lliSilSil^^^ CORNELL UNIVERSITY LIBRARY Given to the COLLEGE OF ENGINEERING ly the Dept. of Machine-Design LJniversity Library Johnson's Materials of construction, 3 1924 004 589 481 Cornell University Library The original of tiiis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004589481 Dean of the College of Engineering of the University of Witconsin 1899-1902 JOHNSON'S MATERIALS OF CONSTRUCTION REWRITTEN Br M. O. WITHEY Associate Professor of Mechanics in the University of Wisconsin AND JAMES ASTON Metallurgist with the A. M. Byers Co. qf Pittsburg EDITED BT r. E. TURNEAURE Dean of the College of Engineering of the University of W^isconsin FIFTH EDITION TOTAL ISSUE, SEVENTEEN THOUSAND NEW YORK JOHN WILEY & SONS. Inc. London: CHAPMAN & HALL, Limited 1919 Copyright, 1897, 1898, by J. B. JOHNSON Copyright, 1919, by PHOEBE E. JOHNSON and M. O. WITHEY PRESS OF SRAUNWORTH & CO. BOOK MANUFACTURERS BROOKLVN, N. Y. PREFACE Some twenty years ago the late Dean J. B. Johnson wrote the following pertinent statement in the preface of the first edition of The Materials of Construction: " The rational designing of any kind of construction involves a knowl- edge of : "The external forces to be resisted, transformed, or transmitted; "The internal stresses resulting therefrom; " The mechanical properties of the materials to be employed to accom- phsh the objects sought. "Of these three coordinate departments of knowledge the first two are founded on the sciences of mathematics and applied mechanics. The last one, however, does not rest on any deductive science, as this informa- tion can only be gained by patient, expensive, and competent research. For this reason the third essential named above has not kept pace with the other two kinds of engineering science; but, on the other hand, it furnishes very much greater rewards to the skilled investigator. "During the past twenty-five years the number of such investigators has increased from a scattering few to hundreds and even thousands, and these are now found in all enlightened nations. The results of their original studies and experiments are pouring in upon us from all countries, in many languages; and no practising engineer can hope to even sc^n, much less to appropriate and assimilate, more than a very small part of this vast wealth of experimental knowledge." The belief that it was essential that students and engineers should have a broad knowledge of this subject led that author to compile his well-known treatise. His good judgment and foresight in so doing were confirmed by extended use of the book both as a text and as a reference for nearly a score of years with little revision. It is obvious, however, to those familiar with the great progress that has been made in recent years in the knowl- edge of the properties of material, that the work no longer adequately meets the need in this field. The number of investigators and the pubhshed data of their researches are now so comprehensive that it is well nigh im- possible for even the specialist in the materials of construction to keep IV PREFACE abreast of the advances being made, and necessarily much of the informa- tion in the former book has now become obsolete. Believing that there is a distinct advantage in presenting to the student of this subject a book which will serve both as a text and as a reference, the authors of the re-written work have maintained in a large measure the broad scope of the former treatise. They have aimed to provide the essen- tial information concerning the sources, manufacture or fabrication of the principal materials; to give carefully selected data covering the more important mechanical and physical properties and the influences of various factors upon these properties; to show the causes of defects and variations and how they may be discovered; to furnish an acquaintance with the technique of testing materials ; and to present to the student some of the more general uses of the different materials. In arrangement, the new book differs markedly from the former work, which was somewhat cumbersome in this respect. The division into parts has been discarded and related subject matter has been more closely coor- dinated than in the previous work as may be seen from the following: In Chapter I is given a rather comprehensive synopsis of the principles of mechanics of materials. Chapters II and III deal with machines and appliances for testing, the technique of testing and the utility of the various tests. Chapters IV to VI consider the characteristics, methods of iden- tification, properties and uses of the more important native woods, also causes of decay and means of preservation. Chapter VII treats of the important stones, their constitution, durability and properties. Chapter VIII covers the manufacture and testing of structural clay products, together with their mechanical properties and uses. Chapters IX to XII deal with the nature, manufacture, methods of testing and properties of the hydraulic cements, the limes and the plasters. Chapters XIII to XV describe very fully methods of making mortar, concrete and concrete products, also the properties and uses of these materials. Chapter XVI provides a brief summary concerning the utility of the principal metals, their ores and the fundamental considerations governing their extraction. Chapters XVII to XIX treat of the reduction of iron from its ores and the subsequent operations of purification and fabrication into final form. Chapters XX and XXI deal with the formation and structure of alloys in general, and the constitution of iron and steel. Chapters XXII to XXIV are devoted to a discussion of the properties and uses of wrought iron, steel, and alloy steels. Chapter XXV takes up the manufacture, molding, con- stitution and properties of cast iron and malleable cast iron. Chapter XXVI treats of the production, properties and uses of copper, zinc, alum- inum, lead, tin, nickel and their alloys. Chapters XXVII to XXIX cover the effects of temperature on metals, the causes and effects of fatigue, and ihe corrosion and protection of metals. It is believed that the new arrange- PREFACE V ment will be considered an improvement over the old and that it will make the work more serviceable as a textbook for students and as a reference for engineers. There have also been some changes in the scope of the new work. The space devoted to the principles of mechanics has been materially- reduced by more concise treatment. In general, discussion of the proper- ties of composite members has been omitted. The writers feel justified in this omission since these subjects are now well treated in many text- books on mechanics, structural design, and reinforced concrete. In the portion devoted to timber, space has been conserved by the omission of the descriptions of trees and by a complete revision and rearrangement of material, thus avoiding the duplications present in the earlier book. The methods of microscopic analysis and magnetic testing of metals have been omitted since it is felt that an adequate treatment of these very important special methods of investigation can not be given in a treatise of this char- acter. On the other hand the new work treats more fully than the former concerning structural clay products, limes and plasters, Portland cement, making and testing of concrete, the methods of manufacture of the metals and the parts made of them, the structure and constitution of metals and alloys, the corrosion and protection of metals, and the decay and preserva- tion of timber. Great care has been taken to illustrate adequately the revised work with material from the best sources. Old figures have been redrawn and, wherever possible, reduced in size. The large use of diagrams and charts in presenting facts and laws, and the omission of tables wherever possible has featured the present volume as it did the previous book. Dean Johnson well said : "A law of relationship cannot be perceived from data arranged in a tabular form. When plotted to significant arguments the law not only becomes evident at a glance, but when once impressed on the mind through the sense of sight it cannot well be forgotten. To obtain this lasting bene- fit, however, the diagram must be intelligently read and understood. The reader is urged, therefore, to give great care to the study of all the diagrams which accompany the text on any subject, for, as a rule, the facts, laws, and conclusions to be drawn from them are not fully expressed in the text. The diagrams must be considered as a part of the text, and they should be read with even greater care than is bestowed on the word-embodied ideas." In the preparation of the present book. Chapters XVI to XXI have been very largely the work of Mr. James Aston, Metallurgist with A. M. Byers Company; Chapter XXVIII has been written by Professor J. B. Kommers of the Mechanics Department, and Chapter XXIX by Professor O. P. Watts of the Chemical Engineering Department of The University of Wisconsin. The remainder of the book has been the work of Professor VI PREFACE M. O. Withey, also of The University of Wisconsin, to whom great credit is due for the vast amount of painstaking work he has done in the prepara- tion of this treatise. In exercising general oversight as editor, the under- signed has endeavored to adhere to the purpose which inspired the first edition and to produce a work which would be of real service to students and engineers. Acknowledgment of the many sources of information consulted in the compilation of this volume have been made in the text. The writers are also greatly indebted to Professors E. R. Maurer and R. S. McCaffery of The University of Wisconsin, to Professor D. A. Abrams of Lewis Institute, to Messrs. J. A. Newlin, C. J. Humphrey and C. H. Teesdale of the Forest Products Laboratory for assistance rendered during the prep- aration of the manuscript. , For courtesies extended in loaning material for illustrations the authors are very grateful to all contributors, especially to Tinius Olsen Testing Machine Co., Riehl6 Bros. Testing Machine Co., The Journal of Industrial and Engineering Chemistry, American Clay Machinery Co., Illinois Steel Co., Harbison- Walker Refractories Co., Ransome Concrete Machinery Co., Steacy-Schmidt Mfg. Co., Lehigh Car Wheel and Axle Works, The W. S. Tyler Co., E. H. Sargent Co., Ludowici-Celadon Co., Weary & Beck, Bradley Pulverizer Co., Alhs-Chalmers Co., Watson-Stillman Co., Shore Instrument and Mfg. Co., The American Railway Engineering Associa- tion, Professor H. C. Berry and Professor J. M. Porter. F. E. TuENEAURE, Editor. Madison, September, 1918. CONTENTS CHAPTER I. SYNOPSIS OF THE PRINCIPLES OF MECHANICS OF MATERIALS GENERAL NATURE OF DEFORMA- TION AND STRESS AETICLE PAGE 1. Definitions 1 2. Kinds of Stresses 1 3. Elastic and Plastic Bodies 3 4. Modulus of Elasticity 3 5. Longitudinal and Lateral Deforma- tion under Direct Stress 4 6. Volumetric Deformation 4 7. Shearing Deformation and Shearing Modulus of Elasticity 5 8. Characteristic Behavior of Materials under Stress 6 MATERIALS UNDER TENSILE STRESS 9. General Phenomena Accompanying Tensile Tests 7 10. The Significant Results of a Tensile Test 8 11. The Elastic Limit 9 12. The Modulus of Elasticity 10 13. Ultimate Strength 11 14. The Percentage of Elongation 11 15. The Reduction of Area of Cross- section 13 16. Failure in Tension 13 MATERIALS UNDER COMPRES- SIVE STRESS 17. Two Classes of Engineering Mate- rials 14 18. Crushing Strength of Plastic or Viscous Materials 14 19. The Law Governing the Strength in Compression of a Brittle Material 14 20. Relation of Crushing Strength to Shearing Strength 16 21. Column Action 16 MATERIALS UNDER SHEARING STRESS ARTICLE PAGE 22. Two Manifestations of Shearing Stress 21 23. Shearing Stress Due to Torsion 21 24. Shearing Deformations 23 MATERIALS UNDER CROSS- BENDING STRESS 25. Fundamental Principles 24 26. Resisting Moment Equals Bending Moment 25 27. Stresses in Ovei-stressed Beams. .. . 27 28. Variation in the Intensity of Shear- ing Stress within a Beam 28 29. Deflection of Beams Due to Bending Moment 30 30. Deflection of Beams Due to Shear , 32 31. Curved Beams 32 32. Approximate Determination of the Strength of Flat Plates under Normal Forces 36 RESILIENCE 33. Resilience Defined 38 34. Resilience of Bodies under Direct Stress 39 35. Resilience in Cross-bending 40 36. Resilience in Torsion 41 37. Resilience a Measure of Shock Re- sistence 41 MATERIALS UNDER COMBINED STRESS 38. Direct and Bending Stresses 44 39. Shears and Direct Stress 44 40. Biaxial Loading 46 41. Conditions Determining Elastic Break-down 47 CHAPTER II. MACHINES AND APPLIANCES FOR MECHANICAL TESTS TESTING MACHINES ■ 42. Definition 49 43. Classes of Universal Testing Ma- chines 49 44. General Conditions which should Obtain in Universal Machines. . 50 45. Olsen Testing Machines 51 46. Riehle Testing Machines 53 47. The Emery Testing Machine 54 CoMPEESSiON Testing Machines 48. A Field for the Hydraulic Press ... 55 49. A Machine for Testing in the Field 55 50. The World's Largest Testing Ma- chine 57 Transverse Testing Machines 51. General Remarks on Transverse Testing Machines 57 52. Descriptions of Various Transverse Testing Machines 58 VIU CONTENTS Cold-bend Testing Machines AKTICLE page 53. Methods of Making the Test 60 54. A Cold-bend Attachment 60 55. Olsen's Cold-bending Testing Ma- chine 61 Shear and Torsion Testing Ma- chines 56. Transverse Shear Test Appliances . . 61 57. Torsion Testing Machines 62 Impact Testing Machines 58. Essential Conditions for Impact Testing Machines 65 59. A Pendulum Impact Testing Ma- chine 65 60. Drop Impact Testing Machines 66 Apparatus for Determining Hard- ness 61. The Sclerometer 68 62. The Brinell Ball Indentation Test. . 68 63. The Shore Scleroscope 69 Endurance Testing Machines 64. Wohler's Repeated-stress Testing Machines 70 65. The White-Souther Endurance Test- ing Machine 71 66. Kommers' Repeated-stress Testing Machine 71 Auxiliary Appliances Employed IN Loading Specimens 67. The Transmission of Load to a Spe- cimen 72 Gripping Devices for Tension Tests 68. Wedges or Grips 73 69. Spherical Seated Holders 74 70. Crossed Knife-edge Suspension 75 Loading Appliances for Compres- sion Tests ARTICLE page 71. Rigid Bearing Blocks 75 72. Adjustable Bearing Blocks 75 Supporting and Loading Devices For Transverse Tests 73. V-blocks 77 74. Adjustable Bearing Blocks 78 Bedments 75. The Use of Bedments 78 76. Plaster of Paris 78 77. Cement Mortar 79 78. Miscellaneous Bedments 79 APPLIANCES FOR MEASURING DEFORMATIONS 79. Essential Features of Extensometers 79 80. A Micrometer-screw Electric-con- tact Extensometer 80 81. A Wire-wound Dial Extensometer. . 81 82. Multiplying Lever Extensometers. . 82 83. Martens' Mirror Extensometer. .. . 83 84. Autographic Stress-diagram Appli- ances 84 85. Essential Features of Compresso- meters 86 86. Brief Discussion of Various Types of Compressometers 86 87. Essential Features of Deflectometers 87 88. A Dial Deflectometer 88 89. Multiplying-lever Deflectometer. . . 88 90. A Wire-mirror-scale Deflectometer. 89 91. Wire-wound dial Deformeters 89 92. Other Types of Deformeters 90 93. Porter's Detrusion Indicator 91 94. A Dial Indicator of Detrusion 92 95. Multiplying Dividers 92 96. A Recording Bridge Deformeter. . . 94 97. A Wire-rope Extensometer 94 CHAPTER III. THE MECHANICAL TESTING OF STRUCTURAL MATERIALS 98. General Observations 97 99. Mechanical Tests Classified 98 THE ACCURACY OF MACHINES AND APPARATUS 100. Methods of Determining the Accu- racy and Sensitiveness of Testing Machines 98 101. The Calibration of Apparatus for Measuring Deformations 100 SELECTION AND PREPARATION OF SPECIMENS 102. Selection of Specimens 101 103. 'The Preparation of the Specimen.. 102 TENSION TESTS 104. Significance of Tension Tests 104 Commercial Tension Tests 105. Object 105 106. Types of Tension Specimens 105 107. Testing 108 108. Observations for Record 109 Extensometer Tension Tests 109. Object Ill 110. Testing Ill 111. Stress-deformation Diagram 112 COMPRESSION TESTS 112. Object of Compression Tests 112 113. The Form of Compression Speci- mens 113 114. Effects of Loading a Portion of the Cross-section 116 115. Apparatus Required for Compres- sion Tests 116 116. Testing 116 117. Observations during Tests 118 TRANSVERSE TESTS 118. Objects of Transverse Tests 120 119. Specimens for Transverse Tests .. . 120 120. Apparatus Required for Transverse Tests 121 121. Observations During Test 123 122. Load Deflection Curves 123 CONTENTS IX IMPACT TESTS ARTICLE PAGE 123. Objects of Impact Tests 124 124. Specimens for Impact Tests 124 125. Considerations Involved in the Se- lection of an Impact Testing Machine 125 126. Testing 126 127. Observations after Rupture 127 HARDNESS TESTS 128. Kinds of Hardness 127 129. Types of Hardness Tests 127 130. Objects of Indentation Tests on Metals 128 131. Relations between Resistance to Indentation and Strength 128 132. Application of Indentation Tests . . 129 133. A Comparison of the Brinell and Scleroscope Methods 129 134. Testing by the Brinell Method 130 135. Testing with the Scleroscope 130 SHEAR TESTS 136. Essential Conditions in Transverse Shear Tests 131 ARTICLE PAGE 137. Objects of Transverse Shear Tests. 131 138. Specimens for Shear Tests 132 139. Testing 132 TORSION TESTS 140. Objects 132 141. Specimens for Torsion Tests 133 142. Testing 133 BEND TESTS OF METALS 143. Significance of Bend Tests 134 144. Various Kinds of Bend Tests 134 145. Specimens for Bend Tests 135 146. Various Methods of Testing 136 147. Influence of Thickness of Specimen 136 148. Observations during Tests 136 DRIFTING TESTS OF METALS 149. Their Character and Significance. , 137 THE VALUE OF MECHANICAL TESTS 150. A Resume of the Utility of the Prin- cipal Mechanical Tests 137 CHAPTER IV. CHARACTERISTICS, PHYSICAL PROPERTIES, USES OF WOOD AND 151. Importance of Wood 140 GENERAL CHARACTERISTICS OF WOOD 152. Structure and Appearance 141 153. Classes of Trees 141 154. Structure of Wood in General 142 155. The Grain of Wood 145 156. Defects in Timber 146 157. Color and Odor 146 PHYSICAL PROPERTIES OF WOOD 158. Density and Specific Weight 147 159. Moisture in Wood 148 160. The Drying of Timber 150 161. Shrinkage and Its Effects 153 162. Amount of Shrinkage 157 PRINCIPAL NATIVE WOODS 163. The Sources, Characteristics, and Uses 157 164. Southern Yeilow Pine. ...'.'.'.'..... 158 165. White Pine 158 166. Norway Pine 158 167. Western Yellow Pine 158 168. Sugar Pine 158 169. Lodgepole Pine 158 170. White Oak 159 171. Red Oak 159 172. Live Oak 159 173. Douglas Fir 159 174. Hemlock 159 176. Spruce 159 176. Cypress 159 177. Hard (Sugar) Maple 160 178. Soft (Red) Maple 160 179. Chestnut 160 180. Red (Sweet) Gum 160 181. Tupelo (Sour) Gum 160 182. Hickory 160 183. Yellow Poplar (White wood) 160 184. Basswood 161 185. Redwood 161 186. Yellow and Sweet Birch 161 187. Larch or Tamarack 161 188. Ash 161 189. Red and White Cedar 161 190. Beech 162 191. Elm 162 192. Cottonwood 162 193. Black Walnut 162 194. Sycamore 162 195. Eucalyptus 162 196. Catalpa 162 THE IDENTIFICATION OF WOODS 197. The Microscopic Structure of Wood 163 198. The Structure of Coniferous Woods 165 199. The Structure of Wood from Broad- leaved Trees 166 200. The Use of a Key in Distinguishing Woods 169 CHAPTER V. THE DETERIORATION AND PRESERVATION OF TIMBER DETERIORATION 201. The Durability of Wood 179 202. Composition of Wood 180 203. Causes of Decay 180 204. Insects 183 205. Marine Borers 183 206. Other Deteriorating Influences. . . . 184 207. The Need of Preservation 185 CONTENTS PRESERVATION ARTICLE PAGE 208. The Relations of Structure to the Penetrance of Preservatives. . . . 186 209. The Treatment of Timber before Preservation 187 SUPEEFICIAL TEEATMENTS 210. Conditions tor Use of Superficial Treatments 188 211. Brush Treatments 188 212. Dipping 188 213. Charring 188 Non-pressure Processes of Impregnation 214. The Value of Non-pressure Proc- esses 189 ARTICLE PAGE 215. Open-tank Process 189 216. Kyanizing 189 Pressure Processes of Im- pregnation 217. Field of Use 190 218. Bethell or Full-cell Process 190 219. Burnettizing 190 220. The Boiling Process 190 221. The Rueping Process 190 222. The Lowry Process 191 223. The Card Process 191 Preservatives and the Effi- ciency OP Presebvation 224. Preservatives 191 225. Economy in Preservation 193 CHAPTER VI. THE MECHANICAL PROPERTIES OF TIMBER 226. Introduction 195 THE STRENGTH OF WOOD 227. Compressive Strength 196 228. Tensile Strength of Wood 199 229. The Shearing Strength of Wood. . . 201 230. The Strength of Wood in Cross- bending 203 231. The Time Element in the Loading of Timber 207 STIFFNESS AND OTHER MECHAN- ICAL PROPERTIES 232. The Stiffness of Wood 208 233. Toughness 209 234. Cleavability 211 235. Hardness 212 CONDITIONS AFFECTING MECHAN- ICAL PROPERTIES OF TIMBER 236. Density 212 237. Effect of Rate of Growth 217 238. Effect of Percentage of Summer- wood 217 239. Relations of Mechanical Properties to Position in Tree 217 240. The Influence of Defects on Me- chanical Properties 217 241. The Effect of Moisture on Mechan- ical Properties 221 242. Effect of Temperature on Strength of Wood 223 243. The Effect of Preservatives on Strength 225 244. Fire-killed Douglas Fir 225 245. Effect of Bleeding on Strength of Longleaf Pine 225 STRENGTH OF NAILS IN WOOD 246. Holding Force of Nails 226 247. Holding Force of Railroad Spikes . . 226 248. The Shearing Strength of Nailed Joints 228 WORKING STRESSES AND GRAD- ING RULES 249. Working Stresses 229 250. Grading Rules 230 CHAPTER VII. BUILDING STONE 251. Uses and Production 234 252. The Mineral Constituents of Rocks 235 IMPORTANT STONES FOR STRUC- TURAL PURPOSES 253. Classes of Rocks 237 254. Granite 238 255. Gneiss 240 256. Trap Rock 2i0 257. Limestone 240 258. Marble 241 259. Sandstone 242 260. Slate 243 THE DURABILITY OF STONE 261. The Weathering of Structural Stone 243 262. Preservative Coatings for Stone Work 245 263. The Value of Durability Tests 246 264. Freezing Tests 246 265. Acid Tests' 247 266. Fire Tests 248 THE PHYSICAL PROPERTIES OF STONE 267. The Thermal Expansion of Stone.. 249 268. Specific Gra\-ity and Specific Weight 250 269. Porosity and Density 251 270. Absorption 254 THE MECHANICAL PROPERTIES OF STONE 271. The Strength of Stone 254 272. The Elastic Properties of Stone . . . 257 273. Resistance to Abrasion 258 CONTENTS XI CHAPTER VIII. STRUCTURAL CLAY PRODUCTS ARTICLE PAGE 274. Introduction 262 MATERIALS, MANUFACTURE AND TESTING OF CLAY PRODUCTS 275. Classes of Raw Materials 263 276. Composition of Clays 263 277. Physical Properties of Clays 265 Method of Manufacture 278. Preparation of the Clay 267 279. Molding 269 280. Drying 270 281. Kilns 270 282. Burning 273 283. Glazing 27* 284. Flashing 274 285. Annealing 274 286. Sorting 274 Methods or Testing Structural Clay Products 287. Tests 274 288. Appearance 275 289. The Hammer Test 275 290. Hardness 275 291. Absorption 275 292. Specific Gravity 276 293. Strength Tests 276 294. The Rattler Tests on PavinR Brick 278 295. The Detroit Pavement Determin- ator 278 296. Alternate Freezing and Thawing Test 278 PROPERTIES OF STRUCTURAL CLAY PRODUCTS Building Brick 297. Manufacture 279 298. Classes of Building Brick 279 299. Requirements of Good Brick 280 300. Tests on Building Brick 281 article page 301. Specific Gravity of Brick 283 302. Crushing Tests on Brick Piers .... 284 303. Resistance of Brick Walls to Fire.. 287 Sand-lime Brick 304. Definition 288 305. Manufacture 289 306. Comparison of Clay and Sand-lime Brick 289 307. Physical Properties of Sand-lime Brick 289 Paving Brick 308. Manufacture 289 309. Requirements of Good Paving Brick 290 310. Physical Properties of Paving Brick 290 Refractory Brick 311. Introduction 291 312. Acid Brick 291 313. Silica Brick 291 314. Basic Brick 292 315. Neutral Brick 292 .Building Tile 316. Hollow Blocks, Partition Tile and Fireproofing 293 317. Tests of Hollow Block Columns. .. 294 318. Roofing Tile 295 319. Floor-tile 296 320. Wall-tile 297 Terra Cotta 321. Decorative Terra-cotta 297 322. Terra-cotta Lumber 297 Clay Pipe 323. Sewer Pipe 297 324. Drain Tile 298 325. Conduit 299 CHAPTER IX. PORTLAND CEMENT 326. The Cements of Construction 301 NATURE OF PORTLAND CEMENT 327. Definition 301 328. The Characteristics of Portland Cement 302 329. The Chemical Elements in Port- land Cement 302 330. The Proportioning of the Main Constituents 303 331. Iron Oxide 304 332. Magnesium Oxide 304 333. Sulphur Compounds 305 334. Alkalies 305 335. Carbonic Oxide 306 336. The Constitution of Portland Ce- ment 305 337. The Setting and Hardening of Port- land Cement 306 MODERN METHODS OF MANU- FACTURE 338. Growth and Importance of the Portland Cement Industry 310 339. Raw Materials 310 The Dry Process of Manu- facture 340. Preparation of Raw Materials. . . . 311 341. Preliminary Grinding 312 342. Proportioning 313 343. Final Grinding 313 344. Burning 315 345. Grinding of the Chnker 317 346. Storage and Bagging of Cement. . . 319 347. Plan of a Cement Plant 319 xa CONTENTS The Wet Process op Manu- facture article page 348. General 319 349. Comparison of Wet and Dry Proc- cesses 319 EFFECTS ON PROPERTIES D0E TO CONDITIONS OF MANUFACTURE OR TESTING 350. Conditions Affecting Soundness ... 320 351. Conditions Affecting Strength 321 352. Conditions Affecting the Time of Set 325 353. Conditions Affecting Fineness 329 354. Conditions Affecting Specific Grav- ity 329 RESULTS OF VAPiOHS TESTS ON PORTLAND CEMENT ARTICLE PAGE 355. General 330 356. Strength Tests 330 357. Expansion and Contraction Due to Variations in Moisture Content. 334 358. Effect of Remixing and Retemper- ing on Strength of Cement 339 359. Effects of Low Temperatures on the Strength of Cement 341 360. Effect of High Temperatures on the Strength of Neat Portland Cement 343 361. Experiments on the Rise in Tem- perature During Setting 344 362. The Resistance of Neat Cement to the Action of Alkali Waters and Sea Water. .... 344 363. Effects of Oils on Neat Cement 347 364. Effects of Sugar on Cement 348 CHAPTER X. NATURAL AND OTHER HYDRAULIC CEMENTS NATURAL CEMENT 365. Definition 349 366. Process of Manufacture 349 367. Characteristics of Natural Cement . 350 368. Properties of Natural Cement. 351 369. Uses and Production 353 MISCELLANEOUS CEMENTS 370. White Portland Cement 353 371. Cements with High Iron Content. 354 372. Blended Cements 354 373. Sand Cements 355 374. Tufa Cement 356 375. Puzzolan and Slag Cements 357 376. Characteristics of Slag Cement .... 357 377. Tests of Slag Cements 357 378. Improved Cements 358 CHAPTER XI. IIMES AND PLASTERS LIMES 379. Quicklime 359 380. Burning of Lime 359 381. Production Statistics 360 382. The Slaking and Hardening of Lime 361 383. Hydrated Lime 362 384. Testing of Limes 362 385. Properties of Lime , 362 386. The Uses of Lime 364 387. Hydraulic Lime 365 388. Latarge Cement 365 GYPSUM PLASTERS 389. Introduction 365 390. Gypsum 366 391. Manufacture of Plasters 366 392. Plaster of Paris 367 393. Cement Plaster 368 394. Hard Finish Plasters 369 395. Other Gypsum Building Materials. 369 CHAPTER XII. METHODS OF TESTING HYDRAULIC CEMENTS 396. Necessity for Testing Cement 371 STANDARD SPECIFICATIONS AND TESTS FOR PORTLAND CEMENT 397. A. S. T. M. Method of Sampling. . . 373 398. Selection of the Sample 374 399. Storage of the Sample 374 400. Mixing Samples 374 401. Quartering 375 402. Purpose of Chemical Analysis 375 403. A. S. T. M. Method for Finding Loss on Ignition 375 404. A. S. T. M. Method for Determin- ing Insoluble Residue 375 405. A. S. T. M. Method for Determin- ing Sulphuric Anhydride 376 406. A. S. T. M. Method for Determin- ing Magnesia 376 407. Purity Test 377 408. A. S. T. M. Method of Finding Spe- cific Gravity 377 409. A. S. T. M. Method of Determin-.-. ing Fineness 378 410. Precautions in Sieving 379 411. Mechanical Shakers 379 412. Other Methods of Determining Fineness 380 413. A. S. T. M. Method of Mixing Pastes and Mortars 382 414. Additional Recommendations 382 415. Kneading 382 416. A. S. T. M. Method of Finding Nor- mal Consistency 382 CONTENTS xm ARTICLE PAGE 417. The Ball Method 383 418. Feret's Consistency Formula 384 419. A. S. T. M. Method of Determin- ing Soundness 384 420. Hints on Manipulation SS.'i 421. Le Chatelier's Test for Soundness. 387 422. The Boiling Test 387 423. The Autoclave Test 388 424. The Value of the Soundness Test. . 388 425. A. S. T. M. Method for Time of Set 389 426. Suggested Precautions 390 427. Comparison of Vicat and Gillmore Methods 390 428. A. S. T. M. Method for Tension Tests 391 429. Reasons for the Tension Test 392 430. Indications Afforded by Neat and Mortar Tension Tests 393 431. The Theory of the Distribution of Stress over the Minimum Section of a Cement Briquette 393 432. Precautions to Observe in .Violding Briquettes 394 433. Mechanical Mixer 394 434. Bohme Hammer 394 435. Types of Testing Machines 395 436. Necessity of Using Roller Clips . . . 396 437. The Effect of Eccentric Loading on the Strength of Briquettes 396 AUTicLE Page 438. The Effect of the Rate of Loading on the Strength of Briquettes . . . 397 439. Number of Specimens 397 440. A. S. T. M. Method of Storage ... 397 441. Moist Closet 397 442.' Storage Bath 398 THE INTERPRETATION OF THE RESULTS OF STANDARD TESTS 443. General Recommendations 398 444. Soundness 399 445. Tensile Strength 399 446. Time of Set 399 447. Fineness 399 448. Specific Gravity 399 MISCELLANEOUS METHODS OF TESTING CEMENTS 449. Methods of Making Cross-bending Tests of Cement 400 450. Methods of Testing the Adhesion of Cement and Cement Mortars to Various Substances 401 451. Methods of Determining Yield. .. . 402 452. Method of Testing Porosity 403 453. Methods of Testing the Permeabil- ity of Cements and Mortars 404 CHAPTER XIII. MAKING MORTAR AND CONCRETE 454. Introduction 406 DEFINITIONS 455. Mortar 407 456. Concrete 407 457. Cement 407 458. Aggregate 407 459. Silt 408 460. Specific Weight 408 461. Voids 409 462. Mechanical Analysis 410 463. Yield 411 464. Density 412 CHARACTERISTICS AND PROPER- TIES OF FINE AGGREGATE 465. Importance of Good Aggregate .... 413 466. Sampling Aggregate 413 467. Requirements for Fine Aggregate. . 414 468. Composition of the Particles 414 469. Impurities 415 470. Gradation of the Sizes of the Par- ticles 416 471. Voids and Specific Weight 417 472. Mortar Tests 419 CHARACTERISTICS AND PROPER- TIES OF COARSE AGGREGATES 473. Requirements for Coarse Aggre- gate 420 474. Characteristics and Properties of Broken Stone 421 475. Characteristics and Properties of Gravels 424 476. Broken Stone and Gravel Com- pared 425 477. Miscellaneous Aggregates 425 THE PROPORTIONING OF MOR- TARS AND CONCRETES 478. The Principles of Proportioning . . . 426 479. The Measurement of Proportions . . 427 480. Arbitrarily Selected Proportions. . . 427 481. Proportions Based on Voids 428 482. Proportions Based on Minimum Yield 429 483. Proportioning by Mechanical Anal- ysis 430 484. Proportions Commonly Used in Different Constructions 432 485. Testing the Quality of Concrete. . . 433 486. Quantities of Materials Required for One Cubic Yard of Mortar and Concrete 434 487. Interpretation of the Meaning of Proportions 438 MIXING, PLACING AND CURING 488. Principles of Proper Mixing 438 489. Hand Mixing 438 490. Machine Mixing 439 491. A Comparison between Machine and Hand-mixed Concretes 440 492. Handling of Concrete 441 493. Placement of Mortar and Concrete 443 494. Joining Old and New Work 444 495. Forms 446 496. Shrinkage in Setting 448 497. Curing 448 498. Protection Against Freezing 449 XIV CONTENTS CHAPTER XIV. THE PHYSICAL PROPERTIES OF MORTAR AND CONCRETE ARTICLE PAGE 499. Introduction 451 STRENGTH OF MORTARS 500. Effect of Proportion of Cement on Mortars 451 501. Effect of Character of Fine Aggre- gate on Mortars 451 502. Experiments on Mortars with Arti- ficially Graded Sands 453 503. Effect of Proportion of Mixing Water on Strength of Mortars . . 457 504. Effect of Mica on Strength of Mor- tar 457 505. Effect of Hydrated Lime on Strength of Mortars 457 506. Adhesion of Mortars 457 STRENGTH OF CONCRETE 507. Effect of Proportion of Cement on the Compressive Strength of Concrete 459 508. The Increase in Strength of Con- crete with Age 461 509. Effect of Density on the Compres- sive Strength of Concrete 462 510. Effect of Size of Coarse Aggregate on Compressive Strength 464 511. Effect of Proportion of Water on Strength of Concrete 465 512. Tensile Strength of Concrete 468 513. The Transverse Strength of Con- crete 469 514. The Shearing Strength of Concrete 470 515. The Effect of Fatigue on Concrete. 472 516. The Strength of Cinder Concrete. . 473 517. The Strength of Slag Concrete 475 THE ELASTIC PROPERTIES OF MORTARS AND CONCRETES 518. The General Characteristics of the Elastic Curves ^ 475 519. Calculation of the Modulus of Elas- ticity 475 520. Values of the Modulus of Elasticity of Mortars and Concretes 477 521. Poisson's Ration for Concrete 480 522. Expansion and Shrinkage Due to Variations in Moisture Content . 480 THE PERMEABILITY AND ABSORP- TION OF MORTAR AND CON- CRETE ARTICLE PAGE 523. Discussion of Terms 482 524. Methods of Testing Permeability. . 482 525. The Effect of the Proportion of Cement on Permeability 485 526. Effect of Density on Permeability. 485 527. The Effect of Consistency on Per- meability 486 628. Effect of Time of Mixing on Per- meability 487 529. Effect of Curing on Permeability. . . 487 530. Other Conditions Affecting Per- meability 489 531. The Absorption of Concrete and Mortar 490 632. Waterproofing Materials 490 633. Effect of Hydrated Lime on Per- meability 491 634. Effect of Finely Ground Clay on Permeability of Mortars 492 635. Integral Mixtures of Alum and Soap 492 636. Oil Mixed Concrete 492 537. Waterproofing by Surface Washes. 493 638. Waterproof Membranes 493 THE EFFECTS OF TEMPERATURE ON MORTAR AND CONCRETE 539. The Effect of Low Temperatures on Setting Concrete 494 540. The Rate of Cooling of Concrete Setting at Low Temperatures ... 496 541. The Effect of Alternate Freezing and Thawing on Hardened Con- crete and Mortar 498 542. The Effect of Adulterants in Low- ering the Freezing Point 498 543. Resistance of Concrete and Mortar to High Temperatures 501 544. The Coefficient of Expansion of Concrete and Mortar 502 545. The Thermal Properties 502 THE DURABILITY OF CONCRETE 646. Effect of Sea Water 506 647. Effect of Alkali Water 509 548. The Effect of Sewage on Concrete . 509 549. Electrolysis of Concrete 510 550. Specific Resistance of Concrete to Electricity Sll CHAPTER XV. PORTLAND CEMENT PRODUCTS 551. General 513 CONCRETE BLOCKS AND BRICK 552. Merits of Concrete Blocks 513 553. Types of Blocks 513 554. Methods of Manufacture 514 555. The Testing of Blocks 515 556. Cement Brick 517 CEMENT DRAIN TILE AND SEWER PIPE 557. The Advantages of Cement Pipe . . 518 558. Method of Manufacture 518 559. The Testing of Cement Pipe 519 560. Poles, Posts and Piles 520 561. Other Forms 520 CONTENTS XV CHAPTER XVI. METALS AND THEIR ORES ARTICLE PAGE 562. Metallurgy Defined 521 563. The MetaJs of Construction 521 564. The Utility of the Metals of Con- struction 521 565. Ores 523 ARTICLE PAGE 566. Economic Value of Deposits 524 567. Preparation of Ores for Extraction of Metals 525 568. Principles of Extraction of Metals . 525 CHAPTER XVII. REDUCTION OF IRON FROM ITS ORES 569. The Economic Importance of Iron and Steel 527 570. The Native Sources of Iron Ores. . . 527 571. Classes of Iron Ores and Their Characteristics 528 572. Elements Associated with Iron Ores 529 573. Preliminary Treatments for Iron Ores 531 574. Fundamental Principles of Ex- traction 531 575. Ancient Methods of Extraction. .. . 531 576. Direct and Indirect Methods of Pro- ducing Ductile Ferrous Metals. . 532 577. The Development of the Blast Furnace 532 578. Description of a Modern Blast Fur- nace 533 579. Accessories to the Blast Furnace . . . 535 580. The Essential Reactions in Ex- tracting Pig Iron 536 581. The Reduction of Impurities in Iron Ores 538 582. Grades of Pig Iron 539 583. Slags 540 584. The Efficiency of the Blast Fur- nace 540 CHAPTER XVIII. MANUFACTURE OF WROUGHT IRON AND STEEL 585. Introduction 542 586. The Purification of Pig Iron 542 THE PUDDLING PROCESS OF MAKING WROUGHT IRON 587. History 544 588. Operation of Process 544 589. Kinds of Wrought Iron and Their Uses 546 STEEL MAKING 590. Classes of Processes 546 The Bessemer Process 591. Principle of the Process 547 592. The Converter 547 593. The Acid Bessemer Process 548 594. The Basic Bessemer Process 550 595. The Tropenas Converter 551 The Open-hearth Processes 596. Essential Features and the Devel- opment of the Processes 551 597. The Open-hearth Furnace 552 598. Smelting by the Open-hearth Fur- nace 554 599. Comparisons of Bessemer and Open-hearth Processes 555 600. The Decline of the Bessemer Proc- ess 556 601. The Duplex Process 556 Minor Processes Used in Making Steel 602. The Cementation Process 556 603. The Crucible Process 557 604. The Electric Furnace in Steel Making 557 CHAPTER XIX. THE MANUFACTURE OF IRON AND STEEL SHAPES 605. Essentials in the Production of Shapes 559 606. Ingots 559 607. Heat Treatment of Ingots 560 608! General Method of Rolling Shapes . 561 609. Rolling Mills 561 610. Plates 563 611. Sheets 563 612. Pipes 564 613. Wire 564 614. Forging and Pressing 565 615. Casting Steel 566 616. Statistics 567 XVI CONTENTS CHAPTER XX. FORMATION AND STRUCTURE OF ALLOYS Alloys in General article page 617. Reasons for Making Alloys 568 618. Mixtures 568 619. Chemical Compounds 568 620. Solid Solution.? 568 621. Methods of Making Alloys 569 622. Allotropy 569 623. Crystalline Structure of Metals. . . 570 624. Effects of Solubility Relations in Alloys 570 625. Evidences of Alloy Constitution Furnished by Thermal Measure- ments 572 626. Cooling Curves 573 Binary Alloys with Liquid Sol- ubility Perfect but Solid Sol- ubility Nil 627. Significance of the Freezing-point Diagram 574 628. Behavior of a Given Alloy in Freezing 575 629. Structure of Alloys of Perfect Liq- uid Solubility — Solid Solubility Nil 576 630. Summary for Alloys with Solid Sol- ubility Nil 578 Binary Alloys with Liquid Sol- ubility Perfect and Solid Sol- ubility Perfect article page 631. Typical Freezing-point Diagram. . 578 632. Behavior of a Typical Alloy in Freezing 579 633. Summary for Alloys of Perfect Sohd Solubility 580 Binary Alloys with Liquid Sol- ubility Complete and Solid Solubility Partial 634. Typical Freezing-point Diagram . . 580 635. Behavior of a Typical Alloy in Freezing 581 636. Summary for Alloys with Solid Sol- ubility Partial 582 Alloys of Moke than Two Com- ponents 637. Complexity due to Metallic Com- pounds 583 638. Difficulties Encountered with Sev- eral Components 584 CHAPTER XXI. CONSTITUTION OF IRON AND STEEL 639. Necessity for Alloying Pure Iron . . 585 640. Classifying Iron and Steel 585 Definitions Proposed for Different Ferrous Metals 641. Cast Iron 586 642. Pig Iron 586 643. Mixer Metal 586 644. Malleable Iron Castings 586 645. Wrought Iron 587 646. Steel 587 647. Blister Bar, Cement Bar, Con- verted Bar 1 588 648. Blister Steel 588 649. Plated Bar 588 650. Single-shear Steel 588 651. Double-shear Steel 588 652. Carbon Steel 588 653. Alloy Steel 588 654. Ferro-alloys 588 655. Semi-steel 588 Composition and Constitution 656. Composition of Iron and Steel. . . . 589 657. Determinations of Constitution of Iron and Steel 589 658. Critical Temperatures 590 659. Cementite, Ferrite and Graphite . . 590 660. Alloying Relations between Iron and Cementite at High Temper- atures 590 661. AUotropic Modifications in Cooling 591 662. The Formation of Graphite 594 663. Structures in Iron-carbon Alloys. . 595 CHAPTER XXII. PROPERTIES OF WROUGHT IRON 664. Structure 598 665. Defects 599 666. The Tensile Strength of Wrought Iron along the Grain 600 667. The Tensile Strength across the Grain 601 668. The Compressive Strength of Wrought Iron 602 669. The Shearing Strength of Wrought Iron 602 670. The Modulus of Elasticity of Wrought Iron 603 671. Effects of Overstrain 603 672. The Toughness of Wrought Iron . . 605 673. The Strength of Wrought-iron Chains 605 674. The Welding of Wrought Iron 606 675. Methods of Distinguishing Wrought Iron from Steel 608 CONTENTS XVU CHAPTER XXIII. PROPERTIES OF STEEL ABTICLB PAGE 676. The Principal Factors Influencing the Properties of Steel 609 COMPOSITION Cahbon 677. Importance of Carbon in Steel . . . 609 678. The Physical Characteristics of Ferrite and Cementite 610 679. The Essential Relations between Carbon Content and Mechanical Properties 610 680. Influence of Carbon on Strength . . 612 681. The Modulus of Elasticity of Steel. 616 682. Influence of Carbon on Ductility . . 618 683. Changes in the Shape of the Stress Diagram 619 684. The Resistance of Steel to Heavy Shocks '. 619 685. The Range in Composition of Structural Steels 620 Effects of Phincipal Impukities ON Steel General Effects 621 Effects of Silicon 622 Effects of Phosphorus 622 Effects of Sulphur 623 Effects of Manganese 624 Copper 624 Arsenic 624 Non-metallic Impurities 624 687. 690. 691. 692. 693. EFFECTS OF HEAT TREATMENTS 694. Effects of Heating above the Crit- ical Range 625 695. Effects of Cooling from above the Critical Range 625 696. Relation of Grain Size to Mechan- ical Properties 626 697. Annealing 626 698. Effects of Annealing on Mechanical Properties 630 699. Overheating and Burning 632 700. Theories of Hardening 633 701. Essentials in Hardening 635 702. Methods of Hardening 635 703. Effect of Carbon on Hardening . . . 636 ARTICLE page 704. Characteristic Microscopic Struc- tures in Hardened Steels 637 705. Tempering 640 706. Relation of Drawing Temperature to Hardness 641 707. Methods of Tempering or Drawing Steels 641 708. Drawing Temperatures for Various Classes of Steels 643 709. Carbon Content for Tool Steels. . . 644 710. Case Hardening 644 711. The Influence of Hardening and Tempering on Mechanical Prop- erties 645 EFFECTS OF MECHANICAL WORK 712. Effect of Hot Work on Structure. . 651 713. Effects of Hot Work on Properties of Steel and Iron 652 714. Methods of Cold Working 654 715. Effects of Cold Work on Proper- ties 656 716. Relief of Distortion Due to Cold Working 658 717. Effects of Overstrain in General .. . 661 718. Grain Growth in Overstrained Metal 661 INFLUENCE OF FORM ON PROPERTIES 719. The Effect of an Abrupt Contrac- tion in Cross-section 663 720. The Influence of Form of Thread on the Strength of Screw-bolts . . 663 721. The Tensile Strength of Grooved Plates 665 722. The Bearing Resistance of Steel and Iron Plates. 666 723. Resistance of Steel when the Com- pressed Area is Confined Later- ally 666 724. Properties of Wire 668 725. Wire Rope , 669 STEEL UNDER COMBINED STRESS 726. Effects of Combined Stress upon the Elastic Limit 672 727. Effect of Combined Stress on the Modulus of Elasticity 673 CHAPTER XXIV. ALLOY STEELS 728. Varieties of Alloy Steels and Their Manufacture 674 729. Nickel Steel 674 730. Manganese Steel 678 731. Chrome Steels 679 732. Tungsten Steel 681 733. Vanadium Steel 682 734. Silicon Steels 682 735. Chrome-nickel Steels 683 736. Chrome-vanadium Steels 684 737. High-speed Steels 686 XVlll CONTENTS CHAPTER XXV. CAST IRON AND MALLEABLE CAST IRON CAST IRON ARTICLE PAGE 738. Importance of Cast Iron 688 Manufacture of Cast Iron 739. Remelting of Cast Iron 688 740. Materials Charged 689 741. The Cupola 689 742. The Air-furnace 690 743. Comparison of Cupola and Air- furnace Processes 691 Molding 744. Patterns 691 745. Cores 692 746. Materials for Molds 692 747. Molds 693 748. Chills 694 749. Cleaning Castings 694 Composition and Constitution 750. The Principal Constituents 696 751. Carbon in Cast Iron 696 752. Silicon in Cast Iron 698 763. Sulphur in Cast Iron 701 754. Phosphorus in Cast Iron 702 755. Manganese in Cast Iron 702 756. Other Elements in Cast Iron 702 757. Defects in Cast Iron. ., 702 758. Composition Suitable to Different Kinds of Castings 704 > Properties of Cast Iron 759. Shrinkage 705 760. Hardness of Cast Iron 705 761. Influence of Composition and Rate of Cooling on Strength 706 article page 762. Tensile Strength of Cast Iron 706 763. The Crushing Strength of Cast Iron 710 764. The Transverse Strength of Cast Iron 712 765. The Modulus of Elasticity of Cast Iron 714 766. Shock Resistance of Cast Iron .... 715 767. Strength of Cast Iron in Shear and Torsion 715 768. Shrinkage Stresses 716 769. Strength of Cast Iron Increased by- Shocks 717 770. Seasoning Cast Iron 717 771. Effect of Repeated Heating on Cast Iron 717 MALLEABLE CAST IRON Nature and Importance 772. Nature 718 773. Importance of Malleable Cast Iron 719 The Manufacture of Malleable Cast Iron 774. Melting the Charge 719 775. Molding and Casting 720 776. The Annealing of the White Cast- ings 721 Constitution and Properties of Malleable Cast Iron 777. Composition and Constitution. . . . 721 77.S, Testing of Malleable Cast Iron. . . 722 779. Mechanical Properties of Malleable Cast Iron 723 CHAPTER XXVI. NONFERROUS METALS AND ALLOYS COPPER 780. Production of Copper 728 781. Properties of Copper 729 782. Uses of Copper 731 ZINC 783. Production of Zinc 731 784. Properties of Zinc 732 785. Uses of Zinc 734 ALUMINUM 786. Production of Aluminum 734 787. Properties of Aluminum 734 788. Uses of Aluminum 736 LEAD, TIN AND NICKEL 789. Lead 736 790. Tin 737 791. Nickel 738 BRASSES AND BRONZES 792. The Brasses — Copper-zinc Alloys . . 739 793. Complex Brasses 742 794. The Bronzes — Copper-tin Alloys . . 744 795. Complex Bronzes 744 796. Cold Working of Brasses and Bronzes 748 797. Season Cracking 748 798. Special Tests for Brasses and Bronzes 749 ALLOYS OF ALUMINUM 799. Utility of Aluminum Alloys 751 800. Aluminum Bronze ^ 751 801. Aluminum-copper .\lloys 753 802. Aluminum-zinc Alloys 754 803. Aluminum-magnesium Alloys 755 ALLOYS OF LEAD, TIN AND ANTIMONY 804. Lead-tin Alloys 756 805. Lead-antimony Alloys 756 806. Lead-antimony-tin Alloys 756 807. Babbitt Metals 757 808. Alloys of Low Fusibility 758 CONTENTS XIX CHAPTER XXVII. THE EFFECT OF TEMPERATURE ON THE MECHANICAL PROPERTIES OF METALS EFFECTS ON IRON AND STEEL ARTICLE PAGE 809. Importance of Temperature Effects on Properties 759 .810. Effects on Strength 759 811. Importance of Effect on Elastic Limit 761 812. The Change in Ductility 762 813. The Change in the Modulus of Elasticity 763 814. Effect on Resistance to Impact . . . 763 ARTICLE PAGE 815. Effect on Hardness 766 816. Effect on Specific Gravity 767 EFFECT ON ALLOYS AND METALS MUCH USED IN MACHINE PARTS 817. Description of Tests 767 818. Effect on Tensile Properties of Alloys 767 819. Effects on Torsional Properties 768 820. Effect on Modulus of Elasticity. . . 769 CHAPTER XXVIII. FATIGUE OF METALS 821. Fatigue Defined 771 822. " Crystallization " of Iron and Steel 771 823. Slip Lines and Fracture 772 824. Experiments on Fatigue 774 825. Effect of Heat Treatment 776 826. Effect of Speed 776 827. Effect of Surface Condition and Change of Section 776 828. Effect of Composition 776 829. Relation to Elastic Limit and Ulti- mate 776 830. Tests beyond the Yield Point 776 831. 832. 833. 834. 835. 836. Rapid Methods for Determining Limiting Stresses 777 Bauschinger's Theory of Failure. . 778 Limits of Maximum and Minimum Stresses for an Indefinite Num- ber of Repetitions 780 A Formula for Dimensioning Mem- bers Subjected to a Great Num- ber of Repetitions 781 Working Stresses by Diagram .... 783 Formulas of Moore and Seely 785 CHAPTER XXIX. THE CORROSION OP METALS 837. Importance to the Engineer of a Study of Corrosion 787 838. Great Variation in the Durability of Iron 788 839. Validity of the Acid Test for Deter- mining the Relative Resistance of Metals to Corrosion 788 840. Relative Resistance to Corrosion of Wrought Iron, Cast Iron and Steel 788 841. Pitting 789 842. Dissolved Air Stimulates Corro- sion 789 843. Local Couples 790 844. Purity a Factor in Corrosion 790 845. Effect of Mill-scale on Rate of Rusting 790 846. Nature of the Process of Rusting. . 791 847. The Function of Hydrogen in Cor- rosion 792 848. The Function of Oxygen in Cor- rosion 792 849. Conditions Affecting Corrosion. . . . 793 850. Rust a Stimulator of Corrosion . . . 795 851. Concentration Cells and Thermal E. M. F. May Cause Corrosion.. 795 852. Effect of Stress and Strain on Cor- rosion 796 853. Puzzling Corrosion of Turbine- driven Propellers 796 854. Effect of Various Elements on the Corrodibility of Iron and Steel . . 798 855. Protection of Iron from Rusting. . . 800 856. Utilization of Passivity to Prevent Rusting 800 857. Protection by Contact with Zinc. . 801 858. Prevention of Corrosion by Cur- rent from a Dynamo 801 859. Corrosion of Non-ferrous Metals. . 801 860. Corrosion by Stray Currents 802 861. The Danger District 803 862. Extent of Corrosion 803 863. Corrosion at Low Voltage 804 864. Joint Electrolysis 804 865. Remedies 804 APPENDICES A. Standard Specifications for Paving Brick of the A. S. T. M 807 B. Abram's Fineness Modulus Method for Proportioning Concrete 815 C. List of Standards Adopted by the American Society for Testing Materials 825 MATERIALS OF CONSTRUCTION CHAPTER I SYNOPSIS OF THE PRINCIPLES OF MECHANICS OF MATERIALS GENERAL NATURE OF DEFORMATION AND STRESS 1. Definitions. — When a solid body is acted upon by external forces, two results are, in general, produced: (1) the body is deformed to a greater or less extent, and (2) there is developed in the body internal resisting forces which balance the external applied forces. The deformation pro- duced is by some writers called strain, but in this work the term deforma- tion will be used; that produced in a unit of length is termed unit defor- mation. The internal forces acting between consecutive particles are called stresses. Unit stress is the amount of internal force per unit area. The stresses acting on any imaginary section taken through the body must be in equilibrium with the external forces acting on either side of such section. If the external forces themselves are not in equihbrium, there is a third result produced, namely, that of acceleration of the body, but in the discussions of this treatise the subject of motion of bodies is not considered; all external forces are assumed to be in equilibrium and the body at rest. 2. Kinds of Stresses. — Depending upon the arrangement and direc- tion of the external forces, the stress produced in a body may be (1) Tensile stresses; (2) Compressive stress- (3) Shearing stress; (4) Bending stress; (5) Torsional stress; (6) Various combinations of the above stresses. Tensile and compressive stresses are frequently called direct stresses. They act perpendicularly to the section in question. In the case of long prismatic bars or members of structures, if the external forces act along the axis of the member, direct stresses of tension or compression are 2 SYNOPSIS OF THE PRINCIPLES OF MECHANICS produced, the section taken being assumed as a cross-section transverse to the axis of the member. Shearing stress is produced by forces tending to shde one particle upon another; it is a stress which acts parallel or tangential to the section in question. Where the resultant of all forces acts in a direction at right angles to a section, the stresses on the section are direct tensile or compres- sive stresses; where it acts at any other angle, there will exist shearing as well as direct stresses. Generally speaking, when a body is deformed under the action of external forces, both shearing and direct stresses will be produced throughout the body; it is only on particular sections that the stresses will be purely direct or purely shearing stresses. Thus, in the case of a tension bar, the stresses on a transverse section will be ten- sile only, but on a section taken through the bar at any other angle, shear- ing stresses will also be present. Tension, compression, and shear may be considered as the elementary stresses. The other kinds of stresses mentioned above are merely com- binations of these elementary stresses resulting from special arrangements of the external forces. Thus, the so-called bending stresses are those which are produced by external forces that give rise to bending moments; the resulting stresses are compressive on one side of a neutral plane and tensile on the other side, while shearing stresses exist, in general, throughout the beam. The result of this combination of stresses is a bending of the member as a whole. Torsional stresses are produced by forces which set up a torsional or twisting moment; this produces a rather complex combination of shearing, compressive, and tensile stresses. The member as a whole receives a twist- ing or torsional deformation. Combined stresses are those resulting from a combination of direct and bending stresses which produce a bending of the member and at the same time an elongation or compression, those resulting from a combina- tion of direct stresses, or those resulting from a combination of direct and shearing stresses. Other common terms, frequently used in defining various conditions under which the external forces are applied, are: impact, repeated stress, and column action. Impact is a term used to describe the application of external forces with such suddenness as to produce a shock or blow. Repeated stresses indicates stresses which are applied and removed, in whole or in part, numerous times and at short intervals. In carrjdng out such tests, stresses are often repeated several millions of times. Column action signifies a compression applied to a relatively long, member so that lateral bending or buckhng is likely to occur, thus giving rise to bending as well as compressive stresses. GENERAL NATURE OF DEFORMATION AND STRESS 3 3. Elastic and Plastic Bodies. — When a body which has been deformed under the action of external forces is released from such action, a greater or less recovery of form takes place. To the extent to which the body recovers its original form, it is said to be elastic, and to the extent to which the body fails to recover its original form, it is said to be plastic. Most engineering materials are in part elastic and in part plastic, the relation between these properties varying widely in different materials. For relatively small unit stresses and deformations, most materials are nearly or quite perfectly elastic, that is to say, they fully recover their form when the load is removed; but as the deformation increases, a point is reached beyond which the original form is not fully recovered. Elastic Limit and Ultimate Strength. — The unit stress within which a body is nearly or quite perfectly elastic is called the elastic limit. Beyond this point, the material will recover only to a certain extent, and will show a certain amount of permanent change of form or set. When the load and deformation are increased still further, rupture generally ensues. The maximum miit stress carried by the material is termed the ultimate strength. The amount of deformation which the material will undergo before rupture, varies widely with different materials. Hard, brittle materials hke glass will show very Uttle deformation between their elastic limit and ultimate strength, while materials like soft steel and wrought iron will undergo a very large deformation between these limits. Under compres- sive stresses materials like soft steel and wrought iron can hardly be said to have any definite ultimate strength, as their resistance to load increases continuously with their deformation. 4. Modulus of Elasticity. — Within the limits of elasticity of solid bodies, the deformation is proportional to the stress, and the ratio of unit stress to unit deformation is a very important function in the study of materials. In general, this ratio is termed the modulics of elasticity, and we have moduli of elasticity in tension, compression, and shear. The moduli in tension and compression are usually equal. The modulus for either direct stress is known as Young's modulus, and is denoted by the letter E. According to notation used in this work, we have the following for direct stresses: P=end axial load; Z = length of bar; A = area of cross-section; e = longitudinal deformation ; 6 = unit deformation; St or (Sc = unit stress of tension or compression; .£= modulus of elasticity. SYNOPSIS OF THE PRINCIPLES OF MECHANICS Then & r, A S, E= — =— or I (1) 5. Longitudinal and Lateral Deformation under Direct Stress. — When a body is subjected to a direct stress, either tension or compression, it undergoes a certain amount of lateral as well as longitudinal deforma- tion. The ratio of lateral to longitudinal deformation is called Poisson's ratio, denoted by X. The values of this ratio for some of the more com- mon materials are as follows: * Glass 0,2451 Steel 0.2686 Copper 0.3270 Brass 0.3275 Delta-metal . 3399 Lead 0.4282 6. Volumetric Deformation. — If the length (l) of a body is increased by el, its lateral dimensions are decreased in accordance with Art. 5 and the new volume of a rectangular bar having lateral dimensions of b and d would be l(l + i)-b{l-eX)-d(l-e\)=lbd{l + e-2€\).^ But the original volume was Ibd, hence the change of volume is lbd{l — 2\)e, and the relative change is lbd(l — 2\)e, divided by the original volume, or (l-2X)e. If we now apply an equal direct tension in the direction of b, we would increase this dimension by eb, and the volume by lbd{l — 2X)e as before. A similar result is produced by a tensile force in the direction of d; hence, for a direct tensile force in all three directions, the volume will be increased by 3(1 — 2X)e times its original volume, and each dimension by (1 — 2X)e times its original value. For a compressive force in all directions the vol- ume will be diminished in the same ratio. The volumetric modulus of elasticity for equal stresses in all direc- tions will be equal to the unit stress divided by the relative strain S 3(1 — 2X)e or, if £^„ =f volumetric modulus, £„ = S 3(l-2X)e But — is the value of Young's modulus or E, hence, E,= E 3(1-2X)' (2) If, for example, X = j, then E^ = IE. * Taken from Wertheim and given in the Report of the French Commission des MHhodes d'Essai des MalMaux de Construction, 1895, Vol. 3, p. 6. For X for concrete and stone see Art. 521 and 271. t Omitting terms containing e^ and e^ as « is a small quantity. GENERAL NATURE OF DEFORMATION AND STRESS 7. Shearing Deformation and Shearing Modulus of Elasticity. — Let ABCD, Fig. 1, represent a very small element of a body subjected to the shearing stresses V. The dimensions perpendicular to the plane of the paper may be taken as unity. For equilibrium the shearing stresses V must be equal on all four faces, the couple formed by the two vertical forces being balanced by that formed by the two horizontal forces. The unit shearing / \ Fig. 1. Fig. 2. Y stress will be y = iSs. Taking a diagonal section on the line AC, it will be found that the stress on this section will be purely tensile and equal in intensity to the shearing stress. That is, St = Ss. Likewise on the diagonal DB, the stress is compressive and has an intensity of Sc = Ss. The element will be deformed into a rhombus, as shown in Fig. 2. Assuming the diagonals to retain their original direc- tions, each side will be deflected through an angle 6, and the total change of angle of each apex of the original figure will be 28. This angular change is a measure of the unit shearing deformation, and the unit shearing stress Ss divided by this relative deformation, is called the modulus of elasticity in shear. Or, ^'-28- (3) The value of d can be calculated by a consideration of the effect of the direct tensile and . compressive stresses Si and Sc. The tensile stress S = force or stress per unit area and £ = modulus of Elasticity (Young's modulus). At the same time its lateral dimensions are reduced in accordance with Poisson's ratio, as described in Art. 5. The rate of elongation in the direction of the force, and contraction in its transverse dimensions, continues in strict proportion to the amount of the external force, until the elastic limit is reached, when both the longitudi- nal elongation and the transverse contraction begin to increase at a more rapid rate, until finally, with the more ductile metals, the condition of perfect plasticity is reached, and the body elongates under a constant force, while the lateral dimensions reduce more and more, until rupture finally occurs. If the external force or load, in pounds per square inch, be represented by vertical ordinates, and the corresponding elongations be represented by horizontal abscissae, then the action of the specimen under test may be indicated by what is known as a stress-diagram, the vertical coordinates representing stress, and the horizontal coordinates the corresponding defor- mations. In Fig. 3 such stress-diagrams are shown for zinc, cast iron, wrought iron, and steel. These Ue on the upper side of the horizontal axis. If the same materials were to be subjected to compressive external forces, corresponding stress-diagrams might be drawn in opposite direc- tions, that is to say, downward and to the left, as indicated in Fig. 3, below the horizontal axis. 8 SYNOPSIS OF THE PRINCIPLES OF MECHANICS In Fig. 4 are shown portions of these same tensile diagrams with the deformation scale largely magnified, so as to bring out more clearly the characteristics of the various curves for small deformations. It will be noted that the diagram for zinc is curved almost from the beginning; the diagram for cast iron is straight for only a short distance; the diagrams for wrought iron and steel are straight until the stress has reached 50 to 60 per cent of the ultimate strength. The diagrams for zinc and cast ^000 \ a 80,000 / ^^ \ 60,000 / ^ ^ \ 40,000 / ^ ^ ^"~~~ ^ \ 20,000 /"cast Iron ?ropo •tlona e Com pressi 3Q /^ ■^jS" Proportionate Elo igatio \ ;8 .2 I .J 6 .1 2 .0 8 .( Zinc ^y .( 20,00 4 .0 B .1 2 .1 6 .'i .: 4 .: 8 .3 40,00 60,00 V=> ^ 1 h 80,00 )£1 nJ voo^ >^ 'M 100,00 -^ -^ / 120,00 / 140,00( o^ %^> y 160,00 ) "-^ 180,00(1 Fig. 3. — Typical Stress-diagrams of Rolled Zinc, Cast Iron, Wrought Iron, and Steel in Tension and Compression. iron are typical for materials of a non-homogeneous nature. Stone, brick, cement, concrete and some of the brasses and bronzes beha-we in much the same way, as shown by the diagrams in Art. 272, 300, 516 and Ch. XXVI. Many of the more ductile metals behave in a manner similar to the wrought iron and soft steel; when the point of plasticity is reached (Y.P.), a considerable deformation occurs with little or no increase of load, thus giving a horizontal notch in the curve. 10. The Significant Results of a Tensile Test. — There are five signi- ficant results of a tensile test, namely: MATERIALS UNDER TENSILE STRESS 9 The elastic limit; The modulus of elasticity; The ultimate strength; The percentage of elongation; The reduction of area of cross-section. 11. The Elastic Limit. — In Art. 3, the elastic Umit was defined as the limit of unit stress below which the material would fully recover its form upon removal of the load. Another definition is com- monly employed, especially in connection with the study of stress diagrams. Under this definition the elastic limit is the limit of proportionaUty of stress and deformation; or it is the unit stress on the dia- gram where the curve departs from a straight line. As a matter of fact, it is found that the two definitions substan- tially correspond; that is to say, the stress at which the limit of proportionality is reached is practically the same as the limit of stress for complete recovery of form. In connection with the study of materials from the usual statie tests, it is more convenient to consider the limit of proportionality as the elastic limit. In the case of such materials as timber, stone, and concrete, the true elastic limit is very low, as these materials will show a small set for very low loads. For most metals, the diagram is sensibly straight for a long distance, and the true elastic Hmit is relatively high. Even in this case, however, the exact point of departure of the curve from a straight line is difficult to determine, and its location will depend to a considerable extent upon the precision of the observations. It is not, therefore, a point which can be very readily determined. On this account it is customary practice in commercial testing of wrought iron and structural steel to determine the point where the deformation increases rapidly. This point is called the yield point. It is also sometimes called the apparent elastic limit. For many purposes it is sufficiently near the elastic Kmit to be used as such, but in other cases, it is very considerably beyond that limit and should be used with caution. 60,000 Y.P. Steel /iE.L. A Y.P. Steel ° 40,000 / n P. Wi^oupht Iron ^ 30,000 a // / //e.L. Cast Iron 2 '^ 20,000 // ^ -^ /// ^ H 1 10,000 /y '/ Rolled Zinc /// "' /^ .0005 .0010 .0015 .0020 TJait ElOQgatlon Fig. 4. — ^Tj^jical Tensile Stress-diagrams for Rolled Zinc, Cast Iron, Wrought Iron and Steel to Enlarged Scale 10 SYNOPSIS OF THE PRINCIPLES OF MECHANICS The original author of this work proposed that, in view of the difficulty of determining the true elastic limit, an apparent elastic limit be taken as the point on the stress diagram at which the rate of deformation is 50 per cent greater than it is at the origin. Under this definition, the apparent elastic hmit would practically correspond to the yield point in materials having such a point and would give a reasonable value for such materials as cast iron or hard steel, for which this diagram shows a very gradual curvature away from the straight line. Such a criterion has much merit, and would accomplish the following results: 1. It would always fix one and the same well-defined point. 2. This point would always correspond to so small a permanent .0050 .0100 .0150 .0200 .0250 .0300 Fig. 5.— Stress-tliagram of Hard-drawn Steel Wire. {Tests of MUals, 1890.) deformation as to be, for many practical purposes, the true elastic limit. 3. It is equally applicable to all kinds of tests, whether on specimens or on finished members or structures, where deformations of any kind can be correctly measured. While the 50 per cent increase in the rate of deformation is purely arbitrary, it is not large enough to fix a point having an appreciable per- manent set, but it is large enough to fix a well-defined point on the stress- diagram. Fig. 5 illustrates the relation between the apparent elastic limit as here proposed and the true elastic limit and yield point. 12. The Modulus of Elasticity. — The modulus of elasticity 's found by dividing any stress per square inch below the elastic limit by the corre- MATERIALS UNDER TENSILE STRESS 11 spending proportionate deformation. Since the stress-diagram is a straight line from the origin to the elastic-hmit point, any point on this portion of the locus may be selected for the determination of the modulus of elas- ticity. In other words, the modulus of elasticity is the tangent of the angle which that portion of the stress diagram below the elastic limit forms with the horizontal axis when the two coordinates are properly evalu- ated by the vertical and horizontal scales, respectively. In the case of materials having a curved diagram almost from the beginning the modulus of elasticity is not so readily defined or determined. For very small unit stresses, it is taken as the slope of the tangent at the origin. Sometimes, however, as in the case of concrete, the actual working stresses lie somewhat above the straight portion of the diagram; there will actually be a slight permanent set in such material under working loads. In such a case it is desirable to consider the modulus of elasticity to be the slope of the secant line (see Eig. 13, Chapter XIV) drawn from the origin to the point in the curve corresponding to the unit stress (S) in question. The slope of this line is 'then called the modulus of elas- ticity at the unit stress S. This use df the term modulus is especially appUcable to problems in reinforced concrete. 13. The Ultimate Strength. — The ultimate strength of a specimen subjected to tensile stress is measured by the maximum load carried, and is indicated on the stress-diagram by the true maximum point in that curve. It is found by dividing the maximum load by the original area of cross-section. In case of the more plastic metals, the area of the broken section is usually about one-half the original area, so that the ultimate strength of the actual section at rupture when found by dividing the break- ing load by the final area of this section would be about twice the ultimate strength as computed on the original section. That is to say, the draw- ing down and pulling of the metal has nearly doubled its strength per square inch. The term " ultimate strength," however, always refers to the original section, and is found by dividing the maximum load hy the original section. 14. The percentage of elongation is found by dividing the increase of length after rupture has occurred, by the original length. By original length is meant a certain portion of the specimen which has been reduced to a uniform cross-section before testing. A standard length for tensile- test specimens in America and in England is 8 inches, while in Germany and France it is 20 cm., these standard lengths being practically identical. The elongation of a test specimen of the plastic metals may be divided into two portions: (a) That part of the elongation which is uniformly distributed over the section; (6) that part of the elongation which occurs in the vicinity of the section which finally breaks. Thus in Fig. 6 are shown four sets of test specimens of mild steel, there being three specimens in each set. All the specimens of one set were originally of the length indi- 12 SYNOPSIS OF THE PRINCIPLES OF MECHANICS cated by the untested specimen which stands on the left side of each group. The specimen next adjoining it on the right has been stretched to the Hmit of the elongation indicated in (a) above, or until there is an indication of a local reduction of area. The right-hand specimen in each group shows the local elongation and reduction, but the specimen has been removed from the testing-machine before rupture occUrrred. The middle specimen of each group has been tested to the ultimate strength of the material, since, when the specimen begins to reduce, locally, the ultimate strength has been passed, and the stress diagram begins to fall, or it is developed under a diminishing load. By the amount, therefore, that the right-hand specimen in each of these groups is longer than the middle specimen of the group, by so much has Fig. 6. — Showing the Necking-down Action of Steel Bars before Rupture. (Tetmajer, vol. 4.) the length been increased by the load drawing out on the section where failure will finally occur. The first elongation, therefore, is that portion which is uniformly distributed over the specimen, and the second is that which is concentrated in the vicinity of the final failure. Both of these elongations are, however, measured and included in the total elongation, from which the percentage of elongation is determined. The total elonga- tion is obtained after rupture has occurred, by placing the two ends together and measuring the distance between the primitive gauge-marks. In the case of specimens having shoulders at their ends the gauge-marks should be at least J in. inside of the shoulder, since the metal adjacent to the shoulder does not elongate fully, because of the strengthening effect of the enlarged cross-section at the ends. It will at once be apparent from a study of these specimens that the MATERIALS UNDER TENSILE STRESS 13 (6) elongation, or that which is locally developed in the vicinity of final rupture, is nearly the same in all these specimens; whereas the (a) elonga- tion, or that which is uniformly distributed over the specimen, is always directly proportional to the length. The total elongation therefore, will not be proportional to the length. In other words, the percentage of total elongation will be greater for the short specimen than for the long ones. This shows the necessity of using standard lengths of these speci- mens when the percentage of elongation is to be found. The percentage of elongation is the result which indicates the ductility of the material, this being one of the most important quahties of the metals iised in structural designing. 15. The reduction of area of cross-section is found by determining the area of the broken cross-section, subtracting this from the original area of cross-section, and dividing the difference by the original area. This is not so important an indication or result as the others described above, but it is customary to determine it, and to add it to the record. For the ductile metals this reduction of area may be as much as from 50 to 60 per cent of the original cross-section. 16. Failtire in Tension.— Illustration of the types of failure common to brittle and ductile metals may be seen in Fig. 6, Chapter III. In general, for ductile homogeneous materials the tensile elastic hmit is reached when the shearing stress on any plane through the bar reaches the shearing elastic limit. Evidence of this is seen in the appearance of fine lines called Luders lines on the surface making angles of approxi- mately 45° with the axis of the test-piece. The fracture of a ductile bar, hke soft steel, shows a full cup and cone, the base angle of the latter also being about 45°. In the medium steels the cone is truncated, showing that the failure is partly shear and partly tensile. For very hard steels and other brittle materials the fracture is square across, showing that failure is due to tension. p Since the unit stress in shear on a 45° plane is ^ it follows that we may expect a cone or truncated cone fracture whenever the ultimate shearing strength is less than half of the true tensile strength * (i.e., tensile load * If we cut an oblique section through a bar under tension or compression and place upon the cut section equilibrating forces normal and tangential to it, the magnitude of the tangential component is P cos 6 and the intensity of shear stress is A P Ss = Pcos8-. , or (13) where P= ultimate load, 4= area of cross-section, /S = the ultimate com- pressive strength of a short prism, 4> = a,n imperial constant depending upon end conditions and kind of material, and - = slenderness ratio. Values of :j> recommended by Merriman are: Material. Both Ends Fixed. Both Ends Round. One End Round, One Fixed. Timber 1 3000 1 5000 1 36000 1 4 3000 4 5000 4 36000 4 25000 1.95 Cast iron 3000 1.95 Wrought iron 5000 1.95 Steel . 36000 1.95 25000 25000 Values of the safe load are obtained by dividing P by a proper safety factor. The formula cannot be used to investigate the unit stress on the concave side of the column when the load is within the elastic limit because 4> and S are usually determined from rupture tests. Straight Line Formula. — T. H. Johnson worked out a straight line formula which, in conjunction with Euler's formula, gives results approxi- MATERIALS UNDER COMPRESSIVE STRESS 19 mating the breaking values gotten by Tetmajer from experiments on medium steel struts. The formula is - = S-C I (14) Here C=the slope of the tangent to Euler's curve at the point where -=\—g-j and j = -^, ox C = ^S|;r^) ; P = the ultimate S \3mEl = slenderness ratio; load; A = area of cross-section; S = ultimate strength of short prism; I r l\i^ and 2^ for round, hinged and fiat ends, respectively. Fig. 9 shows the straight line and the tangent Euler curve. Johnson's constants for his formula are given below. Fig. 9. Kind of Column. S, lb./in.2 C, lb./in.2 Limit of — . r Wrought iron: Flat ends 42,000 42,000 42,000 52,500 52,500 52,500 80,000 80,000 80,000 5,400 128 157 203 179 220 284 438 537 693 28 218 Hinged ends 178 H.ound ends. 138 Structural steel: Flat ends 195 Hinged ends 159 123 Cast iron : Flat ends 122 Hinged ends 99 Round ends Oak: Flat ends 77 128 The straight hne type of column formula has, on account of its sim- pUcity, gained considerable favor among architects and engineers; and many such formulae are found in specifications and in the building laws of our cities. The Parabolic Formula. — From a thorough study of the results of a large number of tests by M. Considere on small steel bars, from tests by Tetmajer on a variety of steel and iron sections and from his own tests on timber, J. B. Johnson concluded that the strength of short columns 20 SYNOPSIS OF THE PRINCIPLES OF MECHANICS was limited by the yield point of the material.* He proposed the follow- ing formula This is the equation of a parabola which is tangent to Euler's curve if 2 /= j;fj;. The ordinate of the point of tangency is -^ and the correspond- -^ j . In the above expressions P = ultimate load; A = area of cross-section; S^ compressive yield-point; -=slenderness ratio; m = l.&r' and 2.5ir^ for columns with hinged and flat ends, respectively; and E — the modulus of elasticity in compression. Constants for Johnson's pajaboUc formula follow. For rectangular wooden columns the (-j term is replaced by its equivalent ( j ) > where d is the least lateral dimen- sion, and / is also modified. Thus for white oak columns with flat ends the formula, in accordance with the tabulated values, is -j=3500— 0.8( jl . p In designing, the values of -j should be divided by a suitable factor of safety. Formulae of the parabolic type in combination with the proper Euler formula appear to be more accurate than any which thus far have been devised. / Kind of Column. Sy, lb./in.2 /, Ib./in.! Limiting — . Value of 4-. a Mild steel: Pin ends 42,000 42,000 34,000 34,000 2,500 3,300 4,000 3,500 0.97 0.62 0.67 0.43 0.60 0.70 0.80 0.80 150 190 170 210 Flat ends *. . Wrought iron: Flat ends White pine: Flat ends. . 60 Short-leaf yellow pine: Flat ends 60 Long-leaf yellow pine: Flat ends 60 White oak: Flat ends 60 * A conclusion which the results of recent tests on large columns at the Bureau of Standards Laboratory reftfiirms. See Engr. News, Vol. 75, p. 190; also Vol. 76, pp. 49 and 81. MATERIALS UNDER SHEARING STRESS 21 MATERIALS UNDER SHEARING STRESS 22. Two Manifestations of Shearing Stress.^When all the opposing external forces which act on a body lie in one plane,* but not in the same line,, the resisting stresses are those of simple shear and cross-bending, without torsional stress. When the opposing external forces do not he in one plane the resisting stresses are those of torsional shear, with or without cross-bending and simple shear. In any case these three kinds of stress are determined separately, as follows: (o) For Parallel External Forces in One Plane. — The moment of resistance of the bending (direct) stresses at any transverse section is equal to the algebraic sum of the moments of the external forces on either side of that section taken about the neutral axis in that section. The simple shearing stress on any section is equal to the algebraic sum of the transverse components of the external forces on either side of that section.. (b) For Parallel External Forces Not in One Plane. — First replace all the forces by equal parallel forces acting in the plane of the axis of the body, and by couples equal in value in each case to the force multiplied by its displacement. Then the moments of resistance and the simple shearing stresses will be the same as in the last case, and in addition there will be the moment of torsion. The torsional moment at any transverse section is equal to the algebraic sum of the moments of the couples of the displaced forces, acting on either side of the transverse section in question. (c) For Non-parallel Forces Acting in Any Manner. — Resolve all forces into horizontal and vertical components at their points of application, and then solve for bending moments, and torsions at any section in these two planes. The bending moment at this section will then be the square root of the sum of the squares of the bending moments at right angles to each other. The total shear will also be the square root of the sum of the squares of the primary shears at right angles to each other. The total moment of torsion will be the algebraic sum of the two moments of torsion found from the two sets of forces. 23. Shearing Stress Due to Torsion. — In a sohd or hollow member of circular cross-section the twisting moment produces shearing deforma- tions which, at any transverse section, vary from zero at the axis to a maximum on the surface. If the member is not deformed beyond its * When a force is distributed over an area it is here supposed to act at the center of gravity of these force-elements. 22 SYNOPSIS OF THE PRINCIPLES OF MECHANICS elastic limit the shearing' deformations vary directly as the distance from the center of the cross-section, consequently the intensity of stress varies in a like manner, Fig. 10a. If Ss is the intensity of stress on the outer fiber of a shaft having a radius r, the moment of stress on any element da at z dis- tance from the axis is -^da r and the total moment of all SJ r ' stresses is where J is Fig. 10. — The Relation of Unit Shear Stress to Unit the polar moment of inertia Deformation in a Sohd Round Shaft (a), Stresses q£ ^jjg gross-section about Within Elastic Limit (6), Overstrained. the axis. This is the resist- ing torsional moment and must equal the external twisting moment M,, or M,= — . r (16) For a sohd round shaft J = ^Trr*, and for a hollow shaft with inner radius ri, Formula 16 does not hold exactly for sections other than circular. For other sections approximate values of the factor - may be computed from the radius of the inscribed circle. Thus for a square shaft, with sides =d, the exact analysis gives Mt = 0.2083SA^ which is about 5.9 per cent greater than the value for a solid round shaft of diameter d. For a solid elliptical shaft of major axis a and minor axis b the exact value for Mt=T7:Ssab^- If a = 26 then the exact value of M, is double 16 that for a round shaft of diameter b. Similarly for a rectangular shaft ^t => 5 — L , where a is the length of the long side and b the length of the oci-rl.oO short side. The greatest intensity of stress in an elliptical or rectangular shaft occurs at the ends of the minor axis. • If the shaft is deformed beyond its elastic limit the shearing deforma- tion increases approximately as the distance of the fiber from the axis but the intensity of stress does not vary directly with the unit shearing deformation, Fig. 106. Values of the ultimate shearing stress in torsion Cannot, therefore, be computed from Ss=-4-^ Upton* has made a * See Materials of Construction by. Upton, p. 52. MATERIALS UNDER SHEARING STRESS 23 mathematical analysis by which the true intensity of shearing stress in a solid round shaft may be gotten as follows: In Fig. 11 the full-line curve represents the relation of unit stress Ss on the outside fiber to the unit deformation of the same fiber. In plotting this curve Ss is computed by formula 16 and es must be deter- mined from experiment. The true stresses are represented by ordinates to the dotted line. To find the true stress DB' corresponding to a unit shearing deformation on the surface =AD, draw BD perpendicular to AD, prolong the tangent at B until it intersects the Ss axis at C; then AC 4 ■ terials the shearing stress-deforma- tion curve is approximately parallel to the deformation axis at the maxi- mum Ss, therefore the true ultimate shearing stress is B^^ 1^2-^""*"^ "42 ■ . IE k \ D ,_ DB'=DB- For ductile ma- CgOD Outside Fiber Fig. 11.— Method of Finding True Unit Shear Stress in an Overstrained Solid Round Shaft (Upton). S/4^ = A77^. 4 J r^ (17) For hollow shafts of ductile material in which the thickness is less than a fifth of the outer radius the intensity of shearing stress is approximately uniform throughout the cross-section when the shaft is stressed to the ultimate, therefore the maximum unit shearing stress is approximately Tr(r-fri)2(r— n) ^ ' 24. Shearing Deformations. — As shown in Art. 7, a shearing action of external forces results in angular deformation of the body. In the case of simple shear, or where the forces lie in one plane, the angular deforma- tion from shear is very small, the bending being mostly due to the longitudinal deformations resulting in the direct ten- sile and compressive resisting stresses on the two sides of the neutral plane respectively. * When the forces do not lie in one plane, or when there is a moment of torsion, the angular deformation gives rise to a twist of the body about the longitudinal axis. Thus in Fig. 12 assume the soUd cylinder, anchored at 0, to have a length I and a radius r. Let the torsional moment be Pa = Mt. * Shear in beams will be discussed in Art. 28. Fig. 12. 24 SYNOPSIS OF THE PRINCIPLES OF MECHANICS Then Ss= -7- =— 3 ■ From Fig. 12 it appears that the unit shearing deformation of an outside fiber is = ^- Also from Art. 7 «s=^, therefore by combining these three equations there results -^ '• • • • (>^> Here is expressed in radians. To obtain the angle of twist in degrees multiply d by 57.3. Formula 19 holds for hollow or sohd round shafts provided the stress on the extreme fiber does not exceed the elastic limit. The angle of twist in radians for a square shaft of side d is 5 = 7.11 ^tti, or 43 per cent more than d for a solid round shaft. For an elHptical section 6 = — .. ' , where 5 is in radians. A is the area of cross-section, and J is the polar moment of inertia. This is also an approximate formula for the twist of rectangular shafts. The fracture of ductile materials under torsion is generally square across. Wrought iron and some of the brasses show a rope-like twisting of the fibers before a square break ensues. Brittle materials hke cast iron, stone, brick and concrete exhibit a hehcoid fracture. These substances being weak in tension really fail through the secondary tensile stresses which are produced by two pairs of shearing stresses acting in planes tangent to the surface of the shaft. One of these pairs of forces acts per- pendicular to the surface elements; the other pair acts parallel to the ele- ments. Consequently on a plane at 45° with the axis of the shaft, there is produced a unit tensile stress St which is equal to the intensity of the shear stress & (Art. 7). MATERIALS UNDER CROSS BENDING STRESS 25. Fundamental Principles. — When a member is bent by forces applied transversely with respect to its axis, cross-bending stresses are produced. The simplest system of forces which will cause such stresses is a coplanar parallel system acting in a plane containing the longitudinal axis of the member. Such a member is called a beam. Frequently beams are horizontal, the loads are produced by gravity pulls on suspended masses and the supporting forces are upward. Under the action of these forces the beam is bent and observation shows that the fibers on its con- vex surface are elongated, those on its concave surface are shortened, and that there must be a plane of fibers between the convex and con- cave surfaces which suffers no deformation. This plane is called the neutral MATERIALS UNDER CROSS BENDING STRESS 25 surface. Hence tension exists in the fibers between the neutral and the convex surfaces and compression exists in the fibers between the neutral and the concave surfaces of the beam. It will be assumed that the beam is symmetrical,- initially straight, homogeneous, of material having equal stiffness in tension and com- pression, that it is not stressed beyond its elastic limit by the loads, that the bending is slight, and that the plane of the external forces coin- cides with a plane of symmetry. If the beam is severed transversely it will be necessary, in order that equiUbrium may obtain, to place a system of forces on either cut surface similar to that shown in the lower part of Fig. 13. Then from the principles of Statics we know that: 1. The vertical shear V equals the sum of the vertical forces on the left of the cut; 2. The total compression C equals the total tension T; 3. The sum of the moments of the tensile and compressive stresses on the portion shown equals the algebraic sum of the moment of the external forces to the left of the section. From experimental evidence it is known that the unit deformations vary directly as the distance of the fiber from the neutral surface, conse- quently the intensity of stress varies in hke manner. From these considerations it is easily shown that the total horizontal stress on the cut is = ~ /, yda, where *S is the unit stress on the extreme fiber at c distance from the neutral axis, y is the distance from the neutral axis to any elementary area (Fig. 13) and the summation is taken for the entire cross-section. Since — is finite it follows that / yda = 0, or the neu- tral axis must pass through the center of gravity of the cross-section. 26. Resisting Moment Equals Bending Moment. — Taking moments of the stresses about the trace of the neutral surface (n—n) and using same notation, we have Mr = - ^^ y'da = -I. Since the resisting moment (Mr) equals the bending moment (M) there results M- SI c ' (20) 26 SYNOPSIS OF THE PRINCIPLES OF MECHANICS For selecting a beam to carrying a given loading S is known and M can be computed by taking the algebraic sum of the moments of all forces on either side of the dangerous section, therefore - may be ascertained and the section designed. To determine the safe load for a given beam; S, I and c are known or may be computed and M is expressed in terms of the unknown load which can then be found. The third type of problem con- sists in finding the unit stress at a certain section of a given beam. In this problem M is computed for the given section; I and c are known and S can be determined. Values of the moment of inertia and resisting moment for several common beam sections appear in the following table. Form of Cross-section. Distance of Center of Gravity, or Neutral Axis, from the Most Distant Fiber. Momenta of Inertia about the Center of Gravity of the Section. =/ Moment of Resistance in Terms of the Stress in the Most Distant Fiber. = Jlf, SI T, Id' 12 isM= 64 -Sd^ 'SI !• 36 24 Sbh^ VT d' 12 6V2 SiP bh'-(b-t')^h-2t)' 12 bh'-(b-t')(h-2t)»S 6A it'h'+Hb-t')(.h-if) i'h+t(.b^t') bh'-(,b-t')(h-t)' ST b+2b' h b+b' '3 ,,T 3b+b' (b+2bV \ ' I 12 18(6 +!>')] S;.'r 3(36+i»')(b+!,') ,. ,,.,,1 MATERIALS UNDER CROSS BENDING STRESS 27 When the plane of the loads does not contain an axis of symmetry of the section, then the neutral axis, is not in general perpendicular to the plane of the loads and the above formulae are inexact. In such cases the principal axes of the section (see Moment of Inertia in Applied Mechanics) may be determined; the bending moment is resolved into the planes of these axes; and the unit stress on a given fiber is found by adding algebraically the stress dueto each moment considered separately. In finding the stress due to a component moment, the neutral plane for that moment is the plane of the principal axis perpendicular to that moment. Thus if x and y are the principal axes of the section and the z-axis coincides with the longitudinal axis of the beam, Si= — 1 — - — . Where Si is the unit stress on fiber whose coordinates are xi and 2/1 Ix ly with respect to the principal axes, Mx is the component of the bending moment in the xz-plane, My is the component in the j/z-plane, I^ is the moment of inertia about the X-axis and ly about the i/-axis. 27. Stresses in Overstressed Beams. — The flexure formula 20 does not hold for beams of materials where Ec does not equal Et nor for beams stressed beyond the elastic limit. In the latter case the intensity of stress to) BENT BEAM (6) STRESS D AGRAMS IN TENSION (T) IN COMPRESSION (C) Fig. 14. does not vary as the distance of the fiber from the neutral axis but follows the law of the variation of the stress ordinates to a stress-diagram in which the extreme ordinate represents the stress on the extreme fiber of the beam. If the ultimate strengths in tension and compression are unequal, the neutral axis will shift toward the stronger side of the beam as the over- stressing proceeds. Thus the stress variation in a beam of cast iron, which is much stronger in compression than in tension, is illustrated in Fig. 14. The unit deformation («() of the outside fiber in tension (Fig. 14a) corre- sponds to a unit stress Si in the stress diagram of Fig. 146. Similarly So for the bottom fiber and the unit stresses for other fibers may be found. If the load is increased until St equals the ultimate tensile strength of the cast iron, failure begins. Concrete, brick, and stone beams fail similarly; but a wooden beam, being weaker in compression, will fail first in com- pression. If formula 20 be applied to find stresses beyond the elastic limit, it is evident from the foregoing that the results will be fictitious. In general the value of Sm, found when Mm is the maximum moment, will he between 28 SYNOPSIS OF THE PRINCIPLES OF MECHANICS the ultimate tensile and compressive strengths for the material. It is called the modulus of rupture. If the shape and size of specimen is main- tained approximately constant, the modulus of rupture furnishes a good index of the strength of different grades of material. For the effect of variations in form on the modulus of rupture of cast iron beams see Art. 11. Upton has also worked out the true value of the unit stress on the extreme fiber of an overstressed beam of rectangular cross-section.* A curve is plotted as in Fig. 15 between the computed stresses on the extreme fiber at the given section and the unit deformations of the same fiber. S for Outside Fiber Fig. 15.— Method of Finding True Unit Stress in an Overstrained Beam (Upton). The true unit stress S' corresponding to a given unit deformation OC OA is CB' = CB-^, AB being tangent to the curve OEB at B. o Ordinates to the dotted curve EB' represents true unit stresses. Use of the above method necessitates measurement of the deflection and calculation of the values of e, or direct measurement of the latter which is cumbersome. For ductile materials the stress-deformation curve is approximately hori- zontal when the maximum moment (Afm) is imposed, therefore the true stress on the extreme fiber is two-thirds of the computed stress or „, _2Mm hd? (22) 28. Variation in the Intensity of Shearing Stress within a Beam. — If a rectangular prism be cut from a beam and the forces necessary to L c^ V bdx J. \/ Surface Fig. 16. equilibrium be placed on the cut surfaces as shown in Fig. 16, the occurrence of a horizontal shearing stress acting along the surface which parallels the neutral plane is noted. We shall now determine the average f inten- * See Materials of Construction, p. 78. t The intensity of shearing stress on a horizontal plane is not always uniform imless the cross-section is rectangular. MATERIALS UNDER CROSS BENDING STRESS 29 sity of this shearing stress Sn- Let M be the bending moment at the left end of the notch, M' the bending moment at the right end, S and S' the unit stresses on the extreme fibers at the left and right end of the notch, respectively, C the total stress on the right end, C the total stress on the left end of notch, b the breadth of the bottom of the notch, and / the moment of inertia of the cross-section about the neutral axis n—n. Then C = -^^yda and C' = —/^ yda; C'-C = Snbdx= \~~-^ ^'yda; therefore but therefore and c c I I I ' Si,bdx= -^j^/ ^ yda; Sn'- dM dxlb ^ yda. ^''=ib2^f''- Since dM dx — V, we have (23) In the above expression ^^ yda is the statical moment of the shaded area in Fig. 16 about the neutral axis n—n.. Since it can easily be shown that the intensity of the vertical and horizontal shearing stresses at any point in a beam must be equal to produce equilibrium (see Fig. 1), it fol- lows that values of the vertical unit shearing stress Sv may also be gotten by formula (23). For a rectangular beam the intensity of the horizontal shear at any section varies, in accordance with the ordinates to a parabola, from zero at the outside fibers to a maximum at the neutral axis. For such beams the maximum value of the horizontal or vertical unit shearing stress is '^ = ^' = Wd' (24) where 6 = the breadth and d the depth of the cross-section. That is, the maximimi intensity is f of the mean intensity of shearing stress. Fig. 17 shows how the total shear and the intensity of the horizontal and vertical ""^- ^^■ unit shearing stresses vary in a rectangular beam under uniform load. In a solid circular section the maximum intensity of shearing stress is f of the mean intensity. Beam uniformly loaded 30 SYNOPSIS OF THE PRINCIPLES OF MECHANICS For an I-beam or plate girder the maximum intensity of shear stress is practically equal to the total shear at the section divided by the area of the web. Shear in Wooden Beams.— li becomes necessary to design wooden beams for horizontal shear when the safe load in shear is less than the safe load in bending. This condition occurs only in short deep beams. Thus for a uniformly loaded rectangular beam of simple span, the safe load in bending is Wi,= „, and the safe load in shear is Ws = ^Sii)d. If Sii Zl s WsKWt, then must ^0.414Z /= 0.0054 for a; =0.5782 EI /= 192£/ wl* ''384:EI 34 SYNOPSIS OF THE PRINCIPLES OF MECHANICS total deformations vary as the distances of the fibers from the neutral surface; but since the fibers are of unequal length the unit deformations, hence unit stresses, will not 39 vary. As a result of this condition the neutral surface does not, in general, include the gravity axis of the beam. Let Fig. 21 represent a small portion of a bent beam.* Consider the end CD fixed and suppose A'B' to be the position assumed by AB after bending. Then the unit deformation of any fiber with cross-section {r-ro)Ede —. 2 '1 i tH Fig. 21. da is rdd-rode and the unit stress tE = The position of rd re the neutral axis is obtained by equating the total stress on the cross-section - f Hr-ro)Ede _, . Edd , . , , ^ . 00 zero; or 0= I 2 "^i smce —r- does not equal zero but is a constant for any given section we have A ro = r^da Jn r The resisting moment is „ Edd C"' -r.^2 (r— ro) ■da. (29) (30) and the unit stress on the inner fiber due to a bending moment M is (ri-ro)M 1 -Si = - n r ir—ro)' da On the outer fiber it is 82 = r2—riM r2 1 /: (r-ro)2 da (31) (32) In solving equations (29) to (32) the form of the section must be known in order that the relation of da to r may be properly inserted in evaluating *The proof outlined is more completely given in Boyd's Strength of Materials, Chapter XVIII. MATERIALS UNDER CROSS BENDING STRESS 35 the integrals. M is given a positive sign when it decreases the radius of curvature. A positive sign before the result in equation (31). or (32) indicates tension. The following table contains values of ro and of the integral of equations (30) to (32) for rectangular, circular and trape- zoidal sections. Section. /; 'ra(r— ro)' ■da ^&->i k Neutral osis '■ a i y 1 log! n+d ;,rj('"2+'"i~4)-o) , ,, ril T 2 +'"°'°s^nj {vvi+v7,y '■(^-^-r) C4^'-^> i-Uloge- n md 'ri+nri+ri' 62—61 '■] The accompanying table shows the ratios of unit stresses computed by eq. (31) and (32) to those gotten from 5=—-, when the curvature is sharp.* ^ * Taken from Boyd's Strength of Materials, pp. 327 and 333. RATIOS OF UNIT STRESS BY CURVED BEAM FORMULA TO UNIT STRESS BY STRAIGHT-BEAM FORMULA FOR EXTREME FIBERS d Rectangle. Circle. n Concave. Convex. Concave. Convex. 0.50 1,00 2.00 1 . 15 1.29 1.52 .87 .81 .73 1.17 1.33 1.62 .86 .79 .70 36 SYNOPSIS OF THE PRINCIPLES OF MECHANICS In many practical problems a curved beam is bent by forces having components which are perpendicular to the cross-section of the member. In such cases the values of ro do not indicate the position of the true neutral surface, but the position which it would occupy if bending only obtained. The bending moment in such cases is computed with respect to an axis through the center of gravity of the section considered and includes the moments of all forces on one side of the given section. The unit stress on any fiber is equal to the bending stress computed as indi- p Gated above plus or minus -j. Example. A 4- by 2-in. rectangular bar is bent in an elliptical arc and loaded on either end with axial pulls of 3000 lb. The center of gravity of the remotest section is 5 in. from the line of action of the pulls. The inner radius (n) of that section is 8 in. and the outer radius {n} is 12 in. Find the unit stiesses Si and Si on the inner and outer faces, respectively. Here A =8 in.^, '■"=, ;^;:+d = 0.1761X2.3026 = l057 = ^-^^^ ""' loge-^ b[d ''+'f^'° +ro' log, r^j = _i.08 in." /o,^ c 8-9,865 (-5X3000) „„,„,.,. , From eq. (31) Si = g — -^^ — ^Qg — ^ = 3240 lb./m.=i Si' = ^+Si=^-+3240 = 3615 lb./in.» tension. «nN c 12-9.865 (-5X3000) oA'7t^^u r 2 From eq. (32) S2 = ^ ^ — j-^g — - = -2470 lb./m.2 S2' = j+-S2 = +375-2470 = 2095 Ib./in.^ compression. 32. Approximate Determination of the Strength of Flat Plates under Normal Forces.* — (a) Flat Circular Plate Supported at the Circumference and Uniformly Loaded. — Assume a diametral strip 1 in. in width to be loaded over its full width at the ends, but the loaded surface to reduce to a zero width at the center, this load to be w lb. per square inch. The total load vyr * on the strip will then be wr, and each end support will be -^. The bending moment at the center will be ,r wr wr 2 wr^ ,„„. ^'>=-2-'—2r=-6 (3^> * These proximate solutions are offered as illustrative of simple approximate methods which may often be applied to very complicated problems of this class. MATERIALS UNDER CROSS BENDING STRESS 37 But for a solid rectangular section we have Mo = iS6<2, or, for 6, =1; -'^o=-g- = -g-, or S=-^; (34) whence no i=^y]s' (35) where <= thickness of plate in inches; r= radius of plate in inches; s = stress in extreme fiber in pounds per square inch; t« = pressure on plate in pounds per square inch. From a very elaborate analysis, Prof. Grashof finds for this case (6) Square Flat Plate Supported at the Periphery and Uniformly Loaded. — Since the corners are more distant from the center and therefore carry a less proportion of the load, we may assume that the opposite sides act inde- pendently, so far as the bending moment at the center is concerned. On this assumption the plate may be regarded as supported at two sides only and loaded with one-half the actual load, whence we have Mo = ^wbF = lSbt^, (36) or _ t = l^ = OMlyj^, (37)( where Z = length of one side of the square plate. (c) Same Cases when the Plates are Fixed in Position at Their Periph- eries. — Since the maximum bending moment on a beam fixed at the ends and uniformly loaded is only f that of a beam supported at the ends and similarly loaded, we may assume the same relations would hold here, thus giving for a circular plate, rigidly held, „ 2wr^ . J2w , -^ = 3"^' °' ^ = '\3S (^^^ For a square plate, rigidly held, c IwP Z Iw) . . (d) For Elliptical and Rectangular Plates. — Here the plate fails by cracking along its greater axis; and since the deflection of a beana for a 38 SYNOPSIS OF THE PRINCIPLES OF MECHANICS given load is as the cube of the length, it is evident that the ends carry but a small part of the total load. Where the longer axis is more than twice the shorter one, we may neglect these end bearings entirely when we have the case of a flat plate supported at two opposite sides, which then becomes a simple beam: and this is the proper assumption to make in such a case. Making this assumption, and calhng b the smaller dimension of the open- ing, we have „ 3 wb^ ; b I3iv x/|° m Prof. Bach gives for this case ^ ia^+b^)fl' ^^^^ where C is somewhere between f and 1. When the longer axis is about 1^ times the shorter, as is common with manhole-covers, assume that J of the total load is carried at the sides, thus giving, from (41), RESLLIENCE 33. Resilience Defined. — Resilience is the work which a body can do in springing back after a deforming force has been removed. Within the elastic limit the work of the forces deforming the body equals the energy stored in the body, that is, it equals the resihence. If a body is stressed beyond its elastic limit some of the work of the forces is spent in perma- nently deforming the body through sHding of the particles over one another, thus causing a loss of heat. Under the latter condition the resilience equals that portion of the total work of deformation which the body can give back upon removal of the forces. Since work is measured by the product of the force and the distance through which the apphcation point moves in the direction of the force, we find the work of deformation by multiplying the average stress by the total deformation. Thus the work of deformation (W) equals the resili- ence (K) for any unit stress (S) which is within the elastic limit and W = K = ^Pe, where P is the maximum total stress and e the corresponding deformation. If in the stress-deformation diagram for a body (Fig. 22) the total stresses (P) are plotted as ordinates and the displacements (e) as abscissa, then the work of deformation (W) equals the area (measured to scales of the diagram) between the curve and the c-axis. Within the elastic Hmit the resilience also is measured by this area. When the elastic limit has RESILIENCE 39 been exceeded experiment shows that the return curve is parallel to the elastic curve — qzqz is parallel to 052, Fig. 22. Therefore the resilience equals one-half of the maximum stress multiplied by the corresponding elastic deformation. In JFig. 22 the shaded triangle marked resihence area represents, to scale, the resili- ence corresponding to a maximum stress 53^3 and an elastic deformation q'sdz, the corresponding total work of the deforming stresses is measured by the area oqiqzdz, and the energy lost through friction by the area oq2qsqs- The total work of deforma- tion to rupture is often called the energy of rupture. If the permanent sets be laid off from the stress-axis opposite to the corresponding stresses — fzqz" equal to oqz', piqi" equal to oqi, etc. — then it may also be shown that the following sets of areas are equal opiqio = oqidio, op2q20 = oq2d20, op2q3"qzq20 = qz'qzdzqz' and op2qz" qi" qiqzq20 = q4,'qidiq4. Therefore the resihence equals the work of the elastic deformations. There are three ^varieties of resihence conimonly met: resihence of direct stress, tension or compression; resilience of cross-bending; and resihence of torsion. Values for these different kinds of resilience will now be determined. In all cases it will be noted that the resilience is directly proportional to the square of the maximum unit stress divided by the modulus of elasticity [^j, the voliune (Al), and a coefficient which depends upon the kind of stress, form of cross-section and the method of loading. 34. Resilience of Bodies under Direct Stress. — Consider a homogene- ous prism of uniform cross-section subjected to end axial pulls or pushes p which are slowly increased until the value P is reached, -j being less than PI the elastic limit. Then the total elongation due to P is e = AE (see eq. 1) and the total work Wj,, which is equal to the resilience K, is Wi, = ^Pe. Therefore 1 SAl 152 '2 ^'• (43) 40 SYNOPSIS OF THE PRINCIPLES OF MECHANICS 1 S^ The factor - -^, where Se is the elastic hmit, is the modulus of resili- ewce for a material under the direct stress considered. P It should be noted in passing that when -j exceeds the elastic limit, the resiUence may be computed by eq. (43), but it does not equal the work of P in this case. The latter can be found from the area of the stress deformation diagram as previously indicated. It may also be approxi- mated as follows: For ductile materials having a stress-diagram like mild steel (Fig. 3), the energy of rupture K, per unit of volume is approximately Kr=P^ 6. (U) For materials hke cast iron having a parabolic stress-diagram, approxi- mately, Kr=^Sn,e„, ^ . (45) In the above Sy and Sm are the unit stresses at the yield point and maximum load, respectively, and em is the ultimate unit elongation. 35. Resilience in Cross-bending. — Consider a homogeneous canti- lever beam of uniform cross-section with an end load which is gradually increased until it reaches the value P, the latter being of such value that the fibers of the beam are not stressed beyond the elastic limit. The p/3 deflection of the free end due to bending is/=;5-gri(eq. 27) and the work (Wp) of the load is TFp = iP/. Therefore the resihence K = ^Pf=^^. Since the maximum unit stress, on the extreme fiber at the support is c Pic . iS = -y- we have Here r = radius of gyration and the other symbols are in accordance with previous notation. The result in eq. (46) also holds for a simple beam loaded at the middle. Eq. (46) does not hold for stresses beyond the elastic hmit because the flexure formula no longer gives the true value of S. The resihence for this case may be computed approximately from K = —^^ , where Pi is the maxi- mum load. RESILIENCE 41 For beams with a uniform load the resiUence may be gotten by K=^iwdxy* (47) Here w is the load per unit of length, y is the deflection at any point and is expressed in terms of x, and the limits of integration include the entire beam. Thus for a simple beam with a uniform load '2iOEr 8SI For the value of y in the above, see eq. (/), Art. 29. Since wl^ = the resilience in terms of the unit stress on the outside fiber at the center of the beam is In all of these discussions the resilience due to shear has been neglected because of its small effect. 36. Resilience in Torsion. — Consider a homogeneous circular shaft held at one end and twisted by a couple, the magnitude of which increases to Pa without overstressing the shaft. Evidently the work of the couple is T^c = — J5-. Substituting in this equation 6 = ^rj, Mt = —^, and J = Ar(? — where ro = polar radius of gyration — we have ^-'-f-m^' («) 1 (S/ For a soUd round shaft K=-t -k-A.1. 4 iLs Zl. Resilience a Measure of Shock Resistance. — The magnitude or effect of a blow, or of a faUing body, is measured by the energy stored in the moving body at the instant of impact. In the case of a body which has fallen freely in space under the action of gravity, its energy is Wh, where W is the weight of the body, and h is the distance through which the body has fallen freely. In any translation, the energy of the body is -^r— , where v is the velocity, and g is the acceleration of gravity. If a 2fif moving body, as a faUing weight, is stopped by striking a fixed solid body, the energy of the moving body is spent in one or all of the following ways: * An alternative method of computing the resihence for such cases is afforded by the equation K= ) — dx where the variables are expressed in terms of z and the limits J EI of integration cover the entire beam. 42 SYNOPSIS OF THE PRINCIPLES OF MECHANICS (a) In deforming the moving body itself, either within or beyond its elastic limit. (6) In a local deformation of both bodies at the surface of contact, within or beyond the elastic limit. (c) In moving the fixed body as a whole, with an accelerated velocity, the resistance consisting of the inertia of the body. (d) In moving the fixed body against its external supports and resist- ances. (e) Finally, in deforming the fixed body as a whole against the resist- ing stresses developed thereby. If there is nearly absolute rigidity in all parts except in the body struck and if this yields only as a whole and not locally at the point of contact, then only can nearly all of the energy of the moving body be absorbed through deformation in the body struck. When the energy of the striking body is due principally to its mass ( measured by — 1 and only in small part to its velocity then 9C per cent or more of its energy may be absorbed by the body struck. Assuming that all the energy of a blow is absorbed by the body struck, then it becomes apparent that the work of deformation of that body must equal the energy of the blow. Studies of the relation- ships of resistance to deformation under impact, where the unit stresses have exceeded the elastic limit, have, in general, shown that a given deformation under impact is accompanied by a higher unit stress than in a static, or slowly appUed, loading. For the tests on soft iron wire illustrated in Fig. 23, the work of deformation in impact, as meas- ured by the area under the impact stress- deformation curve, is about 30 per cent greater than the corresponding value for static stresses. Likewise Russell * found that the average energy of rupture of cast- FiG. 23.— Comparison of Impact iron bars tested in his pendulum impact and Static Stresses when the machine (Fig. 18, Chapter II) was about 44 Deformations are the Same. . _t ji j, ,. , {Report of French Com., Vol. 2, P^^ ^^"^ S^^^t^r than the energy of rupture p. 344.) under gradually applied loads. When the stresses are within the elastic limit it has been customary to assume that the moduli of elasticity for static loadings hold for impact. It has also been customary to argue from the above * See Trans. Am. Soc. Civ. Engr., Vol. 39, p. 246. ,cU^ ^■""""^ •3 ^. .resses ^ 1 ^ :^ a/ 1 .05 .10 .15 .20 Proportionate Deformation o£ Wire RESILIENCE 43 considerations that the modulus of resilience gotten from a static test is a measure of resistance to repeated shocks or blows and that the total area of the stress-diagram (the energy of rupture) is a measure of resist- ance to a single blow. In other words these quantities are considered indexes of toughness. That these conclusions do not apply, however, to all heat-treated materials is evinced by the behavior of burnt steel. This material often exhibits about as high energy of rupture in a static test as properly treated material but is far less tough. (See also Art. 711.) A comprehensive study of the elastic portions of impact stress-defor- mation curves for our various building materials is badly needed in order that true value of the static modulus of resilience as an index of resist- ance to repeated shocks may be ascertained. If we assume all of the energy of the blow is absorbed by the body struck and that the modulus of elasticity is independent of the speed of loading, we have for the case of direct stress under axial elastic impact W{h+e)=^^Al (50) Here W = weight falUng, ^ = distance dropped, e = maximum deformation of body struck (the deformation will oscillate from a maximum to a mini- mum value as in a spring), /S = maximiun intensity of stress corresponding to deformation, £' = modulus of elasticity, A = area of cross-section, and i = length. Sinailarly for a beam under impact of a center load we shall have 1 r^ S^ ^^^+f^^hw'^' (^1) Here /=the maximum deflection and the other quantities have usual significance. When h in either of eqs. (51) or (52) is zero, namely when the load is suddenly apphed, it is easy to show that the maximum intensity of stress is twice that for a static load, W. It may also be shown that the deformation of a bar under axial elastic / 2/i\V2 impact is given by e = e'+e'll-\ — r) , where e' is the elongation due to a static load W and e that due to the impact load W. Similarly for trans- verse impact we have f=f'+f{l+-p-) , where /' is the deflection due to static W and / that due to impact of W. 44 SYNOPSIS OF THE PRINCIPLES OF MECHANICS MATERIALS UNDER COMBINED STRESS 38. Direct and Bending Stresses. — Consider the case o£ a simple beam under a transverse bending moment M and subjected to an eccentric end load P Ijdng in a principal axis, Fig. 24, for example. Consider the p p force P resolved into a force _i I — \-i-^p ri?! along the axis of the beam _Neutnii_ airfare -|^ 1- -j- - -1 g^jj^j g^ couplePc. Then the unit stress on the extreme fiber at the danger section is Fig. 24. given by S=^^f (52) Here M is the algebraic sum of the moments due to end loading (Pe) and transverse loadings taken on either side of the section, I is the moment of inertia of the cross-section about the axis 1-1, c the distance from 1-1 to the fiber considered, A the area of the cross-section. Unless the beam is long, deflection affects the moment arm of P but httle and is, there- fore, not considered in computing M. Equation (52) may also be used in designing short columns ( - < 100 1 which are eccentrically load. It then reduces to =l(l^^) (^3) Here r is the radius of gyration of the section about the principal axis which is normal to the lever arm of P. If P does not lie on a principal axis eq. (53) does not hold. The unit stress on any fiber is theij given by ^=i('+f +f) («> Where xi and yi are the coordinates of the appUcation point of the load (P) with respect to the principal axes (the x-axis and the y-axes), x and y are the coordinates of the fiber with unit stress S, Ix and 7^ are the j)rin- cipal moments of inertia with respect to the x and y axes, respectively. Due account of the signs of x,xi,y and j/i must be taken in using eq. (54). 39. Shears and Direct Stress. — One of the most common cases of combined stress is direct stress with pairs of equal shears perpendicular and parallel to it. Let Fig. 25(a) represent the side elevation of an elementary rectangular parallelopiped, the thickness perpendicular to the paper being unity and the width and height dx and dy, respectively. Let MATERIALS UNDER COMBINED STRESS 45 the intensity of the direct stress be S and that of the shears Ss each. Then it is evident that on any obhque plane cutting the parallelepiped the total stress equals the resultant of Sdy, Ssdx, and Ssdy. Consider the total stress on the plane AC to be resolved into normal and tangential components, Sndz and Spdz, respectively, see Fig. 25(6). We want to find the value of S„ and Sj, in terms of S and Ss and then by rotating the plane AC (allowing d to vary), determine the maximum values for these Sdi ti ^ OS"* c to ^y' .^"f .. s A hi S.dx («) ->%dy Fig. 25. stresses. Resolving the forces on CI> and AB in Fig. 25(&) along AC dv dx and perpendicular to it, substituting sin d=-r, cos S=-j-, and reducing. we have Sj, = ^sm2d+SsCos2e, 'S„ = ^(l-cos 26i)++(f)^ (57) -Sn^liV-S.^+^f)' (58) When the plus sign is used in eq. (58) the magnitude of the maximum unit stress of the same kind as S is found. If the minus sign is used, the minimum normal unit stress is found; but a negative sign obtains for the entire result indicating that the stress thus gotten is of opposite kind to S. These maximum and minimum values of Sn occur at the same point on mutually perpendicular planes. There is no shear stress on either of these planes. 46 SYNOPSIS OF THE PRINCIPLES OF MECHANICS The unit deformation in the direction of max. Sn will be increased by the lateral deformation of min. Sn acting at right angles to the maximum value (see Art. 5, and 6) or e„= — ^ — ^+X — ^— ^. Where e„ is the unit deformation along maximum Sn and X is Poisson's ratio. Substituting values of Sn from eq. (58) and changing sign of min. Sn, there results en = -^{l-\) + {l+\)\ls?+{^^ (59) If X = J, a fair mean for metals, then For analyzing the internal stresses in beams and shafting eq. (57) and (58) are much used. In beams the horizontal and vertical shearing stresses provide the Sdx and S,dy forces of Fig. 25 and the flexure stresses make up the Sdy forces. In horizontal shafts the torsional shears in planes tangent to the shaft provide the pairs of shearing forces, and the stresses due to bending again introduce the normal forces. In vertical shafts the normal stress may be due to both direct stress (from the weight of the shaft) and lateral bending. 40. Biaxial Loading. — Fig. 26 shows an elementary parallelopiped , of unit thickness under two pairs of mutually I perpendicular tensile stresses. The following dx analysis with proper regard to sign holds, in general, whether both pairs of stresses are of like kind or not. We wish to find the value of the normal (S„) and tangential gf (*Sj,) unit stresses on any plane such as AC. Pjq 26 • Resolving Sdy and S'dx parallel to .4C and perpendicular to it and substituting sin 9 = —- and cos B = -r there is obtained dz dz S, = ^^sm2d, (61) S„ = S siii^ 6+ S' cos^ 9 '(62) When 5 = 45° Sp = — ^ — • Note, however, that for this case the greatest value of Sj, = -, if S>Ss. This stress occurs in a plane parallel to S' and making an angle of 45° with S. S„ is a maximum when = 90° if S>S'; when = 0° if ^! (S' ) reached the shearing elastic limit before the maximum unit strain e„ reached its critical value, then failure was conditioned by the maximum shear theory. The two limiting conditions for biaxial tensions are q C/ 1 given by €„' = -g;— X^ and Sp' = ^S, where a„' = maximum unit elastic deformation which material can withstand and >Sj,' = shearing elastic hmit. * See accounts of researches by J. J. Guest, PM. Mag., July, 1900; W. A. Scoble, ThU. Mag., Vol. 12, 1906, p. 583; E. S. Hancock, Proc. A.S.T.M., Vol. 5, p. 179; Vol. 6, p. 295; A. J. Becker, Bulletin No. 85, Univ. of Illinois Expt. Sta. Also see Art. 726. 48 SYNOPSIS OF THE PRINCIPLES OF MECHANICS That the theory advanced by Becker holds for brittle materials cannot be asserted in the present state of our knowledge. For the present it seems safe in designing or investigating members under combined stresses to determine both maximum S„ and Sp and see that neither exceeds the respective allowable working unit stress for the material. CHAPTER II MACHINES AND APPLIANCES FOR MECHANICAL T'iJSTS TESTING MACHINES 42. Definition. — Since it would be obviously impossible to break, or even deform considerably large specimens of strong material by the imposition of dead weights, a mechanical device called a testing machine is employed for this purpose. A testing machine may be said to consist of a base or frame which supports the crossheads used in loading the specimen, a means for applying the load, and a device for measuring it. Universal Testing Machines 43, Classes of Universal Testing Machines. — Universal testing machines— those in which tension, compression or cross-bending tests can be made — are provided with at least one fixed crosshead against which the specimen rests and a movable crosshead by means of which the specimen is deformed. In accordance with the method employed to drive the movable crosshead, such machines may be divided into two classes, hydraulic machines and screw-gear machines. In American laboratories most of the testing machines of less than 600,000-lb. capacity are of the latter type. Many of the larger testing machines, however, are of the hydrauUc type. With the exception of the Emery testing machine, which belongs in a class by itself, the chief advantages of hydrauUc testing machines are freedom from vibration and noise, cheapness, and simplicity of construc- tion and operation. On the other hand, most of the testing machines of this type have one or more of the following disadvantages: leakage of fluid, variable friction at the stuffing boxes and around the ram, or inac- curate means of measuring fluid pressures. * In American screw-gear testing machines the load is generally reduced by a system of compound levers and weighed by balancing with a poise which is moved along a graduated scalebeam. In general these machines * The University of Wisconsin has a 600,000-lb. universal hydraulic testing machine designed and erected by the instructional staff. As a result of calibrations the probable error of results gotten from this machine is not over 2 or 3 per cent for loads above 50,000 lb. The machine cost $3500. (See Proc. of Am. Soc. for Testing Materials, VoL 10, p. 551.) 49 50 MACHINES AND APPLIANCES FOR MECHANICAL TESTS may be made very sensitive and accurate, but when built in large capaci- ties are more expensive than those of the hydraulic type. Owing to the vibration and noise produced by the driving mechanism employed in screw-gear machines, hand power is necessitated when very sensitive apparatus is used to measure deformations. Testing machines are often called horizontal or vertical in accordance with the position in which a tension or compression specimen is held. The advantage of the former type hes in the accessibility of all parts of machine and specimen. In vertical testing machines, however, lateral bending due to the weight of the specimen is obviated. 44. General Conditions which Should Obtainin Universal Machines. — The following considerations apply to testing machines in general: 1. The weighing apparatus should be quite independent of the loading apparatus, the former usually being fixed and the latter movable. 2. In lever machines the length of the knife-edges must be proportioned to the maximum loads in order not to be crushed down, and they should be so placed that all will receive their share of the load. They must also be so mounted as not to change the leverage by any reaction displacement which may occur. To insure this, the knife-edges must be attached to the levers, and the bearings to the platform. Clearance between knife-edge bearings and levers must be sufficient to insure against frictional resistances, which greatly impair sensitiveness. 3. The knife-edges and bearings of any beam must lie in the same straight hne, and this line should lie in the gravity axis of th beam and its rigid attachments. This is especially necessary for the weighing-beam itself, so that its vertical angular movement may not disturb the counter- balancing. If the poise is moved by a cord over a pair of pulleys, this cord should be attached to the poise-hanger in this same axial hne, so that the pulling of the poise may not supply a leverage on the beam to raise or lower it. 4. Manometer machines have many pecuUar errors. For example, any air-bubble in the indicating liquid vitiates the results by its own change in volume under pressure. Again, the exact area of surface sub- jected to pressure is always uncertain. 5. The weighing apparatus should be so constructed as to be readily verified by the imposition of known weights, and the parts should be*open to inspection and easily repaired and kept in order. 6. A precision of 1 in 250 has been considered sufficient.* This is a proportional error of 0.4 of 1 per cent. Also, the imposition of a load equal to one-two-hundred-fiftieth of that on the machine should produce an appreciable indication on the weighing device. * This standard is given by the French Commission and has been accepted by the Am. Soc. for Testing Materials (see Standards, 1916). TESTING MACHINES 51 7. The loading should proceed gradually and uniformly, and not by sudden increments as by large pump-pulsations, or by the adding of overweights by hand to the weighing-beam. The rate of loading should also be under perfect control. 8. The machine should be so constructed as to permit the free use of apphances for measuring distortion of the specimen by some suitable device. 9. For compression tests the speeds of the pulling head should not be over one-tenth or one-twentieth of an inch per min. Pig. 1. — Olsen's Automatic Universal Testing Machine with Direct Motor Drive. 10. The axes of the jaws in the crossheads of the machine should be so placed that they will remain in hne throughout any test provided that the specimen is properly centered in them. 11. There must be no twisting or rocking of the movable head when in motion. 45. Olsen Testing Machines. — The Olsen screw-gear machine shown in Fig. 1, affords a good illustration of the universal machines common to American laboratories. Machines similar to this are built in capaci- ties from 30,000 to 400,000 lb.; others embodying similar principles are built in capacities up to 1,000,000 lb. Power is applied to the machine illustrated through a direct connected motor attached in the rear as shown. 52 MACHINES AND APPLIANCES FOR MECHANICAL TESTS The main shaft (1) transmits power to the gear (2) which, through a shaft and system of gearing, rotates four straining nuts. Each of these straining nuts bears against the underside of the bed plate of the machine (9) and revolves about one of the four vertical screws which are rigidly fastened to the pulling head (5). In ths manner an upward or downward translation may be imparted to the screws and pulling head. A wide range in the rate of mo- tion of the puUing head may be secured by means of the clutch levers (3) and (4). The pull on the specimen (6), which is held in the jaws of the cross- heads by means of grooved wedges or liners, is transmitted downward through the four cast- iron columns (7) to the weighing table (8). The reaction of the straining nuts on the lower end of the screws produces an eqiial upward force beneath the bed plate (9). The weighing table is supported on knife-edges fas- tened in the compound levers (10) and (11), which in tm-n are pivoted on pedestals formed on the bed plate (9); a closed cir- cuit of forces is thus produced. The force on the weighing table is reduced by the levers (10), (11), (12) and balanced by the poise (13) on the scalebeam. The poise (13) is driven by a screw running along the top of the scalebeam. The operator may drive the poise by hand through the wheel (14) qf the motion of the poise may be automatically controlled by the variable speed cone drive (15) which is connected to the driving mechanism on the machine and drives the poise to the right as long as the scalebeam is up. When the beam drops an electric circuit is broken and the poise stops. The load in thousand-pound units or multiples thereof may be gotten from the graduations on the scale beam. Inter- mediate values of the load are read on the dial (16) which is driven by Fig. 2.— a 10,000-lb. Wire-testing Machine. TESTING MACHINES 53 the screw actuating the poise. When a specimen breaks some means must be provided for dissipating the stored energy or serious injury may be done to the knife-edges. Such dissipation of energy is often accom- pUshed by providing long bolts equipped with cushion-seated nuts called recoil buffers (17). Compression tests are made by attaching a compression-block to the lower side of the movable crosshead, and inserting the specimen between it and the weighing table (8). The machine is arranged for cross-breaking tests by placing end bearings on the weighing table (or on an I-beam resting on this table Fig. 3. — ^A Two-screw Universal Testing Machine. if the specimen is long), and attaching a knife-edge bearing to the under side of the moving crosshead. For testing small specimens hand power machines of the type shown in Fig. 2 have proyen very serviceable. These machines are made in capacities ranging from 10,000 to 20,000 lb. 46. Riehle Testing Machines. — An equally well-known American type of testing machine is that manufactured by Riehle Bros. Fig. 3 illus- trates a two-screw, 100,000-lb. automatic and autographic Riehl4 uni- versal testing machine. The main difference in Olsen and Riehle testing machines lies in the method of moving the pulling head. In the Riehle 54 MACHINES AND APPLIANCES FOR MECHANICAL TESTS type the screws revolve in nuts in the pulling head. The main advantage claimed for a two-screw machine is the accessibility of the specimen. This advantage is partially offset by the care which must be exercised in centering compression or transverse specimens to avoid bending the screws. 47. The Emery Testing Machine. — The Emery method of weighing loads is generally considered the most sensitive yet devised. The essential principle of this machine consists in a means of trans- mitting a definite percentage of the force applied to the specimen to the scale beams, and there weighing it accurately, without any friction whatever in the receiving, transmitting, or weighing parts. Hence any very small increment of the force applied is weighed with equal accu- racy, whether this increment is added to a great or to a small previous load. * This is accomplished by means of an hydraulic leverage and through the use of pteel plate fulcra instead of knife-edges. Thus, in Fig. 4, Fig. 4. — A'Schematic Drawing Showing a Side Elevation of an Emery Testing Machine. which is merely a schematic drawing, the load from the ram (1) is trans- mitted through the specimen (2) to the yoke (4), which rests against the hydraulic support (5). A .pressure of equal intensity to that pro- duced upon the liquid in the hydraulic support is transmitted to the hydraulic chamber. In principle, an hydraulic support or chamber con- sists of a very strong shallow nietal cylinder covered by a thin diaphragm or of a plate with a thin diaphragm around the edge. The diaphragm permits a slight movement of the cover without leakage of the fluid. The total force acting against the top of the chamber (7) is to tha force in the specimen as the effective area of the chamber top is to the effective area of the hydraulic support. The force on the chamber top is bal- anced by levers articulating elastically alDOut thin steel plate fulcra (8) * When the first machine was tested, a steel bar 5 in. in diameter was first broken under a load of 722,800 lb., and then a single horse-hair was tested, and the machine gave the strength (16 oz.) of this as accurately as a small spring-balance which was used for a check. Rep. U. S. Test Board, Vol. 2, p. 1. TESTING MACHINES 55 and (9). In an actual machine there are several levers intermediate between the chamber lever and the scalebeam, but for simplicity only one lever is here shown. The hydraulic chamber and levers are inclosed in a glass case to prevent injury. Such confinement does not interfere with the operation of the scalebeam, since a device is employed by which imposition of the poise weights upon the spindles (10) and (11), can be made from outside of the case. The poise weights are generally gold plated to prevent corrosion. To accommodate specimens varying in length the straining head carrying the ram can be moved along the screws (14) by means of the power-driven nuts (15). In making compression tests bearing blocks are placed over the jaws (3), and the hydraulic support (6) is brought to bear against the vertical beam (16) ; valve (12) is closed and valve (13) opened. When machines of this type are cahbrated, allowance is made for the forces required to bend the plate fulcra, and the ratio of the effective area of the hydraulic support to the effective area of the hydraulic chamber is also determined. Since the movement of fluid from the hydrauUc support to the hydrauhc chamber is neghgible the uncertain element, friction, is not present in this weighing system. The largest machine of the Emery type ever built is installed at the Washington Laboratory, of the U. S. Bureau of Standards. This machine has a capacity of 2,300,000 lb. in compression and 1,150,000 lb. in ten- sion. Compression tests can be made in this machine on specimens 33 ft. long.* Compression Testing Machines 48. A Field for the Hydraulic Press. — To ascertain the com- pressive strengths of materials like concrete, stone, brick, and tile, a machine of great precision is not required. For work of this character an hydraulic press provided with an accurate gage for registering the fluid pressure in the ram has been found satisfactory. The chief sources of inaccuracy in the hydrauUc press are the varia- bility of the friction between the piston and cylinder and at the stuffing box. In a well-designed press, however, these variations will be very small and may be neglected in rough work; or an average correction for friction may be made by cahbrating the press with the packing tight and loose. A great variety of testing machines of this type are in use in this country; two will be briefly described. 49. A Machine for Testing in the Field.— A simple and handy form of press for testing small specimens is shown in Fig. 5. This press has a capacity of 60,000 lb.; the lower platen is 8 in. square and the max- *For further information regarding this Emery Machine the reader is referred to American Machinist, Jan. 2, 1913, p. 1; Jan. 9, 1913, p. 50. 56 MACHINES AND APPLIANCES FOR MECHANICAL TESTS imum available height is 8 in. Rapid adjustment of the ram may be secured by the lever at the left. The extensible lever at the right is Fig. 5. — A 30-t.on Hydraulic Press for Crushing Sroall Cubes of Concrete or Stone. Fig. 6. — The Largest Testing Machine in the World. Located at the Pittsburg Laboratory of the U. S. Bureau of Standards. used to load the specimen. The total weight of the press is 425 lb. Presses of this type are especially adapted for work in the field. TESTING MACHINES 57 50. The World's Largest Testing Machine. — In Fig. 6 is shown the 10,000,000-lb. compression machine built by Tinius Olsen & Co, for the Pittsburg Laboratory of the U. S. Bureau of Standards. This machine in its present condition can be used to test specimens less than 25 ft. long and 4 by 4 ft. square within the capacity of the machine. The four screws are each 13| in. in diameter. Connected to the screws by long power-driven nuts is the adjustable upper head, weighing 30 tons. The spherical-seated lower head of the same weight is mounted upon the end of the ram of a huge hydraulic press, not shown in the illus- tration. To obviate uncertainty regarding frictional forces, the packing employed in this ram is so designed that these forces will vary directly with the pressure,, a condition for which due allowance is made in the calibration. The intensity of the fluid pressure in the ram is transferred to a smaller hydraulic chamber which is sealed with a diaphragm and supported on the pump well. The pressure on the diaphragm is balanced through the lever system and screw-driven poise. The scale- beam is graduated to read loads on the specimen up to 2,000,000 lb. directly, and with end weights up to the capacity of the machine. Fluid pressure is suppUed to the ram by means of a triple-plunger variable- stroke pump driven by a 15-h.p. variable-speed motor. This combina- tion makes possible a considerable range in the speed of the lower head of the testing machine when desired. An air reservoir inserted in the supply line leading from the pump to the ram reduces the effects of the pulsations of the pump.* Transverse Testing Machines 51. General Remarks on Transverse Testing Machines. — On account of the large amount of testing done upon beams, it is often convenient to have machines especially adapted for transverse testing. The main conditions, other than those previously mentioned in Art. 44, which should be fulfilled by a transverse testing machine are : ' 1. The parts of the machine should be sufficiently rigid so that the tops of the knife-edges supporting the beam and the bottom of the load- ing knife-edge will remain perpendicular to the sides of the beam through- out the test. 2. The supporting and loading knife-edges should, if necessary, bear upon auxiliary plates to prevent indentation. Also, these knife-edges should be so arranged that longitudinal tension in the specimen due to their rigidity is obviated. (See Art. 74.) 3. The machine should be equipped with a variety of slow speeds by which loads may be uniformly applied to the specimen at a rate which will permit the necessary observations to be made. * This machine is described in the Eng. Record, Sept. 28, 1912, p. 353. 58 MACHINES AND APPLIANCES FOB MECHANICAL TESTS 52. Descriptions of Various Transverse Testing Machines. — Fig. 7 shows a 100,000-lb. Riehle hydraulic transverse testing machine. By means of the valve operated by the hand wheel at the center of the Fig. 7.— a 100,000-lb. Hydraulic Beam-testing Machine. machine fluid from the pump can be forced into either end of the double- acting ram, which moves the loading knife-edge. The support at the left end and the weighing apparatus at the right may be adjusted to spans varying from 4 to 20 ft. To conserve space it will be found advan- FiG. 8. — Johnson's Beam-testing Machine. tageous to install this type of machine with the tops of the I-beams flush with the floor. In Fig. 8 is shown a convenient device for testing small timber or concrete beams. The micrometer-screw deflectometer reading to 0.001 TESTING MACHINES 59 in., is used to measure the movement of the center bearing with respect to the end supports. If due care is taken to prevent crushing at the bearing surfaces, the deflection will be equal to the movement registered by the micrometer-screw. Another form of transverse testing machine, much used in foundry- work, is that shown in Fig. 9. In this machine the deflection is indi- cated on the graduated arc by means of an ingenious lever system not Fig. 9. — Cross-bending Testing-machine for Cast Iron. Deflection correctly measured. shown in the figure. The capacity is 5000 lb., and the length of span 1ft. Fig. 10 shows a transverse testing machine which records the load- deflection curve upon a specially ruled diagram. Imposition of the load is made through the hand wheel at the top. The load on the speci- men actuates a system of levers which move the heavy pendulum along the graduated arc, shown beneath the frame. This motion produces a rotation of the drum. Through a follow pin placed at the center of the span directly under the specimen, a record of the deflection is gotten. 60 MACHINES AND APPLIANCES FOR MECHANICAL TESTS The movement of this pin multiplied tweiity times is transmitted to the pencil which moves vertically. Thus abscissas on the diagram measure loads and ordinates deflections. The machine is built for 12- or 24-in. spans. The capacity is 5000 lb. Cold-bend Testing Machines 53. Methods of Making the Test. — Up to this time, only machines in which the bending is accomplished by static pres- sure have been especially made for cold-bend tests. The power hammer is ordinarily employed when bending is accomphshed Fig. 10. — Olsen's Autographic Cross-bending Machine. by blows. The latter method is subject to much wider varia- tions than the pressure method, but properly made is a more severe test than the former. 54. A Cold-bend Attach- ment. — A bending attachment made by Riehl^ Bros, for use in universal testing machines is shown in Fig. 11. The upper tool, which is clamped in the pulling head of the machine, carries the pin around which the specimen is to be bent. The lower tool is supported on the weighing table and is provided with two adjustable brackets. Before performing a test these brackets are properly spaced to allow clearance for the pin and twice the depth of the specimen. Pins of different sizes are provided with the attachment. The appliance illustrated will bend bars up to IJ in. square through 180 deg. Fig. 11. — A Bending Attachment.i TESTING MACHINES 61 56. Olsen's Cold-bending Testing Machine. — Fig. 12 represents a motor-driven cold-bend testing machine which will bend rods up to 2 in. in diameter or plates less than 6 in. wide. The specimen is held firmly by a wedge be- hind the left end, an adjustable vertical center pin, and an ad- justable vertical pin placed back of the right end. The latter pin bends the specimen. By means of graduations on the table of the machine any bend up to 180 deg. may be determined The wire grating prevents injury to the operator through a sudden break of the specimen, but permits the making of observations during testing. Shear and Toesion Testing Machines • 56. Transverse Shear Test Appliances. — Although it is im- possible to produce in a body a transverse shearing stress un- accompanied by tension or compression, yet, on account of the fre- quent occurrence of shearing stresses in members subjected to cross- bending — ^in rivets, bolts, pins, etc. — and on account of the weakness of timber in shearing along the grain, it is often desirable to obtain an approximate knowledge of the shearing strength of a material. Several devices have been employed for this purpose; two will be briefly described. In' Fig. 13 is shown a double shear apparatus designed to determine the shearing strength of metals. With this appliance the end and central portions of the specimen are tightly gripped by hardened steel bearing plates which minimize bending distortion. However, on account of the small clearance between the central and end portions of the device, some frictional resistance is developed in testing. A comparison of the results of shearing tests on this apparatus with values gotten from torsion tests of very thin cylinders of like material indicates that the shearing device gives about 10 per cent higher unit stresses. The bars used in these tests were uniform in size. Grooving the bars in the planes of shearing would undoubtedly have lessened the error. Fig. 12. — Olsen's Improved Cold-bending Machine. 62 MACHINES AND APPLIANCES FOR MECHANICAL TESTS Fig. 13. — Johnson's Shear Tool. A simple and satisfactory apparatus for maldng shearing tests on timber is shown in Fig. 14. ' 57. Torsion Testing Machines. — Shafting, wire, and elements of machines which are to b§ subjected to twisting are often tested in tor- sion to determine their torsional strength and shearing modulus of elas- ticity. Fig. 15 shows an Olsen 230,000-lb. torsion testing machine. This machine will take shafting up to 2^ in. in diameter and 22 ft. long. The motor, operating through a chain drive and train of gears rotates a large gear carrying the chuck into which the right end of the specimen is securely fastened. The left end of the shaft is gripped by a similai* chuck and transmits the twist to the lever system in the weighing iTead. To allow for longitudinal deformation of the specimen under test, the main lever of the weighing system is mounted on rollers, thus permitting considerable horizontal motion of the chuck. The lever shown at the left is employed to adjust the position of the weighing head on the rails. A very perfect machine for testing wires from 0.05 in. to 0.18 in. in diameter (No. 18 to No. 7 B. W. G.) and for giving (a) the breaking moment, (h) the number of turns, and (c) the complete stress-diagram. TESTING MACHINES 63 Fig. 14. — Shear Test Apparatus Used at the Forest Products Laboratory. Specimen is cut with a projecting shoulder. (Paper by Betts and Greeley at Int. Engr. Congress, 1915.) Fig. 15. — Olsen's Improved Torsion Testing Machine. 64 MACHINES AND APPLIANCES FOB MECHANICAL TESTS is shown in Fig. 16.* This machine was used by Prof. Tetmajer and described by him in Vol. 4 of his Communications. The specimen is kept in tension during the test by a weight suspended by a cord con- FiG. 16. — Tetmajer's Torsion-testing Machine for Wires, giving Autographic Records. nected to the carriage at the resisting (and recording) end of the speci- men. The resisting moment is developed by means of two weights suspended by cords which run in symmetrically arranged spiral grooves. Fig. 17.— a Riehl6 Wire Tw'ister. A simple wire' twisting machine without recording apparatus is shown in Fig. 17. * Made by Messrs. Amsler-Laffon & Sons, Schaffhausen, Switzerland. TESTING MACHINES 65 Impact Testing Machines 58. Essential Conditions for Impact Testing Machines. — Since im- pact tests are made upon car wheels, car-couplers, car-axles, rails and rail joints to determine the resistance of such structural forms to shock, it is very necessary that the machine in which the tests are made shall be so constructed that the energy absorbed by the specimen can be determined. Inasmuch as the effect of a blow on the specimen depends upon the resistance of the specimen as well as the energy and mass of the falling body, it follows that a standard impact test involves a standard anvil resting upon a standard founda- tion, a standard hammer or tup, and a standard fall. Furthermore, in drop machines the axes of the tup, guides, anvil and specimen must be coUinear; and the faces of the specimen, anvil, and tup must be parallel. On account of the im- possibility of providing either an absolutely rigid anvil or tup, true quantitative results can- not be gotten. However, qualitative results of great value may be gotten from standardized tests. In practically all impact testing machines a transverse blow is delivered to the specimen either by a pendulum revolving about a horizontal axis or by a falling weight. 59. A Pendulum Impact Testing Machine. — ^A good representative of this type of impact machine is shown in Fig. 18. The two knife-edge .supports for the specimen are separated by a free passage for the pen- dulum, so that by raising higher than necessary to break the specimen on the first blow, the energy left in the pendulum carries it past the Fig. 18. — Russel's Impact Testing Machine. MACHINES AND APPLIANCES FOR MECHANICAL TESTS vertical position. By registering, or observing in any suitable manner, the final forward position of the pendulum after passing the broken specimen the residual energy left over after rupture becomes known. This, subtracted from the potential energy due to the initial position of the pendulum, after making due allowance for the working resistance to motion, leaves the amount of energy absorbed by the specimen. The specimen supports are massive, and are firmly bedded upon a large body of concrete, so that they are very rigid. The center of percussion of the pendulum is carefully determined and the speci- men placed at this point with the pendulum hang ing vertically, the pivot- blocks being adjustable. The working resistance to motion is made as small as possible. The pendulum itseK should rest on knife- edge bearings and should be a heavy flat bar, swing- ing edgewise, as here shown, to reduce the air resistance. The registering apparatus necessarily has some re- sistance, but all these can be evaluated by swinging the pendulum freely and noting the loss of energy for a single passage. 60. Drop Impact Test- ing Machines. — Fig, 19 illustrates a Turner impact testing machine for either compression or transverse impact tests. In this machine the tup is hoisted by an electric motor placed at the top. Release of the tup is secured by reversing the current through the suspending magnet. A pencil moving over paper fastened to the revolving drum, shown just above the specimen, records the behavior of the specimen. Two sizes of this machine are made, the larger having Fig. 19. — A Turner Impact Testing Machine. TESTING MACHINES 67 Standard Drop Testing Machine. As ADOOTto ev CowWiTTEt O^ Rah. M*NuPACTuoEPS or tme United States 'irl^'rimberi aill'tor^— Hal* Siae Cievation ■ Ma'f SeCon r/trou^f' Center t»tf CM £le¥at-o». 'Moif Sece.on through Cfi/er. . Fig. 20.— Standard Drop Testing Machine for Rails 68 MACHINES AND APPLIANCES FOR MECHANICAL TESTS a capacity for beams 8 ft. long and 12 in. wide; the maximum drop attainable is 6 ft., and the weights of tup range from 50 to 500 lb. With this type of machine tests can be made to ascertain the elastic prop- erties in addition to the energy of rupture of a specimen. In Fig. 20 is presented a drawing of the standard drop testing ma- chine adopted by the American Railway Engineering Association for making tests on rails. A noteworthy fact about this machine is the method of supporting the anvil. The latter weighs 20,000 lb., and is supported on 20 M. C. B. A. Standard " C " springs arranged in groups of five at each corner of the anvil. No connection exists betwe'en the vertical guides and the anvil. For further information relating to this machine see The Manual of the A. R. E. A. Apparatus foe Determining Hardness 61. The Sclerometer. — The scratch test has long been in use by the mineralogist to compare the relative hardness of minerals.* On account of the variability of the miner- alogist's standard it is not satisfactory for the user of metals. Turner's scler- ometer or a modification of it has often been employed by technologists to abrade metals. In this device a diamond point is fixed at the base of a vertical pencil which is carried by a perfectly balanced arm. Provision is made for loading and moving the arm. The weight required to cause the diamond point to visibly scratch the surface of the specimen is taken as an indication of the hardness. Martens in using this apparatus deter- mined hardness by measuring the width of scratch made under a constant load. The method is open to objection on account of the impossibility of grinding the diamond to a standard form. 62. The Brinell Ball Indentation Test. — A great many methods of determining the resistance of materials to indentation have been tried. Among the more note- worthy of these may be mentioned the punch used by Rodman, the knife-edge employed by Unwin, the cone * See Mohs' scale in Art. 252. Pig. 21. — Olsen's Apparatus for Making the Brinell Hardness Test. Cylindrical Hard Steel- Block Recessed lor Brinell Ball T TESTING MACHINES 69 adopted by Ludwik, the ball perfected by Brinell, and the scleroscope invented by Shore. In Fig. 21 is shown a common form of apparatus used by the fol- lowers of Brinell. The specimen is first made smooth and plane at the impression spot. It is then placed on the table (1) and raised until it touches the hardened steel ball (2). The latter is hung on the piston of an hydraulic ram which is used to load the specimen. In order to secure an accurate indication of the test pressure, the ram is provided with an accumulator loaded with dead weights (3). The latter rise when the desired pressure has been imposed upon the test-piece. Fig. 22 shows an inexpensive appa- . ^ ratus for making the test which may be inserted in any compression testing machine. The ball generally used in this test is 10 mm. in diameter, and the pressure most frequently employed for iron or steel is 3000 kg. Brinell determines hard- specimen ness upon the following basis. If the load in kilograms is divided by the area of the indented surface expressed in square millimeters, the average intensity of the ^^°- ^^- Auxiliary pressure is determined. These intensities are called ,, „ . \ „^ ™^ 51 . „, , , _ , . . , . , the Brinell Test m Brinell s hardness numbers. In determmmg the inden- ^ Universal Test- tation the common practice has been to measure the ing Machine, impression left in the specimen by means of an espe- cially constructed microscope (4). A much better method adopted by Devries of the U. S. Bureau of Standards follows. By means of a microscope which is sighted upon a mark on the plunger the operator measures the indentation under a very light initial load, applies the test pressure, and again reads the indentation under' the initial load. The difference between initial and final readings gives the correct indentation. Devries also found that a linear relation existed between load and depth of indentation for pressures less than 3000 kg.* 63. The Shore Scleroscope. f — In this apparatus the specimen is struck by a small diamond-pointed hammer faUing freely from a height of about 10 in. The rebound of the hammer is measured and gives an indication, according to its inventor, of the resistance to indentation or hardness. Fig. 23 shows the scleroscope. The essential features of the instrument are an accurately ground vertical glass tube placed in front of a scale graduated into 140 equal parts, a diamond-pointed hammer within the tube, and a vertical rod which is employed to plumb the apparatus. The hammer can be raised and suspended at the top. of tube by producing a partial' vacuum with the bulb. By again squeezing * Proc. Am. Soc. for Test. Materials, Vol. 11, 1911, p. 709. t Manufactured by Shore Instrument and Mfg. Co., 226 W. 24th St., N. Y. 70 MACHINES AND APPLIANCES FOB MECHANICAL TESTS the bulb a sufficient amount of air is admitted to the tube to release the hammer without giving it initial velocity. The height to which the hammer rises after striking the specimen is noted by the eye. Since slight differences in the sharpness of hammer points greatly affect the rebound, the hammer must be frequently tested on a standard surface. The surface ordinarily used is of hardened steel which gives a rebound of 100 on the scale. Endurance Testing Machines 64. Wohler's Repeated-stress Testing Ma- chines. — Owing to value and importance of the systematic studies of Wohler upon the fatigue of metals, his appliances have received con- siderable attention. Fig. 24 shows his appa- ratus for repeated tensile stresses. Here the specimen {A) is stressed through the lever (L) and spring (s) acting on the auxiliary lever (m). The pull of the spring (s) is measured by the starting of the adjusted calibrated spring (s') through the terminal lever ((/). The nut at the od (d) is adjusted to give the minimum load on the spring (s) by starting the spring (s') when adjusted to a particular tension, and the cam movement of (d) to its extreme downward position is made to give the requisite maximum stress in the specimen by adjusting the Fig. 23.— Shore's Sclero- scope. Fig. 24.- — Wohler's Machine for Repetitions of Tensile Stress. spring (s') so as to just lift at this position of (d). The rod is adjustable by means of a turnbuckle. In this way the bar (A) can be stressed TESTING MACHINES 71 in tension between any chosen limits. Wohler also designed special de- vices for repeating bending stresses and for repeating torsional stresses. * 65. The White-Souther Endurance Testing Machine. — In Fig. 25 is shown a more recent device than those of Wohler for imposing a re- peated bending stress. The speci- men (BB) is wedged firmly in ' ,, '" "^ " i the revolving pulley (A) by ta- pered liners, thus forming a can- tilever on either side of the pulley. The loads are suspended on the rods (EE) which are supported by the bearings (DD) resting on the specimen. Speed counters (CC) are provided to indicate the number of revolutions made by each end of the specimen before rupture. The customary speed used on the machine is 1300 r.p.m. This apparatus takes a specially formed specimen about 14 in. long. The portion of the shaft within the pulley is f in. in diameter; the portion subjected to maximum stress has a diameter of | in. 66. Kommers Repeated-stress Testing Machine. — The repeated stress testing machine shown in Fig. 26 was designed by Prof. J. B. Kommers and built at the University of Wisconsin. The test consists of deflecting the specimen A on either side of the vertical position by means of the slider C, the number of cycles of stress for rupture being automatically recorded. It is possible to set the machine so that the specimen may be stressed within or beyond the elastic limit. When adjusted for the latter condition the machine works to best advantage. The lever B is ordinarily not attached to the machine. It is for the purpose of measuring the load re'quired to produce a given deflection. Slider C has mounted on it two auxiliary sliders D, which are accu- rately located by micrometers reading to 0.001 in. The sUders D carry hardened steel blocks which deflect the specimen. If these blocks are * See Engineering, Vol. 11, p. 199, 221, 224, etc. FiQ. 25. — A White-Souther Endurance Testing Machine. 72 MACHINES AND APPLIANCES FOR MECHANICAL TESTS moved farther apart than the diameter of the specimen, a shght amount of impact is given the test-piece. A scale mounted on the frame at E and a vernier mounted on the slider C permits the measurement of the stroke, and also the setting of the slider exactly at the middle of its stroke with an accuracy of 0.002 in. For most tests a true cylindrical specimen f in. in diameter and 9 in. long is used, a test being made on both ends. The length under test is 4 in.; although it is possible by inserting blocks at K, to obtain a longer length. The hardened steel grip- ' il A / ^ .-n' B Fig. 26. — Kommers' Repeated-stress Testing Machine. ping blocks H can be removed and others inserted so that forms other than rounds may be tested. The crank pin F may be roughly adjusted to give the desired stroke^ by means of a pointer and scale at G; more accurately by the scale E. In testing, the machine is adjusted to give the desired deflection and impact. A specimen is then inserted and the flywheel F is started by a motor. When full speed is reached the test is begim by throwing a clutch at the end of the flywheel shaft. A lever which holds the end and of the specimen after rupture and also stops the counter automatically has been designed, but is not shown in the figure. AUXILIARY APPLIANCES EMPLOYED IN LOADING SPECIMENS 67. The Transmission of Load to a Specimen. — In making tests of materials it is very desirable that the experimenter have control not only of the magnitude but also of the places of application and the direc- tions of the forces applied to the specimen. Unless such conditions AUXILIARY APPLIANCES EMPLOYED IN LOADING SPECIMENS 73 obtain stresses of a different kind or of undesirable magnitude may be produced in the test-piece. In most tension and compression tests an axial load is sought; in most transverse tests a loading which pro- duces bending in a given plane is desired. On account of the devices employed to transmit pressure from the testing machine to the specimen, a brief description of some of these appliances will not be given. Gripping Devices foe Tension Tests 68. Wedges or Grips.- — By far the most frequently used device for holding tensile specimens in the jaws of the testing machine is a set of four serrated wedges. The flat wedges shown in Fig. 27 are for speci- FiG. 27. — Flat and Grooved Wedges for Tensile Tests. mens of rectangular cross-section; the grooved wedges are used with cylindrical test-pieces. Liners are placed in back of the grips in testing thin specimens. Fig. 28d shows the proper method of gripping a test-piece when wedges are employed. To prevent sticking in the jaws of the machine the backs of the grips should be coated with a heavy lubricant. Wedges are often objected to on the ground that they crush the specimen and pull unevenly on opposite sides of a test-piece, thus pro- ducing bending or oblique stresses. However, for rough commercial testing experience has proven such grips to be satisfactory. 69. Spherical Seated Holders. — In scientific testing to determine the elastic limit of a material, it is desirable to secure as close an approach to an axial loading as possible, and a method more refined than indicated above should be employed. For such tests spherical seated holders of the type shown in Fig. 29 have been much used. 74 MACHINES AND APPLIANCES FOR MECHANICAL TESTS The efficiency of this device is dependent both upon the skill of the mechanic in making the apphance and in fashioning the specimen, and upon the care exercised in using the device. To reduce the frictional resistance of the spherical seat to a minimum, the radius of the sphere should be made as small as a proper consideration of the crushing strength of the ball will permit, the ball and seat should be ground to fit, and the bearing should be lubricated with a thin fihn of oil. Even with a well- made holder and careful manipulation, extensometer measurements taken on opposite sides of a specimen will often differ considerably. This dif- ^-,^ (a) -Grips ^tr—Specimea (6) (d) Pig. 28. — Correct (d) and Incorrect (a, b, c) Methods of Gripping Tensile Specimens with Wedges. ficulty may be partly removed by applying a small load, reading the extensions, then removing the load and adjusting the specimen slightly to overcome the eccentricity. A type of holder which is suitable for use with tempered steel specimens is shown in Fig. 30. Portion A is a socket nut which is threaded t Fig. 40. — Berry Strain-gage for Measurements over 8-inch Lengths, Clamp for Attaching Apparatus to Specimen and Center Punch. drilled a short distance into each element at the proper place. In meas- uring, the left pivot which is rigidly attached to the invar-steel side bars is placed in one of the holes and the right pivot, which terminates the short arm of a five-to-one bell-crank lever, is adjusted to the "other hole. The long arm of the bell crank rests against the pin of an Ames dial reading to 0.001 in. The instrument is placed in the pair of holes several times and the average reading of the dial noted; the load is changed and the reading repeated. By exercising great care readings accurate to 0.0001 in. may be taken with this device. Side bars for 2, 8 and 20 in. gage lengths can be procured with this instrument. * Described in Eiig. Record, June 11, 1910. APPLIANCES FOR MEASURING DEFORMATIONS 83 83. Martens' ^Mirror Extensometer. — For greater refinement than 0.00005 in. in the measurement of deformations some form of optical lever is generally employed. One of the most accurate and adaptable instruments is the mirror apparatus devised by Martens. The sketch of this apparatus, Fig. 41, indicates the principle of operation. In this instrument the multiplying levers shown in Fig. 39 are replaced by small mirrors, (4) (Fig. 41), which are attached to the rhombic fulcra (3) so that the axis of each fulcrum passes through the reflecting plane of its mirror. The deformation of the specimen causes slight rotations of the mirrors. The latter are de-^ termined by observing successive positions of the cross-hairs in the telescopes (5) with respect to the images of the scales (6), thus finding e^ and g/. A better idea of the arrangement of the fulcra and mirrors can be ^^^""^ i~ 'T -L K ' Fig. 41. — Diagrammatic Sketch of Mar- tens' Mirror Extensometer. Fig. 42. — Fulcra and Mirrors of Martens' Extensometer. gotten from Fig. 42, which presents a view seen from the telescope. The mirrors (7) may be adjusted about a vertical line through the pivots of the frames (8) by means of screws (9). The springs (10) hold the mirrors against the screws. The mirrors may also be turned about the spindles connecting them with the fulcra (11). To balance the weight of the mirror each fulcra is jjrovided with a counterweight (12). By making the vertical arms (13) parallel to the bars (1), the positions of the fulcra (11) may be accurately adjusted to the gage length for which bars were designed The entire apparatus is very Ught and may be quickly placed upon 84 MACHINES AND APPLIANCES FOR- MECHANICAL TESTS the test-piece. If a flat scale is employed, proper correction to the read- ings must, of course, be made. With careful handUng readings to 0.000002 in. can be taken with this instrument.* 84. Autographic Stress-diagram Appliances.— These fall into two general classes: 1. Those in which the load coordinate is recorded through a move- ment of the poise on the scalebeam. 2. Those in which the load coordinate is recorded through the hfting of the scalebeam against the increasing resistance of a cahbrated spring attached to its free end. The deformation coordinate is m all cases multipUed either by levers or by the principle of the cone pulley. The paper is usually attached to a cylinder, although it has sometimes been attached to a plane board. Generally the pencil moves in a straight line, indicating one of the two coordinates, while the cyhnder (or board) moves to register the other function, and it matters not which of the two movements is made by the deformation of the specimen and which by the increasing load. The location of the paper and its moimtings is a matter of convenience simply. If cords (or wires) are used to transmit the stretch of the specimen, they must form a pair, symmetrically placed on opposite sides of the speci- men; they must be attached to one collar and pass through pulleys similarly placed on the other. They should then pass off in a plane at right angles to the specimen f and connect with the ends of an " evener " (lever), to the center of which is attached the single cord which passes either to the pencil-holder or to the cylinder which carries the paper. If cords are used, they should be such as do not stretch appreciably for such changes of stress as occur in them during the test. Fig. 43 shows the Riehle automatic and autographic recording attach- ments placed on a 200,000-lb. machine. The deformation of the specunen is measured as follows : U-clamps attached to the test piece at the proper gage marks by means of sharp pointed thumb screws support the fingers on the outstanding ends of the horizontal arms. Both arms are supported by a set of telescoping tubes sliding on the vertical shaft. The upper and lower set screws on these tubes are loose but the middle one is fast during a test. With this arrangement any elongation of the specimen produces an equal displacement of the lower arm with respect to the upper» but slipping of the specimen in the grips has no effect. The elongation is transmitted through the vertical rack and pinion on the lower arm to a * For a more complete description and discussion of the Martens mirror apparatus see Martens' Handbook of Testing Materials, translated by G. C. Henning. The apparatus is made by J. Amsler-Laffon & Sons, Schaffhausen, Switzerland. t This is necessary in order that the stretch of the specimen may be fully repre- sented in the shortening up of the cord. The cords should therefore be attached to the moving end of the specimen. APPLIANCES FOR MEASURING DEFORMATIONS 85 set of miter gears which cause a point on the surface of drum B to turn through a distance five times as great as the stretch of the specimen. On the opposite side of the drum is a vertical screw which is geared to the poise beam and drives a nut carrying the recording pencil. Lost motion in the rotating parts is taken up by attaching a weighted cord at the lower end of the drum as shown. Automatic control of the poise is effected through the device at A. The round belt to the left of A is connected to the driving pulley of the machine and turns the small horizontal shaft just below A. At the right Fig. 43. — ^Riehle Automatic and Autographic Recording Attachment. end of this shaft is attached a cast iron disc which drives either of the small fiber wheels placed equidistant from its center. The speed of the fiber wheels is regulated by changing their positions with respect to the center of the disc. A pair of magnets, one of which is shown in the figure, is provided for pulling each fiber wheel against the cast iron disc, and the shaft carrying the fiber wheels is connected by means of sheaves and a round belt to the poise screw. When the scalebeam rises it makes an 86 MACHINES AND APPLIANCES FOR MECHANICAL TESTS electric contact and one of the fiber wheels is forced against the disp, thus causing the poise to move outward and the pencil upward. When the beam drops and hits the lower contact, the poise and pencil are moved in the opposite direction. From Fig. 44 it is evident that the stress-diagrams gotten from this apparatus show yield point, partial elongation, maximum load, and general 0.1 0.2 0.3 0.1 0.5 0.3 0.7 O.S 0.9 1 1.1 1.2 1.3 l.i l.j 1.6 Elongation In Inches FiG.^44. — Autographic Stress-diagrams Made by Riehl6 Bros. Test. Mach. Co., with Device Shown in Fig. 43. Specimens were approximately 1 in. in diameter; gage length was 8 in. Diagram is about one-tliird shape of curve very well. They are not, however, sufficiently precise for finding the modulus of elasticity or limit of proportionality. COMPEESSOMETERS 85. Essential Features of Compressometers. — The conditions men- tioned under essential features of extensometers apply with equal force to compressometers; and the use of an apparatus which measures the relative displacement of the bearing surfaces on either end of the speci- men should never be permitted if the modulus of elasticity of the test- piece is sought. 86. Brief Discussion of Various Types of Compressometers. — Inas- much as the principles of measurement are the same for both extensom- eters and compressometers, only types of the latter in which the method of attachment differs from that employed in the previously illustrated extensometers will be considered. Fig. 45 represents Olsen's cylindrical extension and compression APPLIANCES FOR MEASURING DEFORMATIONS 87 electric-contact micrometer. A similar apparatus is built for rectangular specimens. The upper and lower collars of either device are provided with four points of contact and the apparatus for specimens of any size or length. As shown, the gage frame is in place upon the specimen; this must be removed before a compression test is begun. The apparatus reads to 0.0001 in. In Fig. 46 is shown a wire-wound dial compressometer used at the University of Wisconsin in testing concrete cylinders and columns. The Fig. 45. — A Micrometer Screw Ele(!tric- Fig. 46. — Wire-wound Dial Compres- contact Compressometer. someter for Cylinders and Columns. split rings at the top and bottom have three-point contact and dials may be mounted on these to measure deformations along two or more lines parallel to the axis of the test-piece. This apparatus also measures to 0.0001 in. Deflectometers 87. Essential Features of Deflectometers. — To measure bending of beams, columns, floors and other elements of structures an instru- ment called a deflectometer is employed. The essential conditions which should obtain in a deflectometer designed for accurate measurements are : 1. The apparatus should indicate the relative deflections of points in the neutral surface of the member. In many forms of deflectometers 88 MACHINES AND APPLIANCES FOB MECHANICAL TEST the apparatus itself is suspended from the neutral surface at four points directly above the supports and the deflections measured with respect to a plane through the points. 2. The parts of the deflectometer forming the datum to which the deflections are referred should be unstressed. This principle is often violated. A common practice is to measure deflections with reference to the bed of the testing machine, assuming this to be rigid (see Fig. 48). 3. Provision should be made for determining the deflections of both sides of the test-piece. 4. For most work an apparatus which is sensitive and accurate to 0.001 in. will be found satisfactory. 88. A Dial Deflectometer. — Fig. 47 represents a dial deflectometer which has proven to be a very satisfactory instrument for measuring small deflections. The side bars (1) forming the datum plane of the device are freely supported on pins driven into the neutral surface above SECTION AT 6-6 Fig. 47. — Wire-wound Dial Deflectometer Used at the University of Wisconsin. the end bearings. To prevent the bars from rubbing against the sides of the specimens washers (2) are inserted as indicated. Clamp (3) holds the side bars in place and prevents them from vibrating during the test. Yoke (4) is clamped by means of thumb-screws to the neutral surface at the point whose deflection is to be measured. In transmitting the motion of the yoke to the dial on the side bars, use is made of No. 38 covered copper wire. One end of the wire is attached to the pin (5) driven into the side bar shown at the right of the sectional view. The wire is then carried around the three idler pulleys (6) and wrapped around the drum of dial (7). Weight (8) serves to hold the wire taut. If the parts of the apparatus are properly arranged the increments in dial readings wiU be twice the deflection of the beam. If the deflection of each side is desired the device can be readily modified to meet such requirement. With this instrument readings of deflections to 0.0001 in. may be made. 89. Multiplying-lever Deflectometer.— Fig. 48 iUustrates a common type of lever deflectometer reading to 0.001 inch. Frequently, this device is so arranged that the movement of a point on the lower side APPLIANCES FOR MEASURING DEFORMATIONS 89 of the beam with respect to a point in the base of the testing machine is gotten. Unless the deflection of the base of the machine is known to be of no consequence, allowance should be made for it. Furthermore, the indentation of the specimen at the supports enters into measure- ments made in this manner. Fig. 48.— a Multiplying Lever Deflectometer with Adjustable Short Arm. Other convenient devices employing the lever principle are illustrated in Fig. 9 and Fig. 10. 90. A Wire-mirror-scale Deflectometer. — A very simple and conven- ient form of deflectometer for tests in which large deflections are to be measured is indicated in Fig. 49. In careful work the opposite side of the beam should be equipped with a duphcate of the appUance shown. I -Tf Y- Fig. 49. — A Wire-mirror-scale Deflectometer. The fine wire (1) which is kept taut by the rubber band (2) is attached to pins placed in the neutral surface above the supports and forms the datum from which deflections are measured. The highly poUshed scale (3), ordinarily graduated to 0.01 in., is also suspended from the neutral surface. In reading, the observer brings his eye into the jjlane of the wire and its image and notes the division intercepted on the scale. Beam Depoemetees 91. Wire-wound Dial Deformeters. — The device illustrated in Fig. 50, which is a modification of the extensometer in Fig. 36, is employed to measure the deformations in the longitudinal fibers of a beam. Gen- erally such measurements are made upon the top and bottom fibers. If fibers nearer the neutral surface are to be measured, deeper U-shaped clamps must be provided. 90 MACHINES AND APPLIANCES FOR MECHANICAL TESTS 92. Other Types of Deformeters. — Many experimenters have em- ployed apparatus of the type shown in Fig. 51. Some have replaced the micrometer-screw by dials with friction rollers. An objection to Fig. 50. — Wire-wound Dial Deformeter Device Used to Measure Fiber Stresses in Beams. the form of frame shown is that free motion of the upper and lower points of contact is restricted more or less depending on the rigidity of the frames. Fig. 51. — Micrometer-screw Deformeters. The Berry strain-gage shown in Fig. 40 is a very useful device for measurements of all sorts of deformations in beams. APPLIANCES FOR MEASURING DEFORMATIONS 91 Detrusion Indicators 93. Porter's Detrusion Indicator.* — Essentially, this apparatus con- sists of two rings, each of which is clamped to the specimen by three Fig. 52. — Porter's Indicator with Distance Bars in Place. set-screws, see Fig. 52. The distance between the rings is fixed by gage bars provided with studs for centering the test-piece. The right-hand ring is graduated in degrees and supports, on a ball-bearing, a concentric Fig. 53. — Torsion Indicator Used at the University of Wisconsin. ring provided with a vernier reading to 5 minutes. The vernier ring is moved by a finger attached to the left-hand ring In order that the * Described in Proc. A. S. T. M., Vol. 10, p. 578. 92 MACHINES AND APPLIANCES FOR MECHANICAL TESTS parts of the apparatus may be free to move as the specimen suffers change in length, a ball joint is provided to connect finger and vernier ring. For setting the vernier to read zero the connection between the finger and vernier rinfe is equipped with a slow-motion tangent screw. The instru- ment shown was made for specimens less than 1| in. in diameter and a gage length of 3 in. 94. A Dial Indicator of Detrusion. — ^An apparatus for detrusion measurements which has been in use for several years at the University of Wisconsin is illustrated in Fig. 53. The twist of the section of the specimen between the arms (1) and (2) is transmitted through No. 38 covered copper wire to the drums (3) and (4), respectively. The spindle (5) carrying drum (3) actuates the pointer (6). Similarly dial (7) is connected to drum (4) by spindle (8). From this arrangement it is, therefore, evident that the twist between the two sections of the speci- men can be gotten by noting the relative positions of pointer and dial corresponding to the increment in torque. In the apparatus shown the multiplying factor is 40, and the dial is graduated in one-half degrees. Any deflection produced by bending of the specimen during the test will, of course, affect the readings of this apparatus. However, a rough com- putation quickly demonstrates that such effects are negligible. Miscellaneous Appabatuses for Measuring Deformations 95. Multiplying Dividers. — A very efficient little device for accu- rately locating the yield point in a tension or compression test is Capp's Fig, 54. — Capp's Multiplying Dividers for Detecting the Yield Point. multiplying dividers, shown in Fig. 54. In performing a test with this instrument, the operator grasps the cupped pivot-heads between the thumb and finger of his left hand and places the hard steel pomts on the end of the short arms in punch marks spaced 2 in. apart. By this method the operator's right hand is free to move the poise on the scale- beam if the machine is not provided with an automatic drive. For elastic stresses the motion of the pointer over the scale is hardly appre- ciable, but when the yield point is reached the rapid increase in the rate of motion of the pointer instantly warns the operator of the fact. APPLIANCES FOR MEASURING DEFORMATIONS 93 94 MACHINES AND APPLIANCES FOR MECHANICAL TESTS L_ With such a r'cvice mistakes in the location of the yield point due to slipping of the grips are obviated. In tests of high-carbon steels, wire, and other materials having a high yield point the drop-of-beam method is very uncertain at best. By using the divider method, however, a distinct indication of the yield point can be readily obtained. 96. A Recording Bridge Deformeter. — The apparatus shown in Fig. 55 was designed by the Structural Engineering Department of the Uni- versity of Wisconsin to measure the deforma- tions in bridge . members while subjected to moving loads. The movement between the gage points of the apparatus is transmitted through a long rod to a light, rigid lever actuating a pencil point which records 50 times the deformation on the diagram sheet. The latter is wound about the drum which is turned by an electrically controlled clockwork. A number of these instruments were used with success in a long series of experiments by the American Railway Engineering and Maintenance of Way Association.* 97. A Wire-Rope Extensometer. — A simple and durable device for measuring the elonga- tion of wire-rope is illustrated in Fig. 56. Increments of elongation are determined by taking simultaneous readings on the upper and lower pairs of scales by transits or telescopes set up a short distance from the test-piece. The scales are graduated to 0.01 in., and readings to half -hundredths may be estabhshed. Twist- ing of the rope does not materially affect the results if each telescope be placed on a level with the corresponding pair of scales. Fur- thermore, since the device is not delickte or Extensometer. (a) View expensive and the observer well back from the f rom Telescope ; (t) Clamp test-piece, readings may be taken until the for Attaching Scales to specimen fails. Rope. J (') a. (b) Fig. 56.— a Wire Rope * Bullelin of American Railway Engineering and Maintenance of Way Association No. 125, p. 9; also Engineering News, June 20, 1907. This apparatus is made by A. Wissler Instrument Works, St. Louis, Mo. APPLIANCES FOR MEASURING DEFORMATIONS 95 REFERENCES 1. Handbook of Testing Materials, by A. Martens, trans, by G. C. Henning; Wiley &Sons, N. Y. 2. Handbuch des Material-priifungswesens, by O. Wawrziniok; Springer, Berlin. 3. A Handbook of Testing Materials, by C. A. M. Smith; D. Van Nostrand Co., N. Y., 4. Experimental Engineering, by R. C. Carpenter and H. Diederichs; Wiley & Sons, N. Y. 5. The Testing of Materials of Construction, by W. C. Unwin; Longmans, Green & Co., N. Y. 6. Experimental Engineering, Vol. 2, by W. C. Popplewell; The Scientific Pub. Co., Manchester, England. 7. Commission des Methodes d'Essai des Materiaux de Construction, 4 vol., J. Roth- schild, Editor, Rue des Saints-Peres, Paris. (This is o ten referred to as the Report of the French Commission.) 8. Das Konigliche Materialprufiingsamt der Technischen Hochschule, Berlin, by A. Martens and M. Guth; Springer, Berlin. 9. On the Reliability of Institutions, Machines and Experiments for Testing the Strengths of Materials, by A. Martens, Proc. Sixth Congress Int. Asso. for Test. Materials, 29, 5. 10. The 600,000-lb. screw-gear universal testing machine at the University of Illinois is described by W. C. DuComb in Proc. Am. Soc. for Testing Materials, Vol. 6, p. 476. 11. Special Features of Recently Installed 600,000-^6. Universal Testing Machines (screw- gear machines for the University of Pennsylvania and Bureau of Standards laboratories), by T. Y. Olson, Proc. A. S. T. M., Vol. 8, p. 626. 12. Phoenixville Testing Machine (a 2,400,000-lb. horizontal hydraulic machine), Eng. News, Vol. 30, p. 512. 13. A 3300-ton Testing Machine (a horizontal hydraulic machine built in Germany), Eng. News, Vol. 67, p. 841. 14. A Large Hydraulic Testing Machine for Uniform Loads, by R. Cummings, Proc A. S. T. M., Vol. 5, p. 275. 15. A New Torsion Testing Machine, (an autographic machine designed by W. E. Lilly), The Engineer, Vol. 3, p. 175. 16. Staybolt Iron and a Machine for Making Vibratory Tests, by H. V. Wille, Proc. A. S. T. M., Vol. 4, p. 316. 17. Testing of Metals by the Study of the Abatement of Vibrating Movements, by A. Boudouard, Bull, de la Societe d' Encouragement pour I'Industrie Nationale, Dec, 1910, p. 545. 18. A Fatigue Testing Machine, by J. H. Smith, Engineering, Vol. 79, p. 307, and Vol. 88, p. 105. 19. Alternating Stress Testing Machine at the National Physical Laboratory, by T. E. Stanton, Engineering, Vol. 79, p. 201. 20. A Throw Testing Machine for Reversals of Mean Stress, by O. Reynolds and J. H. Smith, Phil. Trans, of Royal Soc. of London, Vol. 199, p. 265. 21. A Tool Steel Testing Machine and Results, by E. G. Herbert, American Machinist, Vol. 32, Pt. 1, p. 823. 22. Testing the Cutting Quality of Files, by E. G. Herbert, American Machinist, Vol. 30, Pt. 2, p. 946, also Vol. 34, p. 582. 23. Some Apparatus for Tension Tests of Rubber, by P. L. Wormley, Proc. of the Sixth Congress Int. Asso. for Test. Materials, 22, 3. 96 MACHINES AND APPLIANCES FOR MECHANICAL TESTS 24. A Simple Load Weighing Apparatus for Large Testing Machines (a volumetric load-gage), Eng. News, Vol. 67, p. 910. 25. Allowable Unit Loads on Knife Edges, by S. W. Bramwell, Eng. News, Vol. 55, p. 653. 26. Friction in Packings of Hydraulic Testing Machines, Eng. News, Vol. 58, p. 209; Vol. 59, p. 535; Vol. 60, pp. 19 and 154; Vol. 62, pp. 377, 386, 438. 27. On Measuring Small Strains in Testing Materials of Construction, by J. A. Ewing, Proc. Royal Soc. of London, Vol. 58, p. 123 28. A New Mirror Apparatus for Measuring Elasticity, by B. Kirsch, Eng. News, Vol. 62, p. 619, and Proc. Int. Asso. for Test Mat., Congress 5, section 8, 4. 29. An Extensometer Operated by the Volumetric Change Produced in a Diaphragm^ walled Liquid Container is described in Concrete Cement Age, Vol. 2, p. 96. 30. Calibration of Instruments Used in Engineering Laboratories (principally English makes of extensometers), Report of British Asso. for Adv. of Science, 1896. 31. The Optical Determination of Stress, by E. G. Coker, Phil. Mag., Oct. 1910, p. 740, and Engineering, Jan. 6, 1911, p. 1; also articles by the same author on similar subjects in Eng., Vol. 94, pp, 134, 404, and 824. CHAPTER III THE MECHANICAL TESTING OF STRUCTURAL MATERIALS 98. General Observations. — Mechanical tests are those used to discover the qualities of the materials of construction under the action of external forces. Such tests, if they are to be of most value, should be made under conditions approximating as closely as possible those of practice. By standardizing these conditions the results become com- parable wherever or by whomsoever thay are made and are of very great importance in determining the properties and value of building materials. If such results can be made wholly independent of the means employed in making the tests, and hence to furnish a knowledge of the true char- acteristics of the material, they can be used safely in theoretical general- izations on the one hand, and in the practical designing of structures on the other. With many kinds of tests this ideal divorcement of the results from the conditions of the tests can certainly never be attained, as in the case of tests by impact, but it doubtless can be practically attained in some of the more simple tests, as in tension and compression. In the former case the most that can be accomplished is to prescribe uniform condi- tions in order that the results obtained by different experimenters may be comparable, although they may not serve for accurate scientific general- izations. They might also serve to give a relative value to the various materials or samples so tested, and to grade them with some degree of approximation to their true relative merits for a proposed purpose. Such tests, therefore, may serve fully their immediate object even though the results can be given no absolute significance whatever. If, however, the conditions of such tests are allowed to vary, they lose even this rela- tive significance, and therefore become quite worthless. The standard- izing of any particular kind of test evidently depends on the state of the science at the time; and as our knowledge of any particular property of a material increases, it is probable that our standard methods of testing will also have to change. No such standards, therefore, can be fixed per- manently, but certain methods can be agreed on and followed for a time, and when a change is made let all change together. To attain to this kind of unity of action it is necessary to have a world's representative body which will command the confidence and allegiance of both the theo- retical and the practical users of materials in all civilized countries to decide such questions. 97 98 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS The efforts of the International Association for Testing Materials towards securing such unity of action in various countries has not thus far been productive of great reforms although, the outlook is hopeful. However, some of the affiliated societies like our American Society for Testing Materials have been instrumental in unifying the methods of testing and standardizing specifications in force in their respective countries. Evidently no complete standardization can be effected for tests on entire structural forms, since these vary in shape, size, and disposition of parts, but specimen tests can be standardized since all significant condi- tions can be made uniform. 99. Mechanical Tests Classified. — In a general way we may divide tnechanical tests of building materials into the following classes: With reference to the method of applying the loads we have — (1) Static Tests, or those made with gradually increasing loads, such as the ordinary tests in tension, compression, cross-bending, torsion, and shearing. (2) Dynamic Tests, or those made with suddenly applied loads, as by a falling weight. (3) Wearing Tests, or those made for determining resistance to abrasion and impact, as in the case of paving-materials. With reference to the character of the test specimen we have — (1) Specimen Tests, or those made upon specimens of the material, specially prepared and given standard forms and dimensions. (2) Structural Tests, or those made on full-sized structural forms, as floor systems, bridge members, brick piers, pipes, wire ropes, chains, riveted joints, etc., or on the structure as a whole, such as boilers, simple trusses, frames, and various parts of machines. Complete standard rules for making tests of structural materials can be adopted for making all kinds of tests on specially prepared specimens, but they can be only partially prescribed for tests of structural forms. THE ACCURACY OF MACHINES AND APPARATUS 100. Methods of Determining the Accuracy and Sensitiveness of Test- ing Machines. — General considerations of the acciu'acy, sensitiveness, and conditions which should obtain in testing machines have been given in Ch. II. Since it is of vital importance that the user of attesting machine should know approximately at least the accuracy of his machine, a brief statement of methods commonly used for testing accuracy and sensi- tiveness will here be made. In testing the accuracy of vertical static-load machines five to ten equal increments of dead load can be placed on the platform of the machine, or on extensions formed by I-beams, and the corresponding readings of the weighing device compared with the known loads. After each, incre- THE ACCURACY OF MACHINES AND APPARATUS 99 ment of load has been added the sensitiveness may be determined by- finding the additional weight which is required to make a perceptible indication on the weighing device. This method, even when pig iron is used, is too cumbersome and laborious for loads above 10,000 to 20,000 lb. In calibrating machines of the lever type, loads of this magnitude are sufficient to determine the multiplying factor for the lever system and, assuming this factor constant, a correction coefficient applicable to the range of machine may be determined. It is not safe, however, to estimate the sensitiveness at high loads to be proportionately the same as at low loads. In calibrating hydraulic machines in which there is fric- tion at stuffing boxes and around the piston, it is desirable to test the machine to full capacity. Standardized calibrating levers with weights in capacities up to 100,000 lb. can now be purchased from manufacturers of testing machines. These furnish a more expedient and easy means of calibrating over a greater range of loads than the dead weight method. It is often possible to calibrate a very large testing machine by placing a smaller machine of known accuracy and sensitiveness on the weighing table of the larger machine and loading it. Hydraulic jacks of known accuracy may also be used for such purposes. The most inexpensive device for calibrating large testing machines up to full capacity is the calibrated tension bar or compression prism equipped with a permanently attached extensometer. An annealed bar of high elastic hmit and of such cross-section that the capacity of the machine will be well within the elastic limit of the bar is a desirable calibrating apparatus. The extensometer should be preferably of the self-indicating type, measuring deformations on two or more sides of the bar and reading to at least 0.0001 in. It should be permanently attached to the bar and suitably protected from injury. The gage length should be sufficient to permit the least reading of the apparatus to correspond to a change in loading of 0.2 per cent of the capacity of the machine. The bar should be so secured in the jaws of the machine that an axial load is insured, and shpping prohibited. If a compression prism is used the ratio of length to least radius of gyration should not exceed 20, and if a hollow cylinder be employed the ratio of thickness to diameter ought not to be less than 1 : 8. The average unit stress at full capacity of the machine should be less than two-thirds of the elastic limit. The quality of the material, gage length of compressometer and its characteristics should conform to the cor- responding specifications for the calibrating bar. Spherical seats or other means for securing an axial load should be used. Calibrating test-pieces should be standardized at the Bureau of Stand- ards or on machines of known calibration. Care should always be taken 100 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS to standardize such a test-piece under the same conditions as will sur- round the specimen when it is used for calibration purposes. A half dozen or more increments of load may be applied to the calibrating specimen at a speed not to exceed 0.1 in. per minute and corresponding readings of the deformations taken. After each increment of loading, the dead weight required to produce a movement of the weighing device finnishes a measure of sensitiveness. Pressure gages on hydraulic machines should be frequently calibrated throughout the entire range of loading. If the pressure in the jack is measured to determine load on machine, calibrations under increasing and decreasing loadings should be made with the piston at different posi- tions in the stroke. By so doing variations in the frictional resistances can be determined. 101. The Calibration of Apparatus for Measuring Deformations. — For certain classes of testing, a knowledge of the accuracy and sensitiveness of apparatus used to measure deformations is of as great value as similar information concerning the testing machine. For most purposes an accuracy of 1 per cent is sufficient in such apparatus. Essential consider- ations for different types of deformation apparatus have been discussed in the preceding chapter. When conditions permit the calibration of such devices may well be left to standard laboratories such as the Bureau of Standards or the Watertown Arsenal. If calibration is done in the home laboratory, the following method serves for a rough test of accuracy and sensitiveness. The apparatus may be attached to a steel test-piece for which the stress- deformation curve has been accurately determined; and the test-piece gripped in a standard manner by the machine, so that slipping and improper distribution of stress are avoided. Increments of load are very slowly and uniformly applied to the test-piece and the corresponding readings of the apparatus taken. After each increment of loading one may deter- mine sensitiveness by observing the increase and decrease in load required to produce a readable change on the deformation apparatus. If a standardized deformation apparatus is at hand, it may also be attached to a specimen under conditions similar to those surrounding the apparatus which is being caUbrated. The unknown device can then be compared with the standard under loading conditions indicated above. A more accurate method than the above for calibrating extensometers and compressometers consists in clamping one end of the apparatus to a dummy specimen held in a lathe chuck and the other end to the cen- tering spindle of the tail-stock. By using a microscope with a standard- ized micrometer eyepiece the movements of the pivot end of the spindle can be determined and compared with readings of the motions regis- tered by the deformation apparatus. If a precision lathe can be had, SELECTION AND PREPARATION OF SPECIMENS 101 one part of the extensometer may be attached to the spindle on the tail- stock and the other to a specimen held on the lathe carriage. In this set- up the axes of specimen and spindle should be colinear. The lathe may then be set so that the carriage travels .02 or .01 in. per revolution of the chuck and a comparison of the deformation apparatus with the lathe screw determined. Using a standardized linear dividing engine, reading directly to 0.002 mm. or less, still greater refinement may be obtained. With such apparatus it is possible to cahbrate scales, micrometers, and practically all of the devices used in measuring deformations. When calibrating apparatus in which accuracy in fabrication is based directly or indirectly upon the accuracy of a screw, readings of say one- tenth the range should be taken over the entire range of the apparatus to determine the cumulative error of the device. Periodic errors may be ascertained by a large number of readings of small increments of motion over a limited portion, say one-tenth, of the range. Furthermore, to eliminate periodic errors in the calibrating device it is essential that the apparatuses under comparison be shifted several times and the entire range and partial range calibrations repeated. To avoid errors due to lost motion in screw-calibrating devices one must always approach the desired reading from the same direction. To accu- rately detect lost motion or lag and to determine the sensitiveness of the deformation apparatus, observations on minute forward and back motions of the moving part of the apparatus may be made under a microscope provided with a micrometer eyepiece. SELECTION AND PREPARATION OF SPECIMENS 102. Selection of Specimens. — It must be recognized at the outset that specimens are selected for testing with either of two objects in view — to compare the mechanical properties of certain materials or grades of the same material, or to ascertain the influence of certain conditions of fabri- cation, treatment and usage on the mechanical properties. In comparing mechanical properties the size, shape, method of fabrication, and sub- sequent treatment of the specimens are generally standardized, but in ascertaining the effects of structural conditions one or more of these is made variable. When choosing specimens for any kind of test the inspec- tor must constantly bear in mind that the test results are valueless unless the specimens are truly representative of conditions and properties under investigation. The numerous specifications of the American Society for Testing Materials, American Society for Mechanical Engineers, the Society of Automobile Engineers, American Railway Engineering Association, and 102 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS others, in general, cover the method of selecting test specimens of metals and metal elements which are to be used for various purposes. Test- pieces may be cut from the finished casting or rolled product. If the quality of metal is to be ascertained, specimens of cast metals should be separately poured into vertical dry molds. If specimens are cut from castings, it must be remembered that shrinkage strains exert a pronounced effect upon strength at all corners and angles in the casting and that the outside, especially in cast-iron members, is often much stronger than the center. When specimens are cut from rolled structural shapes, one should consider that the metal in the thin parts is harder, tougher and stronger than that of the thick portions which has received less work under the rolls. With wrought iron a great difference will be found in specimens cut with and across the direction of the rolling, the former having much higher strength and a greater ductility. In steel plates there is little difference, and in rolled brass and copper plates there is no difference. In the case of the bronzes it is necessary to have test samples poured from different parts of the same melting, as the mixture changes its characteristics rapidly when in a melted state. Piles of brick or building tile may be subdivided into small piles of approximately 100 each and one sample representing each small pile chosen. If the total number of samples is more than required the number may be reduced in similar manner. In selecting samples, color, depth of kiln-mark, number and position of checks and spalls, and ring under the hammer should be considered. If the sampling is done at the kiln, the position of the specimens with respect to the entrance and exit of the source of heat must be considered. When samples of stone are being selected, it is necessaiy to secure specimens from the different strata which are being worked. If the sur- face has been expose'd to the weather for a considerable time specimens should be cut from the interior. The faces of specimens should be refer- enced with respect to the rift in the rock. Specimens should not be selected from portions of rock adjacent to blast holes. In selecting timber specimens, the rate of growth of the tree as told by the annual rings, position in the tree, the proportion of heartwood and sapwood, the proportion of spring and summer wood, the moisture con- tent, the method of seasoning and the character and position of defects must all be considered. 103. The Preparation of the Specimen. — In order that the specimen may fairly represent the material under examination, or the particular plate, or bar, or rolled form from which it is to be taken, it is necessary to observe a number of rigid requirements. The specimen must be obtained by cutting it out in a way that will SELECTION AND PREPARATION OF SPECIMENS 103 leave it perfectly straight. If a metal test-piece is bent in getting it out, it should be heated to straighten it; but this may often change the original molecular arrangement, and should be avoided if possible. When the speci- men is cut from a larger portion of a plate or rolled form by shearing, it will invariably take a curved form. In this case the plate, or form, should be sheared away from the specimen, in narrow slices, so as to leave the test specimen unbent. If the specimen is bent and then straightened, it raises the elastic limit and hardens the metal, the same as any other kind of cold working. Instead of shearing, some milder process, such as planing or drilling or sawing, should be resorted to to obtain the test specimen. For, besides the bending action on the bar as a whole, the effect of the shearing or punching is to seriously injure the metal for about an eighth of an inch beyond the sheared surface, leaving it so non-ductile, or brittle, that it will not elongate appreciably, and hence under a tensile test these surfaces will be severed very early in the test, and the cracks so started may cause the remainder of the cross-section to tear asunder in detail. To prevent this action on sheared or punched specimens, at least an eighth of an inch of thickness should be removed from all punched or sheared faces, by reaming, planing, or filing. Final finishing of hard metal specimens should be done with a file in order to avoid the torn and bruised surface conditions which result from the use of lathe and planer tools. Soft metal test-pieces should be finished with emery cloth. If the skin is removed from a casting by planer or milling device, it is well to remove the rectangular corners with a file in order that incipient cracks or irregularities caused by the tools may be eliminated. If soft metal specimens must be straightened, wooden or copper mallets should be employed; a steel hammer should never be used. The ends of metal compression specimens should be accurately ground to parallel plane surfaces. To avoid the inclusion of material which may have been weakened in quarrying, it is necessary to saw compression test-pieces of stone from the interior of blocks somewhat larger than the test-pieces: roughing out the specimen with hammer and chisel may cause a large reduction in strength. If the latter method is permitted, care should be taken to make the sides of prismatic specimens plane. If accurate results are desired, it is well to grind to true planes the surfaces which are to be subjected to pressure. Specimens of brick, building tile and concrete will show greater strength if similarly treated. Since the expense of this work is often prohibitive, bedments such as are described in Art. 76, 77 and 78 are often used to overcome the effects of surface inequalities. 104 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS TENSION TESTS 104. Significance of Tension Tests. — Tension tests are more com- mon, more readily made, and more useful in revealing the true char- acter of a metal than any other kind of mechanical ,test. In fact, when other kinds of tests are made it will commonly be well to accompany them with a few tensile tests for the purpose of being able better to co- ordinate the results with those obtained on other materials by similar tests, or on like materials by different tests. In this connection, however, it is well to remember that all metals are wanting in strict homogeneity, and that they may be regarded as aggregations of more or less dissimilar elements embedded in a common matrix, somewhat hke granite. (See Art. 623 and 663.) For instance, the planes of rupture will be different for different kinds of tests on the same specimen, and hence the strength developed will be that of a different combination of elements in each case. Also, the strength to resist various kinds of stress may lie in entirely different elements of the aggregation, as, for instance, in the case of cast iron the strength to resist tension is the strength of the graphitic carbon matrix in which the iron crystals are embedded, while the strength in compression is largely strength of the iron crystals themselves. * What we call the maximum strength of the material, therefore, or its strength at rupture, is not usually the sum of the maximum resistances of the several elementary portions of the cross-section, since they do not all distort equally. It is often the case that actual rupture occurs successively over many elementary portions of the broken section before the final failure occurs. More especially is this true of the elastic limits of the mate- rial, while with iron and steel castings this failure in detail is so prominent as to cause the stress-diagram to be a curve almost from the beginning of the loading. Here, too, the irregular shrinkage often leaves very great internal stresses in the body, which causes some portions to come to their elastic limits and ultimate strength much earlier than others, again giv- ing rise to a curved stress-diagram. The tension test is especially well calculated to show what local irregu- larities may be found in a finished product, and to indicate to what extent the work of forging (rolling or hammering) has produced that degree of homogeneity expected of it. • The tension test is more readily standardized than any other so as to be independent of " personal equation " and of variations in the testing- machines employed. It also demands the least amount of preparation of the test specimen, if tests are to be made only for commercial purposes. Except for the inherent want of uniformity or of homogeneity mentioned above, therefore, the tension test may be made to give typical and uniform • M. Osmond. TENSION TESTS 105 results, and it should be considered as the best single test to make on any of the metals. COMMEKCIAL TENSION TeSTS 105. Object. — In routine testing of metals under tension the ultimate strength, yield-point and per cent elongation are always determined and the character of the fracture noted. Frequently, the per cent reduction in area is also found. From these properties the static tensile strength, the limiting working unit stress, the ductility, and the homogeneity and charac- ter of structure of the metal is judged. * Such tests, therefore, which can be performed with great speed and at low cost, serve a very useful purpose. 106. T3rpes of Tension Specimens. — Experiments have shown that the form of a tension test-piece has an influence upon both the strength and .50 ^ -^ M 4- N \ A? \ .30 .t\ p 1 irai^eo rSS-Te 1 1*6"::-^ / ' \ ■^Ave jagej» mgatic aof S eelSp cimen — Vi ? , perage ^""" ,tion-oi Wron fht-Irc n-Spee menB-)^ K ^ r ' Fig. 1. — The Variation in the Distribution of the Elongation of the Several Inch Spaces of Six-inch Test Bars of Steel and Wrought Iron 0.56 In. in Diameter. {Tests of Metals, 1890.) elongation. The influence on strength of grooving and sudden contrac- tions in area is considered in Arts. 719 to 721. Fig. 1 shows the varia- tion in unit elongation for successive spaces on steel and wrought- iron bars. Fig. 2 illustrates the influence of the length of the gaged position on per cent elongation. Tetmajer proposed that the elongation due to the neck be eliminated by subtracting the elongation in a 4-in. from the elongation in an 8-in. gage length and dividing by the difference in the gage lengths. The func- tion, thus obtained, would be independent of the gage length of the speci- men. This proposal has not, however, been widely adopted. * The character of structure in ductile metals is much better ascertained from tests on specimens around which a V-shaped groove has been turned. With such specimens the lines of stress are concentrated at the bottom of the groove and a square break revealing the character of the crystaUine structure ensues. 106 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS On account of the above considerations it has become quite necessary to prescribe certain types of specimens for commercial tests in which the grading and acceptance of material is involved. M. Barba * has shown that the resistance and per cent elongation remain constant provided the relative dimensions are not changed and the method of gripping and load- ing are identical. As the result of his work and a large number of tests, the French Commission adopted the relation P = 66.67 A or for cylindrical specimens I = 7. 2D, where I is the measured length on which the elongation is computed, D is the diameter, and A the area of cross-section. The German Commissions use l = 11.3VA, which is equal to l=10D if the 80 NOTE Mild Steel Specimen H in. diam. = • Mild Steel Specimen i4 in. diam. = X Mild Steel Specimen 1 in. diam. = o Tool Steel Specimen ^ in. diam.= .^ Mild Steel Specimens were from same bar. o 60 A •» ) ( o * ! s A ' ° f 1 A I ° ! O ^ o I ' o 1 \ n 20 A A t '^ 1 10 .Eatio, 8 w 12 U Gage Len;j:th of Specimen 16 Diameter of Specimen Fig. 2. — The Influence 'of the Ratio — jy on the Per Cent Elongation of Steel Specimens. specimen is cylindrical. Engineering societies in the United States have not rigidly adhered to either of these rules, or even Barba's law, in stand- ardizing the shape of test-pieces cut from plates or other rolled sections. However, they have prescribed fixed standards for cylindrical' and flat specimens (see Figs. 3c and 3e). For flat specimens ON-er j in. thick, the gage length is 8 in. and the width 1| in. The width of specimens cut from material less than j in. in thickness must be five times the tliickness with a minimum of f in., and the gage length must be twenty-four times the thickness with a minimum of 2 in. * Mem. de la SociUi des Ing. Civils, 1880, I, p. of Materials of Construction. 682. See also Unwin's The Testing TENSION TESTS 107 In Fig. 3 are shown seven types of specimens dimensioned in accord- ance with practice. For rough tests on ductile rounds or flats, form (o) (b) kd-^l fur . i 1: ! ht'^l 1 A -^ — '4 H %''i (d) *&♦ I ::i ^'TT-* J_ (e) ^d+X' k^-^- (/) >3i' G) (Sr) Fig. 3. — Types of Specimens for Tensile Tests. is suitable. Form (b) is a more expensive specimen which is less liable to slip in the grips and also receives a lower intensity of compression from the grips than does form (a). For more careful tests in which it is highly 108 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS Bollel 0.80,000 9} a 3 |g 70,000 I 60,000 ti 50,000 40,000 30,000 Steel \=~ : z±z -.^=- _AxleM«i desirable to avoid slipping at the grips, form (c) or (c') is used in con- junction with the holder shown in Fig. 29, Art. 69. Automobile steels of very high elastic limit and great hardness cannot be readily fashioned into form (c) after hardening. If so fashioned before heat treatment, these steels are liable to become warped and weakened at the screw threads. For such steels form * (d) may be used in connection with the holder shown in Fig. 30, Art. 69. An inexpensive casting which makes a very satisfactory test-piece for rough tests on cast iron, mal- leable iron and similar brittle metals is form (/). Form (g) has been used with success by Prof. W. H. Warren of Sydney University, Aus- tralia, in testing the ten- sile strengths of woods. 107. Testing.— The dimensions of cross-sec- tion of the specimen are measured at several places along the gage length. If the test-piece is cyhndrical, mutually perpendicular diameters should be measured at each cross-section. Measurements of metal should be acciKate to of 1 per cent. The 120,000 110,000 .§100,000 a S 90,000 AxleSteel_ :<=^ K-ln. Ultimate Strength.. Yield Point — ■* — ^ ElonsatioD 0--0" ■pofte; Vh I 2 3 4 5 6 Speed of Pulling Head in Inches per Minute 40 c 30 ;S a o 20 « ' 60 S O 10^ OpL, 6M iTT Fig. 4. — The Effect of Speed on the Tensile Strength and Elongation of Steel. (Rept. of Com. O, A.S.T.M., see Proceedings, 1906.) average cross-section of deformed bars can be computed from deter- minations of weight and length. The specimen is then placed in a V-block and punch-marked at intervals of 1 inch along the entire gage length. A laying-off gage or a, multiple punch is a time-Saver in this operation. Fine wire and other small sec- tions which would be seriously weakened by punching may be marked with ink. For variations: in speed of the pulling head of the testing machine up * See description of this type of specimen given by K. W. Zimmerschied in Trans. Soc. Auto. Engr., Vol. 8, pt. 2, p. 161; also see Marten's Handbook of Testing Materiah, p. 10. TENSION TESTS 109 to 6 in. per minute, there is no pronounced effect on the mechanical properties of soft steel as Fig. 4 shows. The higher carbon steel specimens show practically the same properties for speeds less than 3 in. per minute. The greatest effect is produced on the yield-point. However, if one wishes to accurately determine the yield-point a speed of 2 to 4 in. per minute may be applied until about three-fourths of the estimated yield- point load is reached, the speed then may be quickly cut down to about J in. per minute, the yield-point determined, and the high speed again reapplied to rupture. For cast iron and similar brittle materials the speed throughout the test ought not exceed 0.02 or 0.03 in. per minute per inch of gage length. The speed should be constant for any given series of tests on brittle plastic materials. The French Commission recommends that tests be continuously pro- gressive; that the duration of test be proportional to the volume of the specimen (one to six minutes for ordinary sizes of specimen, less than thirty seconds for test-pieces under 0.2 in. thick); that heating of the bar must be avoided, especially with the softer metals. In tests of high carbon steels and in tests in which there is slipping at the grips a pair of Capp's multiplying dividers (see Art. 95) will be found useful. 108. Observations for Record. — The record should contain sufficient information so that the history of the specimen previous to the test may be traced. In inspection at the mill this includes heat number, specimen number, and such other information as may be needed to reference the specimen to the portion of the heat or to the member from which it was taken. The first sign of weakening at yield-point of the specimen should be carefully ascertained. In wrought iron and the low-carbon steels this is readily determined by the drop of beam, by the rapid increase in motion of the divider pointer and, in rolled material, by scaling. If rolled bars of uniform cross-section are used, the scaling will appear first at the grips, owing to the combined stress existing there, and grad- ually extend toward the center of the specimen. It will be noted that the scaling advances on lines at about 45 degrees with the axis of the specimen : i.e., on the surface traces of the planes upon which maximum shear stress exists. The maximum load is next determined. It will be found to occur simultaneously with the commencement of the " necking down " action in ductile materials, with rupture in brittle materials. At present it is not customary to record the actual breaking load for ductile materials, since it is not regarded as an important index of strength. After rupture the test-piece is again laid in the V-block with the fractured ends in con- tact and a record of the length of gage across break is made. b I, b I lEilE no THE MECHANICAL TESTING OF STRUCTURAL MATERIALS If the specimen has a " cup and cone " fracture, it will be found easier to measure the reduced diameter on the lips of the cup than on the cone. The reduced areas of rectangular specimens can be most readily determined by measuring b, di and d2 as shown in Fig. 5. To measure fractures of irregular outline, a micrometer provided with a conical spindle and anvil will be found convenient. Two characterizations of fracture are generally made, one with reference to shape and the other with reference to texture. For example, mild steel fractures are commonly " cup and cone " in shape and " silky " in texture; hard steel fractures break squarely across— " square break " — and are more or less finely crystalline in texture. Fig. 6 shows the fractures commonly observed in metals and suggested Fig. 5. — Reduced Area of a Rectangular Test Pieces b ' . IIUIJllllLi Fig. 6. — Characteristic Fractures of Ferrous Metals in Tension. (1) Common in cast iron, designated as square break and fine or coarsely crystalline; also in very high carbon steel, texture finely crystalline. (2) Common to high carbon steel, called fin cup or flat cone with granular to crystalline texture. (3) Common to soft and medium carbon steels, called full cup and cone with texture silky. (4) and (5) Common in soft and medium steels (especially when eccentrically loaded), designated as three-quarter cup and cone (4), and half cup and cone (5). (6) Common in soft and medium steel bars of flat or square section, designated sheared cone with silky texture. (7) Common in wrought iron, designated jagged and fibrous. (Overheated soft or medium steel may also prcgcnt a jagged break but not fibrous.) characterizations of the same. Unusual features in the fracture should always be recorded and their causes, if possible, ascertained. For the latter purpose the microscope is a valuable aid. TENSION TESTS 111 EXTENSOMETER TENSION TeSTS 109. Object. — In addition to the objects mentioned under commercial tension tests, the extensometer test affords a determination of the stress- elongation curve for the material. Consequently the elastic limit or the limit of proportionality and the resilience may also be measured. 110. Testing. — Specimens like form (c) or (d), Fig. 3, are preferable for extensometer tests; but it is desirable that the gage length for the appa- ratus should be at least 8 in. For steels, a specimen fashioned as indicated with a diameter of 0.798 in. (area 0.5 sq.in.), length between shoulders of 9 in. and a gage length of 8 in. is convenient and satisfactory. To avoid errors arising from the bending of the specimen due to eccen- tricity in loading, non-homogeneity or initial curvature in the specimen, extensometers provided with three-point contact at each collar are prefer- able to extensometers of same type having two-point contact. The accu- racy of the extensometer should be commensurate with the magnitude of the deformation to be measured. Ordinarily the least reading of the appa- ratus should be less than one one-hundredth of the deformation at the elastic limit. For steel this requires apparatus reading to 0.0001 in. General requirements for extensometers may be found in Art. 79. During the test the speed of the pulling head should be very low, not over 0.01 in. per minute per inch of gage length, and the machine may be stopped long enough to secure readings of deformation. It is of great importance to avoid vibration or shocks during the application of the load, since such disturbances greatly impair both the accuracy and sensi- tiveness of the extensometer. There are two methods of loading which may be used, depending upon the nature of the material and the information desired. If the limit of proportionality is to be determined the load is progressively applied in increments equivalent to about one-tenth of the estimated value of that stress and the corresponding deformations observed. When a stress approximating the limit of proportionality is reached the incre- ments are reduced to about one-tenth of their former value until the yield-point has been passed. It is customary to remove the extensometer from the specimen after passing the yield-point in order to avoid injury to the instrument. Subsequent measurements of elongation may be made with a pair of dividers. The second method of loading is more often adopted with materials having a curvihnear stress-deformation diagram than with iron or steel. It consists in determining the maximum total deformation and set correspond- ing to repeated applications of each load. An initial load corresponding to one-twentieth the ultimate strength of the material, or thereabouts, may be applied and removed with determination of accompanying 112 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS deformation and set. If set occurs the load is repeated and readings of deformation and set taken until the set becomes constant. Then the load is doubled and the same cycle of operations is repeated. This proc- ess is applied again and again until the load is reached at which the set continually increases. When this method is applied to a material having a true elastic limit it is well to decrease the increments of load in proximity of the elastic limit. 111. Stress-deformation Diagrams. — It is customary in this country to plot curves using unit stress as ordinates and unit deformations as abscissas with the curve lying in the first quadrant. The scales for such diagrams should be so selected that the slope of the curve will lie between 30 and 70 degrees with the horizontal; otherwise the curvature of the dia- gram is made too flat or too steep and there is also difficulty in determining the modulus of elasticity with accuracy. If the repetition method of load- ing has been employed in testing, curves showing the gross sets, gross deformations, and net deformations are generally plotted against unit stress. On such diagrams in addition to a suitable title and proper label- ing of the coordinates, it is good practice to indicate the value of the modulus of elasticity beside the line from which it was gotten, to indi- cate the elastic limit or limit of proportionality, the yield-point, and ultimate strength. The diagram is, in this way, made to furnish the most essential information secured in the test. COMPRESSION TESTS 112. Objects of Compression Tests. — Whereas tension tests are made for the purpose of determining many of the more significant mechanical properties of materials which are more or less ductile, compression tests are made chiefly to determine resistance to compression and the elastic properties under compression.* In testing materials possessing a high degree of elasticity the elastic limit, yield-point, and modulus of elasticity may be gotten. The determination of the ultimate strength is dependent upon the plasticity of the metal after the yield-point. In the softer varieties of steel there is no well-defined point in the loading at which a complete disintegration of structure takes place. From tests of columns made of such materials it appears that the ultimate strength is limited by the elastic limit. Consequently it is quite common to regard the elas- tic limit as 'a measure of ultimate strength in compression for these steels. Materials, possessing a high degree of plasticity, like the minor metals and their alloys, have poorly defined elastic hmits and the compressive strength is often based upon the load sustained at a given unit deforma- * Herein we shall refer to compression tests as practiced on short prisms. The testing of columns involves consideration of conditions of fabrication, end restraint, form and position of load in addition to the characteristics of the material itself. COMPRESSION TESTS 113 tion. These values furnish a basis of comparison but are far from criteria of structural strength unless determined from long-time applications of load. For brittle materials like concrete, building tile, stone, brick and timber, the compression test is of most value in establishing criteria of mechanical properties of materials. In tests on these substances, the unit stress at first crack or first sign of failure, at elastic limit — if there is one — and at ultimate are found. The position of the first crack, the character of the explosion at rupture and the shapes of the fragments are all note- worthy. The unit stress at first sign of failure coupled with a knowledge of the place of initial weakening may indicate faulty imposition of load or a local defect in material. The character of the explosion at rupture and the shape of the fragments are also of assistance in determining whether the load was axially or eccentrically applied. Flowing of the bedment often produces vertical splitting of the test-piece. 113. The Form of Compression Specimens. — The form of specimen which has been most frequently adopted is the cube. For materials which rupture on planes inclined more than 45° with the horizontal, the cube is not suitable; since the strength is increased by frictional restraint acting at the surfaces under pressure. Prisms or cylinders with a height equal to twice the least lateral dimension are better types of test-piece for such materials. Owing to weaknesses at corners due to the methods of fashioning the specimen and to the impossibility of securing full resist- ance from the material in the corners, a cylindrical test-piece is preferable. In Fig. 7 appears three curves showing the relation of crushing strength to the ratio ; --r—; r-r- • — • The results on cast-iron cylinders least lateral dimension are digested from tests by Mr. Chas. Bouton.* For these tests over 100 specimens were prepared from five bars of each of two kinds of cast iron. Comprehensive tests on Swiss sandstone prisms by Prof. J. Bauschinger f furnished the data for the corresponding curve in the above figure. From these tests on rectangular prisms, Bauschinger derived the following formula, /So =5600 -I- 1400 4; h in which Sc is in pounds per square inch, A is the area in square inches, and h is the height in inches. For a general formula he recommended &= ""' '"^ * M.S. Thesis, Theory and Experiments on Laws of Crushing Strength of Short Prisms, Washington Univ., 1891. t Mittheilungen aus dem Mechanisch Technischen Ldboratorium der K. Technischen Hochschule in MUnchen, von J. Bauschinger, Vol. 6, 1876. 114 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS where w = perimeter of cross-section; a and h are constants, and the other quantities are the same as before. A simpler relation for Bausohinger's tests on sandstone is given by iSc = 5500-|-1565|, h where d is the minimum lateral dimension. 1.7 1.5 d 1.3 g •g 1-1 0.9 0.7 0.5 C = Legend c 8 X 8 in. in cross-section - s= Sandstone prisms 2i^ x 5 in. to 5 X 5 in. in cross-section, i =Cast Iron cylinders. \ \ \\c \ s m '"\V ! '< ^ ~i~~~s i_CaatJ i •■°B..u- i \ ^ ^- s s Sands tone s \ V_ ( c C I c c t ( ( c c ( ( c c 1.0 2.0 3.0 4.0 Eatio of Height to Least Lateral Dimension 5.0 6.0 Fig. 7. — Relations between the Crushing Strengths of Prisms and Cubes. The data for the third curve in Fig. 7 was obtained from 192 tests at several college laboratories in cooperation with the National Association of Cement Users.* From the equation for the curve representing tests on sandstone prisms, Fig. 7, the following relation appears; Strength of prism Strength of cube * Concrete-Cement Age, Vol. 4, p. 141. d = 0.788+0.222 i^ n COMPRESSION TESTS 115 From this equation it appears that a sandstone prism having a height equal to twice its least width has 89 per cent of the strength of a cube of the same material. Whereas from the tests on concrete it appears that such a prism has only 73 per cent of the strength of a concrete cube. It therefore seems essential that a standard prismatic form be adopted for compression specimens. The American Society for Testing Materials has specified for metals a cyhndrical specimen between 1 and 1.129 in. in diameter and from 2.5 to 4 in. high.* At present, sentiment in this country seems to favor 16,000 0.2 0.4 0.6 0.8 Batio o£ Oompressed STi^f ace to Total Arear 1.0 Fig. 8. — Crushing Strengths of Cubes with Chamfered Edges. (Bauschinger.) 0.2 0.4 0.6 0,8 1.0 Katio of Bearing Area to Total Area Fig. 9. — Effect of Loading a Portion only of the Surface of a Cube. the adoption of a 6 by 12-in. cylinder for a concrete test-piece and a 2 by 4-in. cylinder for mortar. In spite of theoretical considerations, however, the necessity of trans- lating into new terms the mass of data which has been accumulated from tests on cubes is an obstacle to the adoption of any other form. Conse- quently, it is very probable that the cube, although improper in form, will still be used in tests of many materials when strength, alone, is wanted. For making tests of the modulus of elasticity, elastic limit, and yield- point on metals, the A.S.T.M.* permits the use of cylinders ranging in length from 10 to 15 diameters. * See Methods for Compression Tests of Metals, El-16, in A.S.T.M. Standards, 1916. 116 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS „26,000 114. Effects of Loading a Portion of the Cross-section. — Tests by Bauschinger on the effect of chamfered edges on the strength of sand- stone cubes gave the results shown in Fig. 8. The tests show that material symmetrically disposed outside of the bearing surfaces increases the strength of the test-piece. This increase is less than 3.2 per cent, how- ever, if the bearing area is more than 80 per cent of the gross cross-section. If the pressed surface is square and symmetrically located on a side of a cube the relations of re- sistances per square inch to the ratio of bearing area over total area are shown in Fig. 9. The effect of loading a rectan- gular zone having a width equal to 5 per cent of the side of the cube and a length equal to the side of the cube was also studied by Bausch- inger. In this case the resistance per square inch is a function of the distance of the zone from the edge of the surface. The results sum- marized in Fig. 10 show that the resistance per square inch of bearing area when the center of the bearing area is 4 per cent of width of the cube from the edge is 9500 lb., the normal strength of a cube. 115. Apparatus Required for Compression Tests. — Descriptions of testing machines, bearing blocks, compressometers, and bedments will be found in Ch. II. For tests on the modulus of elasticity the compres- someter should be accurate and sensitive to one one-hundredth of the deformation in the gage length. It should record deformations on at least two sides of the specimen. The yokes attaching the compressometer to the specimen should be placed not less than half of the diameter of the specimen from the nearer bearing surface. If the jield-point of hard steel is to be gotten, a pair of Capp's multiplying dividers will be found convenient. A spherical seat to permit adjustment due to non-parallehsm of the heads of the specimen is especially desirable in testing brittle tnate- rials. The value of the seat is small, however, unless provision is made for properly centering the specimens with respect to it. 116. Testing. — The cross-section of the specimen should be deter- mined at several points along its length. On cylindrical specimens meas- urements on mutually perpendicular diameters should be made. Metals should be measured to one-one-thousandth part and non-metallic mate- rials to one part in five hundred. Building tile, if scored, should be Fig. 10. — Effect of Loading a Zone on the Surface of a Cube. (Bauschinger.) COMPRESSION TESTS 117 measured outside of the scoring and no allowance made for the area of fillets. Although in specifications for all hollow building block and tile it is customary to demand a minimum strength in terms of the gross sec- tion only, it is worth while to obtain the net area in order that the strength of the material itself may be judged. Great care should be exercised to adjust both the bearing block and specimen so that the line of pressure will pass through the axis of test- piece, bearing block, and testing machine. steel Wrouglit Iron Wrought Iron Steel Fig. 11. — Relative Malleability of Wrought Iron and Soft Steel. All the specimens were originally of the shape of the one remaining undeformed. The wrought iron specimens uniformly show large cracks. (From von Tetmajer's Communications, Vol. 4, PI. 5.) The speed of the movable head of the testing machine ought not to exceed 0.02 in. per minute per inch of height in compressing iron or steel specimens. For plastic and brittle metals, stone, concrete, clay products and wood, speeds should not exceed 0.005 in. per minute per inch of height of test-piece. Where strength only is desired the rate of loading may be made more rapid for loads less than half to three-fourths of the ultimate strength. For very plastic materials a much slower rate of loading should be used if a quantitative determination of the crushing strength is wanted. In any series of tests the method of applying the load should remain con- stant. 118 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS The manner of making compression tests witii a compressometer is the same as that outhned in Art. 110. Also, the method of plotting the curve sheet and the information desired may be gotten from Art. 111. In making a test for crushing strength only, it is well to surround brittle test-pieces with wire meshing to prohibit fragments from flying at rup- ture. Fig. 12.— Bouton's Compression Tests on Cast Iron. 117. Observations During Test.— Care should be taken to determine the position and character of the first crack together with the load at which it occurs. With materials like low-carbon steel and wrought iron the yield-point will be denoted by the drop of the beam, by the rapid increase in motion of the divider pointers, and— in rolled material— by scaling. In tests of brittle materials the shape of the fracture should be stated thus: "pyramidal," "plane inchned S degrees to horizontal," or " cone "; and the texture of the broken surfaces examined and reported. Characteristic fractures of .wrought iron, cast-iron and sandstone speci- COMPRESSION TESTS 119 Fig. 13. — Bauschinger's Compression Tests on Sandstone. Fig. 14. — Typical Failures of 6 X 12-inch Concrete Cylinders. 120 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS mens may be found in Figs. 11, 12 and 13, respectively. Typical fractures of concrete cylinders appear in Fig. 14. TRANSVERSE TESTS 118. Objects of Transverse Tests. — For determining ultimate strength, elastic limit, yield-point, resilience and modulus of elasticity of brittle materials in cross-bending, the transverse test is often used. This test is of especial value in determining the strength, stiffness, and toughness of brittle materials. Since the deflections of brittle specimens are many times larger than the elongation in tension tests, a much more accurate determination of resilience can be made in the transverse test without expensive apparatus for measuring deformations. Furthermore, both the machine and the specimen required are inexpensive and the test may be rapidly made. Cast-iron, brick, stone, and concrete are tested principally for strength, sometimes the resilience and modulus of elasticity are obtained. Timber is tested for its strength, stiffness and resilience. Springs and spring- steel are tested for elastic limit, deflection under given loads, and resiU- ence. Railroad rails are sometimes tested for elastic hmit and ultimate strength. I-beams and other structural shapes used as beams are also tested to determine constants for use in design. Transverse tests are also made for scientific purposes to test the correctness of the ordinary flexure formulae for strength and deflection. In most cases transverse tests of ductile materials are not so well adapted to determine quality as tensile tests. ' Furthermore, the modulus of rupture and transverse elastic limit of such materials vary greatly with the length of span. Since three kinds of "stress, tension, compression, and shearing, are developed when a beam is bent under the action of external forces, the prob- lem is more complex than those thus far considered. Usually the shearing stresses are left out of account in designing both for strength and stiffness, but the conditions under which this stress should be recognized and taken account of are given in Art. 28 for strength, and Art. 30 for deflection. 119. Specimens for Transverse Tests. — For cast metals, the A. S. T. M. recommends a vertically cast cyhndrical specimen IJ in. in diameter with a span of at least 15 diameters.* By employing a circular section, a uniform thickness of slcin is ensured, and in unannealed specimens shrinkage strains due to corners are obviated. For malleable iron, however, the Society permits a test-piece of a rectan- gular section 1 in. broad by i, | or f in. thick with a 12-in. span. As Fig. *See Methods for Transverse Tests of Metah, El-16, A.S.T.M. Standards, 1916. TRANSVERSE TESTS 121 15 shows, the fixing of a standard span for such metals is of importance. The whole problem is now being considered by the I.A.T.M. When tests are made to determine constants for I-beams, T-bars or similar sections, it is necessary that the specimen be geometrically similar (preferably of the same size to avoid differences due to rolling) to the sec- tion under investigation. Tests showing the variation in the transverse es,ooo J2 60,000 15,000 40,000 3S,000 Length of Span, in. Fig. 15. — ^Relation of Span to Modulus of Rupture for Cast-iron Arbitration Test. Bars Differing in Silicon Content. Each Average Represents Nine Tests. (Matthews, in Proe. A.S.T.M., Vol. 10, p. 303). strength properties, due to changing the shape but not the area of cross- section, appear in Table I. For plate glass and flat springs, test-pieces should be flat with a length ten or more times the depth. For timber, rectangular specimens are best. The Forest Products Laboratory uses 2 by 2 by 30 in. specimens with a 28-in. span for small beam tests. In tests of larger timber beams it is advisable to make the span from fifteen to twenty times the depth. For cement and mortar specimens 1 by 1 by 6-in. prisms with a 5-in. span are convenient. 120. Apparatus Required for Transverse Tests. — Descriptions and general considerations of apparatus will be found in Ch. II. A testing machine of capacity equal to two to four times the estimated resistance of the test-piece should be selected. If a deflectometer is used, it should be accurate and sensitive to one one-hundredth of the maximum deflec- tion, for tests involving this determination only, and to one-hundredth of the deflection at the elastic limit for tests on the modulus of elasticity. If deformeters are used to measure fiber deformations, they should have an accuracy and sensitiveness not less than one one-hundredth of the def- ormation in the gaged length when the fibers are stressed to their elastic limit. Care should be taken to avoid fastening deformeters close to appli- cation points of the loads. 122 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS TABLE 1.— THE EFFECT OF SHAPE ON THE TRANSVERSE STRENGTH OF CAST IRON (C. H. Benjamin in Machinery, May, 1906) Beams loaded at center over an 18-inch span Section. Breaking Load, P (lb.). Modulus of Rupture, „ 4.6PC ■s« I ■ (Ib./in.'). Modulus of Elasticity, in 1,000,000 Ib./in.! No. of Results Averaged. Shape. Area (in.'). -^* (in.3). 2 • 4.42 1.31 7,375 25,270 8.28 2 ■ 4.44 1.55 8,125 23,450 9.25 2 1 4.58 3.12 16,150 23,210 6.61 2 o 4.40 2.88 19,900 31,125 7.05 2 o 4.36 3.38 21,400 28,450 5.61 2 4.41 3.22 25,250 35,300 6.49t 2 D 4.38 5.11 28,175 24,840 4.41 2 I 4.56 5.78 24,250 19,400 4.54 2 X 4.84 6.46 31,550 22,010 5.62 2 J. 4.61 6.52 31,750 21,940 4.71 2 J_ 4.88 6.48 34,625 24,060 4.84 •-I 4.51 0.81 5,400 30,000 10.74 u 5.10 1.99 8,350 18,900 •8.57 r^ 4.61 0.69 4,700 30,580 10.17 •-^ 4.80 1.61 8,800 24,600 11.06 •v 4.41 0.83 4,400 23,700 ^. 4.60 2.30 12,250 24,000 9 34 -r 4.47 1.77 7,900 20,050 7.10 JU 5.02 4.36 22,600 23,250 7.88 T 4.50 1.78 10,200 25,800 6.23 JL 5.18 5.95 25,000 18,900 ' 7.28 * c ia the distance to the extreme fiber in tension. | Only one result. Rocker supports or swinging links should be used at the ends of the specimen to prevent longitudinal compression in the lower fibers when the beam is loaded. Also, if a pair of loads is imposed through a loading beam, rollers should be used between specimen and loading beam to avoid compounding of the specimen and loading beam through friction at the load points. A high intensity of compression under the loads and over the reaction should be avoided by the use of metal bearing plates. TRANSVERSE TESTS 123 For transmitting loads to large timber beams, the Forest Products Labora- tory uses heavy maple shoes which rest upon |-in. steel plates. The lower surface of the shoes is cut to a circular arc having a cord length of 13J in. and a mid-ordinate of j^ in. When structural shapes are tested, they should be braced and loaded as far as possible, in accordance with the conditions of use. I-beams and girders should, in most cases, be laterally braced at the supports. For tests of cast and brittle metals, the speed of moving head is limited to 0.2 in. per minute by the A.S.T.M. The Forest Products Laboratory uses a speed of j in. per minute on large timber beams and 0.1 in. per min- ute on 2 by 2 by 30 in. specimens. For tests on brick, stone and similar brittle materials the speed should be such that the rate of deforming the extreme fiber of the specimen will not exceed 0.002 or 0.003 per minute.* In the tests where deflections are being read, it is best to apply the load at a sufficiently low rate to permit the readings being taken without stop- ping the machine. Such procedure is impossible when deformeters are being used, but the time intervals allowed for readings should be con- stant during such tests. It is well to use increments of load of about one-tenth the estimated load at elastic limit and when in the proximity of the elastic limit reduce the increments to one-fifth of their former value. 121. Observations During Test. — The transverse elastic limit of metals as determined from deflections is generally higher than the tensile elastic limit and not so plainly perceived. The yield-point is denoted by the drop of beam and by scaling in the case of rolled sections. The posi- tion of the scaling and its advance over the test-piece are well worth careful note. The ultimate strength of ductile metal specimens is often very hard to determine with exactness; but, if a slow speed is used, the maximum load may be approximately ascertained. In testing brittle materials like cast iron, the observer must be alert if he is to note the load and deflection at failure. The character of the fracture should be recorded with care. When testing timber, concrete, malleable cast iron and like substances, the load at first crack should be noted and the position and character of the crack recorded. 122. Load Deflection Curves. — Ordinarily, loads are plotted as ordinates and deflections as abscissas. The scales should be such that the initial portion of the curve has a slope of over 20 degrees with respect to the load axis. On such diagrams it is good form to indicate the elastic limit, yield-point, modulus of rupture (Sm), modulus of elasticity, and resilience. * Formulas for speed of the moving head of the testing machine appear in Art. 231. 124 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS IMPACT TESTS 123. Object of Impact Tests. — For measuring the abilities of materials to withstand sudden shocks or blows, experience has shown that none of the static tests are entirely suitable. Such determinations can best be made under tests approximating the kind of loading which the material must bear. Although impact tensile and compressive stresses are com- monly encountered in construction, the difficulty of providing suitable means for producing and measuring these stresses has prevented the adoption of tensile or compressive impact tests. Impact transverse tests have, however, been used to determine the shock resistance of struc- tural elements like rails, axles, car wheels and car couplers, and to deter- mine the shock-resisting qualities of both brittle and ductile materials. Of particxilar value is this test in ascertaining the influence of heat treat- ment on the brittleness of steels. Owing to the impossibility of accurately measuring the proportion of the energy of a blow which is absorbed by the specimen, impact tests can- not give absolute indications of shock resistance. Nevertheless, by care- fully standardizing machines, the methods of making tests, and the forms of specimens, it is possible to make comparisons which are very valuable. In tests of structural forms, the acceptance of material is generally based upon the ability of certain selected pieces to withstand an arbitrary number of blows without being deformed beyond a certain limit. In tests of small specimens for the purpose of ascertaining the quality of the metal it is possible to compute with fair accuracy the energy of rupture which serves as a criterion of quality. The Forest Products Laboratory deter- mines the energy of rupture per unit of volume, the elastic limit and modu- lus of elasticity of small timber beams under impact. The energy of rup- ture of ductile materials may be gotten if the shape of the specimen is suitable. 124. Specimens for Impact Tests. — For brittle castings round bars are well adapted for impact specimens. For cast iron and malleable cast iron, the specimens used in standard transverse tests may be employed. If parts are to be used in service as cast, the skin should not be removed from test-pieces. ^ To produce failure in ductile materials, it is necessary to make an abrupt contraction in area at the section under maximum stress. This may be accomplished by nicking, by sawing, or by drilling a hole to serve as the base of a saw-slot. Mr. C. Fremont who made exhaustive experiments to standardize the notched impact test on metals, was led to the adoption of a specimen 30 by 10 by 8 mm. with a 1 by 1 mm. notch extending transversely across the 10 mm. face. A committee of the International Association for Testing Materials appointed to investigate this type of IMPACT TESTS 125 test recommended at the 1908 Congress that two sizes of bar be adopted, one 30 by 30 by 120 mm. with a span of 100 mm. having a nick 15 mm. deep with a base rounded to a 2 mm. radius; the other, one-third of the above dimensions. Small specimens are preferable to large ones, since the effect of segregation and defects are more pronouncedly revealed pro- vided proper precautions are taken in locating the specimen. The previously mentioned committee reported at the 1912 Congress of the I.A.T.M. that nicked test-pieces geometrically similar but differ- ing in dimensions did not give the same energy of rupture per unit of vol- ume. Consequently one must avoid comparing results gotten from nicked test-pieces differing either in shape or size unless the effect of the differ- ence is known. Tests by Fremont * indicate that slight differences in the width of the saw-cut produce negligible effects on the results, while Thomas' f experiments show that the angle between the sides of the nick may be varied from to 30 degrees without materially influencing the energy of ruptiu-e. The experiments of Tetmajer, however, indicate that large variations in the curvature at the bottom of the nick or groove should be avoided. For specimens of the same dimensions, care must also be taken to make the depth of notch constant. In tests on structural forms made of ductile material it is well to mark a nmnber of equal intervals on both sides of the tbst-piece at sections where maximmn stress will occur under impact. After impact, measurements of flow and compression will thus be made possible. 125. Considerations Involved in the Selection of an Impact Testing Machine. — The fundamental conditions which one must consider in selecting an impact machine have been briefly considered in Art 58. It must be pointed out, however, that machines are far from being stand- ardized. In the drop machines, with the exception of the machine for testing rails (see Art. 60), there is a wide diversity of conditions. No standard relations of tup to anvil have been adopted, nor has there been any standardization of the height of drop. Fremont recommends a drop of at least 4 meters and an anvil weighing forty times as much as the tup. Experience seems to show that the hammer should be at least fifteen times as heavy as the specimen. When drop machines are used to apply blows smaller than required for rupture, some means should be provided to avoid secondary effects on the test-piece due to rebounding of the hammer. A standard pendulum machine, Charpy type, has been adopted by the German Association for testing materials, but there are in use a large nmnber of other types in some of which the anvil is much too hght. In * Proc. I.A.T.M., 6th Congress, ^. t Proc. A.S.T.M., Vol. 15, p. 63. 126 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS such machines the loss of energy through vibration must be great. Wide variation also exists in range of the velocity of impact. The cantilever method of supporting a specimen should be avoided, since it is very difficult to duplicate the end conditions in successive tests. Friction losses are also worthy of attention, especially in drop machines. Friction effects in such machines may be made small by keeping the guides free from rust and wiping them with a cloth dipped in powdered graphite. Calibrations for friction losses can be made by measuring the elastic deflec- tion of a spring attached to the anvil of the machine when subjected to different impacts and comparing the energy absorbed with that required to deflect the spring a like amount under static loading. The friction in drop machines equipped with a drum and tuning fork may be gotten by determining the slope of the velocity-time graph and comparing with the acceleration due to gravity. The curvature of the knife-edges on the anvil and especially on the hammer is of importance. The hammer knife-edge on the Charpy machine has a radius of curvature of 2 mm. 126. Testing. — In drop machines where successive blows are to be struck, provision should be made to keep the specimen from jumping off of the supports during the test by means of slots or yokes near the ends; but fixing of the ends should be avoided. In tests on pendulum machines, the specimen must be placed tightly against the anvil. Where rupture is produced by a single blow it is best to adopt a uniform height of drop in order that the velocity of impact may be the same in all tests. Pains should always be taken to see that every specimen is so placed that it receives the blow in the same position as its predecessors. Nicked specimens must be placed with the nick exactly opposite the hammer knife-edge. If such specimens are round, the base of the nick should be parallel to the hammej knife-edge when the latter is in contact with the test-piece. Timber specimens should be placed so that planes tangent to the annual rings will be perpendicular to the direction of the blow. When the elastic limit is to be found, the deflection of the specimen is determined for successive blows in which the energy is progressively increased. The energy of the blow is then plotted against the square of the corresponding deflection. The elastic limit is the unit stress corre- sponding to the point at which the square of the deflection increases in faster ratio than the energy. In such tests it is impossible to measure the total energy absorbed by the specimen. The amount lies between the energy of the final blow and the sum of the energies in all the blows. In general, it is not possible to prescribe which of these quantities will form the better index for comparing ultimate resistance to impact, unless the form of the load-deflection curves are known. Consequently, a single HARDNESS TESTS 127 blow large enough to produce rupture is the preferable method of securing data on energy of rupture under impact.* 127. Observation after Rupttire. — In tests on metals, the shape of the fractured surface, its inclination with respect to axis of the piece, and its texture should all be recorded. If the metal is ductile the relation of the plane of failure with respect to the notch or nick should also be care- fully observed. When a rolled piece is tested the limits of the scaled area are noteworthy. On polished specimens, the area showing lines of strain and the character of these lines should be noted. Microscopic examinations of the portion next to the break are often very useful in determining struc- tural defects which cause peculiar results. HARDNESS TESTS 128. Ejnds of Hardness. — Hardness as appUed to metals, minerals and other solids is a term of variable meaning. Resistance to abrasion, to indentation, and to cutting have all been considered criteria of hard- ness; but no one of these serves in general, as a criterion for the others. Apparently abrasive resistance depends largely upon adhesion between the particles, resistance to indentation upon cohesion and cutting resist- ance upon both cohesion and adhesion. Therefore, it seems likely, and the results of tests f show, that for pure metals which are nearly homogene- ous these different resistances are closely related. However for sub- stances like cast iron, tempered steels, alloy steels, and alloys in which there is a decided difference in the mechanical properties of the constit- uent particles there appears to be no relation between these resistances. Since in practice distinct demands for the different sorts of hardness exist, it is quite desirable to standardize tests for the measurement of these prop- erties. Thus far no single test has been devised which is in general well- adapted to measure all of these different kinds of hardness; nor is it hkely that one ever will be devised. Relative hardness of similar substances may be gotten but no absolute standard appears. 129. Types of Hardness Tests. — The scratch test made with a dia- mond point is the oldest and simplest method of determining abrasive hardness. However, owing to difficulties in standardizing, this test has not come into general use. Probably the most satisfactory method of using it is that of Martens (see Art. 61). For measuring cutting hardness, especially of cast iron, use has been made of the Bauer drill test. In this test the quantity of metal removed by a standard drill operating under constant speed and pressure for a cer- tain time interval, is considered an index of cutting hardness. * For methods of testing axles and rails under impact consult the current Standards of the A.S.T.M.; also see Engr. News, Vol. 75, p. 701. t See T. Turner's tests, Jour, of Iron and Steel Institute^ 1909, No. 1, p. 426 128 THE MECHANICAL TESTING OF STRUCTURAL MATERIALS Resistance to penetration has been experimented upon more scientific- ally than any other phase of hardness. The Rodman pyramidal punch which was attached to a falling weight was standardized by the French Commission and the following law deduced by Lieut. Col. Martel: * " For all forms of pyramids, for all weights of ram, and for all heights of fall, the volume of the displaced material of a given quality is equal to the energy of the blow (wh) divided by a constant, D, which constant is the work or energy necessary to displace (by deformation) a unit-volume of that material. This constant is therefore characteristic of that material and may be taken as its index of hardness, or of its resistance to indenta- tion." At present two forms of test are being widely employed in this coimtry, the Brinell ball method and the Shore scleroscope (see Art. 62 and 63). These methods will be considered in some detail. 130. Objects of Indentation Tests on Metals. — Indentation tests serve two very useful purposes: 1, to determine the quality or condition of parts which — on account of size or shape — cannot be subjected to other mechan- ical tests or which must not be destroyed in testing; 2, to determine hard- ness. In either case comparisons must be made with materials of like nature, since neither test furnishes a satisfactory indication of the com- parative hardness or other mechanical properties of all substances. For example, with the scleroscope soft wood gives as high readings as hard steel, and India rubber gives readings equal to soft steel. Furthermore, comparisons between two dissimilar materials one of which had been tested by the scleroscope and the other by the Brinell method cannot in general be made. As an illustration, Devries showed that an alloy of 90 per cent copper and 10 per cent tin had a hardness greater than annealed tool steel when measured by the scleroscope but when measured by the Brinell method it was slightly harder than copper. 131. Relations between Resistance to Indentation and Strength. — Tests by several investigators, among which those of Abbott f and Tur- ner I are especially noteworthy, show that the ultimate tensile strength and the resistance to penetration of steels are linearly related. Abbott's results are based on about four thousand tests on five types of steel, each of which was heat treated in various ways. The upper limit of the strength for each type reported varied from 250,000 to 300,000 lb. Equations deduced by Abbott correlating strength and hardness appear in Table 2. The tests showed a better agreement between the results of the Brinell * The device was first used by Col. T. J. Rodman (U.S.A.) before 1860; see liis Report of Experiments on Metals for Cannon anil Cannon-Powder, 1861. For standardization, see Commission des Milhodes d'Essai des Matiriaux de Construction, Vol. 3, p. 261. t Proc. A.S.T.M., Vol. 15, p. 43. i Jour, of Iron and Steel Institute, 1909. HARDNESS TESTS 129 and scleroscope methods when the hardness readings were less than 300 (Brinell scale) than for higher values. TABLE 2— RELATIONS BETWEEN THE TENSILE STRENGTHS OF VARI- OUS STEELS AND THEIR HARDNESSES (Abbott) Kind of Steel. Ultimate Strength in 1000 Ib./in.s (.Si) in Terma of Relation of Brinell Hardness Number Brinell Hardness Number (B). Scleroscope Hardness Number (S). to Scleroscope Hardness Number. Carbon steel S( = 0.73B-28 no 130 120 uo 100 \ \ ^ ^ k i \, s N ) n k r~i ?-J >-A [—i — C H kJ ?, '\ led Oa k > k, r ^ f> \ ^ H r^ ' \ — c -^ Ni L( ag ea Pi le I \ % N , ^ ^ ^ --^ ^ n ri N ?—c ti: dg spc le >in J "^ — ' -^ ~ w ^ te= <= ^o -o. ~i3 -o s "-.s- 1— ' _j _r ed a am -*^ ^ 10 18 U 16 18 20 Time Seasoning— Months 24 26 Fig. 6. — Losses in Weight of Ties with Long-continued Seasoning. (W. H. Kempfer in Bull. No. 161, Am. Ry. Engr. Assoc, p. 215.) dried more rapidly than those piled 9 by 9. Coniferous wood may be dried to constant weight in a shorter time and at a more rapid rate than many of the hardwoods. Fig. 6 shows drying charts for a number of tests on different kinds of ties. Large structural timbers of coniferous wood generally require seasoning for two summers, while smaller ones require only one summer in our northern latitudes. On account of the long time required for successful air-drying, a considerable proportion of ceftain woods like maple and gum rot before seasoning is completed. * Bull. 118, Forest Service. 152 PHYSICAL PROPERTIES AND USES OF WOOD There are a great many schemes in use for kiln-drying lumber, but in most of them either warm moist air or superheated steam is the drying medium. Kiln temperatures varying from room temperature to 180° F., and drying periods of a few days to several months are used. In some yards working on hardwoods, a short period of air-drying is followed by kiln-drying. For most successful kiln-drjdng the timber should be brought to as high a temperature as it will stand without injury before drying is begun; otherwise the moisture in the hot outer fibers of the wood will tend to flow toward the cooler interior. The proper condition may be obtained by cir- culating air with a high humidity until the wood is thoroughly heated, and then gradually diminishing the humidity to bring about drying. Tiemann* states that oak, western larch and cypress require a high humidity (80-90 per cent), at the start and should be held at 50 per cent until toward the end of the run. Most of the conifers may, however, be run at lower humidities. With some green timbers initial temperatures of only 120° F. or even less must be used, while others can be started at temperatures above 212° F. Besides control over humidity and temperature, it is essen- tial that the uniformity of both be secured by ample circulation. Air-drying is less expensive in operation but ruins more lumber than kiln-drying. Proper air-drying is preferable, nevertheless, to badly man- aged kiln-drying. It is used very extensively in drying ties and the larger sizes of structural timbers. With kiln-drying there is a smaller loss in timber, usually less than 10 per cent even in timbers like gum. Also, with kiln-drying, the wood is more thoroughly and evenly dried, thus reducing the hygroscopicity of the wood. It is claimed, furthermore, that sap stains may be prevented and the gums and resins fixed by cor- rect kiln-drying. The figures in the following table f furnish an approximation of the amount of water lost in drying green timber: POUNDS OF WATER LOST IN DRYING 100 POUNDS OF GREEN WOOD IN THE KILN Common Names of Species, Sapwood or Outer Part. Heartwood or Interior. (1) Pines, cedars, spruces, and firs 45-65 50-65 60-65 40-50 le-'^s (2) Cypress, extremely variable 18-60 (3) Poplar, Cottonwood, basswood (4) Oak, beech, ash, elm, maple, birch, hickory, chestnut, walnut, and sycamore 40-60 30-40 The lighter kinds have the most water in the sapwood ; thus sycamore has more than hickory. * See previous citation. t Roth in Bulletin No. 10, U. S. Dept. of Agric. PHYSICAL PROPERTIES OF WOOD 153 161. Shrinkage and Its Effects. — For purposes of illustration con- sider a very small, thin transverse section of green wood, Fig. 7 A. If this section is very slowly and uniformly dried no change will be noted in the disc until the water in the pores is evaporated. Then the cell- walls will gradually become thinner and the sides of the disc ab, bd, etc., wUl shorten. No contraction in length of the disc is, however, observable. Furthermore, since the thickness of the end walls of the cells or fibers is very small compared to their length, it is apparent that longitudinal shrinkage of a thicker disc composing several fiber lengths will be negli- gible. If we repeat the experiment with a disc Hke that of Fig. 7B, we Y Pig. 7. — Warping of Wood. Fig. 8. — Formation of Checks. will observe that the side ab shortens more than ed and that the surfaces ab and cd are curved, Fig. 7C. In other words, thick-walled cells shrink more than those having thin walls. We shall, therefore, find that a curved disc of wood one annual ring in width will straighten in drying owing to the fact that the thick-walled cells of summer wood shrink more than the thinner walled cells of spring wood. This inequality in shrinkage between the various cells produces stresses of a serious nature during the drying of timber. Again, if a stream of warm air is directed against the side cd of the moistened , disc. Fig. 7 A, it will be noted that it shortens much more rapidly than ab, owing to the more rapid evaporation of moisture. When all portions of the disc are equally dry, ab and cd are again of equal length. 154 PHYSICAL PROPERTIES AND USES OF WOOD Thus a partially dried board exposed to the sun's rays becomes concave on the upper side, but may be straightened by turning the board over and allowing the moisture in the convex surface to be evaporated. Since water is evaporated more rapidly from the ends of the wood ele- ments than from the sides, a piece of wood like that in Fig. SX will shrink more laterally at ab than at cd. This action produces bending in the piece as shown in Fig. 8F. If the rapidity of drying is sufficiently great, the resulting pull across the grain of the wood will exceed its tensile strength and checking ensues. Fig. 8Z. After the piece has completely dried many of these checks close, although the weakening effect still remains. Rapid drying of the outside logs and timbers often causes similar cracks to appear on the longitudinal surfaces. Not all of these radial cracks close when seasoning is complete; some gradually open and remain a permanent source of weakness for a reason which we shall now explain. Looking at Fig. 14, we note that the cells in medullary rays are elongated in a direction perpendicular to the longitudinal elements. Since cells in the rays obey laws of shrinkage similar to those governing the behavior of the longitudinal elements, it is at once apparent that the rays will shrink in the longitudinal and tangential direction but not radially, whereas the longitudinal ele- ments will shrink radially and tangentially but not longitudinally. Consequently, the lateral shrinkage oi the ray in the longitudinal direction will be hindered by the adjoining longitudinal elements and the length of the ray will be shortened by the radial shrinkage of the longitudinal elements. The mutually perpendicular tensile and compressive forces thus produced are often sufficient to break the bond between the ray and the adjacent longitudinal fibers. Once the bond is broken, further circumferential shrinkage operates to widen rather than to close the breach. In woods like oak, where the number of pith rays is very large, it is probable that the slight longitudinal shrin,kage is due principally to lateral shrinkage of the rays. Also, the resistance offered by the rays to oppose radial shrinkage of the wood and the great shrinkage of the summer wood are the reasons why the tangential shrinkage of wood is always more than the radial shrinkage. The difference in shrinkage in these two directions is the cause of much difficulty in drying. Besides producing the checks in logs and sawn timbers, this difference between the tangential and radial shrinkage also causes the flat surfaces of a sawn log to become con- vex, as shown in Fig. 9. Fig. 9.— Effects of Shrinkage. PHYSICAL PROPERTIES OF WOOD 155 Fig. 10.— "Honeycombed" Board. The checks or cracks form along the pith-rays. When hardwoods, like oak, are quickly dried the water is evaporated more rapidly from the outside than it can be brought to the siu-face. As a result the outer portion of the piece checks; or, if it has sufficient plasticity under the influence of heat and moisture, the surface may take a set and harden just as wood bent in steam retains its shape after drying. If drying continues, the in- terior of the stick shrinks and the circum- ferential tension in the outer shell is re- lieved. Further shrinkage of the piece, as a whole, is diminished by the ri- % - ■ gidity of the outer shell. This brings about a gradual reversal of stress in the shell and causes radial tension in the interior.. If the radial tension becomes excessive, rupture will occur, as shown in Fig. 10. This phenomenon is called case- hardening or honey-combing. It may exist in lumber without the cracks being noticed, but is revealed immediately upon sawing. A simple test for case-hardening is that used by Tiemann (see Fig. 11). Rapid drying of green cedar and red- wood at high temperatures often produces a collapse of the cell walls. This is brought about by the radial tensile stresses pro- duced on the cell walls by the withdrawal of free water. Such defects lower the strength of the timber ; they may be avoided by using lower initial temperatures in drying. Dried pieces of wood greedily absorb water with an increase in volume until the cell walls are saturated, the fiber-saturation point is reached;* subsequent filling of the lumen in the cells is accompanied by no further swelling. Fig. 12. The following average values for per cent moisture at fiber-saturation point ■^'t >l Fig. 11. — Illustrating the Elimi- nation of Case-hardening in Kiln Dry Red Gum by Steam- ing at the End of the Drying Period. No. 1 sawn after no final steaming; Nos. 2 and 3 after eighteen minutes final steaming; No. 4 after thirty- six minutes final steaming. (J. E. Imrie, before Gum Lumber Mfrs. Assoc, Jan. 16, 1916.) * Tiemann reported in Proc. Soc. Am. For., Vol. 8, p. 313, that blue gum is an exception to the above rule, since it "begins to shrink immediately from green con- dition, even at 70 to 90 per cent moisture." 156 PHYSICAL PROPERTIES AND USES OF WOOD were obtained by Tiemann (Cir. No. 108, Forest Service). Each result represents 40 or more tests per species of wood. In some cases individual values varied as much as 10 per cent from the averages. • y .^ " ^r n-^ y ,*-3 ^ H^ >■ ^ ■\ p-c^ •i^ 0^ ^ y y 1 9 y y o \\* i-p ^ y ^ X .,rB ;.^ A^^ 1 _^ ■^ ^ y- f c- } ^ -^ 3<-^ l^ g>^ o ( 2^ ^ f ^ ^^ ^ o " 12 U 16 18 20 22 21 26 28 Moisture Per cent of Dry Weight- Fig. 12. — Relation between Swelling and Moisture. Each point is the average of from five to eleven specimens. Black dots indicate specimens that were kiln- dried and then allowed to reabsorb moisture. The fiber-saturation point is at C. {Cir. 108 of Forest Servfce.) Species. Per Cent. Species. Per Cent. Longleaf pine Loblolly pine Norway pine, heartwood . Norway pine, sapwood . . . 25 24 30 28 23 Red Spruce Chestnut Tamarack Red gum 31 25 3a 25 Douglas fir White ash 20 Repeated wetting and drying weakens timber,, causes expansion and contraction, and, in addition, produces conditions which promote decay. Timber must, therefore, be protected from moisture, if constancy in vol- ume and its life are to be conserved. The swelling of wooden pipes and tanks after water is admitted often produces large stresses in both bands PRINCIPAL NATIVE WOODS 157 and timber. The amount of swelling and the stresses caused by it should be given careful consideration in design. 162. Amount of Shrinkage. — As a rule, if the density of the sapwood and heartwood are the same, the former will shrink more than the latter; but heavy heartwood shrinks more than light sapwood. Coniferous woods like pine, spruce, cedar, cypress and redwood shrink uniformly and do not check much in drying. Oak, beech, chestnut, elm, hickory, gum, and other hardwoods shrink considerably and check more or less depend- ing on the care exercised in drying. In general, the radial shrinkage of wood is about 60 per cent of the tangential, and the longitudinal shrinkage is negligible. Therefore, the volumetric shrinkage is practically 1.6 times the tangential shrinkage. Elaborate experiments by the Forest Products Laboratory show that the shrinkage in either direction varies as the first power of the density and that this relation holds for all species. The following coefficients worked out by Mr. J. A. Newlin give the per cent shrinkage when multiplied by the specific gravity: 26.5 for volume, 9.5 for radial, and 16.5 for tangential shrinkage. Approximate values of the tangential shrinkage of air-dried material are given below, more accurate results appear in Table 1, Ch. VI. APPROXIMATE SHRINKAGE OF A BOARD, OR SET OP BOARDS, 100 INCHES WIDE, DRYING IN THE OPEN AIR Common Names of Species. Lateral Shrinkage Inches. (1) All light conifers (soft pine, spruce, cedar, cypress) (2) Heavy conifers (hard pine, tamarack, yew), honey-locust, box-elder, wood of old oaks (3) Ash, elm, walnut, poplar, maple, beech, sycamore, cherry, black locust . . (4) Basswood, birch, chestnut, horse chestnut, blue beech, young locust .... (5) Hickory, young oak, especially red oak 4 5 6 Up to 10 PRINCIPAL NATIVE WOODS* 163. The sources, characteristics, and uses of the more important woods will now be briefly described. In the list which follows, an attempt has been made to arrange the various classes of wood in order of economic importance. Within a given class, however, there may be individual species which are of less value than species in a class farther down in the list. For example: Sugar pine, lodgepole pine, and tupelo gum are less valuable than hickory; but the pines and gums as groups are more valu- * Compiled largely from Hough's Handbook of Trees, Snow's Principal Species of Wood, and Bulletin No. 232 of the U. S. Dept. of Agric. 158 PHYSICAL PROPERTIES AND USES OF WOOD able than hickory. The mechanical properties of many of these woods can be found in Ch. VI. 164. Southern Yellow Pine is the term appUed to the species of yellow pine which are found in Southern States from Virginia to Texas; most of our supply now comes from Louisiana, Mississippi, Texas and North Carolina. Included in this group are longleaf, shortleaf, loblolly, Cuban and pond pine. Difficulty experienced in separating these species has iDrought about the use of this inclusive term and caused the adoption of grading rules for quality classification. Longleaf and Cuban pine are, in general, heavy, hard, tough, stiff and very strong woods. They are highly durable in dry localities and fairly so in contact with the ground. The other members of the southern yellow pine group are more variable. Most specimens of the latter are inferior in structural properties to long- leaf, but they generally possess good strength and durability when not in contact with the ground. The southern yellow pines are the most important source of dimension timber for all heavy construction. They also provide much lumber for joists, posts, piling, and building con- struction. When treated with preservatives the harder woods of this group make good ties and paving blocks. 165. White Pine is still found to a limited extent in the States north of the Ohio River and east of the Dakotas, most abundantly in Minne- sota, Wisconsin and Maine. A somewhat inferior grade of white pine is obtained along the Rocky Mountains. It is a soft, uniform white wood which shrinks very little in seasoning, works easily, nails without splitting, and takes paint well. It is not very strong but quite durable. For window sash, interior trim and pattern making, the demand for this wood is very great. 166. Norway Pine is now found principally in the States bordering on the Great Lakes. It is a light wood of fair hardness and strength, but is not durable in contact with the ground. Some dimension timber, masts, spars, piling and interior trim are made of it. It is often sold for white pine. 167. Western Yellow Pine grows on the eastern slopes of the Rockies and in country westward to the coast. It is lighter, softer, weaker and less durable than longleaf pine, but heavier and stronger than white pine. It is considerably used for dimension timbers, ties and mine timbers; alttiough unless treated, it is better fitted for trim and pattern making. 168. Sugar Pine, found in California and Oregon, is a light soft wood resembling white pine ; it has similar uses. 169. Lodgepole Pine, a timber found from the Rockies to the Pacific Coast, is a light, brittle, straight-grained wood of low strength. It is also difficult to season. This pine is used principally for poles, posts and ties. PRINCIPAL NATIVE WOODS 159 170. White Oak of commerce includes true white, post, burr, overcup, swamp white, cow and chestnut oaks. Oak of this class may be found in the States east of Colorado, but the principal supply comes from the Vir- ginias, Tennessee, Arkansas, Kentucky, Ohio and Missouri. These oaks are all hard, heavy, strong, tough, dense woods which are durable in con-* tact with the soil. They shrink considerably and are likely to check in seasoning. The wood is capable of receiving a high polish. White oak is much used for furniture, cross-ties, agricultural implements, fence posts, wagon-stock, cooperage and baskets. These oaks are the most valuable of the hardwoods. 171. Red Oak of commerce includes red, pin, Spanish and black oaks. The sources of supply are the same as for white oak. The wood of the red oaks, though hard and strong, is more porous, somewhat lighter and weaker, and far less durable in contact with the soil than white oak. It is used chiefly for interior finish and furniture. It is easily impreg- nated with preservative and when so treated makes excellent cross-ties. 172. Live Oak is found along the coast of the southern Atlantic and Gulf States in California and Oregon. The wood is very heavy, hard, tough, strong, durable and difficult to work. It is used for implements, wagons and in ship buUding. 173. Douglas Fir is grown along the Pacific Coast, the most valuable forests being in Oregon, Washington and British Columbia. The wood is strong, brittle and fairly durable. It is the best structural timber of the northwest. This clear, straight-grained wood is widely used for building construction, dimension timber, ties, piles, boats, paving blocks, tanks, conduits and furniture. 174. Hemlock is found in the Great Lakes States, in southeastern Canada and from Maine to Georgia along the Appalachian range. A Western hemlock grows on the Pacific Coast from Northern California to Alaska. The wood is light, soft and brittle. The Western variety is moderately strong and fairly durable, but Eastern hemlock is weak and not durable in contact with the ground. Hemlock holds nails well and is much used in house framing. Western hemlock is considerably used for dimension timber and cross-ties. 175. Spruce. — Red spruce is found principally in New York, New England and West Virginia; white spruce in nearly all parts of Central Canada and in the Great Lakes States; Sitka spruce in Washington, Ore- gon and Idaho. The woods of these species are light and soft. They have low strength and fair durability. Spruce is used chiefly for paper pulp, railway ties, resonance wood, piles, aeroplanes and lumber. 176. C5rpress grows along the eastern and Gulf coasts from Mary- land to Texas and along the Mississippi Valley as far north as Illinois. Louisiana,. Florida and Georgia are the chief producers. It is a light, 160 . PHYSICAL PROPERTIES AND USES OF WOOD soft wood of medium strength which is rather difficult to season but very durable. Cypress is used for siding, shingles, sash, doors, tanks, silos and railway ties. 177. Hard (Sugar) Maple grows in all of the States east of Colorado "but most abundantly in the Great Lakes region. The wood is heavy, tough, hard and strong, but not durable. The grain is often curly or has " bird's eyes." It is used for interior finish, flooring, furniture, ship and car construction. When treated this wood may be used for cross- ties. 178. Soft (Red) Maple is found in the region with hard maple. The wood is heavy, hard and strong, but inferior to hard maple. It is fairly easy to work and is used for furniture, cabinet making, turnery and gun stocks. 179. Chestnut grows on both slopes of the Appalachian Range, but is produced principally in the Virginias, Pennsylvania, Tennessee, and Connecticut. It is a light, soft, weak and brittle wood which is very durable in contact with the ground. The wood shrinks considerably and checks in seasoning, but works easily. Chestnut is much used for fence posts, poles and cross- ties; also for exposed constructions, furniture, and cooperage. 180. Red (Sweet) Gum grows in the same regions as cypress and is supplied most abundantly from Arkansas and Mississippi. The wood is not durable in the ground, soft, rather brittle and of moderate weight and strength. It is easily worked, but warps and twists in seasoning. When highly pohshed it makes attractive furniture and interior trim. Other uses are for flooring, slack cooperage, turnery and wagon stock. 181. Tupelo (Sour) Gum is found with red gum, but is most abundant in the Gulf States. It has about the same weight and strength as red gum but is tougher. Thjs wood also is difficult to season and finds more or less use in the manufacture of boxes, furniture, wagon boxes, flooring and finishing. 182. Hickory is fast disappearing in this country; the present supply is obtained from Arkansas, Tennessee, and the Ohio basin. The more abundant varieties of hickory furnish very heavy, hard wood which is stronger and tougher than other native woods. Hickory checkg and shrinks largely in seasoning and is difficult to work. It is subject to insect attack and not durable. The chief uses are for wagon-stock, agri- cultural implements, axe-handles, hoops and baskets. 183. Yellow Poplar (Whitewood) is found in nearly all States east of the Mississippi River and south of the Great Lakes; it is gotten from the Virginias, Tennessee and Kentucky principally. The wood is light, soft, brittle, weak and easy to work. It shrinks considerably, but holds nails well and is fairly durable. Whitewood is a very valuable wood for PRINICPAL NATIVE WOODS 161 interior finish, furniture, shelving, drawers, wagon-bodies and boxes; it is also used for siding and paneling. 184. Basswood is scattered over the eastern half of the United States with the exception of the Southern Atlantic and Gulf Coasts; Wisconsin, Michigan, West Virginia and New York lead in production. The wood is soft, light, weak, brittle and not durable. It shrinks considerably, but is very uniform and works easily. Although slightly inferior to whitewood, it is used for similar purposes. 185. Redwood grows abundantly along the coast of California. The wood is light, soft, straight-grained and very durable. In the West it is used for all kinds of lumber; ties, shingles, poles, paving blocks, tanks and conduits. 186. Yellow and Sweet Birch are found in the region east of the Mississippi River and north of the Gulf States, also in Southeastern Canada; Wisconsin, Michigan and Maine lead in production. The wood is heavy, hard, stiff, strong, and tough; but it is not durable when ex- posed. In view of its hardness, it works easily and takes a high polish. Birch is much used for interior finish, furniture, turnery and carving. 187. Larch or Tamarack. — The ea,stern variety of this wood, generally called tamarack, is abundant in the Great Lakes region, New England, northern and eastern Canada. Western larch is found principally along the Columbia River Valley. The Western variety is of medium weight, rather tough, hard and durable, but somewhat less strong than Douglas fir or Western hemlock. It is used for lumber, lath, cross-ties, poles and slack cooperage. Tamarack is slightly less heavy and strong than Western larch. Its uses are similar. 188. Ash. — Varieties of ash are found in nearly all States east of the Rockies. Black ash is confined to the Northern States of this region, but the white and green species are widely found. The wood of the white and green ashes is heavy, hard, strong and fairly tough. It is straight grained, shrinks little in seasoning and can be poUshed. It is used for finishing lumber, in wagon construction, farm implements, fur- niture and cabinet work. Black ash makes a lighter, inferior wood to that of the white or green ashes. It is used as a substitute for them and in basket making. 189. Red and White Cedar. — ^White cedar is found along the eastern coast and around the Great Lakes; red cedar grows in the region east of Colorado and north of Florida. Western red cedar is grown largely in Washington, Oregon, Idaho and Montana. Cedar wood is very Hght, soft, weak and brittle. Its low shrinkage and great durability, when exposed, make cedar' Valuable for shingles, siding, posts, poles and ties. Red cedar is much -used for moth-proof chests. 162 PHYSICAL PROPERTIES AND USES OF WOOD 190. Beech grows in the region east of the Mississippi and in south- eastern Canada. The wood is heavy, hard, strong, tough, but not durable in contact with the soil. It shrinks and checks considerably in seasoning. It is used for furniture, plane-stocks, handles and shoe-lasts. 191. Elm. — White and slippery elms grow in the States east of Colo- rado; rock elm is found largely in Michigan and the States bordering on the Ohio River. The wood of the slippery and rock elms is heavy, hard, strong, tough, durable and difficult to spUt. The wood of white elm is somewhat inferior to that of the rock and slippery elms. Elm wood is used for agricultural implements, wheel-stock, boats, furniture, cross- ties, posts, and poles. 192. Cottonwood is found scattered over the. region east of the Rockies, excepting in Maine; abundantly in Arkansas, Mississippi, Louisiana, and Tennessee. It is a soft, weak wood similar to whitewood but inferior in quality. It is considerably used for slack cooperage, fencing and paper pulp. 193. Black Walnut is found over the eastern half of the United States with the exception of Southern Atlantic and Gulf Coasts; Indiana, Ohio and Missouri are principal producers. Some varieties are obtainable from New Mexico, Arizona and California. The wood is heavy, hard, strong and easily worked. It has a dark chocolate color and is susceptible of a high polish. Owing to scarcity, its usage is confined largely to making of cabinets, furniture and gun-stocks. 194. Sycamore is most abundantly grown in the Ohio and Missis- sippi basin, although common in most States east of Colorado. The wood is of medium weight, hardness and strength. It is rather brittle, diffi- cult to work, and liable to check and warp in seasoning. Sycamore makes a pleasing appearance when quarter-sawn. It is used for interior trim, cabinet making, tobacco boxes, and cooperage. 195. Eucalyptus is a rapidly growing Austrahan tree of which a large number of varieties have been transplanted in California. Blue gum (Eucalyptus Globulus) is the most important of these. This durable wood is very heavy, hard, tough, and strong, comparing favorably in these respects with hickory. It is, however, extremely difficult to season, since it checks and warps very badly. From results obtained in Australia, it is predicted that the American blue gum will furnish a satisfactory wood for cross-ties, fence-posts, poles, piles, paving blocks and wagon- stock. 196. Catalpa is grown in Mississippi, Alabama, Georgia, and Florida; and hardy catalpa in Missouri, Illinois, Indiana, Kentucky and Tennessee. The wood of the two species is similar, being light, soft, and weak. It is very durable in contact with the ground and makes excellent fence posts and poles. If well protected with tie-plates it also serves for cixjss-ties. THE IDENTIFICATION OF WOODS 163 The very rapid growth which is characteristic of the tree has led to the planting of it for such purposes. THE IDENTIFICATION OF WOODS * 197. The Microscopic Structure of Wood. — Thus far we have con- sidered the structure of wood which is readily discerned by the naked eye. With a microscope it has been ascertained that a few definite types of cells and fibers form the structures of all woods. Inasmuch as the recog- nition of these types of cells, as well as their arrangement and condition forms an important aid not only in identifying species, but also in account- ing for mechanical properties, a brief account of them is made. There are four main types of these microscopic elements which, with numerous tran- sitional forms, make up the structure of timber. These are (1) tracheids, (2) 'parenchyma, (3) vessels, (4) wood fibers. The two first-mentioned constitute the wood of the conifers, but all four types are found in vary- ing amounts in broad-leaved trees. Tracheids are slim polygonal cells provided with tapering ends. They are small and of little importance in the hardwoods; but in the conifers where they form the main constituents of the wood they range from 0.05 to 0.35 in. in length with a diameter of one-fiftieth to one one-hundredth of the length. The side walls of the tracheids are perforated with bor- dered pits which are funnel-like depressions most thickly found near the ends of the cell (see Fig. 13). Through the thin walls at the bottoms of these pits the sap flows from one cell to another. In Douglas fir, spiral ridges are found on the inside of the tracheids, while in long leaf and Nor- way pine the ray tracheids have irregular dentations on the inner surfaces. Parenchyma are subordinate elements, which, like the tracheids, may be arranged end to end in a vertical line, thus forming the wood parenchyma fibers; or grouped in bundles with their long axes extending radially, they compose the entire pith rays of the hardwoods and the main part of the rays in softwoods. Sometimes, as in white oak, chestnut and hickory, the wood parenchyma fibers are arranged parallel to the vessels in the rings and appear as fine concentric lines on the cross-section. In some woods they form the boundaries of the rings; in some they are scattered through the wood irregularly; in others they are arranged in radial planes, and in still others they surround the larger vessels. Parenchyma are minute, thin-walled elements tapering at the ends and subdivided by transverse walls into short, prismatic cells. The side-walls of parenchyma are dotted with minute cylindrical depressions called simple pits as in Fig. 13i^. * For a more complete discussion of the microscopic structure and the identification of woods, the reader is referred to Record's Economic Woods and Hough's American Woods. 164 PHYSICAL PROPERTIES AND USES OF WOOD By pressure of large bordering vessels the parenchyma running vertically are sometimes flattened into the conjugate form shown in Fig. IdH. In oak, hickory and walnut the individual ceils of the vertical parenchyma are often separated by crystals of calcium oxalate, see Fig. 13G. Vessels are small pipe-like elements of indefinite length, the walls of which are covered with bordered pits (Fig. 13K). The diameter of ves- sels is quite variable, sometimes reaching 0.02 in oak, but more often it is less than 0.01 in. While growing, constrictions are produced in the side- b.p. Fig. 13.— Types of Wood CeUs. At wood fiber with narrow lumen; B, wood filjcr with wider lumen and simple pita (s. p.); C, wood fiber with saw-toothed end; C, wood fiber with forked end; i), tracheids with bordered pits ib. p.) from pine; E, tracheid from oak; F, wood parenchyma fiber with individual cells and simple pits (s. p.); G, wood parenchyma with crystals of calcium oxalate from walnut; H, conjugate paren- chyma cells; K, part of segment of a vessel with simple perforation (p.t; L, part of segment of a vessel with scalariform perforation {Sc. p.). All much enlarged. (After Record.) walls, thus indicating the segments of growth. These segments may fit together (1) in a perfect transverse plane, (2) in an oblique plane,* or (3) as in oak and gum, the faces of the segments may be oblique and have blind ends extending beyond the main line of constriction. In type (1) the opening from one segment to another is round, but in (2) and (3) the perforations may be scalariform as in Fig. 13L. Vessels in the sapwood serve as vertical water supply lines for the growing portion of the tree, but in the heartwood they are frequently clogged with sac-like protrusions from adjacent parenchyma cells. These protrusions are called tyloses. THE IDENTIFICATION OF WOODS 165 Wood fibers are thin elongated cells tapering to a point at either end. They have thick walls which are ordinarily indented by inclined slit-like simple pits, see Fig. 135. In mahogany the fibers are divided by cross partitions (septate fibers) ; in other woods the fibers are often forked at the ends (Fig. 13C'), a condition which decreases the cleavability of the wood. Wood fibers vary from a fiftieth to a tenth of an inch in length. They are found most commonly in the central portion of the annual rings of the hardwoods and are an important source of strength, tough- ness and hardness. As mentioned before these various types of fibers grade into each other by transitional stages. Thus the wood fibers exhibit forms approach- ing the tracheids in some woods and approximating wood parenchyma in others, and the tracheids sometimes grade into the vessels. 198. The Structure of Coniferous Woods. — In Fig. 14 are shown (1) a sector of spruce in natural size and (2) a part of one ring from the same magnified 100 times but ^ ^ oriented to correspond with piece (1). Looking at the upper face of piece (2) we are at once im- pressed by the regular arrange- ment of the tracheids in radial rows. From left to right they become flattened radially show- ing the increase in density in passing from the spring wood to the summer wood. On the lower front portion of this piece we notice also the bordered pits, of which enlarged types are shown at o, b and c. The dark lines in piece (1) represent the medullary rays of which five are exposed on the right face of piece (2). One of these rays is seen in section on the front face of piece (2). It will be noted that the cells in the rays are elongated radially and that each ray is one cell wide (uniseriate) and several cells deep. In this wood, the top and bottom cells of each ray are tracheids (n), but the intermediate cells are parenchyma (m). The above example is typical of the regularity of arrangement of the cell structure in coniferous wood. In pine, spruce, Douglas fir, and tam- FlG 2, 14. — Wood of Spruce. 1, natural size; small part of one ring magnified 100 times. The vertical tubes are wood-fibers, in this case all "tracheids." m, medullary or pith ray; n, transverse tracheids or pith-ray; a, b, and c, bordered pits of the tracheids, more enlarged. 166 PHYSICAL PROPERTIES AND USES OF WOOD MB arack vertical and radial resin ducts are found, which are interconnected here and there to permit the passage of resin. These ducts are often large enough to be distinguished by the naked eye. They are long canals bounded by groups of thin-walled cells, termed epithelial cells. Fig. 15 shows a cross-section of shortleaf pine which passes through a vertical resin duct. Radial resin ducts are commonly inclosed in multi- seriate rays. Such ducts may often be formed by injury; chip- ping the outer sapwood of long- leaf pine opens the resin ducts and affords a method of securing turpentine and alUed products. Tyloses are sometimes foimd in tracheids adjoining parenchy- matous cells, but in conifers they are more often noticed in the resin ducts. Norway pine, West- ern pine, white pine, and sugar pine, are the main coniferous woods which have abimdant tyloses (see Art. 208). 199. The Structure of Wood from Broad-leaved Trees. — ^As we have previously mentioned, the arrangement of the cell ele- ments in the wood of the broad- leaved trees is far more varied and complex than in the conifers. We shall consider two examples, red oak to illustrate ring-porous woods and sugar maple to illus- trate diffifrie-porous woods. The magnified cross-sectional view of red oak in Fig. 16 shows very clearly the irregular grouping of the large vessels in the spring wood, with a more or less gradual transition to smaller ones scattered here and there through the summer wood. In good oak these vessels occupy less than 10 per cent of the volume of the wood, but in poorer varieties they may amount to 25 per cent. In the middle of the annual ring the dark, sohd looking patches represent the cut ends of the wood fibers. The thicker the walls of these fibers and the greater the proportion of them in the wood, the stronger and tougher will it be. In good timber the fibers constitute one-half of the volume. Two meduUjiry rays are also exposed Fig. 15. — Cross-section of»Shortleaf Pine, Showing Resin Duct Surrounded by • Epithelial Cells. {Bui. 101, U. 8. Dept. Agric, PI. 1. Magnification = 125 diam.) THE IDENTIFICATION OF WOODS 167 MB Fig. 16. — Photomicrograph of Cross-section of Red Oak, a Ring-porous Wood. SP, spring wood (note open pores) ; S, summer wood; F, fibers; V, vessels or pores; MR, medullary- ray. (Prepared by the Forest Products Laboratory Forest Service, U. S. Dept. of Agric. Magnified 40 diameters.) 168 PHYSICAL PROPERTIES AND USES OF WOOD MB in this view. The width of the band of cells composing these rays is a decided contrast to the uniseriate rays of the conifers. In the oaks, rays are often a hundred cells in width and an inch or more in height. It will be observed, however, that they always taper in width, at the top and bottom, to a single cell. Fig. 17 brings out the comparative size of the medullary rays and the ring-thickness in oak. All of the cells in the rays of the dicotyledons are parenchyma. Some of the individual parenchyma can be distinguished in Fig. 16. Beside the me- dullary rays of large size other uniseriate pith rays of parenchymatous cells may also be seen in Fig. Fig. 17.— Block of Oak. CS, cross-section; RS, radial section; TiS, tangential sec- tion; mr, medullary or pith ray; a, height, 6, width, and e, length of a pith-ray. Fig. 18. — Cross-section of Hard Maple. (Note tendency of pores, V, to form radial groups. Spring wood, SP, is much like the summer wood, iS. Narrow q^eduUary ray, MR. Fibers, F. Magnification = 34 diameters. (Photo prepared by Forest Products Laboratory, Forest Service, U. S. Dept. Agric.) 16. The total proportion of rays in good white oak generally lies be- tween 15 and 25 per cent. The arrangement of pores in a ring-porous wood like the sugar maple is more uniform, the diameters are smaller, and the variation in size is less THE IDENTIFICATION OF WOODS 169 than in the oak (Fig. 18). Scarcely any difference is to be noted in the size of the vessels in the spring wood and summer wood, but there is a ten- dency toward radial grouping of two to four cells which is plainly marked. The medullary rays are much narrower than in the oak but broader than in the conifers. When the wood is quarter-sawed these rays produce a silvery appearance. There are, however, numerous intermediate pith rays of one-cell width in evidence. A further distinguishing feature of this wood is the distinct markings which limit the growth rings. Tyloses are abundantly found in the vessels of the following hardwoods: in white, Garry, over-cup, bur, swamp, cow, valley and post oaks, in most hickories, in chestnut, black locust, and osage orange. Tyloses apparently increase the resistance of the wood to the decay and also decreases the penetrance to preservatives.* 200. The Use of a Key in Distinguishing Woods, t — Nobody need expect to be able to use successfully any key for the distinction of woods or of any other class of natural objects without some practice. This is especially true with regard to woods, which are apt to vary much, and when the key is based on such meager general data as the present. The best course to adopt is to supply one's self with a small sample collection of woods accurately named. { Small, polished tablets are of little use for this purpose. The pieces should be large enough, if possible, to include pith and bark, and of sufficient width to permit ready inspection of the cross-section. By examining these with the aid of the key, beginning with the better-known woods, one will soon learn to see the features described and to form an idea of the relative standards which the maker of the key had in mind. To aid in this, the accompanying illustrations will be of advantage. When the reader becomes familiar with the key, the work of identifying any given piece will be comparatively easy. The material to be examined must, of course, be suitably prepared. It should be moistened; all cuts should be made with a very sharp knife or razor and be clean and smooth, for a bruised surface reveals but little structm-e. The most useful cut may be made along one of the edges. Instructive, thin, small sections may be made with a sharp penknife or razor, and when placed on a piece of thin glass, moistened and covered with another piece of glass, they may be examined by holding them toward the light. Finding, on examination with the magnifier, that it contajins pores, we know it is not coniferous or non-porous. Finding no pores collected in the *From researches of Miss E. Gerry. See Jour. Agric. Research, Vol. 1, p. 464. t The remainder of this chapter is mainly the joint product of Dr. B. E. Fernow and Mr. Fihbert Roth. I Hough's Wood Sections will be found both helpful and pleasing. About one hundred and fifty species of American woods are now so prepared by Mr. Romeyn Hough, Lowville, N. Y.— J. B. J. 170 PHYSICAL PROPERTIES AND USES OF WOOD spring wood portion of the annual ring, but all scattered (diffused) through the ring, we turn at once to thg class of " diffuse-porous woods." We now note the size and manner in which the pores are distributed through the ring. Finding them very small and neither conspicuously grouped, nor larger nor more abundant in the spring wood, we turn to the third group of this class. We now note the pith-rays, and finding them neither broad nor conspicuous, but difficult to distinguish even with the magnifier, we at once exclude the wood from the first two sections of this group and place it in the third, which is represented by only one kind, cottonwood. Finding the wood very soft, white, and on the longitudinal section with a silky luster, we are further assured that our determination is correct. We may now turn to the list of woods and obtain further information regarding the occurrence, qualities, and uses of the wood. Sometimes our progress is not so easy; we may waver in what group or section to place the wood before us. In such cases we may try each of the doubtful roads until we reach a point where we find ourselves entirely wrong and then return and take up another line; or we may anticipate some of the later-mentioned features and, finding them apply to our speci- men, gain additional assiu-ance of the direction we ought to travel. Color will often help us to arrive at a speedy decision. In many cases, especially with conifers, which are rather difficult to distinguish, a knowl- edge of the locality from which the specimen comes is at once decisive. Thus, Northern white cedar, and bald cypress, and the cedar of the Pacific will be identified even without the somewhat indefinite criteria given in the key. Key to the More Important Woods of North America I. NON-POROUS WOODS Includes all coniferous woods. A. Resin-ducts wanting.* 1. No distinct heartwood. a. Color effect yellowish white; summer wood darker yellowish (under microscope pith-ray without tracheids) Fibs b. Color effect reddish (roseate) (under microscope pith-ray with tracheids) Hemlock 2. Heartwood preselit, color decidedly different in kind from sapwood. a. Heartwood light orange-red; sapwood pale lemon; wood heavy and hard Yew 6. Heartwood purplish to brownish red; sapwood yellowish white; wood soft to medium hard, light, usually with aromatic odor .... Red Cedar c. Heartwood maroon to terra cotta or deep brownish red; sapwood light * To discover the resin-ducts a very smooth surface is necessary, since resin-ducts are frequently seen only with difficulty, appearing on the cross-section as fine whiter or darker spots normally scat- tered singly, rarely in groups, usually in the summer wood of the annual ring. They are often much more easily seen on radial, and still more so on tangential sections, appearing there as fine lines or dots of open structure of different color, or as indentations or pin-acratches in a longitudinal direction. KEY TO THE MORE IMPORTANT WOODS 171 orange to dark amber, very soft and light, no odor; pith-rays very distinct, specially pronounced on radial section Redwood 3. Heartwood present, color only different in shade from sapwood, dingy-yellowish brown. a. Odorless and tasteless Bald Cypress 6. Wood with mild resinous odor, but tasteless White Cedar c. Wood with strong resinous odor and peppery taste when freshly cut. Incense Cedar B. Resin-duots present. 1. No distinct heartwood; color white, resin-ducts very small, not numerous. Spruce 2. Distinct heartwood present. o. Resin-duets numerous, evenly scattered through the ring. a'. Transition from spring wood to summer wood gradual; annual ring distinguished by a fine line of dense summer-wood cells; color white to yellowish red; wood soft and light. Soft Pines * b'. Transition from spring wood to summer wood more or less abrupt; broad bands of dark-colored summer wood; color from light to deep orange; wood medium hard and heavy. . . .Hard Pines * b. Resin-duots not numerous nor evenly distributed. a'. Color of heartwood orange-reddish; sapwood yellowish (same as hard pine); resin-ducts frequently combined in groups of 8 to 30, forming lines on the cross-section (tracheids with spirals). Douglas Spruce (Douglas Fir) 6'. Color of heartwood light russet-brown; of sapwood yellowish brown; resin-ducts very few, irregularly scattered (tracheids without spirals) Tamarack ADDITIONAL NOTES FOR DISTINCTIONS IN THE NON-POROUS GROUP. Spruce is hardly distinguishable from fir, except by the existence of the resin- ducts, and microscopically by the presence of tracheids in the medullary rays. Spruce may also, be confounded with soft pine, except for the heartwood color of the latter and the larger, more frequent, and more readily visible resin-ducts. In the lumber-yard hemlock is usually recognized by color and the slivery char- acter of its surface. Western hemlocks partake of this last character to a less degree. Microscopically the white pine can be distinguished by having usually only one large pit, while spruce shows three to five very small pits in the parenchyma-cells of the pith-ray communicating with the tracheid. The distinction of the pines is possible only by microscopic examination. The following distinctive features may assist in recognizing, when in the log or lumber- pile, those usually found in the market: The light, straw color, combined with great hghtness and softness, distinguishes the white pines (white pine and sugar-pine) from the hard pines (all others in the market), which may also be recognized by the gradual change of spring wood into summer wood. This change in hard pines is abrupt, making the summer wood appear as a sharply defined and more or less broad band. The Norway pine, which may be confounded with the shortleaf pine, can be dis- tinguished by being much lighter and softer. It ipay also, but more rarely, be con- * Soft and hard pines are arbitrary distinctions, and the two are not distinguishable at the com- mon limit. 172 PHYSICAL PROPERTIES AND USES OF WOOD n. RING-POROUS WOODS [Some of Group D and cedar-elm imperfectly ring-porous.] A. Pores in summer wood minute, scattered singly or in groups, or in short broken lines, the course of which is never radial. 1. Pith-rays minute, scarcely distinct. a. Wood heavy and hard; pores in the summer wood not in clusters. a'. Color of radial section not yellow Ash b'. Color of radial section light yellow; by which, together with its hardness and weight, this species is easily recognized. Osage Obange 6. Wood Ught and soft; pores in the summer wood in clusters of 10 to 30. Cataua founded with heavier white pine, but for the sharper definition of the annual ring, weight, and hardness. The longleaf pine is strikingly heavy, hard, and resinous, and usually very reg- ular and narrow-ringed, showing little sapwood, and differing in this respect from the shortleaf and loblolly pine, which usually have wider rings and more sapwood, the latter excelling in that respect. If the pith is present in the cross-section, the following method, which was pro- posed by Mr. Arthur Koehler of the Forest Products Laboratory, serves to distinguish longleaf pine: Make the pith and surrounding rings clearly visible by smoothing with a knife and moistening the smoothed surface. By the aid of a finely graduated rule and low-power lens measure the diameter of the pith. If it is less than 0.10 in. the specimen is not longleaf. In case the diameter of the pith is over 0.10 in., measure the diameter of the second annual ring, being careful to avoid mistake in identifying the second ring. On a piece of cross-sectional paper mark the diameter of pith as ordinates (y) and the diameter of the second annual ring as abscissas (x). Using scales of 1.0 in. = 0.05 for diameter of pith and 1.0 in. =0.25' in. for diameter of second ring, draw a smooth curve through the following points: a; = 0.40, j/ = 0.09; x = 0.75, y = 0.12; a; = 1.05, 2/ = 0.151; a; = 1.50, j/ = 0.198; x = 2.00, y = 0.257. From the curve find diam- eter of pith corresponding to the measured diameter of the second ring. If this value is smaller than the measured ^iameter of pith, the specimen is longleaf, or very rarely Cuban pine. If the measured diameter of pith is nearly the same as the chart diam- eter, make check measurements on the other end of the specimen. The following convenient and useful classification of pines into four groups, pro- posed by Dr. H. Mayr, is based on the appearance of the pith-ray as seen in a radial section of the spring wood of any ring: Section I. Walls of the tracheids of the pith-ray with dentate projections. a. One to two large, simple pits to each tracheid on the radial walls of the cells of the pith-ray. — Group 1. Represented in this country only by P. re^nosa. 6. Three to six simple pits to each tracheid, on the walls of the cells of the pith- ray. — Group 2. P. tceda, ■palustris, etc., including most of our "hard" and "yellow" pines. .Section II. Walls of tracheids of pith-ray smooth, without dentate projections. a. One or two large pits to each tracheid on the radial walls of each cell of the pith-ray. — Group 3. P. itrobus, lambertiana, and other true white pines. b. Three to six small pits on the radial walls of each cell of the pith-ray. — Group 4. P. parryana and other nut-pines, including also P. balfouriana. KEY TO THE MORE IMPORTANT WOODS 173 2. Pith-rays very fine, yet distinct; pores in summer woods usually single or in short lines; color of heartwood reddish brown; of sapwood yellowish white; peculiar odor on fresh section Sassafbas 3. Pith-rays fine, but distinct. a. Very heavy and hard; heartwood yellowish brown Black Locust 6. Heavy; medium hard to hard. a'. Pores in summer wood very minute, usually in small clusters of 3 to 8; heartwood light orange-brown Red Mulberry 6'. Pores in summer wood small to minute, usually isolated; heart- wood cherry-red Cofpee-treb 4. Pith-rays fine, but very conspicuous, even without magnifier. Color of heart wood red; of sapwood pale lemon Honey-locust B. Pores of summer wood minute or small, in concentric wavy and sometimes branch- ing lines, appearing as finely feathered hatchings on tangential section. 1. Pith-rays fine, but very distinct; color greenish white. Heartwood absent or imperfectly developed Hackberry 2. Pith-rays indistinct; color of heartwood reddish brown; sapwood grayish to reddish white '. Elms C. Pores of summer wood arranged in radial branching lines (when very crowded radial arrangement somewhat obscured). 1. Pith-rays very minute, hardly visible Chestnut 2. Pith-rays very broad and conspicuous Oak D. Pores of summer wood mostly but little smaller than those of the spring wood, isolated and scattered; very heavy and hard woods. The pores of the spring wood sometimes form but an imperfect zone. (Some diffuse-porous woods of groups A and B may seem to belong here.) ADDITIONAL NOTES FOB DISTINCTIONS IN THE RING-POROUS GROUP Sassafras and mulberry may be confounded but for the greater weight and hard- ness and the absence of odor in the mulberry; the radial section of mulberry also shows the pith-rays conspicuously. Honey-locust, coffee-tree and black-locust are also very similar in appearance. The honey-locust stands out by the oonspicuousness of the pith-rays, especially on radial sections, on account of their height, while the black locust is distinguished by the extremely great weight and hardness, together with its darker brown color. Fig. 19.— Wood of Coffee-tree. 174 PHYSICAL PROPERTIES AND USES OF WOOD 1. Fine concentric lines * (not of pores) as distinct, or nearly so, as the very- fine pith-rays; outer summer wood with a tinge of red; heartwood light reddish brown Hickory 2. Fine concentric lines," much finer than the pith-rays; no reddish tinge in summer wood ; sapwood white ; heartwood blackish Persimmon The ashes, elms, hickories, and oaks may, on casual observation, appear to re- semble one another on account of the pronounced zone of porous spring wood. The sharply defined large pith-rays of the oak exclude these at once; the wavy lines of pores in the summer wood, appearing as conspicuous, finely feathered hatchings on tangential section, distinguish the elms; while the ashes differ from the hickory by the very conspicuously defined zone of spring-wood pores, which in hickory appear more or less interrupted. The reddish hue of the hickory and the more or less brown hue of the ash may also aid in ready recognition. The smooth, radial surface of split hickory will readily separate it from the rest. Fig. 20.— .a. Black Ash; B, White Ash; C, Green Ash. The different species of ash may be identified as follows: 1. Pores in the summer wood more or less united into lines by parenchyma fibers. a. The lines short and broken, occurring mostly near the limit of the ring. White Ash b. The lines quite long and conspicuous in most parts of the summer' wood. Green Ash 2. Pores in the summer wood not united into lines, or rarely so. a. Heartwood reddish brown and very firm Red Ash 6. Heartwood grayish brown and much more porous Black Ash In the oaks two groups can be readily distinguished by the manner in which the pores are distributed in the summer wood. In the white oaks the pores are very fine and numerous and crowded in the outer part of the summer wood, while in the black * These fine concentrio lines are the several ends of wood parenchyma fibers. — M. W. KEY TO THE MORE IMPORTANT WOODS ADDITIONAL NOTES — Continued 175 or red oaks the pores are larger, few in number, and mostly isolated. The live oaks, as far as structure is concerned, belong to the black oaks, but are much less porous, and are exceedingly heavy and hard. Fig. 21.— Wood of Red Oak. (For White Oak see Fig. 2.) lilwi»^ Fig, 22.— Wood of Chestnut. Fig. 23.— Wood of ffickory. 176 PHYSICAL PROPERTIES AND USES OF WOOD m. DIFFUSE-POROUS WOODS [A few indistinctly >ing-porous woods of Group II, D, and cedar-elm may seem to belong here.] A. Pores varying in size from large to minute; largest in spring wood, thereby giving sometimes the appearance of a ring-porous arrangement. 1. Heavy and hard; color of heartwood (especially on longitudinal section) chocolate-brown Black Walnut 2. Light and soft; color of heartwood Hght reddish brown Butternut B. Pores all minute and indistinct; most numerous in spring wood, giving rise to a lighter-colored zone or line (especially on longitudinal section), thereby ap- pearing sometimes ring-porous; wood hard, heartwood vinous-reddish; pith- rays very fine, but very distinct. (See also the sometimes indistinct ring- porous cedar-elm, and occasionally winged elm, which are readily distinguished by the concentric wavy lines of pores in the summer wood.) Cherry C. Pores minute or indistinct, neither conspicuously larger nor more numerous in the spring wood and evenly distributed. 1. Broad pith-rays present. a. All or most pith-rays broad, numerous, and crowded, especially on tan- gential sections, medium heavy and hard, diflBcult to split. Sycamoee 6. Only part of the pith-rays broad. a'. Broad pith-rays well defined, quite numerous; wood reddish white to reddish Beech b'. Broad pith-rays not sharply defined, made up of many small rays, not numerous. Stem furrowed, and therefore the periph- ery of section, and with it the annual rings, sinuous, bending in and out, and the large pith-rays generally limited to the furrows or concave portions. Wood white, not reddish. Blue Beech additional notes for distinctions in the diffuse-porous group Cherry and birch are sometimes confounded. The high pith-rays on the cherry or radial sections readily distinguish it; distinct pores on birch and spring-wood zone in cherry, as well as the darker vinous-brown color of the latter, will prove helpful. Two groups of birches can be readily distinguishable, though specific distinction is not always possible. c 1. Pith-rays fairly distinct, the pores rather few and not more abundant in the spring wood; wood heavy, usually darker. Cherry Birch and Yellow Birch i Beech - .Sjcamore I Birclt- FiG. 24. — Wood of Beech, Sycamore, and Birch, KEY TO THE MORE IMPORTANT WOODS 177 2. No broad pith-rays present. a. Pith-rays small to very small, but quite distinct. a'. Wood hard. a''. Color reddish white, with dark reddish tinge in outer sum- mer wood Maple b". Color white, without reddish tinge Holly 6'. Wood soft to very soft. a" Pores crowded, occupying nearly all the space between pith-rays. a'". Color yellowish white, often with a greenish tinge in heartwood Tulip-poplar CUCUMBEK-TKEE 6'". Color of sapwood grayish, of heartwood light to dark reddish brown Sweet Gum 6" Pores not crowded, occupying not over one-third the pith- rays; heartwood brownish white to very Ught brown Basswood b. Pith-rays scarcely distinct, yet if viewed with ordinary magnifier, plainly visible. a'. Pores indistinct to the naked eye. a". Color uniform pale yellow; pith-rays not conspicuous even on the radial section Buckeye 6"- Sapwood yellowish gray, heartwood grayish brown; pith- rays conspicuous on the radial section Sour Gum 6'. Pores scarcely distinct, but mostly visible as grayish specks on the cross-section; sapwood whitish, heartwood reddish. Birch 3. Pith-rays not visible or else indistinct, even if viewed with magnifier. 1. Wood very soft, white, or in shades of brown, usually with a silky luster. Cottonwood (Poplar) 2. Pith-rays barely distinct, pores more numerous and commonly forming a more porous spring wood zone; wood of medium weight. Canoe ob Paper-birch The species of maple may be distinguished as follows: 1. Most of the pith-rays broader than the pores and very conspicuous. Sugab-maplb Fig. 25.— Wood of Maple. 178 PHYSICAL PROPERTIES AND USES OF WOOD ADDITIONAL NOTES — Continued 2. Pith-rays not or rarely broader than the pores, fine but conspicuous. u,. Wood heavy and hard, usually of darker reddish color and commonly spotted on cross-section Red Maple 6. Wood of medium weight and hardness, usually Hght-colored. J Silver Maple Red maple is not always safely distinguished from soft maple. In box-elder the pores are finer and more numerous than in soft maple. The various species of elm may be distinguished as follows: 1. Pores of spring wood form a broad band of several rows; easy splitting, dark brown heart Red Elm 2. Pores of spring wood usually in a single row, or nearly so. a. Pores of spring wood large, conspicuously so White Elm &. Pores of spring wood small to minute. a'. Lines of pores in summer wood fine, not as wide as the inter- mediate spaces, giving rise to very compact grain... .Rock-elm 6'. Lines of pores broad, commonly as wide as the intermediate spaces. Winged Elm c. Pores in spring wood indistinct, and therefore hardly a ring-porous wood Cedar-elm Fig. 26.— Wood of Elm. a, Red Elm; 6, White Elm; c, Winged Elm. -p.r. Fig. 27.— Walnut, p. r., pith-rays; c. l, concentric lines; v, vessels or pores; sM.«i,summerwood;sp.tu, spring wood. Vin. OR — Wood nf flhprrv. CHAPTER V THE DETERIORATION AND PRESERVATION OF TIMBER* DETERIORATION 201. The Durability of Wood. — The durability of wood is a decidedly- variable property. If well-seasoned and kept in a dry place, if immersed in water, or if buried in the ground, it often lasts for centuries. Examples of sovmd wood piling which have been buried over a thousand years, wooden buildings which have stood for centuries, and many wooden reUcs can be cited as proof of this statement. When, however, unprotected wood is subjected to mois- ture, air and moderate warmth it decays. The rapidity with which it decays depends on external condi- tions, the species of the wood, its preliminary condi- tioning, and its structure Thus in mines the life of timber sets of untreated red oak and pine is not over two or three years, in ties or fence posts it may reach four to six years, and unpro- tected pine bleachers may last ten years. In exposed structures decay nearly always starts at the sills and bottoms of posts and columns. Joints like Fig. 1 afford receptacles for the collection of water and snow with the result shown. On the other hand untreated fence posts of osage orange, * Preservation of Structural Timber, by H. F. Weiss, Bulletins Nos. 78, 118, 107, and 126 of the Forest Service, were the principal sources for the compilation of this chapter. 179 Fig. 1. — Decay at Joint and in Strut Supporting a Bleachers. (Teesdale ia Am. Lumberman, Oct. 3, 1914.) 180 THE DETEBIOBIATION AND PRESERVATION OF TIMBER black locust and red cedar often last a quarter century or more;* the life of cedar poles may be estimated at fourteen years but those of loblolly pine are likely to decay in one-third of that time. In general sapwood decays much more rapidly than heartwood. Of the effects of conditioning and structure we shall say more presently. Besides decay, wood may be injured by the attack of insects, marine borers, and woodpeckers. It deteriorates under mechanical abrasion and may, of course, be entirely destroyed by fire. 202. Composition of Wood. — Wood is essentially an organic sub- stance consisting of over 99 per cent organic and under 1 per cent inor- ganic matter. It is made up of a skeleton of cellulose Lmpregnated with lignin and the inorganic material composing the ashes. Cellulose is a whitish substance, like starch (CeHioOs), in composition, but more highly resistant to alcoholic fermentation. Lignin is also composed of carbo- hydrate compounds, but it is more soluble in acid than cellulose. Chem- ically, dry wood contains 49 per cent carbon, 44 per cent oxygen, 6 per cent hydrogen and 1 per cent ash; cellulose is made up of 44.4 per cent carbon, 49.4 per cent oxygen and 6.2 per cent hydrogen. 203. Causes of Decay. — The organic substances in wood are susceptible of attack both by bacteria and by fungi. Bacteria are very low forms of plant Ufe, often only a single cell, which multiply by cell division and subdivision. Often a large mmaber of cells unite to form minute filaments. The method by which bacteria decompose wood is not well understood, but it is probably similar in natiu:e to a fungus attack. Fimgi are also low forms of plant life which live through the destruction of other plants. They reproduce through thousands of minute particles, called " spores," which are blown about by the wind. Whenever one of these spores comes to rest it sends out microscopic filaments, " mycelia," which penetrate surrounding plant life in search of food. Sometimes, when the distance is not too great, mycelia from the fungus on a decaying timber is wafted across to a sound stick, thus communicating the disease. The destruc- tion of the wood tissue is brought about by solvent chemicals " enzymes," which are secreted in the mycelia. Only a small proportion of fungi destroy wood. Of this number some attack the lignin, others the cellulose, and still others consmne both of these substances. The attack may proceed without any external evidence of the injury which the mycelia are inflicting within the wood, or it may be proclaimed by the appearance of mushroom growths, termed " fruiting bodies," on the surfaces of the timbers. In either case, after a consider- able proportion of the cell walls has been destroyed by the mycelia, the wood becomes brittle and weak. Decaying timber is further characterized by si lack of resonance when struck with a hammer, by an abnormal * See Bull. No. 219, Ohio Agrio. Expt. Sta. DETERIORATION 181 capacity for absorbing water, and very often by an unnatural odor and color. For life and propagation, fungi require air, moisture, warmth, and food supply. Not all fungi, however, thrive equally well under the same con- ditions. For example, the house fungus {Merulius lachrymans), Fig. 2 and 3, can live in air-seasoned timber surrounded by atmosphere with less than 70 per cent relative humidity, thrives at normal room temperatures, but is killed in an hour by a tem- perature of 115° F.* This fungus has been known to lie dormant for several years in a seasoned stick of timber. All that is required to revive it is an increase in the humidity of its habitat. Frequently the house fungus furnishes no surface indication of its presence. In such cases boring into beams or planks which are thought to be contaminated may reveal the extent of the rotting. Rotted timber forms brownish chips. If the fungus is alive its presence may be detected by cutting small cubes from the edges of the brown wood region. These should be soaked in a 2 per cent citric acid solution for about six hours; they should then be removed and stored in a closed jar at 75° F. for a couple of weeks. If filaments appear the fungus is aUve. The insidiousness of the attack of the house fungus makes it most dangerous, especially in buildings of mill construction type. On account of the virility of the fungus under somewhat dry conditions, the name " dry rot " has been given to this form of decay. In contrast to the house fungus with its dry habitat and abnormal sensitiveness to heat, the following fungi which are characterized by many pores in their fruiting bodies may be mentioned : the Fames roseus, Trametes serialis and the Lemites sepiaria. The Fames roseus, Fig. 4, has a hard, pink fruiting body covered with small round pores; it lives in a saturated atmosphere and works much mischief to wood exposed in damp * This discussion of the house fungus and dry rot is abstracted from a valuable article entitled "Dry Rot in Factory Timbers," by F. J. Hoxie, of the Inspection Dept. of Assoc. Factory Mutual Fire Ins. Co., Boston. Fig. 2. — Strands of the House Fungus Found on Pine Planks at the Base of a Lumber Pile. (Photo by C. J. Humphrey.) 182 THE DETERIORATION AND PRESERVATION OF TIMBER basements. The fruiting body of the Trametes serialis, Fig. 5, is tough; the surface is white and covered with small pores. It also works in a very moist atmosphere. The Lenzites sepiaria has a semi-circular plate-like Fig. 3. — Portion of tRe Fruiting Body of MeruUus Lachrymans. Taken from a Conif- erous Timber. (Photo by C. J. Humphrey.) fruiting body which has side attachment to the wood. The under side of its fruiting body is covered with gill-Uke pores. It is very active in destroy- ing warehouse platforms and railroad ties. This fungus lives even when the temperature approaches the boiUng point of water. Certain fungi attack with avidity the products stored in the cell walls of the sapwood. This attack is most common in woods which are air-seasoned in a warm humid atmosphere. Despite the fact that no great damage to mechanical properties * appears to at- tend such action, at least in the early stages, yet the discoloration, which goes by the name of sap stain, is objectionable since it decreases the value of the timber. Fig. 4. — Fames Rosens on the End of a Tie. (Photo by C. J. Humphrey.) * See tests in Circular No. 192 of Forest Service. DETERIORATION 183 ■ '*''\. ^^ j€ 204. Insects. — Although decay . is the principal cause of deteriora- tion of timber, an immense amount of danger is done annually by the attacks of insects. Timber with the bark on is especially liable to injury from them, and the attack once started in the green log may con- tinue after the wood has been seasoned. Insects are particularly active in mine timbers, posts, poles, hickory hoops and poles, wagon stock, and pulpwood. Two common in- sects described by Weiss* are ~""'' the powder-post insect and the pole-borer. Both of these in- sects evolve from small beetles. The powder-post variety comes from a small brown or black bug which, when out of doors, deposits its eggs early in the spring on the surface of the wood. The eggs hatch into a small white grub. The grub bores into the wood and trans- forms it into a fine powder while selecting its food. After a period of growth the worm forms a cavity in the wood and lies dor- mant while its legs and wings are being developed. Since this beetle multiplies very rapidly, the deterioration of the infested timber proceeds quickly. The pole-borer comes from a reddish brown beetle about two-fifths to four-fifths of an inch long which deposits its eggs near the ground hne of posts and poles during the late summer and early fall. On hatching, the creamy white grub bores into the wood. It transforms the wood tissue into a reddish brown or yellow dust which is packed into the bur- row behind the worm. Like the powder-post insect, the pole-borer lies dormant in a cell in the wood until converted into a beetle. During the late simuner the latter emerges from the pole through a large hole near the ground Hne. The pole-borer attacks both sound and decayed timber but is not active in the latter if it is water-soaked. It has been found in poles within two years after setting in the ground. 205. Marine Borers. — There are two classes of marine borers infesting the waters of both Atlantic and Pacific Coasts, the moUusk and the crus- tacean types. Of the first class the teredo and xylotrya, which are very similar in appearance and mode of living, aire the most important. Owing * See The Preservation of Stmctural Timber, Ch. II. Fig. 5. — Trameies Serialis. Upper specimen from under side of a floor, lower specimen from side of a girder. (Photo by C. J. Humphrey. Reduced about one-half.) 184 THE DETERIORATION AND PRESERVATION OF TIMBER to their shape they are frequently called " shipworms." Either mollusk tunnels into the wood by means of a pair of shell valves and excretes the borings and a calcareous substance for lining the burrow through a pos- terior syphon. The food supply of the mollusk which consists of low forms of animal life found in the water, is secured through a second posterior syphon. The teredo rarely exceeds a length of 15 in. or a diameter of f in., but specimens of xylotrya 6 ft. long by 1 in. in diameter have been reported. Shipworms infest warm salt water or brackish waters and are said to prefer calcareous shores. They attack piling between mean tide and the low water level; and at the Isthmus of Panama and along the coast of Florida have been known to ruin untreated timber in less than one year. The limnoria or wood louse is the crustacean which is most dangerous to timber. It grows to the size of a grain of rice and bores into the wood by means of sharp jaws. It hves on food gotten from the wood sub- stance which it penetrates radially to a depth of about | in. per year. It is active only in clear salt water and confines its attack to a narrow belt around the piling near the low-water mark. The limnoria is particularly active in the Gulf of Mexico and along the north Pacific Coast. No native timber except the palmetto appears to be highly resistant to the attack of marine borers. The greenheart of South America and the jarrah of Australia are also said to be highly resistant to such attack. Pine and fir are the timbers largely used for piling in this country, but they must be protected to withstand the ravages of these pests. Creosoting by the boiling or Bethell processes, or encasing the piling in concrete jackets are the methods of protection ordinarily used. Impregnation with creosote even when well done is not always proof against shipworms, while concrete casings are expensive and hkely to be cracked. Borers in an attacked pile may be killed by chlorine gas, which is generated as follows: The pue is enclosed with a canvas 'cin-tain and an electric current passed through the pile and the enclosed salt water. The treatment is expensive and requires frequent repetitions in waters which are heavily infested with borers. 206. Other Deteriorating Influences. — Wood cross-ties, mine props and wharf timbers suffer considerable from mechanical wear. It is esti- mated that a tenth of the annual tie loss could be saved by the use of suit- able tie-plates and improved spikes. It is not always possible or econom- ical to protect timbers from mechanical wear, but in some cases iron plates may be effectively employed as shields. Fire decomposes wood into carbon dioxide, water vapor and ash. Wet wood is about twice as resistant to fire as dry wood. Structural timbers which are well-seasoned will ignite with difficulty at temperatures in the vicinity of 400° F., and very quickly at temperatures around 600° F. Wood attacked by dry rot is more combustible^than sound timber. Experi- PRESERVATION 185 ments by the National Fire Protection Association * show that the resist- ance of wood to fire can be much increased by saturating it with weak solutions (5 to 10 per cent) of ammonium sulphate or ammonium phos- phate. Impregnation of the chemicals was accomphshed by heating the solutions to 150° F. and maintaining a pressure of 130 lb. per square inch on the specimens for two hours while they were soaking. For wood exposed to moisture a treatment with zinc borate is effective. In this treatment the wood is first impregnated with a 10 per cent borax solution; 'it is then dried and again soaked in a 3 per cent zinc chloride solution. The two compounds react forming the insoluble borate which remains in the wood. The estimated cost of these treatments per thousand shingles ranged from 11.29 for the zinc borate treatment to $2.48 for a treatment with a solution of 4 per cent ammonium sulphate and 3 per cent am- monium phosphate. In view of the enormous annual fire loss in timber constructions, further experimentation along these lines should be done. Woodpeckers do considerable injury to poles by boring into them and building their nests. Where the holes are well above the ground line, they cause little direct loss in strength or stiffness, but they afford excellent breeding grounds for fungi and thus may foster decay. PRESERVATION 207. The Need of Preservation. — Statistics compiled by the Forest Service f show that the average life in years of untreated structural tim- bers in the United States is approximately as follows: Mine props, 3; piles, 3J; ties, 7; posts, 8; lumber subject to decay, 8; poles, 13; and shingles, 18. Although statistics are not given, it is probable that between seventeen and twenty biUion board feet of structural timber are used annually for replacements. Weiss estimates that the amount of timber cut for such purposes could be decreased annually by nearly seven billion board feet, if proper preservative methods were practiced. This would effect a net saving of not far from a hundred million dollars a year. From a consideration of the low durability of wood and the great cost of the quantity required for replacements, the need of practicing comparatively inexpensive methods of preservation becomes evident. Furthermore, the proper use of efficient protectives would lead to the planting of more rapidly growing trees, the more effective utilization of inferior trees and top logs, the clearing of land occupied by fire-killed timber (since the latter can be effectively used if treated); in short preservation would lead to better forest management in general. At the present time (1916) about one-third of the cross-ties and a hke * Rept. of Common Uses of Wood in Proceedings of 1915. t See Bulletin 78. 186 THE DETERIORATION AND PRESERVATION OF TIMBER proportion of the piling annually used in the United States is given a pre- servative treatment. The proportion of building and bridge timbers which are so treated is, however, quite small. The entire amount of timber treated in this country is approximately a hundred and fifty mil- lion cubic feet per year. To treat this amount of wood about a hundred million gallons of creosote, about thirty-five million pounds of zinc chloride and nearly five million gallons of other preservatives are consumed. 208. The Relations of Structure to the Penetrance of Preservatives. Structure plays a very important role in determining the ease with which preservatives may be forced into wood and also in fixing the quantity injected. In most woods the sap wood is more easily impregnated and absorbs more preservative than the heartwood. However, in hemlock, alpine fir, and white spruce the sapwood is scarcely less resistant to pene- tration than the heartwood. Bark is nearly impenetrable and should always be completely removed from timber which is to be treated. The comparative resistance of the heart and sapwood should be considered in forming timbers which are to be treated. In the diffuse-porous woods and in those conifers which show little demarkation between spring and sum- mer wood, the absorption of preservative is more uniform than in the ring- porous hardwoods or the hard pines. In the ring-porous woods most of the preservative will run into the spring wood, whereas in longleaf pine the greater part will be found in the dense summer wood. Owing to the difference in the absorption of preservative by the spring and summer wood of the hard pines, a minimum limit on the number of rings per inch is often placed in specifications. The purpose of this restriction on rate of growth is to prevent wide variations in the distribution of the pre- servative. Within a given species it is likely that the absorption of preservative varies inversely as the density of the wood, but no such relation exists between timbers of different species. Thus, red oak and hard pine, which are comparatively heavy woods, absorb much more preservative than the hght white spruce. Since nearly all of the preservative is held in the cell cavities and only a small proportion permeates the cell walls, it follows that any condition which causes a plugging of these cells will interfere with the injection of preservatives. Such conditions are effected in many woods by tyloses (Art. 197, 198 and 199). If such woods are treated the preservative is likely to be very non-uniformly distributed. In coniferous wood the resin-ducts, if unclogged by resin or growths, serve as canals for the rapid passage of preservatives. It is probable that the great absorption of the dense summer wood of the hard pines is due to the fact that it contains these ducts. Nearly all of the pines also possess radial resin-ducts which materially assist in the radial penetration PRESERVATION 187 of preservatives. Radial ducts are lacking in the larches, hemlocks, firs and spruces; and it is much more difficult to secure a deep radial penetration in them than in the pines. In some woods it is probable that the radial transmission of preserva- tives is affected through pit membranes in the cell walls. Tiemann and Weiss claim that slits which are opened in the cell walls during seasoning are another possible avenue of transmission. Besides these physical characteristics of the wood structure, the chem- ical composition of the cell walls probably has an important influence on the absorption of preservatives. Among the woods which are most readily injected with preservatives are longleaf pine, shortleaf pine. Western yellow pine, lodgepole pine, lob- lolly pine, red birch, white elm, red elm, soft maple, beech and red oak. White oak, alpine fir, Douglas fir, tamarack and white spruce are treated with difficulty. In this connection it should be recognized that the form of the timber often plays an important part in determining the penetra- tion of preservation. For example, a Douglas fir pole can be easily im- pregnated with preservative because of its sapwood envelope. On the other hand, a large dimension timber of this species having considerable exposed heartwood would be treated with much difficulty on account of the resistance of the heartwood to penetration. 209. The Treatment of Timber before Preservation. — It is generally best to cut timber in the winter in order to avoid the attack of fungus and insects. Also for timber which is likely to check from rapid seasoning the best cutting time is in the fall or winter. Soon after the tree has been felled every bit of the bark should be removed. By so doing danger of attack by fungi and insects is lessened, the weight of the wood is diminished and the surface of the wood is ren- dered much more permeable to preservatives. If, however, the wood is allowed to season too rapidly after the removal of the bark, it may become case-hardened and its resistance to penetration of liquids may be greatly increased. It is desirable that all timber which is to be treated be thoroughly seasoned in order that the penetration of preservatives may be facilitated. With the exception of air-seasoning, exposure to saturated steam is the most-used conditioning process for timber which is to be preserved. Under this process the timber is placed in a large treating cylinder and subjected to live steam at a pressure of 20 to 40 lb. per square inch for two to ten hours, the time being dependent on the size and character of the timber. A vacuum of about 25 in. is then applied for thirty minutes to two hours, after which the timber is treated with preservative. This process is a preliminary stage in several of the common methods of treatment. With a few creosoting processes, seasoning is accomplished by running the timber 188 THE DETERIORATION AND PRESERVATION OF TIMBER into a cylinder and soaking it in creosote. The oil is gradually heated until the temperature is raised above the boihng-point of water. This causes the latter to vaporize. The vapor is drawn off and condensed to free it of oil. After the moisture in wood has been sufficiently reduced, the cylinder is filled full of preservative and impregnation is begun. Superficial Treatments 210. Conditions for Use of Superficial Treatments.— There are three inexpensive methods of treating the surface of timber to protect it against decay and insects. These methods are of value when the amount of timber to be treated is too small to warrant the erection of a treating plant; when it is impracticable to haul the timber to the work from a plant; or when it is necessary to do the work at a minimum cost. Since the value of every one of them is based upon the maintenance of an un- broken film which will resist the attack of fungi, it is very necessary that the timber shall be thoroughly air-seasoned before treating. If the timber is only partially seasoned or green when treated, it is Hkely to check sub- sequently and thus produce passage ways for insects and myceUa. 211. Brush Treatments. — Probably the most-used superficial treat- ments are those in which a liquid is applied to the surface of the timber by means of a brush. Creosote, paint, oil, and whitewash are among the liquids used for the purpose. Creosote should be heated to about 200° F. before applying to the wood, since heating considerably decreases the viscosity of the oil and thereby aids in securing penetration of the preserv- ative. Great pains should be taken to thoroughly coat all defects and fill checks, shakes and joints. This method of treatment has been used considerably for the preservation of mine timbers, poles and posts. It is well adapted to use on farms. 212. Dipping. — By dipping the timber into the preservative and allowing it to soak for a few minutes, it is possible to secure a more com- plete coating of the defects than is gotten by brush treatments. The process requires the use of a large tank for holding the timber and neces- sitates a somewhat greater use of preservative, but the labor cost is less than in the brush process. It can be very effectively used for butt treat- ments on fence posts and poles. When used for this purpose the preserv- ative should cover the pole for at least a foot above the ground line. * 213. Charring. — ^A very old and inexpensive method for protecting wood consists in charring the outer fibers of the timbers by fire. This process produces an envelope of charcoal which, being devoid of food ele- ments, is not attacked by fungi. If the strength of the pieces treated is of great importance this process is detrimental, because it destroys the outer fibers and injures those immediately beneath. It has been us for treating the butts of posts and poles, but is not very efficacious. PRESERVATION 189 NON-PEESSURE PROCESSES OF IMPREGNATION 214. The Value of Non-pressure Processes. — In the non-pressure processes the preservative is drawn into the wood by absorption or it is forced in by atmospheric pressure. By these processes it is not possible to secure as uniform and deep penetrations as with the pressure methods, but with woods like loblolly pine, shortleaf pine, red cedar and beech, they can be successfully used. These processes require a longer time for treat- ment than the pressure processes. On the other hand, since they use no heavy treating cylinder with its expensive equipment, they afford cheap and effective means of preserving small quantities of poles, mine timbers and ties, provided the wood is easily impregnated. The method is also of value when salts which would attack iron treating cylinders are used. 215. Open-tank Process. — In this treatment the timber is placed in a tank and covered with the preservative. The charge is then heated to a temperature just above the boiling point of water. This serves to expel a considerable proportion of air and moisture from the cells in the wood. After soaking at this temperature for an hour or two the timber may be allowed to cool with the liquid, or it may be transferred to a cold tank where it is kept for another hour or more depending on how deep a penetration is wanted. As the wood cools a vacuum is formed in the outer cells and the preservative is injected by atmospheric pressure. Some- times, when a deep penetration is desired with a minimum expenditure of preservative, the timber is drawn from the cooling tank before it has entirely cooled. As the interior of the stick gradually cools vacuums are formed which are filled by the excess fluid held in the outer cells. The process may be used with creosote, zinc chloride, or crude oil. However, if the wood is boiled in the zinc chloride solution, its strength is likely to be impaired. 216. Kyanizing. — In this process the timber, which must be thoroughly seasoned, is immersed in a 1 per cent solution of bichloride of mercury for a number of days. The time of treatment is dependent upon the thickness of the pieces and the depth of penetration desired. Ordinarily the time in days is equal to the thickness of the timber in inches plus one, and the depth of penetration does not exceed a quarter of an inch. Owing to the poisonous character of the salt great care must be exer- cised during the treatment of the timber; and the treated lumber should not be used where it is likely to be licked by animals. As a means of preserving timber used in dry locations, this process ranks high; but on account of the poisonous nature of the salt, the long- time required for the process, and the solubility of the salt in water, it has not been widely used in this country. 190 THE DETERIORATION AND PRESERVATION OF TIMBER Pkessure Processes of Impregnation 217. Field of Use. — In general the pressure processes are the most satisfactory methods of treating large amounts of timber. Furthermore, these methods are the only ones which can be successfully used to impreg- nate many kinds of wood, such as hemlock, Douglas fir and redwood. 218. Bethell or Full-cell Process. — The timber for treatment is placed on small cars and carried into horizontal steel cylinders which are ordinarily about 130 ft. long by 7 ft. in diameter. Green timber is given a seasoning by the saturated steam process; this is unnecessary if the wood is well- seasoned. Coal-tar creosote oil is then admitted to the cylinder and forced into the timber by a pressure of 100 to 180 lb. per square inch. The pres- sure is maintained imtil the oil gages show the required impregnation. Then the oil is blown out of the cylinder into reservoirs, and the timber, after dripping for a few moments, is removed. In some plants dripping is accelerated by drawing a vacuum just before removing the timber. The process is much used both in this country and abroad. It is especially valuable for wood-block and piling where a heavy impregnation of oil is imperative. On account of the large expenditure of oil, 10 to 20 lb. per cubic foot, the process is very costly. The cost of treating cross-ties by it ordinarily runs between 40 and 50 cents each. 219. Bumettizing. — This process is performed in the same manner as the Bethell process, but differs in the preservative. An aqueous solution containing from 2 to 5 per cent of zinc chloride is used and about J lb. of salt per cubic foot is the average impregnation in the process. Owing to the solubility of zinc chloride in water, the process is not suited to treating timbers which are to be placed in damp locations. It is a very inexpensive process costing about one-third as much as the full-cell treat- ment. Burnettizing has been successfully used to treat ties and lumber both in the United States and in Europe. 220. The Boiling Process. — In this process either green or seasoned timber is given a conditioning treatment in creosote oil (see Art. 209) before impregnation with creosote. After the oil conditioning the remainder of the process is much like the Bethell method. The boiling method is used principally in preserving Douglas fir. Tests indicate that it may injure the strength of this wood. (Art. 243.) 221. The Rueping Process. — One of the most important processes both here and abroad is the Rueping empty-cell process with creosote. Air-seasoned timber is preferred, although steam treated material can be used. After placement in the treating cylinder, the cells of the wood are filled with compressed air which is admitted under a pressure of about 75 lb. per square inch. Oil is then admitted at a slightly higher pressure until the wood has been immersed, when the pressure is raised to 150 lb. PRESERVATION 191 per square inch or more. After the proper amount of oil has been injected, the creosote is forced out of the cyhnder and the pressure released. As the pressure is withdrawn the compressed air within the wood expels the excess oil into the cylinder. It is thus possible to secure a deep penetration and to coat the cell walls with 5 to 7 lb. of oil per cubic foot of wood. Treatments by this process cost about two-thirds as much as the full-cell methods. 222. The Lowry Process. — This process, hke the Rueping, is planned to secure a deep penetration of oil with a small absorption. Air-dry timber is run into the cylinder and submerged in creosote oil at a temper- ature of about 200° F. Pressure is then applied, and the temperature and pressure are regulated until the timber has been filled with oil. After withdrawal of the oil a vacuum is drawn until the surplus oil in the wood cells has been removed. When the excess oil has been removed from the cylinder, the timber is taken out. The process is somewhat more expen- sive than the Rueping process but less costly than the full-cell. It is considerably used in the United States for treating cross-ties. 223. The Card Process. — Owing to the high cost of creosote oil and the solubility of zinc chloride neither of these preservatives has been univer- sally adopted. The aim of the Card process is to lessen these objectionable features by using a mixture of 15 to 20 per cent of creosote with a 3 to 5 per cent solution of zinc chloride. In operating the process, air-seasoned timber is run into the treating cylinder and given a vacuum treatment for about an hour. It is next immersed in the preservative at a tem- perature of about 180° F. A pressure of approximately 125 lb. per square inch is then applied for several hours. During this period the mixture of oil and zinc chloride is stirred continuously by a centrifugal pump to prevent separation of the components. After impregnation has been finished, the preservative is drained from the cylinder, and a vacuum drawn to remove surplus preservatives from the wood cells. By the Card method approximately as much zinc chloride is injected as in Bur- nettizing together with about 3 to 5 lb. of creosote per cubic foot. The process costs approximately half as much as the Bethell process and has found favor in this country for the treatment of cross-ties. Preservatives and the Efficiency of Preservation 224. Preservatives. — Inasmuch as fungi cannot thrive without mois- ture, waterproofing of seasoned wood will render it resistant to attack. Crude oil, paint and stains are the common preservatives of this class. A far surer treatment is effected, however, by preservatives which poison the food supply of fungi and insects.' The creosote oils and the inorganic salts, — zinc chloride, mercuric chloride and copper sulphate, — are mem- bers of the latter class. The term crude oil includes three classes, (1) oil with a paraffin base, 192 THE DETERIORATION AND PRESERVATION OF TIMBER (2) oil with an asphaltic base, and (3) the product which is left after the lighter oils are distilled from crude oil called residuum. These oils are all lighter than water but penetrate coniferous wood less readily than creosote. For successful treatment with them, the timber must be fully impregnated, thus rendering it heavy and likely to drip. The cost of sufficient oil to treat a cubic foot of timber runs from 3 to 7 cents. Crude oil is used but little in the United States. Most of the paints used to protect wood consist of linseed oil, turpentine and some inorganic coloring material. Although fungi will not attack a painted surface, most paint cannot be classed as an effective preservative when the wood is in contact with the soil, since it is somewhat parous and permits the passage of moisture. Stains having a creosote base with a vegetable or mineral-oil body are poisonous to fungi. They, also pene- trate further into the wood than do the paints, but are more volatile. Creosote oils of three varieties are used in wood preservation; coal- tar creosote, water-gas-tar creosote, and wood-tar creosote. They are all tar distillates and are very poisonous to fungi and insects. However, the volatile nature of the lighter fractions of these oils, their pungent odor and the fact that they increase the inflammabiUty of wood render them unsatisfactory for some purposes. Creosote is also an expensive preserva- tive; the cost ranges from 5 to 15 cents per cubic foot of treated wood, depending on the price of oil and the process used. Nevertheless, in spite of these objectionable features approximately two-thirds of the timber annually treated in the United States is impregnated with coal-tar creosote. Coal-tar creosote is a complex oil resulting from a double distillation of coal. In the first distillation the products are coke, gas, and tar. If the tar is again distilled three classes of compounds are formed — pitch, oils lighter than water, and oils heavier than water. The latter are the creo- sotes. They consist principally of phenols, naphthalene and anthracene. Tests made at the Forest, Products Laboratory show that from 0.2 to 0.4 per cent of this oil in a culture medium is sufficient to kill fungi. For methods of sampKng and analyzing creosote oil see Proc. A. S. T. M., Vol. 16, Pt 1, p. 564. Water-gas tar is a by-product from the manufacture of water gas. By passing steam over red-hot coke or anthracite coal the fuel is decomposed into hydrogen and oxygen. These gases are then passed through a heated carburetter into which a spray of crude petroleum is simultaneously ad- mitted. Gas and tar are thus evolved. By distillation the tar is sepa- rated into three components, oils lighter than water, pitch, and the creosote oils which are heavier than water. Very little water-gas tar creosote is used as such for preservative purposes, but it is sometimes used as an adulterant of coal-tar creosote. It is probably no more volatile than the coal-tar product, but is less deadly to fungi. PRESERVATION 193 Wood-tar creosote is derived from treble distillation of resinous woods. Owing to the expense of this oil its use has been largely confined to the manufacture of stains and patented coatings. The inorganic salts which are used for wood preservation are all highly- toxic to fungi. They are also non-volatile and odorless. Furthermore, timber into which these salts are injected can be covered with paint, whereas creosoted timber is coated with great difficulty. On the other hand, these salts are soluble in water and are likely to leach out of the timber if it is exposed to moisture. Zinc chloride is the most important of the inorganic salts. It is equal in toxicity to coal-tar creosote but corrodes the iron-treating cylinders to a sHght extent. It is a very cheap preservative costing about 5 cents a pound or 2 to 3 cents per cubic foot of treated timber. About one-fourth of the timber treated in this country is injected with zinc chloride. Mercuric chloride is the most toxic preservative and on this account is often a menace to the users of the treated timber. It is less soluble in water than zinc chloride but much more corrosive to iron. From records it appears to confer a somewhat longer life on treated timber. The cost of mercuric chloride per cubic foot of treated timber is about the same as that of zinc chloride. Copper sulphate is a preservative of high toxicity, but readily leaches from the timber. It is fairly cheap and appears to be about as efficient a preservative as zinc chloride. The depth of penetration is readily determined by the blue stain which the liquid imparts to the wood. Since it attacks iron with great vigor, it cannot be used with the ordinary treat- ing apparatus. The largest use of this preservative is made in France. 225. Economy in Preservation. — Economy is effected by preservative treatment whenever the annual charge against the treated timber is less than the annual charge against any untreated timber (or other material), which would serve the purpose. To furnish examples of the savings which may be made through timber preservation, Table 1 has been inserted. The prices and the estimated life of ties given in this table were largely pre- pared from data furnished by Mr. C. H. Teesdale, of the Forest Service. The prices given are for regions in which the ties are largely used, and the estimated life values are based upon the conditions of usage prevalent in that region. The annual charge (r) was computed from the formula: _ pR(i+pr "" (i+p)"-r Here i2 = initial expenditure, p = rate of interest in per cent divided by 100 (in table p = 0.05), and n = life in years. This formula considers an annual charge sufficient to pay the interest on the first cost of the ties 194 THE DETERIORATION AND PRESERVATION OF TIMBER plus a balance which, with interest compounded annually, will provide a fund at the end of n years equal to the first cost. The estimates show the value of the durable woods and emphasize the importance of treating the inexpensive timber which is not naturally durable. TABLE 1.— ESTIMATED ANNUAL SAVING DUE TO PRESERVATIVE TREATMENT OF CROSS-TIES lA charge of 45 centa for tie-plates and placement was added to the cost of each tie before computing the annual charge. The estimated coat of creosoting waa figured at 45 centa and of Burnettlzing at 15 cents per tie.] Kind of Tie. Redwood -Cedar Cypress White oak Longleaf pine . . Douglas fir ... , Western larch. . Tamarack Hemlock Chestnut. . . .'. Red oak Beech Birch Maple Lodgepole pine Western pine . . Loblolly pine . . Red gum Estimated Life IN Yh. 12 11 10 8 7 7 7 5 5 5 4 4 4 4 4 4 3 3 20 15 15 15 15 12 20 20 20 18 15 15 15 16 11 11 11 11 11 9 12 12 12 12 11 11 10 11 Cost op Ties IN Dollars. 0.60 0.55 0.55 0.80 0.60 0.50 0.40 0,50 0.40 0.50 0.65 0.50 0.50 0.50 0.65 0.50 0.40 0.55 1.05 .95 .85 .95 .85 .95 1.10 .95 .95 .95 1.10 .95 .85 1.00 Annual Charge IN Track. 0.75 .65 .55 .65 .55 .65 .80 ,65 ,65 ,65 ,80 .65 .55 ,70 0.117 0.120 0.128 0,194 0.181 0.164 0,147 0,219 0.197 0.219 0,310 0,268 0,268 0,268 0,310 0,268 0,3120 0.367 120 135 124 135 124 167 124 112 112 119 149 135 124 134 o ■n?. 144 132 120 132 120 155 140 123 123 123 150 132 129 138 Annual Savings. 061 029 023 084 073 062 186 156 156 149 161 133 188 233 0.037 0.032 0.027 0.087 0,077 0,064 0.170 0.145 0.145 0.145 0.160 0.136 0.183 0.229 CHAPTER VI THE MECHANICAL PROPERTIES OF TIMBER 226. Introduction.— In order that the engineer may properly design columns and beams for various parts of wooden structures, he must be thoroughly conversant with the strength and stiffness of the available classes of timber. He must also know how various defects and conditions influence these properties. The architect must not only appreciate the beauty of the various species, the relative ease with which each may be worked, the tendency to shrink, warp and check; but he must likewise be prepared to proportion joists and rafters to carry the imposed loads without excessive deflection. The wheelwright must understand how the toughness and strength of his axles, spokes, and shafts are influenced by species, rate of growth, density, and defects. The carpenter and the craftsman must also have knowledge of the mechanical properties of wood in order that they may work it to best advantage. Furthermore, wood of a given species is extremely variable. Trees differ markedly in their rate of growth, due to climatic conditions, the density of the surrounding forest, the character of the soil and the physi- ography of the region in which they grow. These conditions of growth, the position in the tree, the amount of moisture and the defects all influ- ence the mechanical properties of a piece of timber of a given species. Recognizing the importance of a knowledge of the properties of wood and the factors influencing them. Dr. B. E. Fernow, chief of the Forestry Division of the U. S. Agricultural Department, inaugurated a series of timber tests in 1891. In the beginning, the microscopic and physical tests were conducted at Washington and the mechanical tests were made by J. B. Johnson, at Washington University, St. Louis. Later the mechan- ical tests were distributed among a number of technical laboratories in various parts of the country. In 1909 the major portion of the work done at the various laboratories was transferred to the Forest Products Labora- tory * at Madison, Wis. Mechanical tests of timber are only a portion of the work carried on at this laboratory. Studies of the physical and chemical properties, the microscopic structure, the methods of preservation of wood, and the utili- zation of products are among the other more important lines of investi- gation being conducted by this institution. * This laboratory is run by the U. S. Government; buildings, light, heat, and power are provided by The University of Wisconsin. 195 196 THE MECHANICAL PROPERTIES OF TIMBER On account of the broad scope of these investigations, the great pains which are taken to identify species, to select properly both specimens and trees, and on account of the care taken to eliminate variables in testing, the results obtained are of very great value. Most of the data in this chapter is taken from publications of this laboratory. The mechanical tests which are most commonly made at the Forest Products Laboratory are: compression, shear, both static and impact bending, tension, hardness, and cleavage. Observations are also made on the number of rings per inch, per cent summer wood, per cent moisture, density and shrinkage. Many of the more important conditions per- taining to the methods of testing wood have been considered in Ch. III. Supplementary information will be given, when necessary, in the discus- sions on mechanical properties which follow. THE STRENGTH OF .WOOD 227. Compressive Strength. — When wood is subjected to compress- ive forces acting parallel to the axis of growth (parallel to the grain), it is, in proportion to its weight, one of the strongest of structural materials. Columns and posts are, therefore, often fashioned of it. Inasmuch as the strength of such a member is a function of the compressive strength and the slenderness ratio, information concerning the former is of much importance. Furthermore, a knowledge of the compressive strength is of value in estimating strength in bending, since experiments have dem- onstrated that the yield point of a wooden beam is determined by the compressive strength of the wood. The compression test is not, however, as effective in demonstrating the weakening influences of defects as the cross-bending test. When wood is subjected to compression parallel to the grain it may fail through collapsing of the cell walls or through lateral bending of the cells and fibers. In most of the conifers where the cells (tracheids) have thin walls, failure begins at pits in the walls of one of these cells and grad- ually causes a collapse of the entire cell. The plane of rupture is generally inclined about 60° to 75° with the axis of the cell. From the inclination of the plane of failure it appears probable that final collapse is due to the weakness of the cell wall in transverse shear. Adjacent cells are over- stressed by the failure of the individual cell and a wrinkling of the surface, showing the progress of the breakdown throughout the specimen, becomes visible. In wet wood and in the hardwoods, which are composed of thick-walled fibers and vessels, incipient failure is due to bending of the individual fibers. Occasionally after the wrinkling begins, the specimen is separated into groups of fibers by longitudinal cracks. This condition is brought about by splitting of the fibers and not by failure of the bond (D O) CO CL (Ji THE STRENGTif OF WOOD 197 between fibers.* It will be generally noted that the line of failure on tangential surfaces of the specimen is inclined as previously stated; but on radial surfaces it is approximately normal to the axis of the test-piece. The direction in the latter case is much influenced by the medullary rays. In cross-grained pieces the failxire is Ukely to take place through shear parallel to the grain. The strength of timber compressed across the grain is brought into play wherever a concentrated load is imposed on a beam. Since the compressive strength across the grain is only a small fraction of the com- pressive strength parallel to the grain, proper allowance for this discrep- ancy must be made in designing columns resting on wooden beams or the column must be provided with a footing, to distribute the pressure. Tests on compression across the grain are often made with the pres- sure distributed over only part of one of the loaded surfaces. Thus for tests on small specimens at the Forest Products Laboratory, a 2X2X6-in, block is used and loads are applied over the lower 2X6-in. surface and the middle third of the upper surface. Although such procedure does not give the true cross-grained compressive strength, it more nearly approaches the loading condition ordinarily met in a structure. In such tests, as the load is increased, the upper bearing closes the cell cavities immediately beneath it and gradually indents the surface. Beam action in the upper fibers often produces splitting in planes perpendicular to the line of pres- sure, but there is no well-marked failure. ^ Strictly speaking, timber does not have a well-defined elastic limit, since it takes set after the imposition of low loads. Nevertheless, the initial portion of the stress-deformation curve is approximately straight and it has become customary to record the stress corresponding to the limit of proportionality as the elastic limit. This is the only value of importance in tests across the grain. Values of the compressive strengths of 2X2-in. prisms of 49 woods in green condition appear in Table 1. In Table 2, similar values may be found for larger sizes of the common structural timbers when air-seasoned. Table 3 shows the relation of air-seasoned to green material. Among the species having greatest compressive strength parallel to the grain we note osage orange, hickory, tanbark oak, longleaf pine, white ash, and redwood. Rock elm, maple, several varieties of oak, bald cypress, and shortleaf pine form a second class having good strengths. For most of the conifers the compressive elastic limit across the grain varies between 10 and 15 per cent of the values determined for pres- sures parallel to the grain. Among the hardwoods the elastic limit in compression across the grain bears a higher ratio to the strength in com- pression parallel to the grain, the ratio being about 25 per cent for several * Record, Mechanical Properties o/ Wood, p. 15. 198 THE MECHANICAL •PROPERTIES OF TIMBER TABLE 2.— AVERAGE STRENGTH VALUES FOR COMPRESSION PARALLEL TO GRAIN, COMPRESSION PERPENDICULAR TO GRAIN, AND SHEAR- ING TESTS ON AIR-SEASONED MATERIAL OF DIFFERENT SIZES (Bull. 108, Forest Service.) Compression parallel to grain. Compression parallel to grain. Shear. Species. c s aj P. "o s S 2; 1 'o ■3^4 O II III .sE-g 5 1 i 1 o XI S z u .2 o s ■£„j= to .jj O = « c o 1 E Z g '3 ■si In. p. ct. Lb. 1000 lb. Lb. In. In. p. et. Lb. p. ct. Lb. Longleaf pine . . . 4X5 46 26.3 3480 4800 4X5 4 22 25.1 572 52 20.2 984 Douglas fir 6X6 259 20.3 3271 1038 4258 4X8 16 44 20.8 732 465 22.1 822 2X2 247 18.7 3842 1084 5002 4X8 4X4 4X4 4X4 10 8 6 4 32 51 49 29 ■18.1 20.2 24.0 24.8 584 638 613 603 6X6 29 15.7 4070 1951 6030 8X5 10 4 17.8 725 85 1135 Shortleaf pine. . . 2X2 57 14.2 6380 8X6 8X5 5X5 2X2 14 12 8 2 3 5 6 57 16.3 15.1 lo.O 13.9 757 730' 918 926 6X6 112 16.0 5145 8X6 16 17 18.8 491 193 15.0 905 Western larch. . . 4X4 SI 14.7 6161 8X6 12 18 17.6 526 2X2 270 U.8 5934 3X4 8 22 13.3 735 Loblolly pine . . . 6X6 23 3357 1693 5003 8X5 16 12 19.8 602 156 11.3 1115 5X5 10 22.4 2217 545 2950 8X5 8 7 22.9 679 4XS 8 19.4 3010 633 3920 4X5 8 8 19.5 715 2X2 69 5547 Tamarack 6X7 4X7 4X4 2X2 3 3 57 66 15.7 13.6 14.9 14.6 2257 3780 3386 1042 1301 1353 3323 4823 4346 4790 2X2 2 57 16.2 697 60 14.0 897 Western hemlock 6X6 102 18.6 4840 2140 5814 7X6 15 25 18.2 514 131 17.7 924 2X2 463 17.0 4560 1923 5403 6X6 4X4 6 4 26 6 16.8 15.9 431 4.SS Redwood 6X6 18 16.9 4276 8X0 10 5 25 . 4 548 95 12.4 671 2X2 115 14.6 51 in li XO 7X6 3 X(i -'X6 2X6 2X6 2X2 12 9 14 12 10 8 2 6 5 2 2 4 2 145 14.7 14.8 12.6 16.2 14.3 13.2 13.8 610 500 470 498 511 429 564 e Norway pine 6X7 4X7 4X4 2X2 4 2 56 34 15.2 22.2 16.6 11.2 1 2670 3275 3048 11S2 1724 1367 4212 4575 4217 7650 2X2 36 10.0 924 44 11.9 1145 THE STRENGTH OF WOOD 199 TABLE 3.— RATIOS OF AVERAGE STRENGTH VALUES FOR AIR-SEASONED MATERIAL TO THOSE FOR GREEN MATERIAL. {Bull. 108, Forest Service) Bending. Compression parallel to grain. Com- pression perpen- dicular to grain. Shear. Species. s.s IS, s p. . a IS l-s , ■S.S OS la P. i O o3 O m Crushing strength at elastic . limit per square inch. Mrf a o o OS "1 Mo o 111 u u ft -*» aji sg. m Longleaf pine: Structural sizes Small specimens. . . . Douglas fir: Structural sizes Small specimens. . . . Shortleaf pine: Structural sizes Small specimens. . . . Western larch: Structural sizes Small specimens. . . : Loblolly pine: Structural sizes Small specimens. . . . Tamarack: Structural sizes Small specimens. . . . Western hemlock: Structural sizes Small specimens. . . . Redwood: Structural sizes Small specimens. . . . Norway pine: Structural sizes Small specimens.. . . Lb. 0.99 1.36 1.15 1.28 1.44 1.79 1.05 1.38 1.16 1.26 1.33 2.33 1.25 1.44 .92 1.00 1.63 1.88 Lb. 0.94 1.27 1.06 1.25 1.19 1.57 1.18 1.42 1.19 1.19 1.21 2.26 1.21 1.42 .87 1.12 1.57 1.64 1000 Lb. 1.16 1.13 1.02 1.06 1.17 1.28 1.14 1.19 1.07 1.02 1.10 1.09 1.20 I 17 1.08 1.25 1.21 Lb. 0.77 1.33 1.10 1.18 1.30 1.16 1.07 1.20 Lb. 1.00 1.18 1.10 1.66 1.47 1.40 1.67 1.55 1.48 Lb. 1.00 1.22 1.24 1.76 1.79 1.64 1.60 1.46 1.71 1.34 1.60 1.73 1.69 1.16 1.29 1.66 3.01 1000 Lb. .73 .56 1.26 2.20 .98 1.32 1.11 1.36 Lb. 1.01 1.12 2.26 2.32 1.31 1.31 1.09 1.21 .99 Lb. 1.01 1.08 1.61 1.29 1.77 1.32 1.47 .90 1.94 of the varieties of hickory and oak and reaching 39 per cent for osage orange. With the exception of the longleaf pine specimens, which judging from their moisture content must have been pretty green, the air-seasoned structural timbers of every species were stronger in compression than the green timbers (see Art. 241). 228. Tensile Strength of Wood. — When a properly shaped wooden stick is subjected to tensile forces acting parallel to the grain it is found to have greater strength than can be developed under any other kind of stress. Indeed, the tensile strength of wood parallel to the grain is so 200 THE MECHANICAL PROPERTIES OF TIMBER great that much difficulty is encountered in designing end connections so that the tensile strength of a piece can be developed. Therefore, wood tension members are rarely used. On this account and because the ten- sile strength parallel to the grain is so much greater than the compressive strength that the latter governs the strength of beams, the tensile strength with the grain is rarely tested. The tensile strength parallel to the grain is influenced to some extent by the nature of the wood elements and their arrangement, but principally by the straightness of the grain and the thickness of the walls of the longitudinal elements. When failure occurs these elements are ruptured transversely. Knots greatly reduce the tensile strength parallel to the grain and are a great menace to strength when present in timbers subjected to such stresses (see Art. 240). The tensile strength appears to be less affected by moisture than are other mechanical properties. In the following table the ratio of the tensile to the compressive strength has been tabulated for small specimens of several woods. The moisture content does not appear in the original publication, Bull. 10, U. S. Dept. of Agric, but it is probable that the pieces were air-dry. Species. Ratio, Tensile strength, Compr. strength Ultimate Strength IN Lb. PER Sq.IN. IX Tension. Compression. Hickory Elm 3.7 3.8 2.3 2.2 32,000 29,000 19,400 17,300 8500 7500 Larch Longleaf pine 8600 7400 Across the grain, the tensile strength of wood is sma,ll. It is a prop- erty closely related to cleavability, and it often determines the strength of a beam which has cross-grain or spiral-grain in the tension fibers. Failure in tension across the grain occurs through separation of the cells and fibers in longitudinal planes. Knots, shakes, and checks all reduce the tensile strength of wood across the grain. The form of specimen used by the Forest Products Laboratory in making the test is shown in Fig. 1. An examination of Table 1 shows that the tensile strength of wood across a radial plane is less than the tensile strength across a plane taaigent to the rings. This difference is especially pronounced in the oaks and other hardwoods having large medullary rays. It is probable, therefore, that these rays considerably weaken the tensile strength of wood across a radial plane. For the conifers, from which most structural timbers are secured, the cross-grained tensile strength of small perfect specimens of green wood runs between 200 and 325 lb. per square inch, while for the oaks it varies THE STRENGTH OF WOOD 201 between 600 and 1000 lb. per square inch. The smallness of these values must be remembered in computing the safe strengths of beams having cross-grain in the tension fibers. 229. The Shearing Strength of Wood. — Although shearing stresses are often of small moment in metal beams and other structural elements, they are fre- quently of very great importance in members made of wood. Thus the hori- zontal shear stress at the neutral axis of a short, deep wooden beam may be suffi- ciently great to produce a failure like that of Fig. 2. If the mortise-and-tenon joint, shown in Fig. 3, is loaded so that the tenon presses downward upon the mortise, transverse shear stresses are produced on the tenon ; and shear stresses parallel to the grain are caused in the vertical piece on planes AC and BD. In most cases failure in the tenon is due to bending rather than shear, but the pushing out of the piece ABCD is an example of shear failure. Since the transverse shearing strength of wood is more than half the compres- sive strength parallel to the grain, it is very rarely necessary to design against failure through this stress. Tenons, handles of axes, hammers and mauls, and wooden pins are perhaps the most com- mon examples of wooden pieces which must be proportioned against transverse shear. Not much experimental data on the transverse shear strength of timber has been published, and the results in Table 4 are of interest mainly in showing the varia- tion in the strengths of pieces from trees of different species. The individual values should not be considered representative of the different species. If the shearing stresses act on planes tangent to the growth rings, the resistance of the various woods is quite small, ranging from about 600 to 1000 lb. per square inch for small green specimens of the structural coni- fers and from 1000 to 1500 lb. per square inch for similar pieces of oak, hickory, elm, maple, sycamore, beech, birch, and white ash (see Table 1). Fig. 1.— Type of Test Used by Forest Products Laboratory to Find Tensile Strength of Wood Across Grain. (Betts and Greeley before Int. Engr. Congress, 1915.) 202 THE MECHANICAL PROPERTIES OF TIMBER In the same table it will be observed that there is little difference between the strengths of small pieces of green coniferous wood subjected to shear- FiG. 2.- (CouH esy Forest Products Laboratory.} -Failure of a Large Wooden Stringer by Horizontal Shear. ing parallel to the rings (tangential shear), and the strengths of like pieces subjected to shearing stresses acting on vertical radial planes (radial shear). Among the hardwoods the resistance to radial shear appears to be slightly the greater. In Fig. 4 are shown failures of pieces of green longleaf pine in radial shear (22) and in tangential shear (30). TABLE 4.— THE RESISTANCE OF VARIOUS WOODS TO SHEAR ACROSS THE GRAIN (J. C Trautwine, in Jour. Frank. Insl., Vol. 109, p. 106) Test pieces were cylindrical pins f in. in diameter fairly seasoned and free from defects. They were subjected to double shear. Each result represents two tests. Kind of Wood. Ash Beech Birch Cedar, white Cedar, Central American Cherry Chestnut Dogwood Ebony Gum Hemlock Hickory Shearing Strength (Lb.-In.2) 6280 5223 5595 1446 3410 2945 1535 6510 7750 5890 2750 6665 Kind of Wood. Locust Maple Oak, white Oak, live Pine, white Pine, northern yellow . . . . Pine, southern yellow . . . Pine, very resinous yellow Poplar Spruce Walnut, black Walnut, common Shearing Strength (Lb.-In.!) 7176 6355 4425 8480 2480 4340 5735 5053 4418 3255 4728 2830 THE STRENGTH OF WOOD 203 Turning our attention to the results in Table 5 we find the calculated horizontal shear stresses developed in tests of beams of structural sizes. 3 V These shear stresses were computed from, the formula Sh = ii — ; where (Sft = horizontal shear stress, y = maximum vertical shear and a = area of rectan- gular cross-section of beam. Comparing these results with the values for like woods found in Table 1, we observe that the computed stresses for the large beams are much lower than the shearing strengths of small specimens. This dis- crepancy is due principally to defects, shakes, and checks which cut down the area under shear. Since the formula assumes a full cross-section, the results given by it will be smaller than the stresses in the net sections of wood. The lesson taught is to use values from the tests on large beams faiUng in shear as a basis for design. Both Table 3 and 5 show that air- FiG. 3. — Wood Members Subjected to Longitudinal Shear. Fig. 4. — Shear Failures Parallel to Grain in Green Ijongleat Pine. Nos. 32i and 22i plane of shear radial, Nos. 32 and 30 plane of shear tangential to annual rings. (Bulletin No. 70, Forest Service.) seasoned coniferous timber is, in most cases, stronger than green timber. Longleaf pine and redwood are, however, exceptions to this rule. 230. The Strength of Wood in Cross-bending. — Because of the great use of wood for beams, stringers, joists, rafters and other parts which are subject to bending, the cross-bending test is of much value in determining the quality of wood. By it one can measure the strength, toughness, and stiffness of the timber. Furthermore, the cross-bending test exposes weaknesses caused by defects better than does any other test. Unless very large testing machines are at hand, it is the only test which can be used to find the strength of timbers of structural sizes. It will be remembered from Mechanics of Materials that the modulus of rupture in cross-bending is a fictitious measure of the ultimate unit 204 THE MECHANICAL PROPERTIES OF TIMBER TABLE 6.— CALCULATED SHEARING STRESSES DEVELOPED IN STRUCTURAL BEAMS (From Bull. 108, Forest Service' • Total Number OF Tests. First Failtjhe Shear. BY Shear following OTHER Failure. No Shear Failure. Green. Dry. Green. Dry. G reen. Dry. Species. Is Is 11 a 3 a s d :i o s a 3 a a "a "BS "d ■BS 'rt 3? "ca 3? *« 3? ■3 -3S O .ti O ' O ^ _o " o o -^ o o o o ^ "rt u 4S el u 'rt u d t., +j 'i *^ 1? t~, "o "a •3 "a "o « a) P. o p. •s O 4) Pi o "S ^ Q) , -*i' 0) HJ t. 'I' t. 43 ' <0 I. d s t a a o a u 0) a M g-s.s 2|^ a g 2S^ g-s.a o Q CM ■< PN -• i 3 s 5| a'g °| Sg as 5| JH " d3 o3 2 f) cd o 2 03 oj o « o u O a o. s 'o a ■s.a li 4" •.S.S < 1000 In. In. P.ct. Lb. Lb. Lb. Lb. Longleaf pine. . . 8X16 180 5 22.2 16.0 3390 .50 4,274 0.37 1747 1,00 288 0.75 6X16 132 1 23.4 17.1 3470 .61 6,610 .67 1501 .86 388 1.01 6X10 177 2 19.0 8.8 4560 ,68 7,880 .68 1722 .99 214 .56 4X11 180 1 18.4 23,9 3078 .46 8,000 .69 16tU .95 251 .66 6X 8 177 6 20.0 13,7 4227 ,63 8,196 .71 1634 .94 177 .46 2X 2 30 17 15.9 13.9 6760 1,00 11,520 1.00 1740 1.00 383 1.00 Douglas fir 8X16 180 91 20.8 13.1 4563 .68 6,372 .61 1649 .91 269 .64 6X 8 180 30 14.9 12.2 5065 .76 6,777 .65 1863 1.09 218 .52 2X 2 24 211 19.0 16.4 6686 1.00 10,378 1.00 1695 1.00 419 I. CO Shortleaf pine. . . 8X16 180 3 17.0 12.3 4220 .54 6,030 .50 1517 .86 398 .98 8X14 180 3 16.0 12.3 4253 .55 5,347 .44 1757 .98 307 .76 8X12 180 7 16.0 12.4 5051 .65 7,331 .60 1803 1.01 361 .89 5X 8 180 6 12.2 22.5 7123 ,92 9,373 .77 1985 1.11 301 .74 2X 2 30 67 14.2 13,7 7780 1.00 12,120 1,00 1792 1.00 404 1.00 Western larch . . . 8X16 180 23 18.3 21.9 3343 .57 5,440 .53 1409 .90 349 .96 8X12 180 29 17.8 23.4 3631 .62 6,186 .60 1649 .99 296 .81 5X 8 180 10 13,6 27.6 4730 ,80 7,258 .71 1620 1.04 221 .61 2X 2 30 240 16.1 26.8 5880 1 ,00 10,254 1.00 1564 1.00 364 1.00 Loblolly pine 8X16 180 14 20.5 7.4 4195 .81 6,734 .72 1619 1.10 462 1.45 6X16 126 4 20,2 5.0 2432 .47 4,296 .46 1324 .90 266 .84 6X10 174 '3 21,3 4.7 3100 .60 6,167 .66 1449 .99 173 .54 4X12 174 4 19,8 4.7 2713 ,52 5,745 .61 1249 .86 185 .68 8X 8 180 9 22,9 4.9 2903 .56 4,657 .48 1136 .77 93 .29 6X 7 144 2 21,1 5.0 2990 .58 4,968 .53 1286 .88 116 .36 4X 8 132 8 19,5 9.1 3384 .65 6,194 .66 1200 .82 196 .62 2X 2 30 123 17,6 6.6 5170 1.00 9,400 1.00 1467 1.00 318 1.00 Tamarack 6X12 162 5 23,0 15.1 3434 .45 5,640 ,43 1330 .82 318 .75 4X10 162 4 14,4 9,7 4100 .54 5,320 ,41 1356 .84 262 .69 2X 2 30 47 11,3 16,2 7630 1,00 13,080 1,00 1620 1.00 425 1.00 Western hemlock 8X16 180 44 17,7 17,8 4398 ,69 6,420 ,62 1737 1.04 406 1.06 2X 2 28 311 17,9 19,4 6333 1.00 10,369 1,00 1666 1.00 38» 1.00 Redwood 8X16 180 6 26,3 22,4 3797 .79 4,428 .57 1107 .96 294 1.05 6X12 180 6 16,1 17,7 3175 .66 3,353 .43 728 .64 167 .60 7X 9 180 6 1.5,9 15,2 3S80 .69 4,002 .61 1104 .96 147 .53 3X14 2X12 180 180 6 5 13,1 13,8 24.4 14.4 3928 "!82 6,033 5,336 .64 .68 291 260 1 04 '1249 'i.'og !93 2X10 180 5 13,8 24,8 3757 .79 4,606 .59 1198 1.05 186 .67 2X 8 180 6 13,7 20,7 4314 ,90 5,050 .65 1313 1.15 166 .60 2X 2 28 122 15.2 18,8 4777 1,00 7,798 1,00 1146 1.00 279 1.00 Norway pine. . . . 6X12 162 5 16.7 8.1 2908 ,.56 5,204 ,61 1123 ,97 286 1.02 4X10 162 5 13.7 12,0 5170 ,98 6,904 .82 1712 1.48 317 1.13 2X 2 30 60 14.9 11.2 6280 1,00 8,470 1.00 1158 1.00 281 1.00 THE STRENGTH OF WOOD 207 Results in Table 3 show that air-seasoning is somewhat beneficial to the strength of structural timbers. It is probable that a more complete drying would have made the strengths of the air-seasoned timbers still greater. 231. The Time Element in the Loading of Timber. — Since timber yields more rapidly under heavy loads than most materials of construc- tion, it is quite necessary to standardize the rate of loading in order that test data may not be influenced by this factor. Extensive tests by the Forest Service led it to adopt the following rates of unit deformation per minute for the testing program of the Forest Products Laboratory. Bending tests on timber of structural size . 0007 Bending tests on small beams . 0015 Compression parallel to grain, large prisms . 0015 Compression parallel to grain, small prisms . 0030 Shearing along the grain 0.0150 100 SCHEME OF TEST SPECIMENS T|Q|T|Q|T|Q|TIQ|T|9|T ~ ME OF FI)(ED -OAD IN HOURS Kt 1 < ^ •--i ':. D 3: i. , ' ip Q 5: >• 3- :Biti\ ^^ 5) 2: ti ^ 8 300 400 500 600 700 Pig. 5. — Results of Time Tests on Dry Longleaf Pine in Compression Endwise. The specimens marked Q were tested quickly, as in one or two minutes; those marked T were loaded with various percentages of the breaking load of the two adja- cent specimens, and this load was left on until failure occurred, and the time noted. For the bending tests these rates apply to the extreme fiber at the dan- gerous section. The speed of the movable head {n) of the testing machine eP eP in bending tests is given by n=-prr for a center load, and w = — —^ for a on oAh third-point loading. In these equations e = unit deformation per minute, Z=the span and h = the -depth of a rectangular beam. According to 208 THE MECHANICAL PROPERTIES OF TIMBER Tiemann * variations of 25 per cent in the above rates will not affect strength more than 2 per cent. In order that proper factors of safety may be established on a basis of testing machine results, it is very desirable that the strength of timber under dead loads be determined. A few tests on small beams by the late Dr. R. H. Thurston, indicated that 60 per cent of the progressively applied ultimate load would break beams if left in place for nine months. In Fig. 5 appear the results of approximately seventy-five end compression tests by J. B. Johnson on If Xlf X3-in. prisms. All specimens were cut from a single plank of longleaf pine which was ripped into prisms 40 in. long. The specimens were cut from each long prism as indicated in Fig. 5 and dressed to the above size. All tests were made in a 30,000-lb. universal machine. For dead-load tests the prisms were bedded on a nest of four vertical car springs which deformed about an inch under the imposed loads. By means of this elastic base the yielding of the specimen was taken up and load of almost constant intensity maintained throughout the test. Each plotted point in Fig. 5 represents three to six tests. The horizontal asymptote to this curve would probably be somewhere between the 50 and 60 per cent ordinates. Consequently, as a result of the above tests, it is not safe to assume that the permanent load which timber will "carry is greater than 50 per cent of the short-time ultimate as ordinarily found by the testing machine. STIFFNESS AND OTHER MECHANICAL PROPERTIES 232. The Stiffness of Wood. — Stiffness in a structure is often as of much importance as strength, but it is much more frequently neglected in designing. Floors must be sufficiently stiff so that they will not deflect appreciably under working loads or else they give one the feehng of insecurity. If a floor Sustains a plastered ceiling its deflection under working load should not exceed ^— - of the span. Likewise the deflection of rafters should be limited, if it is desirable to avoid the disagreeable appearance of a sagged roof. Stiffness in compression members is not often of moment in design. It is measured by the modulus of elasticity which is computed from the ratio of unit stress to unit strain. For beams the modulus of elasticity (E) may be computed from the equation E = ——; where P = a certain load within the elastic limit of the beam, /= deflection corresponding to P, Z = length of span, 7 = moment of inertia of cross-section about the neutral axis and j3 = a constant depending on the end conditions and the * For a more complete discussion see Proc. A. S. T. M., Vol. 8, p. 541. STIFFNESS AND OTHER MECHANICAL PROPERTIES 209 method of loading the beam. For a center load on a simple beam, |3 = 48; for the case of a simple beam loaded with two equal concentrated loads iP,P) at the third points of the span, |3 = -^. In general, the denser woods are the stiffer, as may be seen by refer- ence to Table 1. There is not, however, much difference between stiff- ness of the softwoods as a class and the stiffness of the hardwoods, nor are there as wide variations in the stiffnesses of the various species of wood as in the strengths. Values in Table 3 show that green timber is less stiff than air-seasoned; and, from results in Table 6, it appears that the structural sizes of timber are about as stiff as the small clear sticks. Fig. 6 shows typical load-deflection and load-deformation curves for wood. These figures also indicate the method of finding the elastic limit and the correction of curve when it does not pass through the origin. Other load-deformation curves for wood may be seen in Fig. 18. 233. Toughness.^ — ^A wood which has a large capacity to resist shocks or blows is called tough. The spokes of an automobile or wagon, the tongue of a wagon and its axles, the handle of the axe or sledge all must be tough that they may absorb without injury the shocks which they re- ceive. In order to be tough a wood must have both strength and flexi- bility. Toughness is best measured by the energy of the blow required to rup- ture a beam in transverse impact. A less reliable index of toughness is obtainable from the energy of rupture in cross-bending. The latter test, however, is more easily made than the former and of more general value, since static strength and stiffness may also be gotten from it. The tor- sion test has also been used to measure the toughness of wagon spokes. In Table 1 the average work done in deforming a large number of small wooden specimens in both static and impact bending tests has been re- corded. The methods of determining the various results in static bending have been considered in Ch. I and III. In the impact tests the height of drop was increased by 1- or 2-in. intervals until failure took place. The height of drop at the elastic limit was gotten by plotting height of drop (h) against the square of the deflection (/) and determining the value h' at which the curve deviated from a straight line. The fiber stress dWh'l at elastic limit (&) was calculated from Se= ^m > t^® modulus of elasticity (E) from E= nir' ; and the elastic resilience (K) from if =— -J-. The undefined symbols are TF = weight of hammer, Z = length lod of span, 6 = breadth of beam, and d = depth of beam. From the test results on green timber, it wiU be observed that the total 210 THE MECHANICAL PROPERTIES OF TIMBER Klinn pnnoa oool ni pnoi 1 /^ ID \ TS i a 3 N H ^ H J 3 1 -*l ;<_<,-<< PRES REA f 3HT 2 1 "^ ^. s^ ^ h^ fe=^ - r ^ ^ "*>*., BHnfl pnnoa ooOI "I pco-i 1 (I 1 w f ft 1 \ v i t (i (3 ' z • g s UJ CD I U > c •o , -§ S Q- B a \ s 1 S s 43 1 N s N s V k IsSs s V ^V ^k N V c u 5 c ? c 5 i g % 5 a . to R BHiifl panoj oooj ni pooi STIFFNESS AND OTHER MECHANICAL PROPERTIES 211 work in static bending and the height of drop causing complete failure in impact bending vary with different species in approximately the same manner. With these calculated values as criteria, it is obvious that the hardwoods as a class excel the conifers in toughness. Among the hard- woods, osage orange, hickory, rock elm, slippery elm, honey locust and hackberry are very tough; while basswood and sycamore are thore brittle than many of the softwoods. Longleaf pine is the only one of the conifers possessing much toughness. Seasoning when unaccompanied by checking generally increases toughness, but in chestnut, gum and willow it causes a marked decrease in toughness and, to a less extent, adversely affects hickory. In general, greenwood is tougher than seasoned material. 234. Cleavability is the measure of the ease with which wood may be split. This property is of considerable moment in the working of wood, especially in splitting fence rails and firewood. Woods which must be fastened by nails and screws should have a high resistance to splitting. Fig. 7. — Type of Cleavability Test and Specimen Adopted by Forest Products Laboratory. (Betts and Greeley before Int. Engr. Congress, 1916.) Since splitting is accomplished by wedging apart the longitudinal elements, it is closely related to tension, across the grain. At the Forest Products Laboratory, the test-piece of Fig. 7 is used to determine resist- ance to cleavage. From results in Table 1, it appears that most hardwoods split more easily along radial planes than along tangential surfaces. Among the conifers the difference in cleavage strength in the two directions is not great, but for longleaf pine, hemlock and tamarack it is greatest across radial planes. Interlocking of the wood fibers causes high cleavage strength, 212 THE MECHANICAL PROPERTIES OF TIMBER while defects like shakes and checks reduce it. Knots may affect it either way depending upon the number, position and character. Honey locust, hickory, slippery elm, hard maple, and the oaks have the highest resistance to splitting. Basswood and the conifers split with comparative ease. 235. Hardness. — Both resistance to indentation and resistance to scratching are important properties in woods which are to be used for finishing and for furniture. These properties together with the ability to wear without splintering determine the wearing resistance of wood for floors and pavements. Aside from the indentation tests no satisfactorj- type of test has been devised to measure these properties. However, experience shows that woods having marked difference in the character of the spring wood and summer wood (pine and oak), wear best when laid with the edge of the grain exposed to wear. With the fine-grained woods of uniform texture, like hard maple, the resistance to wear appears to be little affected by the method of sawing. The resistance to indentation of a number of green woods is given in Table 1. With the exception of basswood, all of the hardwoods listed are harder than longleaf pine, the hardest of the conifers. In green wood the hardness appears to be independent of the surface indented. Season- ing greatly increases resistance of all surfaces to indentation but affects the resistance of the end surfaces most. CONDITIONS AFFECTING MECHANICAL PROPERTIES OF TIMBER 236. Density. — All of the mechanical properties of clear wood, regard- less of species, are related to its density. Within a given species the relation is closer than between species. This is most pronounced in tim- bers of structural size where defects and moisture content considerably affect interspecies relationships. Thus, from a very large number of tests at the Forest Products Laboratory, it appears that for small specimens of green material, the shrinkage, the compressive strength parallel to the grain, and the stiffness vary with the first power of the density ; the shear- ing strength parallel to the grain and static bending strength vary as slightly higher power of density; whereas, cleavage, work in bending, ten- sion across the grain, hardness, and compression perpendiculai' to the grain vary approximately with the second power of the density. The general law may be expressed by Q = Cp^] where Q is the prop- erty considered, C is a positive constant, n is a positive constant between 1 and 21, and p is the density. In such relationships p is computed from the volume of the wood at the time of testing and the oven dry weight. Fig. 8 shows the relation between modulus of rupture and the dry weight per cubic foot for 113 varieties of wood. In Fig. 9 the relation between CONDITIONS AFFECTING MECHANICAL PROPERTIES 213 0..5 0.6 ■ J O.E SPECIES TESTED-WITH CORRESPONDING LOCALITY DP GROWTH AND REFEllENCE NUMBERS HARDWOODS. CONIFERS :: Sl'.i ~- ■■: -.":'™:::.' " ■-.. ..•..!! <:v;'«i»rs;iS ,■,■ . S"- . 1 9C .»/. .»«».•,:■ > 14 Ul 101 3 / i™-:,--:':^::iJ^-.::-V- ■' 1 rials.:: ■: :=»:..-:. :.:::: J "15 !|pi"^.-::;|:;;:;;:::;:;:;: =) ■• ORA»D-..:- no HEUUICIl. BUCK . TTNN.. .':.:..:' '.:' ::. !: / i|;.™-:='-: a ::■■:::■-- 1 f^n ..tl / -0 ■:^Ka;::;::~;;;s?: : is KS. si aw!::::: ;& s .. M 1:11 ■ / 57 Mfgi^'-::-:ra .... ^l&O <] r° cHkHRv, WILD HED ... TEMii.. :.::::: i:::::::::;' ■■ iSb^lbv;':"'oou) .. ^p^'' ijj, ■ -^ : :: x.?h^w - cal 13E / 108p OH8 / OUd i' C ,13. P / n 04 ri$ "las / io4"a ,f 01 1^^ :::« •• " ybllow;. mont ;:.. :::::::;::;:;::ia u.t- r 01 17 :iS 5ISS88S : ■■ :■ EftaS'.'Sl. 05 ^u y o' 3 ■■ m^i'n^^^!:?*^^^!? '• '" aPBUCE. ENOLEMAN OOLli.,'ORAND 1 :: rag KT-.,- ■::;::::::::; is " EfS' ■■■.;:::■■ ¥ehV.::::::::::::::::::.3 oe / 'loJ 1 ■0 / . . ,::::;:;;::: •.!R : SiS ::::::::■: sii:i;:;;:;;i:;;:s:i;f o: o lO.'n, \-' 14- G4, / 'c son "h / ;,„ -•i- / : iS:-'? ■ is , iCO » / .|70"' 3 158 / ' S!iV°.r',::.-,S,i* IS f '1 'V 1 •^ 1-:1 y .iil 50 > Gi o Si i?' ' 4.1 o 18 la-, / IJX:nrT._ HONEY. S •■■-"■■■"- K J=' ^ '\ i y '•"• ICO !^ <:, •r 5J 70 / o 1 •'li" n / •' > ^ie: III In VI lO ^ 1 Ui CO • 00 / ,,'>• • 1 j7 a? k 11, . ( >17 ■Jl ::^ .P Si 'l\ ■'( ^J^ f^' 0; ^7 °» ?;! '. k 1 • f. i:>i J., .,e „o 5o /a °f.1 f4 .,0 ?;*L"+>, »; 14U :; "'^1 wf^l 5^ i '"r v,*"' I \ J: J'SSffl™' iii 'iW^ 132 .:::..:.:,; /32, 0,« ', ^ii. >i 4 ft-SS. S; :!H 4 / 1133 sol'-'l ,0* •, 10 SrKo,„j^S:::::;:::::::::;:::::£ «5|"««-;:::::;ffiS;:::::::::::;:::::::::a / 'iroifo 4« ffs?. 81 'js' 'J4 is" "i ^•I'n' -1. i piSEH?; 'PT •J7 / '■'■' -S SiLSJL '78 SKa-iJSf^ ;■.:;:■.? i :S N \ It •> li> 111?*! • • r P ^' '^ 3 ^ •J3 JS '/ '^J i« i ^<^ ' ft s ?! - ■* / ^ ?? / / ''( 3 Note:- / I'f % • i neb point 16 the average of lade on Bmall, clear, straight ed pieces cut from tvoicat / ^ grain ^ \** treea, of the same Bpecies,erowil V '^ ^ >■ Usually about 60 pieces frc 5 trees were used. / < X • / /^ / < > ' /' --' 'c>' ^ ' 22 20 18 16 14 d" CO s 12 o 'I 0.1 0.2 0,3 0.4 Specific Gravity 0.5 0.6 0.7- 0.8 Fig. 8. — Relation between Bending Strength (s) and Specific Gravity (p) for 113 Woods. (Specific gravity is based on volume at test and dry weight. Diagram compiled at Forest Products Laboratory,) 214 THE MECHANICAL PROPERTIES OF TIMBER J0,000 9,000 8,000 1.7,000 6,000 5,000 4,000 3,000 2,000 1,000 Modulus of Eupture Ib./in.' Crushing Strength lb./ in.^ Modulus of Elasticity 1000 lb. /in,^ Figures at Q's indicate number of tests averaged. ~ iV" 20 30 40 Weight in Pounds per Cubic Foot Fig. 9.— Relation of Dry Weight to Modulus of Rupture and Modulus of Elasticity in Bending, and to Compressive Strength Parallel to Grain. {.Bull. No, 88, Forest Service.) CONDITIONS AFFECTING MECHANICAL PROPERTIES 215 / / / fe / / CS s / o / ^ s / t; / 1 .«. / o s / ■s ( a ' ii / y a ^, 7 ^ 3 / o / a / rt ? £/ / s g c ;/ a> -rt 'a^ Sj h- i 1 Si ^^ PH 1 s jS >. ^ >. H V y- ce 1 . / s S: ^ ^ y 1 .a P s s a" 1 1 i I / tH \ r y ^ o ( o 1 \ / i?i t \ 1 1 ll \ 1 i/ y \ 1 y t1 \A / I j 1 / I\ /> \ \ 1 1 \\ / V M \ 1 1 \ \ t1 1 \ 1 1 s \ \ \ \ y V K \^ V \ \ ¥ \ s s \ \ V ■l V ^ -V X \ \, \ \ '- •>^ \ \ ja t: K o M e*-< fc4 (1 Pn ^ a rt a o SS ' / S £ / / " / / „ bi / ^ / "I o/ „ 1 1 s s i / h4 5 -^ / a a< = y ^ « fc. / 3 t s (M / ? s s / a5 V. a / =4 t^ to S h ^ 1 /^ y =0 \ ■«< V ('.^ If // ^ -f / X V // s "* // 1 7 2^ F / / / 1 ' / f / °^ 1 1 s/ fS 1 1 1 1 «) jl •n=i ^ s j P^ W V C14 'I \ s^ \ JD \ \ hJ .3 fNI s ^ \, ^ \ ^ \ { \l S, \ ^v\ ^ JD ^^ s. s \ V ^ ^-^ ^^^^^^_^ \y 216 THE MECHANICAL PROPERTIES OF TIMBER various mechanical properties of air-seasoned beams of Douglas fir and the dry weight is shown. Attention should be directed to the difference 12,000 ■^ 3 I 8000 6 8 U 11 17 20 23 26 29 32 35 38 11 4117 HlDgs per Inch k 3 l\ /&^L y^Si ^ 1 §1 sif? 1 i ^ ^ 1^ ~ ft !: 1 s a ^ '■ \i i ' a s " ^\ i \ t 6 8 U 11 17 20 23 26 29 32 35 38 11 11 17 Rings jper Inch Fig. 11.— Bending Strength and Energy of Rupture as Affected by Rate of Growth in Green Hickory. {Bulletin No. 80, Forest Service.) IQOOO ■ " In Lb. perSa. In. ^=_ Fiber Sti-ess at E. L. In Lb. per Sg. In. in 1000 Lb. per Sq. In. ^ A Sho rtlea t Pli le 9000 ( / ^ <^ iSo glas Fii- ^ ^ ^ aooo t* ^ =-Ee Iwo Id A ^ 10O0 A '/ < Wei tern Hei nl oc t ^ V. " 6000 / ^ ^^ pi )0U}: las 'it /^ ' / / ■^ ^' A n '\r. ;dw ood -W 3stei Q H mlo ck ^ -f ^ -^ ^-' =*1t -SI ortl at !me 1000 ^ ^ ^ f ^ ■^ ^ ^ ^ ^ ^ r ^ 2000 -^ Bou ;las Plr - _ii— ^ .^ -" -t- ^W '.stp.l ortl( 11 H At 1 :mlo me " R& iwo Id 10 20 30 10 60 60 70 80 Percent of Summervrood Fia. 12. — Relation of Modulus of Rupture, Fiber Stress at Elastic Limit, and Modulus of Elasticity to Percentage of Summer Wood. (From Bull. No. 108, Forest Service.) in strength values for the large and small specimens. A considerable proportion of these discrepancies is due to defects which were present in CONDITIONS AFFECTING MECHANICAL PROPERTIES 217 4 11,000 ifK.OOO .3 t^ n A^ V ■^, 1 20 i- <{ -,. \ \ 'X Ai k/ -s. V V the large beams. It is also noteworthy that the stiffness is independent of the size of specimen. From tests on other species the latter conclusion appears to be general. Since density is affected by rate of growth, per cent summer wood, position of specimen in tree, and moisture content, the influence of these factors on mechanical properties will next be considered. 237. Effect of Rate of Growth. — Fig. 10 illustrates the previously made statement that coniferous wood having a medium rate of growth is the strongest and stiffest. There is, however, a wide range in the most effective rates of growth for different conifers. In the dense hardwoods rapid growth is more desirable as is shown by the curves of Fig. 11. 238. Effect of Percentage of Summerwood. — With most coniferous wood the summer wood is readily identified and forms a valuable index of the mechanical properties of the timber. The proportion of summer wood in a given conif- erous timber is generally de- termined by estimating the ratio of the sum of the areas of the dark rings to the total cross-section. Fig. 12 shows the relation of per cent summer wood to strength and stiffness for sev- eral coniferous woods. On account of the important relation which the per cent summer wood bears to mechanical properties a minimum percentage limit has been inserted in specifications for structural timber (see Art. 250) . 239. Relations of Mechanical Properties to Position in Tree. — Since wood in the lower part of the trunk of a tree is more dense than that higher up, and since the densest wood at any given height is situated between the pith and the middle ring of the cross-section, a small variation in the strength of wood due to position in the tree will be found. Fig. 13 shows how the strength and energy of rupture of hickory specimens vary due to position in tree. Fig. 14 shows how the strength of wood in Western larch trees varies with the height above ground. 240. The Influence of Defects on Mechanical Properties. — Defects .A, si ^1 5^ S" 'I IJ ^ 8 1 6 8 10 _ _ Inches from center of Tree ^ Inches from center of Tzee Fig. 13. — Bending Strength and Work as Affected by Position in the Tree, as Shown by Tests on Green Hickory. (From BuU. No. 80, Forest Service.) 218 THE MECHANICAL PROPERTIES OF TIMBER are one of the principal causes of variation in the mechanical properties of timber. The discrepancies in the strength values of large and small specimens and the variation in properties of similar test-pieces from the same wood are conditions largely due to defects. Knots destroy the continuity of the wood elements and consequently &.000 SOQO ModnlQB of Bupture Lb. per Sq. In, eUTeBta • Crushtn? Strength at Maximum Load Lb. per Sq. In. , Oompr. 1 1 to Grain U6 Tests 6^000 «,000 8 14 U 1 ii-. ^ 8 16 0/ U —rx 12 J' 25 C c5~~ 26 8,000 y S^OOO 41,000 16 S2 so 28 S6 •^ 7 ^ -<5. .^ 7 ?^ S 70 t 6 '(i^ ?m 21 80 H ^ Lb. per Cu. Ft. 64 Teats 10 20 30 40 50 60 Heiglit of Specimen above Grouud— Peot Fig. 14. — Relation of Strength Values to Height in Tree. Specimens were small clear pieces of green western larch. {Bidl. No. 122, Forest Service.) diminish tensile strength. Such defects are, therefore, a source of weak- ness when present in the lower fibers of a simple beam, and especially so if under the load. Large knots and knots which are incHned to the axis of a member adversely affect the strength of a column or, if in the cen- tral portion of the top fibers, weaken a beam. Table 7 shows the effects of knots on the compressive strength and stiffness of 6X6-in. prisms of CONDITIONS AFFECTING MECHANICAL PROPERTIES 219 TABLE 7.— EFFECT OF KNOTS ON STRENGTH VALUES OF DOUGLAS FIR, WESTERN LARCH, AND WESTERN HEMLOCK IN COMPRESSION PARALLEL TO GRAIN, LARGE SPECIMENS (From Bull 108, Forest Sv=irvice) Kind of knot. Species. Num- ber of tests. Rings per inch. Mois- ture. Weight per cubic foot. At test Oven dry Com- 'proasive strength at elas- tic limit Crushing strength at maxi- mum load per square inch. per square inch. Lb. 3,099 4,390 2,070 Lb. 3,918 4,969 2,850 2,635 3,782 1,710 3,630 4,216 2,956 3,018 3,593 2,204 3,507 3,915 3,045 2,931 3,808 2,017 3,698 4,525 2,875 2,955 3,625 1,815 3,772 4,020 3,445 2,880 3,610 2,630 3,396 3,630 3,190 2,708 3,798 1,832 3,386 4,638 2,428 2,577 3,340 1,643 3,226 3,787 2,800 2,838 3,280 2,350 3,197 3,640 2,775 2,406 3,426 1,669 3,062 4,367 2,129 2,569 3,270 1,778 3,069 3,670 2,380 2,590 3,150 1,945 2,901 3,405 2,300 95 87 78 94 86 78 112 98 98 104 89 85 96 94 86 97 91 83 Mod- ulus of elas- ticity per square inch. No knots. , Pin knots (sound knots ft inch or less in diameter). Standard knots (sound knots, between ^ and li inches in diameter). Large knots (sound knots, 1 ^ inches and over in diam- eter). Comparison of results; clears = 100. Douglas fir: Average High 10 per cent. Low 10 per cent . Western larch: Average High 10 per cent. Low 10 per cent . Western hemlock: Average High 10 per cent. Low 10 per cent . Douglas fir: Average High 10 per cent. Low 10 per cent . Western larch: Average High 10 per cent. Low 10 per cent . Western hemlock: Average High 10 per cent. Low 10 per cent. Douglas fir: Average High 10 per cent. Low 10 per cent . Western larch: Average High 10 per cent. Low 10 per cent . Western hemlock: Average High 10 per cent. Low 10 per cent. Douglas fir: Average High 10 per cent. Low 10 per cent. Western larch: Average High 10 per cent. Low 10 per cent. Western hemlock; Average High 10 per cent. Low 10 per cent. Douglas fir: Pin knots Standard knots.. Large knots. . . . Western larch: Pin knots Standard knots. Large knots. . . . Western hemlock: Pin knots Standard knots. Large knots. . . . 130 13 13 51 5 5 46 5 5 62 6 6 20 2 2 12 1 1 227 23 23 28 3 3 11 1 1 11.8 21.7 5.3 25.4 37.8 17.7 15.7 26.2 6.3 10.4 21.0 4.7 21.7 28.5 12.0 12.5 22.6 7.7 9.0 17.6 4.4 24.2 31.7 14.6 16.7 26.9 8.2 9.4 19.0 3.5 23.8 32.0 16.0 14.6 26.2 10.0 Per ct. 30.4 36.1 26.7 52.3 66.8 39.0 48.5 85.2 30.9 31.6 36.6 27.4 48.1 62.9 36.0 48.4 61.4 30.2 30.9 39.7 24.7 44.6 64.6 32.8 42.0 65.9 30.4 29.9 37.2 24.7 46.2 72.0 33.3 42.0 61.6 29.6 Lb. 38.1 43.4 33.2 44.8 55.7 34.9 41.2 55.3 32.8 37.7 43.6 32.5 42.9 50.8 38.3 38.1 46.2 33.0 37.8 43.8 32.7 39.2 51.3 32.8 36.6 44.0 33.0 38.0 44.5 33.0 40.5 53.7 34.2 37.9 46.3 34.4 Lb. 29.2 33.4 25.8 29.3 34.7 24.3 27.7 32.3 24.0 28.6 33.1 24.5 28.9 32.1 26.9 25.6 29.8 22.8 28.9 33.4 31.0 27.0 31.3 24.1 25.8 28.9 23.8 29.3 33.8 25.5 27.8 31.2 24.6 26.8 29.1 23.8 1,000 lb. 1,321 2,707 623 1,528 1,997 1,101 1,676 2,282 1,111 1,401 2,681 642 1,820 2,479 1,342 1,670 1,957 1,418 1,187 2,467 576 1,521 1,975 1,092 1,624 1,860 1,363 940 2,119 472 1,442 2,189 1,092 1,364 1,688 955 106 90 71 119 ITO 94 100 97 81 220 THE MECHANICAL PROPERTIES OF TIMBER Douglas fir, Western hemlock, and Western larch. From the results in this table it appears that knots I5 in. in diameter or over may diminish the compressive strength and stiffness of structural timbers from 15 to 20 16,000 13 20 25 30 35 40 45 Moisture Per cent Based on Dry Weight 50 55 60 Fig. 15. — Relation between the Crushing Strength Parallel to Grain and the Moisture Content for Several Woods. {Circular No, 108, Forest Service.) per cent. Tests by the Forest Products Laboratory have shown that knots have little effect on the elastic limits and stiffnesses of beams but they decrease the modulus of rupture. Consequently knots in beams will CONDITIONS AFFECTING MECHANICAL PROPERTIES 221 adversely affect ultimate strength and toughness. Sound knots near ^°''""' XI Til 1 T 1 • M'°™ the neutral plane have little in- ^ ^^ ^^ fluence on the shearing strengths S n,ooo of beams. « le.ooo Shakes and checks are most mie.ooo S 11,000 Pi .§ 13,000 g 12,000 o ^ 11,000 g 10,000 §■ 9000 a « 8000 o g 7000 I 6000 g 6000 4000 8000 harmful to strength when they follow the neutral plane of a beam or run diagonally across the tension side of it. -In the first case they' weaken the re- sistance to horizontal shear, and in the second case they lessen the tensile strength. Restrictions on the character, size, and position of defects in structural timbers are given in the grading rules proposed by the Forest Products Laboratory (see Art. 250). ' r \ \, \ i \ \ \ \ \ \i\^ w \ \ .\ \ \ (P \ V ^ ChistDut \ Spr uce \ g 2600 - " 2500- i r 'o o a 03 11 r g?l S Ok. P4 13. Limestone Montgomery County — Pa. /Bed \Edge Lb. 13,112 11,055 Lb. (marble) 4 14. Limestone (marble) Dorset — Vermont. /Bed I Edge 10,506 8,670 2.64 2.68 164.7 167.8 :::: 2 1 15. Limestone (marble) Italy. Bed 12,156 2.69 168.2 .... 1 16. Sandstone Buckhorn (Larimer Co.), Trini- dad (Las Animas Co.), Mani- tou (El Paso Co.), Ralston, Left Hand, Saint Vairus, Fort • Collins (Larimer Co.), Stout (Larimer Co.) — Colo. Thistle —Utah. /Bed I Edge 11,141 12,434 2.13 132.9 6.6 9 17. Sandstone Coal Creek, Oak Creek (Fre- mont Co.), Gunnison (Gunni- son Co.), Manitou (El Paso Co.), La Porte (Larimer Co.), Brandford (Fremont Co.)~Colo. /Bed \Edge 5,481 4,941 2.12 133.0 13.8 9 18. Sandstone Middletown, Portland — Conn. East Long Meadow — Mass. Marquette — Mich. Bed .6,639 2.27 142.2 3.5 3 19. Sandstone Hinckley, Fort Snelling — Minn. /Bed I Edge 16,625 18,750 2.38 139.0 6.0 2 20. Sandstone Dresbach, Jordan, Fond du Lac, ) Dakota — Minn. j /Bed I Edge 5,789 4,102 19.9 124.4 9.9 6 21. Sandstone Taylor's Falls, Kasota, Fronte- \ nac — Minn. /Bed I Edge 7,483 9,725 2.42 142.4 5.9 3 22. Sandstone Haverstraw, Hudson River, Al- \ bion— JV. Y. j /Bed I Edge 8,925 7,687 2.78 142.2 2.6 2 23. Sandstone Medina— AT. Y. /Bed \Edge 17,500 14,812 2.42 2.39 150.8 149.3 1.6 2.0 2 24. Sandstone Vermilion — Ohio /Bed I Edge 7,840 6,876 2.16 135.0 5.2 25. Sandstone Seneca — Ohio. /Bed I Edge 9,687 10,500 2.39 149.3 3.1 26. Sandstone Cleveland— Oto. /Bed I Edge 6,800 7,910 2.24 140 2.8 27. Sandstone Marblehead — Ohio. /Bed I Edge 7,937 6,850 2.31 144.4 5.2 28. Sandstone North Amherst — Ohio. /Bed I Edge 6,212 6,450 2.16 133.7 135.8 6.2 29. Sandstone Berea — Ohio Bed 9,236 2.13 133.0 5.6 2 254 BUILDING STONE 270. Absorption. — Methods for determining the per cent absorption of stone are similar to those outlined in Art. 291. If the per cent water absorbed by volume is desired, it may be gotten by multiplying the per cent by weight by the specific gravity of the rock. The proportion of the pore space filled with water and the rate at which the rock will expel absorbed water are important criteria of resistance to freezing. Rocks which absorb enough water to fill the pores and which expel slowly are very likely to be weakened by freezing. Values of the percentage of absorption for different stones may be found in Table 4. THE MECHANICAL PROPERTIES OF STONE 271. The Strength of Stone. — The compressive strength of building stone is the most commonly tested mechanical property; although shearing and transverse tests are sometimes made.* The preparation of specimens and the methods of performing these tests have been considered in Ch. III. In considering the test results which follow, it must be recognized that many of the values for American stones are subject to variation owing to the uncertainty which exists surrounding the preparation of the speci- mens which were tested. In masonry construction the greatest crushing load allowed on the best grade of granite ashlar does not run over 600 lb. per square inch and for the ordinary grades of coarse rubble laid in cement mortar the allowed stress generally runs between 150 and 200 lb. per square inch. Therefore, if a factor of safety of ten is allowed, the required compressive strength of stone in cubical specimens need not exceed 6000 lb. per square inch for the most severe loading. Although there is no objection to greater strength, it cannot be argued that because one stone has a crushing strength of of 20,000 lb. per square inch and another 30,000 lb. per square inch that the latter is superior to the former for building purposes. A high crushing strength alone is not of great importance. Crushing strengths of the more important stones of the United States are given in Tables 4 and 5. Owing to faulty methods of quarrying, discrepancies between the rift and planes of bedment in the wall, and owing to irregularities in founda- tions and mortar bedments stone is much more likely to crack due to the imposition of bending stresses than by crushing. Cracks in lintels due to transverse stresses and in walls due to excessive shear stresses are quite common. Consequently, the resistance of stone to these stresses is of importance. * The tests made on crushed stone for paving purposes are described in Bvll. No. 44 of the U. S. Dept. of Agriculture; also see Blanchard and Browne's Texl Book on High- way Engineering, Ch. 9. THE MECHANICAL PROPERTIES OF STONE 255 TABLE 6.- -TESTS OF AMERICAN BUILDING STONE MADE AT THE WATERTOWN ARSENAL (Rep. 1894.) Weight per Cubic Foot. Compression Tests. Ratio of Lateral Expan- sion to Longi- tudinal Compres- sion.* Shearing Strength. Coefficient of Expan- sion in Water per °F. Name of Stone. Strength in Pounds per Square Inch. Modulus of Elasticity for Work- ing Loads. Lb. Lb./In.2 Lb. Brandford granite (Conn.)* . .' 162.0 15,707 8,333,300 0.250 1833 , 00000398 Milford granite (Mass.) 162.5 23,775 6,663,000 0.172 2564 .00000418 Milford granite (Mass.) .00000415 Troy granite (N. H.) 164 7 26,174 4 545 400 196 2214 00000337 Milford pink granite (Mass.) 161.9 18,988 5,128,000 1825 Pigeon Hill granite (Mass.) . . 161.5 19,670 6,666,700 1550 Creole marble (Georgia) 170.0 13,466 6,896,500 0.345 1369 Cherokee marble (Georgia) . . 167. S 12,618 9,090,900 0.270 1237 .00000441 Etowah marble (Georgia)., . . 169.8 14,052 7,843,100 0.278 1411 Kennesaw marble (Georgia). . 168.1 9,562 7,547,100 0.256 1242 Lee marble (Mass.).. . . 00000454 Marble Hill marble (Ga.) . . . 168.6 11,505 9,090,900 0.294 1332 .00000194 Tuckahoe marble (N. Y.) 178.0 16,203 13,563,200 0.222 1490 .00000441 Mt. Vernon limestone (Ky.) . 139.1 7,647 3,200,200 0.250 1705 .00000464 Bedford blue limestone (0.) 10,823 7,250,000 0.270 1017 .00000389 North River bluestone (N. Y.) 22,947 6,268,800 .00000519 Cooper sandstone (Oregon) . . 159.8 15,163 2,816,900 0.091 1831 .00000177 Sandstone, Cromwell (Conn.) 10,780 Maynard sandstone (Mass.). 133.5 9,880 1,941,700 0.333 1204 .00000567 Kibbe sandstone (Mass.) 133.4 10,363 1,834,900 0.300 1160 .00000677 Worcester sandstone (Mass.). 136.6 9,762 2,439,000 0.227 1242 .00000517- .00000500 Olympia sandstone (Oregon) , 12,665 00000320 Chuckanut 3andstone(Wash.) 11,389 1352 Dyckerhoff Portland cement. . 00000578 * Poisson's ratio. In Table 5 are given the shearing strengths for a number of American stones. Inasmuch as the majority of these tests were made by a method similar to that outlined in Art. 514 (Fig. 11, Ch. XIV), the values are probably lower than the true shearing strength due to bending. While testing the transverse strength of Wisconsin stones, Buckley found the following ranges in modulus of rupture: Granite, 2713 to 3910; lime- stone, 1164 to 4659, and standstone, 363 to 1324 lb. per square inch. In Table 6 is presented a series of tests on Bavarian building stones. These tests were made with great care and precision by Prof. Bauschinger and reported in his Communications, Vol. 10. The results show that there is no fixed relation between the various kinds of strength of stone. A considerable number of transverse tests were made by Prof. Merri- 256 BUILDING STONE 12,000 10,000 .8000 leooo 4000 8000 Proportionate Compression Proportionate Compression Fig. 2. — The Elastic Properties of Various Fig. 3. — The Elastic Properties of Va- Granites under Compressive Stress. (PTai. rious Limestones and Marbles under Ars. Rept, 1894.) Compressive Stress. (,Wat. Ars. Eept, 1894.) 10,000 6,000 c *t 6,000 c 93 §4,000 8,000 • // A w / !,000,000 ^ 0^ ^- — E= 1,060,01 00 —E= 1,750,001 * E- 460,1 .001 .002 Eroportloiiate ComprGSsion .003 Fig. 4. — The Elastic Properties of Various Sandstones undei- Compressive Stress. {Tests of Metals, 1894.) THE MECHANICAL PROPERTIES OF STONE 257 man * on slate specimens which were secured from a number of the Eastern states. The specimens were 24 X 12 in. in plan and to \ in. thick. They were tested flatwise on a 22-in. span. The values of the average modulus of rupture for nine varieties ranged from 6410 to 9880 lb. per square inch, and the average maximum deflection varied from 0.19 to 0.23 in. It seems reasonable, therefore, to expect good slate to have a modulus of rupture of 7000 lb. per square inch and to deflect 0.20 in. at rupture. Experiments made at the Watertown Arsenal f have shown that a 12,000 Proportionate Compression Fig. 6. — Flastic Properties of Various Stones under Compressive Stress. {Tests of Metals, 1894.) very great loss in tranverse strength results from immersing stone in hot and cold water. The granites were the least affected and the marbles most. The loss in strength of the former, for the most part, was less than 25 per cent while several of the marbles lost 50 per cent of their strength due to this treatment. Consequently, one must be careful that specimens of stone for transverse tests are not subjected to large temperature varia- tions. Furthermore, this fact whould be borne in mind in designing lintels and stone beams which will be subjected to wide variations of temperature. 272. The Elastic Properties of Stone. — Like cast iron, brick and * Bull. No. 275, U. S. Geol. Survey, t Tests of Metals, 1905. 258 BUILDING STONE concrete, stone is a material which does not obey Hooke's law. The gran- ites, limestones and marbles, however, exhibit less curvature and less set in their stress-deformation curves than do the more porous sandstones. These facts will be evident after an examination of Figs. 2, 3, 4 and 5. Bauschinger has shown, however, that for a given specimen the moduH of elasticity in tension, compression and in cross-bending are practically the same. The values which are taken from his tests, Table 6, were found on the first loading. TABLE 6.— PROPERTIES OF THE BUILDING STONES OF BAVARIA. (Bauschinger's Communications, Vol. 10, 1884) Strengths giveii in Pounds per Square Inch. >> '> 2 « cC ■s 1 o u O -^ S3 MP Cross-bending. Compressive Strength. i a t m a H Shearing Strength. Kind of Stone. Modulus of Elas- ticity. Mod- ulus of Rup- ture. Per- pendic- ular to Bed. Par- allel to Bed. Parallel to Bed after 25 Freez- ings. Perpen- dicular to Bed. Par- allel to Bed. Granite 2.65 2.66 2.48 2.23 2.08 2.72 1.80 2.06 2.20 2.28 2.00 2.20 2.23 1.82 1.92 2.15 2.60 2.73 2.29 165.4 166 154.8 139.2 129.8 169.7 112.3 128.5 137.3 142.3 124.8 137.3 139.1 113.6 119.8 134.2 162.3 170.4 142.9 2,986,000 1,621,000 6,420,000 4,906,000 426,600 867,400 1,340,000 341,300 910,000 334,200 512,000 , 270,200 583,000 568,800 2,687,000 1,763,000 1365 1194 882 462 1792 469 469 718 1109 341 483 441 249 135 156 597 967 654 19,200 19,200 8,i30 11,110 4,664 19,340 1,195 7,420 9,040 12,930 6,160 7,636 6,684 3,071 3,029 4,707 13,510 28,860 5,546 18,910 20,050 8,320 7,410 8,760 20,620 2,545 6,010 7,790 13,410 6,100 8,390 6.670 2,247 2,659 4,308 14,500 17,490 4,408 21,470 20,480 6,810 12,290 3,313 18,770 2,076 6,730 7,910 11,520 4,877 5,986 5,900 2,161 4,252 4,038 3,270 619 683 583 448 213 910 227 107 199 576 128 341 213 98 67 , 9* 327 512 242 1379 1450 555 739 498 1479 227 569 512 910 455 640 583 370 242 341 668 995 142 Triassic limestone . . . Jurassic limestone f (marble) \ Oolitic limestone Tuffa stone Variegated sandstone Variegated sandstone Variegated sandstone Variegated sandstone Carboniferous sand- 384 540 299 1138 213 355 313 540 427 284 Carboniferous lime- Slaty sandstone Slaty sandstone Green sandstone Cretaceous sandstone Cretaceous sandstone Quartz conglomerate. 242 185 327 370 768 In Table 5 appear values of Poisson's ratio for stone. With one or two exceptions the values are about the same as those given for the fejrous metals; one-fourth is a fair average. 273. Resistance to Abrasion. — The abrasion of traffic on pavements, sidewalks and doorsteps is a matter of considerable importance in deter- mining the life of stone used for such purposes. A number of tests have been devised for measuring abrasive resistance, but none have been uni- versally adopted. Two types of test have been considerably used. In one a carefully prepared stone specimen with a plane face is held against THE MECHANICAL PROPERTIES OF STONE 259 a horizontal table which revolves about a vertical axis, and abrasion is produced by sand or emery. In the other test the specimen is subjected to the action of a sand blast under a standard pressure. Bauschinger experimented considerably with the first method, using a cast-iron table 5 ft. in diameter. He placed two specimens each 4 in. square at a distance of 19.5 in. from the axis and weighted each with 30 kilograms. The table was run at a speed of 20 r.p.m. and 20 grams of fine emery (No. 3) was fed to the plate every 10 revolutions, the old emery being brushed off. Two attendants constantly kept the emery in the path of the specimen.* The results of some of Bauschinger's preliminary tests to determine proper pressure and rate of feeding the emery are shown in Fig. 6. Table 7 shows the average results which he obtained in testing various materials. They indicate: 1. That the wet grinding was about twice as effective as the dry grind- 400 500 Pressure In Grams per Si|. Cm. TOO Fia. 6. — Showing the Relation between the Abrasion, Pressure, and Energy Used in Abrasion Test. (Bauschinger.) ing, the exact average ratios being given in the last column of the table for each species of stone, f 2. There is no fixed relation between crushing strength and abrasive resistance. 3. The limestones wear about five times and the sandstones about four times as fast as the granites, porphyries, and basalts. 4. The clay-slate shows the best results in abrasion, but only a few specimens were tested. * Bauschinger's test does not differ greatly in principle from the Dorry hardness test used in France and the United States for road metal. In the Dorry test the abras- ive agent is standard quartz sand passing a 30-mesh and retained on a 40-mesh sieve; the diameter of each specimen is 1 inch; and the speed is 30 r.p.m. for 1000 revolutions. t These ratios have been taken from the wet and dry tests on identical material, and therefore are not the ratios of the two general average results in the previous column. 260 BUILDING STONE TABLE 7.— AVERAGE RESULTS OF BAUSCHINGER'S ABRASION TESTS OF PAVING MATERIAL (Communications, Vol. 11, 1884) Four-inch cubes of the material were pressed on an iron plate with a weight of 4 pounds per square inch, and 20 grams of emery fed every 10 revolutions. Results obtained for 200 revolutions at a radius of 19.5 inches. Kind of Material. Average Specific Gravity. Average Weiglit per Cubic Foot in Pounds. Average Com- pressive Strengtli in Pounds per Sq.in. Inch. Number of Results Averaged. How ground: Dry or Wet. Average Loss of Volume in Cubic Inches. Ratio: L oss wet Loss dry Granite Syenite Diorite Hornblende. . . . Porphyry Basalt Gneiss Quartz Clay-slate Breccia Limestone Sandstone Brick and tile. . Artificial stone 1 made with Port land cement . . . Asphalt paving. . 2,63 2.27 2.87 2.82 2.57 3.01 2.61 2.63 2.72 2.61 2.87 2.48 2.98 2.36 2.33 164 142 180 176 161 188 163 165 170 163 180 155 187 148 146 22,400 18,780 26,200 21,900 24,500 34,200 23,000 17,500 26,000 22,600 20,500 17,600 92 8 24 1 18 2 2 93 4 4 9 8 2 10 163 32 44 38 105 34 20 4 2 2 dry wet dry wet dry wet dry dry wet dry wet dry wet dry wet dry dry wet dry wet dry wet dry wet dry wet 0.24 0.46 0.28 0.82 0.27 0.68 0.19 0.20 0.24 0.19 0.47 0.21 0.19 0.16 0.35 0.20 1.10 1.41 0.81 0.64 0.38 0.75 0.51 1.82 0.61 1.62 1.72 1.90 1.90 1.72 2.31 2.76 1.60 2.25 2.50 3.20 2.68 5. The brick and tile wear about twice as fast and the cement c9mpo- sitions about three times as fast as the primitive rocks. 5. The resistance of asphalt paving to abrasion falls between the cement mixtures and sandstone. Prof. M. Gary, of the Royal Testing Laboratory at Berlin, has used the sand-blast method of testing considerably and has reported comparisons of the grinding table and sand-blast methods. Gary used a special sand- blasting device fitted with a nozzle 6 cm. in diameter. The sand was pro- THE MECHANICAL PROPERTIES OF STONE 261 pelled by a dry-steam pressure of 3 atmospheres for a two-minute period directly against the stone. In testing with the table he used specimens 50 sq. cm. (7.75 sq. in.) in area and placed them at 32 cm. (9.6 in.) from the axis of the table. Results obtained by both methods on similar stones are given in Table 8. TABLE 8.— RESULTS OF ABRASION TESTS ON BUILDING STONES (Gary in Baumaterialienkunde, Vol. 10, p. 136) Area of specimens used on grinding table = 7.75 sq. in. Diameter of nozzle on sand-blasting device =2.36 in. Compressive Strengtli Lb./In.2 Volume op Wear in Cubic Inches per Square Inch. Kind of Stone. On Grinding Table. With Sand Blast. • Perpendicular to Rift. Parallel to Rift. Basalt Granite Gneiss Porphyry Graywacke * Sandstone Slate 38,900 21,360 21,230 17,840 15,780 6,640 7,480 0.042 0.041 0.079 0.068 0.085 0.144 0.234 0.024 0.037 0.056 0.046 0.059 0.155 0.111 0.025 0.052 0.045 0.036 0.058 0.117 0.082 * A dense sandstone containing rounded or angular particles of quartz, feldspar or slate. Although the sand-blast test brings out the weak spots in the specimen, it is questionable whether it approximates the action of traffic on the stone. On the other hand, when using the grinding table, considerable trouble is experienced in maintaining the abrasive agent in standard condition and in forcing it under the specimen in a uniform manner. CHAPTER VIII STRUCTURAL CLAY PRODUCTS* 274. Introduction. — Clay products form one of the most important classes of structural materials. In building construction, brick and terra- cotta are desirable on account of their pleasing appearance, strength and durability. Partition and floor tile form walls and floors of Ught weight which possess high strength and resistance to fire.. Paving brick make economical and durable, although somewhat noisy, pavements. Clay pipe on account of their durability, strength, light weight, and cheapness are successfully used in sewers, drains and conduits. Structural clay products may be classified as follows: f Building brick Brick I Paving brick [ Fire brick Hollow blocks Partition tile Fireproofing Roofing tile Floor tile Wall tile ~ , , , Decorative terra-cotta Terra-cotta -^ „, ^, , , I erra-cotta lumber Sewer pipe Pipe ■! Drain pipe I Conduit pipe The total value of the clay products produced in the United States, in 1914, was $164,986,983. Of this amount the value of common 'brick was 27 per cent; fire-brick 10.0 per cent; building tile 8.5 per cent; sewer pipe, 8.5 per cent; vitrified brick, 7.6 per cent; front brick, 5.6 per cent; drain tile, 5.2 per cent, and architectural terra-cotta, 3.7 per cent. *The following texts have been freely consulted in preparing this chapter: Clays: Occurrence, Properlies and Uses; also Building Stones and Clay Products, by H. Ries; Wiley & Sons. The Clay Workers Handbook, hy A. B.Se&rle; Griffin & Co. Modern Brick Making, by A. B. Searle; Scott, Greenwood & Son. 262 Building tile. MATERIALS, MANUFACTURE AND TESTING OF CLAY PRODUCTS 263 MATERIALS, MANUFACTURE AND TESTING OF CLAY PRODUCTS The Raw Materials 275. Classes of Raw Materials. — In addition to the various types of clay there are also many forms of shale which are used in the production of clay products. Clays are those substances resulting from the decay of rocks, which possess plasticity on being tempered with water and which are capable of retaining their shape when molded into various forms and dried. When such bodies are heated to redness or above they resemble rocks in hardness and strength. Shale is a hardened form of clay which has been consolidated by the weight of overlying earth, but which after being reduced to a powder exhibits the above-mentioned characteristics of clay. Residual clays are formed from the decay of the underlying rocks. They constitute important sources of high-grade clays for pottery. Those clays which have been removed from the parent rock by glacial action, by water or by wind are called transported clays. Such clays are often termed sedimentary since they have been carried as sediment by the current and deposited in places where the velocity of flow decreased. On account of the changes in conditions which surrounded the deposition of sedimentary clays, they generally consist of strata of material which often vary considerably in composition and properties. Frequently such clays have sandy laminations or are mixed with sand. Since the largest and most homogeneous deposits of sedimentary clay are those precipitated in large bodies of still water; the marine clays, deposited on former ocean bottoms, or lacustrine clays, found on the bottoms of extinct lakes or in swamps, form the most valuable sources of raw materials for the manufacture of structural clay products. The soft clays, either glacial or residual, which are found at or near the surface are often termed surface clays. Fire-clay is a term, loosely applied, to include those sedimentary or residual clays which vitrify at a very high tempera- ture and which, when so burned, possess great resistance to heat. Impure fire-clays are contaminated with certain fluxes such as lime, iron oxide or the alkaUes which reduce the vitrification temperature. In many of the coal-producing states fire-clays underlie the coal beds. 276. Composition of Clays. — In determining the suitability of clays for the manufacture of clay products a knowledge of both the mineral and chemical constitution is of assistance. From the mineral constitution the proportion of true clay substance may be gotten, whereas the chemical constitution affords indications of the purity, refractoriness, color, and shrinkage or swelling in burning. The minerals most commonly found in clays and shales are kaolinite (2Si02, AI2O3, 2H2O) and other hydrated silicates of alumina; quartz Fluxing Ingredients (generally less than 20 per cent) 264 STRUCTURAL CLAY PRODUCTS (Si02); feldspar (principally silicate of alumina combined with potash, or lime, or soda and lime); limonite (2Fe203,3H20) ; hematite (Fe203); siderite (FeCOs); pyrite (FeS2); calcite (CaCOs); magnesite (MgCOs); gypsum (CaS04,2H20), and sometimes rutile (Ti02). Of these minerals, kaoUnite and other hydrated silicates of alumina are the most desirable constituents. They generally form the major part of those high-grade clays, termed kaolins, which are used in the production of crockery and white burning pottery. These silicates constitute the finer portion of the clay which is called the clay substance. By Seger, clay substance is defined as the material less than 0.004 in. in diameter. Chemical analyses of good clays will show that they consist mainly of the following elements: Silica (SiOo) Alumina (AI2O3) Ferric Oxide (Fe203) Lime (CaO) Magnesia (MgO) Alkalies (K20+Na20) Water (H2O) Carbon Dioxide (CO2) Sulphur Trioxide (SO3 Silica generally forms from 40 to 80 per cent of the raw materials used in making structural clay products other than fire brick. In the latter the silica content may rise to 98 per cent. Although a large percentage of sand or uncombined silica in clay is undesirable, it is sometimes added to decrease shrinkage in burning and to increase the refractoriness of low alumina clays. The alumina content ordinarily ranges from 10 to 40 per cent except in silica brick. Wares having an exceedingly high alumina content are likely to be very refractory. Iron oxide, which in most cases constitutes less than 7 per cent of a clay, is a most important factor in determining the color of the clay and the burned product. It also tends to lower the fusion point of the clay, especially if present as ferrous oxide. Lime normally constitutes less than 10 per cent of clay, but in some glacial deposits, which are successfully used in making common brick and tiling, a higher lime content obtains. In carbonated form lime lowers the fusion point. Since the carbonate breaks up into carbon dioxide (CO2) and lime (CaO) at a temperature of 900° C; it is desirable, in clays burned at this temperature, to finely crush the lime pebbles. If this is done, danger from "popping " in the burnt ware, due to slaking of the lime, may be avoided. If the burning temperature is considerably higher than the MATERIALS, MANUFACTURE AND TESTING OF CLAY PRODUCTS 265 above, complex combinations of lime, silica, and alumina are formed with the result that the lime effects a change in the color of the product. Red- burning wares are often made buff-burning by increasing the lime content. Magnesia rarely exceeds 1 per cent in clay. In burning it causes the clay to soften at a slower rate than does lime and lessens warping. The alkalies, forming less than 10 per cent of the raw clay, are of great value as fluxes, especially when combined with silicates of alumina. Feld- spar is much used as a flux with kaolin in making white ware. A large proportion of free water generally causes clay to shrink con- siderably in drying ; combined water causes shrinkage in burning. Carbonaceous material in the form of bituminous matter or carbon greatly affects the color of the raw clay. Unless proper precaution is taken to effect complete removal of such matter by oxidation, the burned product is likely to have a black core. Sulphur is most commonly found in clay as the sulphate of calcium, magnesium, potassium, sodium or iron, or as iron sulphide. Generally the proportion is small. If, however, there is carbon in the clay and insuffi- cient time is given during biu-ning for proper oxidation of carbon and sulphur, the latter will cause a spongy swollen structure in the burned product. Most of the sulphates are soluble and give evidence of their presence by the formation of a scum on the dried ware. As a result, unless considerable care is exercised in burning, the product will be discolored by white blotches. The use of water containing small quantities of mag- nesium or calciimi carbonates, together with a sulphurous fuel often causes similar effects. Wall white, which appears after brick have been laid, may be due to soluble salts in the brick or in the mortar, which are brought to the surface by absorption of water and -subsequent drying. t 277. Physical Properties of Clays.^ — Plasticity, tensile strength, texture, shrinkage, porosity, fusibility, and color after burning are the physical properties which are of most importance in determining the value of a clay. A knowledge of these properties is of more benefit in judging the quality of the raw material than a chemical analysis. By plasticity is meant the property which wetted clay has of being permanently deformed without cracking. The amoimt of water required by different clays to produce the most plastic condition varies from 15 to 35 per cent. Although plasticity is probably the most important physical property of clay, yet there are no methods of measuring it which are entirely satisfactory.* The simplest and most used test is afforded by feeUng of the wetted clay with the fingers. Personal equation neces- sarily plays a large part in such determination. Since clay ware is subjected to considerable stress in molding, handling, * For a more complete discussion of the physical properties and their measure- ment, see Clays their Occurrence and Uses, by H. Ries, Ch. 3. 266 STRUCTURAL CLAY PRODUCTS and drying a high tensile strength is desirable. The test is made by deter- mining the strength of specimens which have been molded into briquette form * and very carefully dried. The tensile strength of clays will vary from almost nothing in highly silicious fire clays to over 400 lb. per square inch in some common brick clays. Kaolin generally shows low tensile strength. The texture of a clay is measured by the fineness of its grains. In rough work the per cent passing a No. 100 sieve is determined, but for measuring the size of the clay grains a more refined device such as the Schone washing apparatus or a centrifugal separator is used. No numer- ical limit to the grain size or desired relation between sizes has been estab- lished. Tests by Beyers and Williams t indicate that the sizes of grain from 0.004 in. down should be uniformly graded to obtain maximum ten- sile strength. Ries' tests showed that an excess of either very fine material or of sand grains decreased the tensile strength of the clay. Very fine- grained clays free from sand are more plastic and shrink more than those containing coarser material. A knowledge of the shrinkage both in drying and in burning is required in order to produce a product of required size. Also the amount of shrink- age forms an index of the degree of burning. The shrinkage in drying is dependent upon pore space within the clay and upon the amount of mixing water. The addition of sand or ground burnt clay lowers shrink- age, increases porosity and facilitates drying. Fire-shrinkage is dependent upon the proportion of volatile elements, upon texture and the way that clay burns. Tests of shrinkage are made by determining the volume of ben- zine displaced by a small prism of clay when green, after drying at a tem- perature slightly above the boiling point of water, and also after burning. Beyer and Williams, in tests on a number of Iowa clays, reported au- shrinkages varying from 4.86 per cent to 27.00 per cent and fire-shrink- ages from —2.88 per cent (swelling) to 5.92 per cent. By porosity of clay is meant the ratio of the volume of pore space to the dry volume. Since porosity affects the proportion of water required to make clay plastic, it will indirectly influence air-shrinkage. Large pores allow the water to evaporate more easily and consequently permit a higher rate of drying than do small pores. Inasmuch as the rate at which the clay may be safely dried is of great importance in manufacturiag clay products, the effect of porosity on the rate of drying should be considered. The temperature at which a clay fuses is determined by the proportion of fluxes, texture, homogeneity of the material, character of the flame, and its mineral constitution. Owing to non-uniformity in composition, parts of the clay body melt at different rates so that the softening period extends * See briquette molds and testing machines in Ch. XII. t Iowa Geol. Surv., Vol. 15, p. 102, 1904. MATERIALS, MANUFACTURE AND TESTING OF CLAY PRODUCTS 267 over a considerable range both of time and temperature. Wheeler divides the period into (1) incipient vitrification, at which the clay has softened sufficiently to cause adherence but not enough to close the pores or cause loss of shape — on coohng the material cannot be scratched by the knife; (2) complete vitrification, more or less well-marked by maximum shrinkage, coalescence of particles, smooth fracture and no loss in shape; (3) viscous vitrification, produced by a further increase in temperature which results in a soft molten mass, a gradual loss in shape, and a glassy fracture after coohng. Experiments roughly indicate that the higher the proportion of fluxes the lower the melting-point. Fine-textured clays fuse more easily than those of coarser texture and the same mineral composition. The uni- formity of the clay mass determines very largely the influence of various elements; the carbonate of lime in large lumps may cause popping when present in small percentages, but when finely ground 15 per cent of it may be allowed in making brick or tile. Lime combined with silicate of alu- mina (feldspar) forms a desirable flux. Iron in the ferrous form, found in carbonates and in magnetite, fuses more easily than when present as ferric iron. If the kiln atmosphere is insufficiently oxidizing in character during the early stages of burning, the removal of carbon and sulphur will be prevented until the mass has shrunk to such an extent as to prevent their expulsion and the oxidation of iron. When this happens a product with a discolored core or swollen body is likely to result. Since a determination of the fusibility of a clay is of much importance both in judging of the cost of burning it and in estimating its refractoriness, experiments are often made on small prisms to determine the rapidity with which the clay may be burned, the temperatures at which incipient, complete and viscous vitrification occur, how the clay behaves in annealing and the color of the burned product. Temperatures are commonly measured by means of Seger cones,* in refined work by a pyrometer. Method of Manufacture 278. Preparation of the Clay. — Many of the large deposits of clay or soft shale are worked in open cut with a steam shovel. The hard shales adjacent to coal veins are frequently mined. Generally the raw material is drawn from the pit in cars on a narrow-gage track by horses or by dinky engines. For pressed brick and terra-cotta it is sometimes advantageous to weather the clay, before using it. This is accomplished by loosely spreading the clay in a layer a couple of feet thick over a flat surface where * Seger cones are made from mixtures of clay and fluxes so proportioned that their melting-points form a temperature scale. Two or more cones differing in fusibility are inserted in the furnace or kiln and the temperature estimated from their appear- 268 STRUCTURAL CLAY PRODUCTS it will be exposed to the action of the elements. Such action causes a rusting of iron particles and a breaking down of pyrite inclusions. Most clays, however, are hauled directly to a crushing or disintegrating device. For the hard shales jaw-crushers are sometimes used. Dry pans like the one shown in Fig. 1 are often employed to break up the softer Fig. 1.— A"9-ft. Dry Pan. Fig, 2.— a Double-shaft Pug MUl. * shales and tough clays. For certain dry shales, toothed or corrugated rolls are effective where coarse grinding only is required. After the clay has been crushed it is conveyed to a pug-mill (Fig. 2) in which it is tempered with the proper amount of water and thoroughly mixed. Wet clays are generally ground and tempered simultaneously in large ring pits, in pug- mills Or in wet pans. In the ring pits a heavy iron wheel which rolls over the bottom surface of the pit in a spiral path, serves to stir and grind the MATERIALS, MANUFACTURE AND TESTING OF CLAY PRODUCTS 269 clay. This method is used only at small plants. The wet pan is much hke the dry pan, with the exception that the bottom of the wet pan is not per- forated. 279. Molding. — Building brick are molded by the soft-mud, the stiff- mud, or the dry-press process. 'The -stiff-mud process is employed in making nearly all other structural clay products. Fire-brick is sometimes made by the soft-mud process and roofing, floor, and wall tile by the dry-press process. In the soft-mud process the clay, or mixture of clayey materials, is tempered with enough water to form a mass of soft consistency. The mixture is then introduced into wooden molds which are lined with sand to avoid sticking. Either hand or machine molding is employed in this process. Soft-mud brick exhibit five sides to which more or less sand adheres. The soft-mud process can be used with a greater variety of clays Fig. 3.— a Small Auger Equipped with Device for Making Side-cut Brick. than any other method of molding and very uniform brick may be made with it. Less water is used in the stiff-mud process so that the mixture is much more rigid than in the soft-mud process. It is well applied to mixtures which are of medium plasticity. The clay from the pug-mill is forced through a tapered die by means of an auger and the issuing bar is cut into the required lengths. Owing to the motion imparted by the auger and friction on the sides of the die, various portions of the clay bar are given different velocities; consequently more or less laminations are present in the product of auger machines. Brick are made either end or side cut by this machine. Fig. 3 shows a side-cut machine. Auger brick machines have considerably greater capacities than the machines of the vertical press type used in the soft-mud or dry-press processes. For molding common brick, machines equipped with double or triple dies are sometimes used. Partition tile, conduits, fireproofing and the smaller sizes of drain tile are molded in a similar manner to stiff-mud brick. For 270 STRUCTURAL CLAY PRODUCTS sewer pipe and the larger sizes of drain tile, vertical presses are employed. The uniformity in shape and size of stiff-mud or soft-mud brick can be greatly increased by repressing. Repressing increases the density, makes the surfaces smoother and harder, and in some instances, has improved the strength of brick. This auxiliary process is often employed in making high-grade face brick and in molding paving brick. In the dry-press process the proportion of water is small enough to permit pulverizing the clay. The powdered mix is screened through a No. 16 sieve and then fed into molds on a vertical press. The molds are made of hard steel and steam-heated to prevent adherence of the clay. Vents are provided to allow the escape of entrapped air. Owing to the heavy pressures used, it is possible to obtain pieces with sharp corners and of much more uniform shape than can be gotten from auger machines. This process also does away with air drying although considerable free water must be driven off in the kiln. Face brick are commonly made by this process. Terra-cotta is generally hand-molded or is cast into molds made of plaster of Paris. 280. Drying. — Great care is required to dry soft mud and stifif-mud products at maximum rate without causing checking. In the old method of drying, still employed at many brick yards, the ware is dried by the sun. Many plants provide permanent sheds with roofs which can be opened or closed. At some yards open-air driers are provided with artificial means for heating during bad weather. Artificial driers are of two types, the hot-floor drier and the tunnel drier. The former is the older and is used for fire-brick, clay pipe and terra-cotta. The hot-floor drier is heated either by a furnace placed at one end of the drier or by exhaust steam from the engine used to furnish power. Tunnel driers are periodic — filled, dried, and emptied in rotation — or continuous — the green ware being loaded into one end of the tunnel and the dried product removed at the other. Tunnel driers are heated by flues underneath, by steam pipes, or by hot air from cooling kilns. They are more economical than hot-flour driers. In artificial driers the temperature rarely exceeds 120° C. The time required in drying varies from one to three daj-s, de- pending upon the temperature of the drier, the character of the clay, and the shape of the body. In some brick plants the green ware is set in a kiln and dried by waste heat from cooling kilns. This method requires more kilns, but effects a saving in handling of brick. 281. Kilns. — In the brick industry four types of kiln are in use: the scove kiln, the up-draft kiln, the down-draft kiln, and the continuous kiln. Of these types the down-draft and continuous kiln are used in burning other clay products. Terra-cotta is generally burned in round down- MATERIALS, MANUFACTURE AND TESTING OF CLAY PRODUCTS 271 Fig. 4a.— Setting a Scove Kiln. Temporary End and Side Walls Not in Place. {Bull. No. 1-5, Wis. Geol. and Nat. Hist. Surv., PI. 6.) Fig. 46. — Circular Down-draft Kiln Used for Burning Brick. (BuU. No. 15, Wis- Geol. and Nat. Hist. Surv., PI. 6.) TTrr! Ar — TTniirh Oontinuous Kiln f American Clay Machinery Co.) Kilns. 272 STRUCTURAL CLAY PRODUCTS draft kilns provided with muffles to prevent contact of the fiame with the ware. The scove kiln shown in Fig. 4a is much used in burning common brick. Brick are laid about 40 courses high and the entire kiln enclosed with a course or two of special brick containing a small proportion of coal. The outside is then plastered with mortar and fires started in the arches. Wood or oil is used as fuel. The temperature of the outer and inner portions of the kiln is equalized to some extent by the combustion of the coal-brick. Although the cost of the scove kiln is low, the loss in brick and in heat is high. Up-draft kilns provided with permanent walls and roof are an improve- ment over the scove kiln, but they are more wasteful of heat and are heated less uniformly than the down-draft kiln. The down-draft kiln (Fig. 4&) is either rectangular or circular in plan, the former being used largely in burning the better grades of building brick and in burning paving brick. As the name implies, the heat from fire after passing through up-takes to the top of the furnace is drawn downward through the kiln and passes through flues in the floor. Thence the waste gases are led through tunnels either to a stack passing up through the center of the kiln, or to a detached stack serving several kilns. With the down-draft kiln a more uniform distribution and better regulation of heat can be obtained than with either of the previously described kilns. Since the hardest burned ware, which becomes the softest in burning, is found at the top of the kiln, it cannot be misshapen by the weight of overlying courses. Continuous kilns (Fig. 4c), are often built oval in plan and divided by vertical walls into a large number of compartments. These are loaded from the interior of the ring and unloaded from the outside. Each com- partment is provided with an adjoined fire-box, a flue leading to a central stack and by-passes in the side walls through which the compartment can be connected with the adjacent compartments. Pockets are also pro- vided in the top of each chamber for additional fires. Consider a chamber which has been loaded with ware having an unloaded com- partment at the left. The chamber is first isolated from adjoining compartments and fired, until the most of the combined water is driven out of the ware, by heat from the side fire-box or wicket. After this stage has been passed, waste heat from the compartment on the right is admitted until a red heat is attained; then the top pockets are fired by means of slack coal. By this method, chamber No. 1 will be completeh' burned while in No. 8 or 9 setting will be in progress and the intermediate cham- bers are in various stages of burning. The greatest advantage of this type of kiln is the efficient utilization of fuel. It is used to burn brick, fire- proofing and tile. MATERIALS, MANUFACTURE AND TESTING OF CLAY PRODUCTS 273 282. Burning. — The burning of clays may be divided into three main stages: (1) dehydration or "water smoking," (2) oxidation, (3) vitrification, or period of settlement in the kiln. During the dehydration period the water which has been retained in the pores of the clay after drying is driven off, some of the carbonaceous matter is burned, a portion of the sulphur is distilled from pyrites, hydrous minerals like kaolinite and ferric hydroxide are dehydrated, and the carbonate minerals are more or less decarbonated.* The speed with which these eliminations occur is dependent upon the water and mineral content of the clay, its porosity, and its texture, and upon the method of handling the kiln. Too rapid heating causes cracking or bursting of the ware. On the other hand, if alkali is contained in the clay or much sulphur is present in the coal, too slow heating produces a scum on the surface of the product. During the " water-smoking " stage, frequent measurements of the draft and temperature are made in order to stand- ardize the procedure for a given clay. This period is generally com- pleted before a temperature of 700° C. is reached. During the oxidation period, which is nearly always completed at 900° C, the remainder of the carbon must be eliminated and, to promote stability,, the ferrous iron must be oxidized to the ferric form. Although some of these changes begin before the completion of the preceding change, it has been pretty well demonstrated that the removal of sulphur cannot be completed before the carbon has been eliminated. Sulphur, on account of its affinity for oxygen, also holds back the oxidation of iron. Conse- quently, in order to avoid black or spongy cores, oxidation must proceed at such rate as will allow these changes to occur before the heat becomes sufficient to soften the clay and close its pores. Grog or sand is often added to the raw clay to produce a more open structure and thus provide for the escape of gases generated in burning. The different stages in vitrification have already been mentioned. It should be borne in mind that but few clay products are vitrified to the point of viscosity, indeed, many common brick and tile cannot be called vitrified in any sense of the term. On the other hand paving brick must be burned to the stage which Wheeler calls complete vitrification if the maximum combination of hardness and toughness is to result. There is, consequently, a wide range in the maximum burning temperature to which the clay must be submitted depending upon the character of the raw material and the purpose of the ware. In the manufacture of tile and building brick this range varies between 900 and 1200° C. The degree of burning is frequently determined by the settlement of the goods in the kiln, in some cases by pyrometers. For ware which is to be completely vitrified, it is advantageous to have the points of * Prof. E. Orton, Jr. Trans. Am. Ceramic Soc, Vol. 5, p. 393. 274 STRUCTURAL CLAY PRODUCTS incipient and viscous vitrification separated as widely as possible. This is desirable in order that goods from different parts of the kiln may not vary widely owing to non-uniform distribution of heat. 283. Glazing. — By glazing clay products, it is possible to give a pleasing appearance to the ware, to increase its imperviousness to water, or to accomplish both of these ends without incurring the cost of com- plete vitrification. Slip-clays, which have a high fluxing content and which may be so adjusted in composition that different coloring effects can be produced, lead compounds, barium compounds, and common salt are among the substances used for glazes. Decorative terra-eotta goods are sprayed with a thin mixture of slip-clay before burning. Sewer pipe is salt-glazed by the addition of common salt to the fires during the vitrifi- cation stage. Enamel brick are given a coating of slip containing oxide of tin or similar compound to render the glaze opaque. 284. Flashing. — Colors ranging from gold to dark reddish brown may be produced on many kinds of ware by flashing. The process con- sists in exposing the ware to a reducing atmosphere during a part or whole of the burning period. Front brick are often so treated with pleasing results. Flashing, however, is likely to deceive even experts concerning the degree of burning. 285. Annealing. — Great care is necessary in cooling the goods beloT\- a cherry-red heat in order to avoid checking and cracking. Hastening the annealing process may destroy the product of an otherwise successful burn. To make paving brick of maximum toughness requires an annealing period of seven to ten days. 286. Sorting. — In up-draft kilns the over-burned ware is found at the bottom near the top of the arches and the under-burned material is at the top. The converse is true for down-draft kilns. In either kiln, the best of the product is found in the intermediate com-ses. In the man- ufacture of paving brick, high-grade building brick, and drain tile, these different classes of goods are separated in unloading the kiln and the poorer grades of material sold for different pm-poses. Over-burned paving-brick and building brick are used in sewer construction. Soft- burned paving brick are used for exterior walls in building construction, while the soft-burned building brick serve as filling. Methods op Testing Structural Clay Products 287. Tests. — Two classes of tests are used in judging of the quality of clay products: {A) tests which may be readily made on the job; {B) those which require laboratory equipment. The field tests are: (1) appearance, (2) hammer test, (3) hardness, (4) absorption, (5) specific gravity. In the laboratory, the following additional tests are sometimes made: (6) crush- MATERIALS, MANUFACTURE AND TESTING OF CLAY PRODUCTS 275 ing, (7) transverse bending, (8) rattler test* (paving brick), (9) abrasion (paving brick), (10) resistance to alternate freezing and thawing. f 288. Appearance. — Shape, color, kiln marks, checks, laminations and blisters all form more or less valuable indications of quality. The color of the outside of the goods is often misleading in regard to the degree of burning. This also applies to the color of the interior, unless one is familiar with the changes which the given clay undergoes in burning. The presence of lime pebbles over J in. in diameter is undesirable. Black or spongy cores show improper burning as previously mentioned. In brick, well-defined kiln-marks indicate that the brick have been hard burned, but do not serve to distinguish between hard-burned and over-burned brick. Checks and cracks may be due to improper drying or annealing. They decrease the strength and resistance to frost; if well-marked they are sufficient cause for rejection. Checks produced in annealing generally indicate brittleness. Pronounced laminations in the cross-section of the ware are objectionable since they weaken the structure and lessen resist- ance to freezing. Broken blisters on the surfaces of sewer pipe or drain tile are due to air imprisoned in molding. They should not be tolerated on the inner surface. When present on the outer surface they should not exceed i of the thickness of the tile in depth, nor in diameter should they exceed J of the diameter of the pipe. 289. The Hammer Test. When properly burned and free from cracks, dry clay products emit a highly metallic ring if struck with a hammer. A rough notion of the toughness of brick is also afforded by breaking specimens with the hammer. 290. Hardness. — To secure evidence of the degree of burning, the interior of the clay body may be scratched with a knife. Sewer pipe and paving brick which have been burned to incipient vitrification or above cannot be scratched. Well-burned tile will be scratched with difficulty. 291. Absorptioii. — The per cent absorption is a very valuable indi- cation of the degree of burning provided one knows the limit of the given clay corresponding to a properly burned product. According to Orton f vitrification, in the true sense, corresponds to such a degree of compact- ness that the absorption of the product is not over 3 per cent after forty- eight hours' immersion. He also stated that if the absorption was less than 5 per cent danger from frost was negligible. The experiments of Jones § appear to indicate that the rate of absorption is of value in deter- mining resistance to freezing, but the data have not been corroborated by other experiments. It is quite likely that the ratio of the pore space filled * See Appendix A. t Also See Arts. 264 and 296. t Proc. A.S.T.M., Vol. 15, p. 263. § Trans. Am. Ceramics Society, Vol. 9, p. 572. 276 STRUCTURAL CLAY PRODUCTS in the absorption test and the rate of fiUing are properties deserving of careful consideration in determining resistance to freezing (see Art. 264). Experiments by Douty and Gibson * show that a rather high per centage of absorption is favorable to the development of a good bond between cement, mortar and brick. No standardized method of making the absorption test has been specified for all kinds of clay products. Brick and partition tile are gen- erally tested whole, but square fragments weighing a couple of poxmds each are often selected to represent drain tile in absorption tests. What- ever method of testing is employed the specimens are first dried to con- stant weight at a temperature just above the boiling-point of watfer. Weighing should be done on scales sensitive to one-tenth of one per cent of. the weight of the specimen. One of three methods of procedure may now be adopted. (1) The specimen is immersed in water at approxi- mately 21° C. (70° F.) for forty-eight hours. It is then freed of surface water by wiping with a trowel and again weighted. The difference in weight between the soaked and the dry specimen divided by the dry specimen and multiplied by 100 gives the per cent absorption. This method is very commonly used. (2) The dried test-piece is immersed in water at 21 ° C. which is raised to the boihng-point in a half hour, is allowed to boil for five hours, is then cooled to 21° C, surface dried and weighed as before. (3) The dried specimen is subjected to a vacuiun and water admitted without changing the pressure. After immersion for twenty- four hours it is surface dried and weighed. This method is cumbersome and seldom used. Of these methods the first is the most used and appears to be the most valuable for determining absorption imder atmospheric conditions. It does not, however, furnish as satisfactory a determination of porosity as either of the other methods. \ 292. Specific Gravity. — Roughly, the higher the specific gravity, the greater is the strength of clay products. This rule is modified, of course, by conditions in burning and by the degree of burning. Tests by Purdy and Moore f show that the specific gravity of a given clay decreases as the vitrification period advances. The specific gravity is generally found by the following formula: a -n ., Dry weight Specific gravity =- Dry weight— Weight in water when saturated 293. Strength Tests. — The methods of making the crushing and trans- verse tests of brick and building tile are the same as outlined in Art. 112 to 121. The crushing test is generally made on half brick bedded flatwise, *Proc. A.S.T.M., Vol. 8, p. 529. t Trans. Am. Ceramics Soc, Vol. 9, p. 203. MATERIALS, MANUFACTURE AND TESTING OF CLAY PRODUCTS 277 but this method is not satisfactory both on account of the uncertainty in determining the final load and on account of the lack of opportunity for shear failure. These considerations have led some experimenters to bed the brick on the edges. The strength of brick on edge is generally 15 to 20 per cent less than the strength of specimens bedded flatwise. The crushing test affords a means of comparing the quality of brick or tile but is of no value in determining the strength of a wall, since the latter depends primarily on the strength of the mortar. As a criterion of struc- tural strength for brick, the transverse test is of more value than the crush- ing test, since transverse failure in a wall or pavement is likely to occur on account of improper bedment. Brick which are improperly annealed or checked in air-drying exhibit a lower transverse strength than properly J^Sad. At least (a) Sand Bearings. DETAIL OF PLATEN (6) Hydraulic Bearinga. DETAIL OF LOWER BEARING (c) Three-point Bearinga. Fig. 5. — Methods of Supporting Drain Tile for Strength Tests. treated specimens. Moreover, the transverse test can be made in a small machine without the expense of a bedment. Drain tile and sewer pipe are often tested under gradually applied loads placed as indicated in Fig. 5. The tile should be thoroughly wet when tested and not less than five specimens should be tested. The supporting strength (W) is defined as the load per lineal foot which the tile can carry when loaded through sand bearings. Under this condition the moment, M= — , where R is the radius of the center line of the tile in inches. To determine supporting strength from a three-point bearing test, multiply the breaking load per foot by 1.50; if hydraulic bearings are used multi- ply by 1.25. The three-point bearing method is simpler in application, but it is more severe on warped pipe than either hydraulic or sand bear- 278 STRUCTURAL CLAY PRODUCTS ing. Sand bearings also approximate quite closely the loading conditions to which the pipe is subjected in a ditch.* 294. The Rattler Tests on Paving Brick.— Although the rattler test has never been shown to be a true index of the life of brick in a pavement, yet as a means of standardizing resistance of paving brick to combined impact and abrasion it is considered valuable. The standard specification adopted by the American Society for Testing Materials is given in Appen- dix A. 295. The Detroit Pavement Determinator. — Recently considerable interest has been aroused in tests on sample pavements by means of a pavement determinator. The apparatus consists of a central vertical shaft which serves as an axis of rotation for a horizontal shaft. At each end of the horizontal shaft is mounted a heavy broad-faced wheel weighing 1650 lb. Each wheel is shod with five plungers which terminate in calks sim- ilar to those on a horse's shoe. The plungers are actuated by a cam gear and spring mechanism so that a heavy blow can be delivered to the pave- ment through the calks. The horizontal shaft is so driven that the wheels describe spiral paths over a ring 10 ft. 10 in. outside diameter by 8 ft. 7 in. inside diameter. The area is completely traversed in 330 revolutions. Wear is determined by measuring the depth to which the surface of the pavement is abraded. Although a number of tests with this determinator have been run by the engineering department of the City of Detroit on different classes of pavements,! the results thus far published have not been sufficient to establish the value of the test. Tests of this character which will deter- mine in a short space of time the wearing resistance of a pavement are desirable. On the other hand, owing to personal equation involved "in laying the pavement, cost of the apparatus, and difficulties of standardiza- tion, it is doubtful if sijch a test will be widely used. 296. Alternate Freezing and Thawing Test. — Committee C-6 of the A.S.T.M. has prescribed an alternate freezing and thawing test J for drain tile which may be applied to other clay products. The test is made on three or more specimens from each of five separate tiles. The specimens are so chosen that they represent the ends and center of each tile. They must be sound, approximately square, and between 12 and 20 sq. in. in area. After being dried to constant weight at 110° C, or above, the spe- cimens are cooled to 20° or 25° C, reweighed and immersed in pure water. The water is raised to the boiling-point and boiled for five houi-s, after which it is cooled to 10° or 15° C. The specimens are again weighed and * For more oompletp information see Standard Specifications for Drain Tile, Serial Designation: C4-16, A.S.T.M. Standards, 1916. t Engr. Record, Vol. 68, p. 457. t See Std. Spec, for Drain Tile; Serial Designation C4-16. PROPERTIES OF STRUCTURAL CLAY PRODUCTS 279 placed with their concave faces upward in trays of ice water. After the specimens have acquired the temperature of the water, the latter should be drawn off until | in. remains in each tray. The trays are placed in a suitable rack and immersed in a freezer. The freezer temperature must be reduced to — 10° C. or below within thirty minutes after the specimens are introduced, but should not fall below —20° C. during the test. After the water in the trays has been frozen solid, the trays are taken out of the freezer and immersed for thirty minutes in hot water at 85° to 100° C. The specimens are then rapidly cooled to 10° or 15° C. and their condi- tion recorded. The specifications demand ten alternate freezings and thaw- ings for Farm Drain Tile, 15 for Standard Drain Tile, and 20 for Extra Quahty Drain Tile. Failure in this test is conditioned by (1) superficial disintegration or spalling with a loss of more than 5 per cent of the dry weight, or by (2) cracking badly in other than planes of laminations, or by (3) serious loss in structural strength. PROPERTIES OF STRUCTURAL CLAY PRODUCTS Building Brick 297. Manufacture. — ^A variety of clays are used in making building brick ranging from the common surface clays used for common brick to the better grades of shale or impure fire-clays used in producing face brick. The essential properties of the clay are sufficient plasticity for proper molding, low shrinkage in drying and burning, and low fusibility. The clay should not crack or warp during the drying or burning processes and for face brick or ornamental brick it should burn to a uniform color. Common brick are frequently burned in scove kilns, but the better grades of building brick are fired in permanent kilns of the up-draft or down-draft type. The temperature of burning varies from 900 to 1200° C, depending upon the composition of the clay. 298. Classes of Building Brick. — In accordance with the method of molding, brick are often classified as soft-mud, stiff-mud, dry-pressed or repressed brick. By the degree of burning, brick are sometimes sorted into three classes (1) pale or salmon brick which are underburned, (2) body brick which occupy the central portion of the kiln and are well-burned, (3) arch or clinker brick which are overburned. Two irregular forms of brick commonly used in construction are com- pass brick and feather-edge brick. Compass brick have one edge shorter than the other while feather-edge brick have one edge narrower than the other. From the standpoint of usage the following classification may be made: Common brick, front brick and ornamental brick. Common brick com- 280 STRUCTURAL CLAY PRODUCTS prise the poorer grades of building brick which are used for filling, backing, and in walls where appearance is of small moment. They often vary greatly in color, degree of burning and in shape. Front or face brick are made more carefully than common brick. They are generally pressed or repressed and are used in fronts of buildings and in walls for which a pleasing appearance is desired. Red, white, cream, buff-burning brick, and buff-burning brick speckled by the addition of manganese, all of which burn to an even tone, are much used as front brick. Tapestry brick, rug brick and stipple-faced brick are stiff-mud products which have had their edges roughened in different ways in order to create pleasing effects in wall constructions. Ornamental brick include enameled and glazed brick. The former constitutes the major portion of the ornamental brick produced in the United States. 299. Requirements of Good Brick. — The essential requirements for building brick are sufi&cient strength to carry the loads imposed in a struc- ture, durability, and a pleasing appearance when exposed to view. Com- mon brick of good quahty should be free from checks or cracks, should emit a metallic ring when struck with the hammer and should exhibit a fine-grained, uniform, dense structure free from laminations or lime peb- bles. Well-burned face brick should not be easily scratched by the knife. They should possess the previously mentioned characteristics, and also be uniform both in color and size. Regularity in size is of especial importance for brick which are to be used in highly stressed walls, since tests have shown that the strength of such masonry is reduced if the brick vary in size. Good brick should be free from soluble salts such as the sulphates of lime, magnesia and the alkalies, since these compounds are likely to produce eflSiorescence. When uniformly loaded in compression an individual brick is, in gen- eral, sufficiently strong to withstand its proportionate part of any wall or pier load. However, owing to irregularities in the distribution of stress through the wall, the supporting capacity of a single brick may be as small as the transverse center load which it can carry when supported at the ends. Consequently it has been customary, whenever a strength test is specified for individual brick, to demand both crushing and transverse tests. In a structure the durability of brick may be tested by frost 'action, by alternate wetting and drying, and by fire. Tests of fire resistance are generally made on wall-panels. Resistance to frost action is best ascer- tained from alternate freezing and thawing tests, which ai'e, however, quite expensive. The absorption test has long been considered a measure of durability, although the basis for this assumption is questionable. In this connection it should be noted that resistance to freezing is dependent not only upon the porosity of the brick but also upon the size of the pores, PROPERTIES OF STRUCTURAL CLAY PRODUCTS 281 the size of the connecting canals, the strength, and the elasticity of the brick. If the pore space is not entirely filled with water, the common condition, the imprisoned air acts as a cushion and lessens the expansive effect of the freezing water. Thus far, no standards of strength or dura- biUty have been adopted for brick. 300. Tests on Building Brick.— In 1913 Committee C-3 of the Amer- ican Society for Testing Materials proposed the following classification for building brick; Class A (Vitrified) Class B (Hard burned) . Class C (Common firsts) Class D (Common) Average Compreaaive Strength (Flatwise) on Five Samples, lb. per sq. in. 5000 and over 3500 to 4999 2000 to 3499 1500 to 1999 Average Absorption on Five Samples, per cent < 5 <12 <18 Through the aid of a number of laboratories the committee carried out an extensive series of tests part of which are reported in Table 1. Each result is the average of five tests. The compression tests were made on half brick bedded flatwise in plaster of Paris. Transverse specimens were placed flatwise on rocker bearings 6 in. apart and loaded at the center. 3 PI The modulus of rupture (S) was calculated from the formula 8 = ^ rizt where P = center load, Z = span, 6 = breadth, and (i = depth. These tests are very valuable since they afford a notion of the quahties of brick procurable in different parts of the country as well as the range in mechanical properties. From a consideration of the results in the table it appears that minimum moduU of rupture corresponding to classes A, B, C and D, 300, 400, 600 and 900 lb. per square inch, respectively. Results of tests made at the Watertown arsenal indicate that the shearing strength of brick varies from 7 to 30 per cent of the compressive strength. At the University of Wisconsin paving brick tested in single shear with an apparatus similar to the Johnson shear tool (Art. 56) gave an average shearing strength equal to 17 per cent of the average com- pressive strength.* The range in results and the low values obtained in the latter tests indicate that bending must have exerted a considerable influence in both of the above series of tests. * Thesis by W. T. Bolton and W. A. Goss, 1915. 282 STRUCTURAL CLAY PRODUCTS TABLE 1.— RESULTS OF TESTS ON BUILDING BRICK REPORTED BY UNIVERSITY LABORATORIES (Each Value is the Average of 5 Determinations.) Name of Laboratory and Person in Charge of Tests. Place of Manufacture. Corn- Modulus Strength, Rupture, per Lb. per Lb. per Sq.In. Sq.In. 14,964 1926 4.81 9,609 1368 6.50 4,482 733 5.57 8,694 1593 5.12 9,393 1874 1.72 4,653 693 11.99 11,200 1857 4.45 13,507 2308 2.86 8,636 1031 7.56 3,845 468 13.28 3,062 445 13.33 2,442 434 13.82 2,933 791 13.93 3,294 908 14.84 2,740 754 17.44 1,951 501 18.36 2,282 187 23.. 50 3,374 522 18.28 2,771 582 17.86 2,904 251 22.00 7,788 1007 14.18 13,034 848 11.88 2,864 587 24.74 1,687 626 21.26 2,414 628 19.68 2,869 1064 16.60 2,017 580 24.42 2,584 462 25.24 3,054 1094 20.36 3,470 1618 14.74 6,450 1116 14.84 10,145 1303 7.38 14,982 2268 1.51 2,474a 426 19.48 3,9966 805 14.80 5,964c 1238 13.60 9,240d 1926 8.70 7,355 1158 14.39 6,919 1459 10.20 13,740 2891 0.57 2,795 347 21.80 2,502 337 21.80 3,804 499 19.20 9,926 1151 14.00 14,766 1383 11.60 3,110 716 4,134 585 17.95 6,072 478 14.00 9,076 1241 10.55 9,533 1559 8.44 12,013 1085 2.76 3,304 670 16.18 6,302' 721 12.04 7,873 1171 8.74 7,293 814 4.42 4,847 1009 14.59 7,998 1203 11.46 8,200 1283 10.90 9,295 1456 8.06 Remarks Concerning Bbick. Kind. Class, University of Alabama: E. B. Kay University of California: C. Derleth and A. C. Alvarez University of Illinois: A. N. Talbot { and D. A Abrams Purdue Uni- versity: H.H.Scofield University of Maine: C. B. Brown Birmingham, Ala Columbus, Miss . . Lovick, Ala Birmingham, Ata. Fresno, Cal San Francisco, Cal Belleville, III Chicago, 111 Danville, III'. " ." .' .' .* Urbana, 111 New Albany, Ind. . Michigan City, Ind. Crawfordsville, Ind. Lafayette, Ind (?) . Saco, Maine Brewer, Maine. Clay brick . Shale Paving brick. , Not stated Clay brick . Clay brick, stiff mud. ' ' reburned Clay brick, soft mud . stiff mud. Sand-lime brick Shale brick, stiff mud Clay brick, soft mud (?) Clay brick, stiff mud soft mud mud a Tested endwise, 1400 lb. per sq.in, h Tested eodwiae, r926 lb. per sq.in. c Tested endwise, 3137 lb. per sq.in. d Tested endwise, 4280 lb. per sq.in. PROPERTIES OF STRUCTURAL CLAY PRODUCTS 283 TABLE 1.— {Continued.) Name of Laboratory and Person in Charge of Tests. Place of Manufacture. Com- pressive Modulus of Absorp- tion, Strength, Rupture, Lb. per Lb. per cent. Sq.In. Sq.In. 6,264 1440 10.28 5,984 1325 12.70 4,564 1298 17.40 5,094 1028 17.34 3,293 517 21,54 3,881 256 21.20 3,567 255 27.50 4,149 316 24.00 5,404 980 22.10 4,454 577 20.20 3,928 285 22.10 4,341 667 17.80 2,364 323 26.80 7,081 2066 6.67 3,399 1229 10.18 5,468 1190 17.35 3,711 310 20.19 10,981 3354 4.35 6,602 1160 10.83 6,873 1183 8.31 6,720 2119 7.60 1,564 281 17.90 3,718 452 15.00 3,580 659 14.88 5,302 851 10.66 3,147 773 15.76 3,092 812 15.50 4,166 627 13.30 4,474 845 12.21 5,458 1342 10.80 4,780 937 8.36 5,448 1420 6.93 6,024 1522 4.58 2,950 416 14.60 2,278 2,398 1,846 2,145 4,542 438 13.90 4,334 592 12.30 12,780 2329 2.06 9,266 2166 6.04 7,556 1438 6.12 6,122 1124 8.95 7,742 2058 6.84 9,288 1275 10.17 4,758 1609 8.26 5,718 1769 7.15 9,728 2705 5.37 9,052 2226 4.61 4,156 564 17.90 6,250 723 14.53 7,458 918 12 84 7,480 1105 9.01 Remarks Concerning Brick. Kind. Class Iowa State College: R. W. Crura Tulane Tlni- varsity: W. B. Gregory i and W B. Koch Massachu- setts Insti- tute of Technology : C. M. Spof- ford University of Michigan: F. N. Mene- fee University of Pittsburgh: J. H. Smith University of Pennsylva- nia: H. C. Berry University of Washington : A. H. Fuller Mason City, Iowa. Plaquemine, La New Orleans, La Covington, La Pearl River, La. . Fernwood, Miss Slidell, La Norfield, La Tangipahoa, La Baton Rouge, La. . . . Sibleyville, Ala Brookhaven, Miss. . . Slidell, La Novick, Ala Sibleyville, Ala W. Barnstable, Mass. Ganio, N. H... . Worcester, Mass Detroit, Mich . . Watertown, Pa. . Kittanning, Pa . Darlington, Pa. Beaver Falls, Pa Bradford, Pa ... , Pittsburgh, Pa . . Scranton, Pa. . . Spokane, Wash. . Clay bk. stiff mud, side cut Stiff mud, clay brick Soft " Stiff Soft Dry press clay brick hard " " soft Dry pressed Stiff mud Dry pressed. , Clay brick, soft mud . stiff mud . soft mud . ' ' stiff mud . Sand-lime brick Clay brick, stiff mud . " soft mud. Sand-lime brick. Clay brick, stiff mud. Clay brick. Clay brick, salmons . . . •. ' ' medium reds ' ' dark reds . . . ' ' hard burned. A A B A C B B B A B B B C A C A B A A A A D B B A C C B B A B A A C C c D C B B A A A A A A B A A A B A A A Fig. 6 shows stress-deformation curves for three grades of brick tested on end. The softer varieties of brick exhibit stress deformation curves of sharper curvature. The modulus of elasticity of such brick generally lies between 1,500,000 and 2,000,000 lb. per square inch. 301. Specific Gravity of Brick. — The specific gravity of brick ranges from 1.9 to 2.6 depending upon the character of the raw materials and the 284 STRUCTURAL CLAY PRODUCTS degree of burning. Brick made from impure fire-clays generally have a lower specific gravity than those made from shales. Some tests appear to indicate that the specific gravity decreases as the vitrification period progresses. 302. Crushing Tests on Brick Piers. — The main conditions governing the strength of brick piers under concentric loading are: (1) the strength of brick, (2) the strength and elasticitj of mortar, (3) quality of workman- ship in laying, (4) method of laying, (5) regularity in form of brick. The stiffness of piers is dependent largely upon the modulus of elasticity of n1^ ■! 1 V^ 1 N ^ V, v^x N^^ V^\ v;-^ ^"x ^ \ > "''-. ^^~. ^ .,^x •V. V \ "k "^^^ T V ^v \ N \ ^ 'n •J ^ Ss.'V 1 1 ■^^ \ "s'W 1 1 *sj^ ^11 .001 .002 .003 .001 Proportionate Def ormatiou Fig. 6. Fig. 7. Fig. 6. — Elastic Properties of Common Brick Used in Pier Tests. The average crushing strength of these three grades of brick, crushed endwise, was 14,000, 10,500, and 7500 lb. per square inch, respectively. {Tests of Metals, 1885, \i. 1138.) Fig. 7.— Showing Method of Failure of Brick Piers. {Tests of Metals, 1883.) the mortar, the quality of workmanship in laying, and upon the modulus of elasticity of the brick. Tests at the Bureau of Standards Laboratory, at Pittsburgh, on large piers made of Class A (vitrified). Class B (hard burned), and Class C (common firsts)* show very clearly the superiority of the piers made of * See classification in Art. 300. PROPERTIES OF STRUCTURAL CLAY PRODUCTS 285 the stronger brick (see Table 2 *). The same result is also apparent in the tests by Talbot f summarized in Table 3. Fig. 7 shows the typical method of failure of brick columns. Transverse failure of the individual brick commonly begins when 40 to 60 per cent of the maximum load has been applied. The pier then gradually separates into a number of slender col- umns and failure finally ensues. TABLE 2.— THE COMPRESSIVE STRENGTH OF LARGE BRICK PIERS [Tests made at the Pittsburg Laboratory of U. S. Bureau of Standards.] Piers were approximately 30X30 in. X 10 ft. with joints -fg in. thick. Classification of Brick in Column According to Characteristics of Mortar. Age in Mo. Arrangement of Courses of Brick. Ultimate Lab. No. Strength in A.S.T.M. Committee of 1909 Trade Name. Kind of Cement. Mix Ct. :Sd. a -.b ic* Lb./In.2 B 6 c Common Lime 1 :6 4 1:1:5 126 B 5 c Common Lime 1 :6 4 1:1:2 178 B 4 c Common Lime 1 :6 4 1:0:1 210 B12 B Hard Lime 1 :6 4 1:1:5 990 Bll B Hard Lime 1 :6 4 1:1:2 890 BIO B Hard Lime 1 :6 4 } :0 : 1 840 B 9 A Vitrified Lime 1 :6 4 1:1:5 1360 B 8 A Vitrified Lime 1 :6 4 1:1:2 1270 B 7 A Vitrified Lime 1 :6 4 1:0:1 1450 B22 B Hard 15% ■ Lime ■ +85% . Port- land. 1 :3 1:1:5 1760 B28 B Hard 1 :3 1:1:2 870 B20 B16 B A Hard Vitrified 1 : 3 1 :3 1:0:1 1:0:1 1760 2900 B 3 C Common Portland 1 :3 1:1:5 650 B 2 C Common Portland 1 :3 1:1:2 560 B 1 C Common Portland 1 :3 1:0:1 510 B27 B Hard Portland 1 :3 1:1:5 870 B18 B Hard Portland 1 :3 1:1:2 ■ 2070 B17 B Hard Portland 1 :3 1:0:1 2000 B15 A Vitrified Portland 1 :3 1:1:5 2900 B14 A Vitrified Portland 1 :3 1:1:2 2740 B13 A Vitrified Portland 1 :3 1:0:1 2710 * a = header course, 6 = backup course, and 5 stretcher courses in sequence, etc. c=: stretcher course. 1 : : 5 indicates 1 header, 1 backup * Engr, Record^ Vol. 71, p. 460. t Bullef.in No. 27 of the University of Illinois. 286 TRUCTURAL CLAY PRODUCTS TABLE 3.— AVERAGE RESULTS OF COMPRESSIVE TESTS ON BRICK COLUMNS [See Bulletin No. 27, Engr. Expt. Sta., Univ. of III.] Columns were 12^X12§ in.XlO ft. and consisted of 40 to 43 courses of brick laid with |-in. joints. No. of Tests. Characteristics of Columns. How Laid. Mix of Mortar.* Age Days. Average Ultimate Strength Lb./In.2t Propor- tion of Load at which Popping Occurred, t Ratio of Strength of Columns to Strength of Brick First Set. 6-In. Mortar Cubes. Modulus of Elas- ticity in 1000 Lb. /In. 2 Shale Building Brick 3 Well IP :3S 67 3365 .56 .31 1.00 1.17 4783 2 Well IP :3S 181 3950 .37 1.18 5025 2 Well 1 P : 3S 68 2800' .66 .26 .83 4400 2 Poorly 1 P :3S 67 2920 .62 .27 .87 1.05 3525 2 Well IP :5S 65 2225 .52 .21 .66 1.30 3250 1 Well IN :3S 67 1750 .40 .16 .52 5.75 800 2 Well IL :2S 66 1450 .43 .14 .43 104 Undekbuhned Clay Brick Well IP : 3S 63 1060 .76 .27 .31 .37 433 * P=Portland cement; S=sand; N— natural cement. L=Ume. t The maximum range in strength for any set of columns was less than 13 per cent. t Popping was probably due to transverse rupture of brick. 1 These columns were loaded with 1-inch eccentricity. Owing to differences in ratio of height to least width, one would expect a brick tested flatwise to have about 40 per cent more strength than a solid homogeneous pier of the same material having a ratio of height to least breadth of from 6 : 1 to 10 : 1. Therefore a pier which developed 70 per cent of the crushing strength of the component brick would be ideal. Since, however, the mortar of the joints never possesses the same strength and elastic properties as the brick composing the pier, this condition is never realized. Yet on account of the thinness of the joints it is reason- able to expect the strength of the joint to exceed the strength of cubes made from the mortar. The results in Table 2 show that piers of Class A or Class B brick laid in 1 : 3 Portland cement mortars were twice as strong as similar piers laid in lime mortar. The low strength of the lime mortar piers is partly attributed to the fact that the lime mortar in the central portions of the joints did not receive sufficient air to become carbonated. Talbot's tests indicate that the columns laid in 1 : 3 Portland cement mortar were 51 per cent, stronger than those laid in like mortar of 1 : 5 proportions, 92 per cent, stronger than those laid in 1 : 3 natural cement PROPERTIES OF STRUCTURAL CLAY PRODUCTS 287 mortar and 132 per cent stronger than those laid in 1 : 2 lime mortar: Tests made at the Watertown Arsenal * clearly show the advantage of using mortar stronger than a 1 : 3 mix with very hard burned brick. In tests of piers of wire-cut brick having a crushing strength of approximately 13,000 lb. per square inch those laid in neat Portland cement had a strength of 31 per cent of the brick, whereas those laid in 1 : 3 Portland cement mortar only possessed 19 per cent of the strength of the brick. The advantage in stiffness arising from the use of strong mortar in the joints is also well illustrated in the tests by Talbot. Tests at the Watertown Arsenal indicate that the strength of small columns (12X12 in.) is 40 to 50 per cent greater when the brick are laid on edge than when laid flatwise. This shows the desirability of in- creasing the thickness of brick which are to be used in heavily loaded piers. Some tests at Cornell University f and others made at the Bureau of Standards I demonstrate that the strength of a column may be increased by placing a horizontal layer of wire meshing in every joint. A decrease in strength obtained, however, when the four or more courses intervened between layers of meshing. 303. Resistance of Brick Walls to Fire. — In a series of fire tests on 6X9-ft. wall panels at the Underwriters' Laboratories, in Chicago, brick panels showed marked resistance to fire and low conductivity. Tests were made on a 12-in. wall of well-burned Chicago brick, an 8-in. panel of hy- draulic-pressed brick from Indiana, an 8-in. panel of common brick from St. Louis, and an 8-in. panel of sand-lime brick from Indiana. The strengths and absorptive properties of these bricks are given in Table 4. With the exception of the panel made of hydraulic brick which was laid in lime putty, cement mortar was used. The tests were made by subjecting the face of the panel to a temperature which rose to about 800° C. in one- half hour and then varied between 800 and 900° C. for one and one-half hours at which time the panel was removed and the face quenched by water from a fire-hose. Each high temperature recorded in Table 4 rep- resents an average of a number of pyrometer readings, the thermo-couples being arranged to secure the variation in temperature at different parts of the furnace and at various points on the face of the wall. The panels of clay brick withstood the tests better than the panel of sand-lime brick. The panel of hydraulic-pressed brick was in the most perfect condition after quenching. About 18 per cent of the brick on the face of this panel were cracked through and a very few were spalled. The Chicago brick contained lime knots which caused a large percentage of the exposed brick to crack when quenched. In 60 to 70 per cent of these the * Tests of Metals, 1904. t Trans. Asso. Civ. Engrs,, Cornell University, Vol. 8, 1900. j Engr. Record, Vol. 71, p. 460. 288 STRUCTURAL CLAY PRODUCTS TABLE 4.— EFFECTS OF HIGH TEMPERATURE ON BRICK AND BRICK WALLS [Bulletin No. 370 U. S. Geological Survey.] Wall panels fired for two hours, for one hour at maximum temperature. Kind of Brick. Common Clay. Hard- burned Clay. Hyd- pressed Brick. Sand- Lime. Thickness of panel, in Maximum average temperature on exposed face in ° C Maximum average temperature on unexposed face after 2 hr. in ° C Mean temperature of air on unexposed face. . . . No. unexposed brick tested transversely Average modulus of rupture of unexposed brick, lb./in.2 No. exposed brick tested transversely Average modulus of rupture of exposed brick, lb./in.» No. unexposed brick crushed Average crushing strength of unexposed brick, lb./in.2 No. exposed brick crushed Average crushing strength of exposed brick, lb./in.2 No. unexposed * brick immersed Average per cent absorption, unexposed brick, after forty-eight hours' immersion 850 58 23 5 1178 3866 5 6.2 12 770 18 3 2 482 13 2729 13 2793 2 20.2 8 850 35 3 2 718 13 4440 13 3701 2 10.7 790 55 19 5 319 5 56 5 2035 5 1750 5 15.9 * Absorptions of exposed brick were about the same as for unexposed brick. cracks were sufficiently large to permit picking off portions of the brick. About half of the faces of the St. Louis brick were so cracked at the con- clusion of the test that they could be readily removed, and the face of the wall was discolored to a depth of about 1 in. After firing, the face of the panel of sand-lime brick looked soft and chalky. It was washed away to a depth of f to f in. when the hose was applied. Only about 20 per cent of the exposed brick could be removed from the wall intact. Sand-Lime Brick * Although not a clay product, the fact that a million dollars' worth of sand-lime brick are annually used as a substitute for clay brick warrants a brief discussion of their manufacture and properties in this chapter. 304. Definition. — Sand-lime bricks are made from a lean mixture * For further information on sand-lime brick see Cements, Limes and Plasters, by E. C. Eckel. An interesting article on The Chemistry of Sand-lime Brick, by T. R. Ernest appears in Trans. Am. Ceramic Society, Vol. 13, p. 649. PROPERTIES OF STRUCTURAL CLAY PRODUCTS 289 of slaked lime and fine silicious sand, molded under mechanical pressure and hardened under steam pressure. 305. Manxifacture. — The sand should be free from clay or mica. It should all pass a 20-mesh and three-fourths of it should be retained on 100-mesh. If the grains run larger than a 20-mesh, the coarse particles must be screened out or reduced in a tube-mill. A high-calcium lime is preferred to a brown or dolomitic lime owing to the ra.pidity with which the former hardens. The requisite percentage of hme varies between 4 and 10 per cent. Generally the lime is slaked before mixing with the sand by placing it beneath the brick cars in the hardening cylinder and allowing the steam to act upon it. Often the sand and lime are mixed dry in a tube- mill and the mixture is then tempered in a special type of pug-mill. In some plants the quick-lime is slaked, the sand ground, and an intimate mix- iture secured by running the wet sand and lime through a wet and dry grinding mill, an apparatus similar to a dry-pan. Molding is done in powerful presses, some of which can exert a compression of 20,000 lb. per square inch on the surface of the brick. After removal from the press the brick are stacked on cars which are run into the hardening cylinders. In the latter a steam pressure of 100 to 150 lb. per square inch is used. After hardening for six to ten hours the brick are ready for use. 306. Comparison of Clay and Sand-lime Brick. — On account of their smooth surfaces, even shape, freedom from efflorescence, uniform color and satisfactory strength, sand-lime brick are sometimes preferred to clay brick. Some of the American sand-lime brick, however, have not been as durable when exposed to the weather as good grades of clay brick. Unless made with great care sand-lime brick do not resist frost action or fire as well as clay brick. 307. Physical Properties of Sand-lime Brick. — Good sand-lime brick bedded flatwise have a compressive strength between 2500 and 4000 lb. per square inch. In cross-bending the modulus of rupture should exceed 350 lb. per square inch. After immersion for forty-eight hours good brick should not show more than 15 per cent absorption. The specific gravity generally lies between 2.1 and 2.3. Paving Brick * 308. Manufacture. — Paving brick are made from three classes of clay, surface clays, impure fire-clays and shale. Owing to the narrowness of the vitrification range for most surface clays, they are apt to produce either underburned or overburned brick. Impure fire-clays make a good * Additional information on methods of manufacture may be gotten from VitriHed Paving Brick, by H. A. Wheeler, Randall & Co.; and from Burning Brick in Down- draft Kilns, by W. D. Richardson, Randall & Co. 290 STRUCTURAL CLAY PRODUCTS brick when sufficiently vitrified, but require a high temperature. The shales are by far the best source of raw material for paving brick. Wheeler suggests that shales suitable for paving brick should approximate the following analysis: Silica (Si02 = 56, alumina (Al203) = 22, ignition loss = 7, lime (CaO) = l, magnesia (MgO) = l, alkalies (K2O and Na20) = 4 per cent. Fluxing impurities in the above analysis total 13 per cent. Three types of brick are molded with the stiff-mud process; wire-cut, wire-cut lug, and repressed brigk. Wire-cut lug brick are side-cut by a vertical wire. This wire is guided by slots in horizontal plates located above and below the bar of clay. The arrangement of the slots is such that four lugs are formed on one side of each brick; the other side is cut plane. The brick are laid in the pavement so that the smooth side of one brick is in contact with the lugs on the adjacent brick. It is claimed that the ver- tical joints are much stronger in pavements made of this brick than in« those made of plane-cut brick owing to the superior bond between the filler and the lug surfaces. Other types of stiff-mud paving brick may be either end or side-cut. Paving brick are generally burned in down-draft or continuous kilns. From seven to ten days are required in burning and a like period for proper anneahng. The temperature required to bring shales to complete vitri- fication (Wheeler), is 850 to 1100° C. Impure fire-clays require a tem- perature from 100 to 200° C. higher. By employing impure fire-clay, with which danger of over-bm-ning is small, as high as 90 per cent of first-class paving brick may be produced. Using shale it is not possible to average more than 75 per cent of first-class pavers. 309. Requirements of Good Paving Brick. — Every brick should be free from marked distortion, should have one plane edge, and should be free from cracks, checks, and blisters. It should give a high metallic ring when struck with a hammer and should, when broken, exhibit a uniform close-grained structure free from laminations. The interior of a properly bm-ned brick cannot be scratched with a knife. Uniformity in quality is of vital importance in order that the pavement may wear evenly. 310. Physical Properties of Paving Brick. — Good brick should have a crushing strength in excess of 8000 lb. per square inch. Overburned brick are likely to have a very high crushing strength. The transverse strength (modulus of rupture) should not be less than 1500 lb. per square inch. Low transverse strength may be due to either overburning or improper annealing. Shale brick when properly vitrified generally absorb between 0.5 and 2 per cent; brick made of impure fire-clay may absorb as high as 5 per cent. An absorption less than 0.5 per cent generally denotes over-burning. In specific gravity, shale pavers commonly range PROPERTIES OF STRUCTURAL CLAY PRODUCTS 291 between 2.2 and 2,5, impure fire-clay between 2.1 and 2.3. The better grades of paving brick lose less than 20 per cent by weight, in the rattler test. Wide variation in the losses of individual brick indicate non- uniformity in methods of manufacture and are sufficient cause for rejec- tion of brick even though the average loss is small. Refractoky Brick * 311. Introduction. — Certain classes of brick are much employed to line flues, hearths and the various classes of furnaces used in metallurgical processes. Such brick must be able to withstand high temperatures without undue softening or change in volume, must resist the action of gases and slags generated during the process, must resist abrasion when hot, and must possess low thermal conductivity. In accordance with the character of the chemical reaction which different refractory brick resist, they are divided into three classes : acid, basic and neutral. 312. Acid Brick. — The brick which are commonly used to resist the action of silicious and other acid slags are fire-brick and silica brick. Fire-brick are made from fire-clays which are sometimes grogged with small percentages of sand to reduce shrinkage. The clay generally con- sists of J to f silica, i to f alumina and less than 10 per cent of fluxes. The more refractory brick are made from clays having low flux contents and high alumina contents. A very high alumina content, however, gives the brick a basic reaction. The brick are molded by either the soft- or stiff-mud processes and repressed after partial drying. First class fire-brick should have a compressive strength of at least 1000 lb. per square inch and should withstand a load of 50 lb. per square inch at a temperature of 1350° C. without deforming over 11 per cent. They should not soften at a temperature less than 1700° C.f 313. Silica Brick. — Quartzite, sandstone, or silica sand, which con- sists of 95 per cent or more pure silica, are the main constituents used in making silica brick. If the silicious rock contains small percentages of clay it is sometimes possible to mold the brick without artificial additions. The English ganister brick is made from such material. Ordinarily, how- ever, the ground silicious rock or the sand are not sufficiently plastic when tempered with water and are adulterated either with very small percentages of fire-clay or about 1| per cent of high-calcium Hme. Silica brick are burned at temperatures shghtly higher than fire-brick. On account of their brittleness and expansibility when heated, silica brick must be laid with wide joints. The compressive strength of silica * For additional information on refractory materials reference should be made to Havard's Refractories and Furnaces, from which considerable of this material has been drawn. t See Technologic Paper No. 7, U. S, Bureau of Standards. 292 STRUCTURAL CLAY PRODUCTS brick tested flatwise often exceeds 2000 lb. per square inch. The softening temperature ranges from 1700 to 1800° C. 314. Basic Brick. — For lining basic Bessemer converters, basic open- hearth furnaces, blast furnaces, copper furnaces and other vessels subjected to the action of basic slags, magnesia brick are quite generally used. Mag- nesia brick are made from magnesite, nearly pure magnesium carbonate, of which the most satisfactory supplies are found in Greece and in Styria, an Austrian province. The magnesite is first calcined at 800° C, a tem- perature which is sufficient to free the carbon dioxide. This preliminary calcination of Grecian magnesite is generally done at the mines. At the brick plant a large proportion of the calcined product is sintered at a tem- perature of 1800° C. It is then mixed with 1 to 50 per cent of calcined magnesia and the mass is tempered with a small proportion of water. For brick which must resist high temperatures the proportion of calcined magnesia must be low. Since such mixtures are of low plasticity a very little tar or magnesium chloride is sometimes added for a binder. The brick are then hand-molded partially dried and repressed. After further drying, the brick, which have very little tenacity, are carefully stacked m a double layer in a down-draft kiln and burned. Styrian magnesite is sorted, dead-burned, and again freed from impur- ities. The sintered magnesia is then ground, tempered with a small pro- portion of water and molded into brick which are burned at a temperature above 1700° C. Brick made from Styrian magnesite are considered more refractory than others. Their softening temperature is approxi- mately 2000° C. Although not so satisfactory as magnesia, calcined dolomite, the double carbonate of magnesia and lime, is often used to make refractory brick. The natural rock or a mixture of the rock and clay is ground, tem- pered with water and molded into shape. After drying these are burned like magnesia brick. Dolomite brick suffer greater contraction at high temperatures than do magnesia brick. In making bauxite bricks, the bauxite which consists of 50 per cent or more of alumina, with water, iron oxide, and silica for principal impuri- ties is calcined and crushed to a fine powder. It is then mixed with 15 to 30 per cent of fire clay, tempered with water and molded into bricks. Although properly burned bauxite bricks are highly refractory, they have such a large shrinkage when heated to high temperatures that they have not come into general use. In experiments by Kanolt * on eight samples of brick the melting points varied from 1565 to 1785° C. 315. Neutral Brick. — At the slag line in a basic furnace and in certain ports, and flues where the reaction of the surrounding medium may be either acid or basic, refractory brick which are neutral in reaction are used. * Technologic Paper No. 10, U. S. Bureau of Standards. PROPERTIES OF STRUCTURAL CLAY PRODUCTS 293 Chromite, the oxide of iron and chromium, is the principal raw material used for making neutral refractory brick. The ore is crushed and mixed either with fire-clay or with magnesia and tempered with water in a wet- pan. The brick are molded, dried, and burned in much the same way as magnesia brick. Ordinarily the brick contain from 30 to 40 per cent chrome (Cr203), the other elements, alumina, iron oxide, magnesia, and sihca being present in varying amounts. Chrome brick, although very resistant chemically to the' action of slags and gases, are less refractory and weaker than magnesia brick. One sample tested by Kanolt had a melting- point of 2050° C. Building Tile 316. Hollow Blocks, Partition Tile and Fireproofing. — For manufactur- ing hollow blocks, partition tile, and fireproofing, plastic clays or shales mixed with clay are used. The materials employed will burn to a hard, dense structure at a fairly low temperature, generally between 1100° and 1300° C. These forms are molded in machines of the auger or plunger type and are commonly burned in down-draft or continuous kilns. Fig. 8 shows typi- cal shapes of these three classes of building tile. Most of these forms con- tain from 45 to 55 per cent of air space or voids. Sections so made are sometimes inaccu- rately called terra-cotta blocks. Hollow blocks, frequently termed load- bearing tile, are used in load-bearing walls and partitions. For unplastered outside walls they are often salt-glazed. For walls which are to be plastered, blocks, tile and fireproofing are often scored in order to furnish a better bond for the plaster. Hollow blocks are harder burned and stronger than partition tile. The latter are used principally for partitions which carry no superimposed load. Fireproofing differs from partition tile chiefly in shape and size. PARTITION BLOCKS Fig. 8.— Types of Clay Building TUe. 294 STRUCTURAL CLAY PRODUCTS The advantages of hollow block and fireproofing are lightness, low per- meability to water, low heat conductivity and a rough surface to which plaster may be directly applied, thus avoiding the necessity of furring and lathing. Fire tests have shown, however, that partition tile and hollow blocks are likely to split at the junctions of webs and faces, especially when the hose is turned upon hot partitions. * It is, therefore, safe prac- tice to insist on fire tests of hollow block panels when they are to be used for fire protection. Hollow blocks of good quality should have a compressive strength of 1000 lb. per square inch of gross section when the load is imposed in accord- ance with the scheme of design. Many of the best grades of hollow blocks will develop 2000 to 4000 lb. per square inch of gross section depending upon the direction in which the load is applied. After forty-eight hours immersion, good blocks generally absorb less than 12 per cent of water. A notion of the variability of clay building tile and of the necessity for testing them is afforded by a large series of tests made at several laboratories for Committee C-10 of the A.S.T.M. (See Proceedings, Vol. 17, Pt. 1, p. 334.) The manufacturers were requested to select specimens which fairly represented the quality of their product. From the test data, the compressive strengths ranged from 640 to 12,360 lb. per square inch of net section, corresponding approximately to 95 and 6000 lb. per square inch of gross section, respectively. The largest value was recorded for a medium-burned tile tested on end and the smallest for a soft-burned tile loaded flatwise. Absorption, by weight, after boiling five hours, ranged from 1.8 per cent for a hard-burned specimen to 20.3 per cent for a very soft tile. 317. Tests of Hollow Block Columns.— Prof. A. N. Talbot reports two series of tests on columns of hollow blocks laid in Portland cement mortar in Bulletin No. 27 of University of Illinois Engr. Expt. Sta. In the earlier series the end faces of the blocks, which bore the load, were very uneven. This defect caused a marked difference in the strengths of the two series of columns. Most of the blocks were 8 in. high, 4 in. wide and 8 in. long. The cells occupied about 15 per cent of the volume of a block. From compressive tests on 33 single blocks the range in strength based on net area, was 3350 to 9070 lb. per square inch; the average was 5451 lb. per square inch. Transverse tests on seven blocks, tested with cells vertical, gave a range in modulus of rupture of 870 to 1240 lb. per square inch with an average of 1022 lb. per square inch of net section. The seven columns tested in 1907 were approximately 12 ft. high, the twelve columns of the 1908 series were 10 ft. high. Columns of the earlier series ranged in cross-section from 85X8I in. to 171X175 in., all of the columns of the later series were 12JX12| in. in cross-section. The * BulUlin 370, U. S. Geol Survey. PROPERTIES OF STRUCTURAL CLAY PRODUCTS 295 columns of the earlier series were laid in umns of the series of 1908 were laid in 1 : 3 mortar. The strengths of the col- umns tested in 1907 varied from 2710 to 3440 lb. per square inch; those tested in 1908 had strengths ranging from 3040 to 4300 lb. per square inch, the latter value being esti- mated. By reference to Art. 302 it will be noted that the strengths of these hollow block columns com- pare very favorably with the strengths of first-class brick columns. The initial modulus of elasticity of the columns varied between 1,910,000 and 2,860,0001b. per square inch. 318. RoofingTile.— For making roofing tile, the clay must not only be plastic, but it must dry and burn without suffer- ing distortion. Consider- able care is also required in preparing the raw ma- terial. After being ground in a dry7pan and finely screened the clay is pugged in a wet-pan and made into balls which are stored in bins until wanted. The balls are then taken to an auger machine and molded into tile or, if interlocking tile are to be made, they are formed into clots. The clots are then formed into tile on a press. Common 1 : 2 mortar. Most of the col- Terminal SPANISH TILE Ridge Top Fixture GERMAN TfLE CLOSED SHINGLE TILE Fig. 9. — Examples of Various Roofing Tiles. 296' STRUCTURAL CLAY PRODUCTS types of tile are shown in Fig. 9. After drying, roofing tile are burnt in saggers in down-draft kilns. Tile which are to serve as insulation against heat are soft-burned and porous. Where tile are to be subjected to freezing they are burned harder or glazed. Roofing tile should be strong, durable, free from soluble salts, and impervious to water. Roofing tile, when properly made, form a strong, durable, fireproof roof which is a poor conductor of heat. The chief objections to tile roofing are the expense and the heaviness of the con- struction. 319. Floor-tile. — White-burning and red-burning clays, fire-clays and shales are used in making tile for floor surfaces. The chief considera- tions are color when burned, freedom from soluble salts, and absence of r ■ mnr,r j, ^ ,, , , L^J^ 3^ _rZElJ Tl L _i I 1 1 1 ! r 1 1 1 1 1 1 1 1 1 i , 1 1 1 1 i T- 1 1 1 1 1 1 1 1 ! 1 i 1 1 1 i 1 1 1 1 1 1 ! 1 rill 1 1 1 1 1 1 1 1 1 1 1 ' I r '•• 1 ' 1- 1 1 1 JJ n ,-,i,, ^ ; 1 ; 1 — L (a) (b) (c) Fig. 10.— Floor Tile and Wall Tile Designs, (a) and (6) floor tile, (c) wall tile. distortion and checking in burning. The dry-press process is used in molding, and down-draft kilns in burning. Floor-tile may be divided into two classes in accordance with the method of molding the design into the tile. They are face-tile, commonly called encaustic tile because they have a burnt-in design, and plain tile. Plain tile are composed of the same clay or mixture of clay throftghout. Frequently these are made in the form of mosaics. They may be either vitreous or semi-vitreous. Plain face-tile are made by covering the die forming the base of the mold with a thin layer of specially prepared clay, filling the mold with a clay backing and compacting in a hand press. In making inlaid face-tile, a cellular frame is placed on the bottom of the mold and- clays which have been properly colored are screened into the different cells in accordance PROPERTIES OF STRUCTURAL CLAY PRODUCTS 297 with the pattern scheme. The frame is then removed, the backing in- serted, and pressure appUed to compact the tile. Floor-tile should show little absorption, have a high transverse strength and a high resistance to abrasion. 320. Wall-tile, — Tile for surfaces of walls differ from floor-tile prin- cipally in design and degree of burning. Wall-tile are burned at a com- paratively low temperature, glazed, and fired again in a muffle-kiln at a still lower temperature. Wide difference in color, in shades of a single color, and in relief design can be obtained. Wall-tile are much used in wainseotings and to some extent in arches and ceilings. Floor and wall- tile designs appear in Fig. 10. Terra Cotta 321. Decorative Terra-cotta. — For the ornamentation of buildings and structures, decorative terra-cotta is now very widely used. It is made . from a very finely ground mixture of fire-clay and shale, or fire-clay and impure clay, which is adulterated with ground brick or other burnt clay to decrease shrinkage. Plain forms of uniform design are made by hand in plaster molds, but more intricate designs are modeled in the green clay by expert workmen. Terra-cotta is dried very slowly to avoid warping and checking. It is then sprayed with a slip which lends a color to the goods on burning. For certain classes of goods glazes of a bright or dull finish are also applied. Burning is done in muffle-kilns at temperatures between 1100 and 1300° C. To obviate kiln-mark- ing, each piece is so supported by fire-clay tile that it carries only its own weight. 322. Terra-cotta Lumber. — A very different material from decorative terra-cotta is the terra-cotta lumber used for fioor arches and fireproofing (see top of Fig. 8). It is made in much the same way as partition tile with the exception that a considerable quantity of sawdust is incorporated in the raw mix. The goods are burned at a low temperature, which destroys the sawdust but leaves the product sufficiently soft and porous to permit cutting with a saw. The strength and lightness of this material are its chief assets. In compression, good material should withstand 2500 lb. per square inch of net section. Clay Pipe 323. Sewer Pipe. — In the construction of sewers clay pipe has long been successfully used. Sewer pipe must have high strength in order that it may carry the ditch filling. To successfully withstand the action of acids and gases in the sewage, the pipe must be hard-burned and imper- 298 STRUCTURAL CLAY PRODUCTS vious. A smooth interior surface which offers Uttle resistance to flow is also desirable. Sewer pipe is made from red-burning clays, fire-clays, shales and mix- tures of shale and fire-clay. It is generally molded in vertical double- cylinder presses from a stiff-mud mix, although some pipe is made by the dry-press process. Sewer pipe is commonly burned in down-draft kilns at temperatures between 1050° and 1300° C. The term vitrified pipe is often a misnomer, since the burning temperature frequently is insuffi- cient for vitrification. However, the firing should be carried to the stage of incipient vitrification. Salt glazing is generally practiced to insure a smooth and impervious surface. The pipe is made in lengths of about 3 ft. and in diameters up to 42 in. Sewer pipe are commonly provided with a bell on one end into which the small end of an adjacent pipe is fitted. Joints are filled with 1 : 1 Portland cement mortar.* In general, small fragments from good pipe will have an absorption less than 5 per cent after forty-eight hour immersion in water. Results of crushing tests in which the lower portion of the pipe was bedded in sand and the load applied on the top through a hardwood strip 1-in. wide appear in Table 6. TABLE 5.— CRUSHING TESTS ON SEWER PIPE MADE BY THE MUNICIPAL SEWER-PIPE TESTING LABORATORY OF BROOKLYN, N. Y. IN 1909 [See Municipal Journal, Vol. 38, p. 160.] Size of Pipe, In. Total Number Tested. Number Tested to Destruction. Crushing Strengths in Pounds per Linear Foot of Pipe. Required Strength, Lb. per Ft.t Percentage Maximum. Minimum. Average. of Failures. 6 12 15 18 24 30 30* 170 245 72 25 17 2 2 169 245 72 25 14 2 2 2333 2900 2800 3100 3800 3280 3240 1033 933 1300 1734 2200 3240 3080 1537 1542 1935 2389 2825 3260 3160 1000 1150 1300 1450 2000 2.04 * Double strength pipe. t Local standard. 324. Drain Tile. — Clay drain tile are made principally from shales and impure clays. The smaller sizes are molded in auger machines, but the larger ones are made in sewer-pipe presses. The tile arc burned in a * The remarks in Art. 309 concerning appearance, hardness, texture, ring under the hammer of paving brick apply with equaJ force to sewer pipe and the better grades of drain tile. PROPERTIES OF STRUCTURAL CLAY PRODUCTS 299 variety of kilns sometimes with brick or fireproofing. Kiln temperatures are lower than those used in burning sewer pipe, although the better grades of tile are burned until steel-hard. Salt-glazing is sometimes employed. Drain tile are generally cylindrical in form and laid with uncemented butt joints through which the drainage water seeps. The specifications which appear in the following table for the average strength of five specimens of drain tile were adopted by the A. S. T. M. in 1916 (see Standard Specifications for Drain Tile) ; the values for sewer pipe were proposed by Committee C-4 of the Society in the same year. AVERAGE STRENGTH REQUIREMENTS FOR CLAY AND CEMENT DRAIN TILE AND SEWER PIPE Drain Tile. Sewer Pipe. Internal Diameter of Tile, In. Minimum i Strength in Farm Drain Tile (a) Average Ordinary Pounds per Lin Standard Drain Tile (fj). Supporting 3ar Foot for Extra-Quality Drain Tile (c). Internal Diam- eter of Pipe, In. Pressure in Pounds per Linear Foot Applied through Knife-edge Bear- ings. 4 6 8 10 12 14 16 18 800 800 800 800 800 900 1000 1200 1200 1200 1200 1200 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 2600 1600 1600 1600 1600 1600 1600 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 3800 4000 4200 6 8 10 12 15 18 20 22 24 27 30 33 36 42 900 900 1000 1050 1250 1400 1550 1750 20 1950 22 2150 24 2350 26 2500 28 2800 30 3200 32 34 36 38 40 42 (a) Farm drain tile for ordinary private drainage work on farms where the depth and size are moderate. (b) Standard drain tile is for district drainage at moderate depths. (c) Extra-quality drain tile is for district drainage where the depth is large and a first-class pipe ia needed. 300 STRUCTURAL fLAY PRODUCTS Three methods of testing tile are outlined in^ Art. 293. 325. Conduit. — In large cities considerable use is now made of clay conduits for carrying underground cables and wires. Hollow rectangular prisms rounded at the corners and traversed by several longitudinal ducts are much employed in lengths of about 3 ft. Conduits are made of the same material and molded in the same manner as fireproofing. They are, however, hard-burned and salt-glazed to render them impervious to water. CHAPTER IX PORTLAND CEMENT 326. The Cements of Construction.^ — The cementing materials which are most used in engineering constructions may be classified as follows: J. Hydraulic cements 2. Limes 3. Gypsum Plasters 4. Bitumens Portland cement Natural cement Puzzolan cement Blended cement Improved cement . Will set under water Quick lime Hydrated lime Hydraulic lime (sets under water) Plaster of Paris Cement plaster Hard finish plaster Only the first three classes will be discussed herein; for the properties and uses of bitumens reference may be made to Blanchard and Browne's Textbook on Highway Engineering, Baker's Roads and Pavements, or other standard works on pavements. Owing to the widespread use and importance of Portland cement as a material of construction, and on account of the necessity for a thorough knowledge of its properties in order to properly fabricate it into struc- tures, we shall consider at some length its nature, manufacture a^nd properties. NATURE OF PORTLAND CEMENT 327. Definition. — In the revised specifications for Portland cement* the following definition appears. " Portland cement is the product obtained by finely pulverizing clinker produced by calcining to incipient fusion, an intimate and properly proportioned mixture of argillaceous and calcareous materials, with no additions subsequent to calcination excepting water and calcined or uncalcined gypsum." * See Art. 396. 301 302 PORTLAND CEMENT 328. The Characteristics of Portland Cement. — Although the char- acteristics of Portland cement are not measures of quality, they often serve to distinguish differences in brand and to separate Portland from other cements. Typical Portland cement is a flour-like powder which varies in color from a greenish gray to a brownish gray. At the present time, white Portland cement is also being successfully produced. In general, the specific gravity of Portland cement is higher than that of other hydraulic cements and lies between 3.10 and 3.15. Although its specific weight is quite variable, ranging from 75 to 95 lb. per cubic foot, depending upon the compactness, it is considerably higher than the specific weight of natural cement. Portland cement when mixed with water sets much more slowly than natural cement and more rapidly than puzzolan cement. It hardens more rapidly and acquires greater strength than any of the other hydraulic cements. 329. The Chemical Elements in Portland Cement. — The three funda- mental constituents of hydraulic cements are lime, silica, and alumina. In addition to these most cements contain small proportions of iron oxide, magnesia, sulphur trioxide, alkalies and carbon dioxide. From the published analysis of a large number of cements, the table below, show- ing the range in composition and a typical analysis for American Port- land cement, has been compiled. Per cent Element Range Average Lime (CaO) 59-65 62-63 Silica (Si02) 19-25 22-23 Alumina (AI2O3) 5-9 7-8 Iron Oxide (Fe203) 1-5 2-3 Magnesia (MgO) 1-4 1.5-2.5 Sulphur Trioxide (S03) 1-2 1.5 Alkalies (K20>and NaaO) 0-1 trace Water (H2O) and Carbonic Ox- ide (CO2) . . 1-4 Although it is certain that the way in which the chemical elements are combined in the cement exercises a great influence upon its prop- erties; yet, on account of lack of knowledge concerning such combina- tions, the cement chemist has been obUged to rely largely upon -rule of thumb and cut-and-try methods in proportioning raw materials. Despite this fact, careful manufacturers have been able to produce uniform cement of excellent quality. This has been accomplished by the close observance of well-established facts concerning the effects produced by varying per- centages of the elements and by giving especial care to the details of man- ufacture. A brief consideration of the effects of the main chemical ele- ments and the reasons for controUing their proportions will now be given. NATURE OF PORTLAND CEMENT 303 330. The Proportioning of the Main Constituents. — Lime, the element constituting five-eighths of Portland cement, should be very carefully proportioned with reference to the other ingredients. An excessively high lime content tends to make the cement either unsound (i.e., to pro- duce disintegration after setting), or slow setting with a high strength at an early age. On the other hand if the cement is underlimed it will probably be weak and either quick setting if it is underburned or slow setting if hard burned.* A number of formulas for the regulation of the lime content have been proposed and are in use by cement chemists. S. B. Newberry, from the result of an elaborate set of synthetical analyses based upon the work of Le Chatelier, concludes that if proportions are stated by weight, the expression Lime = SiUca X 2.7+ Alumina X 1.0 is a safe rule for proportioning the raw materials commonly used in the United States provided they are finely ground and properly burned.* It will be noted that this formula states only the proportions of the essen- tial elements. It must not be concluded from this, however, that the proportions of the other elements are unimportant. To allow for the effects of magnesia and ferric oxide Eckelf modifies the rule thus Lime -I- Magnesia X L4 = Silica X 2.8 + Alumina X 1 . 1 -|- Ferric oxide X 0.7. Another criterion of more or less value is the hydraulic index which is the ratio — tjtt- in the finished cement. For most Ameri- % lime can Portland cements this index varies between .47 and .53. From a consideration of the form of a hydraulic index it is evident that lowering the siHca necessitates raising the alumina content in a cement. Roughly one can say that a high alumina content tends to ren- der cement quick setting and strong at early ages, whereas a high siUca content produces a slow setting cement of high strength. The relative proportions of these elements also affect the fusibility of the mixture iij the kiln. On account of the marked influence which silica and alumina exert upon the time set, Meade has adopted an Index of activity = -, % alumina' * See Newberry's publications in Jour. Soc. Chem. Industry, Vol. 16, p. 887; Cement and Engineering News, Nov. 1901; Taylor and Thompson's Concrete, Plain and Reinforced, Ch. VI. t Cements, Limes and Plasters, p. 170. X Meade's Portland Cement, p. 33; also E^igr. News, Vol. 61, p. 374. 304 PORTLAND CEMENT He states that this ratio is between 2.5 and 3.0 for most American cements and should always lie between 2.5 and 5. It is evident, however, from a consideration of the effects of lime, that the qmck setting due to a high alumina content may be modified to some extent by increasing the lime content. Furthermore, the time of set may also be affected by iron and magnesia. 331. Iron Oxide. — Ferric oxide (Fe203) exercises a very important influence upon the color of the cement. The pure white Portlands recently placed upon the market are made from materials containing very little of this element. Cements are also being made in which the alumina content is largely replaced by ferric oxide. Such cements have been advocated for use in sea water. Most cements, however, contain 2 or 3 per cent of this oxide. Some authorities, believing that iron oxide behaves hke alumina in promoting compounds of silica and lime, insert it in the hydraulic index; thus the German specifications (1909) in defining Portland cement state that in the mixture of materials, the weight of lime to soluble silica plus alumina and iron oxide should not be less than 1.7 to 1.0. Small percentages of iron oxide render highly silicious raw materials easier to fuse, but a large iron content produces a hard clinker very difficult to grind. 332. Magnesium Oxide. — Magnesia has been the cause of much worry on the part of cement manufacturers and users, since the prevaiUng opin- ion has existed that a large proportion caused unsoundness. The results of experiments by Van Blaese {Thonindustriezeitung , 1899, p. 213) indi- cated that at least 5 per cent of magnesia was not hurtful, while those of Newberry showed that 9 per cent was not harmful to a well made of Portland cement. Butler * reports a satisfactory English cement con- taining 5 per cent of magnesia. Dyckerhoff in Cement Age, Feb., 1909, reaffirmed a previous conclusion that over 4 per cent of this element is injurious. P. H. Bates, of the Bureau of Standards, has conducted tests on cements varying in magnesia content up to 25 per cent.f These were prepared from mixtures of clay, dolomite, limestone and feldspar or kaoUn burnt in a small gas-fired rotary kiln. The results of tests extend- ing over a one-year period show that cements made with less than 7.5 per cent, magnesia are normal in setting, in soundness and in stre'ngth. Clinker containing less than 9.5 per cent, magnesia exhibits no abnormal properties. Tests by Prof. E. D. Campbell at the University of Michigan show that free magnesia is a very undesirable constituent if more than 3 per cent is present in the cement. Neat prisms made from cements con- * Portland Cement, by D. B. Butler, p. 313. t Cement Age, Cement Mill Edition, Mar., 1914. NATURE OF PORTLAND CEMENT 305 taining 3 per cent free magnesia exhibited over 1 per cent expansion after thirteen years storage in cold water, although at an age of one year no unusual expansion was noted. No opinion seems to be advanced indicating that a large percent- age of magnesia is of value in a normally made Portland cement, conse- quently American specifications have hmited its proportion to 5 per cent. 333. Sulphur Compounds.— The presence of sulphides in cement are undesirable, since they are liable to cause unsoundness. The sulphates of calcium, gypsum (CaS04+2H20) and plaster of Paris (CaS04-|-JH20), are used in small percentages to retard the setting. They must be added subsequent to burning, however, in order to be effective. American specifications restrict the presence of sulphur trioxide (SO3) to 2.00 per cent. 334. Alkalies. — The alkalies (K2O and Na20) are found in very small amounts in most Portland cements. Their action is uncertain but, prob- ably not beneficial. 335. Carbonic Oxide. — Since it is common practice to subject the cHnker to aeration before final grinding, all cement contains some carbon dioxide. The percentage absorbed by the cement is dependent prin- cipally upon the completeness of exposure to the air as an experiment by Butler demonstrates. H'e placed a part of a sample of sound cement containing 0.25 per cent CO2 in a cask and part he spread out in a thin layer on a tray. At twenty-eight days the sample in the cask contained 0.57 per cent CO2 and the sample in the tray 1.82 per cent; the cor- responding percentages after three years were 3.21 and 5.60. The ten- sile strength of the original sample showed a progressive increase during this time interval. From these results he concluded that the percentage of carbon dioxide in a cement is not an indication of free lime.* Amer- ican specifications prescribe a limit of 4 per cent for loss on ignition, 336. The Constitution of Portland Cement, f — Although it is a com- paratively simple task to determine the percentages of the various chemical elements in Portland cement, the determination of the combina- tions of these elements which exist in the finely ground clinker is a prob- lem which has baffled the most brilliant experts in physical chemistry. In this connection it should be remembered that the kiln temperature is only sufficient to start fusion and consequently complete solutions of all the elements are not obtained. Among the more prominent investi- gators of the constitution of Portland cement may be mentioned Le * Butler's Portland Cement, p. 317. t For further information on this subject see The Chemistry and Testing of Cement, by Desch, Portland Cement, by Meade, also Fused Portland Cement, by C. Unger (trans- lated article in Cement and Engr. News, Vol. 22, p. 192). 306 PORTLAND CEMENT Chatelier,* the noted French chemist; the Newberry Brothers ;t Torne- bohm,J: the Swedish investigator; W. MichaeHs, Sr.§ C; Richardson;] | and Day, Shepherd, Rankin and Wright at the Geophysical Laboratory of the Carnegie Institute, Washington, D. Clf As a result of the extended researches at the Geophysical Laboratory in which optical, thermal, and chemical properties of a very large number of fused mixtures of pure lime, silica and alumina were investigated, it appears that there are five mixtures of minerals, any one of which may form the main constituents of a Portland cement clinker. In order of lime content in the raw mix these are : First, a high-Umed mixture which solidifies after sintering to a mixture of CaO, 3CaO-Si02 and 3CaO- AI2O3; second, " 'presumably typical Portland cement clinker " a mixture of 2CaO ■ Si02, SCaO ■ Si02 and SCaO -AWz] third, a mixture of 2CaO • Si02, 3CaO-Al203 and 5CaO-3Al203; fourth, a mixture of 2CaO-Si02, CaO-AUOa, 5CaO-3Al203; fifth, a mixture tentatively stated to consist of 2CaOSi02, CaO-AUOa and 2CaO-Al203-Si02. The authors state that these relations will probably remain unaltered by the impurities ordinarily found in the clinker. " Of the effect of magnesia and iron oxide nothing definite is known. Neither seems to form solid solutions with 2CaO • Si02, SCaO • Si02 or 3CaO ■ AI2O3. Nor at the present writing (1911) has any appreciable solid solution been discovered between CaO, AI2O3 and Si02 compounds." II Experiments by P. H. Bates on the constitution of cement clinker, in which burnings were made in a small rotary kiln, indicated that iron oxide entered the beta-orthosilicate (2CaO • Si02) and the 5 : 3 calcium aluminate (5CaO-3Al203) but did not enter the tricalcic siHcate (3CaO-Si02) or the tricalcic aluminate (3Ca0-Al203). In the low- limed mixtures, it formed dicalcic ferrite (2Ca0 ■ Fe^Os) and in the high- limed mixtures, opaque glass and magnetite.** Bates has also shown that magnesia may enter into the beta-orthosilicate (2CaO-Si02) up to 6 per cent and into tricalcic aluminate 3CaO-Al203) up to 10 per cent. In cements carrying less than 7.5 per cent magnesia no separate magnesium compounds were discerned. jj 337. The Setting and Hardening of Portland Cement. — If finely pulverized Portland cement clinker is tempered with the proper amount * * Constitution of Hydraulic Mortars, by H. Le Chatelier (trans, by Mack), t Journal of the Society of Chemical Industry, Nov. 30, 1897. tUeber die Petrographie des Portland Zemcnts, Stockholm, 1897. § The Constitiilion of Hydraulic Cements, by W. MichaeUs, Sr., pub. by Cement and Engr. News. II Engr. News, Vol. 52, p. 127. II Engr. News, Vol. 65, p. 350; also Jour. Industrial Chem., April, 1911. ** Reported in Cement and Engineering News, Feb., 1913. tt Cement Age, Cement Mill Edition, Mar., 1914. NATURE OF PORTLAND CEMENT 307 of water, the resultant soft paste gradually loses its plasticity and becomes stiff and hard. When the paste has lost its plasticity and becomes suf- ficiently rigid so that it will withstand an arbitrarily defined pressure it is said to have set. Generally the period of setting is divided into two stages, the beginning and ending of the setting. The former is called the initial and the latter the final set. After the cement paste has attained final set, it further increases in rigidity, strength and hardness. To the latter transformation the term hardening is applied. Since the setting and hardening of Portland cement is intimately connected with its constitution, there have been as many theories con- cerning the cause of setting as there have been regarding the constitution. Many of these theories have been advanced by the investigators mentioned in the preceding article. A theory which has been accepted by many in recent years was first advanced by W. Michaelis, Sr., in 1893. His own statement of the theory follows.* " The formation of colloidal f calcium hydro-silicate, and to a lesser degree also the formation of colloidal calcium hydro-aluminate and cal- cium hydro-ferrite, is the only essential and important feature in the hardening process of all known calcareous hydraulic cements." Michaelis maintains that when a finely ground hydraulic cement is gauged with water, calcium oxide, calcium aluminate, calcium sulphate, alkali silicate and possible a httle calcium ferrite are dissolved with the production of a supersaturated solution of these components. Calcium sulphate combines with tricalcium aluminate to form calcium sulpho- aluminate. Owing to the insolubility in lime water of the above mentioned compounds, clusters of imperfect crystals of needle or plate-like form are produced. Next the oversaturated solution coagulates about the cement grains, many of which have thus far not been attacked. There is thus formed a soft plastic hydrogel containing calcium hydrosilicate, calcium hydro-aluminate, calcium hydro-ferrite and a very small propor- tion of Ume. Hardening of this soft hydrogel is brought about through the gradual absorption of water by the unattacked cement grains. This * Cement and Engineering News (trans.), Vol. 21, p. 299. t There are a number of solids which when very finely pulverized and mixed with certain Uquids in highly supersaturated solutions will form more or less rigid bodies by coagulation and subsequent desiccation. No crystalline structure is evinced during or after desiccation. On account of the glue-Uke properties which such substances exhibit in hardening, they have been named colloids. Some substances may form either colloids or crystalloids, depending upon the degree of supersaturation of the Uquid solution. Colloidal solutions will not pass through a parchment membrane, whereas crystalloid solutions will. A colloidal aqueous solution is often called an hydrosol. When it becomes gelatinous it is termed an hydrogel. The boiling-point of an hydrosol is the same as the boiling-point of water. 308 PORTLAND CEMENT withdrawal of water leaves the lime in the hydrogel envelope surrounding the cement grains. The hydrogel thus hardens and becomes impervious to the passage of water. The strength of the hardening cement, Michaelis states, is increased by the crystallization of calcium hydrate, calcium hydro-aluminate, cal- cium hydro-ferrite, and to some extent by the crystallization of calcium sulpho-aluminate. These crystalloids are slowly formed from slightly oversaturated solutions, whereas the colloids are produced from highly supersaturated solutions. Although the crystalloids increase the strength of the colloids, they also decrease imperviousness on account of the bound- ary planes between the crystals and the colloids. The hardening of cement in air is hastened by the evaporation of a portion of the water. Owing to the evaporation of water during air hardening, however, more cement grains are imperfectly hydrated than in water hardening, and shrinkage of the colloid is very marked. Since crystals are formed from solutions of low supersaturation, Michaelis reasons that the addition of gypsum which brings on crystalliza- tion, will therefore retard the setting process. This will appear evident when one considers that, owing to the low supersaturation of the initial mixture, some crystalhzation must take place before coagulation of the hydrogel. In speaking of the causes of unsoundness, he states that on account of the non-homogeneity of Portland cement, arising from imperfect con- ditions of manufacture, there will always be more or less uncombined lime within the larger grains. The latter will eventually hydrate with an expansion which may or may not cause disintegration, depending upon the size of the grains and the elasticity of the hardened colloidal crust sur- rounding them. Michaelis' theory has been partially verified by the microscope. Sec- tions of hardened Portland cement paste have revealed the colloidal struc- ture surrounding grains of unattacked clinker. In fact Stern * estimated that only half of the cement grains are attacked by water in ordinary pastes of cement. That the attack of water is incomplete may be proved by holding the broken ends of cement briquettes in contact for several days after which cohesion will have taken place, or by regrinding said pastes and molding new specimens. It has been demonstrated that the pc^wder formed by crushing and grinding neat cement briquettes has cementitious properties and briquettes made after a second regrinding have possessed a low strength. Messrs. Klein and PhiUipsf after extensive microscopic investigations *Chemiker Zeitung, 1908, No. 47 and 85; Slahl u. Eisoi, Vol. 28, p. 1542; Mitt. Kgl. Malerialprufungsamt, Vol. 27, p. 7, and Vol. 28, p. 173. t Technologic Paper No. 43, U. S. Bureau of Standards, April, 1914. NATURE OF PORTLAND CEMENT 309 on the hydration of Portland cement summarized their results as follows : " The hydration of cements is thus brought about by the formation of amorphous hydrated tricalcium aluminate with or without amor- phous alumina, the aluminate later crystallizing. At the same time sulphoaluminate crystals are formed, and low-burned or finely ground lime is hydrated. The formation of the above compounds begins within a short time after the cement is gauged. The next compound to react is tricalcium silicate. Its hydration may begin within twenty-four hours, and it is generally completed within seven days. Between seven and twenty-eight days the amorphous aluminate commences to crystallize and beta-orthosilicate begins to hydrate. Although the latter is the chief constituent of the American Portland Cements, it is the least reactive compound. The early strength (twenty-four hours) of cements is probably due to the hydration of free lime and the aluminates. The increase in strength between twenty-four hours and seven days depends upon the hydration of tricalcium silicate, although the further hydration of aluminates may contribute somewhat. The increase between seven and twenty-eight days is due to the hydration of beta-calcium orthosilicate, but here are encountered opposing forces, in the hydration of any high- burned free lime present and in the crystallization of the aluminate. It is to this hydration that the falling off in strength between seven and twenty-eight days of very high-burned high-limed cements is due, whereas the decrease shown by the high alumina cements is due to the crystalliza- tion of the aluminate. Finally, the iron in the cement is resistive to hydration and does not form any definite crystalline hydration products, but occurs as a rust-like liiaterial." " The last statement is perfectly true for the cements we have examined and contains nothing derogatory to the so-called iron cement." Further researches at the Bureau of Standards by Bates and Klein, (see Technologic Paper 78) indicate that hydrated dicalcic silicate hardens into a granular porous mass which is susceptible to mechanical break- down when exposed to the crystallization of salt solutions; also, that hydrated tricalcic silicate forms a very dense structure of colloidal nature interspersed with crystals of lime hydrate, and consequently is subject to relatively large volume changes if alternately wetted and dried. It appears, therefore, that in good Portland cements these constituents should be well balanced with the dicalcic silicate slightly in excess. Under such conditions a maximum density of structure with a minimum coef- ficient of hydroscopic expansion will result. 310 PORTLAND CEMENT MODERN METHODS OF MANUFACTURE 338. Growth and Importance of the Portland Cement Industry. — On account of the many excellent properties possessed by Portland cement, its great field of usefulness, the widely distributed sources of the raw materials from which it is made, its cheapness, and the decline in the supply of timber, the Portland cement industry has had a marvelously rapid growth. Although the process of manufacture of this material was patented in 1824, by Joseph Aspdin, of Leeds, England, it was not until 1859 that any considerable quantity was used in England, and not until 1875 that any progress was made in the manufacture of this cement in the United States. During the latter year, the pioneer Portland cement plant in the United States was started by Messrs. D. O. Saylor, E. Rehrig and A. Woolever at Coplay, Pa. The plant bearing Saylor's name is still running to-day with a very much increased capacity. An estimate of the rapidity of growth and the economic importance of this industry may be formed by comparing the quantity produced in 1880 — 42,000 bbl. — with the output for the United States in 1916—91,521,198 bbl. The value per barrel at mill in 1880 was $3, in 1916 it was 11.06. 339. Raw Materials. — In general the calcareous ingredients are pres- ent in raw materials in the form of lime carbonate (CaCOa) and the siUca and alumina are combined in the form of clay or other argillaceous ingre- dients. These essential ingredients are proportioned in accordance with Newberry's rule or some similar method. Arranged in order of importance, the raw materials most commonly used in the manufacture of Portland cement and the parts of the United States in which they are employed are: Where Used in Making Port- land Cement Materials Calcaeeods Argillaceoos 1. Limestone + Shale or Clay Widely used. Eastern N. Y., Mich., 111., Ind., Cal., la., Kan., and Tex. 2. Limestone + Cement rock Eastern Penn., N. J., Cal., and Kan. 3. Limestone + Blast furnace slag Illinios, Ohio, Penn. 4. Marl + Shale or Clay Central N. Y., Ohio, Mich., Ind. Limestone for the manufacture of Portland cement should be soft and consist largely of calcite or calcite and clay. If 20 per cent or more of clay is present with the calcite it is called cement rock. The limestone should not contain over 5 or 6 per cent of magnesium carbonate and should be comparatively free from sulphur and quartz. According to Eckel * phosphorus pentoxide (P2O5) is also an undesirable element. * Eckel's Cements, Limes and Plasters, p. 389. MODERN METHODS OF MANUFACTURE 311 Marl, another calcareous substance much used in the wet process of manufacture, is a soft deposit found in the bottoms of shallow lakes, swamps and extinct fresh- water basins. It should conform to the restric- tions placed upon limestone and be free from sand and gravel. For origin and composition of clays, reference should be made to Art. 275, Ch. VIII. With reference to the proportions of the constituents of clay suitable for Portland cement manufacture, Meade states that the ratio of the silica to the alumina content should be between 2.5 and 4 to 1, that there should not be more iron oxide than alumina, and that the alkalies and magnesia should each be less than 3 per cent.* A considerable proportion of sand larger than a 100-mesh sieve renders the clay unfit for cement manufac- ture. Blast furnace slag suitable for the manufacture of Portland cement should be basic in character. The analysis should conform roughly to the following: Two-fifths to one-half lime, one-third silica, one-eighth to one-sixth alumina plus iron oxide, magnesia less than 3 per cent. Calcium sulphide is considered undesirable. The first step in the process of manufacture of Portland cement is the winning of the raw materials from nature. Hard- raw materials are blasted, loaded on to small cars, and drawn to the cement mill. Soft materials like marl or clay are dug or excavated by steam shovel or dredge, depending upon the nature of the deposit. Such materials are often pumped directly to the mill. Slag is granulated into a sand-like substance by running the molten material from the blast furnace into a vat of water. It is then loaded on cars by clam-shell buckets and transported to the cement plant. The Dry Process of Manufacture 340. Preparation of Raw Materials. — In general, only the compara- tively dry raw materials, such as limestone and cement rock, limestone and shale or clay, and limestone and blast furnace slag, are used in the dry process of manufacture of Portland cement. The steps in the process of manufacture are: 1, crushing of raw materials; 2, drying; 3, grinding; 4, proportioning; 5, final pulverizing of raw materials; 6, burning; 7, cooling the clinker; 8, adulteration to retard set; 9, reduction of clinker to an impalpable powder; 10, seasoning of cement; 11, bagging. The order of the first four of these operations varies at different plants and it is dependent to some extent upon the character of the raw materials. Crushing of the hard materials is largely done in gyratory crushers, although a few plants pass material from the quarry through toothed rolls. Generally, the material must be passed through a large and a small crusher * Meade's Portland Cement, p. 54. 312 PORTLAND CEMENT in order that the requisite fineness for successful operation of the grinding mills may result. Since it is necessary to have the raw materials in an approximately dry state before grinding, most of these materials must be passed through some sort of a drying apparatus. In most plants a dryer consists of a hollow steel cylinder about 50 ft. long and 5 ft. in diameter, revolving about its geometrical axis which is inclined at a small angle with the horizontal. The raw materials enter at the upper end and pass out at the lower end of Fig. 1. — A Dry Grinding Preliminator. (AUis-Chalmers.) the cylinder. The source of heat, which is commonly an attached furnace or waste gas from the rotary kilns, enters at the lower end and passesrfiut at the upper. To increase the circulation of the materials through the hot gases, lugs which serve to elevate and scatter the charge, are riveted on the inside of the dryer. 341. Preliminary Grinding. — In order to secure proper combinations in the kiln between the lime, silica, and alumina, it is necessary to have the raw materials ground so finely that 95 per cent will pass a No. 100 mesh. It has been found economical to do this grinding in two stages, designated preliminary and final. MODERN METHODS OF 'MANUFACTURE :3i3 Preliminary grinding is quite extensively done in some type of ball mill. One of the latest forms of such machine is the preliminator shown in Fig. 1. The preliminator consists of a cylindrical steel drum lined with chilled iron or hard steel. To permit revolution of the machine the drum heads at either end are equipped with trunnions. The right end of the drum is also encircled by a large gear by means of which the mill is rotated. Through a hole in the left trunnion raw material is fed into the mill. Pulverizing is accomplished by the rolHng and hammering received from six to eight tons of forged steel balls which range in diameter from 2\ in. to 5 in. The ground material passes through narrow slots in the vertical diaphragm shown near the right end of the mill and Fig. 2.— a Tube Mill. (Allis-Chalmers.) is pitched through the right trunnion by a series of radial fins which are fastened to the center of the vertical diaphragm. Working on 3-in. limestone and shale, a preliminator 8 ft. in diameter and b\ ft. long can pro- duce about 50 bbl. per hour of material which will pass a No. 20 mesh. 342. Proportioning. — Since correct proportioning of the raw materials is of prime importance in securing a clinker of proper constitution, accurate automatic scales are installed for weighing the raw materials. This operation can generally be done to best advantage after the preliminary grinding of the raw materials; although at some plants, where the raw mix runs very uniform in character, the proportioning is done earlier in the process. 343. Final Grinding — At many plants the finishing stage in the grinding process is performed in a tube mill (Fig. 2) . This mill is also steel- jacketed, cylindrical in shape and revolves about its geometrical axis. 314 PORTLAND CEMENT Commonly, such a mill is about 22 ft. long and 5 or 6 ft. in diameter. In order to form a surface with a high resistance to abrasion, the inside of the drum is lined either with trap rock, silex, or chilled cast iron. The mix from the preliminary grinding machines is fed by a worm through the left trunnion of the mill. Pulverizing is accomplished by means of approximately 15 tons of flint stones, the largest of which is about the size of a goose egg. Lately the efficiency of the tube mill has been considerably increased by dividing the drum into two unequal compartments with a vertical diaphragm similar to that used in the Pulley Rim on Lower Half Pulley Body eli minating shearing stress in bolts. Al! wearing parts run in oil maintained by Oil Retainer increasing their life and re- ducing oil consumption. Double Screen allowing total height of 36 inches. Lower half takes most wear, minimizing screen mainte- nance. By removing 4 bolts. Up- per Cross Bar, Pulley Body, and Shaft can be raised, allowing easy replacement of Roll and Die. Lower Journal Bearing separate from Pulley Body, decreasing cost of wearing parts. Increased screening area allows freedom of discharge from mill, making it prac- tically dustless and produc- ing a larger output or a finer material. Fig. 3. — ^A Giant Griffin MiU with Improvements. preliminator. In this type of machine the raw mix is fed through the left trunnion into the longer compartment and ground by means of flint stones. It then passes through the diaphragm into the short finishing compartment where it is acted upon by small metal balls or slugs. From the finishing compartment the powdered mix passes through a second diaphragm into the right trunnion, whence it is discharged onto a belt conveyor. A 6 X 22-ft. tube mill will grind about 5 or 6 tons of raw material per hour, or it will reduce about 24 bbl. of ground chnker to cement in the same interval of time. By making use of a short finishing com- partment in its tube mills, the Allis-Chalmers Company claims that an increase in both quantity and fineness of product can be secured at a somewhat greater expense for power. Fig. 3 shows a sectional elevation of a Griffin mill which is used in MODERN METHODS OF MANUFACTURE 315 many plants as a substitute for the tube mill. In this machine the material enters the pan at the bottom and is forced upward between the circular die and revolving ring. The latter is rotated at approximately 150 r.p.m. by means of the pulley and universal joint at the top of the shaft, so that there i& developed between the die and ring a very large centrifugal force which rapidly pulverizes the material. A current of air car- ries the fine material upward through screens in the top of the pan while the coarse ma- terial falls to the bottom and is reground. Another type of grinding mill often used on raw material is the Lehigh-Fuller, shown in Fig. 4. In this mill four 12-in. steel balls are pushed around an annular die by means of horizontal radial arms set 90 degrees apart on the vertical shaft. Since the shaft runs at 160 r.p.m. the balls exert a large force against the die. The ma- terials are fed to the mill from a hopper on top, which is pro- vided with a feeder operated from the mill shaft. The ma- terial is discharged by the feeder between the balls and the die and is thus reduced to an im- palpable powder. By means of a centrifugal fan operating in the separating chamber just above the pulverizing zone, the powdered material is drawn into the separating compartment. The ground material is drawn through the circumferential screens surrounding the separating chamber and forced through the discharge spout by a lower fan, shown below the ball in the figure. There are several other types of grinding machines, the Maxecon, Huntington, Raymond, Sturtevant Ring-Roll mill, etc., but lack of space prohibits a discussion of them. 344. Burning. — The purpose of burning the raw mixture is to secure a union of the different constituents in the form of mineral compounds, Fig. 4. — A 42-in. Fuller Mill Equipped with Fan Discharge. 316 PORTLAND CEMENT primarily the formation of silicates of lime and alumina as we have seen in Art. 336. After the raw materials have been proportioned, intimately mixed, and very finely ground, the powdered product is conveyed to kilns to be burned. Formerly the vertical intermittent type of kiln, somewhat like that used in the production of natural cement, was employed to burn Portland cement. In Europe, use is still made of this type, and in Ger- many the Hoffman ring kiln, is quite extensively employed. However, in the United States the continuously operated rotary kiln is favored to the exclusion of all others. From Fig. 5 one can obtain a notion of the appearance of a rotary kiln. It consists of a cyhndrical jacket made of riveted steel plates lined with Fig. 5. — A Rotary Kiln. refractory fire bricks. The lower end of this cyhnder is covered by a detachable hood provided with two openings. Through one of these openings is passed a nozzle for the admission of fuel. The fuel most commonly employed is powdered coal. In order to introduce the coal into the kiln and to secure both rapid and complete combustion, it must be so finely pulverized that 95 per cent will pass a No. 100 sieve. The coal is blown through the nozzle by an air blast. The second opening in the hood is provided to enable the operator to observe the interior of the kiln during calcination. The steel jacket is surrounded by two or more heavy steel tires, by means of which it is rotated on friction roller bearings. These bearings are so adjusted that the axis of the kiln has an inclination with the horizontal of about f in. per foot. By thus inclining the axis, the material is slowly moved downward from the upper end as the Idln is rotated. Rotation is produced by a motor placed near the center and geared to a girth gear attached to the jacket. The upper end of the kiln enters a brick flue from which the products of combustion escape to the stack. Passing through this flue is an inclined spout which discharges the finely powdered raw material into the kiln. MODERN METHODS OF MANUFACTURE 317 Soon after the entrance of the material, it begins to ball up into small marble-like shapes. Dm-ing the first half of the passage toward the hood any entrained water is evaporated and the material is heated to a tem- perature sufficient to expel carbon dioxide (CO2) from the limestone. By the time the clinker has reached within a few feet of the lower end of the kiln its temperature has risen to 1400 or 1500° C, all carbon dioxide sulphur, and organic matter have been expelled, and the Uttle soft yellow- ish-brown balls have now partially fused into hard, greenish-black clinker.* At many plants the degree of calcination is left to the skill of the burner, who regulates the speed of rotation of the kiln so that the clinkering zone is kept back a few feet from the discharge end. He is able to judge of the position of this zone by greenish flame which is emitted when the material begins to burn and form clinker. Under ordinary conditions a speed of 30 or 40 revolutions per hour secures the requisite degree of calcination. At the end of about one hour the burning process is completed and the clinker falls out of the kiln through a trap in the lower side of the hood, whence it is conveyed to the cooler. The clinker is quite irregular in shape and varies from the size of a hen's egg down to a buckshot. It is very hard, has more or less vitreous luster, and is generally black or greenish- black in color. Most modern kilns are from 100 to 150 ft. long and from 6 to 9 ft. in diameter. At present the tendency is toward the use of longer kilns. The capacity of kilns of the sizes mentioned will vary from 400 to 800 bbls. per day. In producing a 376-lb. barrel of Portland cement, from 600 to 700 lb. of raw material and 80 to 120 lb. of coal is consumed. 345. Grinding of the Clinker. — To facilitate grinding, the chnker is now cooled by spraying with a water jet and passing through a cooler. Frequently the cooler consists of a vertical or horizontal steel cylinder equipped with devices for agitating the material. As the clinker passes through the cooler, it meets a forced air draft, which rapidly lowers its temperature. At some plants the clinker is cooled out of doors. After ' cooling, about 2 per cent of gypsum is added to retard the time of set of the resulting cement. At many plants the adulteration is done after the chnker has been through the ball mill. In grinding the chnker the same kind of machinery is generally used as is employed in pulverizing the raw materials. Whatever grinding machinery is used, the resultant fineness must be such that 78 per cent will pass a sieve with 200 meshes per linear inch.f On account of the fact that a finely ground cement will make a stronger mortar than a coarsely ground one, many plants endeavor to secure a degree of fineness considerably in excess of *For further information concerning the chemical changes in a rotary kiln, see R. K. Meade's Portland Cement, pp. 176 to 199; •f See Standard Cement Specifications of the A. S. T. M. 318 PORTLAND CEMENT the above figures. At present, however, the economical limit to which fine grinding may be carried seems to be about 85 per cent through a No. 200 sieve. s a o. S o O O •a a o -a 3 to 6 MODERN METHODS OF MANUFACTURE 319 346. Storage and Bagging of Cement. — From the grinding mills a conveyor carries the cement to the storage bins, in which it is generally kept for a few weeks before being bagged for shipment. This seasoning period seems to improve the quality of the cement. In support of this statement, it seems quite possible that unburnt lime might be sealed within the clinker during the burning period and be liberated during the grinding process. Upon exposure to the air such particles of lime would absorb carbon dioxide (CO2) and become calcium carbonate (CaCOs). This substance is not affected by the addition of water, is inert during the setting of the cement, and, therefore, does no harm. In accordance with the demand of the trade the cement is conveyed from the storage bins to the packing house. Here it is automatically weighed and packed by machines sometimes in wooden barrels containing 376 lb., net, but more frequently in cloth sacks which hold 94 lb. net. The cement is now ready for shipment. 347. Plan of Cement Plant. — In order that an idea of the arrange- ment of a cement mill may be gotten. Fig. 6 showing a plan and vertical section of the Hudson Portland Cement Company's plant has been inserted. The Wet Process op Manufacture 348. General. — By far the larger portion of the cement manufac- tured in the United States is made by the dry process. Under favorable conditions, however, the wet process is successfully and economically employed. The raw materials most commonly used in the wet process are marl and clay. Preparatory to mixing the materials, the marl is often screened and pumped, in the form of thin mud, from the deposit directly into large storage basins situated near the kilns. The clay is dried, for convenience in calculating the mixtures, and pulverized in an edge runner or similar mill, Fig. 1, Ch. VIII. Then, proper quantities of the two materials determined by a chemical analysis are weighed out and mixed by passing through a pug mill. This wet mixture, or slurry, from the pug mill con- sists of about two-thirds water and one-third marl and clay. The slurry is next pumped into large vats, in which it is continually agitated to main- tain the uniformity of the solution. From these vats samples are taken for analysis; and, if necessary, additions of marl or clay are made until the desired composition is obtained. The slurry is now pumped into especially constructed rotary kilns and burned. The succeeding stages in the wet process of manufacture are similar to those described under the dry process. 349. Comparison of Wet and Dry Processes. — The chief advantage possessed by the wet process is the well-regulated control which is obtained 320 PORTLAND CEMENT over the raw mixture. On the other hand, the wet process requires about one-third more fuel per barrel of cement than the dry process and the kiln capacity is about 25 per cent less than in the dry process. Although this increase in the cost of production by the wet process is partially offset by the higher cost of grinding the raw materials in the dry process, yet it is only when the raw materials can be gotten under very favorable con- ditions that a wet process cement can be made at a price which can com- pete with a cement made by the dry process. EFFECTS ON PROPERTIES DUE TO CONDITIONS OF MANUFACTURE OR TESTING 350. Conditions Affecting Soundness. — Although some of the effects of the chemical elements present in Portland cement have already been referred to it will not be amiss to recall them in considering the properties affected. The cause most commonly ascribed for unsoundness in Portland cement is the hydration of uncombined lime incased within the cement particles. High burned, coarsely ground, free lime hydrates slowly, but ultimately with sufficient violence to endanger the integrity of the surrounding mortar. Exposed, finely ground, free lime, in small percentages at least, will hydrate before the cement sets and produces no injurious effect. The presence of uncombined lime may be the result of either underburning the clinker or overliming the mixture before burning. Oftentimes freshly ground cement will be unsound due to the presence of uncombined lime which may be partially exposed in the grinding process. By allowing the cement to aerate for two or three weeks, thus allowing the Ume to hydrate, it is often possible to overcome unsoundness.* Other chemical elements which may produce unsoundness are mag- nesia and the alkalies. In most cements the proportions of these elements are well within the danger limit. It is probable that the action of the retardant assists in overcoming unsoundness, since it tends to hold the mixture in a plastic state and permit the hme to slake. Meade cites several examples of unsound cements which were rendered sound by adding from 0.5 to 3.0 per cent of plaster of Paris, f Fine grinding of both raw materials and the clinker are very essential if a sound cement is to be secured. Fine grinding of the raw materials makes possible the production of a more homogeneous mixture before * For example see Proc. A. S. T. M., Vol. 3, p. 376. t Portland Cement, p. 474. See Free Lime in Portland Cement by Kiefer, Chem. Engr., Vol. 15, p. 219; also Soundness Tests of Portland Cement, hy Taylor, Proc. A. S. T. M., Vol. 3, p. 374. EFFECTS OF PROPERTIES DUE TO CONDITIONS 321 burning so that a uniform distribution of the hme content may obtain. It has also been shown that coarsely ground cements which are unsound in the accelerated test may often be rendered sound by fine grinding.* Remembering that the addition of free lime in small percentages does not effect the soundness of a normal Portland cement, it seems evident that the coarser grains of cement may imprison minute particles of uncom- bined lime which do not become hydrated until after the cement has set. The expansion, which then occurs due to the crystallization of calcium hydrate, produces disintegration. This is entirely in accord with Michaelis' views on hardening and unsoundness (Art. 337). The reason- ableness of the above explanation of the action of the coarser particles in promoting unsoundness is made more evident by the experiments of 1000 000 iT 800 d \700 ^ 600 g'500 p ffi WO to I 300 I 200 100 Age = 1 days Age = 28 days ^^«« Vt.,, ^ k. ^ \ _^ ^,--' ^ ^ J-i^^ l;i "^ 90 95 100 80 85 90 Per cent Passing a No. 200 Sieve Fig. 7. — The Tensile Strength of the Same Cement when Ground to Different Degrees of Fineness. Each point represents the average of five briquettes. (Meade in Proe. A.S.T.M., Vol. 8, p. 412.) Brinckley.f The results of his tests show that the particles of a cement passing a No. 100 and caught on a No. 200 sieve may have some hydraulic properties but that pats made of them break down entirely when subjected to the A.S.T.M. accelerated test. (Art. 419.) 351. Conditions Affecting Strength. — Recapitulating what has already been stated concerning the effect of various chemical elements upon the strength of Portland cement, we will remember that either a high lime or high alumina content tends to make the cement strong at an early age. Gypsum and plaster of Paris in small percentages also tend to increase the strength of Portland cement, but when present in quantities larger than 3 per cent these substances produce variable effects, t However, * Portland Cement, p, 472. t Engr. Record, Vol. 61, p. 212. jSee results of experiments given in Eckel's Cements, Limes, and Plasters, pp. 536-544; also a paper by P. H. Bates in Proc. A. S. T. M., Vol. 15, p. 126. 322 PORTLAND CMMBNT it is certain, as has been mentioned before, that the combinations formed by these elements, not the percentages in which they are found, are the factors influencing the strength. In addition to the effects of the chemical constituents, the strength of cement is greatly influenced by the degree of burning, the fineness of grinding and the aeration it receives. If imderburned the cement is liable to be deficient in strength. Assuming that the clinker has been properly burned, increasing the pro- portion of flour or very fine parti- cles will cause an increase in the mortar strength. Sometimes the neat strength is decreased by in- creasing the percentage of flour, but experiments by P. H. Bates * show that this is not, in general, true. The effect of fine grinding is well shown in Figs. 7 and S.f In inter- preting these diagrams one must bear in mind that neither the 200- mesh sieve nor any other which has ever been made is fine enough to separate the flour possessing the maximum cementing power. In fact, Meade has shown that cUnker ground so that it would barely pass the 200-mesh sieve had but httle cementing power. J Since, however, the same cement was subjected to the same method of regrinding in each of the tests illustrated, sittings on the given sieves furnished indices of the fineness of the particles. In Bates' experiment* the effect of fineness of grinding on the com- pressive strength of 1 : IJ : 4J concrete was also determined. Ten brands of cement, varying in fineness from 75.4 to 82.2 per cent, passing a 200-mesh sieve, were used as received and also after being regroimd so that the fineness of the individual brands varied from 86.8 to 92.7 per cent passing the same sieve. At an age of twenty-eight days the concrete made from the finer cements exhibited an average streng^i of 28 per cent greater than the concrete made from the normal cement. At ninety days the concrete made from the finer cement averaged 17 per cent, more strength. * Proc. A. S. T. M., Vol. 15, p. 126. t See also Taylor's Practical Cement Testing, p. 107; Proc. I. A. T. M.. 6th Congress, IBs and ISj. t Engr. Record, Vol. 58, p. 181. 1 ¥r. 2 Yr. 3 Yr. Age of Mortar Fig. 8.— The Effect of Fine Grinding of Portland Cement on the Compressive Strength of 1 : 3 Mortar. (Tetmajer.) EFFECTS OF PROPERTIES DUE TO CONDITIONS 323 From the above it appears evident that a well-burned, finely ground cement can carry a greater proportion of sand than a more coarsely ground cement and will be more economical, provided the cost of the additional grinding does not offset the advantage derived. The amount of " seasoning " or aeration which the cement has received subsequent to final grinding also exercises an important effect upon its strength. In general, it may be said that exposure of cement to the air is beneficial only when it is received in an unsound condition. Further seasoning than that required to remove unsoundness is detrimental to strength. The results of tests made by W. P. Taylor * on cement stored in a cloth sack in his laboratory show that storage beyond three months was detrimental to the strength of both neat and mortar briquettes. 600 S an 100 ^^^ X p ^ __^ ::= ^> V 1000 ..v?^ , ,.— -° s oto* ■sT^J. ^"' '- v2.- ^^ •Jl' •' ^ n — ^■ ■^ r Ver yLu' "py D- I / '<> (fr^ _... ^■ J ^'' ^ f ' / v«- J?-' ^■' ijs \'f ^. V CO if ^■- \j TE NSI 5N \! c 3MP RES SIO < \ f \ 36 70 105 140 176 210 2J5 230 315 350 385 36 70 105 UO 175 210 2J6 280 315 360 386 Age in Days Age in Days Fig. 9. — Effect of Long Storage on the Strength of 1 : 3 Portland Cement Mortar. (Tetmajer's Communications, Vol. 7, p. 15.) (Briquette is the term applied to the standard form of tensile test-piece for cement mortars shown in Fig. 11, Ch. XII.) Both kinds of speci- mens showed the greatest effects at early ages, the mortar briquettes being weakened more than the neat by the aeration. Under the cap- tion, " The Relative Value of Fresh and Caked Cement," Engr. News, Vol. 55, p. 67, may be found the results of tests by a number of different investigators which indicate, in the main, that fresh cement is preferable. A number of tests made at Stevens Institute of Technology f under artificial aging conditions also point to the conclusion, that Portland cement decreases in strength if aerated for a considerable length of time. Fig. 9 shows results obtained by Tetmajer. The effect of the percentage of mixing water on the strength of 1 : 3 standard sand mortars is shown in Fig. 10. From these results it appears * Practical Cement Testing, p. 104. t Stevens Indicator, Vol. 26, p. 158. Missing Page EFFECTS OF PROPERTIES DUE TO CONDITIONS 325 that either very dry or very wet mixes, which are molded in accordance with the A.S.T.M. method, are less strong than the mixtures of medium consistency. If briquettes are removed from the water bath before testing a con- siderable effect, dependent upon the time they are allowed to dry, may be produced upon their strength. Fig. 11 has been compiled from the results of experiments by A. J. Barclay,* on four different brands of cement. Similar tests have been reported by Prof. J. L. Van Ornum in Eng. News, Vol. 51, p. 24, and by Prof. R. P. Davis in Eng. News, Vol. 61, p. 581. 352. Conditions Affecting the Time of Set. — ^As we have already stated the theory of setting and hardening of Portland cement is not completely Time after Bemoval from Bath Fig. 11. — Effects of Drying on the Tensile Strengths of Neat and 1 : 3 Standard Sand Mortars. Age at removal from bath was twenty-eight days. Each result rep- resents four tests. known; it is not possible, therefore, to formulate definite rules for the effect which various chemical elements will produce upon the setting of cement. However, inasmuch as this property is very difficult to con- trol and has such an important effect upon the value of the cement, cer- tain commonly observed facts and the results of trustworthy experiments should be stated. The things which influence the setting properties of the cement are its composition, the percentage of retardant, degree of calcination, fine- ness of grinding, aeration subsequent to grinding of chnker, percentage of water used in gauging the paste, the temperature of the mixing water * Thesis, University of Wisconsin, 1912. 326 PORTLAND CEMENT and cement, the humidity and temperature of the moist closet or of the atmosphere in which the cement paste is placed, and the amount of ma- nipulation the paste receives. The effect of lime, silica and aliimina in controlling the set have already been referred to in Art. 330. In addition to properly regulating the proportions of the above elements, or adjusting hydraulic and activity indexes which amounts to the same thing, some provision must be made by the manufacturer to increase the time of setting of freshly ground cement so that it will be sufficiently slow-setting for use in construction. This is commonly done by mixing gypsum (CaS04+2H20) or plaster of Paris (CaS04+4H20) with the clinker before final grinding, or by adding one of these compounds just after the cUnker has received preliminary grinding. Although these methods are manifestly imperfect since it is impossible to obtain an absolutely homogeneous mixture with either, yet they are the best now devised. (The addition of gypsum before cal- cination causes it to decompose into lime and sulphur trioxide. Since the latter is liberated in the kiln the resulting effect on the time of set is nil.) Experiments by Le Chatelier and later ones by Meade and Gano,* have shown that anhydrous calcium sulphate, plaster of Paris or gypsum may be used as the retardant. The experiments of Meade and Gano, however, indicate that increasing any one of these elements up to 2 or 3 per cent (the limit will vary with the chemical composition of the cement) retards the set but further additions of plaster of Paris cause the setting time to decrease. The introduction of 10 to 20 per cent of plaster of Paris will generally cause the cement to become quick-setting again. The latter effects were not observed in the tests made with gypsum (CaS04+2H20) or dead burned gypsum (CaS04). In addition to the above-mentioned elements, small percentages of calcium chloride f and sodium carbonate also { have a marked influence upon the setting properties of cement. Nihoul and Dufossez showed that strontium sulphate, barium sulphate, calcium sulphate, and calcium aluminate in small percentages also effected a rapid increase in set. Often an underlimed cement will become quick-setting after seasoning. This fault can be overcome by increasing the lime content in the raw mate- rials or the remedy mentioned below may be applied to the cerhent. Examples of cements which become slower setting with age are common, and some cases have been cited where cements slow-setting when fresh have become quick-setting and then slow-setting after aging for some time. * Chemical Engineer, Vol. 1, p. 92; see also the tests of Nihoul and Dufossez, abstracted in Jour. Soc. Chem. Industry, Vol. 21, p. 859. t Engr. News, Vol. 53, p. 13. t Concrete-Cement Age, Nov. 1912, p. 68. EFFECTS ON PROPERTIES DUE TO CONDITIONS 327 Quick-setting may often be avoided by adding to the cement, 1 or 2 per cent of hydrated lime or the fraction of a per cent of plaster of Paris. The fineness to which a cement is ground produces an effect upon its time of set as the results in Table 1 * indicate. In general, it may be said that the more finely the cement is ground the more rapidly will it set. However, the relation between time of set and fineness as measured by 2 Time of Set in Hours Final Fig. 12. — Effect of Percentage of Mixing Water on the Time of Set of Portland Cements, as Determined by the Gillmore and Vicat Methods. the 200-mesh sieve is not rectilinear as inspection of the table will show. The results also indicate that grinding to a fineness of 90 per cent through the No. 200 sieve would not decrease the time of set below the customary limits. The effect of the percentage of mixing water upon the time of set is well illustrated in Fig. 12 f which also furnishes a comparison of the * From a paper by Meade, Proc. A.S.T.M., Vol. 8, p. 410. t From Tests of Metals, 1901, p. 492. 328 PORTLAND CEMENT results gotten with the Gillmore and German methods. The latter is essentially the same as the Vicat method commonly employed in Amer- ica. (The Gillmore and Vicat methods are described in Art. 425). Another comparison of the Vicat and Gillmore methods is afforded in Table 4. TABLE 1.— INFLUENCE OF FINE GRINDING UPON THE INITIAL SET OF CEMENT (Meade) Per Cent Setting Time in Minutes of C ement No. ;■ No. 200 Sieve, 1 2 3 4 5 6 7 8 75 255 105 120 240 240 200 100 115 80 246 106 115 200 210 190 100 105 85 192 100 100 180 110 175 90 100 90 75 100 95 115 55 100 80 75 95 12 22 60 60 15 25 25 30 100 2 6 35 30 5 2 5 10 The influence of temperature upon the time of set is shown in Table 2. Cements stored in warm rooms will, in general, be quicker setting than those stored in a cold atmosphere. Cold mixing water retards set while warm water accelerates it. For the range of temperature ordinarily met in the laboratory say 65° to 75° F., the effect is not very marked. How- ever, due consideration of the influence of temperature should be given TABLE 2— INFLUENCE OF TEMPERATURE ON THE SETTING OF PORTLAND CEMENT f Sample Initial Set in Minutes. Temperature ° F. Final Set in Hours. Temperature ° F. No. 100 80 60 40 100 80 60 40 1 2 3 4* 5 6* 7* 8 9 10 11 12 n 3 4 5 6 7 9 10 11 11 19 15 4 5 10 9 10 12 10 15 15 13 32 35 6 6 15 15 14 15 15 35 20 15 60 70* 13 8 20 30 25 20 17 40 57 30 120 360 U 1 i i 1 li 3J J 3 2i 3 3i u li 3 4 n 2 6 1 5 3 6 6 2 If li 1 2 2i 7 li 6 3i 7 7 21 21 6i 6 2i •2i 12 If 10 6 15 22 * Contain a considerable admixture of Kentish Rag. t From Butler's Portland Cement, p. 267. EFFECTS ON PROPERTIES DUE TO CONDITIONS 329 in reporting on cements which are quick-setting in a hot laboratory but which wQl be used in a colder atmosphere. Cements exposed to a thoroughly saturated atmosphere will set much more slowly than those exposed to a dry atmosphere. If, however, a considerable proportion of moist CO2 is present in the air, the experiments of Gadd * seem to indicate that the setting time will be greatly reduced. By lengthening the time of mixing and by prolonged troweling of the surface mortars it is also possible to considerably delay the time of set. 353. Conditions Affecting Fineness. — The percentage of flour con- tained in a cement is principally dependent upon a number of variables in the method of manufacture. The chemical composition and the degree of calcination influence the hardness of the clinker and conse- quently affect the fineness to which the clinker is ground. Clinker high in iron or silica is apt to be hard and difficult to grind. The same is true of a hard-burned clinker. It does not always follow, therefore, that a difference in fineness indicates the relative quality of two cements since the one more finely ground may have been underburned. Furthermore, the fineness will be influenced by the time of grinding and the character of the pulverizing machinery employed in grinding. To some extent seasoning also affects fineness. It has been found that cement becomes slightly finer with age provided it does not absorb too much moisture. This is probably due to the decrepitation of the coarser grains resulting from hydration of the embedded lime particles. In testing the fineness of cement, the precaution which should be employed and the errors in sieves are mentioned in Art. 409 and 410. 354. Conditions Affecting Specific Gravity. — It is probable that no property of cement has had its importance more overrated than specific gravity. As a matter of fact, in the majority of cases, the specific gravity affords little if any information concerning the relative value of two cements made from different materials, unless the average specific gravity of each brand is known. The test is chiefly used to detect abnormal conditions in a brand of known specific gravity. The detection of adulteration by this test is dependent upon the specific gravity of the adulterant and upon the proportion used. A simple computation reveals that a clinker having a specific gravity of 3.15 may be adulterated with 14.3 per cent of limestone having a specific gravity of 2.8 before the specific gravity of the mixture will be reduced below the requirement of the specifications, 3.10. If, instead of lime- stone, a blast-furnace slag or natural cement with a specific gravity of 3.0 be empiloyed, 6.7 per cent of the adulterant may be used before the specific gravity of the adulterated cement is reduced 0.01. Furthermore, it is *See Cement Concrete Age, Cement Mill Section, Feb., 1914; also paper by G. M. Williams, Proc. A.S.T.M., Vol. 14, p. 174. 330 PORTLAND CEMENT permissible under the above methods of testing to ignite the sample if its specific gravity falls below 3.10. Experiments have shown that this procedure will raise the specific gravity of many adulterated mixtures considerably above the specified hmit. So it is evident that, although adulteration lowers specific gravity, a low result is not necessarily a sign of adulteration, nor is a high value an indication of the absence of it. Long seasoning is the chief cause of a low specific gravity in an im adul- terated cement. This is due to the fact that freshly ground cement when exposed to the air rapidly absorbs moisture and carbon dioxide. A month's seasoning will often reduce the specific gravity from 3.15 to 3.08, or thereabouts, and a long period of seasoning may reduce it to 3.00.* Drying seasoned samples at 212° F. will slightly raise the specific gravity while igniting will, in general, raise the specific gravity to the original value. Seasoning the cUnker lowers specific gravity. The chemical composition of a cement also affects its specific gravity. Cements with high contents of iron oxide will have specific gravities 0.05 to 0.10 higher than those with low iron contents, provided both have been subjected to similar storage conditions. Formerly the degree of calcination was supposed to affect the specific gravity, but numerous experiments have completely disproved this theory, f The effects of fineness of grinding upon specific gravity are shght. Very finely ground cements on account of the readiness with which they absorb moisture and carbon dioxide are likely to have lower specific gravities than cements made from the same materials but more coarsely ground. RESULTS OF VARIOUS TESTS ON PORTLAND CEMENT 355. General. — We shall now consider some results of tests on Port- land cement pastes and standard sand mortars. Only those results which are especially affected by the cement itself will receive attention herein. The effects produced upon mortars by variables in the aggregate will be considered in Ch. XIV.. 356. Strength Tests.— From an elaborate series of tests reported in Bulletin No. 331, of the United States Geological Survey, the strength- age curves shown in Figs. 13, 14 and 15, have been compiled. The brands of cement used in these experiments were Alpha, Atlas (western), Star, lola, Lehigh, Medusa and Vulcanite. The method adopted in making the tests was essentially the same as that advocated by the A.S.T.M. Each plotted point in the figures represents the average of 27 to 30 tests excepting in the diagram of the transverse tests, in which each point represents the averages of 150 tests. Table 3 contains the average results * For example see Chem. Engr., Vol. 6, p. 19; or Taylor's Practical Cement Testing, p. 48. t See Chem. Engr., Vol. 6, p. 17; and Proc. Inst, of Civil Engr., Vol. 166, p. 342. RESULTS OF VARIOUS TESTS ON PORTLAND CEMENT 331 of nine or ten chemical analyses made on each of the seven brands of cement and on the mixture of these brands. Table 4 gives the average results of nine or ten determinations on the physical properties of each of these cements. From these experiments it is seen that those cements 800 S^ ^1000 c ^ 800 600 1000 800 200 / --^ ^ .^ / Brand A '^^ ^ Brand B ^^^ ^^ ."" ""' ' -i -. i "' / r-' ^ ^^^ ^ ^-^^ J Brand C ^ / Brand D ^^^ \ .--' .-^ / / 1 ^^'"--.^ ^ — ^ / Brand E / Brand F ^^^^^ ( y ■"'' ^ /' ^ / f ^ ---^ 1 .^ "-^^^ 1 /^ Brand G ^ / Mixture 3f A - G 1 y ^■^-^ L..._^___ _- / 1 1 1 Neat Cement 1:3 Mortar -"-g % % a c \ i -8 s % ? 2 \ i Age in Days Fig. 13. — Variations in Tensile Strength with Age for Neat Portland and 1 : 3 Standard Sand Mortar Briquettes. developing low strengths when seven days old show the greatest propor- tionate increase in strength at all subsequent ages and that all of these cements exhibit practically the same strength after six months. On the other hand these results do not indicate that the cements which have 332 PORTLAND CEMENT low seven-day strengths become any stronger at the end of one year than those possessing higher initial strengths; neither do the slopes of 12000, 10000 8000 6000 4000 2000 12000 10000 ^ 8000 B ~~- 6000 g 4000 ^ 1 / y / Brand A / Brand B / f , ^-.- ———"'"'""'"" —— -•''' / ^^^ y ^ / / i / Brand C / Brand D / ' ""■ ,/ f '■ " ' ^ " ^ y^ 1 y Brand E / Brand F 1 ' ,,- _— — 1 -' ^^ -' — ^--''^ ^^^^ / ^^ / / Brand G / Mixture of A-G / I — — ,,,-' - ■'•'' / 1:3 Mortar I 2000 £ ^10000 s a 8000 a §> 6000 4000 2000 10000 8000 6000 4000 2000 r^ era ^ CO Age in Days FiQ. 14. — Variations in Compressive Strength with Age for Neat and 1 : 3 Staihdard Sand Mortar. (Specimens were 2-in. Cubes.) the age-strength curve at the one-year period indicate that cements of low early strength will ultimately become the strongest.* * The relative value of those two classes of cements and the advisability of speci- fying that the results of twenty-eight-day- tests should show a percentage increase over the seven-day values has been the cause of much controversy. See Engr. News, Vol. 54, p. 63, 124, 149, 206. RESULTS OF VARIOUS TESTS ON PORTLAND CEMENT 333 TABLE 3.— AVERAGES OF CHEMICAL ANALYSES OF PORTLAND CEMENTS A-G AND MIXTURES (See Figs. 13, 14, and IS) Percentage IN Cement. Element. A B C D E F G Mixture A-G Si02.... 21.99 20.75 20.88 21.61 23.25 22. U 22.47 22.01 AI2O3... 7.24 7.72 7.91 7.88 5.32 7.32 6.94 6.78 FejOs. .. 3.39 2.59 2.69 3.18 3.27 3.02 2.79 3.21 CaO.... 62.53 62.75 62.98 62.56 63.14 62.36 60.42 62.74 MgO.... 2.37 2.61 2.85 2.37 3.01 1.61 3.23 2.64 SO3 1.19 1.66 1.46 1.52 1.32 1.58 1.67 1.46 Undeter. 1.29 1.92 1.22 0.87 0.69 1.98 2.44 1.17 TABLE 4.— AVERAGES OF PHYSICAL PROPERTIES OF PORTLAND CEMENTS A-G AND MIXTURES (See Figs. 13, 14, and IS) I c D E F G 3.129 3.127 3.148 3.104 3.103 74.5 74.4 74,4 74.1 74.1 75.0 75.7 75.6 75.2 75.2 22.0 21.0 21.1 21.5 20.7 169 169 213 144 142 326 357 397 334 346 249 244 261 210 222 361 393 426 375 399 6.6 7.6 7.2 6.3 4.8 23.5 24.5 24.4 20.7 23.4 lAA" 2AA" lA A" I 3A ^" I lA A" O.K. Mix- ture. A-G. Specific gravity Temp. (° F.) Water Temp. (° F.) Air Water (per cent) "s'd f ,,. i / initial o.S Vicat -^ . , tu a ] I nnal c3^ ... 1 .3 \ „., i initial . . . f-i *= Gilmore ( ^ $ [ I final Fineness — % residue / 100 on sieve No. I 200 * iSoundness 3.123 3.103 75.0 74.7 77.1 75.7 20,9 22.5 142 117 338 273 215 195 358 322 7.5 1.0 24.3 15.2 2A A" llAA 3.122 69.6 71.5 21.5 200 383 248 434 6.6 24.3 O. K. * Nine or ten pats were made for each test on every cement: The legend indicates the number, kind of test and amount of warping: thus 2A ^ in. means two air pats had warped ^ in. at twenty- eight days. Complete records of tests of cement extending over a long period of time are rare. In most cases the record of the properties of the cement, other than the strength, and the methods and conditions surrounding the curing of the specimens are very incomplete. Furthermore, the results of such tests are apt to be misinterpreted and a much broader signifi- cance given to them than is warranted by careful consideration of the facts. In general this may be stated of the strength of Portland cement specimens cured in clean fresh water. Usually the maximum tensile strength is attained within one year; thereafter it fluctuates, in most 334 PORTLAND CEMENT cases showing some retrogression. Inasmuch as complete long-time compressive tests are still more rare than long-time tensile tests we can only say that, in general, the compressive strength continues to show a progressive increase for a longer period of time than does the tensile strength. The curves in Fig. 16 show the results of long-time tests on six brands of Portland cement summarized in the Fourth Annual Report of the Metropolitan Water and Sewerage Board of Massachusetts. Fig. 17 illustrates the effects of curing in water and in moist air on the long-time strength of Portland cement mortars. ' These tests were reported by S. W. Hartwell, of the Vulcanite Portland Cement Company, in the Engr. News, Vol. 67, p. 846. Each point represents the average strength ^2400 \,zooo 0^1600 31200 ^^ — -""■"^ f\ 1 Age in Days Fig. 15. — Variations in Transverse Strength witli Age for Neat Cement Prisms Made of a, Mixture of Brands A-G. (Specimens 13X1X1 in. were tested on a 12-in. span with center load.) of five briquettes which were made and tested by the same operator. The sand used in the tests of Figs. 16 and 17 was crushed quartz * which passed a No. 20 sieve and was held on a No. 30 sieve. For other long- time tests on tensile strength see Figs. 2 and 6, Ch. X. In considering the results of long-time tensile tests, one should always bear in mind that the brittleness of cement test-pieces increases with age and that slight errors in the grips or bearing surfaces which produce an eccentric loading, will affect the strength of old specimens more seri- ously than the strength of young specimens. 357. Expansion and Contraction Due to Variations in Moisture Con- tent. — Owing to colloidal nature, Portland cement pastes and mortars * This was the standard fine aggregate in general use in this country until 1904. It was more variable in granulometric composition than Ottawa standard sand. Ac- cording to W. P. Taylor, 1 : 3 briquettes made of standard sand are from 20 to 30 per cent stronger at seven or twenty-eight days than those made of crushed quartz. RESULTS OF VARIOUS TESTS ON PORTLAND CEMENT 335 undergo a volumetric contraction when they harden in air and an expan- sion when hardening takes place under water. A few reliable experiments have been made to determine the magnitude of such action and the dura- tion of time over which it lasts. In a paper by Prof. A. H. White, read before the Am. Soc. for Testing Materials (see Proceedings, Vol. 11, p. 531), there is given a summary of the main experiments upon this sub- ject and an account of some important experiments made by White. The cements used by White passed the standard soundness tests and standard methods of manipulation were employed in making the IXIX 1,000 Fig. 16. — Tensile Strength-Age Curves for Six Brands of Portland Cement. 4-in. specimens. After curing in the moist closet for twenty-four hours an initial reading of the length of each prism was obtained by means of a special micrometer placed in contact with glass plates molded into the ends of the specimen. The probable error of the apparatus was about 0.003 per cent. Fig. 18 shows the average contraction of air-cured neat cement at various ages up to four years. Five or six different brands are represented up to two years and three brands for the remainder of the time period. The effect of prolonged seasoning on contraction was negligible. Fig. 19 * gives the expansion time curves for water-cured neat prisms * Taken from a later paper in Proc. A.S.T.M., Vol. 14, p. 204. 336 PORTLAND CEMENT made of four brands of cement and also shows the effects of removal from water and subsequent immersion. It will be noted that the bars shrank very slowly after removal from water but expanded very rapidly within 600 500 400 300 300 ,100 400 300 '200 100 600 600 400 .^ a 300 H 300 100 600 500 400 300 800 100 OVLr ''\7 «'0 "d Sample No. 1 Sample No. 2 Sample No. 3 Sample No. 4 ■ In Water till broken ■ In Water 6 da., in Uoiet Air till broken — — In Moiat Air till broken S Age FiQ. 17. — The Effect of Storage upon the Tensile Strength of 1 : 3 Crushed Quartz Mortars Made from Four Different Samples of Portland Cement. (Hartwell.) a day when subsequently immersed. The behavior of the dupUcate bars 146A3 and 146A4, well illustrate this phenomenon. The former, after being subjected to short immersion periods and long-drying periods, exhibited no pronounced change in mean length during three years treat- RESULTS OF VARIOUS TESTS ON PORTLAND CEMENT 337 Fig. 18. — The Linear Contraction of Prisms of Neat Cement Stored in Air. (White.) +0.15 + 0.10 +0.05 —0.05 g+0.20 §■+0.15 H 11+0.10 ++0.05 ^ 0.00 a— 0.05 o 'a '3 + 0.15 tn §+0.10 S + 0.05 I 0.00 83—0.05 + 0.10 +0.0S 0.00 -0.05 +0.20 + 0.15 +0.10 +0.05 0.00, •Immersed 1 n Watenatf Ec mm Temperature oin Air of Hoom ©In Desiccator over Calcium Chloride „ In Air Saturated tf ith Water Vapor at Hoom Temperature 131-E . — r, 1 /T f\ / / \ K f ^ ^ \ / \ ^ \ i ^*^ J ^ _. 131-G f ' n /^ A / , n V ^^ \. / f \ \ \.^ \ ,/ \ \1, ■0 © , f- ,--- 181-1 A f\ I ^-— ' 1 I ; V V / / \. ^ "~~- ^\ / ) i J\a K t . % 146-A II y?AA A/' IV \ 'N\ \X\ \f \^ -^ it\ \AAf r 1 \ w \/ ^ "~~~ J i i ^ ^ • > T~°~~ —^ ?A.^ P.i'l ,r" \nii // V r I jii> HYV' A/ IV 14C-A V >© li\ 3 Years Fig. 19. — Changes in Length of Neat Cement Bars when Alternately Wet and Dried at Room Temperature. (White.) 338 PORTLAND CEMENT ment, whereas bar 146A4, which received long periods of soaking and short-drying periods, increased in mean length about 0.15 per cent dur- ing the same time. No diminution in the proportionate expansion or contraction of the bars appeared after repeated applications of the alter- nate wetting and drying process. In several instances the changes in length increased with repetitions of this treatment. White ascribes the water attack on unhydrate cement grains to be the cause of this .Immersed 1 n Water at Koom T€ mperature In Air of Room ©In Desiccator over Calcium Chloride (, In Air Saturated with Water Vapor at Room Temperature 9m 140 -CI « ;v— '\i^ V' ''v^ ~-h- V \' ^^"-^ a;^ fv„ r 146 -C2 Ti -^ ah: —• — -* ' ^^s -^ Ky "~- — A ^ r» ■-< ,46-x: * M - V^ -J ^>^ f^ -^ h, \. — ^>— ^ n U(i-X . • » _, *^Ssr- 1 — « \ K f 1 46-X_5 « ^ ►-• \ r^ ■~~o-^ /Wv ■/ +0.05 0.00 I 0.00 S-0.05 I' +0.05 + '- 0.00 l3 0.00 •9 -0.05 o §'-0.10 ■S +0.05 0) " 0.00 s ^-0.05 -0.10 ""■^^0 1 2 3 4 5 D Years Fig. 20.— Changes in Length of 1 : 3 Standard Sand Mortar Bars when Alternately Wet and Dried at Room Temperature. (White.) action. A saturated atmosphere caused expansion comparable to that obtained by immersion in water. The expansion and contraction of 1 : 3 standard sand mortar prfems subjected to various periods of immersion and drying are shown in Fig. 20.* It will be observed that the mortar bars attained the maximum changes more quickly than the neat specimens but the changes were much less. Alternate wetting and drying caused more rapid changes in the mortar specimens than in those made of neat cement. Prisms cut from sound and strong sidewalk tops, which had seen twenty years' service, * Proc. A.S T.M., Vol. 14, p. 204. RESULTS OF VARIOUS TESTS ON PORTLAND CEMENT 339 exhibited changes in length similar in kind and intermediate in magnitude to the changes observed in the neat and mortar bars. Experiments on compound bars made of equal layers of neat cement and 1 : 3 mortar led White to the conclusion that such specimens expanded and con- tracted together but not at the same rate nor to the same degree, the difference in expansion varying from to 0.15 per cent. Table 5 gives average values of expansions obtained by the U. S. Biu-eau of Standards Laboratory for neat and 1 : 3 mortar prisms made from ten different American brands of Portland cement. TABLE 5.— AVERAGE LINEAR EXPANSION OF NEAT AND 1 : 3 STANDARD SAND MORTAR PRISMS OF TEN DIFFERENT BRANDS OF PORT- LAND CEMENT CURED IN WATER (Proc. A.S.T.M., Vol. 15, p. 141.) Percentage Linear Expansion at Thirteen Weeks. '^ Mix. Normal Cement. Eeground 87-93% 'an g 1000 I J3000 2000 1000 s f V Note;-Main batahes were not disturbed except- ln£r to remove Bamoles or re^ause. \ / •v Initial percentages of mixing: water were Alpha, 26.1; Star, 27.6; Dyctorhofl, 29; Jobbod, 30.5 After molding, Bpecimens aged in air 1 months 1 Iph; _- -^ Jos son ' • I yck ;rho EE Star ■s — i "^ ^ . ' ■ "~^ 6 8 2 4 6 8 10 12 14 16 18 Interval between Mixing and Molding in Hours 20 22 24 FiQ. 21. — Effect of Remixing after Setting upon the Compressive Strength of Neat . Cement Cubes. A remarkable test on the effect of continuous agitation and retem- pering upon the strength of Star Portland cement is recorded in Teste 0/ 7000 10 20 30 40 50 60 70 80 90 100 110 Time Agitated on Mixing Boards in Hours Fia. 22. — The Effect of Continuous Agitation during Setting on the Compressive Strength of Neat Cement Cubes. Age at test, one month. Metals, 1901, p. 508. The main batch of neat cement paste was initially gauged with 32.9 per cent of water, retempered at intervals of one to four RESULTS OF VARIOUS TESTS ON PORTLAND CEMENT 341 hours to maintain initial consistency and was continuously agitated for 102 hours after mixing. Portions of the batch were separated from time to time and molded into 4-in. cubes. Fig. 22 shows the average strength of pairs of cubes plotted against the length of time which they were agi- tated. Table 6 shows the strengths at one month of grouts made from various cements which were allowed to remain for fifteen or sixteen hours in the mixing board and were then remixed with an addition or removal of water, if necessary, to obtain the consistency ordinarily used by masons. TABLE 6.— EFFECT OF RETEMPERING ON THE COMPRESSIVE STRENGTH OF NEAT CEMENT GROUTS * Specimens were 6-in. cubes. Age at test = l mo. Brand. Kind of Cement. Feb Cent Wateh (by Wt.) at Interval between Mixing and Molding CHr.). No. of Spec. Compressive Strength (Lb. per Sq.in.) Mixing. Molding. Max. Min. Average. Alpha Dyckerhoff . Josson Steel Mankato . . . Norton. . . . Portland Portland Portland Slag Natural Natural 44.9 43.3 48.6 50.9 68.8 59 43.9 43.3 43.7 50.9 68.8 64.5 15 15 15 16 16 15 8 8 8 8 7 8 3706 2250 2304 585 316 377 3302 1908 1976 519 255 305 3480 2113 2087 554 294 343 * Tests of Metals, 1901, p. 520. 359. Effects of Low Temperatures on the Strength of Cement. — In general it may be stated that the setting of cement proceeds at a very slow rate when the temperature falls below 40° F. When the tempera- ture falls below freezing the particles of cement in unset specimens are separated by the expansion of water in freezing. A minimum amoimt i of water should, therefore, be used in cement work subjected to freezing | temperature in order that this expansive action may be as small as pos- 1 sible. Alterations in freezing and thawing before the cement has attained I hard set generally cause a loss in cementing power owing to the repeated breaking of the bond between adjacent particles. If the work freezes^ before setting but thaws without refreezing it will in time secure full strength if plenty of moisture is provided for proper curing. From the result of a very large number of compression tests on neat cement made at the Watertown Arsenal, the data in Table 7 have been selected. These tests show that there is considerable chemical activity in neat cement when setting at 0° F. It appears that neat cement speci- mens subjected to such low temperatures immediately after mixing gain strength at a very much slower rate than specimens cured at room tem- 342 PORTLAND CEMENT peratures; but that after several years the test-pieces stored at low tem- peratures develop a considerable proportion of their normal strength. It also appears that specimens hardening at 70° F. for a given period will TABLE 7.— THE EFFECTS OF LOW TEMPERATURES ON THE COMPRESS- IVE STRENGTH OF 2-IN. CUBES OF NEAT PORTLAND CEMENT (Tests of Metals 1901, 1902 and 1907.) Per Cent Water. Time of Setting in Air AT Temperatures op Total Agp. Days. Compressive Strength * in LB.-IN.2 After Storage. Cement. 70° F. Days. 0° F. Days. 70° F. Days. Treatment Indicated. In Air at 70° F' for Total Age. Star 23.4 31 31 32 38 1350 2340 4570 4820 89 90 1720 89 30 119 3620 4410 lyr. 2724 Star 24.0 5yr. 30 3250 Alsen 28.2 31 986 3900 30 37 2440 3450 90 91 1210 4040 90 29 119 2520 3510 lyr. 1580 Alpha 25.0 1 582 1 7 9 2400 4990 1 179 181 3670 5910 25.0 1 5 yr. 6320 1 5 yr. 36 8100 Alpha 23.0 7 6550 7 9 17 5160 5730 7 188 196 5350 5940 7 5yr. 7310 7 5 yr. 41 7650 Atlas 24.0 1 7 1 9 689 2140 4130 1 181 183 2950 5410 1 5yr, 4160 « 1 5yr. 40 6780 Atlas 24.0 7 7 7 15 3730 4210 4890 7 18 192 4500 6790 7 5 yr. 6640 7 5 yr. 40 7410 * Each result is averaged from fi\-c or more tests. RESULTS OF VARIOUS TESTS ON PORTLAND CEMENT 343 attain a greater strength than specimens which are allowed to harden for a like period after an exposure to freezing temperatures. If neat specimens are allowed to set for one day at room temperature before being subjected to freezing temperatures, the rate of growth in strength is more rapid than if immediately frozen. In a paper before the Am. Soc. of C. E.* Matthews and Watson de- scribed experiments on the effect of frost on cement and cement mortar. From their results, it appears that after setting twenty-four hours, at normal temperatures (60° F.), a light frost (29° F.) temporarily lowered the strength of briquettes, but at the end of one month specimens cured in this temperature were equal in strength to those normally treated. Speci- mens frozen immediately after mixing exhibited only two-thirds of the normal strength at the end of either the seven or twenty-eight day period. A heavy frost, temperature 15° F., seriously affected the strength of neat and 1 : 3 mortar briquettes at both of the above periods even though the briquettes had set for twenty-four hoinrs before being subjected to freezing. Mortar briquettes were more speedily weakened by light frost, but they recovered their strength more rapidly than the neat specimens. These experimenters also found that the percentage of water chemically com- bined with the cement was considerably less for specimens hardening in freezing temperatures than for those normally cured. Oilman and Osterbind reported f a series of tests on neat briquettes which indicated that the tensile strength was most seriously impaired by alternate freezing and thawing before setting had taken place, pro- vided such treatment occurred in air and was followed by a storage in air at 70° F. When briquettes were stored in water and subjected to alternate freezing and thawing followed by air-curing . the decrease in strength, although equal to 50 per cent of the strength of specimens water-cured at normal temperature, was not so great as under above conditions. 360. Effect of High Temperatures on the Strength of Neat Portland Cement.- — In Tests of Metals, 1902, a report is made of a number of tests on 4-in. cubes of neat cement which were cured for one year in air or water and then gradually heated to temperatures of 600° to 1000° F. The cubes were cooled in asbestos or sawdust and aged for four days to four months before they were tested. After heating most of the cubes showed faint cracks which gradually enlarged when the cubes were allowed to stand in air for several days. In several of the specimens subjected to temperatures of 900° F. these cracks became so large that the speci- cimens were rendered unfit for testing. Specimens subjected to tem- peratures of 800° F. or above showed a marked decrease in strength, * Trans. A.S.C.E., Vol. 64, p. 320. t Engr. Rec, Vol. 51, p. 388. 344 PORTLAND CEMENT especially those hardened in water. Of the cubes made from Dyckerhoff cement and gauged with 29 per cent of water, those hardened in air showed a loss of weight varying from 7.7 per cent after being subjected to 700° F. to 10.5 per cent after 1000° F.; those hardened in water lost 17.7 per cent after being heated to 1000° F. 361. Experiments on the Rise in Temperature During Setting.— Considerable attention has been devoted to showing a relation between the rise in temperature during setting and the time of set of cement. No such relation has ever been established and it is probable that none exists. However, the possibiHty that the quantity of heat generated in. 100 80 •60 a 40 10 sf V- "\ 1 ./ \ $/ i f-~~/'- ^■■^>, \. "-r--.. -t^ # > ■s. /■' / ^.S> .' / ''^- ^,'\.^^ // "^^ / / 1' N9^ -^ ^?**c::- S,— - .->'' r J .y ^ "*" ""' 8 n 16 20 24 Time after Mixing ia Hours 32 40 Fig. 23. — Temperatures Acquired by 12-inch Cubes of Neat Portland Cement while Setting in Plank Molds in a Room of Normal Temperature. {TesU of Metals, 1907, p. 129.) setting may be an index of the quality of different samples of the same brand of cement is worth consideration.* Furthermore, since the heat generated in setting doubtless affects the resistance offered to freezing, the typical temperature-time records for setting cement pastes presented in Fig. 23 are of interest. The pastes from which these cubes weie made were gauged with 25 per cent of water. With the exceptions noted in the figure, all cements were ground shortly before the tests were made. 362. The Resistance of Neat Cement to the Action of Alkali Waters and Sea Water. — Under laboratory conditions neat cement may be dis- integrated by the combined chemical and mechanical action of waters * See paper by L. N. Beals, Jr., Proc. A.S.T.M., Vol. 13, p. 720. RESULTS OF VARIOUS TESTS ON PORTLAND CEMENT 345 containing various salts such as, the sulphates of magnesia and sodium, the chlorides of magnesia, sodium and calcium, and the carbonate of soda. The sulphates and chlorides are chemically active in removing lime from the cement, while the carbonate of soda alone or in solution with sodium sulphate or sodium chloride withdraws silica.* If the test-pieces are subjected to alternate wetting and drying a mechanical action greatly accelerates the breakdown of the cement. Under such conditions, crys- 1000 104 4 13 26 Age in Weeks 62 104 -o — Fresh Water — » Sea Watec Fig. 24. — Neat Tensile Strengths of Different Cements Stored in Fresh Water and in Sea Water after One Day in a Moist Closet. {Technologic Paper No. 12, U. S. Bureau of Standards.) tals of large size are rapidly formed and expansive forces are produced. Under the action of these forces neat cement pastes are disintegrated more rapidly than lean mortars, j * Action of the Salts in Alkali Water and Sea Water on Cements, Technologic Paper, No. 12, U. S. Bureau of Standards, by Bates, PhiUips and Wig. (Excellent bibhog- raphy.) t The Effect of Alkali Water on Cement Mortars, A. J. Fisk, Eng. News, Aug. 18, 1910. 346 PORTLAND CEMENT Portland cements of high iron content and some of the special slag and tufa cements, in which the silica content is high, are thought by many to possess great resistance to the action of sea water.* In view of tests made at the Bureau of Standards,! however, there appears to be no relation between chemical composition of a cement and its resistance to the chem- ical attack of sea water. In proportions up to 2.5 per cent sulphur tri- oxide has no serious effect upon the resistance of the cement to sea water. J 500 sso BOO aso BOO SBO Cement No. 1 Low Alumina Portland No. 55 Special Slag Cement No. 57b Typical Portland Cement No. 47 [11 £4'ands mixed] White Poi-tland Cement No. 30b 52 4 13 Age ill WeeliS 26 62 — o — Fresh Water , Sea Wata- Fig. 25. — Tensile Strengths of 1 : 3 Standard Sand Mortar Briquettes, Made from Different Cements, Stored 'in Fresh Water and in Sea Water after One Day in a Moist Closet. {Technologic Paper No. 12.) Magnesia combined with the cement is inert, but that contained in sea water is precipitated from a sulphate or chloride solution due to the greater affinity of the lime in the cement for the sulphur or chlorine radical. In construction, however, due probably to the carbonizing of the Ume, thus rendering it insoluble in sea water, and the formation of pro- tective surface coatings, the destructive action is much less rapid. Con- cerning the mechanical disruptive action, it must be borne in mind that * Action of Sea Water upon Hydraulic Cements by Miehaelis, Trans. Inst. C.E., Vol. 107, p. 375; also Engineenng, Vol, 63, pp. 457, 496, and 559. t Action of the Salts in Alkali Water and Sea Water on Cements, Technologic Paper, No. 12, U. S. Bureau of Standards, by Bates, Phillips and Wig. (Excellent bibliog- raphy.) I Report of German Portland Cement Mfg. Asso., Cement Age, Oct., 1911. RESULTS OF VARIOUS TESTS ON PORTLAND CEMENT 347 other porous materials like stone and brick are subject to similar action unless protected by an impervious surface. It, therefore, seems advisable before condemning the use of cement in structures subjected to the action of alkali and sea waters to study methods of rendering the surface impervious. In such studies there should be employed specimens of large mass cured and treated under field conditions. The results of small specimen tests of neat cement are of practically no quantitative value in this connection, however much infor- mation they may yield concerning the nature of the action which takes place. Tests of briquettes of different cements cured in fresh water and in salt water are given in Figs. 24 and 25. Chemical analysis of the cements can be found in Table 8. TABLE 8.— CHEMICAL ANALYSES OF CEMENTS (See Figs. 24 and 25) No. 4. 55 47 43 306 S7 576 32 52 Kind. Iron * Ore Cement. Low Alumina Port- land. Mixed Brands, Port- land. Normal Port- land. White Port- land. Special Slag. Special Slag. Blended. Natural. Si02 AI2O3.... Fe^Os.... CaO MgO SO3 NajO...'. K2O CO2 CaS H2O Ig. loss. . . 23.44 2.98 7.48 61.86 0.50 1.72 0.20 0.28 0.69 0.42 0.09 20.37 3.64 8.97 61.42 0.82 1.19 1.54 0.24 1.01 1.06 21.50 8.12 2.28 62.23 3.24 1.45 0.18 0.38 0.12 0.38 0.39 22.07 6.95 2.31 62.33 2.28 1.54 0.31 0.57 0.45 0.45 0.92 22.66 8.61 0.55 62.46 1.10 1.64 0.40 0.53 0.63 0.36 1.07 27.77 13.87 0.60 44.09 4.49 1.22 0.42 0.11 2.10 2.84 2.68 29.48 15.37 0.64 42.23 4.45 1.83 0.56 0.57 0.64 2.25 2.16 24.00 9.69 2.53 49.15 2.53 1.67 0.71 1.42 4.43 0.45 3.47 22.53 8.98 2.45 45.75 2.92 1.81 0.39 1.20 8.60 3.53 Total . . . . 100.17* 100.26 100.27 100.16 100.01 100.19 100.18 100.05 100.16 * Contains 0.51 % CuO. 363. Effects of Oils on Neat Cement. — In general it may be stated that most mineral oils produce little if any effect upon hard-set specimens of neat Portland cement.* When incorporated into the mixing water they retard the set and decrease the strength. Animal and vegetable oils, which contain acid fats, will attack the lime compounds in neat cement and form hme soap. Toch t states that this disintegration may be the result of expansion * J. C. Hain, Engr. News, Vol. 53, p. 279. t Ibid., 419. 348 PORTLAND CEMENT during the crystallization of oleate and stearate of calcium. Such action is more pronounced in neat cement than in mortar or concrete specimens. It is, therefore, imperative that care should be exercised to use only small quantities of mineral oils for lubricating molds and never employ vege- table or animal oils for such purposes. 364. Effects of Sugar on Cement. — The addition of as small an amount as one-eighth of one per cent of sugar to cement has been reported to produce a marked delay in the time of set and practically to destroy the early strength.* At an age of two or three months additions of sugar, less than 2 per cent, appear to increase the strength. By some, the action of sugar is attributed to the formation of a soluble calcium sac- charate (Ci2H220ii-CaO+2H20). * Parsons, Engr. News, 1887, Vol. 2, p. 461 ; also see series of letters in Vol. 69, p. 126, 127, 478, 1077. CHAPTER X NATURAL AND OTHER HYDRAULIC CEMENTS NATURAL CEMENT 365. Definition. — Natural cement is made by burning a natural argillaceous limestone at a low red heat (1000° to 1300° C), which is suf- ficient to drive off carbonic oxide (CO2). The clinker will not slake to any extent and must be finely groimd before it exhibits hydrauUc properties. 366. Process of Manufacture. — The limestone, containing from 15 to 35 per cent clay, is burnt in vertical kilns 30 to 40 ft. high and 10 to 15 ft. in diameter. The common type of kiln consists of a cylindrical steel shell open at the top and fined with fire-brick. In operating a kiln, thick layers of limestone and thin layers of soft coal are alternately dumped into the top of the furnace and the burnt clinker is drawn off at frequent intervals from the bottom. As the limestone descends in the kiln, water is first driven off from the rock. At a temperature of about 700° C. magnesian carbonate begins to decompose. Lime carbonate dis- sociates at 900° C. and clay at a somewhat higher temperature. The alumina and iron oxide set free by the decomposition of the clay combine with the lime and magnesia and, if the final temperature be high enough, lime and magnesian sihcates will be formed. The process is run con- tinuously and about one-third of the charge, in the form of clinker, is daily withdrawn from the kiln. On account of the variations in the quality of the raw material and on account of non-uniformity in burning different parts of the charge, a considerable portion of the resultant clinker is either under-burned or over-burned. According to Eckel from 10 to 33 per cent of the result- ant product cannot be used. After the clinker has been removed from the kiln it is allowed to season in the air in order that any under-burned chnker may be slacked before grinding. Sometimes slacking is accel- erated by steaming the clinker. The burnt clinker is first passed through a stone crusher and then fed to some form of apparatus for grinding it to the requisite fineness. For- merly, all mills used the miUst-one grinders commonly employed in flour -mills. More j;eGentiy, however, a decided improvement in the fineness 349 350 NATURAL AND OTHER HYDRAULIC CEMENTS of grinding has been effected by the introduction of ball mills, tube mills and other modern equipment used in grinding Portland cement. Natural cement is sold either in barrels of 280-lb. capacity or in 90-lb. bags. 367. Characteristics of Natural Cement. — Natural cement is an impal- pable powder varying in color from yellow to brown and in specific gravity from 2.80 to 3.00. It resembles hydraulic lime inasmuch as it is made from a natural argillaceous limestone and will set when mixed with water either in air or under water. On the other hand, natural cement clinker slakes but little, if any, when water is poured upon it. Most natural cements are not so finely ground as Portland cements although much improvement in this important property has been effected in recent years. Natural cement sets much more rapidly but with a less evolution of heat than Portland cement. For pastes of normal consistency the time era .fl 5 .S 400 He at Katural C luTTifint ■ 300 200 100 ^ — JlortMii- ■ A ^ y ' 21 ! S a 1 e 8 1 » \ 2 '^ — Daya — H^ Fig. 1. — Tensile Strength- Age Curves for Neat and 1 : 2 Natural Cement Mortars (From Taylor's Practical Cement Testing.) of initial set will usually vary from fifteen minutes to one hour and final set will generally occur within three hours. An excess of water greatly retards the setting of natural cement pastes. Aeration also retards the set of natural cement. On account of the variability of the raw materials employed in man- ufacture, natural cements differ considerably in cheihical composition. Even in the same brand considerable differences in the composition are common owing to variations in the rock and degree of calcination. The approximate ranges in amounts of the chief chemical compounds fflund in natural cements, as obtained from over 100 analyses given in Eckel's Cements, Limes and Plasters, Ch. XIX, are as follows: 30 to 60 per cent of lime (CaO); 15 to 35 per cent of silica (Si02); 1 to 25 per cent of magnesia (MgO) ; 2 to 20 per cent of alumina ( AI2O3) ; 1 to 19 per cent of iron oxide (Fe203); and, in general, less than 10 per cent of water (H2O), carbon dioxide (CO2), the alkalies (K2O, Na20), and sulphur tri- oxide (SO3). NATURAL CEMENT 351 368. Properties of Natural Cement. — Because of variations in com- position and manufacture, the properties of natural cements, even those of the same brand, often differ considerably. In Fig. 1 are shown the average tensile strength results of numerous tests rriade by W. P. Taylor on different brands of natural cement. Attention is called to the regu- lar increase in tensile strength which accompanies an increase in the age of briquettes. Although natural cement gains its full strength much less rapidly than Portland cement, it does not, in general, exhibit marked Fig. 2. — The Effects of Age on the Tensile Strengths of Natural and Portland Cements Used in the New Croton Dam. (G. G. Honness, Trans. A.S.C.E., Vol. 76, p. 1038.) retrogression in strength, even when tested neat. This fact is well illus- trated by Fig. 2 which shows the results of long-time tensile tests on three brands of natural and one brand of Portland cement used on the New Croton Dam. In these tests the mortars were made with crushed quartz passing a No. 20 sieve and retained on a No. 30 sieve. The number of specimens per point on the diagram ranged from 15 to 14,740. Nearly all of the tests were made by one operator. In Fig. 3, the reduction in strength of natural cement mortars for increasing proportions of sand is indicated. The results of compressive tests at the Watertown Arsenal on 4-in. 352 NATURAL AND OTHER HYDRAULIC CEMENTS neat cubes made of four different brands of natural cement indicate the following ranges in strength for corresponding ages of specimens. 7 day 1 mo. 3 mo. lyr. 3yr. 51 3T. Compressive strength (Ib.-in.^) Min Max 356 566 840 1090 1110 1530 1040 1590 1320 1866 1290 2440 1.00 Ratio— Saad+Cemeati FiQ, 3. — Showing Reduction of Strength of Natural Cement Mortar Six Months Old for Increasing Proportions of Sand. (Wheeler, Rept. Chf. Engr., 1895, p. 2982.) 300 The specimens were made from pastes of normal con- sistency and were hardened in air. Nearly all of them were badly cracked at the end of the five and one-half- year interval.* Fig. 4 shows the effects of aerating the cement upon the strength of briquettes. The results indicate that natural cement should not be exposed to air over one month. Regauging adversely af- fects the strength of neat natural cement mortars as Fig. 5 plainly shows. Simi- \ V •s \ \ _Jcvg lS;<_M; MhsO Id ^ -ii— = ^^ :6S-I 'ear Q \ zc i2S-28 >iii o 100 Fig. \ \ s w 1 1 1 \ N 3 ja a S a s a ^, a s ,s .a T3 1§ i 00 1 ta ei 1 1 ^, ^ e « K K •y m '0 20 40 60 80 100 Time of Aeration la Days FiQ. 4. — Effect of Aeration on the Tensile Strengths of Natural Cement Mortars. (Wheeler, Rpt. Chf. Engr., 1895, p. 2962.) 5. — Effect of Regauging on the Tensile Strength of a Quick- setting Neat Natural Cement Mortar. Test age was six months. {Rept. Chf. Engr., 1896, p. 2980.) * Testa of Metals, 1902, p. 369; 1904, p. 341; 1907, p. 133. MISCELLANEOUS CEMENTS 353 lar effects are reported in Tests of Metals, 1901, p. 522. In the latter, are also reported results of tests on neat natural and neat Portland cement grouts (see Art. 358), which were gauged with water and allowed to set overnight before retempering. The compressive strengths of these natural cement grouts after hardening in air for one month varied in general between 200 and 300 lb. per square inch. Regauged Portland cement grouts, similarly treated, exhibited about ten times this strength. When subjected to low temperatures neat natural cement pastes are affected like Portland cement pastes' but their strengths are very much lower.* Alternate freezing and thawing, however, is more damaging to natural cement mortars than to those made of Portland cement. Con- sequently natural cement is not so well adapted as Portland cement for constructions which must be carried on in freezing weather. Results of the effects of sea water on the strength of briquettes made froin a brand of natural cement (52) appear in Fig. 24, Ch. IX. 369. Uses and Production. — Natural cement has been extensively used in sewer work, in masonry construction, and in monolithic or massive construction in concrete in which great strength was not required. Since the year 1899, however, the production of natural cement in the U. S. has steadily declined. This decline has been brought about largely by the decrease in the cost of Portland cement. In 1914 the production of natural cement was 751,285 bbl. valued at 46.8 cents per barrel. Only 12 plants reported any production in 1914. MISCELLANEOUS CEMENTS 370. White Portland Cement. — On account of the demand for a stainless white cement of high strength there have recently been placed upon the market several pure white Portland cements. These are em- ployed in ornamental work both interior and exterior and in making build- ing blocks, stucco, stainless mortar, etc. In order to obtain the pure white color it is necessary to use raw materials with a very low content of iron oxide. Generally less than one per cent of this oxide is present in the finished cement. Furthermore, it is necessary to use fuel free of pyrite and to burn at a temperature above the normal. Consequently white Portland cement is somewhat more expensive than the ordinary variety. In physical properties, white Portland cements generally conform to the Standard Specification for Portland Cements, although the strength at one and seven days is sometimes low. Tensile strength-time curves for neat and 1 : 3 standard sand mortar briquettes made from a white • See Art. 359 and Tests of Metals, 1901, p. 540-582. 354 NATURAL AND OTHER HYDRAULIC CEMENTS Portland cement (306) are shown in Figs. 24 and 25, Ch. IX. The chem- ical analysis of this brand is given in Table 8, Ch. IX. * 371. Cements with High Iron Content. — Because of the belief that a high alumina content is undesirable in cements for marine constructions, cements have been developed in which the alumina content has been largely replaced by iron oxide. Two grades of these cements have been marketed by German manufacturers,! the Iron-Portland cements, which are made by grinding a mixture containing 70 per cent or more Port- land cement clinker and slag, and iron-ore cement, which is a true Port- land made from raw materials having a high iron and low alumina con- tent. In this country the latter type of cement has been made from the New Jersey greensand, a ferrous silicate, and shell-marl. | These cements do not ordinarily contain over 2 or 3 per cent of alumina. They have a somewhat higher specific gravity, are slower setting and somewhat weaker at one and seven days than the normal Portlands. Whether such cements do offer superior resistance to the attack of sea water is a question on which authorities differ. The results of bri- quette tests on iron-ore cement (4), and a low alumina cement (55), which were cured in fresh water and in salt water, may be seen in Figs. 24 and 25, Ch. IX. Table 8, Ch. IX, shows the chemical analyses of these cements. From the results of these experiments and those of Candlot, Mr. P. H. Bates, who reports the tests, suggests that a very high silica content is probably of more value than the presence of an unusual proportion of iron oxide. 372. Blended Cements. — In 1893 a patent was taken out by T. L. Smidth for the manufacture of a cement which was made by grinding together silicious rock or sand and Portland cement. Although this cement was successfully employed in a number of constructions, it did not remain long on the market owing to the rapid decrease in price and increase in production of Portland cement. Recently, the U. S. Reclama- tion Service has made use of sand cement on the Arrowrock and Elephant Butte Dam, and the City of Los Angeles has employed tufa cement, a similar blended product, in the construction of a very large aqueduct. In these constructions the cost of Portland cement was made very high on account of the long haul so that the use of a blended cement effected a considerable economy. On the Reclamation projects this g&ving amounted to about 25 per cent of the cost of Portland cement. The cost of producing these blended cements, exclusive of the price paid for Portland, varied from 37 to 50 cents per barrel. In view of the use which *See also Properties of White Portland Cement by P. H. Bates, Trans. Am. Ceramic Soc, Vol. 16, p. 551. t Dr. W. Michaelis, Sr., has been a pioneer in this field. I t Eckel in Eng. News, Vol. 66, p. 157. MISCELLANEOUS CEMENTS 355 these cements have received, both in this country and abroad, a short description of them will be given. 373. Sand Cements. — Generally sand cements have been made by grinding together in a tube mill approximately equal volumes of pulver- ized silicious rock or sand and Portland cement. In the work of the Reclamation service it has been found desirable to use rocks in which there is a high content of soluble silica.* Pure quartz is not a desirable element because it is insoluble, but basalts and sandstones often contain soluble silica, t The reason for a soluble silica requirement is evident if Michaelis' Age Fig. 6. — Tensile Strengths of 1 : 3 Mortar Briquettes of Standard Sand and Blended Cement Compared with Like Specimens Mads of Portland Cement (Paul). explanation of the setting of cement is accepted. From his theory it seems probable that the soluble silica in the rock reacts with the excess calcium hydroxide, which in a pure cement paste would be uncombined and in time crystallized, to form colloidal calcium hydro-sihcate, which is the chief component in the hardening of the cement. It is very probable that the formation of this colloid is promoted by the reduction in the size of both cement and silica particles, which is effected by grinding them together. From Coghlan's experiments * there appears to be produced no reduction in the percentage of voids by the addition of the fine rock. * R. R. Coghlan, Engr. News, Vol. 69, p. 1270. t By soluble silica is meant hydrated silica which in a finely subdivided form is soluble in water. 356 NATURAL AND OTHER HYDRAULIC CEMENTS On the Arrowrock Dam project a mixture of 45 per cent of granite and 55 per cent of Portland cement was so finely ground that 90 per cent passed the 200-mesh sieve. Sand cement so made set slower and hardened much less rapidly than Portland cement, but it passed the Standard tests for soundness and mortar strength. Fig. 6 shows the results of tensile tests on 1 : 3 mortar made from a blended cement and standard sand.* The blended cement consisted of equal parts, by weight, of sand or granite and Portland cement. The progressive in- crease in strength shown by these curves is notable. 374. Tufa Cement. — Tufa is a partially consoHdated pmniceous rock of volcanic origin. On the Los Angeles Aqueduct, the tufa employed con- tained in the vicinity of 70 per cent silica with about 12 to 14 per cent of alumina and small percentages of iron oxide, lime, magnesia and the 600 600 400 ' 300 200 100 Fairmont Tufa Halwee_. Cement _ Tufa Ceme Cement It >* u<=— Monolith r * — F m 1 1 Tufa Cements = 60* Monolith + 50« Tufa 1 Age la Months Fig. 7. — A Comparison of the Tensile Strengths of 1 : 3 Standard Sand Mortars Made of Tufa Cements with Like Mortars Made of Monolith Portland Cement. alkalies. This material contains more or less soluble silica which probably reacts with the lime in the cement as indicated in the discussion on sand cements. At the Aqueduct cement plant the tufa was pulverized and dried and then ground with an equal volume of Portland cement to a fineness of 90 per cent through a No. 200 sieve. The tufa cement passed the Standard Specifications for Portland Cement in time of set and sound- ness, but was somewhat slower than Portland cement in hardening. After ten days, however, the strength of 1 : 3 mortar briquettes made of tufa cement and standard sand was practically equal to the strength of similar briquettes of Portland cement. Fig. 7 shows the results of 1 : 3 mortar briquette tests gotten from two brands of tufa cement and from the Monolith Portland cement, which was used to make the tufa cement, f According to the reports of engineers *See Report of tests by C. H. Paul, Proc. A.S.C.E., Vol. 39, p. 271; also Engr. Newn, Vol. 69, p. 562. t Taken from a report by J. B. Lippincott, Trans. A.S.C.E., Vol. 76, p. 534. MISCELLANEOUS CEMENTS 357 on the Aqueduct, tufa cement gave excellent satisfaction, showed very little shrinkage and made a very impervious concrete. In rich mixes (1:2:4) the compressive strength of concrete made from this cement is about 20 per cent less than that obtained with Portland cement. In leaner mixes the discrepancy is much less. On account of the slower rate of hardening, tufa cement concretes require a longer time for curing than concretes made from Portland cement. In Germany trass, a rock similar to tufa, has been employed to make a blended cement, which has a very consistent growth in strength over a five-year period and which apparently possesses a high resistance to sea water.* 375. Puzzolan and Slag Cements. — Since the beginning of the Chris- tian era the Italians have successfully employed puzzolan cement for various kinds of construction. This cement is made by grinding two to four parts of puzzolana with one part of hydrated lime, f Besides puzzolana, which is a form of volcanic ashes, granulated slag, trass or tufa may ber used. The two latter materials may be classed as partially consolidated pumiceous rocks of volcanic origin. When granulated slag is employed the product is often called slag cement. This is the only puzzolan cement produced in the United States. In 1914 68,311 bbl. of this cement were produced in this country. At the mill, this product sold for 92.6 cents per 330-lb. barrel. 376. Characteristics of Slag Cement. — Slag cement may be recog- nized by its freedom from grit, the extreme fineness to which it is ground, and its lilac color. When a fractured surface of hardened neat paste is exposed to the air its color gradually turns from a bluish green to white, owing to the oxidation of the sulphides present in the slag. When freshly made, slag cement sets in about the same time as Portland cement but hardens much more slowly. If the slag cement is old the effect of the caustic soda, which is added to accelerate the set, disappears and the cement becomes very slow-setting. Slag cements require 2 to 4 per cent less water than Portland cement to form pastes of normal consistency. In specific gravity, slag cements vary from 2.7 to 2.9. The proportions of the chemical elements in these puzzolans range about as follows: CaO, 45-55 per cent; Si02, 27-30 per cent; AI2O3, 10-14 per cent; Fe203< 2 per cent; MgO<4 per cent; CaS<3 per cent. Most of the American slag cements have an hydraulic index between 0.7 and 0.9. 377. Tests of Slag Cements. — The compressive strengths of rich mixes made from slag cement are less than those of similar Portland cement mixes. In lean proportions, however, the differences in strength * See Engr. Record, Vol. 62, p. 237. t In the setting and hardening of these cements, it is probable that the main reac- tions are similar to those discussed in Art. 337 and 373. 358 NATURAL AND OTHER HYDRAULIC CEMENTS Sire not so great. Mortars of puzzolan cements are tough but have httle resistance to attrition. According to the report of the United States Army Engineers * puzzolan cement mortars and concretes should not be used where they will be continually exposed to the air since such exposure produces disintegration by oxidation of the sulphides in the slag. Inas- much as these cements possess hydraulic properties and are highly sili- cious, they are commonly believed to be less affected by sea water than Portland cements. The tensile strength-time curves for briquettes made from a slag cement (57 and 576), when cured in fresh water and in sea water are shown in Figs. 24 and 25, Ch. IX. The Chemical analysis of this cement is furnished by Table 8, Ch. IX. f 378. Improved Cements. — Some manufacturers of natural cement have improved their product by grinding with their natural cement chnker a small proportion of Portland cement chnker. By such adulteration the rate of hardening and the strength at early ages is increased. The com- pressive strength of 4-inch cubes of neat Bonneville improved cement is reported in Tests of Metals, 1902, 1904 and 1907. The cubes were made of normal consistency and set in air. Average values for five speci- mens follow: Age 7 days 1 mo. 3 mos. 5^ jt. Strength (Ib./in.^) 620 1130 1560 2050 * * Average of three cubes. Specimens were cracked. * Engr. News, Vol. 46, p. 180. t For further results see tests by W. K. Hatt, Engr. News, Vol. 45, p. 164. CHAPTER XI LIMES AND PLASTERS LIMES 379. Quicklime. — Pure lime, generally called quicklime, is a white , oxide of calcium. Much of the commercial quicklime, however, con- tains more or less magnesian oxide, which gives the product a brownish or grayish tinge. The specific gravity of pure lime is about 3.10. Essen- tially, the process of making lime consists in heating calcite (CaCOs), or magnesian hmestone (xCaC03)-|-2/MgC03, to a temperature sufficiently high to drive off the carbon dioxide (CO2). For pure lime carbonate the temperature at which such dissociation takes place is approximately 900° C. Since a considerable length of time is required to calcine limestone at such temperatures, it has been found good practice in operating kilns to use higher temperatures, depending upon the character of the impurities of the stone. However, to avoid burning, which seriously injures the setting properties, high magnesian limes should not be subjected to tem- peratures above 1000° C. and high-calcium limes should be burnt at tem- peratures lower than 1300° C* The American Society for Testing Materials in 1915 adopted the fol- lowing classification for quicklime. f (a) High-calcium; (6) calcium (c) magnesian; (d) high-magnesian. The society recognized two grades: Selected — a well-burned lime picked free from ashes, core, clinker, or other foreign material; and Run-of-Kiln — a well-burned lime, without selection. The requirements as to composition appear in the table on the next page: 380. Burning of Lime. — Limestone is usually burnt in some form of vertical kiln. The raw material is fed in at the top and the finished product drawn off through an opening in the side near the bottom. In general the stacks of these kilns consist of cylindrical steel shells lined with refrac- tory brick. Kilns may be operated continuously or intermittently. To secure the greatest efficiency continuous operation is imperative. The common types of kiln are the mixed-feed and separate-feed kilns. In the mixed-feed type, bituminous coal and limestone are fed into the top of * Trans. American Ceramic Society, Vol. 13, p. 618, article on burning of limestones by A. V. Bleininger and W. E. Emley. t See Year Book of A.S.T.M., 1915, Serial Designation C5-15, for the specifications. 359 360 LIMES AND PLASTERS Chemical Composition op Limbs (A.S.T.M.) High Calcium. Calcium Magnesian. High-Magnesian. Properties Considered. Selected. Run-of Kiln. Selected. Run-of Kiln. Selected. Run-of Kiln. Selected. Run-of Kiln. Calcium Oxide, per cent. . . . Magnesium Oxide, per cent. Calcium Oxide plus Magne- sium Oxide, min., per cent. Carbon Dioxide, max., per cent 90 (min.) 90 3 S 90 (min.) 85 5 7.5 85-90 90 3 5 85-90 85 5 7.5 10-25 90 3 5 10-25 85 5 7.5 25 (min.) 90 3 5 25 (min.) 85 5 Silica plus Alumina plus Oxide of Iron, max., per kiln in alternate layers; in the separate-feeci type, the limestone is not brought into contact with the fuel during the burning process. To accomplish this the fuel is burned in a grate which is attached to the sides of the kiln (see Fig. 1), and which is so arranged that the heat produced will ascend into the stack. The majority of the separate-feed kilns burn coal, some wood and a few producer gas. The mixed- feed kiln is more economical of fuel but does not produce as high-grade product as the separate-feed kiln. Most American con- cerns now use the separate-feed kiln to burn lime. The rotary kiln which is widely used in manufacturing Portland cement has not met with favor in burning lime for two reasons. If the rotary kiln is used the rock must be finely crushed. This not only increases the cost of burning but also makes it necessary to grind or hydrate the burnt material. In Germany continuous kilns of the ring type similar to those used in this country for burning clay products are much used. (See Art. 344.) 381. Production Statistics. — Lime is made in nearly every state and territory in the United States. The states which lead in production are: (1) Pennsylvania, (2) Ohio, (3) Maine, (4) New York. Fig. 1. — A Separate Feed Key- stone Lime Kiln. LIMES 361 The total output of the U. S. in 1914 was 3,380,928 short tons, valued at $13,247,676. Nearly one-sixth of the lime produced is sold in hydrated state. About 40 per cent of the total production is used in construction. A considerable proportion of the remainder is utilized in making fertilizer, in chemical industries and in paper manufacture. 382. The Slaking and Hardening of Lime. — When 18 parts, by weight, of water is mixed with 56 parts of pure quicklime the mixture swells with an evolution of considerable heat, increases in volume about 300 per cent and forms calcium hydroxide Ca(0H)2. Limes high in magnesia, poor limes, will require more water and slake more slowly than high-calcium limes, fat limes. However, in order to form a paste easily worked under the trowel and to avoid burning, masons slake hme with a large excess of water. Porous limes or finely ground limes slake more rapidly than dense, lumpy limes. Underburning or overburning causes the lime to slake slowly and injures its strength. When used in construc- tion lime paste is mixed with 1 to 4 parts of sand. By adding the sand, not only is the cost decreased but the shrinkage is also greatly reduced. In the hydrating of lime, part of the calcium hydroxide crystallizes and part forms colloids. These components secure a certain amount of rigidity through evaporation and absorption of the surplus water by the surrounding masonry. Final hardening is attained, however, through desiccation of the water in the crystal or colloid mass and replacement by carbon dioxide from the air. Thus the paste is slowly converted into a carbonate of approximately the same composition as the original lime- stone. Obviously, owing to the inaccessibility of the interior of a masonry joint this hardening action progresses very slowly and, if the wall is quite thick, may take years for its completion. When stored in air, quicklime soon decrepitates due to the absorption of moisture and carbon dioxide and is in time reduced to lime carbonate. Therefore, in order to preserve its hardening power, quicklime must be stored in barrels or other tight containers unless it is to be immediately used. Since experience has shown that ground lime keeps better than lump lime, manufacturers of ground lime can ship their product in open cars, although some prefer to use bags. When ground lime is thus exposed in shipment the outer layer of material air-slakes and thus protects the inner mass. On account of the impurities, silica, alumina and iron oxide often present in limes, the amount of water and the time required for slaking vary. Furthermore, since on the job the paste is often " burned," due to insufficient mixing, or is insufficiently slaked, it is apparent that slaking may be more efficiently done in an especially equipped plant than in the field. Consequently, despite the fact that quicklime works somewhat 362 LIMES AND PLASTERS more smoothly under the trowel, there has arisen within the past decade a considerable demand for hydrated lime. 383. Hydrated Lime. — When quicklime is finely crushed, completely slaked with a minimum amount of water and screened or ground to form a fine homogeneous powder the product is called hyrated lime or " limoid." If the hme from which it is made is pure, hydrated hme is a white powder having a specific gravity of 2.08; the specific gravity of some dolomitic hydrates may reach 2.40. Hydrated lime is in general sold in paper bags of 40-lb. capacity or in 100-lb. burlap or cloth sacks. In such containers it may be stored for a much longer time than lump lime without serious deterioration. 384. Testing of Limes. — In addition to chemical analysis, the Amer- ican Society for Testing Materials specifies a fineness test on slaked lime in order to determine the percentage of inert material in the product. For this test a representative 5-lb. sample of lime broken to pass a j-in. sieve, is carefully slaked with sufficient water to form the maximum amount of lime putty, care being taken to avoid drowning or burning. After standing for twenty-four hours the paste is washed through a 20- mesh sieve. The stream of water should flow under moderate pressure and rubbing of the material through the screen should be avoided. Not over 3 per cent of selected or 5 per cent of run-of-kiln lime should remain on the sieve. Hydrated lime when tempered with water and formed into pats should pass the standard accelerated soundness test prescribed for Portland cement. Tensile strength tests are also sometimes made on lime mortars. For this purpose the standard briquette used in cement testing is the form of specimen which is generally adopted. When compression or transverse tests are made it is necessary to specify a certain size of test-piece, since the rate of carbonation is affected by the thickness of the specimen. Large cubes have greater strengths than small ones. Standard methods of making strength tests have not been formulated. The yield or volume of lime paste which can be made from a given weight of hme is an important factor in estimating the quantity of lime required to make a given amount of mortar. The test can be made in the same manner as indicated in Art. 463, Ch. XII. 385. Properties of Lime. — From a long series of experiments on the strength of Ume-mortars made at Iowa State College the results shown in Table 1 have been derived. For some unknown reason the strength of these mortars was somewhat greater at nine months than at one year, although the carbonation process was still incomplete at the end of a year. In general the greater strengths were obtained with the lower percentages of water and sand. The hardening of the calcium limes was more uniform LIMES 363 and rapid than that of the magnesian hmes, but the latter exhibited higher strengths. * TABLE 1.— RESULTS OF TENSILE TESTS OF LIME-MORTAR BRIQUETTES MADE AT IOWA STATE COLLEGE IN 1907 1 AvEBAGE Strength of 10 Briquettes IN Lb. /IN. 2 *_ Age 3 Months. Ag 3 6 Months. tn o .. Calcium Limes. Magnesian Limes. Calcium Limes. Magnesian Limes. ■M Mason Spring- Eagle Mason Maquo- Mason Spring- Eagle Mason Maquo- fi B? City. field. Point. City. keta. City.t field. Point. City. keta. 1 : 1 65 96 Ill 78 128 63 109 154 159 184 1 :2 100 76 94 100 92 130 68 97 113 137 167 1 :3 55 68 90 86 130 53 73 94 119 154 1 : 1 45 61 98 54 105 47 62 113 75 153 1 :2 200 51 55 90 81 105 53 57 88 98 125 1 : 3 50 55 101 81 100 54 48 104 91 108 1 : 1 43 41 120 75 101 42 45 140 96 123 1 :2 300 41 45 112 77 86 41 ■ 45 114 91 113 1 :3 46 53 87 70 82 48 51 99 88 96 * A river sand passing a No, 20 and held on a No. 30 sieve was used' in all tests, t Calculated in terms of the weight of the dry hydrate. X Age =16 weeks. Analyses of Limes Locality. CaO MgO AUOa-l-FejO., Loss on Ignition. Insol. Res. CO2 Mason City, la Springfield, Mo Eagle Point, la Mason City, la Maquoketa, la 95.40 94.70 58.19 72.40 60.60 0.43 0.40 33.48 15.23 35.70 2.98 1.80 6.60 6.03 2.10 0.00 2.08 slight 3.36 2.30 1.02 1.00 2.01 2.32 0.63 trace 0.10 Compressive tests by W. E. Emley and S. E. Young, of the Bureau of Standards Laboratory, show that the size of the sand grains has a pro- nounced effect upon the strength of Ume mortar, f The tests were made upon 2-in. cubes of 1 part quicklime to 3J parts sand, by weight. The age at breaking was ninety days. The results of these tests appear in Table 2. It should be noted that the mortars of fine sand gave the high- * For further data see Bulletin No. 1, Vol. 4, Engineering Experiment Station, Iowa State College, Ames, Iowa; Report of Chief Engineers, U. S. A., 1896, Pt. 5, p. 2839; Bulletin No. 4, Ohio Geol. Survey; Proc. A.S.T.M., Vol. 10, p. 328-40; also Vol. 14, p. 339. t Reported in Proc. A.S.T.M., Vol. 14, p. 346. 364 LIMES AND PLASTERS est strength, a condition which does not hold true in mortars made of hydrauUc cements. Probably the loss in strength due to the lack of den- sity in the fine-sand pastes is offset by the complete carbonation which is obtained on account of their porous structure. The effect of the proportion of sand on the compressive strength of lime pastes is also shown in Table 2. TABLE 2.— THE VARIATION IN THE COMPRESSIVE STRENGTH OF LIME WITH (o) AMOUNT OF SAND AND (6) SIZE OF SAND GRAINS (Tests by Emley and Young) Each result is averaged from 3 tests. (a) Amount or Sand. (6) Size of Grains. Compressive Strength Lb. per Sq.in. Size of Sand Grains between Meshes No. Compressive Strength Lb. per Sq. in. Sand Parte,. High Calcium Dolomitic. High Calcium. Dolomitic 1 273 151 116 112 116 372 267 217 202 203 10-20 20-30 30-40 40-60 60-80 98 118 138 186 260 166 1 214 2 312 3 335 4 414 High-calcium limes expand more in slaking and shrink more in setting than the magnesian limes. They are also more liable to injviry through " burning " in slaking. The magnesian and dolomitic limes work more smoothly under the trowel and on account of slowness in hardening afford more time for surface treatment in wall plastering. Their slowness in hardening also permits a thorough hydration of the improperly binned particles before the mass has become rigid. Consequently, plaster made of magnesian lime is less hkely to be disfigured by " hme pops " than that made of high calcium hme. 386. The Uses of Lime. — In construction, slaked lime is chiefly used to make mortar for laying brick and stone masonry and for plastering walls of buildings. When used for the latter pirrpose best results are obtained by slaking the lime for a period of three or four days. Hydratedlime is used for similar purposes but may be mixed into mortar and used imme- diately after arrival on the job. Being completely slaked, hydrated lime may be added to natural and Portland cement mortars to increase their plasticity and smoothness under the trowel. It is also used in making the popular stucco finish for exterior walls * and to increase the impervious- ness of Portland cement concrete (see Art. 533). *See specifications for Portland Cement Stucco, Proc. N.A.C.U. Vol. 7, p. 586. GYPSUM PLASTERS 365 387. Hydraulic Lime. — In the middle of the eighteenth century John Smeaton, the celebrated English engineer, was confronted with the problem of finding a cement which could be used in the construction of the famous Eddy stone Lighthouse. The only cementing material then in use was quicklime, which does not harden under water. After a series of experiments he discovered that an impure limestone containing a small amount of clay, if calcined in the ordinary way, would produce a lime which would slake upon the addition of water and. would harden under water. On account of the latter property the name hydraulic lime was given to this material. In France and southern Europe it is still used to a considerable extent. On account of the prevalence of raw materials suitable for the manufacture of Portland and natural cements no hydraulic hme is manufactured in the United States. However, Lafarge cement, a by-product in the manufacture of hydraulic lime, is used considerably in this country. Hydraulic lime is manufactured in the same way as quicklime, although a somewhat higher temperature is required in burning. In slaking, con- siderable care is required to provide just sufficient water and no excess, since an excess would cause the lime to harden. After slaking, the coarse material is screened out and the fine product bagged for market. The coarse particles are finely ground and sold for natural cement. The spe- cific gravity of hydraulic lime is about the same as that of the natural cement. Mortars made from the famous limes of Tiel, France, also have about the same strength as those made from natural cement. 388. Lafarge Cement. — This cement is used in America for stucco work and in laying marble and other masonry which is stained by natural or Portland cement mortars. It is a Grappier cement made as indicated above. Published analyses show it consists principally of lime (58-59 per cent) and silica (27-31 per cent) with 2.6 to 4.5 per cent of alumina and smaller percentages of iron oxide, magnesia and the alkalies. Accord- ing to the manufacturers' circular * this cement has a specific gravity of 2.6, an initial set in 4 hours, final set in 10 hours, and a residue on 100- mesh sieve of 0.6 per cent. Its strength neat and in a 1 : 2 mortar is about 60 per cent of that demanded of a standard Portland cement at 7 and 28 days. At two years the record gives a neat strength of 665 lb. per square inch. GYPSUM PLASTERS 389. Introduction. — On account of the wide use of gypsum plasters in the arts and in building construction a brief resume of some important facts concerning them will be given. In the United States plaster of Paris, stucco, cement plaster, wall plaster, and hard finish plaster are * Eckel's Cements, Limes and Plasters, p. 185. 366 LIMES AND PLASTERS extensively used in wall construction. In Germany flooring-plaster, made by calcining gypsum at a high temperature, has been considerably used. In all of these powders, gypsum in a more or less dehydrated state is the essential element. When water is added to these substances they become rehydrated forming compounds similar to those existing before calcination. 390. Gypsum. — There are two commercial varieties of crude gypsum, rock gypsum and. gypsum earth or gypsite. These substances consist principally of a hydrous sulphate of lime (CaS04+2H20), with varying percentages of silica, carbonate of lime, carbonate of magnesia, and iron oxide. Pure gypsum is a white translucent crystalline mineral, so soft that it can be scratched with the finger-nail. When heated to 400° F., pure gypsum loses its luster and its specific gravity is increased from 2.3 to approximately 2.95 due to the loss of water of crystallization. Deposits of gypsum are numerous and widely scattered. The rock deposits occur in beds commonly traversed by thin strata of limestone and often adjacent to rock-salt deposits. Gypsite formations consist of masses of gypsum crystals interspersed with clay and sand. The states leading in the production of gypsum are New York, Iowa, Michigan, Ohio, Virginia, Texas and Oklahoma. Among the countries of the world the United States ranks first and produces about two-fifths of the total supply. The value of the 2,476,465 short tons produced in the United States in 1914 was $6,895,989 . Of the quantity obtained in this country about two-thirds is calcined and made into plasters; approximately one-sixth is sold in crude state to Portland cement manufactiu-ers. 391. Manufacture of Plasters. — For making the refined grades of plaster of Paris in which a uniform degree of calcination is required the oven process is much used in Europe. In this coimtry, however, on ac- count of expense and time required, this method has been discarded in favor of the kettle and rotary process, the former being used in nearly all plants making plaster of Paris or cement plaster. Hard finish plasters are made in kilns similar to the mixed-feed kilns used in calcining lime. After the raw material has been excavated or mined it is put through one or more crushers, and if the kettle process is used, is then ground by buhr-stones or like mills until about 60 per cent will pass a No. 100 sieve. In the rotary process the final pulverization is omitted until calcination is completed. The kettles employed for calcination are 8 or 10 feet in diameter and about 6 or 7 feet high. The sides are made of sheet steel and the bottoms of cast iron. Each kettle is placed with its top just above the working floor. The lower portion of the kettle is enclosed in a masonry chamber which serves to support the kettle and distribute the heat from the grate fire about it. Two or four horizontal flues running through the kettle increase the circulation of heat. A power-driven stirrer is used to agitate GYPSUM PLASTERS 367 the contents of the kettle and thus prevent the bottoms from burning out. The hot gases and steam are led away through a stack. After the pulverized material has been chuted into a kettle, heat is very slowly applied until the mechanically held water is driven off. At a temperature just above the boiling-point of water the whole mass bubbles up violently and then sinks. At 290° F. the combined water begins to boil out and between 340° and 396° F. the process is stopped. The impure gypsites generally require a higher temperature than the purer rock gypsums. In many plants the final temperature is judged by the appear- ance of the boil, although thermometers are often used in making plaster of Paris. By the kettle process, it requires about two or three hours to calcine a charge yielding 5 or 6 tons. The calcined product is then run from the bottom of the kettle into a cooling vat, whence, after partially cooling, it is sent to the screens. Residues from the screens are reground; the fines are stored in large bins. In the rotary process the raw material is crushed to pass a 1-in. mesh and is then fed into the upper end of a cylinder which rotates about an axis slightly inclined to the horizontal. Calcination is accomplished by the introduction of hot furnace gas, the temperature of which can be regulated by an admixture of a forced draught of air. When properly roasted the material is conveyed to brick-lined calcining vats in which further changes are brought about by the heat within the material. The product from the vats is then finely ground and screened. Continuous operation is the main advantage which this process possesses over the kettle process. In order that the workman may properly handle plaster of Paris or stucco, it is necessary to delay the time of setting. This is accomplished by adding a fraction of one per cent of a retardant like glue, sawdust or blood after the plaster has cooled. To increase the cohesiveness of wall plaster, cattle hair or wood fiber is introduced. For this purpose about 2 or 3 lb. of finely picked hair or 60 to 100 lb. of finely pulverized wood fiber is added to each ton of plaster. Wall plasters made from pure raw materials are generally adulterated with 15 to 20 per cent of hydrated lime to increase the plasticity of the product. The term " stucco " is sometimes applied to a plaster so treated. Wall plasters made from raw materials containing considerable clay do not require such addition. Many of the plasters are packed in jute sacks holding 100 lb. each. Recently a considerable effort has been made to further the use of paper sacks, thus obviating the traffic in empty jute bags, which is a considerable nuisance and expense. 392. Plaster of Paris. — Plaster of Paris is produced by incompletely 368 LIMES AND PLASTERS dehydrating pure, finely ground gypsum at a temperature somewhat less than 400° F. Most plasters closely approach the theoretical composition — CaS04+4H20 — which contains about 6.2 per cent of water. Plaster of Paris is a white powder having a specific gravity of 2.57. When tem- pered with sufficient water to form a plastic paste it sets in 5 to 10 min. The setting of plaster of Paris is attributed to the formation of gypsum crystals from a supersaturated aqueous solution. Why the rapidity of setting is so very much greater when the powder consists of plaster of Paris than when it consists of anhydrous gypsum plus water is a point not yet settled. When substances of a colloidal nature (glue for example) are mixed with the plaster the formation of crystals is hindered and the time of set retarded. In hardening, plaster of Paris first shrinks and then expands. The latter property makes the material valuable in making casts, since a sharp impression of the mold can be secured. Owing to the rapidity of set and difficulty in working this material, its use in structures is limited to orna- mental work. 393. Cement Plaster. — Cement plaster may be made by adding a retardant to plaster of Paris, or very commonly by using impure raw mate- rials which produce a plaster that is slow setting. Ordinarily, less than three-fourths of one per cent of retardant is required. Some of the plasters made from impure materials are so slow in setting that small percentages of accelerators such as sodium chloride, sodium sulphate or sodium carbonate must be added to render the plaster usable. Most plasters are ground so that 60 to 70 per cent will pass a 100- mesh sieve. Tests seem- to indicate that the more finely ground plasters will produce mortars of highest strength. Results of a large number of tensile strength tests on plasters are given in Rept. Iowa Geol. Surv., \o\. 12, p. 232. The plasters were hand mixed and packed into cement briquette molds by the fingers. About 35 per cent of water was used in making the neat specimens. Immediately after setting the specimens were removed from the molds and stored in air or water until tested. The results show that most of the neat plasters stored in air developed over one-half of their strength at one month in one day. Those specimens which were stored in water exhibited little increase in strength after one day and were weaker than those subjected to air-cui-ing. The air-cured specimens gained but little strength after one month. The average strength of air-cured briquettes one month old made of nine different brands of plaster was 370 lb. per square inch. Plaster and sand mortars of 1 : 1 proportions may be expected to develop tensile strengths of about 80 per cent of the neat strength at corresponding ages. Mortar of 1 : 2 proportions generally possess one- half to two-thirds of the neat strength. GYSPUM PLASTERS 369 Compressive strength tests on 2-in. plaster cubes by Slosson and Moody {Tenth Annual Report Wyoming Agric. and Mech. Coll., 1900), furnish values of neat strength varying between 887 and 2236 Ib./in.^ The plasters were one week old and air cured. Those showing the highest strength had no retardant. Specimens of 1 : 1 plaster and sand mortars had about two-thirds of the strength of the neat test-pieces. In the previously cited Iowa report Prof. Marston's tests showed that the adhesion of plaster mortars to a fractured surface of plaster was approximately two-thirds of the strength of the mortar. Gypsum wall plasters have become quite popular in recent years because they are ready for use when brought to the job and also because they harden more rapidly than do the older lime plasters. However, lime plasters are more plastic and may, therefore, be loaded with 3 or 4 parts of sand, whereas the gypsum plasters cannot carry over 2 parts; also, when properly slaked, lime plasters form eventually just as satisfactory walls as those made from cement plasters. 394. Hard Finish Plasters. — By burning gypsum to a considerably higher temperature than the calcining temperature of cement plaster, treating with certain solutions like alum and Glauber's salts and burning again, there may be produced plasters which set slowly but ultimately become very hard. Such plasters may be polished to form a smooth sur- face and make a very satisfactory finish for interior walls. Often walls of these plasters are marked to imitate tiling with pleasing results. Keene's cement is made by burning a very pure rock gypsum at a cherry-red heat, then dipping the calcined product into a 10 per cent solution of alum and burning again at a red heat. Subsequently the material is finely ground. Keene's cement is practically pure calcium sulphate (CaS04) with a very small percentage of calcium carbonate (CaCOa). On account of the care taken in selecting the raw material the plaster is of 'an unusually pure white color. At seven days its neat tensile strength may be expected to be between 500 and 700 lb. Mack's cement is made by burning gypsum at a very high temperature and adding about 0.4 per cent of burnt Glauber's salts (Na2S04) or potas- sium sulphate (K2SO4). It is said to form an unusually hard dense and durable stn-face which will take paint well. 395. Other Gypsum Building Materials. — Blocks and tile made from wall plaster and suitable for floor and interior wall construction are now on the market. These forms are light, can be easily sawn to desired shape, possess sufficient strength for many types of construction and have a high resistance to fire.* Mixed with fine cinders or wood chips and sufficient water to form a thin consistency, wall plaster has been * See Gypsum as a Fireproofing Material by V. G. Marani, Jour. Cleveland Engr. Soc, Vol. 7, p. 213. 370 LIMES AND PLASTERS used in making floors for buildings. Such floors can be much more rapidly constructed than concrete floors, owing to the rapidity with which the plaster hardens.* However, they are neither so resistant to fire nor so strong as concrete floors. Another product of recent origin is plaster board. It is made of thin layers of cardboard or wood cemented together by wall plaster. It is used in place of lath or it may be used in place of plaster wafls by covering the joints with neatly finished wooden strips. * See Bulletin No. 25, Public Works of the Navy, Jan. 1917. CHAPTER XII METHODS OF TESTING HYDRAULIC CEMENTS 396. Necessity for Testing Cement. — Experience has shown that it is practically impossible to make large quantities of cement without any variation in quality. To be sure, some mills working with raw materials which run very uniformly and using the best of equipment and methods of operation will have very few unsuccessful " burns " in a year, while others will be less fortunate. Nevertheless the consumer has little chance of ascertaining how his particular carload of cement was made; therefore, if he has under way a construction of any importance, he ought to satisfy himseK regarding the quahty of his purchase. He should test his cement not only to see that he gets what he has paid for but also to forestall the possibility of a failure through the use of defective material. In engineering construction the main qualifications demanded of a cement are permanency of structure, strength, and a rate of setting suit- able to the demands of the work. To determine these qualifications, both physical and chemical tests are made, the former, on account of importance, more often than the latter. As a result of long experience the physical tests which have come into general use in determining the acceptability of cement are: (1) soundness or constancy of volume, (2) strength, (3) time of set or activity, (4) fineness, and (5) specific gravity. In order that the results of such tests made by different parties may accord as nearly as possible, it is necessary that a standard method be rigidly adhered to and that only experienced operators, who fully appreciate the necessity of eliminating personal equa- tion from all manipulations, be employed. In the fine type of the following sections will be considered the Standard Specifications and Tests for Portland Cement as revised by the American Society for Testing Materials (effective Jan. 1, 1917). The methods of testing are adapted to any of the hydraulic cements with the exception of the accelerated soundness test- which is used with Portland cements only. The sections of the standard methods will be numbered consecu- tively but will be interspersed with comments and references to other methods of testing which will appear in large type. Since it is only by close observance of standard methods that uniformity in testing may obtain, any divergence by the operator from such methods should be stated with full explanation in reporting the results of tests. 371 372 METHODS OF TESTING HYDRAULIC CEMENTS STANDARD SPECIFICATIONS AND TESTS FOR PORTLAND CEMENT * 1917 These specifications are the result of several years' work of a special committee repre- senting a United States Government Departmental Committee, the Board of Direction of the American Society of Civil Engineers, and Committee C-1 on Cement of the American Society for Testing Materials in co-operation with Committee C-1. SPECIFICATIONS 1. Definition.— Portland cement is the product obtained by finely pulverizing clinker produced by calcining to incipient fusion an intimate and properly propor- tioned mixture of argillaceous and calcareous materials, vdth no additions subsequent to calcination excepting water and calcined or uncalcined gypsum. I. CHEMICAL PROPERTIES 2. Chemical Limits. — The following limits shall not be exceeded: Loss on ignition, per cent 4.00 Insoluble residue, per cent . 85 Sulphuric anhydride (SOj), per cent ' 2.00 Magnesia (MgO), per cent , 5.00 II. PHYSICAL PROPERTIES AND TESTS 3. Specific Gravity. — -The specific gravity of cement shall be not less than 3.10 (3.07 for white Portland cement). Should the test of cement as received fall below this requirement a second test may be made upon an ignited sample. The specific gravity test will not be made unless specifically ordered. 4. Fineness. — The residue on a standard No. 200 sieve shall not exceed 22 per cent by weight. 5. Soundness. — A pat of neat cement shall remain firm and hard, and show no signs of distortion, cracking, checking, or disintegration in the steam test for soundness. 6. Time of Setting. — The cement shall not develop initial set in less than 45 minutes when the Vicat needle is used or 60 minutes when the GiUmore needle is used. Final set shall be attained within 10 hours. 7. Tensile Strength. — ^The average tensile strength in pounds per square inch of not less than three standard mortar briquettes (see Section 51) composed of one part of cement and three parts standard sand, by weight, shall be equal to or higher than the following: Age at Teat, Days. Storage of Briquettes. Tensile Strength, Lb. per §^ / / ^ Sands — ' ]/ y / /' 7 y y I P / ^^..--^ ..>^iSS>- ^-""^ .^.s^^l^"-"^ ^ ^^^^ ^ -■^ / /. y s„.4(coavae) 1 y -— "^ Stone Screenings l- 1 1 1 1 1 1 1 o# o# niameters of Particles in Inches and Sieve Numbers Fig. 4. — Mechanical Analyses Curves for Typical Sands and Screenings. 331, U. S. Geol. Survey.) {BvU. No. fine powder is particularly objectionable; since mortars containing such aggregate " dust " and wear badly. 471. Voids and Specific Weight.— Two other criteria of the worth of sands and screenings are afforded by the percentage of voids and the specific weight. Approximately, we may say that for fine aggregates of like chemical and mineral constitution those with the lowest percentage of voids or the highest specific weight are the most desirable, since a less proportion of cement will be required to fill the unoccupied space in such aggregate. One must bear in mind, however, that due to differences in 418 MAKING MORTAR AND CONCRETE gradation two sands which contain the same percentage of voids may produce mortars differing considerably in density and strength. For instance, comparing a fine and a coarse sand containing the same propor- tion of voids, the coarse sand will produce the stronger mortar. Since even a small percentage of moisture tends to hold apart the grains and increase the voids, the moisture content exercises a very important influence upon the percentage of voids and the specific weight. For exam- ples examine Fig. 5, which shows the effect of the percentage of moisture 10 12 14 16 18 Per cent Moisture in Terms of Dry Sand (by wt.) 28 Fig. 5. — The Effects of Moisture on the Voids and Specific Weight of a Fine and a Coarse Sand. upon the voids and specific weights for a fine and a coarse sand. The curves in the diagram serve to illustrate the importance of making the determinations on material containing the per cent moisture ordinarily present in field operations, if the results are to be employed in the'field. If, however, a comparison of different sands is to be made determinations should also be conducted upon dried aggregate. To facilitate the computation of the percentage of voids from the specific weights, the diagram in Fig. 6 is provided. Since a knowledge of the specific gravity of the aggregate is necessary in order to use this dia- gram the following average values are given for sands: Quartz, 2.65; dolomitic sands, 2.65-2.75; calcareous sands, 2.60-2.70. A rough average PROPERTIES OF FINE AGGREGATE 419 value for all sands is 2.65. The specific gravities of stones may be found in Art. 268. For good sands the percentage of voids generally lies between 28 and 35. The corresponding weights per cubic foot range from 120 to 105 lb. In screenings, on account of the angular shape of the particles, a somewhat 146 140 \Sp. Gr. 130 X s\> \ ■S 120 |115 O u 110 « 106 g o ^ 100 d ^ 90 1 1 ^ 80 76 \\ x\ X^>^" \ N ' --\ \*> v\-^ \V \\ """^ \^ \ \X \\1 \ \<.> \\ \\ XV x\ \ \ \ \ \>> s \ ^s \\ \Xs \X \> \ w XX vX^ x\ Xs^ XV vv V \X -X x^ $^ \\ x^^ x^ ^ 65 60 \ "^^X ->^ w \ XV 36 40 46 Percentage of Voids Fig. 6. — Relation of Specific Weight to Voids. higher range in the percentage of voids is to be expected. Screenings of good quality should not, in general, contain over 38 per cent voids. 472. Mortar Tests. — By far the most valuable indices of the efficiency of a fine aggregate are given by the strength and yield tests of mortars made with a cement of known properties. Although tensile tests on 1 : 3 mortar briquettes are ordinarily made, compression tests are of more value. Cross-bending tests are of some value but should only be employed where facilities for testing are limited. The yield test is often made to ascer- 420 MAKING MORTAR AND CONCRETE tain both the yield and density of the mortar. The density forms a much more valuable indication of the probable strength of the mortar than can be obtained from a determination of the voids in the fine aggre- gate. In making these tests a standard consistency should be adopted for the mortars under comparison. Some experimenters beUeve in employing the standard consistency used in cement testing, while others are in favor of a slush consistency comparable to that used in construction. The advocates of the latter claim that the proportionate strength of poor sands is much less for the slush consistency than for the normal. Consequently poor material is more readily detected when the wet consistency is em- ployed.* On the other hand, if density is to be determined, the use of a slush consistency in yield tests produces misleading results due to the excess of water. A rough but satisfactory method of determining normal consistency for mortars made of fine aggregate and cements follows. Weigh the quan- tities of standard sand and cement necessary to make 500 or 600 grams of dry material of the required proportions, mix dry and form into a crater in accordance with the method suggested in Art. 413. Do likewise with a similar quantity of the given sand or screenings and cement. To the standard sand mixture add the proper amount of water to bring the mortar to normal consistency and mix in the standard way prescribed in Art. 413. Next estimate the necessary percentage of water to bring the test mortar to the same consistency, and mix. As an aid to such estimation it should be remembered that a natural sand or screenings will generally require from 10 to 50 per cent more water than standard sand and that the per- centage of water required varies with the proportion of fine material in the aggregate. Two or three trials will ordinarily suffice to obtain the con- sistency which appears and feels Uke that of the standard sand mortar. Mortars of normal consistency suitable for construction purposes should possess strengths at least equal to standard sand mortars. In general, the density of a 1 : 2 or 1 : 3 mortar of standard consistency made of well-graded sand will lie between 0.70 and 0.75; the yield will generally vary between 1.08 and 1.20 for similar mixes, being greater for the richer mix. CHARACTERISTICS AND PROPERTIES OF COARSE AGGREGATE 473. Requirements for Coarse Aggregate. — Any stone or gravel which possesses the strength of neat cement is sufficiently strong for use as an aggregate. In hardness, however, there is a considerable range permis- sible depending upon the kind of construction. In floors, pavements and other surfaces subjected to considerable wear and upon which no top * See Proc. A.S.T.M., Vol. 13, p. 797. PROPERTIES OF COARSE AGGREGATE 421 dressing is placed a uniformly hard and tough coarse aggregate which cannot be scratched by the knife is desired. For other forms of construc- tion extreme hardness is not essential provided the aggregate is tough and strong. The coarse aggregate should also be free from loam, clay, vegetable or organic matter, and other injurious substances previously mentioned in discussing fine aggregates. Preferably, the particles of the aggregate should be approximately cubical or spherical in form. Flat, disc-shaped pieces and long, thin wedge-like particles are objectionable since they cannot be so closely com- pacted as the cubical or rounded stones. To secure a good bond between the mortar and the coarse aggregate, the cleavage planes of broken stone and the surfaces of gravel particles should be uneven and rough. Very porous particles must be saturated with water before mixing with cement. The size of the particles of the coarse aggregate should either be uniform or else uniformly graded from fine to coarse. Material passing a J-in. sieve should either be screened out or, if it is of proper quality, it may be substituted for an equal amount of fine aggregate. Pit-run gravel or other mixed aggregate in which the maximum size of particle is 1 in. should not contain over 50 per cent, by weight, of material passing a J-in. sieve. The maximum permissible size of stone or gravel particles depends upon the character of the construction. For massive work such as heavy piers, abutments, thick walls, footings and similar constructions, aggre- gate passing a 25-in. mesh is often used; but for thin walls, reinforced beams and columns, and small members in general, material passing a 1-in. sieve is frequently specified. The voids in well-shaped broken stone of uniform size generally vary between 45 and 55 per cent. In uniformly graded broken stone, the per cent voids should lie between 40 and 50 depending upon the range in sizes. The per cent voids in well-graded gravel above J in. in size should not be over 38. In well-graded run-of-pit material the voids should not be above 28 per cent. 474. Characteristics and Properties of Broken Stone. — The broken stones commonly used for coarse aggregate are trap rock, granite, dolomite, limestone and sandstone. Trap rock, on account of its hardness, tough- ness, and great strength, is an excellent coarse aggregate. Furthermore, the real trap rocks possess a greater resistance to high temperatures than the other broken stones. The granites also furnish a very good material for coarse aggregate. Both of these classes of rock are very desirable in road or floor construction, or on surfaces which are subjected to consider- able abrasion. Oftentimes, however, these hard igneous rocks crush into elongated particles which cannot be closely compacted. Consequently maximum density cannot be secured in the concrete or mortar into which 422 MAKING MORTAR AND CONCRETE they are made. When such aggregate have very smooth cleavage planes, the mortar will not strongly adhere to the surfaces and the resulting con- crete will be deficient in strength. In spite of these objections, however, these rocks form the most valuable class of crushed aggregates. Crushed dolomite and limestone are extensively used for coarse aggre- gate, and the hard varieties of these rocks form a good material for con- structions requiring high strength. As a class, however, these aggregates have not as high resistance to fire or to abrasion as the traps and granites. Soft limestone is often very porous, and unless thoroughly wetted before mixing will weaken the strength of the surrounding mortar by absorbing water from it while the hardening process is going on. Limestones fre- quently contain large quantities of very fine dust which, in wet weAther, coat the surfaces of the stones. If there is a large proportion of this dust in the coarse aggregate, and if a fine sand is being used, it may be neces- sary to screen out the dust in order to secure a concrete of high strength. However, if the sand is coarse, allowance may be made for this dust in proportioning. The stronger and more dense sandstones make a satisfactory coarse aggregate, but the soft varieties together with the shales and slates should not be used. The latter are likely to be deficient in strength and to con- sist of particles which are improperly shaped for making dense concrete. The voids in crusher-run of broken stone with the dust out generally vary between 43 and 50 per cent. The per cent voids varies with the degree of compacting, but is not materially affected by the way in which the stone is poured into the measure. Dropping from a considerable height tends towards greater compactness. Table 2 contains a summary of results obtained by Prof. I. O. Baker of the University of Illinois * on the voids in different grades of crushed Umestone. Table 3 has been compiled from various reports. The voids or weights per cubic foot for crushed stone may be gotten from Fig. 6; specific gravities of various classes of stone will be found in Art. 268. The best gradation of sizes of coarse aggregate is in dispute. Some authorities claim that coarse broken stone consisting of particles of approximately the same size is preferable to aggregate which is graded from 3 in. to the same maximum size. On account of the tendency of coarse stone to separate from the concrete in which the coarse aggregate is of one size only, it seems preferable to use a graded mixture. Further- more, experiments have shown that concrete made of coarse aggregate which varies uniformly in gradation is just as strong and dense as that made from one-size coarse aggregate. Fig. 7 shows typical mechanical analysis curves for crusher-run broken stone and the desirable form of curve for such aggregates. Since the coarser particles of stone roll to the *Bull. No. 23 Univ. ot 111. Eng. Expt. Sta,, 1908. PROPERTIES OF COARSE AGGREGATE 423 Diameter of Particles in Inches Fig. 7. — Characteristic Mechanical Analysis Curves for Gravel and Stone; also Ideal Gradation Curves. TABLE 2.— PERCENTAGES OF VOIDS AND WEIGHTS PER CUBIC YARD OF CRUSHED LIMESTONE. (Baker) " Size of Stone. Pes Cent Voids. Weights in Lb. per Cu YD. Wagon Loads. Car Loads. Illinois. By Pour- ing in Water. From Specific Gravity. At Crustier. After Hauling i Mile or More. At Crusher. After Hauling 75 Miles or More. Chester Chester .... Chester. . . . Chester. . . . Joliet Joliet Joliet Kankakee. , Kankakee. . Kankakee. . Kankakee. . f-in. scr. J-in. sor. 2-in. to |-in. 3-in. to 2-in. i-in. sor. 2-in. to 5 in. 3-in. to 2-in. f-in. scr. li-in. to f-in. 2i-in. to i-in. 2i-in. to IJ-in- 40.9 43.0 46.6 46.1 42.2 47.9 47.5 39.6 45.7 44.3 46.2 46.8 45.6 46.6 45.1 47.1 46.2 46.1 46.1 44.7 42.9 43.4 2442 2344 2367 2303 2315 2430 2325 2797 2582 2569 2533 2480 2697 2546 2546 2348 2659 2386 2361 2850 2545 2905 2592 2553 * Each value of per cent voids represents a number of tests in which size of vessel varied from 0.7 cu.ft to 27 cu ft. and the height of drop of materials varied up to 20 ft. Percentages of absorption (by weight) for these limestones were Joliet, 0.64; Kankakee, 1.84; Chester, 1.01. Average values of specific gravity were Joliet, 2.71; Kankakee, 2.61; Chester 2.57, 434 MAKING MORTAR AND CONCRETE TABLE 3.— VOIDS AND SPECIFIC WEIGHTS OF COARSE AGGREGATES Kind of Aggregate. Trap Trap Trap Quartzite. . Quartzite. . Granite . . . Granite. . . Granite . . . Granite. . . Granite. . . Limestone . Gravel .... Gravel .... Gravel (Pit-run) Gravel (Lake).. . Gravel Gravel Cinders Bank slag. . . . Bank slag . . . , Bank slag ... Machine slag . Range in Sizes. j-in. scr. IJ-in. to i-in. 3-in. to IJ-in. j-in. scr. li-in. to j-in. i-in. scr. |-in. to i-in. li-in. to i-in. 2-in. to i-in. 1-in. to dust 1-in. to dust 1-in. to i-in. IJ-in. to i-in. { Ij-in. to dust 51 %< i-in. 1-in. to No. |-in. to i-in. Ij-in. to i-in. ( li-in. to dust I 37% < i-in. j^-in. scr. 1-in. to i-in. 25-in. to 1-in. 2-in. to 1-in. 10 Specific Gravity. 2.90 2.90 2.90 2.67 2.67 2.62 2.62 2.62 2.62 2.58 2.49 2.45 2.77 2.77 2.75 2.70 2.70 1.53 Weight per Cu.ft. (Lb.) 98.1 90.0 93.5 92.8 86.4 95.0 86.5 88.9 84.7 95.3 97 7 102.4 110.5 125.9 112.5 105.0 102.4 47.0 117.0 67.0 72.0 96.0 Per Cent Voids. 46.5 50.2 48.1 44.3 48.1 41.8 47.0 45.6 48.1 40.9 37.1 33.0 36.0 27.0 34.4 37.7 39.2 50.7 Authority, W. E. McClintock W. E. McClintock W. E. McClintock M. O. Withey M. O. Withey M. O. Withey M. O. Withey M. O. Withey M. O. Withey U. S. Geol. Sur. U. S. Geol. Sur. U. S. Geol. Sur. M. O. Withey M. O. Withey M. O. Withey M. O. Withey M. O. Withey U. S. G. S. Carnegie Steel Co. Carnegie Steel Co. Carnegie Steel Co. Carnegie Steel Co. lower portions of a pile it is advisable on large jobs to procure the broken stone screened into several sizes and keep the sizes separated until they are placed in the mixer. This is the only way in which the same gradation in the size of particles composing the coarse aggregate may always 'be maintained. Broken stone uniformly graded from 2\ in. down to \ in. diameter makes stronger and denser concrete than similar material vary- ing from 1 in. down to \ in. Likewise broken stone between 21 and 2 in. is superior to the same aggregate ranging in size from 1 in. to 5 in. 475. Characteristics and Properties of Gravels. — The statement pre- viously made in regard to the mineral composition of sands apply equally well to gravels. For concrete pavement subjected to heavy traffic all particles should be of uniform hardness. They should not be scratched by the knife. Somewhat softer material may be employed in making concrete for constructions where strength is the only requisite. Gravels containing considerable proportions of disintegrated rock, pebbles coated with soft limestone, clay, or loam should be avoided. Organic matter even in small percentages is very objectionable. Such impurities are PROPERTIES OF COARSE AGGREGATE 425 often present in gravels gotten from pits in which the overlaying material is covered with leaves and decayed timber. It is possible, however, to remove loam, clay and organic material by thorough washing. The particles composing the gravel should be approximately round; flat, disc-shaped particles are undesirable since the latter do not compact into as dense mixtures as the former. Pit-run gravel generally contains too much material passing a J-in. sieve. If considerable gravel is to be used, it will be found economical to screen such material into two or more sizes and combine the proper proportions of the various sizes with a suitable amount of sand. Further- more, the gradation of sizes in pit-run gravel is decidedly variable, so that it is almost impossible to maintain a uniform quality of concrete when this material is used without screening. As an illustration of the variation in gradation which may exist in the product of a pit the curves for gravel marked No. 1 and No. 2 in Fig. 7 are of interest. The " ideal " curve shown in the figure is based upon the experiments of Fuller and Thompson (see Art. 483). For gravels with the sand screened out, a uniform grad- ation like that shown in curve No. 3 is desirable. Boulders of hard, dense rock may often be economically employed, especially in massive walls, abutments and dams, provided the interstices are thoroughly filled with concrete composed of smaller stones. It is desirable to keep such large rocks back from the surfaces of the work since thin outside shells of concrete sometimes spaU off, especially if they are poorly bonded and are subjected to frost action. The voids and specific weights of a number of gravels differing in gra- dation are given in Table 3. Average values of specific gravity for the different classes of gravel commonly found are approximately the same as the values given for sands in Art. 471. 476. Broken Stone and Gravel Compared. — On account of the spherical shape of its particles gravel makes a more fluid and dense concrete than does broken stone. Furthermore, gravel concrete requires less tamping or puddling than concrete made of broken stone in order to expel entrained air and thoroughly compact the mixture. In compressive strength, con- crete made from gravel seems to attain its final strength somewhat more slowly than broken stone concrete, although after a year's hardening there is little difference in the strengths gotten from good material of either class. On the whole, if equal care is taken in grading the particles of aggregate, gravel concrete seems to be more impervious to water than broken stone concrete. One of the main advantages in using broken stone for concrete is the possibility of securing a product which is of fairly uniform composi- tion. (See also Figs. 8 and 9, Ch. XIV.) 477. Miscellaneous Ag^egates. — Cinders, slag, and mine taihngs are also used as concrete aggregates. Cinders on account of their resistance 426 MAKING MORTAR AND CONCRETE to high temperatures have been employed considerably for making fire- proof concrete. For this purpose the cinders should be a hard, vitreous cUnker, practically free from sulphur, iron oxide, and combustible sub- stances. From the standpoint of fireproofing, a highly porous cUnker is desirable. However, care should always be taken to thoroughly drench the chnker before mixing so that it will not absorb water from the mortar during the process of hardening. Cinders make a very hght concrete but should not be employed in constructions demanding high strength or imper- viousness to water. Slag has been used to some extent both as fine and as coarse aggregate. It is an efficient aggregate for fireproofing. Often, however, the concrete made from it is deficient in strength. The slag sand is formed by running the molten stream from the furnace through a water spray into a large tank. The coarse material is sometimes obtained by crushing the refuse of the slag dump. Freedom from sulphur is also essential in slag aggregates and, like cinders, porous slag should be thoroughly wetted before mixing. Tailings from zinc and lead mines have been considerably used in Missouri and southwestern Wisconsin for concrete aggregate. The chief objection to these aggregates is the presence of pyrites, which causes rust- like spots on the surface of the concrete. THE PROPORTIONING OF MORTARS AND CONCRETES 478. The Principles of Proportioning. — The three most important laws of proportioning may be stated as follows : 1. The strength and impermeability of mortars and concretes of like density and the same constituent materials increase with the proportion of cement in the mixture provided the consistency is constant. 2. With the same proportion of cement, with like consistency and like materials the strength and impermeabihty increase with the density of the mixture. 3. Under common methods of placement the strength and imper- meability of well-cured concrete and mortar are greatest for plastic or mushy consistencies. Mixtures of dry consistency, although strong at an early age, are generally porous. An excess of water produces a weak concrete which hardens more slowly than a plastic mix. * In addition to the above, the following statements appear to be justi- fied by the results of experience and tests : (a) To proportion concrete for the maximum resistance to fire, a porous non-combustible aggregate of high specific heat together with cement sufficient to produce the requisite strength should be thoroughly mixed with a large percentage of water and placed with as little ramming as possible. Such concrete when hardened will be porous and contain a PROPORTIONING Of MORTARS AND CONCRETES 427 high percentage of combined water. These properties are of great value in resisting the transfer of heat through fireproofing. (6) In proportioning concrete or mortar which is to be subjected to freezing temperatures, a minimum amount of water should be used and a quick-setting cement.* Lean mixtures appear to resist freezing better than rich ones. (c) Since the resistance of concrete to abrasion is dependent upon the uniformity, hardness and toughness of the aggregate and the rigidity with which it is held in place, concrete for road construction should be made from a carefully graded, hard, tough aggregate bound together with as small a proportion of rich mortar as is consistent with the required strength and imperviousness. Inasmuch as the density of a mixture is so often a criterion of other physical properties, the more scientific methods of proportioning are essentially schemes for securing maximum density. Two principal aids in proportioning are afforded by a knowledge of the percentage of voids and the mechanical analysis. 479. The Measurement of Proportions. — The most accurate method of measuring proportions is to weigh the required quantities of each material. This may be done whether the proportions are based upon vol- umes or weights. In Europe proportions are generally stated in the terms of weight, but in this country proportions are nearly always expressed as parts by volume. The objections to proportioning by weight are the indefiniteness due to variation in specific gravity of the aggregate and the delay caused by using scales. On the other hand, measuring by volumes, as now practiced, is not satisfactory owing both to the inaccuracies in the methods of measuring and to the large variations in the volume of fine aggregate resulting from small changes in the moisture content. Never- theless in America despite the manifest inaccuracy, volumes of aggregate are generally measured by the wheelbarrowful. Whenever measurements are made by the wheelbarrow or by a similar method care should be taken to specify the size of barrow, how it shall be filled, and the allowance which shall be made for moisture in the sand. In short, the methods of measuring, as well as the unit of measurement should be carefully specified. Cement is usually measured by the bag, one bag containing approximately 1 cu. ft. and weighing 94 lb. In laboratory practice the weight of a cubic foot of cement is commonly assumed to be 100 lb. 480. Arbitrarily Selected Proportions. — Probably the most used method of proportioning is that based upon arbitrary selection. In speci- fying proportions for mortars it is common practice to call for 1 : 2, 1 : 3 or 1 : 4 parts of cement to parts of fine aggregate, depending upon the quality of mortar demanded. In proportioning concrete by this method, * See also Art. 359 and 539. 428 MAKING MORTAR AND CONCRETE the engineer, guided by experience and a knowledge of the requirements for the structure, assumes a mortar of given proportions and selects a proportion of stone such that the voids will be filled with mortar. For concrete made of coarse aggregate containing large percentages of voids, proportions of cement, sand and coarse aggregate similar to the following are often called for: 1 : 2 : 3, 1 : 3 : 5. If the coarse aggregate contains a normal percentage of voids, say 45 to 50 — 1 : 1 : 2, 1 : 2 : 4, 1:3:6, 1:4:8 and like proportions are frequently specified. With an aggre- gate containing still less voids such as a well-graded crushed stone or gravel 1 : IJ : 3J, 1 : 2 : 5, 1:3:7 are sometimes selected. Obviously such methods or proportioning are crude and do not lead to the most efficient use of materials. They may give very fair results when used by a man experienced in judging aggregate, but in the hands of a person inexperi- enced in their use a poor mix or a waste of cement is likely to result. 481. Proportions Based on Voids.^A great variety of rules for pro- portioning based upon the principle of filling the voids in the aggregate with cement have been formulated. There are two main reasons why this method is not accurate. First, the problem of wetting the aggre- gate and bringing it into the same state of compactness which it assumes in the concrete or mortar is very difficult of solution; second, the general assumption that the particles of cement will fit into the void spaces in aggregate is fallacious, especially if particles passing a No. 50 sieve are present in the aggregate. In proportioning mortars, the common appUcation of the above method is to determine the voids in the sand or screenings in the condition in which they are to be used and then find the amount of neat cement paste required to fill the voids. For the latter determination about 112 lb. of cement should be allowed for 1 cu. ft. of paste. In general, this method does not lead to a determination of the densest mixture nor the most effective pro- portions of cement and sand. It is especially unsatisfactory with very fine sand or screenings. One rule advocated for proportioning concrete is to fill the voids in the coarse aggregate with sand and the voids in the latter with cement. Another rule suggests filUng the voids in the coarse aggregate with a slight excess of mortar. A third rule recommends filling the voids in the mixed aggregate with cement. None of these methods is applicable to all classes and gradations of materials with equal efficiency. They are aU faulty if there are particles of the same size in either the cement and sand or in the sand and coarse aggregate. Experiments have been made indicating that such rules do not enable one to secure concrete of the max- imum strength and density with a minimum percentage of cement. The error hes in the assumption that under the above conditions the finer par- ticles of material will occupy the interstices in the larger. Whereas the PROPORTIONING OF MORTARS AND CONCRETES 429 aim should be to select such proportions of cement, sand and stone that the resultant mixture will be the densest. In general we may say that the above methods of proportioning by void filling yield results which are very little better than those obtained by arbitrary selection. 482. Proportions Based on Minimum Yield. — A cut-and-try method of proportioning which possesses considerable merit is that based upon a minimum yield with a given proportion of cement to aggregate. Since the proportion of cement must be based upon judgment, the chief use of this method is to secure the most efficient combination of the different grades of aggregate. Trial mixtures of cement and different grades of aggregate are mixed together on a non-absorbent platform and sufficient water added to form a plastic consistency. The yields are then deter- mined in the ordinary way (see Art. 463). Evidently, if the weights of cement, aggregate and water are kept constant and the specific gravities of the different grades of aggregate are the same, the mixture having the least volume will be the densest. Let us briefly consider the application of this method to proportioning a 1 : 3 mortar, proportions by weight. Suppose that the sand passes a i-in. sieve and has been divided into two grades by an |-in. sieve. We would next assume the following trial proportions: Trial No. PROPOHTIONS. Cement. Fine Sand. Coarse Sand. 1 2 3 1 1 1 1 n 2 2 li 1 From the volumes of mortar gotten in these tests other desirable propor- tions may be estimated and tried. If, for instance, the second trial above gave the minimum volume and the third gave the next lowest, then it would be well to try a 1 : If : IJ mix. The efficiency of this method of proportioning is well shown by the results of Feret's Experiments given in Art. 502. The remarkable sim- ilarity of the triangular diagram, representing the variation in density, to the diagrams showing the variation in compressive strength of mortars made from different gradations of sand forms a very convincing proof of the value of this method for mortars. Trial mixtures for proportioning concrete may be estimated as in the case of mortar. For example, if cement, sand, and gravel are to be used in a 1 : 7 mix, the mixes tabulated below will serve in the preliminary trials. 430 MAKING MORTAR AND CONCRETE Trial No. Proportions. Cement. Sand. C ravel 1 2 3 1 1 1 2 3 6 5 4 For graded aggregate the following variation of the above method has been successfully employed by the Warren Bros. Bituminous Paving Co.* It advocates the use of a graded aggregate containing in compact volume less than 21 per cent voids. In securing a dense aggregate use is made of a yield can shaped like a conical frustum with the large end at the bot- tom. This can is filled with the coarsest aggregate and thoroughly com- pacted by raising it off the ground and letting it fall a number of times. When no more of the coarsest material can be placed in the can, the mix- ture is emptied, an addition of the next finer material is made, and the material is again jostled. This cycle of operations is repeated until no more of this second grade of aggregate can be put into the can and the third and remaining sizes are introduced in a similar manner. Mr. A. E. Schuette, who invented this method, found it satisfactory for all classes of aggregate varying in size from 3 in. down to the material passing a No. 200 sieve. For aggregates differing in shape of particles, he found the pro- portions of the different sizes of particles varied, but after having estab- lished the proper combination for a given set of materials he found it unnecessary to make any large alteration in proportions. 483. Proportioning by Mechanical Analysis, f — From the results of numerous experiments W. B. Fuller and S. E. Thompson J advocate the grading of the aggregate into different sizes and combining them with the cement to form a mixture having a fixed mechanical analysis curve. Their tests indicate that concretes thus proportioned have maximum density strength, and imperviousness. The curve which they propose is a combi- nation of an ellipse and straight line tangent as shown in Fig. 8. To assist in drawing these curves, the table on page 431 was devised by the ex- perimenters. In this table D is the maximum diameter of the stone, a is the length of the semi-major or horizontal axis of the ellipse which is par- allel to the axis of sizes and distant therefrom 7 per cent, b is the length of the semi-minor or vertical axis of the ellipse and is measured upward from the point (o, 7). The abscissa of the point of tangency is 0.1 D. The ellipse can be most easily drawn by the Trammel-point method. * H. P. Bowes in Canadian Engr., Mar. 23, 1911. The method was devised by A E. Schuette of that company. t For a method of more general application see Appendi.t B. I See Trans. A.S.C.E., Vol. 69, p. 67, 1907. PROPORTIONING OF MORTARS AND CONCRETES 431 DATA FOR FULLER AND THOMPSON'S GRADATION CURVES. Intersection of Tangent on Ordi- nate at Zero Diameter, Per Cent. Height of Tangent Point. Per Cent. Axes of Ellipse. Materials. a In. b Per Cent. Crushed stone and sand 28.5 26.0 29.0 35.7 33.4 36.1 0.1502) 0.164D 0.147D 30.4 28.6 Crushed stone and screenings . . 30.8 ffi 70 .1 5 60 Pi 10 / 1 /> i-^ 7 i!{i 7. ■'m' /I 1 Oj 1 m 4" /E A r 1 '^ 1 X /^ c 4 / 5 i4 F c.<0^ ^M^^ S / 1 61 J ^^ / / i 1 jL ^ B f 1 /' ^ :f ^7 7 f \ 1 \ 1 1 / 1 1 1 / 0.1 0.S 0.8 1.0 Diameter of Particles iu Inches Fig. 8. — Fuller and Thompson's Method of Proportioning Concrete by Mechanical Analysis. Cut-and-try methods of combining the various grades of material are employed. For instance, in Fig. 8 mechanical analyses curves are shown for the cement, sand and three grades of gravel. Let us suppose that it is desired to make a 1 : 9 concrete (1 part cement to 9 parts mixed aggregate by weight). An inspection of the curves for the different materials shows that the cement and sand must form the combined curve from to J in., that gravel No. 1 must form the curve between \ and \ in., etc. The theo- retical curve demands that the portion from point (0, 0), to A be filled with cement and sand. Therefore since 10 per cent of the entire weight is cement, the percentage of sand required will be the percentage corre- sponding to A minus 10, or 28. The percentage of No. 1 gravel required to fill the A B portion of the theoretical curve is 12; of No. 2 gravel for the B C portion is 25, etc. In drawing the combined curve the ordinate of 432 MAKING MORTAR AND CONCRETE the point m = 10+28X0.87 (87 = the per cent corresponding to wi')=34.4 per cent. For overlapping curves the process is more laborious. To successfully use this method of proportioning it is frequently necessary to separate the sand into at least two grades and the coarse aggregate into two or more grades depending upon the variation in sizes. These grades should not be remixed until they are placed in the mixer. From a study of the theoretical curve it is apparent that for rich mixes sand passing a No. 50 sieve should be eliminated, but in lean mixes some fine particles are beneficial. Experiments show that greater economy can be realized from the use of this method with lean mixes than with rich mixes. Fuller and Thompson in experiments on 1 : 9 mixes obtained an average gain in strength of about 14 per cent by grading the aggregate. Experiments at the University of Wisconsin * on 1 : 9 mixes of gravel concrete have also demonstrated the beneficial effects of grading the aggre- gate on both the strength and imperviousness. Tests plainly show that a proper grading of the cement-sand portion in the combined mechanical analysis curve is of more importance than an exact grading of the coarse aggregate. From the foregoing it appears that this method of proportioning will effect economy where the increased cost of screening, storing and handling the aggregate is less than the cost of the cement necessary to produce the same quality of concrete. In general, the method is only applied to large jobs. 484. Proportions Commonly Used in Different Constructions. — The proportions listed below are cotnmonly specified when good materials are obtainable. Proportions marked with an * refer to natural cement mortars. Mortar for: Laying brick and stone masonry { " , ^ ,'„... , I 1 : 1* to 1 : 2* ■p.,,. ■ ■ t ■ ■ / 1 : to 1 : 2 Filling joints in sewer pipe < i ■ n* t l • i * Surfaces of floors, sidewalks and pavements 1 : 1 to 1 : 2 Waterproof linings 1 : to 1 : 2 Cement bricks and blocks 1 : 2^ to 1 : 4 Concrete for: Gravity retaining walls, heavy foundations and structures needing mass more than strength (compressive strength • at 28 days = 1000 to 1500 Ib./in^.) 1 : 3 : 6 to 1 : 4 : 8 Retaining walls, piers, sewers, pavement foundations, work requiring strength (compressive strength at 28 days = 1500 to 2000 lb./in.2) 1 : 2 : 4 to 1 : 3 : 6 Floors, beams, concrete pavements, reinforced concrete, arch bridges, low pressure tanks (compressive strength at 28 days = 2000 to 3000 Ib./in.^)! 1 : IJ : 3 to 1 : 2i : 4J * See Jour. Western Soc. of Engr., Vol. 19, p. 813. PROPORTIONING OF MORTARS AND CONCRETES 433 Reinforced concrete columns, conduit pipe, impervious con- crete and work requiring great strength (compressive strength at 28 days = 3000 to 4000 Ib./in.^) 1 : 1 : 2 to 1 : 1} : 3 485. Testing the Quality of Concrete. — Auxiliarj' tests on the aggre- gate are of assistance in making a selection of the proper aggregate, and the use of proper methods of proportioning tends toward economy in cement, but the value of these tests and schemes can only be ascertained by tests on the concrete itself. Such tests show that some fine aggregates, devel- oping a low mortar strength, make very satisfactory concrete when mixed with coarse aggregate. Occasionally a coarse sand having a high mortar strength fails to produce as strong concrete aggregate as a finer grained sand when combined with a certain coarse aggregate. In making such tests, the sampling and proportioning of the materials, the method of mixing, the placing and the curing conditions for the specimens should all be controlled so that the test-pieces will in every way represent the con- crete in the structure. For many structures, strength tests are of most value in determining the quality and uniformity of concrete. They should be made during the construction of every important concrete structure. Occasionally abrasion, absorption, fire or freezing tests are made. (For the methods used in making the latter tests see Ch. VIII and XIV.) We shall now briefly consider the strength testing of concrete. A great variety of shapes and sizes of specimens has been employed in testing the compressive strength of concrete. In the United States practice favors either a 4- or 6-in. cube or a 6X12 or 8X16-in. cylinder. A cylinder is to be preferred to a cube for the reasons mentioned in Art. 113. When the capacity of the testing machine is not over 100,000 lb. the 6 X 12-in. cylinder is preferable. A larger cylinder should be used, however, when the maximum diameter of the coarse aggregate exceeds 2 in. Molds for the specimens should be non-absorbent and should fit tightly together. Means should be provided by which the ends of cylinders can be made plane and perpendicular to their axes. For this purpose it is well to set the molds upon heavy steel plates and to allow the specimen to partially set before leveling the top. Methods of bedding rough ends are suggested in Arts. 76 and 77. Tests on the transverse strength can readily be made in simple machines of low capacity, consequently in the field where apparatus is limited the test can be conveniently used. It is to be hoped that some technical society will standardize this test and determine the proper specifications for different classes of concrete when it is used. A 6X6X42-in. beam loaded at the center over a 36-in. span will be found a satisfactory size of specimen for the transverse test of concrete. Since the modulus of rup- ture of concrete is greatly affected by shrinkage stresses, the test is only adapted to conditions where curing conditions are uniform. In testing, 434 MAKING MORTAR AND CONCRETE care must be taken to make the loading arrangements in accordance with the principles of Art. 116. On account of the curvature of the stress-deformation curve for con- crete and owing to the shifting of the neutral axis toward the concave surface of the beam, the modulus of rupture computed from the flexure / Mc\ formula ((S=— yr-l, averages about 1.8 to 2.0 times the tensile strength. Unfortunately, the ratio of the compressive strength to the modulus of rupture appears to be more variable, ranging from 4:1 to 8:1. The transverse test of plain concrete is not, therefore, an accurate method of determining the compressive strength of this material. For either strength test there should be made, at least, three specimens for each variable covered. Results from seven-day tests are of value in ascertaining the strength developed by the mortar, but rarely is the strength of the latter great enough to shear the coarse aggregate. Tests at twenty-eight days and longer periods are more desirable. 486. Quantities of Materials Required for One Cubic Yard of Mortar and Concrete. — The values given in Table 4 are computed from the results of yield tests on 15 different sands and screenings.* All of these aggre- gates were in air-dry condition at the time of test. It will be appreciated that the values will not apply to all mixes with equal accuracy, since the kind of cement, per cent moisture in aggregate, gradation of sizes, and percentage of particles passing a No. 100 sieve will considerably influence the yield. The greatest variations in yield are produced by variations in the moisture content in the aggregate. If the per cent moisture- is known allowance for such variations may be made by using the informa- tion in Fig. 5 in connection with the yields in Table 4. A rough estimate of quantities of materials required for a given volume of concrete may be gotten by computing the quantity of loose coarse aggregate which will fill the molds and base the computation of the sand and cement upon it. Thus, if the volume of the mold is 10 cu. ft. and the mix is 1:2:4, the above approximation calls for 10 cu. ft. of stone, 5 cu. ft. of sand and 2J cu. ft. of cement. When bank-run materials or mixed aggregates are used this method generally gives results within 5 per cent. If the fine and coarse aggregates are separated it should onl}- be used for rough estimates on small jobs, since for rich mixes the quan- tities may be 10 or 15 per cent too large. A simple approximate formula applicable to the materials and pro- portions commonly used in making concrete is W. B. Fuller's rule,t 10.5 ^ c+s+g' * Proc. A.S.T.M., Vol. 13, p. 834. t Taylor and Thompson's Concrete Plain and Reinforced, p. 16. PROPORTIONING OF MORTARS AND CONCRETES 435 TABLE 4.— YIELD IN MORTAR FOR DIFFERENT PROPORTIONS OF VARI- OUS AGGREGATES BASED ON LOOSE MEASUREMENTS OF VOLUME * All aggregates passed a i-in. sieve and were air dry. Plastic consistency. No.t Per Cent Voids. Pek Cent {by Wt.) Passing Sieve. Yield for Mix. 10 30 50 . 100 1 :2 1 :3 1 :4 1 : 5 St Sdl Sd2 Sd3 Sd4 Sd5 Sd7 Sd8 Sd9 SdlO Sdll Sgl Sg3 Sg4 Tgl 37.0 36.5 35.2 38.2 39.8 45.3 36.6 36.4 36.0 27.9 35 42.0 39.0 40.0 43.6 100.0 86.4 81.2 91.9 100.0 100.0 67.7 82.0 66.8 69.7 72.0 62.8 64.0 69.0 34.6 39.0 61.4 39.7 95.8 99.8 25.9 55.3 13.9 34.0 23.8 35.5 28.0 32.6 15.4 9.1 34.5 13.7 62.5 67.6 11.2 16.1 4.9 17.4 4.3 25.1 19.5 23.8 11.5 2.8 9.7 1.2 8.6 5.7 2.2 1.9 1.4 6.5 0.5 13.0 13.8 15.9 7.5 1.18 1.18 1.25 1.22 1.30 1.22 1.19 1.21 1.14 1.26 1.21 1.13 1.15 1.15 1.07 1.11 1.08 1.15 1.11 1.15 1.09 1.07 1.09 1.03 1.14 1.08 1.01 0.99 1.01 0.97 1.08 1.03 1.10 1.06 1.09 1.03 0.99 1.05 0.98 1.05 1.01 0.93 0.92 0.93 0.89 1.07 1.01 1.07 1.03 1.04 0.99 0.95 1.01 0.95 0.96 0.99 0.88 0.88 0.88 0.84 * Weight per cubic foot of cement was taken at 100 lb. t Sd =sand; sg =screemngs; Tg =zinc mine tailings. t Standard Ottawa sand. Here p = the number of barrels of cement required per cu. yd. of concrete. c = the number of parts of cement by volume; s = the number of parts of sand by volume; g = the number of parts of gravel or broken stone by volume. Having p, the portion of a cubic yard of sand required per cubic yard . s 4p , . , 4p of concrete is -X-^s-; the amount of gravel is -X-^-- In this com- putation a barrel of cement is assumed to contain 4 cu. ft. For exam- ple, if 200 cu. yd. of 1 : 2 : 5 concrete are required for a certain structure, we shall find the quantities of materials needed. 10.5 'l-h2+5 = 1.31 bbl. The required amounts are 200X1.31=262 bbl. of cement, 2X7^X1.31 4 X200 = 77.6 cu. yd. of sand; 5X27 X 1.31X200= 194.1 cu. yd. of gravel or broken stone. More exact computations of quantities may be made by the use of the data in Table 5 which has been compiled from tests by Edwin Thatcher. 436 MAKING MORTAR AND CONCRETE TABLE 5.— PROPORTIONS OF MATERIALS IN CEMENT CONCRETE, MODERATELY RAMMED (From actual experiments made by Edwin Thatcher, M. Am. Soc. C. E.) CONCKETZ WITH Stone 1 Inch and Under. Concrete with Stone 2i Inches and Under. Proportions of Required for 1 Cubic Proportions of Required for 1 Cubic Mixture. Yard. Mixture. Yard. 1 B IB 13 a a CO OJ g 0, 2 III r CO |1| CQ a 0) S o '6 § CO V a o » 3 En o ill 1 ?, 1.42 2.57 0.39 0.78 1 2,0 1.42 2.63 0.40 0.80 1 2.5 1.79 2.29 0.36 0.88 1 2.5 1.79 2.34 0.36 0.89 1 3 ( 2.14 2.06 0.31 0.94 1 3.0 2.14 2.10 0.32 0.96 1 3.5 2.60 1.84 0.28 0.98 1 3.5 2.50 1.88 0.29 1.00 1 5 2 5 1.40 2.06 0.47 0.78 1.5 2.5 1.40 2.09 0.48 0.80 1 5 3 C 1.68 1.85 0.42 0.84 1.5 3.(1 1.68 1.90 0.43 0.87 1 5 3,5 1.97 1.72 0.39 0.91 1.5 3.5 1.97 1.74 0.40 0.93 1 5 4 ( 2.25 1.57 0.36 0,96 1 .5 4.(1 2.25 1.61 0.37 0.98 1.5 4.5 2.53 1.43 0.33 0.98 1.5 4.5 2.53 1.46 0.33 1.00 ?, n 3 1.38 1.70 0.52 0.77 2.0 3.0 1.38 1.73 0.53 0.79 2,(1 3.5 1.61 1.57 0.48 0.83 2.(1 3.5 1.61 1.61 0.49 0.85 ?, C 4.( 1.84 1.46 0.44 0.89 2.(1 4.(1 1.84 1.48 0.45 0.90 ?, r 4 5 2.07 1.36 0.42 0.93 2.0 4.5 2.07 1.38 0.42 0.95 2.0 5.0 2.31 1.27 0.39 0.97 2.0 5.0 2.31 1.29 0.39 0.98 ?, .'i 3,5 1.37 1.45 0.55 0.77 2.5 3.5 1.37 1.48 0.56 0.79 2 5 4.C 1.67 1.36 0.62 0.82 2.5 4.(1 1.57 1.38 0.53 0.84 2 .1 4.5 1.76 1.27 0.48 0.87 2.5 4.5 1.76 1.29 0.49 0.88 2,5 5.( 1.96 1.19 0.46 0.91 2.5 5.(1 1.96 1.21 0.46 0.92 2 fl 5.5 2.16 1.13 0.43 0.94 2.5 5.5 .'.16 1.15 0.44 0.96 2.5 6.0 2.36 1.07 0.41 0.97 2.6 B.O 2.36 1.07 0.41 0.98 3 n 4.0 1.34 1.26 0.58 0.77 3.0 4.0 1.34 1.28 0.58 0.78 ;f,(; 4.5 1.51 1.18 0.64 0.81 3.(1 4.5 1.51 1.20 0.65 0.82 n,(; 5,1 1.68 1.11 0.61 0.85 3.(1 5.(1 1.68 1.14 0.52 0.87 H (1 5.5 1.85 1.06 0.48 0.89 3.(1 5.5 1.85 1.07 0.49 0.90 H.d 6.1 2.02 1.00 0.46 0.92 3.(1 6.(1 2.02 1.02 0.47 0.93 :<,(] 6.5 2.18 0.96 0.44 0.95 3.(1 6.5 2.18 0.98 0.44 0.96 3.0 7.0 2.35 0.91 0.42 0.97 3.0 7.0 2.35 0.92 0.42 0.98 3,5 5.0 1.48 1.05 0.56 0.80 3.5 5.0 1.48 1.07 0.57 0.82 3.5 5.5 1.63 1.00 0.53 0.84 3.5 5.5 1.63 1.02 0.54 0.85 3,5 6.(, 1.77 0.95 ' 0.50 0.87 3.5 6.(1 1.77 0.97 0.51 89 3.5 6.5 1.92 0.92 0.49 0.91 3 . 5 6 5 1.92 0.93 0.49 0.92 3.5 '/A 2.06 0.87 0.47 0.93 3.5 7.(1 2.06 0.89 0.47 0.95 3.5 7.5 2.21 0.84 0.45 0.96 3.5 7 5 2.21 0.86 0.45 0.98 3.5 8.0 2.36 0.80 0.42 0,97 -^ 4,0 6.0 1.57 0.90 0.56 82 4.0 6.0 1.57 0.92 0.66 0.84 4.0 6.6 1.70 0.87 0.53 0,85 4 6.5 1.70 0.88 0.53 87 4.0 V.d 1.83 0.83 0.61 0.89 4 (1 7.0 1.83 0.84 0.51 90 4.0 7.5 1.96 0.80 0.49 0.91 4.0 7,5 1.96 0.81 0.50 0.93 4.0 8.(1 2.10 0.77 0.47 0.93 4,0 S.(> 2.10 0.78 0.48 0.95 4.0 8.5 2.23 0.74 0.46 0.95 4 (1 S 5 2.23 0.76 0.46 98 4.0 y.o 2.36 0.71 0.43 0.97 1 5.0 9.0 1.94 . (Hi 0.50 0.90 5.0 9.0 1.94 0.67 0.52 93 5.0 10.0 2.15 0.(12 0.47 0.95 — 6.0 10.0 11.0 2.15 0.63 0.48 0.96 6.0 11.0 2.04 0.55 0.51 0.93 6.0 2 (14 0.56 0.52 94 6.0 12.0 2.22 0.52 0.48 0.95 — 6.0 7,0 12.0 2 22 0.64 0.49 0.98 7.0 13.0 2.07 0.47 0.50 0.93 13.0 2.07 0.48 0.51 95 7.0 14.0 2.23 0.45 0.48 0.96 7.0 14.0 2.23 0.46 0.49 0.9S PROPORTIONING OF MORTARS AND CONCRETES 437 PROPORTIONS OF MATERIALS IN CEMENT CONCRETE, MODERATELY RAMMED.—iConlinued). CONCBETE WITH 25-INCH Stone, Sckeened. Concrete with Gravel J Inch and Under. Proportions of Required fo,r 1 Cubic Proportions of Required for 1 Cubic Mixture. Yard. Mixture. Yard. 1 a o a CQ 0) a o 03 .2 2 r i t o o .S'S CO>H a B ■6 a 03 m > e a _ hi 2S| .S o ill O 1 2 1.42 2.72 0.41 0.83 1 2,5 1.79 2.10 0.32 0.80 1 2 f, 1.79 2.41 0.37 0.92 1 3 2.14 1.89 0.29 0.86 1 3.0 2.14 2.16 0.33 0.98 1 3,5 2.50 1.71 0.26 0.91 — 1 4.0 2.86 1.55 0.24 94 1 s 2 5 1.40 2.16 0.49 0.82 1.5 3.0 1.68 1.71 0.39 0.78 1 5 3.0 1.68 1.96 0.45 0.89 1 .5 3.5 1.97 1.57 0.36 0.83 1 5 3 S 1.97 1.79 0.41 0.96 1 .5 4.0 2.25 1.46 0.33 0.88 1.5 4.0 2.25 1.64 0.38 1.00 1.5 1.5 4.5 5.0 2.53 2.81 1.34 1.24 0.31 0,28 0.91 0.94 ?, 3.0 1.38 1.78 0.54 0.81 2.0 3.5 1.61 1.44 0.44 0.77 a (1 3 S 1.61 1.66 0.50 0.88 2.( 4.(1 1.84 1.34 0,41 0.81 9. n 4 (1 1.84 1.53 0.47 0.93 2,1 4,5 2.07 1.26 0.38 0.86 2.n 4,5 2.07 1.43 0.43 0.98 2.( 5.0 2.31 1.17 0.36 0.89 2.0 6.0 2.77 1.03 0.31 0.94 ?, 5 3,5 1.37 1.51 0.58 0.81 2.5 4.0 1.57 1.24 0.47 0.75 ? 5 4 ( 1.57 1.42 0.54 0.87 2.5 4.5 1.76 1.16 0.44 0.80 2.S 4,5 1.76 1.33 0.51 0.91 2.5 5.(1 1.96 1.10 0.42 0.83 2 5 5 ( 1.96 1.26 0.48 0.96 2.5 5.5 2.16 1.03 0.39 0.86 2 5 5.5 2.16 1.18 0.44 0.99 2.5 6.(1 2.36 0.98 0.37 0.89 3.0 4.0 2.5 7.0 2.75 0.88 0.33 93 1.34 1.32 0.60 0.80 3.0 5.0 1.68 1.03 0.47 0.78 3 f 4 5 1.51 1.24 0.57 0,85 3.( 5.5 1.85 0.97 0.44 0.81 3 r 5.0 1.68 1.17 0.54 0.89 3.1 6.( 2.02 0.92 0.42 0.84 3 r 5,5 1.85 1.11 0.51 0.93 3.C 6.6 2.18 0.88 0.40 0.87 3.0 6.0 2.02 1.06 0.48 0.97 3.0 3.0 3.0 7.0 7.5 8.0 2.35 2.52 2.68 0.84 0.80 0.76 0.38 0.37 0.35 0.89 91 0.93 3 5 5.0 1.48 1.11 0.59 0.85 3.5 6.0 1.77 0.88 0.46 0.80 3 S 5 5 1.63 1.06 0.56 0.89 3.5 6.5 1.92 0.83 0.44 0.82 3 .■; 6 ( 1.77 1.00 0.53 0.92 3.5 7.( 2.06 0.80 0.43 0.85 3..') 6,5 1.92 0.96 0.51 0.95 3.6 7.5 2.21 0.76 0.41 0.87 3.5 7.0 2.06 0.91 0.49 0.98 3.6 3.6 3.6 8.0 8.5 9.0 2.36 2.51 2.65 0.73 0.71 0.68 0.39 0.38 0.36 0.89 91 92 4 6 1.57 0.95 0.58 0.87 4.0 7.0 1.63 0.77 0.47 0.81 4 6.5 1.70 0.91 0.55 0.90 4.( 7.5 1.96 0.73 0.44 0.83 4 r 7 ( 1.83 0.87 0.53 0.93 4.1 K.( 2.11 0.71 0.43 0.86 4.0 7.5 1.96 0.84 0.51 0.96 4.( 8.5 2.23 0.68 0.42 0.88 4.0 8.0 2.11 0.81 0.49 0.98 4.U 4.0 4.0 9.0 9.5 10.0 2.36 2.49 2.62 0.65 0.63 0.61 0.40 0.38 0.37 0.89 91 93 5 S.O 1.72 0.74 0.57 0.91 5.0 10.0 2.15 0.57 0.43 0.87 5.0 9.0 1.94 0.70 0.53 0.96 5.0 12.0 2.58 0.51 0.38 0.92 fi 9 1.67 0.65 0.59 0.89 6.0 12.0 2.22 0.48 0.44 0.88 6.0 10.0 1.85 0.62 0,56 0,93 6.0 14.0 2.59 0.43 0.40 0.92 7,0 11.0 1.75 0.54 0.58 0,91 7.0 14,0 2.22 0.42 0.44 0.88 7.0 12.0 1. n 0.52 0.55 0.95 7.0 16.0 2.54 0.38 0.40 0.92 438 MAKING MORTAR AND CONCRETE 487. Interpretation of the Meaning of Proportions. — Sometimes it becomes necessary to substitute a pit-run gravel or other mixed aggregate when the specifications call for separate measurement of the fine and coarse aggregate. Since such substitution often causes disagreement, it should be provided for in the specifications. To illustrate, consider a 1:2:4 mix of cement, sand and gravel measured by volume. It has been errone- ously argued many times that the equivalent proportions with pit-run gravel are 1 : 6, whereas volume measurements of 2 : 4 mixture of sand and gravel will generally show that about 1 : 5 or even a richer proportion is the proper equivalent. Furthermore, unless the pit-run material is well graded, it is likely that the- quality of the substituted mix will be inferior to the specified even though the equivalent ratio of cement to aggregate is used. MIXING, PLACING, AND CURING 488. Principles of Proper Mixing. — The first consideration in mixing either mortar or concrete should be to bring all materials into a homoge- neous mixture of uniform consistency in the minimum amount of time and without waste. Whatever method of mixing is used, in order to insure that in the completed batch each grain of aggregate will be coated with cement paste, the aggregate and cement should be dry mixed for a short time. The object of this dry mixing is to distribute evenly the cement throughout the mass and to prevent it from balling-up when the water is added. Since the time of mixing may be somewhat shortened if dry sand is employed, it may be economical on large jobs to cover the storage pile. On the other hand, a porous aggregate should not be allowed to completely dry since it will absorb water from the cement paste and adversely affect the hardening properties of the mix. Instances in which this action has caused a failure of the structure have been recorded. The question of the proper consistency is largely dependent upon the character of the work. At the present time variations from a dry con- sistency which will barely show moisture under heavy ramming to a soupy mix which can be spouted into the molds are in use. The general practice in this country is to employ a wet mix which will readily flow for nearly all reinforced concrete construction. In European countries prac- tice favors a somewhat drier consistency. The effects of different eionsist- encies on the properties of mortar and concrete are discussed in Art. 503, 511 and 527. 489. Hand Mixing. — Mortar can be hand mixed most satisfactorily in a tight wooden or sheet-metal box. For a 3- or 4-wheelbarrow batch a box 4X8 ft. with sides 8 or 10 in. high is convenient. The sand is spread in a layer of uniform thickness over the bottom of the box and covered by a similar layer of cement, or if the batch is large the cement may be MIXING, PLACING, AND CURING 439 sandwiched between equal layers of sand. The dry materials are then thoroughly mixed by hoe or by shovel until the mass is of uniform appear- ance. If shovels are employed the men should work in pairs, partners facing each other on opposite sides of the box. Beginning at one end and work- ing toward the other, both men shovel simultaneously into the pile giving each shovelful a flip which scatters the material as it falls. The entire pile should be given at least three turns in this manner. A long crater is next formed in the pile and filled with water. The batch should then be given at least three more turns with the shovels. Mixing by hoe is not so effective as by shovels, if two or more men are available. If the hoe is employed, water is generally added at the end of the box, the dry mix is rapidly drawn down into it, and the whole mass vigorously worked until the consistency is uniform. For hand mixing of concrete, a tight platform somewhat larger than the mortar box is desirable, and the mixing should be done with shovels. Two methods of procedure are effective. In either method the sand and wetted stone are spread in long, flat piles parallel to each other and about 3 ft. apart. The sand is covered with an even layer of cement, and the dry mortar given at least three turns. In one method the dry mortar is then spread over the wetted stone and two or three additional turns given the mass. A long crater is then formed in the top of the pile and the proper amount of water added. The edges of the pile are gradually turned into the crater until the water has been absorbed and the mixing is finished by three more turns. In the second method the dry mortar is tempered with enough water to make a soft consistency and turned twice. It is then spread over the wetted stone and the batch is given three more turns. By the first method the final consistency of the batch can be more accurately gauged than by the latter. In the second method, however, the batch receives more mixing after the water has been added. 490. Machine Mixing. — Most concrete is now mixed by machine. Although there are a great many designs and forms of mixers, they may all be separated into two classes — batch mixers and continuous mixers. In the operation of a batch mixer a definite charge of materials is mixed and discharged before another batch is admitted. The other type of mixer receives and discharges material continually. In general, concrete made in a batch mixer is more uniform than the product of the continuous mixer for the following reasons: All portions of the charge are mixed together in the batch machine, whereas in the continuous mixer product the uniformity of successive portions depends upon the regularity of the feeding device. Furthermore, in most types of continuous mixer the time of mixing is too short for thorough work, whereas in the batch machine the mixing period can be regulated as desired. 440 MAKING MORTAR AND CONCRETE In selecting a mixer, especial attention should be given not only to the quality of the product and the initial cost of the machine but to other factors which vitally affect efficiency, cost of operation and maintenance, such as — 1, time required in mixing; 2, waste in charging and discharging; 3, rapidity of charging and discharging; 4, ease in cleaning; 5, durability of mechanical parts; 6, capacity of the power drive; 7, visibility of charge during mixing; 8, accuracy of water-feeding device. In general the capacity of a batch mixer should be a little greater than can be handled by the gang employed. In mixing with batch machines, it is desirable to admit the sand, cement and stone in the order named and mix dry for at least 10 or 15 sec. The water should then be rapidly added and the mixing continued for at ^3600 £3400 :3000 2800 ^^■^ — -- -- Note:-All materiab were mixed dry % •^"^"^ of the time indicated below in a No. Smith mixer, nmniag at 26 r.p.m., 8 % water (by wt.) was used. Specimens sprinkled for 2 weeks after removal of molds. Fig. 9. IH 3 5 10 Time of Mixing In Minutes -The Effect of the Length of Time of Mixing on the Compressive Strength of 1 : 2 : 4 Concrete. Age two months. least one minute. When damp sand is being used and a very uniform concrete desired the above mixing period should be doubled. Experi- ments made at the University of Wisconsin * show that the degree of imperviousness of 1 : 9 gravel concrete can be considerably increased by raising the time of mixing from f min. to 2 min., especially if damp sand is used. Fig. 9 shows the effect of increasing the time of mixing on the strength of 1 : 2 : 4 broken stone concrete. The limestone used in these tests passed a 1^-in. screen and was retained on a j-in. sieve. The con- crete was mixed in a No. Smith mixer running at 28 to 30 r.p.m. In Fig. 10 are plotted some results from tests by Prof. H. H. Sconeld.f The test-pieces were made in a cube mixer running at 26 r.p.m. The age of the specimens was one year. 491. A Comparison between Machine-and Hand-mixed Concretes. — If a sufficient number of turns is employed, concrete can be as well mixed by hand as by machine. However, the cost of such thorough work pro- * See Jour. Wesiern Soc. of Engr., Vol. 19, p. 813. t Engr. Contracting, Vol. 43, p. 78. . _ , i MIXING, PLACING, AND CURING 441 hibits its use in practice. With the practiced methods of hand mixing it is not possible to secure so homogeneous mixtures as with machine mixing. This non-homogeneity of the 4S0O 4600 4200 ■4000 a 3600 S 3400 2600 2400 2200 2000 1800 . Water added after 1 min. dry miicing ■ Water added during'first ^ min. of mixing . All materials placed before starting mixer. 10 15 20 25 Time of Wet Mixing (min.) hand-mixed material is especially noticeable when the permeability of the concrete is tested. Table 6 shows the results of tests on the compressive strength of 10X24-in. cylinders made of hand- or machine-mixed con- crete. The materials were a crushed Umestone passing a l;-in. and retained on a J-in. sieve, a good bank sand and a Portland cement of standard quality. Specimens were sprinkled twice a day until tested. In making the hand-mixed specimens the cement and sand were turned twice dry; the cement, sand and stone, twice dry; the whole mass was then wetted and given three more turns. The machine-mixed concrete was tiu-ned for one minute dry and two minutes wet in a No. Smith batch mixer run- ning at 26 r.p.m. A medium consistency was used in making all con- crete, but the hand mixed required more water for this consistency than the machine mixed. 492. Handling of Concrete. — From the standpoint of securing good concrete after placement, certain fundamental principles should be borne in mind in handling the concrete. For conveying concrete, wheelbarrows and two-wheel carts are com- monly employed on small jobs, while elevators with gravity chutes, cars, belt conveyors, and cableways are used on large structures. For lining tunnels, concrete has been transported by compressed air. In using wheel- barrows or carts attention should be given to minimizing the length of haul not only for the sake of economy in labor but to prevent separation of the ingredients in the wheelbarrow due to jarring. The spouting of concrete by gravity requires a very wet, soupy mixture, unless a high pitch is employed; consequently the strength and density of the product suffer when this method is used. Whatever system is employed, the nmnber of changes from one conveying vessel to another should be Fig. 10.— Effect of Time of Mixing on the Compressive Strength of 6-inch Concrete Cubes Mixed in a Chicago Improved Cube Mixer (Scofield). 442 MAKING MORTAR AND CONCRETE reduced as much as possible in order to avoid waste of mortar due to slopping. TABLE 6.— A COMPARISON OF THE COMPRESSIVE STRENGTHS OF MACHINE AND HAND MIXED CONCRETES Proportions Cby Vol.). Method of Mixing. Age (Days). Per Cent * Water (by Wt.). Average Com- pressive Strengtli t (Lb./ln.!). Ratio of Strengths M H' Average M 1:1:2 1:1:2 1:1:2 1:1:2 1:2:4 1:2:4 1:2:4 1:2:4 1:3:6 1:3:6 1:3:6 1:3:6 1 :4 1 :4 1 :4 1 :4 M H M H M H M H M H M H M H M H 28 28 62 62 27 27 58 59 27 27 58 58 26 26 58 58 9.4 11.1 9,4 11.1 9.2 9 6 9.2 9.6 8.7 9.1 8.7 9.1 9.3 9.6 9.3 9.6 3821 2807 4650 3327 2068 1542 2337 2030 1268 1015 1727 1218 645 652 1008 879 1.36 1.40 1.34 1.15 1.25 1.42 0.99 1.15 1.38 1.25 1,33 1.07 * Does not include moisture in sand and stone which were t Each result is the average of three tests. ' air dried.' For placing concrete under water, some method must be used which prohibits the separation of the cement or mortar from the stone. This is sure to occur if the concrete is poured into open water; the stone, sand, and cement will be found in layers one above the other in the order named. Wherever possible the work should be enclosed in a coffer-dam to avoid wave action and prevent currents about the structure. Enclosed buckets holding I cu. yd. or more, which can be lowered to the bottom and emptied without the contents being subjected to the wash of the water, have been successfully used to deposit concrete to depths of 40 ft. In this method a dry consistency is employed and care is taken to create as little disturbance as possible in raising and lowering the bucket. Another device which has been reported satisfactory for depositing concrete under water is a tremie or pipe with a conical frustum at the upper end. This tube is filled with concrete before lowering into place. It is then kept full of concrete and gradually shifted over the work by a crane. A report describing the successful use of this method on the Detroit River MIXING, PLACING, AND CURING 443 Tunnel may be found in Engr. News, Vol. 63, p. 420. Tests of 5-in. cylin- drical cores cut from the outside of the tunnel when two years old gave a range in compressive strength from 1451 to 4060 lb. per square inch, the average for six test-pieces being 2663 lb. per square inch. Air-cured con- crete of the same mix, 1:3:6, had an average strength of 2097 lb. per square inch. When there is considerable current about the work, concrete may be deposited in partially filled, loosely woven cloth sacks. The current washes more or less of the mortar through the sacks into the spaces between them, thus bonding the separate units. 493. Placement of Mortar and Concrete. — Mixtures of dry con- sistency should be placed in layers not over 8 in. thick. Wet concrete can be placed in much thicker layers depending upon the consistency and width of the cross-section. Dry concrete should not be allowed to fall more than a few feet, since the coarse aggregate is liable to become separated from the mortar. When concrete must be poured from a con- siderable height it is desirable to use an inclined chute both to avoid separation of ingredients and to avoid excessive pressure on forms.* With mushy or dry concrete the tamping irons shown in Fig. 11 will be found useful in making a dense mix. Smooth exterior surfaces can be produced on vertical concrete walls by running a spading tool up and down next to the forms. Puddling wet concrete in deep, thin walls or columns with long rods is an effective way of avoiding pockets. Pounding the outside of the forms tends to eliminate voids in vertical faces of walls or columns. In constructing two coarse floors, sidewalks or pavements the base should never be allowed to set before the wearing surface is placed. For the best results, the mortar for the finish coat should be gauged with the minimum amount of water which will admit leveling with a screen. After placement the mortar should not be allowed to partially set but * See discussion in Eng. Record, Vol. 59, p. 279. FiQ. 11. — Facing and Tamping Irons. (a) Gridiron tamper for facing side walls. (6) Flat-faced tamper, (c) Grid tamper for floors or walks. 444 MAKING MORTAR AND CONCRETE should be screened and finished with a wooden float. Opinions differ concerning the methods of surfacing the work. Specifications of the N. A. C. U.* specify that the surface shall be finished before the mix has begun to set, that excessive floating is to be avoided and excess water must be removed by mops. Others claim that the surfaces should be vigorously troweled and that whenever excess water appears it should be absorbed by sprinkling a dry mixture of 1 : 1 mortar upon the wet spots. The dry mortar must then be thoroughly floated until the surface stiffens and drags under the float, f The Cement Gun. — An apparatus which is being considerably used for applying a coat of mortar or grout to large surface is the cement gun. The essential feature of this machine is a vertical tank into which the mixture of sand and cement is admitted through a bell hopper. At the lower end of the tank is placed a horizontal wheel which is provided with radial arms to sweep the dry mortar under an outlet pipe. The dry mortar is driven out of the tank by means of air pressure which also serves to operate an air motor that turns the distributing wheel. From the outlet the mix is driven through a flexible hose, which may be of any length up to 200 ft., to a nozzle. As the mixture is shot through the latter it is tempered with sufficient water to produce a plastic mortar and is then deposited at high velocity in the form of a spray on the sur- face of the work. To facihtate moving, the machine is mounted on a two-wheeled truck. Tensile tests of 1 : 4 gunite, as the mortar from the cement gun is called, show that a product having higher density and strength than hand-molded mortars of hke proportions can be secured, t The cement gun has been used for facing the upstream face of a large dam, for rein- forcing old sewers, for placing a protective coating of motar around structural steel in buildijigs and tunnels, for hning tunnels, and for re- pairing the walls of furnaces and coke ovens. 494. Joining Old and New Work.— Whenever water-tight concrete is desired pouring should be carried on continuously § or a water-tight joint must be provided, see Fig. 12. On less important structures the surface of the old work should be roughened thoroughly, cleaned of all laitance and dirt with wire brushes, saturated with water, and then given a thin coat of neat cement grout before the new concrete or mortar is placed. Tests on 1 : 2 : 4 concrete cylinders 6 in. in diameter show that the full tensile strength of the concrete can be developed by this method * Proc. N.A.C.U., Vol. 7, p. 649. t See Concrete Cement Age, Vol. 8, p. 125. tSee Concrete, Vol. 9, p. 26. § For a good example of what may be accomplished in this way in erecting large standpipes see Concrete Cement Age, Dec, 1913 and Feb., 1914. MIXING, PLACING, AND CURING 445 of bonding a joint. For roughening the surface of the old work a dilute solution of hydrochloric acid is effective. The results of experiments by E. P. Goodrich * on the tensile strength of bonded joints in mortar briquettes are given in Table 7. Tests of a sinilar nature made at Case School of Applied Science, by R. B. Perry, f have been summarized in Table 8. TABLE 7. BOND TESTS ON PORTIONS OF 1 : 2 STANDARD SAND MORTAR BRIQUETTES. (Goodeich) All tests made at thirty days. Average strength of seven whole briquettes = 377 lb. per sq.in. Character of Surfaces Bonded. Age when Bonded. How Treated. (a) Air cured . . . (6) Soaked (c) Grouted. . . . (d) Hydrochloric aciu (e) " Bondsit ". . . Rough Fracture Each. Average. 7 Days. Each. Average. Surface Molded Smooth. 24 Hours. Each. Average. 7 Days. Each. Average. Strength in Lb. per Sq. In. 161 C 92 H H 60 380 315 C 68 C 165 30 60 H 285 162 C 313 205 H 126 343 314 80 149 15 138 165 H 218 90 C 60 212 189 208 154 44 347 98 H 280 43 H 347 200 276 160 100 H 126 87 83 175 232 51 112 221 174 105 141 44 152 79 172 105 54 26 45 95 117 68 67 114 15 44 53 104 H =brokcnin handling before testing. C = broken placing in clips of machine. (a) Half briquettes ox fresh mortar were molded against halves of air-cured specimens. (6) The old portions were thoroughly soaked in ^water before the new portions were molded against them. , r , (c) The old portions were dipped in a creamy grout oi neat cement before the new portions were molded. , . . . , , , (d) The ends of the old portions were washed wjth a 10-per cent solution of commercial hydro- chloric acid, washed in water and then treated as in (a). (e) A patented powder, "Bondsit," was dissolved in water (51b. to 10 gal.) and used as in (d). *Eng. News, Vol. 61, p. 321. t Eng. News, Vol. 60, p. 167. 446 MAKING MORTAR AND CONCRETE TABLE 8.— A COMPARISON OF THE MODULI OF RUPTURE OF 1 : 2 MORTAR PRISMS BONDED IN VARIOUS WAYS. (Pbert) Prisms 2f X2JX13j in. were molded end to end with similar prisms fourteen days old. Twenty-one days after bonding each pair of prisms was subjected to a uniform bending moment and broken (Feret's method). No. Character of Joint. Tension in Outbb Fiber (Ln./lN.!) Per Cent of Full Strength Developed- Individual. Average. Al A2 End roughened with a cold chisel and wet. 158 123 A3 87 A4 124 A5 128 124 49 Bl..... . End smooth and treated with neat 119 B2 B3 cement grout. 131 - 207 B4 82 B5 124 133 53 Dl D2 D3 End roughened as in A and treated with neat cement grout. 279 211 237 D4 225 D5 227 236 94 El End smooth and treated with 232 E2 " Ransomite." * 128 E3 220 E4 231 E5 « 146 191 76 Fl F2 F3 End previously prepared by being molded with a bonding groove. 173 133 120 F4 128 F.5 110 133 53 Gl G2 Full-length prisms, no joint. 255 230 • G3 249 04 271 G5 257 252 * A patented liquid compound which is used to cleanse and roughen the surface of the joint. 495. Forms. — To prevent leakage of water and a loss of fine mortar, the forms should be made as rigid and nearly water-tight as possible. This MIXING, PLACING, AND CURING 447 feature should be given very careful attention when thin, water-tight sections are being constructed. If smooth surfaces are desired tongued and grooved lumber planed on one side should be used. Oiling the forms diminishes warping and shrinkage and reduces labor in removing them. Collapsible steel molds or wooden forms covered with galvanized iron are economical for repeated use. The pressure of unset wet concrete is equivalent to a liquid weighing approximately 150 lb. per cubic foot.* Therefore forms filled before setting begins should be designed for such hydrostatic pressure. After the concrete has begun to set the pressure on the forms decreases. The experiments of F. R. Shunk * Fig. 13, show the maximum pressures obtained on forms under various rates of filling in ^^^^^^^^^^^^^^ different temperatures. The pressures were determined on a board 9.23 in. in o ELEVATION (O) JOINT HORIZONTAL 04- ,'k T / r / r / % I h / h / S, / / ^ f / A ? f' ? / } / / / / ^ y // 'y y ^ y /■ ^ ^ y^ ^ (6J JOINT VERTICAL Fig. 12.— Methods of Making Watertight Joints. 600600 SOO 1000 1200 UOO ICOO 1800 2000 Max. Pre68ure on Form, lb. per sq. ft. Fig. 13. — Relation of Pressure Exerted by Fluid Concrete on Forms to Rate of Filling (Engr. News, Vol. 62, p. 288.) diameter placed near the bottom of a side form supporting a heavy wall. A wet consistency of 1 : 3 : SJ concrete, into which the workmen sank to a depth of 1| ft. was used. Shunk's values have been considered too large,t but later tests by E. B. Germain I corroborate the pressures for wet concrete very rapidly poured. Germain recorded the hydrostatic pressures developed in hot-water bags embedded at the bottom of 18 ft. columns. Mixes of 1 : IJ : 3 and 1:1:1 concrete were employed. The column made from the first mix was poured in 9 min., during which time the weight per cubic foot of the equivalent fluid decreased from 169 to 140 lb. The other column composed of the * Eng. News, Vol. 62, p. 288. tibid. Vol. 63, p. 748; Vol. 64, p. 103. tibid, Vol. 70, p. 294. 448 MAKING MORTAR AND CONCRETE second mix was poured in 14 min., the accompanying pressure change corresponding to a decrease in weight per cubic foot from 148 to 138 lb.* The time at which forms may be removed is dependent upon the rate of hardening of the cement and the temperature of the air. The best index of the proper time for removal of forms is afforded by a series of tests on small beams or cubes made and cured under the same conditions as the structure. Forms should never be removed until the concrete will support 150 per cent of its working unit stress. In warm weather, wall forms not over 10 ft. high can be removed in two or three days, but in the spring and fall when the temperature at night drops to 30° or 40° F., four to seven days should be allowed, see also Art. 539. 496. Shrinkage in Setting. — Owing to the shrinkage which takes place when concrete sets in air, see Art. 357 and 522, and the volume changes which occur due to variations in temperature, provision for contraction and expansion joints should be made. In two-course sidewalks it is good practice to make joints rr to i in. wide, every 4 to 6 ft. Such joints should extend through both surface coat and base. In concrete pavement constructions and in unreinforced walls, joints are placed from 30 to 50 ft. apart. f The width of the joint now used is quite variable. Some engineers advocate simply a plane of separation others make the joint i to ^ in. wide and fill with tar or a prepared fiber board. In thin members where the moisture changes are felt throughout the mass, wider joints will be more necessary than in thick sections. The tongued and grooved joint shown in Fig. 12 is impervious and also serves to preserve alignment when used in a vertical wall. A strip of sheet lead, bent as shown, permits free articulation of the joint. Provi- sion for such joints should be made at all angles in order to avoid cracks due to settlement, contraction or expansion. 497. Curing. — No part of the process of making good mortar or con- crete is more important than thorough curing. It is also one of the opera- tions most frequently neglected. Dusty floors, loose surface coats on side- walks and pavements, weak concrete blocks, leaky conduits and pipes illustrate defects frequently caused by improper curing. The effects of premature drying on the strength and permeability of concrete are dis- cussed in Art. 529. • In warm weather the essential principle is to keep the work damp for a period of two to four weeks subsequent to pouring. Rich mixes do not require so long time for curing as lean mixes and are less affected by pre- * Further evidence corroborating the work of Shunk and Germain is furnished by tests of Prof. A. B. MoDaniel and N. B. Garver, Eng. News, Vol. 75, p. 933. t See Specifications for Concrete Roads, Streets and Alleys adopted by Second National Conference on Concrete Road Building. MIXING, PLACING, AND CURING 449 mature drying. Wet mixes suffer less than those of dry consistency when improperly cured. If provision cannot be made for wetting the work, the forms should be left on for three or four weeks. The following methods of curing yield good results, sprinkling two or three times a day when not exposed to the sun, covering with a canvas wetted twice a day, covering with a 2-in. layer of damp sand, earth or saw- dust wetted once a day, impounding a shallow pool of water over the surface of the work. Of these methods the wet sand treatment is very effective for pavements and floors and is applicable to a wide range of con- ditions. For curing cement blocks and tile, specifications recommending a steatn curing period of forty-eight to ninety-six hours subsequent to initial set have been proposed.* In warm weather the shorter steaming period is recommended followed by sprinkling three times a day for at least one week. Since the object of steam curing is to accelerate hardening the steam should be wet and the temperature of the curing rooms should be kept above 70° F. Wet steam can readily be secured by admitting it to the curing chambers through troughs of water placed on the floor. 498. Protection against Freezing. — In cold weather, concrete should be protected from freezing until it has secured hard set. The effects of freezing on the properties of cements, mortars and concretes are discussed in Arts. 359, 539, and 541. Some of the ways of preventing freezing will be briefly considered. Tests on small 8-in. walls poured in 2-in. plank forms at a temperature of 10° F. have shown that concrete will set before freezing begins pro- vided the temperature of the concrete is above 70° F. when it is poured. This temperature may generally be maintained by heating the mixing water alone. If necessary the aggregates may be heated by building fires in large iron pipes running through the piles of sand and stone. Dol- omitic and calcareous sands, however, may be injured by overheating in this manner. When steam can be had, radiators may be employed or the free steam can be piped into the bottom of the material pile. Since the sand is wetted by use of the latter method, a longer mixing period will be required when it is used. After placement the concrete can be kept warm by covering it with a couple of feet of straw or hay, or a heavy layer of sawdust may be employed. Since these materials get mixed with the surface to some extent their use is often objectionable. For heating buildings in the process of construction salamanders or box-stoves are often used. Exposed walls and floors have been heated by placing a covering of canvas or building paper a few inches from the sur- * Proc. N.A.C.U., Vol. 7, pp. 764 and 768; see also Vol. 6, p. 615; Vol. 7, pp. 770 and 789. 450 MAKING, MORTAR AND CONCRETE face of the concrete and running steam pipes between the covering and work. Precaution should be taken when a structure is being heated to keep the air saturated with moisture in order to prevent too rapid drying of the hardening concrete. Tempering the mixing water with salt or calcium chloride solutions to lower the freezing-point of concrete is a practice to be condemned, especially if the work is reinforced. Either of these ingredients weaken the con- crete and decrease the resistance of reinforced concrete to corrosion. (See Art. 549.) CHAPTER XIV THE PHYSICAL PROPERTIES OF MORTAR ANI> CONCRETE 499. Introduction. — In this chapter we shall consider the effects of various elements and conditions which greatly influence the properties of mortar and concrete, such as strength and elastic properties, permeability to water, absorption, thermal properties, and the durability. In most cases the results given are from laboratory experiments; and it should be kept in mind that only by exercising the utmost care in selecting, pro- portioning and mixing materials and in the placement and curing of the concrete will it be possible to secure similar results under the conditions of practice. Also it must be recognized that many of the results represent only a limited range of variables and deductions should not be made for conditions lying without this range. STRENGTH OF MORTARS 500. Effect of Proportion of Cement on Mortars. — The results of Feret's * tests on mortars made from fine, medium and coarse sands (Fig. 1), show, in a general way, the effect of the proportion of cement on strength. Each tension value is the average from 25 briquettes; each compression result represents five cubes 2.8 in. on a side; each trans- verse value was averaged from tests on 15 prisms, 0.8X0.8 in. in cross- section loaded at the center of a 3.9 in. span; and each shear test repre- sents the average obtained from 15 halves of the transverse specimens. The latter were tested as cantilevers with the load applied close to the support. All mixes were of plastic consistency. The test-pieces were cured in water for five months before testing. The influence of age upon the strength of water-cured mortars made from several of Wisconsin f sands and screenings is illustrated in Fig. 2. Information concerning the aggregates used in these mortars is given in Table 4, Ch. XIII. 501. Effect of Character of Fine Aggregate on Mortars. — From a large number of tests by the United States Geol. Survey {Bulletin No. 331), the results in Table 1 have been drawn. Mechanical analysis diagrams for * Bulletin de la Societe d' Encouragement pour V Industrie Nationale, 1897, p. 1593; article by R. Feret, Chef du laboratoire des Fonts et Chaussfies. t Proc. 'A.S.T. M., Vol. 13, p. 834. 451 452 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE several of these fine aggregates may be found in Fig. 4, Ch. XIII. These tests show in a rough way that the density and strength of mortars made of the same class of aggregates decrease as the proportion of fine grains in the aggregate increases. In strength, the mortars made of stone screenings are slightly superior to sand mortars. From a series of tests on approximately 115 natural sands which were reported in Technologic Paper No. 58,* the relation between density (p) Fig, 2345670123466 Parts ofSandtoOne Part Port 1 and Cement ( by wt.) 1. — Results of Strength Tests on Portland Cement Mortars of Different Propor- tions Made from Fine, Medium, and Coarse Sands (Feret). and the average compressive strength (Sc) of 2-in. cubes of, 1 : 3 mortar was Sc = 26500 p— 14750. Practically all of the strengths were within 30 per cent of the values given by this equation. In these tests a mixture of several brands of cement, a plastic consistency, hand tamping with moderate pressure, and water-storage were used. Variables in these factors as well as the character of the grains of fine aggregate will affect the constants in equations like the above. * By Wig, Williams and Gates of the U, S. Bureau of Stds. STRENGTH OF MORTARS 453 502. Experiments on Mortars with Artificially Graded Sands.— One of the most exhaustive researches on the effects of granulometric eom- 7 28 60 180 300 .7 28 60 180 Age in Days Age la Days Mortar Logend: 1;2 =» ;1;3=A ;W=X ;1:5=» 300 360' Fig. 2. — The Effect of Age on the Strengths of Water-cured Mortars Made with Portland Cement. (Each point represents three or four tests.) position of sands has also been conducted by M. Feret. In an important series of tests he used sands graded as follows: Large grains G (0.2 to 0.08 454 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE TABLE 1.— EFFECT OF GRADATION OF SIZES OF PARTICLES OF AGGRE- GATE ON STRENGTH, DENSITY, AND YIELD OF 1 : 3 MORTARS OF PORTLAND CEMENT (U. S. Geol. Sur., Bull. No. 331) Aggregate No. Pek Cent Retained on Sieve No. Per Cent Voids. Yield. Den- sity. Sthength at 180 DATS IN Lb. per Sq.In. 10 30 so 100 Ten- sile. Com- pres- sive. Trans- verse. Sd. 13 Sd. 16 Sd. 19 Sd. 20 Sd. 11 Sd. 10 Sd. 1 Sd. 21 Sd. 15 Sg. 4 Sg. 6 Sg. 10 Sg. 3 Sg. 12 Sg.7 Sg. 21 Sg. 11 31 40 27 23 32 6 3 1 1 74 68 50 35 31 47 6 10 77 79 70 64 63 33 43 17 5 85 82 78 57 66 82 28 69 93 95 92 83 80 73 79 80 39 90 86 88 73 79 91 47 54 99 99 98 97 94 95 84 99 93 94 88 92 85 87 94 70 80 28.9 29.7 26.9 28.0 36.0 31.6 32.5 40.9 40.5 36.0 33.1 31.8 37.0 35.1 36.1 41.0 42.1 1.21 1.20 1.19 1.16 1.13 1.18 1.18 1.05 1.13 1.08 1.11 1.11 1.09 1.13 1.07 1.14 1.12 .754 .760 .789 .794 .730 .743 .742 .700 .676 .755 .760 .763 .733 .733 .756 .655 .709 668 605 773 670 708 488 415 380 331 939 750 767 809 717 677 683 543 7183 7108 6719 6200 5067 4639 3677 2892 2633 8644 8048 7394 6500 6193 5279 3948 3757 1314 984 1272 1056 792 1602 1326 1218 1410 1446 1206 918 in.), medium grains M (0.08 to 0.02 in.), and fine grains F (0.02 to in.). In analyzing results he plotted points representing the proportions of the Fig. 3.— The Effect of the Gradation of the Fig. 4.— The Effect of the Gradation of Sizes of Sand Grains on the Densities of Mortars of 1 : 3 Proportions (by- weight). (The range in actual size of grain corresponding to a given letter is represented by the pair of circles at each apex in the diagram.) the Sizes of Sand Grains on the Com- pressive Strength of 1:3 Portland Cement Mortars after Storing One Year in Fresh Water. STRENGTH OF MORTARS 455 three sizes on equilateral triangular diagrams, the distance from any side representing the percentage of grains marked at the opposite vertex. The contour lines were then drawn through the points which corresponded to mortars of the same density, strength, etc. A comparison of Figs. 3 and 4 shows the similarity of the contours in the density and strength diagrams of 1 : 3 mortars and indicates that the maximum strength and density obtain when about five-sixths of the sand is composed of the coarse grains with fine grains constituting the principle portion of the remainder. Other tests * by Feret furnished the data for Fig. 5. From the experiments, Feret drew the following conclusions : 1. With cement varying between 10 and 30 per cent of the weight of sand, the strongest mortar for any given percentage of cement was always gotten from a proportion of coarse sand equal to twice the weight of the cement plus fine sand. 2. It requires about twice as much cement mixed with a given quantity of sand to produce a mortar of given strength when fine sand is used as it does with coarse sand. 3. The weight of cement per cubic yard of mortar of a given strength is about twice as much for fine sand as for coarse sand, with the ordinary mixtures. 4. The cost per cubic yard of coarse-sand mortar of a given strength (such as is found for the ordinary ratio 1 c. : 3 s.), is only about 75 per cent of the cost of fine-sand mortar of the same "strength, even when the coarse sand costs six and one-half times as much as the fine sand (coarse sand $1.30, and the fine sand $0.20 per cubic yard). Feret also declared f that " for all series of plastic mortars made with the same cement and of inert sands, the resistance to compression after the same time of set under identical conditions is solely a function of the c c ratio — T— or -z — 7 — ; — r, whatever may be the nature and size of the sand e+v 1 — (c+s)' the proportions of the elements — sand, cement, and water — of which each is composed." In the above law e and v represent the volume of the water and air voids, respectively; the other symbols are defined in Art. 464. He derived the following relations for compressive strength: '^^=4w^-«-4""^'''=Ki^ in which Sc = unit compressive strength in pounds per square inch and j and k are constants. His results indicated a value of fc = 26,000 lb. per * Annales des Fonts et Chaussees, Mar., 1890, July, 1892, Aug., 1896. t Bull, de la Soc. d' Encouragement I'Ind. Nat., 1897, p. 1604. 456 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE 21.00 / > 19.00 / / ,< / / ^ °v / E ^ / fi 15.00 a .9 / ■(■^ / ./V ^> K 13.00 s -/ ..# fp r°* ^^' « rtar per 1 o- ^ ^—R / ..■^ a> V r^ r^" % * 1 ^ 9.00 ^ ^ / / .^'^ 3f-o^ N? ^' \ /< 7.00 / r /^ ^ <'^' '*W. Kl 'q.^ / / V W \^°--n 6.00 / V >| t M^ \ / \ N^ 'f% ^ 3.00 /^ ' i / N \ 1 1 / J \ / ^ 1 h 5,000 V/ 1 1 O cf / 1 1 "a (a ^'/ ,/ i S 3,000 o ,,// #7 7 N^J V ^'/\ -cin ^.A • — / ^ 1 -i . r It A s?' h y: "^i;' 2^ ^ ^ A ^ ■i-" 1,000 ^ ^ '\22 1^ ^ y' ^ 4- %■ si^°^' nc 1.00 0.75 S 0.50 1 0.25 1,000 2,000 3,000 4,000 5,000 6,000 7,000 Compregaive Strength in Pounds per Sq. In. Fig. 5. — Relative Economy of Coarse and Fine t^uiiil in Porlland Cement Mortal after Five Months' Immersion in Sea Water. Coarse sand grains were graded as follows: 52 per cent passing No. 5 and held on No. 15, -tS per cent passing No. 15 and held on No. 46; fine sand grains, 25 per cent passing No. 15 and held on No. 46, 75 per cent passing No. 46 sieve. (M, Feret in Les MatMaiux de Con- struction {Baumaterialen-Kunde, Vol. 1, p. 141.) STRENGTH OF MORTARS 457 square inch. These equations with modified constants have been found to hold in other tests.* 503. Effect of Proportion of Mixing Water on Strength of Mortars. — In general, increasing the percentage of mixing water beyond that required to form a mixture of standard consistency lowers the density and strength. The decrease in strength is most marked, however, at early ages. Experiments by Reinke f show that the niore water required to produce a given consistency the less will be the strength. He found that the ratios of the average strengths of eighteen 1 : 3 mortars taking 12 per cent water for normal consistency to the strengths of twelve like mortars requiring 14 to 15 jper cent were 3.9 : 1, 1.6 : 1, and 1.5 : 1 at three, seven and twenty-eight days respectively. Therefore, it follows that the percent- age of water required to make a mix of normal consistency is a rough index of the strength of mortars made of sands free from impurities. 504. Effect of Mica on Strength of Mortar. — Experiments by W. A. Wilhst on 1 : 3 mortars show that small percentages of mica decrease the tensile strength considerably. An addition of 2J per cent of mica served to reduce the strength at seven days 11 per cent; by adding 20 per cent of mica the strength at the same age was decreased from 180 to 40 lb. per square inch. Feret also found that mica adversely effected the com- pressive strength. The observed effects are probably due to the weak- ness of the mica and to the decrease in density resulting from its presence. 505. Effect of Hydrated Lime on Strength of Mortars. — Tests by E. W. Lazell, § Table 2, show that replacement of less than 15 per cent of the cement by hydrated lime does not decrease the tensile strength of 1 : 3 mortars. The results of E. S. Wheeler (Report of Chief Engineer, U. S. A., 1896, p. 2823) are confirmatory. W. E. Emley and S. E. Young T[ found that both tensile and compressive strengths of 1 : 3 mortars of slush con- sistency were adversely affected by the substitution of only 5 per cent of either high-calcium or dolomitic hydrate, if the specimens were cured in water or exposed to the weather. However, the loss in compressive strength was small for replacement of less than 25 per cent of cement by hydrate. 506. Adhesion of Mortars and Concretes. — Experiments made by E. Candlot for the French Commission show that the normal adhesion block is a satisfactory form of specimen (see Art. 450), but the tests plainly indi- cate that the character of the surface and the kind of cement exert a very * Proc. A. S. T. M., Vol. 13, p. 852. t Proc. A. S. T. M., Vol. 13, p. 797. t Eng. News, Feb. 6, 1908. § Proc. A. S. T. M., Vol. 8, p. 418. \ Proc. A.S.T. M., Vol. 14, p. 339. 458 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE TABLE 2.— THE EFFECT OF THE INCLUSION OF HYDRATED LIME ON THE TENSILE STRENGTH OF 1 : 3 MORTARS OF PORTLAND CEMENT AND STANDARD SAND. (Lazbll) Per Cent Cement Replaced by Hyd. Lime. 5 10 15 20 25 30 100 Method of Curing. in Days. Tensile Strengths in Lb. per Sq.I n. In air, 7 209 203 205 209 133 112 141 10 specimens 28 266 258 255 245 203 170 225 44 moistened 90 286 289 295 297 197 117 177 55 once a 180 382 312 304 281 229 211 219 53 week 270 607 545 441 499 441 397 342 136 360 630 456 513 642 553 444 327 168 In water 7 206 157 189 239 237 173 173 after 28 278 311 364 264 268 259 268 3 days 90 441 389 419 372 374 314 281 m air 180 358 321 341 278 260 207 253 270 390 301 308 279 268 250 232 360 426 336 311 322 299 260 231 5 600 Note. — Each value represents five tests. marked influence upon the adhesion. The tests of Wheeier show that the adhesion of mortar to cut stone is not increased by roughening the surface of the stone. In making adhesion test- pieces Wheeler used small discs, 1 in. square by | in. thick, placed transversely at the center of a briquette mold. These were pulled apart in an ordinary briquette tester. Some of his results on various substances are shown in Fig. 6. For sawn Hmestone and proportions varjang from neat to 1 : 2 he found the adhesion was between 30 and 40 per cent of the ten- sile strength of the mortar. To secure Fig. 6.-Adhesive Strength of Port- maximum adhesion the consistency must land Cement Mortar, 1 C. : 1 S., "^^ considerably softer than standard and Twenty-eight Days Old, to Differ- the surface of the substance should be ent Substances, and the Cohesive thoroughly saturated. Retempering the strength of the Mortar Itself, mortar reduced adhesive strength but, on (Wheder, Rept. Chf. Engr., 1895, ^he other hand, it appears to lessen the shrinkage in setting.* In curing, rapid drying of the mortar should be prohibited. * Cement Concrete Age, Vol. 13, p. 97. STRENGTH OF CONCRETE 459 The adhesion of concrete or mortar to plain round steel bars with surfaces as received from the rolls is about one-eighth to one-tenth of the compressive strength of 6 X 12-in. cylinders of the same material. For bars with polished surfaces the adhesion is 40 per cent less and for square bars about 25 per cent less than the round rods with mill surface. The adhesion of concrete to flat bars is more variable, but may be considered the same as for square bars.* STRENGTH OF CONCRETE 507. Effect of Proportion of Cement on the Compressive Strength of Concrete. — With the density remaining constant and with making and TABLE 3.— THE EFFECT OF PROPORTION OF PORTLAND CEMENT ON THE COMPRESSIVE STRENGTH OF 12-INCH CONCRETE CUBES. (Kimball) Brand of Cement. Compressive Strength (Lb. /In.-) Proportions. 7 Days. 1 Month. 3 Months. 6 Months. 1:0:2... Alpha Germania Alsen . 3294 2734 3118 5053 3246 3240 5047 3858 3710 5129 5332 Average Saylor Atlas 3049 1724 1387 904 2219 1592 3846 2238 2428 2420 2642 2269 4205 2702 2966 3123 3082 2608 5230 3510 3953 1:2:4... Alpha Germania Alsen. 4411 3643 3612 Average Saylor 1565 1625 1050 892 1550 1438 2399 2568 1816 2150 2174 2114 2896 2882 2538 23S5 2486 2349 3826 3567 3170 1:3:6... Alpha Germania 2750 2930 3026 Average Saylor 1311 675 594 564 759 417 2164 800 1090 1218 987 873 2522 1128 1201 1257 963 844 3089 1542 1583 Alpha Germania Alsen. 1532 815 1323 Average 602 994 1079 1359 . Note. — For character of aggregate see Table 4 . * For further information on adhesion and bond see Bulletin No. 71, Engr. Expt. Sta., University of Illinois, and Bulletin No. 321, University of Wisconsin. 460 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE TABLE 4.— PROPERTIES OF AGGREGATES Abbreviations: Sd = sand; Sg = screenings; Gl = gravel; Le = limestone; Ge = granite; Tp = traprock ; Ce = conglomerate Fig. No. Authority. Kind of Aggregate. Coarse Aggregate Fine Aggregate z Range in Size in In. % Voids (Loose). Per Cent Passing % =3 No. 10,. No. 30. No. 100 Voids (Loose), 3 Kimball Sd+Ce 2^-i 49 33 5 Univ. Ill Sd+Le li-s 50 81 35 6.9* 28 5 7 Univ. Wis Sd+Le Sd+Le Sg+Ge U-i ■H-i 2\-\ 52 48 67 83 77 39 38 56 4.0 3.0 15.0 36 Q Univ. Wis 34 6 Fuller and / Thompson | 6 Sd+Gl n-\ 79 50 4.6 Sd+Tp l-f 46 Sand p assed \ -in m. 36 Sd+Tp 3 1 4~2 50 do Sd+Tp 1-1 50 do 7 Tests of Metals, J Sd+Tp li-1 47 do 1898 Sd+Tp Sd+Gl Sd+Gl Sd+Gl 2^-2 l-\ U-1 3-2i 50 33 36 39 do do do do 8 Sd+Ge 1-0.02 41 97 64 1.3 38 and 12 U. S. Geol. Surv. Sd + Gl 1-0.08 33 97 64 1.3 38 13 Bull. 344 Sd+Le 1-0.02 37 97 64 1.3 38 Sd+Cr U-0 51 97 64 1.3 38 15 Withey Sdi 100 96 8 6 40 15 Withey Sds 82 55 1 9 36 36 37 15 Withey Sdg 67 14 1 4 18 Withey Sd+Glf IW [36 138 83 68 57 38 1.6 2.4 34 * No. 74 mesh. t Range of values for different lots of Janesville gravel and sand. curing conditions similar, the strength of concrete increases in nearly direct ratio to the proportion of cement for the mixes commonly used. An illustration of the effect of the proportion of cement upon the strength at various ages is furnished by the comprehensive tests of G. A. Kimball.* The consistency of the concrete was such that, when it was placed in the 12-in. cube molds, water flushed to the surface under vigorous ramming. The specimens were hand mixed at temperatures near freezing and were stored from two to seven days in a room at a temperature approximating 40° F. Thereafter they were cured in wet earth. The properties of the aggregates used in these tests are given in Table 4 and the results of strength tests in Table 3. In nearly all cases each average represents five or six tests. * Tests of Metals, 1899. STRENGTH OF CONCRETE 461 TABLE 5.— TESTS AT THE UNIVERSITIES OF ILLINOIS AND WISCONSIN ILLUSTRATING THE EFFECT OF PROPORTION OF PORTLAND CEMENT ON THE STRENGTH OF BROKEN STONE CONCRETE OF MEDIUM WET CONSISTENCY Average Per Cent Proportions by Volume. Compres- sive Strength (Lb./In.2) Age In Months. Form of Specimen. No. of Tests. Vari- ation from Mean. Method of Mixing. Published in li 3 2303 2 12-in. cube 4 18 Hand Univ. 111. 2 4 1972 2 11 6 12 ( ( Bull. No. 20 3 6 1450 2 ( ( 2 1 ( ( ( ( 4 8 1111 2 ( ( 4 14 ( ( 1 1 14 3 3808 10 • 6-in. cube 9 24 tl (( 2 4 3412 10 ( ( 12 26 it ( I 3 6 2433 10 1 ( 6 7 t( 1 1 4 8 1632 10 ( ( 9 21 ( ( (t li 3i 4433 2 6-in. cyl. 8 20 Machine Univ. Wis. 2 4 2211 2 18-in. high 14 13 ( i Bull. No. 466 3 6 1770 2 ( 1 4 18 i I ( 1 Note. — The 12-in. cubes and cylinders were cured in the respective laboratories, being sprinkled twice daily. The 6-in. cubes were cured under damp sand. For aggregate see Table 4. Similar experiments on both hand- and machine-mixed concrete of wet consistency may be found in Table 6, Art. 491. Other results of tests made at the Universities of Illinois and Wisconsin showing the effect of the proportion of cement on the strength of concrete are shown in Table 5. 503. The Increase in Strength of Concrete with Age. — There is a scarcity of reliable data on the compressive strength of concrete more than two years old. For the proportions commonly used, one may expect the following percentages of the two-year strength when the mixing and curing conditions are good: 25 to 40 per cent at seven days, 50 to 65 per cent at one month, and 70 to 90 per cent at six months. Concrete of dry consistency will show a much quicker growth in strength than con- crete of wet consistency. A series of experiments on the effect of age on the strength of concrete cylinders cured in three different ways was de- scribed in The Wisconsin Engineer, Vol. 19, p. 203. The Atlas cement for these tests was mixed and stored in an air-tight tank; the proportions, amount of water, time of machine mixing and storage in molds were each made constant for the entire series of tests. Specimens from each batch of concrete were distributed throughout the various ages so that the five results gotten for any given test period are representative of different batches of concrete. , The character of the aggregates may be found in 462 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE Table 4 and the results of experiments for a seven-year period are given in Fig. 7. Only specimens cured in cage were exposed to the weather. In Fig. 8 are shown the average results of a large number of com- pressive strength tests * on gravel, granite, and limestone concretes of 1:2:4 and 1:3:6 proportions. These tests were all conducted under comparable conditions. A plastic consistency was used in all tests. The 4800 3 A Time ia Years Fig. 7. — The Effect of Age on the Compressive Strength of Limestone Concrete. figures on the diagrams indicate the number of materials averaged; the number of test-pieces per material was three or more. 509. Effect of Density on the Compressive Strength of Concrete. — If the kind of cement and the proportion of cement per unit volume of *From Technologic Paper No. 58, U. S. Bureau of Standards. STRENGTH OF CONCRETE 463 concrete is maintained constant and if the consistency, shape of aggre- gate particles, age, and method of curing the concrete are the same, the strength will increase with the density. In proportioning concrete it is rarely possible to keep constant the proportion of cement per unit volume of concrete. Experiments have shown that the strength varies directly as the ratio .. _ , the equation being Sc =j c Here Sc = unit com- pressive strength, c=.voIume of cement grains in a unit volume of con- 6000 4000 \A >14 0) 3000 A y \^y .-- 6 U 3 1 20( 2000 8 ? 16 >.-'"" Granite Gravel s 1000 20 12 3 / V t' a " J 4 1 4 13 26 52 4 13 26 62 ' Age in Weeks Fig. 8. — Variation ot Compressive Strength with Age of 1 : 2 : 4 and 1:3:6 Conv cretes in which Granite, Gravel and Limestone Aggregates were Used. (Test Pieces, 8 X 16-inch CyUnders.) Crete, p = density of concrete, and j and n are constants which will vary with the factors mentioned above. * Experiments of the Bureau of Standards verify this relation. The points plotted in Fig. 9 represent data from Tables 1, 23, 25 and 26, of Technologic Paper, No. 58', by Wig, Williams and Gates. The proportions of the concrete varied between 1 : 6 and 1 : 9 (by volume). Other con- ditions surrounding the making, curing and testing of the 6-in. cubes used in these tests were constant. Owing to the fact that the specific gravities of the cements used in these tests were not given, a value of 3.10 was as- * Further verification of this law may be found in Taylor and Thompson's Con- crete Plain and Reinforced, 2d ed., p. 367, and in Jour. West. Soc. Engr., Vol. 19, p. 837. 464 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE sumed in making computations of c. In the figure each number repre- sents the average result for three specimens and the Hke numbers indicate similar aggregates. 510. Effect of Size of Coarse Aggregate on Compressive Strength. — With the largest particles not over 3 in. in diameter, it may be stated that the larger the maximum size of the aggregate the denser and stronger wiU be the concrete, provided other influencing factors are eliminated. The 3000 2000 a 1000 e d fifflOO B a gSOOO t O2000 1000 .1 '. ^ 2 1 ^^ r' • 2 Jv^ < •! 2 1 ij^ • 3 stone C oncrete \j^ fT3 ^ 06^ 6 Gravel ( tonorete 2 03 °2 2^2* °1 1 0.2 0.3 0.4 0.5 Vol. of coment 0.6 0.7 0.8 p„j.i„ vol. or comeni ,j_, c """"• Vol. of voids in Concrete 1? Fig. 9. — The Relation between Compressive Strength and the Ratio (Age of specimens 4 weeks.) 1-p change in strength with the increase in maximum size of aggregate is most marked for diameters under 1 in. The tests of Fuller and Thompson * on 1 : 9 concrete, which illustrate the above statement, are shown in Table 6. The beams used in these tests were 6X6X72 in. and the spans were 60 and 30 in. The compression tests were made on prisms from the beams, approximately 6X6X19 in., which were capped on each end with neat cement. * Trans. A.S.C. E., Vol. 59, p. 115. STRENGTH OF CONCRETE 465 TABLE 6.— EFFECT OF VARIATION IN THE MAXIMUM SIZE OF COARSE AGGREGATE ON THE STRENGTH AND DENSITY OF PORTLAND CEMENT CONCRETE. (Fuller and Thompson) Material.* Character of Mixture. Average Density. Average MonuLUS OF Rupture at 90 Days, in Lb. PER Sq.In. Average Compres- sive Strength at 140 Days, in Lb. per Sq.In. 0.3 £ Stone. Sand. 2i-in. Stone. 1-in. Stone. J-in. Stone. 2i-in. Stone. 1-In. Stone. i-in. Stone. 2i-in. Stone. 1-in. Stone. Hn. Stone. 1 :9 /J. \ Park Park / Ideal 0.851 0.810 0.767 257 226 208 1342 950 915 1 :9 1 :9 Natural Uniform Aggre- gate Various 0.821 0.832 0.798 0.797 0.768 0.769 211 257 171 229 162 180 980 1350 879 950 821 890 1 :9 ( Cowe* (Bay Cowe Bay , 0.859 0.847 0.853 243 246 189 1486 1402 1231 1 :9 (Park Cowe Bay ; " 0.872 0.818 0.784 291 273 207 1798 1585 1185 Averages Ratios 0.847 1.00 0.814 0.96 0.788 0.93 252 1.00 229 0.91 189 0.75 1391 1.00 1153 0.83 1008 0.72 * Jerome Park stone was a crushed mica schist, the sand was screened from the crusher-run material. Cowe Bay material consisted of gravel and sand. Note. — A soft mushy consistency was used in all tests. For character of aggregates in the natural mixture see Table 4. The ideal mixture was graded in accordance with the equations of Art. 483. In Table 7 results from Tests of Metals, 1898, show the effect of variations in the size of aggregate on the strength of 1:1:3 con- crete made into 12-in. cubes. These tests also serve as a comparison of the strengths and specific weights for broken stone and gravel con- cretes. 511. Effect of Proportion of Water on Strength of Concrete. — The greatest strength at an early age can be secured from a concrete of dry consistency in which there is only sufficient water for perfect hydration of the cement. Such concrete requires heavy ramming to make it homo- geneous and dense. A mushy or quaking consistency is more easily han- dled and compacted. Although the growth in strength is less rapid, such concrete gains as great strength eventually as concrete of dry con- sistency. The use of a very wet, sloppy consistency produces concrete of low density and inferior strength. The above conclusions are well estabhshed by Government tests * on wet, medium, and damp concrete made of granite, limestone and gravel. The results of these tests are given in Table 8. The compression tests were made on 6-in. cubes and the transverse tests on 8X11 in. beams supported on a 12-ft. span. Concrete of wet consistency was sloppy enough to splash when struck with the tamping rod; concrete of medium consistency showed no excess water on surface when compacted in the " Bull. 344, U. S. Geol. Survey. 466 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE TABLE 7.— EFFECT OF SIZE OF COARSE AGGREGATE ON THE COMPRES- SIVE STRENGTH OF PORTLAND CEMENT CONCRETE OF 1:1:3 PROPORTIONS BY VOLUME (Tests of Metals, 1898) Bhoken Trap Rock. Gravel. Size of Particles, Age in Days. Crushing Strength in Lb. per Sq.In. Average Weight per Cu. Ft., Lb. Size of Particles, In. Age in Days. Crushing Strength in Lb. per Sq.In. Average Weight In. Single' Tests. Average. Single Tests. Average per Cu. Ft., Lb. 7 1391 7 1298 l-f 19 32 8 2220 2800 1900 2137 147.0 8 i 21 34 2600 2992 2297 148.1 l-i 20 32 7 2769 3200 3390 2623 148.8 1-i 20 34 11 4254 4917 3189 4187 160.3 7 2276 li-1 26 41 7 4006 4562 2400 3919 159.8 n-1 22 29 11 3186 3817 2800 3093 151.0 2i-2 22 32 4143 4140 3561 159.7 3-21 26 41 3400 4200 3467 151.9 Note. — For character of aggregate see Table 4. molds, flowed less smoothly than the wet concrete but could be readily- surfaced with a trowel; 'concrete of dry consistency was very lumpy and granular, under hand ramming it showed no water on the surface, and could not be given a smooth finish with a trowel. After twenty-four hours in the molds specimens were stored in a moist room and sprinkled three times a day. Tests showing 1>he effect of consistency on both tensile and compressive strength of 1 : 2 : 4 limestone concrete made at the University ot Wis- consin are recorded in Table 9. The size, number of results per recorded value, and the curing conditions were the same as those mentioned in the preceding paragraph. The results of experiments initiated by the National Association oj Cement Users * and carried on at different college laboratories are given in Fig. 10. The tests are noteworthy inasmuch as they were made in dif- * Concrete Cement Age, Vol. 4, p. 141. STRENGTH OF CONCRETE 467 TABLE 8.— EFFECT OF PERCENTAGE OF MIXING WATER ON STRENGTH OF 1 : 2 : 4 CONCRETE (U. S. Geol. Sur. Bull. No. 344) THE Percent- age of Water, by Wt. Consis- tency. Weight per Cu. Ft. of Cubes, in Lb. Average Strength op Three Specimens, IN Lb. per Sq.In. Aggregate. . In Compression at Mod. of E.upt ure at 4 Weeks. 13 Weeks. 26 Weeks. 4 Weeks. 13 Weeks. 26 Weeks. Granite 8.9 Wet 147.4 3156 4754 4753 375 501 539 8.3 Medium 147.9 4089 4992 4949 475 536 566 7.0 Damp 147.7 4518 t5445 t5410 499 591 618 Gravel 9.8 Wet 138.8 2299 3814 391 380 435 9.0 Medium 142.7 3547 4808 451 477 520 7.9 Damp 144.8 4612 4989 4884 426 495 496 Limestone 11.0 Wet 144.5 *3072 4008 3460 422 487 507 10.1 Medium 144.1 2975 3939 3896 458 541 566 8.5 Damp 147.8 4367 t5451 5025 537 521 589 * Gotten /rem tests on 8 X16-in. cylinders. t Exceeded capacity of testing machine; did no't fail. Note. — For character of aggregate see Table 4. TABLE 9.— EFFECT OF PERCENTAGE OF MIXING WATER ON THE TEN- SILE AND COMPRESSIVE STRENGTH OF 1:2:4 LIMESTONE CON- CRETE Per Cent Water by Weight. Tensile Strength in Lb. per Sq.In. at Compressive Strength in Lb. per Sq.In. at 14 Days. 28 Days. 34 Days. 60 Days. 14 ■ Days. 70 Days. 350 Days. Dry Dry* Quaking Mushy Soupy 6 61 7 8 10 139 180 153 212 252 168 206 251 204 236 272 219 1774 1945 1709 1283- 2635 3126 2927 2578 4000 4320 4500 3070 * Tensile test-pieces of this consistency had air pockets due to difficulties in molding. Note. — For aggregate .see Table 4. ferent parts of the country by different operators using local materials. Identical instructions regarding method of making and testing were issued to all laboratories. All stone employed in these tests passed a f-in. and was held on a J-in. sieve. Specimens were 6X6-in. cylinders. Each specimen was hand mixed separately. After removal from molds speci- mens were kept damp until tested.* * For further results illustrating the effect of consistency on strength see tests by Mr. C. J. Robinson, Engr. News, Vol. 69, p. 1063; also results of extensive experiments by Prof. D. A. Abrams, Engr. News-Rec. Vol. 80, p. 873. 468 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE 512. Tensile Strength of Concrete. — In general, the tensile strength of concrete varies between one-eighth and one-twelfth of its compressive strength. Besides the affecting conditions discussed under compressive strength tests, imperfections in the fabrication of specimens, the tensile strength and surface characteristics of the aggregate and the method of gripping and loading greatly affect the tensile strength of concrete. Owing to the influence of these factors the results of tension tests are generally less uniform than those gotten in compression. The results of some of the more important tests, showing both tensile and compressive strengths of concrete, appear in Table 10. TABLE 10.— A COMPARISON OF THE TENSILE AND COMPRESSIVE STRENGTH OF PORTLAND CEMENT CONCRETE OF MEDIUM CON- SISTENCY No. OP Tests. Spec. Mix by Vol. Strength (Lb. An'). Ratio (S) Kind of Aggregate. i o a E-i o O Tensile (Si) Com- pres- sive t Fine. Coarse. f 3 1 1 mo. 1 .2:4 218 3020 13,9 1 River 1 ■ Limestone H 2 1 1 mo. 1 :2 : 5 203 2097 10.3 [Sand 34% V. J 46% V. <={ 10 4 1 mo. 1 2 :4 207 2534 12.2 L.S. Scr. ■) Limestone / ^ 1 818 and 10 ■.2:r, o . . Iz; 2 1254 107 Perrine 10 : 2 : 5 'a .S 6 1744 . ill 10 10 : 2 : 5 2 :5 1 1 II 1 2 980 1035 109 Engr. News Vol. 70 10 2 : 5 6 1478 p. 722 10 1 :5* 1 a 1 507 10 1 : 5 's^ 2 662 100 10 1 :5 a 6 754 * Hand-mixed, the other batches of this group were machine-mixed. 474 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE The strength of cinder concrete is decidedly variable and is greatly influ- enced by the strength, granulometric composition, and absorptive proper- ties of the cinders. Table 13 shows the results of tests made by various experimenters. The results of the tests by the U. S. G. S. show that con- sistency has but little effect on the compressive or transverse strength of cinder concrete. From the latter tests on 6-in. cubes and 8Xll-in. beams on a 12-ft. span, the ratio of the compressive strength to the trans- verse modulus of rupture averages 9.8 : 1 for concrete six months old. TABLE 14.— THE COMPRESSIVE STRENGTHS OF SLAG CONCRETES OF 1:3:6: PROPORTIONS BY VOLUME Sand. River No. 1 Slag No. 2 Slag River No. 1 Slag No. 1 Slag River No. 1 Slag No. 2 Slag Coarae Aggregate No. 1 Bank Slag No. 1 Bank Slag No. 1 Bank Slag Ma- chine Slag Ma- chine Slag Ma- chine Slag No. 2 Bank Slag No. 2 Bank Slag No. 2 Bank Slag Age Compressive Strength in Lb. per Sq.In. 28 da 1033 1377 1478 1722 1778 863 1100 1222 1131 959 963 1228 1363 1309 1367 670 928 854 902 1200 561 826 983 1038 836 708 994 1057 1052 960 1028 1307 1440 1328 1888 697 1040 981 666 1030 837 90 da 1076 6 mo lyr 2yr 1225 1232 1348 Wt. in Ib./ft.s 138 121 131 129 120 122 137 129 128 TABLE 15.— PROPERTIES OF AGGREGATES IN SLAG CONCRETES Chemical Analyses. Mechanical Analyses. Element. Per^Cent of Element in Mesh. Per Cent Passing. River Sand. Slag Sand No. 1 Slag Sand No. 2 Bank Slag. Ma- chine Slag. River Sand. Slag Sand Xo. 1. Slag Sand No. 2. Si02 79.28 8.23 5.60 0.92 0.59 5.38 30.31 20.72 44.67 1.48 1.43 1.39 32.24 16,32 46.51 1.45 1.91 1.57 37.26 16.62 39.26 3.06 2.50 1.30 31.28 17.40 46.20 1.43 1.52 1.56 10 20 30 40 50 80 100 87.5 74.6 50.0 28.1 17.2 1.6 0.8 75.0 36.3 15.6 9.8 7.8 4.3 3.1 75 4 AljOs CaO 34.4 16 MgO. . . 11 3 FejOs SO3 10.2 5 5 3 5 Size No. 1 No. 2 1"-2J" l"-2" Wt. inlb./ft.'. 106 55 49 67 72 96 ELASTIC PROPERTIES OF MORTARS AND CONCRETES 475 It will be noted that this ratio is considerably larger than the corresponding value for gravel or broken stone concrete. 517. The Strength of Slag Concrete. — For purposes of construction similar to those mentioned in discussing cinder concrete, slag concrete is sometimes used. The results given in Tables 14 and 15 are taken from Furnace Slags issued by the Carnegie Steel Co., Pittsburgh. Each com- pressive strength result is the average of three tests on 12 X 16-in. cylinders. All specimens were made of standard Portland cement. They were daily sprinkled with water for twenty-seven days after making. The results show that the slag sand No. 2 made by running the molten slag into a water vat is slightly superior to slag sand No. 1 which was run through a spray as it fell into the water vat. The crushed bank slags, No. 1 and No. 2, produced a stronger concrete than the machine slag which was disintegrated by sprinkling with water after it had partially cooled.* THE ELASTIC PROPERTIES OF MORTARS AND CONCRETES 518. General Characteristics of the Elastic Curves. — ^As Fig. 12 shows, the stress-deformation curves for cement and concrete resemble those for other brittle materials like cast iron, brick and stone; Carefully made experiments fail to disclose a limit of proportionality or an elastic limit. Compression tests indicate, however, that after several applications of stresses less than one-half to two-thirds of the ultimate strength of con- crete the set becomes constant. On account of the occurrence of set for low intensities of stress the true elastic stress-deformation curve for these materials may differ considerably from the gross deformation curve. Bach, in finding the true elastic curve in compression repeatedly applied and released each load until the set at zero load became constant. By subtracting the set from the total deformation the elastic deformation for a given load was determined. Although the true elastic curve is of impor- tance in considering the change of shape of concrete after removal of stress, it does not afford information on the amount of total deformation which the material undergoes for a given unit stress. Since in reinforced con- crete construction the unit stress carried by the steel will depend upon the gross deformation of the combination, more appUcation is made of values derived from the gross-deformation curve than of those gotten from elastic deformations. 519. Calculation of the Modulus of Elasticity. — Since mortar and concrete have no elastic limit, the modulus of elasticity must be the slope of the stress-deformation curve at zero stress. For mixes which have a stress-deformation curve of sharp curvature near the origin, the * For additional tests on slag concrete, see Engr. News, Vol. 72, p. 103 and Vol. 75, p. 276. 476 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE initial modulus of elasticity, E, is of little value, except for comparing the stiffness of different concretes; since for all finite values of unit stress, S, Gross Deformations per TTnit of Length Gross Deformations per Unit of Length Fig. 12. — Stress-deformation Diagrams for Mortars and Concretes in Compression. {Tests of Metals, 1904. Technologic Paper No. 2.) S or unit deformation, e, Ei>S and ■p'^e, as may be seen from Fig. 13. For such curves the slope of a secant drawn from the origin through a ELASTIC PROPERTIES OF MORTARS AND CONCRETES 477 CarTO point corresponding to a working unit stress is useful, because the simple relation proposed by Hooke can be applied for neighboring stresses. Also, in reinforced concrete design the use of the secant modulus consider- ably shortens the computations without undue sacrifice of accuracy. Prof. Bach's studies of true elas- tic curves led to an exponential equation for unit deformation in compression, e = KSc^, in which K and m are constants depending upon the material. Morsch * gives the following equations of the true elastic curve for 1 : 2| : 5 sand and gravel concrete and 1 : 2| : 5 sand and broken-stone concrete, Crl.l4 e 116 and € = 9,190,500' Fig. 13 Method of Finding the (Secant) Modulus of Elasticity, E = —. 5,676,100 spectively. Prof. Talbot f developed a form- ula for the elastic curve in compres- sion, based upon the theory that the stress-gross-deformation curve for concrete is a parabola. His formula is Sc=(l — ^q)Ece in which q is the ratio of e (the unit deformation for Sc), to the ultimate unit deformation, and Ec is the initial modulus. 520. Values of the Modulus of Elasticity of Mortars and Concretes. — Table 16 shows values of the moduli of elasticity of neat cement, mortars and concretes compiled from the sources mentioned. It will be noted that the values for neat cement are decidedly variable and that air-cured neat cement and rich mortars have a much lower modulus than similar mixes cured in water. The modulus increases with the density, and to some extent with age, if specimens are water-cured. Morsch's results show that the moduli for wet mixes are less than for dry mixes of the same proportions. For lean mixes of the same aggregate, the modulus like the strength increases with the proportion of cement; but the varia- tion is small for proportions richer than 1 : 2, in the case of mortar, or 1 : 1| : 3, in the case of concrete. For rich mixes, however, the curvature of the stress-deformation line is very slight throughout the range of work- ing unit stress (Fig. 12). The stiffness of the coarse aggregate also considerably affects the rigidity of the concrete. Furthermore, a large difference in the moduli of elas- * Eisenbetonhau, p. 22 (trans.). t Bull. No. 14, Engr. Expt. Sta. Univ. of 111. 478 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE a & m V Pi M cS tn o ^^S2 1^3 OO i-H CO ^1^ oooooooooooooooo ooo o OO OO OO OO OO ooo o o ooo oooooooo o_o o_o_o_o__o__o o__o_o_ o"o~o''o''o''o~o"o"o~o"o''o'"o"o'"o'"o'' o^o'c" Tt< *<*< rH t> iO lO CO I>(N CO IM t^ ■* CD T-H t^ OOIOO Ci OS CO CO '^ '^'^^^'"1,^0 (N^io^ic oo^cq^co^ o cq^ko^ c^r(>rt-r»-rcoc£r»o~cococo"c# ..-*CD rt >-C>-H-H T-H (N CO OOOO'* -* "-Hi-HIN (N IN(NN(N O 0) OH ELASTIC PROPERTIES. OF MORTARS AND CONCRETES 479 .« oi o o g a 2; 36-1 St3 p. ■ till =1^ B O H w w c3 o: tf a C hH »-H hH OOO OOO OOO OOO OOO oooo OOOO oooo oooo OOO OOO OOO oooo oooo oooo OOOO ooo OOO OOO OOO oooo oooo oooo oooo OOO OOO OOO OOO OOO oooo oooo oooo oooo T)00O OOOl^ OS CO CD r^(NOO00 l>00O lO ■* ^ s TS-B T3 e ■73 ^ T3 g S a g a g f1 S !=s a g d g a a So ^o ikO ^•^ cbO ■s J; s ckS ''"^' ' ' ' §& .^ a o. So. ^ a o. a 1 III 1-2 i .3 ■B 0) ' :: ; Ph ^ § CO 'o H ■^ §•■< . . CO s »— 1 rH I— 1 rH i-H i-H 1-1 i-H i-H T-H T-( 1— 1 i-HCCOfN .-HCOCOIM .-(COCCKN ■-HCOON tH I— I 1— 1 1-4 ■^lOcO lOlOlC rft^Tti Tt*TtHTj< ^lJ o m 0-50 40-50 4 57 3 -.eg 8.1 1505 2 26 .000286 .000210 4 69 3 :6o 8.2 1150» 1 27 .031400 .028500 L 4 70 3 :6ff 8.2 1595 1 272 .000516 .000330 21 87 3 :6ff 8.2 1510 2 28 .000440 .000300 21 87 3 -.eg 8.2 1220 2 5 23 .007120 .005800 L 21 88 3 -.eg 8.2 1260 T 23 .012200 .012400 L 2 88 3 :6£t 8.2 1170 2 22 6 .024600 .024500 i 41 71 3 : 6g 8.2 1515 2 23 7 .020600' 11 71 3 :6ff 8.2 1515 2 23 7 .013600 .010700 2 95 3.2ff : 5.8(7 7.1 15.50 2 26 .000218 . 000090 2 3 . 28 : 5 . 8(( 7.1 1550 2 26 .000356. .000180 2 3 . 2|7 : 5 . Sff 7.1 33' . 000286 .000070 2 3.2s :5.8i; 7.1 33 .000420 .000160 2 86 3.29 : 5.8b 8.2 1120 2 27 .001510 .001330 M 2 3.25 : 5.8(7 8.2 29' .001310 .000920 D 2 3.2e :5.8o 8.2 33 .001260 .000800 2 104 3.2g : 5.8g 7.1 6 57" .004140 .003100 L 2 104 Z.2g : 6.8g 7.1 6 57 .009500 .006800 L I iy Volume. 2 110 2 :4b 7.9 1530 1 28 . 005440 .003660 2 110 2 : 4(7 7.9 1935 2 27 .000120 .000050 2 111 2 :4b 7.9 1765 4 25 .001610 .000870 2 111 2 :4b 7.9 2040 6 23 .001100 .000600 2 113 2 :4ff 7.9 2570 13 15 .000373 .000165 2 113 2 :4s 7.9 2620 20 8 .000347 .000140 2 114 2 :4fl 7.9 1750 2 3 24 .001360 .000775 2 112 2 :4s 7.9 2906 2 66 3 .000594 .000180 4 77 U :3b 8.0 2935 2 26 .000080 .000035 4 80 IJ :3b 8.0 3262 1 26 .001900 .000890 21 89 1} :3s 8.0 3460 2 26 .000021 .000014 11 89 li :3s 8.0 3700 2 5 21 .000140 .000088 21 103 1} ;3b 7.9 2810 6 22' .000150 .000097 11 103 li :3s 7.9 2990 6 22 .000326 .000200 21 102 U :3b 7.9 2850 6 57» .000218 .000130 21 102 U :3b 7.9 3550 6 57 . 000682 .000250 11 102 U :3s 7.9 56 .000480 .000210 2 91 1» :3s 7.9 3085 2 26 .000072 .000039 2 91 U :3s 7.9 3325 - 20 .000167 .000103 ^ These specimens were mixed \ min. dry and 4J min. wet; all others were mixed \ min. dty and li min. wet. 2 While being cured in air these specimens were filled with water. ' Results are for intervals from 0-44 and 20-44 hr. respectively. * The tops of these specimens were sprinkled while in the molds. " These specimens were filled with water 7 days before testing after having stood in air for 16 days. They were not sprinkled at any time however. « These specimens were filled with water 10 days before testing. ' Those specimens were filled with water after the 28-day test and stood in air till the 60-day teat " These specimens were full of water during the last 12 days of this period. > Cylinders were removed to the hall after 4 days in the molds. L ^One or more of those specimens leaked. M =One or more of these specimens were wet on bottom. i) =One or more of these specimens were discolored by moisture on bottom. PERMEABILITY AND ABSORPTION 489 at temperature of 120° to 150° F. Therefore structures which are to be subjected to alternate wet and dry periods should be made sufficiently thick to prevent drying, or the work should be sprinkled during dry periods. A short period of saturation following a period of dryness appears to decrease the permeability. The above statements are corroborated by evidence furnished from tests at the University of Wisconsin which are abstracted in Table 18 from the report previously cited. The form of test-piece used in these experiments is shown in Fig. IM. Unless men- tioned there was no visible evidence of flow on the surfaces of the speci- mens. 530. Other Conditions Affecting Permeability. — The water-tightness of concrete or mortar will also vary with the age of the concrete, intensity of pressure, thickness, character of the aggregate, condition of the surface to which pressure is applied, the quality of the water, and the direction in which the pressure is applied. Test evidence shows that the rate of flow for mortars or concretes, which give visible signs of leakage, decreases very rapidly during the first month and somewhat less rapidly for the next two or three months. For specimens which are practically water-tight the decrease in flow between fourteen and twenty-eight days may be 50 to 80 per cent, but the change in flow after one month is small.* Tests on concrete by Taylor and Thompson show that the leakage varies directly with the intensity of the pressure for pressures between 20 and 80 lb. per square inch. Other experiments on concrete, by J. L. Davies, covering the same range of pressures, are confirmatory (see Engr. News, Nov. 7, 1912). A large number of tests by Hyde and Smith (Jour. Franklin Institute), Vol. 128, Sept., 1889 on neat, 1 : 1 and 1 : 2 mortars show, in general, that the rate of flow increases directly with the pressure for the range between 75 and 200 lb. per square inch. With specimens which showed evidence of leakage, Taylor and Thomp- son found the rate of fiow through concrete decreased as the thickness increased. For concrete specimens which show no visible leakage the rate of fiow into the specimen does not appear to depend upon the thickness. The tests of the U. S. Bureau of Standards show httle variation in permea- bility of mortar specimens varying from 1 to 3 in. in thickness. The rate of fiow is materially lessened by the presence of laitance or rich mortar on the surface exposed to pressure. With water containing sediment or a high bacteria content the rate of flow diminishes rapidly with time. There also seems to be a gradual lessening of fiow due to the plugging of the pores by efflorescence. This * The information following was compiled principally from Technologic Paper No. 3, U. S. Bureau of. Standards, Wisconsin tests, and Taylor and Thompson in Trans. A.S.C. E.yol. 59, p. 127. 490 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE is especially noticeable in dry-cured concrete, which leaks badly. Appar- ently calcium and magnesium hydroxide are evolved from the cement and carbonated when washed to the surface, thus forming a more or less impervious crust. Concrete is somewhat more permeable to water when the pressure is applied perpendicular to the direction in which it is cast than when applied in the same direction. This is more pronounced for very wet mixtures placed in deep layers, since, under such conditions, non-homogeneity results from the settlement of the different constituents of the mix. 531. The Absorption of Concrete and Mortar. — A proper method of testing the absorptive properties of concrete or mortar is yet to be deter- mined. By drying these substances at temperatures above 120° to 150° the imperviousness is greatly reduced, and consequently water will pene- trate farther into such material than it would into undried concrete. Nevertheless, the method of conducting the absorption test ordinarily employed for other porous materials is generally used in testing mortar and concrete. A series of tests on the absorption of 1 : 2, 1 : 4, 1 : 6 and 1 : 8 mortars made from three different sands is reported in Technologic Paper No. 2. The test-pieces were 2-in. cubes. They were stored in a damp room between testing periods. Before testing they were dried for several days at a temperature of 212 to 230° F. After cooling they were immersed in water to«a depth of 3 in. They were periodically weighed until they gained less than ^V of 1 per cent, per day; the test was then stopped. The experiments show that the absorption generally decreases with age, the greatest change occurring in the first two months. Mortars of damp consistency absorbed more than those of quaking consistency. Mortars made of coarse sand were somewhat less absorptive than those made of fine sands. The absorption, in general, decreased with the increase in richness of mix. The Results show, however, that some factor, probably porosity, exercised a more important influence than the proportion of cement. Slag sand mortars, on account of the porosity of the aggregate, absorbed much more water than either the fine or coarse sand mortars. Absorption tests made at the University of Wisconsin on mortars vary- ing in richness from 1 : 2 to 1 : 5 have shown that those made from screen- ings and fine sands generally absorb more water than those made of better graded material. Mortars of 1 : 2 to 1 : 4 proportions made of good mate- rials and properly cured ought not absorb more than 10 per cent of water ' after forty-eight hours' immersion. Well-made concrete of dense aggre- gate should not absorb more than 6 per cent of water under the same conditions. 532. Waterproofing Materials. — For a number of years attempts have been made to discover washes and compounds which will waterproof PERMEABILITY AND ABSORPTION 491 concrete and mortar. In general, tests seem to show that if proper atten- tion is given to a proportioning, mixing, and curing these compounds are not needed to secure impermeable concrete for heads under 100 ft. Further- more, if good materials are procurable at average prices it is questionable if the extra expense involved in the use of such compounds will not be greater than the cost of additional cement required for water-tightness. It must also be understood that any beneficial results accruing from the use of these compounds cannot offset poor workmanship or improper _ curing. Furthermore, if the concrete cracks neither a properly made mix nor the use of such washes or compounds are effective. When there is probability of cracking, expansion joints should be used or a water- proof elastic membrane forming an integral part of the wall should be employed. Waterproofing compounds may be divided into two classes: integral mixtures, those which are added before the concrete is mixed; and surface washes, those which are applied after the work is finished. The integral mixtures may be inert, simply void fillers such as finely ground clay or hydrated lime ; or they may be active by virtue of compounds which they form during the hardening of the cement or by their repelling action toward water, petroleum residuum oil and the soap and alum combination, for examples. The coatings comprise paints and varnishes with a linseed-oil vehicle; bituminous compounds — the tars and asphalts; the hydrocarbons — the paraffin gasoline combination for example; and the soap solutions like alum and soap. In Technologic Paper No. 2, U. S. Bureau of Standards, p. 23, the following comment regarding these classes of compounds appears: "As no organic substances can be considered as truly permanent the dura- bility of all of these compounds, except the inert fillers, can be questioned." However, since several of these compounds have been more or less advo- cated and used in construction a very brief consideration of the results of tests on mixes containing some of them will be given. 533. Effect of Hydrated Lime on Permeability. ^ — On account of the plasticity and easy working qualities which hydrated lime imparts to cement mortars, and since it also decreases segregation, it has been consid- erably used as a waterproofing compound. It may be mixed with the cement in proportions less than 15 per cent without producing loss in strength of concrete. Numerous tests on mortars and concretes have indicated that its use decreased permeability. * With a 60-lb. per square inch water pressure, S. E. Thompson's tests * indicated that additions of 8, 12 and 16 per cent of hydrated lime in terms of the weight of the cement gave water-tight concrete for 1:2:4, 1 : 2^ : 4, 1:3:5 proportions, respectively. The concrete was made of run-of -crusher hard conglomerate * Proc. A. S. T. M., Vol 8, p. 500. i92 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE rock below 2 in. size with dust remove. All of the sand passed a }-in. mesh, 26 per cent passed a No. 40 sieve and 4 per cent passed No. 100 sieve. Specimens of the type shown in Fig. 14a were used, the thickness of wall subjected to flow was 8 in., and leakage through the specimens was caught and weighed. Thompson contended that hydrated lime paste is a more efficient void filler than Portland cement paste, since the volume of the former is about 2| times that of the latter. Tests of lean concrete made by J. L. Davies * on specimens 8-in. thick, similar to Fig. 146, showed that the rate of flow was decreased by replacing _ 20 per cent of the cement, by weight, with high calcium lime. The results with dolomitic lime were not so satisfactory. Davies used mixtures varying from 1.1 : 3 : 6 to 1.3 : 3 : 6 by weight and pressures of 40 and 80 lb. per square inch. From a study of his results and the cost per cubic yard of the different concretes based on New York City prices, it does not appear that such use of lime is economical. Tests by E. W. Lazell f and by the U. S. Bureau of Standards t show that the replacemeut of 10 per cent of the cement with hydrated lime increases the imperviousness of 1 : 3 and 1 : 4 mortars. 534. Effect of Finely Ground Clay on Permeability of Mortars. — R. H. Gaines § made a number of tests on 1 : 3 mortars in which he replaced 10 per cent of Cowe- Bay sand with finely ground clay. Under pressures of 80 lb. per square inch he found no leakage for test-pieces containing the clay, although the normal specimens leaked considerably. Davies also made tests on the efficiency of finely ground clay for waterproofing con- crete, but he concluded that this method also was not economical. 535. Integral Mixtures of Alum and Soap. — In experiments at the University of Illinois 1 1 on 1 : 6 mortar under 40 to 45 lb. per square inch pressure the permeability was greatly reduced by the use of a soap and alum mixture amounting to 1.2 per cent of the cement. The experimenters recommended a 1 : 3 mixture of alum sulphate and hard soap. Com- pressive tests showed a small reduction in the strength of the mix due to the alum content. The lasting qualities of such treatment are, however, to be questioned. 536. Oil Mixed Concrete. — Recently there has been considerable agitation concerning the use of oil-mixed concrete. L. W. Page, of the Dept. of Public Roads, is the proponent of this material. He advoftites % the use of a petroleum residuum oil for which he draws the set of specifica- * Engr. News, Vol. 68, p. 866. t Proc. A.S.T. M., Vol. 6, p. 341. t Technologic Paper No. 3, by R. J. Wig and P. H. Bates. § Eng. News, Sept. 26, 1907. II Engr. News, Vol. 62, p. 390. H Bulletin No. 46, Office of Public Roads, U. S. Dept. of Agriculture. PERMEABILITY AND ABSORPTION 493 tions below *. He recommends 5 per cent of oil in terms of the weight of cement for dampproofing purposes, or 10 per cent of oil for water- proofing. His tests with 10 per cent of oil show that the time of setting is considerably lengthened, that the early strength is lowered, that the toughness and stiffness are not materially affected, but that the absorption is rendered very small and the permeability under low pressures is nil. Results of extensive tests by Feret t and by Taylor and Sanborn + fail to substantiate the claims of Page concerning the waterproofing properties of oil-mixed concrete. The discrepancies, however, may have been due to differences in the character of the oils employed by the experi- menters. 537. Waterproofing by Surface Washes. — The Sylvester surface washes have been considerably used, although the durability of the process is questionable. Before applying the washes, the surface of the concrete which is to be exposed to water pressure must be clean and dry. A boiling-hot aqueous solution of castile soap (9 per cent) is brushed over the surface, care being taken to avoid froth. After twenty-four hours a 1| per cent aqueous solution of pure alum is applied cold. After another twenty-four hour period, the alternations in washes are repeated. The claim is made that the two solutions combine to form insoluble compounds which fill the voids in the surface. By ap- plying several sets of washes reports § state that good results have been secured. A neat cement or 1 : 1 mortar grout applied with a whitewash brush to the surface of the work exposed to pressure makes an impervious surface wash. To secure a good job the surface should be roughened and thor- oughly soaked before the grout is applied. Three or four coats should be put on, care being taken to allow each coat to harden before applying the next. If sand is used it should be screened through a No. 20 sieve. For the best results the work should be frequently sprinkled after the grouting has set. 538. Waterproof Membranes. — Absolute imperviousness can be secured by the use of several layers of fabric like the better grades of roofing felt cemented to the work by hot asphalt or coal tar washes. To prevent * The oil shall have: 1, specific gravity 0.93 to 0.94 at 25° C; 2, 99.9 per cent solu- bility in carbon disulphide at air temperature; 3, bitumen insoluble in 86° B. paraffin naphtha between 1.5 and 2.5 per cent; 4, residual coke between 2.5 and 4 per cent; 5, viscosity between 40 and 45 when tests are made on the first 100 c.c. emerging from an Engler viscosimeter after heating for 3 min. at 50° C; 6, less than 2 per cent loss in weight when 20 grams is heated for five hours in cylindrical tin pan 2i ins. deep and 1 in. high at a constant temperature of 163° C. t Engr. News, Vol. 70, p. 1228. tProc. A.S.C.E., Mar., 1913. § Engr. Record, Vol. 55, p. 395. 494 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE deterioration it is well to cover the alternate layers of pitch and felt with a protective layer of concrete or mortar. * THE EFFECTS OF TEMPERATURE ON MORTAR AND CONCRETE 539. The Effect of Low Temperatures on Setting Concrete. — Tests show that the rate of setting and hardening of concrete decreases as the temperature falls below 70° F. The rate of variation and way in which the set varies with the decrease in temperature differs with the cement used. Fig. 17 f shows strength-age curves for 1:2:4 gravel concrete 7 14 30 60 90 9 Age in Days Fig. 17. — Effects of Low Temperatures on Compressive Strengths of 8-inch Cubes of 1 : 2 : 4 Gravel Concrete. Ten Brands of Portland Cement are Represented. made from ten different brands of cement and cured at different temper- atures. It will be observed that the maximum and minimum curves of strength, for concrete cured at 68° F. are closer to the average than those for a temperature of 35° F. This well shows the range in the activity of different brands of cement at temperatures just above freezing. If concrete is allowed to freeze before setting has begun, it will lie dormant until thawed. The long-time strengths of some Portland cements appear to be harmed by such procedure, others are affected but little. * For further information concerning methods of waterproofing concrete see Proc. Nat. Asso. Cement Users, Vol. 3, Vol. 5, p. 143, and Vol. 7, p. 667. Results of tests on concrete waterproofed by fabrics may be found in BuUetin No. 336 of The University of Wisconsin. t Compiled from tests by the Universal Portland Cement Co. See Engr. and Con- tracting, Vol. 34, p. 448; also Engr. Record, Vol. 67, p. 66. EFFECTS OF TEMPERATURE 495 Natural cement concretes are badly injured by freezing prior to hardening. The results in the lower part of Fig. 17 show that freezing for different periods of time before initial set followed by a seven-day curing period at 50 to 60° F. produces a weaker concrete than would normally be obtained at an age of seven days. The magnitude of this weakening effect appears to be less when the freezing period is from one to two months than for either a shorter or longer time. Drying of the specimens may be responsible for the dropping of the curve between sixty and ninety days. TABLE 19.— A COMPARISON OF THE STRENGTHS OF 4-INCH SAND- MORTAR CUBES FROZEN AT DIFFERENT AGES. (Rath) Age AT Crushing Strength in Lb. PER Sq. In. for Mixes. Per Cent of Normal Strength. Testing. Days. Freezing. Days. 1 : 2 1 :3 1 :5 1 ; 2 1 :3 1 :5 2 22 1837 1193 657 91 100 91 3 21 1590 1102 526 74 94 80 4 18 1420 792 332 76 73 53 8 16 1537 788 372 85 77 64 15 17 1630 933 477 89 89 78 Age when Thawed, in Daya 18 15 13 9 6 3 In Table 19 are given the results of tests by W. C. F. Rath * on mortars made from various proportions of Medusa cement and pit sand. The purpose of these tests was to determine the effect of age at freezing on strength. The mortars were of plastic consistency. Speci- mens were allowed to set in air at room temperature before freezing ; they remained frozen one day and were then allowed to cure in the air of the laboratory until tested. The data show that under this treatment the maximum injury to the compressive strength of mortars three weeks old was produced when they had set for three or four days before freezing. It is probable that this effect would have been less marked if the specimens had been allowed to age for two or three months after freezing. The effect of freezing for varying lengths of time immediately after making is illus- trated in Fig. 18. The ratios of the lengths of the ordinates to the two curves for the same mix furnish a comparison between the strength of * Thesis, University of Wisconsin, 1906. 13 15 18 31 Age ol Normal Spec, in Days Fig. 18.— The Effect of the Length of Freezing Period on the Com- pressive Strength of 4-inch Sand- mortar Cubes. 496 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE mortars normally cured and the strength attained in an equal period after thawing. Evidently freezing prior to setting more seriously affects the strength of mortar or concrete than freezing after setting. Table 20 * shows the effect of freezing on the strength of 1:2:4 concrete both before and after initial set has taken place. As would be expected, the effects on the seven-day strengths are much more severe than upon the two-month strengths. After final thawing these specimens were sprinkled twice a day until tested. The tests also show that the final strength of Portland ce- ment concrete of wet con- sistency is not destroyed by a small number of freez- ings before or after setting, nor by a small number of alternate freezings and thawings, that the magni- tude of the effects of such treatment varies with the cement. Other freezing tests by Rath on plastic mortars show that the effect from alternate freez- ing and thawing is greater than from freezing once, and that the effect of such alternations on the strength is greatest when the intervening thawing periods are from four to six days long. Experimental evidence further indicates that lean mixtures suffer less loss in strength by freezing than rich mixtures. Concrete of dry con- sistency resists freezing better than one of wet consistency. After frozen concrete or mortar has been thawed it should be kept wet for three or four weeks in order that it may harden properly. 540. The Rate of Cooling of Concrete Setting at Low Temperatures. — The change in temperature at different points in a concrete wall sub- * Compiled from results of tests made by classes electing work in concrete at the University of Wisconsin. 40 60 Hours after Pouring Fig. 19. — Diagram Showing the Rate of Coohng for a 12-inch Wall of 1:2:4 Gravel Concrete. Con- sistency was medium. EFFECTS OF TEMPERATURE 497 TABLE 20.— EFFECT OF FREEZING ON THE COMPRESSIVE STRENGTH OF 1 : 2 : 4 PORTLAND CEMENT CONCRETE All concrete was made of Universal (U) or Alpha (A) cement, good pit sand, and broken limestone passing a IJ-in. mesh. The consistency was wet, not sloppy. The 6 X18-in. cylinders, used as speci- loens. were made in iron molds. No. of Testa. Brand of Cement. Age when Alternately Frozen and Thawed. Placed in Re- ■ friger- ator in Hours. Re- moved from Re- friger- ator. in Days. No. Cycles. Total Time, in Days. Time Age Ave. Sprinkled at Temp. Twice Test, in a Day, in Refr. in Days. Days, °F. Com- pressive Strength, Lb. per Sq.In. Specimens Made with Normal Watei 12 2 U 7 7 16 114 13 2 A 7 7 8 12 2 U 6 7 7 16 167 15 2 U 6 ■ 6 7 10 20 13 2 A 6 7 7 8 12 2 U 18 6 7 15 284 13 2 A 17 6 7 7 267 15 2 U 30 5 7 12 219 13 2 A 28 6 7 7 310 12 2 U 66 4 7 12 797 15 2 u 54 4 7 15 440 13 2 A 67 4 7 7 645 15 2 U 78 3 7 16 684 12 2 u Not Fro zen 7 7 1146 15 2 u 7 7 862 13 2 A 7 7 830 12 2 U 7 70 77 16 2775 15 4 U 6 57 63 "10 985 13 2 A 7 56 63 8 970 12 2 U 6 7 70 77 16 2605 15 2 U 7 7 56 63 11 870 13 2 A 3 7 56 63 8 1200 12 2 U Not Fro zen 77 77 2370 15 2 U 63 63 2323 13 2 A 63 63 1460 Specimens Made with a Seven Per Cent Salt Solution. 12 2 U 7 7 16 375 15 2 U 6 7 10 155 13 2 A 7 7 8 124 12 2 U 7 70 77 16 2284 15 2 U 6 56 63 10 678 13 2 A 7 56 63 8 900 12 2 U Not Fro zen 77 77 2055 15 2 U 63 63 1625 13 2 A 63 63 800 498 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE jected to freezing temperature while setting is shown in Fig. 19.* The forms of this wall were pine boards, I5 in. thick. A cover of the same thickness was placed on top of the wall immediately after pouring. Tem- peratures were measured by resistance thermometers connected to a Callendar recorder. This wall was withdrawn from the freezer when four days old and the 12X12X24-in. prism (P) tested at six days. The strength of the prism was 415 lb. per sq.in. or 65 per cent of the strength of concrete from the same batch cured for six days in the molds at room temperature. From a number of tests like the above, in which different cements and walls 6 and 12 in. thick were used, it appears that concrete of medium consistency placed in 2-in. plank forms at a tem- perature of 80 to 100° F. will set before freezing providing the waU is at least 6 in. thick and the outside temperature is not less than 0° F. Over- heating of the materials should be avoided, since in the above tests heating to 150° F. caused a decrease in the normal strength. 541. The Effect of Alternate Freezing and Thawing on Hardened Con- crete and Mortar. — To test the resistance of concrete to frost, specimens are sometimes subjected to alternate periods of freezing and thawing. The lower temperature is often about 10° or 15° and the thawing is commonly done by plunging into the water at 150° to 200° F. Ten alternations under such conditions should not lower the crushing strength of good concrete or mortar more than 30 per cent. From tests on mortars and concretes at the University of Wisconsin it appears that rich mixtures suffer a greater proportionate loss in strength under the alternate freezing and thawing test than lean mixtures; also wet mixes suffer more than dry ones. 542. The Effect of Adulterants in Lowering the Freezing Point. — Small percentages of salt or calcium chloride dissolved in the mixing water serve to lower the freezing point of the mix and thereby permit hardening at temperatures lower than 32° F. With some cements the use of small percentages of salt appears to diminish the strength; with others the reverse is true. So far as published results show, the use of a 10 or 12 per cent (by weight) solution of common salt has rarely decreased the long-time strength over 25 or 30 per cent, and in most cases the weak- ening in final strength is much less. The use of salt in reinforced concrete should be prohibited, since in damp locations it may cause rusting df the steel. A common rule for the use of salt is: Add 1 per cent of salt to the mixing water for each degree Fahrenheit below 32. Tests by H. E. Pulver and S. E. Johnson f at the University of Wis- consin, on the effects of calcium and sodium chloride solutions on the * From a thesis by Messrs. O. A. Bailey and F. D. Bickel at the University of Wisconsin, 1915. t Concrete Cement AcjC, Vol. 3, p. 256. EFFECTS OF TEMPERATURE 499 TABLE 21.— THE EFFECT OF CALCIUM CHLORIDE AND SODIUM CHLOR- IDE ON THE COMPRESSIVE STRENGTH OF 1:2:4 CONCRETE Materials: — Atlaa cement, good pit aand weighing 108 lb. per cu.ft., and limestone passing a IJ-in. mesh and weighing 90 lb. per cu.ft. Consistency : — Wet. Storage: — Normal specimens stored in air one day, in water 13 days. Low-temperature specimens, placed out of doors or in a refrigerator immediately after molding, remaining frozen until tested. Testing: — Each result represents tests on 4-in. cubes. Specimens were embedded in blotting paper on a spherical bearing block. Per Sa Cent LT. Specimens Cured at Room Temp. Specimens Cured IT Low Temp. Temp, of Batch at Mixing, o ^ Compressive Strength in Lb. per Sq.In. at Temp, (in °F.) at Mixing. NaCl. Compressive Strength in Lb. per Sq.In. at CaCU 14 Days. 60 Days. 360 Days. Batch. Out of Doors. 14 Days. 60 Days 52 1910 3010 3580 52 13 213 427 6 52 1684 2620 2895 51 13 482 685 9 65 1525 2385 3055 51 13 680 942 12 68 1270 2060 2485 51 13 813 1192 IS 58 1335 2220 2740 42 13 614 1060 2 .0 59 1920 3220 3740 41 17 420 466 4 60 2105 3510 3880 44 17 444 564 6 60 1725 3280 3670 55 18 349* 367* 8 61 1510 3070 3155 46 1 286* 334* 10 61 1655 3025 3330 46 1 234* 348* 2 6 59 1600 2650 3150 52 15 817 992 2 9 63 1695 2590 3100 52 15 848 1185 2 12 64 1420 2440 2805 41 7 690 1045 2 15 60 1320 2350 2725 38 7 583 801 4 6 56 1685 2550 2960 52 21 785 914 4 9 58 1550 2390 2965 51 20 755 926 4 12 58 1710 2935 3680 45 15 766 1215 4 15 65 1245 1880 2410 45 15 713 1200 6 6 60 1310 2475 2575 43 20 680 988 6 9 54 1305 2370 3025 38 20 480 850 6 12 54 1345 2420 52 21 505 615 6 15 52 1380 2415 52 21 527 863 8 6 60 1120 2075 2490 51 21 390 580t 8 9 58 1135 2085 2445 50 30 487 654 8 12 60 1110 1995 2525 52 30 402 589 8 15 59 1550 2605 2940 44 14 535 658t * Badly disintegrated. t Edges were spalled to some extent. 500 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE TABLE 22.— RESULTS OF COMPRESSION TESTS MADE ON PORTIONS OF PORTLAND CEMENT MORTAR BUILDING BLOCKS TAKEN FROM WALLS SUBJECTED TO A TEMPERATURE OF 900° C. FOR ONE HOUR Wall No. Kind of Block. Consistency. Crushing Stkength in Lb. per Sq.In.* From Exposed Face Proportions. 1 :2 1 :4 1 :i From Unexposed Face Proportions. 1 :2 1 :4 10 1 piece, double air-space 1 piece, double air-space 1 piece, single air-space 1 1 piece, single 1 air-space 1 piece, single air-space 1 piece, single air-space 1 piece, single air-space 1 piece, single- air-space 2 piece 2 piece Damp Medium Wet Damp Medium Wet Damp Medium Wet Damp Medium Wet Damp Medium Wet Damp Medium Wet Damp Medium Wet Damp Medium Wet Damp Medium Wet Damp Medium Wet 885 1328 880 1165 1507 1957 1016 971 1949 1422 1846 1843 1034 1482 2116 1141 1550 2215 1153 1370 2143 1202 1812 1873 952 1201 1244 464 663 788 752 831 897 552 1155 918 653 812 779 1205 1240 466 774 1542 505 922 1163 578 974 928 792 800 1204 350 802 992 348 622 462 376 493 464 401 482 482 512 617 408 665 671 502 509 521 307 495 539 552 472 398 1709 2182 1891 1874 2694 2477 1650 1530 2391 2181 2309 2310 1773 2047 2518 1189 1502 2397 1411 1548 2467 1208 2628 3307 1242 1358 1345 885 1253 1503 1140 1415 1692 909 1932 1494 714 1078 1088 1484 1518 987 843 2067 663 1044 1108 615 1159 1043 841 837 1922 669 932 1223 1132 1329 581 771 933 502 765 681 714 643 651 405 870 939 353 585 780 636 877 933 372 647 874 315 615 528 537 406 719 * In most cases values in the table represent four or more tests of pieces from three blocks. strength of 1:2:4 concrete subjected to freezing conditions, are ab- stracted in Table 21. The combination of 2 per cent calcium chloride with 9 per cent sodium chloride gave the best results of any of the salt EFFECTS OF TEMPERATURE 501 solutions under freezing temperatures. Since calcium chloride alone greatly hastens the set, its employment in the field will require very rapid handling during pouring. 543. Resistance of Concrete and Mortar to High Temperatures. — Observations after conflagrations like the San Francisco, Baltimore and Chelsea fires have shown that concrete possesses a high resistance to fire. Many examples have been cited of concrete buildings which were left standing alone in fire-swept areas of these cities. Tests reported by R. L. Humphrey, in Bulletin No. 370, U. S. G. S. show that mortar blocks and concrete beams have equal, if not superior, resistance to fire of any of the building materials employed for fire pro- tection. The tests were made on wall panels at the Underwriters' Labor- atories in Chicago. Specimens were well cured and two months or more old. The temperature of the furnace was gradually raised to 800° C. in one-half hour and maintained between 800 and 1000° C. for one and one- half hours. Careful records of temperature of the furnace, front and rear of the wall were obtained by means of pyrometers. Immediately after the panel was withdrawn from the furnace, the face exposed to the fire was soaked with a hose. A summary of the effects of this treatment on the strength of portions of mortar blocks taken from both sides of the walls is given in Table 22. These tests show that the resistance of mortars to fire increases with the richness of the mix for proportions between 1 : 2 and 1 : 8, and that generally wet mixtures stand a high temperature slightly better than medium mixes and much better than dry mixes. Humphrey's fire tests on 1 : 2 : 4 concrete from the plain beams used in the tests tabulated in Table 8 indicate no marked difference in the resistance of the granite, limestone, and gravel concretes. The cinder concrete showed less conductivity but it suffered greater disintegration than the above-mentioned concretes. This was due to the softness of the cinders and the presence of 24.5 per cent, of combustible material. Obviously, the resistance to fire of a wall heated on one face only will be much greater than the resistance of a small cube heated on all sides, yet tests on the latter type of specimen afford information on the relative resistance of various kinds of concrete. In Table 23 have been placed results showing the effect of fire upon the compressive strength of con- crete. These were gotten by I. H. Woolson.* For these tests the furnace was heated at a rate of 500° F. in forty-five minutes. Specimens were held at the temperature indicated for ten minutes. Prof. Woolson found that the modulus of elasticity for both trap and limestone concrete was reduced over 60 per cent by heating to 500° F. In other tests f on 1 : 2 : 3 concrete heated to 1500° F. in forty-five min- * Proc. A.S.T. M., Vol. 5, 335. t Proc. A.S.T. M., Vol. 7, p. 404. 502 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE TABLE 23.— EFFECT OF FIRE ON THE COMPRESSIVE STRENGTHS OF 4-INCH CONCRETE CUBES. MADE OF TRAP ROCK AND LIMESTONE Concrete was of medium consistency and consisted of 1 part mixed Portland cement 2 parts sand and 4 parts |-in. broken stone. Age of specimens four to six weeks. Each value represents three tests. Time between Heating and Testing, Days. Temper- ature of Furnace "F. comphesbive Strength IN Lb. per Sq.In. Condition after Heating. Trap. Lime- stone. Trap. Lime- stone. Trap. Limestone. 2 2 3 3 3 3 3 3 3 3 500 750 1000 1250 1500 1750 2000 2250 1903 1920 1840 1410 1244 1556 923 847 501 1817 1234 ,1244 1043 973 765 813 Slightly brittle Brittle Stone partly calcined Calcined throughout Full of cracks Fragile "1 Crumbled on / cooling 2 2 2 10 10 9 Slight cracks Brittle, cracks Brittle, cracks Sound Full of cracks Full of cracks Partly fused utes and maintained at that temperature for fifteen minutes he proved that the modulus of elasticity may be reduced to one-tenth of its normal value. The latter experiments were made on trap, quartz gravel, and cinder concretes and showed that the relative loss in stiffness was least for the cinder concrete and most for the quartz gravel. In general, it may be stated that concrete heated above 1000° F. will lose a large portion of its strength and stiffness. If it is then exposed to the air it will show marked surface disintegration; in small specimens the entire structure may disintegrate in the course of two or three weeks. Such disintegration is very pronounced in concretes made from limestone or dolomitic aggregates. Lean mixes suffer disintegration more quickly than rich ones. On the other hand, if the specimens are wet while hot, an arrest of the disintegrating influences is brought about. 544. The Coefficient of Expansion of Concrete and Mortar. — Table 24 contains values of the linear coefficient of thermal expansion of concrete for atmospheric ranges of temperature. For mixes commonly usad an average value is 0.000006 per ° F., which is approximately the same as the coefficient of expansion for iron and carbon steel. 545. Other Thermal Properties. — Tests by C. L. Norton * on the specific heat of various mixtures of ce noi'o to gave tbo r°^"1t i i in Ta.ble "2^ In these tests he employed Regnault nary double calorimeter. ' Proc. Nat. Asso. Cemet s me; ( Us£Ti DEP, lol TMENT E DESTCf^' EFFECTS OF TEMPERATURE 503 TABLE 24.— LINEAR COEFFICENT OF EXPANSION OF CONCRETE AND MORTAR AT NORMAL TEMPERATURES Mix. Aggregate. Coefficient per "F. Authority. Reference. .0000070 .0000056 .0000058 .0000053 .0000059 .0000066 .0000055 .0000054 .0000053 .0000066 .0000056 Keller Keller Keller Keller Bonniceau Bonniceau Pence Pence Pence Hallock Hallock 2 4 8 2 2 :4 2 :4 5 .2:5 :2 Pit gravel Pit gravel Pit gravel 1 Tonind'z't'g, No. 24, 1904 1 Ann. Fonts Chaus. J 1863, p. 181 1 Jour.W. S. E., Vol. 6, J p. 549 j Reid, p. 171 •Sand Sand and limestone Sand and gravel Pit gravel Sand and gravel Sand TABLE 25.— THE SPECIFIC HEAT OF CONCRETE. (Norton) Range of Temp. ° F. 1:2:5 Stone Con- crete. 1:2:4 Stone Con- crete. 1:2:4 Cinder Con- crete. 72 to 212 72 to 372 72 to 1172 72 to 1472 0.156 0.192 0.201 0.219 0.154 0.190 0.210 0.214 0.180 0.206 0.218 TABLE 26.— THE COEFFICIENT OF THERMAL CONDUCTIVITY OF CON- CRETE. (Nohton) Temperature of Hot Side of Plate in Degrees. Mixture. Coefficient in Calories per 1 Deg. C. per Sq.Cm. per Cm. per Sec. Coefficient In B.T.U, per 1 Deg F. per C. F. Thick per 24 Hr. 35 95 Stone 1:2:5 0.00216 150 50 122 Stone 1:2:4 not tamped 0.00110 to 0.00100 76 to 114 60 122 Cinder 1:2:4 0.00081 56 200 392 Stone 1 2 :4 0.0021 146 400 752 Stone 1 2 :4 0.0022 153 500 . 932 . ■ ,,'Stoiie 1 2 :4 0.0023 160 1000 ■ 1832 Sfone 1 2 :4 0.0027 188 1100 2012 Stone 1 2 :4 0.0029 202 504 PHYSICAL PROPERTIES OF MORTAR AND CONCRETE Norton also determined the coefficient of thermal conductivity (K) for concrete. Qd K = {tl-t2)As 1,500 1,000 500 21,000 p d £ B ■£ 500 a a 1,000 500 ^ — / C NDER CONCRETE / ' // V ^^ " / ^ ,--' . / *^ ^ __ / y O ^^ / / ^ - / / y .,^-— / / / ,, / y ^ y ^J>-^ "^L—- / ^_^^ ..jX- ^'-^ ' >^^ _^^ "y^ -i^ ^ — -Ti-" "^ — ^^ ^ / GRAVEL CONCRETE / / / __^ „ / / sll^^ " ______ // ,/ -" «?/ / i ^ / / / I / / / / -^ ■ 1 / / / '-l^'^' / ^^ — ^ y /4" ^^ 1 V^ ■^ ZA :^ ^ ^^^^== '-A „ h .„ ~ " ^.)" /^ / TRAP ROCK CONC RETE / / . ' 1 / ___ — -— ■ / . -^ <,„„^c„ vj f t xTi li. °f metal forms the closed secondary circuit i»" / x^- ^ / i f / 1 / ( i i 0.01 0.02 Proportionate. Elongation for open links. for stud links, -S,= St = 2P A' 1.6P where St is the maximum unit tensile stress, P the load on the chain, and A the area of the stock. For either of the above chains the com- pressive stress on the inner fibers at the link ends is approximately double the maximum tensile stress. However, since the length of link under compression is very short and since additional security is affected at these points by the pinching action of the adjoining links, it appears practical to base the design upon the tensile strength of the hnk If 15,000 lb. per square inch is considered a safe value for tensile stress in chains, then the above formulas reduce to P=6000 d? for open links and P = 7500 d^ for stud links, whore d is the diameter of the iron. 674. The Welding of Wrought Iron. — One of the most valuable properties of wrought iron is the facility with which portions of * Bull. No. 18, Engr. Expt. Sta. Univ. of 111. - . THE WELDING OF WROUGHT IRON 607 it may be united by squeezing or hammering while at a high heat. This characteristic renders the iron very useful to the smith. The property is due to the high plasticity of the iron throughout a consid- erable range of temperature extending below a white heat. However, if the iron parts are heated to such temperatures in the presence of much air their surfaces soon become coated with a film of iron oxide. Consequently it is difficult to bring the welding surfaces into perfect contact. To avoid imperfect cohesion it is necessary that the central portions of the surfaces in the weld be first brought together so that the oxide forming at the joint may be expelled outward and not entrapped as the seam is closed under the hammer. The evil effects of the oxide may be greatly reduced by using borax or other flux which acts as a solvent of the oxide and renders it more easy to expel from the joint. Moreover, by maintaining a thick fire in which most of the oxygen is combined with carbon, or by heating, the parts in a muffie it is possible to considerably reduce the amount of slag formed. One of the advantages of electric welding lies in the fact that no air blast is employed, and by having the parts in contact during the lap Weld Cleft Weld Butt Weld Fig. 8. — Common Types of Welds. heating period, air is largely excluded from the welding surfaces and hence little oxide is there formed. Fig. 8 shows the common types of welds and the shapes of the parts prior to welding. After the parts have been shaped and upset as required by the work in hand, they are reheated, if necessary, and then rapidly hammered until the metal is below a red heat. This hot work reduces the grain size and renders the metal at the weld more ductile and tough. Inasmuch as there is likely to be overheated metal on either side of the joint which has not been properly worked during the welding, it is best, wherever possible, to anneal welds and thus secure uniformity in structure and properties of the metal in the vicinity of the joint. On account of the difficulties encountered in welding, the strength of welded joints is likely to vary from 30 to 100 per cent of the strength of the parts joined. With the most careful hand welding Kirkaldy reports the following average efficiencies: For the strengths of joints in round tie-rods 1| to 3| in. in diameter 60 per cent; for flat plates 2J to 6-in. wide and J to 1-in. thick 71 per cent; for chain- 608 , PROPERTIES OF WROUGHT IRON link welds on §- to 2|-in. iron 216 tests gave an average efficiency of 83 per cent.* Carefully conducted tests by Bauschinger showed an average efficiency of 95.6 per cent for wrought-iron and 89.2 per cent for soft- steel joints. Hand-forged welds of wrought iron gave an average efficiency of 87.9 per cent; those forged by steam hammer had an average efficiency of 91 per cent. With soft steel the hand-forged welds had an average efficiency of 84 per cent, while the power-forged welds developed an average efficiency of 97.2 per cent. The efficiency of the steel welds varied much more than those of wrought iron. These tests represent what can be done under best conditions in welding bars which vary in size up to 3j by 1.2 in. in cross-section. Tests at the University of Illinois f on low-carbon steel welded by an oxyacetylene torch indicate that the efficiency of the material in the joints under static tension will average about 75 per cent when the work is done by a skilled operator. By slightly building up metal around the welds it is possible to make the strength of the joint equal to the strength of the solid section. Under impact the efficiency of oxyacetylene welds was about 50 per cent. 675. Methods of Distinguishing Wrought Iron from Soft Steel. — Often the mechanical properties as revealed by the tension test are ample to differentiate steel' from wrought iron. Generally wrought iron exhibits lower elastic limit, ultimate strength and elongation than steel and a very mudb less reduction in area. The fracture is jagged and fibrous whereas steel is cup-cone and finely crystalline, or silky. The nick-bend test (Art. 144) serves as a determinator if the iron has a pronounced fibrous fracture. Compression tests on short prisms of wrought iron and steel generally furnish indications as shown in Fig. 11, Ch. III. Resistance to corrosion is another basis of distinguishing between these metals. The ends of small rods are turned or filed smooth and suspended for about a half hour in a solution of one part hydrochloric acid, three parts sulphuric acid and nine parts water. After immersion steel will be found to have been evenly attacked, whereas wrought iron specimens show ridges parallel to the axis of the specimen.. The ridges are slag filaments which resist the attack of the acid much better than the intervening grains of iron. Probably the best proof of well-puddled wrought iron is afforded by a determination of the manganese content. In good iron man- ganese will run under 0.D5 per cent, but in steel it is generally above 0.30 per cent. * Kirkaldy's System of Mechanical Testing, London, 1891, Report K.K. ^Bulletin No. 45 and 98, Eng. Expt. Sta. University of Illinois. CHAPTER XXIII PROPERTIES OF STEEL 676. The principal factors influencing the properties of steel are: (1) chemical composition, (2) heat treatment, and (3) mechanical work. Composition bears a vital relation to the constitution of the metal and through structure has a most important bearing on physical properties. Heat treatment may be influential, (a) in altering the solubility rela- tions of the constituents, (6) in changing the crystallization either with respect to form or degree of aggregation, (c) in introducing or relieving internal stresses in the metal. Mechanical work may be hot or cold; it has an effect (a) in altering the form of the crystalline aggregate, (b) in introducing internal stresses. We shall now consider the effects of these main factors together with certain other influences on the physical and mechanical properties of steel. Although for the sake of simplicity, we study these influences separately; yet we must continually bear in mind that combinations of all of them will, in general, affect the properties of a given piece of steel. COMPOSITION Cakbon 677. Importance of Carbon in Steel. — ^We have already noted in studying the constitution of the iron-carbon alloys how very marked are the changes in structure which are produced by adding small per- centages qf carbon to pure iron. Indeed it is the presence of these small quantities of carbon which make it possible to secure the high degrees of hardness and strength that differentiate steel from ingot iron or wrought iron. On the other hand, the addition of carbon to iron decreases the malleabihty and ductility of the metal, and reduces its permeability to magnetic forces. If we refer to the Roozeboom Diagram, Art. 660, it will be noted that for a carbon content above 2 per cent there is always a heterogeneity of structure with separation of cementite, at temperatures below 1130° C, or completion of solidification. On the other hand, with a carbon content below 2 per cent, it is possible to have all of the carbon or cementite in soHd solution in the iron, at sonie temperature below fusion. This limit of solid solubility at 2 per cent of carbon marks the theoretical dividing line between the steel 609 610 PROPERTIES OF STEEL and cast iron; the latter being non-malleable at any range of tem- perature. 678. The Physical Characteristics of Ferrite and Cementite.— Again referring to regions IX and XII of the Roozeboom Diagram we note that slowly cooled steels and cast iron consist of pure iron (ferrite) and iron carbide (cementite), a portion or all of the ferrite and cement- ite always being intimately associated in the eutectoid, pearlite. Fer- rite is a relatively soft, ductile and malleable metal of low elastic ratio. Cementite, on the contrary, is extremely hard, brittle, non-malleable at any temperature, and has a high elastic limit equaling its tensile strength. It is to be expected, therefore, that the relative properties of these two constituents, together with the nature of the association and degree of aggregation, will determine the physical properties of steels and cast irons. In fact the strengths of normal carbon steels of less than eutectoid composition are in direct ratio to the percentage of pearlite, whereas in the hypereutectoid steels the strengths diminish sUghtly as the excess cementite increases. 679. The essential relations between carbon content and mechanical properties for the carbon-iron alloys containing 4 per cent or less of carbon are shown in Fig. 1. From the figure it will be observed that White Cast Iron 1.5 2.0 2.5 3.0 Percentage o£ Carbon Fig. 1. — Theoretical Relations between Mechanical Properties and Carbon Content in Iron-Carbon Alloys. (Howe.) the tensile strength increases to a maximum when the metal is approxi- mately of eutectoid composition. This is probably due to the rela- tively intimate mixture and fine state of aggregation of the cdnstit- uents of the pearlite. With a decrease or increase of carbon the ferrite or cementite, respectively, becomes an excess substance forming a grain network which has a weakening influence on the metal. The relation of hardness to carbon content is dependent upon the kind of hardness. In Fig. 1 hardness is shown as varying directly with the increase in cementite. As measured by. the Brinell ball method the resistance to indentation increases much more rapidly for COMPOSITION 611 carbon contents up to the eutectoid ratio (0.90 per cent C.) than for the higher percentages. Thus the Brinell number for soft iron lies between 75 and 80, for eutectoid steel it is approximately 250, and for 60,000 4S), c=o .81^ / C = fl .71 !4 / ■s> — ■ -^ 60,000 J \s° ?ji. / fj / 1 } // 40,000 4 m 20,000 / / # f Y ' « P ^ V / ^ J r ^ ' / / .•I!- % / A y^ / ^7 3 120,000 7 J / Load In V / / / ^or IP. C = ( sn 80,000 k'\ Tm — .—-. _a — v^ C=0 mi y f^ Z^=ii .... — o / ^ 60,000 / / V \ . 287.) j ^ c .■> , , , pendent of the carbon content. This is shown in Figs. 2 and 3. Table 3 from Marshall's carefully conducted experiments * also furnishes comparisons of the moduli of elasticity for steels varying in carbon content. * Reported in Trans. Am. Soc. Civ. Engr., Vol. 17, p. 62. .50 .75 Per cent CarboD COMPOSITION 617 TABLE 3.— MODULI OF ELASTICITY OF STEEL ON FIRST LOADINGS, WITH VARYING PERCENTAGES OF CARBON, ONE SPECIMEN FROM EACH HEAT. (Marshall) Number of Heats and Average Percentage of of Carbon. Moduli of Elasticity E, in Square Inch. Pounds per Kind of Steel. Tests. Lowest Value. Highest Value. Average Value. 33 8 107 89 25 .09 .11 .24 .34 .72 28,750,000 29,210,000 28,310,000 28,140,000 28,680,000 31,540,000 30,670,000 31,180,000 30,910,000 30,860,000 29,924,000 30,020,000 29,996,000 29,672,000 29,919,000 29,866,000 Bessemer Open-hearth Bessemer Open-hearth Weighted mean value = TABLE 4.— COMPARISON OF MODULI OF ELASTICITY IN TENSION AND COMPRESSION. (Marshall) All results given in one-thousand-pound units, identical material. Steel. — Tensile Strength less than 100,000 Pounds per Square Inch. Spring-steel. — Tensile Strength 144,000 Pounds per Square Inch. Tension. Compression. Size of Bar, In. Tension. Compression. Size of Bar, In. El First Loading. Second Loading. El First Loading. Ei Second Loading. El First Loading. E2 Second Loading. First Loading. E, Seconu Loading. Ird. Ird. frd. 30,190 29,850 29,280 29,830 29,420 29,550 29,240 29,400 30,000 34,420 29,850 29,500 29,150 29,640 29,630 29,960 30,420 30,370 29,450 28,070 38,780 28,580 28,380 28,680 30,070 28,980 29,260 29,740 29,010 29,420 29,420 28,670 28,830 30,490 29,790 29,810 Ird. Ird. ■nrsq. ■nrsq. 29,480 29,390 28,880 29,200 29,760 29,.580 29,420 29,200 28,880 28,880 29,090 29,090 29,300 29,200 29,220 29,350 T%sq. Ird. Ird. Ird. Ird. Mean 29,237 29,490 28,985 29,267 Mean 29,529 30,371 28,884 29,464 Table 4 shows that the modulus of elasticity of steel on second loading is likely to be slightly higher than on first loading due to very small set, although the primitive loading does not exceed the limit of proportionality. If the primitive loading exceeds the proportional limit, the modulus of elasticity is lowered, in some cases from 10 to 20 per cent. From a consideration of the available experimental data, it appears that the modulus of elasticity of steel in tension or compression 618 PROPERTIES OF STEEL generally lies between 28,600,000 and 31,000,000 a mean value being about 29,500,000 lb. per square inch. A very large number of tests by Brinell on the modulus of elas- ticity of steels show also that heat treatment has little effect on the modulus of elasticity of carbon steels regardless of their carbon con- tent. Annealed steels and quenched steels gave moduli averaging from 3 to 4 per cent higher than the bars received from the rolls.* The modulus of elasticity in shear (often called the modulus of rigidity) is determined from torsion tests. Bauschinger reported tests j on Bessemer steels varying in carbon content from 0.19 to 0.96 per cent and on open-hearth steels of five degrees of hardness. For the Bessemer steels the shearing modulus varied from 11,900,000 to 12,700,- 000 lb. per square inch, and for the open-hearth varieties it ranged between 11,500,000 and 12,250,000 lb. per square inch. Piatt and Hayward % also reported values of the shearing modulus of elasticity for high- and low-carbon steels, — ^Bessemer, crucible and open-hearth varieties being represented. Their results ran from 12,350,000 to 14,- 000,000 lb. per square inch. For low- and medium-carbon steels an average value of the shearing modulus is 12,000,000 lb. per square inch. 682. Influence of Caibon on Ductility. — The ductihty of steel de- creases markedly as the carbon content increases (Figs. 4 and 5). Since ductility is also much influenced by variations in heat treatment and by the gauge length (Art. 711 and 106) it is not possible to give an accurate equation between ductility and carbon content. The following equations between per cent elongation (e) and per cent carbon (C), or strength (S;), are examples of some of the attempts to express such relationships. 3 , by Howe for elongation in 8 in . . (1) C^+O.l e = 32 — 30C, by Upton for specimens having diameter of 0.8 in. and 8 in. gauge length. (2) e = 50— 48 C, by Upton for 5-in. standard test-piece . . . . (3) 1,800,000 5,-10,000 1,500,000 - 10, by J. B. Johnson for elongation in 8 in. . . . . . . (4) , by a Committee of Am. Soc. Civ. Engr . . . ... (5) The range of values for C in Eq. (1) to (3) is from to 1 per cent. Eq. (1) gives values about 6 per cent to low for medium-carbon steels. Equations of the same type as 5 are common in specifications. For the high-carbon steels, however, this equation calls for too great elongation. Therefore, the constant is reduced in specifications for such steels. *Jour. It. and St. Inst., Vol. 60, p. 234. t See Unwin's Materials of Con.slructioH, p. 241. i Proc. Inst. Civ. Engr., Vol. 90, p. 409. COMPOSITION 619 Fig. 8 shows the elongation field as worked out from a table in Howe's Metallurgy of Steel, which gives values of greatest and least elongations for different steels. It is plain from the figure that Eq. (4) has a much wider ,„,„„„ 1jJ,UUU J t il 1 1 range of appHcation \ j \2-\ thanEq. (5) or others of that type (5). The per cent re- duction in area {R) also decreases as the carbon content in- creases. In Fig. 4 the relation may be ap- proximately expressed by 13 R- C2+0.18" 15 20 Percentage of Elongation « no i-ii- • Fi°- ^- — Relations of Elongation to Strength for Steels. bod. Cnanges in the Shape of the Stress diagram. — The effects of carbon on the tensile properties of steel are well shown by the changes in the shape of the stress-diagram. Thus, in Fig. 9 the increases in the elastic limit and ultimate strength and the accompanying decreases in the elongation cause the diagrams to increase in height and decrease in width. The horizontal portion of the curve for low-carbon steel, which follows the drop in the load after the yield point has been passed, disappears in the diagrams for the high-carbon specimens. The downward slope of the portion of the stress-deformation curve beyond the maximum stress becomes less pronounced in the high-carbon steels and disappears in the diagrams of the very hard steels which break without necking. Furthermore, the area of the diagram, representing the energy of rupture, decreases as the carbon increases (Fig. 9). 684. The resistance of steel to heavy shocks or blows decreases as the carbon content increases. The decrease in shock resistance is most rapid as the carbon is increased from 0.15 to 0.40 per cent. Fig. 33 shows some of BrinelFs impact results which emphasize this conclusion. The figure also shows that the energy of rupture com- puted from tensile tests is a poor measure of resistance to impact. Similar evidence showing discrepancies between the energies of rupture in tension and impact is furnished by data of the Alloys Research Committee * as compiled by Howe in the discussion of a paper on impact testing before the Institute of Mining Engineers, f * Proc. Inst, of Mech. Engr., 1904-1, p. 160. t Trans. Am. Inst, of Min. Engr., Vol. 53, p. 218. 620 PROPERTIES OF STEEL Although it appears that the soft and medium-carbon steels as rolled, or in the annealed state, have much superior resistance to impact than the high-carbon steels, we must not infer from this conclusion that the low-carbon steels are best suited to withstand repeated stress or a succession of Hght blows. Under such loadings, the harder steels with a higher elastic limit have proven more satisfactory. (See Art. 828.) Unit £longatloQ,ln. per In. Fig. 9. — Tension Stress-cJia-grams of Carbon Steel Bars Used for Endurance Tests of Shafting. {Tests of Metals, 1889, p. 389; 1891, p. 603.) 685. The Range in Composition of Structural Steels. — Practically all steels used in engineering construction in the normal or annealed condition are of less than eutectoid proportion (0.9 per cent carbon). The carbon content is the result of experience whereby the proper combination of strength, elasticity, hardness and workability have been obtained to fit the material for the particular service. Increased tenacity and elasticity are gained at the sacrifice of ductility and soft- ness. In structural steels, boiler plate, and the hke, where some in- crease of strength is desirable, provided there is not too great loss of ductility and softness, a carbon content of about 0.20 per cent is customary. The tensile strength of the iron is thereby increased by about 15,000 lb. per square inch (from 45,000 to 60,000) without COMPOSITION 621 material loss of the ductility and softness so essential to the require- ments for manufacture and service. In steel rails, there is little fabri- cation of the finished product and the stresses are heavy shocks at intermittent periods. Hardness is essential for wear, and high strength and elasticity are necessary to enable the steel to withstand the load and recover its alignment; yet ductility cannot be sacrificed to the extent of dangerous brittleness. The carbon content of rails varies from 0.50 to 0.70 per cent, the larger amounts having been introduced in special cases in recent years, particularly in heavy sections and where the steel has the minimum of phosphorus, sulphur, or other associated detrimental elements, which lower ductility without the compensating advantage of adding much strength. The following table shows classifications, approximate composition and mechanical properties of some of the more important steels used in construction. Carbon contents for tool steels may be found in Art. 709. Classification Based on Usage. Hardness. Manufac- ture. Per Cent Carbon. Tensile Strength (lb./m.=). Percent Elongation in in. 2 in. Rivet Tubing and Pressed Metal Screw stock Boiler plate Structural Structural Machine Rail Tire Extra soft Extra soft Mild or Soft Medium Medium Hard Hard O. H. O. H. JO. H. I Bess. O. H. O. H. O. H. O. H. /O. H. \ Bess. O. H. 0.08-0. IS 0.08-0.15 0.10-0.20 0.10-0.20 0.10-0.20 0.20-0.35 0.20-0.30 0.40-0.75 0.50-0.80 45- 55,000 45- 55,000 55- 65,000 55- 65,000 55- 65,000 65- 75,000 60- 70,000 85-125,000 110-130,000 10-16 10 Effects of Principal Impurities on Steel * 686. General Effects. — ^As we have seen in Chapter XVIII, it is not feasible under present practice to remove impurities entirely in making either iron or steel. Therefore, the final product always con- tains, besides iron and carbon, small percentages of the metallic im- purities, — silicon, manganese, sulphur, and phosphorus, — ^together with lesser amounts of the oxides of silica, manganese and iron, silicates of manganese and iron, and some occluded gases. Occasionally very * For an extended discussion of the effects of impurities on steel the reader should consult the excellent paper and bibliography compiled by J. E. Stead, See Jour. Ir. and St. Inst., Vol. 94, p. 5-136. 622 PROPERTIES OF STEEL small percentages of copper and arsenic are also present. In well- made steel the total amount of these impurities generally ranges between 0.2 and 1.0 per cent and their resultant effect on the consti- tution of steel is often very small. Of the common impurities, phos- phorus and sulphur are injurious elements present in the ore which cannot be eliminated in the process of manufacture, whereas most of the silicon and manganese are introduced to improve the metal. The non-metallic impurities are objectionable substances which find their way into the steel during the process of refining. 687. Effects of Silicon. — Silicon probably in the form of iron- silicide, forms soHd solutions with iron in all proportions up to 20 per cent. It is often added to molten metal to remove oxygen and diminish blowholes. In the carbon steels silicon rarely exceeds one-half of one per cent and in structural steels it is generally under a quarter of a per cent. With such small proportions of silicon the microscope reveals no peculiarities in constitution. Silicon up to 1.75 per cent appears to increase both ultimate strength and elastic hmit without decreasing duc- tility.* BrineU's researches show that silicon increases the hardness of steel. For silicon varying between 0.10 and 0.20 per cent the increase in hardness was approximately 6.4 (Brinell scale) per 0.1 per cent in- crease in sihcon. Silicon is, therefore, about one-third as effective as carbon in increasing hardness. On account of the marked tendency of silicon to prevent solution of carbon in iron (Art. 662) it is very necessary to avoid prolonged heating at high temperatures in treating steels having high silicon and carbon contents. Instances have been recorded where steel castings have been ruined by soaking for a long time at a temperatm-e consid- erably above the recalescence point, the combined carbon being thus transformed into graplyte and the casting thereby greatly embrittled. However, with normal percentage of silicon and good heat treatment graphite is not present in steel. 688. Effects of Phosphorus. — When present in the low proportions common to steel, phosphorus exists in a sohd solution of iron-phos- phide (FeaP) and iron. In thiis form it permeates both the free ferrite and that composing the pearUte (Sauveur). By some it is considered to promote enlargement of the grains and thus produce brittleness. Howe maintains that the presence of phosphorus in ferrite makes the ferrite more mobile when it is slowly cooUng through the transforma- tion range. This mobility results in the banding of the ferrite into thin rods or layers which, upon etching, are revealed as light-colored Unes, called ghost lines. Such formations, of course, render the metal less homogeneous. * The properties of silicon steels are discussed in Art. 734. COMPOSITION 623 In wrought iron much of the phosphorus content is held in the slag fibers in the form of iron phosphate. As a constituent of the slag its effect is probably less detrimental than as a phosphide in the ferrite. Although the ductility of low-carbon steel may be slightly decreased by the presence of 0.3 to 0.5 per cent phosphorus, the yield point, ultimate strength and hardness are increased. Resistance to shock is, however, markedly reduced by such high percentages of phosphorus. Tests by D'Amico on low-carbon steels show that toughness is adversely affected (i.e., the metal is rendered cold short) by 0.1 per cent phos- phorus and very much decreased. by 0.2 per cent of this element. The evil effect on toughness appears to be more pronounced in high-carbon than in low-carbon steels. Although it is very probable that many failures have been errone- ously ascribed to a high phosphorus content which, if all facts were known, were traceable to other causes, yet a due regard for the ten- dency to produce cold shortness requires that phosphorus be kept low in steel. At present the maximum limits are: for inferior grades of structural steel 0.1, for best grades of structural steel 0.05, and for tool steels 0.02 per cent. 689. Effects of Sulphur. — Sulphur readily combines with iron to form iron sulphide (FeS) which, when present in iron or steel, has a tendency to segregate and form brittle networks at the grain boun- daries. On account of its low melting-point, iron sulphide causes a lack of cohesion between adjacent grains of the metal when it is heated above a red heat. Such brittleness at high temperatures is termed red shortness. Since red shortness makes steel or iron hard to roll or forge, it is a serious defect in the metal from the standpoint of the manufacturer. Manganese sulphide has a much higher-melting point than iron sulphide and does not render ferrous metals red short. Therefore, inasmuch as manganese has a very powerful Affinity for sulphur, it is possible to relieve red shortness by adding sufficient manganese to the molten metal to combine with the sulphur. Theo- retically the ratio of manganese to sulphur should be 1.7 to 1 in order to form manganese sulphide (MnS) and completely satisfy sulphur. Levy contends, however, that even if manganese is present in sufficient quantities to form the sulphide some iron sulphide will still remain and will be found mixed with the manganese sulphide. Since man- ganese sulphide also segregates and forms brittle masses, more or less rounded in castings and elongated in mechanically worked pieces, it appears that either sulphide causes a, lack of homogeneity. If sufficient manganese is present to prevent red shortness there is little evidence that sulphur in quantities less than 0.15 per cent exer- cises any appreciable effect on the mechanical properties of structural 624 PROPERTIES OF STEEL steel.* For screw-stock a high sulphur content (0.10 to 0.15 per cent) is commonly specified, since chips of such metal crumble without curling and the stock threads nicely. There appears to be a feehng, even though there is little direct evidence to support it, that percent- ages of sulphur too small to produce red shortness in rolHng may develop invisible flaws in the finished metal. Specifications for steel, therefore, stringently limit sulphur to practically the same amounts as phosphorus. 690. Effects of Manganese. — Marfganese is one of the main elements of the recarburizers used in manufacturing steel. Through its strong affinity for oxygen and sulphur manganese acts as a cleanser of the molten metal by withdrawing much of these undesirable impurities into the slag. When more manganese is present than required to satisfy sulphur and oxygen the excess manganese forms the carbide, MnaC, which is associated with cementite. If present in this form it acts as a hardener. In carbon steels, the manganese content is generally under 1 per cent and ordinarily runs about 0.3 to 0.6 per cent. Brinell's tests show that manganese, when under 1.0 per cent, hardens steel slightly, the average increase in hardness due to an increase of 0.1 manganese being about 4.0 on the Brinell scale. Howe f claims that a maximum fineness of grain together with a minimum of injury in hardening can be secured for carbon steels by maintaining manganese high, say around 1.25 per cent. In high-carbon alloys manganese increases the solubility of carbon in iron and hinders the precipitation of graphite in cooling. 691. Copper up to 0.5 per cent appears to have little if any effect on the mechanical properties of steel. A small percentage of it is said to increase resistance to corrosion. In most steels the proportion of copper is negligible. 692. Arsenic is occasionally found in very small proportions in steels made in Europe. It has a tendency to raise the strength and cause brittleness. It is considered undesirable when more than 0.1 per cent is present. 693. Non-metallic Impurities. — Steel and iron also frequently con- tain very small percentages of the oxides and silicates of both iron and manganese. These impurities are mechanically suspended in the metal and are often called slag inclusions. They appear to arise from trap- ping of the slag, from the cleansing action of the rccarburizer, and from the spalling of the ladle and furnace linings. In well-made steel such inclusions are slight and of small moment. If segregated they are likely to cause brittleness. * See data presented by J. S. Unger in Engr. News, Vol. 75, p. 363. t Proc. A.S.T. M., Vol. 17, Pt. 2, p. 8. EFFECTS OF HEAT TREATMENTS 625 From time to time the opinion has been advanced that nitrogen and hydrogen are present in iron and steel, especially in Bessemer steel, and that they embrittle the metal. Quantitative evidence of these facts is, however, lacking. EFFECTS OF HEAT TREATMENTS 694. Effects of Heating above the Critical Range. — On heating steel past the critical range of temperature,, there is a structural change from an aggregate of ferrite and cementite to a homogeneous sohd solution. This transition effectively destroys all pre-existing crystalliza- tion, not only as to type of aggregate, but of size as well. Referring to the Roozeboom Diagram, Fig. 1, Ch. XXI, it will be noted that so long as a steel of carbon content to 2 per cent is not heated above Ar\ (690° C.) there will be no change in the structural relations of the iron and the cementite.* With rise of temperature above this critical point, however, formation of austenite will begin, and proceed to a degree dependent upon the carbon content of the steel and the temperature attained above the critical one. Solution of all of the pearlite is completed immediately the temperature exceeds Aci. For hypoeutectoid (below 0.9 per cent C) or hypereutectoid (above 0.9 per cent C) steels the solution of the excess ferrite or cementite, respectively, proceeds with each degree of temperature rise above Aci, but is not completed until the temperature reaches the upper transi- tion hmit, marked by GP and PS, respectively, corresponding to the particular carbon content of the steel under treatment. In other words, the austenitic state in a steel of eutectoid composition (0.9 per cent C) is entirely brought about by heating to or just above the constant critical temperature of transition; while for a steel of other carbon content, a range of temperature is necessary, which is greater the farther the carbon content is removed from 0.9 per cent. The temperature necessary to accomplish complete solution of the cementite is higher the more the steel varies either way from eutectoid propor- tions. The transition, as noted heretofore, is the result of aUotropy in the iron; cementite is immiscible in alpha iron, but is completely sol- uble in gamma iron, within the saturation limits, marked by region IV in the Roozeboom Diagram. 695. Effects of Cooling from above the Critical Range. — ^There will be progressive aggregation of the austenite into grains which increase in size with rise of temperature, up to the fusion stage. That grain size which is attained as a result of the maximum temperature reached * On account of lag in reaction the change takes place at Ac^ which is sHghtly higher than An. 626 PROPERTIES OF STEEL during heating, will be retained during the cooling of the steel to ordinary temperatures, and, although the transition from the austenitic to the pearhtic (or some intermediate) form will take place during the critical temperature range, the final structure will exhibit such coarse- ness of texture as was inherent in the austenite when cooling began. Coarseness of grain is a function of temperature rise above the critical point Arz] but diminution of graia is not an accompaniment of tem- perature fall. Rate of cooling through and somewhat below the transition zone influences the final structure, however; (1) the reversion from austenite to ferrite-cementite requires time for its completion, and the quicker the cooling for a given composition, the less complete is the transi- tion, and the more nearly the final product approaches austenite in structure and properties; this will be treated more fully in the dis- cussion of tempering of steel; (2) the ferrite-cementite aggregate, par- ticularly the pearhtic portion, will have opportunity for greater coa- lescence of like to like, the slower the cooling. 696. Relation of Grain Size to Mechanical Properties. — It is con- sidered almost an axiom that, other things being equal, strength and ductihty are inversely proportional to the size of grain. The grains are aggregates of crystals, each of the same form and of like orientation which latter is not the same, except by coincidence, in the adjoining grains. The larger the separate aggregates making up the individual grains, the less there are for a given cross-section of material, and the more direct wiU be the path of fracture along the cleavage planes within the grain, or following the boundaries of contact of the separate grains. The weakness due to coarse grain is likely to be especially pronounced under vibratory or repeated stresses, since a fracture, once started, has a le§g broken course in attaining such dimensions that failure becomes inevitable even under loads which are apparently within the margin of safety. Coarse grain also lessens the resistance of steel to impact. 697. Annealing.^ — Practically all steel is actually cast into a mold as a Hquid mass, and cools through the solidification, austenitic and pearl- itic temperature ranges at rates which vary with the bulk of the sec- tion and the mold conditions. At best, the metal of necessitj' has cooled from a temperature of maximum intensity, which will tend to promote coarseness of crystalUzation, and consequent loss of strength and ductility. Slow cooling, particularly near the solidification zone, will aggravate the effect, because of the increased time under favor- able conditions for growth of the austenitic aggregate. Untreated cast steel is inherently relatively weak, and in large measure this weakness is a function of the size of the casting. EFFECTS OF HEAT TREATMENTS 627 (two 875 \ 1 1 1 1 1 1 _ Sanveur'B OriE>iTiaIOnrve -for annealing and hardening B««cl forgingB ^_ ^.^ Stead's Upper Cnrve - for tieat'treatmen normalizing, etc. ^_^_ Stead's Lower Curve— for refining, tool hardening, etc. „__« A.S.T.M. Curve-for annealing rolled and forced carbon etcelfl. V. nsj The structure and properties may be improved by judicious anneal- ing, by taking advantage of the obhteration of previously existing structure on heating just above the critical range (690-900° C). The operation consists of heating the steel to the minimimi tempera- tuTe and for the minimum time needed to insure complete change of grain to the desired fine texture; then cooHng it from this tempera- ture at such a rate as will best conserve the wished-for structure and properties. The rate of heating should be slow enough to permit uniform diffusion of heat throughout the piece. The specific treatment will vary with the amovmt of carbon and other constituents in the steel, with the size of the object, and with the relations of hard- ness, strength, and ductihty, which are desired in the final product. Soft steels require a higher tem- perature than those more nearly approach- ing eutectoid propor- tions, since the com- plete conversion to austenite is affected only by heating past the upper critical temperature. Simple annealing of mild steels does not pro- duce as great a refin- ing of grains as is obtained with eutectoid steels, since the aggregation of the eutectic begins at the common lower critical temperature, while the higher end- temperatures for tfee |pwer-carbon steels allow greater coarseness of the newly-formed grainj^.The range of annealing temperatures suitable to various carbon steels is well shown by curves 1, 2 and 3 of Fig. 10.* These diagrams show that authorities agree pretty closely on proper anneaHng temperatures for medium and high-carbon steels but there is * Modified from a figure by Stead {Jour. Ir. and St. Inst., Vol. 94, p. 50) by the addition of the curve representing the anneahng temperatures recommended by the A.S. T. M- for forged and rolled carbon steels. Fig. 10.- .4 .5 Canbon, percent. -Temperatures for Annealing and Hardening Carbon Steels. 628 PROPERTIES OF STEEL Fig. 11. — Coarse Structure in a Steel Casting Due to Slow Cooling. a wider diversity of opinion concerning the most beneficial temperature for annealing low-carbon steels. For steels with a man- ganese content greater than 0.75 per cent, sUghtly lower temperatures than indicated by the A. S. T. M. curve sufiice. Heating should be by gradual approach to the desired temperature, and the object should be held at this temperature for a sufficient time to reach a uniform condition throughout. This time varies with the size of object, about an hour for 12 inches of thickness should suffice. Temperature of aimealing fixes the grain size of the product. It should always be the lowest possible to effect complete refining. Rate of cooling from this tempera- ture also has a pronounced effect on the physical proper- ties. Rapid cooling results in incomplete reversion of the austenite to pearhte to a degree which varies with the carbon content of the steel and the rapidity of cooling. This is a process of hardening, and is treated in greater detail later. Pro- vided cooling is slow enough to enable the steel to revert to the pearlitic condition, the aggregation of its cementite ferrite constituents will be coarser the slower the cool- ing, and the greater soft- ness and ductility are thus obtained at a sacrifice of some strengh and elasticity. Coolmg in the furnace or imbedded in lime, clay, etc., is slow; quiet air or an air' Fig. 12. — Same Steel Casting after Forging Showing a Much Finer Grain than Fig. 11. EFFECTS OF HEAT TREATMENTS 629 Pig. 13. — Same Steel Casting Annealed at too High Temperature (1100° C). Note the Coarse Grain. blast is more rapid, and is usual for large objects unless abnormal softness is desired, or the carbon content of the steel is high. ■ Small pieces should always be protected from oxidation and consequently decarburi- zation of the surface during annealing. This may be par- tially accomplished by sur- rounding the parts with lime, sand, or pulverized charcoal. It may be very effectively done by the Jones method. This consists in placing the material in a closed tube from which the air is expelled by a non-oxidizing gas which is kept constantly flowing through the tube. Surfaces of parts thus treated are bright and untarnished. Metcalf also uses a tube closed with a loosely- fitting cap. The air is al- most entirely expelled from the tube by the volatilization of resin which is placed in the end of the tube farthest from the cap. Parts annealed by the Metcalf method are slightly tarnished but de- car burization is negligible. The changes in size of grain brought about by certain heat treatments of a piece of 0.50 carbon steel are shown in Figs. 11 to 16. The coarse structure of the steel as cast (Fig. 11) was materially reduced by forg- ing (Fig. 12), but reheating of the forged steel to 1100° C. A fine grain (Fig. 14) was given this overheated steel by annealing at 800° C, which is approx- FiG. 14.- -Steel Casting of Kg. 13 after Anneal- ing at 800° C. again produced a coarse grain (Fig. 13). 630 PROPERTIES OF STEEL Fig. 16.— Same Steel Casting Heated to 1000° C. and Quenched in Cold Water Shows a Mar- tensitio Structure. Structure indicates high strength, hardness, and brittleness. imately the proper temperature for annealing this grade of steel. (See Fig. 10.) A still finer grain showing a very tough steel was produced by .a double quenching treatment. The steel was first quenched in water from a temperature of 1000° C. which made it very hard and gave it a fine structure appearing like in- terlacing needles and called martensite (Fig. 15). Subse- quently it was heated to 650° C. and again quenched in water, with the result shown in Fig. 16. This represents the fine porcelainic structure of sorbite in which the transition from martensite to pearlite plus ferrite has been practically completed but without opportunity for coalescence of pearlite masses and ferrite grains as in anneahng at higher temperatures. Sorb- ite is the structure which is characteristic of the toughest steels. 698. Effects of Annealing on Mechanical Properties. — Referrmg agam to Figs. 4 and 5 it will be observed that annealing from tem- peratures specified by the A. S. T. M. (See Fig. 10) reduces the strength, hard- ness, and elastic ratio but increases the ductility. The effects are most pronounced iii steels having more than 0.5 per cent carbon and are of small moment in the very low-carbon steels. The effect of temperature of annealing on the mechanical property Fig. 16. — After Reheating the Casting of Pig. 15 to 650° C. and Quenching, a Sorbitic Struc- ture Results. This structure connotes high strength and toughness. EFFECTS OF HEAT TREATMENTS 631 of several tool steels is well illustrated by the experiments of S. v. Fabry, from which Fig. 17 has been prepared. Here again it will be noted that the properties of the high-carbon steels are much more affected by annealing than thofee of the medium-carbon steel. For all cases, it will be noted that the ductility is a maximum for tempera- tures at which the strength is a minimum and that the elevation in the per cent reduction in area is also most prominent at the same temperatures. These temperatures range from 700° for the 0.58 per cent carbon steel to 800° C. for the steel of 1.36 per cent carbon. It should also be observed that the minimum strengths of these steels are nearly the same but the corresponding percentages of reduction in area diminish as the carbon content increases. In general, the 1112 1832 600 700 800 000 ^Temperature, ° C. 700 800 000 Temperature, ° C 700 800 900 Temperature, ° 0. Fig 17. — The Influence of Annealing Temperature on the Mechanical Properties of Tool Steels. (Fabry in Froc. I. A. T. M., 1912.) Specimens 1.18 in. square were held at temperatures indicated for three hours. curves of hardness and strength are nearly parallel. The microscopic data accompanying the original report indicate that the most uniform and the finest grained structures were produced by annealing at the temperatures corresponding to maximum ductility or minimum strength. The effects of variations in annealing temperature on the strength and ductility of steels differing in carbon content are also shown in Fig. 29 and 30. From these data by Brinell it appears that the strength of the low and medium-carbon steels was little affected by any of the annealing temperatures. The strengths of the high-carbon steels were shghtly increased by anneahng at 350° C, shghtly dimin- ished by annealing at 750° C, and considerably increased by annealing at 1000° C. The ductility of all grades of steel was raised somewhat by annealing at 350° C. Further increase in ductility was secured 632 PROPERTIES OF STEEL Fig. 18. — Showing Coarse Grain Produced in Rail of Fig. 19 by Overheating. by annealing at 750° C. Annealing at 850° C. produced the most marked increase in the ductility of the high-carbon steels. Annealing at higher temperatures effected a corresponding slight in- crease in the ductility of low- carbon steels, but the curves plainly show that these tem- peratures were too high to secure maximum ductility from the high-carbon steels. 699. Overheating and Burning. — Exposing steel to high temperatures for long periods develops a very coarse grain; but so long as the temperature does not enter region II of the Rooze- boom Diagram (Fig. 1, Ch. XXI) for the particular car- bon content, it is possible to effect complete refining by reheating above the critical range. The structure of Fig. 18 could be restored to that of Fig. 19 by proper anneahng. If, however, the temperature of heating is such as to take the steel into region II, partial fusion results, and the steel becomes " burnt." There is mechanical separation of the grains due to the partial fusion and gas evolution, with prob- able accompaniment of some oxidation of the boundaries. Thus the steel becomes brittle or " rotten." Such an effect is not curable by reheating, or even by reheating and forg- ing. The differences between burnt, overheated, and nor- mal grains of a steel casting are well shown in Fig. 20.* Fig. 19.— Structure of Rail after Rolling. Although microscopic examination of sections of the metal subjected to overheating or burning will reveal the defective structure, it is not always convenient to make such an examination. The Metcalf test is simpler and effective in detecting overheating * For effects of overheating on rivet steel, see Engr. News-Record, Vol. 82, p. 280. EFFECTS OF HEAT TREATMENTS 633 or burning in steels containing over 0.30 per cent carbon. For this test it is preferable to use a bar of steel about a foot long having the same carbon content as the mal- treated piece, although the piece in question may be used. On opposite faces of the bar saw slots are cut to a depth of approximately one-eighth of the thickness of the piece at intervals of about one inch. One end of the piece is then struck in a fire and heated until it scintillates. Upon removal it may be quenched or allowed to cool in air, depend- ing upon treatment accorded the piece in question. The test-piece is then broken and, beginning at the burnt end, the fractures at the notches show a gradual change from very coarse grain to a fine silky structure for the section which was at the proper restora- tion temperature (i.e., just above the critical range) ; sections nearer the cooler end will show the original structure of the bar. A comparison of the fracture of the piece in question with the series of fractures indicates the treatment accorded. 700. Theories of Hardening. — It has been known for centuries that some kinds of iron become very hard after heating to a bright red heat Burnt. Overheated. Normal Structure. Actual width =0.08 in. Fig. 20. — ^A Steel Casting of 0.40 Per Cent Carbon Cut by an Oxyhydric Torch. Note gradation in structure from burnt mgtal at cut (on the left) to normal structure at right end. and quenching in water. In fact, this property was the basis of the older classification of certain products as " steel." Also, it has been recognized for a long time that this property is a function of the car- bon content of the steel, and that no appreciable hardening accom- panied the quenching of iron with negligible or very small amounts of carbon. But it is only since the development of our understanding of the iron-carbon relations that the hardening of steel by quenching has been put upon our present-day fairly rational basis, and that the heat treatment of steel has deviated from the method of "rule of thumb." Heat-treatment methods have reached a high degree of perfection; and the phenomenon as a whole is fairly well understood. Several theories of hardening are to-day in existence, each having its adherents and points of merit; yet none offer satisfactory explanation of all of the observed facts. Sauveui' * classifies them as follows : * Metallography and Heat Treatment of Iron and Steel, p. 308. 634 PROPERTIES OF STEEL f Beta Iron or AUotropic Theory. Retention Theories Solution Theories ^ ^^j^^ j^^^ ^^^^^ Amorphous Iron Theory. ^ , ^, . I Hardening Carbon Theory. Carbon Theories | g^b-carbide Theory. (Early Stress Theory. Interstraiti Theory. Twinning and Amorphous Iron Theory. The retention theories are based upon the restraining of certain reactions which take place normally when steel cools through the critical temperature ranges. Very quick cooling through the transformation ranges suppress the change, and the condition stable only at higher temperatures is retained to a greater or less degree in the cold rigid steel. According to the several theories, this may be (a) a hard, beta allotropic form of iron normal only to a limited temperature range between 780° and 880° C, which is assisted by solution of iron carbide FeaC, and its influence in restraining the normal transition; (6) a metastable solution of FejC in alpha iron, suppressing, therefore, the separation of the carbide, but not the change from gamma to alpha iron; (c) a hard amorphous transition form, which is intermediate to the complete allotropic change in the iron, and which is aided in its effect by the solution of the combined carbon and its influence in slowing down the reaction velocity; (d) an allotropic form of iron carbide, inherently hard, or conferring hardness because of its forced solution in the iron; (e) a hard sub- carbide of iron FezjC, stable only above the critical range. According to the stress theories, steel cooled quickly from above the critical range is subjected to stresses due to the shrinkage of its outer shell on the interior, and to the increased volume accompanying the transformation of gamma into beta and alpha iron. Hardening accompanies the resultant straining of the metal. Theories in this class were among the first to be put forward to explain the hardening of steel and have recently attracted renewed attention. Hypotheses are advanced that (a) the transition of com- bined carbon from solution in gamma iron to non-solution in alpha iron is not com- pleted, non-homogeneity of crystalline orientation is caused, and a hardness similar to that caused by interstrain is the result; (b) that severe internal strains due to quenching steel, cause crystal twinning and hard amorphoiis layers. Many of the theories have much in common, and in some cases the distinctions are in large part technical or a matter of definition. The technical points are exceedingly complex and involve the highest principles of metallography in experimentation and elucidation. To quote Sauveur (Metal, and Hard, of Steel — Int. Eng. Cong., 1915). " It will be obvious from the foregoing that the many attempts at arriving at a satis- factory explanation of the hardening of steel are based on one or more of the following conceptions; (1) existence of a hard allotropic variety of iron, (2) existence of sohd solu- tions involving the occurrence of so-called 'hardening' carbon, and (3) existence of strains in quenched steel causing or not an amorphous condition of the iron.'' • "It will likewise be obvious that nothing so far presented fully satisfies our craving for a scientifically acceptable explanation of the many phenomena involved." '•'It would seem as if the methods used to date for the elucidation of this complex problem have yielded all they are capable of yielding and that further straining of these methods will only serve to confuse the issue, a point having been reached when this juggling, no matter how skillfully done, with allotropy, solid solution, and strains, is causing weariness without advancing the. solution of the problem. The tendency of late has been to abandon the safer road of experimental facts and to enter the maze of excessive speculations, in which there is great danger of becoming hopelessly lost. The EFFECTS OF HEAT TREATMENTS 635 conclusion seems warranted that new avenues of approach must be found if we are to obtain a correct answer of this apparent enigma." Many of the theories are founded upon special or unusual conditions; others, again, fit the general observations but fall short of covering all of the facts. It seems logical to assume that since hardening in metals (including steel) can be the result of several physical effects, observed phenomena are not to be explained by theories based upon one principle only; there may be several contributing causes. 701. Essentials in Hardening. — The operation of hardening of steel consists of two essential steps: (1) Heating above the critical range of temperature; (2) cooling rapidly from that temperature. No change in the iron-carbon relations will take place until the steel is heated to the lower critical temperature Aci (about 700° C). Austenite will then begin to form, and the reactions will be completed at the upper transition temperature GPS of the Eoozeboom Diagram, Fig. 1, Ch. XXI. As indicated by the diagram, and discussed more fully Art. 661 complete conversion of a eutectoid steel (0.9 per cent C.) may be effected by heating to just above the constant temperature Aci; while for steels of other carbon content, a range of temperature is necessary, which becomes greater as the carbon content is farther removed either way from eutectoid proportions (Fig. 10). The above transitions are reversible, under normal conditions, and the reactions will reach a condition of equilibrium with rise or fall of temperature, in accord with the constitution diagram. ' The essential reaction is ferrite plus cementite to austenite, or the reverse; or com- bined carbon (FesC) into or out of solution with gamma iron. The reaction requires time; separation is relatively much slower than solution, and naturally requires longer time in proportion to the quan- tity of cementite to separate; that is, with increase of carbon content in the steel. Again, the reaction velocity of separation becomes less as the steel becomes colder and more rigid. Therefore, by suddenly cooling a steel which is in the austenitic temperature range, it is pos- sible to bring it to such a temperature and state of rigidity that the reaction velocity becomes nil, and the austenite will be forcibly re- strained in the steel at normal temperatures, in its entirety or in such intermediate transition form as might result from the carbon content and cooling conditions. 702. Methods of Hardening. — The quenching capacity of a medium for hardening steel depends upon its specific heat, conductivity, vola- tility, viscosity, and temperature. The hardening bath should always be kept at a uniform temperature, especially if water is used, and should be continually circulated to prevent the formation of vapor envelopes about the metal, since these materially retard the withdrawal of heat. In order of hardening capacity the more common quenching media rank thus: water spray, brine, water, oil and molten lead. The 636 PROPERTIES OF STEEL first two of these are used commercially on small parts only, when an extremely hard surface is desired. Files are often hardened in brine. Water quenching likewise is so drastic that its use is restricted to the low-carbon steels or to very small parts of simple shape made of high- carbon steel. With the heavy sections of high-carbon steel these drastic hardening agencies are likely to cause cracking. On account of the wide range in quenching power which various oils possess and because their action on the steel is less severe than water quenching, they are much used for hardening tools, machine and structural parts where toughness is an important consideration. In some works the drastic cooling of the water-bath is somewhat reheved by floating an oil bath above it; in others the parts are partially cooled in water before being quenched in oil. The principal use of molt- en lead is for toughening the metal. Parts of irregular form are likely to warp and crack when rapidly hard- ened. Long pieces should be immersed in the bath end first wherever possi- FiG. 21. — The Relations between Carbon Content, \y[Q Jf very lone such H .60 Per cent Carbon Hardness and Hardening Capacity, -j Jour. Ir. and St. Inst, Vol. 59, p. 243.) (BrineU in pieces may be allowed to roll into the bath. Inas- Figures beside plotted points indicate number of results aver- "^^Cll aS it IS akaOSt aged. The silicon content varied from 0.1 to 0.5 and manganese impossible tO harden Uni- from 0.2 to 9.6 per cent in the steels represented by the mean f l ■ f i curve. The discontinuity in curves H, C, and A at 0.66 per cent lOrmJy pieCCS 01 large SeC- carbon is due to the lower manganese contents in the higher tion they should whei'CVer carbon steels. - .,1 , , , , « possible, be bored before hardening. This is often advantageously done in heavy shafts and axles. The inferior metal at the center of the piece is thus ren^oved; and, by forcing a stream of oil through the hole during quenchhig, a much more uniform hardening treatment is gotten. 703. Effect of Carbon on Hardening.— The influence of carbon in hardening steel is well brought out by the experiments of BrineU, some of the results of which are presented in Fig. 21.* It will be observed that the hardening capacity is greatest and nearly constant for steels ■ See also Figs. 4 and 5. EFFECTS OF HEAT TREATMENTS 637 containing 0.40 to 0.80 per cent carbon, but the maximum hardness is found in hardened steels of approximately eutectoid composition. 704. Characteristic Microscopic Structures in Hardened Steels. — Austenite, a solid solution of cementite in gamma iron, is hard; that is, it is harder than the ferrite, but not so hard as the cementite, which is the hardest of the constituents usually found in steel. Again, the hardness of the austenite increases with the amount of cementite in solution. In reverting to the pearlitic conditions normal at ordinary temperatures, the separation of ferrite and cementite from solution, Fig. 22.— a 1.5 Per Cent Carbon Steel Quenched in Brine from 1200° C. Mag. = 150 d. Showing troostite in black rounded areas with surrounding dark needle-like particles of martesite set in a white background of austenite. (Courtesy of Sau- veurand Boylston, see Fig. 286 in Metal, and Heat Treatment oj Iron and Steel.) with subsequent re-arrangement into the final state of aggregation, is a process of gradual progression, and requires for its completion an interval of time, or of temperature, or both. While these transitory stages of dissolution and of coalescence are not to be considered as new constituents, and there are no well-defined hmits of division, convenience in description has led to the introduction of the names, martensite, troostite, and sorbite for certain fairly characteristic struc- tures in the re-arrangement. The transition found in hardened steels have the following distinguishing features: AvMenite is a solid solution of FeaC in gamma iron. It may also include other ele- 638 PROPERTIES OF STEEL ments, manganese, nickel, etc., in association in the solution. The carbon may vary from traces to 1.75 or 2.0 per cent. Austenite is a normal constituent of all carbon steels above the critical temperature range, and may be retained in varjdng propor- tions by rapid cooling by quenching from these high temperatures. These proportions depend upon the amount of carbon, temperature of quenching, and speed of cooling. In plain low-carbon steels, there is no retention of austenite, due to the rapidity of transformation; with high carbon (above 1 per cent) a proportion up to about 50 per cent may be checked in association with marten- site, the first transition product. The structure of this type is given in Fig. 22. Associated metals, as manganese, nickel, tung- sten, . etc., in sufiBcient amount lower the critical temperature or slow down the rate of transition, so that it will not take place at all or will be checked by moderate cooling, with retention of austenite alone. Being a homo- geneous solid solution it exhibits the characteristic polygnal grain 'structure, Fig. 23, is a, typical mi- FiG. 23.— Cast Manganese Steel Quenched in Water from crosection. 1000° C. Nearly 100 per cent austenite. Mag. = 100 d. ^he physical proper- (From Fig. 325, Sauveur's Metal, and Heat Treatment of ties of austemte vary with Iron and Steel.) ?^e carbon content; an increase of this element increases the hardness, strength and elasticity and lowers the ductility. Austenite is hard relatively to ferrite, buit is softer than cementite, or than martensite of the same carbon content. Austenitic steels are non-magnetic, tenacious, rather ductile, and tough. Martensite is the first stage in the decomposition of austenite. It is the principal constituent of hardened carbon steels, and the cause of their great hardness. There is conflict with regard to its constitution; allotropists contend that it is a solution of carbon in beta iron, with some reversion to alpha iron, the latter accounting for its mag- netic susceptibility. The greater hardness of martensite compared with austemte is the bulwark of the defense of a hard, allotropic form of iron (beta) and its influence on the hardening of steel. On the other hand there is strong support of the argument that beta iron does not exist, and that the hardness of martensite is the natural accompani- ment of the solid solution state, augmented in turn by the metastable condition resulting from complete or partial reversion of the gamma to alpha iron, wherein the latter caimot assume its molecular symmetry and orientation, thus bringing about interstrain and correlative hardness. Martensite is obtained, associated with austenite, by quenching very high-carbon steels from high temperature in ice water, or in total by water-quenching eutectoid or hypereutectoid steel from the austenitic temperature range. Microscopically, as shown EFFECTS OF HEAT TREATMENTS 639 in Fig. 22, the structure appears as a network of interlacing needles of triangular distribution, assumed to be cleavages of octahedra. Martensite is very hard, very strong, brittle, and non-malleable when cold. These properties are intensified with increasing additions of carbon. Troosiite is the second transition stage, associated with martensite as a result of partial tempering after hardening or of quenching medium carbon steels in the austenitic region, or high-carbon steels within the transition range. It appears as nodular aggre- gates bordering the martensite grains (see Fig. 22), or associated with sorbite, and is darkly colored by etching. The constitution of trootsite is a matter of controversy, but the physical and chemical properties, between those of mar- tensite and sorbite, indicate that it is a mixture of cementite and fer- rite, differing from pearlite only in the state of division. Sorbite is the last stage in the transition from austenite to cem- entite-ferrite, and considered to be pearlite in a minutely granular form. It etches to a uniform dark-colored mass, with finely granular structure at high magnifications, as indicated in Fig. 24. Sorbite forms in lighter sections of steel cooling in air from above the critical range, by oil quenching pieces of medium carbon, or by water quenching from the lower parts of the transition zone, or by Fig. 24.- reheating hardened steel almost to the critical temperature. Because of their fine and homo- geneous state of aggregation, sor- bitic steels have high strength and elasticity coupled with maximum ductility compared with those of normal pearlitic structure. The fundamental reaction which takes place when a quenched steel is restored to equilibrium is solid solution to separation of cementite and ferrite. This occurs in progressives steps thus: Austenite — > martensite — > troostite -^ sorbite -^ cementite + ferrite . Naturally, with no sharp boundaries between the constituents, tempered steel may be relatively complex, and consist of various associations of the transition forms. The extreme hardness and brittleness of martensite steels make them practically unsuited for industrial uses, except cutting tools; even here, and to a much greater extent in structural products, varying proportions of the other transition forms are desired. They are obtained by proper selection of composition of steel, maximum tem- perature of heating, nature of cooling medium,' and by tempering; that -A 1.1 Per Cent Carbon Steel Quenched from 900° C. Reheated to 600° C. and Quenched, Showing Nearly 100 Per Cent Sorbite. Mag. = 150 d. (Courtesy Sauveur and Boylston.) 640 PROPERTIES OF STEEL TOO— Normal-Pearlite rr^85:i sorbite 7-400_- Troostite 200" Martensite ;100" " - Anstentite is, reheating of the product to a prescribed temperature, followed by slow cooling or quenching. 705. Tempering. — Howe {Iron, Steel and Other Alloys) draws an analogy between the tempering of steel and a spring. A force of 700 lb. bends the spring to the position shown in Fig. 25, where it is held by friction F just sufficient to prevent slipping. It will hold this position of apparent equi- librium so long as the restrain- ing force is not disturbed. The spring is analogous to a steel (0.9 per cent carbon to be specific) heated above the critical temperature and quenched in cold water; for simphcity assume the austenitic condition to be retained, a condition of metastable equilibrium only. Release of the frictional resistance by 100 lb., or one-seventh of the total force, will cause the DegreeB Cent. IBUinff Points 1500 1100 1300 "White Heat 1200 ' 1100 telloS? Heat 1000 900 Fig. 25. 700 600 000 100 Red Heat Fiiintly Red Blue Straw Steel orlginolly [" abhardenod, faeated J to Iht KiDpeiuHire I ,„„„bta indicated, aad L gtecl orlglnallj f slowly liardeDcd, heated J cooled '° 1 ' 212 S2 1 1 1 \ 1 1 1 ' Structure unchanged PrcvloUB fltnicturc oblSteratcd und reaultinR BtrurtuM Very tine Less fine Coaioe Vn» cMir*. Bnrei K Very flno Steel liardenod leBsflno Steel bardoned Uoarw Steel hardened Very Coarse AuFloQlto or nulcDsIte cbugod to nurloatllo DDd trootilM AuiloDito or mBrtaDalle-chugoi to troo«lt8 Uildiampor AuflvDilc or Dmr- tcDiHc cbuDsed to BorbltB or sorbite + rcnrllli.'No tcmpor pniBt-toughowi Same reeulte as with unhardened steel _ Fig. 26. — A Modification of Brinell's Hardening Chart, Showing the Changes Pro- duced in High-carbon Steels by Heat Treatment. end of the spring to move upward to position 100, or one-seventh of the distance to normal; again in an apparently stable position. Further releases of frictional restraint will enable the spring to approach more and more its normal position, which will be reached when an upward force of 700 lb., or its equivalent in frictional release, is applied. Reheating of EFFECTS OF HEAT TREATMENTS 641 the steel to 100, 200, 300 or more degrees of temperature will cause it to revert more and more from the austenitie condition; at the critical tem- perature {Acz) it will reach the normal pearlitic state, by having passed successively through the intermediate transition forms. Checking of the heating at any of the intervening temperatures will leave the steel in a corresponding stage of reversion. The rationale of hardening and tempering, and its correlation with the grain structure, is illustrated in Fig. 26. 706. Relation of Drawing Temperature to Hardness. — The effect of varying temperatures of reheating upon the hardness of water- quenched spring steels of different carbon contents is noted in Fig. 27. 1000 3 204 31 G 427 5 ^8 649 760 "C -.^ ■v A = .30 C. ' B = .51 C. C = .72 0. D = .90 C. E=1.10C. MQ.ineacli = .35-.50 , S. in each = under .045 'p. ine:ich= under .045 SI. in each =.10 -.20 800 700 .§ 600 5 500 1 n A _c .^ \ _,B ^\ s^ A \ n: r ; — - -\ ^ \. ^ . ^. \. ^ — — "~~~" ^ == 100 ' " ^ 20O 100 600 800 1000 liOO 1400 Tempering Temperature in Degrees Falirenlieit FiQ. 27. — Effect of Tempering on the Hardness of Water-quenched Spring Steels. (Tinsley.) Similar data for small specimens of steel oil quenched and drawn at various temperatures in a bath of sodium and potassium nitrates were secured by Nead in his experiments, see Fig. 28. From a comparison of these curves it becomes evident that water-quenched specimens are much harder than oil-quenched of like composition and size. The extreme hardness of the water-quenched pieces is diminished by very low drawing temperatures whereas the hardness of oil-quenched pieces remains unaffected until the drawing temperature is raised consider- ably — ^above 350° C. in Nead's tests. 707. Methods of Tempering or Drawing. Steels. — In all heat treat- ment operations, the aim is to secure a minimum size of grain. The maximum temperature of heating (for hardening) should be held as 642 PROPERTIES OF STEEL close as practicable to the critical range. The latter varies somewhat with different steels, and is best determined from cooling-curve data obtained with a pyrometer. For steels of moderate or high-carbon content (above 0.50 C.) loss of magnetism in the heated steel coincides with the critical temperature; thus a magnet serves as a detector, since it will not be attracted by the heated object if the transition zone has been passed. The drawing temperature is most accuiately indicated by a pyrom- eter; but in tool dressing, color methods give a simple and reasonably accurate control. If a piece of hardened cold steel is brightened and 213 300 500 700 900 300 500 "TOO 9QD 100 J>rawlng Temperature in Degrees Centigrade-. Fig. 28. — The Effect of Drawing Temperatiire on the Hardness and Elongation of Oil-quenched Steels. (Nead.) placed in a hot furnace, the surface will assume oxide tints vai-ying through pale straw color, brown and blue to the final blackish scale color, as the temperature of the steel rises; and. it wiU become pro- gressively softer. The approximate relations of temperature and color, both oxide and incandescence, are noted in the accompanying table. Color of Oxide. Deg.C. Deg.F. 221 430 232 450 243 470 254 490 266 510 271 520 277 530 288 550 293 560 316 600 Degree of Incandescence. Red — ^visible in dark.. . . . Red — visible in twilight. . Red — visible in daylight.. Red — visible in sunlight . Dull cherry red Cherry red Bright red Orange yellow Yellow white Welding white Deg.C. Deg.F. Light straw. . . Straw Dark straw . . Yellow brown Dark brown . Brown purple Dark purple . Bright blue . . Full blue.... Dark blue . . . 400 752 474 885 524 975 581 1078 800 1472 900 1652 1000 1832 1200 2192 1300 2372 1400 2552 EFFECTS OF HEAT TREATMENTS 643 Most tools of ordinary carbon steel are treated by heating to a temperature slightly above the critical range (Fig. 10); the edge of the tool is hardened, by quenching in water or oil, withdrawn from the bath and brightened. The surplus heat in the red-hot unquenched portion is allowed to reheat the hardened quenched part until the proper temper color has reached the edge, the whole tool is then quenched to check further drawing of temper. This method is best for edge tools, such as lathe tools, since it gives the proper hardness at the edge, backed by a softer and tougher portion better adapted to withstand shock. However, it is unsuited for taps, milUng cutters, etc., which must have uniform or distributed hardness; in this case quenching of the entire tool and subsequent reheating in the furnace are necessary. To avoid cracking, large sections, such as axles or shafts, should never be quenched to room temperature if they are to be placed in a hot drawing furnace, but should be held at 100 to 150° C. For carbon steels, the initial heat for quenching is preferably carried to the lowest temperature at which hardening will take place, since there will be the accompaniment of minimum coarsening of grain, and resultant maximum toughness of product. Reheating of the hardened steel parts may.be done in a furnace on a hot plate, in a sand bath or in a liquid bath. For drawing tem- peratures xmder 300° C. oil is commonly used. For higher tempering temperatures a salt bath made of 2 parts potassium nitrate to 3 parts sodium nitrate or a lead bath is often employed. Heating of the metal either in hardening or drawing should be at a sufficiently slow rate to secure a uniform temperature throughout the piece. 708. Drawing Temperatures for Various Classes of Steels. — The degree of tempering will vary with the nature of service, being greatest for tools subjected to shock, and where great hardness is less essential than toughness. Stoughton * gives the following drawing temperatures for various classes of tools: Tools for metal planers, small turning "steel, and wood engraving. 225° C. Faint Straw to to 235° C. Dark Straw ) I Punches and dies, taps and dies, milling cutters, boring tools, „-„„ ^ T • 1 1 Ti I reamers, wood machine tools rock drills. 250 C. Light Brown J 251° C. Light Brown ^ to to [ Twist drills, wood tools. 275° C. Purple J 276° C. Purple -j to to I Cold chisels, wood chisels, axes, metal and wood saws. 300° C. Blue J * The Metallurgy of Iron and Steel, p. 384. 644 PROPERTIES OF STEEL Springs are drawn at temperatures between 300 and 450° C. and axles and shafts are toughened by drawing between 400 and 650° C. 709. Carbon Contents for Tool Steels. — Plain tool steels have a carbon content varying with the service requirements. United States Navy specifications (L. H. Kemmey, Soc. Nav. Arch, and Mar. Engrs.) are as follows: Class 1. Class 2. Class 3. Class 4. Carbon Manganese Phosphorus Sihcon 1.25-1.15 0.35-0.15 0.015 0.40-0.10 0.020 1.15-1.05 0.35-0.15 0.015 0.40-0.10 0.020 0.95-0.85 0.35-0.15 0.020 0.40-0.10 0.020 0.85-0.75 0.35-0.15 0.020 max. 0.40-0.10 Sulphur 0.025 max. Vanadium and chromium optional. Class 1 — Lathe and planer tools, and tools requiring a keen cutting edge combined with great hardness; drills, taps, reamers and screw-cutting dies. Class 2 — Milling cutters, mandrels, trimmer dies, threading dies, and general machine-shop tools, requiring a keen cutting edge combined with hardness. Class 3. — Pneumatic chisels, punches, shear blades, etc., and in general tools requiring hard surface with considerajDle tenacity. Class 4. — Rivet sets, hammer, cupping tools, smith tools, hot drop forge dies, etc., and, in general, tools which require great toughness combined with the necessary hard- ness. 710. Case hardening. — Certain steel parts such as armor plate, safes, plowshares, special types of gears, pinions, and bearing surfaces must combine toughness with a high resistance to indentation or abrasion. Large surfaces, as in safes, armor plate and plowshares, are often made from three- or five-ply plates. They are fabricated from separately rolled plates of wrought iron and high-carbon or hard- alloy steel. The soft, tough plates are sandwiched between the hard plates, heated to a welding temperature and rolled to the required thickness. A heat treatment is then given to harden the exterior plates. Case-hardening is a simpler and a more generally appUcable method than the above for securing hard surfaces. Case-hardening consists in producing a hard skin or shell on the surface of a wrought iron, malleable cast iron, or low-cai-bon steel part by subjection to a modified form of the cementation process. The principle of this process is the readiness with which the surface of red-hot iron will absorb carbon from carbon monoxide gas. To successfully operate the process, the metal should not contain over 0.20 per cent carbon. The objects to be case-hardened are packed in a medium rich in carbon and heated to a temperature between 900 and 950° C. They are then held at this temperature for several hours, the EFFECTS OF HEAT TREATMENTS 645 time depending upon the character of the packing material and the thickness of the case desired. After the required case has been formed the parts may be heat-treated in several different ways. For example, if a hard surface is wanted and toughness is of small moment the objects may be withdrawn from the furnace and immediately plunged into cold water or oil. Such treatment will result in hard case but both case and core will be coarsely crystalline. If toughness is of great importance then the objects should be allowed to cool below the critical range. They should then be heated above the upper critical point for the core (900° C.) and quenched in water or oil. This procedure hardens and refines the grain in the core but makes the case coarse- grained. By heating to a temperature just above the critical range of the case (775 to 825° C.) and again plunging in water or oil the core will be annealed, the case hardened and its grain refined. Among the substances used for packing materials are granulated bone, wood char- coal, burnt leather, a mixture of 2 parts barium carbonate to 3 parts wood charcoal, potassium cyanide, and gases rich in carbon monoxide, such as illuminating gas. SoUd substances appear to be preferred to the liquids or gases. Granulated bone is the base of most of the packings used in this country. Although the rate of penetration of car- bon is slower with wood charcoal than with burnt leather or the barium carbonate and charcoal mixture, yet it gives good satisfaction when a deep case is required. The potassium cyanide compounds are often used for the production of thin uniform cases; but they evolve poisonous gases which render them dangerous. The thickness of the case varies from 0.02 to 0.2 in. Ordinarily the case wanted is less than 0.1 in. thick. It is generally held that best results are obtained when the carbon content of the case is slightly above the eutectoid ratio, or about 0.9 to 1.0 per cent. There is very little absorption of carbon when the temperature is held below Aci. Above that point the rate of penetration increases with the temperature and decreases with the time of exposure. The time required to secure a case will vary, in accordance with the factors mentioned, from one to eight hours. The alloy steels containing manganese, tungsten, chromium, and molybdenum are very susceptible' to case-hardening; but those of nickel, sihcon and aluminum are treated with greater difficulty. 711. Influence of Hardening and Tempeiing on Mechanical Prop- erties. — We have already pointed out the effect of carbon in hardening steel and also its great influence on the capacity of the steel for hard- ening through heat treatment. (See Figs. 21, 27 and 28.) It is also possible to alter greatly other mechanical properties by suitable heat treatment. Thus in the normal or annealed condition there is an increase in strength and elastic limit and a loss in ductility with an increase of carbon content. Heating above the critical zone and quenching in water intensifies these effects, and in a ratio which is much higher for the medium- and high-carbon steels than for those of low-carbon content. Tempering effects, whether they are accom- plished by drawing, or by controlling the rate of cooling through the 646 PROPERTIES OF STEEL critical zone, result in physical properties which can be varied within wide limits between those of the hardened steel and those of the normal peariitic state. BrineU's Strength Tests. The data furnished by Brinell's * experi- ments provide some good illustrations of characteristic influences of various heat treatments on the mechanical properties of steels. Some of his data have been plotted in Fig. 29, 30, and 33. From Fig. 29 and 30 it follows that water quenching from above the critical zone without subsequent drawing causes an increase in the strength and a loss in the ductility of the low- and medium-carbon steels and for these steels is more effective than oil quenching. (It should be borne in mind, however, that such quenching when apphed to larger pieces of steel is hkely to produce heavy internal stress and may even cause cracking.) For the high-carbon steels the oil-quenching treatments gave greater strength and ductihty than quenching in water at correspond- ing temperatures. Water quenching of the high-carbon steels caused warping and heavy internal stress. Under such conditions the speci- mens were eccentrically loaded in testing and, being very brittle, broke at comparatively low stresses. In Brinell's quenching and drawing treatments it appears that drawing at 250° C. after quenching in oil at 80° C. had about the same effect on strength and ductihty as quenching in water at 20° C. and tempering at 550° C. Qu^nchmg from 850° C. followed by tempering gave the best combination of strength and ductility of the treatments tried by Brinell. This is especially true for the water-quenched specimens. It is hkely that quenching the high-carbon steels at a somewhat lower temperature and the low-carbon steels at a somewhat higher tempera- ture could have given still better results. It will be observed that in the case of water-quenched specimens the drawing temperature neces- sary to give the greatest strength increases with the carbon content. For example, consider the plotted data in Fig. 29 for steels water- quenched from 850° C. The 0.09 per cent carbon steel was strongest when quenched, the 0.25 and 0.44 per cent carbon steels were strongest when drawn at 350° C, and the other steels had highest strength when drawn at 550° C. It is hkely that high-carbon steels would have had stiU greater strength if drawn at 400 or 450° C. * The influence of tempering on the strength and ductility of oil-quenched steels is weU brought out by the results of Nead's tests, f In these experunents quenching was done in accordance mth the recommenda^ tions of the A. S. T. M. (see curve in Fig. 10) and the results are very uniform. In Fig. 31 it will be observed that the ultimate strength * Jour, of Ir. and St. Inst, 1901, Pt. 2. p. 234. t Trans. Am. Inst, of Min. Eng., Vol. 53, p. 218. EFFECTS OF HEAT TREATMENTS 647 and yield point are not materially affected by tempering at tempera- tures under 400° C. Fig. 28 shows that the ductility, excepting the •qoni a.TBnbg jod spuno j OOOI "! H^Snang atisnaj; -^ o o o o o 04 ^ S S S O O O O O O ^ CO M rH O CD £ u a d M OSS 0S8 ^d sg S 3 g g a:. ^' ^•' ■>i ."^ / 899 ^^ ■k V- " * 1 ^O* '^ "^ ^ ^ ^ '^ p 1° 0S9 OSS OSE »d s 3 3a g ^^ .-- .--■ ■' ^ii -^ ^ 1 , ^ — -^' ^-^' " 1 ■ ~~~~. ^ ^ , ^d • 3 ^ S5 s s i g a d II 31 OSS OSS ^d S 3 ^ ^. ^ = ^ ^ J> ^ ,-'''' / / f / \ y y ^o SS. S 3 S § II 0S9 OSS 0S8 «ad 5= S 3 S S ____ -= '^ t^ -;^ 'T^ ,1^" •" / Ji- =^ =;:; r - --■ — -"" / W ^ ^ — — _ ,-- ■''' ^d 3 iS S 3 S S d °P ■a V c a d II 5 OSS OSS )3qonsn5 ^o ;2 S S 3 a S N 1 1 / / ' 1 / f 1 / ,,'■' ^o qa g 3 a s d s a a M 0S9 OSS OSS «Rd 33 § 3 S. g wsi / \ \ \ 1 1 1 ) ■ /^ / N ■ \ ,/ / y ^ / \ \ / ^d ". "i". ^. ^. ^ ^ ^ 03 oo ^r S lO CO (M rH •qOTii aJBnbg jad spanoj OOOT ni ii:jSna-ug aiTSuaj] 0.63 per cent carbon steel, is also unaffected by tempering within this range. There is produced, however, a marked decrease in strength and elastic limit and a corresponding increase in ductility as the drawing temperature is raised above 400° C. These effects are most pro- 648 PROPERTIES OF STEEL nounced in the high-carbon steels, as would be expected. For larger pieces strength and ductility would be less affected by quenching, and constant for a greater range in drawing temperature. S (•m eo'i ) ■rata 08I ui nonBSnoia ^naa laj On OSS OSS gfi ms -♦• m -K I '.1= Txai 0S9 OSS 0S8 U OSS OSS ZZOl S99 a M 0S9 OSS OSS a - son gj SMI ;§ s s 299 299 pa r2 OSS OSS loqanan?) n 3 2 ffl c4 a OSS OSS S99 O EH o an . a te §9 ooxx 0001 GS8 OSi OSS poiioa «¥ ^ s a o , Cni 60'iJ "Him 08X nj nojijisSnoia; ^nao jsa TAe toughening effect of quenching followed by drawing at various temperatures is admirably illustrated by the tests of Grard * which are summarized in Fig. 32. The curves for energy of rupture in impact * Proc. I. A. T. M., 1912, III2. EFFECTS OF HEAT TREATMENTS 649 show that the low-carbon steels are the toughest and that maximum toughness in each of the steels tested was produced by drawing at a temperature about 50° C. below the upper critical point (Acs). IflO 300 500 700 100 300 500 Drawing Temperature la Degrees Centigrade^ 700 900 FiQ. 31. — The Effect of Drawing Temperature on the Strength of Oil-quenched Steels. (Nead.) S92 762 1118 1472 1832 32 392 762 1112 1472 1832 2192 °T. 200 400 600 1000 200 400 600 800 1000 200 400 Drawing Temperature in Degrees Centigrade 800 1000 1200 Fig. 32. — Effects of Drawing Temperature on the Mechanical Properties of Three Grades of Steel. (Grard.) Impact tests were made on notched specimens. For drawing temperatures below 400° C. the energy of rupture of the semi-hard and hard steels is low and constant. Again when the anneaUng temperatures are reached in the drawing process the tough- PROPERTIES OF STEEL .40 .60 .80 1.00 1.20 1.40 Per cent Carbon Fig. 33. — The Influence ot Carbon on the Toughness of Steel as Measured by the Energy of Rupture in Tensile Tests and in Impact Tests. ness abruptly decreases. It appears, therefore, that the quenched steels in the martensitic state, and those which have been tempered into a troostitic state are very strong and hard but they do not possess the toughness of the sorbitic steels formed by drawiag at higher temperatures (500° to 700° C). Furthermore, the pearlitic steels formed on annealing after quenching, although more ductile, have less shock resistance than those in the sorbitic state. Results of some of Brinell's impact tests have been plotted in Fig. 33 (6) and (c). These also indicate the superior resistance of low-carbon steels imder impact and show that the mediupa and high- carbon steels are materi- ally improved by quench- ing and drawing at a high temperature. They do not show, however, that such treatment is so beneficial for the low- carbon steels. By comparing Fig. 33 (a) with Fig. 33 (6) and (c) it becomes evi- dent that the energy of rupture computed from tension tests is not a EFFECTS OF MECHANICAL WORK 651 measure of the efficiency of a heat treatment in toughening steels. In other words the efficiency of a toughening treatment should be judged by the results of impact tests. In general the nicked impact test with the blow apphed normal to the root of the nick is the most severe type of test for such purpose. In Fig. 33 (d) are plotted results of Charpy impact tests made on the same steels as used by Nead (see Fig. 31). The results are more consistent than those of Brinell and, likewise, show the beneficial effects of drawing oil-quenched steels at 650° C, thus producing a fine- grained sorbitic structure giving maximum toughness. EFFECTS OF MECHANICAL WORK 712. Effect of Hot Work on Structure. — The mechanical working of steel may be hot or cold; it may be carried out at temperatures above or below the transition zone. In heating steel above the critical tem- perature, there is a complete obliteration of existing grain^ and a pro- gressive increase in grain size of the newly formed austenite with tem- perature rise above the critical range, and with time intervals which will allow of normal crystallization. Symmetry of crystallization is the tendency in the austenitic zone, and the size and character of grain thus attained is not destroyed during the reverse transition in cooling to normal temperature. Mechanical work results in distortion of the grains causing flatten- ing in the direction of the pressure and consequent destruction of the normal symmetry. Within the austenitic range the metal will split up into a mass of grains of symmetrical character, and approximately of the dimensions determined by the distortion; these will in turn grow into an aggregate of larger symmetrical grains conforming to the temperature and time conditions. If, therefore, as is usual in mechan- ical work operations, distortion and reduction of grain size within the austenitic temperature range is accompanied by a gradual decrease of temperature of the metal, the resultant grain must be finer than the original, since there has been mechanical reduction, accompanied by a lower end temperature which will largely determine the size of the final grain. This size will be a function of the amount of reduction of the initial grain by the mechanical operations, and the finishing tempera- ture as compared with the critical. Heavy reductions will tend to result in a fine-grained structure; this in turn will tend to increase in size the higher the finishing temperature is above the critical one, and the more the time approaches that needed for complete aggre- gation. From the standpoint of the doctrine of grain size — that strength and ductility are the accompaniment of fineness of structure— 652 PROPERTIES OF STEEL the importance of hot work in improving the physical quality of steel is obvious, and it is especially beneficial if the reductions are heavy and at finishing temperatures as close as practicable to the critical zone. A comparison of Figs. 11 and 12 shows the marked improvement in refining the grain which has been accomplished by forging a piece of cast steel. The specifications of the United States Navy for steel forgings demand that the diameter of the grains in the finished part, as deter- mined under the microscope, shall not exceed 0.0.05 in. 713. Effects of Hot Work on Properties of Steel and Iron. — It is evident that the rate of cooling of a steel section will have an impor- ^ tant influence upon the structure and physical properties, provided the mechanical work is finished at a tempera- ture above the critical range. That is, in addition to the direct effect of mechanical refining of the grain, there is the accom- paniment of the effects of hardening and tem- pering, because of direct treatment or the equiv- alent result due to natural cooling condi- tions. The tempering effects conform to the principles set forth heretofore, and are pro- FiG. 34. — Showing the Varying Character of Metal in portionately greater in Different Parts of the Cross-section of a Large Steel high-carbon or special- mild steels which are of greatest importance in usual construction. The best results are ob- tained by the proper correlation of mechanical work and heat treat- ment of a steel of suitable chemical composition, all determined by consideration of the service conditions. A few examples illustrating the effects of hot working follow. In Fig. 34 is shown the cross-section of a steel shaft 16 in. in diam- eter '(which broke soon after being put in service) from which eight 0.10 O.IS 0.20 0.25 G.05 0.10 0.15 ProportloDate Eloogtloa EFFECTS OF MECHANICAL WORK 653 test-specimens were cut, lying symmetrically in a diametral section as shown. Four of these were tested as cut from the shaft. The other four were forged down after cutting ^Dut. The plotted results show: The elongation of the unforged specimens varied from 21 per cent in the specimen taken from near the surface of the shaft to 2 per cent in the specimen coming from near the center. In the forgpd specimens, however, taken from the opposite side of the disc, the elongation varied from 28 per cent near the surface of the shaft to 24 per cent near the center, thus showing that the material was identical through- out when it had been similarly worked. In other words, the material near the center of the shaft was in its primitive condition when first cast, while that near the surface was that of well-rolled steel. This shows the necessity of forging large shafts under enormously heavy ham- mers, or, better, the necessity of using only hollow-forged shafts for such service. The amount of reduction which a piece receives in rolling materially influences the mechanical properties. Bullens * cites tests of bars ranging from | in. to 3 in. in diameter all rolled from the same ingot. The tensile strengths of these bars varied from 137,000 to 100,000 lb. per square inch, respectively. In Fig. 35 the characteristic influence of thickness on the properties of mild steel bars is well shown. It will be observed that the strength and elastic ratio decrease slightly but the ductility increases as the thickness of the metal is increased. Anneal- ing greatly reduces these effects. From Fig. 36 it may be seen that the variation in ultimate strength and in the elastic Umit for various thicknesses of metal is much greater when the metal leaves the rolls at a dull red heat. Working at this temperature shghtly increases the ultimate strength and ductility and raises the elastic limit from 8 to 10 per cent above the values gotten at normal finishing temperatures (a bright red). After annealing, Campbell's tests show that specimens finished at a dull red heat still have properties superior to normal specimens similarly annealed. In general the apparent elastic limit rises as the thickness of section * Steel and Its Heat Treatment, p. 229. HUH Thickness of Bar la In, Fig. 35.— Effect of Thickness on the Mechanical Properties of Mild Steel, Natural and An- nealed. {Campbell's M'f'g and Prop, of Iron and Steel.) 654' PROPERTIES OF STEEL diminishes. Since steel columns are built from comparatively thin sections of metal (generally from i to J in. in thickness), and since the ultimate strength of these .is dependent wholly on the apparent elastic limit, and not at all upon the ultimate strength, it is necessary to evaluate this elastic limit for the particular thicknesses of sections used, rather than from special test bars, which are usually not less than f in. in thickness. Differences in the amount and character of work which various parts of a steel shape receive during rolling often cause considerable discrepancies in mechanical properties. From Fig. 3, Ch. XIX, it will be noted that the material near the center of the web and in outer portions of the flanges of an I-beam is worked more in rolling than the portions at the junction of the flange and web. Results in Table 5 show variations in the properties of test-pieces cut from these parts of several I-beams.* 714. Methods of Cold Working.— Cold work- ing of steel, or reduction of area at tempera- tures well below the critical zone, results in distortion of the grain in accordance with the io,ooo }i 'A % i^ Thickness of Bar in In. Fig. 36.— Influence of Thick- ness on Mechanical Proper- ties when the Percentage of Reduction in RoUing is Con- stant, Last Passage in Rolls applied forces, and this distortion remains being at Normal and Dull because of lack of mobility or tendency to Red Heat, Respectively. acquire symmetry at temperatures much (Campbell's Manufacture , _ ,, .^ . , _,. „_ ^ , , ,. and Properties of Iron and ^elow the critical. Fig. 37. Cold distortion Steel.) causes increased density and produces an internally strained condition in the steel. It is accompanied by increased hardness, tensile strength, and, if a period of rest is allowed, by an increase in elastic limit, j The ductility and shock resistance, however, are lowered by cold working. Cold drawing, cold roll- ing, cold pressing (or flanging), and cold twisting are the usual methods of cold working metals. The drawing and rolling processes are very effective in securing parts of exact cross-sectional dimensions. The cold-drawing process is used mostly on pieces of small cross-sectional ai-ea, — -such as wire, automatic screw stock, small shafting and tubing, — where a large reduction in area can be made in a single draft. For large shafts and axles cold rolhng is more efficient than cold drawing. Cold rolling impairs the ductility of the metal less than cold drawing, probably *From the carefully conducted tests of E. L. Hancock, Proc. A. S. T. M., Vol. 10, p, 248. t Elastic limit is used synonymously with proportional limit in Arts. 714 to 717. EFFECTS OF MECHANICAL WORK 655 (a) The distortion is much less in the hot-rolled metal (7) than in the cold-rolled (8). (&) Distortion due to cold punching. Hole at left. Pig. 37.— Distortion Due to Cold Work. (Mag. = 50d.) TABLE 5.— TENSION TESTS OF STEEL SPECIMENS CUT FROM I-BEAMS. (Hancock). The specimens were taken from the center of the web, from the flange near the web, and from the root of flange and web. Elastic limit was determined by an extensometer reading to 0.0001 inch. Depth of Beam (in.) Weight per Foot (lb.). Elastic Limit (lb. /in. 2) Web. Flange. Root, Maximum Strength (lb./in.2). Web. Flange. Root. Per Cent Elongation IN 8 In. Web. Flange. Root. Standard Beams 6 10 10 12 12 12 15 15 15 18 20 13.5 32,000 34,000 34,000 68,300 65,300 64,300 18.7 29 25 30,000 25,500 33,000 56,500 54,600 58,600 28.3 28.1 25 24,750 26,600 27,000 72,300 61,200 66,400 20.2 34.4 31.6 29,500 22,500 19,500 61,800 59,500 63,700 31.3 26.6 40 31,500 24,000 19,500 59,800 62,500 61,500 31.2 21.9 40 28,500 18,700 24,000 62,200 62,200 61,700 30 18.7 42 31,500 29,900 22,500 68,700 56,000 28.2 60 19,500 24,000 16,500 53,300 55,200 53,800 29 29 80 27,000 19,500 19,500 54,300 55,300 55,000 36 31 55 31,500 25,500 19,500 55,800 56,700 60,400 28.5 29 65 34,500 22,500 13,500 62,700 63,800 64,000 28.5 28 29 25 25 25 31.2 31 26.6 29 33 28.5 30 Bethlehem H-Beams 24 18 12 73 48.5 36 33,000 19,500 31,500 24,000 21,000 33,000 22,500 28,500 24,000 72,600 59,600 72,600 70,000 57,300 66,000 67,300 56,200 68,400 25 26.6 21.9 28 31.3 26.6 28.1 31.3 25 Mean Values 28,875 25,050 23,107 62,893 60,738 61,236 27.39 27.82 28.40 Based on Web 1.00 .865 .800 1.00 .965 .974 1.00 1.018 1.039 656 PROPERTIES OF STEEL because the total reduction in area is effected by a large number of light passes through the rolls. The reductions in either of these processes are very much less than in roUing or drawing hot. Cold pressing is much used in fashioning thin parts in car construction, and in making of sheet metal forms. Cold-pressed parts which must withstand shock require annealing. Cold twisting is used to raise the elastic hmit and ultimate strength of square steel bars for reinforcing con- crete. Cold punching of holes in boiler plate, in structural steel and forms made of wrought iron and soft steel is very commonly practiced. The method is rapid and cheap but causes heavy distortion in the vicinity of the holes as shown in Fig. 376. Since the metal on the die side of the hole is considerably embrittled by this process (see Fig. 16, Ch. Ill), and is also rendered more susceptible to corrosion (see Fig. 1, Ch. XXIX), good practice demands that the holes be ptmched about | in. undersize and reamed to required dimensions. 715. Effects of Cold Work on Properties. — Tests on hot-rolled and eold-roUed shafting by Thurston at Cornell University * show that cold rolling increases the elastic limit in tension from 15 to 97 per cent, the tensile strength from 20 to 45 per cent. Under cross bending the elastic limit is raised 11 to 30 per cent and the yield point 13 to 69 per cent. The elastic limit in torsion is raised from 28 to 40 per cent. That the effect of cold rolling on the strength penetrates undiminished to the axis of the bar is demonstrated by a portion of Thiu-ston's results, given in Table 6. The ductility of the metal at the surface is greater than that at the center but the discrepancy is most marked in the cold-rolled metal. In elastic resilience the cold-rolled metal is superior to the hot-rolled; in energy of rupture it is inferior to the hot-rolled metal. The .modulus of elasticity is slightly increased by cold rolling, in these tests by about 1,000,000 lb. per square inch. From a series of tests by A. J. Woodf on cold-drawn steels of low- carbon content the following conclusions seems justified. Cold drawing by reducing the diameter about re in. in one draft increases the max- imum strength of bars less than 1\ in. in diameter about 10 to 1^ per cent. It increases the elastic limit about 100 per cent, reduces the elongation by 75 per cent and the reduction in area by about 15 per cent. Cold drawing raises the strength and elastic limit both by direct stretching of the metal and by lateral compression which also causes lengthening of the piece. The properties of the metal are approxi- mately uniform throughout the piece. * See abstract in Machinery, April, 1917. t Engr. News, Vol. 59, p. 63. EFFECTS OF MECHANICAL WORK 657 TABLE 6.— RESULTS OF TESTS ON COLD-ROLLED AND HOT-ROLLED STEEL BARS. Resilience in Inch ^ stress n Pounds per Square Inch. Pounds per Cubic ■fJ Inch. o a CO-*J g ■SSJ m n'^-a" •" H Hj3 o s-g 3 S B .3 on. .2.2 3 a lis 1 ■3 M §5 S 1 1^^ a W ? s « H « H fq s Cold-rolled Steel 0.349 54,000 62,600 73,637 51,613 7.50 53.70 48.14 6,600 30,393 0.526 59,500 66,000 75,739 55,060 10.12 54.10 66.21 7,340 31,560 0.772 53,500 66,000 76,636 64,648 12.31 55.70 47.02 9,000 30,476 1.019 52,000 62,000 73,778 50,205 14.87 57.80 42.25 10,480 30,056 Sot-bolled Steel 0.356 30,000 35,250 58,606 40,164 22.06 68.0 15.32 10,900 29,418 0.509 31,900 35,500 58,809 41,569 24.31 61.7 17.61 12,860 29,073 0.754 29,750 35,760 59,747 41,793 29.25 64.2 15.67 15,280 28,337 1.010 30,250 35,260 61,210 43,392 30.00 63.8 14.43 16,740 29,126 In the above tests by Thurston and by Wood the properties were determined from pieces turned down to various proportions of the original diameter of the rolled section, but no direct measurements of the relief of internal stress due to the machining are reported. From the experiments of Heyn * and others, however, it seems certain that cold-worked metals, especially those which are cold drawn, are liable to severe internal stress. In a cold-drawn piece the core is placed under compression and the outer layers under tension. Thus, in one of the Heyn tests on a steel bar (Ni = 25, C = 0.3 per cent) which was reduced in diameter from 1.34 to 1.22 in. by cold drawing, the maxi- mum tensile stress near the surface of the bar was 50,000 lb. per square inch and the maximum compressive stress along the axis amounted to 54,000 lb. per square inch. By annealing at 850° C. the maximum internal stress was made less than 3500 lb. per square inch. Heyn also cites instances of failures of cold-drawn parts of steel and brass caused by internal stress. From the foregoing it appears that a material increase in elastic limit and ultimate strength of steel with a corresponding loss in duc- tility and toughness may be secured by light reductions in cold draw- * The Jmir. Inst, of Metals, Vol. 12, p. 12. 658 PROPERTIES OF STEEL ing, but if the reductions are large the internal stresses thus induced may adversely effect the strength as well as toughness and ductiUty. The effects of cold twisting on the strength and ductility of mild steel bars is illustrated in Fig. 38.* The elastic limit in these tests was increased from 10.5 per cent for the f-in. bars twisted one turn in 12d to 80.5 per cent for the f-in. bars twisted 3j turns in 12d. For manufacturing twisted rein- forcing bars one turn in a length of 6 to 12 diameters is commonly used. In a pa- per before the A. S. T. M, J. J. Shuman, a manufacturer, advocated 1 twist in 8 to 10 diameters for Bessemer steel of 60,000 lb. per square inch tenacity and 1 turn in 5 to 7 diameters for basic open- hearth material of Uke strength. The data in Fig. 38 indicate that twisting a bar of mild steel through one turn in 8 diameters causes an increase in strength of 13 to 22 per cent but produces a decrease of 50 to 70 per cent in elonga- tion. Under such treatment the elastic hmit will be raised 40 to 60 per cent. It becomes apparent that cold twisting produces a large increase in elastic ratio and a considerable increase in strength. These changes are accompanied by a marked re- duction in ductility and a prob- able loss in shock resistance. 716. Relief of Distortion Due to Cold Working. — In wire drawing, * Abstract in Jivir. Am. Soc, M. E., Dec, 1916, of tests by Whitney and Dohner at Universily of Colunido. 1 2 3 number ot Twists ln.l2 d. Fig. 38.— The Effect of Cold Twisting on the Strength and Ductility of Mild Steel Bars. (Whitney and Dohner.) EFFECTS OF MECHANICAL WORK 659' several passes through the dies makes the steel so brittle that annealing is necessary to restore ductility and ensure further reduction without rupture. It is usually considered that temperatures above the critical are necessary to remove the distortion of structure due to cold work. (a) Steel rod annealed. (6) Steel wire after one draft. Area of rod reduced 15%. (c) Steel wire after several drafts. Area of (d) Steel wire hard-drawn and then annealed rod reduced 60%. at a temperature below critical range. Fig. 39. — Effects of Drawing and Annealing on the Structure of Soft Steel Wire (0.08% C). Magnification 95 diameters. (J. F. Tinsley.) However, in the manufacture of wire, the annealing temperatures (process anneaUng) are approximately 600° C. or well below the Aa point. That there is effective removal of grain distortion and restora- tion of ductiUty is indicated by Figs. 39o to 39c and Table 7, repre- senting typical practice in the drawing and annealing of mild steel wire 660 PROPERTIES OF STEEL of 0.10 per cent carbon content. (J. F. Tinsley before Am. Ir. and St. Inst., May, 1914). Corresponding results in drawing and patenting 0.50 carbon steel wire are given in Table 8. The patenting operation consists in draw- ing the wire through a heated tube, at a speed and temperature regu- lated according to the carbon content and size of the rod and wire; then cooUng it in the air or in a bath of molten lead, depending upon the final structure and properties desired. The process is in effect one of combined annealing and tempering, and serves to obliterate the distortions of drawing' and to give to the finished product the required combination of strength and toughness, mainly by preventing coarse TABLE 7.— THE EFFECT OF COLD DRAWING AND ANNEALING ON THE PHYSICAL PROPERTIES OF 0.10% CARBON STEEL. (Tinsley) 1^ .CJ .So Condition of Material. 15 a,— < Eh is Green Rod 68,000 25 No. 5 gage, d = .207in. First draft 47 113,000 2h Third draft 82 15P,000 H Process annealed 60,000 30 First draft 35 93,000 3 Third draft 70 isosooo 2 Fifth draft 85 145,000 11 Process annealed 62,500 28 First draft 21 82,000 3| Third draft 62 124,000 2 Fifth draft soi 143,000 1^ Seventh draft . . . 88J 151,500 1 Annealed 68,000 25 Dead soft an- nealed after first and sec- ond annealings 50,000 32 TABLE 8.— THE EFFECT OF COLD DRAWING AND PATENTING ON THE PHYSICAL PROPERTIES OF 0.50% CARBON STEEL. (Tinsley) Condition of Material. s ha -2 ".3 a. Green Rod No. 5 gage, d = .207in. First draft Second draft. . . . 28i 51 95,000 122,000 146,000 10.0 2.9 2.8 Patented 115,000 8.2 First draft Third draft Fourth draft. . . . 30 50J 65 143,000 163,000 176,000 2.8 2.7 2.6 Patented 128,000 7.8 First draft Third draft Fourth draft. . . . 30 66 76 156,000 190,000 208,000 2.0 1.9 . 1.8 Patented 156,000 6.0 First draft Third draft 30 66 184,000 218,000 2.0 1.9 Annealed after first patenting . 70,000 18.0 EFFECTS OF MECHANICAL WORK 661 coalescence of the pearlitic constituents. It is chiefly adapted to medium- or high-carbon steel products such as piano wire or wire for rope strands. 717. Effects of Overstrain in General. — The various methods of cold working, previously discussed, all stress the metal beyond its elastic limit and each produces a particular kind of overstrain. In a general way it has been shown that overstraining a bar in a certain direction, say in tension, will raise the yield point to the overstraining load and will slightly increase the ultimate strength. The magnitude of the effect on the ultimate will depend upon the amount of overstrain. The limit of proportionality is greatly lowered immediately after over- strain.* There is, however, more or less complete recovery as time elapses, and the proportional limit may be eventually raised above the normal value. If the overstrained bar is put under the opposite kind of stress (compression) the yield point and proportional limit of the bar are lowered, they may even vanish if the period of rest after overstrain is small. (See Fig. 6, Ch. XXI.) There is also evidence to show that the effects of overstrain are felt in all directions. Howe f has shown that the ball hardness of a tensilely overstrained steel bar is increased in all directions, in other words, that the effects of simple overstrain are isotropic in hardening the metal. Evidence of influence of overstrain in directions inclined to the overstrain axis is also afforded by Table 9. From these results it appears that the effect of tensile overstrain on tensile properties is greatest in the direction of the overstrain and least at right angles to it. On the other hand, tensile overstrain effects the greatest increase in compressive elastic limit and strength in direc- tions normal to the overstrain. (See also Art. 671.) 718. Grain Growth in Overstrained Metal. — When a pure metal or alloy of solid solubility is heated subsequent to overstrain a growth in the grain may be produced at temperatures below the critical range. Thus very low-carbon steel, or ingot iron, exhibits a decided growth of its crystal grains after overstrain, on heating to a temperature which varies inversely with the magnitude of the overstrain. For example, McAdam J in experimenting on ingot iron containing 0.034 per cent carbon found that this metal when reduced 30 per cent in thickness began to recrystalhze when heated for SJ hours at 900° F. (482° C), when reduced 15 per cent crystallization commenced at 1000° F., and when reduced 10 per cent crystallization began at 1100° F. In no case, however, did coalescence of grains take place in the recrystallized * See Tests o/ Metals, 1915, p. 127. t See Howe's paper on simple overstrain in Proc. A. S. T. M., Vol. 14, p. 8. t Proc. A. S. T. M., Vol. 17, p. 59. 662 PROPERTIES OF STEEL material until the temperature of annealing was raised above 1475° F. (801° C). TABLE 9.— COMPARISON OF TENSION AND COMPRESSION TESTS ON ANNEALED AND UNANNEALED STEEL BARS OF IDENTICAL MATE- RIAL WHICH HAD BEEN STRESSED BEYOND ITS ELASTIC LIMIT.* Tension Tests. Compression Tests. S O w i g .-aS G OS -^. '+3 t- u i li III P 1 w a O h § 5-3 d ^ TO ^ c Ill 1 2 5 6 9 10 Crosswise Diagonally tt Lengthwise tt Uhannealed Annealed Unannealed Annealed Unannealed Annealed lb. 40,000 40,000 40,000 42,000 63,000 47,000 lb. 66,320 63,160 66,760 62,840 73,000 64,000 % 12.0 22.0 16,0 27.5 18.0 26.0 % 24.6 33.5 59.3 61.5 61.5 61.5 30.2 31.2 30.2 30.7 31.2 .30.7 3 4 7 8 11 12 lb. 51,000 43,000 47,000 40,000 35,000 42,000 lb. 58,100 43,000 54,380 43,000 48,940 45,000 34.3 33.0 .34.3 31.8 34.9 32.4 I^O.SSi Tension Specimen * These specimens were cut from an eye bar which had been stressed to 54,350 lb. per square inch, 3 years and 3 mos. before these tests were made. The original elastic limit was 34,400 lb. per square inch. The position of the specimens in the original bar is shown in the figure above. The compression specimens were approximtely 0.92 in. in diameter. (From Tesls of Metals, 1890, p. 731.) The presence of impurities such as slag in wrought iron or carbon, in the form of pearlite, in steel appear to prevent grain growth. Con- sequently wrought iron and steel containing over 0.1.5 per cent carbon are not subject to grain growth. Inasmuch as coarse grain makes the metal very brittle the phenom- enon of grain growth bears an important relation to the properties of susceptible metals when worked in the cold and subsequently reheated. The phenomenon is often called "Stead's Brittleness," after J. E. Stead, who first investigated it. Brittleness is also caused in low-carbon steel and wrought iron by prolonged worldng at a blue heat (225-300° C). It appears quite likely that the crystal growth so produced originates from causes sim- ilar to those producing " Stead's Brittleness." INFLUENCE OF FORM ON PROPERTIES 663 INFLUENCE OF FORM ON PROPERTIES 719. The effect of an abrupt contraction in cross-section of a bar under tension or bending is to cause iiigh concentration of stress at the periphery of the groove or notch; also the shoulders of the groove or notch prevent free elon- gation of the metal at the con- tracted section and increase its strength. Fig. 40 shows the effects of various types of grooves on the distribution of stress in rectangular bars under tensile stress. The yield point of the iron used was 36,900 and the ultimate strength 56,500 lb. per square inch. The mean tensile stress in each case was 10,650 lb. per square inch. It will be noted that the calculated stresses at the root of the V-shaped notches exceeded the yield point of the metal. The superior resistance per unit area of the steel at root of groove as compared with steel in uniform bars is shown by the tests of M. Duguet on hard steel and M. Barba on soft steel which are plotted in Fig. 41. 720. The Influence of the Fonn of the Thread on the Strength of Screw-bolts. — This subject has been investigated by Prof. Mar- tens,* and his results are here given. Two grades of mild steel were used for these bolts, all of which were cut from round bars originally 35 mm. (1.4 in.) in diameter. The softer material, qoni QjBnbs J^d spanoj OT ssaj;s oiTsnax * At the request of the German Society of Civil Engineers. The results were pub- lished in Zeits. d. Ver. deutsch. Ing. for April 27, 1896. The abstract here given was made by J. B. Johnson and published in the Digest of Physical Tests for July, 1896. 664 PROPERTIES OF STEEL 120;000 uo.ooo fllOO.OOO jj 90,000 1-1 g 70,000 ca t 80,000 EO'.OOO No. 1 to 5=Rouna SectionB of Hard SteeL " No, 6 to ll=RectanEriilar SectionB of Soft Steel, having a tensile strength of 53,500 lb. per square inch, was used for screw- bolts approximately 1 in. in diameter, and the harder material, having a tensile strength of 62,000- lb. per square inch, was used for the screw-bolts, which were reduced to approximately 5 in. in diameter. Four such bolts were made of each of these sizes for each of the four styles of thread shown in Table 10, making in all 32 bolts with screw-threads which were tested. Two of each of these sets were tested in plain tension, the pulling force being applied to the iimer face of the nut at one end, and in- creased until rupture oc- The outer two pimensloQS of Reduced Sections In mm, (^ mm. =.03931 in,\ Fig. 41. — ^Effect of the Form of the Reduced Cross-section curred. on the Tensile Strength of Two Kinds of Steel. {French bolts of each set were Com. Rep., Vol. 3, p. 40.) tested also in tension, but TABLE 10.— ABSOLUTE AND RELATIVE STRENGTHS OF THREADED BOLTS IN POUNDS PER SQUARE INCH. (Martens) Kind of Thread. Form of Base of Thread. Stress Applied bt Machine. G.* T.* Nut. T. Proportion. Test Bar =100. = 100. s: (a) Sharp. (6) Whitworth... (c) Sellers. (d) German Soc. of Engr 62,430 71,100 62,160 67,000 60,300 70,250 60,730 69,260 (e) Normal test bar 61,580 70,400 61,300 69,400 60,020 68,120 61,160 73,670 53,480 61,860 49,920 62,720 44,800 58,880 52,330 62,720 47,640 62,720 116.8 114.9 116.2 109.4 112.8 113.6 113.6 112.0 115.2 114.0 114.6 112.2 112.2 110.1 114.4 119.1 93.4 101.4 83.8 95.2 97.9 94.5 89.1 101.4 100 100 98.9 99.2 98.9 100.3 99.6 96.9 100.7 106.4 80.0 88.2 72.2 86.9 86.9 83.2 78.6 90.8 *G. = grooved; T.= threaded. INFLUENCE OF FORM ON PROPERTIES 665 under a torsional action resulting from the continuous turning of the nut as the load increased to rupture. In this case the distortion resulting from the permanent elon- gation of the bolt v/as nearly all taken up by the movements of the testing-machine, the distortion taken up by the turning of the nut being the least possible to maintain a continuous torsional action at this point. The same bars were also tested as plain tension-test specimens with cylindrical bodies, and again with grooves turned into them of the same shape as the corresponding screw-threads, leaving the same diameter at the bottom of the groove as obtained at the base of the threads. The actual and comparative average results of all of these tests are given in the table, from which the following conclusions may be drawn: 1. 'When subjected to plain tension both the screw-threads and the grooved sections were stronger than the plain bars of the same net area of cross-section, this excess of strength having an average value of about 14 per cent. 2. There is no very marked difference in the average strength of the bolts on which the several styles of thread were cut, the perfectly sharp groove shown at (a) in table being slightly stronger than the others. 3. The weakening effect of the turn- ing of the nut under stress at rupture is much less than might have been pre- dicted, when the distortion of the screw below the nut by permanent elongation is taken into consideration. The tests indicate for this case a strength of the 1-in. bolts about 20 per cent less than §65,000' 060,000i 0< 45,000 10,0«0 1.6 2.0 2.S 3,0 Width ia Inehes at3ottom otQxooTes 3.5 that of the plain bars, and of the ^-in. bolts about 15 per cent less than that of the plain bars. 4. In general it may be said that the turning of the nut upon the bolt at rupture reduces the strength of the net section of the bolt by about 30 per Fig. 42.— Variation in Strength of j-in. Plate cent. for Varying Widths at Bottom of Groove. 5. It is very probable that the four Each point represents 3 to 8 tests. {Tests forms of screw-threads here shown of Metals, 1882.) would show very different results under fatigue tests from repeated stresses, and also for static loads on high-carbon steel. Under repeated loads and under shock it is probable that the sharp re-entrant angle of thread (a) would develop incipient cracks much earlier than either of the other forms, and that probably the Whitworth thread (6) would be the last to develop this kind of weakness, either with soft metal under repeated loads or with high-carbon steel under static loads. 721. The Tensile Strength of Grooved Plates is a measure of the tensile strength of a riveted joint when failure occurs by tearing the plate. This strength is found to be a function of the width of the net section at the bottom of the groove, as well as of the method of making the hole, and of the character of the material. These effects are all shown in Fig. 42 for j-in. plates of wrought iron and of 56,000- 666 PROPERTIES OF STEEL lb. steel. The steel, being more ductile, is stronger in the grooved than in the plain (standard) section, while the reverse is the case with wrought iron, except with drilled specimens, where the width of the net section was less than If in. 722. The bearing resist- ance of steel and iron plates is shown in Fig. 43. This is seen to increase directly with the distance of the hole from the edge of the plate. When this distance agrees with ordi- nary practice the resistance is so high that it would seem a working bearing stress of 16,000 lb. per square inch might be employed for iron, and of 24,000 lb. per square inch for steel plates. The stresses here plotted were the bearing stresses at rupture, where the plates had so reduced in thickness as to 40,00(['^ Loo 1.25 1.50 1.75 2.00 2.25 Dietaaeelrom centre of Hole to edge of Plate in Inches FiQ. 43.— Bearing Resistance on Rivet Holes destroy all frictional resistance. at Rupture when Failure Occurs by Tearing Much more, then, could high Out of Hole. Tensile strength of steel working stresses be employed, plat|s = 60,000 1b. persq.in. {Tests of Metals, gj^ce for these the frictional resistance is very great. It appears that ,the ordinary rules for proportioning riveted joints might well be modified so as to allow higher bearing stresses, especially on steel. With wrought iron, especially when the stress is transverse to the fiber, more care must be exercised, as this material is liable to be very weak in this direction. 723. Resistance of Steel when the Compressed Area is Confined Laterally. — When a compressive load is applied over the full cross- section of a short prism or cylinder \l (a) FroB Flow I t M t I (6) Reetrictcd Flow (c) Confined Flow Fig. 44. as in Fig. 44a the metal is free to flow laterally at all cross-sections excepting those in close proximity to the ends. If the load is uniformly applied over a portion of the surface as in Fig. 44& the metal under the loading surface must flow laterally against a ring of unstressed metal. INFLUENCE OF FORM ON PROPERTIES 667 The flow is therefore restricted and the elastic hmit will be higher than in the first case. Again, if Fig. 44c represents conditions of loading, Direction along the Rail ooOOOOO Lb.-- 5,000 10,000 15,000 20,000 25,000 30,000 40,000 New Chilled 'Wheel 33 In. In Diameter 50,000 Lb. I 5,000 10,000 15.000 20,000 25,000 30,000 40,000 Steel Driver 44 In, In Diameter with Flat Tread. 50,000 Fig. 45. — Wheel Impressions on a 75-lb. Rail. Top Radius, 14 in. Areas are One- half Size. it is evident that the metal near the center of the compressed surface is under greater compression and greater lateral restraint due to the wider ring of metal and will have a higher elastic hmit than in the second case. In Fig. 45 are shown a series of actual areas of contact obtained by pressing sections of a cast- iron car-wheel and of a locomotive steel driving- wheel upon the cylindrical top surface of a steel rail. This was done in a testing-machine in such a way that there was no rocking motion and the area of contact was clearly distinguished.* The areas of these surfaces of contact were determined by a planimeter, and these are plotted to their corresponding loads in Fig. 46. It wiU be seen that these plot in nearly a straight hne through the origin. If such a law be assumed, it follows: 1. Thai the area of contact increases directly with the load. 2. That the mean intensity of pressure is a constant for all loads. * See a full account of these tests, showing other areas of contact, in Trans. Am. Soc. Civ. Engr., Vol. 32, p. 270, 1894. 60,000 7 1 _/ 1 -i 7 / s / y / ■d a g 6 If; ■a'T t? , J A s"- J / Jl J y \l 0.3 0.1 0.6 Areas oi Contact in Sq. In. Fig. 46. — Showing Relation between Total Load and Area of Contact between Wheels and Rails. (Johnson, Trans. A.S.C. E., Vol. 32.) 668 PROPERTIES OF STEEL 3. That in these experiments this mean intensity of compressive stress, for all loads, was about 82,000 lb. per square inch. 4. Since the maximum deformation (at the centers of these areas) is twice the average deformation (assuming the volumetric deformation to be that of a segment of a paraboloid of revolution) then the maximum compressive-stress intensity for all loads is about 164,000 lb. per square inch. 5. Since no measurable permanent set was produced by any of these loads on either wheels or rail, it follows that the " apparent elastic limits " of the materials had not been reached for this con- dition of contact, although the ordinary elastic limit of the rail material, for a free flow as in Fig. 45a wcls about 50,000 Ih. per square inch. These are important con- clusions, and should be sup- plemented and supported by further observations of this character. In Fig. 47 are shown the results of tests made by Prof. Fig. 47.— The Elastic Limit per Lineal Inch of Crandall and Marston to find RoUers of Various Diameters. (Crandall and the elastic-lunit loads on steel Marston, in Tran.. Am. Sac. Civ. Engr.,^o\.^2, cyUnders resting on or be- tween steel plates. These results show that the elastic loads vary directly with the diameters, these loads per hneal inch of rollers, for naild structural steel, being 14,000 5 10,000 g 6,000 -S 4,000 ® y/Xi --^1 -^^' syf i'^\ 6 8 10 12 Diameter iQ Inches p = 880d, (1) where p = elastic-Umit load in pounds per lineal inch, and d= diameter of roller in inches. 724. Properties of Wire.— We have already considered the effects of drawing, patenting and annealing on the properties of wire in Art. 716. To determine the quality of wire it has been customary to subject specimens to tensile, cold bending and torsion tests, 'if the tension test is so made that a complete stress-deformation diagi-am is obtained, it appears to furnish the essential information. From such a test the strength, elastic hmit, and ductihty can be read directly, and the toughness can be roughly estunated from the area of the diagram. The per cent elongation is not only an index of ductihty but is also a valuble criterion of the wearing quaUty of the wire when made into rope, The cold-bend test is usually made by clamping one end of the INFLUENCE OF FORM ON PROPERTIES 669 wire between jaws having a radius of | in., or equal to the diameter of the wire, and bending the projecting portion back and forth through an angle of 180° until failure occurs. The number of bends required for rupture constitutes a measure of the capacity of the wire to receive cold work and also indicates its ductility. Torsion tests are usually made on a gauge length of 8 in., and the number of turns which the specimen can withstand under a constant tension is determined. With autographic machines, like Fig. 16, Ch. II, the stress-diagram in tor- sion is gotten. The torsion test appears to be of doubtful value except as a measure of uniformity in the material. The strength and ductility of wire depend upon the drawing and heat treatment and also upon the diameter of the finished wire. Annealed iron wire has a tensile strength of 50,000 to 60,000 lb. per square inch. The same material hard drawn with a diameter of an eighth of an inch will have a strength of 70,000 to 80,000 lb. per square inch, when drawn to a very fine wire t may have a strength of a 100,000 lb. per square inch. The strength of steel wire is of even greater range, depending upon composition in addition to the previously mentioned factors. Thus we find low-carbon hard-drawn wire with an ultimate strength of 90,000 to 100,000 lb. per square inch and high-carbon hard-drawn piano wire with a strength of 300,000 to 400,000 lb. per square inch. A strength of 447,000 lb. per square inch is recorded for a piano wire 0.03 in. in diameter containing 0.80 per cent carbon.* Mr. J. Bucknall Smith gives the following average values of strength for wire used in wire rope: f ^r• J e TXT' - Ultimate Strength Kind of Wire. (Ib./in.!) Bright hard-drawn iron wire 80,000 Bessemer steel wire 90,000 Mild open-hearth steel wire 130,000 High-carbon open-hearth steel wire 180,000 Crucible cast-steel wire (patented) 220,000 Crucible cast-steel wire (plow quality) 240,000 " Bright wire " is that which remains untreated after the final drawing; it annealed or tempered it is left black. Plow-steel wire is so called because it was first used for drawing machine-plows in England. The proportional limit of hard-drawn wire is from 65 to 80 per cent of its ultimate strength. 725. Wire Rope. — Common wire rope is twisted from six strands, each of which consists of 7 to 19 individual wires. In ordinary rope the strands are twisted in the opposite direction to the twist of the wire in the strands; but in rope which must have high resistance to abrasion both wires and strands are twisted in the same direction, thus forming * Tests of Metals, 1894, p. 347. t Mining Journal, June 6-July 11, 1896. 670 PROPERTIES OF STEEL the Lang-lay rope. Where great flexibihty is desired the rope is pro- vided with a hemp core, or, if the wear is not great, a larger number of wires may be used in the strands. For elevators and other hoisting purposes where the loads are light, the speeds high and the wear on sheaves is considerable, an iron wire rope gives good service. For derricks, mine hoists, cableways, conveyors and uses where considerable strength and abrasive resistance is required, cast-steel wire rope has the requisite strength and durability. Plow-steel wire rope is used in deep mine hoists, on dredges, stump pullers, and under conditions where maximum strength and toughness are wanted. For the fixed hues in aerial cableways where very great wearing resistance is wanted, a rope with a smoother surface is sometimes used. One of the two common types is the steel-clad wire rope in which each strand is spirally wound (c) Babbitt Cast, Specimen Compieted Fig. 48. — Method of Socketing Wire Rope. with flat steel strips. The other is the locked-wire rope in which the surface layer is made of wires drawn to such a shape that they inter- lock when twisted about the rope and form a true cyhndrical surface. Flat ropes are also used for hoisting purposes. The strength of wire rope is difficult to obtain from short specmiens because of the small stretch of the wires and the non-uniformity in stretch due to variation in the rigidity with which they are held. A fairly satisfactory method of gripping the ends follows. A length of 5 ft. or more should be marked off on the rope and two sets of four servings (or windings) with black iron wire should be made at each end of the marked length as shown in Fig. 48a. The rope should be cut at the marks by means of a cold chisel and the servings will prevent unravehng. Conical sockets may now be shpped over the ends of the rope, the outer servings removed and the wires broomed as shown in Fig. 486. If there is a hemp core it should be cut back to the inner servings. The wires are cleansed by dipping in gasoUne INFLUENCE OF FORM ON PROPERTIES 671 followed by hot caustic potash. After cleaning, the wires should be dipped in zinc chloride and thoroughly tinned in the molten babbitt used to fill the socket. The sockets can then be pulled over the cable ends and the babbitt poured into the socket in such manner as to completely fill it. Alloys used with success at the University of Wis- consin are: Lead, 83 per cent; tin, 7 per cent; antimony 10 per cent, also lead, 60 per cent; tin, 30 per cent; antimony, 9 per cent, and bis- muth, 1 per cent.* Both of these melt below 550° F. The second alloy was previously used with good results at the Watertown Arsenal. After socketing, the specimen is ready for the testing machine. In Table 11 is given a summary of several hundred tests on high- grade wire and on ropes made of it. These tests were conducted with great care by Tetmajer. The tension and torsion results on wires were TABLE 11.— RESUME OF TESTS ON CRUCIBLE CAST-STEEL WIRE AND WIRE ROPE USED ON CABLE RAILWAYS IN SWITZERLAND. (From Tetmajer's Communications, Vol. 4, p. 272.) Test of Entire Cable. (Each the Mean op Two Tests.) Test of Individual Wires. (Each the Mean OF Eleven Tests.) ■s s a a S Tensile Strength in Pounds per Square Inch of Actual Wire Section. o Tension Test. Torsion Bending. Ratio of Number of Cable. CO • if o a ■ ig« eS.s "11 1^^ o.fl (U o 111 Strength of Cable to Average Strength of Wires. 1 2 3 4 6 6 7 8 9 10 1.65 1.67 1.18 1.43 1.00 1.00 1.38 1.30 1.26 1.00 220,000 117,000 205,000 191,000 184,000 184,000 180,000 226,000 210,000 190,000 3.12 7.45 2.61 3.30 3.92 3.28 2.37 3.00 3.15 2.40 265,000 122,000 213,000 207,000 191,000 190,000 222,000 247,000 238,000 190,000 3.4 9.4 3.0 3.4 3.85 4.0 3.0 3.3 3.3 2.7 6,400 9,500 4,600 5,000 5,300 5,700 4,600 5,700 5,400 3,400 27.5 61.5 35.1 44.5 52.6 33.7 21.7 31.1 48.1 11.4 11.8 17.8 18.0 15.1 14.8 11.0 9.6 9.4 18.8 83 96 96 93 96 97 77 92 89 100 Average (omit- ting No. 2). 199,000 2.98 217,000 3.29 5,100 36.8 14.0 92 determined from autographic diagrams, consequently the ductility meas- urements include the elastic deformations. For a wire having a strength * Tetmajer used an alloy of 8 parts tin, 1 part antimony and 1 part copper for iron and mild steel wires; for hard steel wires he used 9 parts lead, 2 parts antimony and 1 part bismuth. 672 PROPERTIES OF STEEL of 200,000 lb. per square inch the elastic stretch amounts to 0.7 per cent. Consequently the per cent elongation as measured across the break after rupture was about 0.7 or 0.8 per cent less than the values recorded in the sixth column of the table. In long wire ropes on a straight pull the strength of the rope may be taken as about equal to the average strength of the individual wires if these are all of about the same ductility and ultimate strength. If the wires differ greatly in ductility, the ultimate strength of the rope is the average resistance of the wires at that percentage of elonga- tion which corresponds to the total elongation of the least ductile sam- ples. It is common to assume the rope to have 85 per cent of the total strength of the wires when tested individually. The total area (a) of the wires in a rope may be calculated from the following: Or- dinary rope with hemp core, a = A%(P] ordinary rope with steel core, a = .50d^; locked wire rope, o = .74d^; where d = diameter of rope. The weights in pounds per Uneal foot {w) of the same ropes may be esti- mated by the following equations: w = \.5%cP, w=l.lQd?, and w = 2.bd?, respectively. A factor of safety of 5 is commonly used in figuring woi;king loads, but for passenger elevators and conditions where failure in the rope may endanger hfe, the factor should be increased to 8. The modulus of elasticity of ordinary wire rope varies between 7,000,000 and 10,000,000 lb. per square inch of metal in the cross-section. Wire-rope pulleys, sheaves, and barrels should have a diameter not less than thirty times the circumference (or say one hundred times the diameter) of the ropes running upon them, to prevent excessive bend- ing strains in the ropes. STEEL UNDER COMBINED STRESS 726. Effects of Combined Stress upon the Elastic Limit. — A state- ment concerning the theories underlying the causes of elastic break- down has been made in Art. 41. We shall now briefly consider some experimental evidence showing the weakening effects produced by a combination of torsion and direct or bending stresses. The influence of combined stress in lowering the elastic limit is shown in Fig. 49. These results were obtained by Hancock at Purdue University * from experiments on steel tubing and steel shafting. The deformations both in tension and in torsion were measured with appa- ratus of sufficient accuracy to permit the determination of the elastic limit (really the limit of proportionality). It seems rather doubtful if the measurements of deflection were sufficiently accurate to detect the overstrain in the extreme fibers of the specimens under flexure. • Reported in Proc. A. S. T. M., Vol. 7, p. 267. STEEL UNDER COMBINED STRESS 673 Curves 1, 2 and 3, represent the effect of an initial torsional mo- ment in lowering the elastic limit in flexure, compression and tension, respectively. Thus, if an initial twisting moment sufficient to stress the outside fiber of a round bar to one-half of its elastic limit in shear is apphed and the bar is then axially compressed under progressively increasing loads, curve 2 shows that the elastic limit in compression will be found at 79 per cent of the load which the bar could carry under simple compression. It appears that curve 1 is too high, probably J- JL A _ (66666 Torrional (0 ) i,„^^, ^^^^^ ^imlt Initially Applied i A A i. i. _ 6 6 6 6 6 6 Proportion of Stress Applied in lerms of Elastic Limit { Torsional (IJ \ Torsional (2) . Proportion of < Torsiooal (3) f ( Tensile or J Compressive (1) Fig. 49. Fig. 50. Fig. 49. — The Influence of Combined Stress on the Elastic Limit. (Hancock.) Fig. 50. — The Influence of Combined Stress on the Modulus of Elasticity. (Hancock.) due to the difficulty of determining by deflection increments when the outside fiber had been overstrained. Curve 4 shows the influence of an initial tensile or compressive stress on a round bar subjected to torsion. 727. Effect of Combined Stress on the Modulus of Elasticity. — Hancock's tests also show that the modulus of elasticity in tension and in torsion is considerably decreased by combined stress, whereas the effect of combined stress on the modulus of elasticity in flexure is less. Fig. 50. The results are, however, much more irregular than those from which Fig. 49 was derived. CHAPTER XXIV ALLOY STEELS * 728. Varieties of Alloy Steels and Their Manufacture.— Those steels which owe their peculiar properties to the presence of one or more elements besides carbon, or to the joint action of such elements and carbon, are termed alloy steels. In a general way we may say that these alloying elements influence the properties of steels through the changes which they affect, (1) in constitution and structure, (2) in shifting the position of the critical ranges on heating and cooling, and (3) in promoting stability of structure under wide temperature variations. When the distinctive properties are produced by the addition of one element to a carbon steel, a ternary alloy, consisting of iron, carbon and the element, is formed. When two such elements are added to a carbon steel a quaternary alloy results. The more important alloy steels are nickel steel, manganese steel, chrome steel, tungsten steel, vanadium steel, silicon steel — all of which are ternary alloys — the quaternary alloys, chrome-nickel and chrome-vanadium steels, and the high-speed steels which are more complex alloys. The alloy steels which are turned out in large tonnages Uke the nickel, silicon, chrome-nickel, chrome-vanadium and manganese steels are generally manufactured in the acid open-hearth furnace. Nickel may be added with the charge, but the other elements are added just before pouring, or in the ladle, to prevent losses through oxidation. Tungsten steels and high-speed steels are generally made in the crucible or electric furnace. 792. Nickel Steel is, from the standpoint of tonnage and variety of uses, the most important of the ternary alloys. Although additions of nickel to pure iron f effect large increases in strength and hardness with corresponding losses in ductility, the commercial alloys generally contain carbon with small percentages of the other impurities common to carbon steels. Nickel apparently forms a solid solution with iron, reduces the solubility of carbon in iron, and produces marked changes in the position * References : Sleel and Its Heat Treatment, by D. K. Bullens; " Topical Discussion on the Role of the Several Alloying Elements in Alloy Steels," Proc. A. S. T. M., Vol. 17, p. 5-57; Bull. No. 100 U. S. Bureau of Mines; Manufacture and Uses of AUoy Steel, by H. D. Hibbard; The Physico-Chemical Properties of Steel, by C. A. Edwards. t Bull. No. 346, Univ. of Wisconsin, by Burgess and Aston. 674 NICKEL STEEL 675 of the critical range. On account of these influences the constitution, the mechanical and the electrical properties of nickel steel are greatly altered by variations in the nickel content. The relation of nickel and carbon content to the constitution of nickel steel as cast is shown in Fig. la. Fig. 16 shows the influence of nickel on the magnetic point {Ar2 or AC2) or nickel-iron alloys. It will be noted that alloys containing less than 25 per cent nickel are irreversible (transformations' in heating take place at much higher temperatures than in cooling), but alloys containing over 25 per cent of nickel are reversible. Although evidence is incomplete, the critical ranges of nickel steels are Peavlite (and Ferrite or Cementiteys L ^sl3 ) . \ ^1 1 D \ Vb' ^ ^^ X \ 1 m / X. 3 w ^ i // y \ / i V/ c'4 0.5 1.0 1.5 l.f Percent Carbon Fig. 1 a. 40 60 60 Percent Nickel Fig. 1 h. 90 100 Fig. lo. — The Constitution of Nickel Steels. (Guillet, Jmw. Ir. and St. Inst, Vol. 70, p. 4.) Fig. 16. — Effect of Nickel on Critical Points. (Osmond, Comptes Rendus, Vol. 128, p. 306.) effected in somewhat the same manner as the above. Since nickel lowers the solubiUty of carbon in iron, it is not possible to carry over .50 to .60 per cent carbon in nickel steels which are to be annealed on account of the tendency of carbon to separate on slow cooling from above the critical range and form graphite. From a consideration of the constitution diagram (Fig. la) we should expect the low-nickel (pearlitic) steels to possess high strength and good ductility, those of medium-nickel content (martensitic) we should expect to be much stronger and far more brittle while those of high-nickel content (austenitic) should be strong and ductile. These expectations are roughly borne out by the experimental results of Giesen which are plotted in Fig. 2. In toughness the austenitic nickel steels of a given carbon content 676 ALLOY STEELS are superior to the pearlitic, which in turn greatly surpass the martensitic steels. Because of these mechanical properties, the low and high-nickel steels are of most use. Low-nickel Steels. — On account of the high cost of nickel only the low-nickel steels have entered the structural field. Most of the structural nickel steels contain 3 to 4.5 per cent of nickel and 0.15 to 0.40 per cent carbon. Advocates of structural nickel steel claim that it has greater toughness and ductility than a carbon steel of equal strength. It is also claimed that it is freer from segregation but is more liable to blow-holes 7- Iron + Pearlite 7-1^11 + Martensito y-Iron Pearlite y-hoi,-\- /-Iron + MartenBite y-Iron Pearlite jiartens^te 7- Iron 10 20 30 Per cent Nickel FlQ. 2. — The Influence of .Nickel on the Strength and Ductility of Steel. Carnegie Fellowship Memoirs, Vol. 1, p. 1.) (Giesen, and fissures than carbon steel. It possesses excellent machining qualities but cannot be welded. Low-nickel steels are somewhat superior to car- bon steels in resisting corrosion; high-nickel steels are very markedly superior. Abbott * states that each per cent of nickel added to the low-nickel steels (Ni<8 per cent) lowers Aci about 10.3 C°. The other critical points are also depressed nearly as much. On cooUng, the lowering effect on the critical points of these steels is nearly twice as great as in heating. When heat-treating nickel steels it is necessary to hold them longer than carbon steels at temperatures above the upper critical point in order that transformations may be completed. Since nickel steels are less liable • Proc. A. S. T. M., Vol. 17, p. 13. NICKEL STEEL &11 to injury through overheating than carbon steels, double quenching affords an excellent although somewhat costly method of equalizing the structure in hardened steel. Double quenching consists in heating the steel to a temperature considerably in excess of the upper critical point, quench- ing, reheating to a temperature just above the upper Ac point to refine the grain and again quenching. Otherwise the heat treatment of low- nickel steels is carried on in manner similar to treatment of carbon steels. Abbott also states that the strength of a given carbon steel is increased by 4200 lb. per sq. in. for each per cent of nickel added up to 8 per cent and the elongation is reduced by 1 per cent. Thus a 0.30 per cent carbon steel having an ultimate tensile strength of 70,000 lb. per sq. in. would have its strength increased to 85,000 lb. per sq. in. by the addi- tion of 3.5 per cent of nickel and its elongation reduced 3.5 per cent. With f-in. bars he states that the tensile strength of hardened and drawn nickel steel is increased by (29400-21.4 T) lb. per sq. in. for each per cent increase in nickel, T indicating the drawing temperature in degrees C. The elastic limit is likewise raised by (28700-17.4 T) lb. per sq. in. for each per cent of nickel added. Hardening lowers the per cent elongation about 0.73 per cent for each per cent of nickel and drawing does not affect this reduction appreciably. Comparing with carbon steels, we note that structural nickel steels have greater resistance to impact than carbon steels * for like uses. Heat treatment seems to make the superiority of the nickel steels more marked. These steels are used considerably in long-span bridge construction, for shafting, rifle barrels, ordnance, axles, bearings, forgings, and castings. High-nickel steels containing from 30 to 35 per cent of nickel and less than 0.40 per cent carbon possess great resistance to shock, a tensile strength of 85,000 to 95,000 lb. per'sq. in., an elastic limit of half that amount, and an elongation of 35 to 40 per cent in 2 in. The modulus of elasticity of these steels is low, being about 23,000,000 lb. per sq. in. Since these high-nickel steels have very good resistance to corrosion they are well adapted to valves and spindles for gas engines, boiler tubes, and for wire netting and cables which are to be used in salt water. Steels with 25 per cent of nickel are practically impermeable to mag- netism vmless cooled below —50 °C. when they become magnetic and remain so after returning to atmospheric temperatures (see Fig. 16.) Steels of 30 to 35 per cent nickel are magnetic at ordinary temperatures but have much lower permeability than carbon steels. They do not suffer mate- rial change in permeability due to heat treatment. Invar, an alloy of iron with 36 per cent nickel and 0.50 per cent car- bon, has a coefficient of expansion of only 0.000001 per °C. It is most useful in making steel measuring tapes and bars, clock pendulums and * See Tests by W. K. Hatt in Trans. Am. Soc. C. E., Vol. 63, p. 307. 678 ALLOY STEELS 1 1 1 N^__^ yiron V 1 Martensite N,^^ aiavtensit^ " Pea & Troostite i-Ute ^^ ^ (and Ferrite ar Cementite) ""^"^^^^^^^^V other apparatus in which dimensional changes due to temperatiu-e must be made as small as possible. Platinite, a nickel steel containing about 46 per cent nickel and a low percentage of carbon, finds useful appUcation because it has the same coefficient of thermal expansion as glass. 730. Manganese steel is the term appUed commercially to alloys of iron containing from 10 to 14 per cent of manganese and 1 to 1.3 per cent of carbon. Inasmuch as manganese exerts twice as powerful an influence as nickel in lowering the critical temperatures of the iron-carbon alloys and also renders the rate of transformation at the critical points 15 1 ) 1 1 — I 1 very sluggish, it exercises a most 13.6 (.^ potent effect on the constitution and properties of the metal. Fig. 3 shows the variations in structures of the alloys due to changes in manganese and carbon content. It win be noted that the commercial manganese steels are austenitic and experiments have shown that they have no well-defined critical points. In cast or rolled form, the steel is glassy brittle owing to the separation of manganese-iron car- bide which, in slow cooling, forms a weakening network around the austenite grains. By reheating the steel to a temperature between 1000 and 1100° C. and quenching in water, separation of the carbide is prevented and a fine-grained uniform austenitic structure is secured. As a consequence of this heat treatment the ductility and toughness is wonderfully improved. Fig. 4 shows the pensile properties of various manganese steels as determined by Hadfield, who first investigated their properties. It will be observed that the ultimate strength of the water-toughened specimens of the commercial alloys is about 140,000 lb. per sq. in. and the elonga- tion between 40 and 50 per cent. The elastic limit is, however, quite low, being only 50,000 lb. per sq. in. The steel exhibits no necking in the tensile test and consequently has a low per cent reduction in arf a. In shock resistance, it is far superior to carbon steels of equal strength. The Brinell hardness number of the commercial steel is only 200, or thereabouts, but it possesses extremely high resistance to certain types of abrasion. Howe * attributes this resistance to its capacity of hard- ening under deformation. The austenitic manganese steels are non- magnetic and possess high electrical resistance. On account of the impossibility of softening by heat treatment, man- *Proc.A.S. T.M., Yol. 17, p. 7. 0.6 1.0 1.65 20 J»ercent Cacbon Fig. 3. — The Constitution of Manganese Steels (Guillet, Jour. It. and St. Inst., Vol. 70, p. 7.) MANGANESE AND CHROME STEELS 679 ganese steel cannot be machined. Therefore it can only be used advan- tageously in shapes which can be cast or rolled to approximately final form and finished by a comparatively small amount of grinding. Water-toughened manganese steel is effectively utilized for rails on curves where wear is severe, for frogs and switches, for vaults and safes, for screens in separating stone, for crusher jaws and rolls. 6 8 10 12 14 16 18 V , Per cent.Manganese ^. Fig. 4. — The Influence of Manganese on the Strength and Ductihty of Steel. Specimens were j in. in diameter. (Hadfield, Proc. Inst. Civ. Engr., Vol. 93, p. 1.) The martensitic manganese steels are of little commercial value on account of their excessive brittleness. 731. Chrome steels containing 0.5 to 2 per cent chromium and 0.2 to 1.5 per cent carbon find considerable application for parts where great hardness, high strength and a fair degree of toughness are required. The great hardening capacity of the chrome steels is due to the combination of chromium with cementite, thus forming a double carbide with iron. Chromium also promotes a very fine-grained structure in the metal. 680 ALLOY STEELS Steels of the composition mentioned above are pearlitic in the normal state. In the annealed state they have somewhat greater ductility than carbon steels of equal strength, but subsequent to proper quenching and tempering, they are much stronger and harder, and somewhat tougher and more ductile than carbon steels. Chrome steels also have a very high elastic ratio. In toughness, however, they are excelled by the chrome- nickel and chrome-vanadium steels. Since austenite does not readily dissolve the double carbide it is necessary in annealing chrome steels to soak them for several days at a temperature just above the critical range, which is 25 to 50° C. higher than for carbon steels of like carbon content, and then cool very slowly. Excepting the differences in critical points, hardening and drawing of chrome steels are accomphshed in much the same way as with carbon steels. Table I shows the influence of hardening and tempering on the properties of several varieties of chrome steel. TABLE 1.— MECHANICAL PROPERTIES OF CHROME STEELS Chemical Treatment. Strength in Pounds Per Square Inch. Percent Elongation in 2 Inches. Brinell Hardness. Analysis. Quenched at, " C. Drawn at, ° C. Ultimate. Elastic Limit. Authority. C = 0,64 Cr = 1.04 870 400 227,500 170,000 5.0 477 Mn = 0.28 870 500 212,000 155,000 8.0 444 ♦Bullens Si =0.17 870 600 186,000 78,800 127,500 51,100 10.0 30.5 387 As forged AC, C = 0.20 800 400 153,600 150,100 12.5 Cr = 1.98 800 550 130,000 123,200 16.0 822°C. Mn = 0.12 800 700 92,300 71,600 28.0 t McWilliam Annealed 73,900 35,800 40.5 As forged 120,500 71,700 20.5 C=0.50 800 400 255,700 251,000 9.0 Cr = 1.99 800 550 201,000 190,500 13.0 778°C. and Mn = 0.24 800 700 139,800 127,700 21.0 Annealed 84,200 28,700 28.0 » As forged 170,000 116,500 10.0 C=0.85 800 400 Barnes Cr = 2.00 800 550 214,200 207,000 8.5 Mn = 0.24 800 700 141,100 128,800 20.0 777°C. Annealed 1 89,800 42,100 32.0 * Specimens used by BuUens (see Sleel and Its Heat Treatmeiil, p. 302) were 1 inch rounds quenched in oil. t Specimens of MoWilliam and Barnes (see Jour. Iron and Steel /nB(., Vol. 81, p. 253) were quenched is water. They were 0,564 inch in diameter. TUNGSTEN STEEL 681 Like nickel steels, the chrome steels are also highly resistant to cor- rosion. Steels with about 0.5 per cent of chromium and 0.60 to 0.90 per cent carbon are used for chipping chisels, drills, razors and saw-blades. Files are made from 0.5 per cent chrome steel containing about 1.5 per cent carbon. Steels containing about 1.0 to 1.5 per cent chromuim and 0.90 to 1.10 per cent carbon are used in balls and rollers for bearings, also for safes and crusher jaws. Armor-piercing projectiles, rolls for cold-rolling metals, and drawing dies are made from steels containing about 2 per cent chromium. 732. Txmgsten steel is the oldest of the alloy steels but is of minor importance at the present time. The chief use now made of this ternary alloy is in permanent magnets, for which purpose the steel is unexcelled. Magnet steels usually contain about 0.6 per cent of carbon and 6 per cent of tungsten. After the magnets have been formed they are hardened and then soaked for a long time at the temperature of boiling water in order to stabilize their magnetic properties. Steels with about 3 per cent of tungsten and 1 per cent of carbon are used to some extent for lathe tools for rapidly finishing iron and steel parts. Such steels are best treated in much the same manner as carbon steels. Tungsten steels are very complex in constitution. According to results which Arnold and Read * obtained by experimenting on steels containing 7.0 per cent carbon, if in annealed steels the ratio of carbon to timgsten is 1 ; 15.3 these elements are united as a carbide (WC) ; if the carbon is in excess of this ratio both carbides of iron and tungsten are present; if tungsten is in excess there is no carbide of iron, but a mixture of carbide of tungsten and tungstide of iron (Fe2W) is present. When the timgsten steels are heated to temperatures above 1000° C. the lower critical point is depressed very markedly. This effect of tungsten on the critical point Ai has a very important bearing on the properties of the high-speed steels of which tungsten is a part. Swinden's researches f show that the strength of 3 per cent tungsten steels increases from 74,000 to 139,000 lb. per sq. in. as the carbon content is raised from 0.2 to 0.9 per cent, the per cent elongation in 2 in. falling from 28 to 13.5 per cent for the same change in composition. Further increase in carbon produced a decrease in strength. With steels containing 0.8 per cent carbon and tungsten ranging up to 19 per cent Portevin J obtained a maximum strength of 192,000 lb. per sq. in. with a timgsten content of 10 per cent. The steel was, however, quite brittle. * Proc. Inst. Mech. Engr., 1914, Pt. 2, p. 223. t Jma-. Iron and Steel Inst., 1907, Pt. 1, p. 294. t Carnegie Fellowship Mem., Vol. 1, p. 261. 682 ALLOY STEELS Both the strength and hardness of tungsten steels can be raised materially by heat treatment. 733. Vanadium Steel. — ^Although the strength and hardness cf steel is improved by additions of vanadium up to 1 per cent, the element is so expensive that the content usually is kept much lower, running from 0.10 to 0.20 per cent in commercial vanadium steels. Vanadiima is one of the most powerful of the alloying elements in raising strength and hardness. Vanadium is also a powerful scavenger of oxygen but is too costly to use for such purposes. In low percentages, vanadium combines with both the ferrite and pearlite of the steel. In the latter it enters the cementite as a double carbide with iron and thus exerts a pronounced hardening influence. Vanadium exerts a more powerful effect than chromium in raising the upper critical points {A2 and A3). Consequently vanadium steels require higher temperatures (30 to 40° C.) for hardening and annealing than carbon steels. Vanadium renders the coalescence of the pearlite and cementite much more sluggish and, therefore, promotes the formation of globular or sorbitic pearKte in the normally cooled steels. On accoimt of this tendency, also common to the chrome steels, vanadiima steels are much tougher than carbon steels of like strength. Vanadium also raises the temperature to which a steel may be heated without material loss of strength and hardness (Art. 815-819). This latter property renders vanadium a useful alloying element in high-speed steels. Experiments by McWilliam and Barnes * on 0.2 per cent vanadium steels show that the tensile strength of untreated steels varied directly from approximately 85,000 to 157,000 lb. per sq. in. as the carbon con- tent increased from 0.09 to 0.71 per cent. The elongation in 2 in. was reduced from 23 per cent with 0.09 per cent carbon steels to 9.5 per cent with 0.98 per cent carbon steels. When quenched from 850° C. and tem- pered at 400° C. the strength increased from 61,000 to 208,000 lb. per sq. in. as the carbon content was raised from 0.09 to 0.98 per cent. The duc- tility of the treated steels was reduced from 33 to 11 per cent for the same increase in carbon. The yield point of these steels ranged between 75 and 85 per cent of the ultimate strength. Carbon beyond 1 per cent does not appear to benefit the strength of vanadivun ^teek. Vanadium steel is used to some extent in making castings for loco- motive frames, for forgings, automobile axles, springs and battering tools. The ternary vanadium steels have been displaced very largely, however, by the superior chrome-vanadium steels. 734. Silicon Steels.— Owing to difficulty in rolling, steels containing more than 5 per cent silicon are not of commercial value. The influence of silicon on the mechanical properties of steel is similar to that of carbon * Jour. Iron and Steel Inst., Vol. 83, p. 294. CHROME-NICKEL STEELS 683 but is proportionately much less powerful. Hadfield * found that the effect of silicon in increasing the strength of unannealed steel rose from 8000 lb. per sq. in. for IJ per cent silicon to 27,000 lb. per sq. in. for 3i per cent silicon. In his experiments the elastic ratio varied between .73 and .80 and the elongation in 2 in. decreased from 31 to 14 per cent with increase of silicon from IJ to 3j per cent. By alloying silicon with pure iron, Yensen f found that the strength was increased from 38,000 to approximately 85,000 lb. per sq. in. as the silicon content was increased from to 4 per cent. Silicon steel is used to some extent for automobile gears and springs. For such purposes it contains carbon 0.40 to 0.50, manganese 0.50 to 0.70 and silicon 1.25 to 2.00 per cent. These steels are often termed silico- manganese steels, although there appears little justification for the term, since the manganese content is not abnormally high. After suitable quenching and drawing treatment silico-manganese steels have tensile strengths of 200,000 lb. per sq. in., or more, with an elongation in 2 in. of 8 to 10 per cent. Silico-manganese steels are less expensive than the chrome-nickel or chrome-vanadium alloys but do not appear to be as tough and, according to Bullens, are quite difficult to heat treat success- fully. On account of its cheapness, low hysteresis loss, and high permeability to magnetism, steel containing about 4 per cent of silicon and very little carbon or manganese is the best material known for pole pieces of dynamos and for transformer cores. 735. Chrome-nickel steels constitute one of the most important classes of alloy steels. The properties rendering these steels of high commercial value are very high strength, elastic limit and hardness combined with good ductility, and a high degree of toughness, all of which may be secured by proper heat treatment. The most valuable steels of this class are those which are normally pearlitic, those containing pearlite and ferrite (C<0.85 per cent) being used much more than steels containing pearlite and carbide (00.85 per cent). In the commercial chrome-nickel steels the composition ranges are about as follows: Type Cr Ni C Mn Si P s ^ Low Medium. . . High 0.5-0.7 0.9-1.2 0.7-1.8 1.0-1.5 1.5-2.0 2.5-3.5 .20-. 40 .20-. 50 .20-. 50 .50-. 80 .30-. 60 .50-. 70 Low Low Low <.04 <.04 <.04 <.04 <.04 <.04 * Jour. Iron and Steel Inst., Vol. 2, p. 212. t Bull. No. 83, Engr. Expt. Sta., Univ. of Illinois. 684 ALLOY STEELS Bullens * says that the most effective ratio of nickel to chromium is ap- proximately 23 to 1. In steels of the above composition it appears that the influences of nickel and chromium on strength are cumulative. In comparing with nickel steels of like strength the quaternary alloys have greater hardness and higher elastic limit due to the presence of chromium; furthermore they are somewhat less costly. Again comparing with the chrome steels of equal strength, it appears that the chrome-nickel steels are less hard and have a somewhat lower elastic ratio but are much tougher, more ductile and less liable to injury through overheating than the former. Bullens states that the critical range of these steels is lower than for carbon steels and suggests the following as a suitable method for heat treating gear stock of chrome- nickel steel: " (1) Quench in oil from 175 to 200° F. over the critical range. " (2) Quench in oil from about 50° F. over the critical range. " (3) Anneal at about 75° F. under the critical range. " (4) Machine. " (5) Quench in proper medium from about 50° F. over the range. " (6) Draw the temper to suit the work in hand." For shafting and axles requiring a toughening treatment the above set of operations may be abridged by following operations (1) and (2) with a drawing treatment at 900° F. The effects of drawing temperature on the mechanical properties of a low-carbon low-chrome-nickel and a medium-carbon low-chrome-nickel steel are shown in Fig. 5. The strength and ductility of steels containing larger percentages of chromium and nickel are practically the same as those of low-chrome-nickel provided the carbon content is constant. Bullens claims, however, that the dynamic and endurance properties of the high-chrome-nickel steels after heat treatment are materially superior to those of the low-chrome-nickel varieties. Chrome-nickel steels are much used for automobile shafts and gears, also for large axles and shafts. Rails and track bolts made of steel smelted from the Mayari ores of Cuba, which contain enough of the ele- ments to form a low-chrome-nickel steel, have given very good service. On account of the very fine case which these steels will take and the great toughness of the high-chrome-nickel they have been considerably used for heavj^ armor plate. With suitable heat treatment these steels are also used for medium armor plate, for protective decks and projectiles. For armor plate and projectiles a tenth of a per cent of vanadium is often introduced into the chrome-nickel steel. 736. Chrome-vanadium steels, one of the most recent developments among the alloy steels, have acquired extensive recognition on account of their excellent mechanical properties, uniformity in structure, sim- * Steel and Its Heat Treatment, p. 308. CHROME-VANADIUM STEELS 685 ^i)egrees Eahrenhelt IW 800 000 "lOOO 1100 1400 800 plicity with which they can be heat treated, ease of machining and sound- ness of the cast metal. The composition, of chrome-vanadium steels used for structural purposes generally varies between the following limits: carbon, 0.20 to 1.0; chromium, 0.75 to 1.25; vanadium, 0.12 to 0.25; manganese 0.40 to 0.75 per cent, with silicon, phos- phorus and sulphur low. For many structural purposes the carbon is kept between 0.20 and 0.30 per cent, the chromium is held in vicinity of 1.0 per • cent with vanadium about 0.15 per cent. Griffiths* points out that chrome- vanadium steels have a higher critical range on heating and a lower range on cool- ing than ordinary steels of like carbon content. Also pro- longed heating at high temperatures appears to have little deleterious effect. This sluggishness in pj^ 5 structural transfor- mation and capacity to withstand high temperatures ren- ders these steels comparatively easy to heat treat, a single quenching and drawing treatment being sufficient. For most purposes, chrome-vanadium steels, like the chrome-nickel, are heat treated. The excellent strength and hardness and the high ductility of certain * Proc. A. S. T. M., Vol. 17, p. 41. 370 425 480 540 595 Degrees Centigi-ade -The Effect of Drawing Temperature on the Strength, Ductility and Hardness of Chrome-Nickel Steels. Values are average minimum, excepting hardness values which are average, applying to round specimens § to 1^ in. in diameter. No. 3120 were heated to 1585-1615° F., No. 3140 to 1485-1515° F., for 15 to 30 min., quenched in oil, reheated for 30 min. at temperatures indicated, and air cooled. (From Adopted Report of Standards Committee of Soo. of Automotive Engr. See Trans. Vol. 11, p. 18-20.) 686 ALLOY STEELS of these alloy steels after different tempering treatments is typified by the results plotted in Fig. 6. The test-pieces used by Griffiths in these experi- ments were | in. in diameter over the standard 2-in. gage length with a total length of 18 in. With larger sections the strengths and hardness of steels of like compositions would be less and the ductilities greater. Untreated chrome-vanadium steels are sometimes used for castings and shafting. For automobile springs and gears the steels are quenched and drawn. Chrome-vanadium steels may be readily case hardened, taking a glassy hard surface with a very fine-grained tough core. This property renders them valuable for dies and bearing raceways. C. = 0.24 Mn.=0.e9 Cr. =iao V. =0.16 Heated to 850 ° C.,cooIed very slowly to 800°C . and water quenched. C. =0.31 Mn.=o.67 Cr. =0.96 V. =OJi Heated to 850^ C, cooled to SOO^C. and oil quenclied. C. =0.48 Mn.=0.85 Or. =1J8 V. =1J1 Heated to 87&-900 Ccooled to 825 C . and oil qnenclied. is r II .560 21 540 20 520 19 500 18 480 17 160 16 440 15 420 14 400 13 380 12 360 11 340 10 600 600 200 300 400 500 6il0 100 DX&wiDg Xjemperature in Degrees Centigrade Fig. 6. — The Effect of Drawing Temperature on the Strength, Ductility and Hard- ness of Chrome-vanadium Steels. (Griffiths, Proc. A. S. T. M., Vol. 17, p. 37.) 737. High-speed Steels. — One of the greatest advances in promoting rapid machining of metal parts has come about within the past twenty years through the introduction of steels for tools which can cut four, or five times as rapidly as the simple carbon steels. Most of these steels can be run at a red heat without losing their hardness. In fact, many work to best advantage only when run at high temperatures and within a given range of cutting speeds. Most high-speed steels contain from 15 to 20 per cent of tungsten, 3 to 5 per cent of chromium, 0.5 to 2.0 per cent of vanadium, 0.60 to 0.80 per cent of carbon with silicon, sulphur, and phosphorus running low. Some makers have used molybdenum to replace tungsten, but this prac- HIGH-SPEED STEELS 687 tice seems to have been largely abandoned. More recently there has been a strong tendency to insert 3 to 5 per cent of cobalt in high-speed steels, the claim being made that cobalt increases the red-hardness of the steel. Although the critical points and the changes in constitution which the high-speed steels undergo in heat treatment is still largely a matter for further research to settle, there appears to be evidence,* however, that at temperatures near the melting-point the carbon is in combination with the tungsten and chromium as a double carbide of these elements, but if the steel is slowly cooled the carbon combines with the iron at lower temperatures. What changes in constitution are effected by the intro- duction of vanadium is not known. It seems likely that it also forms car- bides like chromium and tungsten. By cooling these steels rapidly from a temperature near the melting- point, approximately 1250° C, down to a temperature below the ordinary critical range of the carbon steels, it is possible to retain the carbon in combination with the tungsten and chromium and to prevent the forma- tion of the carbide of iron. Since these carbides impart great hardness and are very stable for all ranges of temperature up to a red heat, it follows that steels in which they are the essential components will retain their, hardness at much higher heats than carbon steels in which hardness is conferred by the unstable carbide of iron. The heat treatment generally given high-speed lathe and planer tools consists in heating to incipient fusion in a non-oxidizing atmosphere and quenching in an oil bath. For milling cutters and tools of accurate form, the quenching temperature is made slightly less to avoid injury to the shape of the tool. Where considerable toughness must be imparted, tools are quenched in molten lead and air cooled, or reheated in molten lead after oil quenching and air cooled. High-speed steels may be annealed by soaking for a long time at a temperature just above the critical range of carbon steels. After such treatment they possess high strength and good ductility. Aside from tools, high-speed steels are also used in parts which must withstand high heat and wear, as in the exhaust valves of gas engines, and in dies through which brass is extruded. * Carpenter, H. C. H. in Jour. Iron and Steel Inst., 1905, Pt 1, p. 433; aLso Edwards, C. A., in Jour. Iron and Steel Inst, 1908, Pt. 2, p. 104. CHAPTER XXV CAST IRON AND MALLEABLE CAST IRON CAST IRON 738. Importance of Cast Iron. — On account of cheapness, strength, ease with which it may be melted and cast into more or less intricate shapes, ease of machining, and ease with which its hardness may be varied, cast iron is the most-used of the cast metals employed in engineering construc- tions and machines. It is very extensively fabricated into water-pipes, cyhnders, car-wheels, agricultural machinery, stoves, hardware, machine frames, bed plates, and column bases; and to a lesser extent for columns, grate bars, ornamental castings, pipe fittings, and agricultural implements. Further uses are indicated in Table 1. Where toughness is necessary cast iron is displaced by the more expensive malleable cast iron or by the still more costly cast steel. Again in constructions where the metal must withstand corrosion, brasses, bronzes and other alloys, all of which are very much more expensive than cast iron, displace it. As an indication of the great use of cast iron, we note that about one-fifth of the pig-iron annually made in the United States is remelted and made into cast iron. From this pig iron and about a miUion tons of scrap approximately seven million tons of gray-iron castings are produced. Manufactuee of Cast Iron 739. Remelting of Pig Iron. — Although pig iron from the blast furnace is sometimes molded into final form, most of the pig iron used for castings is remelted before being molded into final shape. Remelting is necessi- tated by the variability in the pig iron run from a given furnace, by the difficulty of adjusting the composition of the molten iron, and by the necessity of mixing different grades of pig iron in order to secure the desired grades of castings. Most of the ordinary gray iron used in machine parts is remelted in the cupola, the better grades of gray iron — often called gun iron — and the white iron used in making malleable cast iron are generally remelted in the air-furnace. Some use has also been made of small open-hearth furnaces to remelt pig iron for high-grade cast iron and malleable cast iron. 688 CAST IRON 689 The function of the remelting furnace is simply to produce homogeneity in the charge which has been proportioned with reference to the use of the product. Changes between the average composition of the metal charged and that of the castings are, in general, small although sometimes impor- tant. 740. Materials Charged. — Compositions of the pig irons commonly used in smelting cast iron are given in Art. 582. In many parts of the country the chemical analysis of the pig iron serves as means of grading it and purchase is made on this basis. Generally the silicon content is speci- fied and the sulphur limit prescribed. Some foundrymen still rely on the character of fracture exhibited by the pig iron as a criterion of composition. Special pig irons containing high percentages of silicon, the Scotch irons and ferro-silicons, are sometimes added to soften the iron; while others containing high percentages of manganese, ferromanganese, for example, are used as hardeners. Besides pig iron, from a tenth to a half of the metal charged con- sists of the refuse from previous heats and whatever old machinery or parts of cast iron the foundrymen can purchase. All of this heterogeneous mass is termed scrap. On account of variability in its composition the proportion of scrap is generally less than 25 per cent of the metal charged when the best grades of castings are being made. Coke is the fuel most commonly used in the cupola, bituminous coal in the air-furnace. Under favorable conditions with large furnaces the ratio of fuel to iron is about 1 : 8 or 1 : 10 for the cupola and 1 : 4 for the air-furnace. A flux consisting of crushed limestone or other form of lime carbonate is some- times added in very small amounts to slag off the earthy impurities and reduce the sulphur content of the cast iron. 741. The cupola is a sort of small blast furnace. It consists of a vertical cylindrical steel shell of nearly uniform diameter lined with fire-brick. Fig. 1 shows an elevation of a cupola. At the bottom is placed the hearth or crucible which extends upward a short tuyeres. Fig. 1. — Cupola. distance to the level of the At the bottom of the hearth is located the taphole and opposite 690 CAST IRON AND MALLEABLE CAST IRON to it several inches above the bottom is the slag-hole. The tuyeres are placed in one or two circumferential rows. Air at a pressure of 1 lb. per square inch or less is served to the tuyeres through the wind box which surrounds the hearth. Above the tuyeres is the melting zone which is surmounted by the stack, a door for charging being placed in the latter. Cupolas vary in internal diameter up to 10 ft. The common sizes are from 4 to 6 ft. in diameter with their charging doors 12 to 25 ft. above the hearth bottom. Cupolas of these sizes will run from 10 to 20 tons of metal per hour. In operating a cupola, kindling is first placed on the hearth and a thick layer of coke on top of it. Alternate layers of pig iron mixed with scrap and layers of fuel are then dumped in until the stack is filled to the level of the charging door. If flux is used it is charged immediately after each layer of metal. After the fire has been kindled and the bed of fuel well ignited the blast is turned on, and in about ten minutes molten iron trickles from the tap-hole. The tap-hole is then closed with a plug of fire-clay. As the slag accumulates it runs off through the slag-hole and from time to time the iron is tapped into a large ladle. Ordinarily a cupola is charged and discharged several times a day, but at some plants they are run continuously for several days. The necessity of repairing the lining at frequent intervals prohibits long runs. During the melting process a small amount of iron and 0.2 to 0.3 per cent of silicon is oxidized, while 0.05 to 0.10 per cent of sulphiu- and, under certain conditions, a little carbon is absorbed from the fuel. 742. The air-furnace is somewhat like the puddling furnace used in making wrought iron, but larger in size (Fig. 2). At one end it is provided Fig. 2. — Showing Principal of Air-furnace. • with a fire-box and at the other a stack; between is a shallow rectangular hearth, served by a door in the side. Separating the hearth and the fire- bojc is a low vertical wall called the fire-bridge. The opposite end of the hearth is formed by the flue-bridge which rises to the same height as the fire-bridge. Air-furnaces range in capacity from 5 to 40 tons. Before the charge is introduced into the furnace the bottom of the hearth is covered with an even layer of sand ; then the scrap and pig iron are CAST IRON 691 placed upon it. The furnace door is sealed with clay and the fire started. Melting of the iron is accomplished principally through radiation from the sloping roof and, in part, through the heat of the hot gases which sweep over the hearth. During the melting process the bath is rabbled occa- sionally with iron bars to promote uniformity in melting and in composition. If much slag forms on the bath it is partially skimmed off to raise the temperature and promote oxidation of the carbon and silicon. In order that the top metal, which is the hottest, may be run from the furnace, tapping is done through a set of holes placed at different elevations in the hearth. The usual rate of producing iron with the air-furnace is 3 to 4 tons per hpur. 743. Comparison of Cupola and Air-furnace Processes. — The cupola process is quicker, cheaper in installation and in operation; the metal is hotter and more uniform in temperature — conditions which mean much in casting; the loss of metal through oxidation is also less than in the air- furnace. On the other hand the air-furnace produces a larger quantity of high-grade iron at a single tapping. The metal in the air-furnace not being in contact with the fuel absorbs neither sulphur nor carbon. The air-furnace process is under better control and permits better regulation in the composition of the iron. In neither process, however, has there been a successful attempt at utihzation of the latent heat in the escaping Molding 744. Patterns of the castings are made either of wood coated with shellac or metal. Wood is largely used when only a few castings are desired. When the number of castings is to be great, it is preferable to use a brass pattern and thus avoid imperfections likely to be found in the castings due to damaging of wooden patterns. If a number of castings of similar shape are to be made it is customary to join several patterns in such way that they may be poured simultaneously. Such patterns are said to be gated. Patterns are always made larger than the casting to allow for contraction in cooling. For ordinary gray cast iron an allowance of an eighth-inch per foot is a common rule. White cast iron and steel shrink double this amount; brass and copper about 50 per cent more and lead and zinc two and one-half times as much as gray cast iron. The funda- mental considerations in designing a pattern are: (1) make the pattern of such shape that it may be removed from the sand without damaging the mold, if of intricate shape it may be necessary to make the pattern in two or more parts; (2) use fillets of large radius at all sharp angles and corners and thus avoid planes, of weakness arising from the crystalliza- 692 CAST IRON AND MALLEABLE CAST IRON tion of the metal; * (3) avoid joining heavy and hght sections wherever possible, since these parts, cooling at unequal rates, will be highly stressed at their junction (if sudh design is necessary some provision should be made for rapidly cooling the heavy section); (4) when possible avoid shapes where the ends of the casting will be rigidly held by the mold and contraction stresses or checking thus produced in the intermediate parts of the casting. 745. Cores. — When it is necessary to make a hollow casting some sort of core is used. This is located in proper place in the mold by pro- jecting fins which rest in core prints that are made by corresponding pro- jections of the pattern. If the core is of such size or shape that it cannot be held in place by core prints, iron supports called chaplets are placed in the mold. Generally cores must be so made that they will offer little resistance to shrinkage of the metal and will not burn on to the iron. They are commonly molded of dry sand mixed with flour, molasses, lin- seed oil or patented compound and baked in an oven. Sometimes green sand cores are used. When it is particularly necessary to avoid all stress- ing of the casting, cores are made with centers of crushed coke or of pipe wound with hay rope, the outside being of sand. Cores are vented to permit the escape of gases generated in pouring. 746. Materials for Molds. — Not only must the material composing the mold retain the metal and give it a smooth and true surface but it must also be sufficiently porous to allow the escape of air and gas. Sand is the most refractory cheap material for this purpose. A good molding sand generally contains not less than 80 per cent silica and 5 to 10 per cent of alumina. The higher the temperature of the molten metal, the more refractory must the sand be. Consequently the sihca content must be higher for steel than for cast-iron castings. Some alimiina, however, is needed to furnish reqiysite cohesiveness in the sand. Small proportions of magnesia, lime and iron oxide are usually present also in molding sands. More than 2 or 3 per cent of the carbonates is objectionable owing to the gas formed in calcination of them, while metallic oxides render the sand less refractory. Another important factor which affects the cohesive- ness and the porosity of molding sand is the gradation in sizes of particles. The smoothness of the surface of the casting is also affected by the fine- ness of the sand grains. Therefore, molding sand is generally screened through a 20-mesh sieve, the gradation in sizes below that opening being determined by the work in hand. * When a metal cools the crystals form perpendicularly to the surfaces. If a corner is left sharp there will be a plane of separation between crystals bisecting the angle at the corner. Since the cohesion across these planes is less than in the crystals, a pro- nounced weakness is thus produced. Fig. 3 shows such planes for a square bar. By rounding the corners interlocldng of the crystals is promoted and a stronger, more homogeneous casting is obtained. CAST IRON 693 Parting sand is a highly refractory sand which cannot be rendered cohesive by the addition of water. Facing materials are shaken over the pattern or surface of the mold to prevent the sand from being burnt and to make the castings leave the mold freely, thus preserving a bright surface and avoiding expense in cleaning. Fine soft coal, graphite, charcoal and talc are among the substances which are mixed with six to fifteen times as much fine mold- ing sand to make facings. Loam is the name for a soil carrying a high content of silicious sand, considerable clay and more or less decayed vegetable and animal matter. The term is also used to designate artificial mixtures made of sand and clay with some sawdust or rye meal. 747. Molds. — The kind of castings and the number, size and shape determine the character of the molds. The common types of molds are green-sand, dry-sand and loam molds. Besides these, cast-iron molds are considerably used when a permanent type of mold is desired. Green-sand Molds. The pattern is surrounded by a flask of wood or cast iron which serves to hold the sand in place. Generally the flask consists of two, sometimes three or more, rectangular frames of equal size which may be doweled or locked together to form a bottomless box. In molding many simple objects, half of the pattern is bedded in the lower frame, called the drag, and the other half is covered by the upper part of the flask, called the cope. The procedure is to place the drag on a mold board bottom-side up with the pattern or portion of the pattern resting on the mold board. Molding sand moistened with sufficient water to render it coherent is ramm.ed about the pattern and several small vent holes are punched through to the pattern. A bottom board is put over the drag and the drag is turned over. The remainder of the pattern is inserted and a bit of parting sand is sifted over the top of the drag, the pattern being kept clean. Next, the cope is put in place and plugs for the runner * and riser * are properly located. Molding sand is tamped about the pattern and vents provided. The plugs are then withdrawn, the cope carefully lifted and gates from plugs to pattern are cut. A draw spike is attached to the pattern, and tapped until the pattern can be removed. After the loose sand has been removed a facing may be smeared on the surfaces of the mold; the cope is then placed on top of the drag and locked in position for pouring. Green-sand molds are much used, especially for articles of like shape, because they can be rapidly made at low cost. When there is * A runner is the canal through which the molten metal is poured. It is provided with a basin at the top and a hble at the bottom connecting with the mold called a gate. , A riser is a vertical canal leading from the mold to the top of the cope. It serves to vent the mold, supply metal as the casting cools, and to carry off dirt. 694 CAST IRON AND MALLEABLE CAST IRON a large demand for a certain type of casting, molding machines are frequently used. Dry-sand molds are fashioned in iron flasks in much the same way as those of green sand. A rather coarse loamy sand is used and the molds are dried at 300 to 400° F. After baking, the surface of the mold is generallj'- coated with a wet mixture of graphite, or. charcoal with clay. Such molds are 'strong, will withstand hard usage, and, if properly vented, produce sound smooth castings. Dry-sand molds are well adapted for the production of cylinders, rolls, engine beds and other heavy castings where the pressure of the metal is great, or where a smooth wall of uniform thickness must be obtained Dry-sand molds are likely to be somewhat distorted during drying and cause heavier shrinkage stresses in castings than do green-sand molds. On the other hand, castings made in dry-sand molds are more sound, smoother, and freer from inclusions of sand and dirt than those cast in green sand. Loam molds are used principally for very large castings which are bounded by surfaces of revolution. Castings of heavy engine cylinders and fly-wheels are generally made in loam molds. The outer casing of the mold is ordinarily built of brick, sometimes of iron. To the interior of this casing dampened mixtures of loam are plastered. The surface of the mold is generated by revolving a sweep, the end of which is fashioned in conformity with the surface desired for the casting. The mold is then baked and faced. Owing to the rigidity of loam molds, provision is made during the fabrication to permit rapid destruction of certain parts immediately after the casting is poiued in order that the latter may contract freely. 748. Chills. — Sm-faces of castings which are subjected to heavy wear are made hard by rapidly Qoohng them in chills. Chills consist of pieces of cast iron which form the sm'face of the mold in contact with the part of the casting to be hardened. Sticking of the iron to the chills is prevented by coating the latter with shellac and plumbago or with a thin film of light oil. To avoid explosions resulting from contact between the molten metal and the chill, it is necessary to heat the latter to 300 or 400° F. before pouring. The treads of car wheels and the bearing surfaces of rolls are cast against chills. Changes in composition due to chilUng are explained in Art. 751. Fig. 3 shows the effect of chiUing on structure. The depth in inches of white iron produced by chilling is termed chill. 749. Cleaning Castings. — Flasks are removed as soon as the castings have solidified, but the pieces are generally allowed to remain in the sand until cool. Sand and dirt adhering to the surfaces of the castings are re- moved by rattling, by pickling in acid or by sand blasting. Rattling is done in a device similar to that used in testing paving brick. (Appendix CAST IRON 695 A.) It can only be successfully employed on sturdy regular-shaped pieces. Rattling also produces a hard skin on the castings. Pickling is used on fragile or intricate castings and on pieces which must be (a) Sand-mold, not Chilled. (6) Chilled on One Side. (c) Chilled on Four Sides. (d) Chilled on Opposite Sides. Fig. 3. — Showing the Effect of ChiUingon Car-wheel Iron. (Jour. Frank. Inst., April, 1897.) machined. Dilute solutions of hydrochloric or sulphuric acid are often used for pickling, but they attack the iron. Hydrofluoric acid in a 5 per cent solution is more efhcacious since it attacks the sand. Sand blast- ing is an effective means of cleaning heavy work. 696 CAST IRON AND MALLEABLE CAST IRON Composition and Constitution 750. The Principal Constituents. — Cast iron is really unrefined steel contaminated with larger proportions of impurities. As in the carbon steels, the five main impurities in cast iron are carbon, silicon, sulphur, phosphorus and manganese. They constitute from 5 to 8 per cent of cast iron, by weight. Besides these elements oxygen, nitrogen and copper are often present in small percentages, while, to irons used for certain purposes, vanadium and titanium are sometimes added. Since the properties of cast iron are dependent principally upon the proportion of the different impurities and the combinations which they form in the iron, the influence of each of the essential constituents will be considered. Owing to the variety of forms and combinations in which carbon is found in cast iron (see Art. 659 and 662), the influence of this element is of the most importance in determining the properties and the value of the iron. Thus we find three main types of cast iron — gray, white, and mottled iron — which owe their characteristics and prop- erties to variations in the form of carbon content. 751. Carbon in Cast Iron. — The proportion of carbon in cast iron gen- erally lies between 2^ and 4 per cent by weight. Carbon, as has been shown in Art. 662, occurs in two- forms — either free as graphite, or chemically combined with the iron as iron carbide (FesC). When free, the proportion of the volume of the metal occupied by the graphite, due to its specific gravity being much less than that of iron, is about 3.5 times as much as the percentage by weight. Therefore the spaces occupied by the flakes of graphite aggregate 8 to 14 per cent of the bulk of the iron. When the carbon is combined with the iron the proportionate bulk of the iron car- bide is still greater, being over fifteen times the percentage of combined carbon. The amount of carbon which the molten iron will retain in solidifying is dependent upon the composition of the iron. Again the proportion of the carbon which is retained in combined form is influenced greatly by the presence of other elements and by the rate of cooling. Thus by adding manganese or chromium the solubility of carbon in iron is increased and much of it is combined with the iron. On the other hand, additions of silicon or aluminum reduce the solubility of carbon in iron and promote the formation of graphite. Rapid cooling tends to cause combined carbon, slow cooling furthers increase in graphite. When the composition is properly adjusted it is possible to retain the carbon as carbide of iron by rapid cooling or to precipitate it by slow cooling. If in cooling the carbon is largely precipitated, more or less uniformly in the form of graphite flakes, the iron is soft and presents a dull gray fracture which is brightened here and there by glistening iron crystals. CAST IRON 697 This is gray cast iron. When the carbon is retained in combined form, the cast iron is very hard and brittle; and the silvery white fracture has led to the name, white cast iron. In some irons the major portion of the carbon is retained in the combined form while a lesser part is precipitated as graphite. Such irons exhibit a white fracture spotted with dark (a) Gray Cast Iron with finely divided graphite more or leas globular in form ( X 50) . (Aston.) (&) Gray Cast Iron with graphite in large flakes (XSO). ^Harbison Walker Refractories Co.) (c) White Cast Iron. The white constituent is cementite and the dark one is pearlite (XlOO). (Storey.) (d) White Cast Iron under higher magnification (X500); showing lamellar pearlite (banded 'structure), flakes of graphite, and cementite. (Wiist.) Fig. 4. — Photomicrographs of Gray and White Cast Irons. gray patches and are termed mottled cast irons. Photo-micrographs of gray and white cast irons appear in Fig. 4. From the foregoing it follows that irons containing large amounts of manganese or chromium are hkely to be permanently white while those having a high silicon content are gray. With proper adjustment in com- position, cast iron may be rendered white by cooling rapidly or gray by cooling slowly from the molten state. 698 CAST IRON AND MALLEABLE CAST IRON The proportion of carbon and its form influence more or less most of the physical and mechanical properties of cast iron. The fusibility varies inversely with the carbon content and inversely with the percentage of combined carbon.* Therefore white cast iron has a lower melting- point than gray iron, but it is less fluid when molten. Shrinkage varies inversely as the carbon content, but white iron shrinks nearly twice as much as gray iron. The specific gravity of gray iron increases with the decrease in carbon content and varies from 425 to 450 lb. per cubic foot. White cast iron is heavier than gray due to the chemical combination of the carbon and weighs in the vicinity of 475 lb. per cubic foot. The influence of the proportion of combined carbon on the consti- tution and mechanical properties of cast iron containing 4 per cent of carbon is very well illustrated by Howe's diagram in Fig. 5.t It will be noted that the tenacity of the iron (the whole) is governed by the strength of the matrix which is a maximum when the matrix contains 1.2 per cent combined carbon. The hardness also varies with the hardness of the matrix and increases directly with percentage of combined carbon (cementite). Fig. 5 also brings out the effect of variations in the pro- portion of combined carbon on the machining qualities and general uses of cast iron. Similar diagrams might be worked out for irons with less total carbon. In such cast irons, the weakening effect of the graphite will be less and the influence of the properties of the matrix wiU be stiU more pronounced; therefore, the points G, A and F will be higher. The size and shape of the graphite plates also exercise an important effect upon the strength of the cast iron. Large thin plates of graphite weaken the iron much more than small round grains (see Fig. 4). 752. Silicon in Cast Iron. — Next to carbon, siHcon exercises the most important influence on the properties of cast iron. It combines with the iron, forming iron sihcide, which in turn is dissolved in the ferrite. The proportion of silicon in cast iron usually runs between 0.5 and 3.5 per cent, although certain special castings for acid containers are made with a much higher silicon content. Silicon in small percentages increases the fluidity of the molten iron, decreases blow-holes and increases the density of castings. Silicon also reduces the solubility of carbon in iron. Accord- ing to Wust and Peterson each per cent of silicon throws out of solu- tion 0.27 per cent carbon. Furthermore, since silicon indirectly promotes the decomposition of hard cementite into soft ferrite and graphite J * From results given by Porter in Trans. Am. Foundrymen's Assoc, Vol. 19, p. 113, the following equation is derived: f = 2175— 62.5C, where F=melting tenaperature in F.° and C =per cent combined carbon (less than 3.5). . t Proc. A.S.T.M., Vol. 2, p. 252. t Porter claims that the insertion of 1 per cent of silicon into cast iron effects a precipitation of 0.45 per cent carbon as graphite. (Previous citation.) CAST IRON 699 it acts as a softener and also decreases shrinkage. However, when pres- ent in excess of the' amount required to decompose cementite, the direct hardening influence of iron sihcide becomes noticeable; and with 5 or 6 per cent of silicon the iron is hard and has a mirror-like fracture. In short, by varying the silicon content the foundryman exercises a most important control over a wide range in the properties of cast iron. The combined influence of carbon and silicon upon the structure of cast iron is well illustrated in Fig. 6.* The manganese in all of the test Name of matrix 3|l High carbon steel White cast iron Name of the cast iron i.e., of the whole Very open gray Close Mottled White "■■ ,.,. eray ^^^j ^^^^ very graphitic cast cast iron iron "'°" '"'^'^ Combined carbon per cent Graphite per cent 4.0 StrcQgth aod duotllitj Euited to UHEB V In which it j r will have "^ to uDdergc or resist much maahlnlog in prepatation but little abrasioD In UEe Soft (hi moderate shock ) suited to most engineering purposes moderate machiulDg Id prepaTalloD not osccssivo abrasion in use Hardest no shook unleas metal la Strongly supported no maohinlng in preparation, much abrasion in use Fig. 5. — Influence of Carbon on Constitution and Properties of Cast Iron. (Howe.) heats ranged from 0.25 to 0.35; sulphur averaged about 0.06 and phos- phorus from 0.13 to 0.18 per cent. Cylindrical specimens 2 in. in diameter and 12 in. long were poured in green-sand molds with proper regard for disturbing influences due to variations in pouring temperatures. They were cooled in the molds two hours before quenching in water. In the diagram, the line G-G represents limiting combinations of silicon and car- bon at which the test-pieces were gray. The line M-M shows the varying combinations of carbon and silicon producing a mottled fracture, while the line W-W represents the boundary for white fractures. For smaller * G. M. Thrasher in Met. and Chem. Engr., Vol. 13, p. 40. 700 CAST IRON AND MALLEABLE CAST IRON 3.2 3.0 2.8 2.6 Per cent Carbon Fig. 6. — Relation of Carbon and Silicon Contents to Structure of Cast Iron under Normal Cooling. (Thrasher.) 220,000 r 200,000 - test-pieces or for more rapid rates of cooling these lines would be shifted upward to the left; for larger test-pieces or for slower cooling the lines would be displaced toward the lower right corner of the diagram. The influence of silicon on the mechanical proper- ties of irons containing about 2 per cent total carbon is well shown by Fig. 7. These experiments were very carefully made on specially prepared irons under the direction of Thos. Turner, Associate of Royal School of Mines, England. The hardness tests were made by a sclerometer, the weight necessary to produce a scratch of given width with a standard diamond point being the criterion of relative hardness. Fig. 7 shows that maximum hardness and' crushing 'strength obtained when the castings were ren- dered sound and the per cent graphite was a minimum, per cent silicon being about 0.80 per cent for the„ iron tested. Further increase in silicon to 1 per cent produced maximum stiffness, when in- creased to 1.4 per cent maxi- mum transverse strength resulted, at 1.8 per cent the greatest tensile strength ob- tained, and at 2.5 per i,cent silicon the maximimi soft- ness. Increasing the silicon beyond 2.5 per cent caused an increase in hardness and brittleness. The very important influence of silicon in reducing shrinkage is well 131,000,000 1 KEY TO SYMBOLS Test of Compression • ' Tension o " CroGS Brealcing ^ ..Mod. of Elast. a '< Hardness ■ 30,000 a' 25,000 j Percentage ot Silicon. Fig. 7. — Influence of Silicon on Mechanical Prop- erties of Cast Iron. Specimens were Ij in. in diameter and were tested with skin on. (From Turner's Iron.) CAST IRON 701 brought out in Fig. 8, showing results of W. J. Keep. From other data by Keep, Fig. 9, which shows the variation in transverse strength for different sizes of bars and different siHcon contents, has been prepared. The data emphasize the necessity of testing bars of the same thickness as the finished casting, if a knowledge of the strength of the metal in the casting is wanted. Diameter of Square Bar la laches-. .10 .201.30 .40 .60 .60 .701.80 .901.00 Ratio: Area of Cros3.aectloa-^;Perliaeter Fig. 8. 65,000 Diameter of Squa V4" f" ! re I Sarin Inches " 1 60,000 ll S 55,000 I \ 45,000 \ \\ \\ 3 "S 40 000 ^\ k 3 \ -\ 1 35,000 i^ ^•Ss ^^ ^- a \ ^ ^ l.UU o 30,000 ■::; •-. -liT foo" mi .5() 25 000 v ■-^ ^^ sT -- -^-^ 1 R ) 0. atio ip 0. : A 20 0. rea 30 oiC 40 r.uab 50 iseo 60 0, tiOB 70 80 0.90 1. jrimete DO r Fig. 9. Fig. 8. — Influence of Silicon on Shrinkage of Cast Iron Specimens of Various Areas of Cross-section. (Keep.) Fig. 9. — The Variation in Cross-breaking Modulus of Rupture of Cast Iron for Different Sizes of Bars and for Varying Percentages of Silicon. (Keep.) 753. Sulphur in Cast Iron. — Sulphur is an undesirable element in cast iron and is generally limited to less than 0.1 per cent. Since it is believed to promote the formation of combined carbon the above limit is often doubled on irons cast in chills. It combines with manganese to form the sulphide (MnS) or, if the manganese is very low and not sufficient to satisfy the sulphur, iron sulphide (FeS) may be formed. Since these sulphides solidify at considerably lower temperatures than cast iron they tend to make castings brittle and weak at high temperatures. Sulphur in high percentages (0.5 per cent or over) also increases shrinkage and causes hard, brittle iron. These evil effects may be neutralized by proper additions of silicon. 702 CAST IRON AND MALLEABLE CAST IRON 754. Phosphorus in Cast Iron. — According to Stead, phosphorus occurs in gray iron in a eutectic of iron phosphide plus iron, and in white iron in a eutectic of iron carbide, iron phosphide and iron. Since phosphorus in these eutectics is under 10 per cent, a small proportion of the element generates a large amount of this alloy. When phosphorus does not exceed 0..5 per cent it has no marked effect upon cast iron. If more than 2 per cent of phosphorus is present the iron is embrittled and the strength diminished. High-phosphorus irons are somewhat more fluid and shrink much less than irons low in phosphorus. High-phosphorus irons, there- fore, take a good impression of the mold and are much used in making thin stove castings and ornamental castings where great strength and toughness are not essential. 755. Manganese in Cast Iron. — The proportion of manganese ordinarily found in cast iron ranges from 0.1 or 0.2 up to 2 per cent. When present in such proportions manganese combines with sulphur, forming man- ganese sulphide (MnS), and — having satisfied sulphur — with carbon to form manganese carbide (MnsC). The latter is found in cementite united with iron carbide. Ferromanganese is often added to the molten iron to reduce the sulphur and oxygen contents. This is accompUshed by combination and partial withdrawal of the oxides and sulphides of manganese into the slag. Manganese increases the solubility of carbon in iron and opposes the liberation of graphite. Increased shrinkage and hardness are promoted by increasing the manganese content beyond that required to satisfy sulphur. Therefore manganese must be kept low in gray iron which is to be machined, while in parts which must withstand abrasion a high manganese content is desirable. The effect of manganese on strength is not material. 756. Other Elements in Cast Iron. — Copper is foimd in some ores, and when under 1 per cent appears to make cast iron more dense. About a tenth of 1 per cent of titaniimi or vanadium is occasionally added to the molten iron while in the ladle to cleanse it of oxygen. Such additions have in some instances produced considerable increases in strength. The high cost of these metalloids has, however, prohibited extensive use. Aluminum has much the same effect on cast iron as sUicon, but being more expensive has been little used. Nickel and chromiimi have been added to molten cast iron but no beneficial results appear to accrue from additions of less than 1 per cent of either element. 757. Defects in Cast Iron. — Checks, segregation, blow-holes and coarse grain, the principal defects in cast iron, originate during the cooling of the castings. Checks are small parallel cracks in the surface of a casting. They generally run transverse to the long axis of the piece. Checks may arise from errors in designing the shape of the casting or mold which prevent contraction during cooling. Irons of high sulphur content are CAST IRON 703 liable to have this defect owing to their great shrinkage and lack of strength while at a red heat. Segregation is very pronounced in high phosphorus irons, where the eutectics of iron phosphide and iron separate from the main part of the metal and form brittle masses which are more or less well connected, de- pending on the amount of phosphorus present. Even with smaller per- centages of phosphorus there appears to be a well-marked tendency to the formation, here and there, of little knots of metal which are found attached within gas cavities. Analysis of the knots show that the phos- phorus and sulphur contents are very much above the mean compositions. The sulphides are also found in greatest proportion in the top of the cast- ing and in the parts cooled most slowly. Carbon and silicon sometimes segregate in such manner that interior portions of the metal are white and exterior parts are gray. When such segregations occur at different parts of the surface of a casting, they render it very difficult to machine- Sometimes relief of the non-uniformity can be had by annealing the piece. Segregations make it very difficult to secure representative samples of castings for chemical analysis. Since sulphur segregates on the top of a casting, drillings should be made through the castings from the top and the sample thoroughly mixed. Variations in size of section will cause changes in the combined carbon content; more combined carbon will exist in the skin than in the interior; these conditions must all be kept in mind in locating drill holes for borings or in cutting samples from the casting. Blow-holes are generally due to improper venting of the mold or to a high proportion of sulphur. If pronounced, they seriously affect both strength and toughness of the casting. A coarse or open grain in the iron is caused by too slow cooling, or it may be due to a very high phosphorus content. In thick parts a coarse open grain is generally found near the center of the section (see Fig. 2a) and is quite difficult to prevent. A more compact structure is often gotten by lowering the silicon content or by charging turnings or chips of cast iron along with the pig iron. Besides the above-mentioned defects, spongy spots and " cold shuts " sometimes result from lack of fluidity in the iron or from improper gating. Cold shuts are fault planes in the metal produced by the solidification of part of the casting before the remaining molten metal was run into place. Spongy spots are exaggerated forms of open grain; they are often due to a solidification of metal in the risers before the interior of the casting has solidified. The interior is thus cut off from the supply of metal which is needed to fill voids caused by shrinkage in cooling, and a porous structure results. 704 CAST IRON AND MALLEABLE CAST IRON 758. Compositions Suitable to Different Kinds of Castings. — From a study of the compositions of castings used for different classes of work Table 1 has been prepared.* TABLE 1.— SUGGESTED COMPOSITIONS FOR CAST IRONS SUBJECTED TO VARIOUS USES. (Porter) Kind of Castings. and Acid resisting Agric. machinery, ordinary Agric. machinery, very thin Air cylinders Ammonia cylinders Automobile Automobile cylinders Brake shoes Car, gray iron Car wheels, chilled Chilled Collars and couplings for shafting. . . Crusher jaws Dynamo and motor frames, base spiders, large Dynamo and motor frames, base and spiders, small Electrical Fly wheels Gas engine cylinders Gears, heavy Gears, small Grate bars Gun iron Heat resistant iron Hydraulic cyUnders, heavy. ...... Hydraulic cyUnders, medium Locomotive, heavy Locomotive, light Locomotive cylinders Machinery, heavy Machinery, medium Machinery, light Pipe fittings Pipe fittings for superheated steam Pulleys, heavy Pulleys, light Railroad Rolls, chilled Stove plate Valves, large Valves, small Wheels, large T. Wheels, small Per Cent Composition. Silicon. 00-2.00 00-2.50 25-2.75 00-1.75 00-1.75 75-2.25 75-2.00 40-1.60 50-2.25 .60- .70 .75-1.25 1.75-2.00 .80-1.00 2.00-2.50 50-3.00 00-3.00 50-2.25 00-1.75 00-1.50 00-2.50 00-2.50 00-1.25 25-2.50 80-1 . 20 20-1.60 25-1.50 50-2.00 00-1.50 00-1.50 50-2.00 00-2 . 50 75-2.50 50-1.75 75-2.25 25-2.75 50-2.25 60- .80 25-2.75 25-1.75 75-2 . 25 50-2 . 00 75-2.00 Sul- phur. <.05 .06-. 08 .06-. 08 < .09 < .09 < .08 < .08 .08-. 10 < .08 .08-. 10 .08-. 10 < .08 .08-. 10 <.08 < .08 < .08 < .08 < .08 08-. 10 < .06 < .09 08.-10 < .08 06-. 08 < .08 < .09 < .08 < .09 < .08 Phos- phorus. <.40 .60-. 80 .70-. 90 .30-. 50 .30-. 50 .40-. 50 .40-. 50 .30 .40-. 60 .30-. 40 .20-. 40 .40-. 50 .20-. 40 .50-. 80 .50-. 80 .50-. 80 .40-. 60 .20-. 40 .30-. 50 .50-. 70 <.20 .20-. 30 <.20 .20-. 40 .30-. 50 .30-. 50 ,40-. 60 .30-. 50 . 30- . 50 ,40-. 60 ,50-. 70 50-. 80 20-. 40 50-. 70 60-. 80 40- . 60 20-. 40 60-. 90 20-. 40 30-. 50 30-. 40 40-. 50 Man- ganese. 1 . 00-1 . 50 .60- .80 .50- .70 .70- .90 .70- .90 .60- .80 .60- .80 .50- .70 1.60-.80 .50- .60 .80-1.20 .60- .80 .80-1.20 .30- .40 .30- .40 .30- .40 .50- .70 .70- .90 .80- 1.0 .60- .80 .60-1.00 .60- 1.00 .80-1.00 .70- .90 .70- .90 .60- .80 .80-1.00 .80-1.00 .60- .80 .50- .70 .60- .80 .70- .60- .50- .60- 1.0 - .60- .80- .10 .60- .80 .60- .80 .50- .70 Com- bined Carbon. 55-. 65 60-. 80 20-. 30 20-. 30 20-. 30 <.30 80-1.00 <.30 Total Carbon. 3.00-3.50 3.00-3.30 3.00-3.30 3.00-3.25 low 3.50-3.70 low low low 3.00-3.30 low low low low low low low low 3.00-3.25 low ' Condensed from Porter's report Trans. Am. Foundrymen's Assoc, Vol. 19, p. 134. 759. Shrinkage. — At the moment DEPARTMENT CAST XBotf^^cHJNE DESIGN SIBLEY SCHOOL Properties oJ C$^^^(^^^ UNIVERSITY f)r4rrfp^(ft^°^1ift4T4 + i>^r» gray onot iron expands, due to the precipitation of more or less graphite from the eutectic of austenite and cementite. Since graphite occupies more space that if chemically combined in the molten metal the total volume upon solidification is greater than that of the molten metal just before solidi- fication. If phosphorus is high in the iron the initial expansion is soon augmented by the solidification of the phosphide eutectic which occurs at approximately 1000° C. As the temperature falls these expansions are gradually offset by contraction due to cooling. At 700° C, if the composi- tion is suitable and __the rate of cooling slow, another precipitation of graphite with consequent expansion takes place. With high sihcon and high total carbon the latter expansion is very pronounced. The casting then shrinks continuously until it reaches room temperature. With proper regulation of the phosphorus, silicon and total carbon content, it is possible to avoid a coarse open-grained metal and still control shrinkage quite closely. Fig. 8 indicates the variations in shrinkage due to changes in silicon and size of casting. In order to measure shrinkage. Keep has devised a sand mold with chills at each end for making a §-in. square bar 12 in. long.* He deter- mines the shrinkage by inserting a taper-scale between a chill and the adjacent end of the bar. By comparing the shrinkage of bars made in this mold with that of castings from the same metal it is possible to stand- ardize the mixture which is best suited for a given purpose. A simple shop test to determine sponginess or shrink cavities consists in molding a K-shaped casting. By breaking the branches of the K and noting the fracture, the soundness and density of the metal is revealed. 760. Hardness of Cast Iron. — From the machinist's point of view no property of cast iron is of more importance than its hardness, since the hardness determines the ease with which the iron can be filed or machined. We have seen that hardness increases with the proportion of combined carbon (Fig. 5) and is much influenced by the proportions of manganese and sulphur; that silicon up to about 3 per cent acts as a softener (Fig. 7) because it promotes the formation of graphite. Therefore, to secure an easily worked iron the proportion of combined carbon must be reduced to the lowest value consistent with requisite strength. In irons where high strength, closeness of grain, and ease of machining are properties much desired, the total carbon is kept low and silicon high. For determining the hardness of cast iron, Keep has invented a drill *CastIron,p.l82. 706 CAST IRON AND MALLEABLE CAST IRON test.* In making this test a |-in. straight-fluted drill is pointed vertically upward and rotated at 200 r.p.m. The test-piece is held upon it with a pressure of 150 lb.; and an autographic record, showing the penetration of the drill in terms of the number of revolutions, is gotten. Variations in the slope of the traced curve indicate changes in hardness of metal, or dulling of the drill. The diagram is so set that a slope of 0° means that the rate of penetration is infinite while a slope of 90° indicates no pene- tration. With this device the hardness of white iron is 90° while machinery iron will vary between 25 and 50°, the value for a given iron depending upon the rapidity of cooling and the per cent siHcon. With the Brinell ball apparatus, which is perhaps the most satis- factory apparatus for measuring the resistance to indentation, the hard- ness number of machinery iron rims from 90 for very soft iron up to 200 for the dense, strong irons; the number for white iron ranges between 380 and 500. 761. Influence of Composition and Rate of Cooling on Strength. — We have already noted that the strength of cast iron is dependent upon the proportion of combined carbon, the proportion and form of the graphite, and upon the closeness and fineness of the grain of the iron. From a consideration of these facts Sauveur advances the following argument. The maximum strength will be obtained when the matrix of the cast iron is approximately of eutectoid composition (i.e., pearlite), the graphite reduced to a minimiun and the cooling done as rapidly as consistent with the attainment of the foregoing, in order that the graphite flakes may be small and the grain of the iron both close and fine. These conditions necessitate the use of mixtures having low total carbon and high silicon contents. The proportion of sihcon should be suflficient to produce a eutectic of carbon in iron in order that the solidification period may be a minimum and the graphite finely divided. On the other hand, if the proportion of siHcon is too high, the combined carbon content wUl be re- duced below that required for a eutectoid matrix and the strength consequently impaired. The above conception is, of course, modified by the influences of the other impurities present in the iron, by imperfections due to irregularities in molding, and by strains set up in cooling. Nevertheless it affords a rough basis for proportioning a mixture. Influences of other factors can best be ascertained by trial. 762. Tensile Strength of Cast Iron. — Although not commonly deter- mined in the foundry, the tensile strength of cast iron is both an important * A similar apparatus has been perfected by A. Kessner. See Jour. Iron and Steel Institute, Carnegie Fellowship Mem., Vol. 5, p. 10. A very small diamond drill has also been devised for such tests; see Jaggar drill described by H. C. Boynton, Jour. Iron and Steel Inst., Vol. 70, p. 291. CAST IRON 707 property and a valuable index of the quality of the iron. In making the test it is quite necessary to avoid eccentric or oblique loading; therefore, a specimen provided with threaded ends like Fig. 3c; Chapter III, will furnish more precise results than the cheaper type of test-piece shown in Fig. 3/, Chapter III. The size of bar from which the test-piece is taken win exert a marked influence upon its strength, bars from large sections in most cases giving lower strengths than those from smaller sections of the same metal. The tenacity of gray cast iron ranges from 12,000 lb. per square inch for soft, coarse-grained irons to 35,000 lb. per square inch for the hard, close-grained irons. Occasional reports are found of low-carbon cast irons with strengths above 40,000 lb. per square inch. The American Commission on Metal for Cannon in 1856 reported a maximum value of 46,000 lb. per square inch, and a tenacity of 47,500 lb. per square inch has been reported by the Wassiac furnaces of New York.* White iron such as used for making malleable cast iron has a much higher strength than gray iron, commonly varying between 40,000 and 50,000 lb. per square inch. In small sections the strength of white iron may reach 60,000 or 70,000 lb. per square inch. TABLE 2.— TENSILE STRENGTHS AND COMPOSITIONS OF STRONG CAST IRONS. (Porter) Reported by G. Dillner R. T. Cunningham H. E. DUler H. E. Diller F. J. Cook and G. Hailstone W. Hatfield W. Hatfield G. A. Blum F.J.Cook : J. A. Murphy J. A. Murphy J. A. Murphy J. A. Murphy T. D. West D. West D. West D. West D. West D. West Carbon. Total. G.C 3.15 3.10 2.50 2.70 2.15 2.44 2.29 2.68 2.75 2.50 2.28 2.44 1.40 3.10 .96 2.05 1.62 C.C. .65 .40 1.08 .51 .90 .55 .50 .70 .72 .63 1.10 .42 .76 1.13 1.38 .90 1.91 2.36 1.83 1.31 1.96 2.19 1.25 1.31 1.66 1.60 1.70 1.70 .94 1.00 1.53 .98 1.19 .71 .060 .064 .100 .101 low low 0.70 .056 .065 .063 .070 .075 .050 .050 .050 .060 .055 .058 P. .33 .65 .91 low low .70 .66 .70 .72 .70 .60 .44 .30 .29 .43 .41 .54 Mn. .30 .74 .24 .55 .33 low low 1.00 .43 .90 .85 .75 .92 .31 .60 .45 .43 .42 .39 Tensile Strength Ub./m.2) 35,600 31,890 31,560 36,860 36,600 33,376 34,944 high 35,430 36,000 37,300 30,400 31,300 31,350 33,000 30,000 34,700 37,100 30,100 ■ Inst, of Civ. Engr., Vol. 74, p. 373. 708 CAST IRON AND MALLEABLE CAST IRON Table 2 shows the analyses and tensile strengths of a number of strong cast irons reported by various authorities. Another set of data on tenacity and comparative hardness of high grade irons made and tested at the Watertown Arsenal is given in Table 3. TABLE 3.— COMPOSITION AND STRENGTH OF HIGH-GRADE CAST IROI^S MADE AT THE FOUNDRY AT THE U. S. ARSENAL AT WATERTOWN, MASS. TEST-SPECIMENS GROOVED. {Rep. 1894, p. 247> Carbon. Man- ganese. Silicon. Sulphur. Phos- phorus. Tensile Strength, Lb. per Sq.in. Hard- ness. Kind of Furnace. Graphi- tic. Com- bined. Cupola Cupola Cupola Cupola Cupola Air-furnace .... Cupola Cupola Air-furnace .... Cupola Cupola Air-furnace. . . . Air-fuanace. . . . Air-furnace .... Air-furnace .... Air-furnace .... Air-furnace .... Cupola Air-furnace .... 2.440 2.391 2.487 3.558 2.279 2.492 2.393 2.727 2.058 2.255 2.890 2.538 2.770 2.751 2.538 2.577 2.116 2.825 2.481 0.900 0.960 0.744 0.608 0.366 0.739 0.432 0.299 0.778 0.731 0.458 0.979 0.256 0.357 0.634 0.185 0.640 0.479 0.687 0.335 0.342 0.461 0.451 0.353 0.448 0.450 0.462 0.464 0.458 0.388 0.348 0.470 0.435 0.355 0.361 0.450 0.361 0.454 1.137 1.081 1.511 1.212 1.024 1.231 1.090 1.363 1.560 1.297 1.645 1.316 2.444 1.908 1.222 1.146 1.419 1.062 1.175 0.113 0.134 0.118 0.125 0.118 0.125 0.140 0.125 0.115 0.114 0.105 0.130 0.110 0.095 0.090 0.115 0.125 0.076 0.120 0.572 0.505 0.521 0.655 0.496 0.816 0.497 0.477 0.619 0.491 0.487 0.642 0.587 0.420 0.766 0.762 0.678 0.238 0.673 27,700 27,990 31,980 32,400 34,450 32,980 31,110 31,810 29,100 30,750 27,320 26,480 28,010 29,120 28,520 31,020 31,140 32,010 31,990 16.07 15.20 17.35 15.83 20.47 18.09 15.67 11.08 21.04 17.44 16.82 TABLE 4.— COMPOSITION OF CAST IRON HAVING A HIGH TENSILE STRENGTH. (Turner) Woolwich Experi- ments, 1858, Average. Silicon Experi- ments, 1885. Rosebank Irons, 1886. Dumbarton Irons. Wassiac Iron. Average. Tensile strength. . Pounds per sq.in.. }...... 35,000 40,700 38,200 37,200 36,700 37,000 34,000 41,200 37,500 Graphitic carbon . Combined carbon. % 2.59 1.42 0.39 0.06 0.58 % 1.62 0.66 1.96 0.28 0.03 0.60 % 0.36 1.29 0.56 0.06 1.00 % 0.58 1.50 0.47 0.07 1.00 % 0.52 1.13 0.41 0.06 1.33 % 0.40 1.33 0.70 0.05 0.65 % 2.90 0.32 1.34 1.09 0.14 1.38 % 2.60 0.30 1.63 1.10 0.12 1.29 % 2.31 0.78 1.31 0.29 0.08 1.51 % 0.475 1.434 PhosphoruB 0.587 0.074 Manganese 1.037 CAST IRON 709 Some test results on excellent cast irons reported by Turner are pre- sented in Table 4. In specifying strength for sectiohs thicker or thinner than the test- piece by which the quality of the metal is to be gauged, allowance must be made for the effects of differences in cooling. In standard specifications this has been done. Castings have been grouped into three classes: (1) light — maximum thickness under § in.; (2) medium — ^thickness between | in. and 2 in.; (3) heavy — minimum thickness over 2 in. The following minimum strengths for test-pieces like Fig. 3c, Chapter III, 30,000 ,0005 ,0010 .0015 .0020 _ Elongation, Jn^ per.In, .0025 .0030 .0035 Fig. 10. — stress-diagrams for Gray Cast Iron in Tension. (Tests of Metals, 1899.) cut from 1| in. round bars are standard: Light castings 18,000, medium castings 21,000, and heavy castings 24,000 lb. per square inch. The general characteristics of stress-deformation curves for gray cast iron are shown in Fig. 10. As the curves show, the material has no well-defined elastic limit, but the apparent elastic limit determined as suggested in Art. 11 is found at approximately 60 per cent of the ultimate strength, which corresponds closely to the elastic ratio for structural steel and wrought iron. The stress-deformation diagram for white cast iron is a straight line. Inasmuch as the maximum unit deformation of cast iron is less than 0.005, it cannot be gotten from a tension test without the use of an accurate extensometer. Since measurements with the latter are 710 CAST IRON AND MALLEABLE CAST IRON impractical in commercial work, no index of ductility or toughness is furnished by a tension test of cast iron. 763. The crushing strength of cast iron is remarkably high, and it is th IS property which is considerably utilized in building constructions. Or- dinarily, owing to the necessity of using a testing machine of high capacity, tests of the crushing strength are not made. Since the crushing strength of small prisms is rarely less than five times the tensile strength, a rough estimate of the former may be gotten if the tenacity is known. When tests are made on small prisms with height at least one and one-half times the least lateral dimension, the crushing strength will range from ^^^^ 35,000 lb. per square inch for the soft open-grained gray irons to 200,000 lb. per square inch for the hard close-grained gray irons. (See also Fig. 7.) Machinery gray iron of good quality will have a crushing strength of 90,000 to 150,000 lb. per square inch. White cast iron is one of the strongest metals when subjected to com- pression, and often has a strength of 250,000 to 275,000 lb. per square inch. As in tensile tests, the posi- tion of the test-piece in the cast- ing influences the compressive strength. Pieces cut from near the surface of a casting are stronger than those from the interior. Specimens from small castings are stronger than those from large castings of the same metal. Sometimes variations in strength due to these causes amount to 100 per cent of the smallest values. The stress-diagram of Fig. 11 is representative of good gray iron in compression, being the average of results from twenty-two tests of gun- iron. The specimens were 10.5 in. long and only 1 sq.in. in cross-section. Consequently thay all failed by triple flexure, as columns, at an ^verage stress of 63,000 lb. per square inch before the true crushing strength was reached. (The tensile strength of this iron averaged 33,500 lb. per square inch.) In Table 5 are given the results of available tests on full-size cast iron columns. The very low strength of these columns is noteworthy and shows the necessity for testing full-size pieces, rather than small prisms, in order to gauge the strength of large members. The remarkable discrep- ancy here shown between the crushing strength of small specimens of cast .^ -^ 40,0U0 ^ ^ ^ ^ 30,000 / / a 20,000 1 1 / 10,000 / / i .002 .001 .006 .008 Froportioaate Compressioa. Fig. 11. — Average Results of Twenty-two Compression Tests on Gun Iron, (rests 0/ Afetais, 1894.) CAST IRON 711 TABLE 5— TESTS OF FULL-SIZE CAST-IRON COLUMNS (Results of Tests made at Phoenixville, Pa., by New York Department of Buildings, 1897) Number of Column. Diameter. Inches. Thickness of Metal, Inches. Area in Sq uare Inches. Length in Inches. CO. Actual Breaking Load per Square Inch in Pounds. Radius of Gyration w r Breaking Load by Formula p =34000-88^ I 15 1 43.98 190i 30,830 4.962 38.341 30,630 *- 11 15 li 49.03 190i 27,126 4.92 38.668 30,600 B2 15 li 49.03 190i 24,434 4.92 38.668 30,600 B4 15i U 49.48 190i 25,182 4.965 38.318 30,630 (5) 15 m 50.91 190i 35,435* 4.936 38.543 30,610 (6) 15 lA 51.52 190i 40,411 4.899 38.834 30,580 XVI 8 1 21.99 160 29,604 2.50 64.00 28,370 •- XVII 8 lA 22.87 160 28,229 2.486 64.361 28,340 (7) 6,^ lA 17.64 120 25,805 1.786 67.189 28,090 (8) 6A le^ 17.37 120 26,205 1.805 66.483 28,150 G4 8 3 4 17.083 1471' 25,969 2.741 53.903 29,260 F4 9 1 25.133 150 21,181 2.872 52.226 29,410 D4 12 1 34.588 162 30,810 3.906 41.475 30,350 C2 14 1 40.841 159i 25,401 4.609 34.661 30,950 * Did not fail. Results of the Watektown Arsenal Tests (Reports for 1887 and 1888) Number of Column. Least Diameter in Inches. Approxi- mate Thickness of Metal in Inches. Least Area in Square Inches. Length in Smmte Inches. «) Actual Breaking Load per Square Inch in Pounds. Radius of Gyration w. r Breaking Load by Formula p =34000-88- 990 5.94 0.98 13.19 131.6 38,860 2.11 62 28,540 991 5.90 0.95 12.27 146.7 43,350 2.12 69 27,930 992 5.09 0.85 12.08 150.0 33,500 1.77 85 26,520 " 993 4.74 0.91 11.75 151.5 26,840 1.61 94 25,730 994 4.84 0.91 11.89 128.6 30,370 1.63 79 27,050 995 4.87 0.90 . 11.80 129.5 29,830 1.64 79 27,050 996 5.72 0.66 8.94 127.6 63,310 2.12 60 28,720 997 2.97 0.87 5.19 118.5 31,850 .97 122 23,270 998 3.00 0.88 5,27 118.7 29,990 .97 122 23,270 999 3.00 0.90 5.50 118.4 33,350 .97 123 23,180 1000 4.27 1.00 10.92 84.6 32,130 1.31 65 28,280 "^ 2000 8.66 1.36 31.10 157.0 (25,720)* 2.63 60 28,720 2001 7.87 1.31 26.33 156.9 (30,380)* 2.37 66 28,160 2002 7.17 1.16 21.75 156.9 25,470 2,16 73 27,540 2003 6.35 1.13 17.28 156.9 27,210 1,89 83 26,650 2004 5.57 0.77 13.22 156.4 25,100 1,71 97 25,360 * Did not fail. 712 CAST IRON AND MALLEABLE CAST IRON iron and that of full-size members is doubtless due to hidden defects such as shifted cores, blow-holes, and segregation. Nevertheless such defects are always likely to be present. As the computations in the table P I indicate, the straight-line formula, j = 34,000 — 88-, very closely fits the observed results. In view of these data one is not warranted in using the commonly advocated formulae which permit much higher loads than given by the above straight-line formula. Furthermore, the residts emphasize the importance of carefully calipering cast-iron colmrms and pipes in order that variations in wall thickness due to shifting of cores may be detected. 764. The Transverse Strength of Cast Iron. — Transverse tests are pre- ferred to other mechanical tests by foundrymen. The test has foimd much favor because the specimens are quickly and inexpensively prepared; the required testing machine is simple and readily operated by inexperienced men, and the results measure both strength and toughness. Tests are commonly made on the standard "arbitration bar," which is a cylinder 1 J in. in diameter and 15 in. long. Strength is measured by the center load which this bar will carry on a 12-ui. span. An approximate measm-e of toughness is found by roughly estimating the energy of rupture from half of the product of the maximiun load times the corresponding deflec- tion. The modulus of rupture of cast iron is not ordinarily computed in the foundry, but it forms the only satisfactory means of comparing bars of the same shape which differ slightly in size. Comparisons cannot well be made between bars differing considerably in size or in shape, since the rate of cooling causes radical changes in the grain structure of the interior. Variations in the moduli of rupture of square bars due to differences in area and? in siKcon content are well shown in Fig. 9. Square bars, in general, exhibit a slightly higher modulus of rupture than round bars of equal area. In a series of 152 tests by a committee of the A.S.M.E.* in which bars | in. and 1 in. square and round bars of equal area were broken, the modulus of rupture of the square bars averaged about 5 per cent higher than that of the round bars. Variations in the modulus of rupture due to differences in shape of cross-sections are illus- trated in Table 1, Chapter III. Machined bars are generally weaker than unmachined specimens. Tumbling in a rattler materially improves the strength and increases the hardness of the skin. Bars cast horizon- tally are strongest when the load is applied against the cope face. The modulus of rupture varies from one and one-half to two and a quar- ter times the tensile strength in solid rectangular sections. (For the causes of this discrepancy, see Art. 27.) A comparison of the moduU of * Trans. Am. Soc. M.E.', Yol 16, p. 542, 1066; Vol. 17, p. 675. CAST IRON 713 rupture and tensile strengths of round bars of machinery iron is given in Table 6.* TABLE 6.— A COMPARISON OF THE RESULTS OF TRANSVERSE AND TENSILE TESTS ON GRAY CAST IRON. (Mathews) Each result represents nine tests. The standard threaded-end tensile specimens were turned from portions of bars tested transversely Span, Inches. Mean Center Load, Pounds. Modulus op Rtjptuhe. Tensile Strength. Per Cent Si. Mean Value Lb./in.2. (-S„) Maximum Per Cent Variation from Mean. Mean Value Lb./in.2 Maximum Per Cent Variation from Mean. 1.5 2.0 2.5 12 18 24 12 18 24 12 18 24 3000 1935 1425 2900 1835 1265 2880 1905 1400 47,100 45,600 44,700 • 45,500 43,200 39,700 45,200 44,900 44,000 15.9 10.7 11.2 13.4 9.5 7.6 6.4 16.7 17.5 25,600 ■ 24,370 [ 24,660 5.2 3.2 7.5 ^ 1.84 1.78 1.75 1.87 1.78 1.63 1.83 1.82 1.78 It will be noted that the modulus of rupture for these irons averages about 1.8 times the tensile strength; furthermore, that the maximum variation in the results is much greater for the transverse tests than for the tensile tests. For Math- .ur ews' tests the tensile strength is ,fl approximately 8.5, 13, and 18 times the average center loads on the 12, 18 and 24-in. spans, respectively. The effect of variation in span on the modulus of rupture is shown in Fig. 15, Chapter III. Fig. 12 shows that the energy of rupture per cubic inch de- creases as the span is increased. Here the energy of rupture was approximated by taking half the product of the maximum load times the corresponding deflection and dividing by the volume of the specimen between the supports. Thick sections will, in general, have lower energies of rupture per unit volume than thin ones. * Compiled from Mathews' tests, see Proc. A.S.T.M., Vol. 10, p. 299. 18 21 Length of Spaa, Inches. Fig. 12. — Influence of Length of Span on the Energy of Rupture of Ij-in. Round Bars of Cast Iron. (Mathews.) 714 CAST IRON AND MALLEABLE CAST IRON In Fig. 13 are shown autographic stress-diagrams of four kinds of cast iron. The tests were made on bars | in. square and 12 in. long. They all withstood a load of 450 lb. at the center, which gives a modulus of rupture of 64,800 lb. per square inch. Owing to the great differences in ultimate deflection, however, their resistances to shock vary greatly. By computing the areas under the load-deflection curves and dividing by the voliune of the test-piece between supports, we find their resistances are 10.0, 21.5, 28.9 and 35.1 in.lb. per cubic inch. For these four cases, the greatest error which would arise, due to approxi- mating the energy of rupture by the method previously outlined, is 16 per cent. In the form of the standard arbi- tration bar, gray iron should have a maximum deflection of at least 0.1 in. The minimum center loads should be 2500, 2900 and 3300 lb. for light, medium and heavy castings, respectively. These requirements, which are standard * in this country, are equivalent to a demand for energies of rupture of 8.5, 9.8 and 11.2 in.lb. per cubic inch for these grades of metal. Good gray iron specimens of round or square section under I5 sq.in. in area should have a modulus of rupture "oi'i of at least 45,000 lb. per square inch. 765. The modulus of elasticity of cast ^. , „ ^^. , , iron varies quite as much as its strength. Stress Diagrams of Four Kinds of ^ ii ■ ^^ -x i-/v in ,. Cast Iron all of Equal .Strength. ^^ ^^'^ ^^spect it differs markedly from (Keep, Trans. A. S.M.E.,\ol. 17, all rolled iron or steel which, although p. 677.) varying greatly in ultimate strength, shows little variation in stiffness. From the curves of Fig. 7 it appears that the stiffness and strength vary in the same way. Inasmuch as the stress-diagrams for cast iron are not straight lines the modulus may be calculated by dividing the working unit stress by the corresponding unit deformation. (See Art. 517.) If 10,000 lb. per square inch be the stress used to enter such diagrams, the modulus of elasticity for good gray cast iron will gen- erally vary between 12,000,000 and 15,000,000 lb. per square inch. Strong irons occasionally have moduli of 20,000,000 lb. per square inch. The * See Specifications of the A.S.T.M. and Am. Foundrymen's Assoc. 450 ioo 350 300 Ph250 150 100 50 / / / / 1 f ^ /^7 7 Ujt /V / 5/ / / f 1 ' 0.1 0.2 0.8 DeflectloQ in Inches Fig. 13. — Cross-bending Autographic CAST IRON 715 modulus for white cast iron is considerably higher, commonly 20,000,000 to 25,000,000 lb. per square inch. Cast iron appears to have the same modulus of elasticity in tension, compression and cross-bending. 766. Shock Resistance of Cast Iron. — With the exception of tests on car wheels, few impact tests of cast iron are made. The resistance to shock is generally calculated from the energy of rupture in the cross-bending test. Where castings are likely to receive hard usage the impact test is valuable, especially if phosphorus or sulphur run high in the iron. Good quality of gray iron in standard arbitration specimens will exhibit an energy of rupture of 12 to 20 in.-lb. per cubic inch. 767. Strength of Cast Iron in Shear and Torsion. — Occasionally thin castings are punched, and therefore, a knowledge of the shearing strength of cast iron is valuable. Unfortunately there is little data on this prop- erty. G. Fremont records * 267 tests in which he compared the trans- verse bending strengths (Sm) with the shearing strengths (Ss) for a wide variety of machinery cast irons. His bending tests were made on rect- angular prisms 0.32 in. thick, 0.4 in. wide and supported over a 1.2 in. span; and the shear tests were made on fragments of the prisms used in the bending tests. Fremont's report contains values of Ss varjang from 11,400 to 32,700 lb. per square inch and he states that good machin- ery iron should have a shearing strength above 25,600 lb. per square inch. From the diagram in his report the mean ratio of Ss to Sm is 1 to 2.6. Fremont believes that the shear test of cast iron is very useful and has devised a very unique form of test. He secures a cylindrical specimen 0.3 in. in diameter from. the casting by a core drill. He then fashions the cylinder into a square test bar 0.2 in. on a side and, beginning at the end of the bar nearest the surface of the casting, he shears off pieces at intervals of 0.12 in. By this method he readily secures a bar which truly represents the casting and also determines the variation in strength of the casting. Since the diameter of the hole bored in the casting is only 0.56 in., the structural damage to the casting due to sampling would in many cases be negligible. A few tests on the shearing strengths of three grades of machinery iron are summarized in the table below. The shear specimens were approx- imately f in. thick and between | and f in. in width. They were tested in double shear in the Johnson shear tool. Art. 56. Each result repre- sents two tests. Kind of Cast Iron. Brinell Hardness. No. Shearing Strength (Lb. /in.') (1) Soft and coarse-grained 92 150 217 20,500 33,700 (3) Rather hard, fine-grained • 39,900 ' Proc. A.I.T.M., Vlth Congress, \1,. 716 CAST IRON AND MALLEABLE CAST IRON Under torsion, cast iron fails through weakness in tension, the plane of failure making an angle of about 45 degrees with the axis of the bar. Round bars of good quahty of gray cast iron 5 in. to f in. in diameter should exhibit a computed twisting strength (*Sj) of 35,000 to 45,000 lb. per square inch. Three bars of a good grade of machinery iron 1 J in. in diam- eter tested by J. B. Kommers * had a tensile strength of 29,000 lb. per square inch and a computed twisting strength of 33,800 lb. per square inch. (Computed by formula 16, Art. 23.) The modulus of elasticity in torsion for the three bars varied from 6,430,000 to 8,220,000 lb. per squ^e inch. From four tests on hollow cylinders 0.66 in. in outer diameter and 0.05 in. thick made of iron No. 2 (see above table) the computed twisting strength averaged 31,500 lb. per square inch, and the tensile strength 25,000 lb. per square inch. Since these cylinders were very thin, the com- puted twisting strength was practi- cally the same as the actual unit stress on the outside fibers. There- fore, for this iron the actual shearing strength in torsion was about 93 per cent of the transverse shearing strength and 126 per cent of the tensile strength. 768. Shrinkage Stresses.— The shrinkage of cast iron after it crys- talhzes is so great that, if not pro- vided for, it causes excessive defor- mations which may develop very great stresses, even to rupture. The heavier or the thicker the casting the greater are these shrinkage stresses. These have been studied in the case of cast-iron gims, and one such analysis is shown in Fig. 14. Here the metal was over 11 in. thick. The outer and inner surfaces cooled first, and the subsequent shrinkage of the interior put these parts in compression. But since the total internal stress across any diametral section must be zero, there being no external force acting, it follows that the total tensile stress must equal the total compressive stress. These were all found directly by cutting off a zone included between two transverse sections, and by cutting this up into a series of concentric rings as shown by the dashed lines in Fig. 14. Before cutting these, four diam- eters of each ring were carefully measured, and these same diameters were again measured after cutting out. An increase in mean diameter indicated * See paper on torsional strengths of various sections of cast iron in Am. Machinist Vol. 40, p. 941. Fig. 14. — Shrinkage Stresses in Cast Iron Cannon 11 in. thick. (Tests of Metals.) CAST IRON 111 an initial compression, and vice versa, the initial stresses being found from the equation S=tE, where jS=unit stress in pounds per square inch; 6 = proportionate change in circumference; £= modulus of elasticity of the material. In this way the stress-diagrams shown in Fig. 14 were computed and drawn by J. B. Johnson from the data furnished in the original report. It indicates that the interior surface was under an initial compressive stress of some 7000 lb. per square inch, the outer surface of some 13,500 lb. per square inch; while the interior was under a tensile stress of some 2000 lb. per square inch. Evidently the tension and compression areas on these diagrams must equal each other. This is a very simple illustration of such shrinkage stresses, because of its simple and symmetrical form. In com- plex forms it would be impossible to study or predict the character of these stresses. They are evidently less when all parts are made of approximately the same thickness. 769. Strength of Cast Iron Increased by Shocks. — Mr. A. E. Outer- bridge has shown * that castings which have been subjected to a great num- ber of shocks or blows are from 10 to 15 per cent stronger under a static load and over 20 per cent stronger under impact than they are before receiving such treatment. He attributes this result to a sort of molecular rearrange- ment by which the cooling stresses are relieved. In other words, such treatment is equivalent to an annealing process. However, Keep has shown that this increase in strength is due to a densification of the surface produced by a smoothing and peening action of hammer or tumbling barrel, t 770. Seasoning Cast Iron. — If castings are allowed to age for several months before machining, the initial stresses caused by unequal con- traction in cooling may be somewhat relieved. Such relief is probably due to molecular readjustments. Advantage of the improvement due to seasoning is taken by concerns making castings which must be accu- rately shaped or planed to a true surface, f 771. Effect of Repeated Heating on Cast Iron. — Outerbridge § has shown that cast irons having high contents of graphite and silicon swell markedly in volimie, weaken, and finally crack when repeatedly heated between 1400 and 1600° F. With white irons this phenomenon does not occur. However, the brittleness and extreme hardness of white iron make it of * Trans. Am. Inst. Min. Engr., Vol. 26, p. 176. t Trans. Am. Soc. Mech. Engr., Vol. 19, p. 366. I See paper by R. Moldenke before Inst, of Min. Engr., Feb., 1917. § Trans. Am. Inst. Min. Engr., Vol. 35, p. 223. 718 CAST IRON AND MALLEABLE CAST IRON little value for heat resisting castings. When castings are likely to be severely heated, expansion troubles can be considerably reduced by using a fine-grained dense gray iron, low in graphite. If castings are contin- ually exposed to such high temperatures, steel is a better material than cast iron. MALLEABLE CAST IRON Nature and Importance 772. Nature. — White cast iron of suitable composition can be rendered somewhat malleable and ductile, and very greatly toughened by surround- ing it with a suitable packing material and annealing at a bright red heat for several days. The iron before annealing should have all of its carbon in combined form, but the silicon,- sulphm-, and manganese con- tents must be so adjusted that the annealing may be accomplished at temperatures just above the critical range (1300 to 1500° F.). By the heat treatment the combined carbon is transformed into a special type of graphitic carbon, called temper carbon. The temper carbon is made up of finer, more-rounded, and more-uniformly disseminated grains than the graphite of gray cast iron. If the packing material is loose and the furnace gases strongly oxidiz- ing, practically all of the carbon will be removed from the outer layer of iron, the percentage removed decreasing toward the center of the casting. In American practice the entire annealing period is only five or six days and the carbon removal is small. Examination of a fractured cross-section of malleable cast iron reveals a thin white shell of impure carbonless iron about ^ to ^ in. thick surrounding a black core in which the grains of temper carbon are imprisoned among ci ystals of iron (ferrite). The color of the core in the fractured casting gives rise to the name black heart. In Europe the annealing process is carried on at a higher tem- perature and for a considerably longer time. This results in the pro- duction of a much thicker shell of decarburized iron, and a greater reduc- tion in total carbon than in American practice. The castings so produced have a ivhite heart, and are coarser grained and somewhat less strong than black-heart castings. By providing chills it is possible to make much thicker castings with the black-heart process than with the white heart, the latter being best adapted to the production of sections under ^ in. in thickness. In strength, malleable cast iron is considerably superior to gray cast iron but inferior to steel castings. It is \'ery much tougher than gray iron and, when well made, compares favorably with cast steel. Owing to lower melting temperature white cast iron shrinks slightly less than steel and in the annealing process an expansion takes place, due to the separa- MALLEABLE CAST IRON 719 tion of the temper carbon, which makes the net shrinkage of mallealjle cast iron about the same as gray cast iron. Malleable castings are in general somewhat smoother and freer from blowholes than steel castings, and also more resistant to corrosion. 773. Importance of Malleable Cast Iron. — On account of good strength, high toughness, and moderate cost, malleable cast iron is much used for a large variety of small castings. About one-half of the million tons of malleable cast iron annually produced in the United States is used by railroads on rolling stock for car couplers, journal boxes, brake wheels, levers, door fasteners, hinges, pipe hangers, etc. A large tonnage is used in making parts of agricultural machinery and implements, while most of the remainder is used for pipe fittings, stove plate, hardware, orna- mental castings and cheap tools. About two hundred foundries in the United States produce several times as much malleable cast iron as is made in all the rest of the world. The Manufacture of Malleable Cast Iron 774. Melting the Charge. — The cupola, the air-furnace and the open- hearth furnace are the types of furnaces most used for melting the charge. Baby Bessemer converters and crucibles are used to some extent in Europe and the electric furnace is also forcing its way into this field. The principal use of the cupola in malleable iron works is for making small castings. The process is run in much the same way as in smelting gray cast iron excepting that a larger proportion of fuel is required in order that the white iron, which is less fluid than gray, may be very hot when poured. The composition of pig iron for such castings according to Moldenke should be about as follows: SiUcon 1.00 to 1.50, manganese <0.60, phosphorus < 0.225 and sulphur <0.05 per cent. Small amounts of pig iron and sprues are charged between thin layers of coke or anthra- cite coal. Malleable or steel scrap cannot be advantageously used in this type of furnace. Iron is run continuously from the tap hole into ladles and poured as rapidly as possible. The cupola is the cheapest in installation, in upkeep and in operation, and the quickest smelting process in general use. However, owing to contact between the fuel and the iron and lack of means of control, burnt metal is sometimes produced. Furthermore, the annealing temperature required for cupola iron is higher than for the air-furnace or open-hearth product. The air-furnace is used most in this country for making malleable castings. It is less expensive to install and operate than the open-hearth, although requiring a slightly longer time for smelting. It may be built in a wide variety of sizes, and can be operated discontinuously without impairing the quality of the iron. One of the main difficulties in air- 720 CAST IRON AND MALLEABLE CAST IRON furnace operation is the possibility of burning the thin portions of the bath and consequent production of weak metal. By proper use of the air- furnace it is possible to produce a very good grade of malleable iron with less skill than required to run an open-hearth furnace. The charge of metal for the air-furnace consists of pig iron, white-iron scrap, and malle- able scrap. When necessary to reduce carbon to proper limits (2.25 to 3.00 per cent) a small proportion of steel or wrought iron scrap is added after the pig iron has melted. For heavy castings the silicon content in the pig iron is run lower than indicated for cupola iron in order to avoid mottling of the hard iron castings. Fig. 6 indicates ranges in car- bon and silicon contents in hard iron for making different grades of mal- leable cast iron. The open-hearth furnace for malleable iron is built upon the same principle as that used in steel making, but in smaller sizes. With the open-hearth furnace the charge of metal is similar to that used in the air furnace. The fuel, however, is usually producer gas and air, both of which are separately heated by passage through hot checker works before they enter the furnace. Natural gas and vaporized fuel oil are sometimes used instead of producer gas. Although the most costly process on account of high cost of installation, upkeep and skilled labor for operation, the open- hearth furnace provides well-controlled melting conditions and furnishes the best malleable cast iron. 775. Molding and Casting.— Because of the lack of fluidity in white cast iron and the rapidity with which it chills, patterns must be provided with large runners and sprues. This should be done in order that the metal may be rapidly poured, also in order that a good head of metal may be provided to keep the mold full during solidification. Owing to the high shrinkage of white cast iron about double the allowance ordinarily made for gray iron patterns must be made in patterns for malleable iron. Con- sequently more care must be taken about joining thin and heavy parts. Suitable chills are often required to cool heavy sections with sufficient rapidity to make the iron white and to avoid excessive shrinkage strains at junctions with thin parts. The molds used for malleable cast iron are similar to those made for gray castings but, owing to the number of castings made from the'same pattern, there is a better opportunity for the effective use of molding machines and core-making machines. Metal molds, on account of the chilling action which they exert, are also successfully used for malleable castings. In casting, it is quite necessary that the white iron be poured at a temperature sufiiciently high to render it fluid; yet, on account of danger of burning, the metal cannot be held too long in the furnace. The narrow range of pouring temperature makes it necessary, therefore, to have MALLEABLE CAST IRON 721 the metal handled and cast very promptly when it has arrived at a white heat. After the white castings have cooled they are shaken out of the sand and cleaned by the methods used for gray castings. They are then trimmed of sprues, ground smooth, where nedessary, and sorted. 776. The annealing of the white castings is an exceedingly important operation in the production of good malleable castings. The hard castings are carefully packed in rectangular boxes, called saggars, which are 16 by 24 inches in plan and a foot high. Mill scale from wrought-iron squeezers and silicious slag are often mixed to form the packing material. Hematite and pulverized magnetic ore are also used for this purpose. Leasman and Storey's * experiments show that the oxidizing character of the packing material exercises no influence upon the decarburization of the iron, but that such change is due to the penetration of carbon dioxide generated in the furnace. The permeability of the packing to this gas is therefore the important factor in determining the carbon content in the skin of the castings. The saggars are stacked 4 deep in an annealing furnace, which, in form and in principle of operation resembles a rectangular down-draft brick kiln. Gas, coal or oil is used to slowly heat the annealing furnace until the temperature of the castings is above the critical range. Storey states the latter is between 700 and 775° C. The temperature is held just above this range from sixty to seventy-two hours and then the castings should be cooled very slowly until well below the critical temperature. For black-heart castings about five days are required for annealing. After removal from the saggars, the malleable castings are placed in a rattler, which is partly filled with bits of discarded malleable castings, and cleaned. They are then given whatever finishing is necessary. If crooked they are straightened but without heating. Constitution and Peoperties of Malleable Cast Iron 777. Composition and Constitution. — Good black-heart malleable cast- ings will generally contain about 2.0 to 2.8 per cent of temper carbon, 0.25 to 1.25 per cent of silicon, manganese under 0.30 per cent, sulphur below 0.5 per cent, and phosphorus under 0.25 per cent. The higher percentages of silicon are in most cases to be found only in small castings. For intricate patterns where fluidity of the molten metal is of great importance phosphorus may run to 0.3 per cent. If the annealing is properly done no combined carbon will be found and the entire structure will consist of two main elements, ferrite and tem- per carbon, as shown in Fig. 15a. Such castings should possess maximum * See account of experiments at University of Wisconsin in Foundry, Vol. 42, p. 474. 722 CAST IRON AND MALLEABLE CAST IRON (a) Good Malleable Iron. Note ferrite shell (top) free from temper carbon which appears as black patches farther in from the surface. (Harbison Walker Refr. Co.) (6) Temper carbon in ferrite masses which are in turn surrounded by pearlite. (Storey.) (c) steely shell (top) caused by close com- pacting of packing miiterial and lack of oxidation. Fig. 15. — Photomicrographs of Good and Bad Malleable Iron (X70). ductility. If the annealing period is too short or the temperature too low, cemen- tite will be present in addition to ferrite and temper carbon and the castings will be more brittle, although they may be stronger than the fully annealed iron. When the castings are cooled too rapidly after correct annealing, the structure shows the temper carbon embedded in ferrite which is in turn surrounded by pearlite, Fig. 156. With too low anneal- ing temperature followed by rapid cooling the structure consists of cementite par- ticles embedded in pearlite masses with more or less temper carbon imprisoned in ferrite. * Such iron is likely to be very brittle and non-uniform. In order to determine whether the iron is of proper constitution a small rectangular lug is cast on the work. After anneaUng the lug is broken off with a hammer, the toughness of the iron judged by the energy required to remove the lug, and the fracture examined. Good black-heart iron will show a very thin white skin from ts^ to ^ in. in thickness surrounding a bluish black or black core. The core should present a velvety ap- pearance and be free from shrink cavities or white crystals. 778. Testing of Malleable Cast Iron.— In the foundry, the breaking of hard cast- ings to determine whether the iron is mottled or white and the lug test of the malleablized iron are the principal me- chanical tests. It is customary'' with more important work to run both tensile and transverse tests. For the former a bar shaped about like Fig. 3/, Chapter III, with a minimum diameter of | in. is specified. Recent specifications of the A.S.T.M. demand a tensile strength of 38,000 lb. per square inch and an elon- *Storev's Exneriments. MALLEABLE CAST IRON 723 gation of 5 per cent in 2 in. For the transverse tests rectangular bars |, i and f in. deep, 1 in. wide, and 14 in. long are supported over a 12-in. span. These bars must withstand center loads of 900, 1400 and 2000 lb., respectively. The maximum deflections for the |, | and f in. bars must not be less than IJ, 1, and | in. respectively. Moduli of rupture cor- responding to the above loads range from 64,800 to 64,000 lb. per square inch and the energies of rupture (by approximate method) from 93.6 to 83.3 in. -lb. per cubic inch. A simple test for toughness and ductility, which seems to have found some favor in the foundry, is the curling test. This test is made on a wedge 6 in. long, 1 in. wide, and tapering from 5 in. to t& in- in thick- ness, which has been cast and annealed with the given heat. The thin edge of the wedge is bent over with a hand hammer. It is then gripped rigidly at the thick end and held thin edge up under a drop hammer. The hammer is dropped on the specimen from a constant height giving blows of 70 ft.-lb. each. These cause the specimen to curl into a spiral. 0.4 0.8 1.2 0.0 0.4 0.8 1.2 Diameter of Cross-section, Inches. Diameter of Cross-section, Inches. ** Fig. 16. — The Effect of Size of Specimen on Strength of Malleable and White Cast Irons. (Hathaway.) Lack of ductility is signified by cracking of the wedge, toughness by the number of blows required to break it.* 779. Mechanical Properties of Malleable Cast Iron. — Good black-heart malleable iron will have a tensile strength of 40,000 to 50,000 lb. per square inch with an elongation in 2 in. of 5 to 10 per cent. The per cent reduction in area is quite variable, usually being between 5 and 15 per cent for good iron. In compression, the strength of small prisms of good iron (load line parallel to skin) will range from 100,000 to 150,000 lb. per * Described by E. Touceda in Foundry, Vol. 43, p. 13. 724 CAST IRON AND MALLEABLE CAST IRON square inch. Compression tests on struts * where the ratio of Z : d = 15 : 1 show that such pieces buckle hke wrought iron at an average unit stress of about 30,000 lb. per square inch. Fig. 16 shows the effect of variation in size of cross-section on the strength of round specimens for both white cast iron and malleable cast iron made by the air ftu-nace, open hearth and cupola processes, t All specimens representing a given kind of fmnace were taken from one melt. Each point on the diagram represents two or more tests. TABLE 7.— MALLEABLE CAST IRON CHEMICAL COMPOSITION (UNANNBALED AND ANNEALED) AND PHYSICAL PROPERTIES ffi 391 395 400 406 422 433 436 445 451 458 459 469 474 495 510 Av. Unannealed or Annealed. f Before annealing I After / Before I After / Before 1 After f Before I After / Before I After / Before I After / Before I After / Before I After / Before I After f Before I After / Before I After 1 Before I After ( Before 1 After / Before \ After / Before \ After Before annealing After 3.02 .95 3.09 2.93|o 3. .09 2.56 3.07 2.91 3.26 2.95 2.85 2.77 2.88 2.58 2.97 2.66 3.08 2.15 3.08 2.03 3.03 .06 .09 .86 .08 .67 .84 .58 .26 3.12 3.04 2.85 2.660.31 O 0.06 2.80 0.10 2.45 0.13 2.25 0.30 2.83 0.61 2.59 0.13 2.05 0.15 2.07 0.22 2,35 9.23 2.07 0.26 1.75 0.22 1.79 0.09 2.54 0.16 2.58 0.22 2.52 0.03 2.59 0.19 Mn. 2.350.21 0.72 0,69 0.69 0.60 0.62 0.75 0.74 0.65 0.64 0.69 0,61 0.74 0.72 0.90 0.87 0.77 0.76|0 0.96 0.96 0.74 0.71 0.7010 0.70|o 0.77 0.75 0.70 0.70 0.63 0,66 0,64 0.67 0.21 0.73 138 140 133 13010 142|o 142 163 16410 156 151 16l|o 162 196 192 148|0 145 123 129 1510 154 153 066 064 060 061 065 061 064 064 071 068 073 071 069 069 073 075 033 039 036 037 038 037 022 023 023 023 014 018 040 039 .050 .050 Loss of Car- bon. 0.07 0.11 0.53 0.16 0.31 0.08 0.30 0.31 0.93 1.05 0.97 0.23 0.41 0.26 0.14 0.38 Tests of Annealed Speci- 5^03 -joj:: 55,100 43,800 44,900 47,000 45,300 64,500 38,900 69,100 45,400 56,700 44,200 51,600 46,600 48,100 46,000 49,810 5.5 6.1 7.7 7.2 9.1 1.3 4.3 2.6 7.2 8.4 2.1 7.7 9.8 8.6 5.9 6.2.3 a c3 OH 5.2 6.3 10.3 6.2 8.2 2.8 6.2 4.0 8.0 8.2 4.2 7.0 8.5 8.7 5.3 IS? 108 108 108 108 108 108 108 108 108 108 108 108 108 108 108 108 * C. H. Day in Am. Machinist, Vol. 29, pt. 1, p. 458; also see report by Miner and Blake in Railway Age, Vol. 31, p. 68. t From a thesis by W. Hathaway, 1912, University of Wisconsin. MALLEABLE CAST IRON 725 Table 7 shows results of tensile tests and analyses for a large number of tests by H. R. Stanford. In Stanford's tests the specimens were plain cylinders xf in. in diameter while those used by Hathaway for tensile tests were proportioned like Fig. 3/, Chapter III. Stanford reports five tests on bars which were turned down until the cross-section had two-thirds of the area of the original piece, Fig. 17. From these tests it appears that the strength of the skin was twice as great as the tenacity of the interior. Tests by Hathaway on sixteen bars of malleable cast iron made by the air-furnace and a like number made by the open-hearth furnace indicate that black-heart castings as now made are approximately of the same tenacity, compressive strength and ductility throughout. 50,000 m 40,000 3 30,000 g20,000 510,000 Fig. 17.- Iron each 4 5 6 7 Time of ADDealiQg, ia Days Fig. 17. 50,000 ffi 40,000 3 30,000 / J\ / 'h jtsiai. bgL 1 ^ -f / / A-t^ 1 uf^sr 1 i ? s. \.i 111 Percentage of EloDgatioa In 8 Inches, Fig. 18. -Tensile Strength and Elongation of Cylindrical Bars of Malleable Cast 16 in. in Diameter. Numbers show how many tests were averaged for plotted point. (Stanford.) Trans. Am. Soc. C. E., Vol. 34, p. 1. Fig. 18. — Tensile Tests of Malleable Cast Iron. Each curve represents two or three tests. {Berlin Testing Laboratory, 1886.) Fig. 18 shows the results of tension tests on malleable cast iron of \ in. and X6 in. thickness, and also of j-in. plates which had been welded together. The latter show a greater strength than the unwelded bars. The modulus of rupture of first-class malleable cast iron in cross- bending will run from 65,000 to 90,000 lb. per square inch. The energy of rupture (by approximate method) will vary' from 100 to 400 in.-lb. per cubic inch. Fig. 19 shows load-deflection curves for If-in. round bars of white, malleable and gray cast irons. The white and malleable specimens from a given furnace are from the same melts. Each curve represents two tests, excepting for the gray cast iron which represents only one. The open-hearth malleable represents very good iron but the air- furnace malleable is of poor quality. The energy of rupture values in Fig. 19 represent the areas under the load-deflection curves; for the malle- 726 CAST IRON AND MALLEABLE CAST IRON able specimens the tabulated values are about 50 per cent larger than the product of maximum load times corresponding deflection divided by twice 6,000 ^i,0 ■52,000 j^ Oj^ CROSS BENDING TESTS OF MALLEABLE, WHITE. GRAY IRONS SpecimeoBlHin. diam. Span 12 In. Mean Values from Teste ,r. / /^ "7 Kind of Iron UoduluB of Ruptutf {lb./lii.i) Eoeigy of Rnptare [Ill.lb./CU.lD.) Bfoduliu of ElBEticit; (1I)./I».') / / f / O.H.Mali. O.H.White A.r;MaU. A.r.-White Gray 85,900 68.400 57,900 61,300 47,600 274.6 7.6 30.9 7.4 9.0 17,000,000 27,000OT0 12,000,000 24;0OO,0O« 11.600/)00 ' / 0.2 0.4 0.6 Deflection at Center In Inches Fig. 19. — ^Typical Load-deflection Curves for White, Gray and Malleable Cast Irons. the volume of the specimen between supports. The difference here shown between the energy of rupture of the malleable open-hearth iron and the Fig. 20. — Examples of Cold-bending, Forging and Welding of Malleable Cast-iron Specimens, all being Originally like the Undeformed Bar in the Center. (Berlin Testing Laboratory Communications, Vol. 4, PI. 3.) corresponding white iron is representative of what may be expected with malleablizing. MALLEABLE CAST IRON 727 For several years the students in the Materials Testing Laboratory at the University of Wisconsin have broken 1-in. round bars of air-fur- nace malleable cast iron over a 12-in. span in a Russell impact machine (Fig. 18, Chapter II). The majority of these specimens had energies of rupture in impact in excess of 350 in. -lb. per cubic inch and quite a number have withstood 500 in.-lb. per cubic inch without rupture. The malleability and toughness of malleable cast iron made in Germany is well illustrated in Fig. 20. The plain bar represents the original shape from which all other forms were worked. In one case the ends of the bar were folded over and then welded together, while in another the metal forged like wrought iron. The remaining forms were deformed without heating. PROPERTY DEPARTMENT MACHINE DESIGN ■ SIBLEY SCHOOL CORNELL UNIVERSITY RECEIVER. CHAPTER XXVI NON-FERROUS METALS AND ALLOYS * COPPER 780. Production of Copper. — Copper ores are among the most widely disseminated. Valuable deposits are found in nearly all countries of continental Europe, in Japan, Chile, Mexico, Canada, Spain, Peru, Aus- traha and Africa. The United States, however, produces more copper than all other countries combined. The states which lead in the pro- duction of smelted copper are : Arizona, Montana, Michigan, Utah, Alaska, and Nevada. In general, copper ores carry a much larger proportion of earthy mate- rial than the ores of iron and rarely contain more than 10 or 15 per cent of copper. The three principal groups of copper-bearing ores in order of importance are: The sulphides, native copper and the oxidized ores. Among the sulphides chalcopyrite (CuFeS2, 34.5 per cent copper) and chalcodte or copper glance (Cu2S, 79.8 per cent copper) are the chief min- erals. Native copper is very extensively mined in northern Michigan; it is also found in New Mexico, Peru and China. In the Michigan deposits, native copper is found scattered through the lodes in particles of widely varying size. It constitutes up to 4 per cent of the ore mined and is generally very pure, although occasionally contaminated with arsenic; it is often called "Lake'* copper. The oxidized ores are derivatives of the sulphides which have been broken down bj^ the action of air and water. The more important are: Cuprite, the red oxide of copper (CU2O, 88.8 per cent copper), and the green carbonate, malachite (CuC03+Cu(OH)2, 57.3 per cent copper). Nearly all copper is extracted by smelting; a small proportion is derived by wet methods in which the copper is withdrawn from the ore in the form of a sulphate or chloride. The oxidized ores are readily smelted in a special type of blast furnace using coke as fuel. Lake copper ores are first concentrated to form a mineral containing 70 per cent or more copper, which is then smelted in a reverberatory furnace. The sul- phides, however, require a more complicated treatment, since it is not possible to reduce them directly to metallic copper. Smelting of the sulphide ores is commonly done as follows: The coarse lumpy ore is smelted in a blast furnace with or without previous roasting of a whole or part of the ore charged. The fine portions are usually roasted in * References: The Metallurgy of the Non-Ferroiis Metals by W. Gowland, Alloys and their Industrial Applications by E. F. Law, Metallic Alloys by G. H. Gulliver. COPPER 729 reverberatory furnaces. These operations serve to concentrate the copper of the ore into a matte consisting principally of copper and iron sulphides with more or less of the sulphides of nickel, zinc, silver, and lead. Removal of the major portion of the iron and sulphur compounds is effected by placing the molten matte in a converter and oxidizing it with an air blast which enters just above the bath. After the smelting operation the crude copper ("bhster copper") is cast into small pigs. Refining of the crude copper may be accomphshed by melting in a reverberatory furnace, or electrolytically. Refining in the reverberatory furnace is brought about by further oxidation of sulphides and by the cleansing action exerted by cuprous oxide on the base metals in the crude copppy, the oxide being formed by air blown upon th^ molten bath. Since a large excess or a deficiency of cuprous oxide in the copper will make it weak and brittle it is necessary to remove any excess which remains after the impurities have been skimmed oif . This is accomplished by additions of charcoal, and greenwood to the bath until the fracture of test ingots presents a flat salmon-red surface of silky texture. The copper is then at " tough pitch " and is ready for casting. Fire refining is used to give crude copper the malleability, ductility and toughness essential in plates, tubes and wires. It is also ^sed to refine copper for alloys and to partially refine metal for anodes in the electrolytic process. Electrolytic refining is used when an especially pure grade is wanted for electrical purposes, also when there is a considerable quantity of gold or silver associated with the crude copper. It is accomplished by passing a current through a copper sulphate solu- tion from an anode consisting of crude copper, or partially refined copper, to a cathode of pure copper. By this method pure copper from the anode is plated upon the cathode and the precious metals settle to the bottom of the bath. 40,000 S 30,000 g 20,000 Copper for electrical purposes should contain less than 0.1 per cent of impurities (silver being counted as copper). Copper for castings generally carries less than 1 per cent of impurities. 781. Properties of Copper. — ^Besides possessing high resistance to at- mospheric corrosion and high electrical conductivity, copper may be made very strong or very tough and mal- leable by suitable treatment. The first and ' most general error to guard against in the matter of the strength of copper and its alloys is that of ignoring the mechanical treat- ment to which the material has been subjected. Thus, in the case of copper plate, as shown by Fig. 1, a hot -rolled plate has an elastic limit of only some 7000 or 8000 lb. per sq. in., with an elongation of 50 per cent, while the same plate, cold-hammered, has an elastic limit of over 20,000 lb. c !A_^ nmere I Copi er Pj, te r y. -gs^ "fwJ^ \ /4 4^" 10 15 20 25 30 35 Percentage of Elongaflon 40 45 SO Fig. 1. — Typical Stress Diagrams for Copper Plate |-in. Thick. (Martens, Berlin Testing Lab. Communications, 1894.) 730 NON-FERROUS METALS AND ALLOYS per sq. in., with an elongation of 30 per cent. Both have an ultimate strength of about 33,000 lb. per sq.in. When simply cast, without rolling or forging, both the elastic limit and the ultimate strength are much less, but copper is seldom used in this way. The combined effects of mechanical and heat treatment on strength and ductility are well illustrated in the process of wire drawing. Thus the strength of hard-drawn copper wire will vary from 50,000 lb. per sq. in. for wire 0..5 in. in diameter to 70,000 lb. per sq. in. for wire 0.05 in. in diameter and the elongation will decrease from approximately 4 to 0.9 per cent. When annealed, wire of the above sizes will have a strength TO.OOO 30,000 ■20,000 g 10,000 1 1 20,000 " r / — Ant). E]a( tic Lin lit / t - - Tn e Elastic Limit J' / / ' S2 SO 18 IS 11 Gross Section in Sq. mm. Fig. 2. 0.1 in. 0.2 0.3 0.001 in. 0.002 0.003 £leDgatlon per In. Fig. 3. 0.i in. 0.004 in. Fig. 2. — Showing a Linear Relation between Reduction of Area of Section and the Unit Stress on the Actual Section of Rolled Copper Plate \ in. Thick. {Reipl. French Com., Vol. 3, PI. 4.) Fig. 3. — Typical Stress Diagram for Drawn Copper. {Tests of Metals, 1886, Vol. 2, p. 1673.) of 35,000 to 40,000 lb. per sq. in. and an elongation of 35 to 25 per cent, being stronger and less ductile in the smaller sizes. If the stress in a copper rod be computed for the actual cross-section at every stage of a tensile test, and the values so gotten be plotted against the diminishing cross-sectional area, the points will he in a straight Une, as shown in Fig. 2. This shows that the tenacity of copper increases regularly up to rupture with the reduction in area due to cold drawing. The elastic limit of medium and hard-drawn copper wire lies between 50 and 60 per cent of its tensile strength. The metal does not, however, exhibit a well-defined yield point hke steel, see Fig. 3. The modulus of elasticity of hard-drawn copper wire generally runs between 14,000,000 and 17,000,000 lb. per sq. in. Hard-drawn, copper may be annealed by heating to a temperature of 400° C. (752° F.). Rapid cooling does not interfere with softening of the ZINC 731 60,000 50,000 0140,000 t3 B 30,000 metal but repeated alternations of overstrain and annealing at the higher temperatures cause a marked growth in crystal structure. Effects on strength of wire of heating to various temperatures and quenching are shown in Fig. 4. The electrical resistivity of copper having less than 0.1 per cent of non- metallic impurities lies between 0.155 and 0.159 ohm per meter gram at 20° C. The resistivity increases with the content of impurities and with amount of wire drawing. 782. Uses of Copper. — The major portion of the copper produced in this country is used for electrical purposes on account of its high conductivity. About one-fourth is used in making brasses and bronzes, and a smaller proportion is rolled into sheets for tubes for conductors '^°^ ^ ^ N / 752° T. ^ 12 3 4 Percentage of Klongation roofing and sheeting, into condensers and for other which must withstand corrosion and possess fair strength and flexibility. Copper is also cast and beaten into various ornamental forms Fig. 4. — Effects of Heating Hard- drawn Copper Wires to Various Temperatures and then Quench- ing in Water. (Martens, Berlin Testing Lab., 1894, PI. I.) ZINC 783. Production of Zinc. — Like copper most of the world's supply of zinc is obtained from sulphide ores, zinc blende or black jack (ZnS, 67 per cent zinc), which ordinarily carry from one-third to one-half zinc. The ores are very often found associated with the sulphides of lead (galena), iron (pyrites), and copper. The principal sources of supply are the Rhine districts of Germany, Great Britain, Spain, Sweden and within the United States, — Missouri, Colorado, Wisconsin and Kansas. Zinc carbonate, calamine (ZnCOs, 52 per cent zinc); the zinc silicates Hemimorphite and Willemite, and Franklinite (an ore of iron, manganese and zinc) form less important sources of supply. The carbonate is of chief importance in the Mediterranean countries while the sihcates and Franklinite are the sources of an important supply in New Jersey. The principal features in the extraction of zinc from its ores are the reduction of the sulphides and carbona-es to the oxide form and the subsequent distillation of the oxide. The sulphide ores are finely ground and slowly roasted in reverberatory furnaces until nearly all of the sulphur is expelled. Carbonate ores and silicate ores are often calcined 732 NON-FERROUS METALS AND ALLOYS in shaft furnaces before being distilled. After roasting or calcination, the ore is mixed with a nearly equal amount of finely ground coal and shoveled into fire-clay retorts. By carefully controlling the temperature of the retorts at a white heat, carbon monoxide is produced and the zinc, thus relieved of its oxygen, is collected and cooled to Uquid form in condensers. From time to time molten zinc is tapped from the condensers, skimmed and poured into molds. The zinc so cast is called spelter. Most of the spelter made in the United States is sufficiently pure for industrial purposes. When contaminated with lead or iron, it is further refined by melting at as low temperature as possible. By so doing a separation of these metals is effected through the differ- ences in their specific gravities. In 1915 the electrolytic refining of zinc on a commercial basis was successfully begun at several places. 784. Properties of Zinc. — The most important property of zinc is, without doubt, its resistance to atmospheric corrosion. However, in order to make use of it for protective purposes, as in fruit jar covers, cans and battery zincs where it must be deformed into the shape wanted, zinc must possess considerable ductihty and strength. Like most metals the strength and ductihty of zinc are much influenced by composition, heat treatment, and mechanical work. Observations show that lead tends to make spelter roll easier but it also softens, weakens and reduces ductility. Consequently it should not exceed 0.1 per cent m spelter used for making cartridge brass or condenser tubes. Iron and cadmium em- brittle and harden zinc and are, therefore, a detriment in spelter which is to be rolled or used for galvanizing. For such purposes the content of these elements in the spelter should be very low, probably not over 0.02 or 0.03 per cent. , Data for estimating the strength of cast zinc are afforded by the tests of Rigg and Williams * which appear in Table 1. They found that small differences in the casting temperature of the spelter and slight variations in the temperature of the cast-iron molds caused marked changes in the sizes of the crystals and in the tenacity of the specimens. For example, note the wide variation in the tenacity of the specimens of the first samples of Prime Western No. 1 and No. 2 spelters. The specimens having the maximum strength were much finer grained than those of minimum strength. Similar results were obtained in the transverse tests. In compression, however, the loads carried at a given deformation were far more uniform. The compression specimens also exhibited a high degree of plasticity which was wholly absent in the tensile specimens. Rigg and Williams attribute the high compressive strengths of the first samples of Prime Western No. 1 and Prime Western No. 2 to the high cadmium contents in these spelters. The influence of the reduction in rolling on the tenacity of zinc was investigated by Prof. H. E. Moore, f He found, for example, that the ten- * Proc. A.S.T. M., Vol. 13, PI. 19. ^Bulletin No. 52, Engr. Expt. Sta. University of 111. ZINC 733 sile strength of the zinc, which was 9060 lb. per sq. in. when cast, became approximately 22,000 lb. per sq. in. when rolled into plate 1 in. thick, and 25,000 when rolled into sheets 0.006 in. thick, both being pulled in the direction of the rolhng. The strength across the grain (transverse to the rolhng) was somewhat higher, especially for very thin sheets, than the strength in the direction of the rolling, but the ductility was pronouncedly lower. In the direction of the rolhng the elongation in 8 in. varied from 4.85 to 21 per cent for specimens ranging in thickness from 1 in. to 0.006 in. Zinc either cast or rolled shows no well-marked yield point. Moore found the limit of proportionality in tension varied from 2900 to 5800 lb. per sq. in. for the specimens he tested but nearly all of his specimens exhib- ited permanent set at much lower stresses. TABLE 1.— THE STRENGTH OF CAST ZINC (Riggs and WiUiams) Most of the values represent four tests, some only three. Tension test-pieces were like Fig. c' Ch. Ill, with 1-in. gage length. Transverse specimens were li-in. cylinders 15 in. long with 12-in. span. They were not machined. Compression specimens were 1 in. in diameter and 2.6 in. long. AH test- pieces were gotten from IJ-in. cylindrical rods 17^ in. long cast on end in cold iron molds. In all cases the upper 2J in. of the castings were discarded. d .2 'p. E Analysis, Pek Cent. Mean Stkength, LB./IN.2 o 'ii l§ Maximum Variation FnoM Mean IN Per Cent. Grade of Spelter. Pb Fe Cd 1 s o O 0) 11 1 ft B a 1 i Hiffh. ffrade 1 2 1 2 1 2 1 2 1 2 .041 .040 .194 .190 .474 .484 1.19 1.42 .68 1.15 2.09 .014 .016 .016 .017 .013 .031 .032 .087 .010 0.11 3.51 .000 .000 .000 .000 .000 .000 .250 .079 .274 .046 .043 6,262 4,330 4,340 6,095 11,980 4,330 7,710 3,700 10,800 4,670 7,340 24,230 23,640 23,030 23,150 28,070 24,830 38,770 29,970 39,490 28,450 34,380* 11,630 10,570 10,160 12,360 16,550 13,110 11,020 10,050 16,250 10,370 15,300 0.25 0.25 0.30 0.31 0.29 0.21 0.13 0.13 0.18 0.19 0.05 35 15 25 19 20 24 46 19 34 22 13 3 2 5 4 3 5 0.3 5 2 6 11 5 5 5 Intermediate Brass SDecial. 20 S"! Prime Western No. 1. . . . Prime Western No. 1. . . . Prime Western No. 2. . . . Prime Western No. 2. . . . 23 7 18 9 10 * Faile d con ipletely Moore found the average ultimate shearing strength of eleven specimens of rolled zinc in punching tests was 19,400 lb. per sq. in. and for twelve specimens in double shear 17,100 lb. per sq. in. From a large number of tests by Moore, the modulus of elasticity of rolled zinc hes between 10,000,000 and 15,000,000 lb. per sq. in., averaging about 12,000,000 lb. per sq. in. Six tests on cast zinc in tension gave 734 NON-FERROUS METALS AND ALLOYS 11,025,000 lb. per sq. in. Four tests on cast zinc in compression gave an average modulus of only 6,900,000 lb. per sq. in. 785. Uses of Zinc— As a protective coating zinc is much used on iron and steel plate, boiler tubes, fruit jar covers, cans for resisting corrosion. It is used in making shoe nails, zinc etchings and the negative pole pieces of batteries. As a constituent of brass, German silver and some of the bronzes, zinc is also much used. ALUMINUM 786. Production of Aluminum. — Aluminum is derived from bauxite of which the principal constituents are hydrated oxides of aluminum and iron with some siUca. The important deposits of bauxite which are being worked are located in the United States and in France. Arkansas, Ten- nessee, Alabama and Georgia are the producing states. Between 30 and 35 per cent of aliuniniun is the proportion generally found in the ores which are being mined. The first step in the process of extraction of aluminum is the production of its oxide alumina from bauxite. Alumina is obtained by roasting the coarsely granulated bavix- ite at a temperature sufficient to drive off the water from the iron oxide. The treated bauxite is then finely ground and heated under pressure for several hours with a solution of sodium hydrate. This solution is diluted and filtered and a little sodium hydrate added to the filtrate. It is then agitated for several hours to precipitate the hydrate which is separated, washed, and calcined at a temperature of approximately 1000° C. The process results in the production of alumina with perhaps 1 per cent of the oxides of sodium, iron and sihcon as impurities. Aluminum is extracted by electrolytic decomposition of alumina in a molten bath of cryolite (a fluoride of alumina and sodium). The cryolite is placed in a shallow rectangular hearth provided with a coke bottom which serves as the cathode, and several vertical carbon rods suspended in the bath, which serve as anodes for the elec- tric current. After the cryolite is introduced into the furnace and melted by the pas- sage of the electric current, the alumina is thrown onto the bath. As it melts it is dis- sociated into aluminum and oxygen, the former settling onto the cathode at the bottom of the bath while the oxygen goes to the anodes and, forming carbon monoxide, escapes from the bath. From time to time a portion of the aluminum is tapped from the fur- nace and alumina and cryolite are added to replenish the bath. The metallic aluminum thus obtained usually contains from 0.2 to 2 per cent of siUcon and iron as impurities. "Pure," or No. 1, aluminum usually carries about J per cent of these impurities. Refining of alumina is done principally in the United States, France, Norway, Switzerland, Canada and Austria. The production of aliuninum is increasing very rapidly, especially in the United States and Norway. The entire production of the world is about 150,000 tons. 787. Properties of Aluminum. — Aluminum is a v/hite metal of high metallic luster. It is harder than tin, having in rolled form a hardness of approximately 40 on Brinell's scale. Being second only to gold in malle- ability, it can be rolled into sheets 0.0005 to 0.0006 in. in thickness and may ALUMINUM 735 be hanunered into leaves much thinner. Aluminum is one of the lightest of the metals of construction and, in proportion to its weight, very strong. The specific gravity ranges from 2.56 for castings to 2.7 for the densest types of mechanically worked parts. It is less ductile than copper but excels zinc, tin, and lead in this respect. The results given in Table 2 TABLE 2.— TENSILE PROPERTIES OF ALUMINUM (Alloys Research Committee) Composition:— Al = 99.53 -99.54, Si = 0.24-0.31, Fe = 0.12-0.14 per cent. Condition of Metal. Strength in Lb/in. ^ at Maximum Load. Yield Point. Per cent Elongation in 2 in. Per cent Reduction in Area. Cast (cooled slowly) Cast (cooled quickly) Cast in chills Rolled to 1^-in. round bars Rolled to if-in. round bars Cold drawn to rf-in. diameter Cold drawn to rl'ii- diameter and an- nealed Rolled into sheets j-in. thick RoUed into sheets J-in. thick and an- nealed Rolled into sheets iV-in. thick Rolled into sheets rff-in. thick and an- nealed Rolled into sheets ^-in. thick Rolled into sheets w-in. thick and an nealed 10,270 11,310 11,700 14,560 16,130 19,500 16,620 18,750 13,240 20,290 13,220 20,450 13,060 4,260 5,380 5,150^ 9,850 14,570 19,050 15,690 17,700 6,050 19,270 6,720 18,820 ■7,170 1.9 22.0 37.0 35.5 30.5 19.5 23.0 In 3 in. 10.6 41.0 6.3 31.0 3.7 36.3 27.3 33.8 60.7 79.3 81.2 73.3 82.0 show the tensile properties of pure aluminmn as determined by the Alloys Research Committee.* When hard-drawn into very fine sheets or wire the ultimate tensile strength may reach 40,000 to 50,000 lb. per sq. in. The compressive strength of cast alimiinum in cylindrical specimens with length twice the diameter is 12,000 per sq. in. and the elastic limit 3500 lb. per sq. in. according to reports of the Aluminum Company of America, f The modulus of elasticity of cast aluminum is approximately 9,000,000 lb. per sq. in. The coefficient of electrical conductivity of aluminum is about 62, silver being 100. On account of its light weight, a bar of given length is * See Eighth Report, Proc. Inst. Mech. Engr., 1907, Pt. 1, p. 57. t See Properties of Aluminum, published by the company. 736 NON-FERROUS METALS AND ALLOYS twice as good a conductor as a copper bar of the same length and weight. However, owing to the superior resistance of copper to repeated stress and its lower coefficient of thermal expansion, it is generally preferred to aluminum for transmission purposes. Almninum castings contract about 0.2 in. per foot in coohng from the molten state and are quite brittle (hot short) when sohdifying. Aluminum may be cast either in sand or chill molds. With sand molds great care must be exercised to use sand as dry as can be worked and to avoid hard ramming of molds and cores. In pouring, the temperature of the metal must be kept as low as possible and the rate of pouring must be very slow. Aluminum castings are quite open grained, consequently due allowance for porosity must be made in designing the thickness of cylinder walls and pressure tanks to be made of it. Aluminum parts can be annealed by gradually heating to temperatures between 350 and 500° C. and allowing them to soak for a short time at the temperature which has been found suitable for the given class of work. According to manufacturers statements,* aluminum is highly resistant to the attack of nitric acid, is slowly dissolved by concentrated sulphm-ic acid and is soluble in hydrochloric acid. At ordinary temperatures sul- phur, carbohc acid, salt water, vinegar, sea water, carbonic oxide, and sul- phuretted hydrogen do not attack it; but it is rapidly corroded by the caustic alkaUes. 788. Uses of Aluminum. — On accoimt of the softness and porosity of aluminum castings and the superiority of its alloys with copper or zinc, little aluminum is used in cast form. However, it can be worked at much lower temperatures than iron or copper; and, inasmuch as its density and mechanical properties are greatly improved by rolhng, heating, draw- ing, extruding or drop-forging, it is much used after such treatment. Very light ubing and wire are drawn from extruded sections of aluminum. It is rolled into sheets which in turn, may be stamped into a variety of shapes, in many cases without annealing. Aside from the uses mentioned, aluminum is employed for portions of automobile bodies, for cylinders and pistons in automobile and aferoplane engines, for tips on bullets, for rivets, and kitchen utensils. LEAD, TIN AND NICKEL 789. Lead. — Nearly all lead is derived from ores containing lead sul- phide, galena (PbS, 86.6 per cent lead). Lead carbonate, cerussite (PbCOa), and lead sulphate, anglesite (PbS04), are ormed by decomposition of galena and sometimes constitute the outcropping portions of the galena ore deposits. Lead ores are comparatively lean, averaging in the United * See Properties of Aluminum. LEAD, TIN AND NICKEL 737 States about 5 to 6 per cent of lead. The United States, Spain, Germany, Mexico and Australia normally produce over four-fifths of the world's supply of lead. Within the United States the chief sources of lead are Missouri, Idaho, Utah and Colorado. Lead is extracted from its sulphide o'res, generally in two steps. The preliminary operation consists in reducing the sulphur content by roasting the raw ore in pots or sintering it in shallow pallets. It is then smelted in a blast furnace. The products of the blast furnace are: lead bullion, containing more or less antimony, arsenic, copper, iron, silver and gold as impurities; a matte carrying copper and the remainder of the lead; sometimes a speise containing arsenides of iron and traces of the precious metals; and slag. If the buUion carries much of the impurities or the precious metals it is refined in reverberatory furnaces. The matte and speise are further treated to remove the lead which they carry. Lead has a blue gray color and exhibits a dull metallic luster when freshly fractured. Exposure to moist air causes oxidation and loss of luster. Lead is so soft that it may be scratched with the finger nail and so malleable that it can be readily rolled into very thin sheets as in thin foil. It lacks ductility, however, and cannot, therefore, be drawn into fine wire. Lead is formed into pipes with hydraulic presses which extrude the hot metal through dies. Both the softness and the specific gravity of lead are reduced by the pre ence of the common impurities antimony, arsenic, zinc and copper. Magnesia, however, has a still more powerful hardening influence, only 2 per cent being required to raise the Brinell hardness of pure lead from about 6 to 20. Pure lead pigs have a duU, dead sound when struck with the hammer, but the presence of impurities increases resonance. Lead castings shrink about ^s in- per foot in cooling. The tenacity of cast lead general'y lies between 1500 and 2000 lb. per sq. in. ; in hard lead wire the strength may reach 3000 lb. per sq. in. For the nlanufacture of sheets, pipes, solder, pewter and white lead a pure grade of lead containing less than 0.1 per cent impurities is wanted. For bearing metals and some of the alloys, hard lead which carries from 15 to 20 per cent of antimony is often used. 790. Tin is obtained in the Federated Malay States, BoUvia, Dutch East Indies,' Siam, England, Australia and Africa from the black oxide of tin, cassiterite (SnOa, 78.6 per cent tin). The total output of tin is about 112,000 tons annually. The principal deposits of the ore are found in alluvial sands, whence the name stream tin, and in veins or lodes, called lode tin. Stream tin deposits commonly contain less than 1 per cent, whereas the lode ore carries about two-thirds tin. Stream tin ores are concentrated by washing and roasting processes and lode ores are crushed. Ores containing large amounts of sulphur or arsenic are roasted to oxidize these impurities. After these preliminary treatments the dressed or roasted ore is smelted at a high temperature (1000° C.) in a reverberatory furnace, or, if the ores 738 .NON-FERROUS METALS AND ALLOYS are very pure, a blast furnace is sometimes used. The crude tin thus produced carries more or less iron, copper, lead, arsenic, antimony, and tungsten. Since many of the alloys of tin and its impurities have higher melting-points than the pure metal, the latter can be separated by raising the temperature of the crude tin just above the melt- ing-point of pure tin. Further refining is brought about by aeratij g the molten tin through violent agitation, thus producing more complete oxidation of the impurities. This is accomplished by submerging logs of greenwood in the bath of molten tin (poling) or by repeatedly pouring the molten tin from ladles (tossing). Considerable quantities of tin are now recovered by electrolytic and chemical methods from scrap tin plate. The best grades of Asiatic tin carry less than 0.1 per cent of impurities; but the lower grades from China and Bolivia, and tin recovered from scrap, may contain from 1 to 5 per cent of impurities, — lead, antimony and cop- per being the principal associated metals. Tin is a silvery-white, lustrous, and extremely malleable metal as is evidenced by its form in tin-foil. Its specific gravity is 7.3 and it melts at 232° C. but does not volatilize until the temperature is raised above 1200° C. Tin is harder, more ductile and somewhat stronger than lead. The presence of iron, copper, or lead renders tin harder and more brittle, whereas small percentages of arsenic and antimony reduce its strength and hardness. The ductility of cast tin is influenced by the casting tempera- ture, too high or too low temperature causing brittleness. Reported values of the tensile strength of tin vary from 2500 to 5000 lb. pei' sq. in. In duc- tility it equals soft steel. Tin is somewhat stronger in compression than in tension. On account of the resistance of pure tin to corrosion it is much used in sheet form for roofing, for coating cans, and as a coating on soft steel sheets. Considerable tin is used in maldng the bronzes and other alloys and a small proportion is made into tin-foil. 791. Nickel is gott^ almost entirely from two sources, the nickelifer- ous magnetic pyrites found in the Sudbiiry District of Ontario, Canada, and to some extent from the hydrated nickel-magnesium silicate of New Cale- donia, an island east of Australia. The pyrite ore usually contains about 3 per cent nickel, 2 per cent copper, with iron and sulphur constituting the major portion of the residue. The silicate ores generally carry from 6 to 8 per cent of nickel. About 50,000 tons is the world's yearly produc- tion of metalhc nickel. In order to extract nickel from the sulphide ores, it is first necessary to roast the ore to reduce the sulphur content. The roasted ore is then smelted in a blast furnace and a crude matte of nickel, iron and copper is formed. By Bessemerizing this matte the iron is removed, leaving a more pure matte of copper and nickel sulphides. Nickel with 1 to 2 per cent of impurities may be obtained from the Bessemerized matte by smelting in a roverberatory furnace with coke and sodium sulphate. By this process the copper and iron are formed into a matte of lower specific gravity than nickel sulphide. The nickel sulphide is withdrawn from the bottom of the molten bath and resmelted until BRASSES AND BRONZES 739 the desired purity has been obtained. It is then roasted to form nickel oxide which can be reduced to metallic nickel by smelting with charcoal in iron tubes. The Bessemerized matte may be more completely purified by the Mond process. In the latter process the matte is first crushed, ground and roasted. The oxides are then treated with dilute sulphuric acid to remove the major portion of the copper. The residue is partially reduced by hot producer gas and volatilized at a lower temperature into nickel carbonyl. By passing the latter through a heated tower the pure nickel is deposited in granular form. Nickel is a brilliant metal approaching silver in color. It takes a good polish and does not tarnish or corrode in dry air at ordinary temperatures. The melting-point of nickel is about 1500° C, its specific gravity is about 8.3, when cast, and 8.7, when rolled. Nickel, if attracted by a magnet, becomes magnetic but loses its magnetism when heated to 340° C. It is almost as hard as soft steel, far more malleable, and when rolled and annealed, is somewhat stronger and almost as ductile. Nickel is rendered brittle by the presence of small percentages of carbon, arsenic, nickel oxide and sulphur. Small amounts of magnesium render it more ductile and iron makes it hard. The tenacitj^ of the metal ranges from 75,000 lb. per sq. in. for thin sheets of annealed nickel to twice that value for very fine hard-drawn wire. Nickel is used chiefly in making nickel steel, coins, German silver, resist- ance wires, and in plating. Monel metal is an alloy carrying about 66 to 68 per cent nickel, 2 to 4 per cent iron, 2 per cent manganese, and the remainder copper. It can be cast, forged, rolled, drawn into wire, electrically welded, soldered or brazed and is easily machined. The melting- point is 1360° C. and the specific gravity in cast form is about 8.87. The shrinkage of castings in cooling is about the same as for steel, j in. pei foot. Monel metal has about one-fifth the heat conductivity of copper and one-twenty-fifth of its electrical conduc- tivity. In appearance it is not distinguishable from nickel. The tensile strength of Monel metal in castings is 60,000 to 80,000 lb. per sq. in., in hot-rolled bars 80,000 to 100,000 lb. per sq. in. The yield point is about 50 per cent of the ultimate strength in cast metal, and 75 per cent in rolled form. In ductility it compares favorably with soft steel, the elongation in 2 in. ranging from 18 per cent in cast metal to 40 per cent in rolled rods. The modulus of elasticity is approximately 23,000,000 lb. per sq. in. Monel metal is highly resista^nt to corrosion and the action of sea water. This val- uable property coupled with its great strength, ductility and toughness make it a very useful metal for propellers, pump rods and pump linings, roofing metal and for castings and wrought parts which must withstand attack of sea water or mine waters. Inas- much as the metal costs about ten times as much as the steel, extended use has been limited by the expense involved. BRASSES AND BRONZES 792. The Brasses — Copper-zinc Alloys. — The most valuable brass alloys contain from 60 to 90 per cent copper and 10 to 40 per cent zinc. The color of brasses ranges from a silvery-white for alloys carrying little 740 NON-FERROUS METALS AND ALLOYS copper to a copper-red for those containing little zinc. The color is also affected by the rate of cooUng. Brass may be either cast or wrought. Brass for castings usually con- tains from 30 to 40 per cent of zinc. The addition of 2 or 3 per cent of tin serves to increase hardness, but it also lessens ductility. One or 2 per cent of lead renders brass more easily turned, filed and pohshed, but reduces the ductility and strength; while 1 to 6 per cent of aluminum mate- rially raises the strength but may lessen the ductiUty. In all cases, when melting copper, brass or bronze, great care must be exercised to keep the air from the metal, in order to prevent oxidation. This is done by covering the metal, in the crucible, with a thick layer of powdered charcoal. The copper is first melted alone, in a deoxidized flame, and then the scrap brass and zinc (previously melted, these fusing at a much lower temperature) are added and the whole stirred vigorously to effect a thorough mixing. Sometimes this mixing is done after the crucible is removed from the furnace. If it is done in the furnace, the dampers should be nearly closed to prevent an excessive heat, which would vaporize the zinc. If iron molds are used they should be heated and the interior surfaces coated with a mixture of resin (3 pts.) and lard-oil (1 pt.) to prevent adhesion. In pouring, the metal must be very carefully skimmed. The pattern should be made to allow a shrinkage of J in. per foot. For common castings green sand is used, but for fine work the molds are dried. The leaded brasses are poured quite hot and chilled rapidly, but the bronzes are poured at as low a temperature as possible and into heated molds in order to avoid contraction cracks. The mechanical properties of cast brasses of aU compositions are shown in Fig. 5. It will be observed that the commercial brasses are stronger and more ductile than either of their components, copper and zinc. Electrical conductivity for the brasses is, however, very much less than for copper, being only 0.20 for brass containing 70 per cent copper. Brasses suitable for hot working, by forging, rolhng or extruding, carry from 37 to 45 per cent zinc. Those which are to be extruded often contain 2 to 4 per cent of lead to make them flow easily through the dies. Lead, however, lessens the amount of reduction in working, which these alloys will withstand without cracking, makes the metal more porous and more susceptible to burning during melting. The brasses wrought intcf shape by cold working carry less than 40 per cent zinc, usually the ratio of copper to zinc runs between 2 to 1 and 3 to 1. Brasses containing equal parts of copper and zinc are used principally for brazing brass goods. They have a very high crushing strength but are too brittle to be mechanically worked. Alloys carrying 57 to 63 per cent copper, often called Muntz Metals, are used for bolts, rods, tubes and various extruded shapes. These alloys BRASSES AND BRONZES 741 may be hot-worked but harden considerably when cold-worked and are very liable to season cracking. When slowly cooled from a cherry-red temperature these alloys have a tenacity of 55,000 to 65,000 lb. per sq. in. with an elongation in 2 in. of 50 to 60 per cent. The limit of propor- tionality is low, being in the vicinity of one-third of the ultimate strength. 130,000 15,000,000 10,000 Copper 100 Zinc 10 90 100 Zinc 70 60 50 30 40 50 60 70 Composition in Per cent Fig. 5. — Properties of Cast Brass for Varying Proportions of Copper and Zinc, from U. S. Test Board Rept, 1881, Vol. 2.) (Data The strength, hardness and ductility of these alloys appear to be somewhat increased by quenching. Perhaps the most useful brasses are those containing approximately 2 parts copper to 1 part zinc, often termed "common" or "standard brasses." They are used for sheets, wire, and many stamped and drawn articles. A notion of the wide range of properties exhibited by these brasses may be obtained by comparing the properties of castings. Fig. 5, with the plate specimens of Fig. 6 and the hard-drawn specimens subjected to various annealing treatments, Fig. 7. Brasses of this composition annealed at 742 NON-FERROUS METALS AND ALLOYS 7o;ooo , 60,000 S 50,000 40,000 S 30,000 m 20,000 g 10,000 ,^Ver} Hard Bi aB9 A j;^ ^j^^^r'Tt^ U- / ■^ ^ opper Ai ncaled /. ';:^ 1— 1 1 1 r f E> ;ctic - ^ (Jor per \ ^ j_ ercenl HAoafr K;°» / c_ ■ ■CPSl e Strent^ h '^s < ^ \ J ' — — "'If Limi 1 . , Co pper so Per ct nt \ Zi IC 10 Per o< nt \ v \ >*= ^ ^ / / j7 sf;^; ITfh y — . -S sf 'c: r ;_ — / ~~^ Cc ppet 071 or 01 nt "X Zi ic 33F er ci Dt ~\ jjCso^ .o^H )^i \ 1 N ^: /] fe Ir^n rth i \ \ i> 1 ^ «'■-., -1 — J 60 40 a 20 a cherry-red heat have a Brinell hardness number of 45 to 55; when hard- drawn the hardness may reach 150 to 160. Brasses carrying 70 to 75 per cent copper find use in cartridge cases, condenser tubes, tubes for brazing and in spinning '" '° ?e.centto,.l.a«o^ " ^ °Pe-tions. They have Fig. 6.— Stress Diagrams of Rolled Brass (Cu=67 good resistance to corro- per cent, Zn=33 per cent) and Copper. (French sion and excellent cold Com. RepL, Vol. 3, PI. 5.) working qualities. In cast form, alloys of this composition are very ductile. Their strength and ductility are not materially changed by quenching. Cold working, however, raises the strength of the annealed brass from about 45,000 to 80,000 lb. per sq. in. but decreases the elongation in 2 in. from approxi- mately 50 to 5 per cent. With 80 to 95 per cent copper the brasses take a good polish and have a color somewhat like gold. They are used for medals, cheap jewelry and as gilding for percussion and primer caps. The tensile properties of a hard-drawn 90-10 brass under various anneal- ing treatments are shown in Fig. 7. 793. Complex Brasses are alloys of copper and zinc with one or more other metals. The more important of these are manganese bronze, naval brass, sterro-metal, delta metal and Tobin bronze. Manganese bronze is really a brass containing very small per- 60,000 .20,000 a 60,000 iS 40,000 I 20,000 EO.OOO o 60,000 40,000 20,000 60 S 40 200 400 600 800 A-Qneallng Temperature "^O. 20 1000 Fio. 7. — ^The Influence of Annealing on the Tensile Properties of Cold Rolled Copper and Brass (Grard, Proc. LA.TJL, 6th Congress IIij.) BRASSES AND BRONZES 743 centages of tin, iron and manganese. The usual range in composition is about as follows: Copper, 57-62; zinc, 36-40; tin, 0.5-1.5; iron, 0.5-1.0; manganese less than 0.5 and lead under 0.2 per cent. Besides exercising a deoxidizing influence while in the bath of molten metal, manganese, by virtue of its association with iron strengthens, hardens, and slightly em- brittles the brass. Tin also increases hardness. The tensile strength of cast manganese bronze ranges from 70,000 to 80,000 lb. per sq. in. with an elastic limit of about one-third of the ultimate strength. The elongation in 2 in. generally lies between 20 and 30 per cent. In rolled or forged form its strength is slightly increased, its elastic limit raised to 30,000 or 40,000 lb. per sq. in. and the elongation in 2 in. is raised to 30 or 40 per cent. In compression the strength runs from about 90,000 lb. per sq. in. for castings to 150,000 lb. per sq. in. for rolled or forged parts. The modulus of elasticity of manganese bronze is about 16,000,000 lb. per sq. in. On account of its high strength, the facility with which it may be forged or rolled, and its resistance to corrosion and salt water, manganese bronze is used considerably in marine engine parts, for hydraulic rams, cyhnders, valve stems, propellet blades and bolts, and condenser tubes. Wrought manganese bronze parts are subject to season cracking and should always be annealed. Naval brass is used for similar purposes and is much like manganese bronze in composition but lacks manganese and iron. It is slightly weaker and more ductile than manganese bronze. The tenacity in wrought form ranges from 55,000 to 70,000 lb. per sq. in. with an elongation in 2 in. of 30 to 45 per cent. Naval brass is also subject to season cracking and should be annealed when used in wrought form. Sterro metal is an iron-brass containing about 38 per cent zinc with 1.5 to 2 per cent iron and the remainder copper. It has been used for hydraulic cylinders working under heavy pressures. Delta metal, which is an improvement on sterro metal, is a proprietary composition, or brass, placed on the market since 1883 by a Mr. Alexander Dick (England). His process consists in incorporating a fixed amount of iron by making first a saturated solution of iron (about 5 per cent) in molten zinc. To prevent oxidation a Uttle phos- phorus is added to the melted copper. The proportions are varied for different pur- poses, having from 50 to 65 per cent copper, 50 to 30 per cent zinc, 0.1 to 5 per cent iron, and sometimes 0.1 to 1 per cent tin. This metal is as strong and ductile as mild steel, having a tensile strength, when rolled and annealed, of 60,000 to 80,000 lbs. per sq. in. with elongations in 8 in. of 40 to 14 per cent, respectively, at these limits.* When cast in sand its tensile strength is 45,000 lb. per sq. in. with an elongation of 10 per cent. It is also highly resistant to corrosion. Tohin Bronze is very similar to sterro metal and delta metal, the iron ingredient being somewhat less. Its composition is approximately 60 per cent copper, 38 per cent zinc, 1 to 2 per cent tin, with small portions (0.1 to 0.3 per cent) of iron and lead. Its * Tests made at Lloyd's Proving House, as given by Hiorns. 744 NON-FERROUS METALS AND ALLOYS remarkable properties are due to rolling and annealing. As placed on the market, its tensile strength is from 60,000 to 80,000 lb. per sq. in., with an elastic limit of 60 per cent of its ultimate strength, and an elongatiori of from 25 to 15 per cent in 8 in. at these Umits, respectively. It may be regarded as having the strength and ductility of structural steel, with the advantage of being non-corrosive. It can be procured in sheets from fj in. to I5 in. thick, and in round rods from j in. to 5 in. in diameter. Tobin bronze is readily forged at a cherry-red heat either by hand or by machinery, and also works well in the lathe. The elastic properties of this material are shown in Fig. 9. 794. The Bronzes — Copper-tin Alloys. — Since tin is added to copper principally to harden it,^ — ^it strengthens copper very Uttle, — the copper- tin alloys may be regarded as a kind of hardened copper. The ancients used these alloys for their cutting-tools, and they are used now largely on account of their hardness and non-corrosive properties. The useful range of composition is 5 to 25 per cent of tin and 75 to 95 per cent copper. In cast form the tensile strength of these alloys varies from 28,000 to 35,000 lb. per sq. in., maximum tenacity occurring for a tin content of about 18 per cent. The crushing strength of cast bronze rises from approxi- mately 42,000 lb. per sq. in. for pure copper to a maximum of 150,000 lb. per sq. in. for bronze carrying 25 per cent of tin. The ductility of the bronzes is low. Cast bronzes carrying about 4 or 5 per cent of tin are the most ductile, elongating about 14 per cent in 5 in. With more than 5 per cent of tin the alloys lose most of their malleability when cold. The alloy having 12 per cent of the tin has an elongation in 5 in. of only 3 or 4 per cent and with 20 per cent tin it becomes practically nil. The tenacity also diminishes rapidly as the tin content, of the alloy is raised above 20 per cent. Gun metal is one of the strongest bronzes. It contains about 10 per cent tin and was formerly much used in casting guns. It is now used to some extent for strong castings. Bell metal is the hard sonorous bronze carrying about 20 per cent tin, used in making beUs and gongs. By alloy- ing 2 parts copper with 1 part tin a beautiful, hard, perfectly white metal is produced, called speculum metal. When pohshed this metal can be used for mirrors and reflectors. 795. Complex bronzes, are alloys of copper and tm with one or more additional metals. Among the more useful are zinc bronzes, phosphor bronzes, and lead bronzes. The Copper-tin-zmc Alloys. — As shown in Fig. 8, the valuable ternary alloys are those in which copper forms the controlling element. This diagram is based on that principle in geometry which makes the siun of the normals from any point on the interior of an equilateral triangle equal to the altitude of the triangle. If the three altitudes be each taken as a scale of equal parts on which are indicated proportions (percentages) of copper, zinc, and tin respectively, these ranging from zero to 100, then to the same scale the sum of the three normals from any point in the triangle BRASSES AND BRONZES 745 will be 100, and hence these three normals may be used to indicate the percentages of the three metals which unite to form the alloy which is represented by that point in the triangle.* An alloy of any two of these finds its place along one side of the triangle, of which the three apices make the 100-per-cent ends of the three metal scales. A little study of Fig. 8 will make this clear. The contour-lines on this figure were drawn by J. B. Johnson after plotting on this triangle the tensile strengths of cast bronzes of known com- Oopper 100 Fig. 8. — The Tensile Strength in Pounds per Square Inch of Copper-zinc-tin Alloys in Form of Castings. (Compiled by J. B. Johnson, from Records of U. S. Test Board, 1881.) position from all reliable sources. From an examination of this chart it is at once evident that only those alloys near the copper apex are of any value, the strongest being, however, near the copper-zinc side, where the composition is about 59 per cent copper, 39 per cent zinc and 2 per cent tin. The tensile strength of such a casting, if properly made, is about 60,000 lb. per sq. in. It is too brittle, however, to be of much value. The most valuable alloys are those having an ultimate strength of from 35,000 to * This method of representing these triple alloys was first used by Dr. R. H. Thurston, Trans. Am. Soc. C. E., 1881. 746 NON-FERROUS METALS AND ALLOYS 40,000 lb. per sq. in. tensile strength, with 20 to 30 per cent elongation. This is found in the vicinity of 75 to 85 per cent copper, 17 to 5 per cent zinc, and 8 to 10 per cent tin. It must be understood, however, that so much depends on the purity of the ingredients and on the manipulation of the process of melting and cast- ing, that this chart, or any similar record, must be taken as showing what may be obtained rather than what will be obtained from the use of these particular mixtures. Government bronze or Admiralty metal, consisting of 88 per cent copper, 10 per cent tin and 2 per cent zinc, is a zinc bronze much used for valves, fittings, gears, and nuts where good strength is wanted. This metal has, when cast in sand molds, a strength of 30,000 to 35,000 lb. per sq. in. with a poorly defined yield point of 15,000 to 17,000 lb. per sq. in. The elonga- tion in 2 in. is about 14 to 16 per cent. When annealed for a half hour at a temperature of 700 to 800° C. the ductilitj' of the metal is much increased but the tenacity is practically unchanged. Government bronze cast in sand molds is considerably more ductile than that cast in chills. The ductihty of the latter may be greatly improved, however, by annealing, at the above-mentioned temperatures.* Govermnent bronze is not a satis- factory metal for parts subjected to temperatures above 260° C. Phosphor bronze is any copper-tin alloy made with phosphorus as a deoxidizer. Besides deoxidizing, it is also claimed that the phosphorus causes the tin to form a crystalhzed compound with the copper. It is mainly, however, as a cleanser of the melted metal from the oxide of copper that it is valuable. The phosphorus is added in the form of phosphor- copper or phosphor-tin, these containing phosphides of copper or of tin. For a malleable product, to be rolled or drawn into wire, the tin should not exceed 4 or 5 per cent, and the phosphorus should not exceed 0.1 per cent. For hard castings of great strength, as for pinions, valves, bearings, or bushings, use 7 to 9 per cent of tin and ^ to 1 per cent of phosphorus. A greater amount of phosphorus, up to 4 per cent, increases the hardness and brittleness. More than 4 per cent phosphorus will make the product use- less. Stress diagrams for phosphor bronze are shown in Figs. 9 and 10. The great toughness and high elastic limit of wrought phosphoP bronze render it valuable for making springs which are subject to coiTOsion. The best grades of phosphor bronze carr>'ing about 95 to 97 per cent copper, 31 to 4 per cent tin and somewhat over 0.1 per cent phosphorus are used with good success in turbine blades, f The United States Nav>' Department specifies for best grades of phos- phor bronze castings a minimum tenacity of 45,000 lb. per sq. in. and an * See Technologic Paper No. 59, U. S. Bureau of Standards, t Jour. Insl. Metals, Vol. 14, p. 56. BRASSES AND BRONZES 747 elongation in 2 in. of at least 20 per cent. The composition ranges for this metal are copper = 85 to 90, tin = 6 to 11, zinc<4, iron < 0.06, lead 0.2 and phosphorus < 0.5 per cent. This metal is used for gears, driving and main nuts on steering gears, and castings requiring good bearing qualities and high resistance to corrosion. Lead bronzes are much used for bearings, under heavy pressures. In most cases these bronzes are smelted with a very small percentage of phosphorus and are called phosphor bronzes, although the amount of phosphorus re- maining in the bronze is generally well under 1.0 per cent. When more than 70,000 60,000 60.000 -/ il' r ~ " a' 50,000 fl/ EtsW " ^ 1 , ^ r* ' cc to ' '/■ y / //i ' S 30j000 f 20,000 ii'< !y f '/1 ' jl '' a.'ll_SB_ 6Z Is coiApoi tion ii :onz ■"" H 10,000 ^ '" p L'OP )rtl >na «.= Ion ati ^ ,i = In ■) ^50,000 40,000 g 30,000 S. 20,000 10,000 Fig. 10.- 10 15 20 25 PerGBntage of Elongafion -Tension Stress Diagrams of Cast and Rolled Bronzes. {Tests of Metals, 1885.) Fig. 9. — ^Results of Tension and Compression Tests on Three Alloys Used for Valve Stems. Tobin bronze specimens were rolled, others were plain castings. (Russell, Jour. Assoc. Eng. Soc, Vol. 15, p. 207. Tests by J. B. Johnson.) 3 or 4 per cent lead is present in bronze bearings it segregates, forming soft spots in the hard matrix which rapidly wear and form cavities for the lubri- cant. For bearings in contact with hard steel and sub- jected to pressures over 1500 lb. per sq. in., phos- phor bronze carrying about 80 per cent copper, 20 per cent tin, and less than 1 per cent phosphorus works well. It is, how- ever, unsuited to high speeds, since it is likely to 30 748 NON-FERROUS METALS AND ALLOYS run hot. This metal is suited for turntable bearings and center bearings on swing bridges. For heavy tninnion bearings in contact with soft steel carrying less than the above pressure and operating at slow speeds the copper content may be raised to 83 or 85 per cent. A very common mix- ture for accurately lined machinery bearings is the 80-10-10 of copper, tin and lead with less than 1 per cent phosphorus. This bronze is easy to ma- nipulate but heats and wears more than Dr. C. B. Dudley's "Alloy B," con- sisting of 77 per cent copper, 8 per cent tin and 15 per cent lead. On the other hand the lead in the latter alloy has a pronoimced tendency to seg- regation during pouring and much skill is required to secure good bearings with it. It is used by the Pennsylvania Railroad for car journal bearings. 796. Cold Working of Brasses and Bronzes. — As with the ferrous metals so with the non-ferrous, cold working causes densification of the metal, decreases grain size, promotes an increase in tenacity, and decreases duc- tility. Thus Davis * has shown that sheet brass (2 Cu to 1 Zn) varying from .01 to .06 in. in thickness increases in strength directly with the per cent reduction in area produced by rolling. For a reduction in area of 60 per cent the average strength was doubled, the per cent elongation in 2 in. was decreased to between xo ^-nd t^ of the normal value, and the duc- tility as measured by the cupping test (Art. 798) was reduced to about \ of its normal value. Further examples of the effect of cold roUing and cold drawing of the non-ferrous metals appear in Figs. 2, 6, 7 and 14. It is probable that cold drawing causes more dangerous internal deformation within parts which are to withstand tensile stress than cold rolling or hammering, since cold drawing produces tensile stress in the surface layers and compressive stresses within, whereas stresses of opposite character are set up by cold rolling or by hammering. The magnitude of the internal stresses so produced is quite variable ranging from 3000 or 4000 lb. per sq. in. to 50,000 or 60,000 lb. per sq. in.f When above 5000 or 10,000 lb. per sq. in. such stresses seriously impair the strength of the metal. Steps should, therefore, be taken to remove internal stress by annealing or springing as mentioned in the next article. Although there are, in general, internal stresses — necessarily of opposite sign — induced by cold working, the results gotten by E. H. Peirce % work- ing on hard-drawn copper wire show that the hardening effect of suclj treat- ment is practically uniform throughout the mass of the metal and is not confined to the skin as has sometimes been stated. 797. Season cracking § is a type of failm-e common to rods, tubes, * Proc. A.S.T. M., Vol. 17, p. 165. t See Technologic Paper No. 82, U. S. Bureau of Standards. t Proc. A. S. T. M., , Vol. 17, p. 115. § See E. Heyn in Jour. Inst. Metals., Vol. 12, No. 2, p. 3; Technologic Paper 82, U. S. Bureau of Standards; Topical Discussion in Proc. A. S. T. M., Vol. 18. BRASSES AND BRONZES 749 sheets, cartridge cases and other articles made of brass or bronze. It is especially prevalent in brasses containing 60 to 80 per cent copper, in manganese bronze, Tobin bronze, and has been observed in aluminum and aluminum bronze. It may take place when the part appears to be under no stress; it may occur in a bolt or rod after it has carried a normal load for a considerable time, or it may happen when the brass is put into the annealing oven. The essential cause of "season cracking " is initial internal stress — produced by cold work, by burning in of defects, by quenchirig or by coohng strains induced in molding, coupled with one or more of the following: (a) Corrosion, the metal being under no external stress; (6) Applied stress of less intensity than the normal elastic limit; (c) Temperature changes. Although acting in different ways these combinations effect an over- stressing at a certain region in the metal and cracking finally ensues. Considering the predominating cause of failure, "corrosion cracking" seems a more exact term to apply to the phenomenon. Season cracking may be avoided by proper annealing, or by springing or by a combination of springing and annealing. Annealing at low tem- perature effects a removal of the greater part of the internal strain without producing material loss in hardness or strength. Indeed there is evidence to show that, in some cases, such annealing raises these properties.* To be effective in preserving high strength and good ductility the annealing temperature must be less than the temperature at which grain growth begins in the metal. This temperature varies inversely (but not in direct ratio) with the amount of permanent deformation which the metal has suffered and with the time the metal is held at a given temperature. For brasses containing 2 parts copper to 1 part zinc the range of annealing temperature which is effective in relieving initial stress without diminishing hardness is 200 to 300° C. Springing consists in bending a bar backwards and forwards in radial planes until all outer fibers have been permanently lengthened. This treatment reduces the intensity of tensile stresses which exist at the sur- face in cold-drawn bars, and is sometimes a necessary preliminary treat- ment to prevent cracking of parts in annealing. 798. Special Tests for Brasses and Bronzes. — On account of the large internal stresses present in many cold-rolled and hard-drawn objects of brass and bronze and the harm which may come from them, simple tests for their detection are needed. The most precise method with a rod or tube specimen consists in making accurate measurements of length on three or more surface elements, turning off or boring out a predetermined j_ *Mathewson and Phillips, Trans. A. I. M. E., Vol. 54, p. 608. 750 NON-FERROUS METALS AND ALLOYS amount of metal and measuring again. Knowing the modulus of elasticity of the metal, the cross-sectional area before and after machining, and the original length, it is possible to compute the unit stress in each layer re- moved. Since this method necessitates taking a large number of readings with a comparator or strain gage and since the machining cuts must be very small and slowly and accurately done, it requires too much time for commercial purposes. A more rapid method of measuring the internal stress in a bar has been devised by Mr. S. W. Miller. A specimen is cut from the straight bar, which is to be examined, as shown in Fig. 11. If the outer surface of the TH ,. uTii . a •„ bar was in tension that surface of the speci- FiG. 11. — Miller's Specimen . ^ for Measuring Initial Stress men Will be concave after its removal from in Brass Rods. the bar, the reverse would be true if the stress was compression. By measuring the mid- ordinate to the curve, assuming circular curvature and the neutral plane passing through the gravity axis the change in unit stress on the outer and inner fibers may be computed from these formulas: 8Efr WEfr So=^ and S^=^^. Here So and Si = changes in unit stress at the outer and inner fibers respectively; ^ = modulus of elasticity; /= deflection at center of specimen; r = radius of rod; « I = length of rod. For thin sheets the procedure advocated by Merica and Woodward * is still more simple. A strip about 6 in. long and ^ in. wide is coated with paraffin excepting one of the broad surfaces and etched with acid until one-quarter the depth is removed. If the strip curves the mid-ordinate of the arc is measured and the average value of the original internal stress is computed from Z6tEf S=- 7P where i = original thickness of strip, /= mid-ordinate of arc after etching, and other symbols have same meaning as before. ♦Topical Discussion on Season Cracking of Brass, Proc. A. S. T. M., Vol. 18, Pt. 2. ALLOYS OF ALUMINUM 751 Detection of the presence of high initial tensile stresses in the surface layers of a piece of brass may sometimes be accomplished by immersing the part in a solution of mercurous nitrate (65 gr. HgNOs and 15 cc. cone. HNO3 per liter) for fifteen minutes to a half hour.* Badly strained pieces will frequently crack after this procedure. The cupping test has recently been strongly advocated f for determining the ductility and drawing qualities of thin sheet metal, especially brass. The test is made on a small sample of metal sup- ported between a die and annular holder. A round- nosed tool is gradually forced against the specimen and forms it into a cup as shown in Fig. 12. By determining the depth of the cup at fracture, a direct measure of the drawing quahty of the metal is obtained. Davis claims that this rapid test is far p^^ ^g — showine Ar- more accurate than the tensile test or scleroscope hardness test. It is also superior to the Brinell ball test for brass sheets under 0.05 to 0.08 in. thick. The Brinell test, however, is very satisfactory for determining the drawing qualities of thicker sheets. He also states that the roughness of the surface of the cup and the character of the fracture afford evidence of the grain size and will reveal defects. rangement of Speci- men, Tool and Dies on Erichsen Cupping Machine. (Proc. A.S.T.M., Vol. 17, PI. 2, p. 200.) ALLOYS OF ALUMINUM 799. Utility of Aluminum Alloys.^Owing to the softness of pure alum- inum, it is commonly alloyed with copper or zinc to improve its mechan- ical properties. About one-fourth of the entire alumimmi production is now utilized in making light, stiff alloys with these metals, a large portion of which are used in the automobile industry. Thus we find the light aluminum copper alloys used for pistons, cylinders and crank cases for both automobile and aeroplane engines, also for cooking utensils and strong hght parts which are die cast. The light alloys of alumimmi and zinc are used to less extent for gear cases, light castings of high strength, and for portions of scientific instnmients requiring lightness and rigidity. With small additions of manganese and copper the alimiinum zinc alloys have been used in the frames of Zeppelins. The heavy aluminum bronzes find use in steam valves, pump rods, spindles, springs, propellers, motor and engine gears where good strength and resistance to corrosion are essential qualities. 800. Aluminum Bronze is the rather inappropriate name applied to copper-aluminum alloys containing less than 11 per cent of alimainimi. It * Technologic Paper 82. f C. H. Davis, Proc. A. S. T. M., Vol. 17, p. 165. 752 NON-FERROUS METALS AND ALLOYS is made from the finest grades of copper and pure aluminum and is said to be improved by resmelting. On account of the rapidity with which alum- inum oxidizes, the alloys must be smelted under a layer of charcoal and should be poured into the molds with as Uttle agitation as possible. Cast- ings must be provided with large gates and risers to provide against exces- sive shrinkage. The ductility of the almninum bronzes is very high and nearly con- stant for variations in aluminum content up to 7.3 per cent. Bronzes with more than 7.3 per cent aluminum show decrease in ductihty as the aluminum increases and those containing 12 per cent are very brittle. The tenacity of these bronzes, however, increases directly with the alum- inum content up to approximately 10 per cent aluminum. The tensile properties of these alloys * are shown in Fig. 13. It will be observed that the ductility of small castings of these alloys is about the same as in the rolled rods. The bronzes containing less than 7.3 per cent alimiinum are highly resistant to torsional stress and readily rolled, forged and cold- drawn. Since they consist of a solid solution, the rate of cooling influences their mechanical properties very httle. Bronze with 7.3 per cent alimainum exhibited great toughness under impact and remarkable resistance to alternate bending stress. Bronzes containing over 7.3 per cent alumimma contain, besides the solid solution, a dark needle-like constituent, which is imstable and much influenced by heat treatment. The marked influence of quenching on the properties of bronze with 10 per cent aluminum is also well shown in Fig. 13. This alloy in rolled form has about the same tenacity, elastic ratio, hardness, hardening capacity and toughness as 0.35 per cent carbon steel. Experiments by Corse and Comstock f have shown that cast rods of 10 per cent aluminiun bronze quenched at 850° C. and annealed at 600° C. have an ultimate strength and elastic limit of approximately 95,000 and 45,000 lb. per sq. in, respectively, with an elongation of 10 per cent in 2 in. and a capacity to endure over 5,000,000 bending reversals producing an extreme fiber stress of 33,000 lb. per sq. in. Other tests by the Alloys Research Committee show that the 10 per cent alimiinum bronze has almost constant strength for increasing temperatures up to 700° C. but the alloy is much more brittle above 400° C. than at nonnal temperatures. The insertion of 1 per cent of manganese into a 10 per cent aluminvun bronze increases the yield point and ductility of the allo>' without producing material change in its strength or endurance under reversals of stress. J * From Eighth Report of Alloys Research Com. Proc. Inst. Mich. Engr., 1907. Pt. 1, p. 57. t Proc A. S. T. M., Vol. 16, p. 134. t See Alloys Research Com. Ninth Report Proc. Inxt Mech. Engr., 1910, Pt. 1, p. 130. ALLOYS OF ALUMINUM 753 Aluminum bronzes are almost incorrodible in sea water and are superior in this respect to Muntz metal or naval brass. The modulus of elasticity for aluminum bronze is about 18.000,000 lb. per sq. in. Per cent Aluminum Fig. 13. — The Influence of Aluminum on the Tensile Properties of Aluminum Bronze. (Alloys Research Com., Proc. Inst. Mech. Engr., 1907, pp. 113-133.) 801. Aluminum-copper Alloys. — By the addition of a small proportion of copper, generally less than 5 per cent, to "pure" aluminum, it is possible to secure a metal which is less liable to burning and to produce light castings that are stronger, harder and tougher than those made from aluminum. 754 NON-FERROUS METALS AND ALLOYS Some of the mechanical properties of these alloys are listed in Table 3. They do not possess as high resistance to corrosion in sea water as the aluminum bronzes, nor are they as satisfactory as " pure " aluminum for cooking utensils. As mentioned before these alloys are much used in the automobile industry. TABLE 3.— TENSILE PROPERTIES OF ALUMINUM COPPER ALLOYS (From AUoys Research Com., 8th Report) Per cent Copper. Condition. Diameter of Specimen. In. Ultimate Strength. Lb. per sq. in. Yield Point. Lb. persq.in, Per cent Elongation on 2 in. Per cent. 0.0 1.90 3.76 4.97 0.00 1.90 3.76 4.97 0.00 1.90 3.76 4.97 0.00 1.90 3.76 4.97 0.00 1.90 3.76 0.564 Sand cast. Slowly cooled. Sand cast. Quenched from 450° C. in water Hot rolled from 3 in. to Ij- rounds. Cold drawn. Ij-in. rounds. Annealed and drawn with anneal- ing to H in. 0.564 1.250 3^ M 10,250 10,400 16,840 17,560 11,300 11,210 15,790 16,360 14,550 24,400 37,700 32,850 19,460 33,600 44,800 39,700 16,600 30,900 37,850 4,256 7,390 10^960 12,310 5,375 8,060 12,760 13,880 9,850 14,320 20,300 19,920 19,030 31,370 41,450 35,600 15,660 28,900 34,700 19.0 6.0 4.0 4.0 22.0 7.0 4.0 4.0 35.5 27.5 20.0 19.5 19.5 13.0 7.5 6.0 23.0 16.5 8.0 802. Aluminum-zinc alloys containing less than 25 per cent of zinc are of the most commercial importance of the alloys of this group. As a class all of these alloys are very sensitive to high temperatures in melting and in solid form exhibit low strength and brittleness when heated above 50° C. Those having less than 15 per cent zinc are much used in constructions where a light, sound casting, which can be easily machined or forged into proper form, is desired. Alloys containing from 15 to 25 per cent of zinc are harder, stronger, but less ductile and more difficult to roll or draw. The alloys of high zinc content appear to suffer a decrease in strength when excessively worked either hot or cold. For example, the strength of alloys ALLOYS OF ALUMINUM 755 containing 26 per cent of zinc decreased when the bars were hot-rolled or cold-drawn below IJ in. in alloys are indicated in Fig. Unlike most of the minor metals and their alloys the aluminum- zinc alloys have well-defined yield points characterized by dropping of the scale beam during test. The modulus of elasticity for all of the light alloys is approximately 9,000,000 lb. per sq. in. Aluminum and zinc alloys containing about 5 per cent of aluminum are added in small percentages to the zinc baths used in galvanizing in order to render them more fluid. 803. Aluminum - magnesium alloys {magnalium) containing small percentages of magnesiimi., have been widely used as deoxi- dizers in copper smelting opera- tions. The alloy containing 6 per cent magnesium has very good mechanical properties and is somewhat lighter than piure alumimmi. It is easy to work, exceptionally strong, and duc- tile. Schirmeister f reports a tenacity of 42,000 lb. per sq. in., an elongation of 21 per cent and a Brinell hardness number of 69 for an alloy of this composition rolled at 450° C. diameter.* 14. The tensile properties of these 20 30 40 Per cent Zinc Fig. 14.— The Effect of Zinc on the Tensile Properties of Aluminum Zinc Alloys. (Alloys Research Com., Proc. Inst. Mech. Engr., 1912, p. 449, 472, 494.) Duralumin is another light alloy of exceptionally high strength. It con- sists X of aluminum alloyed with 0.5 per cent magnesium, 0.5 to 0.8 per cent manganese and 3.5 to 5.5. per cent copper. It has a tensile strength of 50,000 to 60,000 lb. per sq. in. and an elongation of about 8 per cent. * Tenth Report Alloys Research Com., Proc. Inst. Mech. Engr., 1912, Ft. 1, p. 331. f Stahl u. Eisen, June 24, 1915. t Mineral Industry, 1915, p. 21. 756 NON-FERROUS METALS AND ALLOYS ALLOYS OF LEAD, TIN AND ANTIMONY 804. Lead-tin alloys are principally used in making solder, pewter and toys. These alloys have rather low melting-pojnts, that of the eutectic containing 37 per cent lead being only 183° C. By adding tin to lead the strength and hardness are considerably increased. Fiuthermore, the alloys carrying more than 50 per cent lead remain pasty over a considerable range of temperature before completely solidifying. The latter property renders these alloys of value for plumbers' solder which ordinarily contains from 2 parts lead and 1 part tin to equal parts of each. For soldering tin, the alloy containing 2 parts tin and 1 part lead is much used, whereas for electrical work the best solders carry less than 10 per cent lead. 805. Lead-antimony alloys. — Antimony, like tin, serves as a hardener when added to lead but the useful binary alloys of these two metals cover only a limited range in constitution. The more useful of these alloj's contain from 10 to 25 per cent of antimony. The alloys richer in lead than the above are very soft; those richer in antimony are too brittle and hard to be of value for most piu'poses. Alloys containing over 13 per cent antimony consist of a comparatively soft eutectic in which are embedded hard cubical crystals of antimony. In bearing metals the presence of a limited mount of these hard crystals increases resistance to wear, but a large proportion causes the bearing to heat. The softer eutectic, on the other hand, readily adjusts itself to inequalities in pressure and, wearing more rapidly than the antimony, allows space for the lubricant. Alloys containing 12 to 17 per cent antimony are inexpensive and are used to some extent for bearings carrying Hght loads. For properties of some bear- ing metals of this class, see Table 4. Shot and bullets arq made from lead containing a small proportion of antimony to increase the hardness. 806. Lead-antimony-tin alloys are of great value for type metal. A satisfactory type metal must take a full sharp impression of the mold and be sufficiently rigid to withstand press action. The alloys of lead and anti- mony containing over 15 per cent antimony satisfy the former require- ment since they expand slightly on heating but they require a Uttl^ tin to increase their compressive strength and render them less brittle. The range in composition for these alloys varies from 2 parts lead, 1 part anti- mony and 1 part tin to 7 parts lead, 2 parts antimony and 1 part tin. Linotype and monotype machines use cheaper alloys containing 12 to 18 per cent antimony, 3 to 8 per cent of tin, and the remainder lead. Alloys containing 10 to 20 per cent antimony, 5 to 20 per cent tin and the remainder lead may also be used for bearings subjected to moderate loads (Table 4). Magnolia metal containing approximately 78 per cent ALLOYS OF LEAD, TIN AND ANTIMONY 757 lead, 16 per cent antimony and 6 per cent tin is one of the common bearing metals of this class. The range in pouring temperatures for these alloys is, however, more limited than for the equally serviceable but somewhat more expensive bearing metals consisting principally of tin. TABLE 4.— SHOWING PHYSICAL PROPERTIES OF WHITE METAL BEARING ALLOYS (From Rept. of Com. B-2, Proc. A. S. T. M., Vol. 18, Pt. 1.) AUoy FOBMDLA. Deformation of Cylindeh li in. Diam. by 2^ in. High at 70° F., in. Brinell Hardness. Melt- ing- Point. Deg. Cent. Com- plete Liqua- tion Point. Deg. Cent. Wt. Oz. per cu. m. Proper Pour- ing Temp- No. Cop- per, per cent. Tin, per cent. Anti- mony, per cent. Lead, per cent. At 1000 Jb. At 5000 lb. At 10,000 lb. At 70° F. At 212° F. era- ture, deg. Fahr. 1 2 3 4 5 6 7 1 10 11 12 4.5 3.5 8.3 3.0 2.0 1.5 n 91.0 89.0 83.33i 75.0 65.0 20.0 10.0 5.0 5.0 2.0 4.5 7.6 8.33S 12.0 15.0 15.0 16.0 15.0 10.0 15.0 15.0 10.0 ib'.o 18.0 63.5 75.0 80.0 85.0 83.0 85.0 90.0 0.000 0.0000 0.0010 0.0005 0.0010 0.0015 0.0010 0.0020 0.0040 0.0010 0.0010 0.0025 0.001 0.0015 0.0045 0.0025 0.0030 0.0050 0.0050 0.0090 0.0120 0.0100 0.0100 0.0170 0.015 0.0120 0.0070 0.0090 0.0090 0.0180 0.0230 0.0620 0.0840 0.1540 0.1190 0.2850 28.6 28.3 34.4 29.6 29.6 24.3 24.1 20.9 19.5 17.0 17.0 14.3 12.8 12.7 15.7 12.8 11.8 11.1 11.7 10.3 8.6 8.9 9.9 6.4 225 238 239 185 185 185 240 243 243 245 247 247 371 362 422 291 280 267 260 260 255 260 260 265 4.24 4.27 4.31 4.35 4.48 5.39 5.62 5.80 5.92 5.82 5.94 6.17 824 808 916 680 661 638 625 625 616 625 625 634 807. Babbitt metals are alloys with a tin base containing small propor- tions of copper and antimony. They are so called from the inventor Isaac Babbitt. The important babbitts consist of crystals of the rather hard antimony-tin compound (SnSb) surrounded by softer masses of tin. Soft varieties of babbitt carry about 4 or 5 per cent of copper and 6 to 8 per cent of antimony, whereas the harder alloys contain 6 to 10 per cent of copper and 8 or 10 per cent of antimony. An idea of the mechanical and physical properties of the more valuable of these alloys is furnished in Table 4 abstracted from Report of Com. B-2 of A. S. T. M., 1918. Since the rate of heating of such bearings under service conditions is dependent upon the size and distribution of the crystals of the copper-antimony compound, the temperature of pouring and rate of cooling must be care- fully controlled. Rapid chilling or very slow cooling causes heating of the bearing.* By heating the core of the mold it is possible to secure an inter- mediate rate of coohng such that the crystals will be well-defined, uni- formly dispersed throughout the mass and not over .01 in. in size. Such treatment leads to a more serviceable bearing. * Behrens and Baucke, The Metallographist, Vol. 3. 758 NON-FERROUS METALS AND ALLOYS 808. Alloys of Low Fusibility. — The following remarkable alloys, all of which fuse at very low temperatures, may be used as safety-plugs in automatic fire-spraying pipe-systems in mills and for similar purposes. TABLE 5.— FUSIBLE ALLOYS Name. Percentage of Ingredients. Fusing Tempera- Bismuth. Lead. Tin. Cadmium. ture, Deg. Cent. Newton's Rose's Darcet's 50 50 50 50 50 31 28 25 24 27 19 22 25 14 13 12 10 95 100 93 Wood's 66-71 60 Lipoirtz's CHAPTER XXVII THE EFFECT OF TEMPERATURE ON THE MECHANICAL PROPERTIES OF METALS EFFECTS ON IRON AND STEEL 809. Importance of Temperature Effects on Properties. — ^At the present time the ferrous metals are the principal materials for boilers, grates, fire-boxes, staybolts, engine cylinders and pistons, ladles, shaftingj rails, axles, refrigerating machinery and other machine parts, which are subjected to considerable variation in temperature or to long periods at higher or low temperatures. Often the breakage of such parts would result in loss of life or large financial loss. It therefore is imperative that the properties of these metals under such conditions be well under- stood. We shall next consider the more important effects of temperature on the mechanical properties of iron and steel. 810. Effects on Strength. — This subject has been very fully and carefully investigated at the Watertown Arsenal, and a full series of stress diagrams, siaiilar to that of Fig. 1, is shown in the report for 1888. The curves of Fig. 1 exhibit the action of a structural steel (0.20 per cent carbon) having a normal tensile strength at 70° F. of 70,000 lb. per square inch and an elastic limit of about 37,000 lb. per square inch. Elastic limits and ultimate strengths may be gotten from this figure. A better notion of the variation in strength of different carbon steels, wrought iron and cast iron with temperature, can be formed from Fig. 2. Study of Fig. 2 reveals that the ultimate strength of the steels and wrought iron does not vary greatly for temperatures between and 300° F., there being a slight sag in strength at 200° F. As the temperature is raised above 300° F. the strength increases until a maximum 10 to 15 per cent higher than the normal strength is reached at 500° F. Further increase in temperature is accompanied by a proportionate reduction in tenacity until at 1600° F. the strength is only 15 or 20 per cent of the normal. Corroborative evi- dence is also furnished by the data in Figs. 4, 5, 6, and 10. For information regarding strength of alloy steels at high temperatures see Art. 815. It is noteworthy that the tenacity of cast iron is not materially affected by variation in temperature up to 900° F. For increases in temperature above 900° F. the strength falls proportionately until at 1600° F. it is approximately 20 per cent of the normal value. 759 760 THE EFFECTS OF TEMPERATURE ON METALS 80,000 70.000 60,000 t; 50,000 • 40,000 CO 30,000 20,000 10,000 .4 6 8 10 12 U Eercentage o£ Elongation, in 5 Inches 16 18 Fig. 1. — Stress-diagrams of Steel Bars at Various Temperatures. Carbon =0.20"^, Manganese =0.45%. (Teste o/ Me«ais, 1888.) 180,000 400 600 800 1000 1200 Temperature in Degrees Fahrenheit Fig. 2. — Variations in Tensile Strength of Ferrous Metals with Temperature. {Tests of Metals, 1888.) EFFECTS ON IRON AND STEEL 761 In Fig. 3 may be seen the relative effects of slow and rapid applica- tions of stress on wrought iron and steel at different temperatures. At ordinary temperatures the quick loading develops a greater tensile strength than the slow loading. Between 250° and 600° F. for steel, and between 150° and 500° F. for wrought iron (figure at left), the quick loading gives a lower ultimate strength, while beyond these higher temperatures the quick loading again gives the greater strength. Similar effects for both ultimate strength and yield point of soft steel wire, under temperature variations between —90° and +200 °F., are indicated in the right portion of Fig. 3. When homogeneous steel or wrought-iron specimens are exposed to temperatures below the freezing-point of water the static strength] is higher and the ductility lower than at normal temperatures. As an example we cite a test* on a steel bar having a normal elastic limit and 100 200 300 400 500 600 TOO 800 900 1000 -50 , -100 Temperature in "Degrees Fahrenheit +50 +100 +150 +200 Fig. 3. — The Effects of Rate of Loading on the Strength of Steel and Wrought Iron when Tested at Various Temperatures. {French Commission Report, Vol. 2, pi. 20.) ultimate strength of 52,800 and 72,400 lb. per square inch, respectively, and an elongation of 29.3 per cent. This bar tested at the temperature of liquid air (—220° F.) exhibited an increase of 51 per cent in elastic limit and 35 per cent in ultimate strength, but in elongation it showed a de- crease of 63 per cent. 811. Importance of Effect on Elastic Limit. — In Fig. 4 combined curves for carbon steels showing mean variations in mechanical properties with temperature indicate that whereas the mean ultimate strength varies less than 15 per cent from the normal for temperature variations between and 700° F., the mean elastic limit decreases in direct proportion to the increase in temperature above 0° F. Therefore the ratio of the elastic limit to the ultimate strength — the elastic ratio — is much less at high temperatures than at ordinary temperatures. For 100° F. the mean * Test made at Watertown Arsenal, See Engr. Rec., Vol. 64, p. 65. 762 THE EFFECTS OF TEMPERATURE ON METALS value of the elastic ratio is 0.57, while at 500° F. it is only 0.36. Figs. 1, 3, and 5, showing results of tests on individual classes of steel, substan- tiate the above statements. For structural purposes, therefore, the working strength of wrought iron and steel must he regarded as regu- larly diminishing, while the tempera- ture increases, the rate of diminution per ' F. terrir- 120,000 a 80,000 g 40,000 200 400 600 800 1000 1200 Temperature In Degrees Fahrenheit Fig. 4. — Grand Mean Curves from Temperature Tests on heing about 4 Steel Rods. Cg^^ pgr 100' Diameter of rods, li in., of specimen 0.8 in. Ten degrees of hardness, . from 0.09 to 0.97% C. (resis o/ Afetois, 1888, p. 245.) inCTeaSe in perature. 812. The Change in Ductility. — Steel and wrought iron both exhibit a marked reduction in per cent elongation for temperatures in the vicinity 150,,000 30,000 100 200 300 400 500 600 700 Temperature of Speoimens.iu Deg. Fahrenheit 800 Fig. 5. — ^Variations in Strength and Ductility of Wrought Iron and Steel at Different Temperatures. (From Cornell University Tests in Jour. West. Soc. Engr., Vol. 1.) EFFECTS ON IRON AND STEEL 763 S 30 of 300° F., as the curves of Fig. 5 show. At this temperature wrought iron and soft steel have elongations of approximately one-third to one- half of the respective values at normal temperatures. The re- duction in elongation at this temperature for high carbon steels is not quite so marked. Minimum values for the per cent reduction in area of wrought iron and steel occur at somewhat higher temperatures, generally between 400 and 500° F., as indicated in Fig. 6. 813. The Change in the Modulus of Elasticity. — The results plotted in Fig. 6 and 7 show that the modulus of elas- ticity of wrought iron and of steel decreases as the tempera- ture increases. This decrease amounts to approximately 2 per cent per 100° F. increase of temperature up to 500° F. For higher temperatures the reduc- tion in stiffness is more marked, being about 20 per cent at 800° F. and 55 per cent at 1100° F. 814. Effect on Resistance to Impact.— The variation in the resistance to a single blow of eight varieties steel tested at different temperatures is well shown in Fig. 8. The composition of these steels is given in Tabic 1. a 30,000,000 I-! .c? an u at ^ 25,000,000 i 20,000,000 m o <» 3 15,000,000 ■o ,_^ / .#_ N \ / 05/ \ / SI \ / "v \ / -^. ) N^j, / y \ !>■ / \ -^ / \ '"•/,? / \ w . \ Nt^ N b MoJuluh ~sr~Ejl \ "'"'^ ^ V V \ " ' 200 400 600 800 1000 1200 Temperature in Degrees Fahrenheit Fig. 6. — The Effects of Variations in Tempera- ture on the Elasticity and Strength of Mild Steel. (Lea and Crowther, Engineering, Vol. 98, p. 488.) ' -o_ Ste 1 Ay 10 Te ts Carbo nO.lJ, to 0.8 f^ o— . Wro ffht I on -A Its ° —Gas >-Irou- -A-vrS Tests' 1 100 200 300 Temperature in Degrees Fahrenheit .m Fig. 7. — Effects of Moderate Variations in Temperature on the Modulus of Elasticity of Iron and Steel. (Tests of Metals, 1887.) 764 THE EFFECTS OF TEMPERATURE ON METALS Each curve represents tests on 50 to 60 specimens. Each 0.4X0.4X2.4-in. test-piece was made with a milled notch 0.08 in. wide and 0.08 in. deep, the notch being provided with a round bottom. Specimens were broken in a Guillery* machine over a 1.6-in. span and under an initial energy of 5000r 4000 U 3000 o. 3 P3 ' 2000 a 1000 400 600 800 lemgeraturein Degrees.E. 1200 Fig. 8. — Effects of Temperature on the Resistance of Various Annealed Steels to Impact. (Guillet and R^villon in Proc. I. A. T. M., 5th Congress, III4.) TABLE I.— COMPOSITION OF STEELS SUBJECTED TO IMPACT AT VARIOUS TEMPERATURES. (Guillet and RAvillon) Steel Per Cent op Annealing C Si Mn s P in Air at (°C.) 0.218 0.345 0.491 0.725 1.224 0.085 0.162 0.105 0.26 0.20 0.44 0.40 0.05 0.01 0.18 0.11 0.24 0.51 0.34 0.33 0.04 0.15 0.20 0.34 0.041 0.048 0.044 0.025 0.040 0.017 Ni=7.10 Ni = 4.38 0.013 0.068 0.062 0.013 0.023 Ni=2.99 Cr = 0.85 850 Soft 800 Half hard 800 Martin (hard) Tool 750 f Plane bars at I 700° 850 600 750 2 per cent Ni 7 per cent Ni Nickel-chrome 5210 in. lb. The tests show that the resistance of these steels increased slightly as the temperature rose from room temperature to a value between 250° and 400° F. The resistance to a single shock then diminished with increasing temperatures until a minimum resistance was reached at a temperature in the vicinity of 900° F., and that with further increase in temperature the resistance again rose. * This machine is provided with a fly wheel to which is attached a knife for breaking the specimens. The energy absorbed in breaking the test piece is measured by the diminution caused in the speed of the fly wheel. EFFECTS ON IRON AND STEEL 765 200 400 600 800 1000 °F. Temperature of AxLeB Tests have demonstrated that repeated blows or working at tempera- tures between 500° and 600° F. (a blue heat) greatly impair the ductility and toughness of wrought iron and structural steel. Experiments by C. E. Stromeyer* showed that the structural steel and wrought-iron bars, which in normal condition could be bent cold through an angle of 45° first on one side of axis of the test-piece and then on the other for 12 to 26 bends, stood only IJ to 3 bends at a blue heat. Tension tests by R. Krohn f on wrought iron, soft steel, and medium steel showed that the decrease in energy of rupture due to working at a blue heat was 56, 30.4, and 26 per cent, respectively, while the elongation decreased 53, 31 and 28 per cent, respectively. In certain experiments by T. Andrews t wrought-iron car axles heated to various temperatures suffered im- pact from a 2240-lb. tup dropping through a distance of 30 in. ; they were then turned over, the temperature restored and the blow repeated. Although the material itself was very non-uniform the results plotted in Fig. 9 demonstrate that the resistance was a minimum when the axles were tested at 570° F., a blue heat. „. „ 1 1. J.1- -J. r Fig- 9- — Effects of Temperature on the Fig. 9 also shows the necessity of E^^uranee of Wrought Iron Rail^yay making impact tests at the same tem- Axles to Alternate Bending under perature if the results of different tests Impact. (T. Andrews.) are to be compared. Although comparatively few impact tests have been made at low temperatures, the available information indicates that the resistance to shock diminishes as the temperature drops below room temperature. Andrews found in other tests § on wrought-iron axles that the number of blows required to produce rupture at 100° F. was 50 per cent greater than at 0° F. Axles broken at —18° F. exhibited a crystalline fracture perpendicular to the axis of the piece; those broken at 300° F. showed a fibrous uneven fracture. Impact tests by Goerens and Hartel || on mild steel show a great increase in brittleness over the results at normal temperatures when the specimens were broken at —103° F. and below. The bar (Art. 810) tested under tension at the temperature of Hquid air required approximately one-half as much energy to rupture it as at * Proc. Inst, of Civ. Engr., Vol. 84, p. 114. t Reported by G. Henning in Engr. News, Vol. 27, p. 42. J In a Bessemer Premium Paper before the Soc. Engr. (London), 1896. § Proc. Inst. Civ. Engr., Vol. 94, p. 209. II Zeitschrifi fiir anorganische Chemie, Vol. 81, d 130. 766 THE EFFECTS OF TEMPERATURE ON METALS normal temperature, thus showing its increased fragihty at low tem- peratures. 815. Effect on Hardness. — An elaborate series of tests by F. Robin (reported in Rev. de Metal, Vol. 5, p. 893; Vol. 6, p. 180) in which the Brinell method was used, show that the curves between hardness and tem- perature are of of the same general character as the curves between tensile strength and temperature. TABLE 2.— BRINELL HARDNESS OF SPECIAL ALLOY STEELS AT VARIOUS TEMPERATURES. (Robin) ALL STEELS TESTED AS RECEIVED EXCEPT AS NOTED Hardness at Composition in % Kind of steel. -60 -58 100 212 400 752 600° C. 1112° F. C. Cr. w. Co. Va. High sDeed 385 315 355 655 540 415 375 640 300 340 545 355 625 335 165 350 660 515 465 350 345 430 290 300 340 345 445 250 135 320 415 480 400 315 295 290 225 170 180 250* 250 160 80t 230 160 .65 .50 1.00 .30 .30 .30 .80 .80 1.2 1.2 6.06 3.20 8.00 18.5 14.0 20.8 6.0 5.0 High speed High speed Mo. 2.0 2.0 0.5 Molybdenum (N) Molybdenum .... (H) Molybdenum Vanadium (A^) 7 Vanadium (H) 7 6.0 6.0 Tungsten (N) Tungsten (H) Nickel Ni. 16.0 27.0 Nickel Chrome (N) 1.18 1.18 1.37 1.37 Chrome (H) 50° C. • 250° C. 400° C. 600° C C. Mn. Si. P. S. 1 Carbon (N) 'Carbon (H) 2 Carbon (A^) 2 Carbon {H) 'Carbon (N) « Carbon {H) Wrought iron 290 350 265 690 205 630 105 320 400 280 520 240 560 155 285 325 245 325 225 355 125 180 160 110 120 35 2.02 2.02 1.08 1.08 .60 .70 .04 .28 .28 .30 .30 .72 .53 .14 .25 .25 .12 .12 .11 .34 .11 .013 .013 .012 .012 .022 .077 .018 .017 .017 .020 .020 .018 .053 .020 N = a.s received. i?=hardened. * Estimated, t At 900° C. i Hardened in water at 1150° C, austenitic. » Hardened at 820° C. ' Hardened at 850° C, mar- tensitic. uT^J''^ u ^"'""iFi^es the more important results of Robin's work. The high, uniform hardness ?'inno 'I.'' -^y. "'° nieh-speed steels and by the molybdenum and tungsten steels at temperatures up to Lff.n.H„'?7m5'S' TK°?-Tt *''j"'° hardness of the hardened carbon steels which were materially softened at 700° F. The high hardness of the 27 per cent nickel steel at 900° C. (1652° F.) is also note- worthy. Since certain comparisons by Robin indicate that the hardness is proportional to the strength for temperatures up to 400° C (752° F.), this series of experiments furnishes important intormaS concerning the relative strengths of alloy and ordinary carbon steels at high temperatures EFFECT ON ALLOYS AND METALS 767 816. Effect of Specific Gravity. — Tests by Langley * show that specific gravity of steel increases from 7.76 at white heat to 7.83 as the tempera- ture falls to a black heat. EFFECT ON ALLOYS AND METALS MUCH USED IN MACmNE PARTS 817. Description of Tests. — Owing to the extensive use of brasses, bronzes and other alloys in valves, shafting, parts of pumps and engines often subjected to temperatures from 400 to 700° F., a knowledge of the effects of such temperatures upon the mechanical properties of these metals is also essential if safe and economical designs of such parts are to be made. One of the most extensive series of tests thus far made on the effects of high temperatures on the mechanical properties of alloys was reported by Bregowsky and Spring to the Sixth Congress of the I.A.T.M.f We shall now present the main results of these investigators. Their experiments included both tensile and torsion tests. Round bars with the gauged portion turned down to a constant diameter of 0.65 to 0.85 in., depending on the size of bar as received, were used. The gauged length of the tension specimens was 2 in.; of the torsion test-pieces, 8 in. All metal was obtained from commercial foundries and all specimens for a given series of tests were from the same heat. Temperatures were secured through resistance coils which were placed around the specimens, due care being taken to insulate the specimen and to reduce the heating effect due to magnetic induction to a minimum. Each point on the diagrams rep- resents from 2 to 10 results. In the tension tests the yield point was gotten by dividers; in the torsion tests a troptometer was used to measure detru- sions. The compositions of the various metals tested may be found in Table 3. 818. Effect on Tensile Properties of Alloys.— Fig. 10 shows the effects of variations in temperature from room temperature to 1000° F. on 16 commercial alloys. It should be noted that both the ultimate strength and yield point of the copper-tin bronzes and the aliuninum bronzes remain fairly constant for temperatures between 70° and 400° F. For increasing temperature both of these stresses decrease. The brasses, manganese bronze, and Monel metal exhibit a considerable falling off in strength as the temperature is raised above 70° F. It should also be noted that with the exception of manganese bronze and Monel metal the duc- tility of the brasses and bronzes is very little at temperatures above 600° F. The high strength and ductility exhibited by the rolled Monel metal at all temperatures is remarkable. * Am. Chem., 1876. t A good bibliography on this subject may be found in the Proc. of the Fifth Congress of the I.A.T.M,, entitled "The Influence of Increased Temperatures on the Mechanical Qualities of Metals," by M. Rudeloff. 768 THE EFFECTS OF TEMPERATURE ON METALS TABLE 3.— CHEMICAL ANALYSES OF ALLOYS AND METALS USED IN TESTS AT VARIOUS TEMPERATURES. (Bhegowsky and Spring) Material. Composition in Per Cent. Mark. Name. Cu Sn Zn Pb Fe Al Alloys used in Tensile Tests. 1 2 3 4 5 6 7 8 9 10 16 18 G H I J K Copper-tin bronze (3) Copper-tin bronze Brass Aluminum bronze Aluminum bronze Cast manganese bronze . . . . U. S. Navy brass S-C U. S. Navy bronze M(2) . . U. S. Navy gun bronze C. Cast Monel metal Rolled rod brass Rolled Monel metal S7 02 HH 50 8H 19 H4 H4 8S 86 ■W 10 m 32 HH 92 «7 HO 27 11 fi2 30 27 22 12.46 0.20 0.06 10.22 0.00 tr. 5.69 5.03 3.02 0.03 0.16 0.48 0.15 0.17 0.51 39.05 tr. 3.98 12.80 2.78 7.72 3.62 1.22 10.40 1.31 0.39 0.08 . 64.79 0.13 0.00 34.84 2.53 (Ni 68.64) 0.30 0.38 0.20 0.14 0.75 2.21 0.24 0.23 0.11 5.46 0.15 2.38 4.90 9.67 0.32 0.225 0.035 Alloys used in Torsion Tests. Parsons' managnese bronze . IJ in. rolled Monel metal. . Rod brass Tobin bronze Elephant (phosphor) bronze . Delta-metal 59 58 27 08 Rl OS 59 86 95 52 56 5B 64 (C 0.186) 18 80 3 87 76 38 08 (Mn 1.52) 35 72 38 94 39 36 0.00 0.28 2.34 0.00 0.00 0.56 1 Al 1.220.34 2.50 ... 0.42 0.46 0.16 40 Mn 0.055 2.33 1.56 Ni 68.40 P 0.0015 0.307 0.004 Material. Mark. Composition in Per Cent. G C C C 11 14 15 17 A B C D E r p N Soft cast-iron (3) Cast steel (2) Cold-roUod shafting. . . . 30% nickel-ateel, rolled. Ferrous Metals used in Pensile Tests. 3.31 0.302 0.140 0.285 Ni 30.92 Ferrous Metals used in Torsion Tests. Cold-rolled shafting Cumberland C. R. shafting. O. H. Machinery steel 3i% nickel vanadium steel. 2b% nickel-steel *. 30% nickel-steel 35% C. Cumberland C. R . Vanadium Tool Steel .... 0.093 0.083 0.084 0.365 0.IS6 0.275 0.375 0.722 3.25 25.03 30.92 Cr 0.49 Va 0.145 2.57 0.22 0.031 0.14 O.OII 0.024 0.024 0.132 0.140 0.120 0.160 0.60 0.61 0.80 2.80 0.73 0.50 0.49 0.45 2.80 0.51 0.32 0.103 0.068 0.108 0.017 0.117 0.110 0.029 0.042 0.017 0.50 0.034 0.73 0.045 0.079 0.011 0.198 0.101 0.013 0.032 0.011 0.013 014 The behavior of the cold-rolled shafting and the cast steel is in accord- ance with the data of Art. 810 and 812. The 30 per cent nickel steel shows similar changes in strength properties but exhibits much higher dijctility at temperatures under 600° F. than either of the other steels. 819. Effect on Torsional Properties. — Data on the strength and angle of twist under torsion is given for 15 metals in Fig. 11. With the excep- tion of the carbon steels, all of the metals tested show a progressive falling off in torsional strength as the temperature is increased above 70° F. The curves for the carbon steels are somewhat similar to the tensile strength — temperature curves. In these tests also, the Monel metal shows both high-shearing strength and ability to withstand severe overstrain. EFFECT ON ALLOYS AND METALS 769 820. Effect on Modulus of Elasticity. — It is to be deplored that the effects of temperature on the stiffness of these metals was not noted. From tests made at the Berhn Testing Laboratory in 18P3 it appears that the . Tensile Stren^h . Yield Point ..Reductloa of Areot . Elongation (Temperatures in Degrees Fahrenheit Fig. 10. — Effects of Variation in Temperature on the Tensile Properties of Different Commercial Alloys. (Bregowsky and Spring.) modulus of elasticity copper and cast delta metal increase 10 to 15 per cent as the temperature increases from 70 to 200° F. and then fall off rapidly as the temperature is further raised, reaching room-temperature values again when the temperature reaches 400° F. Rolled delta metal 770 THE EFFECTS OF TEMPERATURE ON METALS exhibited more pronounced diminution of stiffness with increase in tem- perature than did the cast delta metal. A 4 per cent manganese bronze had as high modulus at 600° F. as at 70° F. soooo liOOOO 40000 30000 20000 .10000 V70000 coooo i 50000 I 40OOO '• 30000 \ 20000 I 10000 t i 130000 I \ 120000 • iioooo 100000 90000 soooo 70000 60000 soooo 40000 30000 .^fForeional Modulus of Haptare , Total Twist in Turns — Torsional Yield Point Ino.'e 25y l (5) i ^S'l '■ ^P In these formulas P and P' may be either of the same or of opposite signs. If of opposite signs, then the second term of the denominator becomes positive. The use of the diagram will be illustrated by two examples. Example 1. — Let the minimum load = 0.7 of the maximum load, and of the same sign; the ultimate strength of the material = 60,000 lb. per square inch; and let the factor of safety be 4. Find the maximum working stress. P' Here p- = 0.7. Enter the diagram for this ratio, on the right hand side because P' and P are of the same sign (both tension, both compression, or both shear in the same direction), pass up on the 0.7 ordinate till the curve of 'actor of safety of 4 is intersected * The Sibley Journal, Dec, 1901. 784 FATIGUE OF METALS thence horizontally to the 60,000 lb. strength line, and thence upward to the scale of working unit stress at the top, determiniBg a value of 11,500 lb. per square inch. This SCALE OF WORKING STRESSES \ \ V \ \ \ I \ \ \ / B \ \ \ \ \ \ l\ \ \ \ \ / ^ \ «, \ \ \ \ . 1 \ \ # \ \ S \ / / \ \ \ ^ \ % \ f \ \% \ / V. \ ^ s \ \ \ \ V \ \ \ \ / 1 % \ \ s \ \ \ \ \ \ \ \ \ \ / \ \ \ \ \ \ \ \ \l \ \ \ \ \ I , / \ \ \ \ S, \, \^ k \ \ \ \ \ Y / C \ \ \ \ \ \ \ 1 \1 \ \ \ \ 1 \ \. \ / \ \ s s \ \ \ \ \ \ \ \ \ \ \ \ / / \ \ \ \ s \l 1 \ \ \ \ \ \ \ \ / \ \ \ \ N\ \ \ \ X ' \ \ \ / \ \, \ ix- V \- ^- \I\_ r f / \^ \^ N^ S^ A X A\ \ \ / / \ \\ .\ \ \ \^' \x \ \, / \ X \\^ vW \K A > \ X^ k x- \\\ Vl A <0^ P^ \ \\ V w \V\ \ \\ i^ loj ><^ \\ \\V \\\ \\ \ \ f tit ^^ ^ ^. s\' \\\\ \ \\ \ n? ^ ^ ,^ n\ A \\\\ \\ \\ \ ^ ^^ ^^ roi -■^ ^\ \\ \\ \ ^ n^ r-?? k-\^ o \ n\\\\ ^^ \V w ■pCf C^ UJ 11 ^ w \\ ^w \\\ t; < t/1 LU 5 LiJ S o < D UJ S I y CC < > ^ KIMlj M AND r n cc OP >os FE SIGN SAME SIGN A -1.0 -0.8 -0.0 -0.4 -0.2 +0.2 +0.4 RATIO OF MINIMUM TO MAXIMUM LOAD + 0.6 + 0.8 +1.0 FiQ. 8. — Diagram for Finding Working Stresses for Variable Loads. (Designed by John H. Barr.) is the working unit stress for this material for a real factor of safety of 4, when 0.7 of the maximum load is removed and replaced an indefinite number of times. FORMULAS OF MOORE AND SEELY 785 Example 2. — For the same material, let 0.5 of the maximum load be imposed in the opposite direction an indefinite number of times, and find the worldng unit stress for a factor of safety of 4. Enter the diagram for the ratio 0.5 on the left side, pass up to the factor of safety of 4, thence horizontally to the 60,000-lb. line, and thence vertically to the scale of working unit stress at the top, determining the value of 6000 lb. per square inch. This is the working unit stress for this material, for a real factor of safety of 4, when 0.5 of the maximum load is imposed an indefinite number of times in the opposite direction. In using the Barr diagram it must be remembered that the diagram is based upon formula (3). Experimental results upon which this formula rests were determined from repetitions which were practically all within 10,000,000. The stress as determined from the Barr diagram with a factor of safety of 1 would be such a stress as would cause failure for repetitions within 10,000,000. Moore and Seely * have found that a factor of safety of 1.8 corresponds to an increase in repetitions for failure of something over 100 times A factor of safety of 2 on the stress as found from the Barr diagram should, therefore, ordinarily be ample to take care of the matter of repetition of stress. Judgment must determine the additional factor of safety necessary to take care of the possibility of sudden shocks or imexpected stresses. As has been stated previously, Bairstow found that when the mean unit stress employed is tensile, there is a permanent elongation even when the maximum unit stress is less than the ordinary static yield point. For this reason, when using the Barr diagram for ratios of minimum to maximum stress from to 1, no stress determined from the diagram should be used as a working unit stress unless it is well within the static elastic limit of the material. 836. Formulas of Moore and Seely. —Very often in practice in the design of piston rods, connecting rods, hne shafts, turbine shafts, automo- bile axles, and many other machine parts, the number of repetitions of stress which a part may be called upon to withstand can be calculated. Moore and Seely f have developed formulas which may be used in such cases, one of the variables in the formula being the niunber of repetitions required for rupture. The formulas are as follows: ^"il-Q)Ny> ^^^ * Proc. Amer. Soc. Test. Mat. 1916, Vol. 16, p. 470. t Proc. Amer. Soc. Test. Mat. 1916, Vol. 17, p. 470. 786' FATIGUE OF METALS in which S is the upper limit of unit stress in pounds per square inch which will cause rupture after N repetitions of stress; Q is the ratio of the minimum stress to ;S; and B is a constant depending upon the kind of material. Formula (6) is recommended for use in designing members whose failure would endanger life or limb; formula (7) for cases in which danger to life or limb is not involved. The following tentative values of B have been suggested by Moore and Seely: Material Structural steel and soft machinery steel Wrought iron Steel, 0.45 per cent carbon Cold-rolled steel shafting Tempered spring steel Hard-steel wire Gray cast iron Cast aluminum Hard-drawn copper LogB. 250,000 5.39794 250,000 5.39794 350,000 5.54407 400,000 5.60206 400,000 5.60206 to 800,000 5.90309 600,000 5.77815 100,000 5.00000 80,000 4.90309 140,000 5.14613 In using these formulas the same precaution must be observed as was mentioned in connection with the Barr diagram; that is, no stress calcu- lated from either formula should be used if it is greater than the ordinary static elastic limit. To illustrate the use of the formula, suppose that a member is expected to withstand 10,000,000 repetitions of stress. Moore and Seely are of the opinion that a factor of safety of 100 as based upon the number of repe- titions is not too large to use. Therefore, knowing B and Q, use 1,000,- 000,000 for A'', and solve for S. An alternative method is to calculate S for 10,000,000 repetitions and then divide it by a factor of safety of about 2. CHAPTER XXIX THE CORROSION OF METALS* By O. p. Watts! 837. Importance to the Engineer of a Study of Corrosion. — For nearly a century the problem of preventing the corrosion of metals has engaged the attention of scientific and practical men, and an enormous amount of experimental work has been done on this subject; yet we are still far from a satisfactory solution of the problem. With the enormous present use of metals this subject has become more important than ever before to every manufacturer and user of metals, to all owners of structures in which metal is largely employed, and to every engineer who has to deal with the construction or use of modern buildings or machinery. Even reinforcement deeply buried in concrete is not immune from corrosion. The statement of an eminent chemical engineer, that " rust taxes the people of the United States 5i)7,000,000 annually," is probably an under- rather than an over-estimate. Over 60 per cent of the zinc produced in and imported into this country is used for galvanizing, t to fight rust. Each year sees a larger extent of metal surfaces exposed to corrosive influences, and therefore the tax levied on human industry by the corrosion of metals is continually increasing. When to the direct loss due to the destruction of metal there is added the cost of paints and other coatings used to prevent corrosion, the total tax chargeable to this source is stupendous. Since the rusting of iron is the most important case of corrosion, and because it has been through the study of this phenomenon that our present conceptions of the nature of the process of corrosion of metals has been chiefly derived, it is fitting that this should receive special attention. * References: Sang's Corrosion of Iron and Steel. McGraw-Hill, 1910. Cushman & Gardner's Corrosion and Protection of Iron and Steel. McGraw-Hill, 1910. Friend's Corrosion of Iron and Steel. Longmans. 1911. Metal Corrosion and Protection. A very complete bibliography. Published by Carnegie Library of Pittsburgh. 1909. 64 p. 10 cents. t Associate Professor of Chemical Engineering in The University of Wisconsin. I W. A. Cook in Metal Worker, 1916, 85, 849. 787 788 THE CORROSION OF METALS 838. Great Variation in the Durability of Iron. *— Cast-iron water pipe laid in France between 1664 and 1668 was in use in 1904, and probably still supplies water to the great fountains of Versailles. London and Glasgow have records of 120 years of service from cast-iron water pipe. One of the most remarkable examples of the durability of iron is the column of Kuntab Minar erected at Delhi, India, 900 B.C., which is still in excellent condition after nearly 3000 years exposure to the weather. An American example of remarkable longevity in wrought iron was the suspension chains of the old bridge over the Merrimac River at Newbury- port, Mass., which was removed in 1909 after 99 years of service. The chains were seemingly good for another century of use, in spite of the fact that they had been exposed to the weather without any protection for the greater part of this period. On the other hand " in 1869 the British troop ship Megaera had to be beached at St. Paul's Island to prevent her sinking. Among other serious defects was a copper strainer fitted to a bilge suction pipe in a remote part of the ship. The action set up by it was sufficient to eat a hole right through the plates, and so admit water to such an extent that the ship had to be run ashore to save the crew." f Cases of the corrosion of boilers and of the copper and brass tubes of the condensers of marine engines have been described frequently, but at too great length to be quoted here. 839. Validity of the Acid Test for Determining the Relative Resist- ance of Metals to Corrosion. — Until comparatively recently most experi- mental work on the resistance to rusting of various kinds of iron and steel was based on corrosion by acids; but it is now generally admitted that the acid test is not capable of determining the relative durability of dif- ferent varieties of iron and steel under atmospheric conditions, and although this test will doubtless still be frequently employed, its findings will not be considered conclusive. The only reliable test appears to be that of subjecting the materials to actual working conditions, a process which usually defers the verdict for a number of years. 840. Relative Resistance to Corrosion of Wrought Iron, Cast Iron, and Steel. — In the last 75 years numerous tests have been carried out for the purpose of ascertaining the relative resistance to corrosion under various conditions, of wrought iron, cast iron, and steel. The most exten- sive of the early investigations are those of Mallet J on the action of air and water on a hundred different makes of these three materials. Summaries of many later experiments may be found in Chapter 15 of Friend's Corrosion of Iron and Steel. From more recent experiments * Mech. Eng., 34, 372; Am. Soc. Civ. Eng., 1867 (1), 26; Inst. Civ. Eng., 1853, 12, 487. t Admiral Corner in Jour. Inst, of Metals, 1911, 5, 115. t Report of Brit. Assoc, 1839, 1840, 1843. DISSOLVED AIR STIMULATES CORROSION 789 there appears to be little choice between good, modern wrought iron and steel as regards resistance to corrosion when exposed to the atmosphere, to sea water, or used as boiler tubes, or as pipes in water systems. Stahl * finds that " steel and iron tanks for storing sulphuric acid last equally well." The remarkable durability of cast-iron water mains has been shown by the examples already cited. In cases of corrosion by current straying from street railway tracks a similar leaching out of the iron often occurs, so that it is possible to drive a nail deeply into, or even entirely through a pipe that appears sound. Besides showing a lesser rate of corrosion both inside and outside, cast iron has an advantage over steel for water pipes in an initial thickness six or seven times as great. Another factor in the greater durability of cast-iron pipe appears to be the scale formed on the outside of the casting by contact with the sand of the mold. The removal of this increased two to four fold the rate of corrosion by air and by sea water, t 841. Pitting. I — In the use of metal for roofing, pipes, tanks, etc., the way in which the corrosion is distributed over the surface may be quite as important a factor in determining its usefulness as the actual weight of metal removed or converted into rust. If corrosion takes the form known as pitting, it is evident that the removal of a very small amount of metal may end its usefulness; whereas, if the corrosion takes place uniformly over the whole surface, very many times this amount of metal may be removed before the apparatus fails to serve the purpose for which it was intended. In neutral or faintly alkaline solutions in which the rust initially formed remains attached to the metal, the rusting of wrought iron and steel almost invariably takes the form of pitting, i.e., deep cor- rosion confined to small spots here and there on the surface. An explana- tion of this peculiar type of corrosion is given under the effect of rust. Art. 849. 842. Dissolved Air Stimulates Corrosion. — It is generally recognized that the presence of air in solutions stimulates the rusting of iron and the corrosion of many other metals and alloys. In 1843 Mallet § said, " It would be desirable that the feed-water of marine boilers were heated to above 190° F. before entering them, and means provided for the escape of the air disengaged, which now enters the boilers and aids much in corrosion." Since that time the same recommendation has been reiterated again and again.ll Not only is the corrosion of iron by hot water greatly * Sang's Corrosion of Iron and Steel, p. 59. t Thwaite, Jour. Iron and Steel Inst., 1880, (2), 667. t Matheson, Jour. Iron and Steel Inst., 1909 (1), 105; Rosenhain, Trans. Faraday Soe., 1916, 237. § Rep. Brit. Assoc, for Adv. Sci., 1843, 12. II Walker, Trans. Amer. Electrochem. Soc, 1908, 14, 186; Speller, Mech. Eng., 1916, 37, 245. 790 THE CORROSION OF METALS lessened by removal of the air, but pipes carrying aerated cold water are often similarly benefited. 843. Local Couples. — Whenever two electrical conductors of unlike materials are in contact with each other in an electrolyte a voltaic cell is formed, and there is a flow of current in the solution between them, one being anode and dissolving, if it is soluble in that particular solution, and the other being the cathode by which the current leaves the elec- trolyte. The effect of such short-circuited voltaic cells, or " local couples," in accelerating the corrosion of ordinary metals and alloys has been recognized and studied for nearly a century. An example of this is found in a report on the Panama Canal under date of January, 1915.* " The top gate-valve seal is of cast steel and is held in place by bronze bolts. In practically every instance corrosion has been excessive around the heads of the bronze bolts, cutting away the metal and in some cases allowing the bolts to loosen and fall out." 844. Purity a Factor in Corrosion. — It is evident from a consideration of the corrosive effect on iron of contact with many other metals and alloys, that electro-negative materials present as impurities in iron and steel, or intentionally added as in making alloy steels, are likely to have an accelerative effect on corrosion. From this standpoint wrought iron of the highest grade would be expected to resist corrosion better than steel, and the superior endurance of ancient iron over modern steel has often been attributed to the greater purity of the former. Several manufac- turers have adopted " purity " as their slogan, and have put on the mar- ket iron of exceptional freedom from impurities, claiming that their products resist rusting better than any other sheet iron or steel. In direct opposition to the advocates of highest purity are those who add 0.1 to 0.25 per cent of the electro-negative metal, copper, to iron, claiming that experiment f shows such " impm-e u'on " to resist atmos- pheric corrosion and attack by acids better than the pure irons. It is even contended that the remarkable durabihty of the iron of our fore- fathers, whose praises have been sung by many recent writei-s, owes its durability to the presence of a small amount of copper. | 845. Effect of Mill-scale on Rate of Rusting.^ — One of the most com- monly occurring negative materials which comes in contact with iron is the scale of black oxide which forms whenever iron is heated in contact with the air. This was early recognized as an accelerator of the rusting of iron, and its complete removal is specified, not only before pamting or coating iron with some other metal, but whenever it is to be exposed to corrosive conditions. Although mill-scale itself is very resistant to * Eng. News, 1916, p. 1005. t D. M. Buck, Jour. Ind. and Eng. Chem., 1913, 5, 447; 1916, 8, 209. jo. W. Storey, Trans. Amcr. Electrochem. Soc, 1917, 32, 211. NATURE OF THE PROCESS OF RUSTING 791 corrosion, it is brittle and therefore liable to be broken off in spots, and always contains cracks, so that when wet a short-circuited voltaic cell is formed, in which iron as anode corrodes more rapidly per unit of area exposed to the electrolyte than if the scale were not in contact with it. Oxide dissolved in steel should also accelerate rusting. Speaking of specimens of steel polished for metallographic examination, some of which contain oxide and others do not. Law says:* " If these are kept side by side in an ordinary room, it will be seen that the steels containing oxide begin to show signs of rusting long before the others, and in dilute acid solutions they corrode far more readily." 846. Nature of the Process of Rusting. — In spite of its occurrence for ages, it is only recently that the process of the formation of rust has been understood. It has long been known that oxygen and moisture are necessary for the rusting of iron, but the exact part played by each was not known. The two modern theories of the rusting of iron are the Add and the Electrolytic Theory. According to the former the presence of an acid is necessary to the formation of rust, but even so weak an acid as carbonic may serve. The acid causes the metal to dissolve, and the oxygen changes the dissolved metal to rust, thereby liberating the acid, which is then capable of dissolving more metal, and so the process goes on. After several years of careful experimenting by different investi- gators, it now seems to be established that moisture and oxygen are suffi- cient for the continued rusting of iron, so that the electrolytic theory of rusting is the one more generally accepted. The electrolytic theory postulates that when a metal dissolves it goes into solution as ions, i.e., atoms each carrying one or more (according to its valence) electric charges, and that it is only by giving up its charge that a metallic ion can escape from solution and become metal again. In the electrolytic cell this is merely visuaUzing Faraday's law, that the passage of a given quantity of current through an electrolyte is accom- panied by the dissolving of a definite amount of material from the anode, and the deposition of a chemically equivalent amount at the cathode. All that the electrolytic theory of the solution of metals has done is to extend the operation of Faraday's law, previously confined, in men's minds, to electrolytic and voltaic cells, to every case of the dissolving of metals. Although no flow of current can be detected when a piece of iron is dissolving in acid, it is believed that the ions of metal still carry electric charges into the solution and that the hydrogen displaced from the acid also carries its normal electric charge, just as if the metal were caused to dissolve as anode and the hydrogen to be deposited at some cathode by the application of an electromotive force external to the cell. * Jour. Iron and Steel Inst, 1907 (2), 103. 792 THE CORROSION OF METALS 847. The Function of Hydrogen in Corrosion. — The statement is sometimes made that it is the hydrogen of acids that corrodes metals. It is evident that this is not so. The function of the hydrogen of acids in corrosion is merely to supply ions that are easily displaced from solution by metals, and which also escape from their surfaces and so do not prevent free access of the electrolyte, as is the case with many metaUic ions, which, though more easily displaced than hydrogen, adhere more or less firmly to the surface of the metal on which they are deposited. 848. The Function of Oxygen in Corrosion.^ — So far there seems no need for oxygen in the electrolytic theory of the rusting of iron; but the dissolving of iron or any metal in an acid or any other electrolyte is (except where a change from a higher to a lower valence can occur, as with ferric salts) a case of displacement. Solution and deposition are inseparable; if deposition is prevented, the process of solution is also halted. It is here that oxygen comes into play as a deciding factor in corrosion. If two sheets of copper connected by a wire are suspended in a solution of copper sulphate, copper neither dissolves nor is deposited; the tendency toward solution or deposition at one plate is balanced by an equal tendency at the other. That solution shall occur it is necessary that a slight E.M.F. be applied to the system, when not only does copper dissolve from one sheet, but an equal weight of metal is deposited at the other. In order that a metal shall dissolve in an electrolyte, e.g. hydrochloric acid, it is necessary that the forces tending toward solution and deposition shall be unequal. This idea has been stated in various ways: that the chemical affinity of the metal for the acid radical must exceed that of hydrogen for the same; that the potential of the metal must be greater than that of hydrogen; that the potential of the metal must be greater than the discharge potential of hydrogen on it; or that the solution pressure of the metal must exceed that of hydrogen. Not only does it require a greater driving force to displace hydrogen on one metal than on another, but the force or potential required increases with the amoimt of hydrogen already displaced and present on the surface of the metal. It follows then, that the dissolving of a metal may begin in some electrolyte from which it displaces hydrogen, but may be brought to a standstiE before gas becomes visible and escapes, because the potential of the metal, or driving force, is no longer great enough to continue displacing hydrogen on a metal already highly charged with it. The only way in which dis- solving of the metal can then continue is for a portion of the hydrogen to be removed by some means, so that the force required to deposit more of it may again be less than the potential of the metal. To do this is the function of oxygen in the rusting of iron, first clearly stated by W. H. Walker in 1907.* " It was formerly thought that the action of oxy- * Jour. Amer. Chem. Soc, 29, 1264. CONDITIONS AFFECTING CORROSION 793 gen as a factor necessary in corrosion was simply to oxidize the iron ions thrown into solution, and to precipitate them as rust. While it is true that this reaction does take place, and is indeed the most striking function that oxygen performs, it is really a secondary one, which is simply inci- dental to corrosion and not a necessary part of the action. Its real accelerative effect is due to the fact that it depolarizes the hydrogen which is set free by the reaction, and separates out on the metallic iron.* Con- firmation of this view of the function of oxygen in corrosion is seen in experiments on the corrosion of metals in acids, f in which the addition of oxidizing agents caused the rapid dissolving of several metals by acids which alone have little or no action on them. 849. Conditions Affecting Corrosion. — The corrosion of metals, includ- ing the rusting of iron and any other process which involves as a pre- liminary step the dissolving of a metal, requires an electrolyte. The rate of corrosion is determined by Ohm's law, i.e., it varies directly as the E.M.F. and inversely as the resistance. Other conditions being equal the lower the resistance of the electrolyte the more rapidly is the metal attacked. The rapid increase in the rate of corrosion observed with rise of temperature is due in part at least to the lessened resistance of electro- lytes at high temperatures. It is of course to be expected that a metal will not dissolve in an acid which forms an insoluble salt with it; why acids attack some metals readily, but not others, although the salts of both are soluble, may be understood by a study of the following table; TABLE 1 Element. Potentials * in Normal. Discharge Potential of Hydrogen on Metal. Diff Sulphate. Chloride. Zn 0.524 0.162 0.093 -0.238 -0.515 -0.980 -0.974 0.503 0.174 0.087 -0.085 -0.095 -0.249 -0.550 -1,140 -1.356 Hg 0.548 Zn 0.468 Pb 0.408 Sn 0,298 Cd 0.248 As 0.152 Cu -0.002 Ni -0.022 Ag -0.082 Pt -0.112 Au -0.218 PtPt -0.238 Fe Zn Ni Cd Sn Pb Cu As Ag Pt Au Hg Cd 0.056 Fe .000 Sn -0.083 Pb -0.383 H -0.503 Cu -0.516 As -0.708 He -0.882 Ae -1.028 Pt -1.144 Au -1.528 * Neuman, Zeit. filr Phys. Chem.. 1894; 14, 203. * W. H. Walker, Jour. Iron and Steel Inst, 1909 (1), 69. t Trans. Amer. Elecirochem. Soc, 1917, 32, 17. 794 THE CORROSION OF METALS Corrosion of a metal by acids and by solutions of the salts of other metals can be predicted from Table 1. Except as limited by the insolu- bility of its salt, a metal is corroded by solutions of all metals below it in potential. If the potential of a metal exceeds the discharge potential of hydrogen on it, this metal is readily corroded by acids whose salts of the metal are soluble; but if its potential is less than the discharge potential of hydrogen, acids dissolve it only at the rate at which the dis- placed hydrogen dissolves in the electrolyte, is removed by the oxidizing action of the air, or is otherwise disposed of. The special power possessed by nitric acid of dissolving lead, copper, silver, etc., whose potentials are less than the discharge potential of hydrogen on them, is due to its being an oxidizing agent as well as an acid. The order and relative magnitude of the potentials of the metals not only foretells what metals will displace others from solution, but gives the order of chemical activity, and the stability of compounds of the dif- ferent metals, those of higher potential being more active and forming more stable compounds. The discharge potential of hydrogen is the potential produced by the accumulation of hydrogen on the metal to such a degree that it begins to escape in visible bubbles. The column marked " difference " is the result of subtracting the discharge potential of hydrogen from the potential of the metal, and its magnitude should be an index of the rate of corrosion of the different metals by acids, provided no oxygen or oxidizing agent is allowed access to the metal. For example cadmium is very high in potential, and from this consideration alone might be expected to be corroded rapidly by acids, but the negative value of the " difference " indicates that it should dissolve in non-oxidizing acids only at the rate at which the displaced hydrogen is removed by the electrolyte; this accounts for its slow corrosion when used as a reference electrode in the 30 per cent sulphuric acid of a lead storage battery. The protection of iron from rusting by immersion in a 5 per cent solution of sodium hydrate is predicted by the value —0.90 for the "dif- ference " ; iron is incapable of displacing hydrogen from this solution, hence does not dissolve, and no rust can form. The effect upon the cor- rosion of iron of electro-negative impurities such as particles of graphite, bits of scale left on the surface, or the cementite present in steels, is not simply a matter of the initial E.M.F. between the iron and the other substance, but depends on the diffrence between the potential of iron and the discharge potential of hydrogen on these materials. There are doubtless many incorrect values in the table, as most of the data is old, so that conclusions drawn from it can be relied on only in a broad and general sense. The effect of amalgamation in preventing the dissolving of zinc by acids is due to the fact that the discharge potential of hydrogen on mer- CONCENTRATION CELLS AND THERMAL E.M.F. 795 cury exceeds the potential of zinc; the remarkable diminution in the rate of attack of iron by sulphuric or hydrochloric acid, caused by the addi- tion of a solution of arsenic, is due to a similar action — arsenic is precipi- tated on the surface of the iron and serves as cathode in the voltaic cell of which iron is anode; but the discharge potential of hydrogen on arsenic exceeds the potential of iron, hence iron is unable to displace hydrogen from the electrolyte except as an infinitesimal layer, and corrosion ceases. 850. Rust a Stimulator of Corrosion.— In 1849, R. Mallet * said, " As every metal is positive to its own oxides, the adherent coat of rust upon iron, while it remains, powerfully promotes the corrosion of the metal beneath." Experiments on atmospheric corrosion of wrought iron, open hearth and Bessemer steels by Aston and Burgess t showed rust to have an accelerating effect in every case. In a later paper Aston { ascribes the accelerating effect of rust on the corrosion of iron to its acting as a screen to prevent free access of air to the metal beneath it. " The underlying feature appears to be the relative access of oxygen to the surface of the electrodes. The electrolyte must reach both; then that to which oxygen has the more free access becomes the cathode, and the other is the anode. If two bare iron electrodes are separated by a parti- tion of porous earthenware, parchment, etc., either may be made the cath- ode by bubbling air into this compartment, and not into the other. . . . Wet rust or a similar coating upon one electrode plays the role of a dia- phragm permeable to the moisture, but preventing or slowing down the oxygen penetration." This theory of the function of rust seems adequate to account for the observed tendency for the corrosion of iron and steel to take the form of pits when it corrodes imder such conditions that the first-formed rust is not continually removed. Pitting does not occur in the corrosion of iron or steel by acids or as anode in the refining of iron electrolytically, but the corrosion of these materials almost invariably takes this form when they are buried in the ground or immersed in a stagnant, neutral electrolyte, so that the patches of rust first formed can adhere. Whether steel corrodes uniformly or in pits, is then determined, not by the nature of the steel, but by its surroundings. Given uniform surroundings corrosion will be uniform ; with freer access of the depolariz- ing air to some spots than to others pitting results. 851. Concentration Cells and Thermal E.M.F. May Cause Corrosion. — It has long been known that an E.M.F. exists between two pieces of the same metal immersed in an electrolyte that differs in concentration at the electrodes; this constitutes a " concentration cell," and although * Report of Brit. Assoc, for Adv. of Sei., 1849, p. 111. t Trans. Amer. Electrochem. Soc, 1912, 22, 233. t Trans. Amer. Electrochem. Soc, 1916, 29, 449. 796 THE CORROSION OF METALS the E.M.F. is small, its continued action in good-conducting electrolytes is often responsible for serious corrosion. Burgess and Engle * have shown that an E.M.F. is produced between two pieces of iron in an electrolyte when one of them is heated to a higher temperature than the other, and have suggested that this may explain many cases of corrosion ot the tubes of locomotive boilers. Several years ago a severe case of corrosion occurred in the steel water-jacket of a cop- per blast-furnace at Douglas, Ariz.,t the inner plates of which were deeply corroded, while the outer plates and stiffeners were unattacked. The absence of acidity in the water, and the entire freedom from corrosion of boilers using the same water were puzzling features of the case. The corrosion can be fully accounted for by the existence of an E.M.F. between the highly heated inner shell as anode and the cooler outer part as cathode, the water, which was foimd to contain much sodium and potassium as sulphate, chloride, and carbonate, furnishing the electrolyte. On accoimt of its alkalinity the water could not attack iron except the metal was anode, and hence did not corrode the boilers, where the E.M.F. was lacking, or at least was very much smaller due to more uniform heating. 852. Effect of Stress and Strain on Corrosion. — Several investigators have studied the effects of stress and strain on the potential and corrodi- bility of iron and steel, t as a result of which it may be concluded that the cold-working of steel or iron raises its potential and increases the rate at which it is corroded by acids. Fig. 1 shows results obtained by Thickens in corroding, in N/4 hydrochloric acid, cylinders of iron and steel that had been strained by torsion or in tension, A and B being mild steel, C, electrolytic iron, and D a cylinder of mild steel that was stretched until necking down occurred, when it was machined to a true C3f]inder and suspended in the acid. Fig. 2 shows the effect of corrosion by acid on a punched plate of half -inch steel; not only was there severe corrosion of the strained metal at the hole, but curious lines of strain are seen to extend to a distance of an inch from the hole. With regard to stresses which do not produce permanent distortion of the metal, i.e., which are within the elastic limit, the results of different experimenters are so conflicting that this question must be regarded as still undecided. 853. Puzzling Corrosion of Turbine-driven Propellers. § — ^With the * Trans. Amer. Electrochem. Soc, 1908, 13, 37. t Trans. Amer. Inst. Min. Eng., 1908, 38, 877. I Bams, BuU. U. S. Geol. Survey, No. 94, 48-73; Andrews, Proc. Iiut. Nav. Eng., 1894, 118, 356; Hambuechen, Bull. Univ. Wis., No. 42; Richards and Behr, Pub. Carnegie Inst., 1906; Walker and Dill, Trans. Amer. Electrochem. Soc, 11, 153; Thickens Thesis, Univ. Wis., 1908; Trans. Amer. Electrochem Soc, 1908, 13, 7. § The Engineer, 1908, 105, 535, 539; 1909, 107, 397; 1910, 110, 252. Engineenng, 1912, 93, 33, 687, 884; 1913, 96, 690, 726, 761; 1914, 97, 535. PUZZLING CORROSION OF TURBINE-DRIVEN PROPELLERS 797 general adoption of bronze instead of cast iron or steel for the propellers of steamships it seemed as if the former troubles from corrosion were forever ended, and that the propeller might be regarded as a permanent piece of equipment. In 1908, however, The Engineer announced a new variety of corrosion which, in a few weeks or even days, destroyed the best bronze propellers. In consisted of pitting to the depth of three- quarters of an inch or more over an area of 40 to 50 square inches on the driving or astern face of the wheel. 'This peculiarly destructive form of corrosion was first noticed on the propellers of ocean-going , destroyers of the British navy, and, curiously, was confined to vessels driven by turbine engines. Corrosion was so Fig. 1. Fig. 2. serious that a propeller was often ruined during the trials, and before the vessel was put into service. Later it was found that this form of corrosion was also taking place, but much more slowly, on the Mauretania, Lusitania, and a few other " liners." In the interesting and lengthy discussion which followed the cause was assigned to faulty material, segregation of impurities, oxidation of the metal by air drawn from the water by " cavita- tion," erosion by the water due to the high speed of turbine engines, and to electrolytic action between strained and unstrained metal. A study of the examples shown in the several articles leads to the conclusion that the true cause is that last mentioned, and that corrosion may be prevented by (a) lessening the power transmitted by a single wheel, (6) the sub- stitution of a stronger material for that used, (c) increasing the thickness of the wheel. In many cases bending of the blades was found to have occurred at the places corroded. Corrosion was the result of a rise in potential of 798 THE CORROSION OF METALS the metal caused by cold-working, and illustrates the serious damage that may be caused by an exceedingly small E.M.F., provided a good electrolyte is continually present. It is still an open question whether or not a portion of the observed corrosion is due to that bending of the blades within the elastic limit, which must occur while the vessel is running, but which does not result in permanent distortion of the propeller. These examples of corrosion induced by strains indicate the desirability of annealing all metals and alloys which are likely to be subjected to corrosive influences. 854. Effect of Various Elements on the Corrodibility of Iron and Steel. — From the nature of the constitution of alloys it is evidently impos- sible from a mere knowledge of the resistance to corrosion of the alloying elements to predict correctly regarding corrosion of alloys, either by acids or on exposure to the atmosphere. Corrosion will be affected, not only by the chemical activity or resistance of the element added, but by the state in which this exists in the alloy. Whether the alloying element unites with the original metal forming a compoimd, forms a solid solution with it, or separates in the elemental state, are quite as important factors in determining corrosion as is the chemical nature of the alloying element itself. The quantity of the alloying element added will also influence profoundly the corrodibility of the alloy; if the added element forms with the original metal a compound which is strongly resistant to corro- sion, and on which the discharge potential of hydrogen is less than on the original metal, its addition in small amounts will accelerate corrosion by forming active local couples; but as the amount added is continually increased a point is finally reached at which the alloy consists entirely of the compound, when the resistance of the alloy to corrosion will be far greater than that of the original metal. When the constitution of alloys is thoroughly known and their cor- rosion has been more fully studied, it will probably be possible to predict correctly the corrodibility of many alloys before making tliem; but at present experiment is the only safe guide regarding the corrosion of most new alloys. Heat treatment is an important factor in the corrodibility* of alloys, for besides removing differences of potential due to strain, it often produces changes in the constituents of the alloy. The effect on corrosion of adding other elements to iron has been extensively studied, but lack of space permits mention of the effects of only a few of the more common ingredients of steel. Corbon.— Corrosion of annealed steel in water and dilute sulphuric acid rises with the carbon content to a maximum at the eutectic point (89 per cent C). Quenched and tempered steels show a continuous EFFECTS OF VARIOUS ELEMENTS ON COBRODIBILITY 799 rise in corrosion with increase of carbon up to 0.96 per cent.* The tem- perature to which a quenched steel is reheated has a marked effect on its corrosion in 1 per cent sulphuric acid,t a steel containing 0.95 per cent carbon showing a sharp rise in solubihty when reheated to 400° C, amount- ing to six times the rate of attack on untempered steel. Copper. — The remarkable lessening of the corrosion of iron by the atmosphere, water, sea water, and acids, caused by the addition of very small amounts of copper, has been the subject of many investigations. J Although resistance to corrosion increases with the copper content up to 2 to 3 per cent of copper, for resisting atmospheric corrosion there appears to be no advantage in exceeding 0.25 per cent of copper, and quantities as small as 0.05 per cent are said to have a marked influence on the rate of corrosion of iron. Manganese. — It is generally accepted that manganese in steel causes increased corrosion. Hadfield and Friend § found 0.7 per cent of man- ganese to cause a great increase in the rate of corrosion of carbon steels in tap water and in artificial sea water, but above 2 per cent of manganese corrosion is much decreased. In 0.1 and 0.5 per cent sulphuric acid corrosion increases with the manganese content up to 12 per cent man- ganese, the highest manganese used. Oxygen. — From theoretical considerations combined oxygen would be expected to accelerate the corrosion of iron, and Law || corroborates this by observations on rusting and corrosion in dilute acid. Silicon. — Sihcon-iron alloys containing about 15 per cent of the for- mer element are now extensively used under various trade names for the construction of chemical apparatus, although their hardness and brittleness are a serious drawback to their usefulness. Up to 20 per cent of siUcon, iron silicide (Fe2Si) forms a solid solution with iron, which fact, in connection with the small weight of silicon needed to produce a large quantity of the highly resistant iron silicide, accounts for the great resistance to acids secured by the addition of only a moderate amount of silicon, in comparison with additions of other elements for protection. Sulphur. — " Sulphur is universally regarded as a stimulator of cor- rosion." If * Chapelle, Jour. Iron and Steel Inst., 1912 (1), 270. t Hadfield and Friend, Jour. Iron and Steel Inst., 1916 (1), 48. JF. H. Williams, Proc. Eng. Soc. West Penn., 1900, 16, 23; Stead and Wigham, Jour. Iron and Steel Inst., 1901 (2), 122; P. Breuil, Jour. Iron and Steel Inst., 1907 (2), 1; Burgess and Aston, Trans. Amer. Electrochem. Sac, 1912, 22, 244; D. M. Buck, Jour. Ind. and Eng. Chem., 1913, 5, 447; Jour. Ind. and Eng. Chem., 1916, 8, 209. § Jour. Iron and Steel Inst., 1916 (1), 48. II Jour. Iron and Steel Inst., 1907 (2), 103. ^ Friend, Corrosion of Iron and Steel, p. 321. 800 THE CORROSION OF METALS 855. Protection of Iron from Rusting. — It is evident from the elec- trolytic nature of corrosion that the rusting of iron may be prevented by keeping it from contact with electrolytes, by rendering the iron " passive," or by making it cathode, the last being accomphshed by contact with a more positive metal such as zinc, or by the application of an external E.M.F. The first method is carried out by painting, enameling, covering with another metal, or forming on the surface of the iron by chemical action a coat of oxide or other compound. For success by this method it is' necessary that the coating be impervious to moisture, and remain unbroken. These are difficult conditions to fulfill, particularly when the object is exposed out of doors and subjected to wear. Paints soon lose their insulating power, and are readily scratched, enamels become chipped, electro-plate usually contains thin spots which soon wear through, and the compounds formed in the Bower-Barff and other similar processes must be kept so thin in order to prevent chipping and peeling, that their serviceability is less than if they could be given a considerable thickness. The subject of rust-resisting paints is receiving much attention from the technical societies interested, and marked improvements are to be expected. At first sight it might seem that coating iron with a less corrodible metal, either by dipping it in the melted metal or by electro-plating, should be a perfect remedy for rusting; but experience has shown that of all the metals so applied to iron, only zinc or cadmium affords satisfactory pro- tection, and when exposed to a good electrolyte like sea water even zinc fails to protect for more than a year or two. In coating by dipping, the thickness of the coating is limited, and only metals and alloys of low melting-point can be used. Galvanized iron, tin plate, and terne plate, the latter consisting of iron coated with an alloy of lead and tin, are made in enormous quantities by this method, but the durability of the last two is hampered by the corrosion induced by " local action " between the coating and the iron whenever the latter becomes exposed. In protecting iron by electro-plating there is a much wider choice of materials than in the dipping process, and theoretically the coating may be made of any thickness desired, but in practice its thickness is restricted by the increas- ing roughness of thick deposits and their liability to peel, for these reasons, coupled with the cost of producing heavy deposits, commercial electro-plate is usually thinner than the heaviest coatings made by dipping. 856. Utilization of Passivity to Prevent Rusting. — Kier in 1790 observed that iron, after treatment with fuming nitric acid, had lost its power of precipitating silver from a solution of silver nitrate, in other words, that the iron had been rendered immune to corrosion by silver nitrate. Chro- mic acid and several other oxidizing agents have since been foiuid to PROTECTION BY CONTACT WITH ZINC 801 exercise a similar effect in preventing iron from reacting as usual toward many reagents. Attempts have been made to prevent rusting by ren- dering iron passive, but, unfortunately, passivity soon ceases after removal of the iron from the passivifying solution, and the presence of certain salts may entirely prevent passivity; for these reasons the utilization of passivity for preventing the rusting of iron is as yet very limited. Although small amounts of alkalies accelerate the corrosion of iron, a strong solution entirely prevents rusting, and this passivity of iron in alkaline solutions has been very successfully applied to the prevention of corrosion in boilers.* Certain pigments used in paint, e.g. the chro- mates, are often classed as " inhibitors " from their supposed effect in preventing rusting by rendering iron passive. 857. Protection by Contact with Zinc. — The protection of metals from corrosion by placing a piece of zinc in contact with them seems to have been discovered by H. Davy f in 1824, and was first applied by him to prevent the corrosion of the copper sheathing of wooden ships. Since that time protection by contact with zinc has been applied to boilers and marine condensers, and plates of zinc are usually attached to the hull of steel vessels in the vicinity of bronze propellers, sea cocks, etc., which otherwise would induce serious corrosion of the steel in immediate contact with them. The principle involved is that corrosion of a metal is lessened by the passage of current to it as a cathode, but there are two difficulties to be overcome in applying this method; first, a good electrical connection must be maintained between the two metals; and second, in some elec- trolytes a coating forms on a zinc anode which may lower its potential to such an extent that the protective action is entirely nullified. For the protection of copper and brass in sea water iron appears to be a better contact metal than zinc, in spite of the higher initial potential of the latter. 858. Prevention of Corrosion by Current from a Dynamo. — In the generation of current for plating the corrosion of zinc in primary cells long ago gave way to the dynamo, and in the prevention of corrosion in large boiler installations by cathodic action, voltaic action has recently been abandoned in favor of the dynamo. Wherever corrosion is severe such protection results in a very considerable saving in the cost of repairs, less interruptions in service, and a higher efficiency of boilers from pre- vention of the formation of scale. The method seems destined to a wide usefulness. 859. Corrosion of Non-ferrous Metals. — The observed behavior of the non-ferrous metals in regard to corrosion is in fairly good agreement * F. Lyon, Jour. Amer. Soc. Nav. Eng., 1912, 24, 845. t Phil. Trans. Royal Soc, 114, 151. 802 THE CORROSION OF METALS with the principles set forth on page 23, modified by the formation of insoluble coatings upon them. The highly positive metals, aluminum and zinc, owe their durability entirely to the formation of an insoluble compound on their surfaces, and although durable in air, dissolve in all electrolytes which remove the protective coatings. Because of the high potentials of these metals, purity and freedom from " local couples " are especially important. Aluminum is corroded rapidly by the halogen acids, seriously by their salts, and vigorously by alkalies. Lead, tin, copper, brass, bronze, Mimz metal, Monel, and silicon-iron alloys are the materials most depended on to withstand severe corrosive conditions when platinum cannot be used on accoimt of cost, as in sea water, for conveying corrosive liquids, etc. Exclusion of oxygen, annealing to remove strains, and freedom from contact with more negative electrical conductors are highly important in minimizing corrosion. In neutral electrolytes brass is subject to the peculiar form of corrosion known as " dezincification," in which the zinc dissolves, leaving a skeleton of porous copper that is utterly lacking in mechanical strength. 860. Corrosion by Stray Currents.— In addition to the chemical or natural corrosion to which metals buried in the earth are subject, any continuous length of metal, such as a water or gas main, or the lead sheath of telephone cables, may suffer from electrolytic corrosion. This may be so serious as to destroy in a single year a cast-iron water main that should normally have a life of 50 to 100 years, while the thinner service pipes may last only a few months in especially bad situations. This damage results from the practice of using the rails for returning to the power station the electric current used for operating street railways. A greater or less proportion of the tota! current flows from the rails through the soil to the pipes, follows the latter to the vicinity of the power station, where it returns to«the rails once more in order to reach the negative ter- minal of the dynamo. Whenever " direct current " leaves a metallic anode to enter an elec- trolyte the metal is liable to be corroded, the extent of such corrosion depending on the same principles which control the corrosion of anodes in the electro-plating and refining of metals. The most important factors in the corrosion of anodes are: the chemical nature of the particular metal or alloy which serves as anode, the amoimt of current flowing, the time, the nature, amount, and concentration of salts in the soil, the tem- perature, current density, and rate of circulation of the electroh-te. With alternating current corrosion is usually negligible in comparison with that produced by direct current. Faraday's and Ohm's laws are of fundamental importance in electrolytic corrosion. According to the former the amount of corrosion should be proportional to the current which leaves the anode, to the time, and to the chemical equivalent of the metal; the THE DANGER DISTRICT— EXTENT OF CORROSION 803 amount of current being determined by Ohm's law, that the current equals the electromotive force divided by the resistance. Current which enters the system of pipes at different points through- out a city will leave the pipes in the vicinity of the power station. Two electrolytic cells are thus formed by the rails, earth, and pipes; one where current enters the pipes, in which the rails are anodes, and the other near the station, in which the pipes act as anodes, and are corroded. Although nothing is made public concerning corrosion of the rails, it is evident that this must occur to about the same extent as corrosion of the pipes, but will be distributed over a much larger area of the city. Soil conducts electricity only as an electrolyte, and by virtue of solutions contained in it, so that the resistivity of different soils varies greatly, as does that of the same soil under different conditions of moisture. Temperature is an important factor in the resistance of electrolytes, and when the ground is frozen to the depth of a few feet corrosion of the pipes by stray currents is at a standstill. 861. The Danger District. — This is the portion of the pipe system from which current flows into the earth on its way to the rails, and it may be located by taking measurements with a voltmeter between the rails and hydrants. Wherever the pipes are positive to the rails the former are in danger of corrosion; but a high voltmeter reading at one place does not always mean a greater flow of current than a smaller reading elsewhere, for the voltmeter reads only the IR drop produced by flow of ciurent in the earth, and there is the possibility that in a soil of high resistivity a small current may produce a greater fall of potential than is caused by a larger current which flows in a better-conducting soil. 862. Extent of Corrosion. — The amount of current flowing in a single pipe has been found to vary from a few amperes to several hundred, and in the case of " bonded pipes " in some of the largest cities, to several thousand amperes. Faraday's law predicts the dissolving of 15 pounds of iron by one ampere flowing from the metal 18 hours a day for a year, which leads one to wonder, not that damage to the extent of hundreds of thousands of dollars is caused annually by stray currents, but that any pipes remain uiidestroyed. The discrepancy between the amount of current known to be carried by pipes, and the relatively slow rate of their destruction, has given rise to much controversy and misunderstanding. The dissolving of 15 pounds of iron per ampere-year is for a current effi- ciency of 100 per cent, and requires that the entire current be spent in dissolving iron, and none of it employed in liberation of oxygen at the anode. Experience with plating and refining solutions has shown that the current efficiency of anode corrosion is greatly affected by the current density (number of amperes per sq. foot of anode surface), by the con- centration of the electrolyte, and its rate of circulation, — ^low current 804 THE CORROSION OF METALS density, high concentration, and rapid circulation tending toward a high efficiency, and vice versa. While the exact current density and the con- centration of the electrolyte is unknown in the corrosion of underground pipes, the extreme dilution and stagnation of the average electrolyte in the soil of city streets should lead to a low efficiency of anode corrosion, except where the bad practice of applying salt to switches to thaw ice has been indulged in. 863. Corrosion at Low Voltage. — The statement is often made that the voltage between pipes and rails must exceed the E.M.F. of decomposi- tion of water (1.7 volts) before corrosion can occur. This is an error. It is only- with- insoluble electrodes, if both are of the same metal, that this voltage is necessary for the passage of current; -with a soluble anode any voltage, however small, will cause some current' to flow. No fixed value can be given for polarization (the counter E.M.F. caused by products of electrolysis) that 'Will ajiply to" strdiy-current corrosion in general; this varies from 0.01 to 2.0. volts, i according to the current density, and the material, conpen|;ration, and freedom to circulate of the electrolyte, — factors which are difficult to determine in el^trolysis of pipes buried underground.- • .. , - 864. Joint Electrolysis. — ^A peculiar form of corrosion sometimes occurs in water pipes, known as joint electrolysis. The average lead joint in water mains has a very low resistance, so that no appreciable current is driven from the pipe at the joint; but when a joint of high resistance is encountered a considerable proportion of the current may pass from one section of pipe to the next by way of the soil instead of through the packing of the joint, causing corrosion on the anode side of the joint. Since this process is repeated at every bad joint, the damage done by a definite amount of current may be many times greater than in ordinary stray-current corrosion. Fortunately high-resistance joints are rather rare. 865. Remedies. — ^Because of lack of space it is only possible to men- tion some of the more important remedies that have been used or proposed for prevention of stray-current corrosion: 1. Lowering the voltage drop on the track by: (a) Better bonds. (b) Use of copper cables in parallel with the rails. (c) Insulated negative feeders attached to the track at suitable points. (d) Negative " boosters " to draw off current at desired points on the track. 2. Bonding of pipes near the station to the rails or to the negative terminal of the dynamo, so that current leaves the pipes by a metallic instead of an electrolytic conductor. REMEDIES 805 3. Insulation of the pipes from the earth. 4. Insulation at pipe joints. 6. Use of the double trolley, i.e. carrying the return current on an insulated overhead wire. 6. The use of alternating instead of direct current for the operation of street cars. CEFARTM ZNT SIBLLY i:.CH0OL CORN&.LL. UNi VARSITY 5^^.-^^ v: Si,:sL APPENDIX A STANDARD SPECIFICATIONS FOR PAVING BRICK OF THE AMERICAN SOCIETY FOR TESTING MATERIALS Serial Designation: C7-16 The specifications for this material are issued under the fixed designation C7; the final number indicates the year of original issue, or in the case of revision, the year of last revision. Adopted, 1915 The quality and acceptability of paving brick, in the absence of other special tests mutually agreed upon in advance by the seller on the one side and the buyer on the other side shall be determined by the following procedure: I. The Rattler Test, for the purpose of determining whether the material as a whole possesses to a sufficient degree strength, toughness and hardness. II. Visual Inspection, for the purpose of determining whether the physical proper- ties of the material as to dimensions, accuracy and uniformity of shape and color, are in general satisfactory, and for the purpose of culling out from the shipment individually imperfect or unsatisfactory brick. The acceptance of paving brick as satisfactorily meeting one of these tests shall not be construed as in any way waiving the other. I. THE RATTLER TEST THE SELECTION OF SAMPLES FOB TEST 1. Place of Sampling. — In general, where a shipment of bricks involving a quantity of less than 100,000 is under consideration, the sampling may be done either at the brick factory prioi to shipment, or on cars at their destination or on the street, when delivered ready foi use. When the quantity under consideration exceeds 100,000 the sampling shall be done at the factory prior to shipment. Bricks accepted as the result of test prior to shipment, shall not be liable to subsequent rejection as a whole, but are subject to such culling as is provided for under Part II, Visual Inspection. 2. Method of Selecting Samples. — In general, the buyer shall select his own samples from the material which the seller proposes tc furnish. The seller shall have the right to be present during the selection of a sample. The sampler shall endeavor, to the best of his judgment, to select brick representing the average of the lot. No samples shall include bricks which would be rejected by visual inspection as provided in Part II, except that where controversy arises, whole tests may be selected to determine the admissibiUty of certain types or portions of the lot having a characteristic appearance in common. In cases where prolonged controversy occurs between buyer and seller and samples selected by each party fail to show reasonable concurrence, then both 807 808 APPENDIX A parties shall unite in the selection of a disinterested person to select the samples, and both parties shall be bound by the results of samples thus selected. 3. Number of Samples per Lot. — In general, one sample of ten bricks shall be tested for every 10,000 bricks contained in the lot undei consideration; but where the total quantity exceeds 100,000, the number of samples tested may be fewer than one per 10,000, provided that they shall be distributed as uniformly as practicable over the entire lot. 4. Shipment of Samples. — Samples which must be transported long distances by freight or express shall be carefully put up in packages holding not more than twelve bricks each. When more than six bricks are shipped in one package, it shall be so arranged as to carry two parallel rows of bricks side by side, and these rows shall be separated by a partition. In event of some of the bricks being cracked or broken in transit, the sample shall be disquaUfied if there are not remaining ten sound undamaged bricks. 5. Storage and Care of Samples. — Samples shall be carefully handled to avoid breakage or injury. They shall be kept in the dry so far as practicable. If wet when received, or known to have been immersed or subjected to recent prolonged wetting, they shall be dried for at least six hours in a temperature of 100° F. before testing. THE CONSTRUCTION OF THE RATTLER 6. General Design. — The machine shall be of good mechanical construction, self- contained, and shall conform to the following details of material and dimensions, and shall consist of barrel, frame, and driving mechanism as herein described. Accompany- ing these specifications is a complete drawing of a rattler which will meet the require- ments, and to which reference should be made (Plate I). 7. The Barrel. — The barrel of the machine shall be made up of the heads, head- hners, staves and stave-Kners. The heads may be cast in one piece with the trunniors, which shall be 2j in. in diameter, and shall have a bearing 6 in. in length, or they may be cast with heavy hubs which shall be bored out for 2i^-in. shafts, and shall be keyseated for two keys, each 2 by t in. and spaced 90 degrees apart. The shaft shall be a snug fit and when keyed shall be entirely free from lost motion. The distance from the end of the shaft or trunnion to the msidef ace of the head shall be 15f in. in the head for the driving end of the rattler, and llf in. for the other head, and the distance from the face of the hubs to the inside face of the heads shall be S-J in. The heads shall be not less than f in. thick, nor more than | in. thick. In outline, each head shall be a regular 14-sided polygon inscribed in a circle 281 in. in diameter. Each head shall be provided with flanges not less than J in. thick and extending outward 21 in. from the inside face of the head to afford a means of fastening the staves. The surface of the flanges of the head shall be smooth and give a true and uijiform bearing for the stsves. To secure the desired true and uniform bearing the surfaces of the flanges of the head shall be either ground or machined. The flanges shall be slotted on the outer edge, so as to provide for two J-in. bolts at each end of each stave, said slots to be tI in. wide and 2f in., center to center. Each slot shall be provided with a recess for the bolt head, which shall act to prevent the turning of the same. Between each two slots there shall be a brace i in. thick, extending down the outward side of the head not less than 2 in. There shall be for each head a cast-iron headliner 1 in. in thickness and conform- ing to the outline of the head, but inscribed in a circle 28i in. in diameter. This head- liner shall be fastened to the head by seven l-in. cap-screws, through the head from the IVC.P., 30E.P.M. 3'Face END ELEVATION SIDE ELEVATI 1?^' Plate i. HEAD LINER GEAR GUARD ^ Z. \l I I I VX Holes 11 Lm] K- f>|2 L- _ ^ One R.H. Make ■Jj'vJir fourteen i ^j_ x -^ ->t3"|»0neL.H. SUPPORTS FOR GUARD STAVE ' jixj^"'" ... J m f ^ ^t-ii^ H^H I 3_l^#^'^\g|^Jil_«_ M^e one CLUTCH LEVER Core'Jli^l SIDE FRAME STANDARD RATTLER FOR TESTING PAVING BRICK PROPOSED BY THE MHOML PAVIHS BRICK lANUFACTURERS' ASSOCIATION December 1, 1910 To face page 808. APPENDIX A 809 outside. Whenever these headhners become worn down i in. below their initial sur- face level at any point of their surface, they shall be replaced with new ones. The metal of these headliners shall be hard machinery iron and should contain not less than 1 per cent of combined carbon. The staves shall be made of 6-in. medium-steel structural channels, 27i in. long and weighing 15.5 lb. per lineal foot. The staves shall have two holes H in. in diameter, drilled in each end, the center line of the holes being 1 in. from the end and If in. either way from the longitudinal center line. The spaces between the staves shall be as uni- form as practicable, but shall not exceed ys in. The interior or flat side of each stave shall be protected by a liner f in. thick by 5| in. wide by 19| in. long. The hner shall consist of medium-steel plate, and shall be riveted to the channel by three 4-in. rivets, one of which shall be on the center line both ways and the other two on the longitudinal center line and spaced 7 in. from the center each way. The rivet holes shall be countersunk on the face of the Hner and the rivets shall be driven hot and chipped off flush with the surface of the liners. These liners shall be inspected from time to time, and if found loose shall be at once re-riveted. Any test at the expiration of which a stave-liner is found detached from the stave or seriously out of position shall be rejected. When a new rattler, in which a complete set of new staves is furnished, is first put into operation, it shall be charged with 400 lb. of shot of the same sizes, and in the same proportions as provided in Section 9, and shall then be run for 18,000 revolutions at the usual prescribed rate of speed. The shot shall then be removed and a standard shot charge inserted, after which the rattler may be charged with brick for a test. No stave shall be used for more than seventy consecutive tests without renewing its lining. Two of the 14 staves shall be removed and relined at a time in such a way that of each pair, one falls upon one side of the barrel and the other upon the opposite side, and also so that the staves changed shall be consecutive but not contiguous; for example, 1 and 8, 3 and 10, 5 and 12, 7 and 14, 2 and 9, 4 and 11, 6 and 13, etc., to the end that the interior of the barrel at all times shall present the same relative condition of repair. The changes in the staves should be made at the time when the shot charges are being corrected, and the record must show the numbers of charges run since the last pair of new lined staves was placed in position. The staves when bolted to the heads shaU form a barrel 20 in. long, inside meas- urement, between head hners. The liners of the staves shall be so placed as to drop between the headliners. The staves shall be bolted tightly to the heads by four |-in. bolts, and each bolt shall be provided with a lock nut, and shall be inspected at not less frequent intervals than every fifth test and all nuts kept tight. A record shall be made after each inspection showing in what condition the bolts were foimd. 8. The Frame and Driving Mechanism. — The barrel shall be mounted on a cast-. iron frame of sufficient strength and rigidity to support it without undue vibration,. It shall rest on a rigid foundation with or without the interposition of wooden plates, and shall be fastened thereto by bolts at not less than four points. It shall be driven by gearing whose ratio of driver to driven is not less than one to four. The counter shaft upon which the driving pinion is mounted shall not be less than 1x1 in. in diameter, with bearing not less than 6 in. in length. If a belt drive is used the pulley shall not be less than 18 in. in diameter and 6J in. in face. A belt at least 6 in. in width properly adjusted, to avoid unnecessary slipping, should be used. 9. The Abrasive Charge. — The abrasive charge shall consist of cast-iron spheres of two sizes. When new, the larger spheres shall be 3.75 in. in diameter and shall weigh approximately 7.5 lb. (3.40 kg.) each. Ten spheres of this size shall be used. These shall be weighed separately after each ten tests, and if the weight of any large 810 APPENDIX A sphere falls to 7 lb. (3.175 kg.) it shall be discarded and a new one substituted; pro- vided, however, that all of the large spheres shall not be discarded and substituted by new ones at any single time, and that so far as possible the large spheres shall com- pose a graduated series in various stages of wear. When new, the smaller spheres shall be 1.875 in. in diameter and shall weigh approx- imately 0.95 lb. (0.43 kg.) each. In general, the number of small spheres in a charge shall not fall below 245 nor exceed 260. The collective weight of the large and small spheres shall be as near'y 300 lb. as possible. No small sphere shall be retained in use after it has been worn down so that it will pass a circular hole 1.75 in. in diameter, drilled in an iron plate \ in. in thickness, or weigh less than 0.75 lb. (0.34 kg.). Fur- ther, the small spheres shall be tested, by passing them over the above plate or by weighing, after every ten tests, and any which pass through or fall below the specified weight, shall be replaced by new spheres; provided, further, that all of the small spheres shall not be rejected and replaced by new ones at any one time, and that so far as possible the small spheres shall compose a graduated series in various stages of wear. At any time that any sphere is found to be broken or defective it shall at once be replaced. The iron composing these spheres shall have a chemical composition within the following limits: Cotibined carbon Not under 2 . 50 per cent Graphitic carbon Silicon Manganese Phosphorus Sulphur For each new batch of spheres used, the chemical analysis shall be furnished by the maker or be obtained by the user, before introducing into the charge, and unless the analysis meets the above specifications, the batch of spheres shall be rejected. THE OPERATION OF THE TEST 10. The Brick Charge. — The number of bricks per test shall be ten for all bricks of so-called " block-size," whose dimensions fall between 8 and 9 in. in length, 3 and 3| in. in breadth, and 3 J and i\ in. in thickness.* No brick should be selected as part of a regular test that would be rejected by any other requirements of the specifications imder which the purchase is made. 11. Speed and Duration of Revolution. — The rattler shall be rotated at a uniform rate of not less than 29.5 nor more than 30.5 revolutions per minute, and 1800 revolutions shall constitute the test. A counting machine shall be attached to the rattler for counting the revolutions. A margin not to exceed ten revolutions will be allowed for stopping. Only one start and stop per test is generally acceptable.* If, from acci- dental causes, the rattler is stopped and started more than once during a test, and the loss exceeds the maximum permissible under the specifications, the test shall.be dis- quahfied and another made. 12. The Scales. — The scales must have a capacity of not less than 300 lb., and must be sensitive to 0.5 oz., and must be tested by a standard test weight at intervals of not less than every ten tests. * Where brick of larger or smaller sizes than the dimensions given above for blocks are to be tested, the same number of bricks per charge should be used, but allowance for the difference in size should be made in setting the limits for average and maximum rattler loss. ' ' over 0.25 " " 1.00 11 it 0.50 Cl li 0.25 " " 0.08 APPENDIX A 811 13. The Resxdts. — The loss shall be calculated in percentage of the initial weight of the brick composing the charge. In weighing the rattled brick, any piece weighing less than 1 lb. shall be rejected. 14. The Records. — A complete and continuous record shall be kept of the operation of all rattlers working under these specifications. This record shall contain the follow- ing data concerning each test made: 1. The name of the person, firm or corporation furnishing each sample tested. 2. The name of the maker of the brick represented in each sample tested. 3. The name of the street, or contract, which the sample represented. 4. The brands or marks upon the bricks by which they were identified. 5. The number of bricks furnished. 6. The date on which they were received for test. 7. The date on which they were tested. 8. The drying treatment given before testing, if any. 9. The length, breadth and thickness of the bricks. 10. The collective weight of the ten large spherical shot used in making the test at the time of their last standardization. 11. The number and collective weight of the small spherical frhot used in making the test, at the time of their last standardization. 12. The total weight of the shot charge, after its last standardization. 13. Certificate of the operator that he examined the condition of the machine as to staves, liners, and any other parts affecting the barrel, and found them right at the beginning of the test. 14. Certificate of the operator of the number of charges tested since the last stand- ardization of shot charge and last renewals of stave liners. 15. The time of the beginning and ending of each test, and the number of revolu- tions made by the barrel during the test, as shown by the indicator. 16. Certificate of the operator as to number of stops and starts made in each test. 17. The initial collective weight of the ten bricks composing the charge and their collective weight after rattling. 18. The loss calculated in percentage of the initial weight; and the calculation itself. 19. The number of broken bricks and remarks upon the portions which were included in the final weighing. 20. General remarks upon the test and any irregularities occurring in its execution. 21. The date upon which the test was made. 22. The location of the rattler and name of the owr.er, upon which the test was made. 23. The certificate of the operator that the test was made under the specifications of the American Society for Testing Materials and that the record is a true record. 24. The signature of the operator or person responsible for the test. 25. The serial number of the test. In the event of more than one copy of the record of any test being required, they may be furnished on separate sheets, and marked duphcates, but the original record shall always be preserved intact and complete. For the convenience of the pubhc, the accompanying blank form, which provides space for the necessary data, is furnished and its use recommended. 812 APPENDIX A Serial No REPORT OF STANDARD RATTLER TEST OF PAVING BRICK Identification Data Name of the firm furnishing sample Name of the firm manufacturing sample Street or job which sample represents Brands or marks on the brick Quantity furnished Drying treatment . . . Date received Date tested Length Breadth Thickness. Standardization Data Weight of Charge. (After Standardization.) Condition of Locknuts on Staves. Condition of Scales. Number and Position of Fresh Stave Liners. Repairs. (Note any re- pairs aiTecting the con*- dition of the barrfel.) 10 Large spheres . Small spheres. Total Number of charges tested since last inspection Running Data Time Readings. Revolution Counter Readings. Hours. Minutes. Seconds. Stops, etc. Beginning of test . Final reading .... Weights and Calculations Initial weight of ten bricks Final weight of same Loss of weight Percentage Loss. (Note. — The Calculation Must Appear.) Number of broken bricks and remarks on same I certify that the foregoing test was made under the specifications of the American Society for Testing Materials, and is a true record. (Signature of tester) Date Location of laboratory APPENDIX A 813 ACCEPTANCE AND REJECTION OP MATERIAL 15. Basis of Acceptance or Rejection. — Paving bricks shall not be judged for accept- ance or rejection by the results of individual tests, but by the average of no less than five tests. Where a lot of bricks fail to meet the required average, it shall be optional with the buyer whether the bricks shall be definitely rejected or whether they may be regraded and a portion selected for further test as provided in Section 16. 16. Range of Fluctuation. — Some fluctuation in the results of the rattler test, both on account of variations in the bricks and in the machine used in testing, are unavoid- able, and a reasonable allowance for such fluctuations should be made, wherever the standard may be fixed. In any lot of paving brick, if the loss on a test computed upon its initial weight exceeds the standard loss by more than 2 per cent, then the portion of the lot repre- sented by that test shall at once be resampled and three more tests executed upon it, and if any of these three tests shall again exceed by more than 2 per cent the required standard, then that portion of the lot shall be rejected. If in any lot of brick, two or more tests exceed the permissible maximum, then the buyer may at his option reject the entire lot, even though the average of all the tests executed may be within the required limits. 17. Fixing of Standards. — The percentage of loss which may be taken as the stand- ard, will not be fixed in these specifications, and shall remain within the province of the contracting parties. For the information of the public, the following scale of average losses is given, representing what may be expected of tests executed under the foregoing specifications: General Average Loss, Per Cent. Maximum Pt^imissible Loss, Per Cent. 22 24 26 24 For bricks suitable for medium traffic 26 28 Which of these grades should be specified in any given district and for any given purpose is a matter wholly within the province of the buyer, and should be governed by the kind and amount of trafiic to be carried, and the quality of paving bricks avail- able. 18. Culling and Retesting. — Where, under Sections 15 and 16, a lot or portion of a lot of bricks is rejected, either by reason of failure to show a low enough average test or because of tests above the permissible maximum, the buyer may at his option permit the seller to regrade the rejected brick, separating out that portion which he considers at fault and retaining that which he considers good. When the regrading is complete, the good portion shall be then resampled and retested, under the original conditions, and if it fails again either in average or in permissible maximum, then the buyer may definitely and finally reject the entire lot or portion under test. 19. Payment of Cost of Testing. — Unless otherwise specified, the cost of testing the material as delivered or prepared for delivery, up to the prescribed number of tests for valid acceptance or rejection of the lot, shall be paid by the buyer. (See also Section 23.) The cost of testing extra samples made necessary by the failure of the whole lot or any portion of it, shall be paid by the seller, whether the material is finally accepted or rejected. 814 APPENDIX A II. VISUAL INSPECTION It shall be the right of the buyer to inspect the bricks, subsequent to their dehvery at the place of use, and prior to or during lajdng, to cull out and reject upon the follow- ing grounds: 20. All bricks which are broken in two or chipped in such a manner that neither wearing surface remains substantially intact, or that the lower or bearing surface is reduced in area by more than one-fifth. Where bricks are rejected upon this ground, it shall be the duty of the purchaser to use them so far as practicable in obtaining the necessary half-bricks for breaking courses and making closures, instead of breaking otherwise whole and sound bricks for this purpose. 21. All bricks which are cracked in such a, degree as to produce defects such as are defined in Section 20, either from shocks received in shipment and handling, or from defective conditions of manufacture, especially in drying, burning or cooling, unless such cracks are plainly superficial and not such as to preceptibly weaken the resistance of the brick to its conditions of use. 22. All bricks which are so off-size, or so misshapen, bent, twisted or kiln-marked, that they will not form a proper surface as defined by the paving specifications, or ahgn with other bricks without making joints other than those permitted in the paving specifications. 23. All bricks which are obviously too soft and too poorly vitrified to endure street wear. When any disagreement arises between buyer and seller under this item, it shall be the right of the buyer to make two or more rattler tests of the brick which he wishes to exclude, as pro\'ided in Section 2, and if in either or both tests, the bricks fall beyond the maximum rattler losses permitted under the specifications, then all bricks having the same objectionable appearance may be excluded, and the seller shall pay for the cost of the test. But if under such procedure, the bricks which have been tested as objec- tionable, shall pass the rattler test, both tests falling within the permitted maximum, then the buyer cannot exclude the class of material represented by this test and he shall pay for the cost of the test. 24. AH bricks which differ so markedly in color from the t3rpe or average of the shipment, as to make the resultant pavement checkered or disagreeably mottled in appearance. This Section shall not be held to apply to the normal variations in color which may occur in the product of one plant among bricks which will meet the rattler test as referred to in Sections 15, 16, and 17, but shall apply only to differences of color which imply differences in the material of which the bricks are made, or extreme differ- ences in manufacture. APPENDIX B ABRAMS' FINENESS MODULUS METHOD FOR PROPORTIONING CONCRETE Acknowledgment. — Since writing Chapters XIII and XIV, the authors have been accorded the privilege of pubhshing the following brief abstract of certain results of tests made under the direction of Professor D. A. Abrams, of Lewis Institute, Chicago.* Inasmuch as these data establish definite relations between the consistency of the mix, the sieve analysis of the aggregate and the strength of the concrete, and, since they also furnish a much more scientific basis for proportioning concrete and mortar, we feel very grateful to Professor Abrams for this privilege. We are especially indebted for the figures, tables and the notes which he has furnished for this brief discussion. The Effect of Proportion of Mixing Water on the Strength of Concrete. — As the result of about a dozen extensive series of tests in which the water content, the size of the aggregate and the age of the test pieces were vari- ables. Professor Abrams concludes that the use of the correct amount of mixing water is fundamental. Fig. 1 shows the relation between com- pressive strength of concrete and the ratio of the volume of water to the volunie of cement in the mix for one of these series of tests. It should be noted that the maximum size of aggregate in the mixes ranged from that which passed a No. 14-mesh to that which passed a 2-in. opening. The variation in the richness of the mixes is noted in the legend on the figure. Only mixes of plastic or wetter consistency form a basis for this figure. If the data for dry mixes had been plotted, there would have resulted a series of hooked curves extending downward to the left from the main curve in Fig. 1. A study of this figure shows very clearly how greatly the strength is decreased by using an excess of mixing water, f The Fineness Modulus may be defined as the sura of the percentages in the sieve analysis divided by 100, using Tyler standard sieves and expressing * The laws developed are based upon approximately 50,000 tests of mortars and concretes. The Structural Materials Research Laboratory at Lewis Institute is run under the co-operation of the Portland Cement Association and Lewis Institute, Professor Abrams being in charge. t For further information concerning this series of tests see Engineering News- Record, May 2, 1918; for additional data on other series, see Canadian Engineer, Vol. 35, p. 73, 103, 132. 815 816 APPENDIX B the analysis in terms of the total quantity of material coarser than each sieve. The sieves used by Professor Abrams are the 100, 48, 28, 14, 8, 4, I, f , 1| in., made of square-mesh wire cloth. (See Art. 462.) This fineness modulus has been shown by Professor Abrams to be a remarkable index of the strength-making quality of any aggregate. Also it furnishes a means of proportioning two or more given aggregates so that the resultant mixture will make the best concrete which can be obtained from the given materials. If the fineness modulus method of proportioning is compared with the Fuller method, which also makes use of mechanical analysis (see Art. 483), it will be found that the Fuller method ensures mixes of high fine- ness modulus but it requires the use of aggregate graded in a fixed manner. 8000 r 7000 . GOOO ■ 5000 '4000 1 3000 2000 1000 ; LEGEND 1-16 Ml 1- " 1-5 " '1-3 " 1-2 .. 1-1 " 1-14 ' I + '- «-" + Yt 'm - Neat • + ^ o ""*■«(-%. «~f-*. i—iko *• ^■.■- *• .50 1.00 1.50 2.00 2.50 3.00 Katlo of Volume of Water to Volume of Cement (~) = X Volume of Water 3.50 i.OO Fig. 1.— Effect of Ratio Volume of Cement on Strength of Concrete. ConsiBtencies normal or wetter; proportions by volume, 1 cu. ft. of cement = 94 lb. Data represent 1600 tests on 6 X 12 In, cylinders. (Abrams in Concr.te Highway Magazine, May, 1918.) In many instances such gradation is prohibited by the expense involved in screening or by the grading of the natural aggregates. The Abrams method, however, enables one to use to best advantage any given set of materials. If, however, it is necessary to screen the aggregate, in order to secure the very best strength, then the Abrams method will in general require less screening than the Fuller method. Table 1 shows the method of computing the fineness modulus for several different grades of sand and gravel. For material of one size — standard sand for example — the fineness modulus may be computed from the equation : m = 7.94-1-3.32 logiorf. Here m = fineness modulus and dl = average diameter of particles in inches. This equation holds for any single size of aggregate provided the- sieves above mentioned are used. APPENDIX B 817 TABLE I.— METHOD OF CALCULATING FINENESS MODULUS OF AGGREGATES. (Abbams) The fineness modulus of an aggregate is the sum of the percentages given by the sieve analysis divided by 100. The sieves used are coihmonly known as the Tyler standard sieves. It will be noted that the clear opening of each sieve is just double that of the preceding one. The sieve analysis mii,y be expressed in terms of volume or weight. Size of 3QUABE Sieve Analysis of Aqghegates, Percentage Coahseh than A Given Sieve. Sieve Size. Sand. Pebbles. Concrete In. Mm. Fine Medium Coarse (C) Fine Medium (B) Coarse (F) gate 100 48 28 14 8 4 f 3 4 .0058 .0116 .0232 .046 .093 .185 .37 .75 1.5 modulus. .147 .295 .590 1.79 2.36 2.70 9.4 18.8 37.6 82 52 20 91 70 46 24 10 97 81 63 44 25 100 100 100 100 100 86 51 9 100 100 100 100 100 95 66 25 100 100 100 100 100 100 86 50 98 92 86 81 78 71 48 20 Finpness 1.54 2.41 3.10 6.46 6.86 7.36 5.74 * Concrete aggregate G is made up of 25 per cent of sand B mixed with 75 per cent of pebbles E. Equivalent gradings would be secured by mixing 33 per cent of sand B with 67 per cent of coarse p^b^les JF; 28 per cent of sand A with 72 per cent of pebbles F, etc. 5000 4000 rSOOO £ 2000 1000 Relation of Fineness Modulus to Strength of Concrete. — Fig. 2 shows the relation between the fineness modulus of the aggre- gate and the strength of concrete of varying proportions made from different aggregates. It will be noted that the peak in the curve occurs for higher values of the fineness modulus with rich mixes than with lean mixes. If, however, a curve showing the relation between compressive strength and fineness modulus Fi^- 2.— Effect of Fineness Modulus of Aggre- 1 i.4. J -i7;„ o f«„ „ gate on Strength of Concrete. (Abrams.) were platted on hig. 2 tor a _, , . ^ f ^ * » . ^^^n- ,■ j ^ ^ ° Each point represents 5 tests of 6X12-in. cylinders; VerV rich mix, like a 1 : 1 mor- consistency normal (=1.00); age =28 days; aggregate '^ ' . was sand and pebbles graded up to li in. in diameter. tar, it would be nearly horizon- tal, showing that there is little advantage in careful proportioning of extremely rich mixes. The curves ,-— ^ ^ ^ ^ „ -D o ° .^ ^ ^ X 0-- -^ --^ o— - 4.00 4.50 5.00 5.50 6.00 6.50 Fineness Modulus of Aggregate 7.00 818 APPENDIX B 4000 3000 ' 2000 1000 in Fig. 2 are representative of the relation which exists for concrete mixes ordinarily used and for aggregate of a given maximum size. Fig. 3 illustrates the relation between the compressive strength of concrete and the fine- ness modulus of the ag- gregate when the maxi- mum size of aggregate is variable. The pro- portion of cement to aggregate was in all cases 1 : 5. Inspection of Figs. 2 and 3 indicates that within the range of sizes and proportions com- monly used the strength of concrete increases di- rectly with the fineness modulus. Maximum Permissible Values for the Fineness Modulus. — Experience in using the fineness modulus as a means of proportioning concrete has shown that it is not practicable to increase the fineness modulus beyond certain limits, these limits depending upon the character of the aggregate, the maximum size of the coarse aggregate, the gradation of the fine aggre- gate, the richness of the mixture, and the "use for the concrete. The desirable maximum limits for various mixes and sizes of aggregate are tabulated in Table 2. )-2In.x O-l'/zln. •/ ^/C%1 1. X /^ ^ X<0-96in J-^No.4 • O-No.14 3 4 5 FiDenesa Modulus of Aggregate -Effect of Gradation of Aggregate on Strength of Concrete. (Abrams.) Each point represents 5 tests on 6Xl2-in. cylinders of 1 : 5 pro- portions at 28 days. Aggregate was sand and pebbles. Consistency was normal. Fig. 3.- APPENDIX B 819 TABLE 2— MAXIMUM PERMISSIBLE VALUES OP PINENESS MODULUS OF AGGREGATES. (Abhams) For mixes other than those given in the table, use the values for the next leaner mix. For maximum sizes of aggregate other than those given in the table, use the values for the next smaller size. This table is based on the requirements for sand-and-pebble or gravel aggregate composed of approximately spherical particles, in ordinary uses of concrete in reinforced concrete structures. For other materials and in other classes of work the maximum permissible values of fineness modulus for an aggregate of a given size is subject to the following corrections: (1) If crushed stone or slag is used as coarse aggregate, reduce values in table by 0.25. For crushed material consisting of unusually fiat or elongated particles, reduce values by 0.40. (2) For pebbles consisting oi flat particles, reduce values by 0.25. (3) If stone screenings are used as fine aggregate, reduce values by 0.25. (4) For the top course in concrete roads, or other work requiring a smooth finish, reduce the values by 0.25. If finishing is done by mechanical means, this reduction need not be inade. (5) In work of massive proportions, such that the smallest dimension is larger than 10 times the maximum size of the coarse aggregate, additions may be made to the values in the table as follows: for |-in. aggregate, 0.10; for IJ-in., 0.20; for 3-in., 0.30; for 6-in., 0.40. Sands with fineness modulus lower than 1.50 are undesirable as fine aggregate in ordinary concrete mixes. Natural sands of such fineness are seldom found. Sand or screenings used for fine aggregate in concrete must not have a higher fine- ness modulus than that permitted for mortars of the same mix. Mortar mixes are covered by the table and by (3) above. Crushed stone mixed with both finer sand and coarser pebbles requires no reduc- tion in fineness modulus provided the quantity of crushed stone is less than 30 per cent of the total volume of the aggregate. Size of Phoportions (by Volume). Aggregate: Cement. Aggregate. 1 2 3 4 6 6 7 9 12 Sieve No. m 0-28 2.25 2.00 1.85 1.70 1.60 1,50 1.40 1.30 1.20 ii 0-14 3.00 2.70 2.50 2.30 2.15 2.05 1.95 1.85 1.80 1 0-8 ■^0-4 3.80 3.40 3.10 2.90 2,75 2,65 2.55 2.45 2.40 4.75 4.20 3.90 3.60 3.45 3.30 3.20 3.06 2.95 In, 0-3* 5.25 4.60 4.30 4.00 3.80 3.65 3.55 3.45 3.35 0-1 5.60 5.05 4.70 4.40 4.20 4.05 3.95 3.85 3.80 0-^* 6.05 5.45 5.10 4.80 4.60 4.45 4.35 4.25 4.20 S 0-1 6.50 5.90 5.50 5.20 5.00 4.85 4.75 4.65 4.60 1 0-1* 6.90 6.30 5.90 5.60 5.40 5.25 5.15 5.00 5.00 § 0-1^ 7.35 6.70 6.30 6.00 5.80 5.65 5.55 5.40 5.35 O 0-2.1* 7.75 7.10 6.70 6.40 6.20 6.05 5.95 5.80 5.75 0-3 8.20 7.55 7.15 6.85 6.60 6.50 6.40 6.25 6.20 0-4|* 8.65 7.95 7.55 7.25 7,00 6.90 6.80 6.65 6.60 0-6 9.10 8.40 8.00 7.65 7.45 7.30 7.20 7.05 7.00 * Half sieves; not used in computing fineness modulus. 820 APPENDIX B Method of Determining the Amount of Mixing Water. — In view of the extremely important influence of the consistency of the mix on the strength of the resulting concrete it is very necessary to carefully proportion the mixing water. From many thousands of tests Professor Abrams has evolved the following formula: : = 4 3 , .30n + (a — c)n. .2^^ 1.26"' X = ratio of the volume of water to the volume of cement in mix. p = the amount of water required for normal consistency in the standard test for cement, expressed as a ratio of the weight of the cement. m = fineness modulus of the mixed aggregate. a = the ratio of the volume of water absorbed by the dry aggregate to the volume of the aggregate, after immersion in water for three hours. (An average value for crushed limestone and gravel is 0.02. Porous sandstones may absorb 0.08.) c = the ratio of the volume of moisture in the aggregate to volume of aggregate (c = for air-dry aggregate) . n = ratio of volume of aggregate to volume of cement in mix. i2 = relative consistency of concrete. (i2=1.00 — a normal consistency obtains — when the quantity of mixing water is such that a 6 X 12-in. cylinder made in a smooth metal mold by puddling with a small rod will just stand, if the form is removed immediately after molding by a steady upward pull. A relative consistency of 1.20 means the use of 20 per cent more water than required for normal consistency.) This equation gives the proper amount of water to make concrete of the same plasticity or workability, regardless of the proportion of cement or size and grading of aggregate, provided the relative consistency R is made constant. The amounts of water required for concrete or mortar of normal con- sistency made from cement requiring an average amount of water for nor- mal consistency and an aggregate in semi-dry condition have been tab- ulated in Table 3. For any other relative consistency multiply all values in the table by the desired factor. For common mixes and ranges in aggregate gradation, the following equation is sufficiently exact and more simple to use: x=R (»-^^-5 )' |p+l0.22 + (a — c)n. APPENDIX B 821 TABLE 3.— PROPORTIONATE AMOUNTS OP WATER REQUIRED TO SECURE CONCRETE OR MORTAR OF NORMAL CONSISTENCY Computed from formula x=R 2*^ 1.26'" + {a-c)n. R = l, p=0.22, (a-c) =0.01. P In Terms of Volume op Cement FOB Fineness Moduli of Gallons of Water per Sack of Cement FOR Fineness Moduli of < 2 3 4 5 6 7 2 3 4 5 6 7 1 2 3 4 5 6 7 8 9 10 .53 .73 .93 1.12 1.32 1.52 1.72 1.92 2.12 2.32 .49 .65 .81 .97 1.13 1.29 1.45 1.61 1.77 1.93 .46 .59 .72 .85 .98 1.10 1.23 1.36 1.49 1.62 .43 .54 .64 .75 .85 .96 1.06 1.17 1.27 1.38 .41 .50 .58 .67 .75 .84 .92 1.01 1.09 1.18 .40 .47 .54 .61 .68 .75 .82 .89 .96 1.03 4.0 5.5 7.0 8.4 9.9 11.4 12.9 14.4 15.9 17.4 3.7 4.9 6.1 7.3 8.5 9.7 10.9 12.1 13.3 14.5 3.5 4.4 5.4 6.4 7.4 8.3 9.2 10.2 11.2 12.1 3.2 4.0 4.8 5.6 6.4 7.2 8.0 8.8 9.5 10.3 3.1 3.8 4.4 5.0 5.6 6.3 6.9 7.6 8.2 8.9 3.0 3.6 4.1 4.6 5.1 5.6 6.2 6.7 7.2 7.7 Outline of Method for Designing Concrete Mixes. — The following steps have been suggested by Prof. Abrams as a guide in designing concrete mixes. " 1. Knowing the approximate compressive strength required of the concrete and the maximum size of aggregate which may be used in the work, estimate the dryest ' relative consistency ' which may be used in the mix. (The mix is expressed as 1 volume of cement to a given number of volumes of aggregate; that is, the combined fine and coarse aggregate.) " 2. Make sieve analysis of fine and coarse aggregates, using Tyler standard sieves of the following sizes: 100, 48, 28, 14, 8, 4, f, f , and I5 in. Express sieve analysis in terms of percentages of material, by weight (or separate volumes), coarser than each of the standard sieves. " 3. Compute fineness modulus of each aggregate by adding the per- centages found in (2) . "4. Determine ' maximum size ' of aggregate by applying the following rules: If more than 20 per cent of aggregate is coarser than. any sieve the maximum size shall be taken as the next larger sieve in the regular series; if between 11 and 20 per cent is coarser than any sieve, maximum size shall be the next larger half sieve;* if less than 10 per cent is coarser than any sieve that sieve shall be considered the maximum size. " 5. From Table 2 determine the maximum value of fineness modulus which may be used for the mix, kind and size of aggregate under consid- eration. * Half sieves are listed with an * in Table 2. 822 APPENDIX B "6. Compute the percentages of fine and coarse aggregates required to produce the fineness modulus values desired for the aggregate mixture by- applying the formula : where 2/ = percentage of fine aggregate in total mixture; A = fineness modulus of coarse aggregate; B = fineness modulus of final aggregate mixtiu'e; C = fineness modulus of fine aggregate. (See also Fig. 5.) " 7. With the estimated mix, fineness modulus and consistency enter Fig. 4 and determine the strength of concrete produced by the combination. If the strength shown by the diagram is not that required, the necessary readjustment may be made by changing the mix, consistency, or size and grading of the aggregates. " Important Note. It must be understood that the values in Fig. 4 were determined from compression tests of 6 by 12-in. cyUnders stored for twenty-eight days in a damp place. The values obtained on the work will depend on such factors as the consistency of the concrete, quahty of the cement, methods of mixing, handhng, placing the concrete, etc., and on age and curing conditions. " Strength values higher than th9,t given for relative consistency of 1.10 should seldom be considered in designing, since it is only in unusual cases that a consistency dryer than this can be economically used. For wetter concrete much lower strengths must be considered." The method of using the chart in Fig. 4 is indicated by the dotted hnes. For example, suppose the strength of a 1 : 3 mixture of mortar made from a sand having a fineness modulus of 3.00 is required. Draw a Une from the point marked 1 : 3, on the line of mixes at the left of the diagram, through the point marked 3 on the line designated " fineness modulus of aggregate." Mark the intersection of this line with the " reference line for consistency," and read the strength. In this case it is 3000 lb. per square inch. If a consistency other than normal is to be used, the strength may be found by drawing a horizontal line through the intersection of the fii-st line and the reference hne for consistency. In this problem the strength for the relative consistency of 1.20 is approximately 2200 lb. per square inch. By the chart it is also possible to compare the strengths of different mixes made from aggregates varying in fineness modulus. For example, the 1 : 3 mortar mentioned above is somewhat less strong than a 1 : 5 mix made from aggregate having a fineness modulus of 5.7. (See lower dotted line in chart.) Again it is possible to determine the proper proportions when bank-run gravel is substituted for a mix containing fine and coarse aggregate and APPENDIX B 823 having a known strength. For example, suppose a specification requires 1:2:4 concrete with the strength of 2000 lb. per square inch and it is proposed that a bank-run gravel having a fineness modulus of 4 be sub- 1.00 1.10 1.20 1.30 1.40 1.50 1.60 1.70 Relative Consistency Fig. 4. — Abrams' Chart for Designing Concrete Mixes Diagram shows relations between proportions, fineness modulus, consistency, and strength. stituted for this mix, the " relative consistency " being 1.20. By inspec- tion of the chart we find that the proportions should be approximately 1 : 3.9. 824 APPENDIX B For a typical problem in mix design, suppose that a mix with a strength of 3000 lb. per square inch at one month is wanted for reinforced concrete columns. The available aggregates are sand B and pebbles D of Table 1. Assume proportions of 1 : 4.5 and a relative consistency, 1.20. Since only 9 per cent of the pebbles is coarser than a f-in. sieve, we enter Table 2 on the line marked 0-J-in. and find that the maximum permissible fineness modulus for the above mix is 5.10. Then y= (77^-77; — 7:^)100 = 34 \6.46 — 2.41/ per cent. Consequently we should use 34 per cent of sand B and 66 per cent of pebbles D in making the aggregate mixture. Entering Fig. 4 with a 1 : 4.5 mix, 5.10 fineness modulus, and a "relative consistency " of 1.20 we find that the strength of this mix is only 2300 lb. per square inch. A 1 : 3.5 mix which allows a fineness modulus of 5.35 for the aggregate, gives the required strength, the proportion of sand B and pebbles D in the aggre- gate being 27 and 73, respectively. If the reinforcement in the colimins is widely spaced and it is possible to thoroughly puddle the columns, the relative consistency might be reduced to 1.10. With this consistency a 1 : 4 mix containing an aggregate with 31 per cent of sand B and 69 per cent of pebbles D has sufficient strength. By interpolating in Table 3 we find that the amount of water required for normal consistency by the last mix, having a fineness modulus of 5.2, is 5.5 gal. per sack of cement. For a " relative consistency " of 1.1, 6.05 gal. per sack of cement is required. Fine Aggregate - Per cent of TotaKy) 10 20 300405060 70 80 90 100 ■Ttn So, Explanation. Assume fineness modulus of sand (C)=3.0, of gravel(A)=7.00,of desired mixed aggregate(B)=575.Findpoints (E) and • on cliart and prolong line thru them to D. Then f sand =32, and $ gravel=68 (both by wt.) . Ratio of sand: gravel in desired mixed aggregate = 1:2; J (l>y wt.) VI I I I I I I . I . I , I 8.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 6.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.6 Fineness Modulus of Mixed Aggregate(B) Fig. 5. — Diagram for Determining Quantity of Sand Required in Concrete Mixes. A—B (Abrams.) Solution of Equation y = . _- 100. APPENDIX C LIST OF STANDARDS ADOPTED BY THE AMERICAN SOCIETY FOR TESTING MATERIALS These Standards are all copyrighted In the name of the Amencan Society for Testing Materials. Permission to reprint any ol these Standards can be obtained only from the Executive Committee on application to the Secretary-Treasurer. ^ The designations A 1, A 2, etc., of the Standards are fixed; the final numbers 14, 12, etc.. Indicate the year of adoption as standard, or in the case of revision, the year of last revision. The serial designations of Standards which have for any reason been discontinued are permanently dropped. In ordering Standards, the complete serial designations should be stated, thus: A 1-14, A 2-12, etc. A. FERROUS METALS Steel (See also Wrought Iron: A 56-18) Standard Specifications Steel Rails and Accessories A 1-14. For Carbon-Steel Rails. A 2-12. For Open-hearth Steel Girder and High Tee Rails. A 3-14. For Low-Carbon-Steel Splfce Bars. A 4^14. For Medium-Carb on-Steel Splice Bars. A 5-14. For High-Carbon-Steel Splice Bars. A 6-14. For Extra-High-Carbon-Steel Splice Bars. A 49-15. For Quenched High-Carbon-Steel Splice Bars. A 50-16. For Quenched Carbon-Steel Track Bolts. A 51-16. For Quenched Alloy-Steel Track Bolts. A 65-18. For Steel Track Spikes. A 66-18. For Steel Screw Spikes. Structural Steels A 7-16. For Structural Steel for Bridges. A 8-16. For Structural Nickel Steel. A 9-16. For Structural Steel for Buildings. A 10-16. For Structural Steel for Locomotives. A 11-16. For Structural Steel for Cars. A 12-16. For Structural Steel for Ships. A 13-14. For Rivet Steel for Ships. Spring Steel and Springs A 14^16. For Carbon-Steel Bars for Railway Springs. A 68-18. For Carbon-Steel Bars for Railway Springs with Special' Silicon Require- ments. For Carbon-Steel Bars for Vehicle and Automobile Springs. For Silico-Manganese-Steel Bars for Automobile and Railway Springs. For Chrome-Vanadium Steel Bars for Automobile and Railway Springs. For Helical Steel Springs for Railways. For Elliptical Steel Springs for Rail- A 58-16. A 59-16. A 60-16. A 61-16. A 62-16. ways. A 69-18. For Elliptical Steel Springs for Auto- nnobiles. Reinforcement Bars A 15-14. For Billet-Steel Concrete Reinforce- ment Bars. A 16-14. For Rail-Steel Concrete Reinforcement Bars. Steel Blooms, Forgings and Axles A 17-18. For Carbon-Steel and Alloy-Steel Blooms, Billets and Slabs for Forg- ings. ' A 18-18. For Carbon-Steel and Alloy-Steel Forg- ings. A 19-18. For Quenched-and-Tempered Carbon- Steel Axles, Shafts, and Other Forg- ings for Locomotives and Cars. A 63-18. For Quenched-and-Tempered Alloy- Steel Axles, Shafts, and Other Forg- ings for Locomotives and Cars. A 20-16. For Carbon-Steel Forgings for Loco- motives. A 21-18. For Carbon-Steel Car and Tender Axles. A 22-16. For Cold-Rolled Steel Axles. Steel Wheels and Tires A 57-16. For Wrought Solid Carbon-Steel Wheels for Steam Railway Service. A 25-16. For Wrought Solid Carbon-Steel Wheels for Electric Railway Service. A 26-16. For Steel Tires. Steel Castings A 27-16. For Steel Castings. Steel Tubes and Pipe A 28-18. For Lap- Welded and Seamless Steel Boiler Tubes for Locomotives. A 52-18. For Lap-Welded and Seamless Steel and Wrought-Iron Boiler Tubes for Stationary Service. A 53-18. For Welded Steel Pipe. Automobile Steels (see also Spring Steel) A 29-18. For Automobile Carbon and Alloy Steels. 1 The Secretary-Treasurer has headQuarters at the University ot Pennsylvania, Philadelphia, Fa, 825 826 APPENDIX C Boiler Steels A 30-18. For Boiler and Firebox Steel for Loco- motives. A 31-14. For Boiler Rivet Steel. Cold-Drawn Steels^ A 32-14, For Cold-Drawn Bessemer Steel Auto- matic Screw Stock. A 54-15. For Cold-Drawn Open-hearth Steel Automatic Screw Stock. Standard Tests A 34-18. For Magnetic Properties of Iron and Steel. Standard Methods A 33-14. For Chemical Analysis of Plain Carbon Steel. A 55-15. For Chemical Analysis of Alloy Steels. Recommended Practice A 35-11, For Annealing of Miscellaneous Rolled and Forged Carbon-Steel Objects. A 36-14. For Annealing of Carbon-Steel Cast- ings. A 37-14. For Heat Treatment of Case-Hardened Carbon-Steel Objects. Wrought Iron (See also Steel: A 52-18) Standard Specifications A 38-18. For Lap-Welded Charcoal-Iron Boiler Tubes for Locomotives. A 72-18. For Welded Wrought-Iron Pipe. A 39-18. For Staybolt Iron. A 40-18. For Engine-Bolt Iron. A 41-18. For Refined Wrought-Iron Bars. A 42-18. For Wrought-Iron Plates. A 56-18. For Iron and Steel Chain. A 73-18. For Wrought-Iron Rolled or Forged Blooms and Forgings for Locomotives and Cars. Pig Iron, Cast Iron, and Finished Castings A43- A 44- -09. -04. A 74-18. A 45-14. A 46-05. Standard Specifications For Foundry Pig Iron. For Cast-iron Pipe and Special Cast- ings. For Cast-iron Soil Pipe and Fittings. For Cast-iron Locomotive Cylinders. For Cast-iron Car Wheels. A 47-15. For Malleable-lron Castings. A 48-18. For Gray-Iron Castings. Standard Methods For Sampling and Analysis of Pig and Cast Iron. B. NON-FERROUS METALS Standard Specifications Ingot Copper B 4-13. For Lake Copper Wire Bars, Cakes, Slabs, Billets, Ingots, and Ingot Bars. B 5-13. For Electrolytic Copper Wire Bars, Cakes, Slabs, Billets, Ingots, and Ingot Bars. Spelter B 6-18. For Spelter. Bronze B 7-14. For Manganese-Bronze Ingots for Sand Castings. B 10-18. For the Alloy: Copper, 88 per cent; Tin, 10 per cent; Zinc, 2 per cent. Wire and Cable. B 1-15. For Hard-Drawn Copper Wire. B Hard-Drawn Copper 3-15. 8-16. 2-15. For Medium Wire. For Soft or Annealed Copper Wire. For Bare Concentric-Lay Copper Cable : Hard, Medium-Hard, or Soft. B 9-16. For High-Strength Bronze Trolley Wire, Round and Grooved: 40 and 65-per-cent Conductivity. Copper and Brass Plates, Tubes, etc. B 11-18. For Copper Plates for Locomotive Fireboxes. B 12-18. For Copper Bars for Locomotive Stay- bolts. For Seamless Copper Boiler Tubes. For Seamless Brass Boiler Tubes. For Brass Forging Rod. For Free-Cutting Brass Rod for Use in Screw Machines. B 13-18 B 14-18, B 15-18, B 16-18, C. CEMENT, LIME. GYPSUM. AND CLAY PRODUCTS Standard Specifications C 9-17. Standard Specifications and Tests for Portland Cement. C 10-09. For Natural Cement. C 4-16. For Drain Tile. C 5-15. For Quicklime, C 6-15, For Hydrated Lime. C 7-15, For Paving Brick. C 19-lS. For Fire Tests of Materials and Con- struction. Standard Definitions C 8-15. Of Terms Relating to Sewer Pipe. APPENDIX C 827 D. MISCELLANEOUS MATERIALS Standard Specifications Preservative Coatings D 1-15. For Purity of Raw Linseed Oil from North American Seed. D 11-15. For Purity of Boiled Linseed Oil from North .American Seed. D 12-16. For Puritv of Raw Tung Oil. D 13-15. For Turpentine. Coke D 17-16. For Foundry Coke. Timber D 10-15. For Yellow-Pine Bridge and Trestle Timbers. Rubber D 14-15. For 2|-in. Cotton Rubber-Lined Fire Hose for Private Department Use. D 26-18. For 2^, 3, and 3^-in. Double-Jacketed Cotton Rubber-Lined Fire Hose for Public Fire Department Use. D 46-18. For Air-Line Hose for Pneumatic Tools. Standard Tests Preservative Coatings D 28-17. For Paint Thinners Other than Tur- pentine. D 29-17. For Shellac. Lubricants D 47-18. For Lubricants. Road Materials D 2-08. For Abrasion of Road Material. D 3-18. For Toughness of Rock. D 30-18. For Determination of Apparent Speci- fic Gravity of Coarse Aggregates. D 4-11. For Soluble Bitumen. D 5-16. For Penetration of Bituminous Mate- rials. D 6-16. For Loss on Heating of Oil and Asphal- tic Compounds. Standard Methods Preservative Coatings D 34-17. For Routine Analysis of White Pig- ments. D 49-18. For Routing Analysis of Dry Red Lead. D 50-18. For Routing Analysis of Yellow, Orange, Red and Brown Pigments containing Iron and Manganese. Road Materials D 7-18. For Making a Mechanical Analysis of Sand or Other Fine Highway Mate- rial, except for Fine A,ggregates Used in Cement Concrete. D 18-16. For Making a Mechanical Analysis of Broken Stone or Broken Slag, except for Aggregate Used in Cement Con- crete. D 19-16. For Making a Mechanical Analysis of Mixtures of Sand or Other Fine Material with Broken Stone or Broken Slag, except for Aggregates Used in Cement Concrete. D 35-18. Form of Specifications for Certain Commercial Grades of Broken Stone. D 20-18. For Distillation of Bituminous Mate- rials Suitable for Road Treatment. Coal and Coke D 21-16. For Sampling of Coal. D 22-16. For Laboratory Sampling and Analysis of Coal. D 37-18. For Laboratory Sampling and Analysis of Coke. Timber Preservative D 38-18. For Sampling and Analysis of Creo- sote Oil. Rubber D 15-15. For Testing of Cotton Rubber-Lined Hose. Standard Definitions D 16-15. Of Terms Relating to Paint Specifica- tions. D 8-18. Of Terms Relating to Materials for Roads and Pavements. D 9-15. Of Terms Relating to Structural Tim- ber. E. MISCELLANEOUS SUBJECTS Standard Methods E 1-18. For Testing. I. For Tension Tests of Metals. II. For Compression Tests of Metals, III. For Transverse Tests of Metals. IV. For Brinell Hardness Tests of Metals. V. For Metallographic Tests of Metals. 828 APPENDIX C LIST OF TENTATIVE STANDARDS PUBLISHED BY THE AMERICAN SOCIETY FOR TESTING MATERIALS The term Tentative Standards Is applied to a proposed Standard which Is printed In the Proceedings for one or more years with a view of eliciting criticism, of which the committee concerned will take due cognizance before recommending final action towards the adoption of such Tentative Standards by formal action of the Society. These Tentative Standards^are all copyrighted in the name of the American Society for Testing Materials. Permission to reprint any of tliese Tentative Standards can be obtained only from the Executive Committee on application to the Secretary- Treasurer. The designation A 67, A 70. etc., of the Tentative Standards are fixed; they follow In numeric sequence the designations of the Standards, and are retained when a Tentative Standard is adopted as Standard. The final numbers, as 18, indicate the year of original issue, or in the case of revision, the year of last revision. The letter " T " Is appended to the designation of all Tentative Standards. The serial designations of Tentative Standards which have for any reason not been adopted as standards, and have been discontinued, are permanently dropped. In ordering Tentative Standards, the complete serial designation should be stated, thus A 67-18 T, etc. A. FERROUS METALS Steel Tentative Specifications A 67-18 T. For Steel Tie Plates. A 70-18 T. For Boiler and Firebox Steel for Stationary Service. A 71-17 T. For Carbon Tool Steel. A 76-18 T. For Low-Carbon-Steel Track Bolts. A 77-18 T. For Electric Cast Steel Anchor Chain. Cast Iron Tentative Specifications A 75-18 T. For Malleable Castings. B. NON-FERROUS METALS Tentative Specifications B 17-18 T. For Non-Ferrous Alloys for Railway Equipment in Ingots, Castings, and Finished Car and Tender Bearings. For Cartridge Brass. For Cartridge Brass Disks. For Naval Brass Rods for Structural Purposes. B 22-18 T. For Bronze Bearing Metals for Turn- tables and Movable Railroad Bridges. B 23-18 T. For White Metal Bearing Alloys (known commercially as " Babbitt Metal"). B 19-18 T, B 20-18 T, B 21-18 T, B 24-18 T. Aluminum Ingots for Remelting and for Rolling. B 25-18 T. For Aluminum Sheet. B 26-18 T. For Light Aluminum Casting Alloys. Tentative Methods B 18-17 T. For Chemical Analysis of Alloys of Lead, Tin, Antimony and Copper. B 27-18 T. For Chemical Analysis of Manganese Bronze. B 28-18 T. For Chemical Analysis of Gun Metal. C. CEMENT, LIME, GYPSUM, AND CLAY PRODUCTS Tentative Specifications C 9-16 T. Specifications and Tests for Compres- sive Strength of Portland-Cement Mortars. 1 C 13-18 T. For Clay Sewer Pipe. C 14-18 T. For Cement-Concrete Sewer Pipe. C 15-17 T. For Required Safe Crushing Strengths of Sewer Pipe to Carry Loads from Ditch Filling. C 6-17 T. For Mason's Hydrated Lime." Tentative Tests C 16-18 T. For Refractory Materials under Load at High Temperatures. C 17-17 T. For Slagging Action of Refractory Materials. Tentative Methods C 18-18 T. For Ultimate Chemical Analysis of Refractory Materials. C 20-18 T. For Determination of Porosity and Permanent Volume # Changes in Refractory Materials. Tentative Definitions C 11-16 T. Of Terms Relating to the Gypsum Industry. Tentative Recommended Phactice C 12-17 T. For Laying Sewer Pipe. ^ To bo added, when adopted, to the Standard Speolflcatlona and Tests for Portland Cement (Serial Designa- tion: C9-17). 3 To replace, wben adopted, the Standard Speclfloatlona for Hydrated Lime (Serial Designation: C 6-16). APPENDIX C 829 D. MISCELLANEOUS MATERIALS Tentative Specifications Preservative Coatings D 51-18 T. For Foots Permissible in Properly Clarified Pure Raw J^inseed Oil from North American Seed. Timber D 23-lG T. For Selected Structural Douglas Fir Bridge and Trestle Timbers. D 24-15 T. For Southern Yellow-Pine Timber ^ I to be Creosoted. D 25-15 T. For Southern Yellow-Pine Piles and Poles to be Creosoted. D 52-18 T. For Wooden Paving Blocks for Exposed Pavements. Waterproofing D 40-17 T. For Asphalt for Use in Damp-proof- ing and Water-proofing. D 41-17 T. For Primer for Use with Asphalt for Use in Damp-proofing and Water- proofing. D 42-17 T. For Coal-Tar Pitch for Use in Damp- proofing and Water-proofing. D 43-17 T. For Creosote Oil for Priming Coat with Coal-Tar Pitch for Use in Damp-proofing and Water-proof- ing, Shipping Containers D 44-17 T. For Canned Foods Boxes, Nailed and Lock-Corner Construction. D 45-17 T. For Cnnned Foods Boxes, Wirebound Construction. Rubber Products D 27-16 T. For Insulated Wire and Cable: 30- per-cent Hevea Rubber. D 53-18 T. For Rubber Belting for Power Transmission. D 54-18 T. For Steam Hose. Tentative Tests D 28-18 T. For Flash Point of Paint Thinners Other than Turpentine.^ D 55-18 T. For Determination of Apparent Specific Gravity of Sand, Stone, and Slag Screenings, and Other Fine Non-Bituminous Highway Materials. D 48-17 T. For Molded Insulating Materials. Tentative Methods D 36-16 T. For Determination of Softening Point of Bituminous Materials Other than Tar Products. D 39-18 T. For Testing Cotton Fabrics. E. MISCELLANEOUS SUBJECTS Tentative Definitions E.2-18 T. Definitions and Rules Governing the Preparation of Micrographs of Metals and Alloys. To be added, when adopted, to the Standard Tests for Paint Thinners other than Turpentine (Serial Designa- tion: D 28-17). INDEX Abrams' method of proportioning concrete, 715 Abrasion tests on stone, 258 Absorption tests on brick, 275, 282 Absorption tests on concrete blocks, 516 Absorption tests on stone, 252, 254 Acid test for corrosion, 788 Adhesion of Portland cement mortar, 401 , 457 Adhesion of nails to wood, 226 Admiralty metal, 746, 767 Age in storage, effect on cement, 305, 323, 329, 330 Air furnace for cast iron, 690 Aggregate for concrete or mortar: broken stone, properties of, 421—425 cinders, 425, 473, 503 clay in, 415 composition of, 414 definition, 407 effect of moisture on sand voids, 418 fire resistance of, 502 gradation of erains in, 416, 422, 430 granite for, 422, 460, 463, 47" gravels for, 424, 440, 460, 466, 467, 468, 479, 486-490, 494, 504 gravel vs. broken stone 425 impurities in, 415 limestone for, 422, 441, 460, 463, 468, 472, 478,497,499,504 mechanical analysis of, 410 mine taihngs, 425, 435, 453 mortar tests for fine aggregate, 419 organic acid in, 415 requirements for, 414, 420 sands for, 414 sandstone for, 422 sieves for, 410 slas 425 specific weight, 408, 417, 423, 424 specific weight, relation to voids, 419 test for impurities in, 416 trap rock for, 422, 460, 466, 472, 478, 4S1, 502 503 voids in, 409, 417, 424 yield in concrete or mortar, 411 Alloys : aluminum bronze, 751, 767 aluminum-copper, 751, 753 aluminum-magnesium 755 aluminum-zinc, 7i,4 behavior of, in freezing 575, 579, 581 constitution furnished by thermal meas- urement 572 cooling curves for, 573 copper-tin, 744. 767 copper-tin-zinc. 744 copper-zinc 739 767 definition of, 568 lead-antimony, 756 831 Alloys (Continued) lead-antimony-tin, 756 lead-tin, 756 method of making, 569 significance of freezing-point diagrams for, 574, 578, 580 silicon-iron to resist corrosion, 799 solubility relations in, 570 structures of, 576 Alloys of low fusibility, 758 Alloys of more than two components, 583 Alloy steel, 588, 674, 766 ' Allotropy, 569 Aluminum, 523, 734 Aluminum, alloys of, 751 Annealing, see steel, copper brasses and bronzes Annual rings in wood, 142 Ash, 161 ; also see timber Austenite, 591, 637 Autographic stress diagram apparatus, 84 Axles, iron, temperature tests on 765 Babbitt metal, 757 . Basalt, 240 Basswood, 161 also see timber Beams, curved, 32 Beams, maximum deflections in, 33 Beams, moments, 33 Bearing bronzes, 746, 747, 757, 767 Bearing metals, 747, 756, 757, 767 Bearing resistance of plates, 666 Beech, 162; also see timber Bend tests, 134 Bending stress combined with direct stress, 44 Bessemer process for making steel, 547 Birch: also see timber Blast furnace, 532 Blast furnace, efficiency of, 541 Blended cements, 354 Blister steel 588 Bohme hammer, 394 Brasses, 739 complex, 742 composition of, 740 cupping test for, 750 Delta metal 743, 768 manganese bronze, 742, 768 Muntz metal, 740 768, 802 naval brass, 743, 768 properties of, 741, 742, 743, 769, 770 smelting of 740 Sterro metal, 743 Tobin bronze, 743 768 uses of, 740, 741, 742, 743 Brasses and bronzes: annealing of, 741, 742, 743, 746, 749 cold working of, 742, 748 corrosion of, 742 797 801 832 INDEX Brasses and bronzes {Continued) effects of high temperatures on, 767 season cracking of, 748 special tests for, 749 Breccias, 242 Brick, building: absorption of 281 cement, 517 classes of, 279 elasticity of, 284 fire resistance, 287 manufacture, 279 piers, strength of. 284 requirements for, 280 sand lime, 2SS strength classification, 281 tests on, 282 Brick, paving, 289 specifications for, 807 Brick piers, strength of, 284 Brick, refractory, 291 acid, 291 basic, 292 bauxite, 292 chrome, 293 magnesia, 292 silica, 291 Brick, see clay products also Brick walls, fire resistance of, 287 Brinell ball test, 68 Briquettes, cement, 391 Brittle materials, definition of, 6 Bronzes : admiralty metal, 746", 767 ■' bearing bronzes, 746, 747, 757, 767 complex, 744 composition of, 744 copper-tin-zinc alloys, 744 government bronze, 746, 767 gun metal, 744. 768 lead-bronze, 747 phosphor bronze, 746, 768 properties of, 744, 746, 748, 750. 767, 707 801 Calibration of testing machines, 98 Carbon in cast iron, see cast iron Carbon in steel, see steel Case hardening of steel, 644 684 Cast iron, 586 air furnace for, 690 carbon in, 696 eastings, cleaning of, 694 composition for different uses, 704 constituents of, 696 chills, 694 cupola for, 689 defects in 702 durability of, 788 effect of repeated heating, 717 gray cast iron, 697 hardness of, 705 importance of, GSS malleable, see malleable cast iron manganese in, 702 manufacture of, 688 molds for, 693 mottled cast iron, 697 phosphorus in, 702 patterns for, 691^ seasoning of castings, 717 segregation in, 703 shrinkage of, 701, 705, 716 silicon in, 698 Cast i;!on (ConHmied) stress diagrams for, 709 structure of, 697 sulphur in, 701 testing of, 707, 712, 715 white cast iron, 697 Cast iron, strength of: crushing strength, 710 effect of composition on, 706 effect of rate of cooling on, 706 effect of silicon on, 12i, 700 effect of repeated blows on, 717 effect of temperature on, 717, 760, 769 modulus of elasticity of 714 shearing strength, 715 shock re.sistance, 715 shrinkage stresses in, 716 tensile strength, 706 torsional strength, 715 transverse strength, 712. 121, 122 Cast-iron columns, strength of, 711 Catalpa, 162 Cedar, 161 Cement brick, 517 Cement drain tile, 518 Cement gun, 444 Cementite, 590, 610 Cement pipe, testing of, 519 Cement plaster, 368 Cement testing of, see Portland Cement Cement, see various kinds of Cements of construction, 301 Chemical compounds, 568 Chains, strength of, 605 Chestnut, 160 Chills for cast iron, 694 Chrome-nickel steel, 683, 764 Chrome steel, 679, 766 Chrome-vanadium steel, 684 Cinder concrete, 473 Clay pipe, see pipe Clay products: annealing, 274 burning, 273 classes of, 262 clays for, 263, 265 constitution of, 264 drying of, 270 flashing, 274 glazing, 274 kilns for burning, 270 manufacture of, 267 molding of, 269 popping in, 264 raw mafeiials for, 263 Soger cones, use of, 267 shales for, 263 sorting, 274 uses of, 262 value of, 262 wall white in, 265 Clay products, testing of: abrasion test, 278 absorption test, 275 appearance 275 freezing tests, 27.'^ hammer test, 275 Iiardness test, 275 kinds of tests, 274 rattler test, 27S specific gravity test, 276 strength tests, 276 Clay tile, see tile Column action, 2, 16 INDEX 833 Column formulas: Euler's, 17 parabolic 19 Rankine's, 18 straight line, 18 Column tests, cast-iron, 711 Column tests, hollow tile, 294 Cold working of brasses and bronzes, 742, 748 Cold working of steel, 654-656 Compression tests, apparatus for, 116 adjustable bearing blocks for, 75 bedments for, 78 effect of chamfered edges, 116 effect of loading portion of specimen, 116 form of test piece, effect of, 113 fractures in 117 method of testing, 116 objects of, 112 rigid bearing blocks for, 75 speeds in, 117 Compressometer, types of, 86 Concrete : absorption of, 490 aggregate for, 407 alkali water, effect of, 509 coefficient of expansion of, 502 contraction due to drying, 480 cracking in pavement, 482 curing of, 448 definition of, 407 density of, 412 durability of, in sea water, 506 elastic properties of, 475 electrical resistance of, 511 electrolysis of, 510 expansion due to moisture, 480 fatigue, effect of, 472 forms for, 446 freezing and thawing, effect of, 498 handling of, 441 hand mixing, 438 hand vs. machine mixing, 440 joining new and old work, 444 joints in, 447 machine mixing, 439 measurement of proportion for, 427 mixing, principals of, 438 modulus of elasticity of 475, 477 placement of, 443 Poisson's ratio for, 480 pressure against forms, 447 preventing freezing of, 498 proportioning by Abrams' fineness modulus, 815 proportioning by Fuller's method, 430 proportioning by sieve analysis, 430, '815 proportioning by voids, 428 proportioning of, 426 proportions arbitrarily selected, 427 proportions based on yield, 429 proportions commonly used, 432 proportions, interpretation of, 438 protecting against cold weather, 449 quantities of materials required for, 434 resistance to fire, 501 setting of in cold weather, 497 sewage, effect of, 509 shear tests on, 471 shearing strength of, 470 shrinkage in setting, 448 tensile strength of, 468 testing, necessity for, 406 testing of, 433 thermal properties of, 503 Concrete (Continued) transverse strength of, 469 use of salt in, 498 variations in, 406 waterproofing of, 490 Concrete blocks, 513 Concrete blocks, specifications for, 516 Concrete blocks, testing of, 515 Concrete, cinder, strength of, 473 Concrete, compressive strength of, 462 density, effect of, 462 effect of age on, 462 effect of per cent cement, 459 effect of per cent water, 465 effect of storage conditione, 448, 488 size of coarse aggregate, effect of, 464 Concrete, permeability of : alum and soap, effect of, 492 clay, effect of, 492 curing, effect of, 487 density, effect of, 485 effect of per cent cement on, 485 fabrics for decreasing, 493 hydrated lime, effect of, 491 oil mixed concrete, 492 other conditions effecting, 489 per cent water, effect of, 486 surface washes, 493 testing of, 482 time of mixing, effect of, 487 waterproof membranes, 493 Concrete poles, posts, piles, 520 Concrete, slag, strength of, 474 Conduit, clay, 300 Conglomerates, 242 Copper: annealing of, 730, 742 cold working of, 729, 730 extraction of, 728 production of, 522, 728 properties of. 522, 729, 742 uses of, 522, 731 Cores for cast-iron molds, 692 Corrosion cracking of brasses, 749 concentration cells may cause, 795 conditions effecting, 793 danger district, 803 dissolved air stimulates, 789 effect of elements on corrosion of iron and steel, 798 effect of stress and strain on, 796 extent of corrosion, 803 importance to engineer, 787 joint electrolysis, 804 jnill scale, effect of, 790 nature of, 791 non-ferrous metals, 801 of metals, 787 protecting against, 800 purity, a factor in, 790 relative corrodibility of metals, 794 rust stimulates, 795 stray current corrosion, 802 turbine driven propellers, 796 validity of acid test, 788 Cottonwood, 162 Critical temperature in steel, 590 Cross bending: breaking stresses in. 27 laws of stressing, 24 resisting moment equals bending moment, . 25 resisting moment for various sections, 26 true ultimate stress in (Upton), 28 834 INDEX Cross bending tests, see transverse tests Crushing strength of brittle bodies, 14 Crushing strength of plastic bodies, 14 Crushing strength, relation of to shearing strength, 16 Crystallization of iron and steel, 599, 771 Cubes and cylinders, relative strength of, 113 Cupola for cast iron, 689 Cupping test for brasses, 749 Curved beams, stresses in, 32 Cypress, 159 Decay of wood, 180 Defiectometer, dial, 88 Defiectometer, multiplying-lever, 88 Defleetometer, wire-mirror scale, 89 Defiectometers, features of, 87 Deflection curves, plotting of, 123 Deflections due to shear, 32 Deflection of beams, formulas for, 30 Deflection of beams, table of, 33 Deflections under impact, 43 Deformation apparatus, calibration, 100 Deformation due to torsion, 23 Deformations, instruments for measuring, see extensometer, compressometcr, torsion indicator, multiplying dividers, deformeter. Deformation, volumetric, 4 Deformation, lateral, 4 Deformeter for bridges, 94 Deformeters for beams, 89 Delta metal, 743 Density, see material in question Detrusion indicators, 91 Diabase, 240 Diorite, 240 Drain tile, cement, 518 Drifting tests, 137 Drying of timber, 150 Ductile materials, definition, 6 Duralumin, 755 Eccentric loading, effects of, 44, 116 Eccentric loading of briquettes, 396 Elastic bodies, 3 Elastic break-down, factors causing, 47 Elastic limit, apparent, 9 Elastic limit, apparent, advantages of, 10 Elastic limit clianged by overstrain, 604, 656, 661 Elastic limit, definition of, 3 Elastic limit obtained from stress diagram, 9 Elastic limit, variability of, 788 Elastic limit, also see steel, wrought iron and other materials Electrolysis of concrete, 510 Elongation, gauge length effects, 106 Elongation, significance of per cent of, 13 Elongation, the percentage of, 11 Elongation, variation of, along test piece, 12 Elm, 162 Endurance testing of metals, 772, 776, 770 Eucalyptus, 162 Extensometer : autographic, 84 Berry strain gauge, 82 calibration of, 100 essential features of, 79 Martens' mirror, 83 micrometer-screw, 80 multiplying lever, 81 wire rope, 94 wire- wound dial, 81 Failure, Bauschinger's theory of, 778 Failure, factors influencing, 47 Fatigue, experiments on, 772 Fatigue of metals : composition, effect of, 620, 776 designing for, 781 heat treatment, effect of, 774 limits of stress for an indefinite number of repetitions, 780 relation to elastic limit and ultimate, 776 repetitions, number required to cause failure, 773 speed, effect of, 776 surface condition, effect of, 776 Ferrite, 590, 610 Ferro alloys, 588 Flat plates, strength of, 36 Flexible materials, definition of, 6 Fineness modulus method for proportioning concrete, 815 Fir, 159 Fire resistance of brick, 287 Fire resistance of concrete, 426, 501 Fire resistance of stone, 248 Forging of ferrous metals, 565 Forms for concrete, 446 Fractures in bend tests, 134 Fractures in compression tests, 117 Fractures in tension tests, 110 Freezing, effects of, on cement and concrete, 341, 494 protecting concrete against, 449 tests t9 determine resistance to, 246, 278, 516 Fusible alloys, 758 Gabbro, 240 Gneiss, 240, 245, 260 Grain growth in steel, 661 Granite, 23S, 245, 24S, 250, 252, 255, 260 Granite, also see aggregate Graphite, 590 Gray cast iron, 697 Gillmore needles, 389 Government bronze, 746, 767 Grappier cement, 365 Grips for tension tests, 73 Gum (wood), 160 Gun metal, 744, 768 Gypsum, 366 Gypsum plasters: cement plaster, 368 hard finished plaster, 369 manufacture of, 366 plaster of Paris, 367 uses of, 365 Gypsum products, 369 Hardening of cement, 306 of lime, 361 of plaster of Paris, 362 of steel, see steel Hard materials, definition of, 7 Hardness, kinds of, 127 Hardness tests: Brinell method, 130 Brinell vs. scleroscope, 129 hardness vs. strength, 128 indentation tests, 128 scleroscope method, 130 Heartwood, 144, 180, 186 Hemlock, 159 Hickory, 160 INDEX 835 High speed steel, 686, 766 Hot blast stoves, 535 Hydraulic cements, 301 Hydraulic lime, 365 I-beam, rolls for an, 561 I-beams, tests of steel cut from, 655 Impact, deformations in, 43 Impact, stresses in, 43, 209 Impact tests, methods for, 126 Impact tests, selection of machines for, 125 Improved cements, 358 Indentation, tests, 128 Ingot iron, 587 Iron; corrosion of, 788, 790 critical temperatures, 590 importance of, 527 protection of, 800 structures of iron-carbon alloys, 595 Iron and steel, classification of, 585 composition of, 589 effect of elements on corrodibUity, 798 production of, 542 Iron and steel, constitution of: alloying relations of iron and cementite, 590 austenite, 591 cementite, 590 critical temperatures, 590 ferrite. 590 graphite, 590, 594 pearlite, 592 structures in iron-carbon alloys, 595 Iron ores: - associated elements, 529 classes of, 528 production of, 529 reduction of impurities in, 538 sources of, 527 treatment of, 531 Keene's cement, 369 Key to species of wood, 170 La Farge cement, 365 Lateral deformation under direct stress, 4 Lead, 522, 736 Lead-antimony alloys, 756 Lead-antimony tin alloys, 756 Lead-bronzes, 747 Lead-tin alloys, 756 Le Chatelier's tongs for testing soundness of cement, 387 Lime: burning of, 359 classes of, 359 hardening of, 361 high calcium, 359 hydrated, 362 hydraulic, 365 kiln, 360. quick lime, 359 slaking of, 361 testing of, 362 uses of, 364 Lime mortar, properties of, 363 Limestone, 240 resistance to abrasion, 260; also see aggregate strength of, 255-258 structure of, 240 Limits of stress for an indefinite number of repetitions, 780 Loading, effect of rate of, 109, 207, 761 Mack's cement, 369 Marble, 241 Magnalium, 755 Malleable cast iron : annealing of, 721 casting, 720 composition of, 721 importance of, 719 malleability of, 726 melting charge for, 719 molding, 720 nature of, 718 strength of, 723 structure of, 722 testing of, 722 Malleable materials, definition of, 7 Manganese bronze, 742, 748 Manganese steel, 678 Magnolia metal, 756 Maple, 160 Marble, 241, 255-260 Mayari steels, 684 Measurement of deformation, see different tests Mechanical tests, classification of, 98 Mechanical tests, observations on, 97 Mechanical tests, uses of, 138 . Metallurgy defined, 521 Metals, crystalline structure of, 570 Metals for bearings, 747, 756, 757, 767 Metals of construction, the, 521 Metals, principles of extraction, 525 Minerals in stone, 235 Mixing of concrete, see concrete Mixtures of metals, 568 Modulus of elasticity, definition, 3 Modulus of elasticity, determination of, 10 Modulus of elasticity in shear, 5 Modulus of elasticity, secant modulus, 11, 477 Modulus of elasticity, volumetric, 4 Moist closet for cement testing, 397 Molds for cast iron, 693 Monel metal, 739, 768, 770, 802 Mortar, lime, 362 Mottled cast iron, 697 Multiplying dividers, 92 Muntz metal, 740, 768, 802 Mortar, Portland cement: absorption of, 490 adhesion of, 445, 457 alkali water, resistance to, 344 contraction of, 334 definition, 407 effect of freezing on strength, 495 elastic properties of, 475 expansion of, 334 modulus of elasticity, 475, 478 oils, effect of, 347 placement of, 443 proportioning of, 427, 432, 815 sea water, resistance to, 346 sugar, effects of, 348 temperature changes in setting, 344 yield in, 412, 435 Mortars, Portland cement, strength of: age vs. strength, 330 effect of character of fine aggregate, 451 effect of gradation of aggregate, 453 effect of hydrated lime, 457 effect of mica, 457 effect of per cent of cement, 451 effect of per cent of water, 323, 457 fine vs. coarse sands, 455 836 INDEX Mortars, Portland cement, strength of {Con.) high temperature effects strength, 343 low temperature effects strength, 341 remixing, effect of, 339 retempering, effect of, 339 tensile strength of, 330 transverse strength, 334 Nails, holding force of, 226 Natural cement: characteristics of, 350 definition of, 349 manufacture of, 349 uses of, 353 Naval brass, 743, 748 Nickel : extraction of, 738 production of, 738 uses, 523, 739 Nickel-chrome steel, 683 Nickel st«el, 674, 764, 766, 768, 770 Oak, 159; also see timber Open-hearth furnace, 552 Open-hearth process for making steel, 551 Ores, 523 Ores of: aluminum, 734 copper, 728 iron, 528 lead, 736 nickel, 738 tin, 737 zinc, 731 Ore deposits, value of, 524 Ores, preparation for extraction of metals, 525 Overstrain, in steel, 661 Patterns for cast-iron molds, 691 Paving brick, 289 Pearlite, 596 Permeability of concrete, see concrete Pig iron, grades of, 539 Pig iron, manufacture, 532 Pig iron, purification of, 542 Pig iron, reactions in extracting, 536 slags, 540 Pine, 158, see also timbei;. Pipe, clay, 297-299 Pipe, clay, testing of, 277 Pipe, conduit, 300 Plates, grooved, strength of, 665 Plastic materials, definition of, 3 Plaster of Paris, 367 Phosphor bronze, 746, 768 Phosphorus, effects of, see steel, cast iron wrought iron Poisson's ratio, definition of, 4 Poisson's ratio, values of, 4, 255, 480 Poplar, 160 Portland cement: alkalies in, 305, 320 alumina in, 303, 321 carbon dioxide in, 305 characteristics of, 302 colloids in, 307 composition of, 302 constitution of, 305 effect of adulteration on specific gravity 329 effect of exposure to air, 330 effect of detrcc of burning, 322 effect of temperature on setting, 328 Portland cement {Continued) fineness, conditions effecting, 329 hydraulic index for, 303 index of activity, 303 iron cement, 354 iron oxide in, 304 lime in, 303, 320 magnesia in, 304, 320 nature of, 301 proportioning of, 303 seasoning, effect of, 323 setting and hardening of, 306 silica in, 303 soundness, conditions influencing, 320 specific gravity, conditions effecting, 329 strength, conditions effecting, 321 sulphur in, 305 time of set, conditions effecting, 325 white Portland, 353 Portland cement, manufacture: burning, 315 comparison of wet and dry processes, 319 grinding clinker, 317 grinding raw materials, 312 importance of, 310 kilns, 316 materials for, 310 plan of plant, 319 storage of cement, 319 wet process, 319 Portland cement, testing of: adhesion tests, 401 autoclave test, 388 ball method for consistency, 383 boiling test, 387 briquette, rate of loading, 397 briquettes, eccentric loading of, 396 briquettes, molding of, 394 briquettes, stresses in, 393 chemical analysis, 375 clips for, 396 consistency for, 382 Feret's consistency formula, 384 fineness, 378 interpretation of results, 398 Le Chatelier's tongs for soundness test, 387 machines for testing, 395 mixer for mortars, 394 mixing of pastes, 382 moist closet for, 397 necessity for, 371 per cent v.'ater in, 382 permeability of mortars, 404 porosity of mortars, 403 sampling, 374 sieving of, 379 soundness, 384 specifications for, 372 specific gravity, 377 storage of specimens, 397 tension test, method, 391 tension test, reasons for, 392 tension test, value of, 393 time of set, 389 transverse testing, 400 value of soundness test. 3SS Vicat method for consistency, 383 Vicat vs. Gillmore test, 390 yield in mater, 402 Portland cement mortar, see mortar Portland cement products, 513 Preservation of timber, 185 Prisms and cubes, crushing strength of, 113 INDEX 837 Proportioning concrete, see concrete Puddling furnace, 544 Punching and shearing, injurious effects of, 656, 665, 134 Puzzolan cement, 357 Quantities of aggregate for concrete, 434 Quartering of samples, 375 Quenching of steel, see steel, hardening of Rails, pressure of wheels on, 667 Rate of loading specimens: effects of, in tension tests, 109 in cement testing, 392, 397 in compression tests, 117 in timber testing, 207 in transverse tests, 123 Rattler test of paving brick, 807 Reduction of area, percentage of, 13 Reduction in rolling, effect of: on brass, 748 on copper, 729 on steel, 753, 756 on wrought iron, 600 Red wood, 161; also see timber Refractory brick, 291 Repeated stress, designing of parts subjected to, 781, 784 Repeated stress, limits for, 780 Repeated stressing of steel, effects of, 771 Resilience a measure of shock resistance, 41 Resilience defined, 38 Resilience in cross bending, 40 Resilience in impact. 43 Resilience, in tension and compression, 39 Resilience in torsion, 41 Resilience of different materials, see material in question Rock, kinds of, 237 Rusting of iron and steel, 788, 790 Salt, effect of, on concrete, 498 Sand cements, 355 Sand for cast-iron molding, 692 Sand for mortar and concrete : effect of composition, 414 effect of grading sizes of grains, 416, 452, 454 effect of impurities in, 415, 457 effect of increasing proportions of, 451, 485 Sand lime brick, 288 Sandstone, 242, 250, 251, 253, 255, 256-260; also see aggregate Sapwood, 144 Schone washing apparatus for determining fineness of cement, 380 Sclerometer, 68 Scleroscope, 69 Screenings for mortaj and concrete, 416 Screw bolts, strength of, 663 Season cracking of brasses, 748 Sea water, effect on concrete, 506 Semi steel, 688 Setting of cement, see cement in question Sewer pipe, cement, 518 Shakers for cement and sand, 379 Shear stress, in wooden beams, 30 Shear stress, Upton's method for true, 23 Shear stress, variation in beams, 28 Shear tests, objects of, 131 Shear tests, specimens for, 132 Shock resistance, measured by resilience, 41 Shrinkage of timber, 153 Silico-manganese steel, 683 Silicon, effect of, on metals, see metal in question Silicon-iron alloys to resist corrosion, 799 Silicon steels, 0S2 Silt, 408 Single shear steel, 588 Slag cement, 357 Slag concrete, 474 Slags from blast furnace, 540 Slate, 243 Slip lines, 771 Solder, 756 Solid solutions, 568 Specifications for paving brick, 807 Specifications, list of A. S. T. M., Appendix C Specimens, also see various tests Specimens for tension tests, 105 Specimens, loading of, 72 Specimens, preparation of, 102 Specimens, selection of, 101 Spikes holding force of, 226 Spring wood and summer wood, 143, 186, 217 Spruce, 159 Standard sand for cement testing, 391 Steel: annealing effects, 630 annealing of, 626 arsenic in, 624 carbon content, relation of to properties, 610 carbon in, 609 carbon, effect on ductility, 618 carbon, e^ect on elasticity, 616 carbon, efSfect on hardening, 636 carbon, effect on strength, 612 carbon, effect on stress-diagram, 619 carbon, effect on toughoess, 619 carbon range of content in steels, 620 cold rolling of, 657 cold twisting, 658 cold working of, 654 cold working, distortion due to, 659 composition of structural, 621 compressive strength of, 614 compressive strength of when confined, 666 copper in, 624 corrosion of. see cortosiau distinguished from iron, 608 ductility of, 618 durability of, 788 effects of cold work on properties, 656 effects of combined .stress on, 674 effect of contraction in crosS'Section on strength, 663 effects of impurities, 621 effects of hot work on, 651-653 effect of reduction in rolling, 653 elastic limit of, 614 elastic limit under combined stress, 672 endurance of, 771-786 factors influencing properties, 609 grain growth, 661 grain size, relation of, to properties, 626 hot work, effect of, 651 manganese, effects of, 624 modulus of elasticity, 616 modulus of elasticity under combined stress, 673 non-metallic impurities in, 624 overstrain in, 661 phosphorus, effect of, 622 protection of, 800 resistance to wheel pressure, 666 shearing strength of, 61.5 silicon, effects of, 622 838 INDEX Steel (Continued) structures of, 595, 628, 637 sulphur, effects of, 623 tensile strength of, 613, 631, 646, 649, 662 theories of hardening, 633 toughness of, 619 under repeated stress, 771 wire drawing, 659 Steel, effects of temperature on- ductility, 762, 769 elastic limit, 761, 769 haraness. 766 modulus of elasticity, 763 resistance to iinpact, 763 strength, 759, 769 Steel, heat treatment of: annealing, 626 burning, 632 case hardening. 644 cooling from above critical range, 625 critical range, 590 drawing, method of, 641 drawing temperature, 643 effect of, on corrosion, 798 grain size, relation to properties, 626 hardening, effect of carbon on, 636 hardening, essentials in, 635 hardening, methods of, 635 hardening, theories of, 633 hardness, effect of drawing, 641 heating above critical range, 625 influence of hardening on properties, 645 influence of tempering on properties, 646 over heating, 632 tempering, 640 Steel, manufacture of: acid Bessemer process, 548 basic Bessemer process, 550 Bessemer process, 547 Bessemer vs. open hearth process, 555 casting steel, 566 cementation process, 556 orucilDle process, 557 decline of Bessemer process, 556 duplex process, 556 electric furnace, 557 forging, 565 ingots, 559 ingots defects in, 560 , ingots, heat treatment of, 560 open hearth process, 551 pipes, 564 plates, 563 pressing, 565 production of shapes, 559 processes used in, 546 rolling of shapes, 561 rolling mills, 561 sheets, 563 statistics, 567 Tropenas converter for, 551 wire, 565 Steel plates, bearing resistance of, 666 Steels, alloy: chrome, 679 chrome-nickel, 683 chrome-vanadium, 684 high speed, 086 manganese, 678 Mayari, 684 nickel, 674, 764, 766, 768, 769, 770 nickel-chrome, 683 silico-manganese, 683 silicon, 682 Steel, alloy (Continued) tungsten, 681 vanadium, 682, 769 Sterro metal, 743 Stiff materials, definition of, 6 Strength in testing machines compared with dead load strength, 113 Stress, combined, direct and bending, 44 Stress, combined, due to biaxial loading, 46 Stress, combined, due to shears and direct stress, 44 Stress-deformation diagrams, plotting of, 112 Stress, general method of finding, 21 Stress, kinds of, 1 Stresses, repeated, diagram for calculating endurance under, 775 Stresses under repeated loads, 778 Stresses, working, diagram for, 784 Stresses, working, in timber, 229 Stone : abrasive resistance, 258 absorption of, 252, 254 acid tests for, 247 basalt, 240 Brards test for, 247 breccias, 242 classes of, 237 conglomerates, 242 cross bending strength, 258 crushing strength, 252, 255, 258, 260 density of, 251 diabase, 240 diorite, 240 durability of, 245, 246 elasticity of, 257 expansion in water, 255 freezing test for, 246 fire test on, 248 gabbro, 240 gneiss, 240 granite, 238 limestone, 240 marble, 241 mineral constituents in, 235 Poisson's ratio for, 255 porosity of. 251 preservation of, 245 production of, 235 sandstone, 242 selection of, 234 shearing strength, 258 slate, 243 sources of production, 234 specific gravity of, 250, 252, 258, 260 strength of, 254 structure of, 239 thermal expansion of, 249 transverse strength of slate, 257 trap rock, 240 , wearing resistance, 258 weathering of, 243 weight of, 250, 252, 255, 258, 260 Storage bath for cement test, 398 Structure of: cast iron, 595 copper, 571 steel, 595, 628-638 stone, 235, 239 wood, 163-170 wrought iron, 598 Sulphur, effect of, in metals, see metal in question Sycamore, 162 INDEX 839 Tailings, for aggregate, 426, 435, 453 Tamarack (larch! , 161 Temperature, effects of, on properties of metals, 759 Tempering of steel, 640 Tensile tests: cross knife edges for, 75 extensometer tests, 111 fracture characterization in, 110 general phenomena accompanying, 7 grips for, 73 methods for commercial tests, 108 objects in commercial tests, 105 observations in commercial tests, 109 results obtained, 8 significance of, 104 speeds in commercial tests, 108 spherical seated holders for specimens, 73 types of, 13 Terra-cotta, 297 Test for season cracking of brasses. 749 Testing apparatus, references on, 95 Tests for determining resistance to repeated stress, 776, 70 Tests of various materials, see material in question Tests, also see tensile, compressive, etc. Testing machines; calibration of, 98 cold bend, 60 conditions which should obtain in, 50 Emery, 54 endurance, 70 for cement, 395 hardness, Brinell ball tester, 68 sclerometer for, 68 scleroscope for, 69 hydraulic press, 55 impact, drop type of, 66 essential conditions in, 65 pendulum types, 65 Kommers' repeated stress, 71 Olsen, 51 Riehle, 53 shear test appliances, 61 torsional, 62 transverse, 68 transverse, essentials in, 57 universal, types of, 49 World's largest, 57 White-Souther, 71 Wohler's, 70 Thickness of rolled shapes, influence on properties, 653, 730, 735 Threads on screw-bolts, influence of form of, 663 Timber: annual rings in, 142 broad-leaved trees, 141 case hardening in, 155 classes of trees, 141 cleavability of, 211 color of, 146 composition of wood, 180 compressive strength of: across grain, 197 influence of seasoning on, 199 parallel to grain, 196 coniferous, 141 cross bending strength, 203 decay, causes of, 180 defects in, 142, 146, 218, 220, 232, 233 deflection curves for beams, 209 density of, 147 Timber (Continued) deteriorating influences, 184 drying of, 150 durability of, 179 failure of beams, 205 fungi in, 180 grading rules for, 230 grain of wood, 145 hardness of, 212 hard wood, 141 heartwood, 144 honeycombing in, 155 identification by key, 169 importance of, 140 insects attacking. 183 knowledge of mechanical properties required, 197 knots in, 142, 218, 220, 232, 233 limnoria in, 184 marine borers in, 183 modulus of rupture of, 203 moisture in, 148 nail joints, strength of, 228 odor of, 146 rays in, 144 sapwood, 144 seasoning of, 150 shearing strength across grain, 201 shearing strength, in beams, 203 shearing strength, tangentia , 201 shrinkage of, 153, 157 soft wood, 141 spring wood, 143 stiffness of, 208 strength of nails and spikes in, 226 structure and appearance, indexes of value, 141 structure of wood in general, 142 summer wood, 143 tensile strength of: parallel to grain, 199 across grain, 200 teredo in, 183 toughness measured by impact, 209 transverse strengths of wood, 205 volume changes due to moisture, 156 weight of, 147, 149 working stresses for, 229 Timber preservation : Bethell process. 190 bi-ohloride of mercury for, 189 boiling process, 190 Burnetizing, 190 card process, 191 copper iTulphate for, 193 creosote oil for, 190, 192 economy in, 193 kyanizing, 189 Lowry process, 191 need for, 185 open tank process, 189 penetrance of preservatives, 186 preservatives for, 191 pressure processes for, 190 Rueping process, 190 superficial treatments for, 188 treatment before preserving, 187 Timber, sources, characteristics and uses of: Ash, 161 Basswood, 161 Beech, 162 Birch, 161 Black walnut, 162 Catalpa, 162 CIVIL ENGINEERINC3 — Continued Se Highways; Municipal Engineering; Sanitary Engineering; Water Supply. 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