k*u OAK S i. nUor .. THE UNIVERSITY OF ILLINOIS # J i i i INTERNATIONAL LIBRARY of TECHNOLOGY A SERIES OF TEXTBOOKS FOR PERSONS ENGAGED IN THE ENGINEERING PROFESSIONS AND TRADES OR FOR THOSE WHO DESIRE INFORMATION CONCERNING THEM. FULLY ILLUSTRATED AND CONTAINING NUMEROUS PRACTICAL EXAMPLES AND THEIR SOLUTIONS SANDS AND CEMENTS PLAIN CONCRETE BUILDING STONE AND BRICK ELEMENTS OF STONE MASONRY ELEMENTS OF BRICK MASONRY FIELD OPERATIONS AND CONCRETE WORK TESTS ON CEMENT CONCRETE BUILDING BLOCKS - HEAVY FOUNDATIONS PILING STEEL AND OTHER METALS LOADS IN STRUCTURES ' INSURANCE ENGINEERING WATERPROOFING OF CONCRETE SCRANTON: INTERNATIONAL TEXTBOOK COMPANY 108 Sands and Cements: Copyright, 1909, by International Textbook Company. Entered at Stationers’ Hall, London. Plain Concrete: Copyright, 1906, 1909, by International Textbook Company. Entered at Stationers’ Hall, London. Building Stone and Brick: Copyright, 1904, 1909, by International Textbook Com¬ pany. Entered at Stationers’ Hall, London. Elements of Stone Masonry: Copyright, 1898, by The Colliery Engineer Company. Copyright, 1907, 1909, by International Textbook Company. Entered at Sta¬ tioners’ Hall, London. • Elements of Brick Masonry: Copyright, 1898, 1899, by The Colliery Engineer Company. Copyright, 1907, 1909, by International Textbook Company. Entered at Stationers’ Hall, London. Field Operations and Concrete Work: Copyright, 1910, by International Textbook Company. Entered at Stationers’ Hall, London. Tests on Cement: Copyright, 1910, by International Textbook Company. Entered at Stationers’ Hall, London. Concrete Building Blocks: Copyright, 1910, by International Textbook Company. Entered at Stationers’ Hall, London. Heavy Foundations: Copyright, 1904, 1910, by International Textbook Company. Entered at Stationers’ Hall, London. Piling: Copyright, 1910, by International Textbook Company. Entered at Sta¬ tioners’ Hall, London. Steel and Other Metals: Copyright, 1906, 1909, by International Textbook Com¬ pany. Entered at Stationers’ Hall, London. Loads in Structures: Copyright, 1904, 1909, by International Textbook Company. Entered at Stationers’ Hall, London. Insurance Engineering: Copyright, 1910, by International Textbook Company. Entered at Stationers’ Hall, London. Waterproofing of Concrete: Copyright, 1910, by International Textbook Company. Entered at Stationers’ Hall, London. All rights reserved. 24853 108 PREFACE The International Library of Technology is the outgrowth of a large and increasing demand that has arisen for the r Reference Libraries of the International Correspondence Schools on the part of those who are not students of the Schools. As the volumes composing this Library are all printed from the same plates used in printing the Reference Libraries above mentioned, a few words are necessary regarding the scope and purpose of the instruction imparted to the students of—and the class of students taught by— these Schools, in order to afford a clear understanding of their salient and unique features. The only requirement for admission to any of the courses offered by the International Correspondence Schools, is that the applicant shall be able to read the English language and to write it sufficiently well to make his written answers to the questions asked him intelligible. Each course is com¬ plete in itself, and no textbooks are required other than those prepared by the Schools for the particular course selected. The students themselves are from every class, trade, and profession and from every country; they are, almost without exception, busily engaged in some vocation, and can spare but little time for study, and that usually outside of their regular working hours. The information desired is such as can be immediately applied in practice, so that the student may be enabled to exchange his present vocation for a more congenial one, or to rise to a higher level in the one he now pursues. Furthermore, he wishes to obtain a good working knowledge of the subjects treated in the shortest time and in the most direct manner possible. iii 343C03 IV PREFACE In meeting these requirements, we have produced a set of books that in many respects, and particularly in the general plan followed, are absolutely unique. In the majority of subjects treated the knowledge of mathematics required is limited to the simplest principles of arithmetic and mensu¬ ration, and in no case is any greater knowledge of mathe¬ matics needed than the simplest elementary principles of algebra, geometry, and trigonometry, with a thorough, practical acquaintance with the use of the logarithmic table. To effect this result, derivations of rules and formulas are omitted, but thorough and complete instructions are given regarding how, when, and under what circumstances any particular rule, formula, or process should be applied; and whenever possible one or more examples, such as would be likely to arise in actual practice—together with their solu¬ tions—are given to illustrate and explain its application. In preparing these textbooks, it has been our constant endeavor to view the matter from the student’s standpoint, and to try and anticipate everything that would cause him trouble. The utmost pains have been taken to avoid and correct any and all ambiguous expressions—both those due to faulty rhetoric and those due to insufficiency of statement or explanation. As the best way to make a statement, explanation, or description clear is to give a picture or a diagram in connection with it, illustrations have been used almost without limit. The illustrations have in all cases been adapted to the requirements of the text, and projec¬ tions and sections or outline, partially shaded, or full-shaded perspectives h'ave been used, according to which will best produce the desired results. Half-tones have been used rather sparingly, except in those cases where the general effect is desired rather than the actual details. It is obvious that books prepared along the lines men¬ tioned must not only be clear and concise beyond anything heretofore attempted, but they must also possess unequaled value for reference purposes. They not only give the maxi¬ mum of information in a minimum space, but this infor¬ mation is so ingeniously arranged and correlated, and the PREFACE v indexes are so full and complete, that it can at once be made available to the reader. The numerous examples and explanatory remarks, together with the absence of long demonstrations and abstruse mathematical calculations, are of great assistance in helping one select the proper for¬ mula, method, or process and in teaching him how and when it should be used. This volume is devoted principally to a description of stone and brick masonry and plain concrete. It also embraces the allied subjects of heavy foundations and piling. The text is so complete and the details so numerous that such a treatise can hardly be found in one volume elsewhere. Special attention has been given to the waterproofing of concrete. The subject of concrete building blocks has been exhaustively treated from the standpoint of the block manu¬ facturer and the small contractor who is about to embark in the block business. This volume should therefore prove useful to both the contractor and the architect. As it forms the basis for information on reinforced concrete, it will be found valuable if used in connection with volumes of this library that relate to that subject. The method of numbering the pages, cuts, articles, etc. is such that each subject or part, when the subject is divided into two or more parts, is complete in itself; hence, in order to make the index intelligible, it was necessary to give each subject or part a number. This number is placed at the top of each page, on the headline, opposite the page gumber; and to distinguish it from the page number it is preceded by the printer’s section mark (§). Consequently, a reference such as § 16, page 26, will be readily found by looking along the inside edges of the headlines until §16 is found, and then through §16 until page 26 is found. International Textbook Company CONTENTS Sands and Cements Section Page Cementing Materials.29 1 Limes.29 2 Cements.29 G Miscellaneous Cementing Materials ... 29 12 Sand and Its Mixtures.29 14 Mortars.29 18 Plain Concrete Materials Used in Concrete.30 1 Cement Mortar.30 2 Aggregates Other Than Sand.30 3 Proportioning of Ingredients ...... 30 15 Properties of Concrete. 30 20 Working Stresses and Strength Values of Concrete . 30 24 Concrete Mixtures . .. 30 29 Working of Concrete. 30 33 Building Stone and Brick Physical Properties of Building Stone . . 31 1 Classification of Building Stone.31 5 Durability of Building Stone.31 14 Selection of Building Stones.31 22 Clay Brick.31 30 TerraCotta. 31 37 Sand-Lime Brick.31 38 Size and Strength of Brick.31 39 m IV CONTENTS Elements of Stone Masonry Section Page Stone-Cutting Tools.32 1 Finish of Stonework ..32 5 Rubblework.32 17 Ashlar. 32 21 Care of Stonework. 32 28 Trimmings.'. 32 31 Footings. 32 43 Thickness of Walls . 32 54 Sidewalks. 32 55 Elements of Brick Masonry Methods of Laying Brick.33 1 Bond in Brickwork. 33 4 Difficulties in Bricklaying.33 14 Thickness of Brick Walls.33 15 Walls for Dwelling Houses.33 16 Walls for Warehouses.33 19 Types of Brick Walls. 33 28 Field Operations and Concrete Work Duties of the Superintendent ...... 34 1 Handling of Materials.34 5 Materials Used in Concrete Work .... 34 8 Devices Used in Concrete Construction . 34 10 Batch Mixers.34 11 Continuous Mixers.34 19 Quantitative Mixers. 34 24 Power Equipment for Mixers. 34 27 Hand-Cart Mixers. 34 29 Operation of Mixers. 34 31 Hauling Devices. 34 34 Hoisting Devices . . . •. 34 37 Combined Hoisting and Mixing Devices . . 34 43 Tools Used in Placing Concrete. 34 47 Machinery for Bending Steel. 34 48 Notes for the Superintendent ...... 34 51 Finish of Concrete. 34 53 CONTENTS v Tests on Cement Section Page Field Inspection.35 1 Sampling.35 3 Primary Tests.35 5 Tensile Strength.35 14 Secondary Tests. 35 24 Fineness . 35 27 Specific Gravity .. 35 32 Chemical Analysis. 35 34 Natural and Slag Cements. 35 36 Specifications. 35 36 Concrete Building Blocks Manufacture of Concrete Blocks.36 4 Essential Qualities of Concrete Blocks . . 36 12 Factors Affecting the Quality of Blocks 36 17 Materials of Manufacture.36 IS Manufacturing Processes. 36 21 Arrangement and Equipment of Factory . 36 39 Footings and Foundations.37 1 Laying and Fitting of Concrete Blocks . . 37 2 Wall Construction.37 4 jCauses of Failures in the Block Industry . 37 9 Cost of Concrete Blocks.37 10 Specifications.37 13 Heavy Foundations Single Footings.38 1 Compound Footings. 38 20 Rectangular Footings. 38 20 Fan-Shaped Footings. 38 35 Details of Cantilever Foundations .... 38 44 Design of Cantilever Foundations .... 38 50 Piling Varieties of Piles.39 1 Wooden Bearing Piles.39 2 Sand Piles.39 13 Metal Bearing Piles.39 14 SheetPiles.39 16 VI CONTENTS Piling —Continued Section ■ Page Methods.of Driving Piles.39 23 Strength of Piles. 39 29 Concrete Piling. 39 35 Construction and Driving of Concrete Piles 39 42 Special System of Concrete Foundations 39 57 Cost of Concrete Piles. 39 59 Strength and Reinforcement of Piles . . . 39 02 Reinforced-Concrete Sheet Piling .... 39 05 Steel and Other Metals Production of Iron.40 2 Cast Iron .40 5 Wrought Iron.40 7 Manufacture of Steel.40 10 Blister Steel and Shear Steel.40 14 Alloy Steels.40 15 Copper, Zinc, and Alloys.40 17 Loads in Structures Floor, Roof, and Wind Loads.41 1 Dead Load.41 1 Live Load.41 13 Snow and Wind Loads.41 * 27 Disposition of Loads.41 35 Insurance Engineering Purpose of Fire Insurance.42 1 Cause and Prevention of Fires.42 2 Extinguishment of Fires.42 14 Adjustment of Insurance Rates.42 16 Limits of Insurance.42 18 Waterproofing of Concrete Requirements of Waterproofing. 42 21 Classification of Systems. 42 23 Integral Method of Waterproofing .... 42 25 Superficial Method of Waterproofing ... 42 29 Membrane Method of Waterproofing ... 42 32 Roof Waterproofing. 42 35 Subsurface Waterproofing. 42 41 CEMENTING MATERIALS INTRODUCTION 1. Definitions. —Any substance that becomes plastic under certain treatment and subsequently reverts to a tena¬ cious and inelastic condition may, in a broad sense, be termed a cement. However, nearly all the cementing materials that are employed in building construction are obtained by the heating, or calcination , as it is called, of minerals composed wholly or in part of lime. The different composition of these minerals, as well as the properties of the calcined products, enables the various resulting substances to be classified as limes , hydraulic cements , plasters , and miscellaneous cements . Although all these materials have cementing properties, the term cement is commonly used to apply only to the group made up of hydraulic cements, hydraulic meaning that these substances possess the ability to set . or become hard, under water. 2. Uses of Cementing Materials. —Cementing mate¬ rials, in building construction, have three principal uses, namely, (1) as materials to hold other bodies together; (2) as materials with which to coat parts of structures; and (3) as building materials in themselves. The first use is illustrated by the mortar in the joints between stone and brick; the second, by a plastering material to coat walls; and the third, by concrete footings, walls, piers, pavements, etc. COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS' HALL, LONDON § 29 211—2 2 SANDS AND CEMENTS §29 3. Classification of Lames and Hydraulic Cements. Limes and hydraulic cements (which will hereafter be called simply cements) are composed essentially of oxide of calcium, or lime, generally called quicklime , with which may be combined certain argillaceous, or clayey, elements, notably silica and alumina, it being to these elements that the hydraulic properties of certain of these materials are due. The quantity of silica and alumina present in these substances enables them to be classified as common limes , hydraulic limes, and cements. The ratio of the quantity of silica and alumina present in these materials to the quantity of lime is called the hydraulic index. In common limes, this index is less than iW; in hydraulic limes, it lies between -nr 0 “ and and in cements, it exceeds ToV These limes merge into each other so gradually, however, that it is often difficult to distinguish the dividing line between them. LIMES CLASSIFICATION OF LIMES 4. The commercial varieties of lime may be classified as common, hydrated, and hydraulic. The common limes, also called quicklimes, may be subdivided into rich, or jat, lime , and meager, or poor, lime. 5. Common Limes.— The grade of common lime known as fat, or rich, lime is almost pure oxide of calcium, CaO, and contains only about 5 per cent, of impurities. It has a.specific gravity of about 2.3 and a great affinity for water, of which it absorbs about one-quarter of its weight. This absorption is accompanied by a great rise in temperature, by the lime bursting, and by the giving off of vapor. The lime finally crumbles to a powder. This powder occupies from two and one-half to three and one-half times as much volume as the original lime, the exact amount depending on its initial purity. When the lime is in this plastic state, it is § 29 SANDS AND CEMENTS 3 said to be slaked. It is then unctuous and soft to the touch, and from this peculiarity it derives the name of fat or rich. 6. Meager, or poor, lime consists of from 60 to 90 per cent, of pure lime, the remainder being impurities, such as sand or other foreign matter. These impurities have no chemical action on the lime, but simply act as adulterants. Compared with fat lime, poor lime slakes more slowly and evolves less heat. The resulting paste is also thinner and not so smooth, greatly resembling fat slaked lime mixed with sand. Poor lime is not so good for building purposes as fat lime, nor has it such extensive use. ¥ 7. Hydrated Lime. —The class of lime called hydra¬ ted lime (calcium hydrate) is merely thoroughly slaked fat lime in the form of a fine powder, Ca(OH) 2 . It is used extensively in conjunction with cement for making mortar, and also in the sand-lime brick industry. 8. Hydraulic Himes.— Limes that contain enough quicklime to slake when water is added, and enough clay or sand to form a chemical combination when wet, thus giving them the property of setting under water, are called hydrau¬ lic limes. Limes of this class are made by burning limestones con¬ taining from 5 to 30 per cent, of clay or sand. They are often considered as divided into three classes, namely, feebly hydraulic , ordinarily hydraulic , and eminently hydraulic , in proportion to the quantity of argillaceous materials present. The slaking qualities vary from slaking in a few minutes with considerable heat after water is added, in the feebly hydraulic, to slaking only after many hours, with practically no evolution of heat and without cracking or powdering, in the eminently hydraulic. The time of setting under water also varies from setting as hard as soap in 2 years, with the feebly hydraulic, to becoming as hard as stone in 3 or 4 days, with the eminently hydraulic. If carbonate of magnesia is present in the lime, it reduces the energy of the slaking, but increases the rapidity of the setting and the ultimate strength when set. 4 SANDS AND CEMENTS §29 As the quantity of clay is increased, hydraulic lime gradu¬ ally merges into hydraulic cement, so that it is often difficult to determine whether a material about on the border line is a lime or a cement. Hydraulic limes, however, are but little used in the United States, their place being taken by natural cement. These limes, therefore, will not be discussed further in this Section. MANUFACTURE OF TIME 9. Common lime is made by the calcination, or burning, in kilns, of limestone that is composed of pure or very nearly pure carbonate of lime, CaC0 3 . The burning is made at a temperature of from 1,400° to 2,000° F., which drives off part of the constituents in the form of carbon dioxide, C0 2 , leaving a product composed of practically pure oxide of calcium, CaO. The lime is prepared for use by the addition of water, which converts it into calcium hydrate, Ca(OH) 2 . This process is called slaking. If lime is underburned, it will not slake evenly, and hard pieces will be left that will not disintegrate when water is first added. If such lime is used in any work, the unslaked particles will disintegrate after being incorporated in the building, resulting in swelling, or blowing , and thus injuring the appearance and weakening the strength of the work. Blowing is particularly disastrous in plastering work, as it spoils the smooth surface that is necessary. Overburned lime also slakes slowly and cannot be employed to advantage. 10. Hydrated lime is prepared by crushing and grinding lump lime to a fine powder and then hydrating, or slaking, it by sprinkling water over it. The operation is performed in a shallow pan provided with plows, which keep turning the lime over so as to insure a thorough and even wetting. The heat drives off the surplus water, leaving the hydrated lime as a fine powder. Hydrated lime is considered better for use with Portland cement than ordinary slaked lime, both because it is more §29 SANDS AND CEMENTS 5 easily handled and measured and because it is thoroughly slaked. The latter property prevents the mortar from disintegrating. PROPERTIES OF TIME 11. Lime is slaked by spreading it on a suitable bed and then moistening it with water. This moistening gives rise to various phenomena. The lime almost immediately cracks, swells, and falls into a fine white powder, with a hissing sound and the evolution of heat and steam. The same process takes place slowly by the absorption of moisture from the atmos¬ phere. The lime falls into powder with increase of volume, but without perceptible heating. Lime slaked in the latter way is said to be air-slaked. It is deficient in setting proper¬ ties, however, and should not be employed for structural purposes. The quantity of water required for slaking is about one- third the volume of the lime. The entire quantity should be applied by sprinkling at one operation. The addition of cold water after the slaking has commenced lowers the temper¬ ature of the mixture and renders the lime granular and lumpy. An excess of water reduces the binding qualities. 12. The quality of common lime is indicated by the readiness with which the lumps fall to powder during slaking. Good lime should be free from unslaked lumps, the presence of which indicates that the limestone was not pure or that the process of calcination was imperfect. In order to obtain complete reduction, lime should be slaked several days before it is to be used. The resulting paste may be kept indefinitely, provided it is protected from the elements by being covered with the sand with which it will subsequently be mixed to make mortar. 13. Meager limes act similarly to fat limes, except that they are less energetic. Lime containing more than 5 or 10 per cent, of magnesia produces a mortar of greater strength, but such limes are slower slaking and less smooth, and for these reasons they are not liked so well by builders. 6 SANDS AND CEMENTS §29 14. Lime hardens by reason of the gradual absorption from the air of carbon dioxide, C0 2 , which slowly changes the lime from the form of calcium hydrate, Ca(OH ) 2 , to calcium carbonate, CaC0 3 , so that the final result is to restore the material to its original condition prior to burning, hardened lime mortar being practically limestone containing sand. To secure this result, however, all parts of the mortar must be readily accessible to dry air. If placed in damp situations or under water, or if excluded from contact with the air, lime mortars will not harden. Even in the interior of thin building walls of brick laid in lime mortar, the lime will be soft, crumbly, and sometimes even plastic after several years, although the edges of the mortar, where exposed, are per¬ fectly hard. It is chiefly for this reason that lime mortars are not employed in important work. CEMENTS CLASSIFICATION OF CEMENTS 15. Cement may be divided into four general classes: Portland , natural , puzzolan (also called pozzuolana ). and mixed. The relative importance of each cement is indicated by the order in which it is named. 16. Portland cement may be defined as the product resulting from the process of grinding an intimate mixture of calcareous (containing lime) and argillaceous (containing clay) materials, calcining (heating) the mixture until it starts to fuse, or melt, and grinding the resulting clinker to a fine powder. It must contain not less than 1.7 times as much lime by weight as it does of those materials which give the lime its hydraulic properties, and must contain no materials added after calcination, except small quantities of certain substances used to regulate the activity or the time of setting. 17. Natural cement is the product resulting from the burning and subsequent pulverization of an argillaceous lime- §29 SANDS AND CEMENTS 7 stone or other suitable rock in its natural condition, the heat of burning being insufficient to cause the material to start to melt. 18 . Puzzolan cement is a material resulting from grinding together, without subsequent calcination, an intimate mixture of slaked lime and a puzzolanic substance, such as blast-furnace slag or volcanic scoria. 19 . Mixed cements cover a wide range of products obtained by mixing, or blending, the foregoing cements with each other or with other inert substances. Sand cements , improved cements , and many second-grade cements belong to this class. Mixed cements, however, are of comparatively little importance, since they are rarely encountered in the market. CEMENT MANUFACTURE 20 , Portland Cement. —Portland cement is made from a great variety of materials, the most common combi¬ nations of ingredients used in the United States being argilla¬ ceous limestone and pure limestone; limestone and clay; marl or chalk and clay; and blast-furnace slag and limestone. After the separate ingredients have been subjected to chemical analysis and their composition determined, they are mixed in suitable proportions and ground together to an extremely fine powder. The powdered mixture is then burned in rotary kilns, which consist of long, slowly revolving, horizontal cylinders. The mixture is fed into one end of the kiln and passes toward the other end, where it is met by a blast of flame, which calcines the mixture and changes it into a clinker before it passes out of the kiln. The temperature of burning averages about 2,700° F. The burned clinker is in the form of irregular round balls about the size of a walnut, and after cooling, this clinker is ground to a fine powder. Cement made in this manner is usually extremely quick-setting and hardens so rapidly that it cannot be properly handled. To overcome this condition, 8 SANDS AND CEMENTS §29 a small quantity of calcium sulphate (plaster of Paris, or gypsum) is mixed with the finished cement, the result of this addition being to retard its activity, or rate of setting. Cement made by this process from blast-furnace slag and limestone is considered to be a true Portland cement. If, however, the material is not burned, the product is classed as puzzolan. The distinguishing characteristics of the manufacture of Portland cement are the use of an artificial mixture, the grinding before calcination, and the calcination to incipient fusion. 21. Natural Cement. —Natural cement is made by the direct burning of an argillaceous limestone, without the admixture of any other substances. The rock is not ground before burning, but is fed into the kilns just as it comes from the quarry. The kilns consist of vertical, stationary cylinders, into the top of which the cement rock and the fuel are placed in alternate layers, the burned cement being drawn finally from the bottom. After pulverization, the material is ready for the market. The process is characterized by the use of a single variety of material in its natural condition, the lack of grinding before burning, and the lower heat, about 1,500° F., employed, as compared with that required for Portland cement. 22. A large portion of the natural cement made in the United States is produced in the Rosendale district of New York State, and in the Louisville district lying in Indiana and Kentucky. Natural cement, accordingly, is often referred to as Rosendale or Louisville cement, but this usage is incorrect, unless applied merely to the cements pro¬ duced in those districts. Certain natural cements made in Europe are known as Roman cements. Natural cement is cheaper than Portland, but it is neither so reliable nor does it possess such good qualities. 23. Puzzolan Cements. —The only variety of puzzo¬ lan cement employed at all extensively in American practice §29 SANDS AND CEMENTS 9 is slag: cement. This cement is made by grinding together a mixture of blast-furnace slag and slaked lime. The slag used for this purpose is granulated, or quenched, in water as soon as it leaves the furnace, which operation drives off most of the dangerous sulphides and renders the slag puzzolanic. Slag cooled slowly in air is not suitable for cement. The lime employed is a fat quicklime that is thoroughly slaked and then dried. A small quantity of caustic soda is also generally added to the mixture, so as to hasten the otherwise rather slow time of setting. The distinguishing feature of the process is the absence of any burning. The orginal puzzolan cement was made by mixing lime with scoria that was obtained at the foot of Mount Vesuvius in Italy. It was the latter material that was used by the Romans in their famous constructions. A volcanic material called trass , found in Germany and Holland, and a sand known as Arenes, found in France, are other examples of puzzolanic substances. 24 . Mixed Cements. —A mixed cement known as silica, or sand, cement is made by grinding together Portland cement and sand, usually in equal parts. The sand is merely - i an adulterant, but the extra-hne grinding that the cement receives increases its sand-carrying capacity, so that its resulting strength is but little less than that of Portland cement. 25 . Improved cement is made from a mixture of Portland and natural cements. The mixture usually contains from 10 to 25 per cent, of the former and from 75 to 90 per cent, of the latter. The combination possesses many of the good features of both materials, and increases the value of natural cement in a proportion greater than the increased expense. 26 . Other varieties of mixed cements are often sold as second-grade Portlands , and consist of cement mixed with raw rock, cinders, sand, or inferior clinker. The use of such cements should not be tolerated in important structures. 10 SANDS AND CEMENTS §29 PROPERTIES OF CEMENTS 27 . The hydraulic cements differ from the limes in that they do not slake after calcination, and that they set, or harden, under water. They can be formed into a paste with water without any sensible increase in volume and with little, if any. disengagement of heat. They do not shrink appreci¬ ably in hardening, so that the sand and broken stone with which they are mixed are employed merely through motives of economy and not, as with limes, of necessity. 28 . Composition. —Hydraulic cements are composed essentially of silica, alumina, and lime, and also contain, in smaller quantities, iron oxide, magnesia, and sulphuric acid. In Portland cement, the active ingredients are certain silicates and aluminates of lime. The iron oxide acts similarly to the alumina, but is usually present in much smaller quantity. The gray color of cement is due to the presence of this iron, since the silicates and aluminates of lime are white. Magnesia acts as an adulterant, and if present in excess of 4 or 5 per cent., may impart injurious properties to the material, espe¬ cially if it is used in sea-water. The presence of sulphuric acid is principally due to the addition of calcium sulphate, which is employed to control the time of setting. Like magnesia, sulphuric acid is injurious if present in excess. 29 . When water is added to Portland cement, the silicates and aluminates of lime are decomposed and go partly into solution, from which calcium hydrate is precipitated and crystallized in the form of long, needle-like, interlocking crystals. The strength of cement is due to the formation of these crystals, and the continued process of this crystallization gives the cement its property of increasing in hardness and strength. The setting of cement, then, is due to the solution of the aluminates of lime, while the slower decomposition and crystallization from the silicates gives the cement its strength, which increases with age. The precise chemical reactions that take place in the setting and hardening of hydraulic cements are still, however, disputed questions. §29 SANDS AND CEMENTS 11 30 . Color. —The color of the different grades of cement is variable, but in certain cases it is distinctive. Portland cement is a dark-bluish or greenish gray; if it is a light yellow, it may indicate underburning. Natural cement ranges in color from a light straw, through the grays, to a chocolate brown. Slag cement is gray with usually a tinge of lilac. In general, however, the color of cement is no criterion of its quality, except when a certain brand shows a variation in color, thus indicating a lack of uniformity in the raw materials or in the process of manufacture. 31 . Weiglit. —Cement is packed either in wooden barrels or in cloth or paper bags, the latter being the form of package most commonly employed. A barrel of Portland or of slag cement contains the equivalent of four bags, while but three bags of natural cement equals a barrel. The average weights of the various cements are given in Table I. TABLE I AVERAGE WEIGHTS OF HYDRAULIC CEMENTS Kind of Cement Net Weight of Bag Net Weight of Barrel Weight per Cubic Foot Pounds Pounds Pounds Packed Loose Portland. 94 376 100-120 70-90 Natural . 94 282 75-95 45-65 Slag. 82I 330 80—100 55-75 In proportioning mortar or concrete by volume, the com¬ mon assumption is that a bag of Portland cement occupies .9 cubic toot. 32 . Physical Properties. — Hydraulic cements are characterized by the properties of specific gravity, time of setting, fineness, strength, soundness, and composition. A discussion of these properties, the methods of testing employed in determining them, and the specifications used for cements 12 SANDS AND CEMENTS §29 that are based on these properties will be given in another Section. 33. Distinguishing Characteristics. — Portland cement may be distinguished by its dark color, heavy weight, slow rate of setting, and greater strength. Natural cement is characterized by lighter color, lighter weight, quicker set, and lower strength. Slag cement is somewhat similar to Portland, but may be distinguished from it by its lilac-bluish color, by its lighter weight, and by the greater fineness to which it is ground. 34. Adaptability. — Portland cement is adaptable to any class of mortar or concrete construction, and is unques¬ tionably the best material for all such purposes. Natural and slag cements, however, are cheaper, and under certain con¬ ditions, may be substituted for the more expensive Portland cement. All heavy construction, especially if exposed, all reinforced-concrete work, sidewalks, concrete blocks, founda¬ tions of buildings, piers, walls, abutments, etc., should be made with Portland cement. In second-class work, such as is used in rubble masonry, brick sewers, unimportant wx>rk in damp or wet situations, or in heavy work in which the working loads will not be applied until long after completion, natural cement may be employed to advantage. Slag cement is best adapted to heavy foundation work that is immersed in water or at least continually damp. This kind of cement should never be exposed directly to dry air, nor should it be subjected either to attrition or impact. MISCELLANEOUS CEMENTING MATERIALS 35. Plaster is probably the most important of the miscellaneous cementing materials. It is made by burning a sulphate of lime known as gypsum. By this treatment most of the water is drawn off and the material is rendered cementitious. The most common varieties of plaster are known as plaster of Paris or stucco , flooring plaster , and wall §29 SANDS AND CEMENTS 13 plaster (prepared by mixing with hair). Keene's cement and Parian cement are varieties of plaster used for hard finishes in buildings. 36 . Since the common hydraulic cements will often destroy the appearance of the stone at the joints, the non- staining: cements have been devised for use in exterior walls of buildings made of cut stone. These cements are either of the Portland type from which the iron has been eliminated or of the puzzolan type. Several imported and one or two American cements of this kind are to be found on the market. 37 . For waterproofing purposes, cements have been devised that, when hardened, tend to resist the action of water and keep the interior of the construction dry. 38 . Bituminous cements and coal-tar cements are materials used in laying cellar floors, or for waterproofing walls, arches, tunnels, etc. These materials are the only ones that combine elasticity with the property to resist water. 39 . Numerous cementing materials are made for other special purposes, but their use is comparatively limited and hence will not be discussed in this Section. 14 SANDS AND CEMENTS §29 SAND AND ITS MIXTURES SAND INTRODUCTION 40. Sand is an aggregation of loose, incoherent grains of crystalline structure, derived from the disintegration of rocks. It is called silicious, argillaceous, or calcareous, according to the character of the rock from which it is derived. Sand is obtained from the seashore, from the banks and beds of rivers, and from land deposits. The first class, called sea sand, contains alkaline salts that attract and retain moisture and cause efflorescence in brick masonry. This efflorescence is not at first apparent but becomes more marked as time goes on. It can be removed temporarily at least by washing the stonework in very dilute hydrochloric acid. The second, termed river sand, is generally composed of rounded particles, and may or may not contain clay or other impurities. The third, called pit sand, is usually composed of grains that are more angular; it often contains clay and organic matter. When washed and screened, it is a good sand for general purposes. 41. Uses of Sand. —The principal reasons for using sand in making mortar are that it prevents excessive shrinkage and reduces the quantity of lime or cement required. Lime adheres better to the particles of sand than it does to its own particles; hence, it is considered that sand adds strength to lime mortar. On cement mortar, on the contrary, sand has a weakening effect. Sand is also used as a cushion to dis¬ tribute the pressure of structures over soft soils, as in a foundation and joint filling for pavements, and for plastering. § 29 SANDS AND CEMENTS 15 TESTING OF SAND 42 . The quality of sand intended for use in mortar is ascertained by determinations of its weight, specific gravity, percentage of voids, character of grain, fineness, purity, and by strength tests of the actual mortar. For mortars and concretes of cement, the character of the sand employed is most important, since it vitally affects the strength, density, and permanency of the finished structure. 43 . Weight. —The weight of sand is determined by merely filling a cubic-foot measure with dried sand and obtaining its weight. Dry sand weighs from 80 to 120 pounds per cubic foot; moist sand, however, occupies more space and weighs less per cubic foot. The weight of sand is more or less dependent on its specific gravity and on the size and shape of the sand grains, but, other things being equal, the heaviest sand makes the best mortar. 44 . Specific Gravity. —The specific gravity of sand is found by a method similar to that used for finding the specific gravity of cement, and will be described in another Section; it ranges from 2.55 to 2.80. For all practical purposes, the specific gravity may be assumed to be 2.65 with little danger of error. 45 . Percentage of Voids. —By percentage of voids is meant the amount of air space in the sand. Struc¬ turally, it is one of the most important properties of sand. The greater these voids, the more cement paste will be required to fill them in order to give a dense mortar; or, conversely, with a given proportion of cement and sand, the sand that has the smallest voids will produce the strongest, the densest, and the most impervious mortar. The percentage of voids may be determined by observing the quantity of water that can be introduced into a vessel filled with sand, but it is best computed from the specific gravity and the weight per cubic foot of the sand to be tested. The weight per cubic foot of sand containing no voids at all 16 SANDS AND CEMENTS §29 is evidently equal to the product of its specific gravity times 62.5, or the weight of water per cubic foot. Therefore, it follows that r • 100 X weight per cubic foot percentage of voids = 100-;- : - 62.5 X specific gravity Example.— What is the percentage of voids in a sand having a specific gravity of 2.65 and weighing 105 pounds per cubic foot? Solution.— Substituting in the formula, the percentage of voids is 10 °-6^H= 100 - 63 ' 4 - 36 ' 6 - AnS ' The percentage of voids is dependent principally on the size and shape of the sand grains and the gradation of its fineness, and hence will vary from 25 to 50 per cent. Sand containing over 45 per cent, of voids should not be used to make mortars. 46 . Sliape of Sand Grains. —The shape of the grains of sand is of chief importance in the influence that the sand exerts on the percentage of voids. Obviously, a sand with rounded grains will compact into a more dense mass than one whose grains are angular or flat like particles of mica. Therefore, the more nearly the grains approach the spherical in shape, the more dense and strong will be the mortar. This fact must be carefully remembered, as it is contrary to the common opinion on the subject. 47 . Fineness. —The fineness of sand is determined by passing a dried sample through a series of sieves having 10, 20, 30, 40, 50, 74, 100, and 200 meshes, respectively, to the linear inch. The result of this test, expressed in the amount of sand passing each sieve, is known as the granulometric composition of the sand. Material that does not pass a |-inch screen is not considered to be sand, and should be separated by screening. Sand that is practically all retained on a No. 30 sieve is called coarse, while 80 or 90 per cent, of sand known as fine will pass through this sieve. Fine sand produces a weaker mortar than coarse sand, but a mixture of fine and coarse sand will surpass either one. §29 SANDS AND CEMENTS 17 48 . Purity. —The purity, or cleanness, of sand may be roughly ascertained by rubbing it between the fingers and observing how much dirt remains. To determine the per¬ centage of the impurities more accurately, a small dried and weighed sample is placed in a vessel and stirred up with water. The sand is allowed to settle, the dirty water poured off, and the process repeated until the water pours off clear. The sand is then dried and weighed. The loss in w T eight gives the quantity of impurities contained in the sand. The presence of dirt, organic loam, mica, etc. is decidedly injurious and tends to weaken the resulting mortar. Clay or fine mineral matter in small proportions may actually result in increased strength, but excessive quantities of these mate¬ rials may be a possible source of weakness. The best modern practice limits the quantity of impurities found by this washing test to 5 per cent. 49 . Strength of Sand Mortar. —It is also advisable, prior to the selection of a sand, to determine what its strength will be when made into mortar. Sands that appear excellent are sometimes incorporated into work, with the result that a weak and soft mortar is obtained, thereby causing the loss of considerable time and money. Proper care in the selection of sand, even if costly, will generally prove to be true economy, especially if the sand is to be used in important structures. PREPARATION OF SAND 50 . Sand is prepared for use by (1) screening to remove the pebbles and coarser grains, the fineness of the meshes of the screen depending on the kind of work in which the sand is to be used; (2) washing, to remove salt, clay, and other foreign matter; and (3) drying, if necessary. When dry sand is required, it is obtained by evaporating the moisture either in a machine, called a sand dryer , or in large, shallow, iron pans supported on stones, with a wood fire placed underneath. 18 SANDS AND CEMENTS §29 MORTARS PROPORTIONS OF INGREDIENTS 51 . Mortars for structural purposes are composed of lime or cement and sand mixed to the proper consistency with water. The proportions of the ingredients depend on the character of the work in which the mortar is to be used. The quality of the mortar depends on the quality of its con¬ stituents, the proportions in which they are combined, and the methods by which they are mixed and used. In proportioning mortar, it is customary to designate the quantities of the separate ingredients by a ratio, such as 1-1, 1-2, 1-3, etc. Thus, 1-1 signifies that the mortar is composed of 1 part of lime or cement to 1 part of sand; 1-2, that 1 part of lime or cement is used to 2 parts of sand; etc. These measurements are usually made by volume instead of by. weight. The first number of the ratio always indicates the quantity of lime or cement, which for con¬ venience, is taken at unity of volume. LIME MORTARS 52 . Ingredients.—Sand is added to lime or cement to increase its bulk and thus cheapen the material. In lime mortar, however, besides effecting an economy, the presence of sand is necessary to prevent the shrinkage that would otherwise occur during the hardening of the paste. When a mortar is made of lime and sand, enough lime should be present to just cover completely each grain of sand. An excess of lime over this quantity causes the mortar to shrink excessively on drying, while a deficiency of lime produces a weak and crumbly mortar. The correct quantity of lime depends on the character of the ingredients, the method of treatment, and, to some extent, on the judgment of the builder, the mixtures employed varying from 1-21 to 1-5. Building laws in many municipalities require the SANDS AND CEMENTS 19 $ 29 use of a 1-3 mixture, and for most materials this proportion will be found satisfactory, although for rich, fat limes a l-3£ or a 1-4 mixture is sometimes preferable. 53 . Mixing. —In mixing lime mortar, a bed of sand is made in a mortar box, and the lime distributed as evenly as possible over it, first measuring both the lime and the sand in order that the proportions specified may be obtained. The lime is then slaked by pouring on water, after which it should be covered with a layer of sand, or, preferably, a tarpaulin, to retain the vapor given off while the lime is undergoing the chemical reaction of slaking. Additional sand is then used, if necessary, until the mortar attains the proper proportions. Care should be taken to add just the proper quantity of water to slake the lime completely to a paste. If too much water is used, the mortar will never attain its proper strength, while if too little is used at first, and more is added during the process of slaking, the lime will have a tendency to chill, thereby injuring its setting and hardening properties. Rather than make up small batches, it is considered better practice to make lime mortar in large quantities and to keep it standing in bulk so that it can be used as needed. 54 . Use of Dime Mortar.— Lime mortar is employed chiefly for brickwork of the second class, and its use is contin¬ ually decreasing as that of cement increases. It is absolutely unsuitable for any important construction, because it possesses neither strength nor the property of resisting water. It cannot be used in damp or wet situations, nor should it ever be laid in cold weather, as it is very susceptible to the action of frost, being much injured thereby. Moreover, since it hardens by the action of dry air, only the exterior of lime mortar ever becomes fully hardened, so that anything like a concrete with lime as a matrix is impossible. However, for second-class brickwork, such as is commonly used in the walls of smaller buildings, lime mortars are economical and sufficiently good. 20 SANDS AND CEMENTS §29 55. Strength of Dime Mortars.— The strength of lime mortars is extremely variable, depending on the ingredients themselves and on their treatment, environment, etc. More¬ over, it is unsafe to figure a lime-mortar joint as possessing much strength, since only a part of the joint is hardened and capable of developing any strength at all. The tensile strength of thoroughly hardened 1-3 lime mortars averages from 40 to 70 pounds per square inch, and the compressive strength from 150 to 300 pounds. CEMENT MORTARS 56 . Ingredients.—Cement mortars consist of cement, sand, and water, and the character and proportions of these ingredients vitally affect the properties of the resulting prod¬ uct. As has been stated, the cement for all structures of importance should be Portland, although natural and slag cements may occasionally be employed to advantage where the conditions permit. 57 . The sand for all mortars should be clean, of suitable size and granulometric composition. For structures designed to withstand heavy unit stresses, or for those intended to resist either the penetration of moisture or the actual pressure of water, the selection of the sand should be most carefully made. Generally, it is not advisable to use a sand containing over 5 per cent, of loam by the washing test, nor one that soils the fingers when it is rubbed between them. These points should be especially considered when the sand is to be used for mortars intended for facing, pointing, or waterproofing. Moreover, for most classes of work, the preference should usually be given to a rather coarse sand, although sand containing all sizes of grains, from coarse to fine, more nearly approaches the ideal in producing the densest and strongest mortar. Very fine sand, such as is found on the seashore, should not be employed in mortar unless it is intended simply for pointing or for grouting. §29 SANDS AND CEMENTS 21 A simple method of determining the best sand for cement mortar is to prepare mixtures of the cement, sand, and water, using the same quantities in each case, and then to place each mixture in a measure; that mixture giving the least volume of mortar may be considered to contain the most desirable sand for use. Limestone screenings, brick dust, crushed cinders, etc., are sometimes substituted for sand in making mortars, and, if care is taken in their selection, they may prove economical and entirely suitable for the purpose. 58 . The water used in mixing cement mortar should i be clean, fresh, and free from dirt or vegetable matter. Water containing even small quantities of acid may seriously injure the mortar. The presence of oil will result in slow setting and decreased strength. Salt water may be used if necessary, but it also retards the setting, and decreases the strength. 59 . Proportion of Ingredients. —The theory of the composition of a correctly proportioned mortar is that the cement paste will just a little more than fill all the voids between the particles of sand, thus giving an absolutely dense mortar at the least expense. If more cement is used, the cost will be increased, while less cement will result in a weaker and porous mortar. The correct proportion of cement to sand, therefore, is more or less variable, depending on the granulometric composition of the sand. Since, however, Portland-cement paste that has set weighs nearly as much as sand, and since the average sand contains about 30 to 40 per cent, of voids, it is evident that 1-3 mixtures most nearly approach the best and most economical proportion. This mixture is in fact most generally employed for mortars used in buildings, walls, etc. and is the proportion commonly specified by corporations and municipalities for such work. 60 . Mortars, however, are made in proportions varying from 1-1 to 1-8. The richer mixtures are used for facing, pointing, waterproofing, granolithic mixtures, etc., the 22 SANDS AND CEMENTS §29 1-2 mixture being usually made for such purposes. The leaner mixtures are used for rough work, filling, backing, etc., but should never be employed where either much strength or much density is desired. Natural-cement mortars are commonly made 1 part of sand less than Portland-cement mortars intended for the same purpose; that is, where a 1-3 Portland-cement mortar would be used, a 1-2 natural mortar would be required, although natural-cement mortars should be decreased by about 2 parts of sand to equal the strength of Portland. In other words, a 1-4 Portland mortar closely equals the strength of a 1-2 natural mortar. Puzzolan cements are usually proportioned the same as-Portlands. 61 . Cements are commonly proportioned by volume, the unit volume of the cement barrel being assumed. Various values for this unit volume are taken by different authorities, but the general practice is to assume that the Portland- cement barrel contains 3.6 cubic feet, and that the bag contains .9 cubic foot. If a 1-3 mortar is desired, a box having a capacity of 10.8 cubic feet is filled with sand and mixed with 4 bags or 1 barrel of cement. A box 3 feet 3^ inches square and 1 foot deep will have a capacity of very nearly 10.8 cubic feet and besides makes a convenient size of box for actual work. 62 . The quantity of water required varies with the richness of the mixture and the character of the ingredients, so that it is difficult, if not impossible, to state just how much should be used at all times. For general purposes, the mortar should be of a plastic consistency—firm enough to stand at a considerable angle, yet soft enough to work easily. Wet mortars are easiest to work and are, as a rule, the strongest and most dense when hardened. However, they are subject to greater shrinkage, are slower setting, and are more easily attacked by frost. Dry mortars, on the other hand, are often friable and porous. The consistency of the mortar, therefore, should vary with the materials used and with the conditions to be met. §29 SANDS AND CEMENTS 23 63. In Table II are given the quantities of materials required to produce 1 cubic yard of compacted mortar. The proportions are by volume, a cement barrel being assumed to contain 3.6 cubic feet. Of course, the quantity of mortar produced from any mixture of materials will vary with the character of the ingredients, but the data given in the table will serve as a guide for the quantities required under average conditions. TABLE II MATERIALS REQUIRED PER CUBIC YARD OF MORTAR Kind of Mixture Portland Cement Barrels Loose Sand Cubic Yards I—I. 4-95 1-2. 3.28 .88 l ~3 . 2.42 1.01 i -4 . 1.99 1.06 i -5 ... 1.62 1.11 i-6. i -34 i*i 5 . 1.18 1.17 i-8. 1.05 1.18 Example. —How much cement and sand will be required to obtain 8.5 cubic yards of 1-3 Portland-cement mortar? Solution. —According to Table II, 1 cu. yd. of a 1-3 Portland- cement mortar requires 2.42 bbl. of cement; therefore, 8.5 cu. yd. will require 8.5X2.42 = 20.57 bbl. of cement. Also, since 1 cu. yd. of a mixture of this kind requires 1.01 cu. yd. of sand, the quantity of sand required will be 8.5X1.01 = 8.59 cu. yd. Ans. 64. Mixing:. —It is essential in making cement mortars to secure a complete and uniform mixture of the separate ingredients. This kind of a mixture is of course best obtained by means of mechanical contrivances; but since mechanical mixers are expensive to install and operate, it is only on extensive works, where large quantities of material can be used in a short time, that such appliances can be employed to advantage. 24 SANDS AND CEMENTS §29 65 . Mortar that is to be mixed by hand is prepared on a platform or in a mortar box. The sand is first measured by means of a bottomless barrel, or, better, by means of a low, square, bottomless box with handles on the sides and of such a size that it will give the correct proportion of sand. After filling the box, the sand is struck off level, the box lifted up, and the sand spread in a low, flat pile. The required number of bags of cement are then emptied on the sand and spread evenly over it. The pile is then turned over and mixed with shovels, working through it not less than four times. After this operation, the dry mixture is formed into a ring, or crater, and the water intended to be used is poured into the center. The material from the sides of the basin is then shoveled into the center until the water is entirely absorbed, after which the pile is worked again with shovels and hoes until the mixture is uniform and in a plastic con¬ dition. In mixing, the mortar should be completely turned over not less than four times dry and from four to six times after the water has been added. 66. Another method of mixing, where a mortar box is used, is to gather the mixed dry materials at one end of the box and pour in the water at the other end, drawing the mixture into the water with a hoe a little at a time, and hoeing until a plastic consistency is obtained. 67 . Good results can be secured by either method, provided sufficient care is exercised. If a batch of mortar is once made too wet, it cannot be brought back properly to a drier consistency; also, an excessively wet mortar is difficult to work and is often productive of poor results. The best plan, therefore, in adding the water is to pour in first a little less than is required and then make up the deficiency by means of a watering can or a sprinkling hose. In this way, an excess of water is guarded against. §29 SANDS AND CEMENTS 25 PROPERTIES AND USES OF CEMENT MORTARS 68. Strength. —The strength of a mortar is measured by its resistance to tensile, compressive, cross-breaking, and shearing stresses, and also by determinations of its adhesion to inert surfaces, its resistance to impact, abrasion, etc. In masonry construction, although mortar is generally subjected only to compressive stress, it is also at times called on to withstand stresses of tension, cross-breaking, and shear. Therefore, in practical design, it is necessary to know the resistance of mortar to each of these forms of stress. There is no definitely fixed ratio between the strengths of mortar subjected to these different stresses, but there is nevertheless a close relation between them, so that, practically, it may be assumed that if a mortar shows either abnormally high or low values in any one test, the same relation will develop when tested under other stresses. In practice, therefore, the strength of mortar is commonly determined TABLE III TENSILE STRENGTH OF CEMENT MORTARS Proportions Tensile Strength, in Pounds per Square Inch Portland Cement Natural Cement Cement Parts Sand Parts 7 Days 28 Days 3 Months 7 Days 28 Days 3 Months I I 45 ° 600 610 160 245 280 I 2 280 38° 395 115 I 75 2I 5 I 3 170 245 280 85 130 ^5 I 4 !2S 180 220 60 IOO J 35 I 5 80 140 175 40 75 110 I 6 50 115 145 2 5 60 90 I 7 3 ° 95 120 15 5 o 75 I 8 20 70 IOO 10 45 65 2G SANDS AND CEMENTS §29 through its resistance to tensile stresses, and its resistance to other forms of stress is computed from these results. 69. The tensile strength of mortar has been shown to vary with the character of its ingredients, with its consistency, its age, and with many other factors. In Table III is given a fair average of the tensile strength that may be expected from mortars of Portland and natural cements that are made in the field and with a sand of fair quality but not especially prepared. The strength of Portland-cement mortar increases up to about 3 months; after that period, it remains practically constant for an indefinite time. Natural-cement mortar, on the other hand, continues to increase in strength for 2 or 3 years, its ultimate strength being about 25 per cent, in excess of that attained in 3 months. The strength of slag- cement mortar averages about three-quarters of that of Portland-cement mortar. 70. The compressive strength of cement mortars is usually given in textbooks as being from eight to ten times the tensile strength. This value is rather high for the average mortar, a ratio of from 6 to 8 being one more nearly realized in practice. The ratio increases with the age and richness of the mortar, and varies considerably with the quality of the sand. Portland-cement mortars of 1-3 mixture that are 3 months old develop, on an average, a compressive strength of about 1,800 pounds per square inch, while 1-2 natural-cement mortars average about 1,600 pounds. The strength of mortars in cross-breaking and shear may be taken at about one and one-half to two times the tensile strength, with a fair amount of accuracy. 71. The adhesion of mortars to inert materials varies both with the character of the mortar and with the roughness and porosity of the surfaces with which they are in contact. The adhesion of 1-2 Portland-cement mortar, 28 days old, to sandstone averages about 100 pounds per square inch; to limestone, 75 pounds; to brick, 60 pounds; to glass, SANDS AND CEMENTS 27 § 29 50 pounds; and to iron or steel, 75 to 125 pounds. Natural- cement mortars have nearly the same adhesive strength as those made of Portland cement. 72. The resistance to abrasion is difficult to measure exactly, but experiments appear to show that mortars of all cements develop the best resistance to abrasion when mixed in the proportion of 1-2. Sidewalks and similar construc¬ tions, therefore, are usually made of this mixture. 73. Lime-Cement Mortars.—In bricklaying and in other places in which mortar is employed, it is frequently desired to use a material that is more plastic or smoother than pure cement mortar. This quality is usually obtained by adding from 10 to 25 per cent, of lime to the mortar. This addition of lime not only renders the mortar more plastic, and hence easier to work, but also increases both its adhesive strength and its density, which assists in making the mortar waterproof. The strength' of cement mortars, moreover, is generally increased by small additions of lime, such as 10 per cent., while even 25 per cent, causes no sensible weakening. • Great care should be taken that the lime is. thoroughly slaked when used in this manner, for any unslaked particles may. through their expansion, ultimately cause disinte¬ gration of the mortar. For this reason, hydrated lime is to be preferred for use in cement mortar, because its complete slaking is assured. Hydrated lime may also be more readily handled and measured on the work. Occasionally, small quantities of cement are added to lime mortars so as to make them set quicker and to increase their strength. Such mixtures, however, are not especially economical nor are they convenient in practice. For these reasons, they are very seldom employed. 74. Retemperlng. —Sometimes, during building oper¬ ations, more mortar is mixed than is required for immediate use, and for this or some other reason batches of it are allowed to stand. In such cases, mortar composed of cement, sand, 28 SANDS AND CEMENTS §29 and water soon begins to set and finally becomes hard. Thus, when it is desired to use this material, more water has to be added and the mixture worked until it again becomes plastic. This process is called retempering. Laboratory tests generally show that retempering slightly increases the strength of mortar, but the reworking is more thorough as a rule in the laboratory than would be the case in actual work. Any part of the hardened mortar that is not retem¬ pered is a source of weakness when incorporated in the building. The adhesive strength of cement, moreover, is greatly diminished by this process. For these reasons, it is generally inadvisable to permit the use of retempered mortars; but if they are allowed, great care should be taken to see that the second working is thorough and complete. 75. Laying Mortar in Freezing Weather.— Frost or even cold has a tendency to retard greatly the set of cement mortars. When the temperature, moreover, is so low that the water with which the mortar is mixed freezes before it combines with the cement, it may, if care is not exercised, result in complete destruction of the work. A single freezing is not particularly harmful, because when thawing occurs, the arrested chemical action continues. A succession of alternate freezings and thawings, however, is extremely injurious. Nevertheless, Portland-cement mortars may be laid even under the worst conditions if certain precautions are observed, but mortars of natural cement should never be used in extremely cold weather, as they are generally completely ruined by freezing. The bad results that arise during mild frost may be success¬ fully guarded against by heating the sand and water and by using a quick-setting cement mixed rich and as dry as possible. In extremely cold weather, salt must be added to the water, so as to convert it into a brine that requires a temperature lower than 32° F. to freeze it. The common rule for adding salt is to use a quantity equal to 1 per cent, of the weight of the water for each degree of temperature that is expected below 33° F. Thus, at 32° F., a 1-per-cent, solution would §29 SANDS AND CEMENTS 29 be used, while at 25°, an 8-per-cent, solution would be required. Solutions greater than 12 per cent, should not be employed, and if a temperature below 20° F. is expected,- heat must be used in addition to the salt. The finished work should also be protected with canvas or straw. Manure should not be used for this purpose, because the acids it contains tend to rot the cement. Unless the conditions are such as to make it imperative, it is not advisable to lay mortars during freezing weather. 76. Shrinkage. —Cement mixtures exposed to the air shrink somewhat during the process of hardening, while those immersed in water tend to expand. The shrinkage of ordinary cement mortars is slight, and when they are used as a bonding material it need not be considered. When used as a monolith, as in sidewalks, shrinkage, as well as temper¬ ature changes, is to some extent guarded against by means of expansion joints. However, in such cases, the best plan is to keep the mortar wet during setting. This can be done by means of moist straw or by sprinkling the mixture with water. Water is the life of cement and a liberal application of it during setting not only prevents excessive shrinkage, but materially increases the strength and durability of the mortar. 77. Pointing.— In the process known as pointing, pro¬ jecting joints of mortar are formed in stone masonry. Walls finished in this manner have not only a better appearance, but they are protected from injury by frost, as no water can accumulate in the joints. In pointing, the joints are raked out an inch or two from the face of the wall and the pointing material introduced. The best pointing mortar is made of Portland cement mixed with 1 or 2 parts of very fine sand. The addition of a little lime to the mortar also makes it waterproof, more adhesive, and easier to work. The joints formed in pointing should be kept wet for several days by sprinkling. Pointing should never be attempted in freezing weather. 30 SANDS AND CEMENTS §29 78. Grouting. —By grouting is meant the process of filling spaces in masonry with a thin, semifluid mixture known as grout. This mixture consists of cement, 1 or 2 parts of sand, and an excess of water. Grout can be used for filling the voids in walls of rubble masonry, for backing arches and tunnels, and for filling the joints between paving brick. In fact, it can be used in all places where it is imprac¬ ticable to lay mortar in the ordinary manner. When hard¬ ened, grout is weak, friable, and porous; therefore, it should not be employed if it can be avoided. 79. Waterproofing of Mortars. —All cement mortars to a greater or less degree absorb water. They therefore not only permit dampness to penetrate a building, but tend also to permit of destruction by frost. Cement mortars may best be made almost impermeable by using only sand that has been carefully graded and by adding hydrated lime. To waterproof mortars by other means, two classes of materials may be made—one to be used as a surface wash on the finished building, and the other to be incorporated into the mortar while it is being made. Surface washes are generally based either on a mineral wax, like paraffin, or on silicate of soda, both of which fill the voids in the mortar and tend to render it waterproof. Another wash that is often used consists of solutions of soap and alum. These solutions are applied alternately and combine to form insoluble fatty acids. The compounds that are incorporated into the mortar while it is being made depend, as a rule, on the chemical formation of a lime soap, which fills the interstices of the mortar. Silicate of soda, paraffin, Japan wax, hydrated lime, and other similar materials are also used. A water¬ proofing cement is to be found on the market that is made by introducing wax into the clinker during the process of manufacture. Practically all these compounds are slightly beneficial in increasing the property of water resistance, but carefully graded sand, as previously mentioned, will usually produce $ 29 SANDS AND CEMENTS 31 far more effective and permanent results than any of these compounds. 80. Coloring of Mortars. —Colors are often used in mor¬ tars to effect contrasts, or to subdue the glaring tone of cement in sidewalks or in similar situations. For the latter purpose, lampblack is commonly employed, 1 or 2 per cent, changing the color of cement to gray, or slate. In order to produce architectural effects, colors consisting of various mineral substances are added to the mortar in proportion of from 1 to 10 per cent. Red lead weakens mortar and should not be used. The color of hardened mortar is quite different in appearance from one that is still wet, so that where it is important to secure the correct tints, preliminary trials should be made until the proportions desired have been determined. The various materials employed to produce different colors in mortar, together with the quantity required per barrel of cement, are as follows: For gray, 2 pounds of lampblack; for black, 45 pounds of manganese dioxide; for blue, 19 pounds of ultramarine; for red, 22 pounds of iron oxide; for bright red, 22 pounds of Pompeian or English red; and for violet, 22 pounds of violet oxide of iron. • . . . * . ■ PLAIN CONCRETE MATERIALS USED IN CONCRETE DEFINITIONS AND TERMS 1. Concrete is usually made of cement, sand, and broken stone. The cement in a plastic state, either by itself or with the sand that is generally mixed with it, is called the matrix, while the broken stone, gravel, or other material used as a filler is called the aggregate. The sand is correctly classed as a part of the aggregate, although some engineers include it with the matrix. The aggregate is used to cheapen concrete. Pure, or neat , cement, when wet with water, would in a way fulfil all the physical requirements of concrete, but it would be too expensive. 2. In the concrete of today, hydraulic cement is used almost exclusively. For this reason, the term concrete , as commonly used, refers only to that variety. In specifying any other kind of concrete, the usual custom is to mention it by its full name, as bituminous concrete , lime concrete , etc. Such varieties, however, are of comparatively little impor¬ tance, and will not be treated here. The term concrete, besides being restricted to hydraulic- cement concrete, has another restriction: the aggregate must not be sand alone, although it may be partly sand. A mix¬ ture of hydraulic cement, sand, and water is called by the special name of mortar. COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS’ HALL, LONDON § 30 211—4 2 PLAIN CONCRETE §30 Concrete is usually named from the kind of aggregate used. For example, stone concrete embodies the use of broken stone or coarse pebbles, while in cinder concrete, the aggre¬ gate consists of cinders or broken slag. 3. The proportions of the several ingredients used in mixing concrete depend on the purpose for which the concrete is to be used, as well as on the strength-resisting properties required by the construction. The proportion of cement and sand to the broken stone depends on the spaces between the stones, which are known as voids. In all instances, there must be sufficient mortar to till the voids entirelv and to cover all surfaces of the separate stones. All concrete in use in modern construction has the property of hardening, or setting, either under water or in the air. Concrete is now extensively used for all important foundation construction, and to a large extent in the erection of rein- forced-concrete buildings and engineering structures. CEMENT MORTAR 4. Portland cement is almost exclusively used for making concrete, and is extensively manufactured for that purpose. In general, Portland cement is made by mixing limestone and clay materials and grinding to a fine powder. The mixture is then calcined, or clinkered, in a rotary kiln at a high temperature. The clinkers are then ground to make the commercial cement. Portland cement possesses the valuable property of hardening, or setting, when mixed with w’ater. This action of setting is not a drying process, but is a chemical action that takes place between the ingredients of the cement and water. The sand used in making cement mortar or concrete .should be a good, clean, river sand, though as a substitute for sand a clean gravel may be used without impairing the strength of the mortar or the concrete. Both of these materials are treated at length in Sands and Cements and in Tests on Cement. PLAIN CONCRETE 3 §30 The .mixture of Portland cement with sand and water forms a mortar, which is the cementing material of concrete. This mortar holds and binds together the broken stone that is used, and fills the voids between the separate pieces. As the mortar composed of the cement and sand is the cementing material to the broken stone, so is the neat cement to the sand, cementing the smaller particles together. AGGREGATES OTHER THAN SAND 5. Desirable Properties. —The aggregates or broken stone used in concrete work should possess three qualities: (1) They should be hard and strong, so as to resist crushing and shearing or transverse stresses; (2) they should have surface texture that will permit the cement mortar to adhere to their surfaces; and (3) where the concrete is to be used for building construction, such as in reinforced-concrete work, and for fireproofing, they should possess refractory, or fire- resisting, qualities. Usually, aggregates that break in such a way as to allow the smallest spaces, or interstices, between the particles, will make the strongest concrete for construction purposes because the voids can be most economically filled with cement mortar. 6. Size of Aggregates. —In measuring broken stone, the size of the stone is determined by the size of the ring through which it will pass. For instance, a 2-inch stone is one that will pass through a ring, or hole, that is 2 inches in diameter. In Figs. 1, 2, 3, 4, and 5, the several sizes of broken stone ordinarily used ill concrete work are shown, full size, compared with a washer that is 2 inches in diameter and has a 1-inch hole in the center. These illustrations are here given to show how deceptive the actual sizes of broken stone may be. The broken stone shown in Fig. 1 is known as 2 h-inch stone; that in Fig. 2, as 2-inch stone; that in Fig. 3, as 1 \-inch stone; and that in Fig. 4, as 1-inch stone. The broken stone shown in Fig. 5 is 4 inch and under, and is known as screenings. Fig. 1 4 §30 PLAIN CONCRETE 5 The broken stone used in concrete work varies in size with the nature of the work. For foundation and mass construc¬ tion, it is the custom to use broken stone of a size that will Fig. 2 pass through the 2- or 2^-inch ring. For filling the spandrels of bridges or the spaces between walls, where mere mass is desired, broken stone of a much larger size is used. 6 PLAIN CONCRETE §30 7. In reinforced-concrete work, the broken stone must be small, owing to the narrow spaces in the forms and to the fact that the concrete mass must penetrate to all parts of the mold and fill in around all the numerous reinforcing rods. Fig. 3 For columns and wall work, stone that will pass through a 1- or f-inch ring is suitable, while for filling the beam and girder forms, where numerous reinforcing rods occur, the broken stone is sometimes so small as to pass through a ^-inch ring. It is sometimes specified that the broken stone PLAIN CONCRETE 7 §30 used for concrete work near the bottom of beams and girders shall pass through a Winch ring, and that the balance of the broken stone used in the beams and girders shall be of a size that will pass through a f-inch ring. It is hardly practicable, however, to use two grades of mixture in filling the forms for concrete construction; therefore, it is advisable, where Fig. 4 the beams are narrow and where considerable reinforcement is employed, to use a small size of aggregate throughout. 8. The latest practice in making concrete is to use stone as it comes from the crusher, without screening it. While such stone, termed the run of crusher , contains broken stone of a size specified, it also has smaller particles of stone and such stone dust as is carried along with the broken stone 8 PLAIN CONCRETE § 30 from the crusher. Where the run of crusher is used, the proportion of the cement and sand must be changed, because the stone dust takes the place of sand; and if mixed with the broken stone, using the same proportion as was specified for Fig. 5 clean broken stone, a much poorer concrete will result. In using run of crusher the very finest dust should be washed or screened out, as it tends to coat the large pieces and prevent the cement from adhering to them. §30 PLAIN CONCRETE 9 9 . Selection of Aggregates.— Usually, the character of the aggregate used in mixing concrete depends on the availability of the supply; that is, in each locality there are places from which broken stone or gravel may be secured at a minimum cost, and this determines the use of the par¬ ticular aggregate for the concrete to be used in that locality. Where there is much choice in the selection of the aggregates, those which are hardest and which break with a cubical fracture will make the best concrete, although rounded pebbles are considered by some engineers to possess great advantages. The claim of these engineers is that such stones pack more closely together and embed more perfectly than sharper or more angular stones, so that while the concrete in which pebbles are employed is inferior in strength after » three months to concrete in which trap or broken rock has been used, at the end of a year the concrete with pebbles will assume greater strength. 10 . The size of the aggregate has much to do with the quality and strength of the concrete. In mass work, aggre¬ gate of the largest size that it is possible to work should be used, but in all instances the aggregate must be proportioned to the work. For instance, in heavy retaining-wall work, aggregates, or broken stone, that will pass through a 3-inch ring could well be used, but such broken stone would be entirely impracticable for reinforeed-concrete floor con¬ struction or for thin partitions or walls. It can, however, be stated as a general proposition that the larger the stones, up to about 3 inches, the stronger will be the concrete. This fact is clearly shown by Table I, which gives the results of tests made at the Watertown Arsenal in 1898, and published by the United States government. The general increase in strength with the increase in size of broken stone or gravel used will be noted. It is also interesting to note that the concrete becomes heavier per cubic foot, or, in other words, more dense, the larger the stone used. This is, as would be expected, because the stronger the concrete is, the less voids, or air spaces, it has in it. All these tests CO W % O H co Q w N M CO ■ H fc W D5 W E fe M 0 6k 0 S <1 w fi 3 s w H H 05 O fc o o Ek 0 H o fc w 05 H co W k CO co W 05 Ok o o a 3 2 o Ih 3 O fei & *f> £ < Q a 3 o a O 33 u IS H a 3 o Vh o 33 C o o J-i xl o c 3 „ „ O - *-> Q. 5co ^ a« S * H > M £ < Q a 3 o a O -a B a x o C '53:5 J2 a « S +* geo O 3 X a O ^ ctf a 3 C3* co x: , .o . .5? «5X) . vO O o CJ ro o ^3 t'-. 00 m O m ■3 p» 00 m co 3 O io o N vOOOOair^wt^.aroPO 3 3 'O O vo vo *3 io >o 6 6 6 o 6 M 6 ''t Tj- to VO vO to to to to M M M M M M w M M k-l o o o VO CM M Cl v O o M CM CM CM CM CM CM CM o w o o O' o CO VO o On On o o 00 o Cn o CM CO O' PO M CM CM 00 CO M M PO PO CM M CM P4 Cl vO M vO o 1 ^ vO CO vO O to O CM 00 CO vq CO On to cP 00 vd cP M to to to io to M M M M M w w M M M 00 M M M M M co C/J o o C • o c • rH o o o c c c?joo rH|C 4 a a C • tH • l-H • ?—< • rH • rH Hp> HCM - - Hcm wH#* W M CM C /5 0 cc Shear Pounds per Square Inch Stpuoyi 9 <0 -t ‘O O -t* O xo O OO h (j\ \0 rj- <0 >-t OoC rOdddddddM stpjuoj^ £ O m fO 00 1-1 tTOO po 0000 tJ- d m On O COdddddMHCHl q;uoj\[ i a + ifioo O lO 00 O io O 't « O O' f'' >0 *+ d ddddMHMHM sAbq L O 0000 fO O tj - m io O N V) pf) N o OOO t'- d Hi M W M t-H Compression Pounds per Square Inch sipuoj^ 9 ooooooooo O io O 00 »o d o O »o co d O OOO t^O xo CSCNOIOJMMMMM sq^uoj^ £ OOOOOOOOO O to O O d O lo d o Tt- d M OOOO lo 't fO dddHiHHHMHM qiuoffl x ooooooooo to to O O d OO d o M OOOOXDTTd M O CNMMMMMMMM sAuq 4 ooooooooo O <0 to O 00 to vo vo O O rt d m O' 00 O O HI M Hi HI Tension Pounds per Square Inch si^uopj 9 O to O CO 1-0 -f d o O in fPj d O O' 00 t-» O to ddddWHHHH sq^uoj^ C OxoOO d O xo d O tT d m O'OOOvo^tfO dddMMH.HMH m;uoj^ i O 'O O O d OO d O M O' 00 O LO^td M O dtHMMMMMlHM sAuq L O < 0 X 0 0 00 to IO to O O rj-d m O' 00 t>* O O M HI M HI Proportion of Ingredients 9UO}g •^■LOVO CO ON O m cs M M M pung o xoO to O to O to O d d ro <0 P rr io >o o ^uauiaQ 28 i PLAIN CONCRETE 29 §30 MIXING AND WORKING OF CONCRETE CONCRETE MIXTURES CONSISTENCY AND PROPORTION OF INGREDIENTS 44. Consistency of tlie Mixture. —In construction work, two kinds of concrete mixtures may be used—one employing a considerable quantity of water, and the other using only sufficient water to cause the necessary chemical reaction required for the setting of the cement. The first is known as a wet mix , and the other as a dry mix. Wet mix has the consistency of very soft mortar, and is so nearly liquid that it cannot readily be shoveled, but is poured into forms. The forms , which are wooden molds into which the concrete is poured, are often called the centering. A dry mix of concrete is mealy in consistency, with no visible superabundance of moisture. The former would flow if placed on a mortar board, while the latter would remain in a pile on the center of the board. A wet mix is used in nearly all concrete work in the United States, and especially in the construction of reinforced- concrete columns and floor systems. The advantages of a wet mix are that the concrete is in such a liquid state that it can be poured into forms, and that it will enter all parts of the forms and between the rods, or bars, of the metal reinforcement. In reinforced-concrete work there is a multi¬ plicity of steel rods, stirrups, and other auxiliary reinforce¬ ment, and these are usually placed so close together that it is only by the use of a wet mixture that all of the voids between the metal and the forms can be filled. One dis¬ advantage of a wet mixture, as stated in Art. 28, especially 30 PLAIN CONCRETE §30 for concrete wall construction, is that the broken stone is liable to separate from the mortar and form a honeycombed sur¬ face, or a line of demarcation, between the several layers of concrete. 45. Proportion of Ingredients in Concrete. —The proportion of cement to aggregates in a concrete mixture determines its physical characteristics and its structural uses. A concrete mixture may be either rich, medium , ordinary , or lean. In designating the proportion of the ingredients in concrete, it is customary, as stated in Art. 10, to use the cement as a unit, naming this material first, following with the sand, and finishing the notation with the proportional parts of the aggregates. For instance, 1-2-4 mixture would indicate that 1 part of cement is to be used to 2 parts of sand and 4 parts of aggregate, the quantities being measured by bulk. 46. A concrete mixed in the proportion of 1 part of cement to 2 parts of sand and 4 parts of broken stone is usually called a rich, mixture. This mixture is generally used for rein- forced-concrete work and all important structures subjected to great strains or vibratory loads. 47. A concrete mixed in the proportion of 1 part of Portland cement to parts of sand and 5 parts of aggregates, known as a medium mixture, is commonly used for mass concrete, such as foundation walls, building walls, sidewalk bases, and machine foundations. This mixture has also been used with success for reinforced-concrete construction, and if the work is well designed and the construction carefully supervised, it will give excellent results. 48. For large masses of concrete, where the structure depends for its stability on mass, or weight, rather than on compressive or transverse stress, a mixture of 1 part of cement to 3 parts of sand and 6 parts of broken stone is used. This mixture, which may be designated as an ordinary, or common, mixture for plain concrete, is used in the con¬ struction of heavy foundations, retaining walls, railroad §30 PLAIN CONCRETE 31 abutments or wing walls, solid concrete foundations for stacks, and similar structures. 49. In heavy engineering work, such as emplacements, bulkheads, and work of this character, a lean mixture of concrete is sometimes used. This mixture is made up of 1 part of Portland cement, 4 parts of sand, and 7 or 8 parts of broken stone, and answers every purpose where mere weight and mass are the requirements. MEASURING AND ESTIMATING INGREDIENTS 50. Methods of Measuring Ingredients. —After deciding what proportions of ingredients will be used for the concrete, the engineer must be able to calculate the exact quantity of each material that he must order. Cement is bought by the barrel, but is usually shipped by the bag. Four bags of Portland cement make a barrel. Natural cement comes in bags of the same size, or in larger bags, three of which make a barrel. An ordinary box car holds from 400 to 600 bags. The purchaser is charged for the bags by the manufacturer, unless they are of paper, but he gets a rebate for those which are returned. A barrel of Portland cement weighs about 376 pounds, and a barrel of natural cement about 282 pounds. Cement is usually measured by the barrel just as it comes from the manufacturer, or as four bags to the barrel, while broken stone and sand are measured loose in a barrel. Port¬ land cement, after it is taken out of its original package and stirred up, fills a larger volume than when packed. It is therefore necessary to state just how the cement is to be measured; and, as said before, the custom is to measure it by the barrel, compact. A cement barrel contains about 3.8 cubic feet. $ , 51. Fuller’s Rule. —A practical rule has been devised by W. B. Fuller whereby, after the proportions of ingredients have been fixed, the quantity of material for a certain work 32 PLAIN CONCRETE §30 may be obtained. It is called Fuller’s rule for quantities, and may be expressed in mathematical symbols as follows: Let c = number of parts of cement; 5 = number of parts of sand; g = number of parts of gravel or broken stone; C — number of barrels of Portland cement required for 1 cubic yard of concrete; 5 = number of cubic yards of sand required for 1 cubic yard of concrete; G — number of cubic yards of stone or gravel required for 1 cubic yard of concrete. Then, C = —+— (1) c + s + g q q S- — C s (2) 27 G = \leg (3) If the broken stone is of uniformly large size, with no smaller stone in it, the voids will be greater than if the stone were graded. Therefore, 5 per cent, must be added to each value found by the preceding formulas. Example.— If a 1-2-4 mixture is considered, what will be: (a) the number of barrels of cement, ( b ) the number of cubic yards of sand, and (c) the number of cubic yards of stone required for 1 cubic yard of concrete? Solution. — (a) Here, c— 1, 5 = 2, and g = 4. Substituting these values in formula 1, 11 C — --=1.57. Ans. 1 + 2 + 4 (6) Substituting the values of C and 5 in formula 2, 3 8 5 = -—X 1.57X2 = .44. Ans. 27 (c ) Substituting the values of C and g in formula 3, 3 8 <7= - X 1.57X4 = .88. Ans. 27 §30 PLAIN CONCRETE 33 EXAMPLES FOR PRACTICE 1. How much (a) Portland cement, (b ) sand, and ( c ) broken stone will be required to make 1 cubic yard of 1-3-6 concrete? '(a) 1.10 bbl. Ans.< ( b ) .46 cu. yd. ( c) .93 cu. yd. 2. A certain concrete foundation is to be 15 feet long, 15 feet wide, and 12 feet deep. If a l-2^-5 mixture is used, how much (a) cement, ( b ) sand, and (c) broken stone will be required? Ans. (a) 129 bbl. ( b ) 45 cu. yd. ( c ) 91 cu. yd. 52. Table of Quantities. —Table V, giving the quan¬ tities of ingredients for concrete of various proportions, has been prepared by Edwin Thacher. It will be noted in this table that the difference in the character and size of the stone or gravel used has been taken into account. These values will be found to agree fairly well with values found by Fuller’s rule. WORKING OF CONCRETE 53. Mixing of Concrete. —Concrete may be mixed either by hand or by machine. To obtain a good concrete, the ingredients should be accurately proportioned to the requirements of the specification, and they should be thor¬ oughly manipulated, so that the matrix will be distributed equally through the aggregates, coating all the surfaces and forming a mixture of uniform consistency. The percentage of water used should be uniform with each batch. Concrete should always be mixed as near the place where it is to be used as practicable, so that very little time will elapse between the completion of the mixing process and the placing of the concrete. In addition to hastening the work of laying, this arrangement will save much labor in conveying the concrete to the forms. 54. For small work, the concrete should always be mixed in small batches, such as would be made up from 1 or 2 bags 211—6 H W H cc fc 0 M H CS c Ph c ss Pi co P o M PC ◄ > h O w H a Pi o K 0 o X 0 p co H fc W M 0 w Pi fc p o / w H fc P O X <+-4 o o • r-t rO 3 O 03 Pi cn v. <0 ’O a P 03 C CS X o a a> > cfl Vh o c/2 1 pjB A oiqnQ o 'O M po oo PO 00 M PO W o O' o 13ABJQ 00 00 O' 00 00 O' 00 00 00 PJB A oiqno m 04 O' vO 04 O' O po W M 00 vO o PO PO 04 04 PO ro PO PO Tf PO PO m puBg • spxiBg O o O' W PO M o o 04 po W 00 00 r>* in PO m PO 04 M PO }U3UI3Q 04 04 M M M M M M M M M M M M M I sdj'b x Otaris po 04 00 m 04 Ov vo o vO W oo PO 00 PO M 00 O' O' o 00 00 O' o o 00 00 Ov O' o 00 suo^g M M M M paB A otqnQ W PO ov O' m M CO in o PO O' 00 puBg PO Po 04 PO PO in m PO in spjJBg 04 M VO 00 vO VO O' M 00 VO PO PO PO w r^- '■f M 00 M O' o in vO m PO m ^U3UI3Q 04 04 04 H 04 M M M H M M M M M M 03 T3 4) C £ £ (fl Vh S c 03 0 r ^ 1 « Cco O in c c O <0 t'O - a> i Go 8 c Oh &i spxiBg PO o 00 O' o M o PO M 00 00 O' 00 vO PO w 00 o O' vO vO PO 04 ^U3UI3Q 04 04 04 W 04 M H H M M M M H M M PJB A oiqno CO 00 CO 00 M o 00 PO Ov PO auo^g 00 O' Ov 00 O' O' O' I ^ 00 00 O' O' • PJB A oiqno O' m M 00 04 O' o PO 04 00 04 O' VO puBg PO PO PO 04 PO PO PO m PO m s]oaaBg O' vO ""f lO m 04 PO o vO vO m in 04 o 00 o 00 in Tf m PO 04 1U0UI0Q C4 04 04 M 04 M M M M M M M M Hi M auo^g O m o m lO o m o VO o VO O VO o VO 04 04 PO PO 04 PO PO PO ro m PO puBg o o o o in in lO m m o o o O o VO H M w M M rH M w M 04 04 04 04 04 04 ^U3UI33 M M M M M - M M M M M M M ►H W 34 m o CO 'O O' 04 vo 00 H-< x^ O' mo oo o 04 vo O' x^ O' Hi cn vo 00 O' ro 1^ 00 oo 00 oo x^ x^ X^ 00 00 00 CO X^ i - oc 00 00 00 00 x^ t'- CO 00 00 00 00 CO 00 X^ 04 O' x^ 04 o x^ ""X 04 o 00 o 00 vO Tf cn Hi O' M O' X^ rX cn C4 o vO cn Tt* CO CO VO VO tX *+ cn vo rt* ^X TX cn vo rX ^X O o ro 00 m O' cn X^ 04 00 Tf \o 04 00 rr> o vO cn cn o X^ cn M 00 VO Hi x^- 04 HH Hi o O' Hi o o O' O' 00 00 O' O' 00 00 00 X^ X^ 00 00 x-^ x^ X^ o vO 'O vo M W M w Hi M M X^ M vO o. CO o VO O' cn W VO VO O' 04 VO 00 M X^ o cn vO 00 M vo o 00 o O' O' o 00 00 00 O' O' o o 00 00 O' O' O' o o CO O' O' O' O' o o O' o M Hi W Hi Hi W M M rt" M 00 ^x Hi o X^ TX M CO in 04 O' o cn M O' X^ m oo vo cn M O' X^ VO cn o in VO vO vo vo VO ^x ^X vo VO VO VO Tf- vo VO VO VO VO VO 04 CO vO CO o 04 ^x X^ w vO O Tf“ W vO / O vO M vO Hi vo Hi -+ W 00 VO o VO CO 04 M H* CO 04 M M o O O' M o o O' O' 00 00 O' O' 00 oo 00 X^ X^ x-. M0 M M M M M M M M M M M Hi H Hi Tf 00 04 vO 00 00 04 X^ o cn vO 00 04 VO O' 04 vo or ; Hi ^X X^ o cn VO 00 Hi cn vO 00 00 Ov O'- O' X^ 00 00 O' O' O' O' 00 00 00 O' O' O' o 00 00 O'- O' O' O' o O' O' r-i M CO O' O) W 00 vo 04 O' X^ ^X 04 X^ TX Hi O' X^ VO ro VO ro M o 00 vO ' r- t* C4 0C VO ^X tX VO vo VO ^x TX ^X ^X VO VO vo ^x *T TX VO vo VO VO 'sf VO Tt* 00 ov i-i in I''- 00 o x^ 04 00 04 X^ 04 X^ cn O' vo 04 04 oo ^X w 00 \o cn X^ cn CO 04 04 M o 04 04 M o o O' O' o o O' O' 00 00 00 O' 00 00' CO x-^ x^ X^ VO MO M M Hi M M M M Hi M Hi ri M 04 x^ M Tf x^ x^ p-4 VO o 04 VO X^ o X^- M cn vO X^ 04 vo O' M cn lO x^ o 00 C0 O' O' O' x^ CO 00 CO O' O' O' oo CO 00 O' O' O' O' 00 00 CO O' O' O' O' O' O' 04 oo VO CO M 00 W 00 vO ^x 04 vO cn o O' X^ VO 04 vo cn Hi O' X-- VO cn o x^ VO Tt- ^X VO VO VO ^X TX vo VO VO •o- "t tX VO VO vo ^X Tj- VO VO x^ O' CO x^ vO CO M vO M vO M VO o VO 04 x^ o o x^. cn o X^ Hi vO C4 CO 04 M M o 04 Hi M o o O' O' o o O' o CO 00 00 O' oo 00 00 X^ X^ X^ vO vo M w M M M M M M M W M o VO o IT. o o vo O VO o VO o o VO o vo o vo o o VO o vo o vo o o o Tf VO in \o ^x vo m vd vd X^ VO vo vO 'd X^ x^ 00 vo vO x>. X^ 00 00 O' dv 6 Hi vo vo VO vo VO o o o o o o o vo vo vo vo VO vo vo o o o o o o o o o 04 04 04 04 04 ro cn cn cn cn cn cn cn cn cn cn cn cn cn ^x ''t Tt’ VO vo M M M M M M M M M Hi M M W Hi M M M M Hi ri Hi H W M M Hi M Hi 35 36 PLAIN CONCRETE §30 of cement. In mixing, hand work should be performed on a flat, water-tight platform. The sand, after it has been measured, is spread over the platform in an even layer. Upon the sand is placed the cement, and these two materials are turned over with shovels at least three times, or until the uniform color of the mixture indicates that they are thor¬ oughly incorporated. The stones, or aggregates, having previously been well w r etted, are then placed on the top of the mixture of sand and cement, and these materials are also turned at least three times, water being added after the first turning. The water should always be added in small quantities. If a hose is used for this purpose, it should be fitted with a sprinkling nozzle, as otherwise much of the cement is liable to be washed out of the mixture. The concrete, when ready for placing, should be of uniform con¬ sistency, either mealy for a dry mix or mushy for a wet mix. 55. In large work, the mixing should be done by machine. The machines used for mixing concrete are of two general types. In one, the materials are proportioned by laborers and then dumped into the machine; in the other, they are proportioned and mixed automatically. The manner of mixing varies with the type of machine. Usually, the machine is driven by a steam engine, or by an electric motor. The subject of machine mixing will be treated at length in a future Section. 56. Retempering of Concrete. —As the cement-and- sand mixture of concrete sets in air in from 20 minutes to 2 hours after it has been mixed, as little time as possible should be lost in conveying it from the place where it is made to the place where it is to be deposited. If concrete is allowed to stand for a considerable length of time on the mixing board or in the bin, the cement will attain an initial set and the concrete will become practically useless. Only as much concrete as can be used at once should be mixed at a time. If the cement of the concrete has attained its initial set— that is, if the concrete has commenced to harden—remixing with water, or retempering of concrete, as it is called, §30 PLAIN CONCRETE 37 should not be allowed; and if concrete treated in this manner has been deposited in the forms, it should be taken out and removed from the site of the operation, because concrete cannot be retempered properly, except in small quantities for laboratory tests. 57. Concreting at High Temperatures. —If the weather is extremely warm, the stone and sand are liable to become heated to a high temperature. Then, in mixing the materials, the water necessary for the crystallization of the • cement is rapidly absorbed by the stone and the sand, or else rapidly evaporated by contact with them. Again, the extreme heat will hasten the setting of the cement, and this tends to cause the concrete to cake in the mixing machine, producing lumpy and inferior concrete. In order to over¬ come such difficulties, the stone should be thoroughly wetted with a hose, and the sand and stone should be kept under cover, away from the direct rays of the sun. Likewise, the mixing platform or machine should be roofed over. It is . well, also, to wet down the finished concrete work with a hose several times a day in extremely hot weather, and less frequently in moderate temperatures. 58. Concreting in Freezing Weather. —While it is entirely practicable to mix and place concrete at a temper¬ ature as low as 27° F., it is not advisable to lay concrete work when the temperature is below 32°; neither should it be mixed and placed even at this temperature, if there is a possibility that the temperature will fall. If concrete is frozen, its setting is retarded and it is liable to become worth¬ less, never properly setting and obtaining the requisite hard¬ ness and strength. There is, however, no certainty of the action of frost on concrete, as frozen concrete will frequently thaw out and set, with apparently little loss of strength. 59. It is not so important to guard against freezing in the construction of large masses of concrete, such as would be used for foundations or retaining walls, as it is in the construction of reinforced-concrete work. In the first case, 38 PLAIN CONCRETE §30 the concrete is protected to some extent by its mass. In the latter construction, however, it is used in comparatively small masses,' and as there must be no uncertainty regarding its strength in compression and shear, every precaution should be taken to guard against freezing. Frozen concrete is especially dangerous in the construction of reinforced-concrete buildings, because it too often possesses the apparent solidity and hardness of concrete that has properly set, and its defectiveness is only apparent on the removal of the forms and the subsequent thawing out of the concrete. No concrete work that is to have a face finish should be placed in freezing weather, as frost will affect the surface, causing exfoliation, spalling, pitting, and discoloration. 60. To prevent the freezing of concrete when the temper¬ ature has fallen below 32°, salt is sometimes used in the mix¬ ture. The addition of 1J pounds of salt to the water used with 1 bag of cement will not decrease the strength of the concrete; or, a 10-per-cent, solution of salt can be used in the water employed in mixing the concrete. The addition of salt, however, is never advisable if a surface finish is required, as it is liable to cause efflorescence, or a white deposit, on the surface, causing the work to become very unsightly. Concrete should never be made from ingredients that have been subjected to freezing weather for some time without first thawing them out. Aggregates that are coated with ice or that have been exposed to severe weather for a long time, as well as the sand used in the mixture of the concrete, should be heated or thawed out before being used. It frequently happens that the concrete will be mixed and placed during the daytime, when the temperature is near 32° F., and then left to set during the night, when the temperature will drop from 5° to 10°. Concrete that is exposed to such conditions should always be protected by placing over it a layer of boards and straw, or salt hay, or cement bags; or, where the work is in the nature of a reinforced-concrete floor system, by heating the interior of the structure by means of salamanders or fires, or in some other convenient way. §30 PLAIN CONCRETE 39 61. Joining of Old Concrete With New. —New and old concrete can be joined only with difficulty, and the strength of such a connection is always uncertain. It is only with the greatest care that a cement-finished coat can be made to adhere to a concrete base that has reached its final set. The joining of old and new concrete work is best done by thoroughly chipping, or cutting away, the old surface, saturating it with water, and working into it thin coats of a 1-1 Portland-cement mortar, and, then, while the coating is still fresh, placing against it the new concrete. There are some high-grade, imported cements that, in the form of cement mortar, more readily adhere to old concrete work than the usual Portland cements. These cements are frequently used for patching and piecing out work already in place. There are also several compounds on the market that are assumed to possess the quality of joining old concrete with the new in a manner to give a strength equal to the mass of the concrete. These compounds, however, have been used with doubtful success. Comparative tests that have been made where such compounds have been used, and where junctions have been carefully made with new concrete, prove in most instances that they have little efficiency. 62. Waterproofing of Concrete. —Plain concrete can . be rendered nearly waterproof by making a very rich mixture of cement mortar. Such a mixture, when carefully manip¬ ulated, will develop waterproof qualities. Generally, a concrete composed of 1 part of cement and 1 part of sand, used in the proportion of from 40 to 45 per cent, of the volume of the concrete, will be impermeable to water. The waterproofing of concrete is necessary in the construction of walls below grade, and also in building bridge arches, where surface water is likely to penetrate the filling and soak through the arch construction, badly marking the surfaces by causing efflorescence. For constructions like these a wet mixture of concrete containing a large proportion of cement is generally used. Such a mixture is not usually sufficient. 40 PLAIN CONCRETE §30 however, to insure waterproof walls or casings for retaining water, such as tanks, dams, and reservoirs. Frequently, these are plastered on the face of the concrete with a rich cement mortar. In placing this mortar, the concrete should be well wetted and the surfaces painted with a coating of neat cement; then the plaster should be applied in layers not over \ inch in thickness, the coats of plaster being put on at intervals of about an hour. 63. A superior method to that just described would be to form the concrete mass work and the cement face work at the same time. This can be done by placing a rich cement mortar between the. concrete and the face of the forms, by plastering the faces of the forms, or by using a .sheet-iron slide, which is raised as the work proceeds. These methods insure a waterproof cement coating over the concrete of such a thickness and so incorporated with the concrete as to pre¬ clude any possibility of its failing. In another method that has been successfully used for some very large work, concrete is rendered waterproof by the use of soap and alum. In this method, a waterproof mortar is made by using 1 part of Portland cement and 2 parts of sand to which f pound of powdered alum has been added for each cubic foot. The cement, sand, and alum are first mixed dry, and then with the proper quantity of water in which f pound of soft soap has been dissolved for each gallon of water used. The mortar is thoroughly mixed and is applied to the concrete as a plaster, to the thickness of about 1 inch. 64. In several instances where a plaster coat of cement has proved ineffectual, the surface has been made waterproof by applying three or four coats of a solution of Castile soap and one coat of a solution of alum. This method effectually stopped the leakage of a concrete stand pipe under a 100-foot head of water. From experience, it has been found that the addition of a small quantity of slaked lime to a concrete mixture will tend to make it waterproof; but, while such an addition does not §30 PLAIN CONCRETE 41 materially decrease the strength of concrete, it does tend to retard the setting. Slaked lime added to concrete crystallizes in the pores of the material and in this way makes it water¬ proof. Attempts have been made to make concrete waterproof by mixing various chemicals with it. Among others, silicate of soda, commonly known as water glass, has been used. This material, however, tends to decrease the strength of the con¬ crete—in some instances as much as 50 per cent. An effectual method of waterproofing concrete is to apply hot pitch to the surface to be waterproofed. The pitch, however, must be very thin, and can only be applied as a thin coating, as it is not easy to make the pitch adhere in any thickness to a vertical surface. There are several concrete waterproofing compounds on the market. These have been successfully used in a number of instances for the construction of waterproof roof -slabs, cisterns, tunnels, walls, and other work of this character. BUILDING STONE AND BRICK STONE PHYSICAL PROPERTIES OF BUILDING STONE 1. In order to be able to decide which kind of stone is best to use under given conditions, a knowledge of the different kinds employed in building construction is very essential. It is not necessary for a builder to determine the exact composition of a stone, but his knowledge should be sufficient to aid him in selecting or specifying the kind of stone best adapted to the purposes for which it is intended. The structural manner in which the constituent parts of * the rocks are grouped together bears a greater relation to the value or quality of the rock than the character of the minerals composing it; or, in other w T ords, the physical char¬ acteristics may be, and frequently are, more important than the chemical qualities. 2. Density. —The weight, strength, and absorptive properties of stone are dependent on the density. Thus, among rocks having the same mineral composition but dif¬ fering as to structure, generally the strongest will be the densest and the heaviest will be the least absorptive. 3. Hardness. —The manner in which the mineral con¬ stituents of a rock are cemented to each other and the individual hardness of such mineral constituents determine the hardness of the rock as a structure. The minerals composing a rock may be hard, but the rock itself as a COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS* HALL, LONDON i 31 2 BUILDING STONE AND BRICK §31 structure will be soft if the particles do not strongly adhere to one another. Thus, some of the softest sandstones are composed of quartz, which is a hard mineral, but the grains are so weakly cemented together that the stone as a whole is soft. 4. Structure.—The structure of a rock depends on the form, size, and arrangement of its component minerals. All rocks may be approximately classified as crystalline , vitreous or glassy, and fragmental. Granite and crystalline limestone may be taken as types of the crystalline group; obsidian and pitchstone may be taken as types of the vitre¬ ous group; while the sandstones are types of the fragmental group. 5. Though all rocks have some common structural char¬ acteristics, certain peculiarities are found only in single types of rock. If the structure can be recognized by the unaided eye, the rock is said to have a macroscopic structure , and such rocks may then be described as being either granular, massive, stratified, schistose, porphyritic, or con¬ cretionary. The term granular, as its name implies, is applied to rocks built up of distinct grains of crystalline, fragmental, or water- worn character. The term massive , or unstratified , is applied to rocks that are not arranged in any definite form in layers, or strata, but have the constituent parts mingled together, as in diabase and granite. The term stratified is applied to rocks composed of par¬ allel layers, or beds, as is frequently seen in limestone and sandstone. The term schistose is applied to stratified crystalline rocks that are in comparatively thin scaly layers. The term porphyritic is applied to rocks that consist of a ground mass of fine or compact and evenly crystallized material, with larger crystals of feldspar scattered through it. A granite fragment has a porphyritic structure, but it is difficult to distinguish owing to the similarity of color exist- §31 BUILDING STONE AND BRICK 3 ing between the crystals and the ground mass. In such rocks as the felsites, it is quite noticeable. In the porphyries of Eastern Massachusetts, the ground mass is of a black or neutral color and very compact and dense, while the large white crystal feldspars are in marked contrast. The porphy- ritic structure is so noticeable that any rocks possessing this characteristic in a marked degree are commonly termed porphyries , without regard to the mineral composition. The word porphyry is now commonly applied as an adjective, because any rock may possess this structure, whatever may be its origin or composition. The term coyicretionary is applied to rocks composed of concretions, or rounded particles built up by the collections of mineral matter around a center, forming a rounded mass of concentric layers like the coating of an onion. When the concretions are small, like the roe of a fish, the structure is called oolitic; when large, like a pea, the structure is called pisolitic. The Bedford, Indiana, limestones are examples of the oolitic type. The concretionary structure is rarely found in crystalline rocks. 6 . Aggregation of Particles.—The hardness of rock depends largely on the aggregation of the particles; therefore, the working qualities of the rock are fixed by the character of this aggregation. If the grains are loosely coherent in a rock composed of hard minerals, it may be worked readily, while a rock consisting of softer materials may be worked with difficulty because the particles tenaciously cohere to each other. The durability of a stone is, to a great extent, a matter of texture. If the grains cohere closely, the stone will be less absorbent and more durable than one in which the cohesion is not so great, as in the friable and loose-textured rocks. The kind of fracture shown by a rock is determined by the fineness or the coarseness of the grain and the relation of the particles to themselves or their state of aggregation. Such rocks as flint, obsidian, and some varieties of lime¬ stone have a compact, fine grain, show a concave or convex 4 BUILDING STONE AND BRICK 31 shell-like face of conchoidal form on fracture, and are difficult to dress. Other stones show, on fracture, a jagged surface or split along certain planes, all dependent on the aggregation of the particles. 7. Rift and Grain.—The rift of a rock is a line of cleavage parallel to the bed and is visible in such rocks as mica schist, gneiss, and other sedimentary rocks. It is along these lines that the rock can be readily split. Rift, however, is commonly found in massive rocks, although it is not so easily discerned as in the examples cited. The grain of a rock is always at right angles to the plane of the rift or the bed. Rocks that do not possess rift and grain cannot be worked into rectangular form without great difficulty, unless they are of a very soft nature, but with rift the hardest rocks can be readily worked; for instance, the South Dakota quartzite, which is one of the hardest rocks known, can be broken into pieces for paving as easily as can a soft sandstone or a granite. 8 . Color. The chemical properties of a rock, as a rule, determine its color. The color of granites, however, is affected by the action of light on the feldspars, which when clear and glassy, absorb the light, making the rock apparently darker than when the feldspars are white and opaque and reflect the light. Iron, the principal coloring matter in rocks, may be found in chemical composition with other minerals or in such sim¬ pler compounds as the sulphides and carbonates, or as an oxide distributed throughout the mass of rock. The brownish or reddish hues are due to the free oxides of iron, while the bluish or grayish hues are caused by the carbonates or the sulphides. The absence of iron in any of its forms is usually indicated by the white, or nearly white, color of the rock. The permanency of the color of the rock depends on the form in which the iron is found. Oxidation is likely to result if it is in the form of a sulphide, carbonate, or other protoxide compound. Therefore, stone containing these forms of §31 BUILDING STONE AND BRICK 5 iron is likely to fade and turn yellowish and stain on expo¬ sure. The sesquioxide, being in the last stages of oxidation, can undergo no further change and is therefore a permanent color; hence, the decidedly red color may be considered as permanent. The blue and the black colors of marbles and limestones are largely caused by the presence of carbonaceous matter, usually of vegetable origin. CLASSIFICATION OF BUILDING STONE 9. Building stones are usually classified according to their geological formation or their chemical composition. The classification given here, however, is strictly in relation to their use in building, and includes the following groups: the granitic , the sandstone, the slate, and the limestone. GRANITIC GROUP 10. The granitic group of rocks is richest in silica and therefore its members are known as silicious stones. In this group are included granite, syenite, gneiss, greenstone, and trap. 11. Granite. —The granites are unstratified and under¬ lie the stratified rocks. They are composed of an aggrega¬ tion, or assemblage, of crystals of feldspar, quartz, and mica, the principal impurities being hornblende and talc. The colors of granite are white, grayish white, yellowish, reddish, rose, flesh color, or deep red, but rarely green. Granite is distinguished by its even and brilliant fracture, • its pearly luster, and its outline, which is seldom regular, but in which may be recognized rectangles and parallelograms. Granite varies in quality according to the proportions of its components and their method of aggregation. Stone of the greatest durability and hardness contains a greater pro¬ portion of quartz and a smaller proportion of feldspar and mica. Hornblende renders the stone tough and heavy. Feldspar renders it lighter in color, easier to cut, and more 6 BUILDING STONE AND BRICK §31 susceptible to decomposition by the solution of potash con¬ tained in it. Mica renders it friable. The durability of granite depends on the quantity of quartz present and on the nature of the feldspar. Potash feldspar is less durable than lime or soda feldspar. Mica, being easily decomposed, is an element of weakness. An excess of lime or soda in the mica or feldspar hastens disintegra¬ tion, as does also an excess of iron. Stones showing large and dark iron stains should be rejected for outside work. Fine-grained granite weathers better than does granite of coarser grain. When mica predominates, granite passes into gneiss. The granites are among the most valuable of the building stones and are extensively used in important works. They can be readily quarried and by reason of the lack of grain in the stone, blocks can be obtained of any size. On account of its great hardness, granite is difficult to work and there¬ fore very costly to use if the stone has to be cut. It weighs about 166 pounds per cubic foot. Granite is found in the eastern part of the United States, in Canada, in many parts of the Rocky Mountains, and, as a rule, wherever the later rock formations and the underlying beds have been left exposed. It is generally classified into gray and red. Gray granite is found throughout New England, the border states, and in Virginia. Red granite is composed of red orthoclase (aluminum potassium silicates), bluish quartz, and a little hornblende, with very little mica. It is hard and takes a fine polish. It is found near the Bay of Fundy, near Lake Superior, on the islands of the St. Lawrence River, in Virginia, Maine, and many parts of the Rocky Mountains. 12. Syenite.—The stone known as syenite derives its name from Syene, in Egypt. It consists of feldspar and hornblende, frequently associated with mica and quartz; is of a granular texture, closely resembling ordinary granite, but somewhat darker; and is hard and tough, somewhat coarse¬ grained, and will not take a polish. It is one of the most §31 BUILDING STONE AND BRICK 7 durable of the granitic rocks when its feldspar constituent is not too readily decomposed by the removal of the potash when exposed to the weather. For this reason, it should be carefully tested before it is used. 13. Gneiss and Mica Slate.—In composition, gneiss and mica slate are similar to granite, but they differ from it in being stratified. Granite, syenite, and gneiss resemble one another so closely that they are all frequently called granite by persons not familiar with their characteristics. Gneiss is not so valuable a stone as granite on account of its stratification, which will not permit it to be split evenly in any desired direction. Although it is not so strong as granite, it is a good building material and often answers just as well. 14. Greenstone, Trap, and Basalt.—The igneous, unstratified rocks, known as greenstone, trap, and basalt, consist of hornblende and feldspar. The term trap has been suggested as a generic name for these rocks. The green¬ stone is not so coarse-grained as granite, and in the trap and basalt the granular structure is not apparent. The green¬ stone and trap break into blocks, and the basalt into columns of prismatic form. They are found in veins and dikes and injected among the stratified rock of all ages. These rocks vary in color, from nearly white in some varieties of greenstone, to nearly black, as in basalt, the difference in color being determined by variation in the proportions of hornblende, which gives a dark color, and feldspar, which gives a light color. The green is due to chromium. These stones, while making very durable build¬ ing material, cannot be obtained in large blocks and are difficult to cut. Trap rock forms one of the best aggre¬ gates for use in making concrete. SANDSTONE GROUP 15. Such material as sandstone consists of fragmen¬ tary rocks, composed mostly of grains of silica (quartz), cemented together by a deposition of silica, carbonate of 211—7 8 BUILDING STONE AND BRICK 31 lime, oxide of lime, and aluminous matter. Sandstone is a stratified rock and belongs to the later geological periods. If the cementing material is silica, the rock is very durable, but difficult to work. Iron oxide in the cementing material, consisting of carbonate of lime and clayey matter, gives the stone a reddish or brownish color. Lime renders the stone particularly liable to disintegration when exposed to an atmosphere containing gases, or when used for founda¬ tions in a soil that is impregnated with acid water. The presence of clay or oxide of iron is also deleterious. Sandstones are variable in character, some being nearly as valuable as granite while others are practically useless for permanent construction. The best stone is characterized by small grains with a small proportion of cementing material, and when broken has a bright, clear, sharp fracture. It is usually found in thick beds and shows slight evidences of stratification. Water can readily penetrate between the layers of this stone; therefore, in foundations it should be laid on its natural bed so that the penetration of moisture and possible disintegration by freezing may be prevented as much as possible. Sandstone of good quality possesses strength and dura¬ bility and can be readily cut and dressed. These qualities make it one of the most frequently used of the common building stones. When the grains are extremely small, it is termed a “freestone” because of the ease with which it can be quarried, cut, and dressed. When quarried, sandstones are usually saturated with quarry water and are very soft; but on exposure to the air and on drying, they become hard. Sandstones vary much in color. The Ohio and Nova Scotia varieties are yellowish and cream color and some¬ times nearly white; the Missouri sandstone is of a yellowish- drab color and possesses durability; the Portland, Connecticut; Newark, New Jersey; Marquette, Michigan; and Bass Island, in Lake Superior, sandstones are of a dark brownish-red color, which is due to the presence of iron, and are termed brow?istones. The Potsdam, New York, red sandstone is § 31 BUILDING STONE AND BRICK 9 durable, hard, highly silicious, and of a reddish color. The Hummelstown, Pennsylvania, sandstone has a brownish color. A fine-grained blue sandstone is known as bluestone. This variety is widely used for trimmings and for stone sidewalks, as it readily splits into slabs. SLATE GROUP 16 . Slate is a stratified rock of great hardness and density, with a laminated structure. It splits readily along planes called planes of slaty cleavage. This facility of cleav¬ age is one of the most valuable characteristics of slate, as it enables masses to be split into slabs and plates of small thickness and great area. The color of slates varies greatly; those most frequently met with are dark blue, bluish black, purple gray, bluish gray, and green. Red and cream-colored slates are also occasionally found. Some slates are marked with bands or patches of color differing from the general color of the stone. These marks are generally considered not to injure the dura¬ bility of the slate, but they lower its quality by detracting from its appearance. Ribs , or veins , are dark marks running through some slates. They are always objectionable, but are particularly so when they run in the direction of the length of the slate, which is very liable to split along the vein. These veins, or ribs, are frequently soft and of inferior quality to that of the slate proper, and slates containing them should not be allowed in good work. Although not strictly a building stone, slate is used exten¬ sively for covering steps and the roofs of buildings, for Wall linings, and for sanitary appliances. LIMESTONE GROUP 17 . All limestones are of sedimentary origin and have for their principal ingredient carbonate of lime, which is combined with various minerals. The presence of these 10 BUILDING STONE AND BRICK §31 minerals gives rise to the division of the limestones into five classes, each of which is designated by the name of the predominating mineral. When clay is present, the stone is called argillaceous limestoiie; when silica predominates, silicious limestone; when it contains iron, ferruginous li?nesto7ie; and when magnesia is present to the extent of 15 per cent., mag¬ nesian limestone. When the carbonate of lime and the car¬ bonate of magnesia are combined in equal proportions, the stone is called dolomite. Limestones are either granular or compact. 18 . Granular limestone consists of carbonate of lime in grains, which are in general sea shells or fragments of shells cemented together by some compound of lime, silica, and alumina, and often mixed with a greater or smaller quantity of sand. Granular limestone is always more or less porous. It is found in various colors, especially white and light yellowish brown. In many cases, it is so soft when first quarried that it can be cut with a knife; it hardens, however, on exposure to the air. The variety of granular limestone called oolitic , from the appearance of the stone, which is that of egg-shaped grains cemented together, is one of the most important of the limestone group, and is extensively quarried and widely used for building purposes. Each grain is usually of concentric structure, the carbonate of lime enclosing a particle of sand or some substance of either animal or vegetable origin. 19 . Compact limestone consists of carbonate of lime, either pure or mixed with sand or clay. This kind of lime¬ stone is generally devoid of crystalline structure, and has a dull, earthy appearance and a dark-blue, gray, black, or mottled color. In some cases, however, it is crystalline and full of organic remains; it is then known as crystalline limestone . The compact limestones are easily worked with the saw and hammer, resemble light granite in appearance, and are extensively used for building purposes. The variety called shelly limestone consists of fossil shells that are cemented together and is sufficiently hard to take a polish; it is much §31 BUILDING STONE AND BRICK 11 used for interior ornamentation. The condition of the minerals combined with the lime also furnishes a basis for distinguishing names. The stone is called hornstone when very fine-grained silica is present; clierty , when the silica is in the form of rounded masses or nodules; ironstone , when the amount of iron and clay is greater than the amount of lime; rottenstone, when the ironstone is decomposed; hydraulic limestone , when the rock is composed of lime, silica, and clay in nearly equal proportions. 20 . The limestones form an important and useful group of stones, but not all are suitable for structural purposes; some are too friable, and others too brittle. The compact and granular varieties, however, are generally suitable for masonry. Their durability depends mainly on the texture; when this is compact, the stone is very durable, except when exposed to the acid vapors of cities. Nearly all the varieties are attacked by sulphuric acid, which forms a soluble sulphate of magnesia that may be easily washed away. 21 . Marble.—Metamorphosed limestone gives the masonry material known as marble, which is easily dressed to a smooth surface and polished. For building purposes, the granular varieties are generally superior to the compact. The impure carbonates of lime are sometimes of great value as marble. The magnesian limestones, or the dolomites, are usually of excellent quality. White marble is found in the Laurentian rocks, Canada, but much of that used in the Northern Atlantic States is obtained from the Green Mountains, which extend through Vermont, Western Massachusetts, Western Connecticut, and Southeastern New York. Quarries exist at Granden, Rutland, Danby, Dorset, and Manchester, in Vermont; at Lanesborough, Lee, Stockbridge, Great Barrington, and Sheffield, in Mas¬ sachusetts; at Canaan, in Connecticut; and at Pleasantville and Tuckahoe, in New York. The snowflake variety of marble is obtained from the Pleasantville quarries, and a fine grade of statuary marble is from Rutland, Vermont. From this place southward, the marbles become coarser and harder 12 BUILDING STONE AND BRICK §31 and more suitable for building purposes. Dolomitic marbles are found in the southeastern part of New York and in Delaware. White dolomite marble is found in Maryland. . The colored marbles used in building construction are of several varieties and are found in Vermont, Connecticut, New York, Pennsylvania, and Tennessee. Brecciated marbles , that is, those in which the conglomerate fragments are angular instead of water-worn, are found in Vermont on the shores of Lake Champlain, and a dove-colored marble with greenish veins is found at Rutland. Black marbles are found at Shoreham, Connecticut, and Williamsport, Pennsyl¬ vania. Black Trenton limestone is found at Glens Falls, New York. The Warwick marble, found in Orange County, New York, is beautifully colored with carmine, with white veins. The Knoxville marble is of a reddish-brown color with lines of blue. Tennessee marble is brown and white mottled. The foreign marbles are largely imported from Italy, Spain, and Belgium. The Bardiglio, of Italy, is of a gray color shaded with black; the Siena, of Spain, is a pale yellow Color; the Lisbon, of Portugal, a pale reddish color; and the Belgian, of Belgium, is black. Verde antique is composed of bands of serpentine and white marble. 22. Chalk.—Soft limestone in which the minute shells composing it have not been entirely destroyed by the pres¬ sure to which it has been subjected in early geological times is called chalk. It is not suitable for constructive purposes, but is very useful in making lime and cement. 23. Quicklime. —The material known as quicklime is obtained by calculation from various limestones and is the basis of common mortar; the act, or operation, of calcination is the expelling, by heat, of carbon dioxide by which the stone is broken down and reduced to the oxide state. 24. Plaster of Paris.—The material known as gypsum, alabaster, or plaster of Paris is a sulphate of lime con¬ taining water of crystallization. The term “plaster of Paris” is due to the fact that large deposits of this stone underlie the city of Paris. This natural sulphate of lime, when raised §31 BUILDING STONE AND BRICK 13 to a high temperature, loses its water of crystallization and is then ground into a fine powder. This becomes the plaster of Paris of commerce, which is used for molds, ornaments, and casts, as well as in wall plaster and staff. Gypsum is found in many parts of the United States, great quantities coming from the state of New York. FIRE-STONES 25. Fire-stones are stones capable of resisting the action of great heat without fusing, exfoliating, or cracking. Lime and magnesia, except in the form' of silicates, are prejudicial to the quality of fire-stones; potash, also, is very injurious because it increases the fusibility of the stone, which, on melting, causes the formation of a fusible glass. Quartz and mica alone or in combination make the most refractory stones. Mica, slate, and gneiss make an excellent combination. Gneiss is particularly refractory when it con¬ tains a considerable portion of arenaceous quartz; that is, quartz in which the particles partake of the nature of sand. Limestones do not stand well in the presence of high tem¬ peratures, as they sometimes explode, owing to the rapid expulsion of the carbonic-acid gas. Granitic and other primary rocks usually contain some water, which, in the presence of fire, causes them to crack and sometimes explode. Sandstones, if somewhat porous, uncrystallized, and free from feldspar, are the most refractory of the common build¬ ing stones. Firebrick is perhaps the most fire-resisting building material now known, while common hard-burned brick is more refractory than any of the building stones. Concrete made of Portland cement is a fire-resisting medium of value. 14 BUILDING STONE AND BRICK §31 DURABILITY OF BUILDING STONE 26. In the structural use of building stones, it is seldom that the full safe strength of the stone is required to resist the stresses imposed, and consequently the range of choice is not limited by this consideration so much as by the factor of durability. While in architectural work color is of great importance, for on it the architect depends to a large extent for the success of his design, it is exceptional in purely structural work for the color of the stone to be a deciding factor. The durability of a building stone depends not only on the physical and chemical formation of the stone, but to a considerable extent on the climate in which the structure is to be built and also the method employed in quarrying the material. Where a selection is to be made of two stones equally durable and structurally fit for their purpose, the economic consideration influences the choice. The cost of structural building stones is regulated by the difficulties of quarrying, the refractory nature of the stone in finishing, and the distance it must be transported. 27. Physical Structure. —The most durable building stones are generally of a compact and uniform texture and show a clean fracture free from earthy or soluble mineral matter. Stones showing lamination, or layers, are not likely to prove as durable as those of a more homogeneous struc¬ ture, especially when laid with the laminations on edge , or perpendicular to the bed of the wall. Non-porosity is not always, a quality synonymous with durability, because many stones that absorb moisture also permit of its rapid evaporation. Such stones are likely to prove more durable than those which absorb less moisture and part with it more reluctantly. Stones showing a streaked appearance and lack of uniform¬ ity in color are usually composed of several minerals of various degrees of hardness, and in some instances one of them may be slightly soluble. Such stones are not likely to weather well, because the softer or more soluble mineral will §31 BUILDING STONE AND BRICK 15 be corroded and washed away, leaving the harder substance to protrude. When the less durable substance is in small pockets, or spots, the stone will, on long exposure, be pitted; while if the softer mineral is in streaks, or veins, the material will be grooved, fissured, or channeled. Small fossils or shells embedded in the substance of a building stone have usually a deleterious influence on its durability and weathering qualities. Such fossils and shells are calcareous in nature and generally soft and partly soluble under atmospheric influences.. 28. Climate and Environment.—Building stones of the most durable character are required in climates where the changes in temperature are great and where there is much moisture in the atmosphere. The structure of a stone consists of minute particles that are surrounded by a matrix that forms the cementing material of the mass or are closely attached to each other by cohesion. In either case, changes in temperature cause these particles to expand and contract with considerable force, thus loosening particles from the matrix or from each other and causing deteriora¬ tion and the ultimate destruction of the rock. The freezing of water in the pores of the stone or in the crevices and the spaces between the laminatibns in stratified stones, is the primary cause of the rapid destruction of some building stones. Water in freezing expands about one-tenth of its bulk and is said to be capable of exerting a pressure of about 150 tons per square foot, which is sufficient, under favorable conditions, to split the strongest rocks. The freezing of moisture within the pores of the stone is very deleterious to the stability of its structure, especially if there is not contained in the rock sufficient reserve pore space to accom¬ modate the increased bulk of the water when frozen. Some¬ times, clay is one of the constituents of sandstone. When acted on by the frost, the clay will swell by reason of the water contained in it, and the stone will begin to disintegrate. The freezing of sandstone when fresh quarried or saturated with water is therefore very injurious. 16 BUILDING STONE AND BRICK §31 When water freezes in the crevices or spaces between the laminations, its action is that of a wedge tending to split the rock and to widen the crevice more and more with each repetition of the freezing process. By this means, stones of laminated or stratified structure, when laid on edge, are particularly liable to disfigurement by exfoliation, or the scaling of the surface. In the large cities, it is not uncom¬ mon to see balusters and carved details partly destroyed from this cause. The damage from the freezing of water in the spaces and crevices between the laminations is not so great when the stone is laid on its bed as when it is laid on edge, because there is not the same opportunity for the space lying in a horizontal plane to collect the moisture and also because the pressure on the stone from the superimposed masonry nullifies to some extent the wedging or bursting action of the freezing water. The severest atmosphere on building stone is one that frequently and for long periods contains great quantities of suspended moisture in the shape of fogs and is also sub¬ jected, by environment, to much smoke and gas from the bituminous coals of manufactories. Such atmospheres are likely to contain carbonic-acid gas and sulphurous fumes, which have a deleterious effect on limestones and marbles. The actions from these sources are especially marked where the atmosphere is extremely moist. It is the opinion of some authorities that, as a cause of decay, the carbonic acid is of little importance compared with sulphurous acid. One of the combustion products of coal is sulphur dioxide, S0 3 . This gas is very soluble in water, and when transferred to a building from the chimney, whence it issues, it will combine with the moisture found on the stone faces and form sulphurous acid, H 3 S0 3 . If car¬ bonate of lime is one of the constituents of the stone, it will be decomposed by the acid and cause disintegration of the stone. The Parliament House, in London, may be cited as an example. The stones of this building, made of dolomite, were selected and tested for durability by the best scientific and technical skill in Great Britain, but the corroding §31 BUILDING STONE AND BRICK 17 influence of the London atmosphere has been such that it is now a question whether the building will last as long as if it were built of timber. Table I, taken from a United States census report, gives the length of time that the several varieties of stone named have lasted in New .York City without material deterioration. TABLE I DURABILITY OF BUILDING STONE Variety of Stone Years Brownstone, coarse. Brownstone, fine laminated . . Brownstone, compact. Bluestone (blue shale) . . . . Sandstone, Nova Scotia . . . Limestone, Ohio, best silicious Limestone, coarse fossiliferous Limestone, oolitic. Marble, coarse dolomite . . . Marble, fine dolomite. Granite. Gneiss. 5 to 15 20 tO 50 100 tO 200 100 tO 200 50 to 100 100 tO 200 20 tO 40 30 to 40 40 to 50 50 to 100 75 to 200 50 to 200 29. Effect of Quarrying and Finishing. —Before stones are used in an important structure they must be thoroughly seasoned. When detached from the rock, stone is generally saturated with quarry water. It should there¬ fore be exposed for some months, preferably under cover, to allow this water to evaporate. If the stone is not seasoned before it is placed in the wall of the structure, it is likely to remain damp, and the excess of moisture, in freezing, will influence the durability of the material. The use of heavy explosives for detaching dimension stone is detrimental to the quality of durability, owing to the fact that the severe concussion is likely to jar the particles and partly destroy their cementation and cohesion, producing 18 BUILDING STONE AND BRICK §31 incipient cracks and flaws that ,make the face of the stone more permeable to moisture and thus hasten the destruction of the stone by freezing and chemical action. For the same reasons, stones sawed to size are more durable than those hammered and broken; and stones taken from the quarry by channeling or cutting are preferable to those procured by wedging. 30. Effect of Fire. —The destructive fires that occur in the large cities frequently subject the stone walls of structures to intense heat. While stone is an excellent non¬ conductor, it is not as a rule so durable, when subjected to intense heat, as brick. The severest test to which a stone can be subjected in a fire is for it to be heated intensely and then cooled by a sudden stream of water from a fire-hose. This rapid change of temperature causes the exterior heated layer of the stone to contract more rapidly than the mass, and from many stones thus treated, large pieces will crack and break off; the process, if repeated several times, results in the entire destruction of the stone. The silicious sandstones are the least destructible by fire, while the granites and conglomerates are probably the most affected by intense heat and the sudden cooling incident to the application of water. Limestones are very refractory, that is, unaffected by heat, in temperatures less than 1,000° F. and at this temperature are not liable to deterioration by sudden cooling, though above this temperature, they may be reduced to quicklime, which crumbles and falls away after a few weeks’ exposure to the air. STRENGTH OF STONES AND MASONRY 31. The resistance of stones to stress varies greatly, and the strength of masonry depends not only on the materials of which it is composed but on the manner in which these materials are handled; that is, on the workmanship. Stones that are the densest usually possess the greatest resistance, §31 BUILDING STONE AND BRICK 19 and masonry composed of squared stones with close joints is the strongest. Many tables, based on the results of tests, give the strength values of building stones, but they differ widely, the dis¬ crepancy being due to the following causes: 1. Samples are taken from different quarries or from different parts of the same quarry. 2. The pieces of stone used for testing are not uniformly seasoned. 3. Test pieces are of different sizes. 4. They are not uniformly dressed or finished. 5. Variations exist in the method of placing the test specimens in the testing machine. Frequently, stones quarried from different parts of the same bed will vary from 20 to 30 per cent, in their resistance to crushing, and stones that have been quarried for some time and exposed will show a different resistance from those lately detached. The larger the test piece, the greater will be the unit stress developed, because small cubes do not develop so great a unit resistance as large ones, and within certain limits the unit stress that test cubes of the same material will sustain varies directly as the cube of the sides. The method of finishing the test pieces and the accuracy and fineness with which the sides are dressed have much to do with the results of the test. Specimens that have been sawed to shape test higher than those that have been finished with a tool or a chisel. A microscopic examination of the surface finished with a chisel reveals numerous minute cracks, caused by the excessive jars, that tend to reduce the crushing strength by starting fractures. The fineness of the surface finish also affects the result, owing to the fact that when the bearing surfaces are rough, transverse stresses that tend to disrupt the specimen are created. 32. It is well determined that from lack of uniformity of texture, building stones and masonry of the same material have variable strength values. This uncertainty regarding the exact strength of masonry materials, together with their / TABLE II STRENGTH OF BUILDING STONES AND MASONRY Material Granite: Colorado. Connecticut. Massachusetts. Maine. Minnesota. New York. New Hampshire. Sandstone: Bluestone. Connecticut, Middletown . . . Massachusetts, Longmeadow, brown. Massachusetts, Longmeadow, red . New York, Hudson River . . New York, Little Falls, brown Ohio. Pennsylvania, Hummelstown, brown. Limestone: New York, Kingston. New York, Garrison Station . . Indiana, Bedford, oolitic . . . Michigan, Marquette. Pennsylvania, Conshohocken . Marble: Pennsylvania, Montgomery County.. . Massachusetts, Lee, dolomite . New York, Pleasantville, dolo¬ mite . Italian. Vermont. Slate . Rubble , in lime mortar. Weight per Cubic Foot Pounds Compressive Strength Pounds per Square Inch Tensile Strength Pounds per Square Inch 1 Modulus of Rupture Pounds per Square Inch 166 15,000 166 14,000 1,500 165 16,000 165 15,000 166 25,000 166 16,000 600 1,800 166 12,000 160 15,000 1,400 2,700 148 7,000 590 1,000 142 10,000 450 149 12,000 450 12,000 10,000 139 8,000 100 479 12,000 168 12,000 164 18,000 Average Average 146 8,000 1,000 1,500 146 8,000 15,000 11,000 22,800 Average Average 22,000 700 1,200 168 12,000 167 10,000 160-180 10,000 10,000 5,000 150 500 20 31 BUILDING STONE AND BRICK 21 usually rapid deterioration, necessitates the use of a high factor of safety, so that in all work of this class, minimum safety factors ranging from 10 to 20 are employed. When, therefore, the average strength values of commercial masonry materials are known and a high factor of safety is used, the basis on which the design is made is assuredly safe. TABLE III ALLOWABLE UNIT STRESSES FOR MASONRY MATER I AES Description of Material Safe Compressive Stress Pounds per Square Inch Safe Bending Stress Pounds per Square Inch Capsto?ie , templets , monoliths: Bluestone . 700 300 Granite. . 700 180 Limestone. 500 150 Marble. 400 120 Sandstone, other than bluestone . 350 100 Slate . . . 700 400 Squa red-stone mason ry: Bluestone .'. 350 Granite. 350 Limestone. 250 Sandstone, other than bluestone . 175 Rubble: Laid in Portland-cement mortar . 150 20 Laid in natural-cement mortar 120 Laid in lime-and-cement mortar . 100 Laid in lime mortar. 80 33. The average strength values of masonry materials, which are sufficiently conservative for good engineering practice, are given in Tables II and III. 34. The values given in Table II are the average ultimate, or breaking, loads for the different materials. 22 BUILDING STONE AND BRICK 31 They are the results of tests made at different times on specimens prepared for the purpose. It will be noticed that the strength values of squared masonry are not given, and though conservative practice recommends that masonry of squared stone may be considered as having an ultimate strength equal to four-tenths the strength of the stone, this is merely an assumption that has not been substantiated by tests. The scarcity of reliable tests on masonry piers and walls is due to the fact that in order to obtain accurate results of the test, specimens must be of full-size dimensions, and when thus built their strength is so great as to resist the ultimate power of the testing machine. 35. In using the values given in Table II, factors of safety of not less than 10 for compression, 15 for tension, and from 10 to 20 for bending stress should be employed. The usual practice in structural and architectural engineering is to use allowable unit values for masonry and masonry materials as given in Table III. These values are considered good practice, and, in most materials, correspond with values recommended by the building laws of several cities. The ultimate unit bending stress is called the modulus of rupture. Its use will be explained in a later Section. SELECTION OF BUILDING STONES METHODS OF SELECTION 36. In the building of important masonry structures, it is of prime importance that the stone employed shall be of sufficient strength and durability. Probably nothing in engineering construction is so neglected as the inspection of the building stone that is to be used. If it is necessary to employ great quantities of building stone at points where the stability of the structure depends on the strength of the stone, an inspection of the quarry from which the stone is to be obtained should be made. §31 BUILDING STONE AND BRICK 23 Besides, it should be the effort of the engineer to inspect some building or structure that has been erected of the same material for a considerable length of time. It is well, however, not to depend wholly on either inspec¬ tion at the quarry or at the building, but to subject the stone to laboratory tests, when it should be tested both chemically and physically, as well as subjected to microscopic inspection. 37. Inspection of Stone at Quarry.— The inspection at the quarry, when carefully made, will frequently reveal the durability as well as the uniformity of the stone. Exposed quarry faces will sometimes show the weathering properties of the stone, besides its liability to disintegration caused by moisture and running water containing deleterious acids and alkalies. Such an inspection will also determine whether there is sufficient stone of a uniform texture and color in sight to supply the amount of material required for the work. By quarry inspection likewise, the several grades of stone are known, and in first-class work it is imperative that the best grade of the quarry be insisted on. Frequently a poor grade of stone is employed in the structure, and on showing deterioration and poor weathering qualities causes otherwise excellent building stone, when of first-class cut¬ tings, to be condemned. 38. Inspection of Stone in Buildings. —By inspecting stone that has been in place in a building or structure for a considerable length of time, an excellent idea may be had of its durability as to structure, color, and weathering properties. If, after years of exposure in the atmosphere of an industrial city situated in the temperate zone, the building stone shows no disintegration and has retained its original luster and color, except for the soil of dust and smoke stains, it certainly can be considered of the best structural value for building purposes. 39. Laboratory Tests of Stone. —While the quarry and building inspections of stone are of the utmost practical importance, they should, as previously stated, be augmented by laboratory tests. When the stone to be used is from a 211—8 24 BUILDING STONE AND BRICK §31 new quarry, the characteristics of the product are little known. The laboratory tests usually consist of chemical analysis , microscopic examinations , and physical tests. 40. The chemical analysis determines both qualita¬ tively and quantitatively the chemical constituents of the stone. Examined qualitatively, the mineral elements and chemical combinations comprising the stone, together with the impurities and organic matter, are determined; while the quantitative analysis shows the proportions of the different elements and chemical combinations. When the chemical composition of a stone is in this way determined, conclusions can usually, though not always, be drawn as to the durability and the weathering properties of the stone. 41. The microscopic examination of building stone is of more importance and is less expensive to conduct than the chemical analysis, for by it is revealed the structure of the stone. By the microscope may be observed the size and shape of the particles or crystals composing the stone, their relative closeness, and the character and compactness of the cementing material holding them together. Usually, the mineral constituents of the stone may be determined like¬ wise by microscopic examination and frequently their pro¬ portions may be estimated, together with the percentage of impurities contained in the stone. Likewise, by the micro¬ scope may be detected any flaws in the structure, such as cracks, cavities, incipient fractures, and gas bubbles. 42. The physical tests of a stone furnish data from which a fair estimate of the durability may be made. It includes the determination of the resistance to crushing and transverse stresses, and the resistance to abrasion, heat, and cold. In making these tests, the object is to impose on the stone as nearly as possible conditions that in the course of a few hours or a few weeks will approximate the effect produced by actual use during a lapse of years. BUILDING STONE AND BRICK 25 §31 METHODS OF TESTING STONE 43. Absorptive Power. — Few of the properties of a stone are of greater importance than the absorptive power, since it is largely through the freezing of the absorbed water that the majority of stones are destroyed. The absorptive power of a stone is usually ascertained by two tests—one to determine the absorption from a moist atmos¬ phere, and one to determine the amount of water absorbed through actual soaking. The first test is performed by keeping samples of the stone in hot, dry air for several days to expel the hydro¬ scopic moisture, after which they are weighed. They are then placed on shelves in a cylinder, the mouth of which is sealed with water by placing the cylinder, mouth down, in a pan of water. The cylinder and the samples are kept for several weeks in a temperature ranging between 60° and 70° F., the water,being replenished from time to time so as to maintain a constant seal at the mouth of the cylinder. At the end of the test period, the samples are weighed. The increase in weight shows the amount of absorption that will take place in moist air. To ascertain the amount of water absorbed by soaking, the specimens of stone are dried and weighed, then immersed in water for 24 hours, removed, and weighed again; the increase in weight will be the amount of absorption. This is usually expressed in a percentage of the weight of the dry stone. An absorption of more than 3 per cent, is regarded as detrimental. The average water absorbed by stones is shown in Table IV. TABLE IV ABSORPTIVE POWER OF STONES Stone Absorptive Capacity Per Cent. Granites . . . .066 to .155 Sandstones . . .410 to 5.480 Limestones . . .200 to 5.000 Marbles . . . .080 to .160 Trap. .000 to .019 26 BUILDING STONE AND BRICK .31 44. The amount o.f water absorbed depends largely on the density of the stone; a dense stone absorbs less than a porous stone. Stones that have already begun to decom¬ pose absorb a much larger quantity of water than those fresh from the quarry. A low absorption is generally con¬ sidered as indicating a good quality; still it does not follow that a stone that absorbs a small amount of water will suffer the least through the action of frost, for the reason that a porous stone of coarse structure will dry more rapidly than one of a firmer grain and open texture, and will permit the expansive action of freezing water to find relief without forcing apart the particles of which the stone is composed. Hence, a high rate of absorption is more detrimental to a fine-grained stone than to a coarse-grained one. 45. Resistance to Freezing. —To ascertain the ability of a stone to resist the expansive action of freezing water, several tests are recommended. Brard’s test, which con¬ sists in boiling weighed samples in a concentrated solution of sulphate of soda, is considered the best. The soda in crystallizing expands, as does water when freezing. After each boiling, the stone is removed from the solution and hung up to dry. The operation is repeated daily during a period of 4 weeks, after which the stone is dried and weighed and the difference in weight and the general appearance are noted. 46. Resistance to Abrasion.— The resistance of a stone to abrasion is ascertained by placing cleaned and weighed fragments of the stone in a metal cylinder and revolving it at the rate of about 30 turns a minute until 10,000 revolutions have been made. As the cylinder revolves, the stones are rolled against one another, and the edges are gradually broken off, the particles thus separated forming a dust. When the required number of revolutions has been reached, the stone is removed from the cylinder and weighed. The difference between the two weighings represents the loss by abrasion. The ability of stones to resist abrasion is compared by the ratio of the weight of the §31 BUILDING STONE AND BRICK 27 dust worn off to the original weight of the stone, and the loss is expressed as per cent, of wear. Thus, if the original weight of the stone placed in the cylinder was 20 pounds, and the weight of the dust produced was 5 pounds, the loss would be expressed as 25 per cent, of wear. Regarding the ability of stones to resist abrasion, it may be stated generally that the granite rocks lose from 2 to 10 per cent.; the range of loss in limestone rocks varies from 10 to 35 per cent.; and sandstones lose about 14 per cent. The resistance to abrasion by wind-blown sand is ascer¬ tained by subjecting weighed samples of the stone to the action of a sand blast operated under a given pressure for a specified time, at the end of which the sample is weighed to ascertain the loss. 47. Crushing Strength. —The crushing strength of a stone is ascertained by subjecting cubical specimens accurately dressed to form and dimensions to a measured force applied in a suitably constructed machine, until they are crushed. 48. Bending Strength. —To ascertain the bending strength of a stone, prisms 1 inch square and from 6 to 12 inches long are supported at each end and loaded in the center until fracture takes place. The breaking load thus found is employed to ascertain the breaking load of any stone under transverse stresses. Owing to the uncertainty regarding the strength of stone, a working strength of from 10 to 20 per cent, of the ultimate strength is used. 49. Permanence of Color. —In order to ascertain the permanence of color of a stone, samples are placed in an air-tight vessel and submitted to the action of the fumes of nitric, hydrochloric, and other acids for a period of 7 or more weeks. At the end of this time the stones are washed and any change in color is noted. 50. Resistance to Acids. —The effect of the acids contained in the atmosphere is determined by immersing samples of the stone for several days in water that contains 28 BUILDING STONE AND BRICK §31 1 per cent, of the acid whose action it is desired to ascertain, and agitating frequently. The usual acids contained in the air are sulphuric and nitric acid, due to the smoke in large cities. i 51 . Specific Gravity.—The determination of the spe¬ cific gravity of stone affords a convenient method of ascer¬ taining the weight per cubic foot. This determination is made by carefully weighing a small piece of the stone in the air and then weighing it in water. The result obtained by TABLE V SPECIFIC GRAVITY AND WEIGHT OF STONE Kind of Stone Specific Gravity Weight Pounds per Cubic Foot Minimum Maximum Minimum Maximum Granite . . . 2 .6 o 2.80 163 170 Sandstone . . 2.23 2-75 137 170 Limestone . . 1.90 2-75 118 175 Marble . . . 2.62 2-95 165 179 dividing the weight in air by the difference between the weight in air and the weight in water is the specific gravity, which multiplied by 62.5, the weight, in pounds, of 1 cubic foot of water, gives the weight of 1 cubic foot of the stone. When it is desired to ascertain the specific gravity of porous stones, or those which absorb considerable water, the speci¬ men is first weighed dry, then immersed in water, and, when thoroughly saturated, removed and weighed, again immersed, and weighed while under water. The quotient obtained by dividing the dry weight by the difference between the weights of the saturated stone in air and under water will be the specific gravity. Table V contains the specific gravity and weight per cubic foot of the usual building, stones. §31 BUILDING STONE AND BRICK 29 52. Resistance to Fire.—The power of a stone to resist the action of high temperatures is ascertained by heating samples to a red heat in a muffle furnace and observing the effect. When slightly cooled, the heated samples are plunged into cold water and the effect in pro¬ ducing cracks or crumbling is noted. ' BRICK INTRODUCTION 53. Brick may be called artificial stone manufactured in small pieces for convenience in laying. Among bricks are included ordinary clay brick , firebrick , terra cotta , and sand- lime brick. While there are many artificial stones manu¬ factured, they will not be discussed in this Section. Terra cotta is much used in modern construction to obtain decora¬ tive and architectural effect, but its chief structural use is in the construction of fireproof floors, partitions, and coverings. The material used in the manufacture of common brick is clay that has a variable percentage of protoxide of iron. Other substances that form part of ordinary clay either do no good or are absolutely harmful, carbonate of lime in any large quantity, for instance, rendering the clay unfit for brickmaking. Sand or silica should not exist in any excess¬ ive quantity, as an excess of sand renders the brick too brittle and destroys cohesion. The protoxide of iron in the brick clay causes the red color in the brick after burning, the color varying with the proportion of iron. With more intense heat, the brick, if slightly fusible, may be vitrified externally and thus become a sort of greenish blue. The presence of magnesia or a small percentage of lime in the clay will change the red color produced by iron to a cream or buff shade. In the mottled brick now largely used, the mottled effect is pro¬ duced by using coloring matter in the clay or by mixing clays of different chemical composition. 30 BUILDING STONE AND BRICK §31 CLAY BRICK IIAND-MADE BRICK 54. In many localities where brick are to be manufac¬ tured for only a short period, or in country districts where, even if the plant were permanent, it would often be idle on account of no building being done, it is sometimes more economical to make brick by hand than to put in brick¬ manufacturing machinery. When making brick by hand, the clay, after water is added, is worked in a circular pit, usually about 2 feet 6 inches deep and 15 feet in diameter. In the center of this pit is a brick or stone pier with a vertical pin fastened in its center. Pivoted to this pin is a horizontal shaft with a wheel, and this wheel rests on the clay that has been thrown into the pit. If a horse, hitched to the outer end of the shaft, is made to walk around the pit, the shaft will swing around the vertical pin, while the wheel will revolve and churn the mixture of clay and water. When the clay becomes soft, it is taken to the molding table and pressed into molds by hand. The molds, which have neither top nor bottom, are usually made of wrought iron and wood or cast iron or brass. When it is desired to make an indentation, called a frog , or kick , in one side of the brick, so as to give a better bond to the mortar, the mold is set on a stock board , or bottom , made to fit it and having a projection the shape of the desired frog. The top of the mold is always struck flush with a steel or a wooden straightedge. When laying brick containing a frog in one side, the frog side is placed upwards. In wire-cut machine brick, of course, there can be no frogs, but frogs are often made even in both sides of pressed brick. Before filling the brick molds, they are either dipped in water (called slop molding ) or in sand (called dry molding) to prevent the clay from adhering to the mold. Sand mold¬ ing gives cleaner and sharper brick than slop molding. I 331 BUILDING STONE AND BRICK 31 After the brick are shaped in the mold, they are laid in the l sun or in a dry house for 3 or 4 days, after which they are stacked in kilns and fired. MAC HIKE-MADE BRICK 55. Where many brick are to be made, the work is usually done by machinery, and one of three methods, known as the soft-mud , the stiff-mud , and the dry-clay process , is employed. 56. Soft-Mud Process. —In the soft-mud process, the clay is thrown into a plank-lined pit, whefe it is soaked in water for 24 hours. The usual custom is to provide several pits, so that one pit may always contain clay that has been softened by the water and is ready for use while the other pits are being filled or the clay is in the process of softening. In some localities where the clay is somewhat wet in the clay bank, or where a lower grade of brick is being made, the clay is not made wet until it is placed in the machine. From the softening pit, the clay is taken by a conveyer and dropped into a hopper, from the bottom of which it passes into one end of a trough. Down the axis of this trough runs a revolving shaft, along the length of which'are knife blades set on an angle, like the blades of a ship pro¬ peller. This shaft with its blades is known in the machine trade as a screw conveyer , or worm. This worm works the clay to the end of the trough farthest from the hopper. If the clay has not been soaked in the softening pits, it is wetted in the trough by means of a spray, which spreads the water evenly and thus prevents unequal wetting. The blades of the worm help to mix the clay completely and make it homo¬ geneous. At the end of the trough is a plunger that works up and down and forces the clay into a wooden mold that is divided into six compartments, each one being the size of a brick. The mold is taken out of the machine at each stroke of the plunger and a new one inserted, the brick being emptied out of the mold on a board and then taken to the drying yard, i where they are allowed to dry before being burned. 32 BUILDING STONE AND BRICK 31 57. Stiff-Mud Process. —In the stiff-mud process, the clay is first thoroughly ground, and just enough water is added to make a stiff mud. After this mud is mixed and tempered in a pug mill , it is placed in a machine having a die the exact size of the brick required. The opening in this die is made the size of either the end or the side of a brick. The machine forces a continuous bar of clay through this die, and as it emerges it is automatically cut into bricks, which are then taken to the drying yard. The soft brick are placed in rows in a yard covered by a rough shed with open sides, where they are sun or air dried for 3 or 4 days. When properly dried and before burning, they resemble somewhat the “adobe” brick that were formerly used for constructing houses and are still employed in the southwestern part of the United States, and also in Mexico and Central America. 58. Dry-Clay Process. —The process often employed in the best work is the dry-clay process. In this method of manufacturing brick, the clay is used just as it comes from the bank, and is apparently perfectly dry. It contains, how¬ ever, about from 7 to 10 per cent, of moisture. The clay is dug from its bed and stored in mounds, sometimes called kerfs , to allow the mass to disintegrate. It is usually kept in this manner for two or three winters, as frost seems to have a good effect on it, and brick made from clay thus weathered will not warp in the kiln. In England, the clay used for making the very best brick is frequently stored in cellars. After the clay has been stored for a sufficient length of time—although often, due to rush of business, it is not kept at all—it is forced through a perforated plate, called a dry pan , and is then screened. In some localities, it is neces¬ sary in making brick to mix several kinds of clay to get the best results. After screening, the clay is filled loosely into molds. These molds are of the same width and length as the brick, but are deeper than the required thickness of the brick. A plunger is then forced in the mold under heavy pressure and compresses the clay to the size of the brick desired. The brick are then removed to the kiln and fired. §31 BUILDING STONE AND BRICK 33 Molded brick are made in the same way, the difference being that the box is made to give the special shape of the brick required. Whenever the term pressed brick is used, it should mean the brick made by the dry-clay process. There are many so-called dressed , or face , brick , however, that are made by recompressing soft-mud brick. BRICK BURNING 59. The brick, after drying, are built in a large mass, or kiln, containing from 100,000 to 300,000 brick. Eyes, or flues, are left at the bottom as receptacles for fuel. The brick are laid loosely together in order to allow the heat to pass in and around them. When ready, a fire is started, slowly at first, but afterwards increased to an intense heat; and after burn¬ ing for a period determined partly by the fuel used, but mainly by experience, the fires are allowed to die out gradually. On opening a brick kiln after burning, the quality of the brick therein contained may be divided into four classes: (1) The extreme outside, or first, layer contains brick that are burnt so little that they are almost worthless. (2) In the second layer the brick are underburned and soft; these are called pale , or salmon , brick , and are unfit for foundation or face work; but are used for filling in between stud parti¬ tions, and sometimes between harder brick in the inside of walls, although their use for this purpose is not recom¬ mended. (3) In the third layer of the mass forming the kiln is found a class of brick well burned, hard, well shaped, and of a good red color; this kind of brick is good for any purpose. (4) The brick in the fourth, or inner, layer of the kiln, just above the flues, are overburnt, very hard, very brittle, and usually distorted, cracked, and even vitrified; they should not be used in any structure subject to shock, but are often employed for paving. 34 BUILDING STONE AND BRICK 31 CLASSIFICATION OF CLAY BRICK 60. Common Brick. —The term common brick includes all brick that are intended for structural and not for ornamental purposes, and that require no special pains to be taken in their manufacture. There are three grades of com¬ mon brick, termed, according to their position in the kiln: arch, or clinker, brick; red, hard , or well-burned, brick; and soft, or salmon, brick. 61. Pressed, or Face, Brick. —The brick called pressed, or face, brick are hard and smooth and have sharp corners. They are usually made by the dry-clay process, or else they are recompressed brick. Owing to the fact that these brick cost more than common brick, they are seldom used except for facing walls built of cheaper grades of brick. The special forms of pressed brick are called molded, gauged, arch, and circle brick. Molded and ornamental brick are now manufactured in a great variety of forms and pat¬ terns, so that cornices and moldings may be constructed entirely of brick. If an architect or engineer requires special patterns of molded brick to carry out designs, most of the larger companies manufacturing pressed brick will make the special shapes desired if drawings are furnished. These should be drawn to a large scale, and full-sized details should be given. 62. Stock Brick.— Hand-made brick intended for face work are called stock brick, and in manufacturing and burn¬ ing them, greater care is taken than with common brick. Stock brick are used extensively for the outside facing of factories, machine shops, and the cheaper class of private dwellings. In the Eastern States, they are sometimes called face brick. 63. Arcli and Circle Bricks. —For circular or seg¬ mental doors and window openings in brickwork, arch brick should be made in the form of a truncated wedge, that is, a wedge with the sharp end cut off. The walls of circular towers, bay windows, etc. are faced with the so-called circle §31 BUILDING STONE AND BRICK 35 brick, or brick molded to the curvature of the circle desired. The radius of the bay or the tower should always be given when ordering the brick. 64. Firebrick.— The brick used for lining furnaces, lime kilns, fireplaces, and tall chimneys in factories are called firebrick. They should be free from cracks, of homoge¬ neous composition and texture, uniform in size, of a regular shape, easily cut, and not fusible. They are usually some¬ what larger than the ordinary building brick, and are made of a very pure clay and clean sand, or sometimes of pure silica cemented with a small proportion of clay. The clay should be silicate of alumina. Oxide of iron in the clay is very injurious, and if it reaches 6 per cent., the brick is not suitable for the purpose. Specifications for firebrick should require that the oxide of iron be less than this amount, and that the aggregate of lime, soda, potash, and magnesia be less than 3 per cent. The sulphide of iron, or pyrites, has a harmful effect on the fireclay, and brick containing it should not be accepted. An excess of silica in the brick makes it refractory in extremely high temperatures. Where the brick has to resist the action of metallic oxides, which would have a tendency to unite with silica, alumina should be in excess. 65. Glazed and Enameled Brick. —Brick that are either glazed or enameled are used largely for lining water- closet and bathroom walls, the wainscoting of halls and staircases, and in many cases the entire walls of stores, restaurants, hospitals, public waiting rooms, and markets, or wherever a non-absorbent surface that is clean and light is desired. Glazed and enameled brick can be used for the exterior of buildings as well as for the interior, as they will withstand the most severe changes of weather, reflect light, acquire no odor, are impervious to moisture, and are fireproof. There are two kinds of enameled brick known to the trade, namely, glazed brick and enameled brick. Glazed brick are made by coating the unburned brick on the side on which it is to be glazed with a slip , and then putting on a coat of transparent glaze closely resembling glass. The 36 BUILDING STONE AND BRICK §31 slip, which gives the brick its white color, is a composition of ball clay, pulverized kaolin, flint, and feldspar. In a genuine enameled brick, the enamel is fused directly into the brick without any intermediate coat, and the enamel in itself is opaque. 66. An enameled surface can be distinguished from one that is merely glazed by chipping off a piece of the brick. The enameled brick will show no line of demarcation between the body of the brick and the enamel, while the glazed brick will show a layer of slip between the glaze and the brick. Brick are enameled or glazed only on one face or on one face and one end. Genuine enameled brick cost more than glazed brick, as they are more difficult to manufacture; but, owing to the enamel being a part of the brick itself, an enameled brick will not chip or peel so readily as a glazed brick, and is therefore more desirable. 67. The genuine enameled brick are made from a certain kind of clay that usually contains a large quantity of fireclay. The enamel is applied to the brick either before or after it is burned, the latter method producing the best brick. For many years all the glazed and enameled brick were made in England, but there are now several factories in the United States. Many of the American manufacturers make the American standard size, which is 8* in. X 4 in. X 2i in., but some of them adhere to the English standard size, which is 8f in. X 4i in. X 2i in. However, the sizes of brick vary a great deal in different sections of the country. 68. Paving Brick. —The stiff-mud process is generally employed in the manufacture of paving brick, the brick being recompressed to give them better shape. They are composed of about three parts of shale clay to one part of fireclay, and are burned to the point of vitrification; that is, * to a heat at which they begin to fuse. These brick have a high crushing strength and absorb very little moisture. They are used principally for paving driveways, and occa¬ sionally for paving flat roofs on fireproof buildings. §31 BUILDING STONE AND BRICK 37 TERRA COTTA 69. Varieties and Manufacture of Terra Cotta. 9 There are three varieties of terra cotta, the porous , the semi- porous, and the de?ise. The degree of density depends on the materials used in its manufacture. 70. The porous terra cotta is produced by mixing a plastic clay with from 25 to 35 per cent, of sawdust, mold¬ ing this mixture into the forms desired, and then subjecting it to intense heat. The heat will transform the sawdust into gaseous products, the remaining cavities giving the burnt clay a porous quality. The finished product should be hard and should give a metallic sound when struck. These quali¬ ties will be absent if the terra cotta is made carelessly or from sandy clays. Porous terra cotta will resist intense heat and will therefore act as a protector for adjoining materials. It is easily workable; that is, it may be per¬ forated with nails and be cut with a saw or other tools. 71. The semiporous terra cotta, used mostly in the form of tiles, is made from a mixture of fireclay and about 20 per cent, of coal dust. When subjected to kiln heat, the coal dust will assist in the burning of the tile and also make it partly porous. It is thought that this variety of terra cotta will resist fire equally as well as porous terra cotta. 72. The dense terra cotta has no admixture of either coal or sawdust, and is made from clay alone; it is, there¬ fore, very dense and of a high crushing strength. Several clays, such as fireclay and good brick clay or plastic clay, are used in its manufacture. Being non-porous and gener¬ ally having a glazed surface, it is a good protector against moisture, but it does not possess the fire-resisting qualities of the preceding varieties. 38 BUILDING STONE AND BRICK §31 SAND-LIME BRICK 73. Methods of Manufacture.—The composition of sand-lime brick is usually 94 per cent, of sand and 6 per cent, of slaked lime. This mixture is forced into molds under a very heavy pressure, and the brick are than hardened by means of superheated steam. These brick can be made in many colors by artificial means, and can thus be used to effect the most pronounced designs. 74. There are several methods by which sand-lime bricks are manufactured. In the Heuennekes system, the lime is burnt in a kiln and crushed into a fine powder, after which, by means of a machine, it is measured into definite quantities- and mixed with sand that has previously been dried and measured. After passing through another machine, which grinds it fine, it is mixed with water in a mixer, whence it is transported to a receptacle where the lime is allowed to slake for about 12 hours. The mixture is now placed in a press, which forms the brick under a pressure of about 5i tons per square inch. The brick are then transported to a large steel cylinder, where they are subjected for 11 hours to chem¬ ically charged steam acting at a pressure of 120 pounds per square inch, when the brick are ready for use. 75. In the Schwarz system, the sand is dried under vacuum in a preparing machine, after which the lime is added and thoroughly mixed with the sand in a specially constructed mixer. The subsequent addition of carefully measured quan¬ tities of water causes the lime to slake, the heat evolved being used for the formation of silica of lime. In this con¬ dition, the mixture is very plastic and is easily molded into brick by means of the press. The brick are finally subjected to a hardening process in which superheated steam is used, and are thus changed chemically into calcium silicate, the hard composition of the brick. There are many other processes of sand-lime brick manu¬ facture, more or less patented, but they all have the essential features of the processes just described. * BUILDING STONE AND BRICK 39 SIZE AND STRENGTH OF BRICK 7(5. Size of Brick. —There is no standard size of brick in America. The dimensions of brick vary with the locality and also with the maker. When ordering brick, a good plan is to specify that all brick shall be over a certain given size; otherwise it will be found that many more brick will be required for a job than was at first expected. Also, as brick are often laid at a certain price per thousand, the cost per cubic yard of masonry will be increased if smaller brick than those figured on are used. In the New England States, the average size of common brick is about 7f in. X 3f in. X 2 t in.; New York and New Jersey brick will run about 8 in. X 4 in. X 2i in.; and the walls laid in them will run nominally 8, 12, 16, and 20 inches in thick¬ ness for 1, If, 2, and 2k brick. Most of the western com¬ mon brick measure 8i in. X 4i in. X 2k in., and the thickness of the walls measures about 9, 13, 18, and 22 inches for thicknesses of 1, lk, 2, and 2k brick. On the seacoast of some of the Southern States, the brick are made with a large percentage of sand, and will average 9 in. X 4k in. X 3 in. Most manufacturers of pressed brick use molds of the same size; hence, pressed brick are more uniform in size. They are generally 8! in. X 4i in. X 2| in. Pressed brick are also made 1^ inches thick. A form frequently used and known as Roman, or Pompeian, brick is 12 in. X 4 in. X li in. in size. In order that a good bond may be secured, pressed brick should be made of such size that two headers and a joint will equal one stretcher. The weight of brick varies considerably with the material used in their manufacture and also with their size. Common brick will average about 4k pounds each, while pressed brick, owing to their greater density, will weigh about 5 pounds each. 77. Strength of Brick. —All brick should be of uniform dimensions, free from cracks, pebbles, or pieces of lime, and should have sharp corners. The brick should be well burned, but not vitrified so that they become brittle. When two 211—9 40 BUILDING STONE AND BRICK §31 good bricks are struck together, they should emit a metallic ring. A good brick will not absorb over 10 per cent, of its weight of water if allowed to soak for 24 hours. Brick suit¬ able for piers and foundations of heavy buildings should not break under a crushing load of less than 4,000 pounds per square inch. The bending strength, or modulus of rupture, of a brick is quite as important as the crushing strength. A good brick 8 inches long, 4 inches wide, and 2 % inches thick, should not break under a center load of less than 1,600 pounds, the brick lying flat, supported at each end only, and having a clear span of 6 inches and a bearing at each end of 1 inch. A first-class brick will carry 2,250 pounds in the center without breaking, and a brick has been tested to 9,700 pounds before breaking. Table VI gives the average ultimate, or breaking, loads for various kinds of bricks. TABLE VI STRENGTH OF BRICKS AND TERRA COTTA Material Weight per Cubic Foot Pounds Compressive Strength Pounds per Square Inch Tensile Strength Pounds per Square Inch Modulus of Rupture Pounds per Square Inch Soft, inferior brick. IOO I .OOO 40 600 Good, common brick. 120 10,000 200 600 Best, hard brick. 125 12,000 400 800 Paving brick. 130 5,000 Philadelphia pressed brick. 150 6,000 200 600 Red sand-lime brick, Arkansas . . . no 5,300 Sand-lime face brick, Maryland . . IOO 3,500 Light-gray sand-lime brick, Iowa . . 115 4,800 Light-gray sand-lime brick, North Carolina. ii 5 5,100 Terra cotta. 110 5,000 §31 BUILDING STONE AND BRICK 41 TABLE Til STRENGTH OF BRICKWORK {Age, 6 Months ) Material Wire-cut brick. Dry-pressed brick. Dry-pressed brick. Recompressed brick. Light-hard, sand-struck brick . . Light-hard, sand-struck brick . . Hard, sand-struck brick . . . . Hard, sand-struck brick . . . . Hard, sand-struck brick . . . . Sand-lime brick. Sand-lime brick. Sand-lime brick. Terra-cotta work. Composition of Mortar Parts Weight per Cubic Foot Pounds Compressive Strength Pounds per Square Inch i cement, 5 sand 136 3,000 1 cement, 5 sand 137 3,400 1 cement, 1 lime, 3 sand 133 2,300 1 cement, 5 sand 124 1,700 1 cement, 5 sand 117 1,900 1 cement, 7 sand 109 853 1 cement, 1 sand 119 2,100 1 cement, 1 lime, 3 sand 1 13 1,500 1 cement, 5 sand 108 1,200 1 cement, 3 sand 112 I, IOO i lime, 3 sand 108 450 neat cement 113 1,400 112 2,000 TABLE Till ALLOWABLE UNIT STRESSES FOR BRICK MASONRY Material Safe Compressive Strength Pounds per Square Inch Safe Bending Strength Pounds per Square Inch 1 Brickwork, laid in Portland-cement mortar; cement 1, sand 3. 250 50 Brickwork, laid in natural-cement mortar; cement 1, sand 3. 150 40 Brickwork, laid in lime-and-cement mortar; cement 1, lime 1, sand 1. 125 30 Brickwork, laid in lime mortar; lime 1, sand 4 IOO 15 42 BUILDING STONE AND BRICK §31 Table VII gives the average ultimate strengths for brick¬ work made of various kinds of brick set in mortar, the com¬ position of which varies from cement to one consisting of 1 part of cement and 7 parts of sand. The values given in Table VII, being ultimate strengths, have to be used in con¬ nection with suitable factors of safety. The usual practice in structural and architectural engineering is to use the allowable unit values for brick masonry given in Table VIII. These values are considered good practice, and, in most materials, correspond with values recommended by the building laws of several cities. The use of the ultimate bending strength, or modulus of rupture, as it is called, will be explained in a subsequent Section. STONE CUTTING AND FINISHING STONE-CUTTING TOOLS 1. Introduction. —Before treating of stone masonry, the preliminary work of dressing the stones for the wall should first be considered. While it is not necessary for a structural engineer to be an expert stone cutter, he should be familiar with the general principles of the art in order to be able to specify the proper treatment for a certain class of work and to know when it is well done. 2. Hammers.— In Fig. 1 are shown the various hammers used for cutting and dressing stone. The double-faced hammer, shown at (a), weighs from 20 to 30 pounds, and is used for breaking and roughly shaping the stones as they come from the quarry. The face hammer, shown at ( b ), is a lighter tool than the double-faced hammer, but it is used for the same purposes when less weight is required. It has one blunt and one cut¬ ting end, the latter being used for roughly dressing the stones preparatory to using the finer tools. The pick, shown at (c), is used for coarsely dressing the softer stones. Its length is from 15 to 24 inches, and the width at the eye is about 2 inches. The ax, or peen hammer, shown at (d ), is about 10 inches long, and has two cutting edges about 4 inches in length. It is used principally for making drafts , or margin COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS’ HALL, LONDON 2 ELEMENTS OF STONE MASONRY 32 lines, around the edges of stones, and also for dressing the faces, being used after the point and before the patent hammer. The tootli ax, shown at (e), has its cutting edges a notched to form teeth, the number of these teeth varying according to the fineness of the work. It is used for roughing soft stones to an approximately flat surface before the finish¬ ing tool is used; but it is not used on hard stones, like granite and marble, as the points would become dull quickly and need constant sharpening. § 32 ELEMENTS OF STONE MASONRY 3 The bush hammer, shown at (/), is from 4 to 8 inches long, with ends from 2 to 4 inches on a side. These ends are cut into a number of pyramidal points, as shown at a. This kind of hammer is used for finishing limestones and sand¬ stones after the surfaces have been made nearly even. The crandall, shown at (g), consists of ten or twelve steel bars a and a malleable-iron handle c. In the end of the handle is a slot b, in which the bars are firmly held in place by a key d. The bars are made of ^-inch steel, are about 10 inches long, and are pointed at each end, as shown. The crandall is used to complete the finish of sandstone after the surface has been partly worked with a tooth ax or a chisel. Fig. 2 The patent hammer, shown at (h), is made of from four to ten thin steel blades. These blades are ground to an edge and are held together by means of bolts, as shown at b. This hammer is used to finish granite or hard limestone. The number of blades required to give the proper fineness to the cutting is usually specified as four, six, eight, or ten cut. The hand hammer, shown at (i), is used in drilling holes and in pointing and chiseling the harder rocks. It is about 5 inches in length and weighs from 2 to 5 pounds. The mallet, shown at (/), is used in cutting the softer stones. It is made of wood, the head being about 7 or 8 inches in diameter and 5 or 6 inches in height. 4 ELEMENTS OF STONE MASONRY §32 3. Chisels. —In Fig. 2 are shown the different chisels used for dressing stone. The point, shown at (a), is made of round or octagonal steel, 8 to 12 inches long, with one end pointed. It is used for chipping off the rough faces of the stone and reducing them to approximately plane surfaces, ready for the peen hammer, and also to give a rough finish to stone in broached and picked work. The tootli chisel, shown at (6), is used only on soft stones, serving much the same purpose as the tooth ax. The drove chisel, shown at (c), is 2 or 3 inches wide at the end. It is used for cutting or driving the rough surfaces of the stone. The pitching chisel, shown at (/), is used for making pitched-face work. Other forms of chisels used for dressing soft stone are shown at (d), (e) , (g), and (k). 4. Machine Tools. —Besides the hand tools just described, there are many machine tools employed to pre¬ pare the stone for the finer treatment to be given by hand work. The machine tools include saws, planers, grinders, and polishers. The saws used for cutting stone are merely thin sheets of steel, the edges of which are not sharp. There are three styles of stone-cutting saws, namely, the drag, the circular, and the band saw. The drag saw, which is similar in shape to the ordinary cross-cut saw, has a forward-and-backward movement The circular saw, as the name implies, is a circular disk that revolves on an axis through its center. The band saw is a continuous steel band, or belt, that runs on two driving wheels. These saws are aided in cutting by feeding sand and water in the groove that is being made in the stone. The planer is a machine used in reducing the inequalities in rough stone. It consists of a table that moves horizontally under a cutter, the stone to be trimmed being fastened on the table by means of clamps. §32 ELEMENTS OF STONE MASONRY o The grinder and the poll slier are practically alike so far as construction is concerned. They differ only in the fineness of surface they are capable of producing. The machine used for grinding or for polishing consists principally of a circular horizontal table on which the stone is fastened, the face to be polished being always turned upwards. This table, with the stone, revolves about a vertical axis through its center, and a horizontal metal plate that can be moved up and down, but will not revolve, is pressed on the stone. Sand and water are supplied between the plate and the stone, whose surface is thus abraded until the proper degree of smoothness is attained. FIXISII OF STONEWORK 5. Stereotomy.-— The science of making patterns, or templets, to which a stone is to be cut to fill a certain place in an arch or other complicated piece of stonework, is called stereotomy. In practice, the engineer makes a drawing of the intended stone¬ work, showing where the joints in the face are to be located, and the stone cutter then details each block and cuts it to fit exactly with the others. It is therefore impor¬ tant for the engineer to understand the different finishes to which stone is dressed, but it is* not necessary for him to be able to make the templets for each stone. 6. Rock-Faced Work. —In Fig. 3 is shown rock¬ faced, or pitcli-faeed, work, and the method of using the pitching chisel. The face of the stone is left rough, just as it comes from the quarry, and the joints, or edges, are pitched off to a line, as shown at a. As this finish requires very little Fig. 3 6 ELEMENTS OF STONE MASONRY §32 work, rock-faced dressing is cheaper than any other kind, especially when granite or hard limestone is used. 7. Margins. —Building stones are often faced an inch or so from their edges. This dressed strip, shown at a, Fig. 4, is known as the margin, or draft line, to distinguish it from the rock-faced work at b. This margin is cut on soft stone with a chisel, but on extra-hard stone, such as granite, it is usually cut with an ax, or peen hammer. 8. Pointed Work.— In producing pointed work, a pointed chisel is run over the face of a stone to knock off any large projections. This work is called rough- or fine-pointed work , according to the number of times the work is gone over. In Fig. 5 is shown an example of rough-pointed work, while in Fig. 6 is shown an example of fine-pointed work that is also margined. 9. Tooth-Chisel Work. — The finish called tootli- cliisel work is produced by dressing stone with a tooth chisel. The surface of a stone finished in this way resembles pointed work, but it is not so regular. Working stone with a tooth chisel is one of the cheapest methods of stone dressing known. 10. Broached Fig - 4 Work. —Fig. 7 illus- »» trates what is known as broached work. In this kind of work the stone is dressed with a point so as to leave con¬ tinuous grooves over the surface. At a is shown the margin, or draft line, and at b, the broached center, which is cut in two directions in order to illustrate right- and left-hand broaching. 11. Tooled Work.— For tooled finish a tooth chisel from 3 to 4^ inches wide is used. In this kind of work, Fig. 5 Fig. 0 7 Fig. 7 Fig. 8 8 Fig. 9 Fig. 10 9 t Fig. 11 Fig. 12 10 §32 ELEMENTS OF STONE MASONRY 11 the lines are continued across the width of the stone to the draft line (when one is used). When well done, tooled work makes a very good finish for soft stones. 12. Drove Work.— The finish known as drove work is somewhat similar to tooled work, but it is generally exe¬ cuted on harder stone. There are two general classes of drove work, namely, hand drove and machine drove , the former being shown in Fig. 8 and the latter in Fig. 9. Machine-drove work, as will be noticed, is more regular than hand drove; also, the cuts are a little deeper, although this is hardly apparent from the illustration. For a large quantity of cut¬ ting, machine work is cheaper than hand work; it is not so pleasing in appearance, however. 13. Crandalled Work. — In Fig. 10 is shown cran- dailed work, which, when well done, gives the stone a fine, pebbly appearance. This finish is especially effective for the red Potsdam and Longmeadow sandstones. In the Eastern States, it is used for sandstones probably more than any other finish. 14. Rubbed Work.— In producing the finish known as rubbed work, the surfaces of stones are rubbed with a piece of softer stone, together with sand and water, until per¬ fectly smooth. Sandstones and most of the limestones are finished in this manner, and if granite, limestone, and marble are rubbed long enough, they will take a beautiful polish. The operation of rubbing can be performed either by hand or by machine. If the rubbing is done soon after the stones are sawed into slabs and are still soft, it is cheaply and easily performed, as the sawing makes the face of the stone comparatively smooth. 15. Bush-Hammered Work. —In Fig. 11 is shown the finish of a stone after having been bush-hammered. This finish, which leaves the surface of the stone full of points, is a very attractive one for hard limestones and sandstones, but should not be used in dressing the softer kinds. 12 Fig. 13 ELEMENTS OF STONE MASONRY 13 § 32 16 . Patent-Hammered Work. —A stone finished by a patent hammer, which is generally used on granite and hard limestone, is shown in Fig. 12. The stone is first dressed to a fairly smooth surface with the point and then finished with the.patent hammer. The degree of fineness in the finish is determined by the number of blades in the hammer, the usual number being eight or ten. The ax may be used instead of the hammer, but more time is required to obtain an equally good finish. 17 . Vermiculated Work. —In Fig. 13 is shown a stone having a somewhat elaborate finish, which is known as ver¬ miculated from the worm-eaten appearance. Stones cut in this manner are used principally as quoins, or corner stones, and in base courses. Owing to the cost, this style of dressing is not often used in the United States. A simple method of obtaining the vermiculated effect is by the use of a patented sand-blast process. The sand employed in this process is carborundum dust, which is one of the hardest substances known. It is blown against the stone with high velocity by means of compressed air. While this sand will rapidly cut and wear away hard surfaces, such as stone, it will not cut soft, yielding surfaces, because the latter do not suddenly stop its motion, but, by giving way slightly, permit it to sink in a short distance and then rebound. For this reason, the nozzle of the blowing machine is made of soft rubber and those portions of the stone that it is desired to have raised are covered with beeswax, asphalt, or even heavy paper. The remainder of the face of the stone is eaten away by the sand blast. When the proper depth has been reached, the sand blast is stopped and the material * used to cover the raised part of the stone is removed. It is then necessary to put on a few finishing touches with a pointed chisel, when the stone is ready to go in the structure. The sand .blast is also used to clean stonework that has become soiled and stained by smoke and dust. 18 . Seale Work. —A pleasing and novel method of stone dressing, presenting a striking effect of light and shade, 211—10 14 ELEMENTS OF STONE MASONRY §32 is illustrated in Fig. 14. The finish shown at (a), known as scale work, is obtained by cutting out rows of shallow flutes between the drafts of the stone with about a 1-inch tool. The flutes are about 1 inch wide, and are alternated so that each successive course “breaks into” the preceding one and forms with it a series of hexagonal hollows, giving a honeycombed appearance. The application of this finish to a window jamb is shown at (b). This unique method is Fig. 15 Fig. 16 applicable, of course, only to soft stones, such as limestone; but to these it gives a beautifully crisp and varied surface. The cutting can be done either by hand or by machinery. §32 ELEMENTS OF STONE MASONRY 15 19. Rusticated Work. —The term rusticated work is generally used to designate sunken or beveled joints. Two examples of this finish are illustrated in Figs. 15 and 16, the former showing the stones with recesses a having sharp edges and the latter with recesses a having rounded edges. This style of work is expensive, and is usually employed in the finish of basement work or to emphasize piers and other projections. STONE MASONRY GENERAL CONSIDERATIONS 20. The stonework entering into the construction of build¬ ings may be divided into three classes: rubble , ashlar , and trimmings. Before describing these, however, a few general observations, applying to all classes of stone masonry, are necessary. Whatever may be the quality of mortar used, the wall should contain as much stone and as little mortar as possible, as the former is the stronger material. In rough walling, if the stones are pressed together until the more prominent angles on their faces come almost into contact, the interstices being filled with mortar, there results better work than if a thick, yielding mass of mortar is allowed to remain in the joints. Absolute contact, however, is not advisable, as the mortar in drying shrinks and may leave the stones bearing only on the projecting angles. The joints in stonework vary in thickness from ^ to I inch. A *-inch joint is probably the best for ordinary work, while a h-inch joint should be used for rock-faced work only. 21. Stone being of a brittle nature, the longer pieces in a wall must be properly supported and well bedded in order to prevent them from breaking. It is also best to avoid extremely long stones, although the length of a stone should be greater than its height, especially in ashlar work, on 16 ELEMENTS OF STONE MASONRY §32 account of the vertical bond. There is a certain medium that should be observed; and while a compact mass, broken as little as possible, is most desirable in stone as well as in brick walls, the mason will often find it better to break a very long stone into two or more shorter ones, even though by so doing additional joints are made. However, in laying very long stones, as in steps or co¬ pings, it is customary to bed them only at the ends, so that when the mortar joint shrinks there will be no danger of the stones being broken by bear¬ ing on some obstruction at their middle. The best stones should be used for piers, jambs, sills, lintels, cornices, band courses, etc. in the order mentioned; and all stones in which the length of the face is greater than its height should be so quarried that they can be laid on their natural beds, except, of course, piers and long jambs, which necessarily have the bed of the rock vertical. Fig. 17 22. Defective Methods.—A stone with a hollow cut in it, as shown at a, Fig. 17, should never be used in a wall, because when the mortar shrinks, the stone will bear only at the edges and is liable to spall, or chip off, with the result shown in the illustration. If not closely watched, careless || stone masons are tempted to cut stones in this manner, as it is much easier than cutting them to a true bed. Another improper method often carried out by masons is to cut the stone as shown in Fig. 18 and underpin the back with spalls. This practice is § 32 ELEMENTS OF STONE MASONRY 17 also liable to lead to disaster, as ]the stone may split as shown at a. On account of the liability of spalling, as illustrated in Fig. 17, rusticated joints are often used in the basement and first story of tall buildings. RUBBLE WORK 23. Rubblework consists of stones in which the adjoin¬ ing sides are not required to be at right angles. It is used for rough masonry, as in foundations, backing, etc., and fre¬ quently consists of common field stone, roughly dressed; but whenever possible, quarried rubble should be used, as better bedding can thus be secured. Conglomerate and slate stones Fig. 19 abound in many localities, and are cheap and durable, but they do not cut easily. Such stones are often used with good effect, however, in walls with cut-stone or brick trim¬ mings; or, when good lengths can be had, they are used for rock-faced sills, lintels, and trimmings. 18 ELEMENTS OF STONE MASONRY §32 24. Rubble Walls. —Fig. 19 illustrates a good rubble wall, the stones being bonded about every 4 or 5 feet, as. shown at a. The largest and best stones should be placed at Fig. 20 the bottom and at the angles, as indicated at b, and should be laid up in alternate courses of headers and stretchers. Such work is generally laid with beds and joints dressed but very Fig. 21 little, the rough angles only being knocked off. The stones are set irregularly in the wall and the interstices are filled with spalls and mortar. If better work is desired, the joints H) ELEMENTS OF STONE MASONRY and beds of the stonework should be hammer-dressed. Such walls arc frequently pointed with colored mortar, showing raised joints. 25. Fig. 20 shows a form of rubble masonry much used for country and suburban work. The quoins, or corner stones, a are hammer-dressed on top and bottom, and may be either cut stone or rock face. The latter finish harmonizes well when stones similarly dressed are in the body of the wall. Fig. 22 All joints should be hammer-dressed, as shown at b , and no spalls should show on the face, while the mortar joints should not exceed \ to f inch in thickness. This makes an effective wall, especially for country churches, lodges, and other small buildings; but the work is expensive, owing to the labor required in dressing the joints. 26. Field-Stone Walls.—In Fig. 21 is shown a field- stone wall. Walls of this kind are built of small, uncut 20 ELEMENTS OF STONE MASONRY §32 boulders, and are frequently employed for fences and rustic- house work. Such walls should be made quite thick on account of the round and unstable shape of the stones used in their construction. 27. Walls With Brick Quoins.— Fig. 22 shows a rub¬ ble wall with brick quoins, or corners, at a. In this case, all the top and bottom joints of the rubblework have level beds , as at b. This kind of construction makes a very effect¬ ive wall, and can be built quite cheaply when the stone used splits readily, or can be laid on its natural bed, thus'requiring but little dressing. 28. Coursed Bubble.— In walls of coursed rubble, some effort is made to produce a coursed effect. Stone of ran- Fig. 23 dom sizes is used, but little or no attention is paid to uniform¬ ity of height in the different courses. For such walls, the stones are generally roughly dressed before the wall is begun. Care should be taken to get as nearly parallel beds as possible, and to bring the face of each stone to a fairly even surface at approximately right angles to the beds. The quoins in coursed rubble are usually dressed and laid with more care than the remainder of the work; they also serve as gauge §32 ELEMENTS OF STONE MASONRY 21 courses. Coursed rubble, when well built, makes a very solid wall and is extensively used. Fig. 23 illustrates a coursed rubble wall, the rubblework being shown at a; the quoins, at b ; the bond stones running through the walls, at c; and two of the course joints, at d e f and d' e' f. ASHLAR 29. Stonework that is cut on four sides so that the adjoining sides will be at right angles to each other, is known as ashlar, no matter whether the face is dressed or not. From Fig. 23 it is evident that some stones of this form are also found in coursed rubble. The latter may therefore be considered as the connecting link between rubble and ashlar stonework. In the following description it should be understood that the style of ashlar designated has nothing to do with the finish on the face of the stone, but simply the manner in which it is laid, although certain kinds of ashlar are generally made with the styles of dressing shown in the illustrations. Ashlar is usually laid either in regular courses with contin¬ uous horizontal joints, as shown in Figs. 24, 25, and 26, or in 22 ELEMENTS OF STONE MASONRY § 32 broken courses, without regard to continuity of the joints, as shown in Figs. 28 and 29. All ashlar should have straight and horizontal bed joints, and the vertical joints should be kept plumb. If the work is not done in this manner, ashlar walls will present a poor appearance. 30. Coursed Aslilar.— A class of stonework in which the blocks are uniform in size and the bed joints are con¬ tinuous is known as coursed aslilar. When such stones can be obtained readily, this kind of work is not very Fig. 25 expensive. A coursed-ashlar wall is shown in Fig. 24, in which 12" X 36" ashlar is shown at a, and the backing, which consists of 12-inch rubble, at b. 31. A good effect is produced by making the courses of two heights, but cut in regular sizes, and having the vertical joints in alternate courses directly over one another. This class of work is illustrated in Fig. 25. In this figure, a 14-inch course is shown at a; a 6-inch course, at 6; and the backing, at c. The latter may also be brick, as the ashlar can be well bonded into it. If the narrow band course b is rock-faced, or § 32 ELEMENTS OF STONE MASONRY 23 has some different finish than the wide courses a, the appear¬ ance of the work will be further improved. 32. The stonework of many public and office buildings has rustic quoins and base or band courses, as shown in Fig. 26. Here, the quoins, which have a 1-inch bevel, or chamfer, at the joints, are shown at a; the plain, rubbed, or tooled stones forming the face of the wall, at b; the rustic band course, having a li-inch chamfer cut on it, so as to project beyond the quoins, at c ; and the stone or brick backing, at d. This ♦ Fig. 26 method of construction is very expensive, owing to the great amount of dressing required. 33. Block-In-Course Ashlar.— In block-in-course, or blocked-course, ashlar work, all blocks of stone are cut the same height but in different lengths, and no attempt is made to have the joints come over one another. The length on the face is usually two or three times the height, and about one-fifth of the face should show headers, as at a, Fig. 27. These headers should rest on long stretchers below them, in order that the wall may be better bonded. As a 24 ELEMENTS OF STONE MASONRY rule, this style of work looks best in rock-faced finish, but any finish desired may be used. Many quarries have stratified ,»»YTT*-. ■" Vo". y. . . Y ~— 1^0, ^ { \ v - Sa>- >vsrjrt ~ HH&WVf _ a» i //• ; J //, ^n. -3? u <- ,-A‘ .*^\V 4, ,\«i/«»’ "Th ;'.:'“iVtrv- v •• • Fig. 27 stone that is just the proper thickness for this class of work, but unless the stone can be found in such shape, block-in¬ course ashlar work is generally quite expensive. Fig. 28 34. Random-Coursed Ashlar.— The method of laying random-coursed ashlar walls is illustrated in Fig. 28. §32 ELEMENTS OF STONE MASONRY 25 In this class of work, no attempt is made to have the vertical joints over one another, and it has only a general arrange¬ ment in courses, as shown. In regard to the best methods of proportioning the blocks and arranging the same so as to produce a harmonious effect, it is first necessary to consider what the various heights of the blocks must be in order to form good longitudinal bond. Assume the lowest height at 4 inches—as a stone any thinner than this presents an appearance of weakness—and the greatest height at 16 inches—as any higher than this looks too heavy for random-coursed ashlar. The gradations may then be 4, 5, 6, 7, 8, 9, 10, 11, 12, 14, and 16 inches, thus giving eleven distinct heights—a variety that, when well arranged, produces a most pleasing effect. If the three highest numbers are taken as jumpers, or course levelers, combinations may be made of the other stones so that their combined thickness will equal that of the jumper. In this manner, several arrangements are possible. The next point to be considered is the lengths of the blocks. The bond, or the lap of the stones over one another, should be, for the thinner blocks, at least 6 inches, and for the thicker ones, 8 inches. 35. Broken Ashlar.— In broken-ashlar stonework, no attempt is made to have the stone run in courses, but each block is cut for the location in which it is to go. It 2G ELEMENTS OF STONE MASONRY § 32 generally takes more time to build broken ashlar than coursed work; hence this kind of wall is more costly, owing to the increased amount of labor required to fit and lay the dif¬ ferent sizes of stone. Broken ashlar, when properly executed, presents a pleasing appearance. It is generally laid up as rock-faced work, but in some cases, it is tooled or hammer- dressed. It should have no horizontal joints more than 4 feet long, and several sizes of stone shotdd be used. Fig. 29 shows an ordinary broken-ashlar wall, 2 feet thick, the sizes of stones used being 4, 6, 8, and 12 inches in height. The quoins are shown at a, and the body of the wall at b. 3G. Best Stone for Ashlar.— The hardest kinds of rock are best suited for ashlar masonry, as, in pitching, the spalls fly off more easily and leave the fracture in sharp lines; whereas, with the softer kinds of rock, the fracture has a bruised and crushed appearance, which is not at all pleasing. The best stones to use are the granites and the most compact b luestones and sandstones. 37. Laying Out Ashlar.— If ashlar in regular courses and sizes is to be used, drawings should be made showing each stone of different size, the heights of the courses, and other necessary details. The drawings for public and office buildings usually show every stone, unless broken ashlar is used, in which case it is only necessary to show the quoins and jambs, together with enough of the ashlar to indicate the character of the work desired. It is almost impossible to follow carefully a drawing showing all the stones laid as broken ashlar. 38. Backing. —The expense of ashlar masonry is such that it is commonly used merely as a facing, being backed with either rubble, masonry or brickwork. It is only on works of great importance and solidity that ashlar masonry is used throughout the whole thickness of the wall. In general, the term ashlar applies*to the facing, or veneering, of stone, or to the stones that constitute the facing. § 32 ELEMENTS OF STONE MASONRY 27 Both stone and brick are used as backing, but in most cases, brick is the cheaper and is therefore more extensively employed. When using brick for the backing, the joints should be made as thin as possible, employing cement mortar so as to avoid shrinkage. Backing of this kind, however, should never be less than 8 inches thick. When a hard, laminated stone with flat, parallel beds can be obtained, it should be used, as it is considered to be a stronger backing than brick. Irregular rubble backing should not be used for dwellings higher than two or three stories, unless the walls are made at least one-fourth thicker than Fig. 30 when brick backing is used. All backing, whether of brick or of stone, should be carried up at the same time and built in courses of the same thickness as the ashlar. This kind of construction is illustrated at a, Fig. 30 (a) and ( b ). If the courses are not over 12 inches high, they are usually bonded sufficiently to the backing by making every other course wider, and by having one through bond stone to every 10 square feet of wall, as shown at b, Fig. 30 (a) and ( b ). This method is called a toothed bonding. 39. Method of Fastening Thin Ashlar.— Although not so strong as a toothed bond, an ashlar facing of from 2 to 4 inches in thickness is often used, especially when marble or 28 ELEMENTS OF STONE MASONRY §32 other expensive stones are employed in the construction. In such cases, each piece of ashlar should be tied to the backing by at least one iron clamp , or anchor , similar to that shown > iiirfife, in Fig. 31, while if the stones are more than 3 feet long, two an¬ chors should be used. All iron clamps, or an¬ chors, should be either galvanized or dipped Fig. 31 in hot tar or asphalt, to prevent the formation of rust on them. Belt courses extending 8 inches or more into the wall should also be laid about every 6 feet in height, so as to give support to the ashlar. When a wall is faced with thin ashlar, the effective bearing strength is only that given by the thickness of the brick or stone backing, the facing not being relied on for that purpose. CARE OF STONEWORK 40. Pointing.— The effects of the weather on the exposed edges of the joints in masonry usually cause the mortar to crumble and fall out. For this reason, it is cus¬ tomary to refill the joints to a depth of from b to 1 inch, with specially prepared mortar. This operation is called pointing. In work that is to be pointed, no mortar should be placed within an inch of the front edges of the stone, as this saves raking out the joints preparatory to pointing. Sometimes, strips of wood the exact thickness of the joint are set on the edges of the lower course. Then, in setting the stone, the superfluous mortar is pressed out and the stone rests on the wooden strips, which are removed when the mortar is hard. Pointing is generally done as soon as the walls are com¬ pleted, but, if the season is too far advanced, it should be deferred until spring. Under no circumstances should point- §32 ELEMENTS OF STONE MASONRY 29 ing be done in freezing weather, nor in extremely hot weather, as then the mortar will dry too rapidly. The most durable mortar for pointing is made of equal parts of Portland cement and sand. These materials are mixed with just enough water to give a plastic consistency, and to this mixture are added a little slaked lime to make the mortar stick and such coloring matter as may be desired. Portland and Rosendale cements discolor most limestones and marbles, and some sandstones. However, by exercising care, the mortar may be kept from the face of the stone, and the joints may be pointed afterwards with mortar that will not stain. A cement made of plaster of Paris, lime, and mar¬ ble dust, called Lafarge cement , is sometimes used for setting marble and limestone; it is claimed that this cement will not cause discoloration. 41. Cleaning. —After pointing, it is usually necessary to remove the mortar stains, etc. from the face of the wall. This may be done by scrubbing the stonework with water containing muriatic acid, the proportions being about 20 parts of water to 1 part of acid. For cleaning granite and limestone, wire brushes are used, and for sandstones and other soft stones, stiff bristle brushes usually serve the pur¬ pose. The stonework should be scrubbed until all mortar stains are removed. As previously stated, the sand blast, operated by either steam or compressed air, does the work of cleaning walls very effectively and rapidly. It not only removes the outer layer of the discolored stone, but leaves a fresh, bright surface. Even fine carvings have been very successfully cleaned by this method. 42. Stone Defects.— Granite may contain cracks, black or white lumps known as knots , and a brownish stain called sap. When such defects are found, the stone should be rejected, provided the importance of the work justifies it. Cracks are the main things to guard against, however, and they may be detected by the absence of the clear ringing sound when the stone is struck with a hammer. 211—11 30 ELEMENTS OF STONE MASONRY §32 Sand holes are frequently found in sandstones. These are bodies of uncemented sand, that become dislodged by jarring or by the action of water, and produce a pitted appearance and an uneven color. Attention must also be paid to secur¬ ing uniformity of color, as sandstone from different parts of the same quarry may vary greatly in this respect. • 43. Faults in Dressing Stone. —The common faults of cut stone are coarseness and poor workmanship. In dress¬ ing stone, builders will avoid any work beyond that necessary to make the material barely acceptable to the inspector. Frequently, the ends of cornices, belt courses, etc. will not match properly. It should be strictly required that the utmost care be taken in cutting all similar pieces to the same pattern, and that the abutting surfaces be closely dressed. 44. Laying of Stonework.— In erecting stonework, care should be exercised to have the stone set on the natural bed, with good joints, and not in too small nor in too thin pieces. The bed joints in ashlar work should be square to the face of the work, and not less than 4 inches wide at both top and bottom. The proper bonding of the w T alls, especially for the ashlar and for the trimmings, should be given very careful attention, as should also the placing of lintels, copings, wall anchors, etc. Another point that requires attention is the formation of the joints on which great pressure comes; also, the mortar should be kept back from the face, so that the edges of the stones will not be chipped off. In pointing, the joints should be well raked out and the pointing mortar properly laid. Many other precautions for the good performance of the work will doubtless suggest themselves to the careful superintendent'. §32 ELEMENTS OF STONE MASONRY 31 TRIMMINGS SPECIAL STONES 45. The term trimmings, as generally used, includes moldings, belt course, sills, caps, and other cut stone (except ashlar) used for ornamental purposes. The stones for such work should be of good quality, having the beds closely dressed and the ends square and properly matched. The faces may be pitched off, but all washes, soffits, etc. should be cut or rubbed. When a brick building is trimmed with stone, great care should be taken to have the trimmings set properly, so that it will not be necessary to split the courses of brick below or above, for such a procedure will spoil the appearance of the building. 46. Bond Stones and Templets. —All piers above a certain size require bond stones, that is, stones the full size of the pier, to prevent them from splitting. The course of brick placed underneath should be brought to an exact level to receive the stone; otherwise, the weight above may cause it to crack or become displaced. Only strong stones, such as granite, bluestone, and hard trap rock, should be used, and they should be cut to the full size of the pier. 47. Bearing stones placed under the ends of beams and girders to distribute the weight more evenly on the wall are called templets. The pressure per square inch allowed on the brickwork or stonework in the wall under the templet, as specified by the building laws of the town in which the building is being erected, governs the size of the templet required, and is usually from 100 to 200 pounds. It is better, however, to make templets too large rather than too small. A hard, tough stone should always be employed, and the usual rule is that the thickness of the stone should be one-third of the smallest surface dimension, except when very large stones are used; but the least thick¬ ness should be 4 inches. When a wooden girder rests on a 32 ELEMENTS OF STONE MASONRY §32 templet, a good plan is to place a flat stone above the end of the girder, so that the wall will rest on the stone and not on the wood. This is advisable for the reason that when the wood shrinks the settlement may cause cracks in the wall. Strictly construed, bond stones and templets are not ashlar; but as they require more or less dressing, they are considered as being ashlar. 48. Quoins. —The corner stones of a wall, as already inferred, are known as quoins. They are often dressed differently from the other stones in order to make them more prominent. Quoin stones should always be equal in size to the largest stone used in the wall; otherwise, the effect of strength and solidity that they are intended to produce will be lost. Sometimes, the quoins of a rubble-stone wall are built of brick. 49. Jamb Stones.— The stones used in the sides of a door or window opening are called jamb stones. The alternate ones should extend through the width of the wall to §32 .ELEMENTS OF STONE MASONRY 33 insure a good bond. Fig. 32 illustrates cut-stone jambs in a rubble wall. The jamb stones bonding into the wall trans¬ versely are shown at a; those bonding longitudinally, at b\ the stone window sill, at c\ and the rubble wall, at d. Fig. 33 Fig. 34 50. Occasionally, when stone piers or pilasters are built on the outside of the building, the windows are recessed so that the projection of the sills and lintels will not be so i iSSfe, ilMMl if## noticeable. This is illustrated in Fig. 33, in which a shows the lintel; b , the sash; and c, one of the jamb stones. Jambs and quoins are often finished with a draft, or angle, line l especially when the softer stones are used. Fig. 34 34 ELEMENTS OF STONE MASONRY §32 illustrates this method of finishing, the quoin or jamb stone, as the case may be, being shown at a; the angle draft, at b\ and the broken ashlar wall, at c. 51. Washes and Drips.— The tops of all cornices, belt courses, etc. should have an outward and a downward pitch from the walls, as shown at b, Fig. 35. If the top is level or slopes inwards, rain will collect, and in time will cause the disintegration of the mortar in the adjacent joints and finally penetrate the w T all. The beveled sur¬ faces are called washes. On the under side of the cor¬ nices, etc., drips should be made, to prevent rain water from flowing down the face of the wall. At a, Fig. 35, is shown the drip; at 5, the wash of the cornice; and at c , the stone cut to a sharp angle, so as to shed part of the water from that edge. Window sills should also have a drip cut in them, as shown at a, Fig. 36, so as to keep the walls below from becoming dis¬ colored by dirt washed off the sills by rain. LINTELS 52. A lintel, often called a cap , is a stone that supports the wall over a door or a window opening; and, as it must resist bending stress, it should be a strong, tough stone having an ample cross-section. The ends of stone lintels should not be built into the walls more than is necessary to give -sufficient bearing; 4 to 6 inches at each end is the usual allowance. There should be a little play allowed at each end, so that the lintels can yield slightly without cracking if the walls on either side settle unevenly. ELEMENTS OF STONE MASONRY 35 §32 53. Relieving Lintels. —Often, when a long lintel is used over an opening, the stonework above the lintel is arranged as illustrated in Fig. 37, in which a shows the lintel, and b the relieving lintel, or stone above it cut with c c 1 ~1 1 Pig. 37 two diagonal joints, as at c. In this way, some of the load is taken off the lintel and transferred to the wall on both sides of the opening. When a lintel extends through the wall and is not sup¬ ported by angles or beams, the strength may be increased, provided the stone is stratified, by cutting it in such a manner that the layers will set on edge, as shown at a, Fig. 38. This procedure, however, may cause the face of the lintel to flake off if the layers of stratification are thin and not securely joined together. 36 ELEMENTS OF STONE MASONRY §32 54. When considerable weight rests on a stone lintel, a brick relieving arch may be used; but unless much skill is exercised in its construction, this arch will detract from the appearance of the building, especially if it extends through the entire thickness of the wall. To avoid this result, if stone of sufficient depth cannot be used, the lintel may be strengthened by the use of iron beams or angles. When the lintel is of moderate length, it is sufficient to use a piece of angle iron, as in Fig. 39, in which a shows the stone lintel; b, the angle, which should have its longer side vertical; c, a wooden beam to which the interior woodwork is nailed; d, the brick wall; and e , the window reveal, or side. 55. I-Beam Supports.— When the width of the opening is considerable, stone lintels should be supported on I beams. Fig. 40 e Fig. 41 If only the weight of the lintel and wall is to be carried, a single I beam may be used, as shown in Fig. 40, in which the §32 ELEMENTS OF STONE MASONRY 37 stone lintel is shown at a; the I beam, at b ; the wooden beam to which the wood finish is attached, at c\ the reveal, at d\ and the brick wall, at e. If, in addition to the walls, the floorbeams over openings must be carried, it is best to use two I beams, as in Fig. 41. Here, the stone lintel is shown at a; the I beams, held together by bolts and separators, at b\ an iron plate on which the wall rests, at c\ a floorbeam, at d; the window reveal, at e\ and the brick wall, at /. When it can be avoided, the best plan is not to support the weight of a wall on both stone and steel or wooden beams, as the deflection of each material is different, making it prac¬ tically impossible for each to carry its proper share of the load. The weight should preferably be borne by the steel beams alone. 56. Built-Up Lintels.— It is sometimes necessary to use a stone lintel that is 10 or 12 feet long. Since it is difficult to obtain a single piece of stone of this length, the lintel may be made in sections, as in Fig. 42. At least three stones should be used, and the joints should be cut as shown at a. When cut in this manner, the stones are self-supporting. The end pieces may be built into the wall for a considerable length, so as to act as cantilevers supporting the middle sec¬ tion. If such long lintels are used, however, it is better to carry them on I beams, as shown in Figs. 40 and 41. In stonework it is best to avoid placing a pier directly on top of the lintel; all openings should preferably be directly above one another. 38 ELEMENTS OF STONE MASONRY §32 SILLS 57. Lug and Slip Sills.— In masonwork, sill is the name given to the stones that form the bottom of the win¬ dow and door openings in stone or brick walls. Lug sills have flat ends, or lugs, built into the wall. These lugs should not enter the walls a distance of more than 4 inches, and should be bedded on mortar only at the ends. If a sill is bedded solid and settlement occurs, it will probably be fractured at the jamb line, as the pier or side walls will likely settle more than the wall under the opening. The joints under the sills should be filled when the finished walls are cleaned down. Slip sills are made just the width of the opening, and are not built into the walls, being put in place after the frame is set. Such sills are cheaper, but they do not look so well as lug sills; besides, there are exposed vertical joints at the ends into which water will penetrate. However, any settlement of the masonry is not liable to break a slip sill, and they arc therefore often used in the lower parts of heavy buildings. §32 ELEMENTS OF STONE MASONRY 39 58. All sills should have a bevel, or wash, about 1 inch to the foot, extending to the back of the reveal, as shown in Fig. 43. They sometimes have a beveled surface the full length of the sill, the brickwork being made to fit the stone. The latter construction, however, is not good practice, as it permits water running down the jamb to enter the joint between the brick and the stone; the sloping upper face also forms an insecure bearing for the wall resting on it. In Fig. 43 is shown the proper method of cutting the surfaces. As shown at a, the flat end of the lug sill carries the brickwork reveal c. At b is shown the bevel, or wash, and at d, the drip. COPING 59. If no cover is put on the top of a wall, rain will wash out the joints. For this reason, parapet walls are capped Fig. 44 with a wide stone called coping. Terra cotta is also occa¬ sionally used for this purpose. The upper surface of the coping should be pitched, as shown at a, Fig. 44, and should have a drip on the under side, as shown at b. The coping should be about 3 or 4 inches wider than the wall. Hori¬ zontal coping stones are often clamped together at their ends to prevent them from becoming displaced. 40 ELEMENTS OF STONE MASONRY §32 Gable copings should be anchored either by bond stones or by long iron ties. A form of coping that is extensively used is shown in Fig. 45, in which the coping is shown at a, and the corbel, at c. The bottom stone b , sometimes known as the kneeler, should always be well bonded into the wall. In some cases, the coping is cut in steps, so that each stone §32 ELEMENTS OF STONE MASONRY 41 will have a horizontal bearing on the wall. This method of coping is objectionable, however, on account of the increased number of joints. It is well to have long pieces of coping, so as to reduce the number of joints—a common length is 6 feet. A short piece of coping cut as shown at a, Fig. 46, should be inserted at intervals to bond the coping securely to the wall. Gable copings do not necessarily have to be pitched on top, but they should project on both sides of the wall and should have a drip at each edge so as to shed rain water. STONE STEPS 60. In laying stone steps, it is important to see that they are firmly supported at each end, but left free in the middle. If the stones forming the steps have a bearing along Fig. 47 their entire length, they might, after a slight settlement in the foundations, rock from side to side when stepped upon, or they might crack. In order to strengthen extra long steps, however, it is sometimes necessary to insert a middle bearing; great care must then be taken to have the middle and two end supports exactly on a line. Each step should overlap the one below at least \\ inches, and should have an outward pitch of about -§- inch. Steps having a nosing, as shown at a, Fig. 47, make a good appearance, but they are more expensive than the ordinary steps. 42 ELEMENTS OF STONE MASONRY §32 A hard stone, such as granite or bluestone, should be used for steps; but for private residences, where the wear is not great, limestone or a fairly hard sandstone may be employed. 61. Stone stairs are sometimes made w T ith only one end supported. This end is built solidly into the wall, and each step is carried on the next lower one, as illustrated in Fig. 48. As shown at a, the landing is rabbeted into the tread of the top step. The manner in which each step is cut and supported by the lower one is shown at b. To be safe, the bearing dimensions should not be less than are indicated in the illus¬ tration. The bottom step should be firmly held in place by 1 Fig. 48 dowels set into the floor, as shown at c, as this step must sustain the thrust of the whole flight.- The stone blocks forming the steps are usually cut in the triangular cross- section shown, which method of cutting gives a good appear¬ ance to the soffit, or ramp, of the stairs. 62. Iron staircases are extensively used in fireproof construction. In such cases, the treads, and sometimes the risers, consist of marble slabs, while slate, which is cheaper, is also used. Staircase railings for stairways having stone or iron steps are often elaborately finished. They are generally made of iron, which is doweled into the ends of the steps. § 32 ELEMENTS OF STONE MASONRY 43 FOOTINGS PURPOSE OF FOOTINGS 63 . If a man stands on soft mud, marshy ground, or quicksand, he sinks to a greater or less depth, proportional to his weight. If, however, he stands on a plank or a wooden platform, or on a post or posts driven through the mud or marsh to firmer ground, his weight is distributed over a larger area in the first case and carried down to a better foundation in the second. The same thing is true of the footings of buildings. By spreading the load, or weight of the structure, over a larger area or bearing surface, the weight of the building is more evenly distributed, and the likelihood of a settlement, due to compression of the ground, is greatly diminished. For this reason, the higher and heavier the building is to be, the wider and deeper the supports or footings for the founda¬ tion must be; and if extremely soft or yielding ground is encountered, piling should be resorted to in order to carry the weight of the building to a more solid base. 64 . Footings may be of iron, timber, or large, flat build¬ ing stones-laid directly on the ground or on a bed of concrete, or they may be of concrete alone or with reinforcement, or of concrete and stepped-up brickwork. Where piling is used, heavy capping timbers are often placed on the heads of the piles, with either stone or concrete footings resting on them; or large footing stones may be laid directly on the piles. TIMBER FOOTINGS 65 . Timber is often used for footing courses where a large bearing surface is necessary and can be obtained, pro¬ vided, always, that the timber can be kept from rotting. In some cases, the timber is charred on the outside; and, again, it is coated with asphalt. If the ground is continually wet, there is little to fear, as timber will not decay when kept con- 44 ELEMENTS OF STONE MASONRY §32 stantly saturated with water; but when alternately wet and dry, unprepared timber cannot be depended on. A good method of placing planks under walls for foot¬ ings is to use 3" X 12" plank cut in short lengths and laid crosswise in the trench. A layer of plank of the same size is then laid lengthwise, followed by a third layer placed transversely. In Fig. 49, the stone footing b rests on the Fig. 49 footing planks a and carries the stone foundation wall c between the sides d of the trench. CONCRETE AND STONE FOOTINGS 66. Fig. 50 shows a 20-inch brick wall b erected on a con¬ crete footing a that is 20 inches thick and 36 inches wide. Figs. 51 and 52 show concrete bases a and stepped-up brick footing courses b. In Fig. 51, each step of brickwork is set back 2 inches for each course, while in Fig. 52, each step is set back 4 inches for each two courses. At c is shown a 20-inch brick foundation wall resting on the stepped-up brick footing. Fig. 53 illustrates a stone footing a, composed of three courses of flat stone, each course being 8 inches thick. The top course projects 6 inches on each side of the 20-inch brick foundation wall b, and the middle and bottom -courses each project 3 inches making the width of the bottom stone 3 feet 8 inches. § 32 ELEMENTS OF STONE MASONRY 45 Fig. 54 shows a stepped-stone footing a similar to that shown in Fig. 53, but supporting a 24-inch stone foundation wmm Fig. 50 Fig. 51 wall b. Each base course advances 3 inches beyond the one above. W&MMM '■lav- 1 Fig. 52 Fig. 53 Fig. 55 shows a footing consisting of a single course of stone a, 8 inches thick and 28 inches wide, carrying the stone wall b, 20 inches thick. 211 — 12 46 ELEMENTS OF STONE MASONRY §32 67. As a rule, concrete, when of sufficient depth and width, and when properly made and laid, makes the best footing course. Concrete for footings should be made of Fig. 54 Fig. 55 1 part of good cement, 3 parts of clean, sharp sand, and 6 parts of sharp, broken stone. In very important work, such as bridge piers and the footings of very tall buildings, chimneys, etc., a mixture consisting of 1 part of cement, 2 parts Fig. 56 Fig - 57 of sand, and 4 parts of broken stone is sometimes used. The New York building laws call for 1 part of cement, 3 parts of sand, and 5 parts of broken stone. ELEMENTS OF STONE MASONRY 47 In localities where stone cannot readily be obtained, broken brick or terra cotta may be used in the same propor¬ tion as stone, but care should always be taken to use good, hard-burned material. - Well-broken foundry slag and scoriae,, clean steam-boiler ashes from anthracite coal, and clean-washed gravel, mixed in the proportions given, also make good concrete. 68. Quicksand, when confined, can be safely built on. Fig. 56 shows a method of confining quicksand by sheet piling and placing concrete between the piling. In this case, the sheet piling show T n at a is placed 4 feet apart. The con¬ crete, shown at b, is 2 feet thick and extends the full width of the piling. The quicksand, through which the sheet piling is driven, is shown at c, and the 20-inch brick foundation wall, at d. 69 . Fig. 57 illustrates a footing composed partly of timber. The footing from which this was taken was placed near the water-line of a marsh in New York state, to carry a factory building 50 ft.X80 ft. and 40 feet high. The soil was a stiff, black muck, and at a depth of about 5 feet, water- soaked sand was found. After the trenches were dug, a bedding of concrete a 12 inches thick was laid. On top of this concrete, 2-inch spruce planks b were placed crosswise, followed by 8"X8" timber c, laid parallel, with the trenches filled in between with concrete. On these planks and concrete were laid the base stones d, and on top of these stones was built a 20-inch foundation wall e. The trenches on each side of the wall were filled in with sand, rammed down, as shown at /. This factory building contains an engine, shafting, boiler, and machinery, and, besides, over one hundred employes are constantly at work, yet no settlement has occurred, though it has been built a number of years. 70. Stone-footing courses should be laid with large flat stones not less than 8 inches thick. If more than one course is laid, the joints should never come over each other, as that 48 ELEMENTS OF STONE MASONRY §32 would defeat the object of bonding, which is to tie together firmly the parts of the wall. All stone footings should lie on their natural, or quarry, beds, and all joints and spaces between the stone must be well filled with mortar. The mortar acts as a bedding between the stones, and unless it is interposed, the uneven pressure of one stone on another might cause a fracture of one and produce settlement. 71. All footing courses, as indeed all masonwork below the ground level, should be laid in cement mortar. The usual proportion of cement and sand for cement mortar is 1 part of cement and 3 parts of sand. The proportions just stated are from the building laws of New York, and have been found suitable for general masonwork. 72. Stepped-up brick footings having concrete and stone bases, as shown in Figs. 51 and 52, are often used. The pyramidal form of stepped-up brickwork carries the load of the superstructure more evenly to the footings and reduces the risk of settlement or fracture. Nothing except good, hard, well-burned bricks should be used, and these should be laid in cement mortar, and should break joints—that is, no two joints should come over each other. SPECIAL FOOTINGS 73. Footings on Rock and Gravel.— In placing foun¬ dation footings on rock, it is sometimes found that some portions of the footings will rest on the rock, and others, owing to the diversified character of the surface, will rest on clay, sand, or gravel. The settlement of the foundation walls—and as a necessary consequence, that of the whole building—will then be uneven, as the walls resting on the rock will not settle, while those resting on the sand, gravel, or clay, by compressing the material on which they are carried, will settle. §32 ELEMENTS OF STONE MASONRY 49 74. Fig. 58 illustrates the method employed to obtain equal settlement. In (a) are shown the rock and gravel before leveling or excavating, the clay or sand being shown at a and the rock at b. It is customary to remove the rock to a certain level, as shown in ( b ). The softer soil a is then removed and leveled off, as at c c, and a bed of concrete about 3 feet thick, as shown at d, is then put down. This concrete is brought to the level of the rock, as at b b, and on this base the brick or stone foundation wall e is built. In erecting footings on solid rock, it is not considered necessary to cut the footing bed level over the entire surface Fig. 58 of the rock, nor even to cut a series of horizontal surfaces resembling steps, as is frequently done in softer soils; but it is necessary to roughen the surface of the rock so as to prevent the footing from slipping on its foundation. After this is done, concrete may be put in to bring the foundation to its proper level. If the structure is to be only three or four stories in height, stone or brick may be used instead of con¬ crete, but a concrete base is usually preferable. 75. Footing on Sloping Ground.— Footing courses built on slopes—especially of clay—are always liable to 50 ELEMENTS OF STONE MASONRY §32 slide. This tendency to slide, however, may be overcome by cutting horizontal steps in the slope, as shown in Fig. 59, where the slope e f is stepped off, as shown at a, in order that Fig. 59 the footings b may have a horizontal bearing. These footings may be either of stone or of concrete, but if the former material is used, great care must be exercised to secure a perfect bond at the stepping places, and the foundations should be laid in as long sections as possible. i 76. Inverted. Arches.— When a wall is composed of isolated piers, it is well to combine all their footings into one, and to step the piers down, as shown in Fig. 60. In this Fig. 60 figure, the concrete footing course is shown at a; the stepped- up foundations of the piers, at 6; and the piers resting on the footings, at c. ELEMENTS OF STONE MASONRY 51 77. If there is not sufficient depth to step the founda¬ tions, use is sometimes made of inverted arclies. Such arches, however, are to be avoided unless the foundation wall is from necessity very shallow, as great care is required to lay them properly, and the slightest settlement in the arches has a disastrous effect on the piers. The end arch of the building must have a pier or other support of sufficient weight or strength to resist the thrust of the arch; otherwise, the weight might throw out the pier, as shown by the dotted lines at a, Fig. 61. 52 ELEMENTS OF STONE MASONRY §32 This difficulty, however, can be overcome by using an iron rod, with iron plates and nuts, as shown in Figs. 62 and 63, thus securing the skewbacks in place. The inverted arches turned between the piers should be at least 12 inches thick, or should extend the full width of the piers. They should also rest on a continuous bed of con¬ crete of proper area, and at least 18 inches in thickness; or, they may rest on two footing courses of large stone, the bottom course being laid as stretchers and the top course as headers. Fig. 63 78. Fig. 62 illustrates two piers, each 3 feet square, con¬ nected by a brick-and-concrete inverted arch. At a is shown the 18 inches of concrete under the 12 inches of brickwork b. At c and c' are shown the stone skewbacks from which the brick arches spring, and at d is shown the 2-inch iron rod that ties the end pier e' to the second pier e , and thus prevents the thrusting out of the end pier. Fig. 63 shows an inverted arch built of stone, 24 inches thick. At a is shown the stone arch maintained in position by the iron tie-rod b , and at c the brick foundation piers are shown on the skewbacks d. ELEMENTS OF STONE MASONRY 53 stem M$0M U* \lvAi vj '.r‘> , ?a.'i4 y/*vyv wr ?#.<*% 79. The best form of inverted arch is the three-centered, or elliptic; next, the pointed; third, the circular; and lastly, the segmental arch. The method of getting the lines for the centering in an elliptic arch is as follows: Divide the space shown on the line from a to b, Fig. 64, into three equal parts, at d, d; then draw three circles with centers c, so that the circumferences of these circles will be tangent at d. From the center of the middle circle draw the perpendicular c ); the point f where it intersects the circle is the center of the arch from g to h. From f draw lines / g and / h of indefinite lengths through points d, d. With a d as the radius, draw arc a g intersecting line f g at g. Then, with f g as the radius, draw the arc g h; and from h, arc h d with b d as the radius. At k is shown the brick arch, which is 12 inches deep, and at l, the concrete under it. This form of arch is used fre¬ quently in the construction of sewers. Fig. 64 54 ELEMENTS OF STONE MASONRY §32 THICKNESS OF WALES 80. Foundation Walls.—A very good rule to fix the thickness of rubble-stone foundation walls is, that they shall be at least 8 inches thicker than the wall next above them, for a depth of 12 feet below grade or curb level; and they should be increased 4 inches in thickness below that point, for every additional 10 feet or less in depth. Thus, if the first-story walls are 12 inches thick, the stone foundation walls would have to be 20 inches thick for 12 feet in depth, and 24 inches thick below that point for 10 feet or less. Rubble-stone foundations walls are seldom made less than 18 inches in thickness. A wall 18 inches thick is not always needed to carry the superimposed weight, but smaller walls are more expensive to build and consequently are seldom constructed. The thickness of foundation walls in all the large cities is controlled by the building laws. Where there are no existing laws, Table I will serve as a guide. TABLE I THICKNESS OF FOUNDATION WALLS Height of Building Dwellings, Hotels, Etc. Warehouses Brick Inches Stone Inches Brick Inches Stone Inches Two stories. 12 to 16 20 16 20 Three stories. 16 20 20 24 Four stories. 20 24 24 28 Five stories. 24 28 24 28 Six stories. 24 28 28 32 81. Stone Walls. —The laws regarding the thickness of stone walls differ in the various cities, and no uniform rules can be given, ^or ashlar work, the New York law states that, “where walls or piers are built of coursed stones, with dressed level beds and vertical joints, the Department of §32 ELEMENTS OF STONE MASONRY 55 Buildings shall have the right to allow such walls or piers to be built of a less thickness than specified for brickwork, but in no case shall said walls or piers be less than three-quarters of the thickness provided for brickwork.” The following regulations apply to the District of Columbia for rubblework: “Walls laid with rubble work shall be one- fourth thicker than required for brick walls, but never less than 18 inches thick; they must be constructed with flat stone, sound and durable, laid on their natural beds, and brought to a level every 3 feet in height. They must be built between two lines, shall have bond stone or headers extending through the thickness of the walls at intervals not exceeding 3 feet, and shall be laid in cement mortar composed of 2 parts of sand and 1 part of cement. No rubble wall shall be located as a party wall unless the written consent of the adjoining owner shall first be filed in the office of the Inspector of Buildings. The restriction as to location of the party wall above mentioned shall not apply to stone foundation walls which support brick walls.” For ashlar facing, the requirements for the District of Columbia are as follows: “Thin ashlar facing shall not be counted in determining the thickness of walls. If stone facing is used with bond courses alternately, not less than 8 inches thick, on the beds, then such facing shall be counted as forming part of the wall, and the total thickness of the wall and facing shall not be required to be more than that herein specified for walls (meaning brick) but never less than 13 inches thick.” The thickness of brick walls will be considered in a later Section. SIDEWALKS 82. Sidewalks may be made of flagstones, concrete, or brick. A flag: is a thin slab of stone, which is generally used in sidewalk work. Concrete sidewalks are usually finished on top with cement and sand. The bricks used for sidewalk work should be hard and of the variety known as paving brick. 56 ELEMENTS OF STONE MASONRY §32 83. Stone Sidewalks. —If stone of a texture that readily splits into flags can be obtained, it will probably make a better and cheaper sidewalk than will concrete. A Fig. 65 flag sidewalk can be taken up and relaid better than one of concrete, is easier to repair, and is also more durable. ‘84. The stone for sidewalks should be 2 or 3 inches thick when used in areas or similar places, and the flags should be cut rectangular. They should be laid on a sand or a cinder bed that is 2 or 3 inches in thickness. The edges of the stones usually rest on a small bed of concrete, or 1-to-l cement mortar is put into the cracks as shown at c, Fig. 65. In this way is obtained a joint that will prevent water from soaking down between the flags and freezing. In countries where there is no frost, this concrete and cement may be omitted, and the sidewalk may simply be laid on the sand bed. 85. Sidewalks located between the curb and the building line are subjected to more traffic than pavements found in areas, etc. and should therefore be built in a more substantial §32 ELEMENTS OF STONE MASONRY 57 manner. The flags used for this class of sidewalks are gener¬ ally 3 or 4 inches thick. It is always best, if possible, to have the stones of the same width as the sidewalk, but for wide sidewalks this is impracticable. When there is danger of frost getting under the sidewalk and thus causing it to heave, the flags should be supported at the ends only, as shown in Fig. 6G. A 12-inch dwarf wall should be built at the curb line, as shown at a, and carried below the frost line. The curbstone b is from 4 to 6 inches thick, and is rabbeted into the dwarf wall. At c is shown the gutter, and d, the stone pavement, which is supported at its center by a dwarf wall e. If the sidewalk is laid in two courses, or if it extends to the building line, it may rest on a break in the foundation wall /, as shown. Under the sidewalk at g is a bed of sand or ashes. 86. Brick Sidewalks. —In constructing brick side¬ walks, good, hard paving bricks, sound and square, should be used. These bricks should be laid flat, herring-bone fashion, on a bed of sand that is from 4 to 6 inches thick. After the bricks are laid and graded, the entire surface should be cov¬ ered with sand, which is swept over the bricks until the joints are thoroughly filled. If extra thickness of wearing surface is desired, the bricks may be set on edge, and cov¬ ered with sand as described. 87. Cement Sidewalks. —The method of laying cement sidewalks is as follows: The ground should be leveled off from 12 to 15 inches below the finished grade of the walk, and should be well settled by ramming, care being taken that the excavation is drained to one side. A foundation consisting of about 8 or 10 inches of coarse gravel, stone chips, sand, or cinders, should then be laid and well tamped or rolled with a heavy roller. An attempt often is made to economize on this kind of foundation by making it only 5 or 6 inches thick. However, foundations of such thick¬ ness generally allow the frost to penetrate to the ground and heave up the pavement in spots. 58 ELEMENTS OF STONE MASONRY § 32 After the foundation has been rolled, the concrete should be prepared in the proportion of 1 part of cement, 3 parts of sand, 5 parts of broken stone, and a sufficient quantity of water to make a stiff mortar. It should be thoroughly mixed and worked while being laid. The top, or finishing, coat should be laid immediately, and only as much concrete should be laid as can be covered with cement on the same day, because if the concrete gets dry on top, the finishing coat will not adhere to it. The top coat should be prepared by mixing 1 part of the best Portland cement with 2 parts of fine sand or 2 parts of clean, sharp, crushed granite or flint rock. A ^-inch space should be left between the curb and the pavement and between the building line and the pavement, to allow for expansion and contraction. This space should be filled with cinders or ashes. The pavement itself should be laid off into blocks 6 feet square or less. These blocks should be separated from one another by sheets of tar paper, which should extend all the way through the concrete. It is very essential that grooves be made with a trowel in the top coat directly over the tar paper, so that if the concrete cracks while drying out, it will be sure to part in these grooves and not in the body of the pavement. 88 . Hair cracks are often caused by the mortar in the top coat being too rich in cement. If the pavement is trow¬ eled too much, it has a tendency to make the cement float to the top; this is as liable to cause hair cracks as the use of too much cement. If the top coat is put on too wet, it has the same effect. 89. In many cities, the law requires that concrete side¬ walks be finished with a rough surface. Such a surface is not so slippery in winter as a smooth finish; it also possesses the additional advantages that it is easier to construct and does not show any hair cracks. In laying such a surface, the top coat is leveled with a straightedge running on battens, one set on each side of the walk. The battens are arranged so that the part of the walk at the curb will be lower than the §32 ELEMENTS OF STONE MASONRY 59 part at the building wall. (This pitch is controlled by city ordinances, and is usually 4 inches in 10 feet for all sidewalks.) The sidewalk i& then left until it has almost set, before it is troweled. It should be troweled as little as possible, and with a wooden trowel instead of one made of steel. After troweling, it should be covered with straw and kept moist for at least a week. The less the sidewalk is smoothed with the straightedge or trowel, and the more it is rammed instead, the better it will be. Fig. 67 shows a section of a concrete sidewalk, the ashes or spalls being shown at a; the first coat of concrete, at b\ the finishing coat, at c\ the street paving, at d \ and the joints with tar paper in them, at e. STRUCTURE OF BRICK MASONRY WALLS METHODS OF LAYING BRICK DEFINITIONS 1. Bonding. —By the bonding of brickwork is meant the process of laying brick across one another so that one brick will rest on parts of two or three bricks below it. When built in this manner, it is difficult for a wall to fail by simply parting at the joints without breaking the brick. In bricklaying, all corners and joints should be carefully plumbed, the courses of brickwork kept perfectly horizontal— which necessitates uniform mortar joints—and the wall surfaces, both exterior and interior, kept in perfect aline- ment. All these conditions may have been complied with, and yet the work may be imperfect; the merit of the brick¬ work must be judged by the thoroughness of the bond observed in every portion of the wall, both lengthwise and crosswise. This bond must be maintained by having every course perfectly horizontal, both longitudinally and trans¬ versely, as well as perfectly plumb. Aside from the quality and character of the material, the bonding of a wall con¬ tributes most to its strength. A brick is designated by different terms, according to its position in the wall. When placed lengthwise on the face of the wall, as at a, Fig. 1, the brick is termed a stretcher; COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS' HALL. LONDON § 33 211—13 i 2 ELEMENTS OF BRICK MASONRY §33 when placed crosswise with one end only exposed to view, as at b, it is called a header. A course means the vertical thickness of a brick and a mortar joint. 2. Keeping the Perpends.— To obtain the best results in bonding throughout the mass of the wall, strict attention must be given to the location of every joint in the brickwork. On the faces of the wall, the vertical joints in each course throughout the height should be kept perpen¬ dicular, or directly over those in the second course below. This is called keeping the perpends. The joints across the top of the wall should also be kept in line, so that Fig. 1 if the perpends are observed on one face of the wall, the other face will also work up correctly. Even when the wall is exposed on only one face, the importance of having the joints on top of the wall kept in line is just as essential; otherwise, its effective longitudinal bond will soon be lost, since at best the heading bond furnishes a lap of only 2 inches. 3. Necessity of Preserving Bonding.— The impor¬ tance of having the bond in brickwork preserved in the whole wall can be understood by referring to Fig. 1, which, as already inferred, shows a section of a wall consisting of §33 3 ELEMENTS OF BRICK MASONRY alternate courses of stretchers and headers. By placing the brick as shown, no longitudinal bond exists, and the wall is simply a series of contiguous piers that join one another at the vertical lines c d, and have no bond or union between them other than that obtained by the adhesion of the mortar. This is because none of the brick in one pier overlaps any brick in the adjoining piers. This method manifestly lacks strength and stability. In order, therefore, to overcome this constructive difficulty and to secure a continuous bond in the length of the wall, recourse is had to a different arrange¬ ment of the bricks and also to the use of blocks that vary in size from the ordinary brick. Fig. 2 4. Closers and Bats. —The brick of different sizes used for bonding are called closers, the term meaning that they perfectly finish, or close, the length of the courses that have been adjusted to obtain the bond. The vertical joint, which is shown at c d, Fig. 1, is avoided, and no two adjacent courses have joints that are immediately over each other. The closers are made by cutting the brick to such dimensions as the situation requires, the operation being performed by striking a brick a sharp blow with the edge of a steel trowel. The cut brick are called bats, and are designated according to the proportion that each bat bears to the whole brick. Pressed and enameled brick are often cut with a cold chisel so as to get a more even fracture. 4 ELEMENTS OF BRICK MASONRY §33 The different bats, or closers, used in brickwork are shown in Fig. 2, (a) representing a whole brick of the usual size. If a brick is cut longitudinally, as at (6), on the line a b, each half is called a queen closer; but as it is difficult to cut the full length in this manner, the usual mode is first to cut the brick on the line c d e, and then cut each half on the # line a b. If the brick is cut as at (c), it is called a king closer, and is a form well adapted for closers at door and window jambs. If one-fourth of the whole length of the brick is cut off, as at (d), the remainder is called a three- quarter bat; and, in a like manner, the portion remaining at ( e ) is called a half bat; and at (/), a quarter bat. BOND IN BRICKWORK 5. In connection with the use of closers, whereby the lap is properly secured, there are several methods of placing the brick in the wall, each method having its own name to indicate the kind of bond used. 6. Heading Bond.— When all the courses present the end of the brick in the face of the wall, the wall is then Fig. 3 composed entirely of headers , and is known as the heading bond. This method of bonding, however, is suitable only for sharp-curved walls, as it possesses little longitudinal bond. §33 ELEMENTS OF BRICK MASONRY 5 7. Stretching Bond.— When all the courses consist of stretchers, the stretching bond is the one employed. The wall formed by this - method should be used only for par¬ titions that are not greater than 4 inches in thickness. If the wall is to be thicker, the method should not be followed, as there would be no transverse bond. 8. English Bond.— In the English bond, the header and stretcher courses are laid alternately, as shown in Fig. 3. Joints are broken in the longitudinal bond courses by the use of quarter-bat closers, as shown at c. The joints can also be broken by the use of three-quarter bats. It will be observed that the heart of the wall consists entirely of heading bond, and that the joints of the heading course, as at a, are well bonded by the headers of the stretching course, as at b. 9. Flemish Bond.— In the method known as Flemish bond, only two-thirds of the number of headers that occur in English bond are exposed, and each course is composed of a header and a stretcher laid alternately. The method of laying the brick in Flemish bond is shown in Fig. 4. The lap in this case is obtained by the use of three-quarter bats both at the external and at the internal angles of the wall, as shown at a on the external and at b on the internal angles. In Flemish bond, the closers occur in the heart of the wall, just as was shown in English bond; these are quarter, half, and three-quarter bats, as shown at c. 6 ELEMENTS OF BRICK MASONRY §33 By referring to the illustration, it will be seen that, owing to the headers and stretchers being placed on the inner side of the wall immediately opposite those on the outer face, both faces will appear exactly alike when thus arranged. The wall is then said to be built in double Flemish bond. 10. Garden, or Running, Bond.— The bond most extensively used in the United States, known as the garden, or running, bond, is shown in Fig. 5. This bond, which enables the bricklayer to build a larger amount of wall in a given time than does either the English or the Flemish bond, is sometimes called American bond. It consists in laying from four to seven courses as stretchers and bond¬ ing with a row of headers at regular intervals. The longi¬ tudinal lap is secured by closers, as shown at c. The heading course in the heart of the wall is shown at a, being placed immediately over the heading course b exposed on the face. The principal defect of the running bond is that the wall, is practically composed of a series of 4-inch layers from 12^ to inches in height that have no transverse bond to the adjoining layers. It fulfils the requirements, however, if every joint throughout the body of the wall is well filled with good mortar and the vertical joints are well rammed with the edge of the trowel. The New York building laws require that every sixth course shall be a header course; that is, that five courses of stretchers must come between two courses ELEMENTS OF BRICK MASONRY 7 §33 of headers. For factory and warehouse purposes, where the walls have to sustain heavy weights, it is better to have every fourth course a header course, thus giving three courses of stretchers between the header courses. The wall is not so liable to split in its thickness, however, as it is to crack longitudinally, as would be shown by a crack up and down the face. In such a case, the garden bond is really stronger than either the English or the Flemish a n-1-r— rz i r i _ rz ZZL L rz 1 1 1 1 b (a) a J L I b (b) a J L nz ~\ 1 I - 1 1 i L rz -l_i.. i _ b (c) Fig. 6 bond. Of course, if the wall cracks exactly vertically the brick will be broken and in any bond the same number of brick will crack. Usually, however, a crack in brickwork follows the mortar joints, as shown in Fig. 6, in which view (a) represents English bond; (6), Flemish bond; and (c), gar¬ den bond. Nine courses of brickwork are considered in each example, and in each case the probable path of the 8 ELEMENTS OF BRICK MASONRY §33 crack is indicated by the line a b. As can be seen from the illustration, the total length of vertical crack in each case is the same. However, the length of the line of fracture, or the contact area, will be found greater in the garden bond than in either the English or the Flemish bond, because the lap of the brick is greater. 11. Bonding; of Face Brick.— When either face or pressed brick are used for the exterior facing of a wall, it detracts from the uniform appearance of the brickwork if the bonding headers appear on the exterior face of the wall. This difficulty can be avoided either by cutting the face brick and the rough brick or by using steel-wire ties to bond the brick together. If no tie or bond is used, the whole 4 inches of brickwork on the face of the wall will have no other connections with the rest of the brick than that given by the adhesion of the mortar, and might be pushed away bodily from the rough brick. 12. In Fig. 7 is shown a 12-inch wall with the face brick bonded to the common brick by what is known as diagonal, or herring-bone, bond. At a is shown the front brick cut at the angles; at b, the bonding brick laid diagonally; at c, the different-shaped bats laid to form the closers of the bond brick; and at d, the inside course of stretchers. It is cus¬ tomary to lay an inside course of headers immediately over the course shown in the figure. ELEMENTS OF BRICK MASONRY 9 §33 The New York building laws require that “where walls are faced with brick in running bond, every sixth course shall be bonded into the backing by cutting the corners of Fig. 8 the face brick and putting in diagonal headers behind, or by splitting the face brick in half and backing the same with a continuous row of headers.” The second method just mentioned is illustrated in Fig. 8. The face brick cut lengthwise are shown at a, and the three- quarter bats bonding in back of the face brick are shown at b. The whole brick c bond on the inside of the wall, and the closer d closes up the angle. The whole face brick on the corner of the wall is shown at e. Fig. 9 13. In Fig. 9 is shown one method of bonding face brick with metal ties. The ties, or bonders, b are made either of steel or of galvanized-iron wire and are twisted at the ELEMENTS OF BRICK MASONRY §33 JO ends, as shown. They are laid in every sixth course of brick and are placed so as to hold together the outside course a and the inside course c. The principal objection to the use of steel or iron bonders is the danger of rust, although by the time their efficiency has been destroyed by the action of rust, the mortar used should have hardened sufficiently to keep the face brick in place. A better method of tying front brick to the common brick in the back of the wall is to use perforated steel ties that are from - 3 - 2 - to | inch thick and have about half the metal punched out. The brick may be brought down to a very close joint, and the clinching spaces make a very firm and satisfactory Fig. 10 binder. Fig. 10 shows the application of these bonding strips. Here the pressed-brick facing is shown at a, the common brick in the back of the wall at b, and the perforated steel ties that bond the pressed brick to the common brick at c. 14. Bonding of Hollow Walls.— While hollow walls are more expensive to build than solid walls, they are sometimes used, particularly for dwellings. They are supe¬ rior to solid walls in that moisture cannot penetrate them; also, since the intervening space acts as an insulating medium, a house built of hollow walls is cooler in summer and warmer in winter than one built of solid walls. §33 ELEMENTS OF BRICK MASONRY 11 In the ideal hollow wall, the air space is uninterrupted, having no braces connecting the inner and outer parts. Of course, in practice, it is necessary to have some bonding Fig. 11 between the two parts, but the style of bonding should be carefully considered. By permitting the passage of moisture through the wall where it is bonded, brick bonding neutral¬ izes some of the benefit derived by making the walls hollow. To provide a continuous air space when a wall is penetrated by openings is practically impossible, though it may be closely approximated. 15. Fig. 11 shows one form of hollow wall with an 8-inch outer wall a, a 2-inch air space b, and a 4-inch inner wall c. Except at the corners, this wall is bonded every sixth course in height and every 12 inches in length, as shown at d. The header brick e that join the bond d are three-quarter bats, and the bond brick have a bearing of 2 inches on the front wall. Fig. 12 shows a 10-inch wall that has a 4-inch outer wall a, a 2-inch air space b, and a 4-inch inner wall c. The bond brick are cut at an angle, as shown at d, and where they miter 12 ELEMENTS OF BRICK MASONRY §33 in the front wall, the front brick are also cut, as at e. The 2-inch spaces left in the rear wall c where the bond brick occur are filled with quarter-bat closers, as shown at /. 16 . Probably the best way of bonding the two sides of a hollow wall is to use metal ties, as they will not carry any moisture across, especially when there is a dip or sudden bend in their length. This method of bonding a double wall is illustrated in Fig. 13. At a is shown the outer 4-inch wall; at b, the air space; at c, the inner 4-inch wall; and at d, the metal ties. These ties are called Morse patent ties. At ( e ), (/), and (g) are shown other forms of ties. The form shown at (g) is probably the best, provided the walls Fig. 13 are more than one brick thick so that the turned-up ends of the tie will not show. When any of the metal ties d, ( e ), or (/) are used, they should be spaced every 24 inches in every fourth course. Since the form of tie shown at (g) is stronger, it need be used only in every eighth course. All metal ties should be dipped in hot pitch to prevent them from rusting. 17. Bonding of Walls at Angles. — In building brick walls, it is necessary that the angles in the walls be properly bonded. When the two walls forming the angle are carried up at the same time, the bonding at the corners is easily effected; if, however, one wall is built a few weeks §33 ELEMENTS OF BRICK MASONRY 13 ahead of the other, owing to a delay in getting materials required for it, particular care must be taken that the two parts will bond together properly. In such cases, the wall first built is generally left toothed, as shown in Fig. 14. In order to unite the two walls more firmly, anchors made of f" X 2" wrought iron, with one end turned up 2 inches, as at a, and the other bent around a f-inch bar, should be built into the side wall about every 4 feet in height, as shown at b. These an¬ chors should be long enough to extend at least 12 inches, or the depth of one and one-half brick laid the long way, into the side wall, and the center of the -f-inch bar should be about 8 inches from the back of the front wall. 18 . In regard to the bonding of angles, the New York building laws are as follows: In no case shall any wall or walls of any building be carried up more than two stories in advance of any other wall, except by permission of the Com¬ missioner of Buildings having jurisdiction, but this prohibition shall not include the enclosure walls for skeleton buildings. The front, rear, side, and party walls shall be properly bonded together, or an¬ chored to each other every Fig. 14 six (6) feet in their height by wrought-iron tie-anchors, not less than one and one-half (if) inches by three-eighths (§) of an inch in size, and not less than twenty-four (24) inches in length. The side anchors shall be built into the side or party walls not less than sixteen (16) inches, and into the front and rear walls, so as to secure the front and rear walls to the side, or party, walls when not built and bonded together. 14 ELEMENTS OF BRICK MASONRY §33 DIFFICULTIES IN BRICKLAYING 19 . Joining New Walls to Old Walls. —In join¬ ing a new wall to one that has been built for some time, especially if the walls come at right angles, the new work should not be toothed, or bonded, into the old work unless the new work is laid up in cement mortar. All masonwork built with lime mortar will settle somewhat, owing to a slight compresion of the mortar joints, and this settlement is liable to cause a crack where old and new work is bonded together. In place of toothing, if lime mortar is to be used, a groove usually the width of a brick should be cut perpendicularly in the old wall, so as to make what is' known as a slip joint. Fig. 15 Fig. 16 The method of bonding just described is shown in Fig. 15. At a is shown the groove, or chase, cut where the new wall is to enter in the old wall, while at c is shown the new wall and d, the old wall. In cheap construction, where new work is bonded into old, the method most commonly used is to nail a piece of 2" X 4" timber against the wall, as in Fig. 16, where a shows the 2" X 4" timber spiked to the old wall b and entering the center of the new wall c. 20. Laying Brick in Severe Weather.— When brick are dry, they absorb moisture from the mortar in which they are laid and thus prevent the mortar from attaining its customary strength. It is therefore very important, espe¬ cially in warm weather, that all brick be wetted with water before they are laid in the wall. §33 ELEMENTS OF BRICK MASONRY 15 As explained in Sands and Cements , neither lime nor cement mortar will set well in freezing weather. In New York City, there is a law against laying brick during freezing temperatures, but the law is not enforced; consequently, in laying brick, it seems to make very little difference to the contractor or architect whether it is summer or winter—the work goes on just the same. On account of this disregard for the laws, many buildings erected during freezing weather either collapse or become weakened as soon as the weather gets warm. On the first warm spring day in 1905, in New York City, six large buildings of the “flat-house” type under construction fell in for no other reason than that just stated. These buildings would probably never have collapsed had proper precautions been taken. THICKNESS OF BRICK WALES i 21. Size of Brick and Mortar Joints. —There is no standard size of brick in America. The dimensions of brick vary with the locality and also with the maker. In the New England States, the average size of common brick is about 7f in. X 3| in. X 2J in.; and New York and New Jersey brick will run about 8 in. X 4 in. X 2^ in. Walls laid in these brick will run normally 8, 12, 16, and 20 inches in thickness for 1, 1^, 2, and 2\ brick. Most of the western common brick measure 8? in. X 4J in. X 2^ in., and the thickness of the walls measures about 9, 13, 18, and 22 inches for 1, 1^, 2, and 2\ brick. On the seacoast of some of the Southern States, the brick are made with a large percentage of sand, and will average 9 in. X 4J in. X 3 in. Most manufacturers of pressed brick use molds of the same size; hence, pressed brick are more uniform in size. They are generally 8f in. X 4J in. X 2f in. Pressed brick are also made 1? inches thick. A form frequently used and known as Roman, or Pompeian, brick is 12 in. X 4 in. X 1 \ in. in size. In order that a good bond may be secured, brick should be made of such size that two headers and a joint will equal one stretcher. 16 ELEMENTS OF BRICK MASONRY §33 In ordinary brickwork, the joints should not average more than i inch in thickness. In pressed brickwork, however, the joints may be made smaller, probably J to A inch, because the brick are smoother and have no irregular projections. 22. Laws Governing Thickness of Walls. —In order that the design and construction of walls for buildings of various dimensions used for dwellings, warehouses, and other purposes may be carried out intelligently, a knowledge of the thickness of walls required is very important. With this object in mind, an extract is given from the building laws of New York City that relate to the thickness of brick walls in proportion to their height. The laws of other cities do not differ very materially from the New York laws, and these may therefore be safely taken as a standard. WALLS FOR DWELLING HOUSES The expression “walls for dwelling houses” shall be taken to mean and include in this class walls for the following buildings: Dwellings, asylums, apartment houses, convents, club houses, dormitories, hos¬ pitals, hotels, lodging houses, tenements, parish buildings, schools, laboratories, studios. 1. The walls above the basement of dwelling houses not over three stories and basement in height, nor more than 40 feet in height, and not over 20 feet in width, and not over 55 feet in depth, shall have side and party walls not less than 8 inches thick [see Fig. 17 (a)], and front and rear walls not less than 12 inches thick. 2. All walls of dwellings exceeding 20 feet in width and not exceeding 40 feet in height, shall be not less than 12 inches thick [see Fig. 17 (6)]. 3. All walls of dwellings 26 feet or less in width between bearing walls which are hereafter erected or which may be altered to be used for dwellings and being over 40 feet in height and not over 50 feet in height, shall be not less than 12 inches thick above the foundation walls [see Fig. 17 (c)]. No wall shall be built having a 12-inch-thick portion measuring vertically more than 50 feet. 4. If over 50 feet in height and not over 60 feet in height, the walls shall be not less than 16 inches thick in the story next above the foun¬ dation walls and from thence not less than 12 inches to the top [see Fig. i7 m o-osr // 0-09 - -> 'O \ § T „0- os — - > r 1 1 1 ^ A 5! L-r n n ±r - W * n U , 07 * T v M'm'w y..^gygT&^siMMi •c 5* — ,, 0 -ot — , t r ,, /.'//'/AS'. ** °0 ' i \) -s 211-14 Fig. 17 <- .0-00! -* L _ n n J _ ^ // w / Jf ~“ [— ^ "0-0t — * HI 2 "8 c Vw /- frl ^ * <0 <\i N- <\i -* -* f • t Z/'ZZ o' $ <\j -- *0-0 9 - „ n -» t , uv ^ * 50 a r«; $ .o-.ot & 18 § 33 ELEMENTS OF BRICK MASONRY 19 5. If over 60 feet in height, and not over 75 feet in height, the walls shall be not less than 16 inches thick above the foundation walls to the height of 25 feet, or to the nearest tier of beams to that height, and from thence not less than 12 inches thick to the top [see Fig. 17 (*?)]. 6. If over 75 feet in height, and not over 100 feet in height, the walls shall be not less than 20 inches thick above the foundation walls to the height of 40 feet or to the nearest tier of beams to that height, thence not less than 16 inches thick to the height of 75 feet, or to the nearest tier of beams to that height, and thence not less than 12 inches thick to the top [see Fig. 17 (/)]. 7. If over 100 feet in height, and not over 125 feet in height, the walls shall be not less than 24 inches thick above the foundation walls to the height of 40 feet, or to the nearest tier of beams to that height; thence not less than 20 inches thick to the height of 75 feet, or to the nearest tier of beams to that height; thence not less than 16 inches thick to the height of 110 feet, or to the nearest tier of beams to that height; and thence not less than 12 inches thick to the top [see Fig. 17 (*)]. 8. If over 125 feet in height and not over 150 feet in height, the walls shall be not less than 28 inches thick above the foundation walls to the height of 30 feet, or to the nearest tier of beams to that height; thence not less than 24 inches thick to the height of 65 feet, or to the nearest tier of beams to that height; thence not less than 20 inches thick to the height of 100 feet, or to the nearest tier of beams to that height; thence not less than 16 inches thick to the height of 135 feet, or to the nearest tier of beams to that height; and thence not less than 12 inches thick to the top [see Fig. 17 (h)]. 9. If over 150 feet in height, each additional 30 feet in height or part thereof, next above the foundation walls, shall be increased 4 inches in thickness, the upper 150 feet of wall remaining the same as specified for a wall of that height. WALLS FOR WAREHOUSES The expression “walls for warehouses” shall be taken to mean and include in this class walls for the following buildings: Warehouses, stores, factories, mills, printing houses, pumping stations, refrigerating houses, slaughter houses, wheelwright shops, cooperage shops, brew¬ eries, light and power houses, sugar refineries, office buildings, stables, markets, railroad buildings, jails, police stations, court houses, observ¬ atories, foundries, machine shops, public assembly buildings, armories, churches, theaters, libraries, museums. 1. The walls for all warehouses, 25 feet or less in width between walls or bearings, shall be not less than 12 inches thick to the height of 40 feet above the foundation walls [see Fig. 18 (a)]. 20 ELEMENTvS OF BRICK MASONRY §33 2. If over 40 feet in height, and not over 60 feet in height, the walls shall be not less than 16 inches thick above the foundation walls to the height of 40 feet, or to the nearest tier of beams to that height, and thence not less than 12. inches thick to the top [see Fig. 18 (6)]. 3. If over 60 feet in height, and not over 75 feet in height, the walls shall be not less than 20 inches thick above the foundation walls to the height of 25 feet, or to the nearest tier of beams to that height, and thence not less than 16 inches thick to the top [see Fig. 18 (c)]. 4. If over 75 feet in height, and not over 100 feet in height, the walls shall be not less than 24 inches thick above the foundation walls to the height of 40 feet, or to the nearest tier of beams to that height; thence not less than 20 inches thick to the height of 75 feet, or to the nearest tier of beams to that height; and thence not less than 16 inches thick to the top [see Fig. 18 (d)]. 5. If over 100 feet in height, and not over 125 feet in height, the walls shall be not less than 28 inches thick above the foundation walls to the height of 40 feet, or to the nearest tier of beams to that height; thence not less than 24 inches thick to the height of 75 feet, or to the nearest tier of beams to that height; thence not less than 20 inches thick to the height of 110 feet, or to the nearest tier of beams to that height; and thence not less than 16 inches thick to the top [see Fig. 18 (e)]. 6. If over 125 feet in height, and not over 150 feet, the walls shall be not less than 32 inches thick above the foundation walls to the height of 30 feet, or to the nearest tier of beams to that height; thence not less than 28 inches thick to the height of 65 feet, or to the nearest tier of beams to that height; thence not less than 24 inches thick to the height of 100 feet, or to the nearest tier of beams to that height; thence not less than 20 inches thick to the height of 135 feet or to the nearest tier of beams to that height; and thence not less than 16 inches to the top [see Fig. 18 (/)]. 7. If over 150 feet in height, each additional 25 feet in height, or part thereof next above the foundation walls shall be increased 4 inches in thickness, the upper 150 feet of wall remaining the same as specified for a wall of that height. 23. Thickness of Walls in Different Cities. Although alike in the main, the building laws of the several cities differ from one another in many points, particularly in the methods of measuring the thickness of walls. For this reason, Tables I, II, and III have been compiled, the first two giving the thickness of warehouse walls and the third the thickness of walls for residences. Some cities, as, for instance, New York and Boston, give the height of walls §33 ELEMENTS OF BRICK MASONRY 21 in feet; others, notably New Orleans and Denver, measure the heights in stories; while still others, as Washington and Cleveland, specify that a certain thickness of wall shall extend to a certain story, but state that this story must not be more than a given number of feet from the foundation. Therefore, in preparing the tables, several heights of stories were selected, so that all the laws could be made to apply to the same case. In every instance where the law required that the walls be thicker as the building is made wider, the minimum width was used; as in New York, 25-foot span for warehouses, and in Philadelphia, 26-foot span. It will be noticed in Tables I and II that dimensions for very high buildings are not given for some cities. This is because the height of buildings in many cases is limited in those localities. In Denver, a building cannot be over 125 feet in height, and in Washington, the government has limited the height to 130 feet. The thickness of the walls in nearly all the cities is given in inches. In Cleveland, however, the law gives the thick¬ ness of the wall in the number of brick, but the size of the brick and the thickness of the mortar joints are also speci¬ fied, so that the figures can easily be reduced to inches. In Washington, the thickness of walls of residences is specified, and a note states that 4^ inches must be added to this thick¬ ness for warehouse walls. In Tables I and II, however, 5 inches instead of 4^ inches is added, so as to eliminate all fractions. It will be noted that some laws call a wall that is evidently a brick and one-half thick 12 inches, while others call it 13 inches. This is due to different customs in different cities and the different sizes of brick used. As the laws gov¬ erning the thickness of foundations differ greatly according to the locality, they cannot be given here; however, they may be found in the ordinances of the city or town in which the build¬ ing is to be erected and are usually from 4 to 8 inches thicker than the wall directly above them. In some of the cities, as, for instance, Philadelphia, Boston, and New Orleans, walls of the same thickness are used for both warehouses and residences Tables I, II, and III apply to brick walls only. TABILE I THICKNESS OF BRICK WALES FOR WAREHOUSES UP TO SEVEN STORIES IN HEIGHT Name of City Number of Stories and Height of Building Story and Height of Each First 19 ' Second 13 ' 4" Third 13 ' 4" Fourth 13' 4" Fifth 13 ' 4" Sixth 13' 4" Seventh i3' 4" Thickness of Brick Wall, in Inches Washington ... 14 14 St. Louis. 18 13 Denver. 13 13 Memphis. 13 13 Boston. 16 12 New York. Two stories 12 12 Philadelphia.. . 32 feet 4 inches l 8 13 Chicago. 12 12 Minneapolis .. . 12 12 New Orleans... 13 1 3 Cleveland. 13 13 San Francisco . 17 13 Washington ... 2 3 18 18 St. Louis. 18 18 13 Denver. 17 1 7 13 Memphis. i7 1 7 13 Boston. 20 16 16 New York. Three stories 16 16 12 Philadelphia. . . 45 feet 8 inches 22 13 13 Chicago. 16 12 12 Minneapolis . . . 16 12 12 New Orleans... 13 r 3 13 Cleveland. 17 13 13 San Francisco . 17 17 13 Washington ... 2 3 18 18 18 St. Louis. 22 18 18 13 Denver. 21 17 17 13 Memphis. 21 17 17 13 Boston. 20 16 16 16 New York. Four stories 16 16 16 12 Philadelphia.. . 59 feet 22 18 13 13 Chicago. 20 16 16 12 Minneapolis .. . 16 16 12 12 New Orleans... 18 18 13 13 Cleveland. 17 r 7 13 J 3 San Francisco . 17 17 17 13 22 TABLE I—( Continued) Name of City • Number of Stories and Height of Building Story and Height of Each First 19 ' Second 13' 4" Third 13 ' 4" Fourth 13 ' 4" Fifth 13 ' 4" Sixth 13 ' 4" Seventh 13 ' 4" Thickness of Brick Wall, in Inches Washington ... 27 23 23 23 18 St. Louis. 22 22 18 18 13 Denver. 21 21 17 17 13 Memphis. 21 21 17 x 7 17 Boston. 20 20 20 20 16 New York. Five stories 20 l 6 16 16 16 Philadelphia.. . 72 feet 4 inches 26 l 8 18 13 13 Ch icago. 20 20 16 16 16 Minneapolis .. . 20 l 6 16 12 12 New Orleans... l 8 l 8 18 13 13 Cleveland. 17 17 17 1 t • it San Francisco . 21 17 17 17 13 » Washington ... 3 1 27 23 23 23 18 St. Louis. 26 22 22 18 18 13 Denver.. 26 21 21 17 17 13 Memphis. 25 21 21 17 17 17 Boston.j . . 24 20 20 20 20 16 New York. Six stories 24 24 24 20 20 16 Philadelphia. . . 85 feet 8 inches 26 22 l 8 l 8 13 13 Chicago....... 20 20 20 l 6 16 16 Minneapolis .. . 20 20 l 6 l 6 16 12 New Orleans... 22 18 l 8 l 8 13 13 Cleveland. 22 17 17 17 13 13 San Francisco . 21 21 17 17 17 13 Washington ... 3 1 27 27 23 23 23 18 St. Louis. 26 26 22 22 18 l 8 x 3 Denver. , . . 26 21 21 21 17 17 17 Memphis. . . , . . 25 21 21 21 17 17 i7 Boston. 24 20 20 20 20 20 16 Seven stories New York. 24 24 24 20 20 l 6 16 Philadelphia.. . yy ICCi 3° 22 22 l 8 18 13 x 3 Chicago....... 20 20 20 20 16 l 6 16 Minneapolis .. . ' 20 20 20 l 6 16 l 6 12 New Orleans... 22 22 l 8 l 8 18 13 *3 Cleveland. 22 22 17 17 17 x 3 13 23 H W o W w W OD W i—i as o H ® W k w £ o H H w o M w H O M K £3 Eh s » PQ H Ph p M O W w K <1 * ti O PH GO Hi hP <1 £ M Q M P5 W Eh O co CO W fc w Q M B H X u a m <« o +> X ‘53 ffi T) C a! Vh o +-> CO J3 V fe n £ h Ch %$- ■ a; s to £%■ C » Z M x'^ .“"to W « X +-> % C ^ 4 ) » > to Q) H co •K*io CO H X +-> «-W S U-. ^ O fo fe M *3* u ^ rC *V) H H *O v O* aj'to CO M C/D « • fa £ C/D a/ rC O G aJ £ .y '£ m u-< O t/D C/D 00 o o to NO NO to to Oi M M \ M CM CM M H W M W 00 o o 00 NO NO 00 CM M M M CM CM W M M W M CM M M o 00 o NO 00 (N CM CM CM CM CM HH CM W M M M CM w M o Tf- CM o o 00 ro o it 0) > a +, « ^ w x H o >* £ CD aS • H XI a »—H u-i M C/3 Ov 0) be C/3 • iH M X t- n aj • H ^G a C/3 • lH *o a TJ G C/3 • rH C/3 • «-H X V-c o aj • rt X a Chicago . in • H *o a *o G G Jq in 0j £ 3 o 4-1 4-> C0 x a 6 a> s Boston £ 'd • H X h< Chicagc aj a> G G • H s aj *—* * £ a) £ QJ 'V • »—< X ex aj a> G G • rH s aj U > 0) O 25 TABLE II —( Continued) ■M 5 t ^ rt PO VO vO ro vO PO * « M M M M M M W • H X! 4-> c* 0) ^ PO NO NO PO VO PO 00 o o PO vO PO > v HH w M M M M M M CM CM M M rO o •c CM CM CM CM CM CM M CM CM CM CM CM CM CM Q> H CO 4-> ^ PQ VM O vO M o Tt CM o CM vO m 00 vO Tf CM >» u in CM CM CM CM CM CM CM CM CM CM CM CM CM CM o -*-> CO M t/i PO CM CM CM PO CM CM PO CM po PO PO CM CM H H •a. o v O' CM CM o 00 vO On CM CM 00 M O V. (V) ^ CO M PO CM PO PO PO CM CM PO CM PO PO PO CM PO |2 "a* Tt- On CM VO 00 00 M On VO VO 00 00 M e* M PO CM 00)00 00 CM PO PO CM PO PO PO CM PO t/5 fcfl o M o c ■Wx s' M * 4-J •*-» O'SS CO a o a> w 00 > (U •g-oW G c > o 0) VM o ^ > <3 03 2: W CM in l to H vo W M o a3 o3 • H • *-« 1 * O in in X u ja a H3 in m X Oh • • *d 6 rt £ St. Loui Memphi; Boston. O >H £ 0) £ 13 T3 ^3 • H X &H Chicago G aS i —< < o 13 T3 • H Oh Chicago. G 13 > ve the mixer h. The materials are delivered to the plant by dump wagons e , which run on channel-iron tracks, and are dumped into the hoppers already mentioned. The cement is conveyed to the mixer by an ordinary dumping-bucket hoist, as shown at i. After the materials pass through the mixer, they fall into the hopper /, from which the mixed concrete may be conveyed to the point of deposit by means of carts or chutes. 49. Another type of concrete handling and mixing plant that was used successfully in the construction of a thirty-span viaduct is illustrated in Fig. 33. As shown at i, this plant has the usual tower construction with the automatic dumping bucket, but the device for conveying the ingredients to the mixer from the hopper b is different from those already described The device used here is known as a skip, and consists of a small open-front car that is drawn up the incline by means of a rope e running to the winding drum /. On the incline are two tracks, one a narrow gauge and the other a wide gauge, built on the same center line. The two rear wheels of the car run on the broad-gauge rails, while the front wheels run on the narrow-gauge rails, similar to the device described in Art. 24. In assuming the dumping position shown at a, the car runs forwards with its front wheels on the narrow-gauge rails, which are bent down to the horizontal position shown at d. The hind wheels, however, continue on the wide gauge, but are stopped by the ends of the track, which are bent upwards. After the car is emptied, the clutch on the winding drum is released and the car is pulled back to its position under the hopper, as at g, by means of the counter¬ weight h. ww CC cc 6 (Z 46 §34 CONCRETE WORK 47 TOOLS USED IN PLACING CONCRETE 50. Tamping Tools. —The concrete most frequently used in reinforced-concrete construction is a wet mixture. For Fig. 34 tamping wet mixtures, the slice bar, or spade, shown in Fig. 34 is generally used. This bar consists of a plate of sheet steel riveted to a round-iron bar handle. With a bar of this character, the concrete can be tamped so as to remove all the air, or voids, from it. By flat spading along the sides of the forms, that is, by pounding on top along the forms with the back of the spade, the broken stone can be jarred away from the form boards and a smooth finish of sand and cement produced. 51. In some instances, a slice bar with perforations in the blade is employed for tamping. When flat spading with a perfor¬ ated slice bar, the liquid cement or mortar is allowed to run through the holes and pass down along the sides of the forms. Other types of rammers, or tamping bars, are shown in Figs. 35 and 3(3. The one shown in Fig. 35 is used for natural cement mixtures, and is suitable for tamping the concrete in small places. The one shown in Fig. 36 is commonly used for tamping such work as con¬ crete basement or cement floors, city pave¬ ments, and other flat surfaces. 52. Concrete Rollers. — Cast-iron or Fig. 35 s heet-steel hand rollers are frequently em- FlG> 36 ployed in the construction of concrete floors or pavements. By some’ engineers rolling is considered to be better and 48 FIELD OPERATIONS AND §34 cheaper than tamping. However, a roller is not always advan¬ tageous to use on reinforced concrete floors, for frequently the tamping is depended on to bring the reinforcing bars or rods up from the centering. By tamping, .the jar forces the con¬ crete under the steel and thus raises it to its proper position. This method is quite frequently employed for reinforced-con- crete work, and the same results could not be accomplished by the roller. 53. A type of roller particularly suitable for sidewalks and the concrete base of cement pavements or floors is illus¬ trated in Fig. 37. This roller consists of a cylinder of sheet steel fitted with a wrought-iron shaft extended fo receive the handle bars. Such rollers are made 30 inches in diameter and about 36 inches wide, and in three weights. The light Fig. 37 roller weighs about 300 pounds; the medium, 375 pounds; and the heavy, 645 pounds. In using the rollers, the light roller is first run over the concrete; this is frequently followed by the medium roller and then by the heavy one. However, the light roller could be used throughout the operation by hanging on it weights properly arranged to make up the weight for the medium and the heavy roller. MACHINERY FOR BENDING STEED 54. Bar-Twisting Machine. —Reinforced-concrete contractors, architects, or engineers, in putting up a building are seldom called on to twist the square reinforcing bars; how¬ ever, with large operations, the steel is sometimes twisted at the site. For such a purpose a bar-twisting machine, such §34 CONCRETE WORK 49 as that shown in Fig. 38, is sometimes employed. This machine consists of a fast and a loose pulley, as at a, carrying a spur pinion that engages with the gear operating a square chuck, as at b, into which the bar fits. The other end of the bar is held rigid in a stationary vise device. When the machine is started, the steel is readily twisted. With these machines are furnished nine sets of dies, varying from £ to 1J inches, inclusive, the sizes advancing by J inches. Different sets of gears are also furnished, so that the machine can be run at the speed required for the different-sized bars. A machine of this kind requires about 12 horsepower. It would be used only on a very extensive operation, and only then after the con¬ tractor has found that he can twist the steel at less cost than he can buy it already twisted. 55. Tools for Bending Rods. On all large rein- forced-concrete jobs, Fig. 38 it is necessary to bend a great number of the steel reinforcing bars or rods. Especially is this true if reinforced floors are to be constructed and if some of the reinforcing rods or bars are to be used in the form of a truss in order to take care of the negative bending moments in the beams and girders. The smaller rods or bars are easily bent, but }-, -J-, 1-inch, and larger bars are difficult to bend, especially if the bend is to be short. In Fig. 39 is shown a device that may be used conveniently for bending steel rods or bars of the usual size used in rein- 50 FIELD OPERATIONS AND §34 forced-concrete work. It consists of a rigid table, or bench, a, upon which is securely bolted a cast-iron vise arrangement consisting of a bedplate b that has pivoted upon it two cams, or clamping devices, c. These cams are arranged eccentric¬ ally upon a pivot, and are provided with a handle so that they can be turned and thus clamp a straightedge d against the steel bar to be bent. The bar is thus held between the straightedge and the flange on the cast-iron plate. The figure shows the bar in position ready for bending. The bar after bending is indicated by the dotted outline. Fig. 39 56. Numerous other devices employed by the contractor to bend steel reinforcement are improvised affairs that depend for their efficiency on the ingenuity of the superintendent or foreman designing them. If the bar is of considerable size, it is liable to bend in a long, easy bend instead of all at one point as desired. When this occurs, a pipe is slipped over the bar to stiffen it so that it can be bent exactly at the point where it leaves the vise. A piece of pipe is also used to increase the leaverage when a short end of a bar is to be bent. §34 CONCRETE WORK 51 If a number of loops, ties, or stirrups are to be bent, it is best to have the work done at the factory. The machines at the factory will bend a J-inch bar or rod and turn it off in a loop on the end with great facility. This class of rein¬ forcement can therefore be bent cheaper away from the operation than it can on the site. NOTES FOR THE SUPERINTENDENT PRECAUTIONS TO BE OBSERVED CENTERING 57. The various methods of constructing forms and notes regarding them are contained in Form Work. There are, however, a number of precautionary measures regarding both form work and concrete work that the superintendent should be familiar with and that he should bear in mind continually. 58. Construction of Forms. —In the construction of forms, observe that the forms, or centering, are built according to the drawings and details and that the steel is properly placed in these forms, so that the amount of steel required by the plans or schedules is sure to be included in the concrete work when finished. Observe that the supports of the forms are well braced and sufficiently strong to carry the dead load of the wet concrete. Many failures have been caused by weakness of the supports for concrete centering. Observe that the forms do not shake or vibrate, as any motion destroys the proper set of the concrete. The superintendent should also observe that the forms are so placed and so supported from the ground where the uprights rest upon the earth as to prevent warping, twisting, or sagging; also, that forms are entirely clean and that proper openings are made in them for cleaning out the foot of columns. 211—18 52 FIELD OPERATIONS AND §34 59. Filling tlie Forms. —In filling the forms with concrete, it should be observed that the concrete is placed in the proper quantities at one time; that is, that the slab is filled at the same time as the beams, and that if it is necessary to stop off the work, good judgment is exercised regarding the position at which such a stop-off is made, so that the structural strength of the finished concrete will not be destroyed. 60 . Stripping tlie Forms. —In no instance should the centering be removed until it has been conclusively deter¬ mined that the concrete has properly dried and possesses sufficient strength to carry its own weight and any weight that may be placed on it during the course of erection. Extraordinary precautions should be taken where it is known, that freezing weather occurred during the placing of the concrete. Cubes of concrete should be made at the same t time as the floor construction. These should be examined later and tested, if necessary, to determine whether the concrete has the proper strength. Even when the forms have been removed, it is better to leave some supports beneath the soffits of beams and girders, leaving where possible, the bottom form boards in place for another week or two after the side forms have been stripped. WORKING UNDER UNFAVORABLE CONDITIONS 61. Work in Freezing and Wet Weather. —No con¬ crete should be laid in weather under 33° F., and whenever possible reports from the Weather Bureau should be obtained, to find out whether or not a cold wave is expected. If such a drop in temperature is looked for, it is better to suspend work than to run the chances of a severe drop in the temperature just after the concrete has been deposited. Where possible, stoves, or salamanders , are used on the floor below to prevent the freezing of the work above. In wet weather, no concrete should be left exposed at night, but should be covered with salt hay, or straw; or, better still, §34 CONCRETE WORK 53 boards should be placed over it, with a space beneath that may be closed in with canvas on the sides and filled with straw or hay. 02 . Protection of Concrete From Rapid Drying. In warm weather or weather in which the concrete is likely to be deprived of its moisture by rapid evaporation, the concrete should be wet down at least twice a day. This can be done by sprinkling or by covering the concrete with wet sand or straw. 03 . Niglit AVork. —The placing of reinforced-concrete work at night is fraught with considerable danger and should be avoided whenever possible. When such work as this comes under the charge of the superintendent, he must depend on the illumination available and take every pre¬ caution to safeguard against the misplacing of steel in the forms and the danger of fire from the .lights. FINISH OF CONCRETE 64 . Brush Finish. —Concrete surfaces may be finished in various ways. The plastic appearance of the concrete as it comes from the forms has always been objectionable, and this pasty, or plastic, appearance can never be reconciled with good artistic finish or effect. About the best but perhaps the most difficult method of finishing reinforced-concrete surfaces is to remove the forms from the concrete about 12 hours after it has been placed and then brush the surface with either a steel brush or a stiff rattan brush. By this means the cement mortar is removed from around the broken stone and the broken stone embedded in the mortar is exposed. The appearance of the finish depends on the broken stone used. A very excellent finish can be obtained if broken trap rock or other dark stone of irregular form is used in the concrete. This finish is shown in Figs. 40 and 41. The difference between these two illustrations is simply in the size of broken stone used, the stone shown in Fig. 40 being larger than that * Pig. 40 54 oo Fig. 41 56 FIELD OPERATIONS AND §34 in Fig. 41. The variation in the size of the stone employed, as can be seen, changes materially the appearance of the surface. If concrete is allowed to set more than 12 hours, so that it is too hard to brush by the ordinary method, hy¬ drochloric acid and water must be used. The acid softens the mortar so that it can be brushed in the ordinary manner. 65. Hand Work. —Besides being brushed, or washed, concrete may be dressed with either a bush or a patent hammer, in the same manner as stonework. These tools, however, do not work so well on concrete surfaces as they do on stone surfaces, because the concrete is not so uniform in texture. Special forms of tools have therefore been devised for the finishing of concrete work. 66. In Fig. 42 is shown the special form of busli hammer designed to dress concrete. The points on the face of this hammer are larger and farther apart than are the points on the face of a similar hammer adopted for stone finishing. The hammer itself, however, is about the same size as a hammer used on stone. In Fig. 43 is shown an ax used for dressing concrete sur¬ faces. This ax consists of a wooden handle and a cast-steel head, to which are bolted steel blades. As the blades are Fig. 43 removable, sharp blades can be easily substituted for dull ones. The dull blades can be sharpened with either a file or 57 Fig. 44 Fig. 45 58 CONCRETE WORK 59 §34 an emery wheel. A laborer can conveniently dress about 100 square feet of surface a day with this type of ax, so that the cost is from I V to 2 cents per square foot, based on a 10-hour day. The effect of dressing concrete with either the special bush hammer or the special ax is about the same. In either case, it is most pleasing. The finish obtained is shown in Fig. 44. 67 . Finishing; With Pneumatic Hammers. —For finishing large surfaces of concrete buildings and structures, a pneumatic hammer or tool is sometimes used. By this means, a very uniform finish is produced, as shown in Fig. 45. This finish is an excellent one for buildings in which the concrete work has various architectural features, such as cornices, mutules, corbels, etc. A bush hammer is used on the intricate portions of the work, and the panels and other plane portions are dressed with a pneumatic hammer. 68. Sand Blast Finish. —The sand blast is some¬ times employed for finishing concrete surfaces. It removes the plastic, or pasty, effect given to the concrete by the forms and produces a granulated finish, somewhat similar to sand¬ stone, but not so uniform, because the aggregates are likely to be brought out irregularly. Owing to the cost of the equipment for a sand blast and the indifferent effect that is produced, it is not much used. * . INTRODUCTION FIEIjD inspection 1. The hydraulic cement used in construction work is of three kinds, namely, Portland , natural , and puzzolan , or cement. In reinforced-concrete construction, however, and, in fact, in all important structural work, Portland cement is employed almost exclusively on account of both its greater strength and its greater uniformity and reliability. Natural cement is used occasionally in repair work or in damp or wet places where its property of quick setting is advantageous, but in structural work, the quantity thus employed is almost negligible. The greater part of this Section will therefore be devoted to Portland cement, and it should be borne in mind that when the unqualified term cement is used, Portla?id cement alone is to be understood. 2 . Condition and Weight of Cement Packages. In order to determine correctly the structural value of a ship¬ ment of cement, an examination in the field is very necessary. Portland cement is packed either in canvas or paper bags or in wooden barrels, which should weigh not less than 94 and 376 pounds, respectively. A number of packages of cement should be weighed at intervals, and the average weight should never be permitted to fall below the stipulated amount; for, since mortar and concrete are usually propor¬ tioned on the assumption of this weight, the resulting mortar COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS HALL, LONDON g 35 2 TESTS ON CEMENT §35 or concrete will be considerably weaker than intended. Each package should also be plainly marked with the brand and name of the manufacturer; those not branded should be dis¬ carded, and, if possible, a mixture of different brands should be avoided. 3. Condition and Color of Cement in Packages. A possible indication of inferiority is the presence of lumps throughout the bulk of the material. On standing, cement gradually absorbs moisture from the air. At first this mois- ture is present in merely a minute and harmless state, but eventually it combines chemically with the cement; that is, in the same manner as when cement and water are actually mixed together in practice. In the first condition, lumps usually appear, but they are so soft that they may be readily crushed with the fingers, and of course would be entirely broken up when mixed into mortar. When, however, the cement contains lumps that are hard and pebble-like and that can only be crushed with considerable effort, it indicates that chemical action has begun. Cement containing any appreciable amount of these hardened lumps is generally of decidedly inferior quality, and it should never be permitted to enter any important part of a structure. For reasons to be explained later, seasoning for a short length of time is beneficial for cement; but on the other hand, storing too long will tend to weaken it. Cement from 2 to 6 months old is usually the safest and will pro¬ duce the best results. 4. The color of Portland cement, ranging from bluish to yellowish gray, affords no indication of quality except in cases where different shipments or different parts of the same shipment show a variation in color, thus pointing to a lack of uniformity. When this occurs, tests of each grade of the material should be made in order to ascertain whether all of it is good quality or a mixture of good and bad. Complete field inspection thus covers an examination of the condition and weight of the packages, and of the condi¬ tion and color of their contents. TESTS ON CEMENT 3 SAMPLING 5. Procuring tlie Sample. —In securing a sample for testing, the essential point is to get one that will fairly represent the entire shipment whose qualities are to be determined. The common practice is to take a small por¬ tion of material from every tenth barrel, or, what is the same thing, from every fortieth bag. Thus, in a carload ship¬ ment of six hundred bags, fifteen bags should be opened and sampled. When tests are to be made, however, on a ship¬ ment of only a few barrels, more packages than one in ten should be opened; and when the shipment is large, say over one hundred and fifty barrels, it should be subdivided and each portion tested separately. The bags selected should be taken at random and from different layers, and not all from one part of the pile. The cement, moreover, should be taken not only from the top of the packages, but from the center and sides as well. When the cement is contained in barrels, a sampling auger, as shown in Fig. 1, is used to extract the sample, a hole being bored in the staves midway between the heads. (>. Care of Sample. —After the samples of cement have been taken from the packages they are thoroughly mixed in a can or basin, and this mixed sample is used for the various tests. To make a complete series of tests, the sample should contain from 6 to 8 pounds. The cement, after sampling and before test- ing, must be well protected, as exposure to heat, cold, dampness, or any other abnormal condition may seriously affect the results. Undoubtedly, many errors in cement testing are due to careless handling of the samples. 4 TESTS ON CEMENT §35 TESTS OF CEMENT PRELIMINARY CONSIDERATIONS 7. Purpose of Testing.—In order that a mortar or a concrete made with cement shall give good results in actual construction, it must possess two important properties, namely, strength and durability. The resulting - concrete must be sufficiently strong to bear any reasonable load imposed on it, and besides must be able to withstand suc¬ cessfully the forces of age, weathering, chemical action, or any other condition that will tend to destroy its permanency or impair its strength. The primary purpose of cement testing, therefore, is to determine whether any particular shipment of cement possesses sufficient strength and dura¬ bility to admit of its use in construction. 8. Classification of Tests.—A determination of the quality of cement necessitates the employment of several tests, which may be classified as primary tests and secondary tests. The former tests, which include tests for sou?idness and tensile strength , are made to give directly a measure of the essential qualities of strength and durability. Unfor¬ tunately, neither of these tests is capable of being made with precision, chiefly because each experimenter, no matter how careful he may be, handles the material and conducts the experiment in a slightly different manner. Therefore, the secondary tests, which include tests to determine the time of setting, the fineness , the specific gi'avity, and the chem¬ ical analysis , are made to obtain additional information in regard to the character of the material. However, with the possible exception of the test of time of setting, the second¬ ary tests have but little primary importance and indicate by their results only indirectly the properties of the material. §35 TESTS ON CEMENT 5 For example, it has been proved that a finely ground cement is more permanent and develops greater strength than one that is coarsely ground; but, otherwise, the actual size of the particles is immaterial. Other special tests, such as those for compressive and transverse strength , for shear, abrasion, absorption, porosity, etc., are made occasionally for special reasons or for research work, but they do not constitute a part of the ordinary routine of cement testing, and will therefore not be considered. 9. Difficulties of Testing. —The reason why tests of cement, and especially the primary tests, are so difficult and admit of so many possible errors is that they are not made on the material as it is produced, but on specimens first made in the laboratory, and in which the material is radically changed from its original condition. Bars of iron and wood, bricks, and such materials are tested in the form in which they are manufactured and used, but cement is made as a powder, tested mostly as a paste, and used as a mortar or concrete. The specimens for testing, moreover, cannot advantageously be made by mechanical means, so that the different style of handling of the operator, or the personal equation, as it is called, becomes an important factor. Accurate cement testing, therefore, is largely dependent on the knowledge, care, and experience of the operator, for an inexperienced man, no matter how careful and conscien¬ tious he may be, can never be relied on to obtain trustworthy results. PRIMARY TESTS SOUNDNESS 10. Soundness may be defined as the property of cement that tends to withstand any forces that may operate to destroy or disintegrate it. This property of soundness, or, as it is sometimes called, constancy of volume, is the most important requisite of a good cement. Although the original strength of the material may have been sufficient, if it is 6 TESTS ON CEMENT §35 unsound and will eventually disintegrate, it is both worthless and dangerous for purposes of construction. 11. Causes of Unsoundness.—The most common cause of unsoundness in Portland cement is an excess of free or uncombined lime, which crystallizes with great increase of volume, and thus breaks up and destroys the bond of the cement. This excess of lime may be due to incorrect pro¬ portioning or to insufficient grinding of the raw materials, to underburning, or to lack of sufficient storing before use, called seasoning. A certain amount of seasoning is usually necessary, because almost every cement, no matter how well proportioned or burned it may be, will contain a small amount of this excess of lime, which, on standing, will absorb mois¬ ture from the air, slake, and become inert. Thus, it fre¬ quently happens that a cement failing in the tests for soundness will pass these tests easily after the expiration of a few weeks. Excess of magnesia or the alkalies may also cause unsound¬ ness, but the ordinary cement rarely contains a sufficient amount of these ingredients to be harmful. Sulphate of lime is occasionally responsible for unsoundness, but this ingredient usually acts in the opposite direction, tending to make sound a cement that otherwise might disintegrate. 12. Methods of Determining Soundness.—Although the presence of free or loosely combined lime is recognized as the most potent factor in producing unsoundness, and although this lime is a more or less well-defined chemical ingredient, it nevertheless is impossible to tell by any known method of chemical analysis what proportion of the total lime present exists in this dangerous condition. Therefore, physical tests must be relied on exclusively for the detection of unsoundness. The property of soundness is determined in one or more of three ways: by measjirements of expansion, by normal tests , and by accelerated tests. 13. Measurements of expansion are made by forming specimens of cement, usually in the shape of prisms, and §35 TESTS ON CEMENT 7 measuring the change in volume by means of a micrometer screw. A crude form of this test, once in common use, con¬ sisted in filling a lamp chimney with cement paste and putting it away until the cement became hard. If the expansion of the paste in hardening caused the chimney to crack, the cement was considered to have failed in the test. At the present time, however, it is believed that expansion is not a sure index of unsoundness, so that these tests are seldom employed. 14. Normal tests consist in making specimens of cement mixed with water, preserving them in air or in water under normal conditions, and observing their behavior. The common practice is to make from a paste of neat, or pure, cement two circular pats, about 3 inches in diameter, i inch thick at the center, and tapering to a thin edge, on glass plates about 4 inches square. These pats are kept in moist air for 24 hours; then one of them is placed in fresh water of ordinary temperature and the other is preserved in air. The condition of the pats is observed 7 days and 28 days from the date of making, and thereafter at such times as may be desired. 15. The most characteristic forms of failure are illus¬ trated in the following figures, which must be carefully studied by any one desiring to make tests, for, while some of the cracks indicate unsoundness and poor material, others 211—19 8 TESTS ON CEMENT §35 Fig. 4 Fig. 5 Fig. 6 Fig. 7 Fig. 8 §35 9 TESTS ON CEMENT show conditions that are entirely harmless. Many cements of excellent quality have been condemned through improper interpretation of the normal pat tests. Fig. 2 shows a pat in good condition. Fig. 3 illustrates shrinkage cracks that are due, not to inferior cement, but to the fact that the pat has been allowed to dry out too quickly after being made. Pats must be kept in a moist atmosphere while hardening, or these cracks, indicative merely of careless manipulation, will develop. Fig. 4 shows cracks that are due to the expansion of the cement. This condition is common in the air pats, and is not indicative of injurious properties. Pats kept in water, however, should not show these cracks. Fig. 5 shows three pats that, for different reasons, have left the glass plate on which they were made. The disk shown in (a) left the plate because of lack of adhesion; the one in (b), through contraction; and the one in (r), through expansion. The condition illustrated in {a) is never dangerous in either air or water; that in ( c) is only dangerous when existing in a marked degree; and that in ( b) hardly ever occurs in water but in air it often indicates dangerous properties. Air pats that develop the curvature shown in ( b) generally disintegrate later. A curvature of about f inch in a 3-inch pat can be considered to be about the limit of safety. Fig. 6 shows cracking of the glass plate to which the pat is attached. This cracking is caused by expansion or con¬ traction of the cement, combined with strong adhesion to the glass. It rarely indicates injurious properties. Fig. 7 illustrates blotching of the pats, the cause of which should always be investigated by chemical analysis or other¬ wise, which may or may not warrant the rejection of the material. Slag cements or cements adulterated with slag invariably show this blotching. Fig. 8 shows the radial cracks that mark the first stages of disintegration. Such cracks should never occur with good material. They are signs of real failure, and cement showing them should never be used. 10 TESTS ON CEMENT §35 In Fig. 9 are shown illustrations made from photographs that illustrate the complete failure of normal pats. The two pats in (a) and ( b ) were kept underwater during the testing period. In these pats, cracks similar to those shown in Fig. 8 have developed. Of the air-dried samples, shown Fig. 9 in (c) and (d), the first shows failure by crumbling and the other by excessive concavity. The concavity of the surface is shown by the shadow thrown by the rubber band that surrounds the pat. A similar pat is shown in Fig. 5 (b). §35 TESTS ON CEMENT 11 1G. The normal pat tests are the only absolutely fair and accurate methods of testing cements for soundness, but the serious objection to them lies in the fact that frequently several months or even years elapse before failure in the cement so tested becomes apparent. To overcome this difficulty, the accelerated tests have been devised. These tests aim to hasten the action of the expansive ingredients by treating the cement with heat or chemical salts, so that if there is any tendency to incipient disintegration, it will occur at once. They are intended to produce in a few hours results that require months in the normal tests. Many forms of accelerated tests have been devised, among which may be mentioned exposure to hot water, boiling 12 TESTS ON CEMENT 35 water, steam, steam under pressure, hot air, direct flame, and chemical salts, such as calcium chloride. At present, however, the only tests employed commercially are the boiling test and the steam test. 17. The boiling test is made by forming specimens of neat-cement paste into pats, such as are employed for the normal tests, or preferably into balls about li inches in diameter. The specimens are allowed to remain in moist air for 24 hours and are then tested. 0 The form of apparatus used for the boiling test is shown in Fig. 10. It consists of a copper tank that is heated by a Fig. 11 Bunsen burner and is filled with water. The water in the tank is kept at a uniform height by means of a constant- level bottle. A wire screen placed an inch from the bottom of the tank prevents the specimens from coming into contact with the heated bottom. The 24-hour-old test pieces are placed in the apparatus, which is filled with water of a normal temperature, and heat is applied at a rate such that the water will come to boiling in about i hour. Quiet boiling is con¬ tinued for 3 hours, after which the specimens are removed and examined. Care must be taken that the water employed is clean and fresh, because impure water may seriously affect the results. The same water, also, should never be used for §35 TESTS ON CEMENT 13 more than one test. A good cement will not be affected by this treatment, and the ball will remain firm and hard. Inferior cement will fail by checking, cracking, or entirely disintegrating, as shown by the specimens illustrated in Fig. 11. 18. The steam test is made in the same way as the boiling test, except that instead of immersing the specimens in water, they are kept in the steam above the water. The apparatus employed is the same as that used for the boiling test. The wire screen, however, is raised so that it is an inch above the surface of the water; also, there must be pro¬ vided a cover that is close enough to retain the steam with¬ out creating pressure. The steam test is less severe than the boiling test, is somewhat less accurate, and is used but infrequently. A combination of the steam and boiling tests is sometimes made by first steaming the specimens and then placing them in the boiling water, but this process has little to recommend it. 19. Results of Tests for Soundness.— The results of the normal tests, if properly made and interpreted, may be considered reliable guides to the soundness of the material, and cement failing in these tests should always be rejected. The accelerated tests, on the other hand, furnish merely indications, and are by no means infallible. A cement pass¬ ing the boiling test can generally be assumed sound and safe for use, but, if failure occurs, it simply means that other tests should be performed with greater care and watch¬ fulness. It often is advisable to hold for a few weeks cement that fails in boiling, so that the expansive elements may have an opportunity to hydrate and become inert; but if the material fulfils all the conditions except the boiling test, and is sound in the normal tests up to 28 days, it is generally safe for use. All things being equal, however, a cement that will pass the boiling test is to be preferred. 14 TESTS ON CEMENT 35 TENSILE STRENGTH 20. The tensile-strength test is for the purpose of, ascertaining a measure of the ability of the material to with¬ stand the loads that the structure must carry. This test is made by forming specimens, called briquets , of cement and cement mortar, and determining the force necessary to rup¬ ture them in tension at the expiration of fixed intervals of time. Cement constructions are rarely called on to with¬ stand tensile stresses, but if the tensile strength is known, the resistance to other forms of stress may be computed with a fair degree of accuracy. The tensile-strength test is the most convenient for laboratory determinations, on account of the small size of the specimens and the comparatively low stress required to cause rupture. Cement is tested both neat, or pure, and in a mortar com¬ monly composed of 1 part of cement and 3 parts of sand. The periods at which the briquets are broken have been fixed by usage at 7 days and 28 days after making, although tests covering much longer periods of time are necessary in research or in investigative work. 21. Normal Consistency.—The strength of cement and cement mortars varies considerably with the amount of water employed in making the briquets. Dry mixtures ordi¬ narily give the higher results for short-time tests, and wet mixtures show stronger with a greater lapse of time. For testing purposes, therefore, it is essential that all cements be mixed, not with the same amount of water, but with the amount that will bring all the cements to the same physical condition, or to what is called normal consistency. Dif¬ ferent cements require different percentages of water because of their varying chemical composition, degree of burning, age, fineness, etc. The normal consistency of neat-cement pastes may be determined by either of the methods that follow. In these tests, the quantities are given in grams. The grain is the metric unit of weight. One kilogram = 1,000 grams = 2.205 pounds; 1 gram = 15.432 grains. TESTS ON CEMENT 15 §35 1. In the first method, 500 grams of cement is weighed and placed on a mixing slab in the form of a crater, and a definite amount of water poured into the center. The cement is turned over from the sides into the center until the water is absorbed. It is then kneaded for 1 minute, after which it is placed in the conical rubber ring under the plunger of the Vicat needle (see Fig. 17). The plunger is brought into contact with the surface of the material, quickly released, and its penetration noted. The penetration should be exactly 10 millimeters, and if the test shows a greater or less amount, other trials must be made, using more or less water, until the correct consistency is obtained. One millimeter is toVo meter, the unit length of the metric system; 1 inch = 25.4 millimeters; 10 millimeters = 1 centi¬ meter = .3937 inch. 2. A simpler method is to form of the paste a ball about 2 inches in diameter and to drop this ball on a table from a height of about 2 feet. If the cement is of the correct con¬ sistency, the ball will not crack nor will it flatten to less then half its original thickness. The percentage of water required will vary from 16 to 25, depending on the characteristics of the material, the average cement taking about 20 per cent. 22. Consistency of Sand Mortars. —The consistency of sand mortars, however, cannot be obtained by either of the foregoing methods, because the sand grains do not permit of the measurement of the consistency by penetration, and the mixture is too incoherent for use of the ball method. For mortars, therefore, it is necessary to employ a formula by means of which the sand consistency can be computed when that of the neat paste is known. Several such formulas have been devised, of which the following is adaptable to the greatest variety of conditions. Let x = per cent, of water required for sand mixture; N = per cent, of water required to bring neat cement to normal consistency; n — parts of sand to one of cement; N = a constant depending on the character of the sand. 16 TESTS ON CEMENT §35 Then, 3iV+ Sn + 1 4 (n + 1) For crushed-quartz sand, the constant N is 30; for Ottawa sand, it becomes 25; and for the bar and bank sands used in construction, it varies from 25 to 35, and must be determined for each particular sand. Example. —How much water is required in a mixture of 1 part of cement and 3 parts of crushed-quartz sand? The neat cement requires 19 per cent, of water to give normal consistency. Solution. —Here, A T = 19, S' = 30, and n = 3. Substituting these values in the formula, x 3X19 + 30X3 + 1 4 X (3 + 1) ' per cent. Ans. EXAMPLES FOR PRACTICE 1. How much water will be required in a mixture of 1 part of cement to 5 parts of Ottawa sand, provided the neat cement requires 20 per cent, of water? Ans. 7.75 per cent. 2. (a) Find the value of S if a mixture of 1 part of cement (JV = 19) and 4 parts of a bank sand requires 8.5 per cent, of water. (5) What percentage of water will be required for a mixture of 1 part of another cement (./V = 22) and 2 parts of the same sand? Ans P°) -S' = 28 s ‘ 1 (b) 10.3 per cent. It is extremely important that all cements have the correct consistency when tested, for if the briquets are either too wet or too dry, the results will be in considerable error and hence valueless. Also, in order to avoid the introduction of possible irregularities, care must be taken that the water is clean, pure, and of a temperature as near 70° F. as practicable. 23. Sand for Mortar Tests. —The size, gradation, and shape of the particles of sand with which cement mortars are made have great influence on the resulting strength. Thus, for testing purposes, it is essential that the size and char¬ acteristics of the sand be uniform. There are two varieties of standard sand for cement testing, one an artificial sand of crushed quartz, the particles of which are angular in shape, §35 TESTS ON CEMENT 17 and the other a natural sand from Ottawa, Illinois, the particles of which are almost spherical. Both sands are sifted to a size that will pass a sieve of 20 meshes to the inch and be retained on a sieve of 30 meshes, the diameters of the sieve wires being .0165 and .0112 inch, respectively. The Ottawa sand will develop strengths in 1-3 mortars about 20 to 30 per cent, greater than those obtained with crushed quartz, and it is theoretically the better sand for testing, but, at present, crushed quartz is more extensively employed. On most important works, tests for purposes of comparison are also made of the actual sand entering the construction. 24. Form of Briquet. —The form of tensile briquet adopted as standard in the United States is shown in Fig. 12. Its length over all is 3 inches, and its cross- section is exactly 1 square inch. This form of briquet is by no means perfect, and often fails under test through stresses that Fig. 12 are not pure tension. Although its defects are recognized, it will probably con¬ tinue as the standard for some time to come, because of the difficulties arising from any change. 25. Molds. —Cement briquets are made in molds that come either single or in gangs of three, four, or five. The gang molds are preferable, as they tend to produce greater 18 TESTS ON CEMENT 35 uniformity in the results. A common type of a four-gang mold is shown in Fig. 13. Molds should be made of brass or of some other non-corrodible material; those made of cast iron soon rust and become unfit for use. 26. Method of Making Briquets. —Many methods of mixing and molding briquets are used in various laboratories, but the following is the one most generally employed and the only one that has been officially adopted by the technical societies: First, 1,000 grams of cement is carefully weighed and placed on the mixing table in the form of a crater, and into the center of this is poured the amount of water that has previously been determined to give the correct normal con¬ sistency. Cement from the sides of the crater is then turned into the center, by means of a trowel, until all the water is absorbed, after which the mass is vigorously worked with the hands, as dough is kneaded, for li minutes. When sand mixtures are being tested, 250 grams of cement and 750 grams of sand are first weighed and thoroughly mixed dry until the color of the pile is uniform; then the water is added and the operation is completed by vigorous kneading. After kneading, the material is immediately placed in the molds, which should first have been wiped with oil to pre¬ vent the cement from sticking to them. The entire mold is filled with material at once—not compacted in layers—and pressed in firmly with the fingers without any ramming or pounding. An excess of material is then placed on the mold and a trowel drawn over it under moderate pressure, at each stroke cutting off more and more of the excess material, until the surface of the briquets is smooth and even. The mold is then turned over, and more material placed in it and smoothed, as before. The mixing and molding should be performed on a surface of slate, glass, or some other smooth, non-absorbent material. During the mixing the operator §35 TESTS ON CEMENT 19 should wear rubber gloves, so as to protect his hands from the action of the lime in the cement. Many attempts have been made to devise apparatus for making briquets by mechanical means, and while some such machinery is on the market and produces fairly good results, the process is much slower and no more accurate than the hands of an experienced operator. 27. Storage of Briquets.—For 24 hours after making, the briquets are stored in a damp closet so that the cement can harden in a moist atmosphere. This condition is con¬ ducive to the greatest uniformity, and also prevents the formation of shrinkage cracks in the material. The damp closet is simply a tight box of soapstone with doors of wood lined with zinc, or some similar arrangement, with a recep¬ tacle for water at the bottom and racks for holding the briquets. Sometimes, when there is no closet, the briquets are covered with a damp cloth, which method answers the purpose but is less uniform and accurate. If a cloth is used, it should be kept damp by immersing the ends in water, and care should be taken that the cloth does not come into actual contact with the surface of the briquets. 28. The briquets remain in the molds while in the damp closet, but at the expiration of 24 hours they are removed, marked, and placed in water until broken. Cement briquets are stored in water rather than in air, because they are thus kept under more uniform conditions, and also because the presence of injurious elements is generally manifested more clearly in this environment. Any suitable receptacle will serve for their storage, provided care is taken to have water that is clean, fresh, and at a temperature of nearly 70° F. If provision cannot be made to keep the water slowly running, it must be changed not less than once a week, otherwise, it soon becomes strongly alkaline and may seri¬ ously affect the results. 29. Testing Machines. —The many machines designed for the purpose of breaking the briquets may be divided into those of the shot-machine type and those of the beam type. 20 TESTS ON CEMENT 35 30. A typical shot machine as made by the Fairbanks Company is shown in Fig. 14. It is constructed on the cast- iron frame a , and is operated as follows: The cup / is hung on the end of the beam d , the poise r placed at the zero mark, and the beam balanced by turning the weight /. The hopper b is then filled with fine shot, and the briquet to be tested is placed in the clips h. The hand- Fig. 14 wheel p is now tightened sufficiently to cause the graduated beam d to rise to the stop k, and the automatic valve j opened so as to allow the shot to run into the cup /. The flow of the shot can be regulated by means of a small valve located where the spout joins the reservoir. When the briquet breaks, the beam d drops and by means of the lever t §35 TESTS ON CEMENT 21 automatically closes the valve j. After the specimen has broken, the cup with its contents is removed, and the counterpoise g is hung in its place. The cup / is then hung on the hook under the large ball e , and the shot weighed. The weighing is done by using the poise r on the graduated beam d and the weights n on the counterpoise g. The result will show the number of pounds required to break the specimen. A mold for a single briquet is shown at c. 31. The Olsen machine shown in Fig. 15 is an example of the beam type of testing machine. In this machine, an electric motor a operates, through a belt d , the step pulleys b and c , which are used to change the speed of operation. A belt (hidden by the frame of the machine) from the step pulley c operates the shaft e, which, through the friction 22 TESTS ON CEMENT §35 wheel /, turns a long screw that runs behind the beam^ and is hidden by it. The weight h is threaded on this screw, the same as an ordinary nut would be threaded on a bolt, and as the motor runs, it revolves the screw and draws the weight out on the beam at a uniform rate of speed. This rate can be changed, if desired, by shifting the belt on the step pulleys b and c. The briquet to be tested is inserted in the clips and drawn tight by the hand wheel i. The weight h is then run to the zero point of the scale, and the hand wheel j is turned until the pointer k floats; that is, touches the frame at neither l nor m. The motor is now started and the weight h moves out on the scale. At the same time the hand wheel j is turned by hand, so as to keep the pointer k balanced, or floating. When the briquet breaks, the motor is stopped immediately by an electrical contrivance at n and the load is read off the scale g. The hand wheel j may also be operated by the motor through a worm-wheel, but it is better operated by hand, as the operator must turn it only enough to keep the pointer k always in mid-position. There are several other machines in the market as suit¬ able for the purpose as those selected for illustration, but, although differing in many minor particulars, all of them are practically of one or the other of these types. 32. Form of Clip. —The standard form of clip for holding the briquet is shown in Fig. 16, the bearing sur¬ faces a being li inches apart, i inch wide, and shaped to fit the curve of the sides of the briquet. Clips are often made with roller bearings, adjustable plate bearings, cushioned bearings, etc., but the results of tests made on these clips are not comparable with those made on the standard clip, and hence their use should not be permitted. §35 TESTS ON CEMENT 23 33. Rate of Loading. —The load should be applied in all tests at the uniform rate of 600 pounds per minute. Variations in this speed will affect the results seriously, higher values being obtained when the rate of loading is increased, and lower ones when it is diminished. The briquets should be broken as soon as they are removed from the storage tanks and while they are still wet, because dry¬ ing out tends to lower their strength. The average of from three to five briquets should be taken as the result of a test. 34. Results of Tensile-Strength. Tests. —The tensile strength of cement tested in the preceding manner should increase with age up to about 3 months, and should then remain practically stationary for longer periods. The average results of tests of Portland cement made in the Philadelphia laboratories, covering a period of several years and based on over 200,000 briquets, are given in Table I. TABLE I TENSILE STRENGTH OF CEMENT BRIQUETS (Pounds per Square Inch ) i Mixture 1 Hour in Air 23 Hours in Water I 1 Day in Air 6 Days in Water _ i Day in Air 27 Days in Water 1 Day in Air 89 Days in Water Neat. 420 710 770 775 i cement, i crushed-quartz sand 360 590 695 700 i cement, 2 crushed-quartz sand 2 10 370 455 465 1 cement, 3 crushed-quartz sand 105 2 10 300 310 1 cement, 4 crushed-quartz sand 60 130 210 230 1 cement, 5 crushed-quartz sand 35 80 155 195 Specifications for strength commonly stipulate minimum values for the 7- and 28-day tests, the customary require¬ ments for Portland cement being 500 pounds at 7 days and 211—20 24 TESTS ON CEMENT 35 600 pounds at 28 days, when tested neat, and 170 pounds at 7 days and 240 pounds at 28 days, when tested in a mortar consisting - of 1 part of cement and 3 parts of crushed-quartz sand. When Ottawa sand is used, the requirements for mortar should be raised to 200 and 280 pounds, respectively. Retrogression in strength of the neat briquets between 7 and 28 days is not necessarily indicative of undesirable properties, but if the mortar briquets show retrogression, the cement should be condemned. Abnormally high strength in the 7-day test of neat cement, say over 900 pounds, may gener¬ ally be taken as an indication of weakness rather than of superiority, because such a condition is usually created by an excess of lime or of sulphates, either of which may be injurious. Neat cement testing from 600 to 800 pounds at 7 days is generally the most desirable. SECONDARY TESTS TIME OF SETTING 35. Reasons for Test. —The time-of-setting test is made to determine whether or not the cement will become hard at the time most desirable in actual construction. If it begins to set too soon, the crystallization of the particles will have begun before the mortar or concrete is thoroughly tamped into place, and working the mixture after setting has begun tends to break up the crystals and to weaken the product. If, on the other hand, the cement sets too slowly, the material is more likely to suffer from exposure to heat, cold, dampness, and frost; also, the progress of the work will be much delayed on account of the greater interval required between different sections, and the longer time the forms must be left up. 36. Cement when mixed into a paste with water and allowed to stand, gradually changes from a plastic state into a hardened mass. This process is known as setting, while the subsequent action resulting in increased tensile strength §35 TESTS ON CEMENT 25 is known as hardening. In the setting of cements, two stages are recognized: (1) When the paste begins to harden, or to offer resistance to change of form, called initial set, and (2) when the setting is complete, or when the mass cannot be appreciably distorted without rupture, called hard set. The time-of-setting test consists, therefore, in deter¬ mining the time required for the cement to reach these two critical points. The test is made by mixing cement with the amount of water required to produce normal consistency, in the same manner as for neat tensile briquets, forming specimens, placing them under one of the forms of apparatus, and observing the time that elapses between the moment the mixing water is added and the moments when the paste acquires initial set and hard set. 37. Forms of Apparatus for Time-of-Setting Test. There are two forms of apparatus employed to test the time of setting, namely, the Vicat needle and the Gillmore wires . The former is the more accurate and the one adopted as standard, although the Gillmore wires are used extensively. 38. The Vicat needle, shown in Fig. 17, consists of a frame k , holding a movable rod /, which carries a cap d at the upper end and a needle h at the lower. A screw / holds the rod in any desired place. The position of the needle is shown by a pointer moving over a graduated scale. The rod with needle and cap weighs exactly 300 grains, and the needle is 1 millimeter in diameter with the end cut off square. When making tests of normal consistency (see Art. 21), the 26 TESTS ON CEMENT §35 plunger b is substituted for the needle h , and the cap a for the cap d y the difference in weight between the needle and plunger being compensated by the difference in the weight of the caps. The mold i for holding the cement paste is in the form of a truncated cone. It has an upper diameter of 6 centi¬ meters, a lower diameter of 7 centimeters, and a height of 4 centimeters, and rests on a 4" X 4" X glass plate j. After the cement paste is mixed, the mold is filled by forcing the cement through the large end; then, after turning it over and smoothing the top, it is placed on the glass plate under the needle. The needle is lowered until it is exactly in contact with the surface of the paste, then quickly released, and the depth to which it penetrates read from the grad¬ uated scale. Initial set is said to have taken place when the needle ceases to penetrate to within 5 millimeters of the bottom of the specimen; and hard set takes place when the same needle ceases to make an impression on the surface. Trials of penetration are made every 5 or 10 minutes, until these points are reached. 39. The Gillmore wires, shown in Fig. 18, consist of two wires, one having a di¬ ameter of iV inch and carry¬ ing a weight of i pound and the other having a diameter of - 2 -4 inch and carrying a weight of 1 pound. The cement paste is molded into any form having a smooth surface, and the wires, or needles , as they are called, are rested upon it from time to time. Initial set takes Fig. 18 place when the light wire ceases to penetrate the surface of the paste, and hard set occurs when the heavy wire ceases to penetrate. Care must be taken to apply the needles in a precisely vertical direction, because if resting at an angle, the area under the pressure will be reduced and the results §35 TESTS ON CEMENT 27 increased accordingly. More accurate results will be obtained if the wires are held upright in a special frame made for this purpose. Tests made with the Gillmore wires give results averaging from one and one-half to two times as great as those determined by means of the Vicat needle. 40. Time of setting varies considerably with the amount of mixing water employed, so that it is essential that every sample tested be brought exactly to normal consistency; otherwise, the results may be in decided error. Variations in temperature, in both environment and in the mixing water, also influence the results. Standard practice requires that both the materials and the room in which the tests are made be at a temperature of as nearly 70° F. as practicable. 41. Results of Time-of-Setting Tests. —In specifying results to be obtained in testing the time of setting, it is obvious that a minimum value should be stipulated for initial set and a maximum, as well as a minimum, for hard set. It must also be remembered that a cement mixed with an aggregate and with an excess of water in the field,, will require from two to four times as long to set as the neat- cement paste mixed with little water in the laboratory. Cement, therefore, showing an initial set at the expiration of 20 minutes with the Vicat needle, will rarely begin to set on the actual work in less than f hour, which gives ample time for mixing and placing the materials; and cement setting in less than 10 hours, will usually have hardened completely in the work in 24 or, at least, in 36 hours. Specifications usually stipulate that Portland cement shall show initial set in not less than 20 minutes, and shall develop hard set in not less than 1 hour nor more than 10 hours. Cement reaching initial set in less than 12 or 15 minutes should never be used for any work. FINENESS 42. Reasons for Fineness Test. —When cement, in the process of manufacture, leaves the rotary kiln after burning, it is in the form of round balls of clinker about 28 TESTS ON CEMENT 35 the size of a walnut. This clinker is reduced by grinding to a powder, and the object of the fineness test is to deter¬ mine the degree of this pulverization. The fineness of cement is important, because it affects both the strength and the soundness of the product. The more finely a cement is ground, the more thoroughly will the cement paste cover the particles of sand; hence, the greater will be the strength of the resulting mixture. Also, because the fine particles are more quickly acted on by the mixing water, the crystal¬ lization is hastened, so that not only is the ultimate strength of the product increased, but the hardening also is more rapid. The strength of neat cement is reduced somewhat when the cement is ground especially fine, but this is of little importance, because cement is rarely used neat; and when it is so used, strength is seldom a factor. Fineness of grinding affects the soundness of cement because the expansive elements contained in the coarse particles are not readily susceptible to the action of season¬ ing, which will hydrate and render inert the unsound material in the fine particles. As a rule, it will be found that only the coarser part of cement is instrumental in causing failure in the soundness tests, as may easily be determined by making comparative tests—one by boiling the cement in its original condition, and another by boiling a sample of the same cement from which the coarse particles have been separated by sifting. Another effect of increased fineness is to hasten the time of setting; thus, with such cement, the set test, as well as the addition of plaster used to retard the set, must be closely watched. 43. Apparatus for Fineness Test. —The fineness of cement is determined by passing it through a series of sieves of different mesh and then measuring the amount retained on each. Three sieves are commonly employed, namely, those having 50, 100, and 200 wires to the linear inch, or 2,500, 10,000, and 40,000 meshes to the square inch, respect¬ ively. The sieves are generally circular in shape, 6 to 8 inches in diameter, 2 to 3 inches deep, and have the wire §35 TESTS ON CEMENT 29 cloth mounted 2 inch from the bottom. A cover and a pan to catch the material passing through the sieve should also be provided. For accurate work, it is necessary that the wire cloth be regular and of exactly the proper mesh, for, because of the uniform gradation of the particles of cement, the least vari¬ ation in the mesh of the sieves becomes noticeable in the results. Sieves for cement testing should never be used until they have been carefully examined and found to conform to the following standard specifications: 1. Cloth for cement sieves shall be of woven brass wire of the following diameters: No. 50, .0090 inch; No. 100, .0045 inch; and No. 200, .00235 inch. 2. Mesh to count on any part of the sieve as follows: No. 50, not less than 48 nor more than 50 per linear inch; No. 100, not less than 96 nor more than 100 per linear inch; and No. 200, not less than 188 nor more than 200 per linear inch. 3. Cloth to be mounted squarely and to show no irregu¬ larities of spacing. 44. Method of Making the Fineness Test. —The method of using the sieves in the fineness test is to weigh Fig. 19 out 50 grams of cement on a scale sensible at least to •To gram and to place it on the No. 200 sieve, on which it is 30 TESTS ON CEMENT 35 shaken until not more than iV gram passes the sieve at the end of 1 minute of shaking. The arrival of this stage of completion can be watched either by using a pan under the sieve or by shaking over a piece of paper. The residue remaining on the sieve is weighed, placed on the No. 100 sieve, and the operation repeated, again weighing the Fig. 20 \ residue. The amount remaining on the No. 50 sieve is then determined similarly. Scales like those shown in Fig. 19 are convenient for this test, and may be so graduated that either the percentage of residue or of the amount passing each sieve may be read directly from the beam. The process of sifting can be accelerated by placing a small quantity of coarse shot or pebbles on the sieves with the cement during §35 TESTS ON CEMENT 31 the shaking. These may be separated from the cement by passing the residue with the shot through a coarse sieve, such as the No. 20. 45. Mechanical sifters like that illustrated in Fig. 20, manufactured by Howard & Morse, of Brooklyn, New York, may be used in the fineness test. The sieves are arranged in nests, the finest being at the bottom, and the coarsest sieve at the top. The cement to be tested is placed on the top sieve. Three or four nests may be placed in the machine at one time, and after turning it until the sifting is complete, the amount remaining on each sieve is weighed. For deter¬ mining the granulometric composition of sands for use in mortar, as described in Sa?ids a?id Cements , this machine is particularly well adapted. By granulometric composition of sand is meant the percentage of the different sizes of grains contained in a given sample. 46. Results of Fineness Tests. —Portland cement should be ground to such a fineness that it will leave a residue of not more than 25 per cent., by weight, on the No. 200 sieve, and not more than 8 per cent, on the No. 100 sieve. Of these two requirements, the first is the more important, because it is only that part of the cement passing the finest sieve that is active in the setting and hardening of the material. The amount remaining on the No. 100 sieve is also important, because this part is most liable to cause unsoundness in the cement, and although specifications do not call for tests with the No. 50 sieve, it is usually employed for the same reason as the No. 100 sieve. Any appreciable residue on this sieve indicates that the material is much more liable to unsoundness. Any cement failing to pass the fine¬ ness test should be watched more carefully in the soundness and strength tests, but if these tests show good results up to 28 days, the cement can as a rule be used safely. It must be remembered, however, that only that part passing the No. 200 sieve is really cement, so that a coarsely ground shipment is practically equivalent to one adulterated with weak and unsound material. 32 TESTS ON CEMENT §35 SPECIFIC GRAVITY 47. Reasons for Specific-Gravity Test. —The object of the specific-gravity test is to furnish indications of the degree of burning, the presence or absence of adulteration, and the amount of seasoning that the cement has received. When Portland cement is burned, the separate ingredients are in close contact and gradually combine by a process of diffusion. The greater the amount of this burning, the more thoroughly are the elements combined. Thus, by their con¬ traction they give, in volume, a higher density or specific gravity. Since, to secure good cement the burning must have been made within definite limits, it follows that the specific gravity must also lie within fixed limits if the cement has been properly manufactured. The common adulterants of Portland cement, namely, limestone, natural cement, sand, slag, cinders, etc., all have specific gravities ranging from 2.6 to 2.75, while the specific gravity of Portland cement averages about 3.15. An appre¬ ciable amount of adulteration, therefore, is at once indicated in the results of the test. For example, suppose a cement whose specific gravity is 3.15 is adulterated so as to contain 20 per cent, of sand whose specific gravity is 2.65. The specific gravity of the mixture would then be .80 X 3.15 + .20 X 2.65 = 3.05, the adulteration thus becoming obvious. Seasoning is indicated because the cement on standing gradually absorbs water and carbonic acid from the air. These ultimately combine with it and thus lower the specific gravity. The amounts of water and carbonic acid combined and absorbed may be approximately determined by making tests of the specific gravity of the cement in its original con¬ dition, on another sample dried at 212° F., and on one ignited over a blast lamp. The difference between the first two tests gives a measure of the absorbed, or hygroscopic, water, and the difference between the last two gives a measure of the combined water and carbonic acid, because igniting the cement restores it more or less to the condition of the original clinker. 35 TESTS ON CEMENT 33 48. Apparatus for Specific-Gravity Test.—Of the many forms of apparatus employed for the specific-gravity test, the Le Cliatelier flask, shown in Fig. 21, is the one most commonly used. It is also the one adopted by the technical societies as standard. It consists of a glass flask about 30 centimeters high. The lower part up to the mark a contains 120 cubic centimeters, and the bulb between the marks a and b contains exactly 20 cubic centimeters. The neck of the flask above the mark b is graduated into tV cubic centimeters. The funnel c inserted in the neck is to facilitate the introduction of the cement. 49. Method of Making the Spe¬ cific-Gravity Test. —The specific gravity of a substance has been defined as the ratio of its weight to the weight of an equal volume of water, or, when the metric system of weights and meas¬ ures is used, the ratio of its weight, in grams, to its displaced volume, in cubic centimeters. The method of conducting the test is as follows: Sixty-four grams of cement is carefully weighed on scales that should have a sensibility of at least .005 gram. The flask, Fig. 21, is filled to the lower mark a with benzine or kerosene, which has no action on the cement, and carefully adjusted precisely to the mark by adding the liquid a drop at a time. The funnel is then placed in the neck of the flask and the weighed cement introduced slowly through it, the last traces of the cement being brushed through with a camel’s-hair brush. The funnel is then removed and the height of the benzine read from the graduations, esti¬ mating to .01 cubic centimeter. The displaced volume is Fig. 21 34 TESTS ON CEMENT §35 then 20 plus the reading in cubic centimeters, and the specific gravity of the cement is 64 divided by that quantity. For example, suppose that the reading on the flask is .54, then the displaced volume will be 20 + .54 = 20.54 and the specific gravity will be 64 -r- 20.54 = 3.116. The apparatus must be protected from changes in temper¬ ature while in use, because even touching the flask with the fingers will change the volume of the liquid noticeably. The flask is sometimes immersed in water during the tests, to prevent these changes of temperature, but this precaution is unnecessary if proper care is exercised. 50. Results of Specific-Gravity Tests. —The specific gravity of well-burned Portland cement averages about 3.15 and should not fall below 3.1. If it falls below 3.1, tests should also be made on dried and on ignited samples to ascertain whether or not this condition has been produced by reason of excessive seasoning. The specific gravity should generally be taken only as an indication of the quality of the cement, and the rejection of a shipment on the ground of failure in this test is rarely, if ever, justifiable, unless of course, that failure has been caused by adulteration or underburning. As a rule, low specific gravity merely indi¬ cates well-seasoned cement, and if sound and sufficiently strong, such cement is the best sort of material for use, as its durability is scarcely open to question. CHEMICAL ANALYSIS 51. The chemical analysis of cement is made by methods that in all essential particulars are similar to those used for limestone or for feldspar, and, as these tests are rarely made, no explanation is required. Portland cement consists primarily of silica, alumina, and lime, but determi¬ nations of the proportions of these ingredients give little or no information as to the quality of the product, for the most perfect combination of ingredients may be so treated by underburning or otherwise as to result in a worthless mate¬ rial, while, by careful treatment, good cement may be made §35 TESTS ON CEMENT 35 from somewhat poorly proportioned raw material. Further¬ more, the ash from the fuel in burning enters into the analy¬ sis and will often so modify the results as to destroy their significance. While chemical analysis of the essential ingre¬ dients is necessary to the manufacturer for the control of his product, it is of little or no value to the consumer, and gives practically no indication of the constructive value of the cement. I 52. Determinations of certain ingredients, notably mag¬ nesia and sulphuric acid, are sometimes valuable, because, under certain conditions, excess of these elements may pro¬ duce unsoundness or disintegration of the product. It is especially necessary for construction that is to be placed in sea-water that these two substances be kept within the speci¬ fied limits, for their deleterious effect reaches a maximum when placed in this situation. Under such circumstances, analysis for magnesia or sulphuric acid may be made at times, but, for ordinary conditions, the test is absolutely unnecessary, any injurious properties being shown much more clearly in the physical tests than by analysis. The limits of magnesia and sulphuric acid in Portland cement are commonly placed at 4 per cent, for the former and 1.75 per cent, for the latter. Complete ultimate analysis of Portland cement will usually give results within the following limits: Per Cent. Silica, Si0 2 .. . . 20.0 to 24.0 Alumina, Al a 0 3 . 6.0 to 9.0 Iron oxide, Fe 2 0 3 . 2.0 to 4.0 Lime, CaO . 59.0 to 65.0 Magnesia, MgO .. . .5 to 5.0 Sulphuric acid, S0 3 . .5 to 2.5 Carbonic acid and water, C0 2 -f H 2 0 . 1.0 to 4.0 Alkalies, K 2 0 and Na 2 0 . 0.0 to 3.0 I 36 TESTS ON CEMENT 35 NATURAE AND STAG CEMENTS 53. The methods of conducting tests of natural and slag cements are, in all important particulars, identical with those employed for Portland cement, although the results obtained and the interpretation to be put on them are often radically different. In the testing, the only essen¬ tial difference is in the amount of water required by these cements to produce normal consistency, natural cement requiring from 23 to 35 per cent, and slag cement taking about 18 per cent., or on an average of 2 or 3 per cent, less than Portland. Tests of natural cement for tensile strength are also frequently made on 1-1 and 1-2 mortars, but recent practice is to test mortars of all kinds of cement in 1-3 mix¬ tures. For these cements, moreover, the specific-gravity test has practically no significance, except in determining the uniformity with which the different brands are made. The requirements for these materials are given in Table II. SPECIFICATIONS 54. The common requirements for high-grade Port¬ land, natural, and slag cements are given in Table II. A complete modern specification for Portland cement is here given. _____ , SPECIFICATIONS FOR PORTLAND CEMENT OO. Kind, —All cement shall be Portland of the best quality, dry, and free from lumps. By Portland cement is meant the finely pulverized product resulting from the calcination to incipient fusion of an intimate mixture of properly proportionated argillaceous and cal¬ careous materials to which no addition greater than 3 per cent, has been made subsequent to calcination. 56. Packages. —Cement shall be packed in strong cloth or can¬ vas bags, or in sound barrels lined with paper, which shall be plainly marked with the brand and the name of the manufacturer. Bags shall contain 94 pounds net and barrels shall contain 376 pounds net. 57. Inspection.— All cement must be inspected, and may be reinspected at any time. The contractor must submit the cement, and §35 TESTS ON CEMENT 37 TABLE II REQUIREMENTS FOR HIGH-GRADE CEMENTS Requirements Portland Cement Natural Cement Slag Cement Specific gravity: Not less than. 3-1 2.8 2.7 Fineness: Residue on No. ioo sieve, not over. 8% 10% 3% Residue on No. 200 sieve, not over. 25 % 30% 10% Time of setting: Initial, not less than . . 20 min. 10 min. 20 min. Hard, not less than . . . 1 hr. 30 min. 1 hr. Hard, not more than . . Te?isile strength per square 10 hr. 3 hr. 10 hr. inch : 7 days, neat, not less than 28 days, neat, not less 500 lb. 125 lb. 35o lb. than. 600 lb. 225 lb. 450 lb. 7 days, 1-3 quartz, not • less than. 170 lb. 50 lb. 125 lb. 28 days, 1-3 quartz, not less than. •240 lb. 110 lb. 200 lb. So2i?id?iess : Normal pats in air andj sound and sound and sound and water for 28 days to bel hard hard hard Boiling test to be . . . j sound and hard sound and hard Analysis: Magnesia, A/gO, not over Anhydrous sulphuric 4 % 4 % acid, S 0 3 , not over . . Sulphur, S , not over . . 1.75% 1.3% 38 TESTS ON CEMENT §35 afford every facility for inspection and testing, at least 12 days before desiring to use it. The chief engineer shall be notified at once on receipt of each shipment at the work. No cement will be inspected or allowed to be used unless delivered in suitable packages properly branded. Rejected cement must be immediately removed from the work. 58. Protection.—The cement must be protected in a suitable building having a wooden floor raised from the ground, or on a wooden platform properly protected with canvas. It shall be stored so that each shipment will be separate, and each lot shall be tagged with identifying number and date of receipt. 59. Quality .—The acceptance or rejection of a cement to be used will be based on the following requirements: Specific gravity: Not less than 3.1. Ultimate tensile strength per square inch: Pounds 7 days (1 day in air, 6 days in water).500 28 days (1 day in air, 27 days in water).600 7 days (1 day in air, 6 days in water), 1 part cement to 3 parts of standard quartz sand.170 28 days (1 day in air, 27 days in water), 1 part of cement to 3 parts of standard quartz sand .... 240 Fineness: Residue on No. 100 sieve not over 8 per cent., by weight; residue on No. 200 sieve not over 25 per cent., by weight. Set: It shall require at least 20 minutes to develop initial set, and shall develop hard set in not less than 1 hour nor more than 10 hours. These requirements may be modified where the conditions of use make it desirable. Constancy of Volume: Pats of cement 3 inches in diameter, ^ inch thick at center tapering to thin edge, immersed in water after 24 hours in moist air, shall show no signs of cracking, distortion, or disinte¬ gration. Similar pats in air shall also remain sound and hard. The cement shall pass such accelerated tests as the chief engineer may determine. Analysis: Sulphuric anhydride, S0 3 , not more than 1.75 per cent.; magnesia, MgO, not more than 4 per cent. CONCRETE BUILDING BLOCKS (PART 1) INTRODUCTION 1. Definition. —A concrete block is a building unit formed from a combination of cement and aggregate mixed with water and molded into required form. This definition is much broader than one that might cover the ordinary commercial concrete block, but the subject must be looked at broadly in order to get proper bearings and to secure a proper realization of the place that the concrete block occupies with respect to the cement and concrete industries. 2. History. —Concrete blocks are generally regarded as something new, and the industry appears to most persons as too young to merit that confidence accorded to forms of construction with which they are more familiar. This new¬ ness is real only in so far as it applies to the particular forms of block recently introduced, or to the particular processes of manufacture that have been developed to meet the needs of the industry during its half dozen years of activity. By carefully looking into the history of building among many ancient and modern peoples, it will be found that concrete blocks were used for certain structural purposes. Although the composition of the concrete does not accord with present practice—cinders, pieces of brick, and various hard substances were often used instead of gravel or broken stone—it may be said that, in general, the substance approx¬ imates the present conception of cement. In fact, every- COPYRIQHTEO BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS' HALL, LONDON § 36 211—21 2 CONCRETE BUILDING BLOCKS §36 where in the ruins of ancient works are found blocks of con¬ crete whose durability, after the lapse of centuries, challenges modern skill. In the middle ages similar blocks were used in fortifications and other work whenever it was more convenient to transport the manufactured blocks than to make the concrete in place. In many places in England such blocks were substituted for stone, and in the United States, very early in the 19th cen¬ tury, they were used for residence construction. In all the instances mentioned, the use of concrete blocks was limited, and the walls, as well as the blocks themselves, were made solid. A hollow wall, it seems, was not thought of until the middle of the 19th century, when hollow blocks came into use. Even then, instead of utilizing the air space as insulation, the builders imagined that it had to be filled with some deadening material. 3. It is unfortunate that the early efforts of block con¬ struction in the United States were along the line of a cement- and-fine-sand mixture, so that cement blocks was the term by which they were designated. So far as is known, no effort was made to use a coarser material, making true concrete, earlier than 1902, and it was some 2 or 3 years later before the term concrete block came into general use. About the same time there arose among block makers a strong desire to imitate natural-stone effects, and the term artificial stone took a firm hold, from which it was not easily dislodged. To persons already familiar with the extensive use of concrete and the variety of its surface finish, this may seem strange. However, it must be remembered that the concrete-block industry, which is now well known throughout America, developed, within a few years, from almost nothing, and, besides, during the labors of the early block makers reinforced concrete, armored concrete, and ferroconcrete were likewise striving for a name and a place. In short, no one seemed to be aware of the merits of concrete blocks for build¬ ing purposes, and for this reason they were not used except as a cheap imitation of stone. This stage, with its delusions, §30 CONCRETE BUILDING BLOCKS 3 has passed, and the concrete block is now valued for its own distinctive qualities. 4. Use aiul Efficiency. —To the fair-minded person, it is apparent that there is a large field for both reinforced concrete and concrete blocks. One of these forms of con¬ struction, however, cannot entirely replace the other. Although the efficiency of blocks cannot be questioned, it would be short-sighted not to recognize their limitations and to note the greater efficiency of reinforced concrete in such struc¬ tures as the Ingalls and Pugh buildings, of Cincinnati, Ohio, or the Marlborough-Blenheim Hotel, of Atlantic City, New Jersey. There are numerous four-story buildings of concrete blocks, occupied as warehouses, hotels, office buildings, etc., that give perfect satisfaction, and there is no reason why blocks should prove unsatisfactory in six- or eight-story build¬ ings. Above eight stories there would hardly be any economy in their use, nor any other advantage adequately offsetting the increased cost resulting from the use of the heavier walls required in a higher building. There are, however, places where blocks are distinctly advantageous and those places are in dwellings and in two-, three-, and four-story business buildings. In all such build¬ ings, the walls may, with perfect safety, be comparatively light and the blocks still afford the usual factor of safety in reference to loading of floors. Consequently, the cost may be kept below that of any other construction of equal quality. It is in the construction of homes that the concrete block is of greatest use, and as the methods of manufacturing and using the blocks are studied in detail the reasons for this will be more clearly seen. 4 CONCRETE BUILDING BLOCKS §36 MANUFACTURE OF CONCRETE BLOCKS CONCRETE BLOCKS IN GENERAL SHAPE OF BLOCKS 5. The accepted shape of the concrete block is such that its exposed surface is a rectangle. The block may extend through the wall, or it may not. In every case, provision is made for an air space in the wall, and the means by which this is accomplished varies widely and is covered by many patents. 6. One-Piece Blocks. —Blocks that extend through a wall are termed one-piece blocks. The outer part is called the face section; the inner part, the back section; and the partitions that unite the face section to the back, the webs , or withes. All such blocks are correctly termed hollow blocks. Fig. 1 shows a gen¬ eral form of a one- piece hollow block. The face section of this block is shown at a; the web, at 6; the hollow spaces, at c\ and the back sec¬ tion at d. The space Fig. i in one block connects with those in succeeding and preceding courses, forming a continuous air space from the top to the bottom of the wall. Of course, different types of one-piece blocks may differ somewhat from this standard. § 30 CONCRETE BUILDING BLOCKS 5 7. In hollow blocks, the number of webs on each block may vary from two to four or more; three is the common number, as it affords two or, as in Fig. 1, three hollow spaces. The fact that this form was the earlier and the more common Fig. 3 has contributed to the general impression that all concrete blocks are hollow blocks, while in many later forms it is not Fig. 4 the block, but the wall, as a result of the arrangement of the blocks, that is hollow. CONCRETE BUILDING BLOCKS 6 8. Two-Piece Blocks. —Blocks in which the face section and back section constitute two separate parts are Fig. 5 known as two-piece blocks. The walls made of these blocks may be spoken of as two-piece walls. These blocks are of a great variety of forms and are often patented. The more common forms are designated as T shape, L shape, and U shape, because their general outlines conform to the shape of these letters. Figs. 2, Fig. 7 3, and 4 illustrate walls made of T-, L-, and U-shaped blocks, respectively. CONCRETE BUILDING BLOCKS 7 § 36 9. Fig. 5 shows a wall that is also made up of U-shaped blocks. These blocks, however, are laid crosswise instead of lengthwise. Fig. 8 The type of block used in the wall shown in Fig. 6 may be considered as an unsymmetrical form of the T-shaped block. In laying two-piece walls, the blocks on the back of the wall break joints with those on the front, so that the only joints extending through the wall are the horizontal ones between the courses. In Fig. 7 is shown a form of block that is a revival, in modi¬ fied form, of a very old style in which two brick-shaped slabs, one forming the face and the other the back, are joined by metal ties a laid in mortar on top of each course. This gives the general effect of a one-piece block, the only difference being a continuous air space throughout the wall, as the trans¬ verse webs are omitted, the metal ties performing their function. 8 CONCRETE BUILDING BLOCKS §36 Another type of two-piece block that produces a continu¬ ous air space is shown in Fig. 8. Each pair of blocks is permanently united by means of four rods a, that are embedded during the forming process. Fig. 9 illustrates a type of two-piece wall in which the face and back portions of the blocks are laid entirely separate, the two halves of the wall being connected by headers a. The wall shown in Fig. 10 is built up of blocks that are triangular in shape. As indicated by the arrows, there is a very free passage of air through the blocks, in both horizontal and vertical directions. SIZE AND WEIGHT OF BLOCKS 10. Size. —The size of a concrete block in respect to the distance from the face section to the back is variable, because the width is regulated by the required thickness of wall. This dimension can be changed by lengthening or shortening the connecting webs. It is customary, however, in wider walls to make some variation in the thickness of the face section and the back, as in this way a larger bearing surface is afforded; in addition, better construction is secured by increased resistance to torsion or unequal expansion in case of excessive heating of one side of the wall. On the other CONCRETE BUILDING BLOCKS 9 §36 hand, the decrease in thickness of face section and the back in narrow walls carrying light weight not only serves to increase the insulation afforded by the interior air space, but also effects some saving of material. The width of walls as customarily specified are as given in Table 1. 1 1. The size of the blocks in respect to the length and height are determined by three factors: (1) Facility in handling and laying; (2) preservation of a unit system; and (3) appearance in the completed wall. Although with the growth of the industry, machinery manufacturers have found it necessary to provide a greater TABLE I WIDTH OF WALDS FOR BUILDINGS OF VARIOUS HEIGHTS (Width of Partitions, 4 to 6 Inches) Kind of Building Width of Walls Inches Base¬ ment First Story Second Story Third Story Fourth Story One story. 12-15 8-10 Two story. I 5~ I 7 10-12 8-10 Three story. 17-20 12-15 10-12 . 8-10 Four story. 20-22 T 5~ x 7 12-15 10-12 8-10 range of adjustability, there yet remains among the many machines offered so wide a difference as to size that no recog¬ nized standard can be said to exist. The general tendency has been to make as large blocks as possible in order to reduce the manufacturing cost per square foot of wall. This practice finally reached a point where the additional labor of handling, hoisting, and laying more than offset the saving in molding, and as blocks came to be used in wider walls and higher buildings this extra expense in handling large blocks became more and more burdensome. Consequently, blocks 30 and 32 inches long are becoming less 10 CONCRETE BUILDING BLOCKS §36 common, and blocks 24, 20, and even 16 inches in length are gaining in favor, often being light enough to be handled by one man. The height, of courses is, or at least should be, determined by adherence to a system of units. For example, in using a block 24 inches in length, courses of 4, 8, or 12 inches will simplify construction and preserve ratios between surface dimensions that are essential to correct building construction. The end to be sought in sizes chosen, so far as appearance is concerned, is geometrical symmetry, and when the pos¬ sibilities afforded by the concrete block are considered, it is deplorable that such variation in sizes has been permitted in many buildings. 12. Weight.—The weight of a concrete block is deter¬ mined by its composition, its size, and its percentage of air space. The composition cannot be varied for the sake of reducing the weight, as that is regulated by more important considerations. The size and proportion of solid matter, however, may be reduced to decrease the weight. Weight is important because of the cost of placing and because of the load on the lower courses and the foundation. A reduction in size, unless it is a reduction in the width of the wall, cannot affect the load, but it does affect the handling cost, while an increased air space affects both. On account of lack of established standards of size, it is difficult to give figures that will apply to the weight of blocks made on dif¬ ferent machines. In general, the aim should be to keep the weight low enough in one-piece blocks so that two men can handle a block on the wall, and in two-piece walls so that one man can handle a block without assistance. When this rule is exceeded, it usually means paying an extra man, who is necessarily idle half his time. § 3G CONCRETE BUILDING BLOCKS 11 AIR SPACE OF BLOCKS 13. The air space in the wall is the indispensable charac¬ teristic of concrete-block construction. It is this air space that renders a building warm in winter and cool in summer; that prevents the passage of moisture through a medium that is frequently more porous than it should be; that pro¬ tects the contents of a building from damage by exterior fire; that deadens a wall against transmission of sound; and that affords that ventilation which makes concrete-block construc¬ tion thoroughly sanitary. The air space is the only part of the block that does not cost anything, and this cost saving was once its strongest recommendation. 14. There has been a great deal of argument about the percentage of air space. In order to provide for the unequal stresses that the front and back of a one-piece block may be subjected to, and to preserve symmetrical proportions between the face section, the back, and the several connecting webs, it is difficult to provide an air space exceeding 33^ per cent. It was found that, assuming all concrete blocks to be made of good concrete, the compressive strength of a block (66§ per cent, of the bearing surface being solid) was more than sufficient. In a wall built of two-piece blocks the air space is not controlled by the proportions of the blocks. Consequently, it is possible in a two-piece wall to give an air space varying according to the width of the wall from a minimum up to as high as 55 per cent. The per¬ centage of air space is often governed by city regulations. An allowance of 33^ per cent, air space has been suggested. 15. In all systems of block construction, the perpendicular spaces are arranged so as to form vertical flues from the bot¬ tom of a wall to its top. They afford, therefore, boundless possibilities for ventilation, as well as convenient receptacles for all sorts of pipe and wiring. ' 12 CONCRETE BUILDING BLOCKS §36 ESSENTIAL QUALITIES OF CONCRETE BLOCKS 16 . Strength. —Strength in a building material is usually of three kinds, namely, compressive , tensile , and transverse. The compressive strength of concrete depends prin¬ cipally on thorough filling of voids, and hence is directly related to density. The compressive strength of concrete blocks varies according to the skill of the individual manu¬ facturer, and in well-made blocks it should average over 2,000 pounds to the square inch of material subjected to pressure. The tensile strength depends on the amount of cement used in the mixture. In average mixtures of concrete, this strength is found to be from one-eighth to one-tenth of the compressive strength. Although concrete blocks will not be subjected to pure tensile stresses, they may be exposed to combined tensile and compressive stresses. This is the case when a block is carrying a heavier load on one end than on the other, generally referred to as eccentric loading. The block may then show compressive stresses at one end and tensile stresses at the other. If the load comes on one or both ends of the block, and these are insufficiently supported while its middle is solidly supported, transverse, or bending, stresses are called into action. If the stresses are maintained up to the point of rupture, it will be found that the upper side has become longer and the lower side shorter. The lower side would be amply safe because of the great resistance of the material to compression, but the upper side is subjected to a tensile stress to which is offered only one-eighth or one-tenth of the resistance that the lower side is offering to compression. Hence, a crack will open in the top of the block and gradually come through unless the stress is relieved. An unreinforced-concrete block should therefore never be laid in such position. When laid truly in a wall, a well-made concrete block will not fail to carry its load, but it must be borne in mind that in direct compres¬ sion lies the strength of the concrete block. § 3G CONCRETE BUILDING BLOCKS 13 17. Density.—Density is a quality that is only indirectly of importance. As already stated, it has a very decided influ¬ ence on the compressive strength. It also affects the per¬ meability of the block. But impermeability to water is not always directly proportional to density. The densest block will not always possess the greatest impermeability, because of certain theoretical considerations in regard to the size of the aggregate; but for practical purposes, density may be considered as closely associated with the power of a block to resist the penetration and transmission of water. Evidently, to obtain the greatest percentage of solids in a block, it is only necessary to fill the voids between the sand and the gravel or other inert material. This is by no means a simple matter, and will in due course be given the attention that it deserves as one of the leading factors in the making of good concrete blocks. 18. Impermeability. — As used in connection with concrete walls, impermeability signifies the resistance offered to the passage of water by capillary attraction. There are three ways in which a wall may be made impermeable: (1) By making a block that will not admit water; (2) by build¬ ing a wall so that there will be no path for water to travel; and (3) by waterproofing the blocks or the wall. To these several methods greater attention will be given later, but here it may be said that one of the most important attributes of a concrete-block wall is its power to produce absolutely waterproof buildings. 19. Durability. — That concrete is the most durable of the world’s structural materials is an authenticated fact. Whether or not as much may be said of concrete blocks depends on how they are made and how they are used. By studying the successes and failures of others, much available data may be collected that will indicate how to make blocks of the highest quality and how to incorporate such blocks into buildings so that they will withstand the ravages of time. Given the factor of intelligent and conscientious manufacture, supplemented by capable superintendence of 14 CONCRETE BUILDING BLOCKS §3G construction, there is no reason why the average concrete- block building should be condemned short of two or three centuries. It is well to draw clearly the line between the bad practice that has characterized much of the concrete-block construction of the past and the more successful methods that have come into use and are destined to inspire greater con¬ fidence toward the industry. It is only necessary to recall the struggle with the cement sidewalk, and the miles of it that disintegrated from defective material or poor workmanship; and yet, to-day the granitoid walk is recognized as the best walk obtainable. The concrete block has had similar dif¬ ficulties to overcome, and eventually it is bound to be the most durable of building materials. 20. Fire Resistance. —The fire-resisting qualities of concrete have been fairly w r ell established, less by laboratory tests than by the practical lessons taught by such catastrophes as the Baltimore fire and the San Francisco earthquake. As is well known, concrete is not only non-combustible, but it is a non-conductor of heat as well. In case of a severe conflagration, its conductivity is still further decreased by dehydration of the outer coating, usually about J inch in an intense fire. There can be no stronger recommendation for the fire resistance of concrete than the prevalent practice of fireproofing structural steel by encasing it in a coating of this material. However, in concrete-block construction an addi¬ tional advantage is afforded by the air chamber in the wall; this air chamber prevents the interior of a wall from becoming superheated by exterior fire. Concrete blocks are freely criticized along this line, their opponents claiming that the expansion of the outer shell under fire exposure will cause the block to break. If blocks are well made, this contention seems more theoretical than practical, and the criticism does not hold good at all in the case of two-piece wails, where the outer and inner sides are not connected by transverse webs. 21 . There have been several cases in which concrete- block buildings have not only passed through fires unharmed, but have saved adjoining buildings from the flames and have §36 CONCRETE BUILDING BLOCKS 15 likewise preserved their own contents from injury. In one case, according to reliable information, the interior of a con¬ crete-block building during the progress of a fire was so cool that the hand could be held against the wall. When a wall is superheated and a stream of water turned on it, it would seem that the sudden contraction of the concrete must cause at least partial disintegration, but the facts do not accord with this theory. A very remarkable case occurred in Nashville, Tennessee, in April, 1907, when the upper portion of the Montgomery Building, a four-story structure filled with furniture, was gutted by fire and the walls in the upper story were heated to incandescence. An examination made the following day by the building inspector and other persons showed that the walls, with the exception of a slight chipping of the window sills and a few of the blocks adjacent to openings, were in perfect condition. This was the more remarkable in view of the fact, that the walls were 16 inches thick and 50 per cent, hollow, except in the upper story where they were 12 inches thick and about 40 per cent, hollow. Before this building was constructed, its site was occupied by a brick building that sustained a fire so badly that it was necessary to tear down the walls. 22. Appearance.—The appearance of a properly designed concrete-block building should surpass that of any other construction of like cost, and yet concrete-block structures have been bitterly criticized—and not without reason— because of their ugliness. The sorry plight of much of the concrete-block architecture is principally due to the following causes: (1) The desire to imitate other materials; (2) the lack of variation in exterior form; (3) the faulty methods of manu¬ facture; and (4) the indifference of architects. 23. The failure to appreciate the possibilities that the concrete block possesses in itself, as well as the desire to imitate the exterior appearance of other building materials, rather than to allow the concrete block to rest upon its intrinsic 16 CONCRETE BUILDING BLOCKS 36 merit, has developed an abnormal style of building that is neither stone nor brick; and while it is in a limited sense con¬ crete, it fails to do justice to the material of which it is com¬ posed. The thought to be grasped is that concrete blocks constitute a distinct class, and their architecture must be developed by due attention to the possibilities offered by the material in hand. Where this idea has been kept in mind the result has been a revelation of symmetry and beauty and a building of characteristic individuality. 24. The selection of a particular style of block, for instance, the prevalent rock face, and the use of similar forms throughout a wall has produced a tiresome sameness of design, offering no relief and presenting no pleasing contrast to the eye. It is scarcely necessary to say that such practice is needless and that it is being rapidly superseded by the intro¬ duction of such varied forms as give to the modern concrete- block building an appearance that will compare favorably with buildings made of more expensive material. It must be understood that the dark, smudgy, porous, or plastered look of many concrete-block walls is merely a matter of ignorance or carelessness in manufacture, and not a thing that should be associated with the concrete block that is rightly made. The fact that architects have.given but little attention to the concrete block as affording a distinct style in construction has made it necessary for concrete-block contractors to rely upon their own resources, and as these have been limited, the results have not been pleasing. This is a matter for which time is the surest remedy, and already the demand for block buildings is drawing to their support, and to the correction of early evils, the skill of some of the most reputable architects. CONCRETE BUILDING BLOCKS 17 §36 FACTORS AFFECTING THE QUALITY OF CONCRETE BLOCKS 25. Composition. —Among the factors that determine whether a concrete block shall be good or bad, the composition of the block naturally appeals as one of the most vital. In the early days of the industry, all blocks were made of fine sand and cement, and this practice is yet common. Such material makes a mortar block, while a concrete block is composed of a fair proportion of gravel or broken stone, with sufficient finer material—either sand or pulverized stone—to fill the spaces between the larger ingredients in a thorough manner and enough cement to bond the whole mass together firmly. There seems to be some misapprehension in regard to the term aggregate. It is well, however, to note that this term properly includes all the material in a block except the cement and water, so that it may with propriety be divided into fine and coarse aggregate. A just appreciation of the relation of fine and coarse materials and the maintenance of uniform and proper proportions between them goes far toward success in block making. It is evident that skimping cement is a prac¬ tice that no wise operator will countenance, as the result is always disastrous, yet there are certain principles of concrete making that effect an enormous saving in cement without loss of quality. 26. Moisture. —The use of the correct amount of water, at the proper time, is a fundamental principle of block making. A mixture too dry to secure the initial set of cement can never give a good block, and it is equally important that the block be constantly, uniformly, and adequately moistened during the curing period that follows its molding. 27. m ixin#.—The thorough mixing of all the ingredients is one of the most essential things in block making. Theo¬ retically, every particle of the aggregate must be cement- coated, and this can only be effected by mixing much more thoroughly than is common. 211—22 18 CONCRETE BUILDING BLOCKS §36 28. Condensation. —After the various ingredients have been well mixed, they are deposited in a mold, and no block can come from the mold strong, dense, and impervious unless it has been condensed to such a degree that air is practically eliminated. The methods of condensation differ, but no matter what method is used, the condensation must be very thorough. 29. Curing.— The forming of the block is only the initial process of its manufacture. The curing period, which follows, is the most critical period in determining the quality of the finished block. The greater emphasis must be placed on cur¬ ing, because it is so easily slighted. There is a common belief that blocks should be allowed to dry out for a week or two after molding. This notion is erroneous. MATERIALS OF MANUFACTURE 30. Cement. —Cement is a very ancient product. Natural cement is produced by burning natural-cement rock as found in various localities. Puzzolan cement is made by grinding together hydrated lime and furnace slag without subsequent burning. Portland cement , as stated in another Section, is made by grinding together definite proportions of material containing lime and clay, then burning the mixture at intense heat, and afterwards grinding the clinker to a very fine powder. The process of manufacturing Portland cement has been brought to great perfection. The materials are selected and propor¬ tioned by chemical analysis, the burning is under constant control, and the grinding is effected by machinery especially designed for the purpose. The rotary kiln and the Griffin mill have been the great factors in the development of the Portland-cement industry in America. Their efficiency has multiplied the number of factories, has reduced the cost of manufacture, and has raised the standard of quality until American Portland cements are today unrivaled in the markets of the world. CONCRETE BUILDING BLOCKS 19 §36 A very recent product is the white Portland cement , which is manufactured at several places in the United States. It is recommended for use in facing blocks because of its lighter color and its waterproofing power. It is an expensive product, however, and is only suitable for special purposes. 31. Sand.—The sand used in concrete blocks should be clean and free from clay or loam. For this reason, river or creek sand is usually preferable to bank sand, although bank sand is sometimes free from foreign matter. If the sand is not clean, it should be washed before using. Sand should pref¬ erably be round and, except for facing, should be fairly coarse. The best sand is hard and not all of one size, but has some grains larger than others. 32. Gravel. —A hard, clean gravel is very desirable in block making. Irregularity in size is an advantage. The gravel will usually be mixed with sand and, provided there is no foreign matter in the natural mixture, it may be used with¬ out screening by adding the required amount of sand or gravel, as the case may be, to secure desired relative proportions between fine and coarse aggregate. If the gravel runs over £ inch in diameter, it will be necessary to screen out the larger sizes, but £ inch sizes can be used in most block molds. It is always an advantage to use as large a size as can be con¬ veniently worked in the mold. 33. Stone. —Broken stone affords a good material for concrete-block work. Limestone is very desirable. Its only fault is that it is liable to disintegrate in fire unless thoroughly coated with cement. The softer sandstones are not so good, because a concrete cannot, in the nature of things, exceed the strength of its aggregate. Granite and trap rock are the best materials obtainable, but in some localities their cost is prohibitive. It has generally been found that there is very little dif¬ ference between the strength of stone and gravel concretes after 6 months or a year, but at shorter periods the stone has the advantage. This is doubtless due to the fact that the 20 CONCRETE BUILDING BLOCKS §36 irregular shape of broken stone offers a somewhat better bonding surface for the cement. 34. Water. —The water used in block manufacture should be clean and especially free from injurious minerals and animal or vegetable matter. Most persons think that any kind of water is good enough for mixing concrete. However, the same care should be given to mixing water as is given to drinking water, and no less care should be given to the water used in sprinkling blocks while curing. 35. Hydrated Dime. —Hydrated lime has been generally recommended for displacing part of the cement in a block. This material is now extensively manufactured, looks like flour, is sold in sacks, and costs about the same as cement. Its recommendation was prompted by a desire to secure greater density and impermeability in the block. Its addition is of greater benefit to a mixture that is poorly graded or low in cement than to one that is rich in cement and so propor¬ tioned as to fine and coarse aggregate that voids are reduced to the minimum. Before employing it, a good plan is to secure a few pounds and note the difference resulting from its incorporation in the mixture. A mixture of 1 part of hydrated lime and 4 parts of cement will be safe, and in some cases beneficial, but reliance must be placed rather on careful proportioning, thorough mixing, and adequate con¬ densation than on the addition of any ingredient to over¬ come the result of neglecting these elementary principles of concrete-block manufacture. 36. Waterproofing Compounds. — Various water¬ proofing compounds are used in the making of concrete blocks, some of which are mixed with cement in the same manner as hydrated lime. These compounds are generally made by a secret process, and their merits can be judged only by results. Some have more worth than others, and the remarks regarding hydrated lime are applicable here, except as to the quantity to be used. This is specified by the manufacturer of each compound. §36 CONCRETE BUILDING BLOCKS 21 37. Salt. —Salt is often added to concrete-block mixtures in freezing weather, 10 per cent, of the weight of the mixing water being generally considered harmless. There are, how¬ ever, other methods of satisfactorily overcoming the dif¬ ficulties attendant upon winter work. 38. Coloring Matter. —If blocks of a particular color are to be produced, it is necessary to color only the face of the block. The more correct way to accomplish this is by the use of an aggregate of the required color. This, however, is sometimes impracticable, in which event resort must be made to coloring matter. Only mineral colors should be used, and even some of these are injurious to the action of the cement. It is good practice to use the colors that are now manufactured for this particular purpose from a base of iron pigment. These colors maybe purchased in the open market. They are backed by reputable manufacturers from whom directions for their use may be obtained. In the use of color¬ ing matter, it is well to remember that the shade will always be lighter in a cured block than in one freshly molded; hence, the color must be made deeper than the one desired in the finished work. MANUFACTURING PROCESSES INSPECTION OF MATERIALS 39. The inspection of materials for concrete-block work comprises the careful selection from available supplies of those best suited to the manufacturer’s needs, and the testing of these materials from time to time to ascertain that there is no falling away from the established standard. The choice between gravel and broken stone often depends on local availability and relative cost. However, the material that is selected must be the best readily at hand in point of strength and freedom from loam, clay, or other foreign mate¬ rial. Due attention must also be paid to its size, and, if neces¬ sary, suitable screening facilities should be provided. 22 CONCRETE BUILDING BLOCKS §30 40 . Selection of Sand. —In the matter of sand for the major portion of the work, care must be taken that the sand is not only clean, but reasonably coarse as well. Of the sand submitted for concrete-block work, it is often unnecessary to do more than throw a little into a glass half full of water and stir for 2 or 3 minutes to prove that there is a percentage of mud that would render it, unless washed, unfit for use. The more expensive grades of sand or marble dust used for facing blocks may, if necessary, be shipped some distance, as the small amount used and the a'dded value of a block with particularly fine finish justify this additional expenditure. These finer grades of sand can be procured from any sand company. 41 . Selection of Cement. —Of the selection of cement a great deal might be written. American Portland cements have generally attained so high a standard that the manu¬ facturer in deciding on a brand may be justified in letting his decision largely be affected by the freight rate from various mills. But, when he has selected a particular brand, he should persevere in its use, unless its quality falls below standard, because changing from one brand to another is liable to cause change of color in the blocks. The difference between raw materials used at the various cement mills and between the proportioning of materials and details of manufacture cause variation in time of setting and in the color of cement. There are very few concrete-block makers that give adequate attention to the testing of cement. Indeed, com¬ paratively few test it at all. It is scarcely to be expected that in the average concrete-block factory such technical tests as provided by the American Society of Civil Engi¬ neers or the American Society for Testing Materials will be employed; yet such tests can be easily made, and besides very little apparatus is required to test the constancy of volume of the cement. The soundness of the cement is also easily tested by making a few flat cakes, or pats, from each ship¬ ment as received, keeping these in moist air for a day, and then immersing some in water, exposing some in moist air, and CONCRETE BUILDING BLOCKS 23 boiling some others. In the case of the specimens in air and water, results are noted at 7, 14, and 28 days. No contractor would hazard the construction of a reinforced-concrete build¬ ing without a cement laboratory, and it would seem that simple tests would raise the standard of block manufacture. PROPORTIONING THE MATERIALS 42 . Proportioning is perhaps the most important, and at the same time the least understood, of the processes involved in concrete-block manufacture. The theory of proportioning the materials contemplates, fundamentally, the elimination of voids by so grading the sizes of material and so regulating the quantity of each size that each will fill the voids between the particles of the next larger size. For example, starting with f-inch gravel, a gallon measure is filled with this material, and then water is added until it is visible at top. If the water is poured from a graduated measure, the volume added is known at once, and it will approximate that of the displaced air. As gravel and sand retain a certain quantity of water after the latter is poured off, it would prevent a thorough mixing of the new material added and an accurate measuring of the voids. A fresh sam¬ ple of gravel and sand should therefore be used for each suc¬ ceeding operation. Next, to the original quantity of f-inch gravel, is added a quantity of the next finer material, say f-inch gravel, equal in volume to that of the estimated volume of voids. The mixing of the two materials is con¬ tinued until the gravel of smaller size occupies the voids of the gravel of larger size. Again a measured quantity of water is added, this time a smaller one. A quantity of finer sand, equal in volume to that of the voids existing at present, is added, mixed as before, and the percentage of voids ascer¬ tained. The latter percentage indicates the amount of cement required to fill the remaining voids. To each of the estimated volumes of gravel and sand 5 per cent, should be added to allow for inaccuracy in testing, but 10 per cent, should be added to the required percentage of cement. 24 CONCRETE BUILDING BLOCKS §36 This method of determining voids is not scientifically accurate, but is recommended because of its simplicity and convenience. It may be checked up in the following man¬ ner: When the relative percentages of different materials have been ascertained, and a quantity of dry aggregate and cement has been thoroughly mixed, fill a vessel full and weigh it. Then vary the mixture by adding more of the fine ingredients or more of the coarse ones, and deposit the same weight of material in the vessel as before. The material of which a given weight occupies the least space will contain the greatest percentage of solid material and the smallest per¬ centage of voids. 43 . At first glance it may appear sufficient to use sand alone in place of graded aggregate to fill the voids. That this is not the case, however, will be seen from the proven fact that the percentage of voids is very nearly the same in any aggregate of uniform size, be it fine or coarse. A block of solid granite has, of course, a greater density than a quantity of granite aggregate occupying the same space, but the aggregate filling this space will approach the former in den¬ sity the more solid material it is made to contain. Let it be supposed that the largest aggregate is 1 inch in size. If the next smaller one is of a size that is just small enough to be conveniently lodged in the voids, and if each succeeding smaller size is chosen as large as the remaining voids will admit, it is clear that in this case there will be more solid material in the mixture than if sand alone is used. It follows, then, that the more carefully the material is screened into different sizes, and the more carefully these are proportioned, the more’nearly perfect will be the mixture. 44 . But not merely in the matter of voids is proportion¬ ing of value. The theory of all concrete work involves the coating of the aggregate with cement, and the bonding of each particle of sand or gravel to the next by means of a film of crystallized cement. If between any two such particles there is no cement, the block will be thereby weakened. If an attempt is made to coat every grain of a straight-sand mix- §36 CONCRETE BUILDING BLOCKS 25 ture with cement, it is evident that a very large quantity of cement will be required. If, on the other hand, a straight- sand mixture with the usual proportion of cement is used, it is impossible to coat every particle with cement, and a weak block will result. If larger aggregate in proper proportion is introduced, then, in the first case, cement will be saved, and in the latter case strength will be gained in the finished block. 45. To one who has grasped this theory of proportioning with respect to either the elimination of voids or to the dis¬ tribution of cement, it must appear impossible to fix arbi¬ trarily a proportion that will be applicable to all the materials available in the many localities where concrete blocks are now made, and in the still greater number of places where they will be manufactured within the next few years. It has generally been customary in the making of blocks of sand and cement to use a l-to-4 mixture. This is usually written 1-4 and means, technically, 1 pound of cement to 4 pounds of sand. However, such a mixture is inaccurately, though almost universally, interpreted to mean 1 sack of cement to 4 cubic feet of sand. The proportions used in making true concrete blocks have not been so arbitrarily fixed. These proportions vary from 1-2-4 to 1-2J-4J, 1-3-4, and l-3^-6J. The last mixture is applicable only in the case of heavy blocks where a large percentage of very coarse aggregate can be used. MIXING THE MATERIALS 46. Mixing by Hand. —The kind of mixing required to make superior concrete blocks involves something more than shoveling for a given period of time and something more than running the ingredients through a mechanical mixer. If the material is to be mixed by hand—and sometimes 0 the exigencies of the small manufacturer demand that it must be so—most careful supervision must be exercised. A thorough turning over is demanded, not a mere hap¬ hazard shoveling. If shovels are to be used, they should be square-pointed rather than round, but many mixers prefer 20 CONCRETE BUILDING BLOCKS §30 hoes, and others use rakes with good effect, claiming for the latter the advantage of separating the material in a manner impossible with shovels, except in a long throw. An expert with a hoe can give to the concrete a motion that not only turns it over, but separates and spreads the particles as well. The only way to secure the desired result in hand work is to use a water-tight platform that is large enough to permit the entire mass to be turned over from its original position into a new pile and then back again. If turning the dry material twice does not bring a uniform color to it, the operation must be repeated before water is added. In adding water, care must be taken not to dash it on in such quantities or with such force as to wash the cement from the aggregate, and after t*he water is added, the turning must be continued until the whole mass becomes homogeneous. Under no circumstances should the batch that is to be wet be of greater volume than can be consumed in 30 minutes, as the average cement takes its initial set within that time, and a block that is to be of good quality must be molded before the initial set. 47 . Mixing by Machinery. —It is desirable that a con¬ crete-block factory be equipped with a power mixer, as a more thorough and more uniform mixture is thus secured, with a saving of labor. In mixing by machinery, the directions sup¬ plied by the manufacturer should be carefully followed. Care should be exercised in the selection of a mixer. Cer¬ tain mixers that operate well on wet concrete are ineffectual when a drier concrete is used. A medium-wet mixture is usually employed for blocks, and a mixer should be selected with reference to this particular service. 48 . The amount of water to use in the mix will depend largely on the type of block machine to be filled. Some machines can handle a much wetter mixture than others. However, the aim should always be to use as wet a mixture as can be conveniently discharged from the mold. Machine mixing should be carefully studied until one knows exactly how much water may be used. CONCRETE BUILDING BLOCKS 27 49. M ixing of Fine Facing. —The mixing of fine facing is a more delicate matter than the mixing of concrete and must be done separately. The operation involves the careful screening of the white sand, marble dust, or other material and the addition of the cement, together with such coloring matter as may be used. All the material should be very thoroughly mixed and then slightly dampened. It is unnecessary to make the face matter as wet as the body of the block, as reliance is had upon surplus water in the block to permeate the face by capillary attraction. An exception to this rule must be made where a waterproofing compound is used. A compound of this kind will not permit the water from the block to penetrate the face, and in that case adequate crystallization cannot ensue unless the face matter has in itself the necessary amount of water. After the face matter has been wet and mixed, it will show a tendency to roll up into little balls owing to the fineness and the richness of the mixture (usually 1-1 to 1-3, the latter preferable because it is not so liable to the formation of crazing cracks). This tendency of the material to form balls must be overcome by again screening the face matter immediately before it is used. DEPOSITING 50. By depositing is meant the process of filling the mold with the materials of wdiich the block is to be made. This process is not so simple as might at first appear, and many of the qualities that the final block is to possess will depend to a great extent on the care displayed during the molding process. The molds may be of three kinds, depending on the position occupied by the face of the block. If the face is formed by the bottom of the mold, it is a face-down mold; if formed by one of the sides of the mold, it is a side-face mold; and if formed by the cover of the mold, it is a face-up mold. The method of depositing the material in the mold will vary somewhat with the kind of mold employed. If a side- face mold is used, the concrete is placed a little at a time, 28 CONCRETE BUILDING BLOCKS §30 filling with some care into the corners and around the cores, and tamping each layer thoroughly so that the bottom of the block will be of like density with the top. If the block is to be faced with a material different from that used in the body, a thin partition is employed and the face matter is placed between the partition and the face plate and the coarse material back of the partition is tamped as the latter is gradually withdrawn. 51. Side-Face Mold. —One type of side-face mold, known as a Miracle block machine , is illustrated in Fig. 11. §36 CONCRETE BUILDING BLOCKS 29 The mold consists of iron end plates a { and a 2 , the face plate b, the back plate c, and the bottom plate d. The end and front of the back plates have pins e v as shown in view (6), that pass through holes e 2 in the bottom plate. Rods k fitted with a nut at one end and a cam-lever i at the other serve to lock the face and back plates together. By turning the cam- levers outwards, these plates may be disengaged and removed. The cores / are bolted to the bottom plate and are made tapering toward the upper end so as to slide easily out of the formed block, or draw , as it is called. In Fig. 11 (a) the mold is shown ready to receive the con¬ crete mixture, which is shoveled in and then tamped down with suitable tamping tools. When the mold is filled, the wooden pallet k, Fig. 11 ( b ) is slid lengthwise over the mold along the flange l, view (a), so as to remove any sur¬ plus material. This pallet is left on top of the mold, and by means of the handles g the mold is turned over so as to occupy the position shown in Fig. 11 ( b ). The bottom plate d may then be lifted, and the cores / withdrawn from the mold. All the side plates may also be removed after unlocking the cam-levers i. After removing the plates the block rests alone on the pallet k and is ready to be transferred to the curing department. On locking the plates together again, the mold is ready for another block. 52. Face-Down Mold. —In Fig. 12 is shown a type of face-down mold known as the Ideal machine. There is a great variety of excellent machines in w'hich the face plate forms the bottom of the mold, but as the operation of all of them is somewhat similar, the one shown will serve as an example. In view (a) the machine is shown in its initial position, ready to receive the material for molding the block; in view (6), the block A is shown formed, ready to be taken to the curing room, technically known as being carried off. Referring to Fig. 12 (a), it will be seen that the mold con¬ sists of end plates a x and a 2 that are hinged to the plate c. The latter plate is connected to a supporting stand q by means 30 CONCRETE BUILDING BLOCKS §36 of hinges and f 2 , while the plate b may be connected to the stand in any suitable manner so as to allow an easy inter¬ change with other plates. It will be noticed that the plate c is backed by another plate c v the latter serving as a support, CONCRETE BUILDING BLOCKS 31 §36 or pallet, for the block when it is transported from the mold while in its plastic state. The end plates a 1 and a 2 are locked to the plate b by means of the cam-levers e x e 2 . 53. The molding is begun by depositing about 2 shovel¬ fuls of the concrete mixture into the mold, using a tamping tool for the purpose of compressing the material If a special face mixture is to be used, a sufficient amount of this mate¬ rial, together with a thin layer of coarse concrete, is first deposited, and thoroughly tamped to insure a bond between the face and the body of the block. The cores o are then moved forwards by pulling forwards on the lever m, which swings around the rod g. One end of each core is sup¬ ported in the openings n 2 n 2 , with the inner end of which they are flush. The other ends have rods k that slide in brackets jj to make them move in line. The cores o are moved in a convenient manner by means of a lever l fast¬ ened to a shaft g. When the latter is turned by the lever m, the cores will move forwards until they project into the openings n x , occupying the positions indicated by the dotted lines, against the stops p. The filling and tamping is now continued until the mold is filled. As the top of the mold represents the back of the finished block, this part of the block is, in general, not given a finished appearance. All that is necessary is to level it with an ordinary wooden float so as to remove all surplus material. The lever m is now pushed backwards so as to withdraw the cores from the block. By swinging the cam-levers e x and e 2 upwards, the mold is released from the plate b, and by using the levers as handles, the mold is swung forwards until it rests on the bracket i and occupies the position indicated in Fig. 12 (6). The doors are then let down, as shown, resting on the curved brackets h, Fig. 12 (a). After the face plate d has been tilted away, the block is free and may be removed on the pallet c. It will be noticed that the block, besides having cavities b 2 and b 2 , has depressions a 4 in the end surfaces. These are formed by the projections a 3 in the end doors a x and a 2 . 32 CONCRETE BUILDING BLOCKS 36 After inserting another pallet c t and swinging the mold into its original position the molding of another block may begin. 54. If a press is used, the entire mold should be filled before pressure is applied. The press is designed to exert sufficient pressure to bring the particles of the mass into intimate contact and to expel the air from the block through numerous vent holes provided in the mold. It is customary in pressure machines to have the face on the top of the mold as it is filled, so that the application of face matter involves only striking out from the top of the mold \ or ^ inch of the coarse material, which is replaced by face matter before pressure is made. There are, however, as has been described, types of machines on the market in wffiich the operation is reversed and the face matter deposited first in the bottom of the mold, in which case the block is discharged with the face on the side. FACING OF CONCRETE BLOCKS 55. As provision must be made for introducing face matter at time of filling the mold, it is well to consider here the general subject of facing. As previously explained, in a face-down machine, the face matter should be deposited first; in a side-face machine, it should be deposited by use of a thin partition, unless the mold is fitted with a tilting device to obviate the use of a partition; and in a face-up machine, it should be deposited last. There has been a great deal of opposition to facing concrete blocks with a finer and richer mixture than that used in the body of the block. This opposi¬ tion has been caused by the belief that it is impossible to put on a face that will not crack, peel, or separate from the body of the block, this apprehension being based on the difficulty of securing an adequate bond between body and face, or on the unequal expansion of the differing mixtures. In practice, the theoretical inequality of expansion has not proved disastrous, and the securing of an adequate bond between the body and the face is merely a matter of method. The essential points of successful facing are two: § 30 CONCRETE BUILDING BLOCKS 33 1. The face and body of the block must be made at the same time. 2. The compression of material must be so thorough that the back of the face and the front of the body of the block will be mashed into each other, so that there will be no distinct line where one joins the other. Thus only may an indestruc¬ tible bond be secured between the two. 56. The advantages of facing are four, namely, better appearance, waterproofing, saving material, and greater strength. The exterior appearance of a block is improved by the use of a liner and richer face, and this face enables the manu¬ facturer to use plates of design that would be impracticable in a mixture of coarse concrete. It also enables him to intro¬ duce into the face matter expensive colors that would make the cost prohibitive if used throughout the block. The advantage of waterproofing is considerable. A block may be rendered nearly waterproof by a mixture of 1-2 or 1-3 cement and fine sand. This is due to the fact that impermeability is determined by the size of openings rather than by the total percentage of voids. The saving of material where blocks must have an exterior of fine texture is enormous, because only £ or £ inch of the finer and more expensive material is required. Greater strength obtains in like cases, for it is impossible, by the use of any quantity of cement, short of that which would bankrupt the block maker, to secure in a block manu¬ factured of fine sand the same strength that is easily obtained in a well-proportioned 1-2-4 or 1-3-5 mixture containing large aggregate. Indeed, a block made entirely of face matter could not be properly called a concrete block. 211—28 34 CONCRETE BUILDING BLOCKS §3(3 COMPRESSING THE MATERIAL 57. Following immediately upon depositing the material, attention must be given to the proper condensation of the material in the mold. To obtain satisfactory strength, density, and impermeability in the block, the various particles in the composition must be .brought into such intimate con¬ tact that the cement will be enabled to perform its office as an adhesive agent, uniting the loose mass into a firm unit. Attention has already been called to the importance of so proportioning the materials that voids will be eliminated as far as possible. This elimination is necessarily imperfect unless adequate care is taken to condense the material in such a way that the air is expelled from it. There are three general methods of securing this condensa¬ tion, namely, lamping , compressing , and pouring. 58. The more common of the methods used in general concrete work is tamping. It was adopted by the early advocates of concrete blocks as the most readily apparent method. Thorough and conscientious tamping will result in ramming the material to place in a satisfactory manner, but it must be observed that tamping should be done in a more industrious and more intelligent manner than is common in many concrete-block factories. There is also difficulty in adapting hand tamping to the use of coarse material mixed wet, which is now generally accepted as better for block work than the dry-sand mixture of the early days. A compara¬ tively dry mixture of cement and sand will pack under the blows of a tamper in a manner impracticable in a wet mixture or in one containing a considerable portion of coarse aggre¬ gate. In the coarse mixture, the blows of the tamper often dislodge adjoining portions of the block, while in a wet mix¬ ture there is always a tendency of the concrete to squash under the blows. To overcome the labor incident to hand tamping and to eliminate the personal factor so disastrous to uniformity, power tampers have been devised by which the quality of the §36 CONCRETE BUILDING BLOCKS 35 product is vastly improved. Of course, the single pneumatic tamper possesses no advantage over a hand tamper except in speed, force, and endurance. To overcome the difficulties attendant upon using the desirable coarse aggregate and the wet mix, a step further is taken by introducing multiple tampers, so that the various parts of the block receive blows almost simultaneously. This is a comparatively new depar¬ ture, but the principle seems to be substantially correct. 59. Compressing. —With the introduction of coarse aggregate and medium-wet mixtures, compressing by means of mechanical and hydraulic presses came into use. The aim of these presses is to overcome the personal equation by providing a machine that will do uniform and effective work. As previously stated, the mold is filled and only one pressure is made on the entire block. The mechanical presses are usually rated to give each block a pressure of 50 tons, which is considered ample for the compression of an ordinary block. Vent holes are provided for the expulsion of air, and these should never be allowed to close. The hydraulic presses commonly used give an ultimate pressure up to 200 tons, but they are slower in action than mechanical presses, because of the time consumed in pumping up the cylinders. This lack of speed in operation is overcome by molding several blocks at one time, as the pressure can be obtained much greater than necessary for a single block. 60. Pouring. — In the condensation method known as pouring, a fluid mixture is poured into molds and allowed to attain a minimum volume by gravity. There are serious objections to pouring, both from a technical and a practical standpoint. As to the former, it is evident that the cement, being heavier, sinks to the bottom and that the block, there¬ fore, is not of uniform strength. As to the latter, the time necessary to leave the block in the mold necessitates tying up a large sum in equipment. The pouring process, however, has its good points,- and it is particularly efficacious in the production of members that are to be especially ornamented. 36 CONCRETE BUILDING BLOCKS §36 These members are usually manufactured either in sand molds or in plaster molds, in which glue negatives are used if there is to be an undercut in the ornamental parts. OFF-BEARING AND CURING 61. Off-Bearing. —The delivery of a block and its off-bearing may seem to be matters that are too trivial to deserve special mention; yet it is in the careless removal from the mold that corners are knocked off, that patches are pulled from the face, and that various irreparable injuries are done to the block. Care and a desire for perfect work, rather than haste in manufacture, are factors that will help to prevent such injuries. But there are two other points that bear vitally on this stage of the manufacturing process. One is the use of a mixture adapted to give best results in the par¬ ticular machine used, and the other is the care of machinery. There are very few plants in which the machinery is carefully cleaned and oiled at the close of the day’s work, and yet these are some of the most essential factors of success. Not much time is required in cleaning and oiling, and if the work is care¬ fully done, a much better and a much larger product will result than if the machinery is neglected. Very many blocks have incipient cracks started while being carried from the machine to the car on which they are to cure. The off-bearer may be careless, but more often he is required to carry a block whose weight, while not heavy in an ordinary sense, is too great to be handled with the care due a freshly made block. The point to bear in mind is the extreme sensitiveness of freshly molded concrete and the necessity of adapting the discharge and handling to this sensitiveness, so that the block will not be deformed in any way before the initial set. 62. Curing. —By curing. is meant more than aging, and something that is entirely different from drying. The curing period is the critical stage of transformation in which a mass of cement, sand, gravel, and water becomes a hard, §36 CONCRETE BUILDING BLOCKS 37 dense, and enduring unit suitable for building purposes. The essential element in curing is moisture, but its applica¬ tion is governed by certain conditions that must be diligently observed. The first condition that the moisture used in curing must comply with is that it shall be sufficient as to quantity. The block must be kept thoroughly wet in order to secure that thorough crystallization essential to ultimate strength. The second condition is uniformity in applying the mois¬ ture. The block must be kept uniformly damp in every part and at all times. This involves sprinkling so frequently that the edges or corners of the block will not become partly dry. No set rule that will govern all conditions of climate and tem¬ perature can be given. The hotter and dryer it is, the more frequent must be the sprinkling. Three times a day should be the minimum. The third condition is that the duration of the curing process shall be sufficient. The sprinkling should begin as early as possible without marring the block. The duration of the sprinkling period depends on the consistency of mix¬ ture used. It should never be less than 1 week, and from that to 2 weeks. After the sprinkling has ceased, the block should be exposed to the atmosphere and allowed to age 1 or 2 weeks longer before going into a building. The fourth condition is that the method of application shall be a suitable one. The water should be sprinkled, preferably by spray from a hose nozzle. In larger plants, the introduc¬ tion of pipes fixed over the blocks will eliminate the expense of a hose tender. The best practice is to cover the blocks with some material that will serve in a measure to retain moisture. Clean hay, straw, or burlap will answer. Any of these materials will add greatly to the maintenance of a uniform condition of moisture in the air immediately sur¬ rounding the blocks. The fifth condition is the provision of climatic protection. The blocks as they come from the mold should be placed on racks or cars and allowed to remain there for 36 or 48 hours, when they will be hard enough to stack. In stacking, no 38 CONCRETE BUILDING BLOCKS §36 block should come in contact with another. This may be arranged by placing lath between them, the idea being to prevent discoloration by contact and to insure a free cir¬ culation of air on all sides of each block. It is absolutely necessary to protect the blocks from both wind and sun during the sprinkling period. In general, the whole idea of curing may be summed up in one word— uniformity. Exposure to wind and sun will ruin the appearance and impair the strength. Consequently, ample curing sheds must be provided to care for blocks until they cease to require sprinkling. 63. The curing of blocks in winter has presented a prob¬ lem so serious that many plants have ceased to operate during cold weather. This, however, is unnecessary. The most simple means of securing a satisfactory cure in winter is by encasing the curing shed with side walls built of blocks and heating it by large stoves. This plan has proved entirely satisfactory. Perhaps the problem of winter work, more than anything else, has prompted the introduction of steam curing rooms, although the practice of the sand-lime brick industry in this regard has undoubtedly had its influence on block makers’ methods. Steam curing differs in some important essentials from the curing process already described. It involves the building of a series of steam rooms, with walls of blocks, floors of concrete, and a roof preferably of the same material. As the blocks come from the mold they are loaded on cars, and each car, when full, is run into a steam room. When the room is full, the doors are not closed, but are allowed to remain open for 24 hours while the steam valve in the room is opened barely enough to moisten the atmosphere by esca¬ ping steam. At the end of 24 hours, the doors are closed and. the carloads of blocks are steamed for 36 hours, exhaust steam being used in the daytime and a low pressure live steam at night. At the end of 36 hours’ steaming, the cars are run into a yard where the blocks are stacked and protected from sun and wind for 48 hours, during which period they are sub- § 36 CONCRETE BUILDING BLOCKS 39 jected to sprinkling. Curing by this method shows results equal to 10 days by sprinkling, and the blocks are consider¬ ably lighter in color. It is apparent that a series of rooms is needed to render the process continuous. Steam curing not only facilitates winter work, but effects a great saving of shed room because of the shorter time required to protect the blocks. This method of curing of course entails some initial expen¬ diture, but it seems to be the method of the future. ARRANGEMENT AND EQUIPMENT OF FACTORY SELECTION OF BLOCK MACHINE 64. In considering the selection and arrangement of equipment for a concrete-block plant, the block machine is generally regarded as not merely the essential feature, but as the only portion of the equipment worthy of study. While admitting the importance of using care in selecting a block machine, it will be shown that other equipment and other considerations also make vitally for success or failure in the plants of the day. 65. In selecting a machine, it is well to analyze the results that it is possible for a machine to effect, to formulate the purposes for which a machine is desired, and to weigh the properties of each particular machine for these purposes. In this way, a machine may be selected that will serve one’s particular purpose more perfectly than can be hoped if a selection is made in a haphazard manner without analysis and comparison. The chief points by which to judge a block machine are as follows: (1) The form of the block; (2) the adjustability as to size; (3) the variation as to shape; (4) the design of the face plates; (5) the facility in filling; (6) the ease of condensa¬ tion ; (7) the adaptability to the use of wet material; (8) the provisions for facing; (9) the perfection of discharge; and (10) the general rapidity. 40 CONCRETE BUILDING BLOCKS §36 It is not the purpose to give a number of illustrations of various machines nor to describe in detail the mechanism or operation of any particular machine, for the reason that such information may be derived from the catalogs of the manufacturers. 66. Form of Block. —First of all, the machine must be selected with reference to the form of block and the style of wall considered best. There are many machines that make the one-piece blocks already described, but the form varies as the machines intro¬ duce one, two, or three interior cores, each of which creates a perpendicular air space. In general, this type is known as the hollow block. The staggered air-space block, shown in Fig. 11, has two rows of air spaces, the air space in one row backing the web in the other and producing the zigzag effect implied by its name. Consequently, no web, or partition, passes directly from the face section to the back, but each takes a roundabout way, the intention being to make more devious the route that the water must travel. The blocks that consist of two slabs united by metal ties go still further by removing the middle portion and using metal rods in its place, thus giving a clear air space in the wall. 67. Adjustability as to Size.—The adjustability as to size is one of the most important items to consider in selecting a block machine. As to the thickness of the wall, this adjustability must cover the range from the thinnest partition wall to a wall as wide as may be required in any building. There must be reasonable adjustment as to the height of courses, in order to secure the pleasing effect of an alternation of wide and narrow courses in a wall, as well as to provide for a course of Unusual height when demanded in building construction. There must also be adjustability as to length of blocks, in order to bring an opening for a window or a door at a particular place. The time has passed when the plan of a house may be changed to fit the blocks. The blocks must be made to fit the plans. §36 CONCRETE BUILDING BLOCKS 41 68. Variation as to Shape. —It must be possible to make wide variation as to shape, involving first the stringer, or main wall, block, then the various fractional blocks, and finally different styles of blocks for the various jambs. There will also have to be made a strong and substantial corner block that will preserve the general plan of bonding the wall. If to these may be added blocks for bay-window angles, as well as blocks for circles, arches, keystones, and the like, it will give the manufacturer a feeling of confidence to undertake con¬ struction that he could not attempt with a machine of limited adjustability. 69. Design of Face Plates. —The design of face plates is a very important consideration, both as to number and quality. Some plates are stamped from metal and others are cast. Cast-metal plates are considered superior to stamped- metal plates, because the lines produced by the latter are indistinct. There is a wide range for selection, and some manufacturers offer a great number of designs. The best practice would seem to be to select plates that display some artistic skill. The rock face has been so popular that often a building has been constructed in which all the blocks present the same design of rock facing. It is clear that to secure any natural effect in rock-face work one must have a considerable variety of plates. The rock face is not only the more common face in general use, but is in greater danger of abuse by the unskilled. The making of an entire building of rock-face blocks should be the exception, rather than the rule. The bevel-edge and tooled-face designs, as well as the perfectly plain, smooth face, present a rich appearance, and, when relieved by a suitable cornice, water-table, and rock-face basement, they give to residences a very handsome exterior. 70. Facility of Filling. —The facility of filling depends largely on the hopper used and on the arrangement of the cores in the mold. A very thin-faced section, or back, or cores very close together will naturally render filling difficult and the operation slower, will require greater care in making and handling the blocks and preclude the possibility of employ- 42 CONCRETE BUILDING BLOCKS §36 ing coarse aggregate. This last consideration is perhaps the most important one in reference to ease of filling. A machine should provide in every section of the mold space sufficient for the working of coarse aggregate without clogging. 71 . Ease of Condensation. —The ease with which con¬ densation may be effected is naturally governed by the process in use; whether tamping, compressing, or pouring. In the case of tamping, if done by hand, the thoroughness of the process depends entirely on the integrity and endurance of the workman. If condensation is attained by compression, it is a matter of adjustment of machinery. In the pouring process it depends on the amount of water used. In the case of any of these methods, it is necessary to see that the machine chosen is perfectly adapted to condense the concrete in an efficient manner. 72 . Adaptability to Use of Wet Material. —In the early days of the concrete-block industry many machines were specially adapted to the use of a dry mix, and in a national convention of a few years ago the advocates of a medium-wet mix were distinctly in the minority. However, conditions are different now, and many concrete-block makers recog¬ nize a necessity of adhering to rules governing concrete construction in general. The danger, therefore, now lies in unscrupulous machinery manufacturers advertising that their machines are adapted to the use of a wet mixture, whereas they may be worked to their greatest capacity only with dry material. The question of the amount of moisture in the mix goes to the very core of the whole subject. It depends on the general process of manufacture and the devices used in connection with filling the mold and dischar¬ ging the material, and is a matter of vital interest bearing directly on the quality of the finished product. In connection with the discharge of blocks, it is necessary to investigate the kind, the cost, and the number of pallets, or bottom plates, on which the blocks are carried away after molding. The pallets vary from pine boards to iron plates, and it is worth while to find out whether one size will answer § 36 CONCRETE BUILDING BLOCKS 43 for all different blocks or whether the particular machine will require several lots of pallets for different sizes of blocks and different widths of walls. 73. Provisions for Facing.— The facility with which a block may be faced is also a matter that should be looked into. As has been noted, there are face-down, face-up, and side-face machines. The latter type is often supplemented by some device for tilting the mold or otherwise rendering facing more easy. The points to be borne in mind in this particular are as follows: (1) The machine should admit of facing without unnecessary loss of time, and (2) it should admit of such methods that an indestructible and absolutely permanent bond will obtain between the body and the face of the block. 74. Perfection of Discharge. — Another point of considerable importance in the selection of a machine is the facility with which the blocks can be withdrawn from the mold. Care must be taken not to buy a machine that is apt to offer difficulties in withdrawing the blocks without breakage. 75. General Rapidity. —Referring to the general rapid¬ ity of manufacture, it is necessary to be able to supply a large demand without using so large a number of machines that the investment renders the business unprofitable. Also, it is necessary to secure from a given number of men an output that will bring profit from their labor and at the same time enable the manufacturer to compete with other building materials common in his locality. The rapidity of a particular machine depends on the mechanical details of operation that have been incorporated into the machine and on the training of the men. The machine selected must be perfect in those almost insignificant labor-saving devices that, in the end, will augment the daily output without any loss of quality in the block. 44 CONCRETE BUILDING BLOCKS §36 SELECTION OF MIXER 76. There are two general types of batch mixer. One agitates the mass by means of interior blades, or deflectors, and the other secures a similar result by the shape of the receptacle in which the material is revolved. The choice between these two types depends on the character of the material used and the consistency of the mix. Both types are being satisfactorily employed in block plants. Continu¬ ous mixers are also often used and if the ingredients are properly fed to the mixer they form an efficient machine. ARRANGEMENT OF MACHINERY 77 . The location of the mixer is a matter of great moment to the block maker. Wherever possible, this machine should be located above the block machine, so that the mixed material can be discharged on a mixture table, from which it can be raked directly into the mold. The location of the mixer in this position naturally involves a still greater elevation of sand, gravel, stone, cement, etc. In the better arranged plants, cement-storage bins are located in the upper part of the building, and a belt conveyer is used to unload the sacked cement from cars. In the upper part of the building also may be located all the screens and other accessories that are brought into use in preparing material for the mixer. The sand, as well as the coarse aggregate, can be brought up as required by an enclosed bucket conveyer located just outside the building and discharging into a chute, which feeds the material to the screens. After leaving the screens the material, with the proper proportion of cement added, is shoveled into a hopper holding one charge for the mixer, and this material, in turn, is controlled by a shut-off operated from below by the man at the mixer. It is contemplated that water will be piped to the mixer from either the city main or a private overhead tank, and that an automatic measuring device will be used to secure a uniform quantity of water in each batch. §36 CONCRETE BUILDING BLOCKS 45 The arrangement just outlined requires a somewhat exten¬ sive building. If such a building cannot be procured, and it is necessary to have all equipment on the same level, the transference of material between the different stages of the process may be accomplished by introducing belt conveyers. It is especially advisable, however, to raise the material from the mixer to the mixture table or the hopper of the block machine in the manner just described, as shoveling the material up by hand is unsatisfactory and expensive. 78. In very small plants, stationary racks serve to hold blocks during the first period of the curing process, but in an establishment designed to turn out large quantities of blocks, it is as essential to have the racks mounted on cars as it is to have a block machine. Steel cars specially designed for the purpose may be procured at reasonable prices. Such cars are usually more satisfactory than cars made of 2-inch lumber mounted on metal trucks. However, such trucks may be procured very cheaply if the manufacturer prefers to build his own cars from lumber. Experience has proved wooden car tracks to be unsatis¬ factory, and a light T rail should therefore be used. The tracks should be arranged systematically, with switches or transfer tables, so that a car when loading may be very close to the machine and may afterwards be pushed to any desired point in the curing shed or steam room. 79. The best appliance for sprinkling blocks is an over¬ head water pipe, with branches extending through the curing shed and equipped with inverted lawn sprinklers at such distances that each car or stack of blocks can be readily sprinkled by turning on the water in a particular branch of the pipe. In this way, the use of the hose can be almost entirely eliminated. Assuming that steam curing is not employed, some provision must be made for a warm room in which to cure blocks in winter, as well as artificial heat in that section of the plant where the machine is located. It is also advantageous to locate the sand bins so that some warmth will reach them. 46 CONCRETE BUILDING BLOCKS §36 In view of the heat required in winter, it is much better to equip a plant with a steam boiler. Lacking steam, however, resort must be made to stoves. These must be looked after / diligently enough to maintain uniform temperature in the curing room during the severest weather. The steam room, however, is the easiest solution of this problem as well as many others. SELECTION OF WORKMEN 80. After the plant equipment has been selected and arranged with a view to securing the best results, there still remains a vital factor to be considered. This factor is the personal intelligence, energy, and integrity of each man employed about the plant, and is one that is sometimes entirely overlooked or underrated in its importance. There must be a foreman who is thoroughly conversant with the uses of cement. On his knowledge depends the constant inspection of material, the proper proportioning of the various ingredients of the block, the consistency of the mix, and the correctness of mixing, manufacturing, and curing. Further than this, the foreman must be a man of such experience in structural work that he can take the architect’s blueprints and make blocks that will fit without cutting or filling. Given such a foreman, the men in each branch of the work will, if of ordinary intelligence and character, rapidly absorb enough of his spirit to do their own part of the work thor¬ oughly well. It is a fatal mistake to employ the cheaper class of ignorant labor in a concrete-block plant because the manu¬ facture of concrete blocks is a business that, in the final summing up, depends on the ability and conscientiousness of the block maker. An entire absence of intelligence cannot be sufficiently overcome by rigid supervision, no matter how effective the latter may be for securing profitable results. A CONCRETE BUILDING BLOCKS (PART 2) DETAILS OF THE USE AND PRODUCTION OF CONCRETE BLOCKS DETAILS OF MAKING AND LAYING FOOTINGS AND FOUNDATIONS 1. The foundation of concrete-block buildings requires as much care in its construction as the foundation of a building of any other material. If the foundation should fail, the blocks would break, developing a crack in the wall. To expect the superstructure to remain intact without adequate attention to the foundation is folly. The rules governing foundations of concrete-block buildings are not essentially different from those governing in any other construction in which walls of equal weight are designed to carry similarly loaded floors. The best practice is to figure the floor load and weight of walls and roof with reference to the resistance of the soil at the bottom of the excavation and to put in concrete footings accordingly. These footings must be of a width that will allow the required factor of safety, and must be thick enough to distribute the load without liability of breaking the footing. Upon this foot¬ ing should be laid a basement wall, or foundation, consisting of blocks. It is unnecessary to make the foundation, or base¬ ment, wall solid, because a hollow wall is especially advan- COPYRIOHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS* HALL. LONDON § 37 CONCRETE BUILDING BLOCKS §37 2 tageous from a sanitary standpoint and may be made amply strong for foundations by employing a width greater than that used for the superstructure. If, in buildings designed to carry heavily loaded floors, the use for which the basement is intended does not permit of bearing partitions, concrete piers should be provided at suitable intervals to support the girders. LAYING AND FITTING OF CONCRETE BLOCKS 2. There is scarcely any danger of placing too great emphasis on the mason’s part in concrete-block construction. The proper placing of concrete blocks in a wall is a factor that determines the ultimate efficiency of this class of construc¬ tion—a factor whose neglect operates to vitiate every good quality of well-made blocks. 3. Mortar Joints. —The first point to be observed in the laying of concrete blocks is uniformity in mortar joints. Very many concrete-block buildings upon close inspection show joints varying from less than \ inch to more than £ inch. Tor such variations there is no valid excuse, and it is a prac¬ tice that is not only detrimental to the strength and durability of a wall, but to the appearance of the building, as well. Machinery manufacturers have found it impracticable to leave the thickness of joints to the judgment of individual masons; therefore, in designing concrete block machines due allowance is commonly made for a constant size of mortar joint. Although this varies in the different makes of machines, f inch seems to be the happy medium, and this thickness is approved as offering a joint sufficiently narrow to afford good construction and pleasing appearance. At the same time, this joint is wide enough to save the mason needless trouble in maintaining it uniformly throughout the wall. Unless a non-staining cement is used, care must be taken not to let any mortar run down on the face of the wall. The pointing as well as the coloring of mortar joints is purely a matter of artistic taste in exterior finish. §37 CONCRETE BUILDING BLOCKS 3 4. Composition of Mortar* —As to the composition of mortar to be used in laying blocks, it is a very serious error to use ordinary lime mortar so commonly employed in bricklaying. A serviceable mortar is composed of 1 part of cement and 3 parts of sand, but as this mixture is some¬ what difficult to work on upright joints, it is now common to add a certain portion of thoroughly slaked lime or of the commercial hydrated lime to the cement mortar. If this plan is adopted, a mortar consisting of 1 part of cement, 1 part of lime, and 3 parts of sand will prove satisfactory. A thoroughly reliable water-proofing compound is a valuable addition to mortar for laying concrete blocks, as it will pre¬ vent rain from penetrating a wall at the mortar joints. Very frequently, the concrete blocks are blamed for collecting moisture when the fault is in the composition of the mortar or the method of laying. 5. Bond. —It is important that there should be a firm bond between the blocks and the mortar. Although the mortar used in a concrete-block wall serves primarily as a bed for the blocks, the intention is that the adhesion between the mortar and the blocks shall be so great that the wall will be almost monolithic. Every person versed in general concrete construction recognizes the difficulty of securing such adhesion between a dry and thoroughly cured stratum of concrete and a layer subsequently deposited. To overcome this difficulty, the blocks should be immersed in water imme¬ diately before laying, so that they will be thoroughly wet when placed in the wall. Otherwise, the dry surface of the block will absorb the water from the mortar and the result will be “dead” mortar in which the cement is only partly crystallized, forming a joint that is weak and easily penetrated by water. 6. Fitting of Blocks. —An important point in con¬ crete-block construction is to use blocks that have been molded to fit in their destined places. The adjustability of the machine or the ingenuity of the foreman in constructing special forms should accomplish this in molding, but if it is 211—24 4 CONCRETE BUILDING BLOCKS 37 not so done, or if there are only a few blocks of a special size required, they can be produced by cutting the freshly made blocks with a large knife. To cut blocks to fit on the job is possible, but it is a practice that should not be followed. It not only wastes blocks and takes too much of the mason’s time, but results in a careless method of filling in pieces that fit more or less perfectly, but never so well as a block made for the place. WALL CONSTRUCTION 7. Width of Walls. —The width of concrete-block walls is often governed by local civic regulations, it being com¬ mon to require the same width as is customary in constructing solid brick walls. If there are no regulations of this kind to follow, it will be safe to use an 8-inch wall for one-story con¬ struction and a 10-inch wall for two-story construction. For a three-story building, the first and second stories should be 12 inches wide and the third 10 inches. For four-story construction, the first and second stories should be 15 inches wide, the third 12 inches, and the fourth 10 inches. The basement walls should, in each case, be from 3 to 5 inches wider than the walls of first story. 8. Supporting of Floor Joists. — The early practice in reference to the placing of floor joists in concrete-block structures was to insert the ends in the wall, supporting them either upon blocks having a face section of extra thickness or upon a metal plate that distributed the load on the under course. The later practice, however, is to employ steel stirrups, or joist hangers, by means of which the joist is hung inside of the wall. An example of a steel stirrup is shown in Fig. 1. The part a hanging inside the wall supports the joist, and the parts h rest on top of the block. This method of sup¬ porting girders is undoubtedly the best, because the wall is relieved from danger in case of failure of floors from over¬ loading or from an interior fire. Some building ordinances require that blocks shall be made solid for several courses underneath the point that bears the joist load. Such blocks, CONCRETE BUILDING BLOCKS 5 however, impair the air space in the wall, and the precaution seems to be an unnecessary one, especially if a metal plate is introduced to distribute the load of the joist. 9 . Fastening of Roof Plates. —For fastening roof plates to the top of concrete walls, Y-shaped pieces of iron, as shown in Fig. 2, are employed. One end of each device is embedded in mortar joints be¬ tween two blocks, and the other end, which is threaded, is passed through the roof plate and secured to it by means of a nut. These devices are made in two lengths and, as shown, are placed so that the strain will not come on a single course of blocks. Fig. 1 10 . Pi lasters.—In any concrete-block construction where the depth of a building exceeds 50 feet and where there are no concrete-block cross-partitions, it is essential to good construction that pilasters, or buttresses, be placed at intervals of 25 to 40 feet. The pilasters not only give lateral strength to the wall, but also provide stiffeners in case of extreme expansion and contraction of a long girder. An example of such walls is shown in Fig. 3, where the building ab f e has long walls a b a^id e f not supported by any cross-partitions. The pilasters c, d, g, and h have been added to strengthen the walls against stresses caused by expansion and con¬ traction of girders extending from the wall a b to the wall e f. The pilasters in ° « this instance are shown on the inside of the building. 6 CONCRETE BUILDING BLOCKS §37 11. Provision for Nailing. —The problem of nailing interior finish, door casings, etc. to concrete-block walls has presented some difficulty and often necessitated the embed¬ ding in the blocks of wooden strips or blocks into which nails or screws might be driven. A more happy and lasting Fig. 3 solution of the problem is the patented metal nailing plug shown in Fig. 4. This comparatively inexpensive device is inserted in the mortar joints as the blocks are laid. 12. Concrete-Block Partitions. —The better practice where fireproof construction is desired demands partitions of concrete blocks. The blocks lend themselves with great readiness to this use, and do not conduct sound so readily as the ordinary partition. The use of block partitions greatly strengthens the entire structure, affording ample bracing of walls and giving great rigidity to floors. BLOCKS FOR SPECIAL USES 13. Blocks for Jambs. Fig. 4 Window and door jambs pre¬ sent a very important part of block construction. The exposed portion of the return at the opening must, of course, have a texture similar to that of the surface of the wall. The various styles of jambs for boxed construction, etc. common in many buildings are provided for in most § 37 CONCRETE BUILDING BLOCKS 7 block machines. It is important that these jamb blocks be especially well made and cured, because they are more liable to severe service than most parts of the building, and in case of an interior fire are directly exposed to the flames. 14. Blocks for Corners. —The cor¬ ner blocks are very important members of a building. As noted elsewhere, their form is determined by the machine selected. Some designs use the stretcher block with the end made flush, as at a , Fig. 5, and others use an L shape with the return half the stretcher length as at a, Fig. 6. The two-piece systems pro¬ vide a special shape for corners. In any system of concrete- block construction, the corner block should be of a shape that will admit of great structural rigidity; and, besides, in manu¬ facturing corners, especial care should be taken to see that each one is as strong and perfect as it is possible to make a block. It is wise to counsel the workmen to disregard speed and to seek absolute perfection in the manufacture of corner blocks. The number used in a building is comparatively small, and the importance of each is relatively great. 15. Blocks for Chimney Flues. Chimney flues are constructed by care¬ fully closing joints in one-piece blocks so that the air cavities will form a perpen¬ dicular, continuous, hollow space that may serve as a flue, except in those cases where the hollow space in the wall does not afford a flue of sufficient size. 8 CONCRETE BUILDING BLOCKS §37 In such cases, it is necessary to use the special chimney block , which is a recognized part of the system of blocks provided in the adjustability of most of the standard makes of machines, and which results in the creation of an interior or an exterior pilaster according to the fancy of the building designer. 16. Blocks for Sills, Lintels, and Ornamental Members. —The making of sills, lintels, caps, coping, steps, belt courses, balustrades, and ornamental work in general is not usually provided for in a concrete-block machine, but the equipment necessary to produce some or all of these members is a necessary adjunct to the thoroughly equipped plant. In the earlier days of the industry, the more plain of these special parts were usually produced in wooden molds constructed at the plant as occasion demanded, while those requiring greater ornamentation were made in plaster molds that were broken to release the undercut, or part of the bottom mold was made of elastic glue to allow the withdrawal of the part of the block that was provided with an undercut ornamentation. In some cases, ornamental work was, and still is, molded in sand. This process is highly satisfactory in the hands of a skilled operator. In molding in sand, there is used a sectional pattern, around which the sand is well tamped, as in iron molding. The pattern is then removed and the concrete, usually of a fine aggregate and made wet enough to run, is poured into the sand mold and allowed to remain for 48 hours or longer, according to the size of the castings. 17. The demand for such members has increased so steadily and the profit in their manufacture and sale has been so satisfactory that there has arisen an active demand for molds in which the work can be produced without the highly skilled labor required in using plaster and glue molds and in casting in sand. To meet this need, several companies have entered the field with a line of iron molds that are simple in construction and operation, and in which the same mixture and methods common in block making produce a satisfactory grade of work. This line of molds is constantly growing, new §37 CONCRETE BUILDING BLOCKS 9 designs being added from month to month, and the pro¬ gressive block maker will not fail to equip his plant with the molds required to meet the demands of his customers. Indeed, a very good business can be done in making orna¬ mental pieces, porch columns, balustrades, lawn vases, etc., independent of general block construction. Such pieces molded in concrete can be produced much cheaper than similar designs in stone, and if well made they will prove to be just about as durable. In the manufacture of sills and lintels, whether made in a mold purchased for the purpose or in one improvised for the particular need, it is well to insert reinforcements in the block near the bottom in case the length exceeds 4 feet. With proper reinforcements, lintels can be made to span any desired opening without noticeable deflection, but an unreinforced lintel with a span of 7 or 8 feet is liable to fail, owing to the load brought upon its center from the walls above. CAUSES OF FAILURES IN THE BLOCK INDUSTRY 18. Although concrete blocks possess the greatest possi¬ bilities of any building material, it is a fact that they-have in many instances fallen far short of the results of which they are capable. There is absolutely no reason for the production of poor blocks, and until good work is done in all concrete- block plants, this building material will not attain the prestige it deserves. One cause of failure in the concrete-block industry is that the manufacture has been regarded as too easy. It has appeared that the mere mixing of sand and cement and the shaping of this mixture into a building block in an iron mold is a process requiring little skill and scant knowledge, while the fact that the product can be sold at a good profit and still come under ruling prices of brick has appealed to very many men who in no wise were fitted for the work. As a result, many plants were started. These plants, however, turned out a product that was unsatisfactory to builders, and in one 10 CONCRETE BUILDING BLOCKS §37 or two seasons caused the block machine to be offered for sale, second hand, or consigned to the scrap heap, while concrete blocks in the community in which the plant was located received a bad name that it might take many years to outlive. Another cause of failure is that there has been too much talk of cheapness in connection with the industry. This talk about the low cost, even below that of frame construction, has taken such a firm hold on the mind of the thoughtless manufacturer that he rushes into contracts without ascertain¬ ing what the blocks really cost. Perhaps he knows the cost of his plain wall blocks, but is unmindful of the added expense incident to special blocks of various shapes required in every building. Under such conditions, a profit is scarcely to be expected, while the temptation is very strong to reduce quality in order to avoid loss. CONCRETE-BLOCK COST AND SPECIFICATIONS COST OF CONCRETE BLOCKS 19. The cost of concrete blocks is an important and prac¬ tical consideration, as no plant is started except with the hope of profit. It was inevitable in the early introduction of concrete-block machines that the low cost of the blocks in comparison with other building materials should be pre¬ sented as one of the chief arguments to those about to engage in the industry. Also, it is unfortunate that the claims made by manufacturers and agents resulted in a widespread belief that concrete blocks were a cheap building material. So eagerly did the public grasp this idea that the block maker, in order to maintain this belief resorted to making blocks cheap at the expense of quality. The results in many cases have been deplorable and sometimes disastrous. But a reaction has come, and the public is now demanding quality, for which it is willing to pay a reasonable price. Persons- that §37 CONCRETE BUILDING BLOCKS 11 have given any study to concrete blocks recognize that their worth places them easily in the lead of building materials, and it is the intrinsic merit of thoroughly good blocks, rather than the low cost of indifferently made blocks, that com¬ mends them to the conservative builder. 20. A careful consideration of cost will give the block maker data by which to calculate the actual cost, for labor and material, of each kind, size, and shape of block that he offers for sale. Few plants have this data so carefully tabu¬ lated that the manufacturer may be sure he is not losing money at some point in the business. It is impossible to give this information in such a form that it will apply to local condi¬ tions. It must be computed at and for each individual plant. The first step is to ascertain the cost per cubic foot of each ingredient used and from these figures compute the cost of each mixture used, being careful to reach the cost of a cubic foot of the mixture at that degree of compression which it attains in the completed block. Then accurate measure¬ ments should be taken to determine the cubical contents of each size and shape of block made, and compute the cost of material it contains. The additional cost of face matter should not be overlooked. To the cost of material must be added the labor cost of each kind of block, figured at the average rate of manufacture. The blocks must also be assessed with cost of curing, power, superintendence, machin¬ ery, repairs, and rent or interest. There are also certain incidentals, such as insurance, advertising, literature, associa¬ tion membership, convention attendance, and the like, that should be charged against the estimated or actual annual out¬ put. Depreciation in machinery is also a very proper charge that is too often disregarded. If all these things are consid¬ ered, it may make the profits appear less, but it will certainly add to the safety of the business. If blocks are sold at the yard, the expense will cease there, but when sold delivered at the building site, hauling must be included. If haulage is done by contract, it should be on a basis of careful handling, with blocks so loaded that they will 12 CONCRETE BUILDING BLOCKS §37 not be defaced. The most convenient method of separating faces in a wagon is by the use of clean straw. If the block maker has teamsters of his own, he will secure greater care in handling blocks, but the cost of transportation may be slightly increased. In very many places, especially when introducing the material, the block maker must also figure on laying the blocks. If this can be done by piece work, a great burden will be taken from his mind, but if it must be done by day labor, he will do well to ascertain from others using the same style of block what results they get from a given number of masons and helpers, and then see that the men he employs come up to the average. 21. As a very rough figure, which varies much with local conditions, the following illustration will serve to show the cost of concrete-block construction: Suppose that the block exposes 2 square feet of surface in the wall, is 8 inches thick, and has an air space of the total volume. The material in this block would be almost 1 cubic foot, and would cost form 6 to 18 cents. The cost of labor varies from 6 to 10^ cents per block. To lay a block in the wall costs from 5 to 10 cents, including mortar. Haulage will cost probably 5 cents. Therefore, the cost per block 8 inches thick set in the wall is as follows: Maximum Cost Minimum Cost Cents Cents Material. 18 6 Labor. 10£ 6 Placing. 10 5 Haulage. 5 None 434 17 These results divided by 2 give the cost per square foot of wall, because each block was assumed to present 2 square feet of surface. §37 CONCRETE BUILDING BLOCKS 13 SPECIFICATIONS 22 . While it is perhaps impossible to submit a set of specifications that may meet the requirements in all cases, the following is an attempt to give certain rules governing the manufacture of concrete blocks, not with any claim to finality or completeness, but rather as a suggestion that may serve as a basis for such standard specifications as may secure safety to the user and justice to the maker of concrete blocks, both in the matter of town and city requirements and in that other really important matter of insurance rates: 23 . Cement. —The cement used shall be a true Portland in the sense in which that term is accepted by the Association of American Portland-Cement Manufacturers. It shall be delivered at the place of manufacture in cloth or paper packages, each containing 1 cubic foot of cement, and each having a net weight of 94 pounds. It shall be kept, until required for use, in good, dry storage. It shall fully meet the requirements of the tests specified by the American Society for Testing Materials. In use, it shall be measured by weight, except that when a sack is taken as the unit it may be considered as 94 pounds. 24 . Sand. —The sand shall be siliceous and clean. It shall include no particles retained on a screen of -|--inch mesh. In the selection of sand, preference shall be given, first, to a sand compri¬ sing graduated sizes of grains, and second, to a coarse sand. The sand shall be free from loam, clay, and vegetable or animal matter. If not free from such foreign matter in its natural state, it shall be washed until the washing water is no longer discolored. 25 . Gravel. —The gravel shall include the particles that will pass through a f-inch ring and be retained on a screen of j-inch mesh. Preference shall be given, first, to gravel graduated in size from fine to coarse; and, second, to gravel that is irregular in shape and of a rough exterior. The gravel shall accord in respect to cleanliness and freedom from foreign matter to the foregoing specification for sand. 26 . Stone .—Crushed granite, trap rock, or limestone may be used, as hereinafter specified, to replace gravel, sand, or both gravel and sand, except that limestone shall not be used in blocks guaranteed against fire. What is commonly known as crusher run shall not be used without rescreening. As a substitute for gravel, the pieces that are retained on a screen of j-inch mesh and pass a f-inch ring may be used. As a substitute for sand, the particles that pass a screen CONCRETE BUILDING BLOCKS 14 §37 of -^--inch mesh may be used, and such particles shall be known as screenings. 27 . Proportions. —In a block the largest aggregate of which passes a screen of ^-inch mesh, the minimum proportion shall be 1 part of cement to 4 parts of sand or stone screenings, and such propor¬ tions shall be by weight. In a block the largest aggregate of which is retained on a screen of -^-inch mesh, the minimum proportion of cement shall be 1 part of cement to 7 parts of mixed aggregate, and said 7 parts of aggregate may vary in proportioning from 2 parts of sand or screenings and 5 parts of gravel or stone to 3 parts of sand or screenings and 4 parts of gravel or stone, and said proportions shall be by weight. The proportioning shall in every case be based on deter¬ mination of voids, either by specific gravity, by relative volume, or by water test. If the last method is used, it shall be subject to check by the preceding. The proportion of sand shall in every case exceed the determined voids in the gravel or stone by at least 5 per cent., and the proportion of cement shall in every case exceed the deter¬ mined voids in the combined aggregate by at least 10 per cent. 28 . Coloring Matter. —All coloring matter other than colored stone or screenings shall be a pure mineral color and shall be mixed dry with the cement before being added to the aggregate. 29 . Mixing .—If mixing is done by hand, it shall be upon a water-tight platform on which the gravel or stone shall first be spread, the sand or screenings spread thereon, and the cement spread on top of the sand or screenings. Before water is added, the mass shall be turned twice, or until of a uniform color. Water shall then be added by spray or by gently pouring into a crater formed of the dry material. The mass shall then be turned three times, or until of uniform con¬ sistency. If mixing is done mechanically, the dry aggregate and cement shall first be placed in the mixer and well mixed before water is added, and when water is added, the mixing shall continue as long as necessary to secure homogenity in the mass. All material to which cement has been added shall be used within 30 minutes from the time water is added. 30. Consistency. —For the purposes of these specifications there shall be three grades of consistency of concrete, as follows: 1. Dry concrete, by which is meant a mixture that on being pressed in the hand retains its shape but does not discolor the hand, shall never be used for the body of the block. 2. Medium concrete, by which is meant a mixture from which, when thoroughly tamped or pressed, free water will flush to the surface, shall be used for the body of all tamped or pressed blocks. §37 CONCRETE BUILDING BLOCKS 15 3. Wet concrete , by which is meant a mixture that can be readily poured from a bucket into a mold, shall be used in all processes where the block or other member is subjected to neither tamping nor pressure, but* acquires the form of the mold by its own settlement and attains rigidity by remaining therein. 31. Condensation. —Condensation may be effected by tamp¬ ing, pressing, or pouring. 1. The material may be condensed in the mold by hand or power tamping. In either case, the material shall be deposited in layers of such depth that the full force of the tamping blow is exerted on every portion of the block, and the tamping shall be so regulated that the density shall be uniform in every part of the block and relatively equal in each block. 2. The material may be condensed in the mold by mechanical or by hydraulic pressure. In either case, the mold shall be filled and the entire block compressed at one time by a minimum pressure of 350 pounds to the square inch of the face surface of the block. 3. The material may be condensed by its own settlement in a mold of metal or of sand. In either case, the material shall be mixed so wet that it is easily poured into the mold and readily acquires the form thereof, and it shall remain therein until it gains sufficient rigidity to maintain its shape without support. 32. Facing. —If a block is faced with a mixture other than that used for the body of the block, the aggregate for the face matter shall be of fine sand, fine stone screenings, marble dust, or other suit¬ able material mixed with the cement in proportions that may vary from 1 part of cement and 1 part of aggregate to 1 part of cement and 3 parts of aggregate. Note.—E ither 1-2^ or 1-3 is recommended as possessing less liability to hair cracks than a richer mixture. In no case shall the face be troweled either before or after molding. Coloring matter may be added as specified in Art. 28. Face matter shall be mixed in consistency of dry concrete, as speci¬ fied in Art. 30. After moistening, the face matter shall have all lumps broken up by rescreening immediately before using. The face matter shall be deposited from a sieve or by loosely shaking it from a shovel, so that it will maintain its loose form until deposited in the mold. The method of condensing the material in the mold shall bear such relation to the face matter that the face will become firmly joined to the body of the block, so that it can be removed only by the destruc¬ tion of the block. 10 CONCRETE BUILDING BLOCKS § 37 33. Curing. —The minimum age of blocks at time of placing in wall shall be 3 weeks. Curing may be by water or by steam. 1. Water Curing .—Sprinkling shall begin as early as possible without defacement—under average conditions 12 hours after mold¬ ing—and shall continue at such intervals as necessary to maintain a thorough and uniform degree of moisture for from 7 to 10 days, during which period the block shall not be exposed to sun, wind, or violent change of temperature. 2 Steam Curing .—The blocks shall be kept in moist air for 24 hours after molding, when they shall be placed in a tightly closed room into which exhaust steam or live steam of low pressure is turned, remaining in said steam room for 36 hours, after which they shall be sprinkled and protected from sun and wind for a further period of 48 hours. 34. Taying. —Blocks shall be thoroughly moistened before laying in the wall, and shall be laid in a mortar consisting of 1 part of cement to 3 parts of sand, or 1 part of cement, 1 part of thoroughly slaked and pulverized lime, and 3 parts of sand. The mortar joints shall be of uniform thickness, not exceeding f-inch 35. Ail* Space. —The air space in the wall shall be governed by the type of block and the thickness of wall, but the minimum thick¬ ness of face section, back, and transverse webs shall in every case be 2 inches. 36. Width of Walls. —The width of walls, in inches, for the several heights of buildings, and for the several stories thereof, shall be as follows: First Second Third Fourth Story Story Story Story One-story buildings. . 8 Two-story buildings. . 10 10 Three-story buildings. . 12 12 10 Four-story buildings. . 15 15 12 10 37. Testing .—Blocks for testing shall be selected at random from those commercially manufactured or delivered at building site. The minimum compressive strength of any block shall be 1,600 pounds per square inch of solid material subjected to pressure in the testing machine, and the average compressive strength of any series of blocks tested shall not be less than 1,800 pounds to the square inch of such solid material. Blocks shall also be subjected to such tensile, fire, freezing, and absorption tests as may be required by the supervising engineer. 38. Identification. —Each block shall be marked with the initials of the manufacturer thereof and the date of molding. §37 CONCRETE BUILDING BLOCKS 17 39. Certificate. — Each manufacturer of blocks shall post in a conspicuous position at his place of business a certified test,of blocks actually manufactured by him in regular course of business, which certificate shall show: (1) The size, number, age and composi¬ tion of blocks tested; (2) the compressive strength of each block tested, and the average result of the.series tested for compression; and (3) the results, in like manner, of such other tests as may be required by the building department of the town or city in which the blocks are offered for sale. I . 4 *■» HEAVY FOUNDATIONS SPREAD FOOTINGS SINGLE FOOTINGS INTRODUCTION 1. The term spread footings is applied to the class of foundations illustrated in Figs. 1 and 2. Foundations of this Fig. 1 kind are best adapted for the substructure of high buildings that are to be erected on soil of a clayey nature, and are i COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS' HALL. LONDON § 38 211—25 2 HEAVY FOUNDATIONS §38 especially necessary where the foundation stratum is of soft clay underlaid with quicksand and the bed rock is so far below the foundation bottom as to preclude the possibility of driving piles to a bearing on it. Spread footings may also be used to advantage on any soil where it is necessary to distribute the load over a considerable area. With such a soil, there are many details that require careful attention and study and involve the incorporation of several features new to the usual stepped masonry foundations. Tall buildings of the skeleton-construction type concentrate great loads on the basement columns; these, in turn, must be supported by footings of considerable area. As the exterior columns in this type of building support the out¬ side, or curtain, walls, they are more heavily loaded than the interior columns; and since some settlement is sure to occur, it is desirable that this settlement be uniform. The simplest way to attain uniformity in settlement is to provide a sepa¬ rate footing for each column or set of columns that acts in unison, the entire building being in this way supported on isolated footings that are accurately proportioned for the loads they must sustain. If, as shown in Fig. 3 (a), (a) 6 5-7- - J ^ - 13-5 4 HEAVY FOUNDATIONS §38 these footings were of the usual masonry type and had the proper proportions and batter for this material, they would be of great depth and of such dimensions as to lessen consider¬ ably the floor space in the basement of the building. This amount of masonry would add greatly to the unit weight on the soil and would form a considerable percentage of the entire load. 2. A recapitulation of the requirements that lead to the adoption of spread footings may be stated as follows: 1. That sufficient bearing may be obtained for the great loads requiring support in the modern tall building resting on a plastic or an unstable soil. 2. That the foundation and footing may be so shallow as not to penetrate the stratum of clay and impair its bearing value when underlaid with quicksand. 3. That no foundation piers of great bulk occupy space in the basement that may be used for engine rooms or even bring in a good rental as cafes or shops. 4. That the weight of the foundation shall be so small a percentage of the entire load on the column it sustains that a considerable portion of the footing area will not be taken up in carrying the weight of the foundation. 5. That the cost of the foundation shall not greatly exceed the cost of the usual stepped footings or foundation piers of masonry. The second and third requirements are of considerable importance, and by referring to Fig. 3, the advantages that the spread footing possesses over the ordinary masonry footing will be evident, especially with regard to space saved in the basement and the depth required for the respective constructions. In (a) is shown the ordinary masonry pier with a concrete footing, while in ( b ) is illustrated a spread footing designed for the same load and conditions of soil. By comparing these views, it will be observed that a depth of nearly 8 feet is saved by the use of the spread footing. 3. Spread footings may be classified as steel-beam gril¬ lage and reinforced-concrete foundations. These two methods § 3S HEAVY FOUNDATIONS of construction are shown in Figs. 1 and 2, respectively. They both produce the same results, namely, a shallow footing that has a large bearing area on the soil and that possesses sufficient transverse strength to transmit a great pressure from the comparatively small area of the column base to the large area of the foundation footing. In the steel-beam grillage foundation, the transverse strength is supplied by the resistance offered by the steel beams to bending, while in the reinforced-concrete footing the necessary transverse resistance is provided by embedding a network of steel tension bars in the lower portion of the concrete, as shown at a, Fig. 2. Reinforced-concrete spread footings are discussed at length in another Section. STEEL-BEAM GRILLAGE 4. The beams originally employed in the construction of grillage footings were steel rails crossed in alternate layers. Undoubtedly, they were used on account of being readily obtainable. The top layer of steel beams, that is, those directly under the cast-iron base, usually have as much projection as any of the under layers, and being fewer in number, are required to offer greater resistance to bending; therefore, in most cases, steel I beams with a section modulus greater than steel rails were used in this position. Now that rolled structural shapes are obtained with facility, it is more economical to use I beams throughout the footing, where its height is not closely limited, as their weight is less for a given section modulus than steel rails. Another advan¬ tage exists in the fact that I beams may be readily secured together with bolts and separators. If the soil is soft and plastic and the load heavy, a large area of footing will be required. To obtain this area, three or more tiers of beams are required, and each tier must be of larger area than the one that rests on it. If the load is light and the soil is of a more stable character, two tiers of beams will usually be sufficient. Grillage foundations are either square or rectangular, depending on their location 6 HEAVY FOUNDATIONS §38 in the footing area. For the support of a single column, square foundations are preferable and more economical. Rectangular footings are used where the space available is narrow and the necessary area must be provided by lengthen¬ ing the footing. 5. The usual design for a heavy grillage footing is shown in Fig. 4. It is necessary to provide first a bed of concrete a from 12 to 18 inches in thickness. This concrete should be tamped in two or three successive layers and should be com¬ posed of 1 part of Portland cement, 2 parts of sand, and 5 parts of broken stone. On this concrete bed, after it has obtained its initial set, the first layer of I beams is placed, the spaces between the beams being solidly tamped with concrete. The beams in each tier are firmly secured to each other by means of separators and bolts. The separators may be of either cast iron or pressed steel; pipe separators should not be used. They should be placed not more than 6 inches from each end of the beam, and one should be placed under each of the outside beams in the tier above. Other separators should be introduced throughout the length of the tier, so that the distance between separators will in no case exceed 5 feet. On the first tier of beams, the second layer of steel beams is crossed; and after these have been filled in with concrete, the third layer is placed in position and embedded in con- §38 HEAVY FOUNDATIONS 7 Crete. The concrete in all cases is placed on the tops, sides, and ends of the steel beams to a depth of from 4 to 6 inches, so that the entire steelwork is completely embedded. Before the steel beams are placed in position, they should be thor¬ oughly painted with several coats of some good preservative paint, thus protecting the steel from corrosion until the initial set of the concrete takes place. When this precaution is adopted, the steel will last indefinitely, provided the concrete contains sufficient cement. In placing the steel beams, they should never be spaced closer than 3 inches in the clear between the flanges, so that the concrete may be thoroughly rammed between them. DESIGN OF SINGLE FOOTINGS 6. In designing steel-beam grillage foundations intended to support columns, it is first necessary to ascertain the column load that is to be transmitted to the footing. It is also necessary to determine the area required for the footing in order that the allowable unit pressure on the soil may not be exceeded. When the area of the footing, and consequently its dimensions, has been determined, the lengths of the steel beams will be known. However, the number of beams required, as well as their size and their weight, must be ascertained by calculation. The steel beams that provide the necessary transverse strength for the footings are subject to failure by the crush¬ ing or buckling of the web or by bending. Since the webs of the beams are secured together at close intervals by separators and bolts, and since concrete is thoroughly tamped between the beams, there is little liability of the webs bulging or crippling, so that the beams may be considered safe from failure if the unit stress on the web due to direct compression does not exceed 10,000 pounds. Some engineers consider the web of the beam as a column and thus determine the allowable unit compressive stress. When column for¬ mulas are applied in this manner to determine the resistance of the web to bulging, the height of the web is considered as HEAVY FOUNDATIONS 8 §38 the length of the column and should be taken as the distance between the fillets. The proper method of determining the bending moment to which the steel beams in the grillage foundation are subjected has been a matter of some dispute among engineers. Some engineers consider the projecting portion of the beam—that is, the length beyond the edge of the cap or the successive layer above—as a cantilever, while others recommend as better practice that the entire length of the beam be considered and •Loac/ o/r Co/umn=w the bending moments cal¬ culated accordingly. It is doubtful whether either method gives the true value of the transverse strength of the successive tiers of the footing, for the beams are necessarily reinforced by the concrete. By disre¬ garding the concrete, how¬ ever, the problem becomes greatly simplified and any error is on the side of safety. The formulas for determining the bending moment on the steel beams in a grillage foun¬ dation may be derived as pages. ■*— V--C • 3HEE: (v H'T x -I- V 1.11 11 l ill I 11 1 LL.I1 J 1’3 !1 II III D s - 1 - V y-n-TTTr LiiJLLE xn XT EX h d b I I i i i. XT I_ Fig. 5 explained in the following 7. In Fig. 5 is shown the plan and elevation of a grillage footing. The area has been determined for the stability of the soil and the magnitude of the superimposed load, and the dimensions of the sides thus obtained. The superimposed load transmitted to the footing through the column may be designated as W. The dimensions of the cast-iron base plate are practically fixed by the design of the column; at any rate, they may be originally assumed, and reduced or HEAVY FOUNDATIONS 9 §38 increased as conditions warrant. It is therefore considered that the distances y and x in the plan are found, so that the length for the top tier of beams is equal to x + y + y = x + 2y. The load on these beams, since they transmit the entire weight on the column, is equal to W, and the load on each unit of length of the tier is, in consequence, equal to W The steel beams in the first tier, being considered x + 2 y as cantilevers with a projection equal to y and having a center of moments about the line a b, sustain the uniformly distributed load acting upwards from beneath, equal to the load per unit of length of the tier multiplied by the distance y, Wy or, as it may be stated, The center of gravity of x + 2 y this uniformly distributed load is along the line c d, the dis- y tance .of c d from a b being therefore, the bending moment • 2 of all the beams in the top tier is equal to the moment of the uniformly distributed load on the projecting portion of the tier between the edge of the cast-iron base and the ends of the beams, or, algebraically expressed, Wf M = 2 (x + 2 y) It is customary to take all the lengths in inches and the weight in pounds; then, the bending moment M will be in inch-pounds. This formula, based on the assumption that the steel beams are cantilevers, may be stated as in the following rule: Rule. —The bending moment on the beams in any tier is equal to the quotient obtained by dividing the product of the load on the footing and the square of the distance that the beams project beyond the base or the tier of beams above , by twice the sum obtained by adding the width of the tier or base above and twice the projection. 8. The resisting moment in any steel beam must equal the bending moment; hence, M = and M t = S s, where 5 10 HEAVY FOUNDATIONS §38 equals the section modulus of the beam section, and 5 the unit fiber stress. When the bending moment has been determined and the number of beams in the tier decided on, the required section modulus for each beam may be obtained by the formula s n in which M t = resisting moment; s = allowable unit fiber stress; n = number of steel beams in tier. This formula may be expressed as follows: Rule.— The section modulus required for each steel beam in a grillage footing is determined by dividing the resisting moment necessary for the entire tier by the product of the safe unit fiber stress and the number of beams. On obtaining the necessary section modulus for each of the steel beams in this manner, the most economical beam §38 HEAVY FOUNDATIONS 11 section may be determined from tables giving properties of sections. Instead of assuming the number of beams in the tier and using formula 1 to find the required section modulus, the size of the beam can be decided on and the number required obtained by transposing the formula thus, n = M, s S If the beams determined in this manner are too great in number to be placed under the cast-iron cap and allow at least 3 inches between the flanges, either the cap must be increased in width or deeper and heavier beams must be adopted. After the first tier of beams has been designed and the size of the beams determined by formula 1, the size of the beams for the second tier, and the other tiers beneath, may be computed. Example. —In Fig. 6, it is assumed that the dimensions of the foot¬ ings are as shown and that the number of beams in each tier and the dimensions of the cast-iron base have been designed as shown on the plan. What should be the size of the steel beams in each tier in order to provide ample support for the load of 400,000 pounds, using a safe unit fiber stress of 15,000 pounds? Solution.— The bending moment on the upper tier of beams a is, Wy 2 by the formula of Art. 7, equal to M, or-. According to y H 2(x + 2 y) the conditions of the problem and the dimensions given in the figure, W = 400,000 lb., y = 5 6 in., and x = 30 in. Then, by substitution, 400,000X56X56 . „ „ r _ 4 M =-= 4,416,901 in.-lb. From formula 1, Art. 8, the 2(30 + 2X56) „ M, required section modulus is equal to S — —. Since M.=M, the 5 n value of Mj in the problem equals the result just obtained, or 4,416,901 in.-lb.; s taken at 15,000 lb. gives a factor of safety of at least 4, which is ample, and n , the number of beams taken from the figure, equals 6, so that by substituting these values in the formula, 4,416,901 S =— ---= 49.08, wdiich is the section modulus required for each 15,000X6 M beam of the first tier. From tables giving the properties of sections, the most economical I beam will be found to be one having a depth of 15 in. and a weight of 42 lb. per ft. By substituting in the formula 12 HEAVY FOUNDATIONS §38 of Art. 7 , the bending moment on the beams b in the second tier is 400,000X36X36 equal to M — ----— = 2,107,317 in.-lb. Then, since M , has 2(51 + 2 + 36) 1 been determined and the safe unit fiber stress is 15,000 lb., and there are fourteen beams, the value of 5, from formula 1, Art. 8, is equal to 2 107 317 —----=10.035. From the tables, it will be observed that 15,000X14 beams having a depth of 7 in. and weighing 15 lb. per ft. may be used in the bottom tier. Ans. 9. The other method of determining the transverse resistance of the steel beams in the grillage foundation is more reasonable than the one just explained and is therefore preferable. In this method, the entire length of the beam is considered in calculating the bending moment, and the loads on the beams are taken as they actually exist. For instance, in Fig. 7 is shown a steel-beam grillage, in elevation, composed of three tiers of beams. In analyzing the bending moment on the lower tier a, it will jfr be seen that the total load from the column acting on the top of the beams in this lower tier is distributed over only a portion of the length of each of these beams equal to c b, while the reactions acting upwards from the bottom of the tier, in oppo¬ sition to the weight from the column, are distributed over the entire length equal to e /, the entire reaction being, of course, equal to the load W. The condition of loading that then HEAVY FOUNDATIONS 13 $ 38 exists on the beams is diagrammatically shown in Fig. 8, in which the total load on the top of the beams is equal in amount to the total force acting upwards from the bottom. The greatest bending moment under such a condition of load¬ ing does not actually occur at the edge of the first tier of beams g, as explained in Art. 7, but exists at the center c of each of the beams, Fig. 8. Then, considering the point c as the center of moments, the bending moment at that point will be equal to the difference between the moment of the force acting upwards and that of the load on the beam acting downwards, and is determined according to the principle of moments. The lever arm of the upward force, or the reaction, is l x equal to - and that of the downward force is equal to -, or 4 4 the distances from the center of moments to the centers of gravity of one-half the respective loads. The positive W l Wl moment is equal to —X- =- and the negative moment 2 4 8' 14 HEAVY FOUNDATIONS §38 , 4 W k/ x Wx is equal to — X- =-; 2 4 8 then the bending moment M equals Wl Wx 8 8 or W M=—(l-x) 8 The method of obtaining the bending moment as explained by this formula may be stated as follows: Rule.— The bending moment on any tier of steel beams in the grillage footing is equal to one-eighth of the entire weight on the column multiplied by the difference between the length of the steel beams considered and the width of the steel-beam grillage , or the cast-iron base above. Example. —According to the formula, what size beams will be required in the steel-beam grillage footing shown in Fig. 9, considering a safe unit fiber stress of 15,000 pounds, provided the load, as in the previous example, is equal to 400,000 pounds? Solution. —In the upper tier of beams, the distance l in this case is equal to their length, or 142 in., while the distance x is equal to the width of the base plate, or 30 in. By substituting these values, together with the total load W, or 400,000 lb., in the formula, 400,000 M = —-— X (142 — 30) = 5,600,000 in.-lb. The bending moment on 8 the beams in the second tier, by the same formula, is equal to 400,000 M— -X (123 — 51) = 3,600,000 in.-lb. The section modulus for 8 each beam may then be determined by applying formula 1, Art. 8, or M S =—. On substituting the respective values in this formula, the s n section modulus for the upper tier is equal to while for the lower tier the section modulus equals 5,600,000 15,000X6 3,600,000 15,000 X 14 62.22, 17.14. From a table of the properties of beam sections, a 15-in. I beam weigh¬ ing 50 lb. will be found most economical for the upper tier, while for the lower tier a 9-in. I beam weighing 211 lb. is suitable. Ans. It will be observed that by this method of calculation heavier beams are required, and the formula consequently TABLE I SAFE LOAD ON ONE BEAM, IN TONS OF 3,000 POUNDS Beam Unloaded Length of Beam, l—x, in Inches Depth in Inches Weight in Pounds per Foot 36 48 60 4 72 84 96 108 120 132 144 156 168 180 24 IOO I5I.I 132.2 H7-5 105-7 96.1 88.1 81.3 75-5 70-5 24 95 146.6 128.3 114.0 102.6 93-3 85.5 78.9 73-3 68.4 24 90 142.I 124.3 no.5 99-5 90.4 82.9 76.5 71.1 66.3 24 85 137-7 120.4 107.1 96.4 87.6 80.3 74-i 68.8 64 2 24 80 132.5 H5-9 103.1 92.6 84.3 77-3 71-3 66.3 61.8 20 75 112.8 96.9 84.6 75-2 67.7 61.4 56.4 52.1 48.3 45-1 20 70 108.4 93-0 81.3 72.3 65.1 59-2 54-2 50.1 46.5 43-4 20 65 104.0 89.1 78.0 69.3 62.4 56.7 52.0 48.0 44.6 41.6 18 70 109.2 91.0 78.0 68.3 60.7 54-6 49-7 45-5 42.0 39-o 36.4 18 65 104.4 87.0 74.6 65-3 58.0 52.2 47-5 43-5 40.2 37-3 34-8 18 60 99-7 83.1 71.2 62.3 55-4 49-9 45-3 41.6 38.4 35-6 33-2 18 55 94-3 78.6 67.4 58.9 52-4 47.1 42.9 39-3 36.3 33-7 31-4 15 60 95-7 76.7 63.8 54-7 47-9 42.6 38.3 34-8 3i-9 29-5 27.4 25-5 15 55 90.8 72.6 60.5 51-9 45-4 40.4 36.3 33-2 30.3 27-9 25-9 24.2 15 50 86.0 68.8 57-3 49-1 43-0 38.2 34-4 31-3 28.7 26.5 24.6 22.9 IS 45 81.1 64.9 54-o 46.3 40.5 36.0 32-4 29-5 27.0 24.9 23.2 21.6 IS 42 78.5 62.8 52.4 44.9 39-3 34-9 31-4 28.6 26.2 24.2 22.4 20.9 12 40 72.9 54-7 43-7 36.4 31-2 27-3 24-3 21.9 19.9 18.2 16.8 15-6 14.6 12 35 67.6 50.7 40.5 33-8 29.0 25-3 22.5 20.2 18.4 16.9 15-6 14.5 13-5 12 3ii 64.0 48.0 38.4 32.0 27.4 24.0 21.3 I9.2 17.4 16.0 14.8 13-7 12.8 IO 40 56.4 42.3 33-8 28.2 24.2 21.1 18.8 16.9 15-4 I4-I 130 12.1 II-3 IO 35 52.1 39-1 31.3 26.0 22.3 19-5 17.4 156 14.2 13-0 12.0 II.2 10.4 IO 30 47.6 35-7 28.6 238 20.4 17.9 15-9 M-3 130 11.9 II.O 10.2 9-5 IO 25 43-4 32.5 26.0 21.7 18.6 16.3 M-5 13-0 11.8 10.8 10.1 9-3 8-7 9 35 44-1 33-1 26.5 22.0 18.9 16.5 14-7 13.2 12.0 II.O 10.2 9-5 8.8 9 30 40.2 30.1 24.1 20.1 17.2 IS-1 13-4 12.1 II.O 10.0 9-3 8.6 8.0 9 25 36.3 27.2 21.8 1S.1 15-5 13-6 12.1 IO.9 9.9 9.1 8,4 7-8 7-3 9 21* 33-6 25.2 20.2 16.8 14.4 12.6 n.2 10.1 9.2 8.4 7-8 7.2 6.7 8 25* 30.2 22.7 18.1 151 13.0 H.3 10.1 9.1 8.2 7.6 7.0 6-5 6.0 8 22I 28.4 213 17.1 14.2 12.2 10.7 9-5 8.5 7-8 7-1 6.6 6.1 5-7 8 20* 26.7 20.0 16.0 13-3 11.4 10.0 8.9 8.0 7-3 6.7 6.2 5-7 5-3 8 18 25-3 18.9 15-2 12.6 10.8 9-5 8.4 7.6 6.9 6.3 5.8 5-4 5-i 7 20 215 l6.1 12.9 10.8 9.2 8.1 7.2 6.5 5-9 5-4 5-o 4.6 4-3 7 17* 19.9 14-9 12.0 10.0 8-5 7-5 6.6 6.0 5-4 5-o 4.6 4-3 4.0 7 15 18.5 13-9 11.1 9.2 7-9 6.9 6.2 5-6 5-0 4.6 4-3 4.0 3-7 6 I7 * 155 11.6 9-3 7-7 6.6 5-8 5-2 4.6 4.2 3-9 3-6 3-3 3-1 6 i4* 14.2 10.7 8-5 7-i 6.1 5-3 4-7 4-3 3-9 3-6 3-3 3-0 2.8 6 12* 130 9-7 7-8 6-5 5-6 4.9 4-3 3-9 3-5 3-2 3-0 2.8 2.6 5 m 3 10.8 8.1 6.5 5-4 4-7 4.1 3-6 3-3 3-0 2-7 2-5 5 12* 9.6 7.2 5-8 4.8 4.1 3-6 3-2 2.9 2.6 2.4 2.2 5 91 8-5 6.4 5.1 4-3 3-7 3-2 2.8 2.6 2.3 2.1 2.0 4 10* 6.4 4.8 3-8 3-2 2.7 2.4 2.1 4 9* 6.0 4-5 3-6 3-0 2.6 2.3 2.0 4 8* 5-7 4-3 3-4 2.8 2.4 2.1 1.9 4 7* 5-3 4.0 3-2 2.7 2.3 2.0 i.s 3 7* 3-4 2-5 2.0 3 6* 3-2 2.4 2.0 3 5* 3-0 2.3 1.8 15 16 HEAVY FOUNDATIONS §38 gives safer results. The principles on which the formula is based are theoretically correct, whereas, in the other method they were not, so that the more conservative rule should be used. Both methods are given here, as they are both used in general practice in the design of these footings. 10 . For convenience in figuring the strength of steel beams in grillage footings, Table I is given. This table gives the safe load on a single beam in tons of 2,000 pounds when < - - / 4-0 l 9-0 ‘ 3-'0' X -- >. / . I 1 J 1 1 1 { • r . ... . \-f-r FT i ZJ 11 1 1 ~1 ■ '• ■ --- 1 i Is i i 1 ! 1 1 1 1 —1-1—i-1— l 1 1 1 - 1 - 1 - 1 - 1 1 i —1 i — i— t— r —i— ill 1 i 1 i ... , 1 r i r Fig. 10 a safe unit fiber stress of 16,000 pounds is assumed. In applying the table, it is necessary to determine the value of l — Xy or the difference between the length of the steel beams beneath and the width of the steel-beam grillage or the cast-iron base above, as shown in Fig. 10. When the required value of l — x is not given in the table, the value next higher should be taken. It is also necessary to determine the total uniform load on each beam in the tier under consideration; this may be found by dividing the total load on the footing §38 HEAVY FOUNDATIONS 17 by the number of beams. In the column giving the existing value of l — x, select the value nearest to the uniformly distributed load, in tons, on the beam and by referring to the columns headed Depth and Weight, the size of the steel beam for the tier will be found. For example, Fig. 10 shows a diagrammatic plan of a three-tier, steel-beam, grillage footing.. The load on the column is 350,000 pounds, or 175 tons, so that the load on each beam in the several tiers is as follows: Top tier = 175^ 5 = 35 tons Middle tier =175^ 8 = 21.875 tons Bottom tier= 175-f-10= 17.5 tons The values oi l — x for the several tiers may be determined thus: Top tier ’= 9 —3 = G feet = 72 inches Middle tier =10 — 3 = 7 feet = 84 inches Bottom tier =14 — 9 = 5 feet = 60 inches Then, referring to Table I, for the first tier of beams, under the column headed 72, it will be found that a 12-inch 40-pound beam is the lightest that will support the required load and that for the middle tier of beams, under the column headed 84, a 12-inch 31^-pound beam will be the most economical, while for the bottom tier of beams, under the column headed GO, the most economical beam will be the 9-inch 21^-pound beam. In calculating the values given in this table, a formula evolved from the elementary equation M = M x has been used. M 1 equals the resisting moment or 5 s, while M equals the bending moment, which, according to the formula of . W Art. 9 , is — (l — x). Substituting these values in the equation 8 W M = M t gives 5^ = —(l — x), and transposing, the equation , 5 5 l — x becomes — =- W 8 In this equation, 5 is the ultimate unit fiber stress, and by dividing by the factor of safety, the 211—26 18 HEAVY FOUNDATIONS §38 safe unit stress is obtained, which, according to the table, is equal to 16,000 pounds. Substituting this value, the TABLE II DEPTH, WEIGHT, AND SECTION MODULUS OF STANDARD I BEAMS Depth of Beam Inches Weight per Foot Pounds ' Section Modulus Inches 3 Depth of Beam Inches Weight per Foot Pounds 1 Section Modulus Inches 3 3 5 - 5 ° i -7 10 25.00 24.4 3 6.50 1.8 10 30.00 26.8 3 7 - 5 ° 1.9 10 35 -oo 2 9-3 4 7 - 5 o 3 -o 10 40.00 31-7 4 8.5° 3-2 12 3 i- 5 o 36.0 4 9 - 5 ° 3-4 12 35 - 0 ° 38.0 4 10.50 3-6 12 40.00 41.0 5 9-75 4.8 *5 42.00 . 58.9 5 12.25 5-4 !5 45.00 60.8 5 14-75 6.1 !5 50.00 64-5 6 12.25 7-3 J 5 55 -oo 68.1 6 M -75 8.0 T 5 60.00 71.8 6 17-25 8.7 18 55 -oo 88.4 7 15.00 10.4 18 60.00 93-5 7 I 7 - 5 ° 11.2 18 65.00 97-9 7 20.00 12.1 18 70.00 102.4 8 18.00 14.2 20 65.00 117.0 8 20.25 15.0 20 70.00 122.0 8 22.75 16.0 20 75.00 126.9 8 25-25 17.0 24 80.00 T 73-9 9 21.50 18.9 24 85.00 180.7 9 25.00 20.4 24 90.00 186.5 9 30.00 22.6 24 95.00 192.4 9 35 -oo 24.8 24 100.00 r 98.3 r , . 16,000 5 l — x . formula becomes-=-. W is m pounds, while, W 8 according to the table, it should be in tons; therefore, by HEAVY FOUNDATIONS 19 § 38 dividing the left-hand member of the equation by 2,000, 8 vS* / % the formula is changed to -= -—and by transposi¬ n' 8 64 5 tion, W = ——, which is the formula by which the values l — x in the table are calculated. 11 . Table II is given for reference. It contains the sizes, weights, and section moduli of standard I-beam sections, and may be used to find the section moduli of beams of various sizes, as required by certain of the preceding formulas. EXAMPLES FOR PRACTICE 1. A grillage footing is composed of two tiers of steel beams; and the column base, which is 30 inches wide, supports a load of 275,000 pounds. The steel beams in the first tier are five in number, the tier is 42 inches in width, measuring between the outside edges of the flanges of the outside beams, and the length of the beams in this tier is 150 inches. The number of beams in the bottom tier is fifteen and their length is also 150 inches. Provided that an allowable unit fiber stress of 18,000 pounds is assumed and that the formula of Art. 9 is employed, what will be the economical sizes of the beams in both tiers? /Upper tier, 15-in. 42-lb. beams Ans. l Lower tier, 8-in. 18-lb. beams 2 . What will be the sizes of the beams required in example 1 if the formula of Art. 7 is used? f Upper tier, 12-in. 35-lb. beams ‘ l Bottom tier, 7-in. 15-lb. beams 3. Determine by means of Table I, without interpolating, the economic sizes of steel beams required for a grillage footing composed of three tiers of steel beams. The bottom tier is 12 feet 6 inches long and 10 feet wide, the intermediate tier has a length equal to the width of the bottom tier and a width of 6 feet, and the top tier extends across the intermediate tier and is 4 feet 6 inches wide. The cast-iron base is rectangular in plan and is equal in length to the width of the top tier and is 3 feet wide. Six beams compose the top tier, while in the intermediate and bottom tiers there are nine and twelve, respectively. The load on the footing is from a principal column and amounts to 320 tons. Bottom tier, 12-in. 31^-lb. beams Ans.< Intermediate tier, 12-in. 40-lb. beams ■ Top tier, 10-in. 40-lb. beams 20 HEAVY FOUNDATIONS §38 COMPOUND FOOTINGS RECTANGULAR FOOTINGS 12. A compound footing; is a footing that supports two or more loads, as, for example, the loads from two or more separate columns. Compound footings may be divided into two classes, namely, those which are square or rectam gular and those which are not so shaped. The latter are usually fan-shaped. The square or rectangular footings will be discussed first. Fig. 11 13. Location of Center of Gravity. —The first point of consideration is to distribute the area of the footing in the proper manner. The requirements are two: (1) that the unit pressure on the soil shall not be excessive, and (2) that it shall be uniform. When the load and the unit bearing value of the soil are known, the area of the footing may be obtained by dividing the former by the latter. But §38 HEAVY FOUNDATIONS 21 the second requirement, namely, the necessity of having the pressure uniform, must not be overlooked; if it is neglected, the footing will settle unevenly and the building is,liable to be cracked, twisted, or perhaps even destroyed. When only one column rests on the footing, all that is necessary is to have the center line of the column directly over the center of gravity of the footing area. When two or more columns rest on one footing, the center of gravity of the combined loads must coincide with the center of gravity of the foot¬ ing area. Fig. 12 14 . In order to illustrate the foregoing principle, the following problem is given: Three columns, as shown in Fig. 11, rest on one footing, and they all carry the loads shown. The soil will carry safely 1^- tons per square foot. Proportion the area of the footing. First, the area of the entire footing may be obtained. The total load to be supported is 42 + 96 + 62 = 200 tons. Since the soil can safely sustain 1 \ tons per square foot, the area of the footing must be 200 14 = 133J square feet. Either the width or the length of the footing may be assumed, although in actual design, the conditions encountered will 22 HEAVY FOUNDATIONS §38 usually limit one of these dimensions. In the case under consideration, assume that the footing can be only 4 feet wide. Then, the length of the footing will be 133^ -s- 4 = 33 feet 4 inches. The next step is to locate the footing under the columns so as to transmit the load uniformly to the soil. First, the center of gravity, or center of action, of the three column loads must be found. To do this, take moments, for instance, about the center line of the left-hand column. The location of the center of gravity is found thus: Load Moment Arm Moment Column 1. 42 0 0 Column 2. 96 12 1,152 Column 3. 62 21 1,302 Total.200 2,454 The distance from the center line of the left-hand column to the center of action of the combined loads is therefore 2,454-r-200=12.27 feet. This point is then the center of gravity of the footing area also. The footing is placed as shown in Fig. 12. 15 . Footings With Two Columns. —After having determined the location and area of a footing, the strength of the steel beams in it may be investigated. d Fig. 13 In order to determine the correct size of beams to use in a footing, simply find the maximum bending moment to which they will be subjected and then proportion the beams to withstand this moment. The maximum moment, as explained in Forces Acting on Beams , occurs at the point of zero shear. In most footings with several columns resting on them, there are two or more points of zero shear, and each of these must be investigated. §38 HEAVY FOUNDATIONS 23 16 . As a typical example of a footing supporting two columns, find the maximum bending moment in the beams d, Fig. 13. It is assumed that the loads on both columns are known and that the area of the footing is properly propor¬ tioned and properly distributed under these columns. The condition of loading to which the beams d in the footing are subjected is illustrated diagrammatically in Fig. 14. The column loads are W l and W 2 , and by means of their bases Fig. 14 they are distributed over the respective lengths x t and x 2 of the beams d. The load per linear foot that these columns exert is W Wo called w x and w 2 , and equals —- and —-, respectively. The total reaction of the earth on the footing is, of course, equal to W x T W 2 , and the pressure per linear foot of foundation, W t + W 2 or p, is equal to l First, the points of no shear must be found. It may be taken as a general rule—although there may be exceptions y x -54- ini y^&4' X 2 =36- ini fO Beams _ . / _ // -£ 2-0 Fig. 15 ■—that there is one point of no shear under each column load and one point of no shear between each two columns. The locations of these points are to be found, and they are assumed 24 HEAVY FOUNDATIONS §38 to be at distances from the left-hand end of the grillage indicated by l lf l 2 , and / 3 . The formulas that give values for 4, / 2 , and 4 are based on principles given in Forces Acting on Beams , and are as follows: hp- w i(h Vi), or k- y ' ' w 1 — p ( 1 ) 7 Tjr , W t 4 p = w 1, or 4 = — 1 P ( 2 ) hP=w l +[l 3 - (.v,++ y 2 y]w 2 or p-W 2 ( 3 ) After these three values have been found, the bending moment at these three points may be determined by the following formulas: M _Ph 2 ^(/,-y .) 2 1 2 2 M 2 =^-W^l 2 - yi -^ ( 5 ) 2 / 2 ' ' These formulas are also obtained by the principles given in Forces Acting on Beams. pi 2 / 17 . As an example of the foregoing principles, determine the most economical I beams that may be used for the bottom tier of the grillage footing shown in Fig. 15, provided that there are ten beams in the tier and that a safe unit stress of 18,000 pounds is assumed. The load from each super¬ imposed column is 375,000 pounds. All dimensions must be put either in feet or in inches. In this case, it will be simpler to use inches, because the section modulus is given in the tables in inches. Thus, / = 22 X 12 = 264 inches; p = 375,000 + 375,000 2 , 840 ** 264 §38 HEAVY FOUNDATIONS 25 say 2,841, pounds; ^ = 375,000-^-36=10,417 pounds, about; and w 2 equals the same amount as w v Substituting the correct values in the formulas 1 , 2 , and 3 , Art. 1G, 54X10,417 10,417-2,841 = 74.25 inches 375,00 0 2,84f = 132.00 inches 375,000 - (54 + 36 + 84) X 10,417 2,841-10,417 = 189.75 inches Now that the values of l v / 2 , and / 3 have been found, the moments of the loads at these points may be determined according to formulas 4, 5 , and 6, Art. 1G. Substituting the proper values in these formulas, _ 2,841 X 74.25 2 10,417 X (74.25- 54 ) 2 1 2 2 = 5,695,494.75 inch-pounds o 041 v/1092 M 2 = » - 375,000 X (132- 54 - *f) 2 = 2,250,792 inch-pounds M 3 = 2,841 X 9 !89,752 - 375,000 X (189.75 - 54 - _ 10,417X[189.75-(5 4 ± 36-f84) ]^ 5i696|90775 2 inch-pounds If the values of p and l v l 2 , and l 3 had been carried to a sufficient number of decimals, M x and M 3 would have been alike. However, both are larger than M 2 ; therefore, in this case, the maximum bending moment occurs under the loads and not between them. This maximum moment may be taken at 5,700,000 inch-pounds. Since there are ten beams in thegrillage, each beam must sustain 5,700,000-r-10 = 570,- 000 inch-pounds. With a fiber stress of 18,000 pounds, the 26 HEAVY FOUNDATIONS §38 required section modulus is 570,000 -s-18,000 = 31.67. Refer¬ ring to Table II, either a 10-inch 40-pound beam or a 12-inch 3Impound beam may be used. As the latter is both stronger and lighter, it is preferable. 18. As a complete example of the design of a footing supporting two column loads, the following problem is proposed: Design a footing to support two columns on a soil that can sustain safely only 2 tons per square foot. The columns are 9 feet apart, center to center. One supports 90 tons, and the other 111 tons. The first step is to find the total area of the footing. The total load is 201 tons. The required area is therefore 201^2 = 100.5 square feet. In order to make the example more interesting, let it be assumed that on account of the special difficulties encountered on this particular job, the footing can be only 6 feet 6 inches wide; then it will be 100.5 -h 6.5 = 15.46 feet long, or say 15 feet 6 inches. Next, the center of gravity of the footing must be found. This may be done by taking moments about the column that supports the 90-ton load. Thus: Load Moment Arm Moment 90 0 111 9 Total, 201 0 999 999 The distance of the center of gravity from the column supporting 90 tons is therefore 999-i-201 = 4.97, say 5 feet. It is next necessary to know the size of the base of the columns. These bases would be known if the columns were designed. Let it be assumed in this case that the bases are each 2 feet square. The grillage may be considered to consist of two tiers of beams, the bottom one of which is 15 feet 6 inches long and 6 feet 6 inches wide. The top tier is in two parts, one under each column. Each part is 6 feet 6 inches long and 2 feet wide. It may be assumed that each part of the top grillage contains four beams, and that the bottom grillage contains twelve beams. The footing of the correct proportions is shown in Fig. 16. The beams, for convenience HEAVY FOUNDATIONS 27 §38 in illustrating, are extended to the end of the concrete. In actual practice, they are stopped short, and the ends are covered with an inch or so of concrete, to protect them from rust. The long beams are the first ones to be investigated, and l v / 2 , and l 3 must be found. From Fig. 16 the following quantities, A „ (90+ 111) X 2,000 in pounds and inches, may be obtained: p = ---——— 186 on v o non = 2,161.29, say 2,161, pounds; iv x — - 1 — = 7,500 pounds; Fig. 16 w 2 = ^ P = 9,250 pounds; ^ = 21 inches; ^ = 24 inches; •24 y 2 = 84 inches; and :r 2 =24 inches. Substituting these values in formulas 1 , 2 , and 3 , Art. 16 , 21X7,500 7,500-2,161 29.50 inches 90 X 2,00 0 = g3 29 inches 2,161 28 HEAVY FOUNDATIONS §38 4 = 90 X 2,000 - (21 + 24 + 84) X 9,250 = 142.93 inches 2,161-9,250 After l v / 2 , and l 3 have been found, M x , M 2 , and M 3 may be found by formulas 4, 5, and 6, Art. 16. Substituting the correct values, 2,161 X 29.5 2 7,500 X (29.5 —21) 2 2 2 = 669,367.625 inch-pounds M 2 = 2,161 X83.29 2 90 X 2,000 X (83.29 - 21 - Y) = —1,556,529.35995 inch-pounds M 3 = 2,161 X142.93 2 90 X 2,000 X (142.93 - 21 - Y) 9,250[ 142.93 - (21 + 24 + 84)] 2 = +1,388,660.52195 inch-pounds It is evident that the maximum bending moment is the negative one of approximately —1,556,529 inch-pounds and is between the two columns. As there are twelve beams in the grillage, each beam must resist 1,556,529 4-12= 129,711 inch-pounds, approximately. If the allowable unit stress is 16,000 pounds, the required section modulus will be 129,711 -r- 16,000 = 8.11. Referring to Table II, it will be found that either a 6-inch 17.25-pound or a 7-inch 15-pound beam will be strong enough. As the latter is the lighter, it will be used. The next step is to design the beams in the upper grillage. The beams under each separate column are designed as the beams of a footing supporting only one column, as they are under the same conditions of stress. As the columns carry different loads, the beams under them will be of different sizes. The column carrying 111 tons will be considered first. To design the beams under it, the formula of Art. 9 is used. Here, w = 111X2,000 = 222,000 pounds; / = 6 feet 6 inches = 78 inches; and # = 24 inches. Therefore, 222 000 M =-—-X (78 - 24) = 1,498,500 inch-pounds 8 §38 HEAVY FOUNDATIONS 29 As there are four beams, each beam must resist 1,498,500 -.-4 = 374,625 inch-pounds. With a safe unit stress of 16,000 pounds, the required section modulus will be 374,625 -v-16,000 = 23.41. Referring to Table II, it will be seen that a 10-inch 25-pound beam is the lightest beam that is strong enough. The beams under the column supporting 90 tons are designed in the same manner. Thus, w = 180,000 pounds; / = 78 inches; and x = 24 inches. Therefore, M = x (78 - 24) = 1,215,000 inch-pounds 8 For one beam, M — 1,215,000-^4 = 303,750 inch-pounds. Therefore, 5 = 303,750 4-16,000= 18.98 According to Table II, a 9-inch 25-pound beam must be used. 19. Footings for Tliree or More Columns. —The method of procedure in designing a footing intended to sup¬ port three or more columns is similar to that followed in designing footings for the support of two columns. First, the footing must be made large enough and with its center of gravity properly located. Next, the points of no shear must be found, and then the bending moments at these points must be obtained and the maximum moment selected. The formulas for finding the points of no shear and max¬ imum bending moment are derived from the principles laid down in Forces Acting on Beams. As will be observed, the first three formulas for both shear and bending moment are the same as those previously given for footings supporting two columns. It is very seldom that more than three columns are placed in a row on one steel-beam grillage. In such a case, the additional formulas for points of no shear and bending moments may be evolved from the principles given in Forces Acting on Beams; or, the following formulas may be used to determine the location of the moments from the right-hand end of the beam. 30 HEAVY FOUNDATIONS §38 The formulas for the points of no shear, using the nota¬ tion given in Fig. 17, are as follows: 4 ^ = Wi(/i-pi), or Zj = y i w i I 2 p IF j, or l 2 w t — p w, p (1) ( 2 ) 4 P = W t +[4 - (y,+* 1 +y 2 )K or 4= ^Fi-(H+^1+T 2 ) W 2 p-w 2 l 4 p = W t + W 2 , or / 4 = TF1 + IF2 P ( 3 ) ( 4 ) 4 /> = TF 1 + TF 2 + w 3 [/ 5 - (h + ^ + ^ + ^ + Ts)] or 4= IFi + 1F 2 — (y t + aq + y 2 + x 2 + y 3 ) P~w 3 ( 5 ) When the location of the point at which the shear changes sign has been determined, the bending moments can be readily found, for they are equal to the algebraic sum of the moments about the points in question. With reference to Fig. 17, the formulas for the bending moments at the several points are as follows: M,= P 4 2 “',(4-^ 1 ) : ( 6 ) M 3 =til _ w, (l,-y t --\- ( 7 ) ( 8 ) Ph X 1 — W 2 l 4 — + x x + y 2 + Xn (9) §38 HEAVY FOUNDATIONS 31 — ^2 j^4 - [y\ + x i + y* + wJ/ 5 - (y 1+ x t +y 2 +* 2 + y 3 ) f ^ 0 2 ^ ; 20. The formulas of Art. 19 may be used to find the bending moment in reinforced-concrete foot¬ ings as well as in footings made of steel beams. To illustrate the appli¬ cation of these formulas, the follow¬ ing problem will be worked out: Proportion the steel beams in the grillage foundation shown in Fig. 18 for the greatest bending moment. The allowable unit stress is 16,000 pounds, and the loads on the col¬ umns and the general dimensions of the footing are given in the figure. 21. It is first necessary to de¬ termine the values of Z lf l 2 , l 3 , etc.; having these distances, which locate the points at which the shear changes sign, the bending moments at these points may be determined by formulas 6 to 10, Art. 19, inclusive, and from this data the greatest bending mo¬ ment is found by inspection and the beam proportioned accor¬ dingly. With reference to the fig¬ ure and by substitution in formulas 1 to 5, Art. 19, the values of * l lt etc. are found as follows: 32 HEAVY FOUNDATIONS §38 k = y x w x 52X5,556 = 84.16 w x — p 5,556 — 2,123 ^ = 200 i 00_0 = 942 i p 2,123 , _W t — (y t + x t + y 2 ) X w 2 _ 200,000 - (52 -f 36 + 82) X 7,500 /-■ - * p-w 2 2,123-7,500 = 199.93 7 _ W t + W 2 _ 200,000 + 300,000_ l a -* ZoO.OZ p 2,123 , _W 1 + W 2 -(y 1 +x 1 +y 2 +x 2 +y 3 )w 3 p — W 3 200,000 + 300,000 - (52 + 36 + 82 + 40 + 65) X 8,333 = 288.49 2,123-8,333 These values may be substituted in formulas 6 to 10, Art. 19, which will give the bending moments at the several points as follows: pi? w^-yj 2 2,123X84.16X84.16 ■ M x = 2 2 5,556(84.16-52) 2 M, pl? = 4,645,314 inch-pounds x x \ 2,123X94.21X94.21 - 200,000 X'(94.21 - 70.00) = 4,579,369 inch-pounds p 4 2 w/, .. wlk-(yi+Xi+yJY 2,123X199.93X199.93 - 200,000X (199.93-70) 7,500X[199.93— (52 + 36 + 82) ] 2 = 13,085,014 inch-pounds pi, X, l, ~ ( >'i +Xi 1-I 2 + Xn = 2'I 23 X 235.52X 235.52 _ 20Q 00Qx (235 -52 _ 70) — 300,000X (235.52-190) = 12,121,055 inch-pounds 33 211—27 34 HEAVY FOUNDATIONS §38 _ w 3 [ 4 - (m+ *1 + y 2 +x 2 +y 3 ) f = 2 4 — (^1 + *1 + ^2 + 2,123X288.49X288.49 9 - 200,000 X (288.49 - 70) - 300,000 X (288.49 -100) 8,333X[288.49-(52 + 36 + 82 + 40 + 65)] 2 __ — 14.o41, # inch-pounds From these calculations it will be observed that the greatest bending moment is at the point M 5 , located under the right- hand column. There are, according to Fig. 18, twenty I beams in the grillage, so that the bending moment on each I beam will be 14,341,729-^-20 = 717,086.45, and since the allowable unit fiber stress is 16,000 pounds, the required section modulus for each beam will equal 717,d86.45 4-16,000 = 44.818. From Table II, it will be observed that the beam having the required section modulus is a 15-inch 42-pound I beam. EXAMPLES FOR PRACTICE 1 . Determine the points of no shear, or the points at which the greatest bending moments occur, in the grillage shown in Fig. 19 when W 1 equals 300,000 pounds; W 2 , 250,000 pounds; and W 3 , 325,000 pounds. The distances y lt x v y 2 , x 2 , y 3 , and x 3 equal, respectively, 58, 40, 80, 3G, 72, 48, and the length of the grillage equals 33 feet. 4 = 82.23 in. = 6 ft. 10£ in. 4=135.75 in. = 11 ft. 3f in. Ans. L= 197.73 in. = 16 ft. 5f in. 4 = 248.87 in. = 20 ft. 8| in. L = 303.99 in. = 25 ft. 4 in. Fig. 19 2. If the values of y v x lf y 2 , x 2 , y 3 , and x 3 in Fig. 19 are, respect¬ ively, equal to 60, 40, 90, 48, 80, and 44 inches, and the length of the bottom tier of beams is 35 feet 4 inches, while the loads W v W 2 , and §38 HEAVY FOUNDATIONS 35 IV 3 are equal to 150, 200, and 175 tons, in the order named, how large should the beams be in the lower tier, provided they are spaced 12 inches from center to center? The footing is 11 feet wide between the centers of outside beams, and the safe unit fiber stress is 18,000 pounds. Ans. 15-in. 55-lb. beams FAN-SHAPED FOOTINGS 22. Consider the case of a footing that supports two columns, one loaded with 150 tons and one loaded with 15 tons, when the columns are 10 feet apart. Suppose the soil can sustain only 1 ton per square foot. The area of the footing will then be 150 + 15 = 165 square feet. If there is some obstruction, say near the column carrying 15 tons, that limits the width of the footing to 5 feet, the footing will be 165-*-5 = 33 feet long. There are two objections to a footing of this length. First, on account of its length, there will be a very large bending moment, which must be resisted by heavy and expensive beams, and, second, it may interfere with other foundations elsewhere in the building. Consider the case of two columns, one supporting 200 tons and one supporting 30 tons, when they are 10 feet apart. The soil can support 10 tons per square foot. The area of the footing is then (200 + 30) -r- 10 = 23 square feet. Suppose the width of the base under the column supporting the heavier load to be such that the footing must be at least 1 foot 9 inches wide; then, its length will be 23-f- If = 13.14 feet. The distance of the center of gravity from the heavier column 10 X 30 must be-=1.3 feet. It can thus be seen that the 200 + 30 footing, if properly placed, will not reach under the lighter column. In cases like the two just cited, rectangular footings are inconvenient or even impossible. Therefore, fan-shaped footings are employed. 23 . Fig. 20 illustrates two fan-shaped footings. The one shown in (a) is strengthened with steel beams, and the one in ( b ) is made of reinforced concrete. The method of 80 Corr. Bars Beef/or? K.K. 36 §38 HEAVY FOUNDATIONS 37 designing these two footings is identical, and along the same lines that were followed with rectangular footings. First, the area of the footing must be made large enough to carry the required load. Then, the area must be so located that its center of gravity will coincide with the center of gravity of the loads. The maximum bending moment must next be found and a sufficiently strong beam grillage designed; or, in the case of reinforced concrete, sufficient steel reinforce¬ ment must be provided. On account of the shape of the footing, its center of gravity is not so easy to find as that of rectangular footings, and, usually, the shape of the footing has to be assumed and then investigated to see whether or not the center of gravity comes in the correct place. Of course, the footing may be shifted a little, but not so much as was done with a rectan¬ gular footing. 24. Shape of Footing. —Various shapes of fan foot¬ ings are in use. A plan view of four styles is shown 38 HEAVY FOUNDATIONS §38 in Fig. 21. The shape shown in (a) is used most, for two reasons; in the first place, the steel beams fit in it better because there are no comers, and, second, the formulas for the points of no shear and bending moment are simpler than with the other shapes. To find the bending moments of footings shaped as shown in ( b ), (c), and (d), the simplest way is to lay the footing out as a beam; that is, lay out its load diagram, its shear diagram, and its bending-moment diagram, as was explained in Forces Acting on Beams. There are no general formulas that will fit all these cases. For the reasons mentioned, the shape of footing generally used is §38 HEAVY FOUNDATIONS 39 that shown in (a). This shape, therefore, is the only one that will be considered in this Section. 25 . Method of Design. —As previously stated, the theory of designing a fan-shaped footing is the same as that of designing a rectangular footing. First, the area must be found; then it must be properly located; and, finally, it must be properly strengthened to resist the incurred bending moment. However, owing to the shape of the footing, the formulas are more complicated than the ones given for rectangular footings. To illustrate their use, reference is made to Fig. 22, which shows a plan view and a conventional side view of a fan-shaped footing. In the side view, the loads and reactions are represented by the shaded areas. Let Q be the pressure per square inch on the soil. Then, n i Q = P l is the pressure per linear inch at one end of the footing, and n 2 Q = P 2 is the pressure per linear inch at the other end of the footing. The letters used in the formulas are shown in the illustration and will be readily understood. The formulas for the points of no shear are: P1-P2I Pi ~ w i + i\-P.X Pi- 2(P,-pji y, 1 1 P —P 1 1 L 2 X P l -w 2 + \2 (P t -P t ) [w 2 (y t + x t + y 2 ) - IUJ + (w 2 - P t ) : ( 3 ) After the values of l lt l 2 , and l 3 have been found, the bending moment at these three places must be obtained by the follow¬ ing formulas: M, = - ( i j_ P 2 )/ L _ (/ - y y. 2 0/ 2 40 HEAVY FOUNDATIONS §38 m 2 =^ 1 -— qf- -- ^-y.-f) (5) M 3 = l±ll- { Z±zIM--W \(l, 3 -y ,-^i) 2 61 \ 2/ -^Ik-fo+xi+yJ? ( 6 ) 26. The design of a footing and the use of these formulas is best illustrated by the following example: Design a fan¬ shaped footing to support two columns. One carries 350 tons, and the other 85 tons. The two columns are 12 feet apart. The soil will safely carry 5 tons per square foot. First, the area must be determined. The total load is 350 + 85 = 435 tons. The required area of the footing is therefore 435 = 5 = 87 square feet. In actual practice, the designer usually tries different sizes of footings until he strikes one of the right area, or he may assume all the.dimen¬ sions but one and solve for that one, as follows: Assume that the width of the small end of the footing is, say, 1 foot 6 inches and that the length of the footing is 18 feet 10 inches. It remains to find out what the length of the wide end will be. Call this x. Then, by the rules of geometry, the area of the footing is %Jr 1 : - 5 X 18 = 87; and % = 8.1667 feet, or 8 feet 2 inches. The next point is to locate the center of gravity correctly. First, the center of gravity of the two loads must be obtained. To find this, take moments about the larger load. The work is as follows: Load Moment Arm Moment 350 0 0 85 12 1,020 Total, 435 1,020 The distance of the center of gravity from the larger load is therefore 1,020 = 435 = 2.34 feet. HEAVY FOUNDATIONS 41 § 3S Next, lay out the area of the footing, as shown in Fig. 23. To find its center of gravity, take moments about the line a b. For convenience, the area abed is divided into two parts, a triangle and a parallelogram, by the line d e parallel to c b. Its center of gravity is then found as follows: Moment Value Arm Moment Area ade .6.667X9 = 60 6 360 Area e b c d . 1.5X18 = 27 9 243 Total. 87 603 The moment divided by the total area is 603-^87, or 6.93 feet. Therefore, the center of gravity of the area is 6.93 feet to the right of a b, and this same place must be 2.34 feet to the right of the left-hand column. The columns may now be located on the diagram, Fig. 23, as shown. It is assumed that the base of the heavier column is 2 feet on a side and that the base of the lighter column is 18 inches square. The last consideration is to find the maximum bending moment and then proportion the beams to resist this moment. The pressure on the soil is 5 tons per square foot, or 5X2,00 0 144 = 69.44 pounds per square inch. From the figure, Wj = 98 and w 2 =18. Therefore, = 69.44 X 98 = 6,805.12 pounds and P 2 = 69.44X 18= 1,249.92 pounds. W x = 700,000 pounds: 42 HEAVY FOUNDATIONS §38 W 2 = 170,000 pounds; w t = 700,000-^24 = 29,167 pounds; w 2 = 170,000 -T-18 = 9,444 pounds; ^ = 43.08 inches; ^ = 24 P —P inches, y 2 = 123 inches; /= 12X18 = 216; and —--- 1 6,805.12-1,249.92 0K _ 0 _ , ™ P x -P* = —-—--—— = 25.7185 pounds. Whenever —- 216 l occurs in the formulas, the value just found may be used; it is also evident that the reciprocal of this value may be used for l P ! P 2 Substituting in formulas 1, 2. and 3, Art. 25, 1 k = X [6,805.12-29,167 25.7185 + V2 X 43.08 X 29,167 X 25.7185 + (29,167 - 6,805.12) 2 ] = 54.48 inches X (6,805.12- V(3,805.12 2 -2 X 25.7185 X 700, OOO) 25.7185 = 139.79 inches L =--— X [6805.12 - 9,444 + a/2 X 25.7185[9,444 25.7185 X (43.08 + 24 + 123) - 700,000] + (9,444 - 6,805.12) 2 ] = 206.73 inches Now that the values of l v l 2 , and l 3 have been found, the bending moments may be found by formulas 4, 5, and 6, Art. 25. Substituting the correct values in these formulas, 6,805.12 X 54.48 2 25.7185 X 54.48 3 29,167 2 6 2 X (54.48-43.08) 2 = 7,510,650.345 inch-pounds M = 6,805.12X 139.79 2 _ 25.7185X139.79 3 _ 2 2 6 X (139.79-43.08-V)= -4,515,822.49 inch-pounds §38 HEAVY FOUNDATIONS 43 M = 6,805.12X2Q6.73 2 _ 25.7185X 206.73 3 _ 7QQ Q()0 X (206.73-43.08—V) 9,444 6 X[206.73- (43.08 + 24 +123) f = 81,322.12 inch-pounds From the foregoing, it can be seen that the greatest bending moment occurs at l t and is 7,510,650.35 inch-pounds. Let it be assumed that only four beams are used in this grillage. Each beam must therefore resist 7,510,650.35-^4 or approxi¬ mately 1,877,663 inch-pounds. If the allowable stress is 18,000 pounds, the required section modulus will be 1,877,663 -T-18,000= 104.3. By referring to Table II, it will be seen that a 20-inch 65-pound beam will fill the requirements. The arrangement of the beams at the small end of the footing is shown in Fig. 24. It will be noticed that two of them are ended short of the column carrying the lighter load, but this grillage is sufficiently strong, as the bending moment at the small end of the footing is not great. The beams, it will be noticed, are placed only 2 inches apart instead of 3, the .usual distance. This is done to save room. The design of the short cross-beams directly under each column may now be considered. The beams under the heavier loaded column will be considered first. The bending moment may be determined by the formula of Art. 9. Here, w = 700,000 pounds; x = 24 inches; and / = / g, Fig. 23. The 44 HEAVY FOUNDATIONS § 38 value of / g may be found by scale or by calculation, and is equal to 82.04, say 82, inches. Substituting these values in the formula, . M = ^5-- x (82 - 24) = 5,075,000 inch-pounds 8 If four beams are used, each one would have to resist 5,075,000 -r- 4= 1,268,750 inch-pounds. If the allowable unit stress is 18,000 pounds, the required section modulus will be 1,268,750-^-18,000 = 70.5, almost. By referring to Table II, it will be seen that an 18-inch 55-pound beam will answer the purpose. On account of the very small overhang of the beams under the base of the column supporting the smaller load, it will not be necessary to figure the size of the cross-beams; as a matter of fact, they may be omitted entirely if so desired. CANTILEVER FOUNDATIONS DETAIIjS of construction 27. In crowded sections of large cities the building sites have great value; therefore, in order to obtain adequate remuneration on an investment it is necessary to utilize every foot of building area. It is sometimes possible to get good rental from basements and subbasements, so that it is quite common for an important building to have three or four floors below the ground level, these basement floors being supplied with artificial light and ventilation. Such unusual conditions require special features of construc¬ tion, and it is therefore not uncommon in the erection of high buildings to employ what are known as cantilever foundations. 28. In Fig. 25, the foundation of an old building that has a building of skeleton construction adjacent to it is shown at a. It is evident that to build close against the HEAVY FOUNDATIONS 45 Fig. 26 iron base of the wall column is carried on a concrete footing course a, and the entire weight of the outside wall of the building line yy and to get adequate foundation area for the support of the column b, all the batter of the footing must be inside the building. In constructing the footings in this manner, the center of downward pressure from the column does not coincide with the center of upward pressure from the soil, and the condition shown by the arrows c and d exists. Therefore, it is evi¬ dent that some special means must be provided to centralize over the foundations the concentrated loads from the outside columns, and at the same time utilize every inch of ground surface by building close to the line. This condition is met by adopting the construction shown in Fig. 26. In this case, the cast- Fig. 25 46 HEAVY FOUNDATIONS §38 new building adjacent to the existing wall at b is carried by the overhang of the girder at c. By this means the new wall is carried close to the old wall, and the center of weight from the combined loads above and the center of pressure from beneath on the combined footings coincide. By inspecting Fig. 26, it will be evident that the girder d is subjected to great bending stress at or adjacent to the point e, and that also, if the wall and the loads supported by Fig. 27 the outside column / are great, there will be an upward lifting tendency, as shown by the arrow g. Therefore, the conditions of loading must be investigated to determine whether the weight on the column h multiplied by the lever arm x is equal to or greater than the weight on the column / multiplied by the lever arm x v Frequently, the overhang is so great and the dead loads on the interior column h are so small that it is necessary to anchor securely the column h to a heavy foundation that supplies the necessary weight so as to §38 HEAVY FOUNDATIONS 47 overcome any tendency of the load on the overhang to lift the interior column. 29. Another condition that sometimes requires the adop¬ tion of the cantilever foundation is shown in Fig. 27. In order to obtain the headroom for the subbasement, it is neces¬ sary to excavate below the foundation of an old building adjacent to it. Such excavation would require either that the old building be underpinned and a new foundation carried down, together with the foundation of the new’ building, as designated by the dotted lines, or that the foundation footings for the new building be located farther within the site. In order to accomplish the latter, cantilever construc¬ tion could be adopted, as shown. When such construction is employed, the excavation for the footings a can be made without disturbing the footings beneath the old building, though such footings must not encroach on the natural slope of the soil on which the old footings are built. 30. In Fig. 28 is illustrated a type of cantilever founda¬ tion used in a large office building. This foundation con¬ struction was used in order to bring the column loads over the center of gravity of the combined footings and to prevent the footings from overrunning the property line. Columns a, b, c, and d are carried on cantilever girders e , which in turn are supported by cantilever girders /. These girders in turn are supported on distributing girders resting on a raft or grillage footing g. In this way the grillage footing is prac¬ tically symmetrically loaded and will produce an approx¬ imately uniform bearing stress on the soil, which will insure its uniform settlement. In Fig. 29 are shown several details of a cantilever grillage footing very similar to that shown in Fig. 28. Over and under each set of girders where there is a concentrated load, each girder is well stiffened by vertical stiffeners a, b , and c. These stiffeners are ground to fit between the flange angles of the girders. The girders d are retained against any tilting tendency that might exist by the gusset- plate brace e. •Secf/ono/ £/erafion X.-X Mam WaJ/ Footing L/evaf/on on Z-Z i_ i~::::::::. Fig. 28 48 - -" *7 I: J r = It—' 0 I—0 -« up \ -2'- 0 N -V-2-0” — AS " 3 o o 5 0 o O' O OOP Lower CanWerer G/re/ers o o o o o Q o o o' o o a 0 o o o o o o o O' 0 0 o o o o (5 0 0 o o 0 o 0 o 0 o D 0 a o a o o o o o 0 0 o 0 °l o 0 0 0 o 0 o e D 0 0 o O O O o O O J o o o o o O O 0 O O 0 o o o o 0 D ,/** 5: ft ::AIS= :<4'.4.4; a 4. A. Qp/Z/age Beams • 4 4 A '-7^- >7^— j ' I * -fc I -tw— XI I CO 6 H £ 211—28 'ng/tudmal Sect/on. 50 HEAVY FOUNDATIONS §38 31. Another type of cantilever foundation construction is shown in Fig. 30. In this case, three column footings are supported on a grillage, the two outside columns forming the support for a cantilever box girder that sustains the outside wall of the building. The plan of the foundation is shown in view (a) and the elevation in ( b ). The outside distributing girder sustaining the column that supports the cantilever is of heavy box-girder construction, while the distributing girders under the interior columns are 20-inch 85-pound I beams. The detail of the cantilever girder is shown in Fig. 31, and on examination should be sufficiently clear as to details of construction without further explanation. DESIGN OF CANTILEVER FOUNDATIONS 32. The design of a cantilever foundation divides itself into two parts: (1) The design of the girder to resist the bending moments, and (2) the design of the footings them¬ selves. It is not within the province of this Section to discuss the design of the steel girders used as cantilevers, while the method of designing reinforced-concrete girders to resist the moment incurred is given in another Section. The maximum moment is usually found to be at the center line of the outside footing, as at e, Fig. 26. The moment is the load on the outside column multiplied by the horizontal distance between the center line of the outside column and the center line of the outside footing; that is, in Fig. 26, it is the load at / times the distance and the girder, whether of steel or of concrete, must be designed to withstand this moment. The greatest care must be exercised both in the selection of the material and in the inspection of the workmanship of these important structural members, for their failure will ordinarily mean the destruction of the entire building. Owing to the fact that steelwork of the cantilever construction is in a location where more than ordinary corrosion may §38 HEAVY FOUNDATIONS 51 take place with little possibility of its discovery or prevention, the steelwork should be designed with a high factor of safety. Such a procedure is at all times a wise precaution and will allow for considerable deterioration without dangerously affecting the safe strength of the foundation. 33. The footing area must be designed by the same method as used before; that is, the common center of gravity of the footing areas must coincide with the common center of gravity of all the loads. The beams in each individual footing are of course designed to support the load on that footing by the methods previously given in this Section. Referring to Fig. 26 and its description, it was suggested that occasionally the load on / multiplied by x l would be greater than the load on h multiplied by x. In such a case, the column h would tend to rise, and it would be restrained only by the rigidity of the building and the weight of the founda¬ tion under it, to which it is anchored. Under such circum¬ stances, it is evident that the unit pressure on the foundation a would be greater than that on the foundation under h, because the foundation a takes the load from f and h, while the foundation under h only supports part of its own weight and yet has to be made of considerable size to insure that the column h, which is anchored to it, will not rise. Therefore, under the assumed conditions, the footing a will settle more than the footing under h, as the latter will hardly sink at all. If, as is usually the case, the location of the columns is fixed by circumstances, there are but two ways of overcoming this difficulty. The first method is either to sink the founda¬ tion a to solid rock or to put piles under it, so that it will not settle no matter what load is put on it. The second method is to extend the girder of the footing to include three columns. Such an arrangement, in which the footing is extended, is shown in Fig. 30, and another example, in which the girder is extended, is shown in Fig. 32. However, such measures seldom have to be taken, as most cantilever foundations have two footings and a load on each one. 1 ■<7 m§mmm V A M Fig. 28 36 §39 PILING 37 meated with the cement to a considerable extent, thus improv¬ ing the character of the soil and increasing the bearing strength of the pile. Another advantage of concrete piles over wooden piles is that they may be reinforced, and the reinforcement embedded in them may interlace with the reinforcement of the footing or capping in such a way as to provide an anchor¬ age for steel chimneys, tank towers, and other tall structures subjected to wind pressure. Concrete piles are also less likely to be damaged when driven and finished than are wooden or timber piles. 55. Soils Best Suited for Concrete-Pile Construc¬ tion. — Concrete piles can frequently be used advan¬ tageously to provide for foundations of buildings to be erected upon a site overlaid with soft clay, mud, or strata of quicksand or other soil of doubtful bearing value. By their use a saving in cost, as well as in time, over the old method of excavating and then erecting concrete piers is frequently possible. Referring to Fig. 28, the columns in both (a) and (6) support the same load. In (a) is shown the usual method of penetrating a soft clay and muddy soil in order to carry the foundations down to the gravel or hard pan, while in ( b ) the same column is shown supported upon con¬ crete piles. From view (a) it is evident that a considerable amount of excavating is necessary before the concrete pier can be constructed. As is usually the case with soft clay soil, the cost of excavation is increased by the pumping necessary to keep the excavation free from water, and, in addition, a large quantity of concrete is required to build from the hard pan to the top of the foundation to provide the necessary strength; there is also danger attached to excavating in this manner on account of the possibility of slides and caves. With the use of concrete piles, all these difficulties are over¬ come, and it is best to use concrete-pile construction even at a slight increase in cost, on account of the time that may be saved. The concrete piles in Fig. 28 ( b ) could probably be driven in one-fourth the time it would take to make the excavation and fill in the concrete in (a). 38 PILING §39 Concrete piles may also be used in unreliable ground, such as that made up of ashes and the usual refuse used to fill up city lots; in fact, they can be used to advantage wherever it is necessary to carry the load of a building or a structure to foundations firmer than can be obtained from the upper strata of the soil. /j lpmum w Fig. 29 56. Capping of Concrete Piles. —It is the custom to cap concrete piles with a concrete capping or a footing course. In order to form the concrete capping, the earth is excavated from around the top of the piles, and a cinder or other cheap concrete is then put around them and made level with the top; above this is constructed a footing course of broken- stone concrete from 2 to 4 feet in thickness. In Fig. 29 is §39 PILING 39 shown a series of concrete piles driven in parallel rows, with the trenches excavated for filling with cinder concrete. Where the thickness of the capping is limited by the conditions of the foundation, the capping may be made shallow—1 or 2 feet in thick- • ness—and reinforced with woven-wire mesh or expanded metal, as shown in Fig. 30. The reinforcement of the foot¬ ing in this manner gives it sufficient strength to distrib¬ ute the weight between the tops of the several adjacent piles. In the capping of piles, a considerable saving is effected by the use of concrete piles ■m# mm -r7.2. Simplex Molded Concrete Pile. —The Simplex system of pile construction also embodies the use of a molded §39 PILING 49 concrete pile. Molded concrete piles arc generally driven with a hammer, in the same manner as wooden piles, with the exception that a buffer is used under the hammer to lessen the shock; however, where the soil will permit, they are driven Fig. 45 with a water jet. The objection to the first method is that the concrete pile is liable to crack badly or become otherwise injured; the latter method can be used only in soils favorable to this process. 50 PILING §39 The Simplex molded piles and the method employed to drive them overcome these difficulties by the method of con¬ struction illustrated in Fig. 44. In this method the driving shell a, view (a), shod with the hinged-jaw device, is driven to the required depth until a solid bearing is reached, when several buckets of concrete are dumped into the driving form, or shell, and the form partly withdrawn, the concrete being well rammed. When this is accomplished, several buckets of soft grout are poured in the form and the previously molded pile is lowered into place. The driving form is then slowly withdrawn, and the concrete pile with the cement grout fills the space formerly occu¬ pied by the driving shell, or form. The finished pile in place is shown in view ( b ). These Simplex piles are molded on end, in the manner illus¬ trated in Fig. 45, and may be rein¬ forced in any desirable manner. The figure shows the derrick and bucket used to hoist the concrete, which is mixed on the ground, to the top of the platform. ■\d. •o' vo-;-.'- • o : c 5>-' 1 ■M :: . ' M : •i. m. : m ■ ;&.■ i ■ 4 •: f ■M o.\* G3. Simplex Sliell, or Wharf, Pile. —There is another Simplex concrete-pile construction known as the sliell, or wliarf, pile; it is used in very soft soil or in water. The method of driving, as well as the form of this pile, is shown in Fig. 46 (a) and ( b ). As in the prece¬ ding case, the driving, or form, shell is driven to the required depth and soft concrete is deposited in the bottom, forming a layer, as shown at a. Then the form is partly withdrawn and inside it is placed a steel cylindrical shell that rests on the con¬ crete at the bottom. The shell is then filled with concrete and (b) Fig. 46 §39 PILING 51 the driving form withdrawn. In this manner, the steel shell protects the concrete until it has set. The shell cannot codapse from the pressure of the soft soil on account of the concrete filling it, nor will the cement be washed from the concrete forming the filling of the shell or the pile. This pile is admirably adapted to the construction of wharf foundations and for the support of the footings of buildings where it is necessary to penetrate a soft mud or quicksand. Piles as large as 36 inches in diameter may be formed in this manner, and when properly reinforced they will sustain thousands of pounds. COMPOSITE PILES 64. A composite pile consists of a wooden pile on the top of which is constructed a concrete pile, the wooden pile being driven to such a depth as to allow its top to be below the permanent water-line. Piles of this kind may be used to advantage when it is necessary to drive piles to a depth of 70 to 100 feet. Ordinarily, with wooden piles, it is necessary to excavate down to the permanent water-line, so that the pile may be sawed off and the concrete pier or footing be completed up from this point. It is not unusual in instances of this kind to excavate 15 or 20 feet, which operation is ordinarily an expensive one. The use of composite piles overcomes this difficulty; besides, they are cheaper than the all-concrete pile, and ordinarily can be used at less cost than by using all wooden piles, cutting them off below permanent water-line, and completing the concrete or masonry piers from this point to the ground level. 65. The method of constructing composite piles is illus¬ trated in Fig. 47. In (a) is shown the first part of the oper¬ ation. The wooden pile is driven until its top is near the ground line, the head of the pile being protected from splinter¬ ing, or brooming, by the cast-steel pile cap a and the cast-steel driving head b. The driving head contains a wooden block c that takes up the shock of the hammer, and by this means the top of the pile is preserved. In order to drive the wooden Fig. 47 52 §39 PILING 53 pile to its final position, with its top well below the permanent water-line, the follower and driving form d, Fig. 47 ( b ), is used. As will be observed, both the follower and the driving form consist of double extra-heavy pipe, which is placed on the top of the wooden pile. This pipe is centered by the iron dowel-pin and casting /, which replaces the cap shown in (a), and is fitted with a driving head b. Both the form and the follower are driven together, forcing the wooden pile to its final position. The driving form, which is reinforced at the lower efid, is provided with a cast-iron ring h, and this is left in position with the completed pile, as shown in (c). When the wooden pile has been driven to the proper depth, the follower is removed and the concrete is dumped into the driving form, which is then withdrawn, forming the concrete pile extension, as shown at i, Fig. 47 (c). It will be noticed that the junction between the concrete pile extension and the wooden pile has considerable lateral strength on account of the cast-iron ring and the dowel-pin. The ring greatly reinforces the end of the concrete pile, and the dowel-pin prevents lateral displacement. 66. One of the advantages of using the composite pile is that a short pile driver may be employed. This is important where piles 70 feet or more in length are to be driven. The concrete portion of the pile may be provided with any neces¬ sary reinforcement and may be used for anchorage. It is claimed for the composite piles that they are excellent in wharf construction, as the marine w’ood borers will not attack wooden piles below the river bottom. The concrete extension in wharf work should be placed by using an iron shell, as described in conjunction with the shell, or wharf, concrete pile. HAMMER- OR JET-DRIVEN CONCRETE PILES 67. Corrugated Piles. —The concrete pile shown in section in Fig. 48 is known as the corrugated concrete pile. It is the invention of Frank B. Gilbreth, and is made and molded in wooden forms. When the concrete has set suf- I 54 PILING §39 ficiently, the pile is driven with a water jet and steam pile driver. As shown in the section, the pile is molded octagonal in form, with fluted sides, and is cast with a hole through the center to facilitate the use of the water jet in driving. The octagonal shape is used in order to cheapen the cost of the form work and the flutes are used to increase the sur¬ face and consequently the fric¬ tional resistance of the pile against settling. The pile is reinforced, in order to strengthen it for handling and driving. The reinforcement consists of Clinton electrically welded wire fabric, the rods running lengthwise of the pile being | inch in diameter, and the rods extending around the pile ■§• inch. The longitudinal, or vertical, rods are placed about 3 inches from center to center, and the J-inch rods, or wires, are 12 inches on centers. The hole through the center of the pile is about inches in diameter, and is molded by using a tapering plug, which can readily be withdrawn. 68. In driving this type of pile, an ordinary pile driver is used, the force of the blow being re¬ lieve d by a cap. This cap, which is about 3 feet in height, fits over the head of the pile and forms a cushion for the blows of the driving hammer. 4 rn d a :.:3x r-Pr- TJ Fig. 49 Fig. 48 5 39 PILING 55 Fig. 50 The cap is constructed as shown in Fig. 49. In this figure, at a, is shown a steel shell of a diameter sufficient to fit over the head of the concrete pile. This shell is slotted at one side, so as to allow the pipe used for the water jet to enter and pass down through the hole in the pile. Directly on the top of the con¬ crete pile a plug of wood b is placed. Several layers consisting of pieces of hose or rope f are inserted between this plug and a wooden plunger c. This plunger is provided with a cast-iron cap d, and this cap is fitted with the wooden plug e, to prevent it from being directly hit by the hammer. The steel shell is provided with channel-iron guides on each side. Ordinarily, the pile, after 8 days, has been found to be set sufficiently to allow driving. In sinking a pile, the water jet is used in conjunction with the hammer. This jet consists of a 1^-inch pipe connected up to a high-pressure pump and passing down through the hole in the pile. The water jet loosens up the gravel and earth and carries them up the corrugations on the outside of the pile, these corrugations acting as an ex¬ haust to the jet. One of these piles successfully withstood the blows of a 2,500-pound hammer falling 25 feet, and striking from 20 to 30 blows. In some instances, piles of this kind have been put in place within 2 minutes after the dri¬ ving has been started. Fig. 50 shows a molded concrete pile of octagonal section with two grooves or corru¬ gations on each side of the octagon. This figure also shows clearly the reinforcement of the pile. The hole down which the water pipe passes is also clearly shown. 5G PILING §39 Fig. 51 69. Clienoweth Steel-Concrete Pile. — The Clien- owetli steel-concrete pile is made by winding a woven- wire cloth with a layer of concrete of plastic consistency and molding - the same to form a reinforced-concrete pile. A section of a finished pile is shown in Fig. 51, which illustrates the method of winding the wire webbing with the con¬ crete to form the pile. As will be noticed, the wire cloth, starting from the steel rod at the center, takes the form of a volute, or spiral, with the center of the volutions at the center of the pile. The piles are made by a special machine, which rolls the concrete and the wire cloth, or webbing, together. These piles may be made from 12 to 1G inches in diameter, and as long as 30 to 40 feet. The average pile is 12 inches in diameter and 30 feet long, and is reinforced at the center with a steel winding rod 1 inch square and about 150 square feet of wire cloth, or webbing, made of wires of No. 17 Brown & Sharpe gauge, woven with lj-inch mesh. The Chenoweth piles, when the concrete has set, have considerable transverse and compressive stress and are driven with the ordinary pile driver, having a sand cushion or other cushioned cap in order to protect the top. Where it is desirable to drive these piles by a water-jet process, a pipe may be substituted for the cen¬ tral winding rod. The usual cushion cap used for dri¬ ving these piles is shown in Fig. 52. As shown, a cast-iron cap, or casing a, fig. 52 fits over the top of the concrete pile. Frequently, a wooden block b is placed over the top of the pile and on the top of this is filled a layer of sand covered by a wooden driving plug c y which fits into the upper end of the iron casing. This plug is §39 PILING 57 protected by a welded wrought-iron ring to prevent brooming. The finished Chenoweth concrete pile is shown in Fig. 53 (a), and the usual steel webbing used for the reinforcement in the flat is shown in ( b ). Bv | if.; .VvWSr-’: ; i p # >-•. ■ f. •. •ijl ' - rv-# I * tm . |;ap i ; K=li • • - SPECIAL SYSTEM OF CONCRETE FOUNDATION CONSTRUCTION 70. A type of concrete foun¬ dation construction that has been somewhat extensively used in France, and which is being intro¬ duced into the United States, is known as the Compressol sys¬ tem of concrete-pier construc¬ tion. While this system is not known as concrete-pile construc¬ tion, yet it is very similar. The distinguishing feature of the Com¬ pressol system consists in driving a hole into the ground by repeatedly dropping a heavy pointed weight, and then filling the hole so formed with concrete. Fig. 54 shows the device used to penetrate the soil. At a is shown the derrick, or dri¬ ving machine, which is somewhat similar in construction to the timber work of the ordinary pile driver, and at b is illustrated the pointed driving weight hoisted to position and ready to drop. This weight when repeatedly dropped pene¬ trates the soil in the manner shown in Fig. 56. When the required depth of pene¬ tration has been reached, the hole is filled with concrete, each lot being tamped by dropping a weight of the shape 211—32 n>) Fig. 53 58 PILING §39 shown in Fig. 55. The concrete is compacted and forced out by this process, so that the hole is spread into the shape shown in Fig. 57 by the concrete forced into it. By this means is formed a solid con¬ crete pier of a more or less cylindrical section and a spread base. Such con¬ crete piers have been known to support with safety as much as 90 tons. One of the advantages claimed for the Compressol system is that the falling Fig. 54 weight compresses the soil around the edges of the hole and prevents water from pene- Fig. 55 Fig. 56 ■■ :.WsF$%A sm&r# k'.e ^ trating. Should the compression of the soil not be sufficient to do this, a quantity of clay or puddle can be placed §30 PILING 59 in the hole, and the blows of the weight will force it out, lining the opening and forming a jacket sufficiently waterproof to keep the hole dry while the concrete is being placed and tamped. COST OF CONCRETE PIEES 71. Comparative Cost of Concrete and Wooden Piles. — Although concrete piles cost several times as much per linear foot as wooden piles, there is frequently a con¬ siderable saving made by using them, not only because fewer are needed to carry the same total load, but also because the amount of the foundation masonry and excavation is materially reduced. One of the largest items of cost involved in the use of wooden-pile foundations is the depth of the masonry foundation required to permit the tops of the wooden piles to be located below the permanent water-line, whereas, concrete piles may extend any distance above the water-line, and therefore require only a capping of concrete or masonry. The cost of wooden piles ranges from 25 to 50 cents per linear foot, depending on the availability of the timber and the conditions encountered in driving. The cost of concrete piles, driven, ranges from 90 cents to $1.50 per linear foot. 72. In the construction of the new United States Naval Academy, it was found more economical to use concrete piles than to employ timber piles; also, in place of 2,193 wooden piles 8S5 concrete piles were found to answer the same pur¬ pose. By using the concrete piles 3,504 cubic yards of exca¬ vation was saved, and the estimated 3,250 cubic yards of con¬ crete footings required for the timber piles was reduced to 986 cubic yards. Besides, it was estimated that the shoring and pumping incidental to making the necessary excavations for the wooden-pile construction and the cutting off of the timber piles would cost $4,000. A comparison of the estimated cost of wooden and concrete piles is as follows: 60 PILING §39 Wooden Piles 2,193.at $9.50 $20,833.50 4,542 cubic yards excavation at .40 1,816.80 3,250 cubic yards concrete . .at 8.00 26,000.00 5,222 pounds I beams.at .04 208.88 Shoring and pumping. 4,000.00 Total cost . $52,859.18 Concrete Piles 855 piles.at $20.00 $17,100.00 1,038 cubic yards excavation at .40 415.20 986 cubic yards concrete . . .at 8.00 7,888.00 Shoring and pumping. 0,000.00 Total cost. $25,403.20 Difference in cost. $27,455.98 From this comparison it is observed that the estimated saving is more than $27,000. Although it is true that these comparative figures, so far as the cost of the wooden piles is concerned, are based on assumptions, it is nevertheless certain that since these assump¬ tions were made on the average of the existing conditions, they were nearly correct, and the conclusion was that in this instance the use of timber piles would be attended with a great increase in cost of the foundation construction. In other localities and with other conditions, it is probable that the difference between the cost of the timber and concrete piles would not be so marked. There are so many factors entering into the cost of both kinds of piles for any particular locality that in designing foundations of this kind it is best, where cost is important, to obtain prices for both timber and concrete-pile construction. 73. Cost of Concrete Piles and Price Quota¬ tions. —Generally, in establishing the price for concrete piles, an average depth of pile is used for the basis of the unit prices per foot, and a minimum number of feet to be driven is also stipulated in the contract. The price is also fixed §39 PILING 61 per foot for piles longer than the average length, and the • reduction in price per foot is made for piles shorter than the average length. For instance, assume that bids are asked on 100 concrete piles, driven to an average depth of, say, 20 feet, but that owing to the nature of the soil and the design of the foundation, some of the piles will be shorter than 20 feet and some much longer. The cost quotations for concrete- pile work of this character will probably stipulate that 100 piles at an average depth of 20 feet, with a minimum total of 2,000 feet, will be driven for say $1.35 per linear foot, or $2,700; and that for piles longer than 20 feet the extra price per foot will be $1, and the deduction for piles of shorter length than 20 feet will be 80 cents per foot. The reason for so arranging the prices is on account of the labor involved in moving the driving machine for the short piles and the cost of getting it to the site and setting it up to commence the driving. On the other hand, the cost of a long pile is greater than that of a short one. It can readily be seen that the deduction for shorter piles cannot, as a rule, be so great per foot as the extra price for piles longer than the average, for if the piles were very short, the profit on the money earned in driving a single pile would be consumed in the labor involved in moving and getting the driving machine in position. Prices have been quoted for the several kinds of concrete piles that are formed in the ground, ranging from $2.25 to $1.35 per linear foot. The former price was high on account of the few piles to be driven, and also because of the severe driving conditions that existed and made the moving and maneuvering of the driving machine difficult. Prices that have been quoted for driving concrete piles of the Simplex and Raymond type are $1.46 and $1.40 per linear foot, based on a total minimum of about 2,000 linear feet, and on piles about 16 inches in diameter and an average length of about 20 feet. 62 PILING §39 STRENGTH AND REINFORCEMENT OF CONCRETE PILES 74. Strength of Concrete Piles. — It is customary to assume that the bearing strength of properly constructed concrete piles is from 20 to 30 tons per pile for piles of the average size, which is about 16 inches in diameter. Concrete piles are generally constructed of concrete com¬ posed of 1 part of cement, 2\ parts of sand, and 5 parts of gravel or crushed stone. As this concrete mixture is a good one and has considerable crushing resistance, it is well within conservative practice to assume that a 16-inch Fig. 58 diameter concrete pile will sustain with safety a load of 25 tons. Bearing tests that have been made on concrete piles have been very successful, showing that they will sustain, with very little settlement, much more than 25 or 30 tons per pile. In Fig. 58 is shown a test load of 300 tons, supported on five Simplex concrete piles each 16 inches in diameter. This test was made on a crane foundation for the Westinghouse Machine Company, Pittsburg, and no appreciable settlement was observed. §39 PILING 63 The Raymond concrete pile has been tested with equal success, as piles 22 feet 6 inches long driven in sand and clay fill, with soft bottom, sustained, under governmental test, at the site of the Annapolis Naval Academy, 133,270 pounds, making a total load on a single pile of over 66 tons. The result of this test showed a very slight settlement, and was particularly remarkable from the fact that the pile did not reach bed rock or hard pan. o* Fig. 59 A Gilbreth molded pile of average size, which is about 16 inches in diameter, has sustained with no appreciable settlement a total load of 45 tons. An important point to observe in the design of concrete- pile foundations is to arrange the piles so that each pile will sustain practically the same load, and choice should be made of the piling plan that most nearly accomplishes this result. 64 PILING §39 For instance, a piling plan that gives a variation of from 17 to 22 tons on the piles would be much better than an arrangement in which the piles were subjected to from 17 to 26 tons per pile. With careful study, the piles can usually be so arranged and spaced as to approach uniform loads on each pile. 75. Reinforcement of Concrete Piles. — Concrete piles formed in the ground are best reinforced by vertical rods. These rods, if required, may be tied together with wire ties as the form is filled. Molded concrete piles may be reinforced with either vertical rods or woven-wire mesh. Concrete piles require reinforcement only when their lateral stiffness has to be increased, as where they are subjected to the severe con¬ ditions of driving by the drop hammer, or in wharf or other structures where the piles might be required to resist a transverse stress. Concrete piles used for stack foundations, or other high structures are usually rein¬ forced with vertical rods, the rods extending above the top of the concrete of the pile, as shown in Fig. 59. These reinforcing rods may be bent over the rods in the footings, in order to form an anchorage, or they may extend into the footing courses or into the foundation itself when the same is of concrete. Concrete piles, owing to the facility with which they may be reinforced, and because of the grip or bond that they have on the earth into which they are driven, make excellent anchorage for stacks, water towers, stand pipes, or other high structures that have small bases and are liable to over¬ turning moments from wind pressure. Sometimes concrete piles are molded square in section, when they are reinforced with four longitudinal rods a, as shown in Fig. 60. These rods are cross-tied with wire ties b. Such Fig. 60 §39 PILING 65 piles as the one illustrated are designed to be driven by means of a drop hammer. Where it is necessary, they are shod with a sheet-iron shoe c. Such reinforced-concrete piles as the one illustrated in Fig. 60 can be driven close together, like sheet piling. REINFORCED-CONCRETE SHEET PILING 76. In some instances, reinforced-concrete sheet piling has been used where a permanent sheathing was required in soft soil, or for wharf work. A type of reinforced-concrete sheet piling is illustrated in Fig. 61. The reinforced- concrete sheet piles shown in view (a) are strengthened by means of four rods b connected with wire -clamps, the latter being cross-tied by flat irons. A projection e, Fig. 61 ( b ), is left near the base of the long side of each pile and a semicircular groove / runs from this projection to the top. The adjacent side of the next pile is provided with a similar groove, so that, in driving, the pro¬ jection on one pile slides in the groove of the last one driven. An iron pipe that fits the grooves of two adjacent piles is connected by means of a hose with a pump- or a water tank. This pipe serves as a guide, and the sand that might jam the grooves is forced out by the water. After the pile is driven, this pipe is withdrawn and a water-tight joint is secured by filling the grooves with cement. (b) 66 PILING §39 While driving the sheet piles illustrated in Fig. 61, the head is protected by a steel cap a previously filled with sand, thus forming a cushion that distributes the pressure of the blow from the hammer. The head should be of smaller diameter than the body of the pile so as to allow a clearance for the application of the steel cap. By this arrangement, the iron rods b may be allowed to project above the head so that they may be connected with other parts of the structure. The cap is closed at the lower end by a clay ring c held by a plug of hemp or spun yarn d. STEEL AND OTHER METALS IRON AND STEEL GENERAL CHARACTERISTICS 1. The materials largely used in structural engineering are iron and steel. Iron may be of two kinds —cast iron and wrought iron. Cast iron can be melted and pbured into molds, after which it again solidifies. This process is known as casting. Wrought iron can be heated until it becomes plastic, when it may be worked into various shapes, either under a hammer or in a press. Steel is simply a special form of iron, and may be divided into several classes, according to the mode of manufacture or the admixture of certain other materials. In order to become familiar with the physical properties of iron and steel, it is desirable to know something of their metallurgy; that is, of the process employed in their manu¬ facture. The methods of producing iron and steel have marked effects on their qualities, while the presence of small quantities of other elements, sometimes as impurities, may have still greater effects. One element that has a very important bearing on the properties of iron and steel is carbon. Other substances affecting them in a greater or less degree are sulphur, phosphorus, tungsten, nickel, chromium, and manganese. Small percentages of some of these ele¬ ments will frequently produce marked changes in the char¬ acteristics of the finished product. These characteristics will be taken up later. COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS’ HALL, LONDON § 40 STEEL AND OTHER METALS §40 9 IRON PRODUCTION OF IRON 2. Ores of Iron.— Iron exists in nature as an ore, which is a combination of iron and other elements in the form of rock or earth. Frequently, the iron is not distinguishable except by chemical analysis. The only ores from which iron is manufactured in large quantities are those containing the oxides and carbonates of iron, the oxides being the richer in iron. The ore known as magnetite , Fe 3 0 4 , contains about 72 per cent, of iron; that known as red hematite , Fe 2 0 3 , con¬ tains about 70 per cent, of iron; while another ore, brown hematite , 2Fe 2 0 3 -\-?>H 2 0 contains about 60 per cent, of iron. These constitute the valuable oxide ores. The carbonate ore, ferrous carbonate, FeC0 3 , contains about 48 per cent, of iron. Magnetite is black and brittle and often has magnetic proper¬ ties, from which characteristic it derives its name, Red hema¬ tite varies in color from a deep red to a steel gray, but all varieties make a red streak when drawn across unglazed porcelain. On account of its abundance and the character of the iron it yields, red hematite is the most important of the ores of iron. Brown hematite varies in color from a brownish black to a yellowish brown. The carbonate varies in color from yellow to brown, but the light-colored ore rapidly becomes brown when exposed to the air. This ore is reduced to Fe 2 0 3 by roasting and exposure to the air, which drives off the carbon dioxide and water, as well as much of the sulphur and arsenic, when these are present. The carbonate is thus changed to an oxide having the same composition as red hematite. 3. Separation of Iron From Its Ores. —Iron in the metallic form is extracted from the ores by the action of heat. The ores are first heated at a comparatively low temperature, so as to drive off all moisture and volatile matter that may be present. Then they are heated to a §40 STEEL AND OTHER METALS 3 comparatively high temperature, in the presence of either car¬ bon, C , or carbon monoxide, CO. At this higher temperature, the oxygen of the ore combines with the carbon or carbon monoxide to form carbon dioxide, C0 2 , thus leaving the iron chemically free. This process is known as the reduction process , since the ores are reduced, or deprived of their oxygen and other non-metallic substances, leaving the metal itself quite free. The fuels used to produce the high temperatures in the reduction process are wood, soft coal, hard coal, coke, and gas. The heating is done in a furnace lined with some material, such as firebrick, which is not easily affected by great heat. The ores charged into the furnace usually contain silica, alumina, or some other substance that is difficult to remove, except by chemical combination with another substance put in especially for that purpose and known as a flux. The flux unites with the impurities in the ore and becomes fluid, when it is known as slag. The slag is lighter than the molten iron, and consequently floats on the surface of the iron, from which it may be removed either by tapping off the iron from below and leaving the slag to be drawn later, or by drawing off the slag through a tap hole at the surface of the molten liquid, without disturbing the iron below. 4. Blast Furnace.— All iron used for manufacturing purposes is obtained by reducing the ores of iron in a special furnace called a blast furnace. The furnace consists of a slightly tapering circular shell, built up of iron plates and lined with firebrick. The lower end of this shell is cone- shaped, with the small end of the cone pointing downwards. When the furnace is in operation, this is the region of highest temperatures, where most of the melting takes place. The ore, fuel, and flux are charged into the furnace at the top, through an opening that can be closed by an iron cone so as to prevent the escape of gases. The lowest tem¬ peratures exist near the top of the furnace, the mass growing gradually hotter as it descends. As fast as the metal at 4 STEEL AND OTHER METALS §40 the bottom melts, the charge above settles, being regularly replenished by charging at the top. Thus there is a con¬ tinuous downward movement of the charge. As the charge in the blast furnace descends into the zone of greater temperatures, the reduction process takes place, and the molten iron collects at the bottom. The slag, which contains much of the impurities and undesirable substances carried in the ore, collects just above the mass of molten iron, since it is lighter than iron. This is especially advan¬ tageous, since it protects the iron from the oxidizing effect of the hot blast entering the furnace. The slag is usually drawn off at intervals through openings near the surface of the molten iron. The air blast, by means of which the combustion is hastened and the higher temperatures obtained, is furnished by blowing engines. It enters near the base of the furnace, through nozzles or so-called tuyeres , at a pressure of from 5 to 15 pounds per square inch. As the blast passes up through the charge, the oxygen of the heated air combines with the carbon of the fuel, forming carbon monoxide, CO, since the amount of oxygen present is insufficient to form carbon dioxide, C0 2 . As carbon monoxide is quite combustible, it is conveyed by a pipe from the top of the furnace to one of the reheating stoves instead of being allowed to escape at once into the atmosphere. The stoves are iron shells lined with firebrick, each one containing two vertical chambers, the combustion chamber and the checkerwork , the latter consisting of numerous columns of firebrick intended to provide a large contact area for the passing gases. The carbon monoxide from the blast furnace is periodically led into one or the other of the stoves, where, during its combustion, it will heat the checker- work. The gas is then turned oft and air is sent through, thus heating it before it enters the furnace. 5. Pig Iron. —After the blast furnace has been started, it is continuous in its operation, the molten iron being drawn oft at regular intervals through a tap hole in the bottom of §40 STEEL AND OTHER METALS 5 the furnace. In the sand floor that surrounds the base of the furnace and sloping away from it, a long trench is dug, leading away from the tap hole from which the molten iron is drawn. From this trench, branch trenches are dug at intervals, and these branches lead to numerous smaller trenches, or molds, about 3 feet long and from 3 to 4 inches wide and deep. When sufficient molten iron has collected in the bottom of the furnace, the blast is shut off and the tap hole opened, thus permitting the iron to run out and fill the trenches and molds. The tap hole is then plugged, and the blast again turned on. The molten iron, on cooling, is known as pig iron. Pig iron contains from 3 to 10 per cent, of impurities, of which the larger part is carbon, although silicon, sulphur, manganese, phosphorus, and other elements may be present. Pig iron is usually classified according to its condition, the impurities it contains, and the purposes for which it is to be used. It is especially valuable because it melts and becomes quite fluid at a temperature of about 2,200° F., which is readily attainable in a foundry cupola. This property of pig iron, combined with its relative cheapness and its exten¬ sive use in the manufacture of wrought iron and steel, makes it the most useful form of iron. CAST IRON • \ 6. Foundry Cupola. —In making iron castings, pig iron is melted in a special form of melting furnace called a cupola, and is then poured into molds of sand. After it has solidi¬ fied, it is known as cast iron. The pig iron that is melted in the cupola and used in foundry work is known as foundry pig. The cupola has an outer shell of iron plates firmly riveted together. The tall cylinder thus formed is lined with fire¬ brick. Near the bottom, the cupola is surrounded by a ring-shaped metal box, which through various orifices supplies the necessary amount of air under pressure. The cupola is charged with alternate layers of coke and pig iron, and as 0 STEEL AND OTHER METALS §40 the iron in the lower end melts, it is drawn oft through a tap hole into ladles and carried to the molds. 7. Characteristics of Cast Iron.— Cast iron is a metal of crystalline formation, very strong in compression and comparatively weak in tension. There are several grades of cast iron that differ chiefly in the amount of carbon con¬ tained, although distinctive properties are given to the iron by other elements, such as silicon, sulphur, phosphorus, and manganese. 8. Carbon in Cast Iron.— Cast iron usually contains from 2 to 4^ per cent, of carbon, but when there is a large percentage of manganese present there may be 6 per cent, or more of carbon. The quality of cast iron depends largely on the condition of the carbon present in the iron. Carbon exists in cast iron in two forms, namely, combined carbon and graphitic carbon. In iron containing combined carbon, the appearance of the fracture, when a piece is broken, is silvery white; while, if an iron containing graphitic carbon is broken, it shows a dark-gray fracture. The melting point of gray iron is about 2,200° F., and that of white iron, about 2,000° F. The average value of the tensile strength of cast iron is about 15,000 pounds per square inch, and that of the compressive strength about 80,000 pounds per square inch. The gray iron, which contains graphitic car¬ bon, is weaker in both tension and compression than the white iron, which contains combined carbon. But since the white iron is very hard and brittle, it is difficult to work, and consequently the softer gray iron is most generally used. A cubic foot of dark-gray iron weighs about 425 pounds, and a cubic foot of white iron about 475 pounds. The appear¬ ance of the fracture of the different grades of cast iron varies from a coarse semicrystalline gray to a fine close- grained white. 9. Silicon, Sulphur, Phosphorus, and Manganese in Cast Iron.— Silicon in small proportions tends to increase the strength and hardness of cast iron, and aids in prevent- §40 vSTEEL AND OTHER METALS 7 ing the formation of blowholes in castings. Sulphur tends to make the iron hard and brittle. On the other hand, this element makes the iron more fusible. Phosphorus also makes the iron more fusible, tends to prevent blowholes, and is supposed to prevent shrinkage in cooling, so that the iron fills the mold more perfectly. On the other hand, phos¬ phorus makes the iron brittle and liable to break under suddenly applied loads. Manganese has the property of increasing the amount of combined carbon in cast iron, and thus gives a harder iron, rendering it less plastic and more brittle. It also increases the shrinkage. However, manga¬ nese unites readily with sulphur, and thus tends to remove the latter from iron. WROUGHT IRON * 10. Purity of Wrought Irou.— Of all the forms of iron obtained from the ores by processes of manufacture, wrought iron is the purest. It not only contains very little or no carbon, but the best grades are also free from the other impurities so common to cast iron and steel. Wrought iron can be produced either from the ore directly or by the con¬ version of pig iron in a reverberatory furnace. In the latter process, called the puddling process , white pig iron is melted and subjected to an oxidizing flame until the carbon is burned out or becomes less than 1 per cent. 11. Puddling Furnace. —The most common type of reverberatory, or puddling, furnace consists of an arched chamber of firebrick containing a shallow receptacle, the hearth, which may hold from 1,000 to 1,500 pounds of molten metal, and a grate. The gases produced by the fuel burning on this grate pass over the hearth into a flue. The heat is reflected downwards by the arched top of the furnace, making the material on the hearth extremely hot, the iron being worked at temperatures ranging from 2,500° F. to 3,000° F. Pig iron is generally used for the charge; it con¬ tains from 3 to 10 per cent, of impurities, while the wrought iron produced contains less than 1 per cent. The loss of iron 211—33 8 STEEL AND OTHER METALS §40 in the process is comparatively small. Scrap iron, machine- shop borings and turnings, etc. are used as a charge when the)" are available; and, as they are in a finely divided state, a heat may be finished in 20 minutes, while with a charge of pig iron it requires from 1^ to 2 hours. 12. Puddling and Rolling.— The iron is heated in the furnace until it melts into a thick, fluid mass. While in this condition, it is thoroughly stirred and worked by means of a long iron bar, to insure all parts of the iron being treated. This working is called rabbling. The puddling process, which is carried on at a high temperature with the iron in a fluid state, causes most of the impurities to be burned out, or else separated as slag. When the process is nearly completed, the iron becomes thicker and is known as a mat. The work¬ man divides this mat into masses of about 160 pounds each, and then with a bar rolls them into balls on the hearth of the furnace. A small amount of slag will adhere to the balls and be rolled up in them. Consequently, as fast as they are formed, these balls are removed from the furnace and passed through a squeezer , which is a form of press. This operation forces out most of the slag remaining in the ball, and welds the iron into a solid mass, after which it is passed through rolls. The rolling process works out more slag and reduces the iron to the form of bars. These bars are then reheated and rerolled to improve their quality. 13. Properties of Wrought Iron. —At a temperature of 1,500° F. or 1,600° F., wrought iron softens; and if the • surfaces of two pieces thus heated are brought together, with a flux to remove the oxide formed on the surfaces, the separate pieces can be welded or made to unite into one piece by hammering or pressing. Good wrought iron can easily be forged and welded, but only with great difficulty can it be melted and poured into molds, like cast iron and steel, since its melting point is about 3,000° F. When broken by a tensile force, its fibrous structure is plainly apparent. When subjected to repeated shocks or loads that exceed the elastic limit, the structure §40 STEEL AND OTHER METALS 9 changes and becomes more crystalline. Wrought iron has a greater tensile strength than cast iron, and can withstand shocks much better. The tensile strength of good wrought iron is about 50,000 pounds per square inch. When cold- rolled under great pressure, the strength of the material is greatly increased. 14. Wrought iron may contain as much carbon as mild steel, but it is far more fibrous and less crystalline than steel. This is due to the manner in which it is made, the successive squeezing and rolling having a tendency to cause the fibers of the iron to lie parallel to the direction in which the bar is rolled. A small amount of slag remains in the finished product, rolled out into fibers that lie between the fibers of the iron. The different grades of wrought iron are termed common bar iron, best iron, double best, and triple best, according to the amount of working each receives. The quality of the pig iron and the methods of manufacture also influence the quality of the wrought iron. Thus, Swedish iron is generally con¬ sidered to be the best wrought iron, because high-grade stock is used and great care is exercised in its manufacture. This grade, however, is too expensive for most classes of work. 15. Defects in Wrought Iron. —Wrought iron pro¬ duced from poor ore and having an excess of phosphorus is said to be cold short; that is, it is very brittle when cold, and is liable to crack when bent. It can, however, be worked very well at high temperatures. If the iron contains sulphur, it is said to be hot short, or brittle and liable to drack when hot, although fairly good when cold. Hot-short iron, some¬ times called red short, is useless for welding, but it is tough when cold and is used extensively in making tin plate. In order to test wrought iron for hot-shortness, a sample may be raised to a white heat and an attempt made to forge and weld it. 10 STEEL AND OTHER METALS §40 STEEL 16 . Definition of Steel.' —It is a difficult matter to give a concise definition of steel that will include all the grades produced, and will at the same time exclude cast iron and wrought iron. However, steel is essentially an alloy of iron and small percentages of carbon, the latter being present in greater quantities than in wrought iron and in smaller quanti¬ ties than in cast iron. Small percentages of other elements are often added in order to give special properties to the product. The question of the proper classification of steels has been given much attention, but thus far no classification proposed has been generally adopted. There are several substances, such as nickel, tungsten, chromium, manganese, molybdenum, aluminum, etc., that have great influence on the quality of the steel containing them. Some of these are added to the molten metal during the process of manufacture, for the purpose of modifying its quality to meet certain requirements. Others of these sub¬ stances may exist in the steel as objectionable impurities, which are derived either from the ore or the fuel, or from both. MANUFACTURE OF STEEL 17. Steel used for manufacturing purposes may be made by any one of three processes, known as the open-hearth process , the Bessemer process , and the crucible process. 18 . Open-Heartli Process.—In the open-hearth process, steel is made by melting a charge of pig iron with wrought iron or steel scrap, or by melting pig iron and iron ore in an oxidizing flame to remove the excess of carbon. The furnace is termed open-hearth because it is open at both ends. It consists of a rectangular hearth, about twice as long as wide, made of firebrick, silica brick, and other refractory material. The roof is arched, so as to deflect the flame on to the charge. In the open-hearth process, the excess carbon in the charge is burned out until only the desired percentage §40 STEEL AND OTHER METALS 11 remains, at which point the process is stopped. Gaseous fuel is used, and (except in the case of natural gas) both the gas and the air before igniting are highly heated by the waste gases in regenerative furnaces. Open-hearth steel is used for the better grades of steel plate, forgings, machine shafts, car axles, structural steel, etc. In fact, the steel made by this process is superior for all work to that made by the Bessemer process. 19 . The open-hearth process divides itself into the acid and the basic systems. In the former, the hearth is made of acid material—silica in the form of silica sand or silica brick. In the latter, the hearth and such portions of the side walls as the slag is likely to come in contact with are made of basic material, such as magnesite or dolomite. The hearth is inert, taking no part in the reactions of the process, and must therefore be made of a material to correspond with the character of the slag produced. In the acid process, only stock containing relatively small amounts of phosphorus and sulphur can be used, as with an acid slag these impurities are not eliminated, or only to a small extent. For this reason, the field of the acid process is limited. The basic process differs from the acid one in that stock higher in phosphorus and sulphur is treated, and basic mate¬ rials, usually lime, are added, so as to give a slag that will effect purification. The only difference in the apparatus used is that the hearth is made of basic instead of a silicious material. The function of the slag is to form a blanket, or covering, for the molten metal, protecting it from oxidation and loss of heat and oxygen, for the removal of silicon, manganese, carbon, etc. 20 . Bessemer Process.— The Bessemer process consists in decarburizing, or taking out the carbon from, a charge of pig iron by forcing a blast of air through it while in a molten condition. The oxygen of the air unites with the carbon, carrying off the latter as C0 2 . A quantity of pig iron rich in carbon and free from objectionable impurities is then 12 STEEL AND OTHER METALS §40 added, so as to give just the required percentage of carbon to the steel, this operation being known as recarburizing. The molten metal is then poured into ingot molds, and the cold blocks of metal, when taken from the molds, are known as ingots. These are afterwards heated and rolled into com¬ mercial shapes. Bessemer steel is used for rails, nails, structural shapes, etc., wherever its cheapness makes it desirable and wherever it will be just as satisfactory as the higher grade and more expensive open-hearth steel. 21. The decarburizing and recarburizing processes used in making Bessemer steel are carried on in a vessel known as a Bessemer converter. The converter consists of a shell of heavy steel plate riveted together and lined with refractory material. It is hung on hollow trunnions, through which the air blast may be conveyed to a receptacle at the bottom of the vessel. From here, suitable pipes, called tuyeres, lead the air to the metal. The vessel is rotated by hydraulic power applied through a rack and pinion. The construction is such that it can be made to revolve completely and empty out any slag after pouring the steel. Converters are made in various sizes, having capacities of from 1 to 20 tons. The metal fills only a small part of the space, as the reaction is so violent that considerable room must be allowed for it. 22. Crucible Process. —The oldest and simplest proc¬ ess of steel manufacture is the crucible process. In this process, the stock is melted in a crucible, which is heated by a fire of coke, hard coal, or gas. The air supply is heated in regenerative chambers. The iron that is melted to form the steel may be either high in carbon, requiring no addition of carbon, or low in carbon, requiring recarburizing. The stock used is chiefly wrought iron and steel scrap, with suffi¬ cient charcoal to give the required percentage of carbon. It is maintained that the highest grade of crucible steel can be manufactured only from blister steel made from the purest Swedish iron. As no sulphur nor phosphorus is STEEL AND OTHER METALS 13 §40 removed from the charge during the melting process, the stock must be free from these impurities. In American practice, the crucible is filled with the stock while cold and before inserting it in the heating furnace. The time required for melting varies from 2\ to 3 hours. Soft steel, or steel low in carbon, requires a longer time to melt than high-carbon steel. The presence of manganese, however, shortens the period of melting. For making tool steel, the molten contents of the crucibles are poured into ingot molds, that are about 3 or 4^ inches square and deep enough to hold the steel from one or more crucibles. These molds open lengthwise, so that the ingot may be easily removed. The cost of making steel by the crucible process is higher than by either the open-hearth or the Bessemer proc¬ ess, for which reason crucible steel is used only in the manu¬ facture of tools and in other cases where its high cost is compensated by the better quality of the product. 23. Comparative Value of tlie Several Classes of Steel. —The Bessemer process was the first to be perfected, and for 35 years, or up to about 1890, it led the open-hearth, both as to tonnage produced and in the perfection of methods and appliances—both metallurgical and mechanical. While the Bessemer process is the older, this is the only direction in which it can claim superiority over the open-hearth. In the order of their metallurgical and commercial importance today, the processes rank: first, the open-hearth; second, the Bessemer; and third, the crucible. The open-hearth process can claim as its own a larger field than the Bessemer. Open-hearth steel is now used for the better grades of plate steel, forgings, car axles, and structural steel. The basic open-hearth process is used where an extra-soft, pure steel is required, as in plates, sheets, rods, wires, etc. Bessemer steel is used for rails, nails, tin plate, light axles, and, in fact, for all articles where cheapness is desired. This grade of steel, however, is being rapidly replaced by steel produced by the basic open-hearth process. The basic 14 STEEL AND OTHER METALS §40 process, by cheaper production than was possible in the acid open-hearth, is a formidable rival of the Bessemer, and seems practically sure to supplant it largely in the next few years. Owing to lower cost of production, the Bessemer process held undisputed sway for years in all lines using a large tonnage of steel. The open-hearth gradually demon¬ strated its superior fitness for special lines. While both the crucible and the open-hearth process have distinctive fields, the Bessemer has no field the open-hearth cannot fill, and only by lower cost does it still produce the greater tonnage. A large proportion of rails are still made of Bessemer metal. While the crucible process is of the least consequence, it holds the most distinctive field metallurgically, and one from which the others seem unlikely to crowd it out. Given the same composition, it is well established that crucible steel is superior to either of the others, but owing to the much higher cost of production, its use is now restricted mainly to the making of high-grade tools, certain mining drills, parts of intricate machines, and, in general, where the first cost of the steel can be ignored. BLISTER STEEL AND SHEAR STEEL 24. Blister Steel. —Wrought-iron bars that have been treated by a cementation process are known as blister steel. This treatment consists in heating the bars to a high temper¬ ature for several hours in an air-tight compartment of a furnace and in contact with carbon. The carbon enters the iron, converting it into steel to a greater or less depth, depend¬ ing on the length of time the process is continued. The surfaces of the bars become rough and spotted with blisters, and the product thus becomes known as blister steel. It i's made in several grades, depending on the percentage of carbon absorbed, which usually varies from .5 to 1.5 per cent. 25. Shear Steel.— Blister steel is used in making shear steel. A number of bars of blister steel are welded together so as to form a single large bar, which is then ham- §40 STEEL AND OTHER METALS 15 mered or rolled down to the desired dimensions. Shear steel is made in different grades, as single shear , double shear , etc., each successive and higher grade being produced by cutting the bars of the next lower grade, welding them together, and working to size. Both blister steel and shear steel are frequently used in making crucible steel. ALLOT STEELS 26 . Tungsten Steel.— When elements other than carbon are added to steel to give it special properties, the product is called an alloy steel. One of the most important of these elements is tungsten, and a steel in which the principal properties are due to this element is known as tungsten steel. The amount of tungsten may vary from .1 to 10 per cent., the usual amount being from 3 to 5 per cent. The tungsten is introduced into the crucible in the form of ferrotungsten, which is simply an alloy of iron and tungsten. The amount of manganese usually runs from 1.5 to 2.5 or 3 per cent., and the percentages of sili¬ con, sulphur, and phosphorus are the same as in carbon steel. 27 . Manganese Steel.— Among all the varieties of steel, the hardest and toughest is manganese steel. The best results are obtained with from 7 to 14 per cent, of manganese. The maximum strength is obtained with about 13 or 14 per cent, of manganese, and the greater amount manufactured contains from 12 to 14 per cent. This steel is high in carbon, because the ferromanganese used in its manufacture is high in carbon. The extreme hardness and toughness of man¬ ganese steel are secured by quenching it in water. This is one of the most noticeable peculiarities of this steel, since the other alloy steels increase in hardness, but decrease in toughness, by quenching. Manganese steel is practically non-magnetic. Its uses are restricted to work that does not require machining, such as castings and forgings for various purposes. It works readily at a red heat, and is used principally for the jaws and plates 16 STEEL AND OTHER METALS §40 of rock crushers and grinding machinery, car wheels, T rails, safes and vaults, etc. This kind of steel may be made in crucibles, but the open-hearth process is more suitable for large quantities. Owing to the large amount of manganese that it contains, the metal is extremely fluid, and solid castings, both large and small, are readily made. The shrink¬ age is excessive, being about f inch to the foot, which increases the difficulties of casting. 28. Nickel Steel. —The addition of nickel to steel will greatly increase its strength, ductility, and elasticity. The amount of nickel added usually varies from 3 to 5 per cent., although alloys containing as high as 30 per cent, are made. The nickel is added to the steel either as metallic nickel or as ferronickel, which is charged with the rest of the stock into the furnace. Nickel steel is made almost entirely by the open-hearth process, though it can be made by either the Bessemer or the crucible process. It is readily worked either hot or cold and is easily forged, but it is harder to machine than ordinary carbon steel. It is used extensively for armor plate, gun barrels, engine and propeller shafts, automobile frames, and a great variety of purposes in which great strength and lightness are required, and in which high cost is not prohibitive. Nickel steel is also especially valuable because it offers a much greater resistance to corrosive influences than does carbon steel. §40 STEEL AND OTHER METALS 17 COPPER, ZINC, AND ALLOYS 29 . Copper. —The metal known as copper is found abundantly in nature, both free and in chemical combination, in such forms as cuprous oxide, Cu 2 0\ cuprous sulphide, Cu 2 S ; and as basic carbonate, Cu 2 (0H) 2 C0 3 . The methods applied for the extraction of copper vary with the ore under treatment. Copper may be drawn into fine wire or rolled into thin sheets. Its tenacity is considerable, being next to wrought iron. It is unaltered in dry air at ordinary temperatures, but it absorbs oxygen in the presence of moisture and carbon dioxide. Green spots then appear on the surface, constituting a basic carbonate of copper, which is the compound commonly known as verdigris. At a high temperature, copper absorbs oxygen very eagerly, being converted into cupric oxide. Weak acids, alkalies, and saline solutions act on it slowly in the presence of air. When hammered or rolled, copper becomes stronger, but also harder and more brittle. This brittleness may be removed by reheating and cooling in water. 30 . Zinc. —As a rule, metallic zinc does not occur free in nature. The chief ores are zinc carbonate, ZnC0 3l and zinc sulphide, ZnS. Zinc is hard and brittle at ordinary temperatures and of great durability. The strength of iron has been combined with the durability of zinc in the so-called galvanized iron. This material is manufactured by coating clean iron sheets with melted zinc, thus affording a protection much needed in large towns, where the oxides of sulphur and the acid emanations from various factories greatly accelerate the corrosion of unpro¬ tected iron. 31 . Brass. —An alloy of copper and zinc is called brass. The zinc promotes solidity, and makes the alloy cast better AVERAGE ULTIMATE STRENGTHS OF MATERIALS, IN POUNDS PER SQUARE INCH O o o o o o o o o o o o o o o o o o o C/3 'o o o O o o o o o o D * 1-4 o o O o' o o o o o 4 c/3 o o O o o o o o o o o O o o lO o o o § M <> 4 o 4 4 o lO oo M w M t-4 M M ►—1 <4-4 O 03 to V* o o o 3 P o o o f—* +-> s a o o_ o^ 'd p 6 co CM cm LO CM S 1 o o o (-> $ tuo o> j-i o o o o O O g; .is cn cs vd O M CO CO O o o o O O o O O o o •js-s o o o o o o o o o o «g 6 aj -P rt j io o o o o o o o o o vO CM vo vO o o 4 o '•O o W M CM rH M CO CM 4 1-4 G 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 1/5 o O o o o o o o O o o o o o G to O 4 O o 1-0 CM o O VO o 4 vO o H r4 4 (N io oo co vO LO VO CO CM CO VO 1 C/5 ag o o o o o o o o o o o o o o o o o o o o o S*i CM 6 o' 6 6 o' o' o M co CM CM CM CO 4 O M w V ^ * * • tuo . bjo G . g • t-H +-> • +j oj • oj 03 • 03 G w • rG • 03 03 Vi HM CL, . U O . ^ GS o Q ‘ 03 «s < W N ' 03 G ► —v K £ M *—» G> _) 13 • T—< ; g 0) ' -4-^ • <4-1 • O . C/3 T3 0) 03 M-> M-l o C/3 T3 T3 ^3 o3 < o u 03 a a o o *03 03 • t-H 4-H o pq C/3 C/3 c C* ' ^3 • 03 ; 13 03 . c rH • a 13 03 G G 03 G P a p G • rH f—< G 13 •13 a G manganese. . u o rG a C/3 O G • f~l C/3 +-> 4> C/3 o3 03 13 03 G G o3 , £> *d CD g 03 +J M-l O w T3 03 *d 'cd JD a; g a CTj c G aj Vh V- O 03 CD 03 V- Vh • *—4 • r-H £ £ G G G G C OOOOO Vh Vh Vh Vh Vh C/3 S 2 n <3 T r w *d l_3 s ^ & O 2 *- ,G 0> C/3 Vi +j 4^ X *G bo bo O O Vh Vh G~ G O O Vh Vh +J C /3 CCJ o -3 W (0 H C/3 G < Pi X H O P 03 H C/3 Q £ <3 (-> C/3 <3 03 O a • H Oh 6 0 bo G • tH CTj 0) ,G 03 Vh & r d 03 G 03 4-9 M-H o C/3 *Tj o C/3 C /3 v- bo G G C/3 03 bo ’d • • £ ^ G O • I-H c/3 03 Vh 03 „ PhH £ 03 G 2 CO +J 03 c/3 c/3 C/3 'd N —' 03 c G -|_>4J+->-|_>+J+J cocococococococo 4-9 C/3 aj o G~ • i-H H 4^ C/3 aj o o G S3 « H O £ 19 Compression values enclosed in parentheses indicate loads producing 10-per-cent, reduction in original lengths. 20 STEEL AND OTHER METALS § 40 than would copper alone. The alloy commonly used for brass castings is composed of 66 parts, by weight, of copper and 34 parts of zinc, although from 2 to 4 per cent, of tin is often added to give strength to the casting. The maximum ductility is secured with about 25 per cent, of zinc. The color of brass varies from a copper red to a gray, according to the amount of zinc used. Ordinary yellow brass contains about 30 per cent, of zinc. 32 . Bronze. —An alloy of copper and tin is called bronze. Tin increases the fluidity of molten copper and the tensile strength of the casting, but decreases its ductility. The quality of bronze depends on its composition, the purity of the materials used, and the care exercised in melting and pouring. The maximum tensile strength is attained when the alloy contains about 18 per cent, of tin, and the maximum ductility when it contains about 4 per cent, of tin. Bronze is harder, denser, and stronger than copper and does not oxidize so easily. 33 . Phosphor-Bronze. —Another alloy of copper and tin containing a very small percentage of phosphorus is known as phosphor-bronze. The phosphorus increases the strength, ductility, and solidity of castings. Copper oxide forms in nearly all alloys containing much copper when they are being melted, and thus reduces the strength and ductility of the alloy. The addition of phosphorus just before pouring the metal reduces the copper oxide and makes the casting more ductile. 34 . Manganese Bronze. —An alloy of copper and man¬ ganese is called manganese bronze. This alloy often contains some iron and may also contain tin. As manganese has a great affinity for oxygen, it tends to make a clear alloy, free from copper oxide. Manganese bronze has great strength and will not corrode easily. Some so-called -manganese bronzes contain no manganese, but are alloys of copper and tin with traces of other metals. §40 STEEL AND OTHER METALS 21 35. Application of Table I.— Table I gives the average ultimate strengths of the various metals employed in building construction. Its application is shown by means of the following examples: Example 1 . —What pull will be required to break a wrought-iron rod 2 inches in diameter? Solution. —The area of the rod is .7854X2 2 =3.14 sq. in.; the ultimate tensile strength of wrought iron, according to Table I, is 48,000 lb. per sq. in. Therefore, the rod will break at a stress of 3.14X48,000=150,720 lb. Ans. Example 2.—What length of wrought-iron bar, if hung by one end, will break of its own weight, assuming the weight of 1 cubic inch of wrought iron to be .227 pound? Solution. —Assume any size of bar; say, lg in. in diameter. The area of this bar is .99 sq. in., which may, for convenience, be called 1 sq. in. Now, as there is just 1 cu. in. in each linear inch in the rod, a length of 1 ft. will weigh .277 X 12 = 3.324 lb. The tensile strength of wrought iron being 48,000 lb. per sq. in., and 1 ft. of its length weigh¬ ing 3.324 lb., the length of rod required is 48,000 3.324 = 14,440.4 ft. Ans. LOADS IN STRUCTURES FLOOR, ROOF, AND WIND LOADS DEAD LOAD 1. The weight of the material used in the permanent structure of a building produces loads on the floor systems, the columns, and the foundations. These loads are called the dead loads and include the weight of the structural frame¬ work, walls, floors, partitions, and roofs. In fact, the weight of every piece of material used in the construction of the building is included in the dead load. Before the dead load can be computed, the weight of vari¬ ous materials must be known, and those in common use in building construction are given in Tables I and II. The units in which these weights are expressed are the ones most often employed in making estimates of loads in engineering calculations. Thus, Table I gives the weight, per cubic foot, of the materials usually measured by that unit, together with the weight, per cubic inch, of a few often measured in inches; while Table II gives the weights of such materials as are used in the construction of floors, roofs, ceilings etc., where the quantities are generally expressed in square feet. 2. Weight of Fireproof Floors. —If fireproof floors are of standard construction, their weights may be deter¬ mined from the weights given by the manufacturers of the particular type to be used. Where the fireproof-floor system is of special construction, that is, different from the standard commercial construction, a careful estimate of the dead load COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED AT STATIONERS’ HALL, LONDON $ 4 1 211—34 c v* TABLE I WEIGHT OF BUILDING MATERIALS (DEAD LOAD) Average Weight Name of Material Pounds per Cubic Inch Pounds per Cubic Foot Asphalt-pavement composition. 130 Bluestone . 160 Brick, best pressed. 150 Brick, common and hard. 125 Brick, paving. I 5 ° Brick, soft, inferior. 100 Brickwork, in lime mortar (average) .... 120 Brickwork, in cement mortar (average) . . . 130 Brickwork, pressed brick, thin joints .... 140 Cement, Portland, packed. 100 to 120 Cement, natural, packed. 75 to 95 Concrete, cinder. 105 Concrete, gravel. 140 Concrete, slag. 135 Concrete, stone. 140 Earth, dry and loose. 72 to 80 Earth, dry and moderately rammed. 90 to IOO Firebrick. 150 Granite . 165 to 170 Gravel . '. I17 to 125 Iron, cast . .260 450 Iron, wrought. .277 480 Limestone. 146 to 168 Marble. 168 Masonry, squared granite or limestone . . . 165 Masonry, granite or limestone rubble .... 15b Masonry, granite or limestone dry rubble . . 138 Masonry, sandstone. 145 Mineral wool . 12 Mortar, hardened. 90 to IOO Quicklime, ground, loose, or small lumps . . 53 Quicklime, ground, thoroughly shaken . . . 75 Sand, pure quartz, drv. 90 to 106 Sandstone, building, dry. 139 to 151 Slate.. 160 to 180 Snow, fresh fallen. 5 to 12 Steel, structural. .283 489.6 Terra cotta. no Terra-cotta masonry work. 112 Tile. no to 120 2 TABLE II WEIGHT OF BUILDING MATERIALS (DEAD LOAD) Name of Material Corrugated (2^-inch) galvanized iron • Corrugated galvanized iron, No. 20, side lap, unboarded. * . . Copper roofing, 16-ounce, standing seam Felt and asphalt, without sheathing . . . Glass, i inch thick. Hemlock sheathing, 1 inch thick . . . . Lead, about i inch thick. Lath-and-plaster ceiling (ordinary) . . . Mackite, 1 inch thick, with plaster . . . Neponset roofing felt, two layers . . . . Spruce sheathing, 1 inch thick. i inch thick . . No. 16. No. 18. No. 20. No. 22. No. 24. No. 26'. No. 27. No. 28. average amount of Slate, single thickness < inch thick i inch thick f inch thick | inch thick | inch thick f inch thick Shingles, common, 6 in. X 18 in., 5 inches to weather . Skylight of glass, ^ inch.to i inch, including frame . . Slag roof, four-ply. Steel roofing, standing seam. Tiles, Spanish, 14^ in. X 10} in., inches to weather . . Tiles, plain, ioi in. X 6i in. X I in., si inches to weather White-pine sheathing, 1 inch thick. Yellow-pine sheathing, 1 inch thick. Gravel roof and four-ply felt. Gravel roof and five-ply felt. Roofing, three-ply ready (asphalt, rubberoid, etc.)- . . . Purlins, wooden, with 12- to 16-foot span. Chestnut or maple sheathing, 1 inch thick. Ash, hickory, or oak sheathing, 1 inch thick. Sheet iron, rg inch thick. Thatch . Average Weight Pounds per Square Foot 2.91 2.36 1.82 1-54 1.27 •99 •93 .86 2 i ii 2 t a 1 4 3 6 to 8 6 to 8 10 j. 2 2 1.81 2.71 3.62 5-43 7-25 9.06 10.87 2 4 to 10 4 1 8i 18 3 4 6 .6 to 10 2 4 5 3 6-5 4 LOADS IN STRUCTURES §41 per square foot of floor surface should be made. The vol¬ ume of all materials that are measured by the cubic inch or the cubic foot should be obtained by the rules and methods set forth in Geometry and Mensuration, and the load obtained by multiplying by the unit weights of the materials found in Table I. The area covered by materials that are measured by the square foot, such as flooring, sheathing, roof covering, etc., should be computed and multiplied by the weight, per square foot, as given in Table II, to obtain the load. 3. In making calculations for the dead load of floors, where the floor construction is of uniform weight and thick¬ ness throughout, as in mill construction, the calculations for Layers of felt ^-l" Yellow Pine floorina 6 - 0 "Celiter to Center Fig. 1 the dead load can be made directly for 1 square foot of floor surface. The size of the girders or floorbeams is seldom known before the dead load has been determined, so that it is necessary to assume their size and to add the weight of the assumed girders or beams in calculating the dead load. When considering the amount of dead weight sup¬ ported by a beam or girder, it is customary to consider the weight as made up of one-half the panel situated on either side of the beam. After the dead load has been found and the size of the girder accurately determined, the assumed weight of the girder can be checked by the actual weight. Example. —In Fig. 1 , what is the total dead load on the girder Bt Solution. —The weight of the materials per square foot may be obtained from Table II and be tabulated, as follows: §41 LOADS IN STRUCTURES 5 Yellow-pine flooring, 1 in. thick . . . 4 lb. per sq. ft. Two layers of felt. 1 2 lb. per sq. ft. Rough spruce flooring, 3 in. thick . . 6 lb. per sq. ft. Assume the weight of the girder . . . 8 lb. per sq. ft. Total dead load of floor surface . . 18 * lb. per sq. ft. The distance from center to center of girders being 6 ft., and the span of the girders being 18 ft., the area of the floor carried by each girder is 6 X 18 = 108 sq. ft. Then, 108 X 18 | = 1,998 lb., which is the entire load on the girder B. Ans. 4. Where the section through the floor shows irregular¬ ities in thickness and, consequently, in volume and weight, it is necessary to consider the cross-sectional area of a panel, which is the space between two floorbeams. The length of section of the floor considered is 1 foot, as designated at xy , Fig. 2, so that when the entire weight of the section has been obtained the average weight per square foot can be found by dividing by the panel width, or the distance between the floorbeams. Example.— What is the amount of dead load per square foot of floor surface on the floor system shown in Fig. 2 , which consists of a brick arch 4 inches deep, covered with stone concrete? Solution. —The sectional area of the brick arch is practically equal to the product of the length of the arc on the center line a b by the thickness of the arch, which in this instance is 4 in. The length of the chord of the arc a b is in., while the rise is 5 in. From these dimensions the length of the arc on the center line a b may be found 6 LOADS IN STRUCTURES §41 by substituting in the formula / = 4 Vr* + 4 h 2 — c given in Geometry and Mensuration , in which c equals the chord and h the rise of the arc. The value of l is found to equal 4 \(47.5 X 47.5) + (4 X 5 X 5)- 47.5 Then, the sectional area of the brick arch equals = 48.8883 in. 48.8883 X 4 144 = 1.358 sq. ft. Since the calculation is for a portion of a floor sys¬ tem 1 ft. in length, the area of the section of the arch also equals, numerically, the cubical contents, so that the weight of the brick arch 1 ft. long is equal to 1.358 multiplied by 130, the weight per cubic foot of brickwork laid in cement mortar, obtained from Table I, or 176.54 lb. The area of the section of the concrete is equal to the area of a rectangle, in this case 7 in. X 47^ in., from which must be deducted the area of the segment of the circle included between the arc ced and the chord cd. In order to obtain the area of this segment, cal¬ culate the radius of the arc ced by applying the formula r = c 2 + 4 8 h r = given in Geometry and Mensuration. The quantities c and h represent, as before, the chord and the rise, and are equal, respectively, to 47.5 in. and 4.875 in. Substituting these values in the formula, (47.5 X 47.5) + (4 X 4.875 X 4.875) 8 X 4.875 ° y m ' The area of the segment is equal to the area of the sector minus the area of the triangle formed by the chord and the radii, or, as desig¬ nated in Fig. 3, the area of the shaded portion is equal to the area cedo minus the area of the triangle cdo. The area of the sector / Y may be found by the formula a — given in Geometry and Mensuration , in which l equals the length of the arc and r the radius. The arc cd has a smaller rise than that of arc a b and will therefore be shorter. Its length, found by the formula just given, is 48.82 in. Inserting this value and that of the radius in the formula, 48.82 X 60.29 2 a — = 1,471.68 sq. in. The area of the triangle to be deducted from the sector is equal to one-half the product of the base and the alti¬ tude. From Figs. 2 and 3, the base equals 47.5 in. and the altitude §41 LOADS IN STRUCTURES 7 equals the radius minus the rise of the arc, or 60.29 — 4.875 = 55.415 in.; consequently, the area of the triangle cdo , as designated in Fig. 3, is 47^5_X5—15 = 1,316.11 sq. in. Since the area of the sector cedo equals 1,471.68 sq. in. and the triangle cdo has an area of 1,316.11 sq. in., the area of the segment ce d equals the difference between these quantities, or 1,471.68 — 1,316.11 = 155.57 sq. in. The area of the rectangle from which this area is to be subtracted is 7 in. X 47| in. = 332.5 sq. in.; hence, the area of the concrete is 332.5 — 155.57 = 176.93 sq. iu. According to Table I, the. weight of the stone con¬ crete used is 140 lb. per cu. ft., and as the length of the concrete sec¬ tion is 1 ft., its weight equals 176.93 144 X 140 = 172 lb. The steel beam shown in Fig. 2 weighs 40 lb. per lin. ft. From these calculations, the entire weight of a panel section of the floor system for 1 ft. in length, or per linear foot, may be itemized as follows: Weight of brick arch. 1 7 6.5 4 lb. Weight of concrete. 1 7 2.0 0 lb. Weight of steel beam. 4 0.0 0 lb. Total weight .... . 3 8 8.5 4 lb. This amount is the dead load on 4 sq. ft.; hence, the dead load per square foot is 388.54 -s- 4 = 97.14 lb. Ans. 5. Pitch. — Fig. 4 illustrates a roof truss in which a b, or Z,, indicates the span and cd the rise. In indicating the slope of the roof, the angle x between the rafter member ac and the horizontal may be used, but more frequently the slope is indicated by the term pitch. As the meaning of this term is open to several interpretations, it is important to understand the methods by which the pitch is determined. The more rational method would be to divide the rise cd 7 • by one-half the span, or —■ = ——. The quotient, which is ad span 2 8 LOADS IN STRUCTURES 41 the pitch, indicates the rise for each foot horizontal. For instance, a roof has a rise of 10 feet and a span of 80 feet. The pitch is nse =40 = 4 , meaning that for every 4 feet span horizontal there is a rise in the rafter of 1 foot; or, when it is said that a roof has a pitch of 4, the meaning is that for every foot horizontal there is a rise of i foot, or 3 inches. The more common method and the one used in this rise Section is to define the pitch by the quotient-. This span may be expressed in the form of a rule, as follows: Rule I.— The pitch of a roof is fo7ind by dividing the rise by the span . According to this rule, the pitch in the preceding example would be 8"o = i. When a roof is said to be of i pitch, it means in this case that in a span of 8 feet there is a rise of 1 foot, and in a span of 10 X 8 feet there is a rise of 10 X 1 = 10 feet. It is thus seen that when using the latter method, the pitch is i of that found by the first method. From this the following rule may be deduced, applicable to the pitch used in the various Sections: Rule II. — To find the rise per foot horizontal imtltiply the pitch by 2. If the pitch is known, the angle x may be found from the rule of trigonometry, by which tan jtr = cd a d rise span Example 1.—A roof has a span of 64-feet and a rise of 8 feet. Find: (a) the pitch according to rule I, and (b) the angle between the rafters and the horizontal. Solution. — (a) According to rule I, the pitch is rise span _ 8 _ 1 ~ 64 ~ 8 Ans. LOADS IN STRUCTURES 9 (b) Applying the formula, tan x = rise span 9. = A = .25 which corresponds to an angle of 14° 2'. Ans. Example 2. —If the pitch of a roof is what is the rise of a rafter for everv foot horizontal? Solution. —According to rule II, the rise per foot is twice the pitch, or 2 X | = i ft., or 4 in. Ans. Another method is to specify the pitch in inches. Thus, by a 6-inch pitch is meant a slope that has a rise of 6 inches to 1 foot horizontal. Likewise, a 3-inch pitch is one in which there is a 3-inch rise per foot horizontal. This method will also be found convenient at times. . It is therefore evident that the engineer should always specify exactly what he means by “pitch” and how it shall be measured. 6. Dead Load on Roof Trusses. —The dead load also includes the weight of the roof covering, the sheathing, and \ the roof trusses. The weight of the roof covering and the sheathing may be calculated from the unit weights given in Table II. The weight of the roof trusses, or principals , as they are termed, is not known until these members have been designed, and must be assumed in the original calcula¬ tion. The weight of roof trusses depends on the material of which they are constructed, the span, and the distance they are placed apart, and also on the rise and the type of construction, though these two latter factors are neglected in the usual empirical formulas. The approximate weight of a wooden or steel roof truss may be determined by the following formula: IV = a£>L(l + j£j, in which W = approximate weight of truss, in pounds; a = constant—for wood .50, for steel .75; D = distance, in feet, from center to center of trusses; L = span of truss, in feet. 10 LOADS IN STRUCTURES §41 This formula may be expressed as follows: Rule. — Multiply the constant {or the material of which the truss is composed by the distance , in feet, from center to center of trusses by the span of the truss , in feet; the product of this result and 1 plus one-tenth of the span of the truss , in feet, is the approximate weight of the truss , in pounds. 7. It is evident that the combined lengths of the slanting sides of the truss are greater than the span of the truss; con¬ sequently, the length of the panel supported by one truss is longer than the span. To ascertain the weight of the frac¬ tional part of the truss that is to be added, per square foot of roof surface, it is necessary to calculate first the length of the slope and then the area of the roof surface supported by each truss. Each of the slopes being a hypotenuse of a right triangle, it is found by trigonometry that if x is the angle between the rafter members and the horizontal and L is the span of the truss, in feet, the combined lengths of the two slopes are equal to ^ cos x The area of the panel between two trusses is therefore ( 1 ) cos jr in which D is the distance, in feet, from center to center. The value of W , as found from the formula of Art. 6, must therefore be divided by that of formula 1 in order to find the approximate weight of the truss in pounds per square foot of roof surface. Designating this weight by w, then W cos jt: w =- D L Inserting the value of W, as found by the formula of Art. 6, a (10 + L) cos x w = a D L 10 (2 Formula 2 may be stated in the form of a rule as follows: Rul q.—M ultiply the constant by 10 plus the span of the truss , in feet , and by the cosine of the angle that the rafter member makes with the horizontal; divide this product by 10. §41 LOADS IN STRUCTURES 11 which gives the approximate weight of the truss in pounds per square foot of roof surface. Example. —Determine the weight, per square foot, that must be added to the weight of a roof covering to provide for the weight of the principals, the steel trusses in this case having a span of 72 feet and a rise of 18 feet. Solution.— According to rules I and II, Art. 5, the roof has a pitch of -y-f = -j. Knowing the pitch, the angle may be found directly riso from Table XII, or from the formula tan x — —-—- = 44 = .5, corre- span Ab 2 ~ sponding to an angle ;r of 26° 34'. cos x in formula 2, Art. 7, .75 (10 + 72) cos 26° 34' t Substituting the values of a, L, and .75 X 82 X .8944 10 . 5.5 lb. Ans. Table III has been calculated from formula 2. This table gives the weight that must be added to a square foot of roof covering to provide for the weight of the principals, or trusses. EXAMPLES FOR PRACTICE 1. A 2" X 3" wrought-iron bar is 36^ inches long. What is its weight? Ans. 60.66 lb. 2. The outside diameter of a cast-iron column is 10 inches, and the thickness of the material composing the column is -f- inch. What is its weight per foot of length? Ans. 68 lb. 3. The wall of a brick building, laid in cement mortar, is 24 inches ; thick, 36 feet high, and 100 feet long; in it are located 20 window openings 2 feet 6 inches wide by 6 feet high. What is the weight of the wall? Ans. 858,000 lb. 4. The roof of a building is made of No. 20 corrugated galvanized iron, laid on 1-inch spruce boarding. What is the weight of the roof covering per square foot? Ans. 3.82 lb. 5. What will be the difference in weight per square foot between a four-ply slag roof laid on 3-inch, tongued-and-grooved, yellow-pine planking, and a steel roof, standing seam, laid on 2-inch hemlock sheath¬ ing that is covered with two layers of Neponset roofing felt? Ans. 8^ lb. 6 . The span of a steel roof truss is 40 feet and its rise is 10 feet. Referring to Table III, what weight per square foot of roof surface should be assumed so as to allow for the weight of the principal, or roof truss? Ans. 3.35 lb. rf) W cc m D 8 H PQ ◄ H * o 0 8 8 0 H 0 8 £ -l|M 32 rf 1—1 00 in 4—< 00 in 04 00 in 04 4-H NO 04 IX 04 tx 04 tx oc co oc 4—* 4-H On O rf 04 On tx m 04 o co 04 CO in 4-H 00 rf 4-H tx rf O tx Oh rf m tx ON 4-H 04 rf NO oo o 4-H 4-H oc NO On l-H rf tx On 01 uc tx fH|-M 4-H 4-H HH 4-H 04 04 04 04 04 oc OC 04 04 04 04 oc oc oc oc rr rf rf 32 O O O O O o O O O o O O uc o uc o UC o in o uc O 4~> o i n o in o in o m O in O o 04 uc tx O 01 LT) tx o 04 uc E 04 oc LO NO CO ON 4-H 04 rf uc lx oo o 04 rf tx On 4-H oc o CO O eq|ro 4-H 4-H t-H 4-H 4—1 1—1 04 04 04 04 04 4-H 04 04 04 04 01 OC oc oc oc rf C"} Q On CO tX in rf 04 4-H O 00 tx NO rf 04 O 00 NO rf 01 o 00 NO rf 4—* O rf CO 04 NO o rf CO 4-H m O' NO lx CO 00 On O 4-H 04 04 OC rf £ 4-H 01 oc in o CO O' o 04 oc rf NO 00 o 04 rf tx On 4-H OC uc tx m|h< 4-H 4-H 4-H 4-h 4-H 4-H 4-H 04 04 04 04 4-H 4-H 04 04 04 04 04 oc OC oc oc 32 rf 04 O 00 NO rf 04 o 00 NO rf NO n o lx rf 4-H 00 uc 04 O'NO O rf O CO O' I—* oc m tx co o 04 4-H On tx rf 04 O tx in oc O 00 On o 4-H 04 rf in no IX co o 4-H Tt* O tx rf 4-H CO rf 4-H 00 LO Oh 00 o 4-H 04 oc rf m no tx On O oc uc NO 00 O 4-H OC uc O 00 O 4-H 4-H 4-H 4-H 4-H 4-H 4-H 4-H 4-H 4-H 04 4-H 4-H 4-H 4-H 04 04 04 04 01 01 OC 4-> C/3 32 o u 13 O O £ O o K- S-H 1 4—• Oh w 01 S Vh O Oh <2> V> + o 12 LOADS IN STRUCTURES 13 LIVE LOAD 8. Besides the dead load, which includes the weight of all the material used in the structure itself, there is a load called the live load. The live load comprises people in the build¬ ing, furniture, movable stocks of goods, small safes, and varying weights of any character. Large safes and extremely heavy machinery require some special provision, which is usually embodied in the construction. Table IV gives the live loads per square foot recommended as good practice in conservative building construction. TABLE IV LIVE LOADS PER SQUARE FOOT IN BUILDINGS Character of Building Pounds Dwellings. Offices. Hotels and apartment houses. Theaters. Churches. Ballrooms and drill halls. Factories. Warehouses. 70 70 70 120 120 120 from 1 150 up from 150 to 250 up The load of 70 pounds will probably never be realized in dwellings; but inasmuch as a city house may at times be used for some purpose other than that of a dwelling, it is not generally advisable to use a lighter load. In the case of a country house, a hotel, or a building of like character, where economy demands it and where the building is likely to be used indefinitely for some fixed purpose, a live load of 40 pounds per square foot of floor surface is ample for all rooms not used for public assembly. For assembly rooms, a live load of 100 pounds will be sufficient, experience having demonstrated that a floor is not liable to be loaded with a greater weight than this. If the 14 LOADS IN STRUCTURES 41 desks and chairs are fixed, as in a schoolroom or a church, a live load of more than from 40 to 50 pounds will never be attained. Retail stores should have floors proportioned for a live load of 100 pounds and upwards. Wholesale stores, machine shops, etc. should have the floors proportioned for a live load of not less than 150 pounds per square foot. The floors of printing houses and binderies, especially where the accumulation of heavy stock, such as bound volumes and calendered paper, is likely to occur, should be proportioned for a live load of at least 250 pounds per square foot. Special provision should be made in floor systems for heavy presses, trimmers, and cutters, and the beams should be proportioned for twice the static load likely to occur from such machines. The static load in factories seldom exceeds from 40 to 50 pounds per square foot of floor surface; therefore, in the majority of cases, a live load of 100 pounds, including the effects of vibrations due to moving machinery, is ample. The conservative rule is, in general, to assume loads not less than those just given, and to proportion the beams so as to avoid excessive deflection. Stiffness is as important a factor as strength. 9. Live Loads on Warehouse Floors. —In the design Af warehouse floors, the character of the material to be stored should be considered and data in regard to the manner of storing, the bulk of the packages, and the weight of the load per square foot should be obtained. With the view of furnishing reliable data to manufacturers, architects, and engineers, the Boston Manufacturers’ Mutual Fire Insurance Company has prepared the table designated as Table V. This table gives the space that the merchandise occupies and the greatest possible loads that can be placed on ware¬ house floors with the usual system of loading. Where the floor space and the cubical contents of the load are given in the table, the height of the load above the finished floor may be obtained by dividing the volume of the load by the floor area that is covered. For instance, the floor space occupied by a bale of white linen rags is 8.5 square feet, §41 LOADS IN STRUCTURES 15 and the cubical contents is 39.5 cubic feet; then the height of the loading is 39.5 4- 8.5 = 4.65 feet. It is hardly pos¬ sible, in the absence of hoists, to place such materials on the floor more than one bale in thickness, and the same thing applies to merchandise in barrels on the side and end. The building ordinances of the principal American cities are particularly emphatic with reference to warehouse floors. For instance, the building laws of Greater New York stipu¬ late that, “in all warehouses, storehouses, factories, work¬ shops, and stores where heavy materials are kept or stored, or machinery introduced, the weight that each floor will safely sustain on each superficial foot thereof, or on each . varying part of such floor, shall be estimated by the owner or occupant, or by a competent person employed by the owner or occupant. Such estimate shall be reduced to writing or printed forms furnished by the Department of Buildings, sta¬ ting the material, size, distance apart, and span of beams and girders, posts or columns to support floors, and its correct¬ ness shall be sworn to by the person making the same, and it shall thereupon be filed in the office of the Department of Buildings. But if the commissioners of buildings shall have cause to doubt the correctness of said estimate, they are empowered to revise and correct the same, and for the pur¬ pose of such revision the officers and employes of the Department of Buildings may enter any building and remove so much of any floor or any portion thereof as may be required to make necessary measurements and examination. When the correct estimate of the weight that the floors in any such buildings will safely sustain has been ascertained as herein provided, the Department of Buildings shall approve the same, and thereupon the owner or occupant of said build¬ ing, or of any portion thereof, shall post a copy of such approved estimate in a conspicuous place on .each story or varying parts of each story of the building to which it relates. * * * No person shall place or cause or permit to be placed on any floor of any building any greater load than the safe load thereof, as correctly estimated and ascertained as herein provided.” TABLE V WEIGHTS OF MERCHANDISE, IN BULK, FOR CALCULATING LIVE LOADS Materials Measurements Approximate Weights Floor Area Square Feet Contents Cubic Feet Total Pounds Pounds per Square Foot Pounds pc Cubic Foot Cotton , etc.: Bale of commercial cotton . 8.1 44.2 5 T 5 64 12 Bale of compressed cotton . 4.1 21.6 550 134 25 Bale of American Cotton Co. 4.0 11.0 263 66 24 Bale of Planters Compress Co. 2-3 7.2 254 110 35 Bale of jute. 2.4 9.9 300 125 30 Bale of jute lashings .... 2.6 10.5 450 172 43 Bale of manila. 3-2 10.9 280 88 26 Bale of hemp. 8.7 34-7 700 81 20 Bale of sisal. 5-3 17.0 400 75 24 Cotton Goods: Bale of unbleached jeans 4.0 12.5 300 75 24 Piece of duck. 1.1 2.3 7 5 68 33 Bale of brown sheetings . . 3-6 10.1 235 65 23 Case of bleached sheetings . 4.8 11.4 330 69 29 Case of quilts. 7.2 19.0 295 4 i 16 Bale of print cloths .... 4.0 9-3 175 44 19 Case of prints. 4-5 13-4 420 93 3 i Bale of tickings. 3-3 8.8 325 99 37 Burlaps. 130 30 Jute bagging. 1.4 5-3 100 7 i 19 Grain: Wheat in bags. 4.2 4.2 165 39 39 Flour in barrels on side . . 4.10 5-40 218 53 40 Flour in barrels on end . . 3.10 7.10 218 70 3 i Corn in bags. 3.60 3.60 112 3 r 3 i Corn meal in barrels .... 3-70 5 - 9 ° 218 59 37 Oats in bags. 3-30 3.60 96 29 27 Bale of clover hay. 5.00 20.00 284 57 14 Clover hay, derrick com- . V pressed. i -75 5-25 125 71 24 Straw ... . i -75 5-25 100 57 19 Tow. i -75 5-25 150 86 29 Excelsior. i -75 5-25 100 57 19 Rags in Bales: White linen. 8.50 39-50 910 107 23 White cotton. 9.20 40.00 7 1 5 78 18 Brown cotton. 7.60 30.00 442 58 15 Paper shavings. 7-50 34.00 507 68 15 Sacking. 16.00 65.00 450 28 7 Woolen. 7-50 30.00 600 80 20 Jute butts. 2.80 11.00 400 M 3 36 Hoot: Bale, East India. 3 -o 12 340 113 28 Bale, Australian .... 5-8 26 385 66 15 10 TABIjE V— ( Continued) Materials Measurements Approximate Weights Floor Area Square Feet Contents Cubic Feet Total Pounds Pounds per Square Foot Pounds per Cubic Foot Wool: Bale, South American . . . 7.0 34-0 1,000 143 29 Bale, Oregon. 6.9 33 -o 482 70 15 Bale, California. 7-5 33-0 550 73 17 Bag of wool. 5-0 30.0 200 40 7 Sack of scoured wool . . . 5 Woolen Goods: Case of flannels. 5-5 12.7 220 40 17 Case of flannels, heavy . . 7 -i 152 330 46 22 Case of dress goods .... 5-5 22.0 460 84 21 Case of cassimeres. 10.5 28.0 550 52 20 Case of underwear. 7-3 21.0 350 48 17 Case of blankets. 10.3 35 -o 450 44 13 Case of horse blankets . . . 4.0 14.0 250 63 18 Miscellaneous: • Box of tin. 2.7 • 5 139 5 i 278 Crate of crockery. 9.9 39-6 I ,600 ] 62 40 Cask of crockery. 13-4 42.5 600 45 14 Bale of leather. 7-3 12.2 190 26 16 Bale of goat skins. 11.2 16.7 300 27 18 Bale of raw hides. 6.0 30.0 400 67 13 Bale of raw hides, com- pressed. 6.0 30.0 700 ii 7 23 Bale of sole leather .... 12.6 8.9 200 16 22 Barrel of granulated sugar 3-0 7-5 317 106 42 Barrel of brown sugar . . . 3 -o 7-5 339 113 45 Hogshead of bleaching powder. 11.8 39-2 1,200 102 3 i Hogshead of soda ash . . . 10.8 29.2 1,800 167 62 Box of indigo. 3-0 9.0 385 128 43 Box of sumac. 1.6 4.1 160 100 39 Caustic soda in iron drum . 4-3 6.8 600 140 88 Barrel of starch. 3 -o 10.5 250 83 24 Barrel of pearl alum .... 3 -o 10.5 350 117 33 Box of extract logwood . . 1.1 .8 57 52 7 i Barrel of lime. 3-6 4-5 225 63 50 Barrel of Portland cement . 3-8 376 100 to 120 Barrel of natural cement . . 3-8 282 75 to 95 Barrel of slag cement . . . 3-8 330 80 to 100 Barrel of English Portland cement. 3-8 5-5 400 105 73 Barrel of plaster. 3-7 6.1 325 88 53 Barrel of rosin. 3 -o 9.0 430 143 48 Barrel of lard oil. 4-3 12.3 422 98 34 Books in library. 30 Crowd of men. 134 to 157 17 211—35 18 LOADS IN STRUCTURES §41 TABLE YI AVERAGE WEIGHTS OF MISCELLANEOUS MATERIALS Name of Material Average Weight per Cubic Foot Pounds Name of Material Average Weight per Cubic Foot Pounds Acid, acetic. 66 Clay, potters’, dry . . . 119 Acid, fluoric. 94 Clinker. 85 Acid, muriatic (hydro- Coal, anthracite, broken 54 chloric). 75 Coal, anthracite, mod- Acid, nitric. 76 erately shaken . . . 58 Acid, phosphoric . . . 97 Coal, anthracite, solid . 93 Acid, sulphuric .... 115 Coal, bituminous, Alabaster, white .... 171 broken, loose .... 54 Alabaster, yellow . . \ 169 Coal, bituminous, Alcohol, commercial . . 52 slaked. 53 Alcohol, grain. 49.6 Coal, bituminous, solid 84 Alcohol, wood. 49.9 Coal, cannel, solid . . . 79 Aluminum . 167 Coke, loose. 23 to 32 Ammonia, 28 percent. . 56 Copper, cast. 552 Antimony. 418 Cork. 15 Asbestos, starry .... 192 Corundum. 244 Ashes. 40 Cotton yarn, in skeins . 11 Asphalt, pure. 80 Earth, common loam, Basalt. 181 loose . 72 to 80 Beer, lager. 65 Earth, common loam, Bismuth . 613 shaken . 82 to 92 Brass. 523 Earth, common loam, Bronze. 546 rammed moderately . 90 to IOO Cement, Portland, Earth, like soft, flowing packed . 100 to 120 mud. 108 Cement, Portland, loose 70 to 90 Earth, like dense mud 125 Cement, natural, Emery. 250 packed . 75 to 95 Ether, sulphuric . . . 45 Cement, natural, loose 45 to 65 Feldspar. 166 Cement, slag, packed . 80 to 100 Flint. 162 Cement, slag, loose . . 55 to 75 Glass, common .... 156 to 172 Chalk. 156 Glass, flint. 180 to 196 Charcoal from birch . . 34 Gneiss, common . . . 168 Charcoal from fir . . . 28 Gneiss, in loose piles . . 96 Charcoal from oak . . . k 21 Gold, cast, 24 carat . . 1,204 Charcoal from pine . . 18 ; Gold, pure, hammered . 1,217 Chrome ore dust, well Grindstone. 134 shaken . 160 Gun metal. 528 Clay, ordinary .... 120 to 150 \ Gunpowder, loose . . . 56 §41 LOADS IN STRUCTURES 19 TABLE VI — {Continued) Name of Material Average Weight per Cubic Foot Pounds Name of Material Average Weight per Cubic Foot Pounds Gunpowder, shaken . . 63 Papei 1 , wrapping . . . IO Gunpowder, solid . . . 105 Paper, writing .... 64 Gutta percha. 6l Paving stone. 1 5 ° Gypsum. M 3 Peat, dry, compressed . 20 to 30 Hematite ore. 306 Petroleum. 55 Hornblende. 203 Pitch. 72 Ice. 1 57 Plaster of Paris, cast . . 80 India rubber. 58 Platinum ...... L 342 Iron, cast. 450 Plumbago. 140 Iron, wrought. 480 Porphyry. 170 Isinglass. 70 Pumice stone. 57 Ivory . 114 Quartz, common pure . 165 Lead, commercial cast . 712 Rosin. 69 Leather, sole, in piles . 17 Rope. 42 Magnesia, carbonate . . 150 Rottenstone .;.... 124 Magnesite, calcined . . no Saltpeter. 131 Magnesium. 109 Salt, coarse. 45 Manganese. 499 Salt, West India, well- Mastic . 67 dried. 74 Mercury, at 6o° F. . . . 846 Sand. 90 to 106 Mica. 183 Silver . 655 Millstone. 155 Slate . 174 Naphtha. 53 Soil, common. 124 Nickel . 548 Soapstone. 170 Niter. 119 Spelter, or zinc .... 437 Oil, linseed. 59 Spermaceti. 59 Oil, olive. 57 Steel. 490 Oil, turpentine .... 54 Sugar . 100 Oil, whale. 58 Sulphur. 125 Ore, hard iron (mag- Talc, block. 181 netite) . 312 Tallow, sheep or ox . . 58 Ore, soft iron (hematite) 306 Tar . 63 Paper, calendered, book 50 Tin. 458 Paper, leather-board . . 59 Trap. 170 Paper, manila. 37 Turf, or peat. 20 to 30 Paper, news. 38 Vinegar . 68 Paper, strawboard . . 33 Whalebone. 81 Paper, supercalendered, Wines. 62 book. 69 Zinc. 437 20 LOADS IN STRUCTURES §41 TABLE VII AVERAGE WEIGHTS OF FARM PRODUCTS Name of Material Weight per Cubic Foot Pounds Name of Material Weight per Cubic Foot Pounds Apples. 38 Fat of mutton .... 58 Apples, dried. 20 Flaxseed (linseed) . . . 45 Apple seeds. 32 Gooseberries. 34 Barley . 38 Grapes with stems . . . 38 Beans, white. 48 Guavas. 43 Beans, castor, shelled . 37 Hay, alfalfa, in bales . 12 . 51014.3 Beeswax . 61 Hay, alfalfa, in rectan- Beets. 44 gular double-com- Beggarweed seeds . . . 50 pressed bales .... 23.53 Blackberries. 32 Hay, alfalfa, in cylin- Blueberries. 34 drical double-com- Blue-grass seeds .... 11 pressed bales .... 36.36 Bran. 16 Hay, clover, in bales . 14 Brorae grass. 11 Hay, clover,compressed 24 Broom-corn seed . . . 30 Hay, clover, in mow 4.6 Buckwheat. 39 Hair, plastering .... 6 Butter . 59 Hemp seed. 35 Cabbage . 40 Hickory nuts. 40 Canary seed. 48 Hominy. 49 Cantaloupe, melon . . . 40 Horseradish. 40 Carrots. 40 Hungarian grass seed . 39 Cheese. 30 Indian corn, or maize . 45 Cherries. 40 Italian rye-grass seed . 16 Chestnuts. 43 Johnson grass .... 22 Chufa. 43 Kaffir corn. 45 Cider . 64 Kale. 24 Clover seed. 48 Land plaster. 80 Corn on the cob, husked 56 Lard. 59 Corn on the cob, un- Lime. 64 husked . 58 Malt. 27 Corn, shelled. 45 Meal. 37 Corn meal, bolted . . . 37 Middlings, coarse . . . 38 Corn meal, unbolted . . 38 Middlings, fine .... 32 Cottonseed. 25 Milk. 65 Cranberries. 29 Millet. 40 Currants. 32 Millet, Japanese barn- Fat of beef. 58 yard. 28 Fat of hogs.. 59 Mustard. 24 §41 LOADS IN STRUCTURES 21 TABLE VII — [Continued) Name of Material Weight per Cubic F'oot Pounds Name of Material Weight per Cubic Foot Pounds Oats. 26 Redtop. II Onions. 45 Rhubarb. 40 Orchard-grass seed . . 11 Rice corn . 45 Osage-orange seed . . . 26 Rice, rough. 35 Parsnips. 38 Rutabagas. 45 Peaches . . 40 Rye . 45 Peaches, dried and Rye meal. 40 peeled . 26 Sage. 3 Peanuts. 18 Sorghum seed .... 37 Pears. 39 Spelt, or speltz .... 34 Peas. 48 Spinach. 24 Plums. 42 Straw. 19 Plums, dried. 22 Strawberries. 32 Popcorn . 56 Sugar-cane seed . . . •46 Popcorn, on the cob . . 34 Tares. 49 Potatoes, white .... 48 Timothy seed. 36 Potatoes, sweet .... 4 i Tomatoes. 44 Prunes, dried. 22 Turnips . 44 Prunes, green. 36 Velvet-grass seed . . . 6 Ouinces. 38 Walnuts. 40 Rape seed. 40 Wheat. 48 Raspberries. 32 10 . Additional information about weights of materials is found in Tables VI, VII, VIII, and IX. Table VI gives the average weight per cubic foot of miscellaneous materials likely to be stored; Table VII, the average weights of farm products; Table VIII, the average weight per cubic foot of various native and foreign woods; and Table IX deals solely with woods found in the Philippine Islands. The weight of woods depends very much on the amount of moisture they contain. The weights given in Tables VIII and IX are for commercially dry, or well-seasoned, wood, and not for green wood. 22 LOADS IN STRUCTURES §41 TABLE VIII WEIGHT OF WOODS, COMMERCIALLY DRY Name of Tree Average Weight per Cubic Foot Pounds Name of Tree Average Weight per Cubic Foot Pounds Alder. 42 Cedar, juniper .... % 35 Apple. 47 Cedar, Palestine . . . 38 Arbor vitae. 19 Cedar, Port Oxford . . 28 Ash, black. 39 Cedar, red. 30 Ash, blue. 44 Cedar, white, or post . 23 Ash, screen. 39 Cedar, white (arbor vitae) 19 Ash, Oregon. 35 Cedar, wild. 37 Ash, red. 38 Cedar, yellow. 29 Ash, white. 39 Cherry, wild black . . . 36 Aspen . 27 Chestnut. 28 Bamboo.'. . 22 Chinkapin. 36 Basswood. 28 Citron. 45 Bay tree. 5 i Cocoa wood . 65 Beech. 42 Cocobolo. 55 Bethabara. 76 Cottonwood . 24 Birch, paper, or white . 37 Cottonwood, black . . * 23 Birch, red. 35 Cucumber tree .... 29 Birch, sweet. 47 Cypress, bald. 29 Birch, yellow. 40 Cypress, Spanish . . . 40 Blue beech (ironwood) . 45 Dagame. 56 Blue gum (fever tree) . 43 to 69 Dogwood. 50 Box elder, or ash-leaved Ebony. 76 maple. 26 Elder tree . 43 Boxwood, Brazilian, red 64 Elm, cork. 45 Boxwood, Dutch . . . . 83 Elm, slippery. 43 Boxwood, French . . . 57 Elm, white. 34 Buckeye, Ohio. 28 Elm, wing. 46 Buckeye, sweet .... 27 Filbert tree. 38 Butternut. 25 Fir, balsam. 23 Buttonwood, or syca- Fir. great silver .... 22 more. 35 Fir, red, or California . 29 Catalpa, or Indian bean 27 Fir, red, or noble . . . 28 Catalpa, hardy .... 25 Fir, white. 22 Cedar, California white 25 Greenheart. 72 Cedar, canoe. 23 Gum, cotton. 32 ’ Cedar, incense. 25 Gum, sour. 39 Cedar, Indian. 82 Gum, sweet. 37 §41 LOADS IN STRUCTURES 23 TABLE VIII- ( Continued ) Name of Tree Average Weight per Cubic Foot Pounds Name of Tree # Average Weight per Cubic Foot Pounds Hackmatack (American • Maple, Oregon .... 30 larch). 33 Maple, red. 38 Hazel. 38 Maple, silver, or soft . 32 Hemlock. 26 Maple, sugar, or hard . 43 Hemlock, Western . . . 28 Mastic tree. 53 Hickory, mocker nut . 53 Medlar. 59 Hickory, pecan .... 49 . Mesquit . 47 Hickory, pignut .... 5 b Missel tree. 59 Hickory, shagbark, or Mulberry, red or black 36 shellbark. 5 i Oak, black. 45 Holly. 36 Oak, bur. 46 Hornbeam . 47 Oak, chestnut .... 46 Ironwood, or blue beech 45 Oak, cow. 46 Iron wood, or hop horn- Oak, English. 5 i beam. 5 i Oak, live, California 5 i Jarrah . 65 Oak, live (found in the Joshua tree. 23 Southern States) . . 59 Jasmine, Spanish . . . 48 Oak, pin. 43 Jucaro Prieto. 67 Oak, post . 50 Juneberry. 54 Oak, red. 45 Karri. 63 Oak, Spanish. 43 Kranji . 64 Oak, white (North- Larch. 38 Central and Eastern Larch, tamarack . . . 46 United States) . . . 50 Laurel, California . . . 40 Oak, white (Pacific Laurel, Madrona . . . 43 Coast from British Lemon. 45 Columbia into Cali- Lignum vitae. 83 fornia) . 46 Linden. 38 Orange, Osage .... 48 Locust, black, or yellow 45 Orange tree . 44 Locust, honey. 42 Paddlewood. 52 Logwood . 58 Palm, Washington . . 32 Madrona. 43 Palmetto, cabbage . . 27 Mahoe. 4 i Pear. 4 i Mahogany . 45 Persimmon. 49 Mahogany, Mexican . . 32 Pine, bull. 29 Mahogany, Spanish . . 53 Pine, Cuban. 39 Mahogany, white . . . 33 Pine, Kauri. 33 24 LOADS IN STRUCTURES 41 TABLE VIII— ( Continued ) Name of Tree Average Weight per Cubic Foot Pounds Name of Tree Average Weight per Cubic Foot Pounds Pine, loblolly. 33 Spruce, black. 28 Pine, long-leaf, or Geor- Spruce, Douglas . . . 32 gia. 33 Spruce, Norway . . . 29 Pine, northern. 34 Spruce, single (balsam Pine, Norway. 3i fir) . . . , . 23 Pine, Oregon. 32 Spruce, Sitka. 26 Pine, pitch. 32 Spruce, white (Northern Pine, short-leaf, or Car- United States) . . . 25 olina. 32 Spruce, white (Rocky Pine, sugar. \ 22 Mountainsand British Pine, white (North-Cen- Columbia). 21 tral and Northeastern Sycamore, or button- States) . 24 wood. 35 Pine, white (Pacific Sycamore, California . 30 States and British Tamarack. 3S Columbia) . 24 Teak. 50 Pine, white (Rocky Tooart. 67 Mountains). 27 Tulip tree. 26 Pingow. 47 Tulip wood. 61 Plum tree. 49 Vine tree. 83 Pockwood. 8 i Walnut, black .... 38 Poplar, or large-tooth Walnut, Circassian . . 35 aspen . 28 Walnut, English . . . 36 Poplar, yellow, or tulip Walnut, Italian .... 42 tree. 26 Walnut, Persian . . . 36 Pomegranate tree . . . 85 Walnut, white .... 25 Quebracho. 82 Wasahba. 76 Quince tree. 44 Whitewood. 26 Redwood. 26 Willow, black. 27 Roller wood. 52 Yarura. 52 Rosewood. 68 Yew, Dutch. 49 Sassafras. 3i Yew, Spanish. 50 Shadblow. 54 Yucca, or joshua tree . 23 Shadbush . 54 41 LOADS IN STRUCTURES 25 TABLE IX WEIGHT OF PHILIPPINE WOODS Name of Tree Average Weight per Cubic Foot Pounds Name of Tree Average Weight per Cubic Foot Pounds Acle . 37 Liusin. 44 Amuguis. 43 Lumbayao. 35 Apitong. 4 i Macaasin. 44 Aranga . 54 Malasantol. 40 Balacat. 33 Malugay. 40 Balacbacan. 34 Mayapis. 25 Bansalaguin. 53 Molave. 49 Banuyo . 33 Narra. 36 Batitinan. 49 Palo Maria. 39 Betis . 49 Sacat. 37 Calantas. 27 Sasalit. 55 Dungon . 49 Supa. 45 Guijo. 43 Tanguile. 30 Ipil. 47 Tindalo . 48 Lauan . 29 Yacal. 52 Example. —What will be the entire live load coming on a large girder supporting a portion of a church floor if the floor area to be supported is 600 square feet? Solution. —From the list given in Table IV, 120 lb. is usually con¬ sidered safe for a live load in a church. Therefore, 600 X 120 = 72,000 lb., the total live load on the girder. Ans. EXAMPLES FOR PRACTICE 1 . What will be the entire live load on the floor of a church 50 ft. X 120 ft.? Ans. 720,000 lb. 2 . What live load will a joist in a city dwelling be required to bear, the distance between centers being 14 inches and the span of the joist 20 feet? Ans. 1,633 lb. 3 . A steel beam in an office building sustains an area of 80 square feet. What will be the live load coming on the beam? Ans. 5,600 lb. 4 . A warehouse used for the storage of South American wool is 40 feet wide and 80 feet long inside. The girders extend across the building and divide it lengthwise into five bays. Provided the floor LOADS IN STRUCTURES 26 §41 construction and the girders weigh 20 pounds per square foot of surface, what is the total dead and live load on each girder? _ Ans. 104,320 lb. 11. In proportioning the live loads on floors, the engineer cannot always exercise his own judgment, for if the building is to be erected in a large city, the live load must comply with the building laws. As such laws are not uniform in the several cities, Table X is given to show the stipulated live loads in the four largest cities in the United States. TABLE X ALLOWABLE LIVE LOADS ON FLOORS IN DIFFERENT CITIES Character of Building Pounds per Square Foot \ New York Chicago Philadelphia Boston Buildings for public assembly . 90 IOO 120 150 Buildings for ordinary stores, light manufacturing, and light storage. 120 100 120 Dwellings, apartment houses, tenement houses, and lodging houses. 60 40 70 50 Office buildings, first floor . . . 150 IOO IOO IOO Office buildings, above first floor 75 IOO IOO IOO Public buildings, except schools 150 Roofs, pitch less than 20° . . . 50 25 30 25* Roofs, pitch more than 20° . . 30 25 30 25* Schools or places of instruction 75 80 Stables or carriage houses less than 500 square feet in area . 75 40 Stables or carriage houses more than 500 square feet in area . 75 IOO Stores for heavy materials, ware- houses, and factories .... 150 150 250 Sidewalks. 300 Note. —In Table X the values given for roofs are for snow and wind loads. In the last column, the roof loads marked with the asterisk (*) do not include the wind load, and the building laws of Boston require that a proper allowance for the wind load exerting a pressure of 30 pounds per square foot of vertical surface shall be made in designing roofs. §41 LOADS IN STRUCTURES 27 SNOW AND WIND LOADS 12 . In calculating the weight on roofs, there are two other loads that must always be considered when obtaining the stresses on the various members of the truss; these are snow and wind loads. When the roof is comparatively flat, that is, when the rise of the roof is under 12 inches per foot of horizontal distance, or is less than \ pitch, the snow load is estimated at 20 pounds per square foot; for roofs of more than 2 pitch, or a rise of more than 12 inches per foot of hori¬ zontal distance, it is good practice to assume the snow load to be 12 pounds per square foot. In northern climates, such as that of Canada, Michigan, and New England, snow loads 50 per cent, greater than the preceding should be assumed. 13 . Wind Pressure. —The wind pressure depends on the velocity with which the air is moving. United States Government tests have determined that the pressure per square foot on a vertical surface is approximately represented by the formula P = .00492 V\ in which p = pressure, in pounds per square foot, of vertical surface; V — velocity of wind, in miles per hour. This formula may be expressed in the form of a rule as follows: Rule. —The wind pressure, in pounds per square foot of vertical surface, is obtained by multiplying the square of the velocity of the wind , in miles per hour, by .00492. The velocity of the wind varies from a pleasant breeze of 2 or 3 miles per hour to a violent hurricane or tornado of 100 or more miles per hour. Careful records, extending over a period of years, show that the velocity of the wind seldom attains 100 miles per hour—probably not more than once in the lifetime of a structure. In cyclonic storms, the velocity of the wind greatly exceeds 100 miles per hour, and structures cannot be built that will withstand their fury. 28 LOADS IN STRUCTURES §41 Table XI was calculated by means of the preceding formula, and it gives the pressure per square foot for various wind velocities up to 100 miles per hour. Though the table indi¬ cates that for 100 miles an hour the pressure per square foot is nearly 50 pounds, modern practice often allows only 30 pounds per square foot for large surfaces, such as the side of a large office building, increasing this to 45 and 50 for unloaded bridges and small surfaces. The reason for this reduction is that the average unit pressure on a large surface is never so great as the maximum unit pressure on a small surface. TABLE XI VELOCITY AND FORCE OF WIND, IN POUNDS PER SQUARE FOOT, ON A VERTICAL SURFACE Strength of Wind Miles per Hour Feet per Minute Feet per Second Force in Pounds per Square Foot Hardly perceptible . . . I 88 I.47 .005 2 176 2-93 .020 Just perceptible .... 3 264 4.4 •044 4 352 5-87 .079 Gentle breeze. 5 440 7-33 .123 io 880 14.67 •492 Pleasant breeze . 15 1,320 22.00 1.107 Brisk gale. 20 1,760 29-33 I.968 25 2,200 36.67 3-075 High wind. 30 2,640 44.00 4.428 35 3,080 51-33 6.027 40 3,520 58.67 7.872 Very high wind .... 45 3,960 66.00 9963 Storm. 50 4,400 73-33 12.300 6o 5,280 88.00 17.712 Great storm. 70 6,l6o 102.67 24.108 8o 7,040 H 7-33 31-488 Hurricane or cyclone . . IOO 8,800 146.67 49.200 14, Curved surfaces, such as would be presented by cir¬ cular towers and stacks, and flat surfaces not in a vertical plane, as roofs, are subjected to less pressure than flat vertical surfaces. The pressure on a cylindrical surface is about one-half the pressure on a flat surface having the same §41 LOADS IN STRUCTURES 29 width as the diameter of the cylinder and the same height. If p\ Fig. 5, represents the direction and strength of the wind pressure against the roof a be, it is the normal com¬ ponent p that must be ascer¬ tained in order to calculate the total pressure normal to the roof, or to determine the stresses in the members of a roof frame or truss. The other component p p is act¬ ing upwards and in a direc¬ tion parallel with the slope. The latter force is not taken into consideration. The wind, supposed to exert a horizontal pressure of 40 pounds, strikes the roof at an angle; consequently, the pressure p , normal to the slope, is considerably less than 40 pounds, unless, of course, the slope of the roof is very steep. On referring to Figs. 5 and 6, it will be evident that the action of the horizontal force p' on the slope of the roof, shown in Fig. 5, is almost as intense as on a vertical surface. How¬ ever, on the very flat roof, as in Fig. 6, the wind exerts hardly any force nor¬ mal to the roof surface, because it strikes the slope at such an acute angle that the force p p is nearly equal to p ', and the tendency of the wind is simply to slide along the slope surface. The more acute the angle between the forces p' and />, the greater is p, that is, the greater the pressure normal to the slope; whereas, the greater the angle between these forces, the smaller will p be, that is, the less the pressure normal to the slope, until they approximate a right angle with each other, when the pressure p may be disregarded. The full discussion of the relation between p’ and p is somewhat more complex than the one given here; however, it shows in a general way why p is more nearly equal to p’ b 30 LOADS IN STRUCTURES 41 when a roof is steep than when a roof is flat. In the design of roof trusses, a horizontal wind pressure of 40 pounds is usually assumed. • TABLE XII NORMAL WIND PRESSURE FROM HORIZONTAL PRESSURE OF 40 POUNDS PER SQUARE FOOT Wind Pressure Horizontal Rise per Angle of Pitch, Propor- Normal to Foot Slope With tion of Rise Slope Inches Horizontal to Spall Pounds per Square Foot 4 . l8° 26' 1 6 23.00 4-8 . to ►—i o 00 1 5 26.11 6. 26 ° 34 ' 1 4 29.82 8.. 33 ° 4 i' 1 3 33-93 12 . 45° o' 1 2 37-71 16 . 53° 8' 2 3 39.02 18 . 56° 19' 3 4 39-33 24 . 63° 26' I 39-75 15. Ducliemin’s Formula.—All necessary data for calculating the wind pressure on a roof with any one of the customary pitches and a horizontal wind pressure of 40 pounds per square foot are given in Table XII. The formula by which these pressures are determined is known as Ducliemin’s formula. Its derivation is not given here, however, as it is rather complicated. Let p — pressure, in pounds per square foot, normal to slope of roof; p' — wind pressure, in pounds per square foot, on a vertical surface; x = internal angle of roof with horizontal (see Fig. 4). Then, according to Duchemin, P 2 sin x 1 + sin 2 x Example. —Find the normal pressure on a roof of 30 ° slope when the horizontal wind pressure is 40 pounds per square foot. 841 LOADS IN STRUCTURES 31 Solution. —Substituting values for the letters in the formula, . P 40 X 2 X sin 30 ° 40 X 2 X .5 1 -f- sin* 30 ° — 1 + .25 ~ 32 lb. per sq. ft. Ans. 16 . The diagram shown in Fig. 7 has been made so as to facilitate the finding of the normal pressure p for the usual slopes and pitches and for horizontal wind pressures of 20, 30, and 40 pounds per square foot. The values given to the three curves shown in the diagram are found by means of the formula of Art. 15 . Wind Pressure Normal to Slope of Roof in Pounds Per Square Foot Fig. 7 The values of the normal pressure for a given slope and a horizontal wind pressure of 20, 30, or 40 pounds may be found as follows: Assume that it is desired to find the normal pressures on a roof having an angle with the hori¬ zontal of 40°. Proceed along the horizontal line marked 40° until it intersects the curve marked 20 lb ., which represents a horizontal wind pressure of 20 pounds. The point of intersection indicates the normal pressure p , the value of 32 LOADS IN STRUCTURES 41 which is found by drawing an imaginary vertical line to the base line, which is marked off in pounds of pressure per square foot. It is found that the normal pressure p amounts to 18.2 pounds per square foot. Proceeding in the same manner, it is found that for horizontal pressures of 30 and 40 pounds, the normal pressures are 27.3 and 36.4 pounds per square foot, respectively. 17. In Fig. 8 , the normal force p has been resolved into its two components, p h and p v , the former acting in a hori¬ zontal direction and the latter in a vertical one. The force p h tends to push the roof in a direction par¬ allel with the wind, while the force p v tends to depress the roof or, in some cases, to press it sidewise. In open sheds, where the wind is liable to strike the inner, far side of the shed roof, as shown in Fig. 9, the effect of the force p v must be considered, as its tend¬ ency would be to lift the roof. Duchemin has deduced the following formulas for p h and p v \ 2 sin’ jr Fig. 8 PH=P' 1 + sin* x . ,,2 sin X cos x pv = p' - —- 1 -f sin x (1) ( 2 ) Example. —A shed roof has an angle of slope with the horizontal equal to 18 ° 26 ' and is subjected to a wind pressure p' — 40 pounds per square foot. Find the values of p h and p v for the lee side of the roof. Solution. —Substituting values in formula 1 , ph = 40 X 2 X sin 2 18 ° 26 ' 80 X .1 1 + sin 2 18 ° 26 ' 1 + .1 = 7.27 lb. per sq. ft. l + .l §41 LOADS IN STRUCTURES 33 Substituting values in formula 2 , p-v - 40 X 2 X .316 X . 949 i + .1 21.81 lb. per sq. ft. Ans. 18 . In order to explain Table XII more fully, assume the conditions shown in Fig. 10. The rise in the slope ab is 6 inches for every 12 inches on the horizontal line ac\ for instance, at 4 feet from a on the horizontal line ac, the rise is four times 6 inches, or 2 feet, the angle included between the line of slope a b and the horizontal base line a c is 26° 34', and the pressure normal to the slope, according to Table XII, is 29.82 pounds per square foot. Since the rise at the center is equal to one-half the length of one-half the span, the total rise is one-quarter of the span. Under these conditions, the pitch of the roof, that is, the ratio of the rise to the span, is I, and the roof is said to be } pitch. Example. — (a) What will be the dead load per square foot of roof surface on a roof with a 12-inch rise per foot horizontal, the span of the iron trusses being 50 feet, and the roof covering being made up of 1 -inch white-pine sheathing, two layers of Neponset roofing felt, and 6 " X 18 " shingles 5 inches to weather? (b) What will be the wind pressure per square foot normal to the slope? (c) If the roof trusses are placed 12 feet apart, what will be the entire dead load on one 211 — 36 34 LOADS IN STRUCTURES §41 truss? Fig. 11 shows a plan with elevation and detail section of the roof. Solution. — ( a ) It is first necessary to obtain the length of the line of slope ad; this is done by calculating the hypotenuse of the triangle, or by laying the figure out to scale and measuring. In the first case it is found that ad measures about 35.36 ft. The area of the roof supported by one truss is 2 X 35.36 X 12 = 848.64 sq. ft. According to Table III, the approximate weight of a roof truss of ^ pitch and with a span of 50 ft. is 3.182 lb. per sq. ft. of roof surface. Using the approximate value of 3.2 lb., the dead load per square foot of roof surface is, then, as follows: Weight of supporting truss. 3.2 lb. per sq. ft. Weight of white-pine sheathing, 1 in. thick 3.0 lb. per sq. ft. Weight of two layers of Neponset roofing felt .5 lb. per sq. ft. Weight of shingles. 2.0 lb. per sq. ft. Total. 8.7 lb. per sq. ft. §41 LOADS IN STRUCTURES 35 The weight of the purlins supporting the sheathing has not been estimated, it being safe in this case to assume that the weight used for the principals, or trusses, is sufficient to cover this item. A snow and accidental load of 12 lb. per sq. ft. of roof surface should also be added to the dead load to get the entire vertical load on the roof. (0 The wind pressure normal to the slope of this roof, according to Table XII, for a -^--pitch roof, is 87.71 lb., say 38 lb. persq. ft. Ans. (c) The area of the roof supported by one truss is, as previously found, 848.64 sq. ft. and the dead load 8.7 lb. per sq. ft. Then, 848.64 X 8.7 = 7 , 383.17 lb. to be supported by one truss, not including the snow load. Ans. EXAMPLES FOR PRACTICE 1 . With the wind blowing at a velocity of 36 miles per hour, what is the pressure in pounds per square foot of vertical surface? Ans. 6.38 lb. per sq. ft. 2 . The area of one slope of a ^-pitch roof is 800 square feet. What is the entire pressure on the slope of the roof provided the maximum horizontal wind pressure is taken at 40 pounds per square foot? Ans. 30,168 lb. 3 . In a ^-pitch roof, the trusses are 20 feet apart and the length of the roof slope is 40 feet. What wind load is there on each roof truss if the horizontal pressure is 40 pounds per square foot? Ans. 23,856 lb. 4 . The purlins supporting a -f-pitch roof are placed 6 feet apart, and the trusses are 12 feet from center to center. What is the load due to the wind on each purlin provided the greatest horizontal pressure is 40 pounds per square foot? Ans. 2,832 lb., nearly 5 . The angle that the slope of a roof makes with the horizontal is 40 °. Provided the wind exerts a pressure of 30 pounds per square foot of vertical surface, what is the pressure normal to the slope? Ans. 27.3 lb. per sq. ft. DISPOSITION OF LOADS 19. In warehouses built especially for the storage of heavy merchandise, where the floors are likely at any time to be fully loaded, the beams, girders, columns, and founda¬ tions are always proportioned for the entire live and dead loads on all floors. However, where the building exceeds four or five stories in height and is used for any other pur¬ pose than for storage, as, for instance, a modern office build- 36 LOADS IN STRUCTURES §41 ing, it is customary to assume that certain members, while proportioned for the entire dead load, carry only a certain percentage of the live load. In an office building, or similar structure, it is highly improbable that all the floors or all parts of the same floor will be fully loaded at the same time, and in view of this fact it is considered good practice, while proportioning the floor- beams for the full live load, to calculate only 90 per cent, of the live load on the girders and columns. The term girders as used here indicates the larger beams that support the floor- beams. It is customary to proportion the columns supporting the roof and the top floor for the full live load. The live loads on the columns, in each successive tier, from the floor above is reduced 10 per cent, until 50 per cent, of the live load is reached, when such reduced loads are used for all the remain¬ ing floors to the basement. The economy obtained by this disposition of the live load is best observed from Table XIII, which gives the distribution of the assumed live loads on the columns in the several tiers of an eighteen-story office building. The following may serve to explain the data given in Table XIII: a represents the live load on each floor, in pounds per square foot; a lf the live load on each floor, in pounds per square foot, reduced by 10 per cent., as a x = .90 a; X a, the sum of all live loads, in pounds per square foot, on a column from all floors above, if no reduction is made; and 2 a it the sum of all live loads, in pounds per square foot, on a column from all floors above, if 10 per cent, reduction is made. The theoretical percentage of saving resulting from the reduction of 10 per cent, on the upper floors is found by the v a _ v a formula---These percentages of saving are given 2 a in the last column of the table. It should be understood that each column supports a given floor area and that the load coming on each column will depend on the extent of this area multiplied by the live load, in pounds per square foot of floor. Each column carries not alone this load, but also the loads transmitted directly from §41 LOADS IN STRUCTURES 37 column to column. Thus, the column supporting the fifteenth floor supports also four other columns above with all their loads. While this system of graduating the live loads on the columns from floor to floor is generally practiced, the amount TABLE XIII REDUCTION OF DIVE LOADS FROM FLOOR TO FLOOR Floors a a, = .90 a 2’a 2 ci ! la - Sa x la Roof 20 20.00 20 20.00 18 6o 60.00 80 80.00. 1 7 6o 54.00 140 134.00 4-3 16 6o 48.60 200 182.60 8.7 15 6o 43.74 260 226.34 12.9 14 6o 39-37 320 265.71 17.0 13 6o 35-43 380 301.14 20.8 12 6o 31.89 440 333-03 24.3 I I 6o 30.00 5,00 363-03 27.4 JO 6o 30.00 560 393-03 29.8 9 6o 30.00 620 423.03 31.8 8 6o 30.00 680 453.03 33-4 7 6o 30.00 740 483-03 34-7 6 6o 30.00 800 513.03 35-9 5 6o 30.00 860 543-03 36.9 4 6o 30.00 920 573-03 ■ 37-7 3 6o 30.00 980 603.03 38.5 2 6o 30.00 1,040 633-03 39-1 I 6o 30.00 1,100 663.03 39-7 of reduction at each floor is a matter that depends on the judgment of the designer. The percentage of reduction is often fixed by the building laws of a city, with which the designer must comply. The reduction of 10 per cent, at each floor, the economy of which is shown in Table XIII, is conservative, and in most cases it will be found to be in 38 LOADS IN STRUCTURES §41 accordance with the rules of the building - departments of the principal American cities. 20 . In the design of the type of building known as skeleton construction, that is, one in which all floors and walls are supported on beams and girders that transmit the loads to columns and, in turn, are supported on ample foundation footings, it is necessary to fix on the general arrangement, disposition, and approximate dimensions of the component parts before the dead load can be computed. After the calculations are made and the structural details are designed, the actual dead load should be checked to see whether it approximates the assumed load. If any consider¬ able variation is found, it can be provided for by increasing or diminishing the weight or thickness of the rolled steel shapes making up the structural members, the sizes of which have already been determined. Where permanent partitions exist, they should always be figured in the dead load; and where they are directly above a beam or a girder, the member should be proportioned to sustain the additional weight without appreciable deflection. Where movable partitions occur or where there is a proba¬ bility of the location of permanent partitions being changed, it is customary to add 20 pounds per square foot of floor surface to the dead load to take care of such contingencies. The foundations of an office building should be propor¬ tioned for the entire dead load and only a portion of the live load, the latter being provided for by making the unit pres¬ sure on the footings and piers well within the safe unit bearing value of the soil. In this way unequal settlement is prevented, as will be explained in a future Section. FIRE AND FIRE INSURANCE PURPOSE OF FIRE INSURANCE 1. Definition and Scope.—Insurance engineering is the modern science of reducing the chances of loss of property by fire to a minimum by confining fires to the smallest limits possible. It was first practiced on an exten¬ sive scale by the factory mutual fire-insurance companies of New England, and has been brought to a high state of development by them. The proof of this statement lies in the fact that under their system of insurance, the average annual cost of $100 of insurance for a period of 6 years end¬ ing December 31 , 1906 , was .0754 cent. Though first applied to individual mills and factories, insurance engineering has been gradually extended to all classes of buildings, even to dwellings and costly residences, and the fire hazard of cities, taken as a whole, is now dealt with according to the same principles. Its successful applica¬ tion may be said to depend on a practical knowledge of a number of the more familiar branches of engineering, as hydraulics, chemistry, electricity, building construction, etc. 2. Relation Between Credit and Fire Insurance. A statement of the close relation existing between business credit and fire insurance will give some idea of the prominent place occupied by insurance engineering today. Thirty years ago F. C. Moore, ex-president of the Continental Fire Insurance Company, of New York, said regarding fire insur¬ ance: “.it has become a necessity of trade; without its assuring protection, undertakings of the magnitude at COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ENTERED A'l STATIONERS' HALL, LONDON 2 INSURANCE ENGINEERING 42 present readily assumed would never be attempted; ventures are made, without hesitation, which would appal those embarking in them if liable to miscarry through a single fire; large values are boldly collected to meet the require¬ ments of commerce, where an accidental conflagration might destroy them in a night; loans are made by the capitalist on insured buildings for many times the value of the land on which they stand, simply because the insurance policy, as collateral between him and loss, makes it valuable for security; merchants sell their goods on extended credits, knowing that, although the misfortune of fire may Overtake the purchaser, his insurance indemnity will enable him to pay for them not less readily than before; vast industries giving employment to thousands of operatives and support¬ ing whole towns by their enterprise testify not more to the energy of their projectors than to the confidence they repose in the protection which insurance extends to their undertakings.” The conflagrations in Paterson, Baltimore, and San Fran¬ cisco, in recent years, demonstrated beyond a doubt the utter dependence of merchants and manufacturers on fire insurance for means with which to replace what was destroyed by fire, and at the same time again emphasized the necessity of preventing conflagrations. By conflagration is meant a fire in which a great number of buildings is involved. Another significant feature of the present situation is the long lists of firms and individuals, published at frequent intervals, who cannot obtain all the insurance they require against fire. _ CAUSE AND PREVENTION OF FIRES FREQUENCY OF FIRES 3 . The underlying cause of the enormous waste of property every year is the frequency of fires. The total loss for the year 1875 was $ 78 , 102 , 285 ; and for the year 1906 , $ 518 , 611 , 800 . If fires occurred only occasionally, there would be little need for costly public fire departments, for §42 INSURANCE ENGINEERING 3 the work of insurance engineers, or, indeed, for insurance against fire losses. But public records show two things; TABLE I FIRE RECORD OF VARIOUS CITIES Name of City Population in 1900 Number of Fires in 1900 Number of Fires in 1906 New York .... 3,437,202 8,405 12,182 Chicago. 1,698,575 5,503 . 4,088 Philadelphia . . . 1 , 293,697 2,944 3,392 St. Louis .... 575,238 2,165 2,264 Boston. 560,892 1,560 2,489 Baltimore .... 508,957 1,438 1,307 Cleveland .... 381,768 1,492 1,8ll Buffalo. 352,387 1,020 1,425 San Francisco . . 342,782 988 685* Cincinnati .... 325,902 1,094 Pittsburg .... 321,616 457 1,200 New Orleans . . . 287,104 428 674 Detroit. 285,704 899 L 499 Milwaukee .... 285,315 i ,073 1,561 Washington . . . 278,718 573 860 Newark. 246,070 620 745 Jersey City . • . 206,433 597 787 Louisville .... 204,731 385 1,004 Minneapolis . . • 202,718 1,002 875 Providence .... 175,597 1,012 1,346 Indianapolis . . . 169,164 1,052 1,130 Kansas City, Mo. . 163,752 1,127 L 732 St. Paul. 163,065 821 909 Rochester .... 162,608 392 638 Denver ..... 133,859 545 * Only a partial record for 1906 , the year of the great conflagration. namely, that the annual number of fires is increasing rapidly, and that the number of fires occurring in any given period is 4 INSURANCE ENGINEERING 42 no indication of the losses of property caused by the fires. Philadelphia may be cited as a case in point. In 1900 there were 2,944 fires, causing - a total property loss of $ 3 , 469 , 063 . In 1904 , the total number of fires was 3 , 395 , but the total property loss was only $ 1 , 640 , 198 . In Table I is given the fire record of the twenty-five largest cities in the United States. This record illustrates the fre¬ quency of fires and the fluctuations in the number that occur in the course of a year. In this table the cities are arranged according to popula¬ tion. It will be noticed that some of the smaller cities have more fires in a year than some of the larger ones. Another phase of the frequency of fires is the number that occur in large manufacturing establishments, the destruction of which would very often mean a much heavier property loss than would result from the burning of the same number of buildings of cheaper construction, or occupied for different purposes. During 1906 , ninety-five fires occurred in a large machine-shop plant in Philadelphia. Fire-marshal laws, which provide for the investigation of fires, have had a wholesome effect, but they have not solved the problem of the annual fire waste. CAUSES OF FIRE 4 . A distinction must be made between the causes of fire and the causes of losses resulting from fires. Losses of property by fire depend, of course, on the occurrence of fire, but the extent of a loss is influenced greatly by other factors, or conditions, that favor the spread of a fire when once fairly started. Generally speaking, carelessness and apathy are the most common causes of fire. “No one can carefully read the figures contained in the Fire Marshal’s report to me,” said Fire Commissioner Francis J. Lantry, of New York City, commenting on the report for 1906 , “without being astounded at the number of fires that could have been prevented by the exercise of very ordinary caution. I think that if the public 42 INSURANCE ENGINEERING 5 mind is sufficiently aroused for the proper exercise of this caution, the people generally can become of great service to this department in the prevention of fires. The Fire Mar¬ shal’s Bureau is for the investigation and determination of the causes of fires, and the head of that bureau reports that in the Boroughs of Manhattan, the Bronx, and Richmond, among the principal causes of fires ascertained by his investi¬ gation, 887 were due to carelessness with matches and 228 due to children playing with matches or fires. Carelessness . in the use of lighted cigars and cigarettes caused 401 fires; overheated stoves, stovepipes, etc. are charged with the responsibility for 419 fires; bonfires, brush fires, etc. are charged with 282 ; carelessness with candles, tapers, etc., 386 ; gaslight in contact with curtains, etc., 216 ; lamps, kerosene, etc. upsetting or exploding, 161 .” 5 . Underwriters divide the causes of fire into two heads: common ca?ises (common hazards) and special causes (special hazards). • . The common causes are artificial lighting (arc electric, incandescent electric, ordinary city gas, gasolene gas, acety¬ lene gas, kerosene-oil lamps, kerosene-oil lanterns, kerosene- oil torches, and candles); heating (steam, hot air, coal stove, gasolene stove, and oil stove); power (shafting and bear¬ ings, steam engines, gas engines, gasolene engines, and electric motors); boiler, or fuel (coal fuel, waste material or refuse used as fuel, overheated woodwork, sparks from stack, defective chimney, and ashes); rubbish, or sweepings; oily material (oily waste and other oily material); smoking; lightning; sparks from locomotives; and miscellaneous. The special causes are those arising from manufacturing processes, as in cotton mills, woolen mills, rubber factories, iron and steel mills, shoe factories, breweries, etc., and may be divided in general as follows: Storage and handling of raw stock; preparing raw stock; making, or general processes of manufacture; finishing; and disposal of waste material. Common causes and special causes of fire are found in all kinds of manufacturing establishments, but they vary greatly. 6 INSURANCE ENGINEERING §42 Special fire hazards consist chiefly in the nature of the raw material worked, the presence of large quantities of raw material and finished goods (when of a highly combustible nature), and the disposal of the refuse resulting from the processes of manufacture. PREVENTION OF FIRES 6. The terrible consequences of fire, as evidenced by the record of the past 35 years or more, is the strongest argu¬ ment that can be advanced for preventing fires. Aside from the enormous losses of property, thousands of persons have lost their lives in recent years in such fires as the Windsor Hotel fire in New York City, on March 17, 1899; the Iroquois Theater fire in Chicago, on December 30, 1903; the excursion steamboat General Slocum fire, in the East River, New York City, on June 15, 1904; also, the many fires in tenements, apartments, hotels, public halls, boarding houses, college dormitories, and even private dwellings might be cited. Another recurring feature of the annual fire waste is the long list of conflagrations in small places, as, for example, the fire in Bisbee, Arizona, on June 29, 1907, which destroyed more than 200 houses; the fire in Coal Creek, Colorado, on the same date, which destroyed more than 100 buildings; the fire in North Lawrence, New York, on July 5, 1907, which destroyed 38 business buildings and dwellings—practically the entire place. 7. Fires may be prevented by observing the lessons taught by fires and anticipating more fires from well-known or similar causes. In large mercantile buildings, factories, and warehouses, probably the greatest precaution is cleanli¬ ness. Accumulations of dirt and refuse are a constant source of fire and favor the spreading of fire. This applies particularly to accumulations of oily refuse, such as cotton waste that has been used for wiping machinery, oily iron turnings, polishing rags, etc., and accumulations of refuse of a highly combustible nature, as dust, shavings, sawdust, packing materials, etc. Such refuse should never be per- i 42 INSURANCE ENGINEERING 7 mitted to remain in a building overnight, or over a holiday. When such refuse is produced in large quantities, it should be removed by an exhaust blower system, with a dust sepa¬ rator and a vault for the heavier refuse. Oily waste should be collected in approved metal receptacles, such as are recommended by underwriters, and these should be emptied frequently. The amount of refuse made in a day will suggest the danger from fire. 8. All woodwork should be kept free from accumulations of oily drippings and from proximity to boilers, furnaces, chimneys, stacks, steam pipes, portable heaters and furnaces, gas jets, etc. Inflammable and volatile oils should not be used near open lights or fires, and lanterns and open lights should not be carried into rooms where the atmosphere is charged with such vapors. Smoking and the carrying of matches (other than safety matches) should be prohibited. Gasolene-gas, acetylene-gas, and electric lighting should be used only in accordance with the latest recommendations of the underwriters. Hot ashes should not be collected in wooden receptacles, nor should they be thrown on wooden floors or piled against wooden walls or partitions. Large quantities of inflammable or volatile oils should not be stored in the main building. Separate small buildings are pre¬ ferred for the storage of the bulk of these oils, and fireproof rooms should be constructed to store during the night the small quantities left over from the day’s work. In most manufacturing processes there are dangers from fire peculiar to each. These the manufacturers and mill superintendents must understand and appreciate. The care, order, and management of a large establishment are an index to the danger from fire._ SPREADING OF FIRES 9. The cause of the conflagrations that have devastated cities and towns and wiped out settlements has been the ease with which the original fire spread to all parts of the first building, passed beyond those limits by working into adjoin¬ ing buildings and by jumping streets, and thence to block 8 INSURANCE ENGINEERING §42 after block of buildings, in every direction, until the fire Was checked in some manner or burned itself out. Sparks and • brands are carried long distances by the wind, and often start fresh fires. The hot gases of a conflagration will ignite buildings located blocks away from the seat of the fire. An earthquake will start a number of fires simul¬ taneously. The occurrence of a number of fires at the same time, or close after one another, produces the most demor¬ alizing effect imaginable on a public fire department. Not only the firemen, but all the safeguards provided for such an emergency, are taxed to the utmost, perhaps to the point of breaking down. Apparatus and hose are destroyed, and large quantities of water are wasted through the breaking of pipes, thus reducing the pressure and the supply. It is not uncommon for cities to ask for help from other cities at such times, but the value of the assistance of other cities depends on whether the same, or nearly the same, standard of hose and hydrant couplings is used. 10. Causes of tlie Spreading: of Fires. —Following are some of the prominent causes of the spreading of fires from the place of origin: Excessive height of buildings; com¬ bustible or weak walls; combustible or weak roofs; lack of parapet walls; the presence of wooden cornices; superstruc¬ tures; awnings, signs, etc.; wooden bridges connecting build¬ ings; combustible or weak division walls; concealed spaces in division walls; inflammable interior surfaces (varnished, oiled, or painted wood, papier mache, etc.); combustible or weak partitions; concealed spaces in partitions; combustible or weak floors; concealed spaces between floors and ceil¬ ings; combustible floor supports; unprotected metallic floor supports; combustible ceilings; concealed spaces in roofs; unprotected windows, doorways, and skylights; open stair¬ ways, elevator shafts, hoistways, and dumbwaiter shafts; chutes without doors at openings; and belt and shaft open¬ ings in walls and floors. Smoke explosions are undoubtedly a factor in the spread¬ ing of fire. They force out windows and thereby increase 42 INSURANCE ENGINEERING 9 the draft; but this danger appears to be confined to build¬ ings several stories in height and of rather large floor areas. 11. Causes of Conflagrations. —Conflagrations are generally due to the poor construction of buildings; unpro¬ tected, exposed window openings; unprotected communi¬ cations between buildings; narrow streets; lack of proper building laws; non-enforcement of building laws; lack of fire limits; lack of proper water supply; lack of sufficient hydrants; lack of modern fire departments; lack of ordi¬ nance restricting the handling and storage of combus¬ tibles and explosives; lack of ordinance compelling the proper disposal of refuse; lack of ordinance compelling safe electrical installations inside of buildings; and lack of ordinance compelling the placing of all outside wires under¬ ground. Too much stress cannot be laid on the importance of window protection, even on street fronts. In the Baltimore and San Francisco conflagrations, modern so-called fireproof office buildings (skeleton steel-frame construction) were badly damaged by fire because the windows were not pro¬ tected against the ingress of fires starting outside of the buildings—“exposure” fires. A building that cannot be damaged by fire makes a good barrier to the spreading of fire. The so-called fireproof buildings in Baltimore and San Francisco only partly served that purpose. 12 . Conflagration Breeders. —The record of the past shows that conflagrations can start in almost any kind of property, but there are classes of buildings that underwriters call conflagration breeders, because fires that get a good start in them are almost sure to develop into conflagrations. Department stores are of this class—buildings of large floor areas, filled with combustible material; especially the type of department store with a large light well extending from the first floor to the roof, making the entire building prac¬ tically one undivided area and “subject to one fire.” 10 INSURANCE ENGINEERING §42 FIREPROOF CONSTRUCTION 13. The development of the United States has been phenomenal. A point has been reached where cities are built to order, as in the case of Gary, Indiana, the new city that has been built by the United States Steel Corporation. But in spite of the great progress in this direction, little thought has been given to the subject of permanency—it has been well said that “we build to burn.” There is no business economy in such a method. Building operations in Greater New York amounted, in 1906 , to $ 228 , 551 , 971 ; in Chicago, during the same period, $ 64 , 822 , 030 ; in Philadelphia, $ 36 , 957 , 520 ; in St. Louis, $ 29 , 938 , 693 ; in Boston, $ 23 , 064 , 741 ; and in San Francisco, $ 33 , 779 , 192 . These amounts include the cost of alter¬ ations and repairs, which in Greater New York in 1906 reached the sum of $ 25 , 000 , 000 . A very small percentage of the buildings in the United States pretend to be fireproof. Wooden construction pre¬ dominates, and a large majority of the brick buildings are of a type that is as easily destroyed by fire as are wooden build¬ ings, because of their combustible interiors—thin wooden floors supported on joists of small dimensions, etc., and roofs of the same construction. Nowadays, wood can easily be dispensed with in the con¬ struction of all classes of buildings. It is no longer required even for trim. A fireproof dwelling costs very little more than one of wood. For buildings located where there is no public fire department, fireproof, construction is imperative. 14. Types of Fireproof Construction. —There are three types of building construction that resist fire success¬ fully, namely, slow-burning , or mill , construction; fireproofed, skeleton steel-frame construction; and reinforced-concrete con¬ struction. 15. Slow-burning, or mill, construction has been employed extensively for mills, factories, and storehouses up to five stories in height, and consists chiefly of substantial l §42 INSURANCE ENGINEERING 11 brick walls; heavy wooden floors without openings, sup¬ ported on heavy wooden beams and posts; and roofs of similar construction. The frame of the building may be supported by the walls, or it may be self-sustaining. Stairs, elevators, and power transmission are placed in brick towers, all openings to the main building being protected by approved fire-doors. The late Edward Atkinson described mill con¬ struction as follows: “ 1 . Mill construction consists in so disposing the timber and plank in heavy solid masses as to expose the least number of corners or ignitible projections to fire, to the end also that when fire occurs it may be more readily reached by water from sprinklers or hose. “ 2 . It consists in separating every floor from every other floor by incombustible stops—by automatic hatchways, by encasing stairways either in brick or other incombustible partitions—so that a fire shall be retarded in passing from floor to floor to the utmost that is consistent with the use of wood or any material in construction that is not absolutely fireproof.” President Atkinson cautioned architects and builders against the misuse and abuse of “mill” construction in the following language: “ 1 . Mill construction does not consist in disposing a given quantity of materials so that the whole interior of a building becomes a series of wooden cells, being pervaded with concealed spaces, either directly connected each with the other or by cracks through which fire may freely pass where it cannot be reached by water. “ 2 . It does not consist in an open-timber construction of floors and roof resembling mill construction, but of light and insufficient size in timbers and thin planks, without fire-stops or fire-guards from floor to floor. “ 3 . It dees not consist in connecting floor with floor by combustible wooden stairways encased in wood less than 2 inches thick. “ 4 . It does not consist in putting in very numerous divi¬ sions or partitions of light wood. 211—37 12 INSURANCE ENGINEERING 42 “ 5 . It does not consist in sheathing brick walls with wood, especially when the wood is set off from the wall by furring, even if there are stops behind the furring. “6. It does not consist in permitting the use of varnish on woodwork over which fire will pass rapidly. “ 7 . It does not consist in leaving windows exposed to adjacent buildings unguarded by fire-shutters or wired glass.” 16 . Mill construction has been abused by architects by adopting only a few of its good features and by disregarding its limitations. On the night of February 11 , 1905 , the new building of the Schwabacher Hardware Company, at the southwest corner of First Avenue (South) and Jackson Street, Seattle, Washington, was practically destroyed by fire. It was eight stories in height, and 70 ft. X 120 ft., with brick walls, two of them being blank. The size of floor posts, the use of combustible material as waterproofing between the flooring, and the fact that the building was 17 feet higher than permitted by law had been criticized by the building department, but it was said at the time that these objections were finally waived. There were no auto¬ matic sprinklers. The fire started in a box of waste or rubbish on the second floor and spread to a light wooden partition. In less than an hour the building collapsed. “The giving way of the roof, which is said to have been able to bear only half the prescribed live weight per square foot, presumably pulled out some of the strap-iron joist hangers, which at the suspension points entered the walls 4 inches. There were no ledges. A large section of the south wall fell out and at intervals other walls fell outward until everything down to the first floor was wrecked.” The fire department lost nearly all its long ladders and 500 feet of hose. 17. Fireproofed skeleton steel-frame construction consists, as the name implies, of a skeleton frame of struc¬ tural steel that is completely encased in fireproofing so as to protect it from the effects of fire. Terra cotta burned at a temperature of from 2 , 000 ° to 2 , 500 ° F. is the fire- §42 INSURANCE ENGINEERING 13 proofing- commonly used. It is made in shapes to fit the various members of the steel frame, and it is used for floor and roof arches and for partitions. It is light and strong— columns of terra-cotta blocks have been used in the place of steel columns for carrying heavy loads. Brick and concrete are also used for fireproofing and for floors and partitions. The concrete is usually reinforced, either with steel rods or with expanded me,tal. The front walls of steel-frame build¬ ings are usually of stone and brick, and the other curtain walls are built of brick or terra-cotta blocks. Without com¬ plete fireproofing, no steel-frame building could withstand the heat coming from an intense fire, and its use for very high buildings, or even buildings more than two stories in height, would probably be prohibited by law. 18. Reinforced-concrete construction produces monoliths—buildings in which the foundations, walls, floors, floor supports, partitions, roofs and roof supports, stairs, etc. are all constructed of concrete reinforced with steel. Terra cotta and reinforced concrete are considered an ideal com¬ bination for fireproof construction. % 19. Object and Requirements of Fireproof Con¬ struction.— The object of fireproof construction should be to confine a fire to certain prescribed limits. To do this, all communications between adjoining rooms and buildings, and between floors, must be protected to prevent the spreading of fire; and all exposed windows should be protected against “exposure” fires. Wooden window frames and sashes should not be used. In New York City, fireproofing systems for floors must pass a test of 4 hours’ exposure to a temperature averaging 1 , 700 ° F., after which the upper side is flooded and water is thrown on the under side. After this a load is put upon the floor. The deflections caused by the temperature are noted with survey¬ or’s instruments. v Comprehensive building laws, properly enforced, are the chief safeguards against poor construction. 14 INSURANCE ENGINEERING §42 EXTINGUISHMENT OF FIRES 20 . Ample facilities for extinguishing fire and good building construction go hand in hand. While the former are doing their work, the latter helps materially by resisting the spreading of the fire. It is a combination of these two features that makes small losses from fire possible. The low cost of insurance under the factory mutual system depends on this combination and its constant maintenance. Fire-extinguishing facilities divide themselves into two heads, namely, private and public. 21 . Private fire protection may consist of casks and pails of water, pails of sand, pails containing a chemical solution; bucket tanks containing a chemical solution and a nest of pails immersed in the solution; liquid chemical extin¬ guishers; inside standpipes extending from the basement to the roof, with hose connections and hose for each floor and with a deluge nozzle on the roof; outside standpipes or connections, with hose; an equipment of automatic sprinklers; outside hydrants with hose houses built over them; a watch¬ man (perhaps several in very large plants) who makes rounds at regular intervals at night, on Sundays, and holidays and records his rounds on a special clock for the purpose; ther- mostats; an auxiliary fire-alarm system connected with the public fire-alarm system; a central-station service for super¬ vising the watchman and automatic sprinkler equipments (in large cities); fire-escapes, ladders, platforms, etc. 22 . Automatic sprinklers are small water valves held shut by fusible solder that will melt at about 165 ° F. They are placed on the ceilings of rooms, and are sup¬ plied with water from two or more sources through a system of piping. The water supplies usually consist of a tank having a capacity of 5,000 gallons or more, located on a trestle above the roof of a building (or on a tower built up from the ground), with the bottom at a height that will give a sufficient water pressure on the highest lines of sprinklers; a fire-pump with a capacity of 500 gallons or more per minute; §42 INSURANCE ENGINEERING 15 a connection with the public water system; etc. The sprinklers are so distributed as to have one for every 100 square feet (10 ft. XlO ft.) of floor area or less, a room 50 ft. X 100 ft. requiring about fifty sprinklers. They are operated by the heat from a fire, the fusible link melting and falling away, thereby opening the sprinkler and allowing the water to be freely distributed on the ceiling and floor immediately above and below it. For a period of 10 years (1897-1907), 75 per cent, of fires in buildings protected by automatic sprinklers were extinguished by the operation of an average of ten sprinklers. It is important that all parts of a building be under the protection of automatic sprinklers, that the water supplies be ample, and that all valves controlling the flow of water in the pipes be kept open. The exceptions to these general rules are clearly stated in the standards of the under¬ writers. The invention of automatic sprinklers revolu¬ tionized the protection of individual buildings against fire, and their use has resulted in a great saving to capital. 23. Public fire protection consists of a waterworks system supplying fire-hydrants distributed throughout the streets of a city or town, a fire-alarm telegraph system for giving alarms of fire, and a fire department equipped with steam fire-engines, hose wagons, hook-and-ladder trucks, water towers, fire-boats, etc. In various cities, salvage corps are maintained. These corps render very valuable service by putting out small fires before they can spread and by covering up perishable goods with tarpaulins, by doing watch service, etc. The greatest need of cities, in view of the grave likelihood of general conflagrations among the buildings in the business sections (the congested districts), is an ample supply of water distributed through large street mains at a high pres¬ sure, so as to prevent fires from becoming conflagrations. The intense heat of spreading fires turns the ordinary hose stream into steam. Volumes of water under a heavy pres¬ sure is the only sure means of extinguishing threatening fires. Such systems are called high-pressure fire-main systems. 16 INSURANCE ENGINEERING 42 Philadelphia has one, and a similar system is installed in the Borough of Manhattan, Greater New York. River water is utilized. Other cities have special fire-main systems that are fed by fire-boats. For small cities or towns, deluge nozzles mounted on battery wagons and supplied by a number of hose streams are invaluable in concentrating a large volume of water on a serious fire. 24. Many large factories are protected throughout with automatic sprinklers, standpipes and hose, casks and pails of water, liquid chemical extinguishers, outside fire-hydrants, watchman service, etc. The employes are formed into private fire companies and are drilled in the use of the private fire appliances. Such private fire protection has given rise to the designation among insurance men of “improved risk.” The term risk as used here means the degree of exposure to fire, improved risk indicating that the chances of loss by fire are lessened. These risks merit the lowest rates of insurance. COST OF INSURANCE ADJUSTMENT OF RATES 25. Insurance rates, or premiums, are the prices charged for insurance against loss by'fire. A rate of 60 cents means 60 cents per $100, or that $1,000 of insurance for one year will cost $6. For a long time no intelligent attempt was made to ascertain the cost of the different ele¬ ments of fire hazards; that is, the difference between the cost of insuring a wooden building and a brick building; the difference between the cost of insuring a building with an elevator in an open shaft and a building with an elevator in. a closed shaft; the difference between the cost of insur¬ ing a building in a city under the protection of a public-paid fire department and a building in a locality not under such public protection; etc. §42 INSURANCE ENGINEERING 17 By carefully studying- the causes of fire and fire losses, underwriters have been able to determine approximately the cost of defects in the construction of buildings that favor heavy losses from fire, the cost of “exposure” from adjoin¬ ing buildings or buildings within a certain distance (due to lack of window protection, lack of fire-walls between adjoin¬ ing buildings, continuous wooden-boxed cornices on a row of buildings, etc.), the cost of management of premises that is conducive to fires due to neglect, the cost of insufficient or unreliable facilities for fighting fires, etc. These numer¬ ous items have been scheduled for the information of owners of property, merchants, and manufacturers, to give them an idea of how the cost of insurance is arrived at and how it may be reduced. 26. All buildings are compared with a standard, and in making insurance rates credits are given for the following desirable features: Small areas, fire-resistive floors, water¬ proof floors, floors arranged for flooding, fireproof floors (especially in the first story), incombustible ceilings and partitions, parapet walls between adjoining buildings (all openings in division and party walls must be protected in an approved manner to make them “fire-walls”) fireproof enclosures for elevators and stairs, fire-resistive coverings for all other openings in floors and walls, approved protec¬ tion for window openings in walls facing other buildings, etc. Credits are also given for the introduction of private fire protection, such as standpipe and hose equipments, casks and pails of water, chemical pails, liquid chemical extinguishers, pails of sand, automatic sprinklers, watchman service, auxiliary fire-alarm service, thermostats, etc. Again, credits are given for improvements in the public fire protec¬ tion, such as increased water supply, increased water pressure, fire-boats, additional apparatus, additional firemen, additional hydrants, larger water mains, approved fire-alarm systems, salvage corps, etc. 27. Until the great majority of poorly constructed build¬ ings that predominate everywhere are torn down and 18 INSURANCE ENGINEERING 42 replaced by structures that are more nearly fireproof, the urgent need of the United States must be the improvement of faulty construction in the sections of cities where con¬ flagrations are liable to occur any day. Schedule rating has shown owners and occupants of buildings how certain com¬ mon defects in the construction of buildings favor heavy losses from fire and the approximate cost of each defect in insurance rates. Schedule rating is not a perfect system of arriving at adequate rates, but it is a vast improvement over the old method of guessing. “A system of insurance rating which does not' discriminate between safe construction and unsafe construction, and between carefulness and neglect, is an injury to the community.” LIMITS OF INSURANCE 28. The wasting of property through destruction by fire is a tax on capital, and so are insurance premiums. The modern system of fire insurance distributes about 65 per cent, of losses on the general public, and 35 per cent, falls on the owners individually. In other words, only about 65 per cent, of losses are covered by insurance. To protect the capital that is invested in the insurance business and to pay losses in full, it is necessary to limit the amount of insurance written on any building and in a certain area taken as a whole. One stock fire-insurance company may be will¬ ing to write a policy for $10,000 on a certain building, whereas another stock company may feel warranted in writing a policy for only $5,000, and so on. A merchant requiring $100,000 of insurance must, in order to cover that amount, get enough companies to insure him. It is a matter of public record that thousands of firms and individuals are unable, every year, to secure all the insurance they require to protect their credit. To be underinsured is to face the most serious consequences of a fire. In many cases the fact that a merchant or a manufacturer cannot secure enough insurance, means that the fire risk of his store §42 INSURANCE ENGINEERING 19 or his mill is so great that some companies will write only the minimum amount and others will write nothing. This situation also means that the amount of insurance to be had from all the companies in the world is decidedly limited: A general conflagration in the wholesale and retail districts of New York City—an impending calamity—would more than equal the loss-paying ability of the entire insurance system. There is not enough insurance capital to provide for the losses that would in all probability occur in that compara¬ tively small area. The fire-insurance business was practically recapitalized after the San Francisco conflagration. 29. The greatest protection to capital and credit is fire prevention and the prevention of undue losses from fire by the adoption of certain simple safeguards. It is a business proposition for individuals and for municipalities. Safe¬ guards cost money, but they constitute an investment in every sense of the word. The high-pressure fire-main system provided by the city of Philadelphia brought about a reduction of 25 per cent, in insurance rates on property in the district protected, and, further, has manifestly brought about a material reduction in the yearly fire loss in that city, even in spite of an increased number of fires. Whatever is done to prevent loss of property by fire must be done thoroughly, or the money invested may be wasted. Thousands of fire-insurance companies have disbanded because the business was unprofitable—not a few have been forced out of existence by general conflagrations. The ( man who cannot shift the liability of loss by fire on the public at large, through the operation of fire insurance, must insure himself in a very true sense. This means that he must do his utmost to prevent losses from fire—losses due to his own neglect and the neglect of his neighbor. The results of insurance engineering as practiced by the progressive underwriters of today bear the highest testimony to the wisdom of fire prevention. WATERPROOFING OF CONCRETE INTRODUCTION REQUIREMENTS OF WATERPROOFING 1. Water-Tightness of Concrete. —Concrete may be considered at first thought to be a waterproof material. Water will not flow through it with a great degree of rapidity, and it may even be used for dams and similar structures where water must be held back. Yet, strictly speaking, concrete is not waterproof. Thin concrete walls are liable to contain small fissures that will permit seepage; also, they are almost invariably sufficiently porous, unless special precautions are taken, to allow the penetration of dampness. The same facts are true, though in a less degree, of mass¬ ive concrete walls. Present engineering practice regards it as essential that some means of resisting water penetration be provided other than the concrete itself. The first rein- forced-concrete roofs were failures until they were provided with additional waterproofing, and although many basements and foundations have been built of concrete or of masonry without waterproofing, there has frequently been difficulty in keeping them free from water, and many of them are subject to dampness. The same remarks apply to the construction of tunnels and subways. Ideas about the necessity of waterproofing have changed greatly in the last few years. In days gone by, dampness was ignored, and the dripping of water from the soffits of arched bridges or the roofs of tunnels was considered of COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY ENTERED AT STATIONERS' HALL, LONDON 22 WATERPROOFING OF CONCRETE §42 little consequence. Modern requirements, however, in the art of waterproofing include the entire exclusion of dampness as well as actual leakage. 2. Degree of Waterproofing. —The term waterproof¬ ing as applied to concrete is relative rather than absolute. There are two aspects from which the variation of the term may be noted. A wall of a culvert or of a sewer may be termed waterproof because it will not allow any large amount of water to percolate through it, yet this same wall might readily allow dampness to penetrate it, and while suitable for a culvert, it would be entirely unfit for a cellar wall. Then, again, a wall of, say, a cellar may keep back moisture and dampness under ordinary conditions because the water pres¬ sure on the outside of the wall is slight; but if this same wall were near the bottom of a tunnel under a river, it would not be waterproof, because the water pressure against it would be very much increased. A structure, therefore, may be called waterproof when it will hold back the required amount of water under the required conditions. To be absolutely waterproof, it must hold back all moisture under the most trying conditions. Of course, if conditions do not require a Structure to be absolutely waterproof, making it so would be only a waste of money. 3. Necessity of Waterproofing. —The importance of waterproofing is so obvious as to require but little explana¬ tion. Plaster and decorations in the basements of buildings, especially modern office buildings in large cities, must be protected from moisture. It is, of course, needless to call attention to the great necessity of waterproofing structural steel in buildings of cage construction. Besides the necessity of waterproofing to protect the materials in the interior of a build¬ ing, so as to prevent their deterioration, waterproofing affects in an important degree the health of a community. Diseases that thrive in damp walls and pools of water in cellars either disappear or are greatly reduced when waterproofing is used. In former times, th'e placing of cellars under houses in the city of New Orleans was considered impracticable, because §42 WATERPROOFING OF CONCRETE 23 they would soon become filled with water owing to the excess¬ ive amount of moisture contained in the soil. Now, how¬ ever, by means of the modern systems of waterproofing, cel¬ lars in New Orleans are kept as dry as those in any other city. 4. In addition to the waterproofing of cellars, it is neces¬ sary in many instances to waterproof sewers, conduits, tunnels, arched bridges, and other engineering structures made of concrete. As an example of the necessity of waterproofing sewers, figures are quoted from a paper read by Myron H. Lewis, C. E., before the Municipal Engineers of the City of New York. These figures show the leakage of ground water into sewers in various localities, and are as follows: Colum¬ bus, Ohio, 100 to 300 per cent, of dry-weather flow; Kalama¬ zoo, Michigan, 20 per cent, of capacity; Norfolk, Virginia, 60 per cent, of pumping; and East Orange, New Jersey, 110 per cent, of dry-weather flow. These figures cannot be com¬ pared with one another because most of them are only estimates and are measured in different ways. Thus, at Kalamazoo the leakage is given as a per cent, of the capacity of the sewer, while in Columbus it is given as a per cent, of the dry-weather flow and in Norfolk as a per cent, of the pumping. All of them, however, ^ show that the useful capacity of a sewer is very much decreased by allowing water to leak into it from outside. c CLASSIFICATION OF SYSTEMS 5. There are three principal methods, or systems, employed in the waterproofing of concrete. They may be termed the integral , the superficial , and the membrane method. The integral method consists in adding something to the concrete when it is placed, or in mixing the concrete in cer¬ tain proportions, so as to make it waterproof throughout. The superficial method consists in coating the concrete with some material that will adhere to the concrete and remain attached. The membrane method consists in putting on the concrete a coating that is distinct from it. While the coating may adhere to the concrete, it does not crack when 24 WATERPROOFING OF CONCRETE §42 the concrete cracks, but is in a distinct membrane usually strengthened by felt or some other fiber cloth. 6. Each of these methods has its advantages and dis¬ advantages. For instance, it is impossible to use the integral method to rectify the seepage of water after a building is already built. In both the integral and the superficial method, a large crack in the concrete will spoil the water¬ proofing effect and will allow water to enter. Again, in both the membrane and the superficial method, care must be exercised not to puncture the waterproof coat. These three methods of waterproofing are closely allied to each other. For example, there are various processes of waterproofing on the market that are about half way between two of the methods. Thus, when paraffin is applied to a concrete surface with a brush, it belongs to the superficial method, and yet the paraffin penetrates the concrete so far as to be almost classed as an example of the integral method. Likewise, some paints may be classed as belonging to the superficial method, and yet they are elastic enough to bridge over minute cracks that may develop in the concrete. '7. It is unfortunate that some manufacturers of water¬ proof compounds make such extravagant claims for their own method while condemning the methods of others. There are so many methods of waterproofing in the market today that the inexperienced engineer is likely to become confused when about to make a selection. Therefore, before trying a method of waterproofing with which he is not familiar, the engineer should satisfy himself, both by laboratory tests and by the examination of buildings that have been made water¬ proof by this method, that the system under consideration is sufficient and will fill the required conditions. It is impossible in this Section to describe all the systems of waterproofing in the market. There are a number of more or less patented or secret processes that have been used with success. Many of these, however, act on the principles to be described and do not differ from each other and from the systems given to a very great extent. §42 WATERPROOFING OF CONCRETE 25 WATERPROOFING METHODS INTEGRAL METHOD MIXING OF CONCRETE 8. According to some authorities, if concrete is properly mixed, it will be impervious to water. The exact mixture to use will depend on the quality of sand and broken stone, and it is only by experiment with the same quality of sand and broken stone that is to be used that this ideal mixture can be arrived at. Of course, it seems hardly necessary to say that this most waterproof mixture is also the densest mixture. Therefore, in searching for the most waterproof mixture of concrete, the engineer really finds the densest mixture. For many grades of sand and broken stone, a 1-1 ^-3 mixture is used. To be impervious to water, concrete must be placed in a wet condition and be well rammed into place. If the concrete is mixed with too little water, it cannot be rammed into a very compact mass with ordinary ramming tools. Concrete, particularly that which is very dense, becomes more impervious to water as it grows older. The first water that penetrates it carries particles of clay and other material that stop up its pores and gradually make it more water¬ proof. 9 . While the method of waterproofing concrete by so proportioning the concrete itself that it is impermeable would appear to be an ideal one, yet the method has some bad features. In the first place, it is much more difficult to proportion the concrete carefully in field work than it 26 WATERPROOFING OF CONCRETE §42 is in the laboratory; and while samples of concrete made in the laboratory might seem impermeable, it is doubt¬ ful whether the same concrete would also seem impermeable when made in the field. Then, again, to obtain a concrete that is entirely impermeable, it must be made fairly rich. Under these conditions, it would often have more strength than is really required; that is, to gain waterproof qualities, it is often necessary to use a better concrete than would otherwise be required. Such a procedure, of course, would not be economical. Concrete, when properly mixed, is waterproof only up to a certain degree. If the water is under great pressure, as at the bottom of very deep foundations in very wet soils, it is probable that moisture will gradually soak through the concrete. Another objection that should not be overlooked is the liability of the concrete to crack. While this danger is under control today, every precaution should be taken to avoid it. ADDING OF DIME OR CLAY 10 . Hydrated Lime. —By hydrated lime is meant lime that has been slaked in water. It can be bought com¬ mercially in the form of a dry powder. For the water¬ proofing of concrete, pqre calcium hydrate, or hydrated lime, as it is called, must be added to the cement. It should be dried and pulverized, however, before adding it to the cement, and in slaking it must be thoroughly mixed with the water in order that no unslaked lumps will remain. Too much water must not be used in slaking, as the extra water is difficult to remove and some of the lime is liable to be dete¬ riorated by it. At present, few contractors slake their own lime, because lime slaked by special machinery, reduced to a fine powder, and packed in bags, can be bought in the market. 11. The purpose of adding hydrated lime to concrete is to fill mechanically the voids in the latter. The lime possesses the property of coating each particle of sand and filling up all the voids around it. WATERPROOFING OF CONCRETE 27 §42 Hydrated lime is a white, soft-feeling, smooth powder that is light in weight. For equal weights, it occupies about two and one-half times the bulk of cement. The results of various experiments differ as to how much hydrated lime affects the strength of the concrete, but it is generally con¬ sidered that the decrease in strength is slight. 12 . If good results are to be obtained with the use of hydrated lime, it must be mixed thoroughly with the dry cement. After the cement and lime are mixed until the color of the mixture is uniform, the sand, broken stone, and water are added as usual. The concrete should be made wet, and great care must be exercised in bonding old and new work. Hydrated lime is intended to assist in making the con¬ crete waterproof. It must not be thought that by adding hydrated lime all care as to the mixing of concrete, the amount of water used, and the placing of the concrete may be dispensed with. These precautions must be taken just the same as if the hydrated lime were not added. 13. The amount of hydrated lime to be added to make concrete waterproof depends on many factors. If fine sand is to be used instead of coarse sand, a smaller quantity of lime will be required. The amount of lime to be employed is usually given as a percentage, by weight, of the cement. Under ordinary conditions, for 1-2-4 concrete, 8 per cent, of lime will be found sufficient, and for 1-3-6 concrete, 17 per cent, of lime will be required. If possible, a good plan is to test the permeability of the concrete that it is intended to use on a certain structure with various percentages of lime before the work is started. For very rich mixtures of concrete, when hydrated lime is to be added, it is well to reduce the amount of cement employed; that is, with rich mixtures, instead of adding the lime as in ordinary mixtures, it is better to substitute the lime for part of the weight of cement. Hydrated lime forms an efficient means of waterproofing concrete under all ordinary conditions. The two most important details to be looked after when using hydrated 211—3S 28 WATERPROOFING OF CONCRETE §42 lime are the careful mixing of the concrete and the intro¬ duction of steel or the use of some other precaution to prevent cracks in the concrete after it has set. 14 . Collodial Clay.—In place of hydrated lime, con¬ crete is often waterproofed by mixing with it finely ground collodial clay. This clay acts in the same manner as the lime and is simply a void filler. It is recommended that clay equal to about 10 per cent, of the weight of the cement be used in a mixture. The clay must be thoroughly dry and well mixed with the cement. If this precaution is not taken, the clay is liable to roll up into little balls. SYLVESTER PROCESS 15 . The Sylvester process of waterproofing concrete is an old one, but it has proved successful on many occasions. It consists in adding powdered alum and soft soap to the concrete. The alum and soft soap combine chemically to form alumina and fatty acids. The compounds are insoluble in water, and they fill up the voids in the concrete with an insoluble, gelatinous mass. In using the Sylvester process, first the sand and cement are mixed together dry, as usual. To this mixture is added alum equal to 1 per cent, of the weight of the mixture. To the water to be used is added 1 per cent., by weight, of soft soap, and this soap is then thoroughly dissolved. The mortar is made wet, and the broken stone is added in the usual manner. Ordinary precautions should be taken to make the concrete dense, and as a rule it is mixed rather wet. METALLIC STEARATES AND OTHER COMPOUNDS 16 . Besides the materials mentioned, various other chemicals are used to make concrete waterproof. One of the most successful of these is calcium stearate, which is a salt of a fatty acid. Calcium stearate fills the pores of the cement and in addition has the power to repel water. §42 WATERPROOFING OF CONCRETE 29 Usually, the quantity of finely ground metallic stearate added to the cement to make the concrete waterproof is about 2 per cent, of the weight of the cement. This material is the base of many well-known commercial waterproofing compounds, and is usually bought under trade names. 17 . Besides the metallic stearates, other substances are used more or less to waterproof concrete by the integral method. A mixture of oil and water has been used with success, as has also chloride of lime. The purpose of the chemicals is usually to fill the voids, and, in addition, some of them are water repellants. SUPERFICIAL METHOD PAINT 18 . If a cement wall leaks after it is built, it cannot be repaired by the integral method. It must therefore be repaired by either the superficial or the membrane method. It is always better, if possible, to put the superficial coat on the side of the wall against which the water presses. This pressure then has a tendency to hold the waterproof coat in place. If the coat cannot be put on the water side of the wall, it must then be placed on the other side. As this is the side that is usually most easily accessible, many inventors have endeavored to obtain a coating that can be success¬ fully put on this side of a structure. 19 . There are many patented waterproof paints on the market that may be used to paint walls on the inside, pro¬ vided the water pressure is not too great. It is impossible to give a complete list of all of them, however, as new ones are being continually manufactured. If the wall develops no large cracks, many of these paints will prove to be very satisfactory. One of the best known of these paints is Toeli’s It. I. W. It is very effective as a waterproof coating if used according to 30 WATERPROOFING OF CONCRETE §42 directions. It sticks to the concrete wall and will not stain stonework. Different grades are made to be used for various purposes and in various locations. Another serviceable paint for concrete is elaterite. It can be painted on the concrete, and plaster may then be put directly on top of it. It is somewhat elastic and forms a film over the concrete, so that hair cracks may develop in the latter without causing the paint surface to open. There are other waterproof paints in the market having about the same properties as the two just mentioned, and they are useful for the same purposes. WAXES 20. To make concrete waterproof, it is sometimes coated with wax. The wax sinks into the pores of the concrete, filling the voids therein and thus preventing the percolation of water. 21. Paraffin is used for waterproofing with considerable success. A paraffin especially hardened to resist the sun’s rays is used. The concrete surface on which the paraffin is to be applied should be thoroughly dry and not very cold. In fact, it is better to warm the surface with a torch if possible. The paraffin is heated and then applied with a brush. The hot paraffin is absorbed by the concrete, into which it penetrates for a short distance. Paraffin will resist the action of acids and alkalies. The treatment just described has been found very effective. Instead of applying paraffin while hot, it may be dissolved in some volatile carrier, such as benzine. The dry wall is painted with this solution, which is readily absorbed. The carrier then evaporates and leaves the paraffin to fill the pores in the surface of the wall. If the carrier is inflammable, care must be taken in using it. 22. There is now in the market an effective waterproofing material known as Minwax. It is a mineral product and contains ozocerite, which, although a mineral, is a near WATERPROOFING OF CONCRETE 31 §42 approach to beeswax. Minwax is not affected by acids and alkalies and is manufactured in various forms. Probably the best form to use is the liquid, which may be applied to the concrete with a brush, the same as paint. Minwax has been successfully used to render concrete waterproof. CEMENTS 23 . One method of waterproofing concrete that is popular is to coat the surface of the concrete with an impervious cement coating. Sometimes this coating is simply a rich, dense cement mortar, sometimes it contains a waterproofing compound similar to those mentioned in connection with the integral method, and sometimes a special waterproof cement is used. There are three features that must be carefully considered in waterproofing by means of cement: (1) The cement coating itself must be waterproof; (2) the engineer must satisfy himself that the walls upon which the cement coating is to be placed will not crack; and (3) the coating must adhere strongly to the wall. To insure that the coating will be waterproof, a proper mixture of reliable materials must be used. Often, the structure is built before the waterproofing problem has been taken up. If there is any likelihood of the walls ever cracking, it is useless to try to waterproof them with an ordinary cement coating, because this will crack also; but if the building has been built properly, the coating of cement should be effective. The third consideration, namely, the adhesion between the coating and the concrete work, requires the most careful consideration. The concrete surface on which the water¬ proof coating is to be placed must first be chipped and scraped to remove all glaze and to obtain a rough texture. The surface must then be washed thoroughly with clean water to remove all dust, and all cracks must be filled with mortar. While the surface is still wet, it is painted with a mixture of cement and water of about the consistency of thick cream. This mixture is applied with a stiff brush and 32 WATERPROOFING OF CONCRETE §42 must be rubbed well into the surface. Before this coat dries the first coat of waterproof mortar is put on, usually about \ inch thick. This coat must be troweled into the surface with great care. Then, before this coat sets, another coat of waterproof mortar of about the same thickness or a little thicker is applied. The successful way of making cement coatings stick is to have the concrete surface very rough and clean and wet, and then to put on each coat before the preceding one has had time to dry or set. BITUMINOUS COATINGS 24. Besides many specially prepared bituminous com¬ pounds sold under trade names, asphalt and coal tar are used for waterproofing by what may be classed as the superficial method. It is sometimes recommended that the surface to be waterproofed should be treated with a preliminary appli¬ cation of dead oil. The material is then applied hot with a mop. Several coatings are usually employed. If a very thick coat is placed on a vertical surface, heat is liable to make it run unless it is supported in some way. Coal tar or asphalt is therefore often used in connection with a cloth fabric, as will be explained under the membrane method. MEMBRANE METHOD MANUFACTURED MEMBRANES 25. There are in the market some excellent waterproofing fabrics and ready-made roofings. It is impossible to describe here the method of using these various fabrics. They are used in different ways, and should be placed according to the directions of their manufacturers. They should be purchased only from reliable concerns who have had success with their product under conditions similar to those which are to be encountered. § 42 WATERPROOFING OF CONCRETE 33 One of the most popular and satisfactory methods of waterproofing is the bituminous membrane that is built into place piece by piece. It is proposed to devote the remain¬ der of this Section to the description and use of this method, as the materials for it can be purchased anywhere and need not be obtained from just one manufacturer. BITUMINOUS MEMBRANES 26 . The common bituminous-membrane method consists in the use of a felt saturated with bituminous material and a bituminous binder. By a binder , as the word would imply, is meant a material that binds two surfaces together; that is, an adhesive material. By a bituminous material is meant any material containing a large proportion of solid or semi¬ solid bitumen, bitumen being that portion of pitch that is soluble in carbon bisulphide, benzol, petroleum, ether, or other similar solvent. The bituminous membrane is built up in place in successive layers, and should form, when finished, a practically homoge¬ neous and continuous waterproof envelope. The functions of the saturated felt and bituminous binder should be clearly understood. The use of the felt is to serve as a retainer of the pitch or bitumen; that is, the felt serves to hold the bitumen in place, while the latter is the waterproofing material. Even though pitch or bitumen appears hard at ordinary temperatures, it is somewhat viscous and has the property of flowing under moderate but continued pressure. This tendency to flow is counteracted by using it in thin layers between successive courses of absorbent felt. The pitch penetrates the felt and the felt serves to hold the pitch in place and to give strength, very much as does the hair used in mortar. The felt also enables the pitch to resist ordinary pressure and to bridge small fissures caused by settlement. The felt is therefore an essential part of the com¬ bination, but, as should be understood clearly, it is not in itself the waterproofing material, and must at all times be com¬ pletely enclosed and protected by an unbroken layer of pitch. 34 WATERPROOFING OF CONCRETE §42 27. Coke is a fuel used largely in blast furnaces. It is made by heating soft coal. Coke bears the same relation to coal as charcoal does to wood. In the manufacture of coke, the heat drives gases out of the coal and, at the same time, a black, viscous bituminous material is obtained from the coal, leaving the coke. This material is coal tar, so useful in manufacturing and waterproofing. 28. Asphalt, or asphaltiim , as it is sometimes called, is a natural bituminous material found in various parts of the world in a more or less advanced state of distillation. The asphalt commonly used in America is obtained either from Trinidad or from Bermudes. That obtained from the former place is known as Trinidad■ pitch-lake asphalt , and that from the latter place as Venezuelan asphalt . Asphalt is also found in some parts of the United States. 29. The exact meaning of the term pitch should be understood, so as to remove some widespread misconcep¬ tions. Pitch is a general term, and it may be applied indis¬ criminately to coal tar, and also to the resinous sap of pine trees, or to asphalt. All kinds of pitch have in common the property of resist¬ ing the penetration of water, although in a greater or less degree, so that the name itself has become synonymous with the waterproofing quality. 30. Qualities of Pitch. —In purchasing pitch or bitu¬ minous waterproofing, only trustworthy companies should be allowed to bid, as it is of the utmost importance to obtain first-class material. Good waterproofing cannot be made from poor pitch. The source of the pitch or bituminous binder is a question of great importance, because on its ability to resist the dissolving action of water rests the per¬ manence bf its waterproofing effect. In underground work, the action of the water is sometimes made more difficult to resist because it contains sewage, drainage from manufactur¬ ing establishments, gas liquor, etc., which have a solvent action on poor pitch. On a roof, it is not only the dissolving §42 WATERPROOFING OF CONCRETE 35 action of water, but also the effects of sun and wind, heat and cold, that must be withstood. The corroding influence of these agencies is so strong that few materials can resist it for longer than a few years. The pitch binders generally used in bituminous water¬ proofing are either coal tar or asphalt. The basis of either of these materials is bitumen, and they differ from each other in the amount and character of the other ingredients present, corresponding to the sources from which they are derived. Crude coal tar and asphalt are put through a process of manufacture or refining before they are used for waterproof¬ ing purposes. 31 . Saturated Felt. —As its name implies, saturated felt is nothing more nor less than an absorbent felt that has been passed through a hot bath of liquid refined tar or pre¬ pared asphalt of such consistency as to penetrate its structure thoroughly, superfluous pitch being squeezed out between rollers. After this treatment the felt is subjected to an aging process, which toughens it and makes it ready for use. It is of course essential that the bituminous binder and the saturating material with which the felt is prepared should be similar in character, in order that the union between the felt and the pitch binder will be as intimate as possible. ROOF WATERPROOFING 32 . In the case of a roof, the layers of felt and pitch are often covered with a coat of gravel or slag embedded in pitch. This coating serves a double purpose, first, that of furnishing as large an amount of mineral surface to withstand the action of the elements as possible, and second, to stiffen mechanic¬ ally the layer of pitch and prevent it from flowing, thereby making it possible to maintain a thicker layer in place on the slope of the roof than would otherwise be the case. A gravel or a slag layer also serves another purpose, namely, that of a fire retardant of no mean efficiency, the particles of 3G WATERPROOFING OF CONCRETE §42 stone serving as an insulating layer and protecting the pitch and felt from the action of sparks or embers. A roof covered with pitch and felt, on top of which is placed slag or gravel, is practically as uninflammable as one covered with tin or tile. 33. Specifications for Coal-Tar Pitch and Felt Roof Over Concrete. —The following specifications, known as Barrett specifications , will be found excellent for placing a coal-tar pitch and felt roof over concrete. Following the specifications are data concerning estima¬ ting, flashings, expan¬ sion joints, etc. rec¬ ommended by the same company. There shall be used five thicknesses of ap¬ proved felt weighing not less than 14 pounds per 100 square feet, single thickness, not less than 200 pounds of approved pitch, and not less than 400 pounds of gravel or 300 pounds of slag from \ to -§ inch in size, free from dirt, per 100 square feet of completed roof. The material shall be applied as follows: (1) Coat the concrete a, Fig. 1, with hot pitch b mopped on uniformly. (2) Lay two full thick¬ nesses of tarred felt c, lapping each sheet 17 inches over the pre¬ ceding one, and mop with hot pitch d the full width of the 17-inch lap, so that in no case shall felt touch felt. (3) Coat the entire surface with hot pitch e mopped on uniformly. (4) Lay three full thicknesses of felt /, lapping each sheet 22 inches over the preceding one and mopping with hot pitch g the full width of the 22-inch lap between the plies, so that in no case shall felt touch felt. (5) Spread over the entire surface of the roof a uniform coat of pitch, into which, while Fig. 1 §42 WATERPROOFING OF CONCRETE 37 hot, embed the gravel or slag h. The gravel or slag in all cases must be dry. Note. —The preceding specifications are designed for roofs having an incline not exceeding 1 inch to the foot, and by adding the words “such nailing as is necessary shall be done so that all naiis will be covered by at least two plies of felt, ” the specifi¬ cations are suitable for inclines not exceeding 3 inches to the foot. For surfaces steeper than 3 inches to the foot, nailing strips of wood must be provided. These should be embedded in the concrete from 3 to 6 feet apart, running at right angles to the pitch of the roof, and the felt nailed to these strips. 34 . Roof Covered With Tile or Brick.—A roof laid in accordance with the preceding specifications will resist the action of the elements without necessity for repair for many years. Such a roof, however, is not calculated to withstand abrasion or traffic. Where it is necessary for persons to walk on a roof, the fabric should be protected from injury by a layer of vitrified tile or brick. This quality of roof is the one generally used on large and important buildings of the first class, and on roof gardens, docks, vaults, and places of similar character. The following are the specifications for this type of work: Over the concrete shall be laid a five-ply coal-tar pitch felt and vitrified tile or brick roof to be constructed as folfows: The tarred felt shall be of approved quality weighing not less than 14 pounds per 100 square feet, single thickness. The pitch shall be approved coal-tar pitch, distilled direct from American coal tar, and there shall be used not less than 200 pounds, gross weight, per 100 square feet of completed roof. The material shall be applied as follows: First, coat the concrete with hot pitch mopped on uniformly. Over this coating of pitch lay two thicknesses of tarred felt, lapping each sheet 17 inches over the preceding one and mopping back with pitch the full width of each lap. Over the felt thus laid, spread a uniform coating of pitch mopped on. Then lay three full thicknesses of tarred felt, lapping each sheet 22 inches over the preceding one. When the felt is thus laid, mop back with pitch the full width of 22 inches under each lap. Then coat the entire surface with pitch uniformly mopped on and finish with a course of vitrified-clay tiles 6 in. X 9 in. X 1 in. laid in and thoroughly grouted with Portland-cement mortar. Note. —The same general specifications apply where bricks arc used instead of vitrified- clay tiles. 35 . Bata for Estimating. —For convenience in esti¬ mating the quantity of felt and pitch required for work according to the preceding and following specifications, the following data are given: 38 WATERPROOFING OF CONCRETE §42 Standard saturated felt is 32 inches wide and weighs from 60 to 65 pounds to the roll. One roll contains sufficient felt for four squares of single-ply waterproofing, allowing for the laps. Standard roofing coal-tar pitch weighs 11 pounds to the gallon, or 180 gallons to the ton. A cement barrel of pitch weighs about 300 pounds. For one square of roof or hori¬ zontal waterproofing, allow 40 pounds of pitch for each mopping. For one square of wall or vertical waterproofing, allow 50 pounds of pitch for each mopping. One square is equal to 100 square feet, or 10 ft. X 10 ft. 36 . Flashings. The connections be¬ tween the flat sur¬ face of the roof and the adjacent parapet walls, chimneys, sky¬ light and scuttle curbs, etc. are termed flashings. Their object is to prevent any water from pene¬ trating the joint Fig. 2 between the roof and the vertical surface. The material generally used is metal, either sheet copper, zinc, or galvanized iron, these materials being named in the order of merit, as well as of cost. The flashings for roofs laid with gravel or slag, or tile or brick, are practically the same; there¬ fore, in Figs. 2 and 3, the finishing course of vitrified brick or tiling is shown, and may replace the gravel or slag coating in the ordinary type of construction. 37 . Fig. 2 shows a flashing laid without nails over con¬ crete. The bottom flashing of copper, zinc, or galvanized iron is 4 inches on the roof, and extends up 8 inches along the side of the wall, with a counterflashing extending down 4 inches on the bottom flashing and 2 inches into the wall. §42 WATERPROOFING OF CONCRETE 39 •Y'