MATERIALS OF CONSTRUCTION UNIVERSITY OF WISCONSIN EXTENSION TEXTS A series of Industrial and Engineering Education Textbooks, developed under the direction of Dean Louis E. REBER, University of Wisconsin Extension Division Norris and Smith's SHOP ARITHMETIC Norris and Craigo's ADVANCED SHOP MATHEMA- TICS Hills' MACHINE DRAWING George's ADVANCED SHOP DRAWING Wooley and Meredith's SHOP SKETCHING Longfield's SHEET METAL DRAFTING Hobbs, Elliott and Consoliver's GASOLINE AUTOMOBILE Norris, Winning and Weaver's GAS ENGINE IGNITION Consoliver and Mitchell's AUTOMOTIVE IGNITION SYSTEMS Shealy's HEAT Shealy's STEAM BOILERS Shealy's STEAM ENGINES Jansky's THEORY AND OPERATION OF D. C. MACHINERY Jansky's ELECTRIC METERS Jansky's ELEMENTARY MAGNETISM AND ELECTRICITY Jansfy's PRINCIPLES OF RADIOTELE- GRAPHY Jansky and Faber's PRINCIPLES OF THE TELE- PHONE Part I. Subscribers' Apparatus Hool's ELEMENTS OF STRUCTURES Hool's REINFORCED CONCRETE CONSTRUCTION Vol. I. Fundamental Principles Vol. II. Retaining Walls and Buildings Vol. III. Bridges and Culverts Blair's SHOW CARD WRITING Pulver's MATERIALS OF CONSTRUC- TION ENGINEERING EDUCATION SERIES MATERIALS OF CONSTRUCTION PREPARED FOR THE EXTENSION DIVISION OF THE UNIVERSITY OF WISCONSIN BY H. E. PULVER, B. 8., C. E. ASSOCIATE PROFESSOR OF CIVIL AND STRUCTURAL ENGINEERING THE UNIVERSITY OF WISCONSIN FIRST EDITION McGRAW-HILL BOOK COMPANY, ING. NEW YORK: 370 SEVENTH AVENUE LONDON: 6 & 8 BOCJVERIE ST., E. C. 4 1922 COPYRIGHT, 1922, BY THE MCGRAW-HILL BOOK COMPANY, INC. THB MAPI-E I'HKSS TOKK PA PREFACE This textbook has been prepared for use in a correspondence- study course offered by the Extension Division of The University of Wisconsin. It is intended that the book will be supplemented by questions and problems and such extra material as is found to be advisable. The book is quite elementary and is suitable for students who have had an ordinary training in English and Arithmetic. It is believed that this text may also be of use for residence courses in technical schools, as the book is of such size that its entire contents may be covered in the length of time usually assigned to this subject. The text should be used in connection with courses in the Strength of Materials and Materials Testing as no attempt has been made to cover any of the subject matter usually included in those courses, with the exception of a few tests and specification requirements. The data in this book have been compiled from many sources and the author has endeavored to give credit where- it is due. The author is indebted to Professor D. A. Abrams of Lewis Institute for material on concrete proportioning and to the several manufacturing companies and individuals for illustrations furnished. H. E. PULVER. THE UNIVERSITY OF WISCONSIN, MADISON, WISCONSIN, June, 1922. 4888-49 CONTENTS PREFACE v CHAPTER I. PLASTERS AND NATURAL CEMENTS A. GYPSUM PLASTERS ARTICLE PAGE t. Definition and Classification 1 2. Manufacture of Gypsum Plasters 1 3. Properties of Gypsum Plasters 2 4. Uses of Gypsum Plasters 8 B. NATURAL CEMENT 5. Definition 8 6. Manufacture of Natural Cement 4 7. Properties of Natural Cement .- 4 8. Uses of Natural Cement 6 C. MISCELLANEOUS CEMENTS 9. Natural Puzzolan Cement 6 10. Slag Cement . . 6 11. Magnesia or Sorel Cement. 7 CHAPTER II. LIMES AND LIME MORTARS A. LIMES 12. Definitions and Classifications. . . 9 13. Manufacture of Quicklime 9 14. Manufacture of Hydrated Lime 12 15. Manufacture of Hydraulic Lime 12 16. Properties of Quicklime. . . 13 17. Properties of Hydrated Lime. 14 18. Properties of Hydraulic Lime . . ... 14 19. Uses of Limes . 15 B. LIME MORTARS 20. Lime Mortar; Definition and Materials 15 21. Slaking the Quicklime 16 22. Proportioning and Mixing of Lime Mortar 17 23. Properties of Lime Mortar 18 24. Common Lime or Wall Plaster 19 25. Uses of Lime Mortar '. ' 19 vii viii CONTENTS CHAPTER III. PORTLAND CEMENT A. DEFINITION AND CLASSIFICATION ARTICLE PAGE 26. Definition of Portland Cement 21 27. Classification of the Principal Cementing Materials 21 B. MANUFACTURE OF PORTLAND CEMENT 28. Raw Materials. . , 21 29. Proportioning of the Raw Materials 22 30. Outline of the Dry Process of Manufacture 25 31. The First Six Steps of the Dry Process of Manufacture 25 32. The Remaining Six Steps of the Dry Process of Manufacture ... 29 33. The Wet Process of Manufacture 31 C. PROPERTIES AND USES OF PORTLAND CEMENT 34. General 32 35. Chemical Constitution and Specifications 32 36. Soundness 33 37. Strength 34 38. Time of Set 35 39. Fineness 35 40. Specific Gravity 36 41. Uses of Portland Cement 36 CHAPTER IV. PORTLAND CEMENT MORTARS A. DEFINITIONS AND MATERIALS 42. Definitions 37 43. The Cement and the Water 37 44. Sand in General 37 45. Properties of Sand 38 46. Sieve Analysis of Sand 38 47. Standard Sand 39 48. Substitutes for Sand 39 49. Specifications for Fine Aggregate 40 B. PROPORTIONING AND MIXING MORTAR 50. Proportioning the Mortar 41 51. Mixing the Mortar. . . - 42 C. PROPERTIES OF PORTLAND CEMENT MORTARS 52. Strength of Portland Cement Mortars in General 43 53. Effect of Density and Size of Sand on the Strength 43 54. Effect of the Amount of Mixing Water on the Strength 44 55. Effect of Various Conditions on the Properties of Mortars 44 56. Effect of Various Elements on the Properties of Mortars 45 57. Tensile Strength .46 CONTENTS ix ARTICLE PAGE 58. Compressive Strength 46 59. Transverse Strength 47 60. Adhesive Strength 47 61. Shearing Strength 47 62. Miscellaneous Properties 48 CHAPTER V. PLAIN CONCRETE A. DEFINITIONS AND MATERIALS 63. Definitions 51 64. Cement, Water, and Fine Aggregate 51 65. Coarse Aggregate in General 52 66. Size of Coarse Aggregate 52 67. Voids, Weight per Cubic Foot, and Specific Gravity of Coarse Aggregates 53 68. Specifications for Coarse Aggregate 54 B. PROPORTIONING OF CONCRETE 69. General Theory 55 70. Proportioning by Standard Proportions 55 71. Proportioning with Reference to Coarse Aggregate 56 72. Proportioning with Reference to Mixed Aggregate 56 73. Proportioning by Maximum Density Tests 56 74. Proportioning by Mechanical Analysis 57 75. Example of Proportioning by Mechanical Analysis ...... 58 76. Proportioning of Concrete Mixes by Abrams' Method ..... 60 77. Proportioning Concrete by Edwards' Surface Area Method ... 65 78. Formula for Estimating Quantities of Materials Required for Plain Concrete 65 C. MIXING OF CONCRETE 79. Hand Mixing '. 66 80. Machine Mixing 68 81. Consistency of Concrete '.>........ 68 D. DEPOSITION OF CONCRETE 82. Forms for Concrete 69 83. Transporting, Placing, and Tamping Concrete 69 84. Bonding New Concrete to Old Work 70 85. Surface Finish of Concrete 70 86. Placing Concrete under Water , . . 71 87. Placing Concrete in Freezing Weather 71 E. IMPERVIOUS CONCRETE 88. Impervious Concrete in General 72 89. Effect of Increasing the Density and Amount of Cement .... 72 x CONTENTS ARTICLE PAGE 90. Using Waterproofing Materials 73 91. Using Foreign Matter in the Concrete 73 92. Use of Surface Treatments 73 F. PROPERTIES OF CONCRETE 93. Effect of Various Impurities Mixed with the Concrete 74 94. Effect of Various Elements on Hardened Concrete 74 95. Effect of Varying the Amount of Mixing Water 75 96. Strength of Concrete in General 77 97. Compressive Strength of Concrete 78 98. Tensile Strength of Concrete 79 99. Transverse Strength of Concrete 79 100. Shearing Strength of Concrete. 80 101. Adhesive Strength of Concrete to Steel 80 102. Elastic Limit and Modulus of Elasticity of Concrete 81 103. Yield of Concrete 81 104. Expansion and Contraction of Concrete 82 105. Miscellaneous Properties of Concrete 82 106. Working Stresses and Factor of Safety for Concrete 82 107. Rubble Concrete 83 G. CONCRETE STONE, BLOCK, AND BRICK 108. Definitions and Classifications 84 109. Materials for Concrete Stone 84 110. Proportions 84 111. Consistency 85 112. Mixing and Molding 85 113. Surface Finishes 86 114. Curing and Aging 86 115. Properties of Concrete Blocks and Brick 87 116. Uses of Concrete Blocks and Brick 88 CHAPTER VI. BUILDING STONE A. CLASSIFICATIONS AND DESCRIPTIONS 117. Building Stone in General 89 118. Classifications of Building Stone 89 119. Granite, Gneiss, and Trap 90 120. Limestone, Marble, Sandstone, and Slate 91 B. STONE QUARRYING AND CUTTING 121. Hand Methods of Stone Quarrying 91 122. Machine Methods of Quarrying 93 123. Explosives Used in Quarrying 93 124. Stone Cutting 94 CONTENTS xi C. PROPERTIES OF BUILDING STONE ARTICLE PAGE 125. Durability 96 126. Action of Frost, Wind, Rain, and Smoke 97 127. Action of Fire 98 128. Mechanical Properties of Building Stone 98 CHAPTER VII. BRICK AND OTHER CLAY PRODUCTS A. CLASSIFICATIONS AND DEFINITIONS 129. Classifications 101 130. Definitions 101 B. MANUFACTURE OF CLAY BUILDING BRICK 131. The Clay 102 132. Hand Process of Making Brick 102 133. Soft Mud Machine Process of Making Brick 103 134. Stiff Mud Machine Process of Making Brick. . 104 135. Pressed Brick Machine Process of Making Brick 106 136. Brick Kilns 106 137. Burning the Brick 108 C. MANUFACTURE OF OTHER BRICK 138. Manufacture of Paving Brick ...... 108 139. Manufacture of Firebrick 109 140. Manufacture of Sand-lime Brick Ill D. OTHER CLAY PRODUCTS 141. Terra Cotta Ill 142. Building Tile ......... ...:... 112 143. Drain Tile 112 144. Sewer Pipe . . . , . . 113 E. PROPERTIES OF BRICK AND OTHER CLAY PRODUCTS 145. General Properties of Brick 114 146. Absorption of Brick and Building Tile 114 147. Compressive Strength of Brick and Building Tile 115 148. Transverse Strength of Brick and Building Tile 115 149. Shearing Strength of Brick and Building Tile 116 150. Modulus of Elasticity of Brick and Building Tile. ....... 116 151. Properties of Drain Tile 117 152. Properties of Sewer Pipes 118 CHAPTER VIII. STONE AND BRICK MASONRY A. STONE MASONRY 153. Stone Masonry in General 119 154. Definitions . .119 xii CONTENTS ARTICLE PAGE 155. Classification of Stone Masonry 120 156. Mortar for Stone Masonry 122 157. Dressing of Stone Masonry 122 158. Bond in Stone Masonry 122 159. Backing in Stone Masonry 123 160. Pointing of Stone Masonry 123 161. General Rules for Laying Stone Masonry 124 162. Waterproofing Stone Masonry , 124 163. Cleaning Stone Masonry 125 164. Strength and Other Properties of Stone Masonry 125 165. Safe Loads for Stone Masonry 126 B. BRICK AND HOLLOW TILE MASONRY 166. Brick Masonry in General 127 167. Mortar for Brick Masonry 127 168. Laying the Brick 128 169. Improvements in Brick Laying 128 170. Bond in Brick Masonry 129 171. Pointing of Brick Masonry 130 172. Waterproofing Brick Masonry 130 173. Cleaning Brick Masonry 131 174. Strength and Other Properties of Brick Masonry 131 175. Allowable Working Loads for Brick Masonry 132 176. Efflorescence 133 177. Hollow Tile Masonry 133 CHAPTER IX. TIMBER A. TREES 178. Timber Trees in General 135 179. Structure of Exogenous Trees 135 180. Growth of Exogenous Trees 136 181. Structure and Growth of Endogenous Trees 137 182. Grain and Texture of Wood 138 183. Color and Odor of Wood 138 184. General Characteristics of Conifers Pine, Fir, and Spruce . . . 139 185. General Characteristics of Conifers Other Species 140 186. General Characteristics of Broad-leaved Trees Oak, Maple, Ash, Walnut 140 187. General Characteristics of Broad-leaved Trees Other Species. . 141 188. General Characteristics of Some Endogenous Trees 143 B. PREPARING THE TIMBER 189. Logging 143 190. Sawing the Lumber 144 191. Classification of Lumber 144 192. Defects in Lumber 145 193. Natural Seasoning of Lumber . 147 CONTENTS xiii ARTICLE PAGE 194. Artificial Seasoning of Lumber 147 195. Shrinkage of Lumber 148 C. DURABILITY AND DECAY OF LUMBER 196. Durability and Decay of Lumber in General 149 197. Dry Rot in Lumber 150 198. Wet and Common Rot 151 199. Injurious Insects 151 200. Marine Wood Borers 151 D. PROPERTIES OF TIMBER 201. Strength of Timber in General 152 202. Influence of Moisture Content in Timber 153 203. Tensile Strength of Timber '. . . 154 204. Compressive Strength of Timber 154 205. Transverse Strength of Timber 154 206. Shearing Strength of Timber 155 207. Cleavability and Flexibility of Timber 155 208. Hardness and Toughness of Timber 156 209. Miscellaneous Properties of Timber 156 210. Factors of Safety and Safe Working Loads for Timber 156 211. Properties of Timber 158 E. SELECTION AND INSPECTION OF TIMBER 212. Selection of Timber 158 213. Inspection of Timber 159 F. PRESERVATION OF TIMBER 214. Preservation of Timber in General 160 215. Creosote Processes for Preservation of Timber 161 216. Zinc Chloride Pressure Processes for Preservation of Timber . . 162 217. Vulcanizing Process for Preserving Timber 163 218. Some Other Pressure Processes for Preserving Timber 163 CHAPTER X. PIG IRON A. DEFINITION OF PIG IRON AND ORES OF IRON 219. Definition of Pig Iron 165 220. Ores of Iron 165 221. Ore Mining 166 222. Preliminary Treatment of Iron Ores 166 B. MANUFACTURE OF PIG IRON 223. The Blast Furnace 168 224. Accessories of the Blast Furnace .171 xiv CONTENTS ARTICLE PAGE 225. The Fuel 171 226. The Flux 172 227. Operation of the Blast Furnace 172 228. Use of the Electric Furnace in Reducing Iron Ores 174 229. Making the Pigs 175 C. CLASSIFICATION AND USES OF PIG IRON 230. Classification of Pig Iron 175 231. Uses of Pig Iron 176 CHAPTER XI. CAST IRON A. DEFINITIONS AND GENERAL CLASSIFICATIONS 232. Definitions of Cast Iron 177 233. General Classification of Iron and Steel 177 234. Howe's Classification of Iron and Steel 177 B. MAKING THE MOLTEN CAST IRON 235. The Materials 178 236. The Cupola 179 237. The Air Furnace 181 C. FOUNDRY WORK 238. Definition of Founding 181 239. Patterns and Cores 181 240. Molds 182 241. Pouring and Cleaning the Castings 183 242. Defects in Castings 184 D. CONSTITUTION AND COMPOSITION OF CAST IRON 243. Constitution and Composition of Cast Iron in General 184 244. Effect of Carbon in Cast Iron 185 245. Effect of Silicon, Sulphur, Phosphorus, and Manganese on Cast Iron 186 246. Effect of Some Other Chemical Elements on Cast Iron . . . 188 E. PHYSICAL AND MECHANICAL PROPERTIES AND USES OF CAST IRON 247. Strength of Cast Iron in General 188 248. Tensile Strength of Cast Iron 189 249. Compressive Strength of Cast Iron 190 250. Transverse Strength of Cast Iron 191 251. Miscellaneous Properties of Cast Iron 192 252. Allowable Working Stresses for Cast Iron 192 253. Uses of Cast Iron . . 192 CONTENTS xv F. MALLEABLE CAST IRON ARTICLE PAGE 254. Definition of Malleable Cast Iron 193 255. Making the Castings for Malleable Cast Iron 193 256. Annealing the Castings for Malleable Cast Iron 193 257. Properties of Malleable Cast Iron 194 258. Uses of Malleable Cast Iron V ......... 194 CHAPTER XII. WROUGHT IRON A. DEFINITION AND CLASSIFICATIONS 259. Definition of Wrought Iron 197 260. Classification of Wrought Iron 197 B. MANUFACTURE OF WROUGHT IRON 261. The Materials for the Wet Puddling Process 198 262. The Furnace Used in the Wet Puddling Process 198 263. Operation of the Furnace Used in the Wet Puddling Process . . 199 264. The Dry Puddling Process 200 265. Mechanical Treatment of the Puddle Balls 200 266. Wrought Iron Made from Scrap 201 267. Defects in Wrought Iron 201 C. CONSTITUTION, PROPERTIES, AND USES OF WROUGHT IRON 268. Composition and Constitution of Wrought Iron 201 269. Tensile Strength of Wrought Iron ........ 202 270. Compressive Strength of Wrought Iron 203 271. Shearing Strength of Wrought Iron 203 272. Transverse Strength of Wrought Iron 203 273. Fracture of Wrought Iron 203 274. Welding of Wrought Iron 204 275. Miscellaneous Properties of Wrought Iron 205 276. Tensile Strength and Ductility Requirements for Wrought Iron . 205 277. Working Stresses for Wrought Iron 205 278. Uses of Wrought Iron 206 CHAPTER XIII. STEEL A. DEFINITIONS AND CLASSIFICATIONS 279. Definitions of Steel. 207 280. Classifications of Steel ......... . . . . 207 B. METHODS OF MANUFACTURE OF STEEL 281. The Cementation Process 208 282. The Crucible Process. 208 283. The Principle of the Bessemer Process and the Plant Equipment . 209 284. The Acid Bessemer Process 211 285. The Basic Bessemer Process. . 212 xvi CONTENTS ARTICLE PAGE 286. The Principle of the Open Hearth Process and the Plant Equipment 213 287. The Acid Open Hearth Process 215 288. The Basic Open Hearth Process 216 289. The Electric Process 217 290. The Duplex Process 218 291. The Triplex Process 218 292. Comparison of the Different Processes 219 C. COMPLETING THE MANUFACTURE OF THE STEEL 293. Casting the Ingots 219 294. Defects in Ingots 219 295. Reheating the Ingots 220 296. Rolling 220 297. Forging and Pressing 221 298. Wire Drawing 222 D. HEAT TREATMENT OF STEEL 299. Hardening of Steel . 223 300. Tempering of Steel 223 301. Annealing of Steel 223 302. Case Hardening of Steel 224 E. STRUCTURE AND CONSTITUTION OF STEEL 303. Normal Constituents and Compounds 224 304. Critical Temperatures 226 305. Slow Cooling of Molten Steel 227 306. Rapid Cooling of Molten Steel 227 307. An Explanation of the Hardening of Steel 228 308. An Explanation of the Tempering of Steel 228 309. An Explanation of the Annealing of Steel 229 F. PHYSICAL AND MECHANICAL PROPERTIES AND USES OF STEEL 310. General 229 311. Effect of Carbon 230 312. Effect of Silicon, Sulphur, Phosphorus, and Manganese .... 231 313. Effect of Mechanical Working and Heat Treatment 232 314. Tensile Strength of Steel 232 315. Compressive Strength of Steei 233 316. Shearing Strength of Steel 234 317. Transverse Strength of Steel 234 318. Average Properties of Rolled Carbon Steels . . . .' 234 319. Effect of Combined Stresses 235 320. Resistance to Impact Loads 235 321. Ductility of Steel 236 322. Hardness of Steel 237 323. Effect of Repeated and Alternating Stresses. . . . 237 CONTENTS xvii ARTICLE PAGE 324. Welding of Steel 238 325. Magnetic Properties of Steel 238 326. Specific Gravity and Coefficient of Expansion of Steel 239 327. Summarized Specifications for Various Steels 239 328. Working Stresses for Structural Steel. 240 329. Uses of Steel. . .' . . . . . . . ... . . ... . . . . . . .241 CHAPTER XIV. SPECIAL STEELS AND CORROSION OF IRON AND STEEL A. STEEL CASTINGS 330. Definition and Uses of Steel Castings 243 331. Founding of Steel Castings 243 332. Properties of Steel Castings .' 244 B. ALLOY STEELS 333. Definition and Classification of Alloy Steels 244 334. Heat Treatment of Alloy Steels 245 335. Nickel Steel 246 336. Manganese Steel. 246 337. Vanadium Steel 247 338. Chrome Steel , . ." 247 339. Silicon and Aluminum Steels 247 340. Tungsten, Molybdenum, and Cobalt Steels . . . . 247 341. Copper Steel .....*.... 248 342. Some Four and Five Part Alloys 248 C. CORROSION OF IRON AND STEEL 343. Definition of Corrosion ...,...,. . . . 249 344. The Life of Iron and Steel under Corrosion 250 345. Theories of Corrosion 250 346. Prevention of Corrosion in General 251 347. Prevention of Corrosion by Painting 251 348. Prevention of Corrosion by Covering with Concrete or Asphalt . 252 349. Prevention of Corrosion by Galvanizing 252 350. Prevention of Corrosion by Aluminum, Nickel, Tin, and Lead Plating 253 351. Prevention of Corrosion by the Inoxidation Process . . . .. . . 253 CHAPTER XV. NON-FERROUS METALS AND THEIR ALLOYS A. THE NON-FERROUS METALS 352. General 255 353. Copper . 255 354. Lead 256 355. Zinc 256 356. Tin. . 257 xviii CONTENTS ARTICLE PAGE 357. Aluminum 257 358. Nickel 258 359. Gold, Silver, amd Platinum 258 360. Some Other Non-ferrous Metals 259 B. ALLOYS OF NON-FERROUS METALS 361. General 259 362. Brasses 259 363. Bronzes 261 364. Various Aluminum Alloys 262 365. Various Nickel Alloys 263 366. Bearing Metal Alloys 263 367. Fusible Alloys 264 368. Solders 265 369. Composition and Use of Some Miscellaneous Alloys 265 370. Corrosion of Non-ferrous Metals and Their Alloys 265 CHAPTER XVI. SOME MISCELLANEOUS MATERIALS 371. Paints, Oils, and Varnishes 267 372. Asbestos 268 373. Glass 268 374. Glue 269 375. Rubber 269 376. Leather 271 377. Paper 272 378. Canvas 272 379. Ropes 272 380. Belts 273 . APPENDIXES A. A. S. T. M. Standard Specifications and Tests for Portland Cement 275 B. A. S. T. M. Standard Specifications for Structural Steel for Buildings 291 C. List of A. S. T. M. Standards and Tentative Standards . 297 MATERIALS OF CONSTRUCTION CHAPTER I PLASTERS AND NATURAL CEMENTS A. GYPSUM PLASTERS 1. Definition and Classification. Gypsum plasters may be defined as those plasters which are produced by the partial or complete dehydration of gypsum. Pure gypsum is a mixture of 1 part of calcium sulphate (CaSO 4 ) and 2 parts of water (2H 2 0). Gypsum plasters may be classified as follows: 1. Those produced by the incomplete dehydration of the gypsum, the calcination being carried on at a temperature less than 400 degrees Fahrenheit, (a) Plaster of Paris (CaSO 4 + KH 2 O), in which no foreign material has been added either during or after the calcination. (6) Cement plaster, which is made from an impure gypsum or by adding certain impurities, during the manufacture, to act as a retarder to the plaster. This plaster is often called hard wall or patent plaster. 2. Those plasters produced by the complete dehydration of the gypsum, the calcination being carried on at temperatures greater than 400 degrees Fahrenheit. (a) Calcined plaster (flooring plaster), a pure calcined gypsum. (6) Hard-finish plaster, which is made by calcining gypsum at a red heat or higher temperature and to which certain substances, such as alum or borax, have been added. 2. Manufacture of Gypsum Plasters. The process of manu- facture is essentially the same for all of the first class of gypsum plasters, variations being made in the temperature of calcination and the purity of the gypsum used. The raw material is a natural gypsum rock usually containing from 1 to 6 per cent of impurities. The rock is crushed, ground to a powder, and then heated in a large calcining kettle. If a rotary calciner is used, the fine grinding is done after the calcination. In making plaster of Paris, a pure gypsum is calcined at a temperature of about 220 degrees Fahrenheit thus driving off three-fourths of the water present. Cement plaster is made in the same way, an 1 2 MATERIALS OF CONSTRUCTION impure gypsum being used. Often a retarder (a substance to make the plaster slow setting) is added after the calcination. Flooring plaster is made by calcining lumps of gypsum in a separate feed kiln similar to the kiln used for the calcination of lime. The temperature of calcination is usually about 850 degrees Fahrenheit and the time required is about 3 hours. Higher temperatures or longer heating will burn the plaster and FIG. 1. Rotary cylinder type of plaster calciner. cause it to lose its powers of setting and hardening. After the calcination, the plaster must be finely ground. Keene's cement is the best-known kind of hard-finish plaster. This plaster is made by calcining a very pure gypsum at a red heat, immersing it in a 10 per cent alum solution, recalcining it, and then finely grinding the calcined material. 3. Properties of Gypsum Plasters. All gypsum plasters will set or harden when mixed with the proper amount of water. The process is a combination of the plaster and the water to form gypsum. The time required varies from 5 minutes to 2 hours according to the plaster used and the conditions of the mixing. The plasters made from pure gypsum are the quicker setting while the hard-burned plasters form the harder substances. Very little data are available concerning the strength of plasters, and the methods and conditions of testing have never been standardized. The strength varies according to the quality of the plaster, the quality of the sand, and the care taken in the mixing. The following table will give an idea of the strength of good plasters: PLASTERS AND NATURAL CEMENTS 3 TENSION TEST Neat paste Age 1 month Strength, about 350 Ib. per square inch 1 : 2 sand mortar Age 1 month Strength, about 175 Ib. per square inch COMPRESSION TEST Neat paste Age 1 month Strength, 1,200 to 2,000 Ib. per square inch 1 : 2 sand mortar . . Age 1 month Strength, 900 to 1,500 Ib. per square inch ADHESION TEST Plaster to paving brick Age 1 month Strength, about 100 Ib. per square inch Plaster to 1 : 2 mortar. Age 1 month Strength, about 130 Ib. per square inch The results of tests have shown that neat plasters gain rapidly in strength for the first few days only, and that the maximum tensile and compressive strength of the plasters is reached in from 2 to 4 weeks. The mortars gain in strength a little less rapidly than the neat plasters. 4. Uses of Gypsum Plasters. Gypsum plasters are not used very much as a material for engineering construction. Plaster of Paris is used as a casting plaster and for making quick repairs, etc., where a quick setting plaster is desired. Wall plasters are made by adding lime and a retarder, together with hair, wood fiber, etc., to a calcined plaster. (Ordinary wall plaster contains no gypsum plaster.) Stucco plaster is a plaster mixed with a dilute solution of glue, and it is usually slow setting. An addition of alum or borax tends to increase the hardness of a plaster. Gypsum plasters are used for interior wall plasters, stucco work, architectural ornamentation, etc. Gypsum blocks, tile, and plaster boards are made from gypsum wall plaster. These materials are used to some extent in building construction. They are light in weight, have good fire resisting qualities, are strong enough for many types of construction, and are easily sawn or cut to the desired shape. Gypsum wall plaster, mixed with water and fine cinders or wooden chips, has been used in making floors for buildings. These floors are usually lighter in weight but less strong and less fire resistant than concrete floors. B. NATURAL CEMENT 5. Definition. Natural cement is the finely pulverized product resulting from the calcination of a natural argillaceous limestone at a temperature below fusion. This temperature should be high enough (from 1,850 to 2,350 degrees Fahrenheit, to drive off the carbon dioxide as a gas, decompose the clay, and cause 4 MATERIALS OF CONSTRUCTION the formation of aluminates, ferrites, and silicates. The burned stone must be finely ground before it exhibits any hydraulic properties. 6. Manufacture of Natural Cement. The rock used is a natural clayey limestone containing from 15 to 35 per cent of clayey material, 10 to 20 per cent of the clayey matter being silica, and the balance alumina and iron oxide. This rock should occur in large deposits and should be fairly uniform in composition. The ordinary form of kiln in which the stone is burned is a vertical steel cylinder lined with firebrick and open at the top. It is about 30 or 40 ft. high and from 10 to 15 ft. in diameter. Thick layers of limestone and thin layers of soft coal are alternately dumped into the top of the kiln and the burned clinker is removed through a door at the bottom. As the lime- stone descends in the kiln it first loses its water and then, when a temperature of about 1,400 degrees Fahrenheit is reached, the magnesium carbonate begins to decompose, freeing carbon dioxide. At a temperature of about 1,650 degrees Fahrenheit the carbon dioxide is driven off from the calcium carbonate. The clay decomposes at a slightly higher temperature and sets free alumina and iron oxide which combine with the lime and magnesia and, when the temperature is raised to about 2,200 degrees Fahren- heit, form silicates of lime and magnesia. The kilns are run continuously. If the stones were all perfectly burned, the weight of the cement produced would be equal to the weight of the raw materials minus that of the carbon dioxide and the water in the rock. However, on account of the overburning and underburning of some of the rock, about 25 per cent of the clinker cannot be used for cement. The amount of soft coal required is about 30 Ib. per barrel of cement made. After the clinker is removed from the kiln, it is allowed to stand in air for a time so that any underburned clinker will be slaked before grinding. The slaking may be hastened by steam- ing in a closed vessel. After slaking, the clinker is crushed in a stone crusher and then ground to a fine powder in other forms of grinding machinery. Finally, the cement is packed in sacks or barrels for shipment. 7. Properties of Natural Cement. The chemical composition of natural cement is about as follows: silica, SiO 2 , 20 to 30 per per cent; lime, CaO, 30 to 60 per cent; magnesia, MgO, 1 to 25 PLASTERS AND NATURAL CEMENTS 5 per cent; alumina, A1 2 O 3 , 5 to 15 per cent; iron oxide, Fe 2 O 3 , 1 to 10 per cent; and small percentages of carbon dioxide, water, alkali, and sulphur trioxide. Because of differences in the chemical composition of the rocks used and in the degree of calcination, the chemical properties are very variable. The specific gravity of natural cement varies usually from 2.70 to 3.10 with an average of about 2.95. When mixed with water, natural cement will set either under water or in air. It usually sets more rapidly than portland cement. Allowing the cement to aerate for some time will cause it to set less rapidly and also to be less strong. Conse- quently, natural cement should not be stored exposed to air for more than a few weeks before using. The addition of gypsum or plaster of paris will retard the set somewhat. The standard specifications require initial set to occur in not less than 10 minutes and final set in not less than 30 minutes nor more than 3 hours, when the Vicat needle is used. The cement should be sound, and test pats stored in air and in water at normal tem- perature should remain firm and hard and show no signs of dis- tortion, checking, cracking, or disintegrating. The cement must be ground so fine that 90 per cent of it will pass a standard 100-mesh sieve and 70 per cent of it will pass a standard 200-mesh sieve. In general, the finer the cement is ground, the stronger it will be. Natural cement pastes and mortars are about half as strong as corresponding portland cement pastes and mortars in tension, and only about a third as strong in compression. When tested in compression at the age of 1 month, neat natural cement cubes should average 800 Ib. per square inch or more, and 1:2 sand mortar cubes should average more than 500 Ib. per square inch. The A. S. T. M. standard specifications for natural cement require* that the tensile strength of neat natural cement and 1 : 3 standard sand mortar should be equal to or more than the following values: TENSILE STRENGTH Age and storage Neat cement, pounds per square inch 1 : 3 standard sand mortar, pounds per square inch 24 hours in moist air 75 24 hours in moist air, 6 days in water 24 hours in moist air, 27 days in water 150 250 50 125 6 MATERIALS OF CONSTRUCTION 8. Uses of Natural Cement. Natural cement is used some- times in structural works where mass and weight, rather than strength, are required, as in sewers, conduits, massive founda- tions, pavement foundations, sidewalks, and rarely in large masonry dams, abutments, etc. Natural cement, when mixed with sand or with lime and sand, makes a suitable mortar for brick and stone masonry that is not subjected to heavy loads. Natural cement should not be used in exposed places or under water or where it will be exposed to the action of frost before the concrete has set and dried. At the present time the use of natural cement is decreasing, due to the decrease in cost and the increase in use of the better and stronger portland cement. C. MISCELLANEOUS CEMENTS 9. Natural Puzzolan Cement. Natural puzzolan cement is the finely pulverized product made by a mechanical mixture of fused argillaceous material and hydrated lime. All natural puzzolanic materials of commercial importance are taken from the deposits of volcanic ash. Hydrated lime must be added to this volcanic dust to form a hydraulic cement. As most deposits of puzzolana vary in quality and fitness for use, a careful selection must be made at the quarry to keep out objectionable materials. The selected material is ground very fine. It is usually mixed with hydrated lime (and also sand) at the place where it is to be used for structural purposes. Good puzzolan cement mortar of a 1:3 mix is about as strong in compression as a like mortar made with portland cement, but it is only about 70 per cent as strong in tension. Natural puzzolan cements were much used in the days of the Roman Empire and at that time they were the only known cementing materials. At the present time these cements are used but very little in construction work. 10. Slag Cement. Slag cement is practically the same as puzzolan cement except that blast-furnace slag is used in place of the puzzolan rock. The slag must be a basic slag, such as is produced in the reduction of iron ores, and the slag should be cooled rapidly when it is taken from the blast furnace so that it will become broken up into small pieces which are easily handled by the grinding machinery. The granulation of the slag PLASTERS AND NATURAL CEMENTS 7 tends to make a stronger cement and also to reduce the amount of undesirable sulphides present. The slag is well dried, finely ground, and then thoroughly mixed with the proper proportion of hydrated lime. The specific gravity of slag cement varies from 2.70 to 2.85 and it is about as finely ground as portland cement, though it is usually slower setting. The following table will give an idea of the strength of good slag cement: STRENGTH OF SLAG CEMENT Mix Age Tension, pounds per square inch Compression , pounds per square inch Neat paste 1 month 450 3,000 1 : 3 sand mortar . . 1 month 175 700 The uses of slag cement are usually limited to the unimportant parts of structural works which are not exposed and which do not require great strength. Slag cement is used but very little at the present time. 11. Magnesia or Sorel Cement. This cement is magnesium oxide, MgO, which, when mixed with a proper solution of mag- nesium chloride, MgClo, forms oxychloride of magnesium. This is often called Sorel stone after M. Sorel, a Frenchman, who was the first to note that this cement exhibited very strong hydraulic properties. Much of the magnesium oxide is obtained from Greece, though some is produced in Canada and the United States. Oxychloride of magnesium is probably the strongest and hardest artificial stone known at the present time. Magnesia cement forms a good, strong, tough mortar when mixed with sand, sawdust, asbestos, and other inert materials. The strength of neat pastes and mortars made with this cement is about twice that obtained by using portland cement. Magnesia cement is used for floors in buildings and railway carriages, for stucco work, architectural ornamentation, etc. This cement should not be used in water or where it will be exposed to a great amount of moisture. CHAPTER II LIMES AND LIME MORTARS A. LIMES 12. Definitions and Classifications. 1. Quicklime. A white oxide of calcium, CaO, or a mixture of calcium and magnesium oxides, CaO and MgO. (a) High-calcium lime contains 90 per cent or more of calcium oxide. (6) Calcium lime contains from 85 to 90 per cent of calcium oxide. (c) Magnesium lime contains from 10 to 25 per cent of magnesium oxide. (d) Dolomitic lime contains more than 25 per cent of mag- nesium oxide. Quicklime may be divided into two general grades as follows: (a) Selected Lime. A well-burned lime containing no ashes, clinker, or other foreign material. It contains 90 per cent or more of calcium and magnesium oxides and less than 3 per cent of carbon dioxide. Sometimes called " white" lime. (6) Run-of-kiln Lime. A well-burned lime containing 85 per cent or more of calcium and magnesium oxides and less than 5 per cent of carbon dioxide. 2. Hydrated Lime. A quicklime to which just enough water has been added to produce a complete slaking. 3. Hydraulic Lime. Obtained from the calcination of an ordinary limestone containing from 10 to 20 per cent of clay. 13. Manufacture of Quicklime. The essentials of this process are the heating of a pure or magnesium limestone (CaCOs or CaCO 3 and MgCO 3 ) until the water in the stone is evaporated; then raising the temperature high enough for chemical dissocia- tion and the subsequent driving off of the carbon dioxide as a gas; and leaving the oxides of calcium and magnesium. The maximum temperature required varies from 1,650 to 2,350 degrees Fahrenheit, depending upon the kind of limestone and the impurities present. 9 10 MATERIALS OF CONSTRUCTION The fuels used in lime burning are wood, bituminous (soft) coal, and producer gas. The soft coal is not so good as wood because it burns with a much shorter flame, thus causing a more uneven heat distribution. The kilns used in heating the limestone are usually vertical kilns of the intermittent or con- tinuous types. Continuous kilns may be of the mixed feed, separate feed, or ring types. In a vertical kiln, the limestone is fed in at the top end and, as it descends, it first loses its water by evaporation; then the stone undergoes dissociation, the car- bon dioxide passing off as a gas; and finally the calcined lime collects in the lower portion of the kiln, from which place it is withdrawn from time to time and the underburned and overburned materials sorted out. The cooled lime is sometimes ground to a powder (fine enough to pass an 80-mesh sieve) before being placed on the market. In the intermittent or old- style form of kiln, the limestone is rarely ever uniformly burned and the fuel consumption is large. Consequently, these kilns are not used very much. In the mixed-feed type of kiln, the mixture of bituminous coal and limestone is fed in at the top and the calcined material removed through a door at the bottom of the kiln. Often the limestone and fuel are charged in the kiln in alternate layers. The fuel consumption of this kind of kiln amounts to from 15 to 25 per cent of the weight of the lime produced. The vertical kiln with the separate feed is made of steel and lined with firebrick, and it is so designed that the limestone does FIG. 2. -Continuous gas fired lime kiln (Glamorgan Pipe & Foundry Co.) LIMES AND LIME MORTARS 11 not come in contact with the fuel during the burning. The fuel is burned in a grate which is attached to the side of the kiln, and so arranged that the heat will ascend into the stack. Compared with the separate feed kilns, the mixed feed kilns are ~-CLEVATOR SKIP FIG. 3. Mount continuous lime kiln plant. (Glamorgan Pipe & Foundry Co.) cheaper to construct, a little more rapid in operation, and more economical in fuel, but they do not produce so high a quality of lime. The ring or chamber type of kiln is much used in Germany. This kiln consists of a series of chambers grouped around a central stack, each chamber being connected with the stack and with the other adjacent chambers by a system of flues. The kiln is charged at the top with a mixture of fuel and limestone. In 12 MATERIALS OF CONSTRUCTION the burning, the flue system is so used that the hot gases gen- erated in one chamber will pass through the other chambers before ascending the stack, thus causing a preheating of the limestone in the other chambers. This kind of kiln is economical in the amount of fuel used. 14. Manufacture of Hydrated Lime. The commercial hy- drated lime is made by crushing lump quicklime to lumps about half an inch in size or less (some factories crush the lime so fine that the larger portion will pass a 50-mesh sieve). The crushed lime is mixed with just enough water to secure a complete hydration. This mixing is usually done with machinery. The lumps of unhydrated lime and other impurities are removed by screening or by air separation, and the hydrated lime, in the form of a very fine powder, is packed in bags weighing about 100 Ib. For every 56 parts of pure quicklime, 18 parts of water are required for the hydration. During the mixing, considerable heat is evolved and the lime increases in volume. The final product is a fine powder having about three times the volume of the original quicklime. The chemical formula is Ca(OH) 2 . 15. Manufacture of Hydraulic Lime. Hydraulic limes include all of those cementing materials (made by burning siliceous or argillaceous limestones) whose clinker after calcination contains so large a percentage of lime silicate (with or without lime alumi- nates or ferrites) as to give hydraulic properties to the product, but which at the same time contain normally so much free lime that the mass of clinker will slake on the addition of water. The limestone rock used should be such that, after the silica has combined with the lime during calcination, enough free lime remains to disintegrate the kiln product by its own expansion when it is slaked. Such a limestone usually contains from 40 to 50 per cent of lime; about 1 per cent of magnesia; from 7 to 17 per cent of silica; and about 1 per cent of alumina and iron oxide. The hydraulic limes are manufactured in continuous kilns in the same way as quicklime except that a higher temperature (never less than 1,850 degrees Fahrenheit) is required. After the burning, the lumps of lime are removed from the kiln and slaked in the same way as quicklime, great care being taken to use just the right amount of water and no more, as an excess of water would cause the lime to harden. The expansion of the quicklime in slaking breaks up the lumps into a fine powder which consists principally of lime silicate with about 25 to 33 LIMES AND LIME MORTARS 13 per cent of hydrated lime. The lime is then screened through a 50-mesh sieve and placed in bags. The underburned limestone and overburned materials (known as grappiers), which are left after the hydraulic lime is slaked and screened, are ground to a fine powder and sold as "grappier" cement. This cement is of value according to the proportion of lime silicate contained in it. Lafarge cement is a hydraulic grappier cement made at Tiel, France. 16. Properties of Quicklime. Before using, quicklime must be slaked by the addition of water which causes the calcium oxide to change to calcium hydroxide, Ca(OH 2 ). As great heat is evolved when quicklime is slaked, it should be stored so that the heat caused by an accidental slaking of a part of the lime will not cause a fire. The rate of hydration and the evolution of heat vary according to the purity of the lime and the percentage of calcium, oxide present. The high-calcium quicklimes slake more rapidly and generate more heat than the other quicklimes. When the slaked lime is exposed to the air, it gradually absorbs carbon dioxide and changes from calcium hydroxide to calcium carbonate (limestone) and water. Dry carbon dioxide will not react with dry hydrated lime, hence an excess of water (moisture) must be present. On account of the large shrinkage in the hardening of lime paste, sand or some other inert material must be added to reduce the shrinkage and cracking. The proportions are usually 1 part of lime to from 2 to 4 parts of sand. The plasticity (quality of being spread easily and smoothly with a mason's tool) or sand- carrying capacity of a lime may be expressed by the number of parts of sand which can be mixed with 1 part of lime paste without making the mortar too stiff or " short" to work well with a trowel. The sand-carrying capacity of a lime appears to vary with its purity and calcium content, the high-calcium limes being able to carry the most sand. The yield of a lime is the volume of paste of a given consistency produced by a unit weight of dry quicklime. The greater the purity and the higher the calcium content of the lime, the greater the yield. The hardness seems to vary inversely, and the shrinkage to vary directly, with the purity of the lime and the percentage of calcium oxide present. The A. S. T. M. specifications for quicklime in regard to 14 MATERIALS OF CONSTRUCTION physical properties and tests are: "An average 5-lb. sample shall be put into a box and slaked by an experienced operator with sufficient water to produce the maximum quantity of lime putty, care being taken to avoid "burning" or "drowning" the lime. It shall be allowed to stand for 24 hours and then washed through a 20-mesh sieve by a stream of water having a moderate pressure. No material shall be rubbed through the screens. Not over 3 per cent of the weight of the selected quicklime nor over 5 per cent of the weight of the run-of-kiln quicklime shall be retained on the sieve. The sample of lump lime taken for this test shall be broken to pass a 1-in. screen and be retained on a J^-in. screen. Pulverized lime should be tested as received." 17. Properties of Hydrated Lime. Hydrated lime is the same as ordinary quicklime which has been properly slaked and, therefore, it should have the same physical properties. However, it has been observed that hydrated lime makes a mortar that is stronger, more rapid setting, and which shrinks less than the ordinary quicklime mortars. The sand-carrying capacity and yield of hydrated lime are usually less than that of quicklime. The better qualities of the hydrated lime may be due to the more perfect hydration. The A. S. T. M. specifications for hydrated lime in regard to physical properties and tests are: "A 100-gram sample shall leave by weight a residue of not over 5 per cent on a standard 100-mesh sieve and not over 0.5 per cent on a standard 30-mesh sieve." "Hydrated lime shall be tested to determine its con- stancy of volume in the following manner: Equal parts of hydrated lime under test and volume-constant portland cement shall be thoroughly mixed together and gaged with water to form a paste. Only sufficient water shall be used to make the mixture workable. From this paste a pat about 3 in. in diameter and J-2 in. thick at the center, tapering to a thin edge, shall be made on a clean glass plate about 4 in. square. This pat shall be allowed to harden 24 hours in moist air and shall be without popping, checking, cracking, warping, or disintegration after 5 hours' exposure to steam above boiling water in a loosely closed vessel." 18. Properties of Hydraulic Lime. Hydraulic lime pastes and mortars are about as strong as those of natural cement. Compared with the values obtained from tests on portland cement pastes and mortars, the strength of hydraulic lime pastes LIMES AND LIME MORTARS 15 and mortars is about J as strong in tension and about y as strong in compression. A 1:3 hydraulic lime and sand mortar is about 70 per cent as strong as the neat mix. The rate of gain in strength is very slow and the maximum strength is not reached in less than a year. Hydraulic limes are about five times as strong in compression as they are in tension. The above re- marks are not true for the feebly hydraulic cements as those cements are very much weaker. 19. Uses of Limes. About half of the lime made is used for various structural purposes, the remainder being used for other industrial purposes and arts. Most of the lime used for struc- tural purposes is mixed with sand to form mortars for laying brick and stone masonry. A large amount of lime is used in plastering the walls and ceilings of buildings. Ordinary wall plaster is a mixture of lime and sand to which hair, fiber, etc. have been added. Some lime is used for whitewashing. A little lime is sometimes used in cement mortars to make them more plastic and impermeable. Hydrated lime is used for the same structural purposes as quicklime, and it is more easily handled, stored, and shipped as there is no danger of air slaking. Hydrated lime requires no slaking before it is ready to be mixed with sand and water to form a mortar. It is sometimes used as an ingredient of portland cement mortars and concretes. Hydraulic limes and grappier cements are sometimes used for the purposes of interior decoration. At one time they were much used in construction work, but they were replaced some time ago by the natural cements, and later by portland cement. Hydraulic limes are not suitable for use in underwater work and they are too slow setting for practical construction work. B. LIME MORTARS 20. Lime Mortar; Definition and Materials. Lime mortar is a mixture of slaked (hydrated) lime, usually in the form of a thick paste, sand, or other fine aggregate, and water. The lime used is usually a quicklime which must be properly slaked or hydrated before the sand or other fine aggregate is added. In general, a high-calcium lime makes the strongest and best-working mortar for ordinary uses. Sometimes a hydrated lime (a lime which has been slaked by the manufacturer) 16 MATERIALS OF CONSTRUCTION in the form of a fine powder is used. This hydrated lime requires no slaking or other preparation and is ready to be mixed at once with the sand and water to form a mortar. The water used should be clean and contain no materials, such as oils, acids, strong alkalis, vegetable matter, etc., which may be injurious to the mortar. The sand used for lime mortar should be clean and sharp and be composed of rather small grains in preference to large ones. The sand should be free from all dirt, loam, clay, and vegetable matter as these impurities tend to decrease the strength and soundness of the mortar. 21. Slaking the Quicklime. When quicklime is used, it must first be properly slaked before being mixed with the fine aggregate. It is important to secure a complete slaking of the lime and no more, because, if too much water is added, some of the binding power of the lime will be destroyed, and if too little water is used or proper care is not exercised by the workman, some of the lime may not be slaked. This unslaked lime may slake after the mortar is in place and cause bad results, especially if the mortar is used as a wall plaster. If the quicklime is properly slaked, the lime paste formed should have about three times the volume of the original quicklime. There are three general methods of slaking quicklime, namely, drowning, sprinkling, and air-slaking. Slaking by the drowning method is the most common way. The lumps of quicklime are placed in a layer 6 or 8 in. deep in a water-tight box and then water is poured on the lumps. The water should be equal to about two and a half or three times the volume of the quicklime. If the proper amount of water is used, the lime will form a thick paste. With a high-calcium (quick-slaking) lime, it is better to add the water all at once, but with a magnesium (slow-slaking) lime, the water should be added gradually. As lime slakes best when hot, care should be taken not to chill the lime after it has begun to slake. Stirring may be necessary to break up some of the lumps, but care should be taken not to chill the lime and retard the slaking. " Burning" occurs when only a little water is present and this water is changed into steam by the heat produced. " Burning" tends to prevent a complete slaking of the lime. Another method of slaking by drowning is to fill a water-tight box with about 8 in. of water and then add lumps of lime in LIMES AND LIME MORTARS 17 sufficient quantity to form a thick paste. The mass must be stirred to assist in breaking up the lumps of lime. Slaking by sprinkling consists of sprinkling a heap of quicklime with water equal to about one-third or one-fourth of the volume of the lime and then covering the mass with sand and allowing it to stand for a day or so. If the slaking is properly done, the hydrated lime will be in the form of a powder. This method requires extra care and expert labor and is, consequently, expensive. Air slaking consists of spreading the quicklime in a thin layer and allowing it to slake by absorbing moisture from the air. Frequent stirring is required. This method produces a good quality of slaked lime, but is rarely used due to the large storage area, labor, and time required. 22. Proportioning and Mixing of Lime Mortar. Sand should be added to the lime paste for four reasons: 1. To prevent excessive cracking and shrinking of the lime mortar when the water evaporates. 2. To give greater strength to the mortar. 3. To divide the lime paste into thin films and to make the mortar more porous, thus aiding in the absorption of carbon dioxide from the air which causes the lime to set or harden. 4. To reduce the cost. The usual proportions vary from 2 to 4 parts of sand to 1 part of lime paste. With most sands and limes, the correct propor- tions will be from 2% to 3 parts of sand to 1 part of lime paste by volume. Care should be taken to secure the proper propor- tions. The volume of the lime paste should be just a little more than enough to coat completely all of the sand grains and fill the voids. In mixing the mortar, the lime paste is first spread out in a thin layer a few inches thick and the sand spread uniformly over the top. The lime paste and sand are then mixed by hoe or shovel until the mass is of a uniform color. A little water should be added, if necessary, to make the mortar of the proper con- sistency. Thorough mixing is required to make a good mortar. When hydrated lime in the form of a powder is used, the lime and sand should be mixed dry until of a uniform color and then sufficient water should be added and the whole mixed until the mortar is of the proper consistency. If too much sand has been used the mortar will be "short" 2 18 MATERIALS OF CONSTRUCTION and "stiff" and will not work properly; while if too much lime paste is used, the mortar will be too sticky to work properly. A mason can tell very quickly whether the mortar is correctly proportioned or not when he starts to use the mortar in his work. The proportions which give the best working mortar are also the best proportions in regard to strength, hardening, and other properties (except when clay or loam is used instead of sand). About 210 Ib. of good quicklime are required to make a cubic yard of 1 : 3 lime mortar. 23. Properties of Lime Mortar. Lime mortar has the import- ant property of " setting" or " hardening" when the water evaporates and the lime absorbs carbon dioxide from the air thus forming calcium carbonate. This setting takes place very slowly, especially if the mortar is placed in thick layers or in places where it is difficult for the air to reach, and sometimes many years are required for the hydrated lime to change to calcium carbonate. In a lime mortar, an excess of lime paste delays the hardening, increases the shrinkage, decreases the compressive strength, and makes the mortar sticky. An excess of sand makes the mortar " short" and hard to work with a mason's tools besides decreasing the strength of the mortar. The freezing of lime mortar delays the evaporation of the water and thus delays the absorption of carbon dioxide from the air. The expansion of the water due to the freezing may damage the mortar. Alternate freezing and thawing decrease the adhesive and cohesive strength. A fine, sharp, clean sand gives the best results in a lime mortar. Clay, loam, dirt, etc. decrease the strength of lime mortar, hence these materials should not be used. Oils, acids, strong alkalis, vegetable matter, etc. decrease the strength and hardening qualities of a lime mortar. The tensile strength of a good 1 : 3 lime mortar, 1 month old, varies from 30 to 60 Ib. per square inch. When it is 6 months old, the strength will probably be from 10 to 15 Ib. more per square inch. The compressive strength of a good 1 : 3 lime mortar, at the age of 1 month, will probably be between 150 and 400 Ib. per square inch., while at the age of 6 months the strength may vary from 17Q to 750 Ib. per square inch. The strength of a lime LIMES AND LIME MORTARS 19 mortar depends upon the quality of the lime and the sand and upon the care taken during the mixing, molding, storing, and testing. A magnesium lime mortar is usually stronger and quicker setting than a high-calcium lime mortar. 24. Common Lime or Wall Plaster. Common lime or wall plaster is a lime sand mortar in which hair, fiber, or some similar material has been thoroughly mixed. The hair or fiber is added to keep the plaster from shrinking and cracking when it sets and hardens on the wall. Wall plaster is usually applied in two coats. The first or rough coat is put on about half an inch thick. It consists of about a 1 : 3 lime mortar to which the fiber, etc. have been added. The exposed surface is troweled smooth, but no effort is taken to make a very smooth surface. The second or finishing coat is added after the first coat has dried. This finishing coat consists of a rich mortar (a 1 : 1 or 1 : 2 mix) made of a very white lime paste and a fine, sharp, clean, light-colored sand. This coat is applied in a very thin layer and care is taken to secure a very smooth-finished surface. It is important that the quicklime used in a wall plaster shall be thoroughly slaked before it is placed on the wall. This is usually made sure of by allowing the plaster to remain in a water-tight box for several days before it is . applied to the wall. If any unslaked lime is placed in the wall, it will absorb moisture, slake, expand, and form "blisters" on the wall surface, often injuring the wall so much that the plastering has to be done over again. A ''whitewash" is a thin paste made of white quicklime and water which is applied to the wall or other surface by means of a brush. As many coats as desired may be applied. A "white- wash" serves the same purpose as a cheap paint. 25. Uses of Lime Mortar. Lime mortar is used as a mortar for stone and brick masonry, where the mortar can be placed in comparatively thin layers and the walls are not very thick, and where great strength is not required. Lime mortar should not be used in massive masonry, under water, or in a wet soil, as the lime will not harden unless it can absorb carbon dioxide from the air. In places where great strength is required, a portland cement mortar should be used. 20 MATERIALS OF CONSTRUCTION Lime mortar is sometimes mixed with portland cement mortar to make the portland cement mortar easier to work and also where a mortar stronger than lime mortar is required. Lime mortar is much used as a wall plaster and for stucco work, etc. CHAPTER III PORTLAND CEMENT * A. DEFINITION AND CLASSIFICATION 26. Definition of Portland Cement. Portland cement is the product obtained by finely pulverizing clinker produced by calcining to incipient fusion, an intimate and properly propor- tioned mixture of argillaceous and calcareous materials, with no additions subsequent to calcination excepting water and calcined or uncalcined gypsum (Am. Soc. Test. Mat.). 27. Classification of the Principal Cementing Materials. At the present time the knowledge of cement chemistry is not complete enough to allow of the classification of cementing materials according to their chemical properties. However, the different kinds of cementing materials may be classified according to their methods of manufacture and physical properties. The following classification brings out the main differences in the manufacturing methods and the slaking and hydraulic properties of the five main-cementing materials. 1. Common Lime. Made by burning relatively pure limestone at a very low temperature. It will slake when mixed with water and it has no hy- draulic properties. 2. Hydraulic Lime. Made by burning slightly argillaceous limestone at a low temperature. It will slake slowly and has feebly hydraulic properties. 3. Natural Cement. Made by burning argillaceous limestone at a com- paratively high temperature. It will not slake but it has hydraulic proper- ties when ground. 4. Portland Cement. Made by burning an artificial mixture of argillaceous and calcareous materials to a temperature of incipient fusion. It will not slake but it has very marked hydraulic properties when finely ground. 5. Puzzolan or Slag Cement. Made by mixing slaked lime with granu- lated blast-furnace slag or a natural puzzolanic material. It will not slake but possesses hydraulic properties when ground. B. MANUFACTURE OF PORTLAND CEMENT 28. Raw Materials. A large number of materials are available for use in the manufacture of Portland cement. The following 21 22 MATERIALS OF CONSTRUCTION are the materials most commonly used and they are arranged about in the order of their importance. ARGILLACEOUS CALCAREOUS MATERIALS MATERIALS Argillaceous limestone (cement and pure limestone rock) Clay or shale and pure limestone Clay or shale and marl Blast-furnace slag and pure limestone Clay or shale and chalk or chalky limestone Clav or shale and alkali waste Cement rock is a soft, impure, argillaceous limestone containing about 20 per cent of clay and 70 per cent of calcium carbonate. Limestone suitable for cement manufacture consists principally of calcium carbonate (90 per cent or more) with small percentages of silica, aluminium and iron oxides, magnesium carbonate, sulphur, and various alkalis. Marl is a deposit of soft and comparatively pure limestone usually found in the beds of extinct and existing lakes. Shales are a soft rock composed chiefly of silica, alumina, and iron oxide. Clays result from decayed shales and, consequently, have about the same chemical composition with a little more water. Slate is a form of shale. Blast-furnace slag is a fusible silicate formed during the reduc- tion of the iron ore in a blast furnace by the combination of the fluxing material (limestone, etc.) with the earthy matter (gangue) of the ore. Chalk is a soft variety of calcium carbonate formed from the remains of minute organisms. It also contains small percentages of silica, alumina, and magnesia. Alkali waste is the precipitated calcium carbonate obtained during the manufacture of caustic soda by the Leblanc process. In order to secure the proper chemical combinations in the kiln, all of the calcareous materials should be free from quartz or sand and should contain but little sulphur or magnesium car- bonate. The clays should also be free from sand and harmful impurities. Soft limestones are more easily ground than hard ones. 29. Proportioning of the Raw Materials. Portland cement has a complex chemical composition consisting for the most part of tricalcium silicate (3CaOSiO 2 ), dicalcium silicate (2CaOSi02), PORTLAND CEMENT 23 and tricalcium aluminate (SCaOA^Oa), with small amounts of other compounds, resulting from the burning of the calcium car- bonates, silicates, and alumina. Hence, the proportions of argillaceous and calcareous materials must be carefully chosen in order to secure the proper results. Eckel's formula for the correct theoretical proportions for Portland cement is: 2.8 Silica (SiO 2 ) + 1. 1 Alumina ( A1 2 O 3 ) +0.7 Iron Oxide (Fe 2 O 3 ) = 1.0 Lime (CaO) + 1.4 Magnesia (MgO) An average portland cement contains about 22.0 per cent of FIG. 4. Flow sheet for a dry process Portland cement plant. (Allis-Chalmers Mfg. Co.) silica, 7.4 per cent alumina, 3.0 per cent iron oxide, 62.0 per cent lime, 1.75 per cent magnesium oxide, 1.3 per cent of sulphuric acid, and about 1.0 per cent of alkalis. 24 MATERIALS OF CONSTRUCTION An excess of lime makes the cement unsound, while too little lime causes the cement to be quick setting and weak. In order to avoid an excess, the lime content is kept a little below the value given by the formula. SLAG CoAL FIG. 5. Flow sheet for a thousand barrel dry process slag Portland cement plant. (Allis-Chalmers Mfg. Co.) The amount of alumina present has a large effect on the clinker- ing temperature, the more the alumina the lower the temperature required. Large amounts of alumina tend to make the cement quick setting and weak as well as to render the cement more liable to disintegration when exposed to the action of sea water. PORTLAND CEMENT 25 Magnesia, up to 4 or 5 per cent, appears to have no bad effect on the cement, but larger amounts are thought to be injurious. Calcium sulphate, as gypsum or plaster of Paris, is added to the cement after burning to retard the set. The amount is usually less than three per cent. Sulphuric acid (SO 3 ) is limited to 200 per cent by the specifica- tions. 30. Outline of the Dry Process of Manufacture. The dry process of manufacture of Portland cement, which is the most important process of manufacture, consists of the following steps (though not always in the exact order as given) : 1. Securing the raw materials. 2. Crushing the raw materials. 3. Drying the raw materials. 4. Grinding the raw materials. 1 5. Proportioning and mixing. 6. Finely grinding the materials. 1 7. Burning the materials. 8. Cooling the clinker. 9. Addition of the retarder. 10. Grinding clinker to a very fine powder. 11. Seasoning the cement. 12. Packing the cement for shipment. 31. The First Six Steps of the Dry Process of Manufacture. 1. Most of the raw materials are obtained by quarrying, after which they are transported to the factory. Blasting is required for the harder materials, while the softer materials may be excavated with a steam shovel. Marl is often dredged. Blast- furnace slag is secured from the blast furnace. 2. Nearly all of the raw materials need to be crushed to smaller sizes before they can be handled by the grinders. The crushing is done by means of jaw, roller, or gyratory crushers and often both large and small crushers are used to make the materials fine enough for the grinders. The gyratory type of crusher is used more than the other types because it is more economical in operation. The raw materials are usually crushed so that they will pass through a 2-in. ring. 3. The drying is usually done in a revolving, hollow, steel cylinder about 5 ft. in diameter and 50 ft. long and which is inclined a little to the horizontal. The materials enter at the upper end and pass out of the lower end. The dryer removes the water from the materials. 1 NOTE. In the newer types of cement mills, both the coarse and fine grinding (processes 4 and 6) are done in one mill. 26 MATERIALS OF CONSTRUCTION 4. The preliminary grinding is often done in a ball mill which is a short, closed, hollow cylinder that revolves about its longitud- FIG. 6. Jaw crusher. (Allis-Chalmers Mfg. Co.) FIG. 7. Gyratory crusher. (Allis-Chalmers Mfg. Co.) inal axis. The grinding is done by a number of hard steel balls, from 3 to 5 in. in diameter, placed in the cylinder. The materials are ground so that they will pass a 20-mesh sieve. 1 1 NOTE. In the later type of cement plants, both the coarse and fine grinding are done in one mill, called a compeb mill. This mill is divided into two parts. The coarse grinding is done in the first part, after which the material passes into the second part for the fine grinding. The use of this type of mill eliminates process 4 (grinding the raw materials). PORTLAND CEMENT 27 FIQ. 8. Direct heat rotary dryer. (Allis-Chalmers Mfg. Co.) CXM^W ffg. Co.) FIG. 10. Coropeb mill. (Allis-Chalmers Mfg. Co.) 28 MATERIALS OF CONSTRUCTION 5. The materials then pass through a weighing machine where they are weighed out in the correct proportions and then dumped in a mixing hopper where they are thoroughly mixed together. FIG. 11. Compeb mill section. (Allis-Chalmers Mfg. Co.) 6. From the mixing hopper, the materials pass into a mill (such as a tube, Gates, Fuller-Lehigh, or Griffin mill, etc.) for a finer grinding. The tube mill, which is more often used than any FIG. 12. Gates tube mill. (Allis-Chalmers Mfg. Co.) other, is a closed steel cylinder about 5 ft. in diameter and 22 ft. long which is lined with a material (that has a high abrasive resistance) such as chilled cast iron or trap rock. The grinding is done by a number of flint rocks, about the size of goose eggs, PORTLAND CEMENT 29 which fill the mill about half full. The materials are ground so fine that about 95 per cent of the powder will pass a 100-mesh sieve. (See footnote, page 25.) FIG. 13. Fuller-Lehigh mill. (Fuller-Lehigh Co.) 32. The Remaining Six Steps of the Dry Process of Manufac- ture. 7. The finely ground material from the tube mills passes into the upper end of a rotary type of cement kiln where it is burned. The rotary kiln is a long steel cylinder, 6 to 9 ft. in diameter and from 100 to 150 ft. in length, which is slightly inclined to the horizontal and is so made that it can be slowly 30 MATERIALS OF CONSTRUCTION rotated. The fuel used is a finely powdered coal which is blown through a nozzle inserted in the lower end of the kiln. A brick flue, leading to a smokestack, is attached to the upper end of the kiln. Soon after the material enters the upper end of the kiln it balls up in small balls and, as it moves slowly down the kiln, the water is evaporated and the most of the carbon dioxide is driven off. As the material approaches the lower end of the kiln, all of the carbon dioxide, sulphur, and organic matter is expelled. A few feet from the lower end the temperature reaches 2,900 to 3,100 degrees Fahrenheit and the little brown balls are FIG. 14. Rotary kiln with taper end. (Allis-Chalmers Mfg. Co.) fused into a hard dark-colored clinker. The time required for the passage of the material through the kiln is four or five hours. 8. After the burning, the clinker is removed from the kiln and sprayed with a stream of water. Then the clinker is passed through a cooler and placed in the clinker storage bins. 9. When the clinker is removed from the clinker storage bins, it passes through a weighing machine where the retarder is added. The reason that something is added to retard the set of the cement is that the high-lime content would make the cement too quick setting for commercial use. The quantity added is about 2 per cent, usually, and never more than 3 per cent. Gypsum is usually used as a retarder though plaster of Paris is sometimes used. 10. After the retarder is added the clinker is ground to a very fine powder in a mill similar to the one used for finely grinding the material before burning. The clinker must be ground so fine that 78 per cent or more will pass a standard 200- mesh sieve. PORTLAND CEMENT 31 11. After the final grinding, the cement is conveyed to a storage bin and allowed to season for a few weeks before being packed for shipment. These storage bins usually have a capacity varying from 1,000 to 5,000 bbl. each. The seasoning seems to improve the quality of the cement. FIG. 15. Flow sheet for a wet process Portland cement plant. Mfg. Co.) (Allis-Chalmers 12. For shipment, the cement is packed in bags or sacks holding about 94 Ib. of cement, or in barrels which hold the equivalent of four sacks or 376 Ib. of cement. Sometimes the cement is placed in bulk in a railroad car and so shipped. 33. The Wet Process of Manufacture. The raw materials most commonly used in this process are clay and chalk or marl. 32 MATERIALS OF CONSTRUCTION The clay is dried and then ground in an edge runner mill, while the other materials are ground in a wash mill where enough water is used to make them into a thin mud or slurry. Then the proper quantities of the materials are weighed out and mixed in a pug mill, the slurry pumped into a large vat, a chemical analysis made, and more materials added if necessary. The slurry is then pumped from the vat to a special rotary kiln in which it is burned. After the clinker is removed from this kiln, the process of manu- facture is the same as that of the dry process. The wet process of manufacture allows of better chemical con- trol and easier grinding, but it requires more fuel for the burning. Because of this the dry process is usually cheaper and, conse- quently, more often used. C. PROPERTIES AND USES OF PORTLAND CEMENT 34. General. Cement is valuable as a structural material because it has mechanical strength after hardening. In order to compare the mechanical strengths of different cements and their fitness for structural work, it is necessary to make stand- ardized tests and laboratory experiments on some of the physical and mechanical properties. These qualities in the order of their importance are: soundness, strength, time of set, fineness, and specific gravity. The determinations of some of the chemical properties by standardized chemical tests aid in deciding whether a cement is suitable or not for structural purposes. 35. Chemical Constitution and Specifications. The latest studies on the chemical constitution of Portland cement seem to indicate that portland cement is made up largely of three compounds, namely: tricalcium silicate (3CaOSi0 2 ), dicalcium silicate (2CaOSiO 2 ), and tricalcium aluminate (3CaOAl 2 O 3 ). There are also small amounts of iron oxide (Fe 2 O 3 ), magnesia (MgO), sulphur in the form of SO 3 , alkalis, etc., together with a little lime (CaO) if the clinker is underburned. A perfectly burned cement clinker consists of about 36 per cent of trical- cium silicate, 33 per cent of dicalcium silicate, 21 per cent of tricalcium aluminate, and about 10 per cent of other com- pounds. If the cement clinker is not perfectly burned, there is less tricalcium silicate and more dicalcium silicate and usually some free lime. The standard specifications for Portland cement specify that, PORTLAND CEMENT 33 in regard to chemical properties, the following limits shall not be exceeded: Loss on ignition 4 . 00 per cent Insoluble residue . 85 per cent Sulphuric anhydride (SO 3 ) . 2.00 per cent Magnesia (MgO) 5 . 00 per cent 36. Soundness. Soundness is a necessary quality for cement that is to be used for structural purposes, as it is not desirable to use a cement that will later disintegrate and cause a failure of the structure. Unsoundness is usually shown by expansion after the cement has set, followed by disintegration. Free lime is the chief cause of unsoundness, causing the cement to ex- pand and disintegrate. An excess of magnesia (more than 5 per cent) is thought to cause unsoundness. An excess of sulphate is thought to have a similar action in some cases. Seasoning helps in making cement sound by giving time for the complete hydration or carbonating of any free lime that is present. Un- soundness is shown by the cracking and disintegration of the cement after setting, due to the expansion of some of its constituents. The amount of sulphates added for a retarder should never be more than 3 per cent. Soundness is promoted by thorough seasoning, fine grinding, and by keeping the amounts of magnesia and sulphates low. The specification requires that a pat of neat cement shall be kept in moist air for 24 hours and then exposed for 5 hours in an atmosphere of steam at a temperature between 98 and 100 degrees Centigrade on a suitable support 1 in. above the boiling water. This pat of neat cement should be about 3 in. in diameter, J^ in. thick at the center, and tapering to a thin edge. To pass the soundness test successfully, the pat should remain firm and hard and should show no signs of distortion, checking, crack- ing, or disintegrating. This test is commonly known as the "accelerated" test. The old specifications required three pats to be tested. One was to be subjected to the accelerated test. One pat was to be kept in moist air for 24 hours and then in water for 27 days, and observed at intervals. The third pat was to be kept in moist air for 24 hours and then in air for 27 days, and observed at intervals. The temperature of the air and water was to be kept as near 70 degrees Fahrenheit as practicable. 34 MATERIALS OF CONSTRUCTION 37. Strength. The tensile strength of cement has but little value as a measure of the suitability of the cement for structural purposes, but it is of value as a means of comparing different cements and also because of the relation of the tensile to the compressive strength. While the ratio of tensile strength to compressive strength varies for different cements and for differ- ent ages, it is generally true that a cement that is strong in tension is also strong in compression. Because of fewer diffi- culties in the making and testing of specimens and because of the lower cost and weight of testing machines required, tension tests have been standardized in preference to compression tests on cement. A slight increase in the lime content increases the tensile strength a little. Fine grinding increases the strength of cement mortar but not that of the neat cement. An addition of more than 5 or 10 per cent of clay is injurious. Hydrated lime will decrease the strength of neat cement. A high-tensile strength does not indicate that the cement is sound. A large retrogression in the strength of cement is a bad sign. The tensile test requirements for neat cement have been discon- tinued in the new specifications. The following are the old specifications (minimum requirements) for the strength of neat cement : STRENGTH, POUNDS STORAGE PER SQUARE INCH 1 day in moist air 175 1 day in moist air and 6 days in water 500 1 day in moist air and 27 days in water 600 The compressive strength of cement is the best criterion to use in choosing a cement for structural purposes, but for several reasons this test has not been standardized. The compressive strength of a good neat cement is about 10 times its tensile strength. The modulus of elasticity for cement in compression is not a constant because the stress strain curve is not a straight line for any appreciable portion of its length. The compressive strength of cement is influenced by the same factors as the tensile strength. The shearing strength of neat cement is about the same as the tensile strength, and it depends upon the same factors. Very little information regarding the shearing strength of neat cement is available. PORTLAND CEMENT 35 38. Time of Set. One of the most important properties of Portland cement is its property of setting and hardening, which is caused principally by the hydration of its three major con- stituents, tricalcium silicate, dicalcium silicate, and tricalcium aluminate. When water is added to Portland cement, these compounds first form amorphous and later both crystalline and amorphous hydrated materials. The tricalcium aluminate sets and hardens very quickly, and the " initial" set of the cement is undoubtedly due to the hydration of this compound. The early hardness and cohesive strength of the cement are due to the hydration of the tricalcium aluminate and the tricalcium silicate. The further increase in strength is due to the further hydration of these two compounds as well as that of the dical- cium silicate. The tricalcium silicate is the most important cementing compound of the three. This setting and hardening will progress under water as well as in air. The actual time of set is of much importance in some work. It is not desirable to have the set occur before the concrete is placed, neither is it desirable to have too long a time elapse before the cement sets, especially if the cement is to be placed under water. In general, the higher the temperature the quicker the set takes place. An excess of water will lengthen the time required. Cement sets slower in damp weather than in dry. An addition of gypsum or plaster of Paris up to about 3 per cent retards the set, while a larger addition of plaster of paris will tend to give the cement a " flash" set. The seasoning of the cement often affects the time of set, sometimes increasing and sometimes decreasing the length of time required. The specifications require that the cement shall not develop initial set in less than 45 minutes when the Vicat needle is used or 60 minutes when the Gilmore needle is used. Final set shall be attained within 10 hours. 39. Fineness. It has been determined that the final particles of cement are the ones which give the cement its cementing values. Fineness of grinding increases the strength of cement mortars, but not that of neat cement pastes. Fine grinding also increases the sand carrying capacity of the cement, shortens the time of set, and is thought to make the cement more sound. The specifications for fineness of cement require that 78 per cent or more of the cement shall pass a standard 200-mesh sieve. 36 MATERIALS OF CONSTRUCTION 40. Specific Gravity. The specific gravity test of Portland cement is not of much importance and is not made unless it is specifically ordered. A low specific gravity may be caused by adulteration in large amounts, but small amounts may not have enough effect to lower the specific gravity below 3.10. There is practically no relation between the degree of burning and the specific gravity. Seasoning tends to lower the specific gravity, due to the absorption of carbon dioxide and moisture from the air. The specifications require that the specific gravity of Portland cement shall not be less than 3.10 (3.07 for white Portland cement). Should the test of cement as received fall below this requirement, a second test shall be made upon an ignited sample. 41. Uses of Portland Cement. At present, Portland cement is used very much in structural work and it is rapidly replacing lime, natural cement, and other kinds of cements in this field. As a part of mortar it is used for stone and brick masonry and for finishing coats, etc. As a part of monolithic concrete it is used for all kinds of heavy masonry work such as foundations, dams, piers, footings, abutments, retaining walls, pavements, sidewalks, etc. As a part of reinforced concrete it is used in walls, buildings, floors, roofs, piles, bridges, tunnels, subways, ships, conduits, pipes, culverts, etc. Portland cement ranks next to steel and timber as a structural material at the present time and it will probably outrank timber in the near future. At present, cement concrete is not so reliable a structural material as steel or timber, due to the fact that not so much is known about concrete and also that unskilled men are often employed for selecting the aggregate and mixing and laying of the concrete. There is no doubt but that the use of Portland cement in structural work will be much more extensive in the future than it is at the present time. CHAPTER IV PORTLAND CEMENT MORTARS A. DEFINITIONS AND MATERIALS 42. Definitions. A Portland cement mortar is a mixture of Portland cement, fine aggregate (sand or its equivalent), and water. Fine aggregates are particles of gravel, crushed stone, sands, or other materials which will pass a Y in. sieve. Silt is sometimes defined as particles between 0.005 mm and 0.05 mm. in diameter; clay as particles less than 0.005 mm. in diameter; and loam as a mixture of any of the fine materials with organic matter, either animal or vegetable. 43. The Cement and the Water. The cement should be a Portland cement capable of passing the standard specifications. On the work, the cement should be stored in a weather-tight building which will protect it from dampness, and so piled as to permit of ready inspection and sampling. Whenever practicable, each shipment of cement should be sampled and tested before being used. The water used for Portland cement mortar should be free from oils, acids, alkalis, and organic matter (either animal or vegetable). The water should not contain any chemical in solution that would be harmful to the mortar. The presence of oil is easily detected by its surface film. Organic matter (usually of vegetable origin) can sometimes be detected by observing floating particles, or by turbidity, though chemical tests are often required. Tests of water for acidity or alkalinity can be made by means of litmus paper. If there is any doubt as to the suitability of the water for use, its effect on soundness, set, and strength of the mortar should be determined by tests. 44. Sand in General. In mortars and concretes it is just as important to have a good sand as it is to have a good cement. Due to the progress in the manufacture of Portland cement, the quality of most Portland cements is such that there are more failures due to the use of a poor sand than to the use of a poor cement. 37 38 MATERIALS OF CONSTRUCTION The sand should be composed of a hard siliceous material free from loam, clay, sticks, animal or vegetable matter, friable materials, etc. ; and the particles of sand should be small enough to pass through a quarter inch sieve. The best sand, as to size, is one which contains both coarse and fine grains in such propor- tions that the percentage of voids will be a minimum. A coarse grained sand is usually better than a fine grained one. While a sand should preferably consist of hard silica grains, other minerals may be present without causing any bad effects. How- ever, sands containing mica, hornblende, feldspar, and carbonate of lime are not durable and should not be used. The physical condition of a sand is of more importance than the chemical compo- sition. A friable sand is worthless. A small percentage of finely divided clay or loam is not usually injurious. Sands may be washed to remove dirt and like materials, but care should be taken not to wash away too much of the finer parti- cles of the sand. 45. Properties of Sand. Other things being equal, the smaller the percentage of voids, the better the sand for use with Portland cement. The percentage of voids in dry sand ranges from about 25 to 45 per cent. The percentage of voids in a sand may be found by dropping a known volume of well-shaken dry sand into water and noting the volume displaced. The difference between the original volume of the sand and the volume of the water displaced gives the volume of voids. Or, as the specific gravity is nearly a constant (2.65) for all sands, the percentage of voids can be approximately determined from the weight per cubic foot. Another way is to pour water on the sand (contained in a water-tight vessel) until the surfaces of the sand and water coincide. The volume of water required is equal to the volume of voids in that amount of sand. Well-shaken dry sand will weigh from 90 to 125 Ib. per cubic foot, but if the sand is in a loose condition it may weigh as much as 20 per cent less. Moist sand, that is not packed, weighs less than dry sand. The percentage of absorption of sand rarely exceeds 3 per cent. The specific gravity of sand is usually between 2.6 and 2.7 and the average value is about 2.65. 46. Sieve Analysis of Sand. The sieve analysis of sand (or fine aggregate) is one of the best tests for determining the suit- ability of the sand for use in a Portland cement mortar. This PORTLAND CEMENT MORTARS 39 analysis consists of sifting a sample of sand through several dif- ferent sieves (five or more) and noting the amount passing each sieve. Sieve openings Ko in. or larger are usually in the form of circular holes, while woven brass wire cloth is used for the sieves with smaller openings. These woven-wire sieves are known by numbers corresponding to the number of openings per lineal inch. For analyzing sands the following sieves are desirable : Diameter Diameter Diameter Sieve of opening, Sieve of opening, Sieve of opening, inches inches inches %in. 0.375 No. 10 0.073 No. 40 0.015 Mm. 0.250 No. 15 0.046 No. 50 0.011 H in. 0.167 No. 20 0.034 No. 80 0.007 Ho in. 0.100 No. 30 0.022 No. 100 0.0055 The results of a sieve analysis may be shown graphically by plotting the sieve openings as abscissae and the corresponding percentages passing each sieve as ordinates. This will give a curve from which the qualities of the sand may be estimated (see chapter on "Plain Concrete" for sample curves, for sand). The uniformity coefficient is the ratio of the diameter of the particles, represented by the point where the curve crosses the 60 per cent line, to the diameter of the particles where the curve crosses the 10 per cent line. A coarse sand has a uniformity coefficient of about 5.2 or more; a medium sand of about 4.2; and a fine sand of about 2.2. A sand that has a uniformity coefficient of about 4.5 is usually considered good for concrete work. 47. Standard Sand. Standard sand is the sand recommended for use in cement testing by the American Society of Civil Engineers and other engineering societies. It is a natural bank sand obtained from Ottawa, 111., U. S. A., and screened to proper size. Only the sand that passes a No. 20 sieve and which is held on a No. 30 sieve is used. The percentage of voids in this sand is about 37 per cent, and the weight per cubic foot is about 104 Ib. 48. Substitutes for Sand. Stone screenings are the fine materials (less than one-quarter of an inch in size) which have 40 MATERIALS OF CONSTRUCTION been screened out from crushed stone. When they are free from clay and dirt, they make a good substitute for sand. They are apt to be a little coarser than sand, but they have about the 0.0+ o.oe o./2 o./6 O/ometer of J/etv Opening in fates FIG. 16. Mechanical analysis of sands. same percentage of voids and weight per cubic foot. Screenings make a strong mortar, but the strength usually decreases more rapidly with a decrease in the amount of cement than in the case of a sand mortar. Well selected and screened mine tailings often make as good a cement mortar as stone screenings. Granulated blast-furnace slag, small cinders, clay, loam, etc. have been used as substitutes for sand in a Portland cement mortar, but they do not make so good a mortar as ordinary sand. 49. Specifications for Fine Aggregate. These specifications are practically the same as those adopted by the New York Public Service Commission. Fine aggregates for use in a Portland cement mortar or concrete should conform to the following requirements. PORTLAND CEMENT MORTARS SIEVE ANALYSIS OR MECHANICAL GRADING 41 Sieve Diameter of opening, inches Per c.ent passing sieve limits Kin. 0.250 100 KG in. 0.187 Between 93 and 100 No. 6 0.138 Between 90 and 100 No. 10 0.073 Between 75 and 93 No. 15 0.047 Between 48 and 80 No. 30 0.022 Between 20 and 50 No. 50 0.011 Between 2 and 30 No. 100 0.0055 Between and 7 Curves for the extreme conditions may be plotted upon cross- section paper together with the curve for the sand tested. If the sand is good, its curve will lie between the two extreme curves. In general, a sand for use in a mortar may be a little coarser than a sand for use in a concrete. SiU. Not over 7 per cent of the dry weight of the sample should pass a No. 100 sieve when screened dry. Strength. Both tensile and compressive strengths of a 1:3 mortar (proportioned by weight) shall be equal to or more than the strengths required for a 1 : 3 standard Ottawa sand mortar in the standard and tentative (proposed) specifications of the American Society for Testing Materials. Organic Matter. The loss on ignition shall not exceed ^{Q of 1 per cent of the total dry weight. B. PROPORTIONING AND MIXING MORTAR 50. Proportioning the Mortar. The proportioning of cement and sand for a mortar is usually done by one of the three following methods: (1) by weight; (2) by volumes of packed cement and loose sand; and (3) by volumes of loose cement and loose sand. The best way of proportioning the materials is by weight, and this method is usually followed in the laboratories, though rarely in practical work. The presence of moisture in the sand may affect the proportioning to some extent if the amount of moisture is not approximately determined and allowed for. Sand rarely contains more than 5 per cent of moisture by weight ; hence, the error due to moisture would usually be less than 5 per cent if no correction were made. 42 MATERIALS OF CONSTRUCTION Proportioning by packed cement and loose sand is probably the second best method. This method is used to some extent on practical work. Usually a sack of cement is considered to be 1 cu. ft. in volume and only the sand is measured. In measuring the sand, it is important to secure the same degree of looseness each time, otherwise the proportions may be changed. The difference in volume between loose and compact material may be as much as 20 per cent in some cases. Proportioning by loose cement and loose sand measured by volume is the least reliable of the three methods due to the inability or neglect of the average workman to secure the same degree of compactness at all times. The common method is to dump the cement and sand loosely into measuring boxes and then empty the boxes on the mixing platform. Often the measuring is done by pails or wheelbarrows and the proportioning is very inaccurately done. The proportions of mortar for masonry work are usually a 1 : 2 or a 1:3 mix, 1 part of cement to 2 or 3 parts of sand. Some- times as rich a mix as a 1:1 is required for finishing or other work while as lean a mix as a 1:5 may be used in some cases. 51. Mixing the Mortar. The mixing should be done either by hand or by machine. In either method it is better first to mix the cement and sand dry and in the proper proportions, and then add the water and mix again. The batches should not be too large. Machine mixing is faster than hand mixing and the quality is more uniform. The cement and sand are first placed in the machine and mixed for a minute or so. Then the water is added and the batch mixed for a few minutes more. A well-handled mixer will turn out a batch of mortar every 5 minutes. For hand mixing, suitable water-tight platforms must be provided to prevent the loss of cement. The sand is first spread out in a layer on the platform and the cement is then placed in a thin layer on top of the sand. The cement and sand are then mixed dry until they are of a uniform color. Then the water is added and the batch is thoroughly mixed again. Shovels and hoes are convenient tools to use in the mixing. Thoroughness of mixing is of the most importance. The mortar should be used before the initial set has taken place. Cement mortar that has reached initial set should not be used. Retempering (remixing) of cement mortar should not be allowed after the initial set is reached. PORTLAND CEMENT MORTARS 43 C. PROPERTIES OF PORTLAND CEMENT MORTARS 52. Strength of Portland Cement Mortars in General. The strength of Portland cement mortar depends upon (1) the pro- portion of cement used; (2) the size and grading of the sand; (3) the amount of water used; and (4) the degree of compactness of the mortar. That is, the strength of the mortar depends upon (a) the amount of cement per unit volume, and (b) the density of the mortar. In order to secure the best results, it is necessary to make tests upon different mixes of cement, sand, and water. Uniform condi- tions of testing must be carefully observed in order to secure relia- ble results. The strength of Portland cement mortar is affected by the temperature of the air and water, the thoroughness of gaging, and the conditions of testing. It is necessary to standardize the methods of testing before trying to determine the influence of the constituents of the cement, sand, and water used in the mortar. This testing should preferably be done by experienced operators in a well-equipped laboratory. The personal equations of different operators will have some effect on the results and care should be taken to minimize this effect as much as possible (see any book on the testing of Portland cement and cement mortars for the standard methods). 53. Effect of Density and Size of Sand on the Strength. Density of the mortar may be defined as the ratio of the actual solid material (absolute volume of the cement and sand) to the total volume of the hardened mortar. The density may be determined by carefully weighing the materials used and assum- ing a value of 3.1 for the specific gravity of the cement and 2.65 for the specific gravity of the sand. If the actual values for the specific gravities have been obtained, these values should be used. In general, the size and grading of the sand that will give the densest mortar will also give the strongest mortar. This requires that the percentage of voids shall be small and that the sand shall have a sufficiency of coarse grains. A low percentage of voids depends upon the grading of the sand and not on the actual size of the grains. With the same percentage of voids, a coarse sand will make a stronger mortar than a fine sand. If a sand is not suitable for use, it may be made suitable by mixing another sand or part of another sand with it so as to give a low percentage of voids. Sometimes a sand may be screened in two or three 44 MATERIALS OF CONSTRUCTION different sizes and these sizes remixed in different proportions so as to reduce the amount of voids. Feret made a study of the effect of the size of sand grains on the strength of Portland cement mortar and his results showed that (1) the densest mortar was generally the strongest; (2) the proportion of fine sand should be small; and (3) if the sand is uniform in size, a coarse sand is better than a medium sand and a medium sand is better than a fine sand. 54. Effect of the Amount of Mixing Water on the Strength. An increase in the amount of water used (above the proper amount needed) in the mixing of the Portland cement mortar will (1) increase the time required for setting; (2) decrease the strength of neat cement mortar, having a greater effect on short time than on long time tests; (3) decrease the strength of the mortar on short time tests (say under 6 months), but will have less effect on the results of long time tests; (4) increase the amount of laitance on the surface; (5) increase the difficulty of bonding the new mortar to the old; and (6) tend to cause a segregation of the materials (sand and cement). A decrease in the amount of water (below the proper amount required) used in mixing the mortar will (1) tend to hasten the set; (2) increase the voids; (3) decrease the strength, except that a slight decrease in the amount of water used may increase the strength, especially on short time tests, provided that the mortar is well compacted; and (4) make the mortar less water-tight. 55. Effect of Various Conditions on the Properties of Mortars. Mortars made and used in dry weather should have their exposed surfaces kept moist for several days so that the water will not be evaporated from these surfaces before the mortar has hardened. Portland cement rnortar will harden a little more rapidly in dry weather. Mortars made and used in wet weather require a little more time to set and attain their strength. Hot weather (high temperatures) decreases the time required for set and increases the rate of gain in strength. Low temperatures increase the length of time required for the setting and hardening of the cement mortar and decrease the strength on short time tests. At a temperature of 40 degrees Fahrenheit, the strength is only about two-thirds of that at 70 degrees Fahrenheit when the mortar is 2 months old. Cement requires about four times as long to set at a temperature of 32 PORTLAND CEMENT MORTARS 45 degrees Fahrenheit as it does at a temperature of 65 degrees Fahrenheit. Freezing of Portland cement mortars retards their rate of hardening and their rate of increase in strength. Exposed sur- faces, that are frozen before the final set occurs, often scale off. It is not good practice to use Portland cement mortar in freezing weather unless special precautions are taken to keep it from freezing. Regaging or remixing a Portland cement mortar after setting has begun is generally not permitted. Experiments on the effect of regaging mortars gave various results, depending upon different mortars and the length of time elapsed between the mixings. Regaging of some mortars within a few hours after the initial set had taken place caused no bad results whatever, but in most cases such regaging seemed to cause a decrease in the ability to harden as well as a decrease in the strength. It is thought that the effect of regaging a Portland cement mortar within 2 hours after mixing is not very injurious. 56. Effect of Various Elements on the Properties of Mortars. A small percentage (2 or 3 per cent) of mica added to a 1:3 Portland cement mortar may cause a 20 per cent loss of strength due to an increase in voids and the inability of the cement to stick to the smooth surface of the mica. Dirt has an injurious effect on the strength of the mortar, especially if it contains any organic matter. As small as ^{Q of 1 per cent of organic matter may be injurious. A small percentage of any friable material is injurious. Clay usually decreases the strength of the mortar, but in some cases a small amount of finely divided clay (say from 5 to 10 per cent), which has been thoroughly mixed with the sand, appears to have a good effect. A rich mortar is generally injured by the addition of clay while a lean mortar may be improved, especially if the mortar contains a large percentage of voids. Good finely divided loam has about the same effect as clay. Lime has about the same effect as clay but is not thought to be so injurious. Small percentages of lime often improve a lean mortar but may injure a rich mortar. A small addition of lime paste makes a cement mortar much easier to work with in laying brick or stone masonry. Salt, when added to the mixing water, lowers the freezing point 46 MATERIALS OF CONSTRUCTION of the mortar and, up to about 10 per cent, appears to have but little effect on the strength. For temperatures below 32 degrees Fahrenheit, the amount of salt required to lower the freezing temperature 1 degree Fahrenheit is about 1 per cent of the weight of the mixing water. 57. Tensile Strength. The statements made in preceding paragraphs on the strength of neat Portland cement apply equally well to the strength of a Portland cement mortar. In determining the qualities of a cement that is to be used, the tensile strength of the mortar is more valuable than the tensile strength of the neat cement. Under normal conditions the strength of Portland cement mortar increases very rapidly during the first few days. The rate of gain of strength gradually decreases. At the age of 7 days, the strength is about one-half or two- thirds of the maximum, which is reached at an age of about 3 months. The specifications (minimum requirements) for a 1 : 3 standard sand mortar are as follows: ONE PART OF PORTLAND CEMENT TO 3 PARTS OF STANDARD OTTAWA SAND TENSILE STRENGTH, POUNDS PER SQUARE AGE AND STORAGE INCH 1 day in moist air, and 6 days in water 200 1 day in moist air, and 27 days in water 300 The proportions are by weight. The temperature of the materials during the mixing, storing, and testing should be as near 70 degrees Fahrenheit as practicable. A good sand and cement should give results much higher than the above minimum requirements for a standard sand mortar. Many mortars show a slight retrogression in strength after 5 or 6 months, but this retrogression is usually not permanent and it does not appear at all in the compression test results. 58. Compressive Strength. Testing a Portland cement mortar in compression is the best way of judging of the suitability of the cement and sand for construction purposes. In general, a mortar that is strong in tension is also strong in compression, but the ratio of the strengths is not a constant quantity. The compressive strength of a good mortar increases steadily with age and shows no retrogression. The modulus of elasticity in compression is a variable quantity because the stress strain curve is not a straight line. At about one-fourth of the ultimate strength, the modulus of elasticity PORTLAND CEMENT MORTARS 47 in compression is approximately 4,000,000 Ib. per square inch for neat cement and about 3,000,000 Ib. per square inch for a good 1:3 mortar. At present there are no standard specifications for the com- pressive strength of Portland cement mortar in America, but the following minimum requirements have been proposed and adopted as tentative specifications: ONE PART OF PORTLAND CEMENT TO 3 PARTS OF STANDARD OTTAWA SAND COMPRESSIVE STRENGTH, POUNDS PER SQUARE AGE AND STORAGE INCH 1 day in moist air, and 6 days in water 1 , 200 1 day in moist air, and 27 days in water 2 , 000 The specimens are cylinders 2 in. in diameter and 4 in. high. Each value should be the average of not less than three specimens, and the average at 28 days must be higher than that at 7 days. A good mortar should give results that are much higher than the above minimum requirements for a standard sand mortar. 59. Transverse Strength. The transverse strength of a Portland cement mortar, as calculated from the formula S = Mv/I, is approximately two times the tensile strength. The cross-bending strength is proportional to the tensile strength, and it depends upon the same factors. 60. Adhesive Strength. The adhesive strength of neat Portland cement and Portland cement mortars, at the age of 6 months, with a few different materials, is shown by the following table: ADHESIVE STRENGTH IN POUNDS PER SQUARE INCH MIXTURE IRON RODS SAWN LIMESTONE BRICK Neat 315 270 50 1:1 290 220 40 1:2 265 170 30 1:3 110 75 15 61. Shearing Strength. The shearing strength is of import- ance, as concretes and mortars are often subjected to shearing stresses in practical work. Shearing tests are rarely ever made on account of difficulties of obtaining a true shearing stress. The shearing strength depends upon the same factors as the tensile and compressive strengths. The shearing strength is usually proportional to the compressive strength. The fineness 48 MATERIALS OF CONSTRUCTION of grinding of the cement and the qualities of the sand are the most important factors. The following table gives the results of some tests upon the shearing strength of neat Portland cement and Portland cement mortars made by Bauschinger in 1879. The specimens were about 2% by 5 in. in cross-section and were stored in water. Each result is an average of nine tests. It is to be noted that the cement used did not pass the tension test requirements of the American specifications; the neat strength being 224 Ib. per square inch for the 7-day and 294 Ib. per square inch for the .28-day tests, while the 1 : 3 mortar results were 95 Ib. per square inch for the 7-day and 169 Ib. per square inch for the 28-day tests. SHEARING STRENGTH IN POUNDS PER SQUARE INCH Mix AGE 7 DAYS AGE 28 DAYS AGE 2 YEARS Neat 271 346 415 1:3 116 188 375 1:5 77 131 364 62. Miscellaneous Properties. Abrasive resistance of Port- land cement mortars depends not only upon the cement but also upon the hardness of the sand grains. Expansion and Contraction. -Cement mortar, when hardening, in air, will contract slightly, and when hardening in water it will keep a nearly constant volume or expand a little. The richer the mortar, the greater the effects of expansion and contraction. Permeability is the measure of the rate of flow of water through a mortar of a given thickness and under a given pressure. An impermeable mortar is a water-tight one. Permeability de- creases rapidly for all mixtures with an increase in the age of the specimens tested; it decreases considerably with a continuation of flow; and it increases with an increase of pressure, leanness of mix, dryness of mixture, and with increased coarseness of the sand used. An addition of a small amount of finely divided clay or loam tends to decrease the permeability. (See the articles on "Impervious Concrete" in the chapter on "Plain Concrete" for methods and materials for decreasing the permea- bility of plain concrete. These articles apply to a Portland cement mortar as well as to plain concrete.) Absorption of water by a Portland cement mortar depends upon the same conditions (but not to so large an extent) as the permeability does. In general, the absorption decreases slightly PORTLAND CEMENT MORTARS 49 with age; increases with an increased leanness of mixture; and the dry mixtures are slightly more absorptive than the wet ones. Voids in a Portland cement mortar depend upon the grading of the materials and the consistency of the mix. A well-graded aggregate with a small percentage of voids will usually give a mortar with a small percentage of voids. If more or less water is used than is necessary to form a proper consistency, the voids in the mortar will be increased. A dry mix usually has more voids than a corresponding wet mix. The voids in a mortar usually vary between 15 and 30 per cent. Weight. A good Portland cement mortar of a 1 : 3 mix will weigh about 140 Ib. per cubic foot; a 1:1 mix about 145 lb.; and a 1:4 mix about 138 lb. per cubic foot. The weight per cubic foot varies directly with the density of the mortar and the specific gravities of the cement and fine aggregate used. CHAPTER V PLAIN CONCRETE A. DEFINITIONS AND MATERIALS 63. Definitions. Concrete is an artificial stone made by mixing cement, water, and an aggregate consisting of large and small particles, such as broken stone or gravel and sand or screenings. Aggregates are those inert materials which, when bound together by cement, form a concrete. Fine aggregate is usually defined as the material that will pass a J-in. sieve, while coarse aggregate is the material which is held on a J^-in. sieve. 64. Cement, Water, and Fine Aggregate. Cement. The cement used should preferably be a Portland cement that will pass the standard specifications of the American Society for Testing Materials (or equivalent specifications) when subjected to the standard tests recommended by the American Society of Civil Engineers. . . After delivery at the work, the cement should be carefully stored in weatherproof buildings having tight floors above the ground level in order to protect the cement from the weather and to allow of ample time for inspection and testing. If kept dry, the cement will not be injured by a long storage and it may be improved, due to the seasoning. Before being used, each shipment of cement should be carefully inspected, sampled, and tested by a competent person. In sampling, one sample should be taken from about every tenth barrel and care should be taken to secure a fair sample. The amount of cement required for the standard tests is about 10 Ib. Water. The water used in making concrete should be clean and free from any impurities which would be injurious to the concrete. See the discussion regarding a suitable water for Portland cement mortars in the preceding chapter (Chap. IV, Art. 43). Fine Aggregate. The fine aggregate used in making concrete should be a good sand, or its equivalent, and should possess those requisites that are given and discussed in the preceding chapter (Chap. IV) on "Portland Cement Mortars." In general 51 52 MATERIALS OF CONSTRUCTION a sand for use in a concrete should possess more fine particles than a sand for use in a Portland cement mortar. The fine aggregate should be stored in bins or piles convenient to the work and, if necessary, be screened to remove large particles and be washed to remove dirt and silt. In washing, care should be taken not to wash out too much of the finer material. 65. Coarse Aggregate in General. The coarse aggregate used for concrete usually consists of crushed stone, gravel, cinders, slag, broken brick, etc. Any stone is suitable for concrete work that is durable and strong enough so that the strength of the con- crete will not be limited by the strength of the stone. Strength, density, hardness, toughness, durability, and cleanliness are desirable properties in a coarse aggregate. As the physical character of a rock depends upon its mineral constituents and structure, only those rocks which have durable mineral constit- uents and a dense, strong structure should be used for concrete. Rocks which are structurally weak or which contain weak mineral constituents should not be used. Granites, traps, and lime- stones are often employed for concrete work, while sandstones are rarely suitable for this work. Soft, flat, or elongated particles do not make a satisfactory material for use in concrete. Clean screened gravel is a good substitute for broken stone, but it often contains some particles of a soft friable nature that will reduce the strength of the concrete. Cinders, and sometimes slag, may be used for a coarse aggregate for a concrete subjected to very low stresses or which may be used as a fireproofing material or where light weight is desired. Broken brick should not be used in concrete work of any importance or where strength is required. After the stone is quarried, it may be broken by laborers with stone hammers or it may be crushed in stone crushers. Jaw crushers are usually used in small or portable plants and gyratory crushers in large stationary plants Screening of the crushed stone or gravel is often necessary to remove the dust and other fine material that will pass a ^i-in. sieve. Sometimes it is neces- sary to wash the gravel to remove the dirt, loam, clay, or organic matter adhering to it. Coarse aggregate may be stored in bins or piled in the open without any special protection from the weather. Care should be taken to keep the coarse aggregate clean and prevent dirt, clay, loam, organic matter, etc. from being mixed with it. 66. Size of Coarse Aggregate. The maximum size of crushed PLAIN CONCRETE 53 stone for concrete work varies according to the use to which the concrete is to be put. When crushed stone is used for massive walls, the maximum size may be 2^ or 3 in.; 2 in. for abutments; 1J4 in. for arch rings; 1 in. for copings, bridge seats, and thin walls; and 1 in. or % in. for reinforced concrete work. Flat, ir- regular, or rough stones are not so desirable as are the more rounded ones. A crushed stone or gravel that is nearly all of one size is not so good as an aggregate that is made up of uniformly graded parti- cles because an aggregate all of one size usually has a larger per- centage of voids. It is often desirable to screen the aggregate into two or more sizes and remix these sizes in different proportions in order to secure the proper grading. A mechanical (sieve) analysis is of value in studying the grading of a coarse aggregate that is to be used in concrete work. The sieves used are preferably ones of 2J^-, 2-, 1%-, lM-> lJ^-> 1-, %-> M-> %-> and 34-in. mesh. Usually all of these sieves are not needed for any one test, but just a sufficient number should be used to give the desired information. The results of a sieve analysis may be plotted on cross-section paper and a curve drawn through the points (see article on " Proportioning by Mechanical Analysis" for further discussion). 67. Voids, Weight per Cubic Foot, and Specific Gravity of Coarse Aggregates. The voids in a coarse aggregate may be- found by pouring a known volume of the aggregate into a known volume of water and noting the displacement. In measuring the volume of the aggregate, care must be taken to secure a uni- form degree of compactness. The volume of the aggregate minus this displaced volume equals the volume of the voids. Another way of determining the voids in a coarse aggregate is to pour water on a known volume of the aggregate, contained in a water-tight vessel, until the surfaces of the aggregate and the water coincide. The volume of the water added equals the volume of the voids. The. percentage of voids varies from 30 to 55 per cent for com- mon crushed stone and gravel, depending to some extent on the shape, grading, and degree of compactness. The weight per cubic foot for coarse aggregate (crushed stone and gravel) usually varies from about 75 to 120 Ib. Crushed stone is often sold by. the cubic yard but it is frequently measured by weight, 2,500 Ib. being considered equal to 1 cu. yd. 54 MATERIALS OF CONSTRUCTION The specific gravity of stone and gravel varies somewhat. Approximate values are as follows: trap 2.8 to 3.0; granite 2.65 to 2.75; limestone 2.6 to 2.7; sandstone 2.3 to 2.6; and ordinary sand and gravel 2.6 to 2.7. The following table shows the relation between voids, weight per cubic foot, and specific gravity: VOIDS AND WEIGHT OF BROKEN STONE AND GRAVEL Percentage of voids Weight in pounds per cubic foot Specific gravity 2.6 Specific gravity 2.7 Specific gravity 2.8 Specific gravity 2.9 Specific gravity 3.0 35 106 110 114 118 122 40 97 101 105 109 112 45 89 93 96 100 103 50 81 84 87 91 94 55 73 76 79 82 84 68. Specifications for Coarse Aggregate. The following speci- fications are those of the American Railway Engineering and Maintenance of Way Association: Stone shall be round, hard, and durable, and shall be crushed to sizes not exceeding 2 in. in any direction. For reinforced con- crete, sizes usually are not to exceed % in. in any one direction, but the size may be varied to suit the character of the reinforcing materials. Gravel shall be composed of clean pebbles of hard and durable stone of sizes not exceeding 2 in. in diameter, and shall be free from clay and other impurities except sand. When the gravel contains sand in any considerable quantity, the amount of sand per unit of volume of the gravel shall be determined accurately, to admit of the proper proportion of sand being maintained in the concrete mixture. The following specifications for coarse aggregate for concrete are practically the same as those adopted by the New York Public Service Commission. Cleanliness. All broken stone aggregate must be so free from dust that the limit of fineness (5 per cent) shall not be exceeded (fine material being the material passing the ^-m. sieve). All gravel must be thoroughly washed, preferably at the plant or pit where it is secured. PLAIN CONCRETE 55 Mechanical Grading. A sieve analysis shall be made of the coarse aggregate and, if the aggregate is suitable for use, the results should be within the limits given in the following table. If so desired, curves for the extreme conditions or limits for the kind of sieves used may be plotted on cross-section paper together with the curve for the coarse aggregate tested. If the coarse aggregate is good for use, its curve will lie between the two extreme or limiting curves. MECHANICAL GRADING SIZE OF SQUARE-HOLED SIEVES, LIMITS, ROUND-HOLED SIEVES, LIMITS, OPENING, PERCENTAGE PASSING PERCENTAGE PASSING INCHES 2 100 100 1> Between 95 and 100 Between 75 and 95 \Y Between 65 and 92 Between 50 and 85 1 Between 40 and 80 Between 35 and 70 % Between 25 and 60 Between 20 and 50 > Between 10 and 40 Between 7 and 35 % Between and 5 Between and 5 B. PROPORTIONING OF CONCRETE 69. General Theory. The theory of proportioning is that the fine and the coarse materials should be so proportioned that the concrete will have the greatest density. This means that the voids in the concrete should be a minimum. This is accomplished when there is just enough cement to fill the voids in and com- pletely coat all of the particles of the sand, and just enough mortar to fill all the voids in and completely coat all of the particles of the coarse aggregate. There must be no excess of water, otherwise water voids will be formed. Proportioning by weight will secure more uniform mixtures than proportioning by volume because the errors due to the measurement of the materials in a loose or compact form are eliminated. These errors may be as large as 20 per cent. In practical work the proportioning is nearly always done by volume because this method is more convenient. 70. Proportioning by Standard Proportions. Proportioning in practical work is commonly done by. "rule of thumb," using certain standard proportions. The materials are measured by volume, the unit of measurement being 1 cu. ft. usually. The following are some of the standard mixes: 56 MATERIALS OF CONSTRUCTION 1:1:2 A very rich mixture used only where great strength and water tightness are required. 1: 1^:3 A rich mixture not quite so strong as the first, but used for the same purposes. 1:2:4 A good mixture used very often in reinforced concrete work and for foundations subjected to vibrations. 1:2^:5 A medium mixture used for floors, retaining walls, abutments, etc. 1:3:6 A lean mixture used for massive concrete structures under steady loads of not great intensity. 1:4:8 A very lean mixture used only for massive concrete work which is not very important. 71. Proportioning with Reference to Coarse Aggregate. The theory of this method is that just enough mortar should be used to fill the voids in the coarse aggregate. In practice, more mortar is required, because of the separation of the coarse aggregate by the mortar and excess water and the consequent increase in the voids. About 10 per cent more mortar is required on an average. If care is taken to secure a properly graded coarse aggregate, the voids will be less, and less mortar will be required to produce a concrete of the required strength and imperviousness. This means a saving of cement and sand. In general, ordinary proportioning by voids is no better than arbitrary proportioning, because of the behavior of the different materials when mixed together to form a concrete. 72. Proportioning with Reference to Mixed Aggregate. The theory of this method is to grade both the coarse and the fine aggregates together so as to reduce the percentage of voids in the mixture to a minimum. Then the amount of cement required will depend upon the strength and imperviousness desired. The amount of cement necessan^ to fill completely the voids of the mixture may be estimated by making a void test on a well shaken mixture of the aggregates. In practical work it has been found that slightly more cement is required to make a concrete of maximum density because of the slight increase in voids formed when the cement and water are added. This method is no better than the preceding one. 73. Proportioning by Maximum Density Tests. Different mixtures of fine and coarse aggregates may be mixed with the required amounts of cement and water and the resulting concrete tested to determine which proportions of fine and coarse aggre- gates are the best. PLAIN CONCRETE 57 The procedure of the test is roughly as follows: A trial mix of fine and coarse aggregates is prepared, the proper amounts of cement and water are added, and the whole thoroughly mixed. The resulting concrete is placed in a water-tight metal cylinder and tamped. Then the volume of the concrete is measured. Other trial mixes of the fine and the coarse aggregates are pre- pared and the volumes of the concretes formed are carefully measured. The same amounts of cement and water should be used each time and the total weight of all materials and water should be the same for all of the tests. The mixture which gives the least volume is the best mixture and will make the strongest, densest, and most impervious concrete. Care should be taken not to use too much water when making the tests as the excess water will increase the voids in the concrete and thus destroy the accuracy of the tests. The test described above is usually called a "yield" test on concrete. 74. Proportioning by Mechanical Analysis. This is a good and accurate method of properly proportioning the concrete materials. A sieve analysis is first made of each of the aggre- gates and the results plotted on cross-section paper, using the percentages passing a given sieve as ordinates and the cor- responding sizes of sieve openings as abscissae. A curve is drawn for each aggregate. It is not necessary to draw a curve for the cement as it completely passes practically all of the sieves. By using the curves, the materials can be so proportioned (by cut and try methods) that they will give a mechanical analysis curve that agrees very closely with the ideal curve, or curve of maximum density. This ideal curve consists of a portion of an elliptic curve and a straigh't line. The straight line is drawn from the intersection of the maximum size of the coarse aggregate and the 100 per cent lines tangent to an elliptical curve. The ordinate of this point of tangency is equal to 33 per cent, and the abscissa is equal to Jio of the maximum size of the coarse aggre- gate. The elliptical curve is drawn from this point of tangency to the origin. Aggregates of apparently unsuitable grading may be studied in this way and the proper proportions determined. Sometimes it is found necessary to screen a coarse aggregate into two or more sizes and then to combine these sizes in different proportions in order to obtain a dense mixture. 58 MATERIALS OF CONSTRUCTION 75. Example of Proportioning by Mechanical Analysis. Suppose that for a 1:9 concrete, it is desired to find the proper r4^ Diameter of sieve opening in inches FIG. 17. Mechanical analyses curves, etc. proportions of sand and stone whose sieve analysis gave the following results: Sand Stone Sieve Per cent passing Sieve Per cent passing Hm. 100 2 in. 100 No. 6 95 1 1 A in. 90 No. 10 86 IK in. 65 No. 15 66 1 in. 54 No. 30 34 % in. 32 No. 50 17 Yz in. 18 No. 100 5 Hin- 3 The sieve-analysis curves for the aggregates and the ideal curve as directed in the preceding article should be plotted. A tabulation similar to the following should then be made: CONCRETE 1:9 Mix PER CENT PASSING SIEVES Material No. 30 No. 15 No. 10 No. 6 K in. Min. H in- 1 in. IK in- IK in. 2 in. Cement. . 10 10 10 10 10 10 10 10 10 10 10 Sand 19^ 22^ 22^ 22H 22^ 22K 22^ 22 H Stone yr fyr? m vduct^re/n ?m tiers re M forcea fu/re V be u com \the \ \ r-With this consists J one-/?a/fthe strt ncy < ngf/? ibout * \ L ^ 1 X ^ to >W/7 /-^(f 's/opf>\/'eoncrete fome~^** % m -f?- used ' /h road work and in Duila/nq constractionj trfo-thirds to three-fourths of the possib/e strength of the concrete /> Josf- ^r ^ * ^ r i Oj tv ov vu itiv 110 {20 /30 I4O 150 ICO J7O JO I3O ZSO Water Used.- F/gures are percent- of Quantify (fit/ing Max'/mum Strength. FIG. 20. Effect of quantity of mixing water on strength of concrete. (Abrams.) Too little water retards the flowing of the concrete and makes it difficult to place the concrete in the molds and compact it properly, while too much water tends to cause segregation of the materials. Enough water should be present for the proper lubrication of the materials and no more. Water occupies space in the concrete and, if too much is used, it tends to push the solid particles farther apart and make the mixture less dense. Further, this excess of water may escape, after the concrete has set, and leave air voids. Excess of water also has the following bad effects on concrete: (1) it tends to cause day-work planes; (2) it tends to cause large deposits of laitance; (3) it makes the concrete less impervious; (4) it increases the difficulty of bonding new to old concrete; PLAIN CONCRETE 77 (5) it tends to make dusty concrete floor surfaces; and (6) it increases the difficulties of concreting in freezing weather. It is very important that just the proper amount of water be used in concrete work and that the engineer in charge of the work regulate the water at all times so as to secure the proper consist- ency. Different cements and different aggregates (and some- times different batches of the same aggregates) often require slightly varying amounts of water for the normal consistency. 96. Strength of Concrete in General. In general, the strength of a Portland cement concrete depends upon: (1) the amount of cement per unit volume ; (2) the density of the concrete ; and (3) in some cases upon the strength of the aggregates. Of course, the strength of concrete increases with its age, but the rate of increase decreases with the age. Any factors which influence any of the above conditions will also affect the strength of the concrete. Some of these factors are: the consistency; the conditions of mixing, placing, and storing or aging; the qualities of the cement, water, fine and coarse aggregates; presence of impurities; etc. Results of tests indicate that concretes stored or aged in damp or moist air are stronger than those aged in water or dry air. Also, that concretes exposed to the weather (sun, wind, and rain) are usually stronger than concretes cured indoors in a compara- tively dry room. A concrete of a slightly dry consistency, well mixed and thoroughly tamped, is generally stronger than a concrete of slightly wet consistency, but the wetter consistency gives better results in practical work and is necessary in reinforced concrete work. Also, a concrete of a slightly wet consistency becomes about as strong as the dry mix at the age of 6 months. A very wet mix or a very dry mix never becomes so strong as a normal mix and should not be used if it can be avoided. With good grading, the actual size of the stone has but little effect on the strength of the concrete. Usually, a small size of stone is less well graded and gives less density when mixed with the sand. For plain concrete, the maximum size of the stone should rarely be less than 1 in. The maximum size in reinforced concrete work depends upon the molds and the spacing of the reinforcement. Tests show that broken stone generally makes a stronger 78 MATERIALS OF CONSTRUCTION concrete than gravel, though this difference is not very great (about 10 per cent). The strength of the coarse aggregate may have an effect on the strength of the concrete if enough cement is used so that the failure takes place in the aggregate. Ordinary stone and gravel have enough strength for most kinds of concrete. Soft, friable stones, such as some of the sandstones, will give a weaker con- crete. Cinders, brick, old concrete, etc. should be carefully investigated as to their strength before being used in concrete. The presence of such materials as will reduce the strength of neat cement and cement mortar will also tend to reduce the strength of the concrete. 97. Compressive Strength of Concrete. The compressive strength of concrete depends primarily upon the amount of cement per unit volume and also upon other conditions such as were discussed in the preceding article. For a 1:2:4 mix of concrete, made under reasonably good conditions as to the character of the materials and workmanship, an average strength of 2,000 Ib. per square inch may be expected at the age of 1 or 2 months. Under similar conditions, a 1:3:6 mix should average about 1,600 Ib. per square inch. Poorer or better results may be obtained, depending upon the quality of the materials and the workmanship. An average of 25 cylinders, each 10 in. in diameter and 24 in. long, of a 1:2:4 mix of machine made concrete tested at the University of Wisconsin gave an average strength of 1,940 Ib. per square inch at an age of 30 days. An average of 44 cylinders of the same kind gave a strength of 2,150 Ib. per square inch at an age of 60 days. A fairly fine sand was used. The consistency of the concrete was soft, and the specimens were stored in air and kept moist by sprinkling. The following table gives results of tests made on 12-in. cubes at the Watertown Arsenal. Standard Portland cement, a clean coarse sharp sand, and crushed stone (having a maximum size of 2J-2 in. and 49.5 per cent of voids) were used. The cubes were buried in wet ground after their removal from the molds. The compressive strength of concrete increases with age, reach- ing about 80 or 90 per cent of its ultimate at the age of 2 months. The compressive strength of a good cinder concrete is about one-third of the strength of a corresponding mix of a good stone concrete. PLAIN CONCRETE 79 COMPRESSIVE STRENGTH OF TWELVE INCH CUBES OF CONCRETE Mix Strength in pounds per square inch Age 7 days Age 1 month Age 3 months Age 6 months 1:2:4 1:3:6 1,565 1,311 2,399 2,164 2,896 2,522 3,826 3,088 From the results of tests it has been observed that the strength of short concrete columns (as long as 10 or 15 diameters) is from 10 to 20 per cent less than that of short concrete prisms. 98. Tensile Strength of Concrete. Satisfactory tensile tests of concrete are very difficult to make. The tensile strength varies from about Ho to Jf 2 of the compressive strength. The quality of the materials and the workmanship both have a very great effect on the tensile strength. The same factors that affect the compressive strength also affect the tensile strength. The tensile strength of a well-made concrete at an age of 60 days is about as follows: 1:2:4 mix of concrete 175 to 275 Ib. per square inch 1:3:6 mix of concrete 125 to 200 Ib. per square inch 99. Transverse Strength of Concrete. The transverse strength of concrete depends upon the tensile strength. The computed modulus of rupture is about twice the tensile strength and from J to % of the compressive strength. The following table gives an idea of the cross-bending strength of good concrete of various mixes at an age of one month: TRANSVERSE STRENGTH OF CONCRETE (ON TENSION SIDE) 1 MONTH OLD Modulus of Modulus of Mix of concrete rupture, pounds per square inch Mix of concrete rupture, pounds per square inch 1:1^:3 1:2:4 475 425 1:3:5 1:3:6 275 225 1:2:5 350 1:4:8 125 80 MATERIALS OF CONSTRUCTION 100. Shearing Strength of Concrete. The shearing strength of concrete is of importance especially in short concrete columns and reinforced beams. Satisfactory shearing tests on concretes are hard to make, due to the difficulty of securing apparatus that will give a pure shearing stress. The shearing strength of concrete usually varies from J^ to % of the compressive strength. Tests on concrete at the University of Illinois gave the following results. The shear specimens were restrained beams and the compression specimens were cubes. The specimens were stored in damp sand. Mixture Shear, pounds per square inch Compression, pounds per square inch Comp. Ratio-- Shear . Shear Ratio Comp. 1:2:4 1,418 3,210 2.26 0.44 1:3:6 1,313 2,428 1.85 0.54 1:3:6 1,020 1,721 1.69 0.59 101. Adhesive Strength of Concrete to Steel. The adhesive strength (or bond) of concrete to steel is of great importance in reinforced concrete work. This strength depends upon the richness of the mix and on the character of the surface of the steel. Corrugated rods usually give greater bond stresses than plain rods. Bond tests have been made in two different ways. One way was to measure the force required to pull a rod out of a block of concrete (pull out test) , and the other method was to determine the force required to make a rod slip in a beam. The tests showed that the bond between the concrete and steel was divided into two parts; the adhesion between the concrete and steel and the sliding resistance. The adhesive strength may be said to have been reached when the first end slip of the rod was observed. This stress is about % or % the maximum stress attained. The beam tests are thought to have given more reliable values than the pull out tests. Results of beam tests gave maximum bond stresses varying from 160 to 375 Ib. per square inch for round rods while square and flat rods were not quite so strong. Corrugated bars gave higher results. The concrete was a 1:2:4 mix. Pull out tests on specimens of the same mix usually gave higher results. There does not seem to be any relation PLAIN CONCRETE 81 between the size of rod and the unit bond stress. The bond strength of a 1:3:6 concrete is about 20 or 30 per cent less than that of a 1:2:4 mix. 102. Elastic Limit and Modulus of Elasticity of Concrete. As the stress strain curve for concrete is not a straight line through- out any part of its length and as the concrete is subject to a permanent deformation even for a small load, concrete may be said to have no true elastic limit. There appears to be a limit, however, to the stress that can be repeated indefinitely without continuing to add appreciably to the deformation. This limit may be taken as the elastic limit, or yield point, for all practical purposes. From the results of tests it appears that this limit is usually somewhere between 40 and 60 per cent of the ultimate. As the stress strain curve for concrete is a curved line, the modulus of elasticity is not a constant through any appreciable range of stress. One way to determine the modulus of elasticity is to take the slope of the curve at the origin. Another, and perhaps a better, way is to compute the secant modulus for a load of 300 or 500 Ib. per square inch, or for a load equal to about J^ of the ultimate. The second way usually gives a value considerably less than that obtained by the first. For a concrete one month old and for a stress of 500 Ib. per square inch, the secant modulus of elasticity for a 1:2:4 mix will generally be between 2,000,000 and 2,500,000 Ib. per square inch, and between 1,500,000 and 2,000,000 Ib. per square inch for a 1:3:6 mix. If the modulus of elasticity is computed from the slope of the curve at the origin, the value obtained will probably be from 20 to 50 per cent higher than the secant modulus at 500 Ib. per square inch. In general, the modulus of elasticity increases with the richness of mix and the age, but varies greatly with different aggregates. 103. Yield of Concrete. Yield may be defined as the volume of concrete that may be obtained from given quantities of cement, fine and coarse aggregates. Other things being equal, those concrete materials should be used which will give the greatest yield of concrete. This means that less quantities of the ma- terials will be required for a given volume of concrete and, conse- quently, the cost of the concrete will be less, assuming that the materials are purchased by volume and that the prices are the same for all varieties of the same kind of materials. 6 82 MATERIALS OF CONSTRUCTION 104. Expansion and Contraction of Concrete. Experiments have shown that concrete will shrink a little when hardening in air, and that when it is hardening under water it will keep about the same volume or perhaps swell a trifle. The coefficient of expansion for concrete is about 0.000006 per degree Fahrenheit. The coefficient of expansion increases but very little with an increase in the richness of the mix. The fact that an average crushed stone concrete has a coefficient of expansion practically equal to that of steel is of importance in reinforced concrete work. 105. Miscellaneous Properties of Concrete. Weight per Cubic Foot. The weight per cubic foot of concrete may vary considerably, due to the kind of materials used for aggregates. The weight also varies directly with the richness of mix and the density. A concrete made from sand and crushed stone usually weighs from 135 to 160 Ib. per cubic foot. For practical purposes, the weight of concrete may be assumed to be 145 or 150 Ib. per cubic foot. Absorption. The absorption of water by concrete may be quite small or very large, depending upon the richness and density of mix, kind of materials used for aggregates, thoroughness of mixing, care in placing, etc. In general, the same factors that tend to make concrete impervious will also tend to make it non-absorptive. Abrasion. The abrasive resistance of a concrete depends primarily upon the abrasive resistance of the mortar. Of course, if the surface of the concrete is worn away so that the coarse aggregate is exposed, the abrasive resistance of the coarse aggregate will have some influence on the abrasive resistance of the concrete. The abrasive resistance of the mortar depends upon the ability of the cement to hold the sand grains together and also upon the abrasive resistance of the sand grains themselves. 106. Working Stresses and Factor of Safety for Concrete. The following working stresses are recommended by the Committee on Concrete and Reinforced Concrete of the American Society of Civil Engineers. The allowable compressive stress on a short plain concrete column or pier (whose length does not exceed 12 diameters) is 22.5 per cent of the strength at 28 days, or 450 Ib. per square inch for 2,000 Ib. concrete. The factor of safety is 4.5. PLAIN CONCRETE 83 The extreme fiber stress in compression in a reinforced concrete beam, calculated on the assumption of a constant modulus of elasticity for concrete under working stresses, may be allowed to reach 32.5 per cent of the compressive strength at 28 days, or 650 Ib. per square inch for 2,000 Ib. concrete. The apparent factor of safety is 3.1 while the actual factor is larger. Where pure shearing stress occurs, uncombined with compres- sion normal to the shearing surface and with all tension normal to the shearing plane provided for by reinforcement, a shearing stress of 6 per cent of the compressive strength at 28 days, or 120 Ib. per square inch for 2,000 Ib. concrete, may be allowed. The factor of safety in this case is between 6 and 7. When the shear is combined with an equal compression, as on a section of a column at 45 degrees with the axis, the stress may equal one-half of the compressive stress allowed. For ratios of compressive stress to shear between and 1, proportionate shearing stresses shall be used. This gives a factor of safety of about 4.5. The bonding stress between concrete and plain reinforcing bars may be assumed at 4 per cent of the compressive strength at 28 days, or 80 Ib. per square inch for 2,000 Ib. concrete; and in the case of drawn wire, 2 per cent, or 40 Ib. per square inch for 2,000 Ib. concrete. The factors of safety are about 4.5 and 2.25. It is recommended that the modulus of elasticity of concrete in compression be assumed as ^5 of that of steel (2,000,000 Ib. per square inch for a good 1:2:4 concrete 1 month old). While this assumption is not accurate, it will give safe results. 107. Rubble Concrete. This is a concrete in which stones of a large size are handled and embedded separately. Rubble concrete construction is suitable only for massive work where the concrete is not less than 3 or 4 ft. thick. The saving over the cost of ordinary concrete is very little except in instances where the large stones cari be very cheaply procured and handled. The usual procedure is to drop the large stones in the concrete and then spade the concrete around the stones so as to release the air and make a good bond. The large stones should be clean and the joints between the stones should be at least 4 in. thick and well filled with wet concrete. The concrete should be wet enough to flow readily around the stones. 84 MATERIALS OF CONSTRUCTION G. CONCRETE STONE, BLOCK, AND BRICK 108. Definitions and Classifications. Concrete stone may be defined as any precast concrete units of ordinary size which are used for construction purposes. Concrete blocks are concrete stones which are considerably larger than ordinary brick. The blocks are of several shapes, varieties, and sizes. Most concrete blocks (except those used for purposes of ornamentation) are hollow so as to form air spaces in the walls and save weight and materials. There is no standard FIG. 21. Cross sections of some concrete blocks. size, though the length is usually 16 or 24 in., the height 8 or 9 in., and the thickness 8, 10, or 12 in. Concrete brick usually are of the same size as ordinary building brick and are usually made solid, though some makes have grooves or hollows in the top and bottom. Concrete stone may be divided into two classes according to use: (1) units for structural use primarily, such as ordinary solid or hollow blocks and brick ; and (2) units designed primarily for purposes of architectural effect and ornamentation, such as the specially molded shapes or specially faced blocks or brick. Concrete stone may also be classified according to the method of manufacture. The three general methods in use are the dry tamp, pressure, and wet-cast methods. Concrete stone for orna- mental purposes is usually made in special molds by the dry tamp method. 109. Materials for Concrete Stone. The materials should be chosen according to the principles governing the selection of materials for good concrete, except that the coarse aggregate should be a well-graded crushed stone or gravel that will pass a %-in. sieve and be retained on a M-in. sieve. 110. Proportions. The proportions for concrete blocks should be 1 part of good portland cement to not over 2}^ or 3 parts of good sand and to not over 3 or 4 parts of coarse aggregate. That is, the leanest allowable mix is a 1:3:4. When the coarse PLAIN CONCRETE 85 aggregate is omitted, the proportions should be 1 part of cement to not over 4 parts of good sand. The limiting proportions for cement brick, which usually contain no coarse aggregate, are the same as those for concrete blocks. In general, the proportions should be such that the concrete stone will pass the specifications given in a following article. 111. Consistency. The best consistency is one where the mixture will just retain its shape when the molds are removed immediately after the concrete has been deposited and pressed in place. This consistency is much wetter than that usually used in the dry tamp method and a little wetter than that used in the pressure process. The consistency used in the wet-cast method is frequently too wet to secure the best results. A con- sistency that is too dry makes the concrete porous and increases its absorptive powers besides tending to reduce the strength. 112. Mixing and Molding. The mixing may be done either by hand or machine. (See articles on hand and machine mixing for discussions of these methods.) The molding may be done either by hand or machine except in the pressure process where a machine is required. Concrete blocks and brick for structural purposes are usually molded by machines while especially molded blocks are usually molded by hand. At present there are many different kinds of molding machines used in the manufacture of concrete stone. The construction of the machines varies with the consistency of the mix and the methods used for compacting the concrete. The following are the three methods most frequently used in the manufacture of concrete blocks and brick: (a) Dry Tamp Process. The materials are first mixed to a damp consistency and are then thoroughly tamped in the molds by hand or machine tampers. Usually too little water is used in this process. This method is nearly always used in making concrete stone of special shape or surface finish as the molds may be made of any desired shape and size. The tamping is usually done by hand. (b) Pressure Process. A somewhat wetter mixture is used than in the dry tamp process. The concrete is then placed in the molds and pressure is applied either by mechanical levers or by a hydraulic piston. (c) Wet-cast Process. In this process the consistency is such 86 MATERIALS OF CONSTRUCTION that the concrete will readily flow. The mixture is poured into the molds and then thoroughly puddled to release any entrained air and to get the large particles away from the sur- faces. No tamping or mechanical pressure is used. Frequently too much water is used. In the first two methods the concrete is dry enough so that the molds can be removed immediately from the blocks, while in the last method the molds cannot be removed until after the concrete has set. If either of the first two methods is used, care should be taken to secure density and uniformity of com- pactness in the blocks. 113. Surface Finishes. A variety of pleasing surface finishes may be secured with concrete blocks and brick. For a descrip- tion of a number of ways of finishing the surface, see article on " Surface Finish." Another way is to have one of the faces of the mold so shaped that the exposed face of the block, when placed in a wall, will have some pleasing shape such as some surface finish of stone masonry, etc. Special molds can be made to give a great variety of designs of cornices, rails, window seats, ornaments, etc. Still another way is to place a facing layer of a selected fine material next to the face mold, this layer becoming intimately bonded with the body of the block in the process of molding. Variety of color may be secured by using different colored stones or sands in the facing layer or by adding coloring matter when the materials are mixed. Only the purest mineral colors should be used, as coloring matter (especially when impure) tends to destroy the binding qualities of the cement. Sometimes the coloring may be secured by applying a cement stain to the desired surfaces. 114. Curing and Aging. In curing, care should be taken to prevent the drying out of the blocks during their first hardening. After the molds are removed, the blocks should be protected from wind currents, sunlight, dry heat, and freezing for at least a week. During this time additional moisture should be supplied to the blocks by sprinkling, or some other method equally as good, at least once a day. After the first week the blocks should be sprinkled, or otherwise moistened, at occasional intervals until they are used. When cured by any natural process, concrete blocks should not be used for construction purposes until they are at least three weeks old. PLAIN CONCRETE 87 The curing of concrete stone products may be accelerated by placing them (as soon as possible after they are removed from the molds) in an atmosphere of moist steam for at least 48 hours. The temperature of the curing room should be between 100 and 130 degrees Fahrenheit. The saturated steam provides heat and moisture and accelerates the hardening or setting of the concrete without causing the concrete to lose any of its moisture. After removal from the steam curing room, the concrete blocks should be stored for at least 8 days before using. 115. Properties of Concrete Blocks and Brick. Concrete blocks and brick are usually not so strong as plain concretes of the same proportions. This is probably due to the fact that the consistencies used are not the ones which will give the greatest strength. Blocks made by the dry tamp and pressure processes often contain too little water while those made by the wet-cast process usually contain too much water. Good concrete blocks and brick should pass the following tests : (a) Transverse Test. When subjected to transverse tests at an age of 28 days, the modulus of rupture should average more than 150 Ib. per square inch and should not be less than 100 Ib. per square inch in any individual case. (b) Compression Test. The ultimate compressive strength of solid blocks at the age of 28 days should average more than 1 ,500 Ib. per square inch and should not be less than 1,000 Ib. per square inch in any individual case. The ultimate compressive strength of hollow blocks at the age of 28 days should average more than 1,000 Ib. per square inch, and should not be less than 700 Ib. per square inch in any individual case. In calculating the results, no reductions shall be made for the hollow spaces in the blocks. The allowable working stress in compression should not exceed 167 Ib. per square inch of gross area for hollow blocks, and 300 Ib. per square inch of gross area for solid blocks. (c) Absorption Test. The samples shall be dried to constant weight at a temperature not exceeding 212 degrees Fahrenheit. After drying, the samples shall be immersed in clean water for 48 hours. The percentage of absorption (weight of water absorbed divided by the dry weight of the sample) should not average over 12 per cent and should not exceed 18 per cent in any individual case. Full-sized blocks or brick shall be tested whenever possible. 88 MATERIALS OF CONSTRUCTION The number of samples for any one test should not be less than three. 116. Uses of Concrete Blocks and Brick. Blocks made of molded concrete can be used to advantage, as a substitute for solid concrete, brick, or stone, in the construction of walls that are thin or which carry only light loads, such as building walls, partitions, etc. Solid concrete is not satisfactory for such pur- poses on account of the expense of forms, the difficulty of securing a proper finish, and the prevention of the formation of cracks Concrete blocks are usually made of such shapes and sizes that they will form a wall containing hollow spaces, thus increasing the stability of the wall and forming dead air spaces as well as decreasing the weight. Concrete brick are usecl as a substitute for ordinary building brick. Especially molded and finished concrete blocks and brick are used for various purposes of architectural detail and ornamentation. CHAPTER VI BUILDING STONE A. CLASSIFICATIONS AND DESCRIPTIONS 117. Building Stone in General. Building stones include all of those stones or rocks that are used in masonry construction. The qualities which are the most important in stone used for construction purposes are cheapness, durability, strength, and beauty. In general, the hardest, densest, toughest, and most uniform stone will be the best stone to use. The fitness of a stone for structural purposes may be approxi- mately determined by the examination of a fresh fracture. This fracture should be bright, clean, sharp, without any loose grains and be free from a dull earthy appearance. An even fracture, when the surfaces of division are planes in definite positions, is characteristic of a crystalline structure. An uneven fracture, when the broken surface presents sharp projections, is character- istic of a granular structure. A slaty fracture gives an even surface for planes of division parallel to the laminations, and uneven surfaces for other directions of division. A conchoidal fracture presents smooth concave and convex surfaces, and is characteristic of a hard and compact structure. An earthy fracture leaves a rough, dull surface and indicates softness and brittleness. The stone should contain no material, either in the form of seams or veins, that is not thoroughly cemented together. Stone containing much mica, pyrites, or glass seams usually are not very durable. Only about half of all of the stone quarried is used for structural purposes, the other part being used for roads and pavements, crushed stone for railroad ballast and concrete, etc. 118. Classifications of Building Stone. Building stone may be classified according to geological position, physical structure, or chemical composition. The geological position of a rock has but very little influence upon its properties as a building stone. 89 90 MATERIALS OF CONSTRUCTION A. Geological Classification 1. Igneous rocks which are formed by a consolidation of the material from a fused or partly fused condition, such as greenstone, basalt, lava, etc. 2. Sedimentary rocks which are formed by a consolidation of material transported and deposited by water, such as sandstones, limestones, and clays. 3. Metamorphic rocks which are formed by a gradual change in the structure and character of igneous or sedimentary rocks due to their expo- sure to heat, water, pressure, etc. Some examples are the marbles and slates. B. Physical Classification 1. Stratified rocks which are formed in layers, such as the sandstones, marbles, limestones, and some of the clays and slates. Their structure is either crystalline or granular or a combination of both. 2. Unstratified rocks which are not formed in layers. These rocks are usually made of crystalline grains strongly adhering together. Some ex- amples are the granites, traps, basalts, etc. C. Chemical Classification 1. Siliceous rocks in which silica is the most important chemical element, such as the granites, syenites, mica-slate, basalt, trap, quartz, sandstone, etc. 2. Argillaceous rocks (clayey rocks) in which the alumina governs the characteristic properties, such as the clays and slates. These stones are usually not very durable. 3. Calcareous rocks in which carbonate of lime is the important element, such as the marbles and limestones. The more compact of these stones are the more durable ones. 119. Granite, Gneiss, and Trap. Granite is used more for structural purposes than any other igneous rock, and is the strongest and most durable of all the stones in common use. It is very hard and tough and, consequently, is difficult to cut and shape. However, it may be quarried in simple pieces with- out much difficulty as it breaks easily along its planes of weakness, which are at right angles to each other. Granite is used for foundations, base courses, walls, columns, steps, paving blocks, etc. Gneiss has the same composition and about the same appear- ance as granite and is found in the same localities. It differs from granite by being usually arranged in more or less parallel layers, which makes the work of quarrying less difficult and expensive. This stone is used for foundation walls, courses, street paving, curbs, etc. BUILDING STONE 91 Trap is the strongest and one of the most durable of all building stones. It is also very tough and usually has no planes of cleav- age. As it is difficult to quarry and work, trap is used very little for structural purposes. 120. Limestone, Marble, Sandstone, and Slate. Limestone is a stone which contains calcium carbonate as its main constitu- ent. It is very widely distributed and much used in building construction, probably ranking next to granite in this respect. Limestone differs greatly in color, composition, and structural qualities, because of the character of the deposits and their chemical composition. Marble is a limestone which has been subjected to a metamor- phic action and has had its structure changed to a more crystal- line form. Its original color is usually changed and sometimes lost during this metamorphic action. Marble has a variety of colors, is very beautiful, and is much used for interior decorations. Often the name " marble" is improperly used by applying it to any limestone that will take a polish. Sandstone is composed of grains of quartz sand which are cemented together by means of silica, iron oxide, calcium car- bonate, or clayey materials to form a solid rock. This stone differs greatly in color, hardness, and durability, but some are very suitable for use in outside construction. The durability of the sandstone depends both upon its physical and its chemical composition. The best has silica as a cementing material and is usually soft wheji quarried but becomes harder upon exposure. Sandstone having iron oxide as a cementing material ranks next in durability, followed by that having calcium carbonate, while the one having clayey matter is the poorest. Sandstone is easier to quarry and work than limestone. Sandstone is used a great deal in building construction. Slate is ordinarily composed of a siliceous clay which has been deposited in thin layers on a sea bed and later metamorphosed and compacted by pressure into a solid rock. Slate can be split into thin sheets and is tough, strong, and non-absorptive. It is used for roofing and some interior work in buildings. B. STONE QUARRYING AND CUTTING 121. Hand Methods of Stone Quarrying. No matter what method of quarrying is used, it is first necessary to remove the surface soil from the rock. The stone may be quarried by 92 MATERIALS OF CONSTRUCTION means of hand tools, machine tools, explosives, or by some combination of these methods. Hand methods may be used when the stone occurs in thin beds. The principal tools used are the pick, crowbar, drill, hammer, wedge, and plug and feathers. In quarrying, rows of holes, which are from % to % in. in diameter and a few inches apart, are drilled in the rock by means of the drill and hammer. The ~* FIG. 22. Cross section of "Jackhammer Sinker" drill. (I nger soil-Rand Co.) distance between rows usually depends upon the dimensions of the desired stone. In drilling, a man holds the drill in one hand and drives it with a hammer in the other hand, rotating the drill a little between blows. Sometimes one man holds the drill and another man drives it with a heavy hammer or sledge. This kind of drill is called a jumper. Another kind of hand drill is the churn drill which is a heavy drill about 6 or 8 ft. long. This drill is raised by the workman who lets it fall in the desired place, then catches it on the rebound, rotates it a little while raising it, and lets it fall again, thus cutting a hole in the rock without the aid of a hammer. For deep holes, a churn drill is more economical than a jumper drill. BUILDING STONE 93 After the holes are drilled, a plug, inserted between two feathers, is placed in each hole. The plug is a narrow steel wedge with plane faces, and the feathers are wedges which are flat on one side and rounded on the other. Then the plugs in all of the holes are pounded in at the same time until they exert a force that is large enough to split the rock along the line of holes. 122. Machine Methods of Quarrying. Machine methods include the use of machines driven by steam, compressed air, or electric motors to drill the holes or cut narrow channels in the rock. The machine drills are divided into two classes percus- sion drills and rotary drills. In a percussion drill, the cutting tool resembles a hand drill. This drill is operated by a cylinder using steam or compressed air, or by an electric motor. An automatic device rotates the drill a little between strokes. In a rotary drill, the cutting tool is a hollow tube with a cutting edge made of sharp teeth or diamonds. This cutting edge is kept in contact with the rock while the drill is revolved, thus cutting a hole through the rock. When large rectangular blocks of stones are desired, a special machine called a "channeler" is often used. This machine operates on a track or guide bars and carries a number of cutters which cut deep narrow channels in the rock as the machine slowly moves along. After the holes are drilled, the rock is broken off by means of plugs and feathers or by means of explosives inserted in the holes. Stone is rarely ever quarried by one method alone. The use of a combination of two methods is very common and that of three methods is not infrequent. 123. Explosives Used in Quarrying. Explosives may be used instead of plugs and feathers to split off the stone after the drill holes have been made. The explosive is placed in the holes in the proper amounts, and the pressure (tamping) is provided by a little moist sand, clay, packed paper, etc. tamped on top. In the case of nitro-glycerine, a little water on the explosive provides all of the tamping necessary. The explosives used in quarrying are usually gunpowder or dynamite and sometimes nitro-glycerine. The gunpowder must be a coarse, slow acting kind (commonly known as " blasting powder"). It is exploded by means of a fuse or electric spark. Dynamite consists of some granular substance (such as saw- dust) saturated with nitro-glycerine. True dynamite contains at 94 MATERIALS OF CONSTRUCTION least 50 per cent of nitroglycerine, while the granular absorbent is an inert material. False dynamite may contain as little as 15 per cent of nitro-glycerine, but the absorbent material contains at least one other explosive. The other explosive is usually oxygen which is liberated in large quantities by the explosion and aids in effecting the complete combustion of the gases of the nitro-glycerine . Nitro-glycerine is a fluid made by mixing glycerine with nitric or sulphuric acid. It is rarely used in quarrying as it acts too quickly and tends to shatter the rock very much. UK 23 3 DOUBLE FACE MAMMS.R | FACE HAMMER ' n MO) SI \ / "1 ~T^ ::> V FIGS. 23-40. Tools used in stone cutting. Dynamite and nitro-glycerine are exploded by means of a percussion cap which is ignited by a fuse or an electric spark. A percussion cap is a hollow cylinder made of copper and has one end closed. This cylinder is about y in. in diameter and 1 or 2 in. long. It contains a cement made of fulminate of mercury and some inert material. 124. Stone Cutting. In stone cutting, various tools are used, such as stone hammers, picks, axes, points, chisels, mallets, pneumatic hammers, etc. These tools are often different in BUILDING STONE 95 shape from ordinary tools of the same name. An examination of the sketches of these tools will furnish all of the description necessary, while their uses will be indicated in the following paragraphs. Building stone are divided into three general classes and various subdivisions according to the finish of the surfaces (from Trans. Am. Soc. Civ. Eng., Vol. 6). FIG. 41. Quarry-faced FIG. 42. Pitched-faced FIG. 43. Drafted squared stone. squared stone. stone. FIG. 44. Rough-pointed FIG. 45. Fine- face finish. pointed face finish. FIG. 46. Crandalled face finish. 1 ^ .-.:. : . I FIG. 47. Axed or pean- hammered face finish. FIG. 48. Bush- hammered face finish. FIG. 49. Raised diamond panel. 1. Rough or Unsquared Stone This class includes all stone that are used as they come from the quarry without any special preparation. 2. Stone Roughly Squared antf Dressed This class includes stone that are roughly dressed on beds and joints with the face hammer or axe. The distinction between this class and the third class lies in the closeness of the joints. When the dressing on the joints is such that the general thickness of mortar required is one-half inch or more, the stone properly belong to this class. There are three subdivisions: (a) Quarry faced stone are those whose faces are left untouched as they come from the quarry. (6) Pitched-faced stone are those in which the edges of the faces are made approximately true by the use of a pitching chisel. (c) Drafted stone are those whose faces are surrounded by a chisel draft, the space inside being left rough. This method is not ordinarily used on stone of this (the second) class. 96 MATERIALS OF CONSTRUCTION 3. Cut Stone or Stone Accurately Squared and Finely Dressed This class includes all stone dressed to smooth beds and joints so that the thickness of the mortar joints is less than one- half inch. As a rule, all of the edges of cut stone are drafted, and between the drafts the stone is smoothly dressed by one of the following methods. In massive construction work, the face of the stone is often left rough. (a) Rough-Pointed. The excess of material is removed by the pick or heavy point until the projections vary from % to 1 in. This method is much used on limestone and granite. (6) Fine-Pointed. The projections are less than J^ in. and the tool used is a fine point. (c) Crandalled. The same effect is produced as in fine pointed stone, except that the tool marks are more regular and with J^-in. projections. A stone is said to be cross crandalled when it is crandalled in both directions. The tool used is a craridall. (d) Axed or Paen Hammered. The face of the stone is covered with parallel chisel marks. (e) Tooth Axed. The same finish as fine-pointed stone, except that the tool used is a tooth axe. (/) Bush- Hammered. Where the roughnesses of the surface are pounded off with a bush hammer. This follows the rough pointing or tooth axing and is usually used only on limestone. (g} Rubbed. Where the sawn surfaces of the stone are smoothed by grit or sandstone. The method is used on marbles and sandstones. (h) Diamond Panels. Where the face inside the draft is cut to flat pyra- midal forms. C. PROPERTIES OF BUILDING STONE 125. Durability. The durability of a stone depends upon its ability to resist the destructive actions due to the weather agencies. The determining factors of durability are the struc- ture, texture, and mineral composition of the stone. Imperfec- tions, such as cracks, joint planes, etc., allow water to enter and disintegration to start through the action of frost. A coarse- grained or porous stone usually disintegrates more rapidly than does a fine-grained stone. Different mineral compounds in the stone also influence the durability. A stone containing silica or silicates is the most resistant to decay; followed by that contain- ing aluminates; calcium and magnesium carbonates; iron com- pounds; and sulphides. An increase in the durability of the stone may be secured by proper seasoning and surface finishing. When the stone is BUILDING STONE 97 green, it contains much quarry sap and disintegrates much faster than after it is seasoned and the quarry sap has evaporated. In dressing the stone, care should be taken not to break up the grains too much and produce very small fissures through which the water may enter. A stone resists the effects of both pressure and weathering much better if it is placed on its natural bed. The best way to determine the durability of the stone is to examine the surfaces of stone structures which have been exposed to atmospheric influences for years. There have been many artificial tests proposed, such as specific gravity, hardness or toughness, compression, cross-bending, shear, absorption, chemical, freezing, acid and microscopical tests, for determining the durability of the stone, but none of these tests give wholly satisfactory results. The following table gives the estimated life of some of the building stones. The values are approximate, depending upon the variety of stone and place where it is used. APPROXIMATE LIFE OF BUILDING STONE Sandstone may last from 20 to 200 years according to kind and place. Limestone may last from 20 to 40 years according to kind and place. Marble may last from 40 to 100 years according to kind and place. Granite may last -from 75 to 200 years according to kind and place. Gneiss may last from 50 to 200 years according to kind and place. 126. Action of Frost, Wind, Rain, and Smoke. Frost action, or freezing, disintegrates a stone only when the pores are practically filled with water before the freezing takes place. As a stone is not often used in such a way that the maximum amount of water is absorbed, it is very rare that a good building stone is injured by frost. Only a stone having a high absorptive power and a low structural strength is liable to be damaged by freezing. A gentle wind has no effect on the stone but a heavy wind blows rain, dust, sand particles, etc. against the face of the rock. The sand and dust particles tend to wear away the surface by abrasion. Rain, falling on the stone, penetrates the pores and tends to dissolve some of the chemicals in the stone. Rain water may contain some acids which are injurious to the stone. Also, there is the effect of pattering raindrops and flowing water wear- ing away the surface. Smoke, which usually contains sulphuric or carbonic acid, has 7 98 MATERIALS OF CONSTRUCTION a bad effect on the stone, as these acids, as well as the nitric acid in the air, tend to cause disintegration. 127. Action of Fire. Fires, such as destroy ordinary buildings, produce temperatures that are high enough to injure seriously the exposed building stone. The injury due to the combined action of both fire and water is usually much greater than that due to fire alone. Rapid cooling, by the application of water, of the exteriors of a highly heated stone tends to cause it to disintegrate. Any stone expands upon being heated, but it only partly returns to its original dimensions on being cooled. This increase or set is very small, being about JK oo of 1 per cent of the length of the stone. Granite usually cracks and spalls badly when exposed to fire. This stone has a low fire resistance. Gneiss does not resist fire so well as granite does. Limestone offers a high resistance to fire until a temperature of about 1,100 degrees Fahrenheit is reached and then the stone starts to decompose and crumble, due to the driving off of the carbon dioxide and the flaking of the quicklime formed. Lime- stone is injured more by slow cooling than by sudden cooling. Marble cracks and spalls to some extent at temperatures below that at which calcination begins. After that temperature is reached, its action is like that of limestone. Sandstone, especially if it is dense and non-porous, offers a better resistance to fire than other building stone. It cracks less than any other stone, and, if properly placed, these cracks will probably be horizontal. Sandstone having silica or lime carbonate for a cementing material resists fire better than a stone bound with iron oxide or clay. 128. Mechanical Properties of Building Stone. The following tables give some average values of the strength and other mechan- ical properties of the principal building stone. It is to be noted that there are several varieties of each kind of stone and that the results obtained by testing any one variety may vary considerably from the average given in the table. However, most any variety of stone of good quality will give results equal to or greater than the average values given. All of the values in these tables were obtained from the " Ameri- can Civil Engineers' Pocket Book," except those in parenthesis which were obtained from other sources. BUILDING STONE STRENGTH OF BUILDING STONE 99 Modulus of Stone Compression, pounds per square inch Shear, pounds per square inch bending, pounds per square inch elasticity in compression, pounds per square inch Granite 15,000(18,000) 2,000 1,500 7,000,000 Sandstone 8,000 1,500 1,200 3,000,000 Limestone 6,000(8,500) 1,000 1,200 7,000,000 (8,000,000) Marble 10,000 1,400 1,400 8,000,000 Slate 15,000 8,500 14,000,000 Marble Slate 10,000 1,400 1,400 15,000 8,500 8,000,000 14,000,000 MECHANICAL PROPERTIES OF BUILDING STONE Stone Weight, pounds per cubic foot Specific gravity Per cent of absorption Coefficient of expansion per degree Fahrenheit Granite 170(165) 150(145) 170(160) 170(165) 175 185 2.72(2.64) 2.40(2.32) 2.72(2.56) 2.72(2.64) 2.80 2.96 0.5 (0.7) 3.0 (6.0) 0.15(4.0) 0.10(0.4) 0.17(0.5) 0.0000040 0.0000055 0.0000045 0.0000045 0.0000058 Sandstone Limestone Marble . . . Slate Trap . . CHAPTER VII BRICK AND OTHER CLAY PRODUCTS A. CLASSIFICATIONS AND DEFINITIONS 129. Classifications. Common brick may be classified accord- ing to use ; as to position in the kiln when burned (see articles on kilns and burning) ; as to methods of manufacture ; or as to form and shape. Brick and clay products are usually classified accord- ing to their uses. Classification of Brick and Clay Products According to Their Uses. 1. Building Brick. Used for ordinary building purposes. (a) Common building brick. (b) Face brick, pressed or re-pressed brick. (c) Enameled, glazed, and ornamental brick. (d) Hollow brick. (e) Sand lime brick. (/) Portland cement concrete blocks and brick. 2. Paving Brick and Block. Vitrified brick or blocks used for paving. 3. Fire Brick. Brick made so that they can withstand a high temperature. 4. Terra Cotta. Used for structural purposes. (a) Architectural or decorative. (b) Blocks and lumber. Used for structural purposes. (c) Hollow building blocks and fireproofing material. 5. Building Tile. Used for structural purposes. (a) Roofing tile. (b) Wall tile. (c) Floor tile. 6. Drain Tile. Porous, non-vitrified, unglazed tile used for drainage purposes. 7. Sewer Tile. Non-porous, vitrified, glazed tile used for sewerage purposes. 130. Definitions. The following are definitions of some of the different kinds of brick. Other definitions will be found in the articles following. 101 102 MATERIALS OF CONSTRUCTION Clay brick are made by molding, drying, and burning a proper mixture of sand and clay. Sand lime brick are made from a mixture of sand and lime. Terra cotta is made in about the same manner as ordinary clay brick, except that selected clays, that will burn to a desirable color with a slight natural glaze, and other materials are used. Building tile are made in about the same manner and from about the same materials as pressed brick. Tile and pipes are made by burning properly selected clay which has previously been molded in a suitable form. Re-pressed brick are those made by pressing soft or stiff mud brick before firing. Sewer brick are hard common brick or No. 2 paving brick used for sewers. Face brick are usually pressed or re-pressed brick that are regular in shape and size and uniform in color. They are used for the outside of walls of buildings. Feather edge brick have one edge thinner than the other. They are used in arches. Compass brick have one edge shorter than the other. They are used for walls with curved surfaces. Glazed or enameled brick have one face glazed or enameled. B. MANUFACTURE OF CLAY BUILDING BRICK 131. The Clay. Only the sedimentary clays are sufficiently homogeneous, fine, and plastic enough to be used in brick making. These clays consist principally of silicate of alumina together with a little lime, magnesia, and iron oxide. An excess of alumina makes the clay very plastic, but causes it to shrink, warp, and crack badly in drying, and also makes the clay very hard after burning. Uncombined silica, if not in excess (not over 25 per cent), tends to preserve the form of the brick, but an excess destroys the cohesion and makes the brick brittle and weak. Iron oxide makes the brick hard and strong. A little magnesia tends to decrease the shrinkage. Silicate of lime decreases the shrink- age, but it also softens the brick so that they will be distorted in burning. Carbonate of lime decomposes in burning and tends to cause the brick to disintegrate. 132. Hand Process of Making Brick. The clay is first cleaned of all pebbles, dirt, etc., by washing, after which it is mixed with BRICK AND OTHER CLAY PRODUCTS 103 a moderate amount of water. To reduce the clay to a plastic mass, it is usually placed in a pug mill and then the proper amount of water is added. The pug mill consists, essentially, of a cylinder with revolving blades inside which cut up and mix the material. The clay may be made plastic by hand labor, but this process is very laborious. After "pugging," the plastic clay is pressed into the molds with the hands and tamped hard. The molds are sometimes sprinkled with water, but they are generally sprinkled with sand to keep the clay from sticking to them. This accounts for the names of "slop" and "sand" molding. After molding, the brick are dried in air, often for several weeks, before they are fired or burned in a kiln. The length of time FIG. 50. Double shaft pug mill. (American Clay Machinery Co.) required for drying depends on the weather conditions as well as on the composition of the brick. If the brick are to be pressed, this must be done before they become too dry and hard. The press is a simple hand machine in which the brick are placed between plates or dies and then compressed by a piston operated by a hand lever. 133. Soft-mud Machine Process of Making Brick. The three important ways of making machine-made brick are the soft-mud process, the stiff-mud process, and the pressed-brick process. In the soft-mud process the clay is prepared as in the hand process and then reduced to a soft mud by the addition of water. The process of manufacture is practically the same as the hand process except that most of the work is done by machinery. The molding is done by a machine which presses the pugged clay into sanded molds by means of a plunger. Gang molds are used 104 MATERIALS OF CONSTRUCTION so that from 4 to 8 brick are molded at a time. Such a machine often has a capacity of from 8,000 to 12,000 brick per day. The soft-mud brick are dried in the same way as the hand-made brick, except that sometimes a drying house is used to accelerate the drying. 134. Stiff-mud Machine Process of Making Brick. In the stiff-mud process just enough water is added to the clay so FIG. 51. Soft mud type of brick machine with pug mill. (American Clay Machinery Co.) that it will retain its shape after being molded under a moderate pressure. The consistency of this clay is like that of stiff mud, hence the name. The. molding is done by machines which are either of the auger or plunger types. In the auger type, the clay is forced through a die by means of an auger or screw working in a cylinder; while in the plunger type a simple piston or plunger is used instead of the auger. The die is an opening equal in size to the dimensions of an end or a side of the brick. When the clay comes through the die, it is forced out on a long table where it is cut in sections the size of an ordinary brick. If the cross-section of the bar of clay is the BRICK AND OTHER CLAY PRODUCTS 105 same as the end of a brick, the brick are called end cut; and if the section is the same as the side of a brick, they are called side cut. FIG. 52. Auger type of brick machine. (American Clay Machinery Co.) FIG. 53. Plunger type of brick machine. (American Clay Machinery Co.) 106 MATERIALS OF CONSTRUCTION Often the brick are burned without any preliminary drying, but this is not good practice as they tend to crack and warp in the burning. It is better first to dry the brick for a time in air, or place them in a drying house where the drying is accelerated by means of steam pipes or hot air. 135. Pressed -brick Machine Process of Making Brick. In the pressed-brick process, the clay is either used dry (containing less than 7 per cent of water) or semi-dry (containing more than 7 per cent of water but not so much water as the clay used in the stiff mud process). The clay is ground to the fineness of flour FIG. 54. Side cut brick table for plunger machine. (American Clay Machinery Co.) before being delivered to the brick machine. This machine feeds the clay into the molds and then compresses it (under an enormous pressure) by means of plungers. These brick require less drying than the other kinds, and, consequently, are often burned without any preliminary drying. Pressed brick are very compact and strong, but they are thought to be less durable than those brick in which more water is used during the making. 136. Brick Kilns. Brick kilns may be classified as intermit- tent or continuous kilns, according to their method of operation. The intermittent kilns are subdivided into updraught, down- draught, and up-and-down-draught kilns. The old style updraught kiln is usually just a pile of brick about 20 or 30 ft. wide, 30 or 40 ft. long, and 10 or 15 ft. high. The brick are so piled as to form a number of arched openings extending through the pile. The sides of the pile are often plastered with mud and the top covered with dirt and some- BRICK AND OTHER CLAY PRODUCTS 107 times roofed so as to keep in the heat. The more modern type of updraught kilns are built with permanent side walls. This updraught kiln is not so economical as the other types, as many FIG. 55. Dry clay brick press machine. (American Clay Machinery Co.) FIG. 56. Hundred and ten chamber Haigh continuous kiln. Five fires. (American Clay Machinery Co.) (about half) of the brick have to be discarded on account of over-and-under burning. A downdraught kiln has permanent walls, a floor, a tight roof, chimney, and furnaces. The floor has openings connecting with flues leading to the chimney. The heat is generated in outside ovens and enters the kiln in such a way that it reaches the top of the brick piles first and passes down through the piles to the open- 108 MATERIALS OF CONSTRUCTION ings in the floor, and then through the flues to the chimney. This kiln burns the brick very evenly and only a few of them have to be discarded on account of over-or under-burning. The up-and-down-draught kiln is so arranged with two sets of furnaces that the heat from one furnace can be made to pass down through the brick while the heat from the other furnace can be made to pass up through r the brick before passing to the chimney. This type of kiln burns the brick very uniformly. Continuous kilns are of many types, but they all consist essentially of a series of chambers with flues between them and also between each chamber and the stack. When one chamber is fired, the heat can be made to traverse several other chambers before going to the chimney, thus preheating the brick in those chambers and securing an economy of fuel. Only one chamber needs to be out of operation at any one time because of the changing of the piles of brick. 137. Burning the Brick. The fuel used usually depends upon local conditions. The furnaces in the kilns may be designed to use wood, coal, or gas. Wood is usually used in the old-style updraught kilns where the fires are built in the archways. The brick are first subjected to a fire giving a moderate tem- perature until the moisture is expelled. Then the temperature is increased until the brick in the hottest part of the kiln are at a white heat, and the other bricks at a red heat. The fire is kept at this temperature until the burning of the brick is complete. Ordinary burning requires from 6 to 15 days. When the burning is completed, the fires are stopped and all of the openings are closed so as to exclude any cool currents of air. Then the kiln and the brick are allowed to cool slowly for several days before the kiln is opened and the brick removed. This slow cooling " anneals" the brick and makes them tough. The brick nearest the fire are usually overburned and are called arch or clinker brick. The brick in the coolest part of the kiln are usually underburned and these brick are called salmon or soft brick. All of the other brick in the kiln, which are properly burned, are called body, cherry, or hard brick and are the brick that are valuable for building purposes. C. MANUFACTURE OF OTHER BRICK 138. Manufacture of Paving Brick. These brick are used for paving purposes and should be hard, tough, and non-absorp- BRICK AND OTHER CLAY PRODUCTS 109 live. Their manufacture differs from that of ordinary clay brick because they are burned at a much higher temperature (high enough to vitrify the brick) and also because the selection of a suitable clay is more limited. Surface clays, impure fireclays, and shales have been used in the manufacture of paving brick, but the shales are the best and most used material at the present time. These clays occur in large bodies and are rocklike, but they are easily reduced to a powder. They are impure and have a range of vitrification often extending over 300 degrees Fahrenheit. The shale banks are usually worked with steam shovels. When the clay arrives at the factory, it is crushed to a powder by grinding machinery and delivered to a pug mill where just enough water is mixed with the clay to make a stift mud. The brick are molded as in the stiff-mud process and are repressed immediately after molding. This repressing makes the brick more uniform, rounds off the corners, and makes lugs on the sides so that the brick will be separated a little from each other when laid in a pavement. Sometimes the brick are wire cut and not repressed. This kind is called "wire cut lug brick." The brick are usually dried in a dry house before they are burned. Paving brick are burned in a down-draught or a continuous kiln. The time required for burning is about ten days. The heat necessary is a bright cherry heat (from 1,500 to 2,000 degrees Fahrenheit) for shales, while only a red heat is reached in burning common-clay building brick. Different clays require different temperatures. After the brick are thoroughly burned, the kiln is tightly closed and allowed to cool slowly for several days. This tends to anneal the brick and make them more tough. Upon emptying the kiln the brick should be sorted into different classes. With shales, about 70 or 80 per cent of No. 1 paving brick are obtained. 139. Manufacture of Firebrick. Firebrick may be classified as follows: 1. Add Brick. (a) Fireclay brick. (6) Silica brick. (c) Canister brick 2. Basic Brick. (a) Magnesia brick. (6) Bauxite brick. 110 MATERIALS OF CONSTRUCTION 3. Neutral Brick (a) Chromite brick. Fireclay brick are made of ordinary fireclay mixed with a little flint clay, sand, burned fireclay, or other refractory material to prevent too great a shrinkage in burning and drying. The molding and drying may be done by any of the ordinary ways, while the firing is usually done in a down-draught or continuous kiln. A temperature of from 2,500 to 3,500 degrees Fahrenheit is required in the burning. The cooling should, be fast until 2,500 degrees Fahrenheit is reached, and then it should be slow. Silica firebrick are made of silica sand mixed with a little lime (about 2 per cent) to act as a binder. These firebrick are usually molded by hand, dried in a drying room, and fired in a down- draught kiln. The temperature required is from 2,600 to 3,200 degrees Fahrenheit. The cooling must be done very slowly and uniformly. A very good grade of silica firebrick can be made by the process used in making sand lime brick. Ganister brick are made from ganister rock, which is a dense siliceous sandstone containing about 10 per cent of clay. The process of manufacture is the same as that for silica brick, except that no lime is added. Magnesia brick are made from a mixture of caustic magnesia and sintered magnesia with a little iron oxide for a flux. The materials are ground and mixed; water is added in the pug mill; and the brick are molded under a heavy pressure. They must be carefully dried before being fired. The temperature required is from 3,300 to 3,450 degrees Fahrenheit. These brick warp and shrink badly. Bauxite brick are made by mixing ground bauxite (containing more than 85 per cent of A1 2 O 3 ) with about 25 per cent of clay in a pug mill; adding water; and molding by hand or with a stiff mud machine. The brick are burned at a temperature of about 2,800 degrees Fahrenheit. They are weak and shrink greatly in drying and burning. Chromite brick are made from a mixture of chrome iron ore and fire clay or bauxite. The mixture contains about 50 per cent of chromium ore, 30 per cent of ferrous oxide, and 20 per cent of alumina and silica. The materials are ground, mixed, and molded under heavy pressure, as in the case of the silica brick. The burning temperature is about 3,000 degrees Fahrenheit. BRICK AND OTHER CLAY PRODUCTS 111 140. Manufacture of Sand-lime Brick. Sand-lime brick consist of a mass of sand cemented together with lime. There are several classes of these brick, but only one is of importance as a structural material. This class of brick is made of a mixture of sand and lime which is molded in a press and then subjected to steam under pressure. The sand used should be well graded so as to have a low percentage of voids. The binding action between the sand and the lime is better with fine sand; hence, the sand should not be too coarse. A well-graded mixture has been found to have a low percentage of absorption. The sand should contain a sufficient proportion of fine quartz sand and it should also be clean and dry when mixed with the lime. The lime used may be either a high-calcium or a dolomitic lime, but the former is preferable. The lime should be hydrated or slaked either before or at the time of mixing with the sand. The amount of lime varies from 5 to 10 per cent of the sand. The thorough mixing of the sand, lime, and water is the most important part of the process of manufacture. It is preferable to mix the dry sand and the dry hydrated lime thoroughly and then add the water and mix again. The mixture is molded into brick in the same manner as in the pressed-brick (dry clay) process. The pressure exerted by the machine on the mixture in the mold is about 15,000 Ib. per square inch. The brick are hardened by placing them in a closed hardening cylinder and subjecting them to steam under a -pressure of about 125 Ib . per square inch. The length of time required for harden- ing at this pressure is about 10 hours. D. OTHER CLAY PRODUCTS 141. Terra Cotta. Terra cotta is made in about the same way as ordinary clay brick, but it requires a carefully selected clay that will burn to a desirable color with a slight natural glaze. Usually, no single clay is used, but a mixture is made of several clays in order to obtain the desired effect. Decorative terra cotta is usually made by hand molding and then dried and burned. Very great care must be taken to prevent distortion and discoloration during firing. Terra cotta lumber and building blocks, which are used for 112 MATERIALS OF CONSTRUCTION structural purposes, are usually made of a mixture of terra cotta clays and finely cut straw or sawdust. The method of manu- facture is like that of the stiff-mud process, except that special care must be taken to prevent distortion and unequal heating in firing. The burning temperature is high enough to burn out all of the straw and sawdust and leave a light porous material. About all of the terra cotta lumber is hollow in construction with outside walls about 1 in. thick and partition walls about % in. thick. Terra cotta building blocks and fireproofing are the same as terra cotta lumber, except that no straw or sawdust is used and the firing temperature is high enough to vitrify the clay. 142. Building Tile. Building tile may be divided according to use into roofing, wall, and floor tile. Roofing tile are made in the same way as pressed brick, except that the flat forms may be made by the stiff-mud process. The clay is selected with greater care than in the case of ordinary brick. The shape of the tile may be flat, curved, or interlocking. There are two kinds of wall tile called dust-pressed tile and plastic tile. The clay used in making dust-pressed wall tile may be a fireclay, shale clay, or a mixture of clays. The materials are ground, mixed, and then made up to the consistency of thin cream and strained through a silk screen. The water is drained off, the material dried, crushed to a powder, and slightly moisten- ed by steam. The molding is done in a dry press and the tile are burned in fireclay -boxes to keep the tile from coming in contact with the flames. After the first burning, a glaze may be applied and coloring matter added and the tile burned a second time to fuse the glaze. Plastic tile are made in the same way as dust- pressed tile, except that a mixture of soft clay and burned clay is used and the molding is done immediately after the mixing and the addition of the water. Most wall tile are dust-pressed tile. An inferior product of building tile (and some kinds of terra cotta) is made from a finely divided clay similar to that used for ordinary clay brick. The stiff-mud process is used, and the tile are wire cut. The burning is the same as that given to ordinary clay building brick and is usually done in a down-draught kiln. 143. Drain Tile. Drain tile are made from a red burning clay BRICK AND OTHER CLAY PRODUCTS 113 (shale clay), fireclay, surface clay, or from a mixture of clays like those used in making terra cotta lumber. The tile are made by the stiff mud process, and the burning is done at a temperature that aids in the production of a strong porous product that is not vitrified or glazed. The tile may be classified according to the materials from which they are made, according to their use, or according to their FULL- $-HALF- JAMB -TILE FIG. 57. Standard wall and jamb tile. general physical properties. Drain tile are used for draining water from fields, roads, ditches, etc., and they must be porous so that the water can pass from the soil through the walls of the tile into the interior of the pipe. 144. Sewer Pipe. Sewer pipe is made from such clays as will produce a non-porous tile with a low percentage of absorption. 114 MATERIALS OF CONSTRUCTION The stiff-mud process of manufacture is used for ordinary pipes, and the dry-press process for those pipes having sockets at the end or which are of some special shape. The pipe is dried in a steam chamber and then burned in a down-draught kiln. When the temperature reaches about 2,100 degrees Fahrenheit, common salt is thrown on the kiln fires. The sodium vapors from the salt combine with the clay and form a hard glaze on the surface of the pipe and thus make the pipe very non-absorptive. Sewer pipe may be classified in the same ways as drain tile. As sewer pipes are used for carrying sewage, it is important that they be non-porous and non-absorptive and that they have good tight joints. E. PROPERTIES OF BRICK AND OTHER CLAY PRODUCTS 145. General Properties of Brick. Requisites of Good Brick. A good brick should have plane faces, parallel sides, sharp edges and angles, a fine, compact, uniform texture, and it should contain no cracks, fissures, air bubbles, pebbles, lumps of lime, etc. A brick should give a clear ringing sound when struck with the hammer or another brick. A paving brick should be hard and tough to resist wear and impact, and it should be free from laminations or seams so that it will wear uniformly in a pavement. Common clay building brick of good quality weigh about 125 Ib. per cubic foot; face or pressed brick about 135 Ib. per cubic foot; sand-lime brick about 115 Ib. per cubic foot; and paving brick about 150 Ib. per cubic foot. The sizes of brick vary in different countries and different localities. The standard size for common brick in America is 8J4 by 4 by 2J4 in., and for paving brick 8^ by 4 by 2^ in. Paving blocks are about 3 by 4 by 9 in. in size. 146. Absorption of Brick and Building Tile. Formerly, it was thought that if a brick would absorb much water it was not so durable as other brick and was more liable to destruction by frost, but this opinion has not been substantiated by tests. The absorptive power of a brick depends somewhat on its compact- ness but more on the chemical composition of the clay. There appears to be no close relation between the absorptive power and the strength and durability of the brick. The following table shows the approximate range of absorption in different kinds of brick which have been immersed in water for 48 hours. BRICK AND OTHER CLAY PRODUCTS 115 ABSORPTION OF BRICK AND BUILDING TILE Percentages are based on the weight of the dry brick KIND OP BBICK PERCENTAGE OP ABSORPTION Common clay building brick 12 to 18 Pressed or face brick : . . . 6 to 12 Sand-lime brick 12 to 15 Paving brick and blocks 1 to 3 Fireclay brick 8 to 12 Unglazed terra cotta blocks and building tiles . . 10 to 15 147. Compressive Strength of Brick and Building Tile. The compression test of brick is only of relative value for comparing different kinds of brick, because, when a brick is used in masonry, its crushing strength is not of much importance unless the mortar used with the brick has nearly the same strength. Ordinary mortar used in brick masonry is generally very much weaker than the brick. Soaking a brick in water tends to decrease its strength in compression. The following table will give an idea of the average compressive strength of good brick: COMPRESSIVE STRENGTH OF BRICK AND BUILDING TILE STRENGTH IN POUNDS KIND OF BRICK PER SQUARE INCH Average good clay building brick 4 , 000 Pressed brick 8,000 Sand-lime brick 3,000 to 4,000 Paving brick and blocks 10 , 000 Fireclay brick 3,000 to 6,000 Terra cotta blocks and building tile 4,000 Architectural terra cotta 3,000 148. Transverse Strength of Brick and Building Tile. The transverse tests are easy to make and they give results that are definite and which furnish the best indications of the quality of the brick. Transverse tests afford an indication of the toughness and also of the ability of the brick to resist ordinary failures in brick walls. In masonry walls the mortar usually fails first and squeezes out, thus setting up bending stresses in the brick which cause them to fail. The appearance of the fractured surface is a good indication of the care with which the brick have been made. The following table gives an average range of values: 116 MATERIALS OF CONSTRUCTION CROSS-BENDING STRENGTH OF BRICK AND BUILDING TILE MODULUS OP RUPTURE IN POUNDS KIND or BRICK PER SQUARE INCH Common clay building brick 500 to 1 , 000 Pressed or face brick 600 to 1 , 200 Sand-lime brick 300 to 600 Paving brick and blocks 1 , 500 to 2 , 500 Fireclay brick 300 to 600 Unglazed terra cotta blocks and building tile 500 to 1,000 149. Shearing Strength of Brick and Building Tile. The shearing strength of brick is of but little importance and the tests are very hard to make properly. Tests made at the Watertown Arsenal gave the following values. Results for terra cotta and building tile were taken from another source. SHEARING STRENGTH OF BRICK AND BUILDING TILE STRENGTH IN POUNDS KIND OP BRICK PER SQUARE INCH Common clay building brick 1 , 000 to 1 , 500 Pressed or face brick 800 to 1 , 200 Sand-lime brick 500 to 1 , 000 Paving brick and blocks 1 , 200 to 1 , 800 Fireclay brick 500 to 1 , 000 Unglazed terra cotta blocks and building tile 600 to 1 , 200 150. Modulus of Elasticity of Brick and Building Tile. The modulus of elasticity of brick in compression is not a constant quantity because the stress strain curve in compression is a curved line throughout its length, similar to the stress strain curves for concretes and mortars. The following are average values of the modulus of elasticity in compression for loads not exceeding one-fourth of the ultimate strength. MODULUS OF ELASTICITY IN COMPRESSION OF BRICK AND BUILDING TILE MODULUS op ELASTICITY IN POUNDS KIND OP BRICK PSR SQUARE INCH Common clay building brick 1 , 500 , 000 to 2 , 500 , 000 Pressed or face brick 2 , 000 , 000 to 3 , 000 , 000 Sand-lime brick 800,000 to 1 ,200,000 Paving brick and blocks 4,000,000 to 8,000,000 Unglazed terra cotta blocks and building tile 1,500,000 to 3,000,000 BRICK AND OTHER CLAY PRODUCTS 117 151. Properties of Drain Tile. Requisites. All drain tile should be free from visible grains of caustic lime, iron pyrites, or other minerals which are known to cause slaking or the dis- integrating of the tile. The drain tile should be of the proper shape, diameter, and length; uniform in structure, smooth on the inside, free from cracks and checks that would appreciably lower the strength ; properly burned ; and should give a clear ring when stood on end and tapped with a light hammer. Drain tile are divided into three classes (farm drain tile, standard drain tile, and extra quality drain tile) according to quality and use. The physical tests include strength and ab- sorption tests and sometimes freezing tests. Any good drain tile should easily pass the following minimum requirements for strength and not absorb more water than the maximum values given below: MINIMUM REQUIREMENTS FOR STRENGTH OF DRAIN TILE Internal diameter of pipe, inches Average supporting strength in pounds per lineal foot Farm drain tile Standard drain tile Extra quality drain tile 4 8 12 16 20 24 30 36 42 800 800 800 1,000 ,200 ,200 ,200 ,300 ,500 ,700 2,000 2,300 2,600 1,600 1,600 1,600 1,700 2,000 2,400 3,000 3,600 4,200 MAXIMUM ALLOWABLE ABSORPTION FOR DRAIN TILE Standard boiling test. All values are percentages of the dry weight. Materials used in making Farm drain tile, per cent Standard drain tile, per cent Extra quality drain tile, per cent Shale and fireclay tile Surface clay tile 11 14 9 13 7 11 Concrete tile 12 11 10 118 MATERIALS OF CONSTRUCTION 152. Properties of Sewer Pipes. Requisites. Sewer pipes should be of the hub and spigot type preferably, properly made and burned, vitrified, and salt glazed. All pipes should be of proper dimensions, straight, sound, well glazed throughout, smooth on the inside, free from blisters, lumps, or flakes which are broken or are larger than allowed by the specifications, and free from fire checks and cracks extending through the thickness of the -pipe. The thickness of the walls should be at least j^2 of the inside diameter. The thickness of the walls of ordinary sewer pipes is less than y\2 of the inside diameter, while that of " double strength" pipes is equal to Y\i of the inside diameter. The following table gives the minimum strength requirements of the Tentative (Proposed) Specifications for Sewer Pipes of the American Society for Testing Materials, the Specifications of the City of Brooklyn for Sewer Pipes and the results of strength tests made in that city. These results are higher than would ordinarily be expected from tests on ordinary salt-glazed and vitrified-clay sewer pipes. Any good sewer pipe should be able to pass the A. S. T. M. specifications. The requirements for the specification for absorption have not yet been decided upon. However, good salt-glazed vitrified-clay sewer pipes should not absorb more than 3 per cent of water on the average or more than 5 per cent in any individual case. MINIMUM STRENGTH REQUIREMENTS AND RESULTS OF TESTS OF SEWER PIPES Average supporting strengths in pounds per lineal foot. Inside diam- eter, inches A. S. T. M. tenta- tive specifications Brooklyn specifications Brooklyn test results 6 1,430 1,000 4,275 8 1,430 9 1,050 3 983 10 1,570 12 1,710 1,150 4,696 15 1,960 1 , 300 5,046 18 2,200 1,450 6,311 21 2,590 24 3,070 2,000 9,866 30 3,690 36 4,400 42 5,030 CHAPTER VIII STONE AND BRICK MASONRY A. STONE MASONRY 153. Stone Masonry in General. Stone masonry includes all masonry in which stone form the most important part. When mortar is used with stone masonry, it is called " wet " or " mortar " masonry. When no mortar is used, it is called "dry" masonry. Stone masonry is one of the oldest forms of construction known to mankind. It has been used by practically all peoples through- out all ages and in all countries where the stones could be readily obtained . Structures made of stone masonry are very durable and some of them have been in use for more than a hundred years. Coping Section A- A FIG. 58. Range masonry. Sketch showing arrangement and names of parts. Stone masonry is used for various buildings, retaining walls, dams, piers, abutments, arches, bridges, paving, culverts, founda- tions, etc. 154. Definitions. The following are definitions of some of the terms often used in connection with stone (and brick) masonry. Other definitions will be found in the articles following. 119 120 MATERIALS OF CONSTRUCTION Batter is the slope of the surface of the wall. Coping is a course of heavy stones laid on top of a wall to protect it. Course is a horizontal layer of stones in a wall. Cramps are bars of iron or steel having their ends bent at right angles to the body of the bar. These ends enter holes in adjacent stones to keep the stones from separating. Dowels are short straight bars of iron or steel which enter holes in adjacent stones which are above each other to prevent one stone from slipping on the other. Face is the front surface of the wall. Back is the rear surface of the wall. Facing is the stone or other material which forms the face of the wall. Filling is the material in the interior of the wall. Backing is the material forming the back of the wall. Quoin is a stone laid in the corner of a wall. 155. Classification of Stone Masonry. The following is a classification of stone masonry: A. Dry Masonry 1. Slope wall masonry is a thin layer of stone, or an inclined wall of stone, built against slopes of embankments, excavations, river banks, etc., to protect them from rain, waves, or weather. 2. Stone paving is a dry stone masonry used for paving the floors or ends of culverts and similar structures. 3. Riprap is stone of any shape or size placed on river banks or around piers, abutments, etc., to prevent wash and scour by the water. The stone may be dumped in place, but they are more effective if arranged by hand. B. Wet or Mortar Masonry 1. Rubble masonry which is composed of rough unsquared stone. (a) Coursed rubble in which the stone are leveled off at specified heights to an approximately level surface. (6) Uncoursed rubble which is laid without any attempt at regular courses. 2. Squared stone masonry is masonry in which the stone are roughly squared and roughly dressed on beds and joints. The STONE AND BRICK MASONRY 121 thickness of the mortar required in the joints is more than % in. This class may be subdivided according to the facing of the stone into: (a) Pitched faced masonry. (6) Quarry faced masonry. Or this class may be divided according to the manner in which the stone are laid: (a) Range work which is laid in courses. (6) Broken range which is laid in broken courses. (c) Random masonry which is laid with no attempt at courses. "59 UNOOURSID RUBBLE RUBBLE Uff ED RUBBLE =55:3 -V- ^ Mi i rM - 1 1 1 1 I l 1 1 1 1 ASHLAR FIGS. 59-67. Stone masonry. 3. Cut stone or ashlar masonry which is composed of any of the kinds of cut stone where the required thickness of the mortar joints is less than J^ in. This class is usually subdivided as follows: (a) Coursed ashlar in which the courses are continuous (range work). 122 MATERIALS OF CONSTRUCTION (b) Broken ashlar in which the courses are broken and not continuous (broken range). 156. Mortar for Stone Masonry. Mortar for stone masonry has three functions: (1) to form a bed or cushion for the stone so as to distribute the pressure uniformly; (2) to bind the wall together into a solid whole; and (3) to fill the spaces and voids in the masonry and keep out the water. Also, a good mortar should be soft and plastic so that it will work properly besides being capable of hardening and becoming strong, dense, and impervious. In general, the kind of mortar used depends upon the kind of masonry and the loads the masonry is to bear. Lime mortar is usually used with rubble masonry, often with squared stone masonry, and rarely with cut stone or ashlar masonry. Probably more lime mortar is used than any other kind as it is very suitable for masonry where the loads are small. This mortar is composed of 1 part of lime paste to 2^2 to 3 parts of good, clean, fine, sharp sand. See chapter on " Limes and Lime Mortars" for a further discussion of this mortar. A Portland cement mortar is usually used with cut stone or ashlar masonry, sometimes with squared stone masonry, and rarely with rubble masonry. This mortar should always be used where the unit load on the masonry is large. The proportions usually vary from 1 part of portland cement to from 1 to 4 parts of sand according to the strength desired. See chapter on " Portland Cement and Cement Mortars" for a further discussion of this mortar. A mortar made of Portland cement, lime, and sand may be used with any of the three classes of stone masonry as conditions permit. This mortar is stronger than lime mortar, and weaker, more plastic, and more impervious than an ordinary portland cement mortar. 157. Dressing of Stone Masonry. Dressing is the cutting of the side and bed joints of the stone to plane surfaces, usually at right angles to each other. Care should be taken to make the bed a plane surface so that the pressure will be distributed evenly over all of the stone and also so that the bending stresses in the stone will be a minimum. Great smoothness is not desirable in the joints as slightly rough surfaces offer a greater resistance to slipping and also tend to increase the adhesion of the mortar. 158. Bond in Stone Masonry. Bond in masonry is the over- lapping of the stone so as to tie the wall together both longitudi- STONE AND BRICK MASONRY 123 nally and transversely, and is of great importance to the strength of the wall. The stone in any course should be laid so that they will overlap or break joints with those in the course below, and in such a manner that each stone will be supported by two (or three) below and will aid in supporting at least two above it in the wall. A very strong bond is made by laying some of the stone with their greatest dimension perpendicular to the face of the wall. Such stone are called " headers." In thin walls the headers should be long enough to extend clear through the wall. Stone laid with their greatest dimension parallel with the face of the wall are called "stretchers." 159. Backing in Stone Masonry. Ashlar or cut-stone masonry is usually backed with coursed rubble masonry and sometimes FIG. 68. Methods of finishing horizontal joints. with brick masonry. Squared-stone masonry is sometimes backed with rubble or brick masonry. Great care should be taken to secure a good bond between the facing masonry and the backing. Headers should be frequently used. For the best bond, the backing should be built up with the facing masonry. 160. Pointing of Stone Masonry. Pointing is the refilling of the edges of the joints in the masonry as compactly as possible and to a depth of about 1 in. with mortar especially prepared for that purpose. Only a very good cement mortar such as a 1:1 or a 1 : 2 portland cement mortar should be used. Sometimes a good lime mortar is used for some classes of masonry. The four general ways of pointing the edges of the horizontal joints in cut stone masonry are flush joints, weather joints, grooved joints, and bead joints. The vertical joints are pointed in the same manner as the horizontal ones, except that in weather joints, the vertical joints are made flush. Care should be taken not to reverse the slope in the weather joint as this would allow water to collect in the joint and tend to weaken the masonry. 124 MATERIALS OF CONSTRUCTION 161. General Rules for Laying Stone Masonry. The following general rules for laying stone masonry are taken from ' Baker's Masonry Construction." These principles apply to all classes of stone masonry. 1. The largest stone should be used in the foundation to give the greatest strength and lessen the danger of unequal settlement. 2. A stone should be laid upon its broadest face, since then there is better opportunity to fill the spaces between the stones. 3. For the sake of appearance, the larger stone should be placed in the lower courses, the thickness of the courses decreasing gradually toward the top of the wall. 4. Stratified stone should be laid upon their natural bed, that is, with the strata perpendicular to the pressure, since they are then stronger and more durable. 5. The masonry should be built in courses perpendicular to the pressure it is to bear. 6. To bind the wall together laterally a stone in any course should break joints with or overlap the stone in the course below; that is, the joints parallel to the pressure in two adjoining courses should not be too nearly in the same line. This is briefly stated by saying that the wall shall have sufficient lateral bond. 7. To bind the wall together transversely there should be a considerable number of headers extending from the front to the back of thin walls or from the outside to the interior of thick walls; that is, the wall should have sufficient transverse bond. 8. The surface of all porous stone should be moistened before being bedded, to prevent the stone from absorbing the moisture from the mortar and thereby causing it to become a friable mass. 9. The spaces between the back ends of the adjoining stone should be as small as possible, and these spaces and the joints between the stone should be filled with mortar. 10. If it is necessary to move a stone after it has been placed upon the mortar bed, it should be lifted clear and reset, as at- tempting to slide it tends to loosen stones already laid and destroy the adhesion, and thereby injure the strength of the wall. 11. An unseasoned stone should not be laid in the wall if there is any likelihood of its being frozen before it has seasoned. 162. Waterproofing Stone Masonry. As most of the stone used for masonry is practically impermeable, the weak or permea- ble part of the masonry is the joints. If good mortar is used and all of the spaces between the stone are filled, practically no STONE AND BRICK MASONRY 125 water will pass through. Care should be taken to see that all joints are carefully pointed and that all cracks are filled with good mortar. Washing or painting the surface of the masonry exposed to the water with a waterproofing compound (such as a soap and alum solution, hot tar, asphalt, etc.) will aid in making the masonry water-tight. Sometimes the masonry is made more water-tight by incorpora- ting a layer of felt or tar paper, painted on both sides with tar or asphalt, in the wall. Care should be taken to make the ends of the felt or paper overlap so that no cracks or holes extend through this waterproofing layer. Such a waterproofing layer is some- times applied to the face or back of the wall instead of being built in the wall. 163. Cleaning Stone Masonry. When the masonry is com- pleted, the surfaces should be cleaned to remove any dirt, mortar, etc. adhering to the wall. The cleaning is usually done by brush- ing with stiff brushes and then washing with water. Frequently, the stone work in buildings or other structures becomes soiled by dirt in the air, or smoke. The stone work may be cleaned with soap and water or by brushing and then washing with soap and water. Sometimes washing with a dilute acid solution aids in cleaning and brightening the surface. The use of the sand blast is very effective for cleaning purposes. 164. Strength and Other Properties of Stone Masonry. The strength of stone masonry depends not only upon the strength of the stone in compression but also upon the accuracy of the dressing, the bond between the stones, and the thickness and strength of the mortar. In practically all of the observed failures of stone masonry under compression, the mortar failed first and squeezed out, thus causing bending stresses in the stone which resulted in their failure by tension in cross bending. About the only practical way of determining the strength of good stone masonry is to note the loads that have been carried by it without failure. There are several structures of first-class masonry carrying loads of approximately 400 Ib. per square inch without showing any signs of failure. Ashlar or cut stone masonry is the best of all stone masonry in quality, and it is used in all important structures where strength and stability are required. The stone used should not be longer than 3 to 5 times their depth, nor wider than 2 to 3 times the 126 MATERIALS OF CONSTRUCTION depth, depending to some extent upon the strength of the stone. The weight per cubic foot of stone masonry may be taken at about 5 Ib. less than that of the stone used. The modulus of elasticity of stone masonry in compression is about 2,000,000 Ib. per square inch for rubble masonry and about 4,000,000 Ib. per square inch for ashlar masonry. These values are approximate only and depend to a large extent upon the stone and mortar used as well as the class of masonry and the care with which it is constructed. The amount of mortar required for ashlar masonry is about 2 or 2% cu. ft. per cubic yard of masonry; for squared stone masonry, from 3J^ to 5 cu. ft. per cubic yard of masonry; and for rubble masonry, from 7J^ to 10 cu. ft. per cubic yard of masonry. The coefficient of expansion of stone masonry is about 0.0000035 per degree Fahrenheit. The tensile strength of masonry is very small, and, therefore, stone masonry should not be designed to carry any tension. As stone masonry is very weak in tension, it is also weak in cross bending, and should not be expected to carry transverse loads. 165. Safe Loads for Stone Masonry. Safe loads for stone masonry in tension and cross bending should be considered as zero, except in special cases where there are special designs and constructions. The working stress in shear should be taken at one-fourth of the safe working stress in compression. See tables following for safe working stress in compression. From an examination of the loads carried by different classes of the best stone masonry without failure, the values in the following table may be assumed, provided that each kind of stone masonry is the best of its class : SAFE LOADS IN COMPRESSION FOR THE BEST STONE MASONRY GOOD ORDINARY PORTLAND CEMENT MORTAR, POUNDS PER MORTAR 1:2 Mix, KIND OF MASONRY SQUARE INCH POUNDS PER SQUARE INCH Rubble 140 to 200 Squared stone 200 to 280 Limestone ashlar 280 to 350 600 Sandstone ashlar 250 to 320 500 Granite ashlar 350 to 400 700 The building laws (1907) of the city of Chicago gave the following allowable safe loads in compression for masonry. STONE AND BRICK MASONRY 127 These values were recommended to the city by a large committee composed of the leading architects and engineers of Chicago. CITY OF CHICAGO ALLOWABLE UNIT STRESSES FOR MASONRY IN COMPRESSION All values are in pounds per square inch PORTLAND CEMENT KIND OF MASONBY LIME MOBTAK MOBTAB Rubble masonry, uncoursed 60 100 Rubble masonry, coursed 120 200 Ashlar masonry, coursed limestone ... 400 Ashlar masonry, coursed sandstone ... 400 Ashlar masonry, coursed granite ... 600 B. BRICK AND HOLLOW TILE MASONRY 166. Brick Masonry in General. Brick masonry includes all forms of masonry composed of brick and mortar, such as walls of buildings, backing for stone and concrete masonry, sewers, tunnels, facing for stone or concrete masonry, arches, etc., and sometimes culverts, piers, abutments, and bridges. At the present time, brick masonry is much used as a building material. Good brick masonry is the equal of stone masonry in strength, durability, and appearance. Some of the advantages of brick masonry are: brick resist the action of fire, weather, and the acids in the atmosphere ; brick can be secured in any locality, and of most any size, shape, and color; brick are easy to lay in a wall; brick masonry is as durable as stone masonry ; brick masonry is as strong as stone masonry, with the exception of cut stone masonry; brick masonry is often cheaper than stone masonry. Some of the disadvantages of brick masonry are : it requires skill to lay a good wall ; poor mortar is often used in the laying of the brick, thus making a wall that is neither strong nor durable. 167. Mortar for Brick Masonry. As in stone masonry, the mortar in brick masonry has three functions to perform : namely, (1) to form a bed or cushion to take up any inequalities in the brick and to distribute the pressure uniformly; (2) to bind the wall into a solid mass; and (3) to fill the spaces and voids between the brick in the masonry and keep out the water. In general, the mortar should be chosen to suit the character of the masonry and the loads that it is to bear. For strong and impervious masonry or masonry which may be under water, a Portland cement mortar (of a mix varying from a 1:2 to 1:4 128 MATERIALS OF CONSTRUCTION according to conditions) should be used. For small loads a good lime mortar is suitable, while for medium loads, a mortar com- posed of Portland cement, lime, and sand may be used. Clay or loam should never be used in place of the sand. At the present time most of the brick masonry is laid in lime mortar on account of its cheapness. The quantity of mortar required for brick masonry depends upon the size, of the brick and the thickness of the joints. As many of the building brick are about of the same size, most of the variation in the quantity of mortar needed is due to the thickness of the joints. The thickness of joints in brick masonry may vary from ^ to Y in., depending on the kind of brick used and the architectural effect desired. For pressed brick, a joint of about ^{Q in. is desirable, while for ordinary brick the joint should be from % to %in. thick for good work. For ordinary backing and filling and rough work, the joints are usually from % to J^ in. thick. 168. Laying the Brick. The following principles apply to all brick laying: 1. All brick should be thoroughly wet before laying, so that they will not absorb the water from the mortar. While this wetting is important, it is often neglected. 2. The brick should be laid in a truly horizontal position except in special cases. 3. The top edge of a brick should be laid to a stretched string. 4. The masonry should be built in courses perpendicular to the pressure it is to bear. 5. Each course should break joints with the courses immediately above and below it. There should be sufficient longitudinal bond. 6. Sufficient transverse bond should be provided. 7. The spaces between the brick should be completely filled with mortar. 8. In laying the brick, a layer of mortar should first be spread over the last course of brick. 9. The brick should be firmly pressed in place in this mortar with a slid- ing motion which will force the mortar to fill the joint. 10. The excess mortar squeezed out on the face of the wall should be removed with the trowel and applied to the end of the brick so as to aid in filling the next joint. 169. Improvements in Brick Laying. During the last few years, the laying of brick has been greatly expedited by the use of three innovations: the packet, the special scaffold, and the fountain trowel. By the use of these innovations, together with proper instructions, a skilled bricklayer can lay three or four times as many brick as he could before. STONE AND BRICK MASONRY 129 The packet is a small wooden frame or tray upon which two rows of ten brick each are placed on edge in such a position that the mason can put his fingers under each brick while it is upon the packet. The brick are placed on the packets when they are unloaded from the wagon or car, and are transported on the packets to the scaffold. The brick may be sorted as they are placed on the packets. The special scaffold is simply a shelf or bench about two and a half feet above the platform on which the mason stands. The packets are placed on this scaffold. Hence, the mason does not have to stoop over and pick up each brick from the floor of the platform on which he stands, thus saving time and energy. The fountain trowel is a metal can shaped something like a low shoe. The heel is used to scoop up the mortar from the box, and the mortar is poured upon the brick through a narrow open- ing in the toe about 4 in. long. This fountain trowel makes it possible to spread a much greater quantity of mortar in a given time, and also permits the use of a softer mortar which fills the joints better. 170. Bond in Brick Masonry. The bond is the arrangement of the brick in courses in such a way as to tie the wall together both longitudinally and transversely. The brick in one course should always break joints with those in the course below. A stretcher is a brick laid with its greatest dimension parallel to the face of the wall, while a header is a brick laid with its greatest dimension perpendicular to the face of the wall. A course is a layer of brick, and is usually horizontal. The three principal ways of bonding are the common, English, and Flemish methods. In the common bond, from four to seven courses of stretchers are laid to one course of headers. The English bond consists of alternate courses of headers and stretchers. In the Flemish bond, the headers and stretchers alternate in each course, and the brick are so placed that the outer end of a header lies in the middle of a stretcher in the course below. Brick veneer consists of a single layer of brick placed on the face of the wall. Great care must be taken in the bonding of this veneer to the rest of the wall if these brick are to carry any of the load. One of the ways of bonding is a secret bond as shown in the sketch. Another way is to use metal ties extending from the joints in the veneer to the joints in the filling. 9 130 MATERIALS OF CONSTRUCTION In hollow walls, the bonding of the outer layers to the inner layers is usually accomplished by long metal ties. Arches in brick work are usually built with a series of header courses in which the brick are laid on edge. Such arches are called row-lock arches. Another method is to lay the brick with continuous radial joints with the brick laid partly as headers and partly as stretchers. Specially prepared brick must be used for this method. 171. Pointing of Brick Masonry. After the wall is built, the edges of the exposed joints are pointed by refilling them to a depth of about one inch with specially prepared mortar. This 1 1 I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I I I I I . i ' i i , i i :r . ' i , 1 1 E ii ii i . i i i i ii ii r~ i L j L_ i i ^^ i i i i FIG. 69. Common bond FIG. 70. English bond FIG. 71.. Flemish of brickwork. of brickwork. bond of brickwork mortar is usually richer than that used in building the wall. Sometimes the pointing mortar is colored so as to secure pleasing effects. The four general ways of refilling the horizontal joints are by making what are known as flush, bead, groove, and weather joints. The vertical joints are pointed in the same way except that when the horizontal joints are weather joints, the vertical ones are made flush. There are several other varieties of pointing which are not known by any general names. When the slope of the weather joint is reversed (sometimes called a struck joint), it allows water to collect in the joint and penetrate into the masonry. 172. Waterproofing Brick Masonry. Brick masonry may be made water-tight by constructing it of impervious brick and mortar. Another way is to incorporate a layer of tarred paper or felt (painted with asphalt or tar) in the wall. If the wall is already built, it can be made more water-tight by painting it with a soap and alum solution, a tar or asphalt preparation, or some other waterproofing compound. Sometimes it is given a coating of impervious mortar or of an impervious bituminous mastic. STONE AND BRICK MASONRY 131 The methods of rendering a stone wall water-tight may be used to make a brick wall waterproof. 173. Cleaning Brick Masonry. Brick masonry may be cleaned by the same methods as are used for cleaning stone masonry (see the article on " Cleaning Stone Masonry"). Mortar sometimes sticks so tightly to the brick that a metal tool is required to remove it. Enameled brick can be cleaned with caustic soda or sodium carbonate, which does not have any effect on the brick or cement and lime mortar. 174. Strength and Other Properties of Brick Masonry. The weight of the best pressed brick masonry with thin joints is about 145 Ib. per cubic foot; of brick masonry of ordinary quality, 125 Ib. per cubic foot; and of soft brick masonry with thick j oints, 100 Ib. per cubic foot. These values are approximate. The strength of brick masonry depends more upon the strength of the mortar, the bond, and the workmanship than upon the strength of the brick. When it is desired to have strong masonry, a portland cement mortar must be used. Occasionally, the transverse strength of the brick masonry is of importance, as in some cases the masonry acts as a beam (fre- quently when door openings are cut in a brick wall after it is built). A few tests have given results varying from 50 Ib. per square inch to 300 Ib. per square inch in cross bending, according to the quality of the brick and the mortar. The modulus of elasticity of good brick masonry in compression is about 2,000,000 Ib. per square inch. The coefficient of expansion is approximately 0.0000030 per degree Fahrenheit for pressed brick masonry. The shearing strength of brick masonry probably varies from 10 to 25 per cent of the shearing strength of the brick, depending upon the quality of the mortar used. The compressive strength of brick masonry is of the most importance. A number of tests have been made on the crushing strength of brick masonry piers. The first sign of failure was usually a popping or cracking sound followed a little later by the appearance of cracks which gradually increased in size until the failure was complete. In nearly all of the tests, the mortar failed before the brick. The following table gives results of compression tests made upon some brick piers at the Watertown (U. S.) Arsenal: 132 MATERIALS OF CONSTRUCTION CRUSHING STRENGTH OF BRICK PIERS Watertown Arsenal tests of 1904 Age 6 months Compressive strength, Per cent of average crushing pounds per square inch strength of the brick Kind of brick Neat Portland cement 1 Portland 3 sand 1 lime 3 sand Neat Portland cement 1 Portland cement 3 sand 1 lime 3 sand Face brick Dry pressed face brick 2,880* 2,400 1,517 26 21 13 Repressed mud brick 1,925 1,670 1,260 28 25 19 Common brick Wire cut stiff mud brick. . 4,021 2,410* 1,420 31 19 11 Hard sand struck brick . . . 4,700* 1,800* 994 42 16 9 Hard sand struck brick . . . 1,969 1,800 733 44 40 16 Hard sand struck brick . . . 1,400 1,411 718 24 24 12 Light hard sand struck brick 1,510* 1,519 732 23 23 11 Light hard sand struck 1,061 1,224 465* 20 23 9 *Age 1 month. 175. Allowable Working Loads for Brick Masonry. Safe working loads for brick masonry in tension and cross bending should be considered as zero, except in special cases where there are special designs and constructions. In the case of a lintel, the actual load on it is very uncertain. This load may be assumed to be the weight of all the masonry vertically above the lintel, including such loads as may be trans- mitted to the masonry from floors, etc. Another assumption is to take the load as the weight of the triangle of masonry above the lintel, considering the span of the lintel as the base of the triangle and assuming that the sides of the triangle make an angle of 45 degrees with the base. This latter assumption may be a little unsafe, but if the angle of the sides is changed to 60 degrees, the assumption gives results that are safe for most cases. If there is any doubt in regard to the safety of the lintel, it is better to construct an arch over the opening. The allowable working stress in shear for brick masonry may be taken at one-fourth of the allowable working stress in compression. The following table gives the safe working stresses in com- pression for brick masonry as recommended by a committee of STONE AND BRICK MASONRY 133 Chicago Engineers and Architects in 1908 for the building laws of that city. This table represents good practice. SAFE WORKING LOADS IN COMPRESSION FOR BRICK MASONRY Safe load in Kind of brick Kind of pounds mortar per square inch Paving brick 1:3 Portland cement and sand. . 350 Pressed and sewer brick, strength 5,000 Ib . . . 1:3 Portland cement and sand. . 250 Select hard common brick, strength 2,500 Ib . 1:3 Portland cement and sand . . 200 Select hard common brick, strength 2,500 Ib . 1 Portland cement, 1 lime, 3 sand 175 inch . 1:3 Portland cement and sand. . 175 Common brick, strength 1,800 Ib. per square inch 1:3 Natural cement and sand 150 Common brick, strength 1,800 Ib. per square inch 1 Portland cement, 1 lime, 3 sand 125 1:3 Lime and sand 100 176. Efflorescence. Efflorescence is a white deposit that frequently forms on the surface of brick masonry, especially in moist climates and in damp places, and spoils the appearance of the brickwork. The mortar in the masonry absorbs water and this water dissolves some of the salts of potash, soda, magnesia, etc. that are in the lime or cement. Then, when the water is evaporated from the surface of the brickwork, it leaves these salts in the form of a white deposit. Generally, there is a greater deposit from a lime mortar than from a natural or Portland cement mortar. A portland cement mortar has the least amount of deposit. Sometimes the efflorescence originates in the brick, particularly if the brick were burned with sulphurous coal, or were made from clay containing iron pyrites. Efflorescence can often be prevented by making the wall as water-tight as possible and by keeping water from leaking into the wall. Painting the wall with a soap and alum solution tends to prevent efflorescence. Efflorescence can be removed from the wall by the use of scrubbing brushes and soap and water or a dilute solution of hydrochloric acid in water. 177. Hollow Tile Masonry. Hollow tile masonry is composed of hollow terra cotta or tile building blocks laid in a portland 134 MATERIALS OF CONSTRUCTION cement mortar. This masonry is light in weight and fireproof. It is used for backing of walls, for entire walls, and for partitions and floors. In walls, the blocks are usually laid with their openings vertical instead of horizontal. When the openings are vertical, wire Metal Ties. Header Courses. Flemish Bond. FIG. 72. Hollow tile masonry wall veneered with brick. screen is often laid in the horizontal joints to aid in holding the mortar in place. The mortar should be a 1:2 portland cement mortar, preferably containing a small amount of lime paste not to exceed ten per cent. Good hollow tile masonry can be safely used for the load-carrying walls of ordinary buildings and dwell- ings that are three stories or less in height. Fireproof floors are often constructed of special hollow terra cotta blocks in buildings of steel or reinforced concrete construc- tion. These blocks are set in portland cement mortar and are used as flat arches between the I-beam or reinforced concrete beam joists. A layer of concrete, about two inches thick, is usually placed on top of the blocks to form a wearing surface for the floor. CHAPTER IX TIMBER A. TREES 178. Timber Trees in General. Wood has long been used as a structural material because it could be obtained in most every locality and was easily adapted for use. While there are hundreds of varieties of trees, yet only a few species (probably less than 25 distinct species) are of great commercial importance. Practically all of the woods used for structural materials are produced by the seed-bearing trees. These trees are divided into three groups : namely, the conifers, or soft woods (pine, spruce, fir, cedar, etc.); the broad-leaved trees, or hard woods (oak, maple, ash, walnut, hickory, etc.); and the tropical trees (bam- boos, rattans, palms, etc.). Of these three groups, the conifers, which are found throughout the northern hemisphere, are the most important structurally. The broad-leaved trees are found practically all over the world, and they are next to the conifers in structural importance. Of the soft- and hard-wood trees, probably the pine, fir, hemlock, spruce, cedar, oak, hickory, ash, poplar, maple, cypress, and walnut are the most important. Possibly the bamboo may also be classed as an important structural timber, especially in the tropical countries. There is no sharp distinction in hardness between the soft woods and the hard woods, as some of the hard woods (such as poplar and bass wood) are softer than some of the pines. According to the manner of their growth, trees may be divided into two classes the exogenous or outward growing trees (coni- fers and broad-leaved trees) , and the endogenous or inner growing trees. 179. Structure of Exogenous Trees. The structure of an exogenous tree consists of three parts the bark, the sapwood, and the heartwood. The bark is a protective tissue found on the outside of the tree trunk and varying from one quarter to two inches in thickness. It is valueless as a structural material and is always removed soon after the tree is felled because it 135 136 MATERIALS OF CONSTRUCTION tends to hasten the decay of the wood. The sap wood is just inside of the bark and is made up of the soft thin-walled cells which form the living part of the tree. The heartwood, which is circular in shape and darker in color than the sapwood, is inside of the sapwood. The heartwood consists of many fibrous bundles which give the wood its strength and stiffness. The wood of the exogenous trees is made up of bundles of long cells and fibers whose long axes are usually parallel to the tree Bar* Heart Wood Sap Woo* Spring lTood(Ly/)V FIG. 73. Cross-section of a tree showing annual rings. trunk. These vertical bundles are crossed in a radial direction by plates of tissue or radial cells extending from the pith at the center of the tree to the soft tissue (sapwood) on the outside. These radial cells are called medullary rays and help to bind the longitudinal fibers more firmly together besides forming com- munications between the center of the tree and the outside. There are resin ducts scattered through the wood of the conifers and hollow ducts or vessels in the wood of the broad-leaved trees. The conifers are more uniform in structure than are the broad- leaved trees, whose structure is often very complex. 180. Growth of Exogenous Trees. The exogenous trees (coni- fers and broad-leaved trees) increase in size by the annual formation of new wood on the outer surface. The conifers can be recognized by their needle leaves, resinous bark, and cones, while the broad-leaved trees can be distinguished by their broad flaring leaves. An exogenous tree grows in diameter when new and branching bundles of hollow fibers appear under the bark and form an annular ring on the outer edge of the sapwood. This happens once during each growing season, which extends through the spring and summer. The growth is more rapid in the spring than in the summer and this variation in growth causes a differ- ent appearance in the wood fibers, the summer wood usually being darker in color and denser than the spring wood. This TIMBER 137 makes the cross-section of the tree look like a number of con- centric circular rings, each ring representing a year's growth. The age of a tree can be determined by counting the number of annular rings. The thickness of an annular ring varies from 0.01 to 0.5 in., with an average of about 0.10 to 0.15 in. The last few rings form the sapwood which is light in color and usually from H to 4 in. thick. The rings inside the sapwood form the heartwood which contains from 25 to 85 per cent of the wood of the tree, according to the kind of tree and the conditions of growth. The time required for the sapwood to change to heartwood varies from a few years in the fir to many years in the oak. The exogenous trees grow in length because each annular layer extends over the others, thus increasing the length. Be- cause of the conical shape of the tip, the increase in length may be much greater than the increase in diameter. Knots in a tree are caused by the encasement of a limb by the successive annual layers of wood. When a board is sawed- out of a tree, the knot is the portion of the branch contained in the board, and the fibers of the knot are usually about perpendicular to the other fibers in the board. A loose knot is one that is. loose or badly cracked or checked so as not to be solid in the board, and it is usually composed of dead wood. A sound knot is one that is solid and contains no appreciable cracks or checks. It is usually composed of living wood. 181. Structure and Growth of Endogenous Trees. These trees are largely confined to the tropical regions, and the palms and bamboo are about the only ones of structural importance. The wood elements of endogenous trees are similar to those of exogenous trees but their arrangement is different. The fibrous bundles do not form concentric circles around the center of the tree, but are scattered throughout the wood where they curve inward and outward among each other thus making a more complex structure. Endogenous trees increase in diameter and length by the intermingling of new wood fibers with the old. The growth of the fibers is apt to be more rapid in the outer part of the stem, thus causing the outer part to be more dense and solid than the inner. When the growth is very rapid, a hollow is formed in the center of the stem, because of the insufficient growth and the rupture of the inner fibers. Knots or joints are often found 138 MATERIALS OF CONSTRUCTION at the places where leaves have issued. The bamboos have hollow centers, while the palms and yuccas have pithy centers. 182. Grain and Texture of Wood. Depending on the charac- ter and arrangement of wood elements, the width of growth (a) Straight grain. (&) Cross grain. (c) Twisted grain. FIG. 74. Showing the grain of wood. rings, etc., wood may be described as fine or coarse grained, straight or twisted or cross grained, curly, " bird's-eye," or mottled grained, etc. Woods are fine grained if their growth rings are narrow, and coarse grained if their growth rings are wide. Woods may be said to be rough or smooth grained according to the appearance of the surface. They are straight grained if the fibers are straight and parallel to the axis of the tree; twisted if the fibers follow a spiral course around the tree; cross grained if the fibers change direction during the growth; curly grained if the fibers tend to form short curves or curls (as in curly birch); mottled if the appearance has a mottled effect. " Bird's-eye" is probably due to the layer of wood next to the bark becoming pitted or marked by small projections, probably caused by the presence of undeveloped buds as in " bird's-eye" maple. Woods may be said to have coarse or fine texture if the ele- ments are large or small. The texture is even if the fibers are all of about the same size, and uneven if the size varies. 183. Color and Odor of Wood. Color helps in identifying the species of wood. Most new wood is almost colorless but becomes yellowed after a few years and usually deepens in color when the sapwood changes to heartwood. The color may be variable or uniform throughout the heartwood and may be TIMBER 139 lighter or darker according to the species and the manner of growth. Deep color is nearly always due to the infiltration of resins, pigments, tannins, etc. into the heartwood. jUl woods darken more or less when exposed for a time to air or immersed in water. Hence, the natural color can only be observed in newly cut wood. Color aids in distinguishing the heartwood from the sapwood, as the heartwood is nearly always darker than the sapwood. All woods possess a characteristic odor, though in some cases it is not readily distinguished. The odor is due to foreign chemical compounds in the wood and is usually more pronounced in heartwood than in sapwood. The odors of green wood, seasoned timbers, and decaying wood are different in different species and aid in identifying the different species. A few of the woods lose most of their odor when they are seasoned. 184. General Characteristics of Conifers Pine, Fir, Spruce. White Pine. Light, soft, straight grained, easily worked, but not very strong. Light yellowish brown color often tinged slightly with red. Used for pattern making and interior finishing. Red Pine (Norway Pine). Light, hard, coarse grained, com- pact, with few resin pockets. Light-red color with a yellow or white sapwood. Used for all purposes of construction. Yellow Pine (Long Leaf). Heavy, hard, strong, tough, coarse grained, and very durable when dry and well ventilated. Cells are dark colored and very resinous. Color, light yellowish-red or orange. Cannot be used in contact with the ground, as it then decays rapidly. Used for heavy framing timbers and floors. Yellow Pine (Short Leaf). Varies greatly in the amount of sap and quality. Cells are broad and resinous with numerous large resin ducts. Medullary rays well marked. Color, orange with white sapwood. Used as a substitute for long leaf pine. Douglas Fir (Oregon Fir). Hard and strong but varying greatly with age, conditions of growth, and amount of sap. Durable but difficult to work. There are two varieties, red and yellow, of which the red is the more valuable. Color, light red to yellow with a white sapwood. Used in all kinds of construction. Black Spruce. Light, soft, close grained, straight grained, and satiny. Color, light red and often nearly white. Resists decay and the destructive action of Crustacea. Used for piles, framing timbers, submerged cribs, and cofferdams. 140 MATERIALS OF CONSTRUCTION White Spruce. Similar to black spruce, but it is not so com- mon. Light-yellow in color with an indistinct sapwood. Used for lumber in construction work. 185. General Characteristics of Conifers Other Species. Hemlock. Soft, light brittle, easily splits. Is not durable, is likely to be shaky, and has a coarse uneven grain. Light brown color tinged with red, and often nearly white. Resistant to attacks of ants. Used for cheap, rough, framing timber and some finishing lumber. White Cedar. Soft, light, fine grained, and very durable in contact with the soil. Lacks strength and toughness. Light- brown color which darkens with exposure. Sapwood is very thin and nearly white. Used for water tanks, shingles, posts, fencing, cooperage, and boat building. Red Cedar. Strong pungent odor, repellant to insects. Very durable and -compact, brittle, but easily worked. Color, dull- brown tinged with red. Used for posts, sills, ties, fencing, shingles, and linings for chests, trunks, and closets. Tamarack (Larch). Hard, heavy, strong, durable. Like spruce in structure and hard pine in weight and appearance. Used for posts, poles, sills, ties, and ship timbers. Cypress. Very durable, light, hard, close grained, brittle, easily worked, and polishes easily. Color, bright clear yellow with a nearly white sapwood. Used for house siding, building lumber, poles, interior finishing, etc. Resists dampness and excessive heat. Redwood (California or Giant) . Light, soft, weak, and brittle. Grain is coarse, even, and straight. Easily split and worked. Durable when in contact with the soil. Shrinks lengthwise as well as crosswise. Color, bright clear red becoming darker with exposure. Used for ties, posts, poles, and as a general building material. 186. General Characteristic of Broad-leaved Trees Oak, Maple, Ash, Walnut. White Oak. Heavy, strong, hard, tough, and close grained. Checks if not carefully seasoned. Well- known silver grain. Capable of taking a high polish. Color, brown with lighter sapwood. Used for framed structures, shipbuilding, interior finish, carriage, and furniture making. Chestnut Oak. A species of white oak. Very durable in contact with the soil. Dark-brown color. Used for ties. TIMBER 141 Live Oak. Very heavy, hard, tough, and strong. Hard to work. Color, light-brown or yellow with a nearly white sap wood. Used in shipbuilding and wagon work. Red and Black Oak. More porous than white oak and softer and less strong. Color, darker and redder than white oak. Used for furniture and interior finish. Hard Maple. Heavy, hard, strong, tough, and coarse grained. Medullary rays are small but distinct. EaSy t& polish. Color, very light-brown to yellow. Used for flooring, interior finish, and furniture. White Maple. About the same as hard maple except that it is lighter in weight and color. Same uses. White Ash. Heavy, hard, very elastic, coarse grained, and compact. Tends to become decayed and brittle after a few years. Reddish brown color with a nearly white sapwood. Used for interior finish and cabinet work. Unfit for structural work. Red Ash. Heavy, compact, and coarse grained but brittle. Color, rich-brown, with sapwood a light-brown sometimes streaked with yellow. Used as a substitute for the more valuable white ash. Green Ash. Heavy, brittle, hard, and coarse grained. Color, brown with lighter sapwood. Used as a substitute for white ash. White Walnut (Butternut). Light, soft, coarse grained, com- pact, and easily worked. Polishes well. Color, light-brown turning dark on exposure. Used for interior finish and cabinet work. Black Walnut. Hard, heavy, strong, and coarse grained. Checks if not carefully seasoned. Easily worked. Rich dark- brown color with a light sapwood. Used for interior finish and furniture. 187. General Characteristics of Broad -leaved Trees Other Species. White Elm. Heavy, hard, strong, tough, and very close grained. Difficult to split and shape. Warps badly in drying. Takes a high polish. Color, light-clear-brown often tinged with red and gray, with a broad whitish sapwood. Used for building cars, wagons, boats, and ships. Used for sills, bridge timbers, ties, furniture, and barrel staves. Hickory. Heaviest, hardest, toughest, and strongest of the American woods. Very flexible. Medullary rays numerous and distinct. Brown in color with a valuble white thin sapwood. 142 MATERIALS OF CONSTRUCTION Used for carriages, handles, and bent wood instruments. Not used for structural purposes on account of its hardness and liability to attack by boring insects. Locust. Heavy, hard, strong, and close grained. Very durable in contact with the ground. Hardness increases with age. Color, brown (and rarely light-green) with yellow sap wood. Used for ties, vehicles, posts, and turned ornaments. Gum. Heavy, hard, tough, and close grained. Shrinks and warps badly in seasoning. Not durable when exposed to weather. Takes a high polish. Color, bright-brown tinged with red. Used for furniture, hat blocks, wagon hubs, interior finish. Mahogany. Strong, durable, and flexible when green, and brittle when dry. Free from shakes. Not very liable to attacks of dry rot and worms. Peculiarly marked by short straight lines or dashes. Rapid seasoning causes deep shakes. Color, red-brown of various shades and often varied and mottled. Used for interior finish, furniture, veneers, etc. Chestnut. Light, moderately soft, stiff, and of coarse texture. Shrinks and checks considerably when drying. Easily worked. Durable when exposed to the weather. The heartwood is dark and the sapwood light-brown in color. Used for cabinet work, cooperage, ties, telegraph poles, and exposed heavy construction. Poplar (Whitewood). Soft, very close and straight grained, brittle. Shrinks excessively in drying. Warps and twists very much but does not split when dry. Easily worked. Light- yellow to white color. Used for vehicles, wooden instruments, toys, furniture, finishing, etc. Lignum-VitcB. Very hard, heavy, resinous, has a soapy feeling, and is difficult to split and work. Color, rich yellow-brown varying to almost black. Used for small turned articles, tool handles, and sheaves of block pulleys. Teak. Tropical wood, durable, heavy, hard, elastic, strong, and easy to work. When seasoned it does not rack, split, shrink, or alter in shape. Aromatic odor. Heartwood is golden- brown in color, seasoning into brown. The sapwood is white. Used in temples, ships, buildings, and for structural timbers. Can be used in contact with iron. Catalpa. Light weight, soft, weak, elastic, and durable in contact with the soil. Used for ties, posts, cabinet work, and interior finishing. Eucalyptus. Very hard, heavy, strong, tough, and close TIMBER 143 grained. Hard to split after it is dried. Not durable in contact with the soil. Resembles ash and hickory in appearance. Resists attacks of marine borers. Used for wharf piling, lumber, parts of vehicles, furniture, flooring, paving, etc. Beech. Hard, heavy, strong, and tough. Not durable when exposed. Subject to attack by insects. Liable to check in seasoning. Takes a high polish. Color, white to light-brown or reddish. Used for furniture, interior finish, ship building, and carriage making. 188. General Characteristics of Some Endogenous Trees. Palmetto. Lightweight. Difficult to work when dry. Very durable under water as it resists attacks by the Teredo and borers. Color, light-brown with dark-colored fibers. Used for piles and wharves. Bamboo. Hollow stem with many joints. Many branches, usually small ones. Used for timbers, columns, masts, poles, rafters, water pipes, furniture, split bamboo work, etc. B. PREPARING THE TIMBER 189. Logging. Logging may be said to be the process of felling the trees, trimming off the branches and vegetation, cutting the trunks and limbs to proper sizes, and transporting the logs to the sawmill. The trees are felled by means of axes or saws and are then chopped or sawn into sizes small enough to be transported to the sawmill. The methods of transportation vary according to conditions. If the sawmill is quite close to the forest, the logs may be rolled downhill, placed on sleds drawn by horses, pulled by a donkey engine and windlass, drawn by automobiles, carried by an aerial tramway, floated down small streams, or carried by a narrow-gage logging railway to the mill. If the sawmill is some distance away, the logs may be transported by railway or assembled in rafts and floated on a river or other waterway to the mill. It is important to choose the proper time for cutting the timber. In the spring and late summer, the sapwood contains an abun- dance of moisture with starches, sugars, and oils in solution, all of which tend to hasten the decay of the timber. In the drier summer months and in the winter, the growing and conducting cells of the tree are less active or altogether dormant, and the best wood is secured if the timber is cut during those seasons. Oak is 144 MATERIALS OF CONSTRUCTION claimed to be more durable if it is cut just after the leaves have fallen. Hewn lumber is thought to be more durable than sawn lumber. Usually, most of the logging operations are carried on during the winter months. 190. Sawing the Lumber. Most of the sawing of lumber is done in sawmills by machine driven rotary or band saws. The manner in which a stick of lumber is sawed from the log has a (a) Flat Sawed (&) Quarter Sawed (c) Quarter Sawed FIG. 75. Methods of sawing lumber. remarkable influence on its qualities and behavior. The kind of sawing is determined by the character of the wood and the purpose for which it is to be used. The two main classes of sawing are flat and rift sawing. Flat sawing consists in cutting the timber tangential to the annular rings. Rift (or quarter) sawing is cutting the boards out of the log in such a manner that the annular rings are cut through as nearly as possible in a radial direction. Quarter sawing is done for the sake of the beauty of the grain thus obtained, as well as to expose the edge of the hard bands of the summer wood. Flat sawing and rift sawing give rise, in the lumber trade, to the terms flat grain and edge grain respectively. Edge grain lum- ber does not sliver, shrinks and checks less, and wears more evenly and smoothly than the flat grain lumber. Ordinary, or bastard, sawing consists of cutting the log into a number of parallel slices and then trimming the edges of these slices with a circular saw. In ordinary sawing, some of the boards will be flat sawn, some quarter sawn, and about half of them will be neither flat nor quarter sawn but a combination of these. 191. Classification of Lumber. All material sawn from logs for structural or other commercial purposes is called lumber. The larger sizes, such as beams, joists, etc., are called timbers, and these timbers are usually resawn in order to obtain the smaller sizes of lumber. Lumber is furnished in all sizes and dimensions such as are suitable for the work at hand. TIMBER 145 The term "resawed lumber" is applied to lumber sawed on all four sides. Rough edge or flitch is lumber sawn on two sides. Planed resawed lumber is called dressed lumber. Dressed planks and boards free from all defects are called clear. Such boards are produced in regular sizes J^ in. less in thickness than the sawed lumber, and ranging from % to 1% in. in thickness. Sawed timbers shall be sound, of standard size, square edged, and straight; and they shall be close grained and free from de- fects, such as injurious ring shakes and cross grain, unsound or loose knots, knots in groups, decay, or other defects that will materially impair the strength. Rough sawing to standard size shall mean that the timbers shall not be over Y in. scant from the actual size specified; for instance, a 12 by 12 timber shall not measure less than 11% by 11% in. Standard dressing shall mean that not more than y in. shall be allowed for dressing each surface; for instance, a 12 by 12 timber after being dressed on four sides shall not measure less than UK by 11^ in- The standard lengths are multiples of 2 ft., running from 10 to 24 ft. for boards, fencing, dimension, joists, and timbers. Longer or shorter lengths than those herein specified are special lengths. Special and fractional lengths shall be counted as of the next higher standard length. The standard widths for lumber shall be multiples of 1 in. All sizes 1 in. or less in thickness shall be counted as 1 in. thick. Flooring shall include pieces 1, 1J^, and 1J^ in. thick by 3 to 6 in. wide, excluding 1% by 6. Boards shall include all lumber less than lj^ in. thick and more than 6 in. wide. Plank shall include all sizes from 1J^ to under 6 in. in thickness by 6 in. or over in width. Scantling shall include all sizes exceeding 1^ in. and under 6 in. in thickness, and from 2 to under 6 in. in width. Dimension sizes shall include all sizes 6 in. and more in thick- ness by 6 in. and more in width. Stepping shall include all sizes from 1 to 2J^ in. in thickness by 7 in. and over in width. Rough edge, or flitch, shall include all sizes 1 in. and more in thickness by 8 in. and more in width, sawed on two sides only. 192. Defects in Lumber. The following defects are adopted 10 146 MATERIALS OF CONSTRUCTION as standard by the American Society for Testing Materials. The diameters of the knots and holes are average diameters. Knots. A sound knot is one which is solid across its face and which is as hard as the wood surrounding it ; it may be either red or black, and is so fixed by growth or position that it will retain its place in the piece of lumber. A loose knot is one not held firmly in place by growth or position. A pith knot is a sound knot with a pith hole not more than Y in. in diameter at the center. An encased knot is one which is surrounded wholly or in part by bark or pitch. Where the encasement is less than J-^ of an inch in width on both sides, not exceeding ^ the circumference of the knot, it shall be considered a sound knot. A rotten knot is one that is not so hard as the wood it is in. A pin knot is a sound knot not over % in. in diameter. A standard knot is a sound knot not over 1^ in. in diameter. A large knot is a sound knot more than 1J^ in. in diameter. A round knot is one which is oval or circular in form. A spike knot is one sawed in a lengthwise direction. Wane. Wane is bark, or the lack of wood from any cause, on edges of timbers. Pitch Pockets are openings between the grain of the wood con- taining more or less pitch or bark. These shall be classified as small, standard, and large pitch pockets. A standard pitch pocket is one not over % of an inch wide or 3 in. in length. A small pitch pocket is one not over ^ of an inch wide. A large pitch pocket is one over % of an inch wide, or more than 3 in. long. A Pitch Streak is a well defined accumulation of pitch at one point in the piece. When the pitch is not sufficient to develop a well defined streak, or where the fiber between grains (the coarse grained fiber, usually termed " spring wood") is not saturated with pitch, it shall not be considered a defect. Shakes are splits or checks in timbers which usually cause a separation of the wood between the annual rings. A ring shake is an opening between the annual rings. A through shake is one which extends between two faces of a timber. Rot, Dote, and Red Heart are forms of decay which may be evident either as a dark red discoloration not found in sound wood, or by the presence of white or red rotten spots, and shall be considered as defects. TIMBER 147 193. Natural Seasoning of Lumber. In the preparation of lumber for construction purposes, it is necessary to expel the sap and moisture from the pores of the wood by some natural or artificial means. This process is called seasoning. It has been found that the drier the timber, the less likely it is to shrink and decay. Natural air seasoning consists in exposing the planks and boards, after sawing, to a free circulation of air. The lumber is placed on skids in large square piles under shelter in a dry place, the layers being separated by three or four narrow strips or boards laid in the opposite direction. The lowest layer should be at least 2 ft. from the ground. At frequent intervals the decayed pieces should be removed and the lumber replied. The time required for thorough seasoning varies from 1 to 3 years, depend- ing upon the character of the wood, the purpose for which it is to be used, and its dimensions. Water seasoning is another type of natural seasoning which consists in immersing the lumber in water. The soluble sub- stances in the sap wood are removed, leaving a timber that is less liable to warp and crack. Water seasoning causes the heartwood to become brittle and lose its elasticity. In this method of seasoning, the timber is immersed for about 2 weeks and then removed and thoroughly dried with an excess of air. If im- mersed too long, the wood becomes brashy when exposed to the air. Water seasoning is not very much used. 194. Artificial Seasoning of Lumber. Artificial seasoning or kiln drying hastens the evaporation of the moisture and the removal of the sap, but it produces an inferior product because it causes a rapid drying of the surfaces and ends of the material and a slow or imperfect drying of the interior. This weakens both the strength and the elasticity of the wood. The timber is stacked in a drying kiln and exposed to a current of hot air, the temperature depending upon the kind of lumber and its dimensions. Sometimes vacuum pumps are used in connection with the heating. The temperature usually varies from about 100 degrees Fahrenheit for oak to about 200 degrees Fahrenheit for pine. The time required depends upon the thickness of the lumber. About 4 days are required for 1 in. pine, spruce, or cedar boards. Hard woods are usually dried in air from 3 to 6 months and then placed in the drying kiln from 6 to 10 days. 148 MATERIALS OF CONSTRUCTION When rapidly dried in a kiln, oak and other hard woods tend to become " case-hardened " as the outer parts dry and shrink before the interior parts have a chance to do the same. Thus there is a firm shell of dry, shrunken, and usually checked wood about the interior. When the interior drys, it tends to become checked along the medullary rays. Lumber that has been properly air dried will not case-harden when placed in a kiln. 195. Shrinkage of Lumber. When a short piece of wood fiber dries, it shrinks; its walls become much thinner and the cavity becomes greater, but the length of the fiber remains about the same. A thick-walled fiber shrinks more than a thin-walled one. As most of the fibers in a tree are parallel to its length, the length of a timber will not change appreciably, but the cross section will shrink when the timber is seasoned. The medullary rays have an effect on the shrinkage of the cross-section, the wood in the cross- section shrinking more at right angles to the rays than parallel to them, due to the fact that the rays themselves shrink in cross- section but not in length. Hence, the greatest shrinkage in lumber will take place tangentially to the annular rings, a little less shrinkage will take place in a direction radially to the annular rings, while the shrinkage in the longitudinal direction of the tree will be inappreciable. The shrinkage of the fibers tangen- tially to the annular rings is known as circumferential shrinkage. Some woods shrink much more unevenly than others. The harder timbers are more compact in structure, with thicker cell walls, and, therefore, produce the greatest shrinkage. Quarter-sawed lumber will shrink less than flat-sawed lumber. A combination of quarter and flat sawing will cause the lumber to shrink unevenly, thus causing a warped surface. Flat sawing produces lumber that checks and cracks to a greater extent in drying than rift sawed lumber does. If the outer fibers of a timber dry out much faster than the inner fibers do, the timber will tend to become checked and cracked. This tendency toward checking and cracking may be reduced by driving S-irons, etc. in the ends of the timbers. If a board shrinks unevenly, it will become warped. This may be due to the fibers on one side drying out faster than the ones on the other side, uneven drying, sawing in such a way that the shrinkage will be more in some directions than in others, or due to the structure of the board itself. The opposite effect to shrinkage is produced by the absorption TIMBER 149 of moisture, and precautions must be taken when applying timber to construction work to allow for this expansion, such as expan- sion joints in a wood-block pavement. A roadway 40 ft. wide (constructed of wood blocks) has been observed to expand 8 in. FIG. 76. Effects of shrinkage. FIG. 77. Formation of checks. (Bull. 10, U. S. For. Div.) (Bull. 10, U. S. For. Div.) The longitudinal shrinkage of timber is usually less than 1 per cent. The change in volume of the timber is due to the radial and tangential shrinkage, and expressed in percentages is approximately twice the figures given in the following table, as the shrinkage takes place in two directions in approximately equal amounts. The following are average values for shrinkage in width: PEH CENT SHRINKAGE 3 4 4 SHRINKAGE OF THE WIDTH OF WOOD KIND OF WOOD Light conifers (soft pines, spruce, cedar, cypress) . . . Heavy conifers (hard pine, tamarack) Honey locust, box elder, wood of old oaks Ash, elm, walnut, poplar, maple, beech, cherry, sycamore 5 Basswood, birch, chestnut, blue beech, young locust 6 Hickory, young oak (especially red oak) up to 10 C. DURABILITY AND DECAY OF LUMBER 196. Durability and Decay of Lumber in General. The life of timber depends upon the way in which it is felled, seasoned, and worked. The timber is subject, in both its growing and 150 MATERIALS OF CONSTRUCTION converted states, to decomposition and attack by animal and vegetable life. Trees should be felled when the growing and conducting cells are less active or are dormant. Seasoning increases the life of timber by removing the sap and moisture. In structural work the timber should be protected as much as possible from the attack of agencies that cause decay. The agencies which produce the decay of wood are: alternate moisture and dryness, heat and confined air, bacteria and fungi, insects and worms. Well seasoned wood in a uniform state of moisture or dryness and well ventilated should never decay. Timber that is kept constantly immersed in water may soften or weaken but it will not decay. Elm, elder, oak, and birch possess great durability when kept constantly immersed. Dryness and ventilation are the best preventives of the decay of timber used for construction purposes. Wood that has been kept dry has been known to last for hundreds of years, though it finally became brittle and lost most of its strength. In construc- tion work it is important that timber be kept completely im- mersed in water or else kept in a fairly dry condition and well ventilated. Water should be prevented from collecting in the joints, and important structural timbers should be protected from weather conditions when practical. 197. Dry Rot in Lumber. Dry rot is directly caused by the fermentation and breaking down of the chemical compounds of the wood, due to the introduction of a certain fungus in the presence of a little moisture. These lower organisms excrete ferments which dissolve out parts of the cell walls, thus causing a crumbling of the wood. The growth of this fungus is stimulated by moderate warmth, presence of dampness, and lack of venti- lation. Dry rot is often found in ill-ventilated places, such as the wall pockets at the ends of floor timbers, and in the core of timber columns in mill construction. The decomposition is often hastened by the use of unseasoned wood. Dry rot is indicated by a swelling of the timber and a change in the color, the wood gradually becoming covered with mold and emitting a musty odor. Sometimes reddish or yellowish spots appear on the timber, and the fibers are gradually reduced to a powder. Dry rot is especially dangerous as it destroys the timber in which it originates and also tends to spread to adjacent woodwork. It is difficult to eradicate, when it is once estab- lished, the only remedy being to remove all of the fungus and TIMBER 151 disinfect the wood. Actual contact is not necessary for the spreading of dry rot. 198. Wet and Common Rot. Wet rot appears only when the wood is kept damp or is subject to alternate dryness and moisture. It will not take place if the wood is thoroughly seasoned and the further absorption of moisture prevented. The decay is caused by the moisture which dissolves out the substance of the cell walls of the sap wood. Wet rot spreads by actual contact only. Wood cut in the spring and early fall is especially subject to wet rot. The remedy is to remove ah 1 of the rotten parts of the timber and keep the remainder dry and well ventilated. Common rot is shown by the presence of external yellow spots on the ends of timber sticks and often by a yellowish dust in the checks and cracks, especially where the timbers are in contact with each other. The cause of common rot is improper seasoning in badly ventilated sheds. 199. Injurious Insects. The larvae of many insects are de- structive to wood. The living trees are attacked by some, and the felled trees and lumber by others. Some of the common insects attacking the wood of living trees are the oak and chestnut timber worms, locust borers, carpenter worms, ambrosia beetles, turpentine beetles and borers, and the white pine weavil. Round timbers with the bark on are subject to attack by the insects mentioned above, and especially 'by the round-headed borers, timber worms, and ambrosia beetles. Seasoned and finished hardwood lumber is especially subject to attack by powder post beetles. Construction timbers are often seriously injured by wood boring larvae, termites, black ants, carpenter bees, and powder post beetles. The damage is caused by the insects, or their larvae, eating or " boring" holes in the timbers, thus breaking the continuity of the fibers and reducing the cross-sectional areas. 200. Marine Wood Borers. The Teredo or ship worm belongs to the mollusk species and is the marine borer which is the most active, and destructive to wood. It bores its way in lumber usually in a direction parallel to the grain and lines the hole with a calcareous deposit as it progresses. These worms vary much in size, some of the largest being about half an inch in diameter and 4 or 5 ft. long. They live in clear salt water, preferably of 152 MATERIALS OF CONSTRUCTION the warmer climates, and are more active near calcareous shores. They work from the ground up to the half -tide level. The lycoris fucata is a little worm with many legs something like a centipede. It crawls up the piles or timbers inhabited by the Teredo, enters the hole, finds and eats the Teredo, and then lives in the hole. The xylotrya also belongs to the mollusk species, and is similar to the Teredo in structure and mode of life. The limnora, or gribble, is a small crustacean resembling a wood louse and is about the size of a grain of rice. It can swim, crawl, and jump. Both air and water are required for its existence; consequently, its attacks on wood are confined to a space between the high- and low-water marks. It devours the wood at the rate of 1 to 3 in. a year, and is found in both warm and cold water. D. PROPERTIES OF TIMBER 201. Strength of Timber in General. The mechanical proper- ties of wood are very variable, not only between different kinds of trees, but between trees of the same kind, and even between specimens cut from different parts of the same tree. In estimat- ing the properties of timber the following things should be con- sidered correct identification of the species and variety, age and rate of growth of the trees, position of test specimen in the tree, moisture content, and freedom of test specimens and commercial timbers from defects. In general, the results of tests have shown that: The influence of defects is very marked. Defects tend to lower the ultimate strength. Knots and cross grains lower the elastic limit. Tests on small specimens usually give results that are at least 50 per cent greater than the results obtained from tests on large specimens. Large checks and seasoning cracks weaken the wood. In general, the strength of wood varies with the specific gravity. Timber treated with creosote, tannin, zinc chloride, etc. is usually weaker than untreated timber. Dry timber is much stronger (about 75 per cent) than wet or green timber. TIMBER 153 The strength parallel to the grain is different than the strength perpendicular (across) to the grain. The strength of timber under any kind of a permanent load is only about one-half of the strength found by short time tests. Rapid loading in tests will give higher results than slow loading. In general, the larger the percentage of summer wood, the stronger the timber. In general, the strength of wood varies with the number of annular rings per inch. It must be remembered that the percentage of moisture is the greatest factor influencing the strength of timber; hence, the percentage of moisture in the specimens tested should always be given. 202. Influence of Moisture Content in Timber. Moisture has a very great influence upon the strength of timber, probably more than any other factor. The strength and weight of timber depend, to a large extent, upon the number of fibers per unit area of cross section; hence, the more fibers per unit area the heavier and stronger the wood. Absorption of moisture by the wood causes the fibers to swell in diameter and thus the number of fibers per unit cross sectional area are decreased and .the wood is not so strong. Further, moisture tends to weaken the cells and make them less firm and strong. Results of tests have shown that, in the seasoning of Southern pines from green wood (33 per cent of moisture) to dry wood (about 10 per cent of moisture), there were variations of over 75 per cent in the average strength, the strength increasing with the decrease in moisture. The strength decreases with increase in the moisture content up to the point where the cell walls become completely saturated. This limit is between 20 and 30 per cent for most woods. The addition of more moisture to the wood fills the cavities and causes no further swelling of the cell walls and has practically no effect upon the strength. The amount of moisture contained in ordinary dry lumber is about 15 per cent, and this value varies greatly with the tem- perature and weather. So-called "dry" wood usually has as much as 8 per cent of moisture, while green and wet woods con- tain over 30 per cent. It is practically impossible to obtain perfectly dry wood. Wood is said to be dry when it has been dried to a constant weight (the variation in weight for a period of 154 MATERIALS OF CONSTRUCTION 24 hours being less than ^ of 1 per cent) in an oven where the temperature was kept approximately at 212 degrees Fahrenheit. 203. Tensile Strength of Timber. The tensile strength of timber is not of much importance except as it is involved in transverse loading. In construction, timber is rarely ever sub- jected to pure tensile stresses, due to the difficulty of designing proper end fastenings. Failure in tension across the grain is due to the tearing or pulling apart of the wood fibers longitudinally. The tensile strength across the grain is only a small part (Jf Q ^ Mo) of the tensile strength parallel to the grain. Failure in tension along the grain is due to the transverse or oblique tearing apart of the wood fibers. That is, the fibers are rarely pulled in two, but they are usually pulled out from between the .others. Knots, cross grain, medullary rays, and other defects weaken the timber in tension. The proportional elastic limit of wood in tension along the grain is usually between 60 and 75 per cent of the ultimate strength. 204. Gompressive Strength of Timber. The compressive strength of timber is important as timbers are very frequently used as columns and compression members in various structures. In compression along the grain ; the fibers act like a number of hollow columns bound together. When failure occurs, the fibers tend to bend or buckle over each other and shear off. The compressive strength along the grain depends upon the density of the wood, the stiffness and continuity of the wood fibers, adhe- sion between the fibers, seasoning, moisture content, straightness of grain, and defects. The proportional elastic limit in compression along the grain is usually between 60 and 75 per cent of the ultimate strength. In compression across the grain the fibers fail by flattening. The strength depends primarily on the density of the wood, though many of the other factors have some influence. The strength across the grain is from % to Y of that along the grain. 205. Transverse Strength of Timber. The transverse strength of timber is important as timbers are often used as beams and joists in structural work. The strength of timber in cross bending depends largely upon the compressive, tensile, and shearing strengths. Consequently, TIMBER 155 the transverse strength of timber depends upon the same factors as the tensile and compressive strengths do. Timber beams rarely have a final failure in compression, though the initial failures are nearly always in compression. Final tension failures are quite common, especially if the beam is long compared with its thickness or if there are defects on the tension side. A large proportion of the failures occur by horizontal shear, especially if the beam is short and thick. The " elastic limit" in cross bending is usually between 66 per cent and 75 per cent of the ultimate strength. A load in excess of the elastic limit will cause a beam to break if left loaded. The modulus of elasticity in cross bending is a variable quantity because the load deflection curve is not a straight line, even as far as the elastic limit. The value of the modulus of elasticity in cross bending is about the same as that in compression. Stiffness is the ability of a beam to resist cross-bending loads without having large deflections. The transverse modulus of elasticity may be considered as a measure of the stiffness. Straight grained lumber is stiffer than knotty or cross-grained pieces, and dry wood is about one and a half times as stiff as green or wet wood. In general, the heavier the wood, the stronger and stiffer it is. 206. Shearing Strength of Timber. The resistance to shear across the grain is from four to ten times that along the grain. The shearing strength is less in wet woods than in dry woods, and it is reduced by defects, such as knots, checks, cracks, etc. The shearing strength along the grain is very small and depends upon the adhesion of the wood fibers to each other, the straight- ness of grain, the medullary rays, etc. The shear across the grain is approximately half of the compressive strength along the grain and depends upon the same factor. The shearing strength of timber is important, especially in beams. 207. Cleavability and Flexibility of Timber. Cleavability is the resistance of wood to splitting, as with an axe or other tool. Elastic woods split more easily than others, while woods with great hardness and transverse tensile strength are hard to split. Wood splits naturally along the two normal planes and a little more readily along the radius. The weight of the wood has but little effect on the cleavage. Defects, especially knots and cross grains, and the presence of moisture, increase the resistance of the wood to splitting. 156 MATERIALS OF CONSTRUCTION Flexibility is the ability of the wood to bend very much without breaking. Hard wood is usually more flexible than soft wood. Moisture softens the wood and makes it more flexible, while knots and other defects make it less flexible. 208. Hardness and Toughness of Timber. Hardness is usually measured by the penetration of a ball or a steel plunger under a load. The hardness is closely related to the shearing strength across the grain. Heavy wood is harder than light wood. Seasoning tends to increase, and moisture to decrease, the hardness. Placing the annular rings in a vertical position appears to help the wood to resist indentation. A tough wood is a wood that is strong and flexible and able to resist shocks and blows. Toughness is often measured in impact tests by finding the amount of work required to cause rupture. Wood which offers a high resistance to tension and longitudinal shear and which is capable of suffering a distortion of more than 3 per cent in tension and compression is usually tough. 209. Miscellaneous Properties of Timber. The approximate chemical composition of all woods when dry is nearly uniform, and consists, by weight, of the following elements: 49 percent carbon, 6 per cent hydrogen, 44 per cent oxygen, and 1 per cent ash. The weight per cubic foot for most dry woods varies between 25 and 60 Ib. A few woods are lighter and some are heavier than these values. Moisture increases the weight per cubic foot very considerably. The coefficient of linear expansion per degree Fahrenheit and for temperatures between 35 and 60 degrees Fahrenheit varies as follows: parallel to the fibers from 0.0000014 to 0.0000054; and perpendicular to the fibers, from 0.0000019 to 0.0000034. 210. Factors of Safety and Safe Working Loads for Timber. The factors of safety (and safe working stresses) vary according to the kind of stress and kind of loading and also according to the judgment of various engineers. In designing, only the net section of the dressed timber should be considered. The following factors of safety for variable loads are considered good practice: 10 for tension, 5 for compression with grain, 4 for compression across grain, 6 for extreme fiber stress in cross bending, 2 for modulus of elasticity in cross bending, and 4 for shear. For steady loads, these factors of safety may be decreased 33 per cent (corresponding to an increase of 50 per cent in the unit TIMBER 157 ' II II ec ec ic * co w O t CO O O O >O . 00 CO t 00 00 W t CO 1C T}* 00 Oi ^ l>- "3 "500 II )COO>C'C ** CO C Tf T}< *# CO "4* CO CO CO US C * 1C 1C 1C C C *< CO CO CO CO CO ^ CO *> 4> I- j :'--': '';'&', FIG. 86. Section of a green sand mold. tool. These molds give better castings than the green sand molds do and they require no patterns, but they are more expensive. Loam molds are generally used for large castings. These molds are built up of brickwork, and the surfaces are finished by plastering with loam. The whole must be thoroughly dried before using. Loam molds are the most expensive molds. Chills are metal molds used for certain castings, or are simply pieces of metal placed in other molds. This metal causes the molten iron that comes in contact with it to chill, or cool rapidly, and form a hard surface. In order to prevent an explosion, when the hot metal comes in contact with the cold, it is necessary to heat the chills to a temperature of about 350 degrees Fahren- heit before pouring the iron. These molds are used in making cast car wheels, chilled rolls, etc. 241. Pouring and Cleaning the Castings. When the mold is ready, molten pig iron is drawn from the cupola into a ladle and conveyed to the mold. The molder holds the ladle as close as he can to the pouring gate and then pours the molten iron into the mold. If it is a top pouring ladle, a bar is used to keep back the slag. The molder stops pouring when the metal appears at 184 MATERIALS OF CONSTRUCTION the top of the riser. Each mold must be filled in one operation, or planes of separation will be formed in the casting. When the castings have become solid, they are removed from the molds and allowed to cool. After the castings have cooled, they usually have to be cleaned of the sand that sticks to them. For small castings, a common method of cleaning is to place them in a tumbling barrel with some pieces of very hard iron. The barrel is rotated slowly and the tumbling about of the castings knocks the sand and scale off of their surfaces. A better method of cleaning is to pickle the castings by immers- ing them in a dilute solution of sulphuric or muriatic acid. The time required is about 12 hours in a 15 per cent solution. When the castings are removed from the pickling solution, they must be carefully washed in water to remove all traces of the acid. The sand blast is a very convenient way of cleaning the cast- ings, especially those which are large or which have irregular surfaces. The irregularities left by breaking off the gates, risers, etc. may be removed with a file, an emery wheel, or a cold chisel and hammer. Sometimes a pneumatic chipping tool can be economically used. 242. Defects in Castings. The most common defects in castings are: 1. Blow Holes. These are caused by the formation of steam when the hot metal comes in contact with the damp sand of the molds. 2. Sand Holes and Rough Surfaces. These are caused by the failure or breaking down of the molds in places. 3. Cracks. These are caused by unequal shrinkage in different parts of the casting when it cools. 4. Cold Shorts or Seams. These are caused by cooling the iron so quickly that it does not completely fill the molds. D. CONSTITUTION AND COMPOSITION OF CAST IRON 243. Constitution and Composition of Cast Iron in General. Cast iron usually contains from 90 to 96 per cent of iron; 2J^ to 4^2 per cent of carbon; 0.5 to 4.0 per cent of silicon; and small percentages of manganese, phosphorus, sulphur, and other chem- ical elements. CAST IRON 185 The most important element in cast iron, besides the iron, is carbon. It may be present as free carbon (graphite) or as combined carbon. Carbon combines with iron and forms cementite, Fe 3 C. This cementite may combine with free iron (ferrite) and form pearlite, which consists of about 6 parts of ferrite to 1 of cementite. Thus a cast iron may be composed of ferrite, graphite, cementite, and pearlite. Ferrite, or free iron, is soft, weak, and tough. Graphite is weak. Cementite contains 6.67 per cent of carbon combined with iron, that is, 1 part of carbon and 15 parts of iron. It has great strength, is very brittle, and is harder than the hardest steel. Pearlite is more ductile, less hard and less strong than cementite, but is stronger and harder than ferrite. If a section of ordinary cast iron is examined under the micro- scope, flakes of graphite will be found enmeshed in a matrix composed of ferrite, cementite, or pearlite, or combinations of these. The proportions of the four materials vary considerably in different cast irons, some cast irons containing practically no free carbon and others containing practically no combined carbon. When the cast iron is in a molten state, the carbon is in solution with the iron. Silicon and aluminum tend to decrease the amount of carbon that can be held in solution, while manganese and chromium increase the solubility. Slow cooling in the solidifying of cast iron allows the carbon to separate out and appear in the form of flakes (graphite). The presence of aluminum and silicon aid in this separation of the carbon and iron during the solidifying. Slow cooling tends to produce what is known as gray cast iron. If cast iron is cooled rapidly from the molten state, the carbon tends to stay combined with the iron (because it does not have time to separate out) and produce what is known as white cast iron. Chromium and manganese, when present, help to keep the carbon in the combined form. 244c Effect of Carbon in Cast Iron. Carbon has more effect on the properties of cast iron than any other element present, excepting the iron itself. Carbon usually varies in amount from 3 to 4 per cent. The properties of cast iron depend to a large extent on the amount of carbon present and also on the form that it is in, i.e., combined or free. Cast iron is usually classified according to the different form in 186 MATERIALS OF CONSTRUCTION which the carbon occurs. There are three different classes as follows : 1. White Cast Iron where the carbon is combined with the iron. 2. Gray Cast Iron where the carbon has separated from the iron and is present in the form of graphite. 3. Mottled Cast Iron a mixture of gray and white cast iron. The amount of combined carbon has a great influence on the properties of cast iron. This influence may be summarized briefly as follows: As the ratio of combined carbon to total carbon increases from zero to one: The name of the matrix changes from low-carbon steel to medium carbon steel, then to high-carbon steel, and then to white cast iron. The name of the cast iron as a whole changes from open gray or very graphitic cast iron to close gray cast iron, then to mottled cast iron, and then to white cast iron. The percentage of ferrite decreases while the percentage of cementite increases. The strength increases for a while (until the percentage of combined carbon is about 1.2 per cent) and then decreases. The hardness and brittleness increase, while the ductility decreases. The ability to resist shock (toughness) decreases rapidly. The ease of machining decreases. White cast iron consists essentially of cementite and pearlite and is harder and more brittle than gray cast iron. In gray cast iron, the amount of graphite varies from 2 to 4 per cent, while the amount of the combined carbon is less than 1^2 P er cent. Gray cast iron is composed of a mixture of ferrite, graphite, and cementite. This iron is softer, tougher, weaker, and less brittle than white cast iron. Mottled cast iron is a mixture of particles of white and gray cast irons and contains ferrite, graphite, cementite, and pearlite in various proportions. Its properties depend upon the relative amounts of gray and white cast iron. 245. Effect of Silicon, Sulphur, Phosphorus, and Manganese on Cast Iron. Ordinary cast iron contains, besides iron and carbon, four other chemical elements that are of importance, namely silicon, sulphur, phosphorus, and manganese. Cast iron also often contains very small percentages of other chemical elements such as aluminum, oxygen, nitrogen, copper, nickel, CAST IRON 187 tin, chromium, etc. These latter elements are not present in large enough quantities in ordinary cast iron to cause any noticeable effect upon its properties. Silicon. The amount of this element present usually varies from 0.5 to 4.0 per cent, and it aids in determining the suitability of the iron for various purposes. A little silicon, from 0.8 to 1.8 per cent, makes the iron soft and tough and gives the best strength results. More or less silicon tends to make the iron brittle and hard. About 3 per cent makes the carbon separate out in flake form (graphite). Silicon aids in foundry work by tending to increase the fluidity, eliminate the blow holes, and decrease the shrinkage when properly used. It reduces the chill in casting. Sulphur. This element helps to keep the carbon in the com- bined form and tends to make the iron hard, brittle, and weak. It also causes "red shortness;" i.e., makes the iron very brittle at a red heat. Such iron is not good for steel manufacture. In foundry work, sulphur reduces the fluidity and increases the chill. Good cast iron rarely contains more than 0.15 per cent of sulphur. Phosphorus. The fusibility and fluidity of the iron are increased by from 2 to 5 per cent of phosphorus, thus helping in the making of fine castings in the molds. From 1.0 to 1.5 per cent of phosphorus is often used for fluidity and softness, but more than 1.5 per cent tends to make the iron brittle and hard. For the best strength results, not over 0.55 per cent of phos- phorus should be present. Phosphorus tends to reduce the shrinkage and chill in castings. If the iron is to be used for steel making by the acid bessemer or open-hearth processes, the phosphorus content should be less than 0.07 per cent. Manganese. The amount of this element present may vary from to 80 per cent, but rarely exceeds 2 per cent in ordinary castings. Iron that is to be used for steel making should have some manganese present, as the manganese tends to prevent the absorption of sulphur in remelting and also helps to neutralize the silicon besides making the steel more workable. Less than 1.0 per cent of manganese has practically no effect on the iron, while about 1.5 per cent makes the iron fine grained and hard to tool. Foundry iron usually contains less than 1.0 per cent of manganese. Manganese increases the shrinkage, decreases the magnetism, and increases the solubility of carbon in iron. Speigeleisen is iron containing from 10 to 50 per cent 188 MATERIALS OF CONSTRUCTION of manganese. It is capable of taking a high polish and is very hard, resisting cutting by hard cast steel tools. If the iron contains more than 50 per cent of manganese, it is called ferromanganese. 246. Effect of Some Other Chemical Elements on Cast Iron. Many other elements are often found to some extent in cast iron in very small quantities, and these elements may have some effect on the properties of the iron. Copper. From 0.1 to 1.0 per cent closes the grain of cast iron, but does not appreciably cause brittleness. It makes the iron unsuitable for making malleable iron. Aluminum. From 0.2 to 1.0 per cent (added to the ladle in the form of a FeAl alloy) increases the softness and strength of white iron; added to gray iron, it softens and weakens it. About 0.1 per cent of aluminum has the same effect as 1.5 per cent of silicon. Aluminum is undesirable. Tin. Increases hardness and fusibility and decreases mallea- bility besides making the iron unfit for conversion into malleable cast iron. Vanadium. Very small quantities increase softness and ductility. As much as 0.15 per cent added to the ladle in the form of a ground FeVa alloy greatly increases the strength of cast iron. Vanadium also acts as a deoxidizer and as an alloying material. Titanium. Increases the strength, when added in small amounts, such as a 2 per cent or a 3 per cent TiFe alloy containing about 10 per cent of titanium. E. PHYSICAL AND MECHANICAL PROPERTIES AND USES OF CAST IRON 247. Strength of Cast Iron in General. In general, large castings are not so strong as small ones. The shape of a casting also affects the strength; sharp reentering angles cause planes of weakness in cooling, while curved surfaces are not so weakened. The design of the castings is of importance. The methods of founding also greatly influence the strength. For example, if a hollow column is cast in a horizontal position, the slag and foreign materials will tend to collect on the upper side and weaken that part of the column. Casting the column in a vertical position will cause the strength of all sides to be the same. As CAST IRON 189 noted in previous articles, the presence of different chemicals, especially carbon and its combinations, have a great influence on the strength and properties of cast iron. 248. Tensile Strength of Cast Iron. The combined carbon (for a total carbon content of about 4 per cent) in cast iron should be between 0.6 and 1.2 per cent to obtain the maximum tensile strength. The tensile strength of cast iron varies from 10,000 to 45,000 Ib. per square inch, but for ordinary castings it may be taken .001 .002 .003 .004 .Strain, Inches per Inch FIG. 87. Stress-strain diagrams for cast irons in tension. between 15,000 and 30,000 Ib. per square inch. The minimum specification requirements for gray iron castings are: 18,000 Ib. per square inch for lightweight castings; 21,000 Ib. per square inch for medium castings; and 24,000 Ib. per square inch for heavy castings. The stress-strain diagram for tension is a curved line which shows no well-defined elastic limit; but, if the elastic limit is considered as the unit stress at which permanent set takes place, cast iron may be said to have an elastic limit which varies from 30 to 60 per cent of the ultimate, according to the grade of the iron. The modulus of elasticity in tension is a variable quantity, depending upon the kind of iron and the unit stress at which it is computed. It will average about 14,000,000 Ib. per square inch with probable variations of 25 per cent or more. 190 MATERIALS OF CONSTRUCTION The percentage of elongation is very small, rarely exceeding 3 or 4 per cent for any grade of cast iron. The reduction of area is so small as to be inappreciable. The fracture of cast iron in tension is square across; that of gray cast iron being gray in color, highly crystalline in appearance, and showing flakes of free graphite, while the fracture of white cast . 90,000 .002 .OO4.0O6 .COO .OIO .OI2 .OK .OI6 .016 .020 -O2 .024 Strain, Inches per Inch FIG. 88. Stress-strain diagrams for cast irons in compression. iron has a white metallic color and a finely crystalline appearance. 249. Compressive Strength of Cast Iron. The compressive strength of cast iron depends upon about the same factors as the tensile strength. For the best results, the percentage of com- bined carbon should be a little more than that for tension, say from 1.0 to 1.2 per cent for a total carbon content of about 4.0 per cent. In compression, the strength of cast iron may be taken from 60,000 to 100,000 Ib. per square inch, though tests have shown variations from 45,000 to 200,000 Ib. per square inch, depending upon the kind of iron, structure, composition, size, etc. The stress-strain diagram for compression shows a fairly well defined yield point, varying from 35 to 60 per cent of the ultimate, depending on the grade of the iron. The modulus of elasticity in compression varies, according to the kind and grade of the iron and the unit stress at which it is computed, from 10,000,000 to 25,000,000 Ib. per square inch with an average of about 14,000,000 Ib. per square inch. When cast iron is stressed to failure in compression, the failure CAST IRON 191 is usually shear along a plane making approximately 55 degrees with the line of loading. 250. Transverse Strength of Cast Iron. At the present time the cross-bending strength of cast iron is the most important criterion of its quality, the tensile strength probably ranking second. The transverse strength is usually expressed by the term "modulus of rupture" and is computed by the formula S = Mv/I. An average value of the transverse strength of cast iron is about 35,000 or 40,000 Ib. per square inch, though tests have shown a variation of from 10,000 to 65,000 Ib. per square inch, depending on the grade of iron, the structure, method of founding, length of span, etc. The percentage of combined carbon for the greatest strength should be between the values for the highest strength in compression and tension. The minimum requirements for strength in transverse tests on the " arbitration test bar" over a 12-in. span are as follows: CENTER LOAD, MODULUS OP RUPTURE, CASTING POUNDS POUNDS PER SQUARE INCH Light castings 2,500 39,000 Medium castings 2,900 45,000 Heavy castings 3,300 52,000 The deflection at the center shall not be less than 0.10 in. The " arbitration test bar" is a bar 15 in. long and \Y in. in diameter, cast vertically in a green sand mold that is cold and thoroughly dry when the iron is poured. Two bars should be cast from each heat. The " modulus of shock resistance" of cast iron is equal to the product of one-half the center load and the deflection divided by the volume of the specimen between the supports. It is approxi- mately the same as the energy of rupture. The failure of cast iron in cross bending is a failure by tension on the tension side of the beam. The modulus of elasticity of cast iron in cross bending is about the same as that in tension and compression, averaging about 14,000,000 Ib. per square inch with large variations depending upon the grade and structure of the iron, etc. The modulus of elasticity in cross bending may be considered as a measure of the stiffness of the cast iron, or its ability to resist transverse loads without bending much. 192 MATERIALS OF CONSTRUCTION 251. Miscellaneous Properties of Cast Iron. The computed ultimate resistance to shear and torsion varies from 20,000 to 35,000 Ib. per square inch for cast iron. The fusibility of cast iron depends upon the percentage of carbon and some of the other elements. An average value is 2,500 degrees Fahrenheit. The coefficient of expansion is about 0.0000062 per degree Fahrenheit. The specific gravity of cast iron varies from 6.9 to 7.5. It is usually taken at 7.22, corresponding to a weight of 450 Ib. per cubic foot. In general, the specific gravity increases with the strength and the number of remeltings. The shrinkage of cast iron in cooling varies according to its shape and purity, varying from J^2 m> P er foot fo r large castings to % in. per foot for bars. Pure cast iron will shrink about %Q in. per foot of length. When dropped on a concrete or stone floor, white cast iron has a bright metallic ring, malleable cast iron a dull ring, and gray cast iron a "dead" sound. 252. Allowable Working Stresses for Cast Iron. Allowable unit working stresses for cast iron depend upon the character of the loads, grade of metal, and size of casting. Large castings are weaker than small ones due to shrinkage, nonuniformity of structure, and chance for defects. For variable loads, the allowable working stresses in tension are 3,000 Ib. per square inch; in compression, 16,000 Ib. per square inch; and in shear about 2,500 Ib. per square inch. Work- ing stresses for steady loads may be taken about 25 per cent greater than those for variable loads. For repetitive loads, changing alternately from tension to compression, the allowable unit working stress should not be over 1,000 Ib. per square inch. Cast iron is too brittle to be used to resist shocks or impact loads. 253. Uses of Cast Iron. For structural purposes, cast iron is not used to so large an extent as wrought iron and steel. Cast iron can be used for posts, columns, column bases and caps, bear- ing plates, etc. Cast iron is much used for parts of machines because it is cheap and can be cast in almost any form. In places where cast iron can be used, it suffers but little from competition by other metals. CAST IRON 193 F. MALLEABLE CAST IRON 254. Definition of Malleable Cast Iron. Malleable cast iron is annealed white cast iron in which the carbon has been sep- arated from the iron without forming flakes of graphite as in the gray cast iron. 255. Making the Castings for Malleable Cast Iron. White pig iron, containing not more than 0.60 per cent of manganese, not more than 0.22 per cent of phosphorus, and not more than 0.05 per cent of sulphur, is used in the manufacture of malleable cast iron. The total carbon content must be more than 2.75 per cent. The amount of silicon varies inversely with the size of the casting; heavy castings require about 1.0 per cent, and light castings about 2.0 per cent of silicon. Sometimes malleable scrap (never over 20 per cent), steel scrap (never over 10 per cent), or wrought-iron scrap (not over 5 per cent) is mixed with the pig iron. Malleable scrap is hard to melt, but it increases the strength of the castings. Steel scrap and wrought-iron scrap tend to make the castings stronger. The white pig iron, with the scrap, is melted in a cupola, an air furnace, or an open-hearth furnace; the air furnace being generally used. The molds are usually green sand molds. The molten white iron must be poured while it is very hot, and the pouring must be done very rapidly in order to secure good cast- ings. After cooling, the castings are cleaned by any ordinary foundry method, and the imperfect ones rejected. 256. Annealing the Castings for Malleable Cast Iron. The castings, which are to be annealed, are placed in annealing pots in such a way that they will not be deformed by any slight settle- ments. The annealing pots are made of cast iron, and are about 18 by 24 in. in cross section and from 15 to 48 in. high. Iron scale, Fe 2 O 3 , is packed in the pots and around the castings. Sometimes the slag squeezed from wrought-iron puddle balls, powdered hematite ore, or magnetite is used instead of the iron scale. This iron scale acts as a decarburizer. Excess space in the annealing pots may be filled with good clean silica sand. The annealing pots are placed in an oven and the temperature raised to a cherry red heat, about 1,450 degrees Fahrenheit, and held there from 3 to 5 days, depending on the size of the castings and the amount of decarburizing desired. Then the furnace is allowed to cool slowly for a few days before the castings are removed and cleaned. 13 194 MATERIALS OF CONSTRUCTION To test the quality of the annealing, test plugs or small pro- jections about ;Hj by % in. by 1 in. long are cast on the more important pieces. These are broken off and the fracture exam- ined. If properly annealed, the interior of the fracture should have a black velvety surface surrounded by a band of dark gray about He m - thick. This dark gray band should in turn be surrounded by a thin white band about ^4 in. thick. The effect of the annealing process is to change nearly all of the carbon from the combined form to a free amorphous form called " temper" carbon, to make the castings " malleable," and to about double their tensile strength. The decarburizer (packing of iron scale) prevents the oxidation and warping of the castings, and also extracts a large part of the carbon from the surfaces of the castings to a depth varying from He to Y% in. 257. Properties of Malleable Cast Iron. Structure. The outermost skin, which is white in color and about %4 in. thick, consists of ferrite with a few impurities. The dark-gray layer, from % to J/f e m - thick, consists of ferrite with a few scattered particles of temper carbon. This layer is much stronger and more ductile than the inner portion. The black interior consists of ferrite and many particles of temper carbon. The tensile strength is the best criterion of the quality of malleable cast iron. Its tensile strength is about 45,000 Ib. per square inch, with a yield point at about 70 per cent of the ulti- mate. The percentage of elongation varies from 2 to 7 per cent over a gage length of 2 in. The compressive strength of small prisms of good malleable iron (load applied parallel to skin) will vary from 100,000 to 150,000 Ib. per sq. in. The average transverse strength (modulus of rupture) is about 60,000 Ib. per square inch. Tests have given results varying from 54,000 to 90,000 Ib. per square inch for a 1 in. square bar over a span of 12 in. The deflection varied from J/ to 1% in. Malleable cast iron is quite tough, and is much more able to withstand shocks and blows than the cast iron from which it is made. Malleable castings can be bent when cold, and can be forged and welded to a greater or less extent. 258. Uses of Malleable Cast Iron. Malleable cast iron has no structural uses, but it is used very much in the manufacture of articles which are too complicated in form to be readily forged, CAST IRON 195 and which must be tougher and stronger than gray cast iron. Malleable cast iron has all of the advantages of gray cast iron, with respect to casting in various shapes, plus toughness, ductil- ity, and strength nearly equal to that of some steels. Only cast or forged steel can compete with malleable cast iron in many of its uses, and then the malleable cast iron is usually cheaper. Malleable cast iron is used in the manufacture of machinery parts, pipe fittings, small pinions, parts of railway rolling stock such as journal boxes, brake fittings, etc., and for various kinds of hardware, etc. CHAPTER XII WROUGHT IRON A. DEFINITION AND CLASSIFICATIONS 259. Definition of Wrought Iron. Wrought iron may be defined as nearly pure iron intermingled with more or less slag. The name "wrought iron" is applied to that commercial form of iron which is obtained by refining pig iron at a temperature not high enough to keep the metal in a molten state after the oxidation of the impurities, but just high enough to keep the iron in a pasty condition. Wrought iron is made in a reverberatory furnace. It is composed principally of pure iron (ferrite) and slag (iron silicate) together with small amounts of impurities. 260. Classifications of Wrought Iron. Wrought iron may be classified according to the method of manufacture, or according to its use. According to Method of Manufacture 1 . Charcoal Iron. Made by using charcoal fuel and a charcoal hearth. The purest grades of wrought iron are made by this method. 2. Puddled Iron. Made by the ordinary wet puddling process of manufacture. 3. Busheled Scrap. Made as described in Article 266. According to Use 1. Staybolt Iron. Made from puddled or charcoal iron. While not the strongest, it is the toughest and most ductile wrought iron. Good for forging and welding. 2. Engine-bolt Iron. Made from the same material as the staybolt iron. It is a little stronger but less tough and ductile. 3. Refined Bar Iron. Made from a mixture of muck bars and iron scrap. Less strong, ductile, tough, and forgeable than the engine-bolt iron. 4. Wrought Iron Plate. Class A. Made from puddled iron. A strong hard iron, but less ductile and tough than the best grades of wrought iron. 197 198 MATERIALS OF CONSTRUCTION 5. Wrought Iron Plate. Class B. Made from a mixture of puddled iron and scrap. Not so good as the class A plate. Neither class A nor class B plate should be used for forging or welding. B. MANUFACTURE OF WROUGHT IRON 261. The Materials for the Wet-puddling Process. Practi- cally all of the wrought iron manufactured at the present time is made from pig iron and various kinds of scrap by the puddling process. There are two kinds of puddling processes wet puddling and dry puddling. The latter process is rarely used. The pig iron commonly used in the manufacture of wrought iron is forge pig. This pig iron contains from 1.0 to 1.5 per cent of silicon, from 0.25 to 1.25 per cent of manganese, less than 1.00 per cent of phosphorus, and less than 0.10 per cent of sul- phur. A large amount of silicon is desired so as to form enough slag to cover the molten iron. The amount of manganese is not important as it is practically all removed in the manufacture. The phosphorus arid sulphur must be kept low as they are not completely removed. The " fettling" is composed of the strong basic iron oxides that are used to line the furnace hearth. Some of these fettling materials are basic slag from the puddling furnace or reheating furnace, hammer slag or scale from a rolling mill, and hematite ore. Enough fettling is used to cover the hearth to a depth of about 5 in. The fuel used is a bituminous coal that burns with a long flame. 262. The Furnace Used in the Wet-puddling Process. The furnace is of the reverberatory type and consists essentially of a puddling or working chamber (hearth), a grate or firebox at one end, and a stack at the other end. The furnace is made of masonry lined with firebrick. The outside is made of cast-iron plates fastened together with wrought-iron bolts. Iron castings support the hearth at some distance above the floor to allow for the circulation of air underneath. The hearth has a sloping roof which deflects the flame from the fire down upon the hearth. The working chamber is provided with openings for the purpose of charging and working the metal, and for the removal of the slag and the puddled iron. The fire grate has about one-third WROUGHT IRON 199 of the area of the hearth, and is separated from the hearth by a cast-iron air-cooled flue covered with a refractory material. Sometimes a steam jet is used to provide more air for the fuel and for the oxidation of the impurities. Dampers, etc. are provided for the regulation of the fire. The stack is connected with the hearth by suitable flue and draft openings, and is also provided with dampers to aid in the regulation of the fire. 263. Operation of the Furnace Used in the Wet-puddling Process. -The charge of the furnace consists of a large amount of fettling, which is uniformly compacted on the hearth, and about FIG. 89. Section of a puddling furnace. 500 lb. of gray forge iron placed on top of the fettling. After a melting temperature has been reached, the reduction of the impurities occurs in four different stages: 1. The " melting down" stage lasts about half an hour after the fire is started, by the end of which time the iron will have melted and nearly all of the silicon and the manganese together with part of the phosphorus and a little of the sulphur will have been oxidized. These oxides leave the metal and join the slag. 2. The " clearing" stage lasts about 10 minutes, and in this stage the remainder of the silicon and of the manganese is oxidized together with a further quantity of phosphorus and sulphur. At this time it is usually necessary to add more red oxide of iron to make the slag more basic, and also to reduce the temperature of the furnace somewhat so that the carbon will not be oxidized before the phosphorus and the sulphur. Vigorous stirring or "rabbling" at this stage tends to help the oxidation. 3. During the " boiling" stage practically all of the carbon and most of the remaining phosphorus and sulphur are oxidized. The iron oxide in the slag unites with the carbon in the pig iron, producing carbonic oxide and iron. The iron combines with the iron on the hearth, while the carbonic oxide gas rises and causes 200 MATERIALS OF CONSTRUCTION the molten metal to swell up and boil. When this gas comes through the surface of the bath, it burns in small flames of a light- blue color. The slag must be strongly basic in order to keep the phosphorus and sulphur in solution. During this stage the slag sometimes boils over the edge of the hearth and is caught and removed by means of a slag buggy. The puddler vigorously stirs or rabbles the charge to prevent the iron from oxidizing, to keep it from settling on the hearth, and also to secure a uniform product. Finally, the iron ceases to boil and " comes to nature 7 ' forming a spongy mass of metal which rests on the bed of slag. 4. During the " balling" stage, which occupies about 20 minutes, the temperature of the furnace is lowered and the FIG. 90. Showing principle of a merchant bar mill. pasty mass of iron is divided into portions small enough to be removed from the furnace by the puddler. Before removing the pasty iron from the furnace, the puddler works each portion into a ball, storing the balls under the protection of the fire bridge to prevent the oxidation of the iron before the balls are taken from the furnace. Each ball weighs about 100 Ib. 264. The Dry-puddling Process. In the dry-puddling process, white pig iron is charged to the furnace and subjected to the action of an oxidizing flame. In this process, the necessary oxygen is supplied by the furnace instead of by the fettling. 285. Mechanical Treatment of the Puddle Balls. Squeezing or Shingling. When the puddle balls are removed from the furnace, they contain much slag. This slag is removed to a large extent by squeezing the balls in a squeezer, which reduces the diameter of the balls about one-half. Sometimes a ball is placed under a steam hammer and the slag pounded or " shingled" out. The squeezing or shingling causes a rise in the temperature of the ball which tends to melt the slag and thus aid in its removal. WROUGHT IRON 201 Rolling Muck Bars. After the squeezing, the balls are taken to a rolling mill and rolled and cut into rectangular bars called "muck" bars. The rolling usually removes a little of the remaining slag. Reheating and Rerolling. The muck bars are piled, tied in bundles with wire, reheated to a welding heat, and rerolled in commercial shapes (merchant bars). Sometimes the operations of piling, tying, reheating, and rerolling are repeated several times, resulting in an improvement in the quality and an increase in the strength of the bars. Not much advantage is gained by reheating and rerolling more than three times. The shapes of the commercial bars are sheets, plates, strips, bars, round and square rods, angle irons, tee irons, channels, I-beams, Z-bars, etc. 266. Wrought Iron Made from Scrap. Sometimes wrought- iron scrap is tied together, heated, and rolled into commercial shapes. Another way is to make a box out of muck bars, fill it with scrap, heat it, and roll it. If the pieces of scrap are too small or too irregular to be tied together as muck bars are, they may be "busheled" together, placed in a small furnace, and treated as an ordinary puddle ball. All of these methods of making wrought iron from scrap result in an inferior product. If some steel scrap is heated with the muck bars, the resulting product will have many of the properties of soft steel. 267. Defects in Wrought Iron. The principal defects in wrought iron are rough edges, spilly places, blisters, and excess of slag. Rough edges are due to careless workmanship, imper- fect rolls, or red shortness. Spilly places are spongy or irregu- larly spotted parts, and are generally caused by imperfect puddling. Blisters are caused by the presence of gas, probably carbonic oxide, in the iron when it is being rolled. An excess of slag is due to imperfect or insufficient squeezing, forging, or rolling of the balls and bars. C. CONSTITUTION, PROPERTIES, AND USES OF WROUGHT IRON 268. Composition and Constitution of Wrought Iron. The following table gives the chemical composition of some kinds of wrought iron. From this table it is seen that wrought iron is nearly all pure iron with a little slag. The strength of wrought iron is affected to some extent by its chemical composition, an increase in the carbon content causing an increase in strength. 202 MATERIALS OF CONSTRUCTION CHEMICAL COMPOSITION OF WROUGHT IRON Chemical element Common wrought iron, per cent Best wrought iron, per cent Swedish wrought iron, per cent Carbon 05 to 10 06 050 Phosphorus 18 to 35 15 055 Sulphur . 04 to 06 0.03 0.007 Silicon Manganese 0.20 to 0.23 about . 10 0.20 0.06 0.015 0.006 Slag 2 . 80 to 3 . 10 2.80 0.610 Swedish wrought iron is a very pure wrought iron made in Sweden. The constituents of wrought iron are ferrite (pure iron), slag (silicates and phosphates of iron and manganese), and a little pearlite due to the presence of the carbon. The little carbon in wrought iron combines with some of the iron to form cementite, which in turn combines with ferrite to form pearlite. The size of the crystalline grains of ferrite in the wrought iron depends on the temperature from which the. hot iron is cooled, the length of time held at that temperature, the rate of cooling, the mechanical working during the cooling, and the temperature at which this working is stopped. High temperatures and slow cooling both tend to increase the size of the crystals. Mechanical working tends to overcome the bad effects of coarse crystals by breaking up the large crystals and retarding their formation and growth. 269. Tensile Strength of Wrought Iron. The tensile strength of wrought iron depends upon the direction of the load in regard to the grain or fibers of the wrought iron. The strength across the fibers is from 60 to 90 per cent of the strength along the fibers. In regard to the effect of the amount of reduction in size due to the rolling, tests have shown that, if the ratio of the finished size of bar to the size of pile of muck bars is kept constant, practically the same tensile properties are shown by all sizes of wrought-iron rods. The effect of previous straining or cold working on the tensile properties of wrought iron is to raise the elastic limit and ultimate strength and to decrease the elongation. Annealing removes the effect of overstrain and also tends to lower the elastic limit and ultimate strength of the original bar. WROUGHT IRON 203 The following values are average results from tensile tests on good grades of wrought iron: Elastic limit About 25,000 Ib. per square inch Yield point About 30,000 Ib. per square inch Ultimate strength About 50,000 Ib. per square inch Elongation in 8 in About 20 per cent Reduction in area About 30 per cent Modulus of elasticity About 27,000,000 Ib. per square inch 270. Compressive Strength of Wrought Iron. The compres- sive strength of wrought iron depends upon the same factors as the tensile strength. The values obtained in compression tests are about the same as those obtained in tension tests. The ultimate strength may be taken as varying from 45,000 to 60,000 Ib. per square inch, and the yield point from 25,000 to 35,000 Ib. per square inch. Overstraining a wrought-iron bar in tension will impair its properties in compression, and vice versa. 271. Shearing Strength of Wrought Iron. Wrought iron offers a greater resistance to shearing forces perpendicular to the fibers than it does to shearing forces parallel to the fibers. The following are general ranges of values for wrought iron in shear and torsion: POUNDS PER SQUARE INCH Ultimate shearing strength parallel to the fibers 20,000 to 35,000 Ultimate shearing strength across the fibers . . 30 , 000 to 45 , 000 Elastic limit in torsion 17,000 to 25,000 Ultimate strength in torsion 45,000 to 60, 000 Modulus of elasticity in torsion about 12,500,000 272. Transverse Strength of Wrought Iron. The transverse strength of wrought iron depends upon the same factors as do the tensile and compressive strengths. The results obtained in cross-bending tests are about the same as those obtained in ten- sion tests. The yield point may be taken as varying from 25,000 to 35,000 Ib. per square inch, and the ultimate strength from 40,000 to 60,000 Ib. per square inch. 273. Fracture of Wrought Iron. When good wrought iron is broken in tension or bending, the fracture is fibrous, and darker in color, more rough, and more jagged than that of mild steel. This is largely due to the presence of the slag in the iron. If the wrought iron is broken very suddenly, as by shocks, sudden blows, or impact, the fracture is more crystalline and granular in appearance. 204 MATERIALS OF CONSTRUCTION 274. Welding of Wrought Iron. Welding is one of the most important properties that wrought iron possesses. It is the joining together of two pieces of the iron by pressing or hammer- ing them while at a very high temperature, but which is not high enough to melt the iron. The ease with which wrought iron is 45,000 4O,OOO c 35,000 t_ 30,000 3 25,000 20,000 I5,OOO 10,000 .OCCK ,0004.00)6 .00 .(X 10 lost if Id Paint Typical Stress-strain Curve for Wrought Iron (Curve 11 is Portion A- 5 of I Enlarged) .Oolg .0014 LOOK [OOB LOoto Loot Oofa .02 .04 .06 .06 .10 .12 .14 .16 .\Q .20 .22 .24 26 Strain Inches per Inch FIG. 91. Typical stress-strain curve for high grade wrought iron in tension. welded is due to two things the absence of a large percentage of impurities such as carbon, silicon, and sulphur, and the ability of the wrought iron to remain in a plastic state (a white heat) through a considerable range of temperature. It is very difficult to make a good welded joint because of the formation of iron oxide (melted slag) at the joint. In order to remove as much as possible of this melted slag in the welding, the surfaces of the two pieces of iron that are to be brought together should be convex. The use of a flux, such as borax, in welding aids the work by making the slag more soluble and, therefore, easier to remove from the joint. Care should be taken not to leave the iron next to the joint in a brittle condition. This brittleness, which is caused by coarse crystals, may be remedied by working the wrought iron under a hammer or press until the critical range of tem- perature has been passed. The welding temperature in practice is about 2,400 degrees Fahrenheit, while the critical temperature is about 1,275 degrees Fahrenheit. WROUGHT IRON 205 The strength of welded joints varies from 30 to 90 per cent of the parts that have been joined. 275. Miscellaneous Properties of Wrought Iron. Wrought iron has the important properties of toughness, ductility, malle- ability, and weldability, but it cannot be tempered. The coefficient of expansion is about 0.0000065 per degree Fahrenheit. The melting temperature is about 2,800 degrees Fahrenheit. The specific heat is 0.0114. The average specific gravity is 7.7. Wrought iron containing much sulphur is "hot short" or "red short," that is, the iron is brittle and liable to break when worked at a red heat. Wrought iron containing much phosphorus is "cold short." It has low ductility when cold, breaks with a crystalline fracture, and is unable to resist impact stresses. 276. Tensile Strength and Ductility Requirements for Wrought Iron. The following requirements for tensile strength, elonga- tion, and reduction in area for the different grades of wrought iron were taken from the American Society for Testing Materials Specifications for Wrought Iron. WROUGHT IRON SPECIFICATION REQUIREMENTS Yield Ultimate Elonga- Reduc- Kind of iron point, pounds per strength, pounds per tion in 8 in., tion of area, square inch square inch per cent per cent Staybolt iron 29 , 400 to 49 , 000 to 30 48 31,800 53,000 Engine-bolt iron 30 000 to 50 , 000 to 25 40 32,400 54,000 Refined bar iron 25,000 48,000 22 Wrought-iron plate: 6 to 24 in. wide, Grade A. . . 26,000 49,000 16 6 to 24 in. wide, Grade B . . . 26,000 48,000 14 24 to 90 in. wide, Grade A. . . 26,000 48,000 12 24 to 90 in. wide, Grade B. . . 26,000 47,000 10 277. Working Stresses for Wrought Iron. It has 'been found that a stress in wrought iron in excess of the elastic limit causes a permanent set and raises the elastic limit. Repeated stresses 206 MATERIALS OF CONSTRUCTION above the elastic limit will cause a loss of strength and even failure if repeated a large number of times. Consequently, the working stresses for wrought iron should never exceed the elastic limit. The following values of the allowable unit working stresses are for an average grade of wrought iron and should be increased about 30 per cent for the very best grades. This table was taken from the "American Civil Engineer's Pocket Book." All values are given in pounds per square inch. UNIT WORKING STRESSES FOR AVERAGE WROUGHT IRON Kind of load Steady stress Variable stress Shocks and impact Tension . ... 14 , 000 10,000 4,000 Com pression 13 000 9,000 3,000 Shear 10,000 7,000 3,500 Torsion 5,000 3,500 1,500 Cross bending 12,500 8,500 3,500 278. Uses of Wrought Iron. Wrought iron is used for spikes, nails, bolts, nuts, wire, chains, chain rods, horseshoe bars, sheets, plates, staybolts, engine-bolts, pipes, tubing, third rails, arma- tures, electromagnets, and in the manufacture of crucible steel. Before 1890, wrought iron was used very much in bridge and structural-building work, but since that date structural steel has replaced it. Structural steel costs less than wrought iron and is about 20 per cent stronger. CHAPTER XIII STEEL A. DEFINITIONS AND CLASSIFICATIONS 279. Definitions of Steel. The Committee of the International Association for Testing Materials has proposed the following definition : Steel is iron which is aggregated from pasty particles without subsequent fusing; is malleable at least on some one range of temperature; and contains enough carbon (more than 0.30 per cent) to harden usefully on rapid cooling from above its critical temperature. The following definition proposed by Prof. H. M. Howe is, perhaps, better than the one given above. Steel is iron which is usefully malleable at least in some one range of temperature; and, in addition, either (a) is cast into an initially malleable mass; or (6) is capable of hardening greatly on sudden cooling; or (c) is both so cast and so capable of hardening. 280. Classifications of Steel. Steel may be classified according to method of manufacture, use, or carbon content. According to the method of manufacture, steel may be divided into cementation steel, crucible steel, acid Bessemer steel, basic Bessemer steel, acid open-hearth steel, basic open-hearth steel, duplex steel, electric steel, etc. According to its use, steel may be divided into the following classes; structural-rivet steel, structural steel, boiler-rivet steel, boiler-plate steel, machinery steel, rail steel, gun steel, axle steel, spring steel, tool steel, cable-wire steel, etc. Steel may also be classified into carbon or alloy (special) steels, depending on the chemical element which tends to control its strength. Carbon steels may be divided into soft, medium, hard, and very hard steel, according to the percentage of carbon present. Alloy or special steels include all other steels, except the carbon steels, and may be divided into many classes. The name of each class depends upon the name or names of the element or elements (other than iron or carbon) governing its distinctive properties. Some examples of alloy steels are: nickel 207 208 MATERIALS OF CONSTRUCTION steel, manganese steel, nickel-vanadium steel, vanadium steel, chrome steel, etc. For general classifications of iron and steel see Art. 233 and Art. 234. B. METHODS OF MANUFACTURE OF STEEL 281. The Cementation Process. The principle of this process is the absorption of the carbon by wrought iron at a high red heat and thus converting the wrought iron into steel. Alternate layers of charcoal and wrought-iron bars are packed in a " con verting pot" (made of a refractory stone or brick) so that the charcoal completely surrounds each bar. Several of these pots are placed in a furnace and the temperature gradually raised to about 1,250 degrees Fahrenheit at the end of 3 days' time. The furnace is kept at this temperature from 7 to 12 days, depending on the carbon content desired in the steel. When the proper amount of carbon has been absorbed, the fires are drawn and the furnace allowed to cool slowly for about a week before the bars are removed. The presence of a little slag in the wrought-iron bars causes the formation of carbon monoxide gas which makes " blisters" on the surface of the bars, hence the name " blister steel" has been given to this product. On account of the cost and the length of time required, very little of this kind of steel is made at the present time. 282. The Crucible Process. The principle of this process is the absorption, by molten wrought iron, of the carbon in such quantities as to change the wrought iron into steel. About 80 Ib. of wrought iron with a little charcoal and manganese is placed in a closed crucible made of some refractory material. Several of these crucibles are placed in a furnace and subjected to an intense heat which melts the metal in 2 or 3 hours. The crucibles are then kept in the furnace for about half an hour longer until the metal is " killed" (has ceased to boil and evolve gases). After the "killing," the crucibles are removed from the furnace and the molten metal poured into ingot molds. The time required for a heat varies from 3 to 5 hours. As the cost of this kind of steel is quite high, it is used only in the manufacture of tools, cutlery, springs, projectiles, etc., where a steel of a high grade is required. STEEL 209 283. The Principle of the Bessemer Process and the Plant Equipment. The principle of the Bessemer process is the oxida- tion of the carbon and some of the other impurities by blowing a blast of cold air through a bath of molten pig iron in a converter. The essential parts of the plant are the blast furnaces or cupolas, mixers, converters, blowers and blowing engines, together with the necessary ladles, ingot molds, etc. The molten pig iron is brought from the blast furnaces or cupolas and stored in a mixer until it is time to charge the FIG. 92. Diagram of a Bessemer steel plant. converter. This mixer is a large steel reservoir lined with firebrick. It has a capacity of from 100 to 600 tons of molten pig iron and is used to keep the molten metal hot and also to allow the mixing of the iron from several blast furnaces so as to secure the desired grade of iron. The converter is a bucket-shaped vessel of steel with an eccentric conical snout. Its capacity varies from 15 to 30 tons of metal. The converter is lined with a refractory material and is supported on trunnions so that it can be tipped. The bottom is pierced with a large number of holes through which the air blast enters. On account of the fact that the lining in the bottom burns out faster than that of the sides, the bottom is made so that it is detachable and can be removed and have its lining renewed 14 210 MATERIALS OF CONSTRUCTION FIG. 93. Cross section of a mixer. FIG. 94. Section through Bessemer converter while blowing. (Stoughtori), STEEL 211 whenever necessary. The average life of the bottom is only about 25 heats. The lining of the converter is of a siliceous brick for the acid process, and of a basic material such as dolomite or limestone for the basic process. 284. The Acid Bessemer Process. About 15 or 20 tons of molten pig iron are brought in a ladle from the mixer and poured into the converter which is tilted to a horizontal position to receive the charge. Then the converter is rotated to a vertical position and the air blast turned on. This air blast, under a 4.00% J.00% 00% 1.00% 0% . C.( tr\ or T * ^ *x, N, \ \ \ \ V \ \ >^ . s ^ - - "'/ f \ s f ^ ^1 "^ ^ V ^ s* 9 ii e, \ '- ^ v 'v s^ \ *v ^ \ g 5 s> \ \ n \ \ ^ ^ nr -0 L % ^ ^^ ^0 ?v5~< - A \ ^ ">- ^ 1 V ~ , c t\ \ \ tp SN \ \ \ t ,^ ^ /tn \ \\ , ~ Jy> \ ^ \ \ J --, ~~ ^ ^>s, cV -^ Sr- / 3 4 567 Hours FIG. 100. Removal of impurities in basic open-hearth process. (Bradley Stoughton.) the phosphorus is oxidized and absorbed by 'the slag, while some of the manganese combines with some of the sulphur and is dissolved in the slag. The charge is tested from time to time by molding and fracturing a small test bar. When the elements are reduced to the proper percentages, the molten steel is drawn off in a ladle. After the slag is skimmed off and a recarburizer added, as in the basic bessemer process, the molten steel is poured into the ingot molds. The total time required to run a heat varies from 8 to 12 hours. The steel scrap used in this process has about the same composi- tion as the steel scrap used in the acid open-hearth process, except that the phosphorus and sulphur contents may be a little higher. The composition of the pig iron used is: less than 1.0 per cent of silicon, more than 1.0 per cent of manganese, from 1.0 to 2.5 per cent of phosphorus, from 0.02 to 0.30 per cent of sulphur, and from 2.5 to 3.5 per cent of carbon. STEEL 217 Open-hearth steel, like Bessemer steel, is used mostly for all kinds of structural purposes. 289. The Electric Process. The principle of this process is the same as that of the open-hearth process except that electricity, instead of gas and air, is used to produce the heat necessary for the oxidation of the impurities. In the electric process, no oxygen is required to supply the heat. This is an advantage over all other processes. The electric furnace is very efficient Hcxrfh Z//7//2? FIG. 101. Section of a Heroult arc type electric furnace. in removing the sulphur and the oxygen from the steel, but it is less efficient in removing the phosphorus. There are three types of electric furnace: 1. Furnaces using an open arc between electrodes above the bath. The Stassano furnace is an example of this type. 2. Furnaces using an arc between the electrodes and the bath. The Giroud, Heroult, and Keller furnaces are examples of this kind. 3. Furnaces of the induction type in which the bath forms the secondary coil (or part of the coil) of a transformer. The Rochling-Rodenhauser and Kjellin furnaces are examples of this type. The power consumption of an electric furnace varies from 218 MATERIALS OF CONSTRUCTION 150 to 1,000 kilowatt-hours per ton of steel produced according to the type of furnace, kind of materials in the charge, and the tem- erature of the charge at the start. The time necessary for a heat varies from 2 to 5 hours, depending upon conditions. In the production of high quality steel, the electric furnace is a strong competitor of the crucible process, because it can produce larger quantities at a heat and at a slightly lower cost. The electric furnace has an advantage over all other furnaces in making special alloy steels, because it does not need to be operated under oxidizing conditions. However, the electric furnace cannot compete in cost with the bessemer and open-hearth processes in the production of steel of a medium or low quality. 290. The Duplex Process. This process is usually a combi- nation of the acid Bessemer and basic open-hearth processes. The molten pig iron is first placed in the Bessemer converter until the silicon, manganese, and most of the carbon are oxidized. Then the molten metal is removed from the converter and placed in a basic open-hearth furnace where the phosphorus and the remainder of the carbon are removed. The recarburizer is added to the steel in the ladle after the slag has been skimmed off, as in the basic open-hearth process. The total time required for a heat is about 6 or 8 hours. The advantages of the duplex process are: a low-grade pig iron with a high phosphorus content may be used; a steel is pro- duced that is better in quality than the Bessemer steel; the time required for a heat is about half the time required by the basic open-hearth process. Another kind of duplex process is where the preliminary refining of the steel is done in a Bessemer converter or an open- hearth furnace and the final refining in an electric furnace. This process gives a steel of a high quality and at a lower cost than when the electric process is used alone. 291. The Triplex Process. In this process the molten metal is taken from a mixer and placed in an acid Bessemer converter where the silicon, carbon, and manganese are nearly all removed. Then the molten metal is transferred to a basic open-hearth furnace where the phosphorus is removed and the steel recar- burized. After this, the molten steel is placed in an electric furnace for the final refining; that is, for the removal of the sulphur and the oxygen. The triplex process gives a very high-grade steel and is less expensive than the electric process. STEEL 292. Comparison of the Different Processes. 219 Quality Cost Length of time for one heat Total quantity produced 1. Electric 2 Triplex Crucible Electric Basic open-hearth Acid open-hearth Basic open-hearth 3 Crucible Triplex Triplex 4. Basic open-hearth 5. Acid open-hearth 6. Duplex (usual) 7. Basic Bessemer 8 Acid Bessemer Acid open-hearth Basic open-hearth Duplex (usual) Basic Bessemer Acid Bessemer Duplex (usual) Crucible Electric Basic Bessemer Acid open-hearth Crucible Duplex (usual) Electric Triplex C. COMPLETING THE MANUFACTURE OF THE STEEL 293. Casting the Ingots. Most of the steel is cast into ingots, which are about 7 ft. high, 18 in. square at the bottom, and about 15 in. square at the top. The ingot molds are placed on small flat cars that run on a track. At the proper time the molten steel is drawn from the furnace into a ladle which is a bucket shaped vessel of steel lined with a refractory material and having a valve at the bottom. The cars carrying the ingot molds are run under the ladle, and each mold is filled by means of the valve. The cars then pass under cranes that remove the molds from the ingots. The molds are washed with clay water to prevent the steel from sticking to them, and are used again. The ingots pass on to a "soaking pit" or a reheating furnace. The average life of an ingot mold is about 100 casts. 294. Defects in Ingots. When the ingots cool, they form a structure that is not very homogeneous as the metal on the outside cools first so that when the metal of the inside cools and shrinks, a cavity or pipe is formed inside the ingot and near its upper end. Oxides of phosphorus,sulphides of iron, and sulphides of manganese, together with some carbon, tend to segregate near the upper por- tion of the central part of the ingot. The gases and slag in the molten metal rise to the top of the ingot and form blowholes. Ingotism is the formation of large crystals of steel and is caused by slow cooling or by casting at too high a temperature. Piping and segregation may be overcome by a proper propor- tioning of the different elements, while the only remedy for blowholes is to cut off the top of the ingot. Careful rolling and forging will remove the bad effects of ingotism by reducing the size of the steel crystals. 220 MATERIALS OF CONSTRUCTION 295. Reheating the Ingots. For good working, it is necessary for the ingot to have the proper working temperature throughout. As the outside of the ingot cools more rapidly than the interior, it is necessary to place the ingot in a furnace where the outside of the ingot may be heated and kept at the proper temperature for working until the interior has solidified and cooled to that temperature. If the ingot becomes too cool during the working, it is necessary to stop and reheat it before going on with the working. The furnaces used for reheating purposes are of three types: the " soaking pit," the regenerative gas-fired pit furnace, and the billet heating furnace. The " soaking pit " is a pit in which the ingot is charged through the top and kept in a vertical position. The purpose of the soaking pit is to equalize the temperature of the ingot. No fuel is used, the interior of the hot ingots supplying the heat. The soaking pit is used. to equalize the temperature of the ingot before the working is commenced. The regenerative, gas-fired, pit furnace is a vertical furnace using gas for fuel. The ingot is charged through the top, and remains in the furnace until it is heated to the proper work- ing temperature. This furnace can be used for equalizing the temperature of the ingot and also for reheating the ingot when it cools during the working. The billet heating furnace is a horizontal gas-fired furnace in which the billets enter at the cool end of the furnace and are pushed through by means of a hydraulic ram, discharging from the hot end. This furnace is used for heating small pieces of steel either before or during the working. 296. Rolling. The rolling is done by rolling mills which consist essentially of two (two high) or three (three high) layers of smooth chilled cast-iron rollers of the desired form. Some- times a mill has a set of vertical rollers, placed just outside the horizontal ones, which keep the edges of the metal smooth but do not reduce it. Such a mill is called a universal mill. The ingot passes through the rolls many times (from 2 to 20) before emerging in the desired form, each passage through the rolls changing the shape of the steel somewhat. The action of the rollers compresses the metal under the rollers and also tends to produce longitudinal tension in the surface fibers of the steel. The speed of rolling is quite great, varying from a few miles per STEEL 221 hour for special shapes, to about 10 miles per hour for rails, and to as high as 30 miles per hour for rods. Too great a speed in rolling causes a heating of the steel, due to the rapid distortion. Rolling HM*ill FIG. 102. "Three High" I-beam roughing rolls. FIG. 103. "Three High" I-beam finishing rolls. mills produce plates, bars, structural steel shapes, rails, and rods. 297. Forging and Pressing. Forging steel is working it under a hammer until it is of the desired size and shape. Most of the hammers used at the present time are steam hammers, and they vary in size from a few hundred pounds up to 30 or 50 tons. Drop forgings are forgings made by using dies in connection with the steam hammer. The metal usually passes through a 222 MATERIALS OF CONSTRUCTION series of dies before becoming of the proper size, shape, and finish. Forging may also be done by using a hydraulic press instead of a steam hammer. With the hydraulic press the force is applied more slowly and acts for an appreciable length of time, while with a hammer the force is applied as a blow. Hydraulic presses vary in size from a few tons pressure up to 1,400 tons pressure or more. The mechanical treatment of an ingot, such as forging, pressing, drawing, or rolling, greatly improves the quality of the steel by solidifying the metal, reducing the blowholes, and increasing the FIG. 104. Rolling mills. (Illinois Steel Co.) strength and specific gravity. For the best results, the work should be done when the ingot has cooled to a low-red heat. Forging works the metal better, but it is more expensive and less rapid in operation than rolling. Much more steel is made by rolling than by forging. 298. Wire Drawing. In making wire, the steel is first rolled in rods and then these rods are drawn through holes in a plate. These holes vary in size from the diameter of the rod down to the diameter of the desired wire. Some thick lubricant is used to reduce friction and to prevent wear of the holes in the draw plate. The diameter of the rolled rods is usually from STEEL 223 H to M in- The sectional area of the rod is reduced about 20 or 25 per cent for each, hole that it is pulled through. Cold drawing makes the metal very hard, and it must be annealed to a low-red heat after it has been drawn from 3 to 10 times. The number of drawings through the holes depends upon the original diameter of the rod and the desired diameter of the wire, and may be as many as 20 or more. D. HEAT TREATMENT OF STEEL 299. Hardening of Steel. The heat treatment of steel by hardening, tempering, and annealing greatly influences its physical properties. Every steel has a certain "critical" tem- perature in the range of which important molecular changes occur in heating and cooling. In general, this range is from a low-yellow heat down to a dull-red heat. Steel is hardened by heating it up to this critical temperature, which is usually between 1,250 and 1,600 degrees Fahrenheit, and then retarding the molecular changes that occur in slow cooling by suddenly plunging the steel into molten lead, oil, water, ice water, or iced brine, etc., according to the degree of hardness desired. The hardness increases with the rate of cool- ing, and, in general, the cooler the quenching liquid, the harder the steel. The degree of hardening, as well as the critical tem- perature, also depends to some extent upon the amount of carbon, manganese, chromium, tungsten, and other elements present. 300. Tempering of Steel. As some hardened steels are too brittle to use, they must be tempered to reduce the hardness to some extent. "Tempering" is accomplished by heating the steel up to a temperature which is less than the critical tempera- ture, and then quenching it in some liquid as oil, water, etc. For most steels, the temperature for tempering varies from 425 to 600 degrees Fahrenheit. This temperature is indicated by the color of the film of oxide that forms on the surface of the steel. This color varies from a pale-yellow (about 425 degrees Fahrenheit) through straw, brown, purple, and blue to dark- blue (about 600 degrees Fahrenheit). Tempering the steel tends to increase its ultimate strength. 301. Annealing of Steel. Annealing consists of heating the steel up to a light red heat and then allowing it to cool very slowly for some (2 or 3) days. The usual annealing tempera- 224 MATERIALS OF CONSTRUCTION ture's are between 400 and 900 degrees Fahrenheit. If the size of grain is to be reduced much, the temperature must be raised slightly above the lower limit of the critical range of temperature. The heating must be done in such a way that the steel will not come in contact with the fuel and flames, and the pieces of steel must be supported so that they will not warp. Small pieces are often packed in charcoal in closed iron boxes. Annealing removes any overstrain caused by the cooling or by the working of the steel; reduces the size of the grains of the steel; makes the steel soft and ductile ; and reduces the elastic limit and ultimate strength. 302. Case Hardening of Steel. Case hardening is accom- plished by heating soft or medium steel in contact with carbon so that the carbon will penetrate the outer skin of the steel. The temperature required is about 1 ,650 degrees Fahrenheit. The time varies from 2 to 12 hours according to conditions. The penetration of the carbon is usually less than ^ in. Case hardening produces a high-carbon steel surface! which is hard and which will resist wear, abrasion, cutting, and indenta- tion, while the interior is left soft and tough and capable of resisting impact. Harveyized armor plate is made by case hardening the side of an armor plate of tough medium steel. E. STRUCTURE AND CONSTITUTION OF STEEL 303. Normal Constituents and Compounds. The normal constituents of iron and steel are ferrite (pure iron), cementite (Fe 3 C), and graphite (free amorphous carbon). These con- stituents appear in various forms and combinations when the iron or steel is in the solid and liquid forms, depending upon the amount of carbon, rate of cooling, presence of other elements, etc. Molten steel is a solution of liquid carbide of iron in liquid iron whose carbon content is less than about 2.0 per cent (some authorities claim 1.7 per cent and others 2.2 per cent). If the carbon content were over 2.0 per cent, the liquid solution would be called molten cast iron. When the carbon is less than 2.0 per cent, there is no separation of the constituents when the solution cools, i.e., it forms a " solid" solution. Steels are solid solutions. When a molten mixture cools, one constituent may solidify STEEL 225 before another, or before the solution freezes as a whole. If the proportioning of the parts is such that the freezing point of the solution is reached before that of any of its parts, it is called a "eutectic" solution, in the case of the cast irons, and a "eutec- CAST IRQ" 5 H,YPER- LIQUID SOLUTION N^ CEMENTITE D Freezing EUTECTIC ALLOY (SATURATED IAUSTENITE +CEMENTITE) Decomposing into Iron | and Graphite I AUSTENITE CEME NTrrd I EUTECTIC AUSTENITE CEMENTITE EUTECTIC (AUSTENITE I CEMENTITE l I I 1 I FtRRITt + CEMENTITE |(WMITECAST IRON3J I n FCRRITE + GRAPHITE I KRARE) | ;RRITE +PtARLITE + GRAPHITE (6RAY CAST PEARLITE PEARLITE ' ! I ! fe)|WiTh Hypo Eutectokj matrix. I (b^WiTh Hyper EuTecToid JmaTrix. CEMENTITE I I PEARLITE 2.0 JO 40 433 3.0 6,0 8.67 *C 30 49 60 73 90 lOO%fe,C PERCENTAGE COMPOSITION FIG. 105. Roberts- Austen iron-carbon diagram. (Slightly modified.) toid" solution in the case of the steels. The substance formed by the freezing of the eutectic solution is called the "eutectic," while that formed by the freezing of the eutectoid solution is called the " eutectoid." If there is an excess of iron carbide (Fe 3 C) present, the steel solution is called " hyper-eutectoid " 15 226 MATERIALS OF CONSTRUCTION and the cast-iron solution "hyper-eutectic." But if there is an excess of free iron present, the steel or solid solution is called "hypo-eutectoid " and the cast-iron solution "hypo-eutectic." 304. Critical Temperatures. It has been found that when a bar of soft steel containing about 0.20 per cent of carbon is gradually heated, the temperature of the bar increases regularly with the time up to a certain point, Aci, at which the increase in temperature is retarded for a short time. After this the temperature will again increase regularly until a second point, Ac 2 , is reached, where a similar retardation will occur. If the heating is continued, a third such point, Ac 3 , will be found before the steel melts. In cooling, the same thing will happen but in the reverse order, the " critical" points found being called Ar 3 , Ar, and Ar\. These latter points are each about 55 degrees Fahrenheit lower than the corresponding points obtained when the bar is heated. If the carbon content is increased, the point Ar s tends to approach point Ar 2 and will finally coincide with it. A further increase in the carbon content will tend to make the point Ar 2 -z approach the point Ari, and, if the carbon is increased sufficiently, all three of these points will coincide. This is also true in regard to the points Ac 3 , Ac z , and Aci. When a high-carbon steel is gradually cooled, the temperature will decrease regularly until the point Ari_ 2 - 3 is reached, and then there will be a sudden momentary increase in temperature, after which the regular rate of cooling will be resumed. This phenomenon is called "recalescence," and the point the "recalescence point." An explanation of this phenomenon is that there is a change in the molecular structure of the steel at each of these critical points. The iron above the Ar 3 point is called gamma iron; the iron between the Ar% and the Ar 2 points, beta iron; and the iron between the Ar 2 and the Ar\ points, alpha iron. The Ari point is at about 1,275 degrees Fahrenheit, while the Ar 2 point varies between 1,400 to 1,275 degrees Fahrenheit, and the Ar 3 point from 1,650 to 1,400 degrees Fahrenheit (after which it coincides with Ar z ) according to the carbon content. Increasing the carbon content lowers Ar 3 until it coincides with Ar 2 , and increasing the carbon content still further causes Ar 2 - to be lowered until it coincides with STEEL 227 Alpha iron is soft, ductile, and magnetic, while -beta iron is hard, glassy, brittle, and^ non-magnetic. 305. Slow Cooling of Molten Steel. When steel cools slowly, it passes from a liquid solution of iron carbide in gamma iron through austenite, martensite, troostite, and sorbite to pearlite. It will be all pearlite if the solution is a eutectoid solution. If there is an excess of gamma iron present (hypo-eutectoid), this excess will gradually separate out in the form of ferrite before the pearlite is formed. This ferrite passes from gamma iron to beta iron and then into alpha iron. At the Ar\ point, pearlite is formed, and the excess iron will be in the form of ferrite (probably a mixture of alpha and beta irons). Thus the resulting steel will be a mixture of ferrite and pearlite. If there is an excess of iron carbide in the solution, this excess will separate out as cementite until the solution is eutectoid in character and until the point Ar\ is reached, when the remainder of the solution will freeze as pearlite, the resulting steel being a mixture of pearlite and cementite. Austenite is a solid solution of iron carbide (cementite) and gamma iron. It is stable above the Ar\ point, may contain carbon up to about 2.0 per cent, and is unmagnetic, ductile, and very hard. Martensite is the first stage in the transformation of austenite. The structure of martensite is needlelike, and is much harder than austenite. Martensite is not very stable. The iron is a mixture of the alpha and beta forms. Troostite is the next stage following martensite. Troostite is not stable. It is not quite so hard as martensite, probably because the proportion of alpha iron has been increased. Sorbite is the last stage before pearlite. Sorbite is softer than troostite and harder and much stronger than pearlite. Pearlite is the last stage in the transformation of austenite. Pearlite is a mixture of 6 parts of ferrite and 1 part of cementite, and it is less hard, less strong, and more ductile than the other forms of austenite. Pearlite' is quite stable below An, except that the cementite tends to form ferrite and graphite. 306. Rapid Cooling of Molten Steel. In the rapid cooling of molten steel the molecules do not have time to go through all of the successive transformations that they do in the case of slow cooling. Hence, various arrangements of the constituents will 228 MATERIALS OF CONSTRUCTION be found in the final structure of the steel due to the rate of cool- ing, initial temperature, amount of carbon, and amounts of other elements present. Hypo-eutectoid steel will always have free ferrite present with the other constituents, while free cementite will be found in the case of hyper-eutectoid steel. Rapid cooling or quenching (as in water) of a solution of molten steel will give a steel whose constitution will be austenite with some martensite. Very rapid cooling, as by quenching in ice water, from the temperature Tl, at which austenite begins to form, will give the same results. A little slower rate of cooling from a molten steel solution, or a rapid cooling from the temperature T2 (of the formation of martensite) gives a steel consisting mostly of martensite with some austenite or troostite or both. A slower rate of cooling (as quenching in air) from a molten steel solution, or a rapid cooling from the temperature T3, of the formation of troostite, will give a steel consisting essentially of troostite with some martensite but with no sorbite. A very slow cooling of a molten steel solution, or a rapid cooling from the temperature T4, of the formation of sorbite, gives sorbite steel which may contain some pearlite. If slow cooling is carried to the temperature T5 (of the forma- tion of pearlite), the constitution of the resulting steel will be mainly pearlite, except that some sorbite will be present if the steel is suddenly cooled from a temperature very close to Ar\. Temperatures Tl, T2, 7 7 3, and T4 are all above, while the temperature T5 is slightly below, the point Ar\. 307. An Explanation of the Hardening of Steel. It is thought that the hardness of steel and iron depends upon the amount of beta iron present, and that any treatment which will increase the amount of beta iron present will also increase the hardness. An increase in the carbon content increases the hardness prob- ably because the carbon tends to hold the iron in the beta form and prevent its transformation into the softer alpha iron. Sud- den cooling, from the temperature of the formation of beta iron, does not give the beta iron time for all of it to change into the alpha form; and the quicker the cooling, the less the change. 308. An Explanation of the Tempering of Steel. In ordinary commercial tempering, the steel is heated to a temperature varying from 425 to 600 degrees Fahrenheit, and then quenched. STEEL 229 The quenching is done to prevent the temperature from increas- ing above the desired degree. The transformation of one constituent to another depends upon the temperature reached, the rate of increase in temperature, and the length of time that the steel is held at that temperature. In heating cold steel, the austenite will be all changed to marten- site when 400 degrees Fahrenheit is reached, and the martensite will be changed to troostite before 750 degrees Fahrenheit is reached. Further heating changes the troostite to sorbite, sorbite alone existing above 1,100 degrees Fahrenheit. Conse- quently, in commercial tempering, the resultant steel will be troostite, with some ferrite or cementite, depending on the carbon content. Only austenite, martensite, austen-troostite, and marten-troostite steels can be tempered, the commercial process having no effect on troostite or trooso-sorbite steels. 309. An Explanation of the Annealing of Steel. In annealing, the steel is heated to higher temperatures than in tempering and is allowed to cool very slowly. This gives a steel which may be essentially sorbite or pearlite (though some troostite may be present if the annealing temperature is low) which is softer and more ductile, though less strong, than the martensite, austenite, or troostite. Ordinary annealing temperatures vary from 400 to 900 degrees Fahrenheit'. To reduce the coarse crystallization in the steel, the annealing temperature must be above the critical point, say from 1,700 to 1,450 degrees Fahrenheit, depending upon the carbon content. Some think that in annealing, most all of the beta iron present is changed over into the alpha form. F. PHYSICAL AND MECHANICAL PROPERTIES AND USES OF STEEL 310. General. The physical and mechanical properties of steel depend upon the methods of manufacture, mechanical working, heat treatment, and chemical composition. The principal chemical elements affecting the properties of steel are carbon, silicon, sulphur, phosphorus, and manganese. Other chemical elements are present, but usually in such small quantities that they have practically no effect on the properties of the steel. Some chemical elements, such as nickel, chromium, 230 MATERIALS OF CONSTRUCTION copper, vanadium, etc., when present in appreciable quantities, also have their effect on the properties of steel. The effect of these elements will be considered in the paragraphs on special and alloy steels. 311. Effect of Carbon. Carbon has a very great effect on the physical properties of steel, depending on the amount present and t 160,000 150,000 t 140,000 s ft uo,ooo ^120,000 110,000 100,000 90,000 ,60,000 70,000 60,000 ^^5 50,000 ^4i 40,000 ^^5 C50.000 X d 20,000 ^ 10,000 1 \ ffOATION 6ETWEEN TENSILE STRENGTH ^ tt ru 0f ) AND YIELD POINT AND PERCENTAGE Of CARBON IN 5 f? . r^ ~j V t ^9 i )(/ ^s ^1, / u ^ X ^ r $ o s Lh . x^ $ re ^ /' ^ -## - ^ j 4 % ^ c t ^/ .> W /* a^| ^('/ > E ~t Ifi K * ^* *** i I ) FIG. 1. Le Chatelier apparatus. ammonium-hydrogen phosphate added, and ammonia drop by drop, with constant stirring, until the precipitate is again formed as described and the ammonia is in moderate excess. The precipitate shall then be allowed to stand about two hours, filtered, and washed as before. The paper and APPENDIX A 281 contents shall be placed in a weighed platinum crucible, the paper slowly charred, and the resulting carbon carefully burned off. The precipitate shall then be ignited to constant weight over a Meker burner, or a blast not strong enough to soften or melt the pyrophosphate. The weight of magnesium pyrophosphate obtained multiplied by 72.5 gives the percentage of magnesia. The precipitate so obtained always contains some calcium and usually small quantities of iron, aluminum, and manganese as phosphates. 27. Permissible Variation. A permissible variation of 0.4 will be allowed, and all results in excess of the specified limit but within this permissible variation shall be reported as 5.00 per cent. VIII. DETERMINATION OF SPECIFIC GRAVITY 28. Apparatus. The determination of specific gravity shall be made with a standardized Le Chatelier apparatus which conforms to the requirements illustrated in Fig. 1. This apparatus is standardized by the United States Bureau of Standards. Kerosene free from water, or benzine not lighter than 62 degrees Baume, shall be used in making this determination. 29. Method. The flask shall be filled with either of these liquids to a point on the stem between zero and 1 c.c.; and 64 grams of cement, of the same temperature as the liquid, shall be slowly introduced, taking care that the cement does not adhere to the inside of the flask above the liquid and to free the cement from air by rolling the flask in an inclined position. After all the cement is introduced, the level of the liquid will rise to some division of the graduated neck ; the difference between readings is the vol- ume displaced by 64 grams of the cement. The specific gravity shall then be obtained from the formula Weight of cement (grams) Specific gravity = - Displaced volume (cubic centimeters) 30. The flask, during the operation, shall be kept immersed in water, in order to avoid variations in the temperature of the liquid in the flask, which shall not exceed 0.5 degree Centigrade. The results of repeated tests should agree within 0.01. 31. The determination of specific gravity shall be made on the cement as received; if it falls below 3.10, a second determination shall be made after igniting the sample as described in Section 20. IX. DETERMINATION OF FINENESS 32. Apparatus. Wire cloth for standard sieves for cement shall be woven (not twilled) from brass, bronze, or other suitable wire, and mounted without distortion on frames not less than \\% in. below the top of the frame. The sieve frames shall be circular, approximately 8 in. in diameter, and may be provided with a pan and cover. 33. A standard No. 200 sieve is one having nominally an 0.0029-in. open- ing and 200 wires per inch standardized by the United States Bureau of Standards, and conforming to the following requirements : 282 MATERIALS OF CONSTRUCTION The No. 200 sieve should have 200 wires per inch, and the number of wires in any whole inch shall not be outside the limits of 192 to 208. No opening between adjacent parallel wires shall be more than 0.0050 in. in width. The diameter of the wire should be 0.0021 in. and the average diameter shall not be outside the limits 0.0019 to 0.0023 in. The value of the sieve as determined by sieving tests made in conformity with the stand- ard specification for these tests on a standardized cement which gives a residue of 25 to 20 per cent on the No. 200 sieve, or on other similarly graded material, shall not show a variation of more than 1.5 per cent above or below the standards maintained at the Bureau of Standards. 34. Method. The test shall be made with 50 grams of cement. The sieve shall be thoroughly clean and dry. The cement shall be placed on the No. 200 sieve, with pan and cover attached, if desired, and shall be held in one hand in a slightly inclined position so that the sample will be well dis- tributed over the sieve, at the same time gently striking the side about 150 times per minute against the palm of the other hand on the upstroke. The sieve shall be turned every 25 strokes about one-sixth of a revolution in the same direction. The operation shall continue until not more than 0.05 gram passes through in 1 minute of continuous sieving. The fineness shall be determined from the weight of the residue on the sieve expressed as a percentage of the weight of the original sample. 36. Mechanical sieving devices may be used, but the cement shall not be rejected if it meets the fineness requirement when tested by the hand method described in Section 34. X. MIXING CEMENT PASTES AND MORTARS 36. Method. The quantity of dry material to be mixed at one time shall not exceed 1,000 grams nor be less than 500 grams. The proportions of cement or cement and sand shall be stated by weight in grams of the dry materials; the quantity of water shall be expressed in cubic centimeters (1 c.c. of water = 1 gram). The dry materials shall be weighed, placed upon a non-absorbent surface, thoroughly mixed dry if sand is used, and a crater formed in the center, into which the proper percentage of clean water shall be poured; the material on the outer edge shall be turned into the crater by che aid of a trowel. After an interval of ^ minute for the absorption of the water the operation shall be completed by continuous, vigorous mixing, squeezing, and kneading with the hands for at least 1 minute. 1 During the operation of mixing, the hands should be protected by rubber gloves. 37. The temperature of the room and the mixing water shall be main- tained as nearly as practicable at 21 degrees Centigrade (70 degrees Fahren- heit). 1 In order to secure uniformity in the results of tests for the time of setting and tensile strength the manner of mixing above described should be carefully followed. At least one minute is necessary to obtain the desired plasticity which is not appreciably affected by continuing the mixing for several minutes. The exact time necessary is dependent upon the personal equation of the operator. The error in mixing should be on the side of over- mixing. APPENDIX A XI. NORMAL CONSISTENCY 283 38. Apparatus. The Vicat apparatus consists of a frame A (Fig. 2) bear- ing a movable rod B, weighing 300 grams, one end C being 1 cm. in diameter for a distance of 6 cm., the other having a removable needle D, 1 mm. in diameter, 6 cm. long. The rod is reversible, and can be held in any desired position by a screw E, and has midway between the ends a mark F which \B FIG. 2. Vicat apparatus. moves under a scale (graduated to millimeters) attached to the frame A. The paste is held in a conical, hard -rubber ring G, 7 cm. in diameter at the base, 4 cm. high, resting on a glass plate H about 10 cm. square. 39. Method. In making the determination, 500 grams of cement, with a measured quantity of water, shall be kneaded into a paste, as described in Section 36, and quickly formed into a ball with the hands, completing the operation by tossing it six times from one hand to the other, maintained about 6 in. apart; the ball resting in the palm of one hand shall be pressed into the larger end of the rubber ring held in the other hand, completely filling the ring with paste ; the excess at the larger end shall then be removed by a single movement of the palm of the hand ; the ring shall then be placed on its larger end on a glass plate and the excess paste at the smaller end 284 MATERIALS OF CONSTRUCTION sliced off at the top of the ring by a single oblique stroke of a trowel held at a slight angle with the top of the ring. During these operations care shall be taken not to compress the paste. The paste confined in the ring, resting on the plate, shall be placed under the rod, the larger end of which shall be brought in contact with the surface of the paste; the scale shall be then read, and the rod quickly released. The paste shall be of normal consistency when the rod settles to a point 10 mm. below the original surface in % min- ute after being released. The apparatus shall be free from all vibrations during the test. Trial pastes shall be made with varying percentages of water until the normal consistency is obtained. The amount of water required shall be expressed in percentage by weight of the dry cement. 40. The consistency of standard mortar shall depend on the amount of water required to produce a paste of normal consistency from the same sample of cement. Having determined the normal consistency of the sample, the consistency of standard mortar made from the same sample shall be as indicated in Table I, the values being in percentage of the com- bined dry weights of the cement and standard sand. TABLE I. PERCENTAGE OF WATER FOR STANDARD MORTARS Percentage of water for neat Percentage of water for one Percentage of water for neat Percentage of water for one cement paste of normal cement, three standard Ottawa cement paste of normal cement, three standard Ottawa consistency sand consistency sand 15 9.0 23 10.3 16 9.2 24 10.5 17 9.3 25 10.7 18 9.5 26 10 8 19 9.7 27 11.0 20 9.8 28 11.2 21 10.0 29 11.3 22 10.2 30 11.5 XII. DETERMINATION OF SOUNDNESS 1 41. Apparatus. A steam apparatus, which can be maintained at a tem- perature between 98 and 100 degrees Centigrade, or one similar to that shown in Fig. 3, is recommended. The capacity of this apparatus may be increased by using a rack for holding the pats in a vertical or inclined position. 1 Unsoundness is usually manifested by change in volume which causes distortion, crack- ing, checking, or disintegration. Pats improperly made or exposed to drying may develop what are known as shrinkage cracks within the first 24 hours and are not an indication of unsoundness. These conditions are illustrated in Fig. 4. The failure of the pats to remain on the glass or the cracking of the glass to which the pats are attached does not necessarily indicate unsoundness. APPENDIX A 285 2/ T- A t*" i TT r " \ ~* c /, K 1 u V o I 1 ""' c c * C 3 q_ ^ J^-S E ^> a i ft io 10 5! M C 1 Q.^ o H , S GO JB \ -*_ 3 \[ J w \_ ^_ / v \ *evj g ^H h ! / \ W in. in thickness above % in., to a minimum of 18 per cent. (b) For structural steel under % 6 in. in thickness, a deduction of 2.5 from the percentage of elongation in 8 in. specified in Section 5 (a) shall be made for each decrease of Ho in- in thickness below ^{Q in. 7. Bend Tests. (a) The test specimen for plates, shapes, arid bars, except as specified in Paragraphs (6) and (c), shall bend cold through 180 degrees without cracking on the outside of the bent portion, as follows: For material % in. or under in thickness, flat on itself; for material over % in. to and including 1^ in. in thickness, around a pin the diameter of which is equal to the thickness of the specimen; and for material over \% in. in thickness, around a pin the diameter of which is equal to twice the thickness of the specimen. (b) The test specimen for pins, rollers, and other bars, when prepared as specified in Section 8 (e), shall bend cold through 180 degrees around a 1-in. pin without cracking on the outside of the bent portion. See Section 6. APPENDIX B 293 (c) The test specimen for rivet steel shall bend cold through 180 degrees flat on itself without cracking on the outside of the bent portion. 8. Test Specimens. (a, Tension and bend test specimens shall be taken from rolled steel in the condition in which it comes from the rolls, except as specified in Paragraph (6). (6) Tension and bend test specimens for pins and rollers shall be taken from the finished bars, after annealing when annealing is specified. ./I . i'J i i ! u^'ij*- /*4<*.4^*i I j*......'*-.....,! ' -About 16' FIG. 1. Tension and bend test specimen. (c) Tension and bend test specimens for plates, shapes, and bars, except as specified in Paragraphs (d), (e), and (/), shall be of the full thickness of material as rolled; and may be machined to the form and dimensions shown in Fig. 1, or with both edges parallel Z'Gage Length H The GagtLengih. Parallel Portions and Filleh shall bat Show, but tht Endt may b of any Form which will Fit the Ho/dery of ffit Testing Machine. FIG. 2. Tension test specimen. (d) Tension and bend test specimens for plates over 1^ in. in thickness may be machined to a thickness or diameter of at least % in. for a length of at least 9 in. (e) Tension test specimens for pins, rollers, and bars over 1^ in. in thick- ness or diameter may conform to the dimensions shown in Fig. 2. In this case, the ends shall be of a form to fit the holders of the testing machine in such a way that the load shall be axial. Bend test specimens may be 1 by H in- in section. The axis of the specimen shall be located at any point midway between the center and surface and shall be parallel to the axis of the bar. (/) Tension and bend test specimens for rivet steel shall be of the full- size section of bars as rolled. 294 MATERIALS OF CONSTRUCTION 9. Number of Tests. (a) One tension and one bend test shall be made from each melt; except that if material from one melt differs % in. or more in thickness, one tension and one bend test shall be made from both the thickest and the thinnest material rolled. (6) If any test specimen shows defective machining or develops flaws, it may be discarded and another specimen substituted. (c) If the percentage of elongation of any tension test specimen is less than that specified in Section 5 (a, and any part of the fracture is more than % in. from the center of the gage length of a 2-in. specimen or is outside the middle third of the gage length of an 8-in. specimen, as indicated by scribe scratches marked on the specimen before testing, a retest shall be allowed. IV. PERMISSIBLE VARIATIONS IN WEIGHT AND THICKNESS 10. Permissible Variations. The cross-section or weight of each piece of steel shall not vary more than 2.5 per cent from that specified; except in the case of sheared plates, which shall be covered by the following permissi- ble variations. One cubic inch of rolled steel is assumed to weigh 0.2833 Ib. (a) When Ordered to Weight per Square Foot. The weight of each lot 1 in each shipment shall not vary from the weight ordered more than the amount given in Table I. (b) When Ordered to Thickness. The thickness of each plate shall not vary more than 0.01 in. under that ordered. The overweight of each lot 2 in each shipment shall not exceed the amount given in Table II. V. FINISH 11. Finish. The finished material shall be free from injurious defects and shall have a workmanlike finish. VI. MARKING 12. Marking. The name or brand of the manufacturer and the melt number shall be legibly stamped or rolled on all finished material, except that rivet and lattice bars and other small sections shall, when loaded for shipment, be properly separated and marked for identification. The identification marks shall be legibly stamped on the end of each pin and roller. The melt number shall be legibly marked, by stamping if practica- ble, on each test specimen. VII. INSPECTION AND REJECTION 13. Inspection. The inspector representing the purchaser shall have free entry, at all times while work on the contract of the purchaser is 1 The term "lot" applied to Table I means all of the plates of each group width and group weight. 2 The term "lot" applied to Table II means all of the plates of each group width and group thickness. APPENDIX R 295 il 8.9 OJ 2-3 5* 3* 50 X 2* 00 C J3AQ J8AQ JSAQ J3AQ rapo.! J9AQ japun J3AQ japna J3AQ japun n 99999999 OiOOOOiCOOC oooooooo -0000000000000000 . .ooooicooo " ' os 06 1- o "3 3 ^ ^ .oooooooo eo co co co eo eo cc n . . . oooooooo : I .'oot>.'< " . -OOOOOOOO5 . .OOO"5OOOOO ' " CO W . .000000000 ' ICOCOCOCOCOCOCOCM'CM .t^tflOO^^COCOfN . CO CO CO CO CO - O o O O t L 3 S XXXXXXKXW Ordered tl i s ^, ^3^313^1 c > CM O -oooooooo '. '. 05 I-i 10' CO -< OS 00 1^ co I CO t, *"" O r ^ V > "S J CM co- X o w i.s : -oooooooo IDERED TO 11 i.s : -00000000 *" CM' d os 06 1>^ ui & 3-g -OOOOOOOiO 1 11 I.2 : - OJ O OS 00 t^ 5O U5 TJ< g 03 3 10 s g-B -OOOOOOOiOO jj o II 1! 2 CM O OS 00 t>- O O * Tj< OVERWEl M -3 o 5 ooooooooooo ^ CN O Os' 00 1^' 10" TjJ Tjl CO 3RMISSIBLE e excess in a expr t>."3 X i.s r ooooooo>oo>oo csocsooi^oio^^co'co' a 8-s 00000000^00 i i i g S * 5 * w * w * w fed oooooooooo>o 5s - " * " i :::::::::!: Ordered thic 1 1 "o "3 ~ "3 "S "c "o "u "o ! xxxxxxxxx ovoo>cevv . o ; |222222222 296 MATERIALS OF CONSTRUCTION being performed, to all parts of the manufacturers' works which concern the manufacture of the material ordered. The manufacturer shall afford the inspector, free of cost, all reasonable facilities to satisfy him that the mate- rial is being furnished in accordance with these specifications. All tests (except check analyses) and inspection shall be made at the place of manu- facture prior to shipment, unless otherwise specified, and shall be so conducted as not to interfere unnecessarily with the operation of the works. 14. Rejection. (a) Unless otherwise specified, any rejection based on tests made in accordance with Section 4 shall be reported within five work- ing days from the receipt of samples. (6) Material which shows injurious defects subsequent to its acceptance at the manufacturers' works will be rejected, and the manufacturer shall be notified. 15. Rehearing. Samples tested in accordance with Section 4, which represent rejected material, shall be preserved for two weeks from the date of the test report. In case of dissatisfaction with the results of the tests, the manufacturer may make claim for a rehearing within that time. APPENDIX C List of Standards and Tentative Standards of the American Society for Testing Materials A. FERROUS METALS A 1-14. Standard Specifications for Carbon-steel Rails. A 2-12. Standard Specifications for Open-hearth Steel Girder and High Tee Rails. A 3-14. Standard Specifications for Low-carbon-steel Splice Bars. A 4-14. Standard Specifications for Medium-carbon-steel Splice Bars. A 5-14. Standard Specifications for High-carbon-steel Splice Bars. A 6-14. Standard Specifications for Extra-high-carbon-steel Splice Bars. A 7-16. Standard Specifications for Structural Steel for Bridges. A 8-16. Standard Specifications for Structural Nickel Steel. A 9-16. Standard Specifications for Structural Steel for Buildings. A 10-16. Standard Specifications for Structural Steel for Locomotives. A 11-16. Standard Specifications for Structural Steel for Cars. A 12-16. Standard Specifications for Structural Steel for Ships. A 13-14. Standard Specifications for Rivet Steel for Ships. A 14-16. Standard Specifications for Carbon-steel Bars for Railway Springs. A 15-14. Standard Specifications for Billet-steel Concrete Reinforcement Bars. A 16-14. Standard Specifications for Rail-steel Concrete Reinforcement Bars. A 17-18. Standard Specifications for Carbon-steel and Alloy-steel Blooms, Billets, and Slabs for Forgings. A 18-18. Standard Specifications for Carbon-steel and Alloy-steel Forgings. A 19-18. Standard Specifications for Quenched and Tempered Carbon- steel Axles, Shafts, and Other Forgings for Locomotives and Cars. A 20-16. Standard Specifications for Carbon-steel Forgings for Loco- motives. A 21-18. Standard Specifications for Carbon-steel Car and Tender Axles. A 22-16. Standard Specifications for Cold-rolled Steel Axles. A 23. Discontinued Replaced by Specification A 57. A 24. Discontinued Replaced by Specification A 57. A 25-16. Standard Specifications for Wrought, Solid Carbon-steel Wheels for Electric Railway Service. A 26-16. Standard Specifications for Steel Tires. 297 298 MATERIALS OF CONSTRUCTION A 27-16. Standard Specifications for Steel Castings. A 28-18. Standard Specifications for Lap-welded and Seamless Steel Boiler Tubes for Locomotives. A 2918. Standard Specifications for Automobile Carbon and Alloy Steels. A 3018. Standard Specifications for Boiler and Firebox Steel for Loco- motives. A 31-14. Standard Specifications for Boiler-rivet Steel. A 32-14. Standard Specifications for Cold-drawn Bessemer Steel Auto- matic Screw Stock. A 33-14. Standard Methods for Chemical Analysis of Plain Carbon Steel. A 34-18. Standard Tests for Magnetic Properties of Iron and Steel. A 35-11. Recommended Practice for Annealing of Miscellaneous Rolled and Forged Carbon-steel Objects. A 36-14. Recommended Practice for Annealing of Carbon-steel Castings. A 37-14. Recommended Practice for Heat Treatment of Case-hardened Carbon-steel Objects. A 38-18. Standard Specifications for Lap-welded Charcoal-iron Boiler Tubes for Locomotives. A 39-18. Standard Specifications for Staybolt Iron. A 40-18. Standard Specifications for Engine-bolt Iron. A 41-18. Standard Specifications for Refined Wrought-iron Bars. A 42-18. Standard Specifications for Wrought-iron Plates. A 43-09. Standard Specifications for Foundry Pig Iron. A 44-04. Standard Specifications for Cast-iron Pipe and Special Castings. A 45-14. Standard Specifications for Cast-iron Locomotive Cylinders. A 46-05. Standard Specifications for Cast-iron Car Wheels. A 47-19. Standard Specifications for Malleable Castings. A 4818. Standard Specifications for Gray-iron Castings. A 49-15. Standard Specifications for Quenched High-carbon-steel Splice Bars. A 50-16. Standard Specifications for Quenched Carbon-steel Track Bolts. A 51-16. Standard Specifications for Quenched Alloy-steel Track Bolts. A 52-12. Standard Specifications for Lap-welded and Seamless Steel and Wrought-iron Boiler Tubes for Stationary Service. A 53-18. Standard Specifications for Welded Steel Pipe. A 53-20 T. Tentative Specifications for Welded Steel Pipe. A 54-15. Standard Specifications for Cold-drawn Open-hearth Steel Automatic Screw Stock. A 55-15. Standard Methods for Chemical Analysis of Alloy Steels. A 56-18. Standard Specifications for Iron and Steel Chain. A 57-16. Standard Specifications for Wrought, Solid Carbon-steel Wheels for Steam Railway Service. A 58-16. Standard Specifications for Carbon-steel Bars for Vehicle and Automobile Springs. A 59-16. Standard Specifications for Silico-manganese-steel Bars for Automobile and Railway Springs. A 60-16. Standard Specifications for Chrome-vanadium-steel Bars for Automobile and Railway Springs. APPENDIX C 299 A 61-16. Standard Specifications for Helical Steel Springs for Railways. A 62-16. Standard Specifications for Elliptical Steel Springs for Railways. A 63-18. Standard Specifications for Quenched-and-tempered Alloy-steel Axles, Shafts, and Other Forgings for Locomotives and Cars. A 6416. Standard Methods for Sampling and Analysis of Pig and Cast Iron. A 65-18. Standard Specifications for Steel Track Spikes. A 66-18. Standard Specifications for Steel Screw Spikes. A 67-20 T. Tentative Specifications for Steel Tie Plates. A 68-18. Standard Specifications for Carbon-steel Bars for Railway Springs with Special Silicon Requirements. A 69-18. Standard Specifications for Elliptical Steel Springs for Auto- mobiles. A 70-18 T. Tentative Specifications for Boiler and Firebox Steel for Stationary Service. A 71-20 T. Tentative Specifications for Carbon Tool Steel. A 72-18. Standard Specifications for Welded Wrought-iron Pipe. A 73-18. Standard Specifications for Wrought-iron Rolled or Forged Blooms and Forgings for Locomotives and Cars. A 74-18. Standard Specifications for Cast-iron Soil Pipe and Fittings. A 75. Discontinued Has become A 47. A 76-20 T. Tentative Specifications for Low-carbon-steel Track Bolts. A 77-20 T. Tentative Specifications for Electric Cast-steel Anchor Chain. A 78-20 T. Tentative Specifications for Steel Plates for Forge Welding. A 79-19 T. Tentative Specifications for Extra Refined Wrought-iron Bars. A 80-20 T. Tentative Specifications for Commercial Bar Steels. A 81-20 T. Tentative Definitions of Terms Relating to Wrought-iron Specifications. B. NON-FERROUS METALS B 1-15. Standard Specifications for Hard-drawn Copper Wire. B 2-15. Standard Specifications for Medium Hard-drawn Copper Wire. B 3-15. Standard Specifications for Soft or Annealed Copper Wire. B 4-13. Standard Specifications for Lake Copper Wire Bars, Cakes, Slabs, Billets, Ingots, and Ingot Bars. B 5-13. Standard Specifications for Electrolytic Copper Wire Bars, Cakes, Slabs, Billets, Ingots, and Ingot Bars. B 6-18. Standard Specifications for Spelter. B 7-14. Standard Specifications for Manganese-bronze Ingots for Sand Castings. B 8-16. Standard Specifications for Bare Concentric-lay Copper Cable: Hard, Medium-hard, or Soft. B 9-16. Standard Specifications for High-strength Bronze Trolley Wire, Round and Grooved : 40 and 65 per cent Conductivity. B 10-18. Standard Specifications for the Alloy: Copper, 88 per cent; Tin, 10 per cent; Zinc, 2 per cent. B 1118. Standard Specifications for Copper Plates for Locomotive Fireboxes. 300 MATERIALS OF CONSTRUCTION B 12-18. Standard Specifications for Copper Bars for Locomotive Stay- bolts. B 13-18. Standard Specifications for Seamless Copper Boiler Tubes. B 14-18. Standard Specifications for Seamless Brass Boiler Tubes. B 15-18. Standard Specifications for Brass Forging Rod. B 16-18. Standard Specifications for Free-cutting Brass Rod for Use in Screw Machines. B 17-18 T. Tentative Specifications for Non-ferrous Alloys for Railway Equipment in Ingots, Castings, and Finished Car and Tender Bearings. B 18-20 T. Tentative Methods for Chemical Analysis of Alloys of Lead, Tin, Antimony, and Copper. B 19-19. Standard Specifications for Cartridge Brass. B 20-19. Standard Specifications for Cartridge Brass Disks. B 21-19 Standard Specifications for Naval Brass Rods for Structural Purposes. B 22-18 T. Tentative Specifications for Bronze Bearing Metals for Turn- tables and Movable Railroad Bridges. B 23-18 T. Tentative Specifications for White Metal Bearing Alloys (known commercially as " Babbitt Metal"). B 24-20 T. Tentative Specifications for Aluminum Ingots for Remelting and for Rolling. B 25-19 T. Tentative Specifications for Aluminum Sheet. B 26-19 T. Tentative Specifications for Light Aluminum Casting Alloys. B 27-19. Standard Methods for Chemical Analysis of Manganese Bronze. B 28-19. Standard Methods for Chemical Analysis of Gun Metal. B 29-20 T. Tentative Specifications for Pig Lead. B 30-19 T. Tentative Specifications for Brass Ingot Metal for Sand Cast- ings. B 31-19 T. Tentative Specifications for Bronze Bearing Metal in Ingot Form. B 32-19 T. Tentative Specifications for Solder Metal. B 33-19 T. Tentative Specifications for Tinned Soft or Annealed Copper Wire for Rubber Insulation. B 34-20. Standard Methods for Battery Assay of Copper. B 35-20. Standard Methods for Chemical Analysis of Pig Lead. B 36-20 T. Tentative Specifications for Sheet High Brass. B 37-20 T. Tentative Specifications for Aluminum for Use in the Manu- facture of Iron and Steel. C. CEMENT, LIME, GYPSUM, AND CLAY PRODUCTS C 1. Discontinued Replaced by Specifications C 9 and C 10. C 2. Discontinued Replaced by Specification C 19. C 3. Discontinued Replaced by Specification C 19. C 4-16. Standard Specifications for Drain Tile. C 5-15. Standard Specifications for Quicklime. C 6-15. Standard Specifications for Hydrated Lime. APPENDIX C 301 C 6-19 T. Tentative Specifications for Masons' Hydrated Lime. C 7-15. Standard Specifications for Paving Brick. C 8-15. Standard Definitions of Terms Relating to Sewer Pipe. C 9-21. Standard Specifications and Tests for Portland Cement. C 9-16 T. Tentative Specifications and Tests for Compressive Strength of Portland-cement Mortars. C 10-09. Standard Specifications for Natural Cement. C 11-16 T. Tentative Definitions of Terms Relating to the Gypsum Industry. C 12-19. Recommended Practice for Laying Sewer Pipe. C 13-20. Standard Specifications for Clay Sewer Pipe. C 14-20. Standard Specifications for Cement-concrete Sewer Pipe. C 15-17 T. Tentative Specifications for Required Safe Crushing Strengths of Sewer Pipe to Carry Loads from Ditch Filling. C 16-20. Standard Test for Refractory Materials under Load at High Temperatures. C 17-19 T. Tentative Test for Slagging Action of Refractory Materials. C 18-20. Standard Methods for Ultimate Chemical Analysis of Refrac- tory Materials. C 18-20 T. Tentative Method for Ultimate Chemical Analysis of Chrome Ores and Chrome Brick. C 19-18. Standard Specifications for Fire Tests of Materials and Con- struction. C 20-20. Standard Test for Porosity and Permanent Volume Changes in Refractory Materials. C 21-20. Standard Specifications for Building Brick. C 22-20 T. Tentative Specifications for Gypsum. C 23-20 T. Tentative Specifications for Calcined Gypsum. C 24-20. Standard Test for Softening Point of Fireclay Brick. C 25-19 T. Tentative Methods for Chemical Analysis of Limestone, Lime, and Hydrated Lime. C 26-20 T. Tentative Methods for Tests of Gypsum and Gypsum Products. C 27-20. Standard Definitions for Clay Refractories. C 28-20 T. Tentative Specifications for Gypsum Plasters. C 29-20 T. Tentative Test for Unit Weight of Aggregate for Cement Concrete. C 30-20 T. Tentative Method for Determination of Voids in Fine Aggregate for Cement Concrete. C 31-20 T. Tentative Methods for Making and Storing Specimens of Concrete in the Field. D. MISCELLANEOUS MATERIALS D 1-15. Standard Specifications for Purity of Raw Linseed Oil from North American Seed. D 2-08. Standard Test for Abrasion of Road Material. D 3-18. Standard Test for Toughness of Rock. D 4-11. Standard Test for Soluble Bitumen. 302 MATERIALS OF CONSTRUCTION D 5-16. Standard Test for Penetration of Bituminous Materials. D 6-20. Standard Test for Loss on Heating of Oil and Asphaltic Com- pounds. D 7-18. Standard Method for Making a Mechanical Analysis of Sand or Other Fine Highway Material, Except Fine Aggregates Used in Cement Concrete. D 8-18. Standard Definitions of Terms Relating to Materials for Roads and Pavements. D 9-15. Standard Definitions of Terms Relating to Structural Timber. D 10-15. Standard Specifications for Yellow-pine Bridge and Trestle Timbers. D 11-15. Standard Specifications for Purity of Boiled Linseed Oil from North American Seed. D 12-16. Standard Specifications for Purity of Raw Tung Oil. D 13-15. Standard Specifications for Turpentine. D 13-20 T. Tentative Specifications for Turpentine. D 14-15. Standard Specifications for 2%-in. Cotton Rubber-lined Fire Hose for Private Department Use. D 15-15. Standard Methods for Testing of Cotton Rubber-lined Hose. D 16-15. Standard Definitions of Terms Relating to Paint Specifications. D 17-16. Standard Specifications for Foundry Coke. D 18-16. Standard Method for Making a Mechanical Analysis of Broken Stone or Broken Slag, except Aggregates Used in Cement Concrete. D 19-16. Standard Method for Making a Mechanical Analysis of Mix- tures of Sand or Other Fine Material with Broken Stone or Broken Slag, except Aggregates Used in Cement Concrete. D 20-18. Standard Method for Distillation of Bituminous Materials Suitable for Road Treatment. D 21-16. Standard Methods for Sampling of Coal. D 22-16. Standard Methods for Laboratory Sampling and Analysis of Coal. D 22-19 T. Tentative Method for Determination of Fusibility of Coal Ash. D 23-20 T. Tentative Specifications for Structural Douglas Fir. D 24-20. Standard Specifications for Southern Yellow-pine Timber to be Creosoted. D 25-20. Standard Specifications for Southern Yellow-pine Piles and Poles to be Creosoted. D 26-18. Standard Specifications for 2%-, 3-, and 3j^-in. Double- jacketed Cotton Rubber-lined Fire Hose for Public Fire Department Use. D 27-16 T. Tentative Specifications for Insulated Wire and Cable: 30-Per Cent Hevea Rubber. D 28-17. Standard Tests for Paint Thinners Other than Turpentine. D 29-17. Standard Tests for Shellac. D 30-18. Standard Test for Determination of Apparent Specific Gravity of Coarse Aggregates. D 31. Discontinued Replaced by Method D 39. D 32. Discontinued Replaced by Method D 39. APPENDIX C 303 D 33. Discontinued Replaced by Method D 39. D 34-17. Standard Methods for Routine Analysis of White Pigments. D 35-18. Standard Form of Specifications for Certain Commercial Grades of Broken Stone. D 36-19. Standard Method for Determination of Softening Point of Bituminous Materials Other than Tar Products (Ring-and- Ball Method). D 37-18. Standard Methods for Laboratory Sampling and Analysis of Coke. D 38-18. Standard Methods for Sampling and Analysis of Creosote Oil. D 39-20. Standard General Methods for Testing Cotton Fabrics. D 40-17 T. Tentative Specifications for Asphalt for Use in Damp-proofing and Waterproofing. D 41-17 T. Tentative Specifications for Primer for Use with Asphalt for Use in Damp-proofing and Waterproofing. D 42-17 T. Tentative Specifications for Coal-tar Pitch for Use in Damp- proofing and Waterproofing. D 43-17 T. Tentative Specifications for Creosote Oil for Priming Coat with Coal-tar Pitch for Use in Damp-proofing and Water- proofing. D 44-20 T. Tentative Specifications for Wooden Boxes, Nailed and Lock- corner Construction, for the Shipment of Canned Foods. D 45-17 T. Tentative Specifications for Canned Foods Boxes, Wire-bound Construction. D 46-18. Standard Specifications for Air-line Hose for Pneumatic Tools. D 47-18. Standard Tests for Lubricants. D 47- 20. Standard Test for Viscosity of Lubricants. D 48-17 T. Tentative Tests for Molded Insulating Materials. D 49-18. Standard Methods for Routine Analysis of Dry Red Lead. D 50-18. Standard Methods for Routine Analysis of Yellow, Orange, Red, and Brown Pigments containing Iron and Manganese. D 51-18 T. Tentative Specifications for Foots Permissible in Properly Clarified Pure Raw Linseed Oil from North American Seed. D 52-20. Standard Specifications for Wooden Paving Blocks for Exposed Pavements. D 53-20. Standard Specifications for Rubber Belting for Power Trans- mission. D 54-20. Standard Specifications for Steam Hose. D 55-19. Standard Tests for Determination of Apparent Specific Gravity of Sand, Stone, and Slag Screenings and Other Fine Non- bituminous Highway Materials. D 56-19. Standard Test for Flash Point of Volatile Paint Thinners. D 57-20. Standard Specifications for Materials for Cement Grout Filler for Brick and Stone-block Pavements. D 58-20. Standard Specifications for Materials for Cement Mortar Bed for Brick, Stone-block, and Wood-block Pavements. D 59-19 T. Tentative Specifications for Block for Granite-block Pavements. D 60-20. Standard Specifications for Leader Hose for Use with Pneu- matic Tools. 304 MATERIALS OF CONSTRUCTION D 61-20. Standard Method for Determination of Softening Point of Tar Products (Cube-in-water Method). D 62-20 T. Tentative Specifications for Workability of Concrete for Con- crete Pavements. D 63-20 T. Tentative Specifications for Commercial Sizes of Broken Stone and Broken Slag for Highway Construction. D 64-20 T. Tentative Specifications for Commercial Sizes of Sand and Gravel for Highway Construction. D 65-20 T. Tentative Specifications for Broken Slag for Waterbound Base. D 66-20 T. Tentative Specifications for Shovel-run or Crusher-run Broken Slag for Waterbound Base. D 67-20 T. Tentative Specifications for Natural or Artificial Sand-clay Mixtures for Highway Surfacing. D 68-20 T. Tentative General Specifications for Wooden Boxes, Nailed and Lock-corner Construction. D 69-20 T. Tentative Specifications for Adhesive Insulating Tape. D 70-20 T. Tentative Test for Specific Gravity of Road Oils, Road Tars, Asphalt Cements, and Soft Tar Pitches. D 71-20 T. Tentative Test for Specific Gravity of Asphalts and Tar Pitches Sufficiently Solid to be Handled in Fragments. D 72-20 T. Tentative Test for Quantity of Clay and Silt in Gravel for Highway Construction. D 73-20 T. Tentative Test for Quantity of Clay in Sand-clay, Topsoil, and Semi-gravel for Highway Construction. D 74-20 T. Tentative Test for Quantity of Clay and Silt in Sand for High- way Construction. D 75-20 T. Tentative Methods for Sampling of Stone, Slag, Gravel, Sand, and Stone Block for Use as Highway Materials, Including Some Material Survey Methods. D 76-20 T. Tentative Methods for Testing Textiles. E. MISCELLANEOUS SUBJECTS E 1-18. Standard Methods for Testing. E 2-20. Standard Definitions and Rules Governing the Preparation of Micrographs of Metals and Alloys. INDEX Aggregate, coarse, 52 fine, 37, 38, 51 Air furnace, 181 Alloy steels, 244 aluminum steel, 247 chrome steel, 247 chromium-nickel steel, 248 chromium-vanadium steel, 248 classification of, 244 cobalt steel, 247 copper steel, 248 definitions of, 244 heat treatment of, 245 manganese steels, 246 molybdenum steel, 247 nickel steel, 246 nickel-vanadium steel, 249 silicon steel, 247 tungsten-chromium-vanadium steel, 249 tungsten, steel, 247 vanadium steel, 247 Alloys, bearing metal, 263 fusible, 264 miscellaneous, 265 Alloys of aluminum, 262 of nickel, 263 of non-ferrous metals, 259 of non-ferrous metals, corro- sion of, 265 of non-ferrous metals in general, 259 Alpha iron, 227 Aluminum, 257 alloys, 262 bronze, 262 copper alloys, 262 copper-tin alloys, 262 copper-zinc alloys, 262 Aluminum, extraction of, 257 magnesium alloys, 262 plating, 253 properties of, 257 steel, 247 uses of, 258 zinc alloys, 262 American Society for Testing Materials, list of standards, 297 list of tentative standards, 297 standard specifications and tests for Portland cement, 275 Antimony, 259 Asbestos, 268 properties of, 268 uses of, 268 Asphalt paints, 268 Austenite, 227 H Bauer drill test, 237 Bearing metal alloys, 263 composition of, 264 requisites of, 264 Belts, 273 canvas, 274 leather, 273 rubber, 273 splicing of, 274 steel, 274 Beta iron, 227 Bismuth, 259 Blast furnace, 168 259 composition of, 260 definition of, 260 delta metal, 261 effect of adding aluminum. 260 lead, 260 305 20 306 INDEX Brasses, manganese bronze, 260 properties of, 260 sterro-metal, 261 strength of, 261 Tobin bronze, 261 Brick, 101 absorption, 114 acid, 109 basic, 109 bauxite, 110 building, 101 chromite, 110 classification of, 101 clay building, 102 compressive strength of, 115 definition of, 101 facing, 101 fire, 101 fireclay, 110 ganister, 110 general properties of, 114 kilns, 106 list of standards and tentative standards, 297 modulus of elasticity, 116 neutral, 110 properties of, 114 requisites of, 114 sand-lime, manufacture of, 111 shearing strength of, 116 silica firebrick, 110 transverse strength of, 115 veneer, 129 Brick masonry, 119, 127 bond, 129 cleaning, 131 definitions, 119 efflorescence, 133 in general, 127 laying, 128 mortar for, 127 pointing, 130 properties of, 131 strength of, 131 waterproofing, 130 working load, 132 Brinell hardness test, 237 Bronzes, 261 Bronzes, aluminum, 262 composition of, 261 definition of, 261 lead, 261 phosphor, 261 strength of, 262 Tobin, 261 Building stone, 89 action of fire, 98 of frost, 97 of rain, 97 of smoke, 97 of wind, 97 classification of, 89 cut stone, 96 cutting, 94 durability of, 96 general, 89 gneiss, 90 granite, 90 limestone, 91 marble, 91 mechanical properties of, 98 properties of, 96 quarrying, 91 explosives used, 93 hand methods, 91 machine methods, 93 sandstone, 91 slate, 91 strength of, 99 trap, 90 Building tile, 112 absorption, 114 compressive strength of, 115 modulus of elasticity of, 116 shearing strength of, 116 transverse strength of, 1 15 Cadmium, 259 Calcined plaster, 1 Canvas, 272 belts, 274 Cast iron, 177 arbitration test bar, 191 blow holes, 184 INDEX 307 Cast iron, cementite, 185 classification of, 177 coefficient of expansion of, 192 cold shorts, 184 composition of, 184 compressive strength of, 190 constitution of, 184 cracks, 184 defects, 184 definitions of, 177 effect of aluminum, 188 of carbon, 185 of copper, 188 of manganese, 186 of phosphorus, 186 of silicon, 186 of sulphur, 186 of tin, 188 of titanium, 188 of vanadium, 188 ferrite, 185 fusibility of, 192 graphite, 185 gray, 186 malleable, 193 annealing, 193 compressive strength of, 194 definition of, 193 ductility of, 194 making castings, 193 properties of, 194 structure of, 194 tensile strength of, 194 transverse strength of, 194 uses of, 194 mechanical properties of, 188 mottled, 186 pearlite, 185 physical properties, 188 rough surfaces, 184 sand-holes, 184 seams, 184 shearing strength, 192 shrinkage in cooling, 192 specific gravity, 192 strength in general, 188 tensile strength, 189 Cast iron, transverse strength, 191 uses of, 192 white, 186 working stresses, 192 Cast iron manufacture, 178 air furnace, 181 chills, 183 cleaning castings, 183 cores, 181 cupola, 179 definition of founding, 181 dry sand molds, 183 foundry work, 181 green sand molds, 182 loam molds, 183 materials, 178 metal molds, 183 molding sand, 182 molds, 182 patterns, 181 pickling castings, 184 pouring castings, 183 Castings, steel, 243 Cement, list of standards and tenta- tive standards, 300 magnesia, 7 miscellaneous, 6 natural, 3 plaster, 1 Portland, 21 Puzzolan, 6 slag, 6 Sorel, 7 Cementing materials, classification of, 21 Cementite, 185 Chrome steel, 247 Chromium-nickel steel, 248 Chromium-vanadium steel, 248 Clay building brick, 102 manufacture, brick kilns, 106 burning of brick, 108 hand process, 102 of building brick 102 pressed-brick machine pro- cess, 106 soft-mud machine process, 103 308 INDEX Clay building brick, manufacture, stiff-mud process, 104 the clay, 102 Clay products, 101 building tile, 101, 112 absorption, 114 compressive strength of, 115 modulus of elasticity of, 116 shearing strength of, 116 transverse strength of, 116 classification of, 101 definitions of, 101 drain tile, 101, 112 properties of, 119 list of standards and tentative standards, 300 properties of, 114 sewer pipe, 113 properties of, 118 sewer tile, 101 terra cotta, 101, 111 Coarse aggregate, general, 52 size, 52 specific gravity, 53 specifications, 54 voids, 53 weight per cubic foot, 53 Cobalt steel, 247 Concrete, abrasion, 82 absorption, 82 adhesive strength to steel, 80 bonding new to old, 70 coarse aggregate, 52 compressive strength of, 78 consistency of, 68 contraction, 82 definitions, 51 deposition of, 69 effect of amount of mixing water, 75 of clay, 74 of dirt, 74 of grease and oil, 74 of lime, 74 of loam, 74 of mica, 74 of organic matter, 74 of regaging, 74 Concrete effect of sugar, 74 of various impurities, 74 elastic limit, 81 expansion, 82 factor of safety, 82 forms for, 69 hardened, effect of acids, 75 of alkali, 75 of fire, 75 of grease and oil, 75 of sea water, 75 impervious, 72 effect of amount of cement, 72 of increasing the density, 72 foreign matter, 73 surface treatments, 73 waterproofing materials, 73 material, 51 cement, 51 fine aggregate, 51 water, 51 mixing, 66 by hand, 66 by machine, 68 modulus of elasticity, 81 placing, 69 in freezing weather, 71 under water, 71 plain, 51 properties of, 74 proportioning, 55 Abrams' method, 60, 61 by standard proportions, 55 Edwards' surface area method, 65 general theory, 55 maximum density test, 56 mechanical analysis, 57, 58 quantities of materials re- quired, 65 reference to coarse aggregate, 56 to mixed aggregate, 56 rubble, 83 shearing strength, 80 strength in general, 77 surface finish, 70 tamping of, 69 INDEX 309 Concrete, tensile strength, 79 transporting, 69 transverse strength, 79 waterproofing of, 72 weight per cubic foot, 82 working stresses, 82 yield of, 81 Concrete stone, block, and brick, 84 consistency, 85 curing and aging, 86 definitions, 84 materials, 84 mixing, 85 molding, 85 properties of, 87 proportions, 84 surface finishes, 86 uses of, 88 Constantin, 263 Copper, 255 extracting from ores, 255 properties of, 255 strength of, 255 uses of, 256 Copper steel, 248 Corrosion, carbon-dioxide theory, 250 definition of, 249 electrolytic theory, 251 moisture theory, 251 of alloys, non-ferrous metals, 265 of iron and steel, 249 life under, 250 of non-ferrous metals, 265 prevention of, by aluminum plating, 253 by covering with asphalt, 252 by covering with concrete, 252 by galvanizing, 252 by inoxidation process, 253 by lead plating, 253 by nickel plating, 253 by painting, 251 by sheradizing, 253 by tin plating, 253 in general, 251 Corrosion, theories of, 250 Cupola, 179 Cut stone, classification, 95 D Delta metal, 261 Drain tile, 112 properties of, 117 E Electric furnace, 174, 217 Electric welding, 238 Explosives used in quarrying, 93 Ferrite, 185 Ferrous metals, list of standards and tentative standards, 297 Fine aggregate, for plain concrete, 51 definition of, 37 specifications, 40 Firebrick, manufacture of, 109 Forms for concrete, 69 Foundry work, 181 Fusible alloys, 260 Galvanized wire, standards test fo r, 253 Galvanizing of iron and steel, 252 Gamma iron, 227 German silver, 263 Glass, 268 properties of, 268 uses of, 268 wire, 269 Glue, 269 properties of, 269 uses of, 269 Gneiss, 90 Gold, 254 Granite, 90 Graphite, 185 Gypsum, 1 310 INDEX Gypsum, list of standards and ten- tative standards, 300 plaster, 1 calcined plaster, 1 cement plaster, 1 classification of, 1 definition of, 1 hard-finish plaster, 1 manufacture of, 1 plaster of Paris, 1 properties of, 2 uses of, 3 products, 3 H Hard-finish plaster, 1 Hollow tile masonry, 127, 133 Hydrated lime, 9, 12, 14 I Inoxidation process, 253 Invar, 263 Iron carbide, 227 Iron, cast, 177 Iron, corrosion of, 249 life under, 250 galvanizing of, 252 general classification, 177 Howe's classification, 177 list of standards and tentative standards, 297 malleable cast, 193 ores, 165 preliminary treatment, 166 pig, 165 wrought, 197 Iron ore mining, 166 Lead, 256 extraction of, 256 properties of, 256 uses of, 256 Lead bronze, 261 Lead plating, 253 Leather, 271 Leather, classification of, 271 .properties of, 271 uses of, 272 Leather belts, 273 Leather, rawhide, 272 Lime, 9 calcium, 9 classification of, 9 definition of, 9 dolomite, 9 high-calcium, 9 hydrated, 9 hydraulic, 9 list of standards and tentative standards, 300 magnesium, 9 manufacture of hydrated lime, 12 of hydraulic lime, 12 of quicklime, 9 properties of hydrated lime, 14 of hydraulic lime, 14 of quicklime, 13 quicklime, 9 run-of-kiln, 9 selected, 9 slaking quicklime, 16 uses, 15 Lime kiln, 10 Lime mortars, 9,15 definitions, 15 materials, 15 mixing, 17 properties of, 18 proportioning, 17 slaking quicklime, 16 uses of, 19 Limestone, 91 Linseed oil, 267 Lumber, artificial seasoning, 147 classification, 144 common rot, 151 decay, 149 defects in, 145 dry rot, 150 durability, 149 inspection of, 159 natural seasoning, 147 INDEX 311 Lumber, sawing, 144 selection of, 158 shrinkage, 148 wet rot, 151 M Magnalium, 262 Magnesia cement, 7 Magnesium, 259 Malleable cast iron, 193 Manganese, 259 bronze, 260 properties of, 260 strength of, 260 Manganese steel, 246 Marble, 91 Martensite, 227 Masonry, 119 Materials, miscellaneous, 267 Metals, non-ferrous, 255 alloys of, 259 Miscellaneous cements, 6 Mixing of concrete, 66 Molybdenum steel, 247 Monel metal, 263 Mortar for brick masonry, 127 for stone masonry, 122 Mortars, lime, 9, 15 N Natural cement, 1, 3 definition of, 3 manufacture of, 4 properties of, 4 uses of, 6 Nickel, 258 extraction of, 258 properties of, 258 uses of, 258 Nickel alloys, 263 constantin, 263 german silver, 263 invar, 263 monel metal, 263 table ware alloy, 263 Nickel plating, 253 Nickel steel, 246 Nickel-vanadium steel, 249 Non-ferrous metals, 255 alloys of, 259 corrosion of, 265 in general, 255 list of standards and tenta- tive standards, 299 O Oils, 267 Ore mining, 166 Ore of iron, 165 Oxygen-acetylene 238 welding process, Paints, 267 asphalt, 268 composition of, 267 drier, 267 linseed oil, 267 solvent, 267 stain, 267 turpentine, 267 vehicle or binder, 267 white lead, 267 zinc white, 267 Paper, 272 classification of, 272 manufacture of, 272 Paving brick, manufacture of, 108 Pearlite, 185, 227 Pewter, 265 Phosphor-bronze, 261 Pig iron, 165 chemical contents, 175 classification of, 175 definition of, 165 uses of, 176 Pig iron manufacture, 168 blast furnace, 168 accessories, 171 operation, 172 casting pigs, 175 electric furnace, 174 312 INDEX Pig iron manufacture, flux used, 172 fuel, 171 hot blast stoves, 171 slag, 174 Pig iron ores, 165 Plain concrete, 51 Plaster, 1 common lime, 19 of Paris, 1 wall, 19 Plasters, 1 Platinum, 258 Portland cement, 21 chemical specifications, 275 classification of, 21 definition of, 21, 275 manufacture of raw materials, 21 standard specifications and tests for, 275 uses of, 36 Portland cement manufacture, 21 adding retarder, 30 burning, 29 crushing materials, 25 dry process, 25 drying materials, 25 fine grinding of materials, 28 flow sheet, 23, 24, 31 grinding clinker, 30 material, 26 proportioning raw materials, 22 wet process, 32 Portland cement mortars, 37 abrasive resistance, 48 absorption, 48 adhesive strength, 47 cement, 37 compressive strength, 46 contraction. 48 definition, 37 effect of amount of mixing water, 44 of density of sand, 43 of size of sand, 43 of various conditions, 44 elements, 45 materials, 37 Portland cement mortars, miscella- neous properties, 48 mixing, 42 permeability, 48 properties, 43 proportioning, 42 sand, 37 shearing strength, 47 strength in general, 43 tensile strength, 46 transverse strength, 47 voids, 49 water, 37 weight, 49 Portland cement properties, 32 chemical constitution, 32 specifications, 32 expansion, 48 fineness, 35 specific gravity, 36 soundness, 33 strength, 34 time of set, 35 Portland cement specifications, 275 fineness, 276 inspection, 276 marking, 276 packages, 276 rejection, 276 soundness, 276 specific gravity, 275 storage, 276 tensile strength, 276 time of set, 276 Portland cement tests, 277 briquettes, 289 molds, 290 chemical analysis, 277 fineness, 281 Gillmore needles, 287 insoluble residue, 278 Le Chatelier apparatus, 280 loss on ignition, 277 magnesia, 279 mixing cement pastes, 282 mortars, 282 moist closet, 290 molding briquettes, 289 INDEX 313 Portland cement tests, normal con- sistency, 283 Ottawa sand, 288 sampling, 277 soundness, 284 steam apparatus, 284 specific gravity, 281 standard mortar, 284 percentage of water, 284 standard sand, 288 standard sieves, 281 storage of test pieces, 290 sulphuric anhydride, 278 tension, 288 testing briquettes, 289 time of set, 287 Vicat apparatus, 283 Properties of concrete, 74 Proportioning of concrete, 55 Puddling furnace, 199 Puzzolan cement, 6 Q Quicklime, 9, 13 R Rawhide, 272 Reverberatory regenerative furnace, 213 Riprap, 120 Ropes, 272 properties of, 273 wire, 273 Rubber, 269 belts, 273 derivation of, 269 properties of, 270 uses of, 271 vulcanizing of, 270 Rubble concrete, 83 Sand, 37 composition of, 38 for Portland cement mortars, 37 properties of, 38 Sand, sieve analysis, 38 standard, 39 substitutes for, 39 Sand-lime bricks, manufacture of, 111 Sandstone, 91 Sewer pipe, 113 properties of, 118 Sherardizing of iron and steel, 253 Shore scleroscope test, 237 Silicon steel, 247 Silver, 258 Slag cement, 6 Slaking quicklime, 16 Slate, 91 Solders, 265 Sorbite, 227 Sorel cement, 7 Special steels, 243 Specifications for structural steel for buildings, 291 Standard sand, 39 Standards, American Society for testing materials, list of, 297 Steel, 207 alpha iron, 227 aluminum, 247 annealing, explanation of, 229 austenite, 227 beta iron, 227 Bauer drill test, 237 Brinell hardness test, 237 coefficient of expansion of, 239 classification, 207 of carbon steels, 230 cold bending test, 236 compounds of, 224 compressive strength of, 233 constitution of, 224 corrosion of, 249 life under, 250 critical temperature, 226 definitions, 207 ductility of, 236 effect of alternating stresses, 237 of annealing. 232 of carbon, 230 314 INDEX Steel, effect of cold working, 232 of combined stresses, 235 of hardening, 232 of heat treatment, 232 of hot working, 232 of manganese, 232 of mechanical working, 232 of phosphorus, 232 of repeated stresses, 237 of silicon, 231 of sulphur, 231 electric welding, 238 elongation of, 233 eutectic solution, 225 eutectoid solution, 225 fatigue of, 237 galvanizing of, 254 gamma iron, 227 general classification, 177 hardening, explanation of, 228 hardness of, 237 Harvey ized armor plate, 224 heat treatment, 223 annealing, 223 case hardening, 224 hardening, 223 tempering, 223 Howe's classification, 177 hyper-eutectic solution, 225 hyper-eutectoid solution, 225 hypo-eutectic solution, 225 hypo-eutectoid solution, 225 iron carbide, 227 list of standards and tentative standards, 297 magnetic properties, 238 manufacture of, 208 martensite, 227 mechanical properties of, 229 molybdenum, 247 normal constituents of, 224 oxygen-acetylene welding proc- ess, 238 pearlite, 227 physical properties, 229 properties in general, 229 properties of rolled carbon steel, 234 Steel, rapid cooling of, 227 recalescence, 226 resistance to impact, 235 shearing strength of, 234 Shore scleroscope test, 237 silicon, 247 slow cooling, 227 sorbite, 227 specific gravity of, 239 strength formulas for carbon steels, 231 structural working stresses for, 230 structure of, 224 summarized specifications for, 239 tempering, explanation of, 228 tensile strength of, 232 thermit process for welding, 238 transverse strength of, 234 troostite, 227 tungsten, 247 tungsten-chromium-vanadium steel, 249 uses of, 241 uses of carbon steels, 241 weight per cubic foot of, 239 welding of, 238 working stresses for, 240 Steel aUoys, 244 aluminum, 247 chrome, 247 chromium-nickel, 248 chromium -vanadium, 248 classification of, 244 cobalt, 247 copper, 248 definitions of, 244 heat treatment of, 245 manganese, 246 molybdenum, 247 nickel, 246 nickel-vanadium, 249 silicon, 247 special, 243 tungsten, 247 tungsten-chromium-vanadium, 249 INDEX 315 Steel alloys, vanadium, 247 Steel belts, 274 Steel castings, 243 annealing of, 243 definition of, 243 founding of, 243 minimum requirements for, 244 properties of, 244 uses of, 243 Steel manufacture, acid Bessemer process, 211 acid open-hearth process, 215 basic Bessemer process, 212 basic open-hearth process, 216 Bessemer process, 209 converter, 209 mixer, 209 plant equipment, 209 billet heating furnace, 220 blowholes in ingots, 219 casting ingots, 219 cementation process, 208 comparison of different proc- esses, 219 crucible process, 208 defects in ingots, 219 duplex process, 218 electric process, 217 forging, 221 gas-fired pit furnace, 220 ingotism, 219 ingot molds, 219 open-hearth process, 213 furnace used, 213 plant equipment, 213 piping in ingots, 219 pressing, 221 reheating furnace, 220 ingots, 220 rolling, 220 mills, 220 segregation in ingots, 219 soaking pit, 219, 22C triplex process, 218 wire drawing, 222 Sterro-metal, 261 Stone, building, 89 Stone masonry, 119 Stone masonry, backing, 123 bond, 122 classification, 120 cleaning, 125 cut stone or ashlar masonry, 121 definitions, 119 dressing, 122 dry masonry, 120 general rules for laying, 124 in general, 119 mortar for, 122 pointing, 123 properties of, 125 riprap, 120 rubble masonry, 120 safe loads, 126 squared stone masonry, 120 strength, 125 waterproofing, 124 wet or mortar masonry, 120 Structural steel for buildings, standard specifications, 291 bend tests, 292 chemical composition, 291 chemical properties, 291 finish, 294 inspection, 294 ladle analysis, 292 manufacture, 291 marking, 294 number of tests, 294 permissible variation in thick- ness, 294 variations in weight, 294 physical properties, 292 rehearing, 296 rejection, 296 tension tests, 292 test specimens, 293 Surface finish of concrete. 70 Swedish wrought iron, 202 Table ware alloy, 263 Tentative standards, American Society for Testing Materials, list of, 297 316 INDEX Terne plates, 253 Terra cotta, 111 Timber, 135 air seasoning, 147 artificial seasoning, 147 bamboo, 143 beech, 143 black oak, 141 spruce, 139 walnut, 141 broad-leaved trees, general characteristics of, 140 butternut, 141 catalpa, 142 chestnut, 142 oak, 140 classification of, 144 cleavability of , 155 color of wood, 138 common rot, 151 compressive strength of, 154 conifers ; general characteristics, 139 Cyprus, 140 decay, 149 defects in, 145 dote, 146 Douglas fir, 139 dry rot, 150 durability, 149 endogenous trees, growth of, 137 structure of, 137 eucalyptus, 142 exogenous trees, growth of, 135 structure of, 135 factors of safety, 156 flexibility of, 155 grain of wood, 138 green ash, 141 gum, 142 hard maple, 141 hardness of, 156 hemlock, 140 hickory, 141 influence of moisture content, 153 injurious insects, 151 Timber, inspection of, 159 kiln drying, 147 knots, 146 lignum-vitse, 142 live oak, 141 locust, 142 logging, 143 mahogany, 142 marine wood borers, 151 miscellaneous properties, 156 natural seasoning, 147 Norway pine, 139 odor of wood, 138 Oregon fir, 139 palmetto, 143 pitch pockets, 146 poplar, 142 preparing the, 143 preservation, 160 A. C. W. process, 161 Allardyce process, 162 Bethell process, 161 boiling process, 161 Boucheri's process, 163 Breant process, 161 brush process, 160 Burnett's process, 162 card process, 163 copper sulphate, 163 creo-resinate process, 162 creosote process, 161 Kreodone process, 162 Kyan's process, 163 Lowry process, 162 non-pressure process, 160 Payne's process, 163 pressure process, 160 Ruping process, 162 Seeley's process, 161 Thilmany's process, 163 vulcanizing process, 163 Wellhouse process, 163 zinc chloride pressure process, 162 properties of, 152, 1'57, 158 red ash, 141 cedar, 140 heart, 146 INDEX 317 Timber, red ash, oak, 141 pine, 139 redwood, 140 rot, 146 safe working loads, 156 sawing, 144 selection of, 158 shakes, 146 shearing strength of, 155 shrinkage, 148 strength in general, 152 tamarack, 140 teak, 142 tensile strength of, 154 texture of wood, 138 toughness, 156 transverse strength of, 154 trees in general, 135 wane, 146 water seasoning, 147 wet rot, 151 white ash, 141 cedar, 140 elm, 141 maple, 141 oak, 140 pine, 139 spruce, 140 walnut, 141 white wood, 142 yellow pine, long leaf, 139 short leaf, 139 Tin, 257 extraction of, 257 plating, 257 properties of, 257 uses of, 257 Tobin bronze, 261 Trap, 90 Trees, 135 Troostite, 227 Tungsten steel, 247 -chromium-vanadium steel, 249 Turpentine, 267 Vanadium steel, 247 Varnishes, 267, 268 Voids, coarse aggregate, 53 in concrete, 53 in Portland Cement Mortar, 49 W Wall plaster, 19 Waterproofing brick masonry, 130 concrete, 72 stone masonry, 124 Welding of steel, 238 of wrought iron, 204 White lead, 267 Wire glass, 269 rope, 273 Wrought iron, 197 busheled scrap, 197 charcoal iron, 197 classification, of 197 composition of, 201 compressive strength of, 203 constitution of, 211 Corrosion, life under, 250 defects in, 201 definition, 197 ductility requirements, 205 effect of annealing, 202 of coal working, 202 engine-bolt iron, 197 fracture of, 203 making scrap, 201 miscellaneous properties, 205 plate, 197 properties of, 201 puddled iron, 197 refined bar iron, 197 shearing strength, 203 staybolt iron, 197 Swedish, 202 tensile strength, 202 requirements, 205 transverse strength, 203 uses of, 206 welding of, 204 working stresses for, 205 Wrought iron manufacture, 198 dry-puddling process, 200 318 INDEX Wrought iron manufacture, reheating muck bars, 201 rerolling muck bars, 201 rolling muck bars, 201 shingling puddle balls, 200 squeezing puddle balls, 200 treatment of puddle balls, 200 wet-puddling process, 198 boiling stage, 199, 200 cleaning stage, 199 furnace operation, 199 furnace used, 198 Wrought iron manufacture, wet pudding process, mate- rials for, 198 melting down stage, 199 Z Zinc, 256 extraction of, 256 properties of, 256 uses of, 257 Zinc white, 267 UBRAEY Return to desk from which borrowed. This book is DUE on the last date stamped below. DEC REC'D LD JUN7 1963 NOV3019658 REC'D HWlfa'65-lDPI LOAN DEPT, LD 21-100v-9,'47(A5702 8 16)476 4888-J9 kLBRARY