water and the immersing in fresh, the difference is not so striking. Although these tests show that cement mortar is weakened by the action of salt water, works have been carried on of sufficient time and extent to make it certain that the deterioration is not dangerous. This becomes important in studying the action of frost on mortars, as it is customary to add salt to the water for mortar-mixing, when it must be used at low temperatures. Mr. James J. R. Croes gives as a rule: " Dissolve 1 pound of rock salt in 18 gallons of water when the temperature is at 32° F., and add 3 ounces for every 3 degrees of temperature." He adds that masonry laid with such mortar stood, well and showed no signs of having been affected by the frost. Mr. Alfred Noble states that a pier was built on the Northern Pacific Railroad near Duluth at a temperature varying from 0 to 20°. Portland cement was used for the mortar in proportions of 1 to 13 for face stone and 1 to 24 for backing. Salt was dissolved in the water, and the sand was warmed. The mortar froze very quickly, and several months afterwards was found to have perfectly set and to be in as good condition as that laid in milder weather. Table No. 30 gives the result of some of his experiments to determine the effect of salt upon the mortar, and Table No. 31 the combined effect of salt and freezing. The amount of salt seems to make no material difference, although the figures are slightly less for the greater quantities, and, as in the previous tables, the salt water gives poorer results than the fresh. These figures show some gain when salt water is used for the mixture and the briquettes immersed in fresh, and decided increase when they were frozen for six days and immersed in water long enough to thaw, but not a sufficient time to gain an additional set. The table would be of more value if it extended over a longer period of time. Table No. 32 is taken from paper read before the Canadian Society of Civil Engineers in February, 1895, by Prof. Cecil B. Smith of McGill University. Set No. 1 was submerged, after 24 hours, in water of laboratory tank. TABLE NO. 30. Proportions: cement 1, sand 1, volume; cement 21 ounces; sand 23 ounces; water 6 ounces. Figures are tensile strength per square inch. Salt. 7 Days. 30 Days. 90 Days. 6 Months. 9 Months. 12 Months 18 Months 2 Years. Immersed in test-room when removed from moulds... Exposed to air and frozen three days, then immersed in test-room four days... Immersed in test-room when removed from moulds... 327 357 375 392 429 402 415 388 402 316 378 411 374 415 405 392,383 409 336 422 421 399 394 384 390 356 387 Exposed to air and frozen six days, then exposed to air in test-room at 70° one day. 169 198 167 217 215 208 221 221 239 Set No. 2 was kept on damp boards in a closed tank for the whole period, and never allowed to dry out. Set No. 3 was allowed to set in the laboratory, and then exposed to the severe frost and left in open air for the whole period. Set No. 4 was exposed in from 8 to 10 minutes to the severe frost and left there for the whole period. The important deductions from the Portland tests are: 1. That mortar immersed in water is stronger than when used in air; 2. That mortar exposed to temperature below freezing and kept there till set is stronger than when allowed to set in air and then exposed to frost; 3. That mortar kept in damp air was the weakest of all the different conditions experimented on. It will be noticed from the results of the tests of the natural cement: 1. That, contrary to the Portlands, these cements should not be used if the mortar must be exposed at once to frosts; 2. That from the neat tests no time deductions can be made of a sand mixture, as in every case when mixed with fresh water the 1-to-1 compound was considerably stronger than the neat; 3. That No. 2 in every case but one was the strongest, while with the Portland it was the weakest; 4. That the addition of salt to the mixing water added very materially to the strength of the briquettes when exposed to the frost. Table No. 33 gives the results of some experiments made by Mr. A. C. Hobart and published in The Technograph, No. 12, 1897-98. In all cases the briquettes were frozen six days after having been allowed to set, as shown in the table. They were thawed from 18 to 20 hours and then broken. The upper line of figures for each mortar is the strength in pounds per square inch of the unfrozen briquettes, and the lower is the percentage of the strength frozen to the strength unfrozen. Table No. 34 gives the result of some tests made on 12-inch concrete cubes by Mr. W. A. Rogers, Assistant Engineer of the Chicago, Milwaukee, and St. Paul Railway at Chicago. "Atlas" Portland and Louisville natural cements were used. The proportions were: Atlas, 1 cement, 3 gravel, and 4 broken stone; and Louisville, 1 cement, 2 gravel, and 4 broken stone. Eight cubes were made of each cement, two being mixed with water to which Clark's Utica neat. 1 to 1 2 to 1..... Louisville Star neat. 1 to 1 2 to 1 Akron neat.... 1 to 1.... 2 to 1.... 1 321 337 341 172 2 3 6 12 24 48 72 168 336 372 374 400 352 379 327 672 79 80 80 67 69 52 100 184 186 187 193 296 331 58 77 75 75 80 79 75 75 105 102 33 43 62 58 Louisville Black Diamond neat.... 1 to 1... 2 to 1..... 260 271 303 391 56 57 58 79 79 82 68 87 102 129 143 138 146 161 226 86 92 116 129 120 108 98 128 26 15 33 48 54 69 74 87 124 46 27 59 86 96 113 114 121 125 43 126 64 80 92 88 107 93 140 132 150 120 116 127 152 163 143 135 140 154 199 one pint of salt to ten quarts of water had been added, and the others with fresh water. Capacity of machine 185,000 pounds. a showed signs of failure, b showed no signs of failure. The cubes kept out of doors were subjected at once to a temperature considerably below zero. During this exposure the weather was the coldest experienced in Chicago for twenty years, but subsequently grew warmer, so the cubes froze during the night and thawed during the day. The deductions the author of the paper makes for the mixture is: "Freezing before setting does not seem to injure the Portland-cement concrete even if, after having frozen hard, the concrete is exposed to freezing and thawing weather. Exposing green Portland cement concrete to a freezing temperature seems to affect its rate of hardening, making it slower, but eventually the concrete will be just as good as if it had not been exposed to the cold. The use of salt seems largely to counteract the effect of cold in causing slow hardening.' He also makes the same deductions for Louisville cement, except that he thinks the use of salt seems to have little if any effect on the strength of the cubes exposed to the cold. Mr. Noble describes the construction of an anchor-block of concrete. This was built during freezing weather, a portion of the time below zero, with about one-half of the mass below water. The mixture was 1 part Milwaukee cement, 2 parts sand, and 4 to 5 parts broken stone. The material and water were heated, a double handful of salt being added to each part of water. Ice formed over the top of the concrete every night until the mass was above the water-level. No attempt was made to protect the concrete from frost, and six months after it was laid it was found to be thoroughly set. These experiments cover quite a period of time and were made by different people under very different conditions. As a rule the same general deductions can be made from them. That is, that with proper precautions good results can be obtained by the use of cement mortar in cold weather; that a freezing temperature |