att : ANNUAL REPORT 
‘cements are open to suspicion. Indirectly the tensile strength is a test for 
fineness of grinding, for, given a certain cement, it will show a greater 
tensile strength the finer it is ground. Silicious cements are occasionally 
looked upon with distrust owing to their comparatively low tensile strength 
in the short time tests. This, however, is due to the slower hardening of 
these cements and not to any inherent weakness, for they show an ex- 
ceedingly high tensile. strength after three months, the writer recollecting 
several instances in which silicious cements pulled considerably higher 
than 1,000 pounds, neat. Ueaeae 
On the other hand, aluminous cements show a very high initial tensile 
strength, but after some time a significant decrease in strength is observed, 
which not uncommonly results in the destruction of the cement structure. 
It is, hence, always preferable to use a cement showing a steady increase 
in strength, though the initial strength may not be high. Very high 
initial tensile strengths are to be regarded with suspicion and will be 
found to be indicative of weakness rather than strength. In American 
practice crushed quartz not coarser than 20 mesh and not finer than 30 
mesh is used as the standard sand and though, owing to the large propor- 
tion of voids, it does not produce the densest and hence strongest mixture, 
it affords a uniform standard of comparison. The following table indi- 
cates the required tensile strengths in American practice: 
A.—Neat cement. 
1 hour in air, 23 hours in water, 100-140 pounds per square inch. 
1 day in air, 6 days in water, 250-550 pounds per square inch. 
1 day in air, 27 days in water, 350-700 pounds per square inch. 
1 day in air, 364 days in water, 450-800 pounds per square inch. 
B.—One part of cement (by wt.) to three parts standard sand. 
1 day in air, 6 days in water, 80-125 pounds per square inch. 
1 day in air, 27 days in water, 100-200 pounds per square inch. 
1 day in air, 364 days in water, 200-350 pound per square inch. 
To indicate how American cements run, the breaking figures of a 
well-known cement might be quoted,* which are interesting, since they 
represent the averages, of many tests. The briquettes were made of 
Giant cement, with standard sand in the proportion of I cement: 2 sand. 
Time. 28 days.| 3 mos. 6 mos. 9 mos. | 12 mos. | 
Number of breakines:) sc.) 9-49: oon} CSO) 215 185 155 165 
Aven break. weight, pounds per sq.inch..| 441 5638 | 657 671 663 
*O. S. Gowen, Proceedings, Amer. Society for Testing Materials July, 1903: 
