making tests of mortar briquets, which have been kept in hot water, seems, to be the most rational accelerated test for soundness. This method was used in Germany several years ago, when it was claimed that a definite relation existed between the results thus obtained and the longer time cold water tests. This theory being disproved, threw discredit on the hot test, but M. Deval1 has since made many experiments showing that it is of much value in detecting bad products.
The method consists in making briquets with three parts sand to one of cement, and after twenty-four to seventy-two hours in moist air, according to the rate of setting, immersing them in water maintained at 80° C, the briquets being broken after an immersion of from two to seven days. These hot water briquets are to be compared with briquets stored in water of the ordinary temperature and broken at seven and twenty-eight days after immersion.
1 "Hot Tests for Hydraulic Cements," M. Deval, Bull. Soc. d'Encouragement, etc., 1890, pp. 560-583.
127. Among other tests M. Deval compared the results obtained with six samples of Portland cement as follows: —
Good finely ground cement of modern make.
Coarsely ground cement of good quality, but partially aerated.
Quick setting cement with low per cent, lime and lighter burn.
Made from clinker having property of disintegrating spontaneously while cooling; large proportion of inert material.
Under-burnt cement; contains free lime. No. 6. Over-limed cement.
The results of the tests are given in the following table: —
Tensile Strength in Kilos per Sq. Cm.
No. 4, when allowed forty-eight hours to set, gave 3.2 kilos at two days, and 4.3 kilos at seven days, when tested hot. Among the cements which disintegrated in the hot water, the only one that gave a high result cold was No. 6, and this sample, it is stated, would crack and swell badly even in cold water if mixed neat. It is quite possible, however, that a sample might be found which, not having quite as flagrant defects as No. 6, would pass all the cold tests but be condemned by the hot test.
128. The conclusions drawn from these experiments have been stated as follows: —
"(1) Tests made cold do not indicate the quality of the cement, inasmuch as cement containing excess of lime, and, in consequence, deplorably bad, may give excellent results".
"(2) Portland cement of good quality, mixed with normal sand in the proportion of one to three, resists water at 80° C. Its strength at two and seven days after setting is about equal to that which it would have at seven and twenty-eight days in the cold".
"(3) Poor cement containing much inert material does not resist the action of water at 80° C. unless the setting be allowed to proceed for some days before immersion".
"(4) Cements containing free lime do not withstand the action of water at 80° C. if immersed twenty-four hours after setting." Comparison of the strength hot and cold will suffice for the detection of even small quantities of free lime.
129. Before passing to the comparison of the tests for soundness already outlined, a few other tests which have been suggested for use may be briefly mentioned.
The Chloride of Calcium Test depends on the fact that slaking of free lime is hastened by feeble solution of chloride of calcium. (See § 107.) Concerning this test, Prof. F. P. Spalding1 says he "has found it to give true indications in a number of cases, including some unsound magnesian cements. It consists in mixing the mortar for the cakes with a solution of 40 grammes chloride of calcium to one liter of water, allowing them to set, immersing them in the same solution for twenty-four hours, and then examining them for checking and softening as in other tests".