LIME, CEMENT, AND CONCRETE 253 



205. Compression tests. Compression tests of cement are made 

 in Europe, but not generally by engineers in the United States, as 

 the tensile test is thought quite as valuable as the compression test 

 in giving results indicative of the strength of the cement. Compres- 

 sion tests are made upon the ends of the specimen broken in tension, 

 or upon specially prepared cement cubes. The use of the broken ends 

 of the briquette insures the same material for the compression test as 

 was used in the tension test. The table on page 252 gives the com- 

 pressive strength of several brands of cement* The tests were made 

 by compressing halves of briquettes broken in tension, and both the 

 tensile and compressive strengths are given. 



206. Standard specifications for cement. The following is a copy 

 of the standard specifications for cement recently proposed by the 

 American Society for Testing Materials. 



NATURAL CEMENT 



This term shall be applied to the finely pulverized product resulting from 

 the calcination of an argillaceous limestone at a temperature only sufficient 

 to drive off the carbonic acid gas. 



Specific gravity. The specific gravity of the cement, thoroughly dried at 

 100 C., shall be not less than 2.8. 



Fineness. It shall leave by weight a residue of not more than 10 per cent 

 on the Xo. 100 sieve, and not more than 30 per cent on the No. 200 sieve. 



Time of setting. It shall develop initial set in not less than ten minutes, 

 and hard set in not less than thirty minutes nor more than three hours. 



Tensile strength. The minimum requirements for tensile strength for bri- 

 quettes 1 in. square in cross section shall be within the following limits, and 

 shall show no retrogression in strength within the periods specified, f 



Neat Cement 

 AGE STRENGTH 



24 hours in moist air 50-100 Ib. 



7 days (1 day in moist air, 6 days in water) . . . 100-200 

 28 days (1 " 27 " '" ) . . . 200-300 " 



One Part Cement, Three Parts Standard Sand 



7 days (1 day in moist air, 6 days in water) . . . 25- 75 Ib. 

 28 days (1 " " " 27 " ".)..,. 75-150 " 



* Watertown Arsenal Report, 1901. 



t For example, the minimum requirement for the twenty-four-hour neat cement test 

 should be some value within the limits of 50 and 100 Ib., and so on for each period stated. 



