254 STRENGTH OF MATERIALS 



Constancy of volume. Pats of neat cement about 3 in. in diameter, \ in. 

 thick at the center, tapering to a thin edge, shall be kept in moist air for a 

 period of twenty-four hours. 



(a) A pat is then kept in air at normal temperature. 



(6) Another is kept in water maintained as near 70 F. as practicable. 



These pats are observed at intervals for at least twenty -eight days, and, to 

 satisfactorily pass the tests, should remain firm and hard and show no signs 

 of distortion, checking, cracking, or disintegrating. 



PORTLAND CEMKNT 



This term is applied to the finely pulverized product resulting from the 

 calcination to incipient fusion of an intimate mixture of properly proportioned 

 argillaceous and calcareous materials, and to which no addition greater than 

 3 per cent has been made subsequent to calcination. 



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

 100 C., shall be not less than 3.10. 



Fineness. It shall leave by weight a residue of not more than 8 per cent on 

 the No. 100 sieve, and not more than 25 per cent on the N<>. _'<() sieve. 



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

 and hard set in not less than one hour nor more than t.-n hour-. 



Tensile strength. Tin* minimum ivi[uirements for tensile strength for bri- 

 quettes 1 in. square in section shall be \vithin the following limits, and shall 

 show no retrogression in strength within the periods sj>ecified.* 



Neat 

 AGE si KI iron 



24 hours in moist air ........... ir0-'JOO Ib. 



7 days (1 day in moist air, 6 days in water) . . . 450-5."><> 

 28 days (1 " 27 ) . . . 550-650 



One Part Cement, Three Parts Sinmlnrd Sand 



7 days (1 day in moist air, 6 days in water) . . . 150-200 Ib. 

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



Constancy of volume. Pats of neat cement about 3 in. in diameter, \ in. 

 thick at the center, and tapering to a thin edge, shall be kept in moist air 

 for a period of twenty-four hours. 



(a) A pat is then kept in air at normal temperature and observed at intervals 

 for at least twenty-eight days. 



(6) Another pat is kept in water maintained as near 70 F. as practicable, 

 and observed at intervals for at least twenty -eight days. 



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

 should be some value within the limits of 1 .TO and 'JOO Ib., and so on for each period stated. 



