68 STANDARD SPECIFICATIONS 



in diameter, -J-in. thick at center, tapering to a thin edge, shall 

 be kept in moist air for a period of 24 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. 



(c) These pats are observed at intervals for a least 28 days, 

 and, to satisfactorily pass these tests, should remain 

 firm and hard and show no signs of distortion, checking, 

 cracking, or disintegrating. 



PORTLAND CEMENT 



300. Definition. 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 cal- 

 careous materials, and to which no addition greater than 3 per 

 cent, has been made subsequent to calcination. 



301. Specific Gravity. The specific gravity of cement shall 

 not be less than 3.10. Should the test of the cement as 

 received fall below this requirement, a second test may be made 

 upon a sample ignited at a low red heat. The loss in weight of 

 the ignited cement shall not exceed 4 per cent. 



302. Fineness. It shall leave by weight a residue of not 

 more than 8 per cent on the No. 100, and not more than 25 per 

 cent on the No. 200 sieve. 



303. Time of Setting. It shall not develop initial set in less 

 than 30 minutes, and must develop hard set in not less than 1 

 hour, nor more than 10 hours. 



304. Tensile Strength. The minimum requirements for 

 tensile strength for briquettes 1 sq. in. in cross section shall 

 be as follows, and the cement shall show no retrogression in 

 strength within the periods specified: 



NEAT CEMENT 

 Age. Strength. 



24 hours in moist air 175 Ibs. 



7 days (1 day in moist air, 6 days in water) 500 ' ' 



28 days (1 27 " " ) 600 " 



ONE PART CEMENT, THREE PARTS STANDARD OTTAWA SAND 



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



28 days (1 " 27 ) 275 " 



