120 



Tensile Strength. 



15. The minimum requirements for tensile strength for 

 briquettes 1 in. square in cross section shall be within 

 the following limits, and shall show no retrogression in 

 strength within the periods specified:* 



Age. Neat Cement. Strength. 



24 hours in moist air 50-100 Ib. 



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

 28 days (1 day in moist air, 27 days in water) . .200-300 Ib. 



One Part Cement, Three Parts Standard Sand. 



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



28 days (1 day in moist air, 27 days in water) . . 75-150 Ib. 



Ponstancy of Volume. 



16. Pats of neat cement about 3 in. in diameter, % 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. 



(b) Another is kept in water maintained as near 70 

 F. as practicable. 



17. These pats are observed at intervals for at least 

 28 days, and, to satisfactorily pass the tests, should remain 

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

 cracking or disintegrating. 



PORTLAND CEMENT. 



18. Definition. This term is applied to the finely pul- 

 verized 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% has been made subsequent to 

 calcination. 



Specific Gravity. 



19. The specific gravity of the cement, thoroughly dried 

 at 100 C., shall be not less than 3.10. 



Fineness. 



20. It shall leave by weight a residue of not more than 

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

 200 sieve. 



Time of Setting. 



21. It shall develop initial set in not less than 30 min- 



For example, the minimum requirement for the 24 hour 

 neat cement test should be some value within the limits of 

 60 and 100 Ib., and so on for each period stated. 



