SPECIFICATIONS FOR PORTLAND CEMENT. 627 



paste that will leave the trowel cleanly in a compact mass. Fresh 

 water is to be used for gauging, the temperature thereof, and of the test- 

 room at the time the said operations are performed, being from 58 to 

 64 F. 



The cement gauged as above is to be filled, without mechanical ram- 

 ming, into molds ; each mold resting upon an iron plate until the cement 

 has set. When the cement has set sufficiently to enable the mold to be 

 removed without injury to the briquette, such removal is to be effected. 

 The said briquettes shall be kept in a damp atmosphere and placed in 

 fresh water twenty-four hours after gauging and kept there until broken, 

 the water in which the test briquettes are submerged being renewed 

 every seven days and the temperature thereof maintained between 58 

 and 64 F. 



Neat tests. (10) Briquettes of neat cement are to be gauged for 

 breaking at seven and twenty-eight days, respectively, six briquettes 

 for each period. The average tensile strength of the six briquettes 

 shall be taken as the accepted tensile strength for each period. For 

 breaking, the briquette is to be held in strong metal jaws, the briquettes 

 being slightly greased where gripped by the jaws. The load must 

 then be steadily and uniformly applied, starting from zero, increasing 

 at the rate of 100 Ibs. in twelve seconds. The briquettes are to bear 

 on the average not less than the following tensile stresses before breaking: 



7 days from gauging 400 Ibs. per square inch of section. 



28 days from gauging 500 Ibs. per square inch of section. 



The increase from seven to twenty-eight days shall not be less 

 than: 



25% when the 7-day test falls between 400 to 450 Ibs. per square inch. 



20% when the 7-day test falls between 450 to 500 Ibs. per square inch. 



15% when the 7-day test falls between 500 to 550 Ibs. per square inch. 



10% when the 7-day test falls between 550 Ibs. per square inch or 

 upwards. 



Sand tests. (11) The cement shall also be tested by means of 

 briquettes prepared from one part of cement to three parts by weight 

 of dry standard sand, the said briquettes being of the shape described 

 for the neat-cement tests; the mode of gauging, filling the molds, and 

 breaking the briquettes is also to be similar. The proportion of water 

 used shall be such that the mixture is thoroughly wetted, and there 

 shall be no superfluous water when the briquettes are formed. The 

 cement and sand briquettes are to bear the following tensile stresses: 



7 days from gauging 120 Ibs. per square inch of section. 



28 days from gauging 225 Ibs. per square inch of section. 



