NK\v YOKE GH 



Portland cement 1 a Blow setting through long Btorag 



though at gain in ita Betting Bpeed if kept in a dry 



plac in drai 



meson ah ea that Borne cement, when taken from the 



mill and gaged with water, La found to be moderately Blow Betting, 



bui after 24 to 30 hours will Bet almost before il can be mixed. 



v it in a cool, dry place and in a few days it will become Blow 



setti 



T] ed of Betting usually decreases with I 



cement, provided it has been b1 >red in a dry place. Borne con- 

 sider that Blow Betting is due to free lime, but other factors a 

 enter into the problem, Buch as the underburning or overburning 

 incut, the underburned setting quicker. A vitrified 



I will never B< 



Boiling test 

 This is the one that has been recommended as the best for 

 ermining the soundness of a cement. At the fifth interna- 

 ti< oal convention for unifying methods for testing construction 

 materials, held in Zurich in September 1895, the rules for con- 

 ducting this test were laid down as follows. 



1 The rapidity test of hydraulic cements for constancy of vol- 

 ume consists in the application of warm Laths at temperatures 

 from 50° to 100° C. 



•1 Manner of making test pieces. Enough water is used to 

 bring the neat cement after proper working into a plastic sfc 

 Two balls from 1.5-2 inches diameter are formed by hand and 

 kept in moist air resting on Borne non-absorbent material. (Sand 

 mixtures are not subjected to this test, neither are briquets that 

 are to be for tensile Btrength.) The employment of ten- 



sion briquets and cylindric disks from 2 to 4 inches in diameter, 

 from \\ inches thick, is likewise permitted. 



:; Duration of previous hardening. Till set has taken place, 

 test pieces must be kept in moist air. Portland, Blag, pozzuolana, 

 and Roman cement will be kept uniformly thus for 24 hours, 



