740 KEW YOEK STATE MUSEUM 



WEIGHT 



The relation of tlie weight of cement to its tensile strength is 

 an uncertain one. In practical work, if used alone, it is of little 

 value as a test, while in connection with the other tests recom- 

 mended it is unnecessary, except when the relative bulk of equal 

 weights of cements is desired. 



We recommend that the cubic foot be substituted for the bushel 

 as the standard unit, whenever it is thought best to use this test. 



SETTING 



The rapidity with which a cement sets or loses its plasticity 

 furnishes no indication of its ultimate strength. It simply shows- 

 its initial hydraulic activity. 



For purposes of nomenclature, the various cements may be- 

 divided arbitrarily into two classes, namely ; quick setting, or those- 

 that set in less than one half hour; and slow setting, or those 

 requiring one half an hour or more to set. The cement must 

 be adapted to the work required, as no one cement is equally 

 good for all purposes. For submarine work a quick setting ce- 

 ment is often imperatively demanded, and no other will answer,, 

 while for work above the water line less hydraulic activity will 

 usually be preferred. Each individual case demands special treat- 

 ment. The slow setting natural cements should not become warm 

 while setting, but the quick setting ones may, to a moderate ex- 

 tent, within the degree producing cracks. Cracks in Portland 

 cement indicate too much carbonate of lime, and in the Yicat 

 cements too much lime in the original mixture. 



SAMPLING 



There is no uniformity of practice among engineers as to the- 

 sampling of the cement to be tested, some testing every tentk 

 barrel, others every fifth, and others still every barrel delivered. 

 Usually, where cement has a good reputation, and is used in largo 

 masses, such as concrete in heavy foundations or in the backing^ 

 or hearting of thick walls, the testing of every fifth barrel seems- 

 to be sufiicient; but in very important work, where the strength 

 of each barrel may in a great measure determine the strength of 

 that portion of the work where it is used, or in the thin walls of 

 sewers, etc., every barrel should be tested, one briquet being 

 made from it. , c. 



In selecting cement for experimental purposes, take the samples^ 

 from the interior of the original packages, at sufficient depth to 



