114 



The Philippine Journal of Science 



191S 



of profit; and, as a result, there are many local officials who 

 believe that the present system for purchasing cement is the 

 most economical and that any expenditure in excess of the lowest 

 bid would be only an unnecessary expense. However, the records 

 of cement testing show that the manufacturers who secure such 

 contracts supply cement which tends to meet the minimum 

 requirements of our specifications rather than those of a high- 

 grade cement. This is especially true of cements imported into 

 the Philippine Islands, where standard, 1 : 3, Ottawa-sand 

 mortars, showing a strength over 400 pounds per square inch 

 between the periods of three months and two years, are as rare 

 as they should be common. 



Careful investigation has shown that practically all of the 

 cements which have been purchased by the local Government 

 from the lowest bidder could have been considerably improved 

 at a very small expense by better burning, by proper seasoning, 

 or by finer grinding. The following instance will serve to show 

 that the same is true of Portland cements purchased in other 

 parts of the world. One of the best-known, high-grade, Amer- 

 ican cements was reground in a tube mill so that 88 instead of 

 78 per cent passed a 200-mesh sieve. Concrete made with this 

 cement before and after regrinding was then molded into six- 

 inch cubes and crushed after three months. In each case the 

 sand, gravel, water, and the proportions by weight were the 

 same. The average results obtained are recorded in Table III, 

 which also includes the tensile and compressive strengths de- 

 veloped by the ordinary briquettes. 



Table III. — The strength developed by a high-grade Portland cement before 



and after regrinding. 



SIX-INCH, CONCRETE CUBES. 



Cement. 



Propor- 

 tions 

 by 

 volume. 



Age in days. 



Compressive strength. 



In moist 

 air. 



Wea- 

 thered 

 outside. 



Total in pounds. 



In pounds per square 

 inch. 



First 

 crack. 



Ultimate. 



First 

 crack. 



Ultimate. 



As received 



1:2:5 

 1:2:5 



21 

 21 



70 

 70 



55,745 

 64,408 



72, 955 

 92, 135 



1,550 

 1,800 



2,027 

 3,659 



Reground 





