CONCRETE CONSTRUCTION IN THE PHILIPPINE ISLANDS. 125 



Many gravels used for concrete structures in other parts of the Phil- 

 ippine Islands have proved themselves to be worse than the poorest 

 material from the Pasig River. From time to time concrete cubes taken 

 from the mixtures used for construction work have been submitted to 

 this laboratory for valuation. In many cases the concrete proved to 

 be of poor quality and almost without exception it was evident that the 

 weakness of the cubes was due to other causes than that of the quantity 

 or quality of the cement, which, it must be understood, had previously 

 been tested and accepted. 



In many cases the gravel was so poor as to crack and crumble under 

 light loads. For instance, two cubes of the concrete used for Bridge 

 jS'o. 14, P. & A. Road, Tayabas, Avere well proportioned and molded 

 concrete. "A" concrete was richer and harder than "B," and yet both 

 cubes possessed the same poor strength. As about 50 per cent of the 

 gravel cracked and crumbled under the light load recorded, it is evident 

 that the strength of the concrete was limited by the inferior quality of 

 the gravel. 



The results obtained were the following: 



Concrete etibes from Bridge Wo. 1>{, P. <G A. Road, Tayabas. 



Dimensions, in inches. 



Propor- 

 tions, by 

 volume. 



Age. 



Total strength, 

 in pounds. 



Total strength, 



in pounds, per 



square inch. 



Mark on cubes. 



First 

 crack. 



Ulti- 

 mate. 



First 

 crack. 



Ulti- 

 mate. 



i 4X4X4 { 



•1 :]2 : 4 

 1:3:6 



Days. 

 28 

 28 



5, 305 

 7,015 



9,900 

 9,800 



331 



438 



619 

 612 



Class "A". 

 Class "B". 



The results obtained with cubes taken from the concrete used for 

 Carcar Bridge, Province of Cebu, project E-16, are especially instructive. 

 The rich class "A" concrete was stored in water two weeks and then 

 exposed in the open air for the remainder of the sixty days. Con- 

 sequently the cement had ample opportunity to harden. The mortar 

 in each case was rich and durable and in each the strength obtained 

 varied directly as the quality of the gravel used. 



