1 34 REIBLING. 



Sand for Bocaue Bridge (dirt and fine material 2.8 per cent by weight.) 



Sand. 



Tensile strength, 7 days. 



1:2 



mortar. 



,.o Per cent 



mortar ; efficiency 

 mortar. 1:3mortar . 



Bocaue Bridge (washed).— 

 Bocaue Bridge (unwashed)__ 

 Standard quartz _ 



283 

 277 



170 | 68.5 

 172 I 69.3 

 248 ' 







1 



Sometimes the granularmetric composition of the sand can be much improved 

 by screenings from the gravel, and vice versa. Thus, samples of the only available 

 sand and gravel for the Trade School building at Malolos, sent to the laboratory, 

 proved of good quality in every respect but that of its granularmetric composition. 

 The sand was very fine, 51.5 per cent passed through the 40- and remained on 

 the 50-mesh sieve. The gravel was clean and hard, but contained 40.7 per cent 

 of sand passing the 4-mesh sieve. 



It frequently happens that aggregates do not permit recomposition, but in this 

 case it was easily accomplished. 



The gravel was screened on a 4-mesh sieve and the coarse sand thus obtained 

 was mixed with the fine in the proportion of 3 to 1. The percentage of voids in 

 the sand thus produced was reduced from 40.4 to 36.2 per cent. 



Comparative compression tests showed a gain in efficiency of almost 60 per 

 cent, and a dense, impermeable concrete was obtained even" with a 1:3:6 mixture. 

 It was found practicable to follow this method in practice and the materials were 

 so used. 



Relative compression strength of Malolos concrete using sand, and a mixture of 

 this sand and sand screened from the gravel. 



M . . Relative compression 

 Mixture. strength. 



1 cement, 3 sand, 6 gravel 



622 



1 cement, 3 sand mixture, 6 gravel (1 





sand, 3 sand screened from the 





gravel ) . 



992 



1 cement, 2 sand, 4 gravel 



1,230 



The examples given, though incomplete and stated briefly, are con- 

 sidered sufficient to show the variable nature of available sands and 

 gravels in the Philippines and to indicate the value of reliable and 

 exact knowledge concerning their characteristics. However, such tests 

 are not to be relied upon implicitly, because they were not made under 

 working conditions, and the time was too short in which to complete 

 them. The material should be tested before the building specifications 

 are drawn up, and not after the materials are delivered. In some cases 

 tests have been put off until the time for construction had nearly arrived 

 and then only a few pounds of the sand and gravel were sent to the 

 laboratory for a five or seven day test, which was necessarily of question- 

 able value. If this work is worth doing at all, it is worth doing well. 



