626 The Philippine Journal of Science 1923 



cannot be separated economically from our bituminous rock 

 and another sand substituted for it. The study of mineral 

 aggregates used in road building requires an examination of 

 fineness of grain and the determination of chemical composition. 

 The mineral matter impregnated with bitumen in our case 

 consisted of loose white grains which were held together be- 

 cause of the cementing bitumen and which crumbled to powder 

 when the bitumen was extracted with solvents. The size of 

 the grains was determined by Mr. A. E. W. King, of the Bureau 

 of Science. The sand sieved as follows: 



Passing 200-mesh sieve 16.95 



Passing 80-mesh 1 



Passing 50-mesh s 



Passing 40-mesh sieve 



Passing 30-mesh s 



Passing 20-mesh i 



Passing 10-mesh sieve 2.73 



Retained on the 10-mesh sieve 0.14 



99.29 



The size of grains desirable in asphaltic pavements depends 

 on the character of the traffic that the pavement is destined 

 to bear. Very fine grains permit the obtaining of closely bound 

 and smooth asphaltic surfaces, but the pavement thus obtained 

 cannot withstand heavy traffic so well as can a pavement made 

 of coarse sand. On the other hand, pavements made of coarse 

 sand must contain a high percentage of bitumen, as otherwise 

 they are likely to crack easily. In general, moderately sized 

 grains, such as those of our samples, are preferable for all 

 purposes. They have a sufficient content of coarse grains and 

 an appropriate amount of fine particles to fill the voids between 

 the coarse grains. 



The chemical composition of our mineral aggregate, as de- 

 termined by Mr. E. Gutierrez, of the Bureau of Science, was 

 found to be as follows: 



Water ^Vlt 



Silica (SiO.) 7.48 



Iron oxide (Fe*0 3 ) 0.96 



Aluminum oxide (A1 : 0,) 4.58 



Calcium oxide 47.44 



Magnesia (MgO) 1.82 



Combined CO, 37.20 



Total 99.96 



