CONCRETE CONSTRUCTION IN THE PHILIPPINE ISLANDS. 137 



In like manner, the sand as delivered was not of uniform character, the per- 

 centages of gravel in it varied from 5.5 per cent to 38.5 per cent. 



Samples of Mariquina River sand and gravel were used for another structure 

 where the specifications called for a 1:3:6 mixture. The sand was screened 

 through a sieve with ^-centimeter rectangular openings, and the gravel washed 

 with water thrown over the pile before it went into the mixture. The effect of 

 the water was to remove the dirt and make the sand adhere more persistently to 

 the gravel. Analysis of the washed gravel gave the following: 



Held on 

 Held on 

 Held on 

 Held on 

 Held on 

 Held on 

 Held on 

 Held on 

 Through 



3.81-centimeter 

 2.54-centimeter 

 1.70-centimeter 

 1.14-centimeter 

 0.76-eentimeter 

 0.51-centimeter 

 0.38-centimeter 

 0.25-centimeter 

 0.25-eentimeter 





Per cent 



openings 



1 



openings 



2.2 



openings 



10.3 



openings 



27.8 



openings 



49.1 



openings 



63.1 



openings 



77.3 



openings 



87.0 



openings 



91.2 



Percentage of voids 



31.5 



This gravel contained 36.4 per cent sand; therefore the 1: 3 mortar relied upon 

 by the designers to bind the gravel was weakened to a 1:5.18 in actual con- 

 struction. 



For similar reasons 1:2:4 concrete made from crusher run Sisiinan stone 

 showed greater strength when the dust and fine mateial had been removed from 

 the stone, 

 tion, division of port works, and tested here. 



The concrete cubes recorded below were made at the Bureau of Naviga- 



Compression tests of 1:2: 4 Sisiman stone concrete. 



No. 



Age. 



Strength, in 

 pounds, per 

 square inch. 



Remarks. 



First 

 crack. 



Ulti- 

 mate. 



1 



2 



3 



4 



Days. 

 24 

 24 



10 



10 



1,080 

 1,309 



427 

 385 



1,319 



1,744 



601 

 771 



Made with Orani sand, a standard cement, and crusher run stone. 



Same as above with all material passing one-half inch screen re- 

 moved from stone. 



Made with Pasig sand, a standard cement, and crusher run stone. 



Same as above with all material passing one-half inch screen re- 

 moved. 



Because of these results it was assumed that the fine material in this stone 

 was detrimental to its value. However, this was not proved. If we measure 

 and consider the fine material passing the one-fourth inch screen as sand and 

 make allowance for it as such in the mortar mixture, different results may be 

 obtained. A 1:1.5:4 mixture may show better results than the best 1:2:4 

 mixture recorded and give as great a volume of concrete as with the fine material 

 screened out. 



