478 ADAMS. 



.UifiRKGATES. 



Pasiij mnd and Mariqiivna gravel. — In most of the coucrete work in 

 Manila, Pasig sand and Mariqiiina gravel are used. In the tests recorded 

 above the sand in tensile strength briquettes showed in a seven-day test 

 but 65 per cent efficiency when compared with crushed quartz, and it 

 has Ijeen demonsti'ated by crushing concrete blocks that a large percentage 

 of tlio gi'avcl breaks under a lower compressive force than the mortar 

 will sustain. Concrete blocks of Pasig sand and Mariquina gi'avel in 

 the propoi'tiDus 1:2:4-1:2:5-1:2:6 showed but little difference in 

 compression tests. This is explained by the fact that the gravel is weak 

 and that the concrete crushed below the ultimate strength of the mortar. 



Sangley sand and Sisiman crushed stone. — This combination has been 

 used extensively, as, for example, in the construction of the sewers. The 

 stone is of good quality since a block of it cnished under a pressure of 

 1,115 tons per square foot. The Sangley Point sand has at seven days 

 an eflSciency of but 55 per cent. The crushing strength of concrete 

 made with this aggi'egate has not been determined, but it is probably 

 low, since the efficiency of the sand is low and the ultimate strength of 

 the mortar will not approach that of the stone. 



Sangley sand and Mariquina gravel. — This is the poorest aggregate 

 which is used in Manila, and yet Mariquina gi'avel has been suljstituted 

 for Sisiman stone in some cases where Sangley sand was used. The 

 crushing strength of concrete made from these materials is yet to be 

 determined. 



Pasig sand and Sisiman stone. — This aggregate has not been much 

 employed. It should prove superior to those above mentioned but 

 concrete made from it will jDrobably fall far beloiv the limit of the stone, 

 since the sand has an efficiency of only 66 per cent in seven-day tensile- 

 strength tests. 



Orani sand and Pasig gravel. — This aggregate has l)een used in the 

 base of concrete paving blocks where but little strength is required. 

 For constructions requiring great strength the coml>iiiation is not desir- 

 able, since the gravel is not efficient. The mortar used in the surface 

 of the paving blocks was found to be superior in finality to those of 

 blocks made with Pasig sand. 



Orani sand and crushed stone. — Orani sand and Sisiman stone have 

 been used in reconstructing the shaft of the Magallanes Monument. This 

 aggregate should develop greater strength than any combination above 

 mentioned. Other crushed stone available for rise in Manila may be 

 substituted for Sisiman stone and some of it may even prove better, 

 as for exaple, the Angono i-ock. The Orani sand showed 97 per cent 

 efficienc}- in seven-day tensile-strength tests, and the strength of good 

 crushed stone is higher than mortar made with this sand. 



