CONCRETE CONSTRUCTION IN THE PHILIPPINE ISLANDS. 121 



the decomposition and abrasion of weathered, poor-grade gravel. It 

 contains but little quartz and a considerable quantity of fine "dead" 

 sand and shells. Its low percentage of voids is its one good feature. 



Dr. George I. Adams, of the division of mines, Bureau of Science, 

 has located several extensive sand beds within practicable distances of 

 Manila. The most promising of these is that from the Orani Eiver, 

 which enters the northwest part of Manila Bay. 



These two sands have been under test for some time in this laboratory. 

 However, it soon became manifest that the commercial products varied 

 so much that it was impossible to report on the relative efficiencies of 

 the material now being obtained if these be considered independently 

 of granularmetric analysis. The best product from the Pasig Eiver 

 is probably a sand obtained from washed gravel screenings containing 

 a large percentage of pea gravel. This sand could be screened on the 

 one-fourth inch mesh. The best grade of Orani sand contains no small 

 pebbles and will all pass through the 0.1-inch mesh. Ordinarily the 

 least efficient grains in the Pasig sand are the fine ones which predo- 

 minate in the so-called "banco," sand dipped up by native divers. The 

 objectionable material in the Orani sand is the small, soft pebbles which 

 are formed on the surface of sand bars exposed at low tide. Sand 

 dredged from the channel of the stream can be obtained free from these. 

 Accordingly, the specifications for obtaining the best quality of the 

 two sands will be quite different. 



Some results leading to the above conclusions have been obtained; 

 more comprehensive tests are under way and it is also proposed to 

 secure information by testing the aggregates used in actual construction. 

 The latter course is necessary because laboratory tests, to be of most 

 value, should be conducted under conditions as similar as possible to 

 those of actual practice. Spackman G found that a concrete which 

 hardened at the laboratory failed to do so in actual construction, 

 because the stone in the rotary mixer ground the hydrated clay in the 

 aggregate to a powder and the paste so produced prevented the cement 

 from hardening. 



Another essential requirement to secure proper results is the develop- 

 ment of standard methods of testing the materials. We have such for 

 iron and steel, cement, stone, and timber, but not for sand and gravel. 

 Specifications should be theoretical enough to insure . uniformity and 

 yet practical enough to meet the conditions of actual construction work. 

 The development of strength in concrete is very elusive and dependent 



8 hoc. cit. 



