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INCHCS IOI530 30 45 67 1 OO ISO 2 25 



DIAMETER OF PARTICLES IN CENTIMETERS AND INCHES 



Pig. 14. — Gkanulaemetbic Analysis of Mabiquina Gravel to Pass a i. 5-inch Opening. 



The analysis iu fig. 14 shows 6 per cent of oversize and 3 per cent 

 passing the smallest sieve. Voids, 31.5 per cent. 



The Maraqnina gravel varies greatly in character since it is not care- 

 fully screened as the analyses aliove will show. 



Efficiency. — There is no standard gravel witli which gravels may be 

 compared after the manner that sands are compared with standard sands. 

 It might be well to select a superior gravel to use as a standard in testing 

 the efficiency of gravels in concrete. Cubes could be made with a good 

 cement, a given sand or standard sand, and the standard gravel, and 

 these could be used for conij)aring the crushing strength of cubes of 

 concrete in which the gravel to be tested is combined with the same 

 cements and sand in the same proportions. This would be especially 

 helpful when a gravel is found to break under a pressure which is less 

 than that required to crush the mortar of the concrete. In most gravels 

 the smaller sizes have a lower crushing limit since they are in a more 

 advanced stage of decomposition. It would, therefore, seem desirable 

 that a standard gravel should be of small size. At Calapan. in Mindoro, 

 a gravel was seen which had been obtained from a beach west of the 

 port. It consists very largely of white qirartz pebbles which will pass a 

 1.14-centimeter circular opening and be retained on a sieve with 0.51- 

 centimeter circular openings. Tliere are at present with the quartz peb- 

 bles some rounded fragments of shells and corals, and a few schist pebbles, 

 but these can easily be jDicked out because of their texture and color. It 

 is proposed to see what results can be obtained by using this material as 

 a standard gravel and if it is satisfactory to recommend it for use. It is 

 believed that quartz pebbles will be superior to crushed stone for the pur- 

 pose of comparative tests of gravels because of the similarity of the 



