CONCRETE CONSTRUCTION IN THE PHILIPPINE ISLANDS. 135 

 CONCRETE SPECIFICATIONS. 



The following quotations will serve to demonstrate the weight laid 

 upon concrete specifications in other parts of the world. 



"In framing concrete specifications, the proportions of the constituents should 

 be stated so distinctly that there can be no misunderstanding between the engineer 

 and the contractor as to the quantities which will be required for the work." e 



"Engineers have placed the volume of a barrel of packed cement all the way 

 from 3.1 to 3.8 cubic feet, corresponding to a variation in the weight of from 

 123 to 100 pounds per cubic foot. Loose cement measurements, on the other 

 hand, are variously fixed at from 3.8 to 4.5 cubic feet to the barrel, or 100 to 

 84£ pounds per cubic foot. The extreme actual variation is therefore from 3.1 

 to 4.5 cubic feet per barrel, or 123 to 84* pounds per cubic foot. The quality 

 of cement should invariably be regulated by its weight", 8 as has been done in 

 France and England. 



At this laboratory we have adopted the American Society standard of 

 100 pounds of cement being assumed as equal to 1 cubic foot. Sand 

 and gravel are measured dry. 



"Without a universal standard there is no means of comparing the concrete 

 in different structures or the results of different experiments, and an unscrupulous 

 contractor may adopt for his unit the volume of cement very loosely measured, 

 and thus produce too lean a concrete." * 



He may also fail to reject "cake" cement, unless such action is 

 specifically designated in the concrete specifications. 



Although the nature of the sand and gravel or stone is as important a 

 consideration as that of the cement itself, many local building specifica- 

 tions simply state that the sand shall be sharp and clean and that the 

 gravel shall all pass a certain sized sieve. There are sometimes no 

 definite statements as to the kind of materials, their chemical composi- 

 tion, the percentage of voids, the percentage of dirt, gradation of the size 

 of the particles, and the strength they should give when mixed with the 

 cement to be used. 



In one instance,- which has come to my notice, the contract called for a 1:2:4 

 mixture. The gravel and sand for the work were piled in two large heaps and 

 samples sent to the laboratory for inspection. As already recorded, it was found 

 not advisable to use the 1:2:4 mixture specified. The gravel being well graded 

 and the percentage of voids correspondingly small, an excess of mortar resulted, and 

 this, working to the top during the "puddling," produced a layer of pure mortar 

 and a non-homogenous concrete. A 1:2:5 mixture was then substituted and gave 

 better results. 



Though they seldom do so, concrete specifications should insist upon 

 sand-free gravel. Sand tends to reduce the percentage of voids in the 

 gravel. Ordinarily a low percentage of voids is desirable, but when a 



8 Taylor and Thompson, page 217. 

 * Loc. cit. 



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