140 



REIBLING. 



sand, gravel, and stone, as well as for cement, in order to guarantee 

 satisfactory results. 



5. Concrete specifications, to insure economy as well as efficiency, 

 must be based upon a comprehensive knowledge of the relative merits of 

 all available material. 



6. To ascertain the relative merits of the available material, a standard 

 method of testing must be adopted. 



7. This standard method of testing must embrace practical conditions 

 of manipulation and exposure, so regulated as to subject the concrete 

 to equal, uniform influences. 



I am indebted to Mr. F. D. Eeyes, assistant in the chemical laboratory 

 of this Bureau, for his assistance in the tests of materials which are 

 reported in this article. 



Note. — Shortly after this article had been prepared for publication, 

 our attention was attracted to the concrete qualities of basaltic rock from 

 the Province of La Laguna. This rock is dense, fine-grained, and hard ; 

 and it possesses an ideal fracture for concrete aggregate as it crushes 

 into cubical fragments. 



The strength of the concrete made with this crushed stone proved 

 far superior to any so far tested at this laboratory. The figures obtained 

 were as follows : 



Compression tests of concrete made from crushed basaltic rock from La Laguna. 



Dimensions of 

 cubes, in inches. 



Proportions, 

 by volume. 



Age. 



Total strength 

 in pounds. 



Strength, in 

 pounds, per 

 square inch. 



Mark on cubes. 



In 



moist 

 air. 



In air. 



First 

 crack. 



Ulti- 

 mate. 



First 

 crack. 



Ulti- 

 mate. 



6X6X6 



6 X 6 X 5J 



6X6X6 



1 : 2.2 : 5 



1:2.75:6.25 



1 : 3.3: 7.5 



Days. 

 21 

 21 

 21 



Days. 

 80 

 80 

 80" 



133, 000 

 76, 010 

 22, 450 



152, 500 

 96, 900 

 36, 890 



3,700 



2,203 



623 



4,236 

 2,808 

 1,025 



"B" concrete. 

 "C" concrete. 

 "D" concrete. 



Good Pasig 



The stone was crushed so that all passed 1.5-inch circular meshes, 

 sand (gravel-screenings) was used. The cement was the same as used in previous 

 laboratory work. 



The strength developed by the leanest mixture recorded above shows 

 the economic possibilities of good aggregate in concrete structures where 

 great strength is not essential. The 1 : 3.3 : 7.5 concrete proved stronger 

 than many 1:2:4 mixtures of poor aggregate. 



The ideal, cubical fraeture of the crushed stone, and the dense, masonic 

 concrete it tends to produce is illustrated by Plate IV, which is a 

 photograph of the crushed, 6-inch, 1 : 2.2 : 5 concrete cube which withstood 

 a pressure of over 150,000 pounds. 



