18, 2 King: Philippine Concrete and its Aggregates 109 
LABORATORY TESTS OF AGGREGATES USED IN CONCRETE 
Percentage of voids—A graduated cylinder about 7 centi- 
meters in diameter with a capacity of 500 cubic centimeters was 
used in determining the voids in the sand. A small quantity 
of the dried sand was placed in the cylinder and compacted by 
striking the cylinder lightly on a cloth pad. About twenty blows 
were given and successive additions of sand compacted until the 
cylinder was filled to the 500 cubic centimeter mark. It is im- 
portant to compact all sands to the same mark in order to secure 
reliable results. The difference between the weight of the 
cylinder containing the sand and that of the empty cylinder gave 
the weight of the 500 cubic centimeters of dry compacted sand. 
Knowing the specific gravity of the sand, the actual volume 
occupied by the sand grains may be easily calculated by sub- 
stituting the proper values in the formula: 
Mass 
Volume= 
Specific gravity 
If the true volume of the sand particles be now subtracted 
from the apparent volume as measured in the graduated cylin- 
der, the difference will represent the void space in 500 cubic 
centimeters of sand. The void space divided by 500 and mul- 
tiplied by 100 will give the percentage of voids. 
The method used for determining the percentage of voids 
in the coarse aggregate (gravel) is analogous to that employed 
in connection with the sands and screenings. On account of 
the larger size of the grain a more spacious and: less fragile 
container was used for weighing a compacted volume of the ag- 
gregate. A wooden box with inside lineal dimensions of 15 
centimeters was filled with gravel, which was compacted by 
subjecting it to gentle percussion. The difference between 
the filled box and the empty box gave the mass of the compacted 
aggregate contained within a space of 3,375 cubic centimeters. 
Knowing the mass and the specific gravity of the gravel, it is 
an easy matter to calculate the true volume of the constituent 
pebbles by means of the formula already mentioned. The true 
volume of the gravel subtracted from the apparent volume 
(3,375 cubic centimeters) gives the void space, and this in turn 
divided by the apparent volume and multiplied “4 100 gives the 
percentage of void space. 
