108 The Philippine Journal of Science. 1921 
Upon arrival at the laboratory, the samples of sand and 
gravel were first thinly spread on a concrete platform and then 
rapidly dried by exposure to the heat of the sun, which at sea 
level in a tropical country is great. When dry, the aggregates 
were ready for testing. Complete sand tests in this laboratory 
comprise the determination of percentage of voids, apparent 
specific gravity, granulometric analysis, comparison of tensile 
and compressive strengths of 1:3 mortar with those of 1:3 
Ottawa sand mortar, and approximate mineralogical composi- 
tion; but sometimes not all of these tests were performed. 
Examinations were conducted in conformity with requests made 
by the Bureau of Public Works and, as Table 2 shows, are not 
complete. Ten years’ testing of sands for concrete work has 
shown that very little practical value has been derived in the 
Philippines from knowledge of percentage of voids, apparent 
specific gravity, and mineralogical composition data, and that 
for ordinary routine examinations these tests might very well 
be omitted, since they tell us nothing regarding the compressive 
strength of the mortar or mortars yielded by the sand. The 
compressive strength of mortar is, after all, of paramount im- 
portance to the designing engineer; with the exception of granu- 
lometric analysis, all other tests play a very inconspicuous role 
in determining the suitability of a sand as a concrete aggregate. 
The size of the grain and the gradation of grain sizes, more than 
any other factors determine the compressive strength obtainable 
from a sand when mixed with Portland cement; so that the 
granulometric analysis of a sand, in nearly all instances, forms 
a valuable, practical criterion of the compressive strength. 
What has just been said with respect to sand may also be 
applied to gravel and crushed stone, which constitute the coarsest 
components of concrete. Specific gravity, percentage of voids, 
granulometric analysis, and mineralogical composition data are 
of secondary importance. Table 3 gives the granulometric 
analyses of some Philippine gravels. 
The most important test of gravel in ordinary routine inves- 
tigation consists in actually making a series of concrete mix- 
tures with this coarse aggregate and then ascertaining the 
compressive strength of the resultant test specimens. The pro- 
portions usually designated by the Bureau of Public Works are 
the standard 1:2:4, 1:2.5:5, and 1:3:6 mixtures; occa- 
sionally requests for other mixtures are received. 
