198 The Philippine Journal of Science 1921 
X 
per square inch, which is practically three times as high as the 
strength of the other 1 : 3 : 6 mixtures from Capiz Province. 
Table 2 shows that the sand used in the construction of Balu- 
cuan Bridge is coarse, and yields a mortar nearly as strong 
as that made of standard Ottawa sand. The high compressive 
strengths of the concretes just cited are due largely to the 
coarse, clean sands used. 
CAVITE 
Compressive strengths of concrete specimens from Cavite 
show a wide degree of variation. Tests of 1 : 2 : 4 cubes from 
Tabon Bridge average 656 pounds per square inch, which is 
poor for this class of concrete. The first lot of specimens from 
Canacao Bridge made of hand-mixed concrete shows still lower 
strengths and averages 488 pounds. These results were ap- 
parently alarming, for the next lot of specimens sent to the 
Bureau of Science show great improvement, having been made 
from machine-mixed concrete; they give the excellent average 
of 1,868 pounds per square inch. Toward the end of the con- 
struction, machine mixing was abandoned and the specimens 
were again made from hand-mixed concrete, the compressive 
strength of which is only l;048 pounds per square inch. The 
same aggregates were used throughout, so that machine mixing 
at first glance seems to account for the high strength. Caution 
must be used in drawing this conclusion, however, because 
details of proportioning are lacking, and it is not improbable 
that on account of the crude methods of measuring aggregates 
in the field, more cement was used in one case than in the other. 
Concretes mixed in the materials testing laboratory of the Bu- 
reau of Science give higher average results than do field-mixed 
specimens. The 1:2:4 laboratory mixtures average 2,251 
pounds per square inch. Field specimens proportioned 1:3:6, 
aged between 31 and 36 days, average 495 pounds per square 
inch, which incidentally is higher than the lowest result already 
discussed in the 1:2:4 series. The mixture 1 : 1.5 : 4.5 was 
used rather freely in constructing Canacao Bridge, and the re- 
sults obtained from ihese test specimens show extraordinary 
variation. The highest average result in this series is 2,203 
pounds per square inch, and was obtained from machine-mixed 
concrete; the lowest, 609 pounds per square inch, was given by 
specimens made from hand-mixed concrete. The. entire group 
of results obtained from 1 : 1.5 : 4.5 concrete specimens gives 
the good average of 1,319 pounds per square inch. Careful 
