18, 2 King: Philippine Concrete and its Aggregates 205 
tent gave, with one exception, much higher results; at 28 to 32 
days the 1.12 :3 : 6 specimens averaged 979 pounds per square 
inch, and the 1.2 : 3 : 6 test pieces at 77 days, 1,974. In general 
the poor results given by concrete made in Leyte are due to the 
fine-grained sands. The unconformable and inconsistent nature 
of the compressive strength values is very likely due to faulty 
proportioning of cement and aggregates. 
MANILA AND VICINITY _ 
Most of the concrete specimens made in Manila were marked 
1: 2:4; and these, like specimens coming from other provinces, 
gave widely variant compressive strengths. Test pieces aged 25 
to 34 days gave minimum and maximum values of 393 and 2,093 
pounds per square inch, respectively, and a mean compressive 
strength of 1,016 pounds per square inch; the latter value is fair. 
Aging increases the strength very little; in fact, the average com- 
pressive strength given by test pieces aged 52 to 61 days is 1,222 
pounds per square inch, which is practically the same as the mean 
value of 1,292 pounds obtained from specimens aged 36 to 49 
days. Laboratory-made 1 : 2 : 4 specimens gave concordant re- 
sults that average 2,797 pounds per square inch, which is more 
than twice the average value given by the corresponding series 
of field-made test pieces. 
The fourteen results obtained from specimens made of concrete 
used in the construction of the United States Quartermaster Pier 
are particularly noteworthy. This concrete is in a class by itself ; 
it is exceptionally resistant, compact, and stonelike, and on rup- 
ture shows no cleavage planes along the surfaces where mortar 
and stone meet. The five cubes aged 1,042 to 1,052 days kept in 
air under the materials testing laboratory eaves gave an average 
compressive strength of 4,393 pounds per square inch. The other 
five specimens in this series, aged 1,041 to 1,051 days and stored 
in a steel cage totally submerged under the pier in Manila Bay 
for a period of 784 days, show marked decrease in average 
compressive strength; the compressive strength of salt-water 
specimens averages 3,781 pounds per square inch. Four other 
specimens, representing concrete from this structure, were rup- 
tured; these were older, and had an age of 1,373 days. There 
is a well-defined difference between the compressive strength of 
the specimens submerged in Manila Bay for 784 days and those 
kept in air, the average being 2,357 and 4,565 pounds per square 
inch, respectively. The relatively low value of 1,941 pounds per 
square inch of one of the salt-water specimens 1s due to the use 
of soft Pasig sand and gravel, which possess neither the hardness 
