a 
18, 2 King: Philippine Conerete and its Aggregates P11 
in aggregate, though the difference between 1,268 and 730 
pounds per square inch for specimens made from the same 
materials is more puzzling. As in other instances, the data 
here given lack certain value that they would have, had the 
district engineer included the source of the aggregate used in 
the concrete. 
RIZAL 
Compressive strength values given by concrete specimens 
from Rizal Province are variable; this variability, however, is 
almost entirely due to the different aggregates used. Specimens 
made of 1:3 :6 concrete having ages between 28 and 31 days 
vary from 397 to 1,091 pounds per square inch, and average 
825. The low values were obtained from test pieces containing 
Pasig River sand, and the high ones from specimens containing 
Mariquina River sand. The same difference is noted in the 
compressive strength obtained from the 1:2:4 specimens, 
though here an appreciable difference in age may have exerted 
some influence on the strength; the concrete specimens con- 
taining the soft, fine-grained Pasig River sand average 558 
pounds per square inch at 28 days, and those containing the 
Mariquina River sand average 1,326 pounds, at 38 to 39 days. 
The use of Pasig River sand was abandoned in the last stages 
of the construction of Angono Bridge, because of the low re- 
sults shown by the concrete containing this sand, and Mariquina 
sand was substituted with better results. 
SAMAR 
Most of the test specimens coming from Samar Province were 
marked 1:2: 4, the rest being labeled 1: 3:6 mixtures. By 
averaging the values given by the latter specimens, a compres- 
sive strength of 696 pounds per square inch is obtained; the 
age of these 1 : 3 : 6 test pieces varies from 28 to 34 days. Two 
low results, 496 and 388 pounds per square inch, characterize 
this series; the highest figure, 964 pounds, is good for this class 
of concrete. The specimens made of 1 : 2 : 4 concrete and aged 
27 to 31 days gave extremely rambling results, varying from 
830 to 2,168 pounds per square inch; this series shows an aver- 
age compressive strength of 957 pounds per square inch. The 
striking irregularity in compressive strengths obtained from the 
1:2:4 specimens made October 30 and December 16, 1914, 
from concrete used in the construction of Arapison Bridge is 
very likely due to carelessness; a variation of from 330 to 1,655 
pounds per square inch could hardly be explained otherwise. 
It will be noted that most of the 1 : 2:4 specimens were con- 
