18, 2 King: Philippine Concrete and its Aggregates 219 
of 2,245 pounds per square inch, and field-made concrete test 
pieces marked 1 : 2 : 4 and aged 25 to 42 days give an average 
ultimate compressive strength of only 980 pounds per square 
inch. The lowest compressive strength, 177 pounds per square 
inch, given by 1 : 2: 4 concrete was obtained from three speci- 
mens coming from Leyte. 
Field specimens made of 1 : 2.5 : 5 concrete and aged 26 to 36 
days average 944 pounds per square inch which, for all prac- 
tical purposes, is the same as the mean compressive strength of 
concrete which is supposedly much richer. No 1: 2.5:5 con- 
crete mixture was made in the laboratory. 
Test pieces made in the field of 1 : 3 : 6 concrete and aged 27 
to 42 days give a mean ultimate compressive strength of 705 
pounds per square inch, which compares favorably with the 
average results of 1,104 pounds per square inch given by the 
laboratory-made 1 : 3 : 6 concrete test pieces. The lowest com- 
pressive strength of 1 : 3 : 6 concrete recorded is 97 pounds per 
square inch and is given by a specimen coming from Capiz. 
The differences between the average ultimate compressive 
strength of the 1:2:4, 1:2.5:5, and the 1:3:6 series of 
test specimens, respectively, are very slight and there are good 
reasons for suspecting that the procedure in proportioning the 
component cement, sand, and gravel was in the majority of the 
Cases grossly inaccurate. 
Aging beyond 28 days in most instances exercised an incon- 
Siderable influence on the strength of the concrete specimens 
tested. Little if any increase in compressive strength accom- 
panies increase in age of the greater part of the older concrete 
test pieces. In several cases an average decrease in compres- 
sive strength is characteristic of old test specimens. 
Most of the low average ultimate compressive strengths may 
be traced to the use of fine sands, some may be attributed to 
faulty proportioning of cement, and in a few cases incomplete 
mixing of the batch accounts for low and erratic results. Care- 
less molding of the test specimens in a few instances has been 
the cause of poor strength. Too much water and faulty storage 
of concrete undoubtedly have contributed not a little to the poor 
yuality generally characteristic of field-made concrete in the 
Philippines, but in the absence of reliable data, it is impossible 
to estimate the influence exercised by these two factors. 
Sands unsuitable for concrete work have been used throughout 
the Philippines and without subjecting them to a preliminary 
laboratory test. It was only after considerable actual con- 
