18, 2 King: Philippine Concrete and its Aggregates 197 
River sands particularly, as Table 2 shows, are coarse and have 
a desirable granulometric composition. The sand used in the 
construction of Santo Nifio Bridge, although rather fine, never- 
theless gave an excellent result in the 1:2: 4 field specimens, 
which averaged 1,574 pounds per square inch. However, field 
specimens, particularly the 1 : 2 : 4 mixtures, show lower com- 
pressive strengths than the corresponding concrete specimens 
made in the laboratory. The results of laboratory-made 1 : 2 : 4 
concrete average 2,158 pounds per square inch, and the corres- 
ponding field-made specimens average only 895. The difference 
in strength of field and laboratory 1:3 :6 concrete is not so 
great; specimens of this mixture made at the Bureau of Science 
average 988 pounds per square inch, and those made on the 
building site, 692. No 1:2.5:5 or 1:2:5 mixtures were 
made in the laboratory; those fabricated in the field average 
557 and 702 pounds per square inch, respectively. In general 
concrete from Bulacan is fair in strength, and in one case the 
results are very good. With the aggregates available, better 
field results should have been obtained in the case of the 1:2: 4 
mixtures. It is reassuring to note that all of the long-time 
tests (90 and 181 days) show substantial increases over the : 
28-day tests. 
CAPIZ 
Two distinctly different series of results for each of the two 
groups of 1:2:4 and 1:3 :6 concrete specimens are charac- 
teristic of the tests from Capiz. The 1:2:4 specimens from 
Ivisan and Pilar Schools and from Libas Bridge average 527 
pounds per square inch, which is about one-third of what con- 
crete of this proportion should test at 28 days. These low 
results are due to the use of fine, dirty sands from Ivisan and 
Panay Rivers and from Pilar beach. The 1 :3 :6 mixtures in- 
volving these sands also give low strengths and average 349 
Pounds per square inch. The lowest result recorded in this 
Paper was obtained from a concrete specimen coming from 
Ivisan School, and has a value of only 97 pounds per square 
inch. Preliminary tests and the exercise of judgment could 
have prevented the use of these sands for concrete work. In 
sharp contrast to these low compressive strengths are those 
obtained from specimens cast of concrete used in the construc- 
tion of Balucuan Bridge and the Capiz water tank. Thel:2:4 
results from these structures are close together and average 
1,427 pounds per square inch. The compressive strength of the 
1:3:6 specimens from Balucuan Bridge average 917 pounds 
