is, 2 King: Philippine Concrete and its Aggregates 213 
ones. Unquestionably, poor sand accounts largely for the un- 
satisfactory concrete strengths. Table 2 shows that the two 
Surigao sands tested are fine-grained, particularly the one 
coming from Surigao River. Specimens made of 1 : 3 Suri- 
gao River sand at 28 days give a compressive strength that is 
46 per cent of that given by the corresponding Ottawa sand 
mortar test pieces. Sand from the wharf site gives a better 
value — 74 per cent of that of the standard specimens. The 
latter sand was apparently used on the job, but the results are 
only one-third of what a good concrete should give. 
TARLAC 
Comparison of results obtained from concrete made in Tarlac 
is not very satisfactory on account of the appreciable differences 
in age of the test specimens. Some results are excellent, 
whereas others are only fair, and still others are incongruous. 
The great disagreement that exists between the average com- 
pressive strengths of 1 : 2 : 4 specimens made of concrete used 
in the piles of San Antonio Bridge is puzzling and is very likely 
due to carelessness in the manipulation of materials. Spec- 
imens cast May 8, 1913, and aged 25 days give the excellent 
average of 2,462 pounds per square inch, whereas another series 
of six specimens (date of manufacture not given) averages 
only 1,045 pounds per square inch at 31 days. It is likely that 
the proportioning of materials varied in these two cases and 
that a difference in cement content probably accounts for the 
difference in strength. Tarlac Province has an excellent build- 
ing sand, which is commonly called Tarlac sand, and which on 
account of its light color makes it a suitable material for or- 
namental concrete. As Table 2 shows, the average compres- 
sive strength of 1 : 3 mortar specimens at 28 days is 1.6 times 
that given by the test pieces made of Ottawa sand. Tarlac 
sand is coarse and well graded, and contains very little quartz, 
the principal constituent being a clear, glassy, plagioclase feld- 
spar. The Tarlac sand deposit is located along the Manila- 
Dagupan Railroad, and the sand has been tranpsorted by rail to 
Manila in fairly large quantities, for use in special work con- 
ducted by the Bureau of Science and the Bureau of Public 
Works. 
TAYABAS 
In general, tests of concrete made in Tayabas give unsatis- 
factory results. The compressive strength of the only 1:2:4 
specimen is low and practically the same as that of the single 
1 : 2.5 : 5 test piece coming from the same job. No information 
