is, 2 King: Philippine Concrete and its Aggregates 201 
mixture used in the Singson Waterworks gave anomalous re- 
sults, the average compressive strength being lower than that 
shown by either of the leaner mixtures (1 : 2 : 4 and 1 : 3 : 6). 
Since no preliminary laboratory tests were made of the aggre- 
gates employed in Ilocos Sur concretes, it is impossible to hazard 
an explanation of these abnormalities. 
ILOILO 
All of the one hundred fifty-six tests of concrete listed under 
Iloilo in Table 8 were obtained from specimens made in con- 
nection with the construction of Molo Bridge. Nine of these 
results were gotten from laboratory-made test pieces, and the re- 
mainder from field-cast specimens molded during the period Jan- 
uary 9 to September 30, 1911, so that ample data are available 
on this structure. More than ordinary care was apparently 
observed in the erection of this bridge. Before beginning the 
fabrication of concrete, the district engineer sent samples of 
several aggregates to the materials testing laboratory during 
November, 1910, for preliminary examination, and mixing of con- 
crete was begun in January, 1911, of aggregates that had given 
the best laboratory results. These steps are shown in Table 8 
under Iloilo. In general all of the field tests show very good 
results ; they are fairly high and uniform. The 1:2:4 speci- 
mens ranging in age between 28 and 34 days average 1,344 
pounds, whereas the corresponding laboratory-made test pieces, 
having an age that varies between 28 and 31 days, average 
2,223 pounds per square inch. However, this catena of results 
taken as a whole is not free from puzzling anomalisms. For 
instance, as stated before, the 1:2:4 specimens aged between 
28 and 34 days give a mean compressive strength of 1,344 
pounds per square inch, while the group of 1 : 2 : 4 results from 
specimens next in age, varying between 36 and 41 days, actually 
show a decrease in compressive strength and average 1,184 
pounds per square inch. The remaining results in this 1:2:4 
series average 1,275 pounds per square inch for those having 
ages between 48 and 50 days, and 1,348 for those aged 57 to 
60 days ; the last result is practically the same as that given 
by the youngest specimens. The same irregularity is found in 
the results obtained from the 1 : 2.5 : 5 and the 1:3:6 speci- 
mens. The former series gives averages of 1,098 pounds per 
square inch at 25 to 28 days, 1,657 pounds at 34 to 40 days, and 
1,408 pounds at 41 to 45 days ; the latter series shows 1,068 pounds 
per square inch at 28 to 35 days, 1,076 pounds at 41 to 51 days, 
