220 
The Philippine Journal of Science 
struction had taken place and samples of concrete had been tested, 
that the poorness of the sands was recognized. Usually a change 
in aggregate was then made. Such a procedure is to be deplored, 
and it often entails loss of time and money. A thorough lab- 
oratory examination of concrete aggregates is always a help- 
ful guide to the engineer in selecting his material, and it is 
hoped that copious reliable data on Philippine concrete aggre- 
gates may be collected in the future. 
Compressive strength results obtained from series of field 
specimens made from the same materials on the same day, and 
from the same batch of concrete, and averaged to give the values 
recorded in Table 8, generally show considerable variation. 
Laboratory-made specimens composed of the same materials, and 
molded from the same batch of concrete, are in much better 
agreement, and show only one-fourth of the average maximum 
variation from the mean that field-made specimens show. 
