Particular attention must be paid to the selection of the materials and
their mixing.
The concrete should be composed of gravel or crushed stone all of
which will pass through a ¾-inch mesh screen, and be collected on a
¼-inch mesh; sand, free from loam and preferably coarse, and a grade of
Portland cement guaranteed to meet all the requirements of the Standard
Specifications as adopted by the American Society for Testing Materials
and the American Society of Civil Engineers.