31. Specifications for Sand.—Tests have seldom been used as means of judging sand for use m masonry construction. The require ments have usually been that the sand be coarse, clean, and sharp; the requirement of sharpness is now commonly omitted.
Mechanical analysis and void tests are frequently made for the purpose of judging the qualities of available sands on important work, and to aid in properly proportioning mortar, but such tests are not usual in specifications.
The Joint Committee of the Engineering Societies on Concrete and Reinforced Concrete has suggested the following as requirements for sand to be used as fine aggregate in concrete work: (a) Fine Aggregate.—This should consist of sand, crushed stone or gravel screenings, graded from fine to coarse, and passing when dry a screen having holes inch in diameter. It is preferable that it be of siliceous material, and should be clean, coarse, free from dust, soft particles, vegetable loam, or other deleterious matter: and not more than G per cent should pass a sieve having 100 m shes per linear inch. Fine aggregates should always he tested.
Fine aggregates should be of such quality that mortar m omposed of one part Portland cement and three parts fine aggr gates by weight, when made into briquettes, will show a tensile strength at least equal to the strength of I to 3 mortar of the same consistency made with the same cement and standard Ottawa sand. If the aggregate be of poorer quality, the proportion of cement should be increased to secure the desired strength.
If the strength developed by the aggregate in the 1 to 3 mortar is less than 70 per cent of the strength of the Ottawa sand mortar, the material should he rejected. To avoid the removal of any coating on the grains, which may effect the strength, bank sand should not be dried before being made into mortar, but should contain natural moisture. The percentage of moisture may he determined on a separate sample for correcting weight. From 10 to 40 per cent more water may be required in mixing bank or artificial sands than for standard Ottawa sand to produce the same consistency.