 Fine aggregate consists of sand or another suitable fine material. A good concrete sand will contain particles varying uniformly in size from very fine up to ¼ in. (6.4mm) in diameter. In well-graded sand the finer articles help fill the spaces between the larger particles. Sufficient fine particles are necessary for good workability and smooth surfaces, but an excess of fines requires an increase in the amount of Portland cement-water paste to achieve a desired strength, thus increasing cost. Failure to increase the Portland cement content when there is an excess of fines in the aggregate will lower the strength of a concrete |