The right type and quality of aggregates are crucial for concrete as they significantly influence its properties, mix proportions, and cost-effectiveness. If different sources are available for sand, the commonly used fine aggregate in concrete, the selection of sand is primarily based on its gradation.
The grading, or particle-size distribution, of sand is determined using sieve analysis, with standard sizes ranging from 150 μm to 10 mm (ASTM No. 100 sieve to 3⁄8 in. sieve). Sand is sampled for gradation from a flowing aggregate stream, conveyor belts, or stockpiles. A single sample typically represents about 45 to 50 tons of sand. Finally, the test portions for sieve analysis are obtained from the field sample using a sample splitter.
Concrete using very fine sands can be uneconomical, and coarse sands can result in less workable mixes. Generally, well-graded sand, without a large deficiency or excess of any size and giving a smooth grading curve within the region bound by the grading curve for fine and coarse sand, is preferred in concrete.
