Fineness of Cement

Fineness of cement is the measure of the average particle size / total specific surface of the cement powder. Finer cement has greater surface area, hydrates faster, releases more early heat and gains early strength more quickly, but is also more prone to shrinkage and to deterioration if stored damp. It is determined by the dry-sieving residue on the 90-micron sieve (IS 4031 Part 1) or, more precisely, by the Blaine air-permeability specific-surface method (IS 4031 Part 2).

IS 269 requires OPC fineness (specific surface) of at least 225 m²/kg by Blaine; modern OPC 53 is often 300-350 m²/kg. Fineness directly influences water demand, setting, heat of hydration (important for mass concrete where lower fineness/low-heat cement is preferred) and the 3-/7-day strength used for early formwork stripping.