Effect of gypsum on properties and internal structure of PC paste

Abstract Gypsum somewhat accelerated the rate of hydration of PC when added below the optimum SO 3 content, but produced significant retardation when the addition exceeded the optimum. At a given degree of hydration, or at a given BET surface area, strength of the paste increased with the increase in the SO 3 content of the cement. No effect of the SO 3 content on the density of the hydration products and pore-size distribution was observed. Further study is required to explain the effect of SO 3 content on strength.