Gypsum Content of Cements Used in Concrete Cured by Accelerated Methods

Abstract The effects of the gypsum content of cement on several engineering properties of concrete cured by accelerated and normal methods were investigated. It is shown that increased gypsum content results in a significant decrease in the slump of concrete and that there is an optimum gypsum content, considerably higher for accelerated-cured concrete than for normally cured concrete, at which maximum strength is obtained. Contrary to prevailing theory, the increase in the compressive strength of accelerated-cured concrete with increased gypsum content is too small to warrant a gypsum content higher than that for normal curing conditions. In addition, insufficient SO3 content cannot be the only cause for the reduction in the later-age strength of accelerated-cured concrete compared with that of normally cured concrete. The optimum gypsum content under accelerated curing conditions may be used without risk of reduction in the durability of concrete caused by excessive, delayed expansion.