Long-term effects of cement SO3 content on the properties of normal and high-strength concrete. Part I. The effect on strength

Abstract Six brands of cement were each manufactured at four SO3 contents, in full scale plants. Strengths were determined, at up to one year, in concretes of high and low water/cement ratio. Strength was usually independent of, or linearly related to, the SO3 content of cement. Only rarely was a well defined optimum SO3 content observed. With each cement, the strength-SO3 relationship at 28 days was usually similar to that at one year. At 28 days the association between strength and the C3A content of cement varied considerably with SO3 content, whereas the corresponding association for C3S did not. With one-year concrete strength, the dominant factor of cement composition was C3A. At this age the correlation coefficient of strength with C3A varied with SO3. Undersulphated cements displayed a strongly negative association between strength and C3A content, which could account for up to 10 MPa difference in strength at either 0.45 or 0.75 water/cement ratio.