Effect of clay content on shrinkage of cementitious materials

Clay-like substances in manufactured sand significantly impact the shrinkage of cementitious materials. This study investigated the effect of clay content on autogenous shrinkage, drying shrinkage, hydration rate, internal relative humidity (IRH), elastic modulus and pore structure of cementitious materials. The water content and self-contraction of clay during desorption were also studied to clarify the underlying mechanism of its influence on shrinkage. The results indicate that the clay slightly alleviated the autogenous shrinkage while significantly aggravated the drying shrinkage. Pronounced self-contraction of clay occurred as RH dropped, but the conversion ratio of the self-contraction of clay to the shrinkage of mortar was very low. It is concluded that the self-contraction of clay obviously influences the pore structure and the evolution of the various performance of mortars. Furthermore, the initial swelling of clay and the gentle decline of IRH are account for the reduction in autogenous shrinkage. Meanwhile, the coarsened pore structure accelerates the drying shrinkage and the self-contraction of clay intensifies the drying shrinkage.