Hydration of internally cured shrinkage compensating cement paste

Modern concrete with low water-to-cement ratio and/or mass volume exhibits increased risk of cracking at early age. Internal curing and shrinkage compensation are two of the innovative technologies developed for reducing shrinkage and enhancing crack resistance of cementitious materials. Hydration characteristics and microstructure of internally cured cement pastes with 10 wt. % replacement of cement by ground low temperature clinker which contained C₁₂A₇, C₂S and anhydrite, and with water-to-cementitious materials ratio of 0.30, were studied by using scanning electron microscopy. Degree of hydration of internally cured cement pastes at 20°C ±2°C was higher than that of the pastes without internal curing because of a higher internal relative humidity in water entrained pastes. Volume of capillary pores in water entrained pastes were reduced for the promotion of cement hydration by internal curing and more ettringite (AFt) formation due to hydration of C₁₂A₇, which implies the efficiency of shrinkage compensation from low temperature clinker and anhydrite may be enhanced by internally water entrained. So, it has significant importance for shrinkage compensating concrete to adopt internal curing.