Effect of C–S–H seeds on the hydration reaction of Portland cement matrices blended with a high-carbon content rice husk ash

The use of Calcium silicate hydrate (C–S–H) seeds is a promising solution to accelerate the hydration kinetics of Portland cement mixtures blended containing supplementary cementitious materials (SCM) with a low initial reactivity. However, the interaction mechanisms between C–S–H seeds and alternative SCM, such as Rice husk ash (RHA), are still not fully understood. In this paper, pastes with three levels of Portland cement replacement (10, 20, and 30% by volume of cement) by a high-carbon content RHA were analyzed, with and without the addition of 3% C–S–H seeds. The hydration process and the mechanical performance of the pastes were evaluated through isothermal calorimetry for seven days, thermogravimetric analysis, and compressive strength after 1, 7, and 28 days. The results showed that the C–S–H seeds increased Portlandite consumption during the first hours of the hydration process and enhanced compressive strength after one day of curing. These finds suggested that the use of C–S–H seeds could eliminate the delay in the hydration process and strength development during the initial hours caused by the high-carbon content and low reactivity of RHA.