Early-age hydration heat evolution and kinetics of Portland cement containing nano-silica at different temperatures

This study investigated the influence of nano-silica dosages and hydration temperatures on the early-age hydration heat of cement using isothermal calorimetry, and a hydration kinetics model was used to analyze the nucleation and growth rates of hydrates. The calorimetry results show that the addition of nano-silica and the increase of hydration temperature can accelerate the process of hydration reaction. As the dosage of nano-silica increases, the induction period decreases, the acceleration period and exothermic rate peak value increase. The fast pozzolanic effect of nano-silica is responsible for accelerating the hydration reaction. However, the excessive addition (5%) of nano-silica may form many agglomerations, thereby inhibiting the modification effect of nanosilica on the cement hydration. The simulating results of kinetic parameters show that, at three hydration temperatures, the nucleation rate of hydrates increase with the increasing of nano-silica dosages, which indirectly confirms the nucleation effect of nano-silica in the early-age hydration. At 20 degrees C and 30 degrees C, the growth rate of hydrates also increases with the increasing of nano-silica dosages. At 40 degrees C, the growth rate of hydrates is decreased gradually, possibly due to the lack of sufficient Ca2+ and H2SiO42- . In addition, the nucleation rate is more sensitive and the growth rate is less sensitive to the hydration temperature.