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

•Nano-silica can decrease induction period and increase acceleration period.•Excessive nano-silica can inhibit its modification effect on cement hydration.•Nucleation effect of nano-silica in the early hydration is confirmed by BNG model.•Nucleation rate is more sensitive and growth rate is less sensitive to temperature. 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 nano-silica 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 °C and 30 °C, the growth rate of hydrates also increases with the increasing of nano-silica dosages. At 40 °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.