Enhancing Portland cement performance with nano-SiO2 for low-carbon winter construction at negative temperature

Cold weather concreting suffers from retarded strength development and frost damage, which lead to increased energy consumption and carbon emissions. This study investigates the effect of nano-SiO 2 on enhancing Portland cement (PC) performance at −5 ℃, with a focus on hydration kinetics. Cement pastes with 0–2.0 wt% nano-SiO 2 were subjected to room-temperature precuring (0, 2, or 4 h) before negative temperature curing. Hydration kinetics were analyzed using isothermal calorimetry and the Krstulović-Dabić model, complemented by strength, freezable water, phase, and microstructure characterization. Nano-SiO 2 shortened the induction period, accelerated early hydration under precuring and freezing, and refined microstructure. Kinetic modelling showed increased nucleation and crystal growth (NG) and phase boundary reaction (I) stage rate constants (up to 29.1 % and 18.8 %) and reduced reaction order n. The optimal mix (1.5 wt% nano-SiO 2 , 4 h precuring) enhanced 28-day strength by 149.5 % compared to unmodified cement without precuring. Nano-SiO 2 with precuring further reduced freezable water content by 32.1 %, thereby mitigating frost damage. This study proposes a low-energy-consumption winter concreting strategy using nano-SiO 2 and short precuring.