Abstract:Carbonated ready-mixed concrete serves as an effective approach to mitigate CO2 emissions in the cement and concrete industry. This paper systematically reveals the impact of CO2 mixing on the early hydration and phase evolution of fresh cement paste. The results demonstrate that CO2 mixing significantly accelerates the hydration process during the initial and induction periods, while exhibiting minimal effects on the heat release and microstructural build-up rate during the acceleration period. Meanwhile, CO2 mixing alters the early reaction pathway and phase assemblage of the paste, increasing the degree of cement reaction by 10.2%, accompanied by a reduction in CH and increases in CaCO3, amorphous phases, and chemical bound water, while promoting the formation of low-calcium C-S-H gel. In addition, CO2 mixing causes Ca2+ to preferentially participate in CaCO3 precipitation, thereby lowering the saturation indices of clinker minerals, gypsum, AFt, and CH, promoting the dissolution of clinker minerals and gypsum while inhibiting the precipitation of CH and AFt. Concurrently, low-calcium C-S-H and nano-CaCO3 advance the early microstructural build-up. These findings provide a theoretical basis for the engineering application of carbonated ready-mixed concrete.
