Modeling of the interaction between hydration and carbonation on reaction kinetics at early age

Although CO2 curing of cement-based materials offers a promising avenue for mitigating carbon emissions in construction, its optimization is limited by the lack of mechanistic understanding of the interaction between hydration and carbonation reactions during curing. This study establishes a unified physicochemical reaction kinetics framework that explicitly captures the coupled interaction between hydration, carbonation, water content evolution, and reaction heat within a thermodynamically consistent formulation. Based on a representative volume element (RVE) at the cement paste level, microdiffusion-reaction equations are developed to describe the coupled reaction kinetics. The interaction is characterized by three dominant mechanisms, including competitive reactant consumption, heat evolution, and water content evolution, each providing physicochemical feedback to the reaction kinetics. The proposed model quantitatively captures the influence of pre-hydration on carbonation kinetics and the evolving influence of carbonation on subsequent hydration. Furthermore, the results reveal that although both hydration and carbonation initially consume water, the carbonation of hydration products subsequently releases chemically bound water, while carbonation ultimately reduces the equilibrium moisture content through pore refinement and microstructural densification. The proposed framework provides a physics-based foundation for understanding and optimizing early-age CO2 curing conditions.