Evaluation of Potential Carbon Storage of Cement-based Material in Aqueous Media Using PHREEQC

Cement-based material has great potential to store carbon dioxide (CO₂) as carbonate minerals (mainly calcite, CaCO₃), through aqueous carbonation, driven by their alkaline nature and high portlandite (Ca(OH)₂) content. The carbonation capacity is influenced by many variables, such as cement mass, particle size, and water volume. However, the mechanistic understanding of how these parameters collectively control carbonation kinetics and long-term CO₂ uptake under dynamically evolving conditions remains underexplored. In this study, we developed a geochemical model using PHREEQC that integrates thermodynamic descriptions of aqueous speciation and mineral equilibria with kinetic rate laws to simulate simultaneous reactions in dynamically evolving systems. Portlandite dissolution releases Ca²⁺ into solution, which subsequently reacts with dissolved CO₂ to form CaCO₃ over time. By tracking phase assemblages involving Ca(OH)₂ dissolution, CaCO₃ precipitation, and pore-solution evolution, the progression of carbonation can be quantitatively resolved. Model results under experimentally relevant conditions indicate that CO₂ dissolution is the rate-limiting step of the overall process. Elevated pH is sustained for a finite duration, which depends on key controlling factors such as cement mass and particle size. This modeling framework provides a mechanistic foundation for upscaling laboratory observations and evaluating the potential performance of cement-based carbonation processes in natural environments, supporting the development and optimization of mineral-based carbon sequestration strategies under environmentally relevant conditions.