Chemical Realkalization of Carbonated Concrete: Influence of Cement Composition on Alkalinity Restoration and Portlandite Formation

This study examines the carbonation and realkalization dynamics of various cementitious systems, with a focus on the influence of cement composition on their susceptibility to carbonation and potential for realkalization. Four cement types were evaluated: CEM I, CEM II/A-LL, CEM II/A-V, and CEM II/B-W. Carbonation depth measurements revealed that blended cements, particularly CEM II/A-LL, showed greater carbonation susceptibility due to their lower portlandite content and increased porosity. In contrast, realkalization experiments demonstrated that blended cements exhibited enhanced ionic transport, resulting in deeper penetration of the alkaline solution. CEM II/A-V showed the highest realkalization depth, while CEM I displayed the lowest, highlighting the role of microstructural characteristics in realkalization efficiency. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) confirmed that carbonation led to portlandite depletion and the formation of calcium carbonate, with limited portlandite regeneration upon realkalization. Thermodynamic simulations further supported the experimental findings, revealing that realkalization only partially restored alkalinity, with no significant dissolution of carbonation products. These results emphasize the need for tailored realkalization strategies, considering cement composition and pore structure, to optimize remediation efforts and enhance the long-term durability of concrete structures.