Structural Evolution and Characterization of γ-C2S (γ-C2S) Compacts during Carbonation

γ-C2S has high potential for use as a construction material with the additional benefit of CO2 absorption due to its high carbonation reactivity. This study quantitatively investigates the evolution and influencing factors of the microstructure of the γ-C2S compact molded by cold isostatic pressing, including microhardness, porosity, pore structure, and carbonation degree at different reaction depths. Results show that the carbonation reaction of the γ-C2S compact is a sequential process from outside-in, and the whole process can be divided into three stages. The carbonation degree decreases gradually with the increase of depth of the compact and finally forms a gradient structure, and the microhardness and backscatter results can also quantitatively demonstrate this evolution. In addition, the γ-C2S compact with a lower forming pressure is beneficial to obtain a higher reaction depth after carbonation; with the progress of carbonation, the reaction depth shows a trend of rapid growth in the early stage, followed by a tapered-off development in the later stage of carbonation. This study provides a meaningful insight and shows the practical significance for the study and development of related γ-C2S-based carbonation products.