Which one among the in-situ formed calcite, aragonite or vaterite is more beneficial to the carbonated γ-C2S performance: Mechanical strength, pore structure

Among the three polymorphs of CaCO 3 (calcite, aragonite, and vaterite) that may form during the carbonation of calcium silicate, it is still unclear which one is most beneficial to the material properties, and this issue is crucial for the performance-oriented design of such materials. This study employed crystal modifiers to prepare three carbonated γ-C 2 S samples dominated by calcite (Type C), aragonite (Type A), and vaterite (Type V), respectively. Their mechanical properties, microstructure were systematically compared. Results showed that, at an equal degree of carbonation, the flexural and compressive strength followed Type A > Type V > Type C. Microstructurally, needle-like aragonite best refined the pore structure, yielding the lowest porosity and most probable pore size, Whereas the cubic calcite in Type C created vertex-to-face, vertex-to-edge, edge-to-face, and edge-to-edge contacts, generating pores around the contact points, and resulting in its highest porosity. These findings indicate that Type A offers the greatest advantage for the mechanical performance. This result offers a novel perspective for producing high-quality bulk building materials from calcium silicate-based waste residues via the carbonation method.