Enhancement of flexural strength of γ-C2S carbonated compacts through in situ synthesis of Mg-calcite

Abstract

To address the inherent brittleness of carbonated gamma calcium silicate (γ-C₂S) material, we controlled the crystal transformation of γ-C₂S during the carbonization process to facilitate the development of Mg-calcite particles as secondary phases. In this study, highly Mg-calcite carbonated compacts were synthesized in situ by modulating the concentration of MgCl₂ in an aqueous solution. The mechanisms underlying the toughening of these compacts are discussed in detail. The resulting carbonated compacts prepared in 0.1 or 0.5 mol/L MgCl₂ solutions exhibited compressive strengths over 100 MPa and flexural strengths exceeding 40 MPa. Additional MgCl₂ introduced a chemical looping that accelerates the carbonation reaction. Simultaneously, the formation of Mg-calcite and aragonite induced structural deformation and internal coherent strain, enhancing the capacity of the γ-C₂S carbonated compacts to withstand high flexural stresses. Furthermore, the interaction of Mg²⁺ ions with silica gels promoted the formation of highly polymerized M-S-H structures, resulting in an increased elastic modulus of the carbonated matrix. This toughening strategy effectively addresses the inherent challenges associated with carbonatable binders and holds promise for developing low-carbon cement alternatives.