Durability and microscopic mechanisms of coal gangue-calcium carbide residue geopolymer binder material

To evaluate the durability of coal gangue (CG)–calcium carbide residue (CCR) geopolymer in aggressive environments, full immersion tests were performed in H2SO4, Na2SO4, and MgSO4 solutions. Changes in compressive strength, mass loss, and performance degradation were examined. Degradation mechanisms were studied using XRD, FTIR, TGA, MIP, and SEM to analyze erosion products, microstructure, and pore evolution. An optimal liquid-to-solid ratio of 0.45 was identified for CG–CCR geopolymers. The material exhibited excellent resistance to Na2SO4 due to ettringite and C-A-S-H gel formation, enhancing pore structure and bonding strength. However, resistance to H2SO4 and MgSO4 was poor, driven by aluminum and calcium leaching and C-A-S-H transformation into non-cementitious M-A-S-H gels. A dense protective layer and corrosion-resistant C-A-S-H gel provided superior durability compared to OPC, with CCR addition further improving structural integrity and C-A-S-H gel generation. These findings highlight the potential of industrial waste-based geopolymers for durable, sustainable construction.