Mechanical Properties and Reaction Mechanisms of One-Part Alkali-Activated Materials Based on Coal-Based Synthetic Natural Gas Slag

Alkali-activated materials (AAMs) have the potential to reduce carbon dioxide emissions in the cement industry. However, the complex preparation process for activator solutions and high production costs hinder their widespread application. This study developed a ternary one-part alkali-activated system composed entirely of waste materials, including coal-based synthetic natural gas slag (CSNGS), calcium carbide slag (CCS), and flue gas desulfurization gypsum (FGDG). The effect of the solid waste ratio and curing temperature on the mechanical properties of CSNGS-CCS-FGDG AAMs were investigated, and various characterization techniques were employed to study the synergistic mechanisms in the ternary alkali-activated system. The experimental findings revealed that the mechanical properties of AAMs were effectively improved by incorporating FGDG, and the 28-day compressive strength and flexural strength can reach up to 21.8 and 4.39 MPa, respectively. This is attributed to the increase in the gels formation within the reaction products, resulting from the dissolution of CSNGS facilitated by the presence of FGDG. It was also found that a reinforcement microstructure of cross-linked ettringite and gels was formed. Consequently, its bridging effects on the gels, as well as the connecting and filling effects, resulted in a matrix microstructure with good integrity and denseness. Furthermore, the curing temperature was a critical factor affecting the morphology and composition of the ettringite and gels reinforcement structure, with the suitable temperature sequence identified as 65°C > 80°C > ambient temperature > 95°C for ettringite generation.