Sustainable application of waste residue from coal gasification process in low-carbon cement: multiscale evaluation,...

The preparation of composite cement using alkali-ground coal gasification slag (CGS) exhibits significant potential for promoting solid waste utilization while reducing energy consumption and carbon emissions. However, the mechanisms governing CGS activity enhancement during alkali grinding and its subsequent influence on hydration behavior and property evolution of composite cements remain insufficiently understood. In this study, a series of CGS-based composite cement samples with graded performance were prepared by regulating alkali grinding parameters. The intrinsic relationships among CGS activation, hydration behavior, microstructural evolution, and mechanical properties were systematically investigated from both optimization and degradation perspectives. The results indicate that alkali grinding effectively activates the latent reactivity of CGS. The introduction of an appropriate amount of sodium hydroxide during alkali grinding significantly promotes cement hydration and accelerates the nucleation and crystal growth of hydration products, whereas excessive sodium hydroxide inhibits hydration. Consequently, the compressive strength of the composite cement initially increases and then decreases with increasing sodium hydroxide dosage. The 28 d compressive strength of the SH-2 group reaches 46.8 MPa, representing a 32.20% improvement compared with the SH-0 group. The dominant hydration products consist of AFt and highly polymerized C-(A)-S-H gels, which markedly enhance matrix densification. Compared with conventional cement, the SH-2 group exhibits reductions of 16.17% in sustainability index (SI), 19.84% in cost, and 14.71% in economic index (EI). These findings provide a mechanistic basis for the rational utilization of CGS in composite cements and offer valuable insights for the synergistic development of solid waste resource utilization and sustainable construction materials.