Particle-Size-Fractionated Coal Gasification Slag as a Supplementary Cementitious Material: Hydration Products, Microstructure Evolution, and Mechanical Performance via Classified Grinding.

To promote the high-value utilization of coal gasification slag (CGS) resources and mitigate the environmental issues caused by its accumulation, CGS was separated into five fractions by particle size (2.36-4.75 mm, 1.18-2.36 mm, 0.60-1.18 mm, 0.30-0.60 mm, and 0.15-0.30 mm) and subsequently ground into CGS powders (CGSPs). The physicochemical properties of both CGS and the obtained CGSP were systematically characterized, and the effects of CGSP on the hydration behavior and engineering performance of ordinary Portland cement (OPC) were investigated. The results revealed significant differences in physical properties and composition among the various particle-size fractions of CGS and their corresponding CGSP. When 40 wt.% CGSP was used to replace Portland cement, the C2.36 fraction exhibited the highest early-age compressive strength (16.91 MPa and 25.3 MPa at 3 d and 7 d, respectively), which is attributed to its favorable chemical composition and abundant glassy components. In contrast, the C0.6 fraction achieved the highest 28 d compressive strength (50.0 MPa). The C0.15 fraction showed the lowest strength at all ages, may be mainly due to its high residual carbon content and low reactivity. Overall, the compositional differences among CGS fractions of different particle sizes govern the formation and evolution of hydration products, and the proposed strategy of "classified grinding and quality-oriented utilization" provides an effective approach for the high-value application of CGS in cement-based materials.