Optimizing coal gasification slag utilization: Predictive modeling and hydration mechanism of blast furnace slag replacement in solid waste cementitious materials

Coal gasification slag (CGS), a by-product of the coal gasification process, is produced in large quantities but remains underutilized, posing environmental challenges. This study investigates the feasibility of partially substituting blast furnace slag (BFS) with CGS in the preparation of solid waste cementitious materials (SWCM), aiming to enhance resource utilization and reduce costs. A constrained mixing test design was employed to optimize the proportions of CGS, BFS, steel slag (SS), and desulphurization gypsum (DG), and a regression model was developed to predict compressive strength at 3, 7, and 28 days. The optimal mix (20 % CGS, 23 % BFS, 37 % SS, 20 % DG) achieved a 28-day compressive strength of 57.1 MPa, with the model demonstrating high predictive accuracy (Adj-R 2 up to 95.27 %). Microscopic analyzes (XRD, SEM-EDS, XPS, TG-DTG/DSC) revealed that CGS contributes abundant aluminosilicate glass, promoting the formation of C-(A)S-H gels and AFt, which enhance strength and densify the microstructure. The study confirms that CGS can effectively replace BFS in SWCM, providing a theoretical basis for large-scale, sustainable utilization of CGS in construction materials. • CGS enriched in [AlO 4 ], [AlO 6 ] and [SiO 4 ] could replace BFS in solid waste binder. • A prediction model with Adj-R 2 of 84.40–95.27 % were built for CGS containing binder. • The optimized ratio of CGS replace to BFS in solid waste binder is nearly 1:1. • C-(A)S-H gels and Aft are the primary hydration products of CGS containing binder.