Activation effects of activator type and coal gasification slag content on mechanical properties and reaction mechanisms of alkali-activated materials

The growing accumulation of coal gasification slag (CGS) poses serious environmental concerns, creating a compelling opportunity for its conversion into a fundamental constituent of alkali-activated materials (AAMs) for sustainable resource recovery. Nevertheless, the effectiveness of common activators (NaOH and water glass) in CGS-BFS systems and their reaction mechanisms requires clarification. This study systematically investigates the influence of CGS content on the properties of AAMs, quantifying the reaction degrees of the precursors activated by NaOH or water glass through XRD-PONKCS analysis. Results indicate that a CGS content of 20–40 % constitutes the optimal replacement level for slag, effectively mitigating early-age rapid setting and shrinkage without compromising compressive strength. Regarding activator suitability, water glass was more effective than NaOH in promoting the CGS reaction, achieving a reaction degree of 15 % compared to only 9 % with NaOH. However, the water glass-activated system exhibited greater sensitivity to CGS content. At a constant Na 2 O dosage of 4 %, increasing the CGS dosage markedly reduced early compressive strength. Samples with up to 40 % CGS showed gradual strength recovery over time, approaching the performance of the pure BFS system. In contrast, CGS contents exceeding 60 % significantly depressed the reaction degrees of both BFS and CGS, thereby strongly limiting strength development. These findings highlight that the effective use of water glass in CGS-BFS systems requires careful control of the CGS-to-alkali ratio to balance reactivity and performance. • Quantification of reaction degrees for both BFS and CGS in composite AAMs was achieved via XRD-PONKCS analysis. • NaOH activation promotes weakly crystalline C-A-S-H, whereas sodium silicate suppresses the formation of crystalline products. • An optimal CGS content of 20–40 % was identified, maintaining mechanical performance while valorizing the solid waste.