Activation of coal gasification slag by alkali fusion for blended cement: phase reconstruction, hydration behavior, and mechanical performance

Alkali fusion is an effective strategy to enhance the reactivity of coal gasification slag (CGS) and promote its high-value utilization in cementitious materials. However, the structural reconstruction of alkali-fused CGS and its influence on the hydration behavior of blended cement systems remain unclear. In this study, CGS activated by different NaOH dosages was incorporated into blended cement systems to investigate the relationships among phase reconstruction, reactive species dissolution, hydration evolution, and macroscopic performance. The results showed that NaOH-assisted alkali fusion altered the phase assemblage and structural characteristics of CGS and promoted the measured dissolution of Si and Al species. SH-8 contained approximately 6.5 wt% Na 2 SiO 3 and exhibited the highest dissolved Si and Al concentrations of 42.81 and 22.59 mg/L, respectively. The subsequent hydration behavior reflected the coupled effects of CGS structural reconstruction and the NaOH-derived Na-containing phases formed during fusion. Consequently, the compressive strength of the CGS-containing blended cement first increased and then decreased with increasing NaOH dosage. SH-8 achieved the highest 28 d compressive strength among the CGS-containing mixtures, reaching 46.6 MPa, although this value remained approximately 8.4% lower than that of the OPC control mixture (50.9 MPa). This study demonstrates the non-monotonic influence of NaOH dosage on alkali-fused CGS and highlights the coupled roles of CGS structural reconstruction and NaOH-derived phase formation in regulating the hydration behavior and performance of CGS-containing blended cement.