Mechanical properties and hydration mechanism of coal gasification slag fly ash alkali‐activated cementitious materials

Abstract Coal gasification slag (CGS) and fly ash (FA), as abundant industrial solid wastes, pose significant environmental risks. In this study, we prepared coal gasification slag–fly ash composite cementitious binders (CF) using CGS and FA as the main raw materials, with calcium oxide (CaO) as an alkaline activator. Through an orthogonal experiment, the effects of the CGS‐to‐FA mass ratio, CaO dosage, and water‐to‐binder (w/b) ratio on compressive strength are investigated, supported by XRD, SEM‐EDS, FTIR, and XPS analyses. Results indicate that the CGS‐to‐FA mass ratio is the primary factor influencing strength; ratios exceeding 60% significantly reduce strength. Compared with the water‐binder ratio, CaO dosage exhibits a significant promoting effect on the long‐term strength; the w/b ratio shows no remarkable influence on compressive strength within the range of 9%–11%. The optimal mix (CF6) comprises a CGS‐to‐FA ratio of 60:40, 6% CaO, and 9% w/b ratio, achieving a 28 d compressive strength of 1.70 MPa. Microscopic analysis shows that CF6 achieves precise calcium‐silicon‐aluminum coupling, forming calcium silicate hydrate (C–S–H gel), Ca(OH) 2 , and ettringite (AFt) during hydration, which increases matrix compactness. This study provides theoretical and technical support for the high‐value utilization of coal‐based solid wastes in cementitious materials.