Hydration properties of activated "coal gangue-fly ash-cement" ternary compound cementitious material

Coal gangue is a solid waste generated from coal selection and washing. This study proposes to improve its utilization rate by enhancing its activity through calcination and mixture with fly ash in a designed proportion to replace 30 % of cement. We investigated the effect of coal gangue-fly ash composite cement on the fluidity and mechanical properties of mortar after replacing cement, and analyzed the hydration mechanism of the composite cement using water heat generation, XRD, TG, and SEM. Results show that with the increase in the amount of activated coal gangue, the fluidity and mechanical properties of the cement mortar first increased and then decreased. When the activated coal gangue accounted for 20 % of the total composite powder, the 28-day compressive strength of the mortar reached 52.27 MPa. The addition of activated coal gangue and fly ash altered the proportion of mineral and chemical components in the composite cement system, consumed the calcium hydroxide generated during cement hydration, and formed additional C-(A)-S-H gel. It also induced the transformation of the AFt phase into the AFm phase. When the mechanical properties of cement mortar is improved, the activated coal gangue exhibits more significant physical filling effect and nucleation effect than its pozzolanic activity.