Exploring calcined coal gangue fines as the total substitute of fly ash in the production of alkali-activated slag/fly ash materials

This paper investigated the feasibility of upcycling coal gangue fines (CGF), a secondary waste generated during the production of coal gangue aggregates, as the substitution of fly ash to prepare alkali-activated slag materials (AASM). CGF was thermally activated by calcining CGF at 500–900 ℃ to enhance its reactivity without grinding. The effects of CGF subjected to various temperatures on the flow, hydration heat, hydration products, compressive strength, and microstructure of AASM were experimentally examined. Experimental results confirmed the feasibility of upcycling CGF as the total substitution of fly ash. By adding calcined CGF, the 3 d and 7 d compressive strengths of AASM gained pronounced increases by 7–32 % and 4–27 %, respectively, where 800 °C was the optimal mixture with the highest compressive strength. Moreover, the addition of CGF brought tiny changes to the development of hydration products and microstructure. The proposed technology enables a more promising way to upcycle CGF into useful material and benefits the application of coal gangue aggregates.