Exploring coal waste-based powder as a substitution for silica fume in cement-based materials

This paper proposes using coal gangue powder (CGP) as an alternative to silica fume (SF) in cement-based systems, towards to high-value recycling of this coal waste. In cement-based systems, CGP offers a more affordable substitute for SF as a supplementary cementitious material. Mechanical activation enhances CGP’s reactivity by inducing structural disorder and increasing surface area, which facilitates its participation in hydration reactions. Additionally, its water retention capacity contributes to prolonged hydration and improved microstructural densification. Employing techniques such as BET analysis, rheological testing, XRD, TG-DTG, hydration kinetics, compressive strength and nanoindentation, the research compares the effects of CGP and SF on paste properties. The results indicate that SF increases plastic viscosity by 9.18 %–30.61 % and enhances compressive strength by 4.68 % at 28d, while CGP-added pastes show slight plastic viscosity to gain more distinctive rheological properties. CGP-added pastes demonstrate a comparable cumulative mass loss in TG-DTG, highlighting its positive impact on cement hydration. Additionally, CGP modifies the pore structure, increasing gel pore volume at lower dosages while maintaining a balanced distribution at higher dosages. These findings suggest that mechanically activated CGP can partially replicate SF’s effects on hydration and microstructural refinement, providing a sustainable and economical approach to enhancing cement-based materials.