Influence of mechanical activation of coal gangue on the strength and microstructure of geopolymer

This study establishes a mechanistic framework linking grinding-induced particle characteristics of coal gangue to its geopolymerization behaviour and microstructure performance, offering a novel pathway to transform this coal mining waste into high-strength, sustainable geopolymers. By systematically grinding coal gangue (1–120 min, 450 rpm, 10 mm grinding media media), we demonstrate how variation of particle size reduction (including aggregation and agglomeration of particles), specific surface area, specific grinding energy E m , and structural defect was investigated in relation to setting time, compressive strength, morphology, and phase composition of the resulting geopolymers. Unground and mechanically activated coal gangue was analyzed via X-ray fluorescence (XRF), particle size distribution (PSD), specific surface area, Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR/FT-IR) and phase analysis by X-ray diffraction (XRD). The mechanically activated coal gangue was alkali-activated with 8 M NaOH and sodium silicate (Na 2 SiO 3 ), and the resulting geopolymers were characterized. A maximum compressive strength of 55.7 MPa was achieved after 28 days with a grinding time of 120 min, which represents an improvement of several orders of magnitude compared to the unground sample (0.92 MPa). Finer particles with increased specific surface area provided more reactive sites for alkali activation, while the generation of structural defects enhanced the dissolution of reactive species, leading to improved geopolymer properties. However, it was also observed that prolonged grinding delayed the setting time of the resulting geopolymer. These results highlight the importance of optimizing grinding parameters to optimize the reactivity and target performance of coal gangue-based geopolymers. This study provides valuable insights into the recycling and sustainable use of coal gangue as a material for geopolymer production and offers practical applications for environmental protection and resource efficiency.