Abstract: Coal gangue shotcrete (CGS), as an eco-friendly construction material, is significantly influenced by the type and amount of admixtures used, among which accelerators and superplasticizers are widely applied due to their effective modification properties. This paper investigated the impact of varying dosages of accelerators and superplasticizers on the mechanical properties and impermeability of CGS through single-factor experiments to determine the optimal dosage. The findings were validated through rebound rate and large plate spraying tests. The results show that the inclusion of superplasticizer causes the compressive strength and splitting tensile strength of CGS to initially increase, then decrease, and rise again, achieving optimum properties at a 2.50% (mass fraction) dosage with no signs of permeability and good compactness. For accelerator content ranging from 0% to 3%, there is a slight increase in compressive and splitting tensile strength at 1 d age, which gradually decreases at 7 and 28 d. When the dosage increases from 3% to 12% (mass fraction), the strengths significantly decrease at all tested ages. Excessive accelerator (12%) notably exacerbates permeability. When the accelerator dosage is 3%, the top of CGS shows permeability. Rebound tests demonstrate that the synergistic effect of the accelerator and superplasticier enhances the flowability and bonding of CGS, reducing the rebound rate to 13.03%. The large plate spraying tests indicate that the optimized mix of CGS significantly enhances compressive strength and splitting tensile strength compared to ordinary CGS, with a 50.72% reduction in average penetration height.

Key words: coal gangue, shotcrete, admixture, mechanical property, impermeability