Upcycling coal gangue in alkali-activated pervious concrete: a sustainable pathway to sponge city infrastructure

Abstract This study explores the use of coal gangue powder (CGP) to enhance the workability of ground granulated blast-furnace slag (GGBS)-based geopolymer pervious concrete (GPCC) and promote the reuse of industrial waste. CGP was introduced as a partial replacement for GGBS at rates ranging from 0 to 50%. The impact of CGP on the multiscale properties of GPCC was evaluated, including rheology, mechanical strength, permeability, frost resistance, and pore structure. Incorporating CGP improved paste flowability by reducing yield stress, plastic viscosity, and thixotropy. However, mechanical strength declined with increasing CGP content. At 40% replacement, the 28-day compressive strength dropped to 17.9 MPa, falling below the C20 strength class defined in relevant specifications. Although CGP increased total porosity, permeability decreased. This was likely due to bottom pore blockage caused by changes in flow behavior. Frost resistance also diminished at higher CGP rates, with over 7% mass loss and 20% strength loss after 25 freeze–thaw cycles. Pore structure analysis revealed a shift toward larger pores, reducing compactness and long-term durability. When CGP content was limited to 30% or less, GPCC maintained a balanced performance across strength, permeability, durability, and workability. These results highlight the potential of CGP-based geopolymers in sustainable infrastructure applications, especially in sponge cities and pervious pavement systems.