Abstract: To address the issues of poor acid resistance of cement-stabilized soft soil and the high pollution, energy consumption, and cost associated with cement production, this study proposes using low-cost industrial solid wastes (ground granulated blast furnace slag (GGBFS) and fly ash (FA) in varying ratios) as precursors, with solid sodium hydroxide as the activator, to prepare geopolymer grout through a ‘one-step’ process for stabilizing soft soil. Subsequently, the geopolymer-stabilized soft soil samples were immersed in HNO₃ and H₂SO₄ solutions with different pH values (2, 4, and 6). The acid resistance of the stabilized soil was evaluated at different erosion ages (30, 60, 120, and 240 days) using four indices: mass loss, unconfined compressive strength (UCS), neutralization depth (ND), and pH value. Furthermore, the changes in microstructure and hydration product composition of the samples under different acidic environments were investigated using scanning electron microscope-energy dispersive spectrometer (SEM-EDS) to reveal the degradation mechanisms. The test results indicate that compared to H2SO4 solution, HNO3 solution exerts a milder acid erosion effect on the stabilized soft soil. This is primarily because the Ca²⁺, K⁺, and Na⁺ ions in the stabilized soil form nitrates in water, which can neutralize the erosion of ions, thereby mitigating the degradation of the soil’s properties. When the mass ratio of GGBFS to FA is 80:20, the acid erosion resistance of the geopolymer-stabilized soft soil reaches an optimal level. This suggests that the appropriate incorporation of FA can form a dense microstructure in the samples, effectively impeding the intrusion of H⁺, NO₃^-  and SO₄^2-  ions. The research findings can expand the application scope of low-cost industrial solid wastes and lay a theoretical foundation for the durability assessment of one-step geopolymer-stabilized soft soil.

Key words: geopolymer, acid resistance, stabilized soft clay, microanalysis