Deterioration Behavior of Geopolymer-Stabilized Soil under the Coupling Action of Freeze–Thaw Cycles and Chloride Salt Erosion

Geopolymer-stabilized soil is a low-carbon material widely used in engineering, but it often faces complex engineering environments. In cold regions, factors such as low temperature curing, chloride salt erosion, and freeze–thaw cycles (FTCs) seriously affect the mechanical properties of geopolymer-stabilized soil, which pose challenges to the stability of the foundation and engineering construction. The deterioration characteristics of geopolymer-stabilized soil were studied by the chloride erosion FTC coupling test and the unconfined compressive strength (UCS) test. The UCS, degradation rate, stress–strain curve, and deformation modulus of geopolymer-stabilized soil were analyzed, and the deterioration mechanism was explained from a microscopic perspective. The results indicated that with an increase in chloride concentration, the UCS of geopolymer-stabilized soil gradually decreased. The critical number of FTCs for the geopolymer-stabilized soil in water and chloride salt solution was three times, and the degradation rate exceeded 25% after three FTCs. The polymerization products of low temperature curing samples were fewer, and there were more unreacted geopolymer materials, making low temperature curing samples more susceptible to chloride erosion and FTCs. The final degradation rate of C(20) ranged from 37.72% to 46.81%, C(-2) ranged from 40.29% to 62.46%, and C(-10) ranged from 47.50% to 62.38%. After FTCs, the polymerization products of geopolymer-stabilized soil decreased. Chlorine salt erosion affected the polymerization rate and the total amount of polymerization products. Due to its high porosity, the low temperature curing sample was more susceptible to chlorine salt erosion, resulting in more corrosion products. By contrast, the internal structure of the room temperature sample was more compact and more susceptible to FTCs.