Investigating the Bond–Slip Behavior of Steel Rebar–Geopolymer Concrete after Freeze–Thaw Damage

Geopolymer concrete, an innovative sustainable construction material, demonstrates distinctive advantages including facile preparation protocols, reduced energy expenditure, minimized carbon footprint, and superior acid–alkali corrosion resistance. The material’s optimized pore architecture contributes to its enhanced frost resistance performance compared to conventional portland cement concrete systems. Nevertheless, the interfacial bonding behavior between steel reinforcement and geopolymer matrices under freeze–thaw (F-T) cycling conditions remains insufficiently characterized in current research literature. To objectify the adhesion performance between rebar and geopolymer concrete in F-T environments, this paper used variables including the strength of geopolymer concrete, the diameter of the deformed rebar, and the anchorage length to design central pullout specimens. The study of rebar and geopolymer concrete’s bonding properties, including failure modes, adhesion strength, and bond stress–slip curves, was conducted using central pullout tests under various F-T conditions. The findings indicate that three distinct failure modes exist for centrally loaded pullout specimens: pullout failure, splitting–pullout failure, and splitting failure. During F-T cycling, the bonding strength exhibits a direct proportionality to the compressive strength of geopolymer concrete and an inverse proportionality to both the diameter of the reinforcing bar and the anchorage length. As the number of F-T cycles increases, the bond performance between the rebar and geopolymer concrete deteriorates progressively, accompanied by an increase in peak slip. After 150 cycles of F-T exposure, Specimen N150-C40-18-5d demonstrated the most rapid decline in bonding strength, with a reduction of 40.4%, whereas Specimen N150-C40-14-3d exhibited the slowest degradation rate, registering a decrease of 24.9%. Sensitivity analysis reveals that during F-T cycles, the compressive strength of geopolymer concrete exerts the most significant influence on adhesive strength, while the rebar diameter demonstrates the greatest impact on peak slip magnitude.