In extremely cold regions with frequent extreme weather conditions, coupled factors make concrete corrosion by garbage landfill leachate become more complicated. Although previous studies have characterized the effects of individual factors, the mechanisms of coupled effects under specific conditions require further research. Therefore, this study analyzed the individual and coupled effects of landfill leachate, salt solution, and freeze–thaw cycles. The corrosion mechanism of landfill leachate was explained by analyzing the mechanical properties, surface morphology, and microstructure of the concrete. The individual factor tests showed that landfill leachate affected the performance of concrete more significantly than salt solution in the short term. In the immersion tests, the strength of concrete specimens corroded by landfill leachate was always minimized throughout the process, and the compressive and flexural strengths of concrete in landfill leachate decreased by 6.40% and 7.83%, respectively. In the coupled tests, freeze–thaw cycles amplified the effect of landfill leachate on concrete, exhibiting more severe damage than that with only landfill leachate. After four test cycles, the compressive strength of the concrete in the coupled test group decreased by 22.5%, 19.7%, and 31.3% and the flexural strength decreased by 40.2%, 26.7%, and 46.3%, respectively. Through surface morphology and microstructure analyses, we found that the inorganic salt ions in the landfill leachate reacted to form expansive ettringite and gypsum, which initially optimized the internal structure of the concrete but caused severe damage in the later stage. Concrete corrosion by landfill leachate was significantly enhanced under the influence of freeze–thaw cycles. The experimental results of this study provide basic data and theoretical support for designing and protecting concrete buildings in extremely cold environments.

The deterioration of concrete buildings in landfills by landfill leachate corrosion has received widespread attention, and this problem is pronounced in cold regions. This study selected landfill leachate, salt solution, and freeze–thaw cycles as the corrosion conditions for the concrete corrosion test under one-factor conditions. At the same time, landfill leachate and salt solution were coupled with freeze–thaw cycles for the concrete corrosion test. The severity of concrete damage was compared by the changes in mechanical properties and microscopic morphology of the concrete during the test. The results of the one-factor corrosion test showed that the landfill leachate would cause more damage to the concrete in the short term. Meanwhile, the coupled-factor corrosion test results showed that freeze–thaw cycles amplify concrete corrosion by landfill leachate, resulting in a significant reduction in the mechanical properties of concrete and damage to the internal structure. In addition, the study characterized the mechanism of action of landfill leachate corrosion on concrete. This could also provide theoretical support for constructing and protecting concrete structures in landfills in cold regions.