Experimental Study on the Mechanical Properties of Molybdenum Tailings Concrete Under Chloride Erosion and High-Temperature

This study investigates the mechanical behavior of molybdenum tailings (MT) concrete circular specimens under combined chloride salt dry–wet cycling and high-temperature exposure, simulating post-fire conditions in corrosive environments. A total of 50 circular cross-sectional specimens were fabricated with varying concrete strength grades (C30 and C40), MT replacement ratios (0–100%), and exposure conditions (NaCl solutions: 20,000 and 50,000 mg/L; temperature: ambient/400 °C). Axial compression experiments were conducted to evaluate their performance. Analysis of mass change rates and post-cycling phenomena indicated that MT content significantly influenced mass variation, with the 100% MT group having a 2.3 times higher mass increase than the 0% MT group. Especially, under coupled conditions, compared with the 0% MT control group, the 25% MT group showed a 28.6% increase in peak stress, 8.3% reduction in peak strain, 12.1% rise in Elastic modulus, and 13.3% decrease in Poisson’s ratio, confirming that MT incorporation mitigates coupled strength degradation. Two failure modes were identified: end-cone failure and overall splitting failure. Chloride salt corrosion markedly reduced the load-bearing capacity of the specimens, decreasing both their peak displacement and peak strain. Furthermore, peak strain decreased as the molybdenum tailings replacement ratio increased. Scanning electron microscopy (SEM) revealed that dry–wet cycling prior to high-temperature exposure promoted hydration product densification, indicating a partial enhancement of hydration reactions and consequent strength improvement. Although high-temperature exposure degraded the strength of MT concrete, the incorporation of MT mitigated this weakening effect. The relationship between the peak stress of concrete and its axial compressive strength under the coupled effects of MT replacement ratio and NaCl solution concentration has been established via fitting. This study reveals the coupled damage mechanism, verifying the mitigating effect of MT on coupled chloride-thermal damage, and establishing a validated bearing capacity prediction model, which provides a valuable reference for assessing the behavior of MT concrete circular specimens subjected to salt corrosion and elevated temperatures.