Frost Resistance of Self-compacting Concrete with Varying Recycled Coarse Aggregate Contents in a Typical High-altitude Cold Region

This study investigates the effect of recycled coarse aggregate (RCA) replacement ratio on the frost resistance of self-compacting concrete (SCC). The experimental program was conducted in Linzhi, Tibet, China, a representative high-altitude region characterized by low atmospheric pressure and cold climatic conditions. SCC mixtures with RCA replacement levels of 0%, 25%, and 50% were prepared and subjected to repeated freeze-thaw cycles (FTCs). The results indicate that increasing RCA content tends to reduce the workability of SCC; however, this effect can be effectively mitigated through the incorporation of polycarboxylate-based superplasticizers. As the RCA replacement ratio increased, the frost resistance of SCC progressively deteriorated, as evidenced by higher mass loss, greater reductions in RDEM, and lower residual compressive strength. After 250 FTCs, the RDEM retention values of SCC-RCA0, SCC-RCA25, and SCC-RCA50 were 77.36%, 71.13%, and 65.39%, respectively, indicating aggravated freeze-thaw deterioration with increasing RCA replacement ratios. Microstructural analyses suggest that higher RCA contents are associated with weaker interfacial transition zones, which may promote damage accumulation and crack propagation under freeze-thaw action. An improved comprehensive evaluation model integrating mechanical performance, material cost, predicted service life, and carbon emissions was proposed to assess the overall performance of the mixtures. The comprehensive performance index is governed by the combined effects of the RCA replacement ratio and the transportation distance. Based on the proposed comprehensive evaluation framework and the conditions considered in this study, SCC incorporating 25% RCA exhibits relatively favorable overall performance when the transportation distance is below approximately 7.4 km; beyond this distance, SCC without RCA becomes the more suitable option. This finding provides practical guidance for selecting RCA replacement levels in SCC for infrastructure construction in such high-altitude cold regions under comparable environmental conditions.