Thermal Performance of Recycled High-Ductility Cementitious Composites Under Various Elevated Temperatures and Cooling Regimes

Driven by the global demand for sustainable construction resources, Recycled High Ductility Cementitious Composites (R-HDCC) exhibit high ductility and cracking resistance, demonstrating significant potential for enhancing structural durability. However, fire resistance remains a critical constraint on its engineering application. To investigate the performance evolution mechanism of R-HDCC after high-temperature exposure, this study examined the effects of different temperatures (200 °C, 400 °C, 600 °C, and 800 °C) and cooling regimes (self-cooling and water-cooling) on R-HDCC. The results indicate that when the temperature exceeded 200 °C, the compressive strength of R-HDCC decreased significantly. At 800 °C, the residual compressive and flexural strengths dropped to below 20% of their initial values. However, water-cooling treatment mitigated the adverse effects on compressive and flexural strength to some extent. In terms of tensile performance, R-HDCC completely lost its functionality at temperatures of 600 °C and above, and the cooling method had minimal influence on tensile behavior. Compared with natural cooling, water-cooling specimens developed fewer microcracks and less interfacial damage, indicating that water-cooling alleviates high-temperature-induced deterioration of the material’s microstructure to a certain degree. These findings provide important insights for the scientific evaluation of the fire resistance of R-HDCC and offer valuable guidance for its practical application.