Residual compressive mechanical behavior of recycled lump-aggregate concrete with alluvial-proluvial sand after exposure to high temperatures

Recycled lump-aggregate concrete (RLAC), incorporating alluvial-proluvial sand, recycled coarse aggregate (RCA) and recycled lumps (RLs), reduces natural resource consumption and offers clear environmental benefits with strong application potential. However, as fire hazards intensify, understanding the evolution of RLAC mechanical properties at elevated temperatures and after heating is crucial for structural safety and performance evaluation. This study thus investigated the high-temperature damage evolution and post-heating compressive behavior of RLAC using 132 cylinders, considering fine aggregate type, RCA and RL contents, and exposure temperature. Mercury intrusion porosimetry was used to quantify mortar pore structure after heating. Results show that: (i) primary compressive cracking is largely unaffected by the variables, while recycled materials mainly increase secondary cracks; (ii) recycled constituents reduce ambient compressive strength and elastic modulus but increase peak strain and property dispersion; (iii) temperature governs post-heating mechanical behavior, with RCA and RLs improving retention of relative strength and modulus, while fine aggregate type has limited influence; and (iv) at temperatures of 600 °C or above, thermal effects dominate degradation, making other factors negligible. A post-heating compressive stress-strain model and conversion relationships among key mechanical indices are proposed, providing a basis for engineering application and fire-resistance evaluation.