Abstract: To explore the influences of different coarse aggregate replacement ratios on the high-temperature performance of recycled concrete with manufactured sand (RCM), RCM specimens were prepared with varying coarse aggregate replacement ratios (0%, 20%, 40%, 60%, 80%, 100%, mass fraction). The surface morphology, mass loss rate, compressive strength, load-deformation curve, and microscopic morphology of RCM were investigated after exposure to high temperatures. Results indicate that the RCM performs well in high-temperature tests below 600 ℃ when the coarse aggregate replacement ratio is between 40% and 60%. At 200 ℃, the specimens in each group show minimal morphological changes, small mass loss rate, and a slight increase in compressive strength. At 400 ℃, cracks begin to appear on the surface of the specimens, with mass loss rate ranging from 4.35% to 6.47%, and compressive strength starts to decline. At this point, the coarse aggregate replacement ratio has a minor impact. At 600 ℃, significant changes in surface morphology are observed, with mass loss rate increasing to 6.42%~8.70%, and compressive strength eventually decreasing to around 80% of the baseline strength. Specimens with coarse aggregate replacement ratio of 40%~60% perform well under these conditions. At 800 ℃, the surface morphology of specimens in all groups intensifies further. The impact becomes particularly pronounced for coarse aggregate replacement ratio exceeding 60%. Simultaneously, various performance parameters indicate that the concrete has experienced a complete loss of effectiveness at this temperature.

Key words: recycled concrete with manufactured sand, coarse aggregate replacement ratio, high-temperature performance, compressive strength, load-deformation curve