Effect of coarse aggregate replacement with structural demolition waste on adiabatic temperature rise characteristics of recycled aggregate concrete from semi-adiabatic tests

Recycled coarse aggregates (RCA) obtained from demolished concrete structures offer a sustainable alternative to natural aggregates; however, their influences on the thermal behavior of concrete remain insufficiently understood, particularly for mass concrete applications. This study investigates the effects of RCA replacement on the adiabatic temperature rise characteristics of recycled aggregate concrete (RAC) through semi-adiabatic tests. The associated variations in apparent density, internal moisture content, and compressive strength were also evaluated with three concrete mixtures, including a natural aggregate concrete (NAC) mixture and two RAC mixtures with RCA replacement ratios of 25% and 50%. The results demonstrate that increasing the RCA content exhibits a linear reduction in apparent density and compressive strength, while increasing the internal moisture content because of the lower density and higher water absorption capacity of RCA. Compared with NAC, RAC mixtures reached lower maximum hydration temperatures, required a longer time to attain the peak temperature, and maintained the peak temperature for a longer duration. These observations indicate that the altered physical characteristics of RAC promote greater internal heat storage, while the porous residual mortar attached to the RCA may contribute to a lower rate of heat conduction. Within the investigated range, the ultimate adiabatic temperature rise demonstrated a preliminary linear decline as the RCA content increased, with an approximately 1.54°C reduction for every 10% increase in RCA replacement. While the delay time of temperature rise remained nearly unchanged, the rate of temperature rise decreased with increasing RCA content. The findings demonstrate that RCA exhibits favorable thermal characteristics that can moderate hydration heat development and reduce temperature gradients in concrete structures, thereby offering potential benefits for mitigating thermal cracking while promoting sustainable construction practices.