Dynamic compressive behaviours of sustainable concrete with recycled aggregates and NaOH pretreated crumb rubber after exposure to elevated temperatures

The utilization of recycled aggregate concrete (RAC) represents a pivotal strategy for waste valorisation and environmental conservation. The efficacy of NaOH pretreatment in enhancing the high-temperature performance of crumb rubber-modified RAC was investigated. Specimens with varying recycled aggregate replacement rates (0, 50%, and 100%) and rubber content (0, 10, and 20%) underwent controlled heating, quasi-static compression, and high-strain-rate impact tests, complemented by SEM micro scale analysis. Key findings reveal that NaOH pretreatment dramatically enhanced rubber-cement matrix bonding, increasing ambient compressive strength by 68.14% and improving thermal stability, with MRRAC100-R20 (100% RA, 20% rubber) retaining 83.18% and 59.66% of its strength at 300°C and 600°C, respectively. Besides, dynamic performance showed elevated crack resistance by adding rubber particles, evidenced by larger fragment sizes. Strain-rate sensitivity was affected by heating temperature, RA replacement rate and rubber content. Specifically, the increase in heating temperature increased the transition strain rate that distinguishes the high and medium strain rate ranges in MRRAC. The RA replacement rate has a weakening effect on the strain-rate effect of MRRAC, but an appropriate amount of rubber reinforces the strain-rate effect of MRRAC due to its flexible material properties. Microscopic experiments revealed that the softening and decomposition of rubber formed a pore structure inside MRRAC, effectively widening the release channels for internal free water and bound water evaporation, and significantly alleviating thermal damage by reducing the pressure gradient between the interior and exterior of MRRAC. These results demonstrate that thermal resistance and impact tolerance of MRRAC, supporting its application in safety-critical infrastructure.