Review of mechanical properties and strengthening mechanism of fully recycled aggregate concrete under high temperature

High temperature impacts on the overall performance of fully recycled aggregate concrete (FRAC). Accordingly, an investigation of the decay rule of the mechanical properties of FRAC is essential to gain insight into damage mechanism of FRAC exposed to excessively high temperatures. This study systematically analyzes the performance of FRAC in resisting stress after its exposure to high temperatures. Then, the effects of excessively high temperatures on the thermal parameters and mechanical properties of FRAC are determined. Measures and mechanisms necessary to improve the FRAC performance at high temperatures are identified such that FRAC mechanical properties at high temperatures can be better understood. Moreover, targeted enhancement mechanisms are proposed. The currently used compressive constitutive model of FRAC at high temperatures is analyzed and results are summarized. Future research trends are also predicted based on the current research status. The results show that the thermal expansion and specific heat of FRAC are observed to increase with temperature, whereas the thermal conductivity decreased. The microstructure of FRAC also changes due to high temperature, resulting in the deterioration of its mechanical properties. Nevertheless, the high-temperature resistance of FRAC can be effectively improved using admixtures, fibers, and steel tube reinforcement. This paper provides a comprehensive summary of the thermodynamic parameters and computational models for the mechanical properties of FRAC at high temperatures. Further research and theoretical modeling of the mechanical properties of FRAC at high temperatures are required to establish a theoretical foundation for future FRAC utilization and promotion.