Effect of elevated temperature on mechanical, and microstructure properties of concrete containing reclaimed asphalt pavement

Structures frequently encounter fires of varying intensities. In cases where the building is not completely burned, a post-fire assessment of its structural integrity is essential to ascertain its future. The addition of Reclaimed Asphalt Pavement (RAP) into concrete mixes is deemed both economically viable and environmentally sustainable, as it conserves natural resources. This research investigates how the inclusion of RAP influences the mechanical properties and thermal expansion strain, in addition to the microscopic structure of concrete mixtures when subjected to temperatures of 23 °C, 200 °C, 400 °C, and 600 °C. Natural Coarse Aggregate (NCA) was substituted with RAP aggregates at four different replacement proportions (0%, 20%, 40%, and 60%) by volume. Results demonstrated a decrease in mechanical properties and thermal expansion strain with increasing RAP replacement proportion at constant temperatures. The worst recorded drops for compressive strength, flexural strength, and modulus of elasticity after exposure to 600 °C were (43%, 40%, and 53%), respectively. All at replacement ratio of 60%. On the other hand, thermal expansion strain was reduced by 40% at the same replacement ratio. Increasing the temperature at the same replacement proportion of RAP results in a decline in compressive strength, flexural strength, and modulus of elasticity, while the thermal expansion strain increases. Furthermore, microscopic analysis using scanning electron microscopy (SEM) indicated that the interfacial transition zone (ITZ) is significantly influenced by the use of RAP, which primarily explains the changes in the behavior of RAP concrete.