Previous research regarding the flexural performance and durability of concrete incorporating hybrid polymeric waste in particular after exposure to heat is scarce. Therefore, this research effort addressed the flexural behavior and durability of concrete incorporating PET and tire aggregates as well as their combination as a volumetric substitution for sand after experiencing elevated temperatures. For this aim, different parameters effective on the post-fire flexural behavior and durability of hybrid recycled concrete such as flexural strength, toughness, fracture energy, flexural stiffness, water absorption, porosity, and density were assessed through different tests. The experimental findings demonstrated that incorporating tire and PET aggregates as well as their combination in the concrete mixture in place of sand degraded the flexural properties of the heated and unheated specimens. Furthermore, although prior to the degradation point of the polymeric waste materials, incorporating tire aggregate in the concrete mixture led to less reduction in the flexural behavior of the specimens, above this point, PET flakes provided a proper and more ductile performance for the heated concrete. In addition, introducing polymeric wastes in concrete and increasing temperature led to increased water absorption and porosity, as well as a decreased density of the specimens. The test results were also compared with the corresponding results estimated by formulas proposed by several codes, and then they were used to develop formulas to predict the flexural behavior of heated concretes incorporating hybrid PET-tire aggregate in terms of temperature and the fraction of the polymeric waste aggregate in volume. Ultimately, based on the response surface method (RSM), an optimum solution was presented for the design parameters, which maximizes the flexural strength of concrete incorporating hybrid recycled waste aggregates at various temperatures.
