Post-fire impact behavior and durability of steel fiber-reinforced concrete containing blended cement–zeolite and recycled nylon granules as partial aggregate replacement

Recycling polymeric waste in concretes to replace a portion of the stone aggregate volume can improve some of the mechanical features of concrete such as impact resistance, while also helping mitigate the associated environmental problems. Thus, this research was aimed at exploring the combined effect of nylon granules (0, 10, and 20%) as a replacement for fine aggregate, steel fibers (0, 0.75, and 1.25%), and zeolite (0, 10, 15, and 20%) as a replacement for cement on the impact resistance and durability of concrete following several heating levels (20, 300, and 600 °C). For this purpose, 432 concrete samples were manufactured, and the concrete features including compressive strength, tensile strength, impact resistance, loss of weight, water absorption, porosity, density, and failure type of concrete samples after different heating levels were investigated. The results demonstrated that the impact energy at the failure level declined considerably with temperature for all the concrete samples containing nylon granules and steel fibers (by 46–94% for 600 °C). However, increasing nylon granule content to 20% in concrete improved the impact resistance at the first and ultimate crack levels following exposure to 20 and 300 °C, while significantly lowering this parameter (by up to 40%) following exposure to 600 °C. Furthermore, the inclusion of steel fibers in concrete and increasing its content led to increased impact energy of the heated and non-heated concretes.