عنوان مقاله [English]
Use of common fibers, in addition to increasing ductility, toughness, first point cracking, and ultimate strain, plays a major role in preventing shrinkage and thermal cracks. The role of temperature in fiber bridging and change of material structure has been investigated in previous studies. Use of waste materials in structural materials can decrease further pollution of ecosystem. On the other hand, increase in oil and polymer-based waste materials, caused some concern in the international community because of the adverse environmental impact of this material. For this reason, in this research, steel fiber (0.4, 0.5 and 0.6), Polypropylene fiber (0.03, 0.05 and 0.1), and recycled Polyethylene terephthalate (PET) fiber (0.2, 0.3 and 0.4) percent of the concrete mixture volume were used. The results of the rheological (V-funnel, T50, Slump and L-Box), mechanical properties (e.g., compressive, flexural, and splitting tensile strength) and Ultrasonic Pulse Velocity (UPV) Test of self-compacting concrete exposed to temperatures of 20, 200, 300, 400, and $600^circ$ showed that high contents of fibers did not satisfy some rheological and mechanical aspects of self-compacting concrete. Steel fibers increased the compressive, flexural, and splitting tensile strengths of concrete with maximum amount of 9.8% and two other fibers cause 15% decrease in strength of unheated specimens at most. Fiber reinforced specimens had an increase in resistance in the range of 8 to 21% by heating specimens to $600^circ$.The flexural strength of steel fiber reinforced specimens had an increase of maximum 30% for unheated ones. PET and P.P. fiber reinforced specimens had 9 to 20% increase in flexural strength. The presence of fibers increases the mechanical strength, toughness, and ductility of concrete and prevents loss of strength and spalling phenomenon at high temperatures, as well as having a fundamental role in the reduction of heat, microcracks, and retaining fundamental structure of concrete.