Effects of high temperatures on mechanical behavior of high strength concrete reinforced with high performance synthetic macro polypropylene (HPP) fibres

•HPP Fibers did not have significant effect on the compressive strength of concrete.•Mechanical properties of HSC were enhanced when HPP fibers were added.•Addition of HPP fibers postponed the spalling of HSC when exposed to high temperatures.•Discussion about the optimum dosages of HPP fibers was made. Today, the advancement of technology and the achievement of increasing innovations in the field of building materials have increased high-strength concrete (HSC) production. The use of this material has been increased due to economic and technical reasons in the construction of concrete sections. However, the more compressive strength of the concrete is, the more concrete becomes brittle and its tensile strength does not increase with increasing compressive strength. HSC is also more vulnerable to high temperatures due to its high density and low porosity compared to conventional concrete. Researchers have proposed different methods including the use of polypropylene fibres in concrete mix designs in order to overcome these defects of HSC. In this study, a new type of polypropylene fibres, called high performance synthetic macro polypropylene fibres (HPP), have been used in dosages of 1, 2 and 3 kg/m3. Tests on hardened concrete include compressive strength, tensile strength and flexural strength at temperatures of 25, 100, 200 and 300 °C. By adding 1 kg of fibres to HSC, its compressive strength, tensile strength and flexural strength increased up to 14, 17 and 8.5%, respectively. Furthermore, the greatest improvement in the mechanical properties of concrete exposed to high temperatures was obtained when 1 kg/m3 of fibres was added to HSC.