The current study investigates the effects of different amounts of polypropylene (PP) and macropolymeric (MP) fibers on the mechanical properties and durability of high-strength concrete containing silica fume and nano-silica. In total, 280 concrete specimens were produced in 28 different test groups, for which the parameters of compressive strength, tensile strength, modulus of elasticity, water absorption, and porosity were evaluated. The macro-polymeric fibers in volume fractions of 0.25, 0.5, 0.75, 1.0, and 1.25%, and the polypropylene fibers in volume fractions of 0.1, 0.2, 0.3, 0.4, and 0.5% were used in this study. Furthermore, one set of specimens with the total fiber volume fraction of 1.0% of the concrete volume was tested in order to examine the effect of hybrid polypropylene-macro-polymeric fibers on the concrete properties. In addition, the nano-silica with the weight percentages of 1, 2, and 3%, and the silica fume with the weight percentages of 8, 10, and 12% were employed in the concrete mix design. In the current paper, first, the effects of macro-polymeric, polypropylene, and hybrid fibers on the physicomechanical properties were comparatively examined, and then the influence of using nano-silica and silica fume in the high-strength concrete with no included fiber was investigated. Finally, the optimum percentages of fibers and pozzolans corresponding to the most significant increases in the tensile strength were chosen, which were subsequently used as the optimum combination of the highstrength concrete. The results of the experimental study suggest an improvement in the concrete mechanical properties and durability following the introduction of nano-silica and silica fume. In addition, incorporating macro-polymeric fibers in the concrete mixture given the volume content of fibers improves the mechanical properties of high-strength concrete. Moreover, high volume fractions of polypropylene fibers in the concrete mixture brought about negative effe
