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In this study, some mechanical and durability properties of concrete specimens, with a water/cement (w/c) ratio of 0.47 and having a reference slump of 40 mm, produced by addition of steel fi bers (SF) and/or polypropylene fi bers (PF), were investigated. The additions of SF were 20 kg/m 3 and 40 kg/m 3 and PF additions were 0.3 kg/m 3 and 0.6 kg/m 3 . Workability and unit weight tests were made on fresh concretes. Compressive stress, elastic modulus, and fl exural tensile tests were performed on hardened concretes. Also, load-defl ection curves and toughness indices were obtained during a three-point fl exure tensile test. Freeze-thaw, abrasion and drying shrinkage tests were also carried out to determine the effects of SF and/or PF on some durability properties of concretes. It was observed that fi ber inclusion to concrete decreases the workability and that the mechanical properties of concrete can be improved by the addition of fi bers. Using hybrid fi bers in the concrete both increases and decreases some mechanical properties of concrete. In order to see a greater effect of both SF and PF on the properties of concrete, different hybrid fi ber volume fractions for different matrix strengths may be examined, since fi ber type and fi ber volume fractions are important parameters to be taken into account in the mix design of concrete for the performance Keywords: durability; hybrid fi ber concrete; mechanical properties; polypropylene fi ber; steel fi ber.

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