Considering increasing growth of using other materials in concrete for increasing its quality, studies on fibres have been recently extended. Existence of fibers can compensate for some of the weaknesses of concrete in terms of its brittleness and fragility. Now, in this study, role of steel waste fibers in compressive strength of cubic samples and tensile strength of cylindrical samples at ages of 3, 7, 28 and 42 days and also tensile strength resulting from flexure of prismatic samples at age of 90 days was investigated. The studied concrete included steel waste fibers with three different diameters of 0.8, 1.0 and 1.2 mm and two weight ratios of 35 and 70 kg/m³, which were compared at different ages with the control sample. It was observed that the concrete containing steel waste fibres had remarkable growth in increasing tensile strength. This strength increasing trend proceeded with increase in the amount and ratio of fibers' length to width.

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