Evaluation of mechanical properties of steel fiber reinforced concrete with different strengths of concrete

Concrete has high brittleness along with low tensile strength and tensile strain capacities. Such unsatisfactory performance can be improved with the addition of steel fibers in concrete. Steel fiber reinforced concrete (SFRC) has gained popularity in the last decades because of its superior performance. Its main advantages include hindrance in macro crack propagation, prevention of growth of micro cracks to macroscopic level, improvement in ductility and residual strength after formation of the first crack, and high toughness. This study investigates the effect of adding steel fibers with different lengths and diameters on the mechanical properties of concrete for three values of concrete strength. In this study, hooked ended fibers of three lengths (40, 50, and 60 mm) and two diameters (0.62 and 0.75 mm) were used with three water-to-cement ratios (0.25, 0.35, and 0.45). Steel fibers were added with three volume fractions, 0.5%, 1.0%, and 1.5%. Thirty concrete mixes were prepared and investigated. The results indicated that the addition of different content and lengths of steel fibers with increasing water-to-cement ratios caused significant change in the mechanical properties of concrete, with an increase of about 10-25% in compressive strength and about 31-47% in direct tensile strength. The increase in the fiber content from 0.5% to 1.5% increased the flexural strength from 3% to 124% for fiber with the smaller aspect ratio of 65, whereas, for the higher aspect ratio of 80, a 140% increase in the flexural strength was observed compared to the concrete without any fibers. With the consideration of steel fibers of different lengths and diameters, an analytical model for stress strain relationship of fiber reinforced concrete under compression is proposed. There is good agreement between the proposed model and the experimental results.