The Effects of Steel Fiber Types and Volume Fraction on the Physical and Mechanical Properties of Concrete

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Different types and amounts of steel fibers have varying effects on the improvement of concrete’s mechanical properties. In order to identify the most suitable steel fiber types for the practical production of prefabricated pavements and derive a formula to predict and evaluate the mechanical properties based on steel fiber volume fraction, this study conducted experimental research on the physical mechanical properties of concrete using the method of equal volume substitution of coarse aggregate. The influence of steel fiber type and volume fraction on the microstructure and failure mechanism of steel fiber reinforced concrete (SFRC) was analyzed through electron microscopy scanning. The mechanical properties of plain concrete were used as benchmark. The results showed that when the steel fiber volume fractions were 0.6% and 1.5%, the bending and split tensile strengths of milled steel fibers were 3.1% higher than those of hooked-end steel fibers and the compressive strength of SFRC was significantly increased by 13.5%. The comprehensive mechanical properties of wave-shaped steel fibers were inferior to the first two types. Considering the requirements of SFRC in engineering, milled steel fibers are more suitable to be concrete components. This is because the tangling property of the hooked-end steel fibers makes them difficult to be shaped. In contrast, the smooth surface of milled steel fibers exerts a smaller impact on the forming of specimen and they are more economical. The mechanical properties of SFRC improve as the volume fraction of steel fibers increases from 0% to 2%, but start to decline when the volume fraction exceeds 2%. A volume fraction of 0.6% for steel fibers is sufficient to meet the standard for bending and tensile strength in heavy-duty concrete pavements. Finally, the relationship expressions between the compressive strength, flexural strength, and split tensile strength of SFRC and the steel fiber volume fraction were obtained through fitting the experimental data using Origin software.