Research on the mix proportion design and mechanical properties of C60 hybrid fiber-reinforced high-strength concrete

Abstract

Based on the actual engineering requirements of a specific metro project, this paper develops a mix proportion design for C60 hybrid fiber-reinforced high-strength concrete. Through compressive strength tests, splitting tensile strength tests, and scanning electron microscopy analysis, the study explores the effects of fiber parameters on the mechanical properties of the concrete and analyzes the underlying mechanisms. Results of the experimental study indicate that the mechanical properties of the C60 hybrid fiber-reinforced high-strength concrete are optimal when the steel fiber dosage is 40 kg/m³, the polypropylene fiber dosage is 1 kg/m³, and the length of the polypropylene fibers is 18 mm. Both types of fibers will reduce the compressive strength of the concrete but enhance its splitting tensile strength. Specifically, the compressive strength of the concrete de-creases gradually with the increase of steel fiber dosage. In contrast, the effect of polypropylene fiber dosage on compressive strength shows an initial increase followed by a decrease. The increase in the dosage of both fibers and the length of the polypropylene fibers enhances the splitting tensile strength of the concrete. Polypropylene fibers make the concrete more “flexible,” and steel fibers do not effectively restrain the lateral deformation of the concrete, leading to a reduction in compressive strength. However, combining both fibers with other admixtures forms a framework that transfers tensile stress, and delays crack propagation and concentration, thereby enhancing the ultimate tensile stress of the composite matrix.