Effect of electromagnetically aligned steel fibers on tensile properties of hybrid steel-macro basalt fiber UHPC

Ultra High Performance Concrete (UHPC) is a new concrete material with excellent performance. Many practices have shown that UHPC tends to have excessive compressive properties but insufficient tensile properties. The electromagnetic alignment technology of steel fibers enhances the efficiency of steel fiber utilization. It greatly enhances the flexural strength, but the ductility of the flexural specimens is poor. Furthermore, it is required to use environmentally friendly fibers to partially replace steel fibers, as the incorporation of steel fibers adds to carbon emissions. This research explores the tensile behaviors of hybrid steel-macro basalt fiber UHPC to search for low-carbon construction materials with great mechanical behaviors. The effects of two key parameters, the alignment of steel fibers and the mixing ratio of steel-macro basalt fibers, on the tensile properties were systematically analyzed. Aligned steel fiber was classified as parallel to the tensile direction, vertical to the tensile direction, and undirected. In the steel-macro basalt fiber blend, the total volume doping of 1.5 % was kept unchanged, and a total of four groups of blend schemes were established. Uniaxial tensile tests were performed, and the elastic modulus, tensile strength, and tensile ductility coefficient of the specimens were calculated to produce the stress-strain relationship curves. The results reveal that the parallel orientation of steel fibers could significantly enhance the tensile strength, and the ductility of the material is increased considerably by blending macro basalt fibers. Carbon emissions can be effectively reduced while maintaining superior tensile properties through an optimized combination of steel fiber orientation and steel-macro basalt fiber blend ratio. Finally, the tensile strength prediction equations for this material are proposed by considering the impact of the two fibers on the tensile properties separately.