Effect of the orientation of steel fiber on the strength of ultra-high-performance concrete (UHPC)

Copper-plated microwire steel fiber is generally added to ultra-high-performance concrete (UHPC) to reduce its brittleness. In the UHPC, the steel fibers are randomly dispersed. When subjected to a specific load, the steel fibers that have an orientation consistent with or close to the direction of tensile stress can take full effect of reinforcement on the matrix, while the reinforcing effect of those steel fibers perpendicular to the tensile is relatively weak. From this point of view, the influence of steel fiber orientation on the strength of UHPC was modeled and analyzed in this investigation. During modeling, the tensile, flexural, and compressive strength of the UHPC were correlated with the orientation efficiency factor of steel fiber. In the tests, aligned steel fiber reinforced ultra-high-performance concrete (ASF-UHPC) specimens were prepared by using electromagnetic field treatment to align the steel fibers in the specimens, and the tensile, flexural, and compressive properties of ASF-UHPC specimens were tested and compared with the modeling results. The reinforcement mechanism of aligned steel fiber on the properties of UHPC was analyzed. The results showed that the mechanical properties of ASF-UHPC specimens are significantly higher than those of UHPC with randomly distributed steel fibers (RSF-UHPC) specimens, and the model can well predict the mechanical properties of UHPC.