Study on Dynamic Impact Mechanical Properties of UHPC with High-Content and Directional Reinforced Steel Fiber

Ultra-high-performance concrete (UHPC) is a kind of building material with ultra-high strength, toughness, and durability. However, under the conditions of ordinary molding technology, most of the fibers cannot play a bridging role in the direction of force. In this study, UHPC specimens with different steel fiber contents (0%, 2%, 4%, and 6% by volume) and directional reinforced fiber were prepared. Based on the split-Hopkinson pressure bar (SHPB), the influence of directional distributed steel fiber on the dynamic impact mechanical properties of the UHPC specimen were systematically investigated. The stress–strain curves, stress peaks, dynamic increase factor (DIF), and ductile energy absorption properties of the specimens at different strain rates were obtained. The results showed that oriented steel fiber significantly increases the dynamic property of UHPC. The dynamic impact peak strain, peak stress, and DIF of the UHPC specimen with 2% oriented steel fiber were 35.78%, 8.8%, and 12.6% higher than that prepared by normal molding technology, respectively. Moreover, with the increase of fiber content, the peak stress, energy absorption, and multiple-impact compression resistance of the specimen were greatly improved. When the fiber content was 6%, the dynamic impact peak strain, dynamic impact compressive strength ratio, and energy absorption capacity of the specimen were 3.09, 1.45, and 4.1 times the reference group, respectively.