Fracture energy of ultra-high-performance fiber-reinforced concrete at high strain rates

The fracture energy of ultra-high-performance fiber-reinforced concrete (UHPFRC) at high strain rates (5–92 s− 1) was investigated, and specimens with 1–1.5% fibers exhibited very high fracture energy (28–71 kJ/m2). Evaluation of the rate effects on the UHPFRC fracture resistance, including fracture strength (ft), specific work-of-fracture (WS), and softening fracture energy (WF), indicated that ft and WS were highly sensitive to strain rate, whereas WF was not. The effects of fiber type, volume content, specimen shape and fiber blending on the fracture resistance at high and static strain rates differed significantly: 1) smooth fibers exhibited higher ft and WS at high rates than twisted fibers; 2) higher fiber volume content did not clearly generate higher WS and WF at high rates; 3) notched specimens generally exhibited higher fracture resistance than un-notched samples at both static and high rates; and 4) UHPFRC blending two fibers produced higher WS and WF than UHPFRC with mono fiber at high rates.