Dynamic fracture toughness of ultra-high-performance fiber-reinforced concrete under impact tensile loading

Abstract

The fracture toughness and fracture energy of ultra-high-performance fiber-reinforced concrete (UHPFRC) at both static and impact rates (43-92 s(-1)) were investigated using double-edge-notched tensile specimens. Two types of steel fiber, smooth and twisted fiber, were used in producing UHPFRC with different volume ratios of 0.5%, 1.0%, 1.5%, and 2%. The results indicated that UHPFRCs produced very high fracture resistance at impact rates, with first stress intensity factor (K-IC) up to 3.995 MPa root m, critical stress intensity factor (KIC*) up to 7.778 MPa root m, and fracture energy (G(F)) up to 86.867 KJ/m(2), which were 2.5, 5.0, and 16.9 times higher than those of ultra-high-performance concrete, respectively. The KIC* was clearly sensitive to the applied loading rate, whereas the K-IC and G(F) were not. Smooth fiber specimens exhibited not only higher KIC* and G(F) at impact rates but also higher dynamic increase factor than twisted fiber specimens. A minimum fiber volume content of 1% should be used in UHPFRC to provide a significant enhancement in crack resistance. The maximum value of UHPFRC crack velocity at impact rates was found to be 527 m/s by using a dynamic fracture mechanic model.