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

Abstract

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√m, critical stress intensity factor ( ) up to 7.778 MPa√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 was clearly sensitive to the applied loading rate, whereas the K IC and G F were not. Smooth fiber specimens exhibited not only higher 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.