Loading rate effect on crack velocity in ultra-high-performance fiber-reinforced concrete.

Highlights • The crack initiation and velocity at high speed were successfully tested by using the modified I-SEFIM. • The crack velocity increased as the applied strain rate increased. • The fiber reinforcement significantly affected on the crack velocity in the UHPFRCs at static rates, but it slightly did at high strain rates. • The strain-rate sensitivity of UHPFRC is strongly correlated with the dynamic crack growth mechanism. Abstract Loading rate effect on crack propagation in ultra-high-performance fiber-reinforced concrete (UHPFRCs) was investigated using a pre-notched three-point bending specimen in an improved-strain energy frame impact machine (I-SEFIM) and image processing techniques. The crack velocity of up to 984 m/s and the crack initiation strain rate of up to 271 s−1 were observed. Crack velocity in UHPFRCs increased as the applied strain rate increased. Fiber reinforcements significantly affected on the crack velocity in the UHPFRC at static rates, but slightly did at high strain rates. There is a strong correlation between the strain-rate sensitivity and the dynamic crack growth characteristics of UHPFRCs. [ABSTRACT FROM AUTHOR]