Investigating the impact resistance of ultra-high-performance fiber-reinforced concrete using an improved strain energy impact test machine

The direct tensile stress versus strain responses of ultra-high-performance fiber-reinforced concretes (UHPFRCs) at high strain rates (10-150 s−1) were investigated using an improved strain energy frame impact machine. The high strain rates (>100 s−1) were achieved by increasing the capacity of the hydraulic jack and coupler and changing the diameter and material of the energy frame. The use of a titanium energy frame (diameter of 30 mm) increased the impact speed. As the strain rate was increased from 0.000333 to 170 s−1, the post-cracking strength of the UHPFRCs containing 2% straight steel fibers increased from 16.5 to 47.1 MPa.