Preliminary Investigation of Ultra-High Performance Concrete Behavior at High Strain Rates using the Split-Hopkinson Pressure Bar

Ultra-high performance concrete (UHPC) displays several enhanced material properties compared to normal strength concrete (NSC). In past research, Split-Hopkinson pressure bar (SHPB) tests have been used for normal strength concrete to determine material behavior at high strain rates. The behavior of advanced concrete materials, such as UHPC, under high strain rates has not been thoroughly investigated. While it is generally accepted that concrete materials experience increases in compressive strength under increasing strain rates, a preliminary investigation was conducted to gain insight into the compressive behavior of UHPC under high strain rate SHPB testing. In this research, 50 specimens were tested in compression using the SHPB equipment at Michigan Technological University. Normal strength concrete, ambient cured UHPC, and thermally treated UHPC specimens were tested at 2:1, 1:1, and 0.5:1 aspect ratios. A dynamic increase factor (DIF), which shows the increase in strength between dynamic and static loading, was calculated for each specimen. Based on results of specimens meeting recommended tolerances, DIFs were found to be between 3.65 and 4 for NSC, 1.73 and 2.95 for ambient cured UHPC, and 1.21 and 2.45 for thermally treated UHPC for strain rates between 102 and 103 s-1. While UHPC experiences a relative increase in dynamic compressive strength, it is less strain rate sensitive than NSC and experiences a lower overall compressive strength increase