Axial impact behaviors of UHPC: The roles of nanomaterials and steel fibres

Abstract

With the gradual maturity of nanotechnology, many nanomaterials have been used to modify ultra-high performance concrete (UHPC) to improve its performance. In the course of use, concrete structures will suffer from various forms of dynamic impact loads, resulting in serious damage. At present, the research on the dynamic properties of nanomaterials modified UHPC is still lacking. This study presents an experimental study on the axial impact behaviors of nanomaterials modified UHPC by Split Hopkinson Pressure Bar (SHPB). The effects of nanomaterials and steel fibres on failure patterns, dynamic compressive strengths, impact toughness, dynamic compression constitutive relationship and dynamic increase factor (DIF) of UHPC under different strain rates were analyzed and discussed. The results show that UHPC is strain rate sensitive. Steel fibre improves the dynamic compressive strength and impact toughness of UHPC, and reduces the strain rate sensitivity of UHPC. The effect of hook-end steel fibre on the impact performance of UHPC is generally better than that of straight steel fibre. Proper addition of nanomaterials can improve the axial compression impact properties of UHPC, but excessive nanomaterials will adversely affect the impact performance of UHPC. Under strain rate of 160 s−1, the dynamic compressive strength and impact toughness of UHPC were improved by 10.05 % and 5.70 % respectively by adding 2 % nano-CaCO3. Based on the experimental results, a recalibrated DIF model considering the coupling effect of nanomaterials and steel fibres is proposed for the UHPC, and it predicted the test results of the modified UHPC reasonably well.