Impact response of RC beams strengthened with ultra-rapid-hardening strain-hardening cementitious composites

Ultra-rapid-hardening strain-hardening cementitious composites (URSHCC) have the potential to significantly enhance the structural performance of reinforced concrete (RC) beams under impact loads. However, there is limited research on their effectiveness in retrofitting damaged RC beams subjected to low-velocity impact loads. This study investigates the impact resistance of large RC beams retrofitted with URSHCC. The damaged cover under the tension reinforcing bar of the RC beam was removed and replaced with URSHCC, following the application of a latex-based adhesion enhancer. To evaluate performance, static flexural and drop-weight impact tests were conducted on seven large beams, including both typical RC beams and those strengthened with URSHCC. Load cells at both supports and the impact weight, along with laser displacement sensors, were used for data acquisition. A high-speed camera captured the impact event for image analysis to correct deflection measurements affected by horizontal cracks. The tests were performed at three impact energy levels: 15, 22.5 and 30 kJ. The results showed that at 30 kJ impact energy, the URSHCC-retrofitted beams increased the reaction force by 41.2 % and decreased the mid-span deflection by 20.0 % compared to non-strengthened RC beams. Additionally, the URSHCC retrofitting reduced the crack propagation. Despite some delamination issues, the overall performance of URSHCC-retrofitted beams under impact loads was significantly improved, demonstrating the material's potential for enhancing structural resilience.