In-situ evaluation on existing RC beam strengthened with GFRP-reinforced UHPC overlay

Ultra-high performance concrete (UHPC) is usually embedded with reinforcing bars to avoid localized cracking, when adopted to strengthen existing reinforced concrete (RC) structures. In this case, indoor test is the most common way to evaluate the strengthening efficiency of UHPC overlay, which is inadequate to describe the real mechanical and degeneration states of existing structures. In this study, seven existing RC beams were first detached from a 15-year-old bridge. Then, three of them were strengthened with GFRP-reinforced UHPC overlay (named GFRP-strengthened beams), other three of them were strengthened with steel-reinforced UHPC overlay (named steel-strengthened beams), and the rest one was used as control beam. The effects of rebar type and reinforcement ratio were studied by in-situ four-point bending tests. Results indicated that the failure modes of steel-strengthened beams were predictable ductile failure, whereas sudden brittle failure was observed in GFRP-strengthened beams. The rebar type within the UHPC layer has little effect on the cracking loads of strengthened beams. When compared to steel-strengthened beams, GFRP-strengthened beams exhibited faster stiffness degradation and crack width development, with fewer crack number and wider crack spacing. Regardless of rebar type, the flexural capacity, stiffness and cracking resistance of existing RC beams were increased with the increase of reinforcement ratio.