Bond properties of GFRP rebars in UHPC under different types of test

Bond properties of Glass Fiber-Reinforced Composite (GFRP) rebars in Ultra-High-Performance Concrete (UHPC) are the key to designing the FRP-reinforced UHPC structures. In this paper, bond properties between sandcoated/deformed GFRP rebars and UHPC within various embedment lengths and covers were estimated using three types of tests, namely the pullout test, modified pullout test and beam test. It was revealed that the dominant failure mode was the pulling-out of GFRP bars, evidenced by interlaminar shearing devastation, showing the shearing of the ribs and a significant reduction of the rebar diameter. Two classes of bond stress-slip relationships were summarized depending on the embedment length. The micro-slip, slip, decline and oscillation parts were captured, with the oscillation characteristic being more related to the ribs of GFRP rebars. Bond strengths of GFRP rebars under the beam test increased by 4.2 %- 10.0 % to the pullout test, and those obtained from the modified pullout test and pullout test remained little difference within 3.3 %. Both increasing the embedment length and lowering the cover could cause a linear decrease in the bond strength. Specifically, regarding beam tests, the bond strength demonstrated reductions of 11.4 % and 29.5 %, respectively, when the embedment length increased from 2.5d to 5d and 5d to 10d. Moreover, the bond strengths under three types of tests were compared with the ones predicted by existing methods, and the design recommendation was presented.