Local bond-slip response of GFRP rebar in ultra-high-performance fiber-reinforced concrete

This study investigates the bond performance of steel and glass fiber-reinforced polymer (GFRP) rebars embedded in ultra-high-performance fiber-reinforced concrete (UHPFRC). The steel rebar showed 2.8-3.6 times higher bond strengths than the GFRP rebar and rebar yielding at embedment length of 2 times the rebar diameter. The bond failure of GFRP rebar occurred by delaminating resin and fiber in GFRP rebar, different to that of steel rebar (shearing off and crushing of concrete). For GFRP rebar, higher bond strength was obtained when a larger rebar diameter and a shorter embedment length were used, and reincrease of pull-out stress in softening branch was observed owing to wedging effect. Equations for normalized bond strength and development length of GFRP rebar embedded in UHPFRC with pull-out failure were suggested. In addition, analytical models for bond-slip response of GFRP rebar proposed in the literature were considered, and adequate parameters were derived from the present test data.