Bond Behavior of GRFP Bars to Concrete in Beam Test

Bond behavior between reinforcing bars and concrete is a key problem to understand behavior of reinforced concrete members. The introduction of the new reinforcing system made of fiber reinforced polymer (FRP) to construction industry forced the study of FRP-to-concrete bond behavior as one of the main mechanical properties. The application of FRP reinforcement in concrete structures increased rapidly in last years. Their excellent corrosion resistance, high tensile strength, good non-magnetic properties were the reason why they have become an alternative to traditional steel reinforcement, especially in harsh environments on bridges, outside garages and off-shore structures. The GFRP bars are very different from steel, mainly due to much lower elasticity modulus and their anisotropic structure. Good performance of FRP reinforced concrete requires adequate interfacial bond between bars and concrete, mainly due to surface preparation. The authors’ own experimental program includes twelve beam bond tests carried out on rectangular beams consisted of two concrete blocks connected by a continuous GFRP bar in tension and by a steel hinge in compression. Two main parameters were investigated in the tests: bar diameter and thickness of a bottom concrete cover. The GFRP bars indicated good bond behavior to concrete, mainly due to the ribs on the bar surface. The results of the test indicated the decrease in the ultimate shear bond stress with the increase in the bar diameter regardless of the thickness of the concrete cover. The decrease in the concrete cover caused the decrease in the shear bond stress for all bars diameters. The increase in bar diameter caused the decrease in the ultimate bond strength.