Investigation on bond behavior of GFRP bar embedded in ultra-high performance polyoxymethylene fiber reinforced concrete

The combination of glass fiber reinforced polymer (GFRP) bars and polyoxymethylene (POM) fiber reinforced ultra-high performance concrete (UHPC) can create a structural system with excellent service performance and exceptional durability. Bond is a critical factor affecting the service performance of structures constructed using GFRP bars and POM fiber reinforced UHPC. Therefore, this paper investigates the bond behavior between GFRP bar and POM fiber reinforced UHPC by using a direct pull-out test. The test variables were reinforcement type, volume fraction of POM fiber, embedment length, diameter of reinforcement, thickness of concrete cover, and compressive strength of concrete. The effects of these test variables on the failure mode, bond stress-slip curve and bond strength of GFRP bar with POM fiber reinforced UHPC were discussed. The test results revealed that the volume fraction of POM fibers and the reinforcement diameter have barely effect on the bond strength. The bond strength initially increases with increasing concrete cover thickness, and then plateaus after the concrete cover thickness reaches 3.35 times the reinforcement diameter. Furthermore, a predictive model for bond strength of GFRP reinforced UHPC specimens was proposed and validated using test data from other literature. A general bond-slip constitutive model was established to accurately describe the bond-slip relationship of GFRP bar and UHPC.