Bond behavior of helically wrapped sand coated deformed Glass Fiber-Reinforced Polymer (GFRP) bars in concrete

Using Fiber-Reinforced Polymer (FRP) bars in reinforcing concrete structures requires understanding the bond behavior between the two materials to ensure adequate force transfer and crack control. Currently, there are no standards for characterizing the surface condition of FRP bars, which results in significant variability on the bond behavior of FRP bars. Thus, this paper presents the experimental investigation conducted to evaluate the bond behavior of helically wrapped sand coated deformed glass fiber-reinforced polymer (GFRP) reinforcing bars. The bond-slip relationship of 96 pullout test specimens were analyzed to determine the effects of bar size and production variability. Test results demonstrated that force transfer between GFRP bars and concrete is achieved by chemical adhesion, mechanical interlock (bearing), and friction. All tested bar sizes demonstrated the same bond-slip relationship; however, small bars developed higher bond strength than large bars. Also, test results indicated that production variability could result in significant differences in the bond behavior of GFRP bars in concrete. Test data were used to calibrate and compare the existing bond-slip models of FPR bars and a new model for the bond-slip relationship of the helically wrapped sand coated deformed GFPR bars was proposed.