Bond behavior of glass fiber reinforced polypropylene (GFRPP) bars in concrete: Effects of surface configuration and rib geometric parameters

Thermoplastic-based fiber-reinforced polymer (FRP) bars have attracted increasing interest in construction engineering because of their recyclability, high toughness, and ability to be reheated and re-bent after forming. In this study, 53 pull-out specimens of glass fiber-reinforced polypropylene (GFRPP) bars were tested to investigate their bond behavior with concrete. The test GFRPP bars had different surface conditions, including smooth, ribbed, grooved and helically wrapped surfaces, as well as different rib geometries, including narrow ribs, wide ribs, shallow ribs and deep ribs. The surface configurations were compared to identify the most effective surface treatment for improving the bond performance, among them, the grooved bars showed the best overall performance. A parametric study was conducted on GFRPP grooved bars to examine the effects of rib geometry on bond behavior. The results disclosed that the ribs and grooves formed on the GFRPP bars improved the bond strength, while the rib geometry had a pronounced effect on the bond response. The maximum bond strength measured in this study was 11.48 MPa. The most favorable rib geometric corresponded to a rib height of 8.3% of the bar diameter (d), a rib width of 0.85d and a concrete lug width of 0.51d, as determined from the bond property within the tested range. The bond-slip curves of the grooved GFRPP bars exhibited a damped oscillatory residual response with a nearly constant wavelength and decreasing amplitude. Three typical residual behaviors were identified: ascending, plateau-like, and descending peak-envelope oscillatory response, according to the evolution of successive residual peaks. Finally, a complete bond-slip constitutive model for GFRPP bars was proposed and verified by experimental bond-slip relationships.