Bond durability between anchored GFRP bar and seawater concrete under offshore environmental conditions

The lower bond strength of FRP bars to concrete compared to steel bars has remained an unsolved barrier to the widespread use of FRP-reinforced concrete under extreme loading. Additionally, the degradation of the bond between FRP reinforcement and concretes in aggressive environments adds to the existing concern. In this study, an innovative anchorage system comprised of polypropylene pipe was used to strengthen the bond between seawater concrete and GFRP bars after 250 days of exposure to offshore environmental conditions. As material factors, two types of GFRP bars (sand-coated and ribbed) and two types of concrete (normal and seawater concrete) were evaluated. Four distinct environmental conditions were used to assess the samples: (i) ambient environment (control), (ii) tap water, (iii) seawater, and (iv) wet-dry cycles in seawater. According to the findings of the direct pull-out tests, the suggested anchor system strengthens the bond and shifts the failure mode from bond failure to bar rupture. Additionally, after exposure to 250 days of seawater wet-dry cycles, GFRP-reinforced seawater concrete lost 5% of its maximum bond strength (developed bar tensile stress). All other samples exposed to different environmental conditions either increased or decreased in bond strength by less than 5% after 250 days, compared to the control samples.