Bond evaluation of GFRP reinforcing bars embedded in concrete under aggressive environments

Technologies developed over the last three decades have facilitated the use of glass fiber reinforced polymer (GFRP) composites as internal reinforcement bars (rebars) for concrete structures, which have proven to be an alternative to traditional steel reinforcement due to significant advantages, such as magnetic transparency and, most importantly, corrosion resistance. GFRP rebar manufacturers have developed different GFRP rebar types, where the surface enhancement to create the bond with concrete varies. However, a knowledge gap exists related to adequate durability of the surface enhancement in composite rebars, needed to achieve a proper bond to concrete. Thus, the durability of the bond enhancement of GFRP rebars to concrete must be addressed. This study evaluates the mechanical and bond to concrete properties of GFRP rebars subjected to accelerated conditioning. To this end, specimens were expose to circulating seawater chambers, at different temperatures (23°C, 40°C and 60°C) for different periods of time (60 and 120 days). The selected GFRP rebars were made from the same glass fibers, but different manufacturing methods and more importantly bond enhancements: i) sand-coated with helical wrap, ii) ribbed/external deformations and iii) external cross fibers. Bond tests after exposure were performed according to ASTM D7913. Preliminary results show that the different surface enhancements for the same nominal size GFRP rebars, result in different bond to concrete strength slip relationships. However, the durability for the different types of surface enhancements for the selected GFRP rebars did not exhibit a significant change in bond to concrete strength over the exposed period of time.