Abstract
Technologies developed over the last two decades have facilitated the use of glass fiber reinforced polymer (GFRP) bars as internal reinforcement for concrete structures, specially in coastal environments, mainly due to their corrosion resistance. To-date, most durability studies have focused on a single mechanical parameter (tensile strength) and a single aging environment (exposure to high alkalinity). However, knowledge gaps exists in understanding how other mechanical parameters and relevant conditioning environments may affect the durability of GFRP bars. To this end, this study assesses the durability of different physio-mechanical properties of GFRP rebars, post exposure to accelerated conditioning in seawater.
In this study, the durability and service life prediction of GFRP rebars directly exposed to seawater was evaluated. Six different commercially available GFRP rebar types were submerged in seawater tanks, at various temperatures (23°C, 40°C and 60°C) for different time periods (60, 120, 210 and 365 days). The durability of these GFRP rebars was assessed by property retention measurements, based on eight different physio-mechanical properties. It was inferred that rebars with high moisture absorption resulted in poor durability. Overall, the tensile strength was the most affected property. Based on the Arrhenius model, at 23°C all the rebars that met the acceptance criteria by ASTM D7957, are expected to retain 85% of the tensile strength capacity.
In addition, a further evaluation of the bond-to-concrete mechanism was conducted. To ensure a proper bond between the reinforcement and the concrete, it is crucial to allow stresses to be transferred. To-date, however, a lack of knowledge exists about the bond behavior of GFRP rebars when subjected to flexure (one of the most common cases in civil structures). This is a critical aspect, for example, to effectively define the minimum embedment length.
In total, 32 beams were tested under 3-point-bending, to check the minimum embedment length, the bond behavior under flexure and the bond coefficient (kb). It was seen that even if the maximum bond strength developed by steel rebars was higher than the one achieved by GFRP, the bond coefficient between the sand coated GFRP rebars and steel was comparable, while it was approximately 26% higher for the helically grooved ones. The theoretically computed minimum embedment lengths based on the currently existing design guidelines, seemed to be very conservative.