Durability under freeze-thaw cycles of concrete beams retrofitted with externally bonded FRPs using bio-based resins

This study examined the effects of freeze-thaw (FT) cycles on the flexural performance of reinforced concrete beams strengthened with externally bonded fibre-reinforced polymer (FRP) laminates fabricated using bio resins. Six large-scale beams including three retrofitted with bio resin-FRP, two with epoxy-FRP, and one control beam, were tested. A fully bio furfuryl alcohol (FA) resin derived from corn cobs and sugar cane, and a partially bio epoxidized pine oil (EP) resin, were investigated. Additionally, 40 FRP tension coupons fabricated with the bio resins and the epoxy resin were tested to assess the effect of FT cycles on their tensile properties. Specimens were exposed to 300 FT cycles over a period of seven months at a temperature range of +6 to −27 °C. The study showed that this aggressive FT regime did not have a negative effect on the ultimate capacities of the beams or the coupons. In fact, all the conditioned beams had peak loads between 7 and 17% higher than their unconditioned counterparts, which may be attributed to the additional curing of concrete during the thawing phase of the FT cycles by submersion in water. The FT conditioned beams with the FA and the EP resin FRPs had 22 and 25% higher yield loads and 25 and 31% higher ultimate loads, respectively, compared to the FT conditioned unstrengthened beam.