The Effects of Bio Content and Type of Resin on FRP Wet Layup Tensile and Bond Strength to Concrete and Durability Under Freeze-Thaw Cycles

Abstract

This study focused on replacing conventional unsustainable resins currently used in the fabrication of externally bonded Fibre Reinforced Polymers (FRP) with bio-based resins. The first two phases of this study explored three partially bio-based resin blends, namely; one with 41% of its content derived from vegetable and wood industry by-products (VW), a cashew nut shell liquid (CN) resin blend and an epoxidized linseed oil (ELO) resin blend. The mix ratios with epoxy were varied to obtain 20 to 40% bio content for the CN resin, and 10 to 40% bio content for the ELO resin. Both glass (G) and carbon (C) fibres were investigated.

Ninety tension coupons and sixty lap splice specimens were tested as part of the first phase of this study. The VW specimens had mean tensile strength (fu) within 9% of the epoxy (E) FRP specimens. The CN30%-CFRP specimens had a similar fu compared to the E-CFRP specimens, while the CN40%-GFRP specimens had a fu, 15% lower than the E-GFRP specimens. ELO20%-CFRP specimens had a fu similar to the E-CFRP specimens and the ELO30-G specimens had a fu, 13% higher than the E-GFRP specimens.

In the second phase, small concrete beam bond test specimens were tested to compare FRP bond strengths. It was found that the VW resin, with the highest bio content of 41%, had similar bond strength compared to epoxy. The ELO resin with 20% bio content showed the highest bond strength, at 30% higher than epoxy. The CN resin, at 20 to 30% bio content, resulted in comparable bond strengths compared to epoxy.

This final phase examined the effects of freeze-thaw (FT) cycling on both FRP coupons and large-scale reinforced concrete beams with externally bonded FRPs fabricated with three different resins – a furfuryl alcohol fully bio resin, an epoxidized pine oil partial bio resin and the E resin. The FT conditioning was found to have minimal effects on the tensile strength and modulus of the FRP coupons. For the beams, the ultimate strengths after FT conditioning increased by 7 to 17%, likely due to the additional concrete curing during thawing in water.