Durability of bond between concrete beams and FRP composites made of flax and glass fibers

- Plain concrete beam specimens with bonded flax and glass FRPs were tested.
- Specimens were designed to fail at the interface of FRP and concrete under bending.
- Effect heat, moisture, and freeze/thaw conditions were investigated.
- Mode of failure, peak load, and ductility of specimens were studied.
- FRP tensile force, strain, and bond strength of specimens were computed.

In this paper, the durability of flax and glass fiber-reinforced polymer (FRP) composites externally bonded to concrete beams is studied. A total of 100 plain concrete beam specimens (75 mm × 100 mm × 400 mm) were prepared and bonded with flax and glass FRP strips to the tension side of the beams. The specimens were designed to have an adhesive debonding failure of the FRP from the concrete. The specimens were aged in water and dry heat conditions at 20 and 60 °C for 21, 42, and 63 days and then were tested under three-point bending. A set of specimens were also aged by freeze/thaw cycles. The load-deflection behaviors of the specimens were evaluated and the effects of heat, moisture, and freeze/thaw cycles on the peak load and ductility of the specimens were quantified. The study shows that the peak load retentions of the specimens with bonded flax and glass FRPs immersed in 60 °C water for 63 days is 72% and 80% of their counterparts kept in dry heat condition, respectively. An analysis of variance was also performed to assess the significance of the aging effects on the physical and mechanical properties of the specimens. Also, a cross-sectional analytical modeling was performed to compute the FRP tensile force, strain, and bond strength of the specimens.