Durability of Concrete Beams with Bonded FRP Composites made of Flax and Glass Fibers

Abstract

Synthetic fibers, such as glass fibers, in the form of fiber-reinforced polymer (FRP) composites have been extensively used for the repair and strengthening of existing concrete structures in the past three decades. As glass fibers come from a non-renewable resource, this research was conducted on flax fibers as a natural plant-based material and a potential replacement to glass fibers. The element of durability is a major concern with natural materials such as flax fibers. In this study, durability tests were conducted in order to investigate the long-term behavior of both glass and flax FRPs externally bonded to concrete beams. A total of 100 plain small-scale concrete beams (75×100×400mm) were prepared and bonded with flax and glass FRPs made of vinyl-ester resin. The test specimens were immersed into water solution and tested after 21, 42, and 63 days. There were also specimens kept in dry conditions and were used as control specimens. The temperature of the solutions were controlled at 20 and 60 °C. Five identical specimens were prepared and tested for each condition. The durability of the bond between the FRP and the concrete were studied under three-point bending. The weight of the specimens and the pH and temperature of the solutions were also observed. In general, the test results showed that the bond strength of the control specimens bonded with flax FRP was 20% weaker than their counterparts with glass FRP in air dry condition. After 63 days in water at 60 °C, the residual bond strength of the specimens bonded with flax FRP was 84% and with glass FRP was 90%; which were compatible with the overall moisture absorption of 2.79% and 2.35%, respectively.