Comparative durability evaluation of ambient temperature cured externally bonded CFRP and GFRP composite systems for repair of bridges

In recent years externally bonded fiber reinforced polymer (FRP) composites have been increasingly accepted as an efficient means of rehabilitating deteriorating and under-strength concrete structures. In the case of the two primary application procedures – wet layup of fabric and adhesive bonding of prefabricated strips, the efficacy and reliability of the approach intrinsically depends on the strength and durability of bond between the FRP and the concrete substrate. This paper presents results from an extensive 24-month study, involving ten different external strengthening FRP systems, to assess the durability of the bond under environmental exposure conditions including immersion in water, immersion in salt water, ponding at different humidity levels, and exposure to freeze conditions of –18 °C. The FRP systems were characterized through determination of moisture uptake characteristics, tensile strength and modulus of the resins and adhesives, and direct tension pull-off testing of the FRP-concrete assembly. As expected from ambient temperature cure systems, both tensile characteristics and pull-off strength show degradation with time under specific environmental exposure conditions. Differences in bond durability are discussed based on system and exposure type and it is seen that exposure to the −18 °C environment results in the highest level of deterioration overall. The results indicate that the use of wet layup, with appropriately selected resins, and well fabricated composites, may at present have advantages over the use of adhesive bonded systems as related to long-term durability of the FRP-concrete bond. They also suggest that the changes in characteristics in resin/adhesive and bond due to environment exposure induced deterioration need to be considered in design to avoid premature failure.