Durability of the bond between CFRP plates and concrete exposed to harsh environment

Abstract

Strengthening and retrofitting structural members using carbon fiber reinforced polymer (CFRP) materials has gained wide acceptance in the civil engineering community because of their superior mechanical properties, light weight, corrosion resistance, and ease of use. Numerous structural reinforced concrete (RC) members have been strengthened with externally-bonded CFRP plates using epoxy adhesives that produce an increase in their load-carrying capacities. However, there are some uncertainties regarding the durability of the bond between the concrete and FRP interfaces when subjected to severe environmental exposure. Most strengthening applications are exposed to outdoor conditions and hence durability under aggressive environments must be considered. This is the subject of this investigation. Several CFRP-concrete prisms have been subjected to several sets of environmental exposure conditions and preloaded with 3 and 5 kN of sustained loading, amounting to approximately 15 and 25% of ultimate load, respectively. Site exposure conditions were an actual marine environment and a seawater splash zone, including direct exposure to sunlight with the associated Ultra Violet (UV). Both exposures were conducted in a well-controlled atmosphere that lasted for more than 150 days (3,600 h). The experimental program consisted of 27 specimens divided among the two exposures and some laboratory control specimens as benchmarks. The specimens were subjected to sustained loading during the whole course of the exposure. The change in ultimate bond characteristics between the externally-applied CFRP and the concrete because load and exposure conditions were used as measures of durability and performance effects. Single-lap shear tests were conducted on all specimens after exposure to failure of the specimens. It was observed that the specimens exposed to the sun and saline environments experienced an increase in both the bond strength and attained peak loads because exposure of the adhesive to elevated temperature increased the bond because of greater polymer crosslinking, thus creating complex interactions in the polymer matrix. The data obtained from this experimental investigation will add to the sound scientific data demanded by the ACI 440.2R-08 design guidelines.