Bond performance of CFRP plated concrete members at elevated temperatures

One of the major requirements in the design of buildings is the provision of suitable fire endurance for structural members. Most structural materials show some degradation in mechanical properties at elevated temperatures. This is also true for CFRP. Few experimental and theoretical works exist on the bond strength of CFRP-concrete joints under high temperatures. Therefore, research into the behaviour of CFRP-epoxy composite members under high temperature is essential if the CFRP is to be recognised in the building industry. In strengthening reinforced concrete structures, CFRP plates or sheets are externally bonded to the concrete surface using epoxy adhesive. Force transfer of the CFRP retrofitted members takes place through the bond. Therefore, the bond between CFRP and concrete is critical for force transfer to be effective. At elevated temperatures, normally beyond the glass transition temperatures of epoxy adhesive, mechanical properties of the polymer matrix deteriorate rapidly. Carbon fibers have high heat resistance. But data available in the literature shows that the epoxy polymer used in bonding applications is more sensitive to temperature. The epoxy matrix will soften at temperatures close to its glass transition temperatures, which is usually in the range of 65 degrees C- degrees150 C (ACI, 2001). Therefore, the load carrying capacity of the composite system at high temperature is determined by the glass transition temperature of the adhesive. Researchers have used shear testing to investigate bond characteristics between FRP laminate and concrete. The testing of bond between CFRP and concrete which form the basis of this paper, were carried out using the single shear test method. Emphasis is placed on the investigation of the relationship between bond length and bond failure temperature. A numerical model for evaluating the temperature distribution of CFRP-concrete composites, based on a purely thermal analysis, was developed and validated against test data. This paper presents the experimental and numerical results of this research