Effect of thermal exposure on carbon fiber reinforced composites used in civil infrastructure rehabilitation

Abstract

In this work, characteristics related to the thermo-oxidative resistance of a wet layup ambient cured carbon-epoxy composite are investigated using dynamic scanning calorimetry, dynamic mechanical thermal analysis, and thermo-gravimetric analysis. Specimens of the unidirectional composite are exposed to temperatures between 121℃ and 232℃ for periods of time between 1 and 72 h. Initial exposure results in post-cure and enhancement of thermal characteristics whereas higher temperatures and longer periods of exposure at the higher temperatures result in deterioration. Degradation is determined through DMTA based on decreases in both peak loss modulus height and activation energy, Ea, and through TGA based on decreases in apparent decomposition activation energy, Ed, using the Coats-Redfern method. In both cases, there appears to be no deterioration within the 72 h period at the two lower temperatures of exposure, and minimal deterioration at the next two levels, whereas initiation of deterioration can be noted as early as between 8 and 16 h of exposure at the highest temperature of exposure, 232 ℃. The reaction order determined using the Kissinger method is seen to remain fairly constant except at the highest temperature level wherein drops are noted after 24 h of exposure. This provides thermal data at the materials level to guide field use within the time–temperature combinations suggesting that residual integrity can be reasonably assumed at all except the highest temperature level.