Durability characterization of wet layup graphite/epoxy composites used in external strengthening

Carbon fabric impregnated in the field using a wet layup process is increasingly used for the rehabilitation of deterioration and understrength concrete structures. Although the wet layup process affords significant flexibility for application in the field, the use of a manual process in conjunction with the field environment can result in substantial variation in material characteristics, higher void content, non-uniform wetout and compaction between layers and a higher propensity for moisture related deterioration. In order to assess the durability of such systems an investigation is undertaken considering a number of exposures including immersion in deionized water, salt and alkali solutions, freeze-thaw, and accelerated aqueous exposure, with composite response being determined over a 100 week period through moisture uptake measurements, mechanical characterization, and dynamic mechanical thermal analysis. It is shown that while strength characteristics can degrade significantly due to deterioration at the matrix and interface levels, modulus is relatively less affected. Changes in mechanical characteristics are correlated with level of moisture uptake and a relationship between uptake and glass transition temperature is demonstrated. The data provides the basis for a fundamental understanding of uptake related correlations and deteriorative mechanisms that could be used for purposes of future reliability and service-life estimation.