Water, saltwater, and concrete leachate solution effects on durability of ambient‐temperature cure carbon‐epoxy composites

Abstract

AbstractWet layup carbon epoxy composites are extensively used for rehabilitation of civil infrastructure. This study focuses on foundation building for understanding durability of such materials through long‐term (up to 5 years) hygrothermal aging in water, saltwater, and concrete leachate, solutions. Moisture uptake is described using a two‐stage model incorporating diffusion and relaxation/deterioration parameters with the concrete leachate solution showing further transitions and the highest value of the relaxation/deteriorative coefficient. Glass transition temperatures decreased with an increase in moisture content reaching an initial minimum followed by fluctuations and small increases with an increase in the time of exposure. Immersion in concrete leachate results in the largest decrease. Tan δ height shows an initial decrease followed by an increase and then a continued decrease indicative of an initial plasticization and post‐cure followed by deterioration at the resin and fiber–matrix levels. Although short‐term response in mechanical properties shows differences with immersion in water having the least effect, solution type had very little difference on residual mechanical characteristics at the end of the 60‐month period of immersion. The results emphasize the need for further understanding of competing effects in ambient‐cured composites and of the need for longer term testing for determination of design factors.