Effects of hygrothermal conditioning on epoxy adhesives used in FRP composites

• Six epoxies were tested to determine curing kinetics in hygrothermal environments.
• Competing effects of added cure and plasticization were observed in all epoxies.
• Significant decrease in Tg from theoretical values was observed in all clear epoxies.
• Average Tg of tested epoxies was below the design temperature for some U.S. bridge locations.

Durability of FRP composites and their bond to concrete is essential to structural integrity of an FRP repair. Epoxy adhesives are used to form FRP composites, and as a bonding medium between the FRP and concrete substrate. Susceptibility of epoxy to the negative effects of water and high temperature affects the longevity of FRP repairs in hygrothermal environmental conditions. The presented work investigates the effects of such environments on the curing kinetics of epoxy. Competing effects of plasticization and post-cure during accelerated conditioning are discussed; recommendations targeting researchers, practitioners, and manufacturers are made based on the research findings.