Assessment of Outdoor Exposure Effects on the Long-term Durability of Epoxy Resin Adhesives Used for Steel-plate Bonding

The steel-plate bonding method used to reinforce concrete slabs in bridges has a long record of adoption, and has played an important role for many years. Favorable conditions have been observed with this method in periodic inspections; however, as part of durability tests, decreases in strength of the epoxy resin adhesive (which is one of its component materials) have been observed following over time outdoor exposure under standard environmental conditions. Investigations into the causes of decreased strength of epoxy resin adhesive are useful for increasing long-term durability in future infrastructure maintenance. The estimation of environmental factors that incorporate exposure conditions and the results of conducting accelerated tests revealed that the performance of epoxy resin adhesive was influenced by humidity. Additionally, decreases in strength accompanying reaction progress of epoxy resin were also observed. These results indicate that the degradation due to water absorption and the generation of internal stress due to the progress of the curing reaction of the epoxy resin are the causes of the decrease in the strength of the epoxy resin.