Effect of Accelerated Curing Conditions on Shear Strength and Glass Transition Temperature of Epoxy Adhesives

This paper presents research on variable curing temperature of commercially available epoxy adhesives used for structural strengthening with externally bonded and near surface mounted fiber reinforced polymer laminates, strips and bars. An innovative technique for anchorage of prestressed FRP laminates called “gradient anchorage” based on accelerated curing of the epoxy adhesive was invented at EMPA in order to avoid the mechanical fastening systems. The main importance of the “gradient anchorage” is selection of the most appropriate conditions for curing of the epoxy resin in terms of different curing and cooling times and temperatures. In order to specify the best curing conditions the research on two commercially available adhesives was performed. The test program consisted of eight series of adhesive specimens prepared in accordance with the producer and stoichiometric composition defined in the simultaneous chemical research. Both compositions were differed in a temperature and a crosslinking time. The following temperature and time of the epoxy adhesive curing were investigated in the shear test joints: 80 °C for 25 minutes (4 series), 80 °C for 35 minutes (4 series). The shear strength of the epoxy joints was tested after 10, 20 and 30 minutes of the adhesive curing in a high temperature. Analysis of variable curing and cooling time enabled to define the best curing conditions to obtain the highest shear strength of the adhesive joints. Simultaneously with the mechanical test, the glass transition temperature of the epoxy adhesive was determined by the Differential Scanning Calorimetry method.