Temporary bond strength of partly cured epoxy adhesive for anchoring prestressed CFRP strips on concrete

Externally bonded Carbon Fiber Reinforced Polymer (CFRP) strips have been used for strengthening reinforced concrete structures. This paper presents an experimental study on the debonding of externally bonded CFRP strips anchored to a concrete substrate by a commercial epoxy adhesive. The study represents the basis for the characterization of an innovative ‘gradient method’, giving the possibility to anchor prestressed CFRP strips to concrete without the use any mechanical anchorage systems such as plates and bolts. Bond between the two components is achieved by an epoxy adhesive able to carry loads after an accelerated curing process under elevated temperatures. The effect of heating configuration/duration, strip thickness and bond length on the temporary bond resistance have been investigated using prestressed and non-prestressed CFRP-strips. Besides the optimization of the heating elements necessary for the curing process, curing parameters for an optimal temporary bond strength could be determined. Twenty-five minutes of heating and curing at 90 °C was found to be an optimum heating configuration, resulting in better short-term mechanical performances than after conventional curing at room temperature for several days. The main reason is a temporarily softer adhesive which allows the use of the full bond length by reducing shear force peaks.