Effects of Ageing on the Bond Properties of Carbon Fiber Reinforced Polymer/Concrete Adhesive Joints: Investigation Using a Modified Double Shear Test

Abstract

Abstract Although externally bonded carbon fiber reinforced polymer (FRP) composites are now commonly used for the strengthening and repair of reinforced concrete structures, the durability of the adhesive bond at the concrete/composite interface is still a matter of investigation and remains a critical issue to be addressed in order to assess the long-term performance of FRP strengthening methods. The proposed paper aimed at presenting the results of an investigation on the time evolution of the adhesive bond strength of concrete/composite assemblies exposed to accelerated ageing. Such an evolution was studied by performing double lap shear tests at several intermediate periods of ageing up to 1 year, while changes in the mechanical properties of the weakest constitutive materials, namely polymer adhesive and concrete, were investigated by means of tensile and compressive tests, respectively. Considering that an increase in the transfer length of aged samples can counterbalance the ageing-induced degradation of the mechanical properties of the bulk adhesive and can finally lead to an unchanged shear capacity of the joint, a new geometry of double-shear test specimens was proposed. This geometry involved a smaller bonded length and consequently restricted the possible increase in transfer length during ageing. Moreover, their reduced size allows the storage of a large number of samples in standard climatic chambers. A specific anchorage device was designed, so that double lap shear tests could be carried out using a conventional universal testing machine. The obtained results showed that the shear tests based on this original setup are able to reveal the evolutions of both the bond strength and the failure mode of concrete/composite assemblies subjected to various accelerated ageing conditions. These ageing conditions were found to have only slight detrimental effects on the mechanical characteristics of samples, and finally a partial recovery was observed.