Bond Behaviour of NSM Strengthening Systems on Concrete Elements Under Sustained Load and High Ambient Temperature

The study of the bond behaviour of FRP strengthening systems under service conditions has become increasingly important during the last years. Previous works have shown that sustained loading jointly with changes in environmental conditions may affect the long-term deformations of the FRP-concrete joint. Therefore, information from long-term tests under high ambient temperatures can provide relevant knowledge to fully understand the bond behaviour of the strengthening systems in real applications. The main goal of this paper is to experimentally study the evolution of the bond behaviour of FRP-concrete joint with time under high service temperature, and how this progression affects the global slip of the strengthening system. For this purpose, an experimental programme of eight NSM pull-out specimens loaded with different levels of sustained load and under high ambient temperature was performed. Slip at the loaded end of the FRP was measured in order to capture its evolution with time. From the short-term experimental campaign, an effect of the groove thickness and the bonded length on the maximum load and the failure mode were observed. Moreover, from sustained loading pull-out tests, a significant increase in the slip was observed during time. High effect of the bonded length and groove thickness on the slip at the loaded end was observed when specimens were subjected to high service sustained loading.