Durability of bond between NSM CFRP strips and concrete under real-time field and laboratory accelerated conditioning

This investigation addresses the durability of the adhesive bond between near-surface-mounted (NSM) carbon fiber-reinforced polymer (CFRP) strips and concrete, under real-time field conditioning and laboratory-accelerated conditioning. Four natural outdoor environments were considered in the experimental program to induce aging mainly by carbonation, freeze-thaw cycles, elevated temperatures, and airborne chlorides from seawater. Additionally, a control environment (20°C and 55% RH) and a water immersion environment under controlled temperature (20°C) were considered. The durability was studied mainly throughout the mechanical properties obtained from (1) the involved materials (concrete, epoxy adhesive, and CFRP strips); and (2) the bond specimens, with a period of exposure up to 2 years. The bond performance of NSM-CFRP strips to concrete was slightly affected by environments under investigation, being water immersion and freeze–thaw cycles the most deleterious ones. A maximum average bond strength decrease of approximately 12% was registered for the specimens immersed in water, while in the case of the outdoor environments, the maximum bond degradation (approximately 8%) occurred for the specimens of freeze–thaw cycles after 2-year exposure.This work was carried out in the scope of the project FRPLongDur POCI-01-0145-FEDER-016900 (FCT PTDC/ECM-EST/1282/2014) and DURABLE-FRP (PTDC/ECI-EGC/4609/2020) funded by national funds through the Foundation for Science and Technology (FCT) and co-financed by the European Fund of the Regional Development (FEDER) through the Operational Program for Competitiveness and Internationalization (POCI) and the Lisbon Regional Operational Program and, partially financed by the project POCI-01-0145-FEDER-007633 and by FCT/MCTES through national funds (PIDDAC) under the R&D Unit Institute for Sustainability and Innovation in Structural Engineering (ISISE), under reference UIDB/04029/2020. The first author wishes also to acknowledge the grant SFRH/BD/131259/2017 provided by Fundação para a Ciência e a Tecnologia (FCT)