Bond durability of concrete-cfrp ebr and nsm systems under natural ageing

Abstract

The use of Carbon Fibre Reinforced Polymer (CFRP) as reinforcement material for strengthening of existing reinforced concrete (RC) structures has been increasing. These materials can be applied mainly by using two strengthening techniques: (i) the Externally Bonded Reinforcement (EBR) by the application of the CFRP on the concrete surface; and, (ii) the Near Surface Mounted (NSM) by the insertion of the CFRP into the grooves on the concrete cover of the RC element to be strengthened. The durability of structures strengthened with CFRP materials is still an open issue. Accelerated ageing protocols under laboratory conditions have been used for the assessment of the durability; however, very few studies have been performed in outdoor environments (natural ageing). Moreover, the relationship between accelerated ageing and real outdoor ageing is not fully understood. The main objective of this paper is to give new insights on the bond durability between concrete and CFRP strips installed according to both EBR and NSM techniques, after a 2-year exposure to natural outdoor conditions. This study includes a reference environment (~20 C / 55% RH) for comparing proposes and four outdoor environments for ageing induced mainly promoting (i) carbonation, (ii) freeze-thaw attack, (iii) elevated temperatures, and (iv) airborne chlorides from seawater. An additional environmental condition, namely continuous immersion in water at ~20 C was also considered. The performance of the bond concrete-adhesive-CFRP was assessed throughout pull-out tests. When compared with the reference environment, small degradation on the bond performance on specimens exposed to outdoor environments has been observed for both strengthening techniques.