Bond characteristics of various NSM FRP reinforcements in concrete

The rehabilitation and strengthening technique using near-surface mounted (NSM) fiber-reinforced polymer (FRP) has proved to be a reliable alternative to the existing methods for deficient concrete structures. To effectively apply this method, bond characteristics at the interface need to be fully understood. This paper presents the results of the bond performance of a wide range of embedded FRP NSM reinforcements with various surface configurations, cross-sectional shapes, material types, adhesive types, and groove sizes. A total of 109 concrete specimens (with a dimension of 350×300×150 mm) were tested under direct pull-out loading configuration. It was found that both specimen sets using NSM bars treated with spirally wound and sand coating with indentation and groove displayed the best performance. Strip shape was more effective than round and square cross-sectional shapes. Higher bond strength was obtained by using carbon FRP than glass and adhesives with higher material bond strength. Increasing the groove sizes was fairly effective in improving the bond capacity. The existing bond strength models were also assessed in comparison with the test data in this paper.