Parametric investigation of flexural performance of concrete prisms retrofitted with near-surface mounted FRP bars

This study investigates the impact of flexural retrofitting on the load-bearing capacity, ductility and failure modes of concrete prisms using the NSM-FRP technique, considering four design parameters. Some specimens were retrofitted with NE only, while others incorporated FRP (i.e. CFRP, GFRP or BFRP) reinforcement bars alongside NE to assess the influence of presence of FRP reinforcement on the specimens' performance. The study also examines changing the position of GFRP reinforcement bars (cantered or along the groove's edge), using different numbers of CFRP bars (one, two or three) and considering three groove dimensions (8 x 8 mm2, 10 x 10 mm2 and 12 x 12 mm2). Results showed that NE-only retrofitting increased the capacity by about 38 % compared to the non-retrofitted specimens, with negligible impact on ductility. Introducing FRP reinforcement led to an approximately twofold increase in capacity and ductility compared to NE-only retrofitting. Placing GFRP reinforcement bars along the edge of the groove minimally affected the capacity but reduced ductility by about 24 %. Increasing the number of CFRP bars from one to three significantly improved capacity and ductility but increased the risk of debonding failures. Using larger groove sizes (10 x 10 mm2) enhanced capacity of the CFRP-retrofitted specimens, slightly reduced GFRP-retrofitted concrete capacity and improved ductility for both. The 12 x 12 mm2 groove size reduced capacity but increased ductility. The 10 x 10 mm2 groove size effectively prevented debonding failures observed with other sizes.