One of the most common methods for flexural strengthening of concrete beams with FRP materials is the Externally Bonded Reinforcement (EBR) method. The main problem that has greatly hampered the use of EBR method is the premature debonding of FRP laminate from the beam substrate. This will shorten the expected lifespan of the reinforced membrane and makes EBR method uneconomical. Near Surface Mounted (NSM) method is another flexural strengthening technique for reinforced concrete structures. The NSM technique can provide a significant increment of the load at serviceability limit state, as well as, the stiffness after concrete cracking. In terms of the debonding issue, experiments have shown that the NSM has a better performance compared to the EBR; however, delamination and debonding of FRP sheets from concrete is highly probable in both methods and still remains as a limitation.

Recently, special treatments on concrete surface prior to using the FRP sheets in the EBR technique, named as Externally Bonded Reinforcement On Grooves (EBROG), has been introduced in Isfahan University of Technology (IUT), Iran; According to this method, longitudinal grooves were first caved on the tension face of the concrete beam, The grooves were then cleaned with compressed air and filled with appropriate epoxy resin and Carbon fiber sheets were adhered to the surface. The EBROG method has shown a great promise in resolving the debonding problem. Based on some experimental investigations, the EBROG method can considerably postpone the debonding and in some cases may completely eliminate it. The aim of the current study is to introduce another improved strengthening procedure by using the EBROG method while the FRP sheet is in direct contact with carved grooves on the tension face of concrete beam in a wet-lay-up application. This method is named Externally Bonded Reinforcement In Grooves (EBRIG). For this purpose, 36 beam specimens with the dimensions of 120 × 140 × 1000 mm were cast. Four distinct strengthening methods, i.e., Externally Bonded Reinforcement (EBR), Near Surface mounted (NSM), Externally Bonded Reinforcement On Grooves (EBROG) and Externally Bonded Reinforcement In Grooves (EBRIG) were examined. A group of specimens were also considered in which FRP laminates were applied to the beams using EBR technique without any surface preparation. The beams were then subjected to four-point flexural loading. Results showed that EBRIG technique performs as good as EBROG when the section area of FRP sheets are relatively low; however it permits for higher failure loads and displacements compared to EBROG method, when multi-layer FRP sheets are used. Thus, the method can be used as a reliable technique to significantly reduce or even eliminate the debonding of FRP sheets from the concrete surface in flexural strengthening of concrete beams.