Fiber Reinforced Polymer (FRP) composites are widely accepted as a promising and easy-to-use construction materials especially for strengthening purposes due to the numerous advantages such as high tensile strength, ease of application, light weight and corrosion resistance. 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.ear 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) and Externally Bonded Reinforcement in Grooves (EBRIG), has been introduced in Isfahan University of Technology (IUT), Iran.The EBROG and EBRIG methods have shown a great promise in resolving the debonding problem. Based on some experimental investigations, the EBROG and EBRIG methods can considerably postpone the debonding and in some cases may completely eliminate it.The aim of the current studyia study on CFRP-to-concrete joint, which results of these studies, is bond-slip relationship for EBROG method. To do so, 48 concrete prisms with dimensions of 150 × 150 ×330 mm were cast with three mix designs for three different compressive strengths. In current study use CFRP sheets with 0.13, 0.17 and 0.26 thickness and use two grooves with 2, 5, 10 and 15 mm depth. The specimens were strengthened using EBR and EBROG methods. Afterwards, all strengthened specimens were subjected to pull out test. In order to benefit from full field deformation measurements, a non-contact image based technique, i.e. Particle Image Velocimetry (PIV), was used to investigate the bond behavior of tested specimens.After the evaluation of results and use common relationship between strain, shear stress and slip, obtain relationship between shear stress and slip. Then for bond-slip relationship in EBROG and EBR methods, a new function was been proposed. The study results showed that proposed function for EBROG and EBR specimens has good fitting with load-slip and bond-slip curves. Also according to experimental data in current study, increasing in compressivetrength concrete in EBR specimens and EBROG specimens with grooves depth equal 2 mm, caused increasing in load capacity; but in EBROG specimens with grooves depth equal 5, 10, 15 mm, with increasing in compressive strength concretethe load capacity not an increased; because the CFRP sheets in most of specimens were rapture and access final tensile capacity. Increasing in CFRP sheets thickness, in all specimens, there was an increase in load capacity. In EBROG specimens, load capacity was increased by increase the depth to 10 mm.increased depth of 10 to 15 mm will be a slight reduction in load capacity which due to the stress concentration around grooves and local fracture in CFRP sheets. Keywords: FRP composites, debonding, single-shear test, bond-slip model, externally bonded reinforcement (EBR), grooving method (GM), Particle Image Velocimetry (PIV).