Bond behaviour of CFRP-to-concrete bonded joints with a GFRP interlayer: An experimental study

This paper presents an experimental investigation into the improvement of efficiency in carbon fibre reinforced polymer (CFRP)-to-concrete bonded joints by an introduction of a glass fibre reinforced polymer (GFRP) interlayer. By introducing a ±45° biaxial GFRP interlayer between the CFRP and concrete, applied force on the CFRP laminate was distributed over a larger area of concrete surface, thereby increasing the load carrying capacity of the bonded joint. A total of 18 single-shear pull test specimens were prepared and tested to investigate the effect of CFRP width (varying from 25 mm to 50 mm) and GFRP/CFRP width ratio (ranging from 2 to 4) on the behaviour of the CFRP-to-concrete bonded joints with a GFRP interlayer. Addition of the GFRP interlayer was found to increase both ultimate load capacity and the deformation capacity significantly. Increase in the GFRP interlayer width, while keeping the CFRP width the same, increased the ultimate load of the bonded joint. Increasing the GFRP width while keeping the GFRP/CFRP width ratio the same also increased the ultimate load of the bonded joint but had little effect on the bond strength. An idealized mechanism was presented to explain the behaviour of the CFRP-to-concrete bonded joints with a GFRP interlayer. It was shown that due to 2D stress transfer of the newly proposed bonded joints, underlying mechanisms may be different to the conventional FRP-to-concrete bonded joints. Therefore, design theories developed for conventional FRP-to-concrete bonded joints may not be directly applicable to the CFRP-to-concrete bonded joints with a GFRP interlayer. Much more investigations are necessary to better understand the behaviour of the newly proposed bonded joints. •A biaxial GFRP interlayer was introduced between CFRP and concrete in CFRP-to-concrete bonded joints to improve the load carrying capacity.•Both ultimate load and the ultimate displacement of the bonded joints were significantly increased.•Fracture area within concrete was significantly increased with the introduction of the biaxial GFRP interlayer.•Width of the GFRP interlayer increased the ultimate load of the CFRP-to-concrete bonded joints.