Improving the Load-Carrying Capacity of FRP-to-Concrete Bonded Joints Using a Biaxial GFRP Interlayer

Abstract

The use of externally bonded (EB) fiber-reinforced polymer (FRP) systems for the strengthening of reinforced concrete (RC) structures is a widely accepted technique. In these strengthened systems, debonding of the FRP laminate from the concrete substrate is a commonly observed failure mode, which controls the strength of the bonded joint. Debonding failure often limits the utilization of the strength of carbon fiber–reinforced polymer (CFRP) laminates, which reduces the efficiency of the strengthening system. This paper presents a novel methodology to improve the load-carrying capacity (i.e., ultimate load) of CFRP-to-concrete bonded joints, therefore improving the utilization of the CFRP material strength. A bidirectional glass fiber–reinforced polymer (GFRP) interlayer is introduced between the CFRP laminate and the concrete substrate, therefore, distributing the load that is applied to the CFRP laminate over a larger bond area than that of typical CFRP-to-concrete bonded joints. A series of single-shear pull test specimens were fabricated and tested to investigate the behavior of the newly proposed bonded joints. A vacuum curing technique was employed to achieve a good quality bonded interface. The test results showed a significant increase in the ultimate load. In addition, the test results showed that the GFRP laminate width and stiffness significantly affect ultimate load (up to 156% increase). Considering the significantly lower cost of GFRP compared with CFRP laminates, the proposed method could provide an economical solution to improve the efficiency of EB CFRP strengthening systems.