Bond between carbon fibre-reinforced polymer (CFRP) bars and ultra high performance fibre reinforced concrete (UHPFRC): Experimental study

Carbon fibre-reinforced polymer (CFRP) bars are currently used to reinforce concrete in an attempt to overcome the corrosion issue encountered with ordinary steel. In order to exploit more efficiently their tensile capacity, it is interesting to use CFRP bars as prestressing tendons. This application requires a high quality concrete matrix. The advantageous characteristics of UHPFRC, such as high strength, good ductility and durability, mean that a UHPFRC structure prestressed with CFRP bars may be lighter and require less maintenance. Since the flexural behaviour of prestressed concrete members reinforced with CFRP bars is highly dependent on the bond between the two materials, an experimental program was carried out in order to investigate the bond of CFRP bars embedded in UHPFRC. Two types of surface, smooth and sand-coated, were investigated. Pullout tests were performed to examine the effect of varying parameters such as embedment length, bar diameter and concrete age. The results clearly show that the bond strength of macroscopically smooth bars embedded in UHPFRC is close to that of sand-coated bars. It was also found that ultimate bond strength decreases with bar diameter and with embedment length. Moreover, the bond strength can be expected during early age (3 days). A post-test examination revealed that damage occurred only in the outer layers of the CFRP bars.