Bond strength of corroded steel bars in reinforced concrete structural elements strengthened with CFRP sheets

The effectiveness of CFRP strengthening to maintain and enhance bond between corroded steel reinforcement and concrete has been investigated through pullout tests. Results indicate that strengthening with CFRP can increase the ultimate bond strength of specimens containing corroded steel reinforcement especially at medium or high levels of corrosion. The failure mode changes under these conditions from brittle bond splitting to more ductile rebar pullout in most cases. The confining effect of CFRP increases with increasing ratio of cover depth to rebar diameter c/db up to a value of about 2.3. But the confining effect is reduced if c/db increases beyond this value. Ultimate bond strength in specimens, which are strengthened before corrosion starts, can be significantly increased up to a degree of corrosion of about 15%. This beneficial effect cannot be observed if structural elements are strengthened after considerable corrosion took place already because in this case corrosion products can leak out of the interfacial zone into expansion cracks. Under these conditions, the reactionary confinement is reduced.