CFRP strengthening of RC beams with corroded lap spliced steel bars

Abstract

Corrosion is the number one deterioration mechanism that decreases the service life of the concrete structures. Many structures in severe environments have experienced an unacceptable loss in serviceability earlier than anticipated due to corrosion. Advanced composite materials in the form of externally bonded fiber reinforcing polymer (FRP) sheets have been successfully used for rehabilitation and strengthening of infrastructure in lieu of traditional repair techniques such as steel plates bonding. FRPs are used because of their light weight, ease of application, non-corrosiveness material, and high strength. The current study comprised of testing eighteen reinforced concrete beams to investigate the confinement provided by carbon fiber-reinforced polymer (CFRP) sheets on the bond strength of corroded tension lap splices under static loading. The beams were 200mm wide by 300mm high by 2000mm. Each beam was reinforced on the tension side with two steel bars (2 M 15 or 2 M20 steel bars) spliced at mid span in the constant moment region. The nominal concrete strength was 43 MPa and the yield stress of the steel reinforcement was 400MPa. The test variables were the concrete cover to bar diameter ratio (c/d) which varied from 1.5 to 2.67, the level of corrosion (0% and 2.5% mass loss), and the presence or absence of transverse CFRP wrapping. The corrosion in the steel bars was induced by means of accelerated technique withan impressed current density of 150mA/cm2. The specimens were instrumented by strain gauges on the steel reinforcement, concrete, and CFRP sheets. Linear variable differential transformer (LVDT) was used to measure mid span deflection. The specimens were tested to failure in four point bending. The test results showed that all beams failed by bond splitting. The reduction in the ultimate bond strength due to a 2.5% corrosion level ranged between 16% and 25% depending on the c/d ratio. The reduction in the ultimate bond strength due to a 5.0% corrosion level ranged between 20% and 45% depending on the c/d ratio. FRP wraps were effective in confining the tension splice region. The failure in the FRP repaired beams was more ductile and more gradual although the final mode of failure was splitting of the concrete cover. A new, (Ktr,f,) accounting for the presence and amount of FRP confining tension lap-splice was proposed.