Efficiency evaluation of electrochemical chloride extraction technique for CFRP-reinforced concrete beams

The corrosion of reinforcing steel is a primary source of deterioration in concrete bridges. In 2006, the Federal Highway Administration statistics showed that approximately one out of every 13 reinforced concrete bridges in the USA is structurally deficient. With the aid of governmental programs such as the American Recovery and Reinvestment Act of 2009, now is a critical time for the rehabilitation of our nation's aging infrastructure. Many efficient repair technologies exist and when properly implemented, they can be effectively and economically used to restore structurally deficient bridges rather than replace them. The application of Fiber-Reinforced Polymer (FRP) composites for retrofitting deteriorated concrete structures has been highly successful, but there are concerns of its long-term performance and durability since chloride ions are still present for two possible reasons: (1) no chloride ion extraction is performed when a bridge is initially retrofitted; and (2) even if chloride ions are initially extracted, they will again accumulate due to available sources such as continual application of de-icing salts. Leaving chlorides within concrete will exacerbate the onset of corrosion during the post-repair service life of the structure.;The objective of this study is to evaluate whether the Electrochemical Chloride Extraction (ECE) technique, which has been proven to be an effective tool for removing chloride ions for regular concrete structures, can be effectively applied to Carbon Fiber-Reinforced Polymer (CFRP) repaired concrete structures. A total of 28 beams (6" x 8" x 78") were tested, with testing variables including intermittent vs. continuous ECE techniques, different CFRP repairing schemes, and applying ECE before and after FRP repair. Parameters assessed during the study included chloride content, pH value around the steel, corrosion potential, and concrete resistance. The beams were tested under static ultimate loading to observe the effects, if any, that ECE had on the bond strength of the component materials. The effectiveness of ECE for CFRP was determined by changes in chloride levels and the pH value around the steel.;The results showed that acceptable chloride removal levels could be obtained from behind CFRP laminates when the intensity and duration of ECE were increased. Removals of 78% of initial chloride were achieved after 900 A*hr/m 2 of current from beams without CFRP repair; values as high as 77% were observed from CFRP-repaired beams after doubling the cumulative applied current (1800 A*hr/m2). Chloride was removed more readily from beams with less CFRP interference; however, those with more CFRP benefitted more from additional ECE, proving that adjustments could be made to the method for its applicability to various CFRP-repaired structures. CFRP pull-off testing showed that the CFRP bond strength was not affected by ECE, even when the cumulative current density reached 1800 A*hr/m2. Static flexural testing demonstrated the same conclusion, with ECE beams actually yielding higher failure loads than the control beams. The evaluations of corrosion rate and resistivity of beams pre- and post- ECE showed that the ECE technique did not significantly affect the corrosion risk and resistivity of concrete.