Electrochemical and Ultrasonic Investigations for Chloride Corrosion Monitoring in RC Structures

Abstract

One of the major causes of catastrophic failures in reinforced concrete structures such as bridges, dams and buildings is the deterioration of reinforcing bars caused by corrosion. Thus, a rigorous inspection of the embedded reinforcements for corrosion related damages on a regular basis is imperative. There is a need for a complete health monitoring system for corrosion related damages in reinf rcing bars embedded in concrete. Electrochemical techniques are useful for evaluating the behavior of steel in concrete because it is non-destructive and can be used to monitor corrosion rate over a period of time. The two important parameters, corrosion potential (Ecorr) and corrosion current (Icorr) are good indicators of corrosion initiation in reinforced concrete structures.Two techniques of electrochemical measurements and ultrasonic guided waves used in combination can reasonably predict the corrosion related damages in steel in concrete. Fall in corrosion potential (Ecorr) and rise in corrosion current (Icorr) is a measure of corrosion initiation. Once initiation of corrosion is picked up, ultrasonic technique of pulse transmission can fairly measure corrosion progression in reinforcing bar in concrete. Surface and core seeking ultrasonic guided wave modes have been identified which were sensitive to delamination and pitting effects of corrosion respectively. These modes were used to ultrasonically monitor reinforced concrete beams undergoing accelerated impressed current corrosion in chloride environment.Effect of different cover depth on ultrasonic voltages also has been studied. This thesis is an attempt to suggest a complete monitoring methodology for corrosion of steel in concrete using electrochemical and ultrasonic measurements.