Development of Distributed Node Electrodes for Corrosion Monitoring of Concrete Rebars, 20-R8084

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Principal Investigators
Kuang-Tsan Kenneth Chiang
Lietai Yang

Inclusive Dates:  07/16/09  – 11/15/09

Background - Corrosion is often the major cause of concrete structural failures. The corrosion rate of the reinforcement bars (rebars) is one of the most important parameters in assessing the failure risk and remaining life of a concrete structure. However, corrosion monitoring for concrete rebars has been a technical challenge. The linear polarization resistance (LPR) method has been used to measure the corrosion rate of actual rebars inside a concrete structure. With the LPR method, large errors may be produced because of difficulties in determining the surface area. The guarded ring method has a mechanism that helps to determine the surface area, but the method may not apply to structures where several rebars are in close proximity of each other. An effective corrosion monitoring system is needed.

Approach - A concrete rebar or a long metal rebar with a composition similar to concrete rebars was used as the working electrode. The long metal bar is coated such that only selected sections (evenly distributed along the axial direction) are exposed to the concrete. Each of the exposed sections has a well defined surface area for corrosion rate measurement using conventional electrochemical techniques, such as the LPR method. The collection of the exposed sections form a network of electrodes, and each exposed section is a node electrode. Counter electrodes that are required for the electrochemical measurements (linear polarization, AC impedance, or current disrupting methods) are attached to the concrete surface near the exposed node electrodes prior to the measurement at each location. Multiple long metal bars can be used to form a network of node electrodes if they are connected together. The network of node electrodes can be used conveniently to detect the health condition of the metal components in a large area.

Accomplishments - An innovative node electrode system was developed to provide corrosion monitoring in concrete structures. The node electrode concept for monitoring degradation of rebar in concrete was demonstrated. The system allows real-time detection of corrosion using few instruments and electrical cables. It is low cost and has high reliability for deployment in large numbers to form a network of monitoring systems. The system can be installed in either new construction or during repairs of existing structures. The signals from the node electrode are easily interpreted by operators and can be easily automated and interfaced with a central data system. The node electrode allows accurate measurement of corrosion rate at locations identified to be high risk by the real-time detection system. Experiments were conducted to determine the effects of the node electrode size, distance between the neighboring nodes, and corrosivity of the environment.

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