Detecting Corrosion in Existing Structures Using Time Domain Reflectometry

The effectiveness of corrosion evaluation of steel strands using time domain reflectometry (TDR) has been established both theoretically and experimentally in previous work. A two-wire transmission line model has been established. The relationship between model geometry and impedance has been under thorough investigation and corresponding experimental results have been obtained. The results have proved its feasibility. TDR instrumentation has been successfully installed in a newly built bridge and periodic data are being collected and studied. It has been proved that for a new structure, if a sensor wire is applied along side the strand/rebar in the process of construction, the future corrosion that could occur on the strand/rebar can be effectively detected and the damage to the strand can be estimated. However detecting corrosion in existing structures in which sensor wires were not applied when the structures were built, is more difficult. External detection methods must be employed instead of internal methods. The theory of time domain reflectometry still applies, but factors such as the non-existence of built-in sensor wires, the presence of concrete layers (which are strong dielectrics and contain non-uniformities) and the distance from the strand to the sensor wire must be considered. They begin to exert strong influence on the TDR results and methods of distinguishing and evaluating their effects have to be found. This project is directed at solving this problem. Possible geometries that can be applied to externally detect steel strand corrosion and factors that influence signal returns from corrosion have been thoroughly studied during the project period.