Corrosion Detection of Steel Cables using Time Domain Reflectometry

Corrosion of steel cables and reinforcing steel in concrete structures is a major cause of structural deterioration. The current methods for corrosion detection suffer from several significant drawbacks. In this paper, a nondestructive evaluation technique is developed that is capable of determining the location and severity of corrosion of embedded or encased steel rebar and cables. This technique utilizes time domain reflectometry (TDR), which has been traditionally used to detect electrical discontinuities in transmission lines. By installing a sensor wire alongside the steel reinforcement, the reinforcement can be modeled as an asymmetric, twin-conductor transmission line. Physical defects of the reinforcement, such as abrupt pitting corrosion, general surface corrosion, and grouting voids, will change the electromagnetic properties of the line. They can be modeled analytically, and identified using TDR. TDR measurement results from several fabricated bridge cable sections with built-in defects are reported. Based on the initial results, the TDR corrosion detection method has proven to be more robust than the existing methods, because it allows one to detect, locate, and identify the extent of corrosion damage.