Signal Profiles and Images of Corroded Steel Bars in Concrete Generated by Inductive Scanning Technique Using Heterodyning Sensor

Abstract
  The inductive scanning system is a non-destructive testing technique that utilizes the phenomenon of eddy current induction and detection for imaging steel reinforcing bars embedded within concrete. In this paper the inductive scanning system using a heterodyning sensor in combination with real time digital signal processing (DSP) has been used to detect and generate images of corroded reinforced steel bars embedded within the concrete. The sensor generates a vector of voltage values of the reinforced bars scanned at a spatial interval. These voltage values are processed by the DSP to produce voltage signals and generate images. The feasibility of exploiting the inductive scanning system to detect and distinguish different amounts of corrosion on steel bars embedded in concrete was investigated by using one-dimensional scanning techniques, such as orthogonal and parallel line, scans for single and multiple corroded steel bars. In these techniques, signal profiles of various amounts of corrosion on steel bars were compared and analysed.  The system shows evidence of very good performance which encourages its development and use in corrosion detection and monitoring.