Inductive and magnetic field inspection systems for rebar visualization and corrosion estimation in reinforced and pre-stressed concrete

Inductive and magnetic field inspection systems are becoming increasing popular for the nondestructive imaging and condition assessment of reinforcing components, such as steel reinforcing bars (rebars) and tendons in reinforced and prestressed concrete structures. In this article, we review the principles of this nascent technology, the research and commercial instruments that are now available, and the directions of future research. Magnetic field imaging technology has in general many potential benefits; it is truly nondestructive and non-invasive, it is non-hazardous, cost-effective and, most important, ignores the concrete matrix in which the reinforcing components are embedded. Most significantly, by analysing the impedance change in an excitation coil, it is also possible to obtain quantitative information (and image data) in relation to regions of corrosion. However, the testing industry has traditionally been reluctant to apply this methodology, for the important reason that the detection range is limited by the rapid attenuation of the magnetic field with increasing distance from the source. This limitation is now being addressed with research into novel coil arrangements, new, more stable and sensitive solid state sensors, and reconstruction algorithms that allow virtual three dimensional reconstruction of embedded components.