Corrosion Detection in Concrete Rebars Using a Spectroscopic Technique
Edward J. Garboczi, Paul E. Stutzman, Shuangzhen S. Wang, Nicos Martys, Dat Duthinh, Virgil Provenzano, Shin G. Chou, David F. Plusquellic, Jack T. Surek, Sung Kim, Robert D. McMichael, Mark D. Stiles, Ahmed M. Hassan
Detecting the early corrosion of steel in reinforced concrete is a goal that has been much pursued. Since 2010, NIST has been working on a large project to develop an electromagnetic (EM) probe that detects the actual corrosion products via spectroscopic means. Several principal iron corrosion products, such as hematite and goethite, are antiferromagnetic at field temperatures. At a given applied EM frequency, which depends on temperature, these compounds undergo a resonance that can be detected, which pinpoints the presence of these particular iron corrosion products. The electromagnetic waves tend to be of order 100 GHz or higher, so getting them through the cover concrete and back out again to the detector has been challenging. We have successfully detected these two iron corrosion products, and are developing equipment and methodologies that will be capable of penetrating the typical 50 mm of cover concrete in the field. The novel part of this project is that we actually detect specific compounds, rather than just look at changes in rebar cross-section. This method has the potential of providing an early-corrosion probe for steel in reinforced concrete, and for other applications where steel is covered by various layers and coatings.