Computed tomography. A new tool studying hidden corrosion: Fid-Bau Portal

Computed tomography. A new tool studying hidden corrosion

Goebbels, Jürgen / Hanke, Daniel / Meinel, Dietmar / Staude, Andreas / Beck, Matthias / Burkert, Andreas

Due to the progress in Computed Tomography (CT) applied for dimensional control new fields in materials characterization are opened. Especially volume properties can be non-destructively and quantitatively analysed which are non-accessible by other methods. These possibilities are used to study time dependent properties of corrosion. As an example concrete cylinders with embedded steel bars as working electrode are investigated. The mass loss of the working electrode is determined by CT and compared with results from electrochemical and gravimetric measurements. The limitations of the evaluation process of corrosion by CT are studied using a simulation program for the radiographic projections. From the observations it can be asserted, that CT is able to observe the ongoing corrosion of steel in concrete. In the case of passive steel cylinders the electrochemistry is able to determine the amount of corrosion much better than the CT. Nevertheless the divergence is also much higher than in the case of active systems. The basic cause is the thin passive layer of about 20-30 micron which can not measured by CT. In this case the EC is the more applicable technique. This observation is like expected; in the case of passive systems the electrochemistry is able to describe the corrosion with limitations. The theoretic background is investigated by Heitz and Schwenck. However in the case of advanced corrosion, especially pitting corrosion with deep and impenetrable pits, the CT seems to be the more dedicated technique. The corrosion promoted by hydrolysis in the pits can not be measured by the EC. In this case the investigation of corrosion by the determined steel volume is the more exact method.