Markus Stoppel

Measurement of Accelerated Steel Corrosion in Concrete Using Ground-Penetrating Radar and a Modified Half-Cell Potential Method

A new approach is presented to evaluate corrosion of steel bars in concrete by 1.5- and 2.6-GHz ground-penetrating radar (GPR) and a modified half-cell potential method. Changes in time-lapsed travel times, amplitudes, and peak frequencies that are associated with short-time Fourier transform spectrograms of the bar reflections were continuously measured. The year-long corrosion process of the reinforcement bar rapidly accelerated within a few days by impressing direct current across a pair of embedded reinforcement bars, which served as the anode and cathode. When corrosion started, the travel times, amplitudes, and frequency spectra of the bar reflection changed. The results were analyzed by dividing the material’s response into three phases (NaCl contamination, depassivation, and corrosion). The writers attribute the phenomena of the first two phases to the ionic conduction and interfacial polarization effect, described in the low-frequency regime of complex dielectric permittivity outlined in the Maxwell-Wagner effect. The remaining phase corresponds with the appearance of large and multiple interfaces among steel, concrete, corrosion product, and cracks, in addition to the upward movement of the corrosion product to the concrete surface that intercepts wider radar footprints. The findings, based on time lapse measurements, provide a basis to further apply the GPR technique to spatial measurements in laboratory and field studies.

CONTROL AND DATA ACQUISITION OF AUTOMATED MULTI‐SENSOR SYSTEMS‐TWO EXAMPLES FROM CIVIL ENGINEERING

A combination of different non‐destructive test methods is often necessary to receive reliable results for material characterization, flaw detection and the determination of component specific geometry parameters. Regarding structures of concrete thickness measurements are combined with flaw detection. Furthermore, additional information about reinforcement and tendon ducts is needed. Therefore, a multi‐sensor measurement approach is required with a high degree of automation. Otherwise a time consuming succession of manual measurements has to be performed. A modular control and data acquisition approach will be described and the application to two different automated measurement devices will be shown. These are results from two collaborative projects dealing with the development of an automobile robot system and a highly flexible scanner system. These different applications are based on a similar kernel allowing the modular use of different contact and non‐contact sensors. Therefore, continuous and point measurement devices can be combined and multiple sensor combinations are possible. This measurement approach leads to results in form of point data and time series. Furthermore, the coordinates of each measurement can be device dependent. Therefore, a flexible analysis concept is needed. Since often only a combination of several methods will lead to significant results the fusion of the analyzed data must also be possible. Several aspects as well as limits and future trends concerning analysis and also flexible data storage will be discussed.A combination of different non‐destructive test methods is often necessary to receive reliable results for material characterization, flaw detection and the determination of component specific geometry parameters. Regarding structures of concrete thickness measurements are combined with flaw detection. Furthermore, additional information about reinforcement and tendon ducts is needed. Therefore, a multi‐sensor measurement approach is required with a high degree of automation. Otherwise a time consuming succession of manual measurements has to be performed. A modular control and data acquisition approach will be described and the application to two different automated measurement devices will be shown. These are results from two collaborative projects dealing with the development of an automobile robot system and a highly flexible scanner system. These different applications are based on a similar kernel allowing the modular use of different contact and non‐contact sensors. Therefore, continuous and point ...