Application of a multi-ring electrode for depth-staggered resistance measurement at varying humidity levels.
Source: BAM
Corrosion is usually the limiting factor in the service life of a reinforced concrete structure. Suitable monitoring methods can detect changes in the corrosivity of the concrete at an early stage and thus allow timely maintenance measures to be planned before significant corrosion damage occurs. The paper presented here results from a collaboration between authors from the DGZfP Subcommittee Corrosion Detection.
Electrochemical potential measurement, elemental current measurement, and resistance measurement methods can be used to monitor reinforced concrete structures. While the first two allow conclusions to be drawn about the condition of the reinforcement, resistance measurement can be used to assess the corrosiveness of the concrete. A depth-graded determination of the corresponding values allows statements to be made about the risk of corrosion at higher reinforcement levels.
The illustrated use of the multi-ring electrode shows changes in the electrical resistance of the concrete. As shown in the figure, the influence of chloride at a humidity above the deliquescence humidity of NaCl (approx. 75% RH at 20° C) is visible. In addition to the change in the conductivity of the pore solution, the hygroscopic effect of the chloride also changes the pore saturation, significantly reducing the electrical resistance of the concrete. The renewed decrease in moisture leads to a significant increase in resistance near the surface despite the presence of chloride. From the measurement depth shown in light blue (top edge of reinforcement), changes in ambient humidity no longer have a significant effect on the electrical resistance of the concrete.
Targeted corrosion monitoring can ensure timely repair measures and thus an extended service life, increasing the structures sustainability.
Corrosion monitoring of reinforced concrete structures: The DGZfP specification B12 Collaboration
Gino Ebell, Till Felix Mayer, Jörg Harnisch, Christoph Dauberschmidt
Materials and Corrosion. 2/2024, 188–196.