The durability of reinforced concrete structures is a key task for engineers in design, execution, and maintenance. Protection of reinforced concrete from corroding reinforcement requires measures such as applying coatings, cathodic protection (CP) or other similar solutions.

When surface-applied anodes are used, typically the anode system is placed on the concrete surface next to the corroding reinforcement layer. This assures that the major part of the applied current polarizes the reinforcement layer that shall be protected. Sometimes this common anode installation is not practicable due to difficult access to this surface or due to unacceptable traffic blocking that would be needed during the installation. In such cases, it would be helpful to know whether an anode that is installed on the opposite reinforcement of the structural element can also protect the reinforcement.

Consulting Engineers Raupach Bruns Wolff, specialized in building maintenance, considered this issue in cooperation with ibac – the Institute of Building Materials Research at the RWTH Aachen University in Germany. In their study, the engineers simulated how the protection current distributes to the reinforcement layers and examined under which conditions the rear reinforcement layer obtains sufficient current to be effectively protected.

A general answer is not possible because the distribution of protection current depends on several parameters such as the geometry and amount of the reinforcement, concrete resistivity, polarization behavior, and the geometry of corroding and passive zones. Thus, the consulting engineers developed a 3D-FEM model of the current and potential distribution in case of CP of the rear reinforcement. The accuracy of the numerical calculations was verified by laboratory tests.

The examinations show that macrocell corrosion at the rear reinforcement can already be suppressed at relatively low anode current densities. At higher concrete resistivity, the concrete resistance between the anode and the reinforcement layers predominantly defines how the CP-current distributes to the reinforcement. The polarization behavior of the reinforcement at lower concrete resistivity and lower protection current densities significantly contributes to a current distribution which leads to higher fractions of the protection current at the rear reinforcement.

Currently two research projects are underway at the ibac and the Federal Institute for Materials Research and Testing (BAM) in Berlin, to study the long term effects of CP in concrete.

M. Bruns and M. Raupach, Mater. Corrosion ; DOI: 10.1002/maco.200905584