Cathodic protection (CP) is a common method for rehabilitation of reinforced concrete structures suffering from Chloride induced corrosion. A sufficient protection of the corroding rebar can be ensured by use of several protection criteria. The use of these assessment criteria, in particular the so called 100 mV-criterion, can lead to erroneous resuits for certain unconventional arrangements of rebar and cp anode.
Therefore a joint research project of the Institute for Building Materials Research, RWTH-Aachen University, Germany, (ibac) and the Federal Institute for Materials Research and Testing, Berlin, Germany, (BAM) has been set up to determine the applicability of CP under arbitrary geometrical conditions. A special focus was set on the applicability of surface applied anode Systems for protection of the reinforcement of structures opposite to the accessible side (e.g. outer side of tunnel Shell, Bridge deck protected from inside a box girder) In this paper, the impact of the time dependent changes of the Polarisation behaviour of the rebar on the current and potential distribution is shown by means of parametric studies using the FEM method.
A joint research project was accomplished by ibac and BAM with the aim to develop a numerical model
of cathodic protection (CP) of reinforced concrete with a special focus on CP of the rear reinforcement
layer. The model was intended to include the effects of chemical alterations within the concrete and the
steel concrete interface, which are induced by long-term application of CP. The investigations presented
in this paper focus on the migration of chloride ions due to small electric fields as applied during cathodic
protection of steel in reinforced concrete structures and its impact on polarisation characteristics. A
comparatively new method, laser induced breakdown spectroscopy (LIBS), was used to determine
chloride profiles on laboratory specimens in order to investigate one of several model parameters to
describe cathodic protection of the rear reinforcement of reinforced concrete structures. These
investigations are described elsewhere, [1].
The paper focuses on long term polarisation tests and their impact on the charge depending cathodic
polarisation behaviour of laboratory specimens.
Although the complex changes at the steel-concrete interface due to cathodic polarisation are widely acknowledged to have a beneficial influence concerning the cathodic protection (CP) of steel in concrete, some questions concerning the repassivation of carbon steel in consequence of cathodic polarisation are still not satisfactorily clarified. In the recent literature, some indications are presented that repassivation occurs after a certain time of polarisation. Therefore, the investigations discussed in this paper aim to clarify, to what extent the re-passivation of carbon steel due to cathodic polarisation occurs, and if the ennoblement of OCP is a sufficient indication for repassivation. In a first step, the corrosion state of five nominal equal test specimens was determined by electrochemical impedance spectroscopy (EIS). After determining the initial corrosion state by evaluating the charge transfer resistance and the polarisation resistance, respectively, the specimens were polarised cathodically. Impedance data were recorded before, during and after polarisation. The impedance data were evaluated by equivalent circuit fitting with special attention to charge transfer resistances and the impact of diffusion on the corrosion and polarisation behaviour. The results indicate that the reduction of oxides and oxygen diffusion during cathodic polarisation has strong impact on the systems behaviour and that repassivation effects occur after switching off the polarisation current and during depolarisation, respectively.
At the Institute for Building Materials Research (ibac) in Aachen and the Federal Institute for Materials Research and Testing (BAM) in Berlin a joint research project is currently running with the aim to develop a numerical model which describes cathodic protection (CP) of reinforced concrete. Special project focus is the CP of the rear reinforcement layer. The resulting model shall include the impact of chemical alterations at the steel surface and within the adjacent concrete on the polarisation behaviour of reinforcement, which are induced by long-term application of CP. The investigations presented in this paper aim to clarify open aspects on the migration of chloride ions due to small electric fields as applied in CP of steel in reinforced concrete structures. A comparatively new method, laser induced breakdown spectroscopy (LIBS), was applied in order to determine chloride concentration profiles on laboratory specimens as one of several model parameters for a mathematical description of CP of the rear reinforcement of reinforced concrete structures. The paper concerns migration tests using non-saturated specimens under laboratory conditions at constant voltage and the application of the experimental parameters on FEM-calculations. The presented results suggest the conclusion that even comparably small electric fields, as applied in CP of steel in concrete, may lead to significant and sustainable reduction in chloride concentration at the surface of the reinforcement.