Electrochemical investigation of carbon-based conductive coatings for application as anodes in ICCP system of reinforced concrete structures

摘要

Carbon based conductive coatings are complex composites, consisting of an organic or inorganic binder and conductive carbon components, for application as anodes in impressed current cathodic protection systems (ICCP) of reinforced concrete structures. These mixtures can be painted as paste or aqueous dispersion at the prepared concrete surface. For current supply of the rectifier to the coating are used different materials like wires made of platinised titanium, copper or mixed metal oxide coated titanium (primary anode). The minus pole of the rectifier is connected to the reinforcing steel (cathode) and the positive pole to the primary anode. By supplying a protective current between anode and cathode, the potential of the reinforcing steel should be lowered below -720 mV (versus Ag/AgCl/0,5 M KCl) into an electrochemical inactive range.An industrial research project in cooperation between the Federal Institute for Materials Research and Testing (BAM, Berlin) and the Institute of Building Materials and Research (RWTH-Aachen University) should assess the applicability of three commercial carbon-based conductive coatings as secondary anode in ICCP systems. As part of this research project, extensive electrochemical and morphological investigations of carbon based conductive coatings were carried out to determine important parameters such as applied current density, pH value of the electrolyte solution, humidity and, type of binder and their influence to the degradation behaviour of these coatings. The electrochemical properties in saturated calcium hydroxide solution were studied by electrochemical methods, such as electrical impedance measurement, measuring of open circuit potential over time and galvanostatic polarisation. For the galvanostatic polarisation with in situ pH-value measurements we designed a special corrosion-measurement-cell (Fig. 1).The dissolved organic and inorganic carbons in electrolyte solution were quantified by using a photometric method. The structures of the coatings were investigated before and after the electrochemical investigations by microscopy and SEM/EDX analysis.