Long term control of corrosion of steel reinforcement by a two-stage cathodic protection method

It has been shown experimentally that corrosion of steel reinforcement can be arrested if sufficient cathodic charge at a current density higher than 20 mA/m2 is applied over a period of weeks. Once corrosion is arrested, a cathodic prevention current density, which requires a current density an order of magnitude lower than for conventional cathodic protection, can be applied for long-term prevention of re-initiation of corrosion. Self-contained products were developed in the laboratory according to the Two-Stage principle, each single product containing a battery-operated ICCP element which produces a high initial current output of between 20 mA/m2 and 50 mA/m2 of steel area during an initial polarisation corrosion arrest phase and a galvanic anode component which delivers the lower cathodic prevention current long-term. Diodes ensure that the current from the battery is delivered to the steel reinforcement and not dumped onto the galvanic anode and allow the galvanic current to flow only when the ICCP element becomes inoperable. This paper describes the principles of the technique, illustrates products developed and presents medium-term field studies to demonstrate the success of the Two-Stage CP technique