Corrosion protection for reinforced concrete
Novel technologies have been developed with the help of the EU-funded project DOSECOPS (Development of sustainable electrochemical corrosion protection systems for reinforced concrete structures), which remove and prevent corrosion while improving the material's bond and tensile strength. The consortium brought together an international team of experts from China and Europe. All partners had a vested interest in the problem given the ageing European infrastructure and the many new buildings in China already showing signs of corrosion. They proposed a solution based on electrochemical remediation together with electrochemical injection of nanoparticles. Two major causes of corrosion of reinforcing steel in reinforced concrete structures are carbonation and chloride attack. Carbonation is the reaction between atmospheric carbon dioxide (CO2) and alkaline components of concrete. It can also release bound chloride, which can alter the physical and chemical characteristics of pore structure and thus the transport properties of concrete. Cement paste is highly alkaline (has a high pH), primarily due to calcium hydroxide or lime content. The alkalinity passivates the steel surface with an oxide film, protecting it from corrosion. Carbonation occurs when CO2 becomes dissolved in rain water and reacts with the limestone in the cement. Chloride ions from contaminated mixes or from ions in the environment such as de-icing salts or saltwater cause localised breakdown of the film. Carbonation and chloride attack lower the pH, rendering the passive film unstable. Electrochemical technologies allow the re-alkalisation of carbonated concrete, chloride removal and nanoparticle injection. Proven cathodic prevention systems enabling current injection to suppress corrosion have also been developed for new reinforced concrete structures. Project partners validated the new processes with experimental and field studies with the goal of making them commercially viable. Carbonated and chloride-contaminated concrete were treated using processes based on carbon fibre-reinforced polymer meshes and embedded microcapsules. DOSECOPS also tested novel performance-based cathodic prevention systems for marine structures. The new technologies target removing chlorides from the concrete and increasing alkalinity. They seal pores, thereby preventing further entry of chlorides and/or CO2 from the environment and enhance mechanical properties for a permanent solution. Carbonation is an increasing problem given the rising levels of CO2 in the atmosphere. DOSECOPS technology will benefit both existing and future reinforced concrete buildings and infrastructure. It is expected to have major socioeconomic impact, reducing the costs of maintenance and monitoring while increasing safety.
Keywords
Corrosion protection, reinforced concrete, DOSECOPS, carbonation, chloride attack