Corrosion protection for reinforced concrete

Most of the existing reinforced concrete building stock in Europe was built before 1970, incurring significant expenses for rehabilitation and renovation due to corrosion. Novel technology under development with EU support of the DOSECOPS project will remove and prevent corrosion while improving the material's bond and tensile strength.

The consortium brings together an international team of experts from China and Europe. Both have a vested interest in the problem given the ageing European infrastructure and the many new buildings in China already showing signs of corrosion. The proposed solution exploits electrochemical remediation together with electrochemical injection of nanoparticles.

Carbonation and chloride ions are the targeted offenders. 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 carbon dioxide (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 both lower the pH, rendering the passive film unstable.

Electrochemical technologies are facilitating realkalisation of carbonated concrete, chloride removal and nanoparticle injection. Proven cathodic prevention systems enabling current injection to suppress corrosion are also under development for new reinforced concrete structures.

Now at its midpoint, the project is validating the new processes with experimental and numerical studies. Carbonated and chloride-contaminated concrete are being treated with processes exploiting carbon fibre-reinforced polymer meshes and embedded microcapsules, respectively. Novel performance-based cathodic prevention systems for marine structures are also being tested.

The technologies will remove chlorides from the concrete and increase alkalinity. They will also seal pores, preventing further entry of chlorides and/or CO2 from the environment and enhancing 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.