Electrochemical chloride removal from concrete prisms containing chloride penetrated from sea water

Abstract

Electrochemical chloride removal tests were carried out in the laboratory of reinforced concrete prisms containing chloride due to 16 years' submersion in the North Sea. After 39 days of treatment using current densities of about 1 and 4 A/m2 steel surface, about 40% to 70% of the initial chloride was removed from the concrete on average. The chloride contents close to the rebars were reduced by 70 to 90% of the initial values. Less than 1% or 0.5% chloride by mass of cement remained around the steel after treatment at 1 or 4 A/m2, respectively. Steel potentials in treated specimens showed a strong shift towards more positive values, indicating passivation, while potentials in control specimens remained strongly negative, corresponding to active corrosion. No influence on the chloride removal efficiency was found from the electrolyte type, the cement type or the water-to-cement ratio. The removal efficiencies were relatively high, corresponding to high chloride ion transport numbers in the pore solution and suggesting quick release of bound chloride. Good overall agreement was found between the removed amounts of chloride determined from chloride in the concrete and from chloride accumulated in the electrolyte. Microscopic examination showed that the number of microcracks had increased slightly in some specimens, probably due to build-up of hydrogen gas pressure.