Electrochemical desalination of cores from a reinforced concrete coastal structure

Abstract

This paper describes a laboratory investigation of the process of electrochemical desalination (chloride removal) applied to cores taken from the splash zone of an eight-year-old reinforced concrete quay wall situated on the North Sea coast. The concrete, which had been made from blastfurnace slag cement in accordance with Rijkswaterstaat specijications, was of high quality and significant levels of chloride contamination were present only in the exposed surface zone of the material at depths well below the thickness of cover to the reinforcement. Segments of steel reinforcement present within cores taken from the structure were subjected to cathodic polarization at current densities in the range 0·6–4 A/m 2 for 3–6 weeks. The anodes, which were placed at the chloride-contaminated end surfaces of the cores, were composed of activated titanium meshes in contact with electrolyte solutions of either saturated calcium hydroxide or 1 M sodium carbonate. Changes in the electrical resistance of the concrete, its chloride content and its pore solution composition projile were measured and the corresponding increases in the chloride concentration of the external electrolyte were recorded. The proportion of chloride ions removedfrom the cores was found to depend on the total charge passed and on the nature of the external electrolyte, the eficiency of the desalination process being much higher when saturated calcium hydroxide rather than 1 M sodium carbonate was used. The mechanism of this effect and the associated changes in pore solution chemistry are examined.