Electrochemical chloride extraction: efficiency and side effects J.C. Orellan, G. Escadeillas * , G. Arliguie Laboratoire Mate ´riaux et Durabilite ´ des Constructions, INSA-UPS Complexe Scientifique de Rangueil, 31077 Toulouse, France Received 27 June 2001; accepted 24 July 2003 Abstract Some specimens of reinforced concrete cast with an alkali-resistant aggregate, previously maintained in a solution of NaCl, were subjected to an electrochemical chloride extraction (ECE). The chloride profiles before and after treatment were determined. Likewise, alkali ions profiles before and after treatment were determined. After treatment, some specimens were stored in a controlled atmosphere (60 jC and 100% RH) in order to accelerate the alkali– silica reaction, if any. Results of chloride content after treatment show that about 40% of the initial chloride is removed within 7 weeks. About one-half of the chloride close to steel was removed, but at the same time, significant amounts of alkali ions were observed around the steel. Microstructural observations by scanning electron microscopy (SEM) showed that after treatment, new cementitious phases containing higher concentrations of sodium, aluminum and potassium were formed. Moreover, alkali –silica gel was observed in the specimens stored at 60 jC and 100% RH. It may be possible that the ECE accumulates locally high amounts of alkali ions that stimulate the alkali – silica reaction even though the concrete contained nominally inert siliceous aggregates. The specimen expansions were not recorded, but no cracks were observed. D 2003 Elsevier Ltd. All rights reserved. Keywords: Electrochemical chloride extraction; Corrosion; Microstructure; SEM 1. Introduction Corrosion of embedded steel in concrete represents a great concern in relation to the durability of reinforced structures. Generally, the steel in hardened concrete is protected by a passivating film. However, the presence of sufficient chlo- ride ions, or carbonation, causes the passivating film to break down. Therefore, steel is no longer protected against corro- sion in the presence of moisture and oxygen. Various protective methods, including epoxy-coated steels, overlays, membranes, impregnation or inhibitor, are used to prevent corrosion in new structures. For old struc- tures, the conventional repair technique consists in locating the corroding areas through the potential mapping tech- nique, determining the chloride content in corroding and passive zones and removing the chloride-contaminated concrete. However, conventional patch repairs have not generally proved to be a lasting solution to this type of deterioration because of the difficulty of effectively remov- ing chlorides from all parts of the structure. One specific method for rehabilitating the deteriorating reinforced concrete consists in extracting the chlorides from concrete by electrochemical means. This process is known as ‘‘electrochemical chloride extraction’’ (ECE) or ‘‘desali- nation’’. The technique involves the application of a high current density (DC) for a short period, typically a few weeks. The steel reinforcement acts as the cathode, and an extended anode is placed in a suitable electrolyte at the concrete surface. The positive terminal is connected to the secondary anode and the negative terminal to the steel. When the negative terminal of the DC power source is connected to the steel, the steel achieves negative polarity; it repulses anions and attracts cations present in the concrete pore solution; the cations and anions present in the concrete pore solution act as the electrolyte that permits movement of current between the anode and the cathode. Therefore, accumulation of sodium, potassium and hydroxyl ions occurs at the cathode. This accumulation has been shown to increase the risk of alkali–silica reaction in concrete containing potentially reactive aggregates [1]. Recent studies suggest that even prolonged treatment would remove only 40–55% of the total chloride [2–4]. This investigation determines the reduction in chloride content, measures accumulation of cations near the steel 0008-8846/$ – see front matter D 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.cemconres.2003.07.001 * Corresponding author. Tel.: +33-561-559-931. E-mail address: Gilles.Escadeillas@insa-tlse.fr (G. Escadeillas). Cement and Concrete Research 34 (2004) 227 – 234