* J. A. Gonza Âlez, E. Otero CENIM, Avda. Gregorio del Amo 8, 28040 Madrid (Spain) A. Cobo, M. N. Gonza Âlez Escuela Universitaria de Arquitectura Te Âcnica de Madrid, Avda. Juan de Herrera 6, 28040 Madrid (Spain) Electrochemical chloride removal from reinforced concrete structures and its ability to repassivate prerusted steel surfaces Elektrochemische Chloridentfernung an Stahlbetonbauwerken und Mo È glichkeiten der Repassivierung vorgerosteter Stahloberfla È chen A. Cobo, E. Otero, M. N. Gonza  lez and J. A. Gonza  lez* Gravimetric and electrochemical measurements were used to ex- pose the relationship between the degree of prerusting of reinforce- ments embedded in chloride-contaminated mortar or concrete and the efficiency with which they are repassivated once depassivating ions are removed. The results show that, above a certain, ill-defined rusting threshold, the electrochemical chloride removal does not ensure effective repassivation of reinforcements in the steel/con- crete system. Once the passivity of reinforcements embedded in re- inforced concrete structures (RCS) is overcome, the typical corro- sion rates of the active state seemingly suffice to maintain an acid pH at the metal/rust interface in the bulk of such a strongly alkaline material as concrete. After this local acidification, the metal inside pits probably behaves similarly as it would in an acid solution. As a result, it does not suffice to remove the rusting agent in RCS in order to stop corrosion; rather, the agent must be removed before the first visible signs of deterioration appear. Gravimetrische und elektrochemische Messungen wurden durchgefu Èhrt, um die Beziehung zwischen dem Grad der Vorro- stung von Bewehrungsstahl, der in chloridhaltigem Mo È rtel oder Be- ton eingebettet war, und der Wirksamkeit einer Repassivierung, nachdem die depassivierenden Ionen entfernt wurden, zu untersu- chen. Die Ergebnisse zeigen, dass oberhalb eines bestimmten, schlecht zu definierenden Rostgrades die elektrochemische Chlo- ridentfernung eine wirksame Repassivierung der Bewehrung in dem Stahl/Beton-System nicht sicherstellt. Sobald die Passivita Èt der Bewehrungen, die in Stahlbetonbauwerken eingebettet sind, verloren gegangen ist, scheinen die typischen Korrosionsgeschwin- digkeiten des aktiven Zustandes auszureichen, um einen sauren pH- Wert an der Metall/Rost-Grenze selbst in einem so stark alkalischen Material wie Beton aufrechtzuerhalten. Nach dieser o Èrtlichen An- sa Èuerung verha Èlt sich das Metall im Loch wahrscheinlich a Èhnlich wie in einer sauren Lo Èsung. Als Ergebnis ergibt sich, dass es nicht ausreicht das Korrosionsreaktionsmittel zu entfernen, um die Kor- rosion zu stoppen; vielmehr muss das Reaktionsmittel, d.h. das Chlorid entfernt werden, bevor die ersten Anzeichen einer Scha Èdi- gung auftauchen. 1 Introduction Reinforcement corrosion is regarded as the primary source of premature deterioration of reinforced concrete structures (RCS) [1, 2]. The enormous technical economic and social significance of these structures has raised the concern in the scientific community about early detection of corrosion and the development of effective methods for the prevention and control of corrosion-related damage, in order to avoid the huge costs of traditional repair procedures. This has recently aroused an interest in electrochemical methods for rehabilitating RCS, which rely on electrochemi- cal chloride removal (ECR) or electrochemical realkalization (ERA) of carbonated concrete [3 ± 6]. These alternatives are more expeditious than traditional cathodic protection (CP) methods as the treatments involved typically take a few weeks to apply at most. Unlike traditional repair methods, these re- habilitation techniques require no removal of carbonated or chloride-contaminated concrete layers, nor thorough cleaning of reinforcements; as a result, they are more economical and also less hazardous to both workers and the environment. In addition to these appealing features, ECR and ERA methods can be used for effective prevention of corrosion be- fore chloride ions or the carbonation front reach reinforce- ments [7]. Whether they can effectively repassivate strongly corroded reinforcements is however questionable [7, 8]. Un- fortunately, the visual inaccessibility of embedded reinforce- ments usually prevents one from detecting any signs of corro- sion before substantial damage has occurred. The problem is worsened by the fact that, construction technicians frequently are unaware of corrosion-related risks, so routine preventive inspections of RCS are the exception rather than the norm as they should. This paper exposes the relationship between the degree of prerusting of reinforcements embedded in chloride-contami- nated mortar or concrete and the ability of effectively repas- Materials and Corrosion 52, 581±589 (2001) Electrochemical chloride removal from reinforced concrete 581 Ó WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001 0947-5117/01/0808-0581$17.50.50/0