Changes in the Composition of Pore Solution and Solids During Electrochemical Chloride Removal in Contaminated Concrete


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Title: Changes in the Composition of Pore Solution and Solids During Electrochemical Chloride Removal in Contaminated Concrete

Author(s): J. Tritthart

Publication: Special Publication

Volume: 154


Appears on pages(s): 127-144

Keywords: chlorides; concretes; porosity; salts; Materials Research

Date: 5/1/1995

Electrochemical chloride removal was applied to a concrete test area of about 36 m 2 in a reinforced concrete hall which had been used for more than 10 years as a depot for deicing salt, in an attempt to extract the chloride that had penetrated into it. Since the salt had been stored loosely and the interior of the hall was frequently exposed to outside air, the concrete was heavily contaminated by chloride (up to about 15 percent Cl - in cement). Chloride removal was performed with an average current density of 1 A/m 2 for a period of 132 days. The studies were aimed at determining the changes in total chloride content and the Cl - and OH - concentrations of the pore solution at varying concrete depths. It was shown that the efficiency of chloride removal decreased in the concrete cover with increasing depth and that it was least efficient near the reinforcement. The factor that was identified as being responsible for this was the change in OH - concentration of the pore solution that had been caused by reactions at the electrodes. The OH - concentration of the pore solution decreased in the area close to the surface during treatment, while it rose dramatically around the reinforcement (up to approximately 2.5 mol OH -/L). This resulted in an increase of the Chloride Transference Number and, thus, the efficiency of chloride removal close to the concrete surface, as well as a drastic decrease close to the reinforcement. Hence, a reduction of the Cl - to "harmless" levels was not possible in this particular case. However, practice has shown that in many cases such a reduction can be achieved as chloride contamination is normally much less severe; thus, most of the chloride can be extracted from the reinforcement area before the rising Cl -concentration of the pore solution has diminished the efficiency of chloride removal. If, however, chloride has penetrated beyond the reinforcement, it can be removed to a limited extent only.