Alkaline hydrogels as ion-conducting coupling material for electrochemical chloride extraction

One method to rehabilitate chloride-contaminated reinforced concrete structures is electrochemical chloride extraction, by which chloride ions are extracted from the pore system of the concrete using an externally applied voltage. Although many factors influence the efficacy of electrochemical chloride extraction, a number of these, such as the concrete cover and the chloride profile, are predefined by the structure. One factor with major influence that can be improved is the coupling material. In this contribution, we present a suitable coupling material in the form of a highly alkaline hydrogel, with which the applied voltage can be reduced from 40–50 to 1 V under laboratory conditions. The reduction is due to the high conductivity of the gel and its excellent electrolytic contact with concrete. In a field test on chloride-infested car-park columns, more than 95% of the chloride could be extracted with 2–3 cycles, each comprising of 21 days of extraction and 7 days of rest. During the entire treatement, the gel did not require any attending to, such as replacing evaporated moisture.