The electrochemical removal of chlorides from reinforced concrete

Results of a 2-year field study performed in Switzerland to evaluate the process and to obtain information on the efficiency of electrochemical chloride removal as a restoration technique for chloride contaminated concrete are presented. It is shown that about 50% of the initial chloride content is removed within 8 weeks (ca 5 × 106 C m-2). In the treated zones of the structure the half-cell potentials became more positive by about 80-100 mV. A comparison with the theoretical efficiency for chloride removal, calculated from the transference number of chloride ions, show that mainly the free chlorides in the pore solution of the concrete are removed. Due to the slow chemical equilibrium between bound and free chlorides, a second treatment after several months also removes originally bound chlorides. For severe and inhomogeneous chloride contamination local zones with active rebars and high chloride content may remain after the treatment.