Electrochemical desalination of salt infected limestone masonry of a historic warehouse

Salt induced decay of porous construction materials can cause severe loss of cultural heritage and can in some cases also develop to structural problems. To get the salts out of the porous building materials in a structure is not a simple task. The present paper reports results from a test scale plant for electrochemical desalination, a method where the driving force is an applied electrical potential. The test plant covered about 25 m2 surface of a limestone wall of a historic warehouse. It consisted of 72 electrode units which were placed in two rows; the one above the other and the mutual distance between electrodes was 50 cm. The wall was severely infected with NaCl and the average concentration of chloride was 0.72 wt%. The test lasted for about a year, and 3.8 kg chloride corresponding to 6.3 kg NaCl was removed during this period. The part of the wall underneath the electrodes was successfully desalinated; however, the Cl concentration was in the same level as initially in samples taken just between sets of anodes and cathodes. The desalination was thus not completed during the test. The removal rate for Cl into the anodes was constant all through the test revealing that the desalination could have continued if the test had lasted longer. The test showed that the overall method works, but it also underlined the necessity for development of a new design, which allow for shorter distance between the electrodes in order to shorten the duration of the treatment.