Electrochemical re-alkalisation, chloride extraction and alkali-silica reaction in concrete

Concrete made with potentially reactive aggregate was artificially contaminated with chloride (two levels) or arti-ficially carbonated (two levels) or both in combination. These nine combinations were either left untreated or electrochemically treated by realkalisation and/or chloride extraction and then subjected for one year to the con-ditions of 38°C and high relative humidity that are known to promote alkali-silica reaction. Expansion measure-ments, pore solution analysis and microscopy confirmed that ASR is unlikely to be a problem in realkalised car-bonated concrete because the hydroxyl ion concentration does not reach the level needed to initiate the reaction. However, ASR is potentially significant in concrete treated by chloride removal: observed expansion increased tenfold. In chloride contaminated concrete, increasing carbonation progressively reduces the expansion, although it may still be unacceptably high in partially carbonated concrete.