Electrochemical chloride extraction: efficiency and side effects

Abstract

Some specimens of reinforced concrete cast with an alkali-resistant aggregate, previously maintained in a solution of NaCl, were subjected to an electrochemical chloride extraction (ECE). The chloride profiles before and after treatment were determined. Likewise, alkali ions profiles before and after treatment were determined. After treatment, some specimens were stored in a controlled atmosphere (60 °C and 100% RH) in order to accelerate the alkali–silica reaction, if any. Results of chloride content after treatment show that about 40% of the initial chloride is removed within 7 weeks. About one-half of the chloride close to steel was removed, but at the same time, significant amounts of alkali ions were observed around the steel. Microstructural observations by scanning electron microscopy (SEM) showed that after treatment, new cementitious phases containing higher concentrations of sodium, aluminum and potassium were formed. Moreover, alkali–silica gel was observed in the specimens stored at 60 °C and 100% RH. It may be possible that the ECE accumulates locally high amounts of alkali ions that stimulate the alkali–silica reaction even though the concrete contained nominally inert siliceous aggregates. The specimen expansions were not recorded, but no cracks were observed.