Effect of electrochemical chloride extraction treatment on the corrosion of steel rebar in chloride contaminated mortar

Abstract

Purpose

This work aims to demonstrate the use of electrochemical chloride extraction (ECE) to remove chloride ions away from the steel rebar in chloride-contaminated mortar and to mitigate the corrosion of the embedded steel.

Design/methodology/approach

To simulate salt contamination in concrete, sodium chloride was added at 0.5 per cent by weight of cement in the fresh mortar featuring a water-to-cement ratio of 0.45. The ECE treatments were varied at two electrical current densities (1 and 5 A/m²), using two electrolytes (0.1M NaOH and 0.1M Na₃BO₃ solutions) and for two periods (2 and 4 weeks). The average free chloride concentration in cement mortars before and after ECE treatment was quantified using a customized chloride sensor, whereas the spatial distribution of relevant elements was obtained using energy-dispersive X-ray spectroscopy. The effect of ECE treatment on the electric resistivity of mortar and the corrosion resistance of steel rebar was investigated by electrochemical impedance spectroscopy and potentiodynamic polarization measurements, respectively.

Findings

The experimental results reveal that the ECE treatment was effective in removing chlorides and in improving electric resistivity and compressive strength of the mortar, when using the sodium borate solution as the electrolyte. In this case, a 4-week ECE treatment at 1 A/m² decreased the free chloride content in the mortar by 70 per cent, significantly increased the Ca/Si ratio in the mortar near rebar, led to a more refined and less permeable microstructure of the mortar and significantly improved its compressive strength. The ECE treatment was able to halt the chloride-induced corrosion of steel rebar by passivation. A 4-week ECE treatment at 1 A/m² using sodium hydroxide and sodium borate solutions decreased the corrosion rate of rebar by 36 and 34 per cent, respectively.

Originality/value

This electrochemical rehabilitation of steel-reinforced concrete under chloride-contaminated condition is very effective in prolonging its service life.

Citation

Nguyen, T.H., Nguyen, T.A., Le, V.K., Dinh, T.M.T., Thai, H., Shi, X. and Nguyen, T.H. (2016), "Effect of electrochemical chloride extraction treatment on the corrosion of steel rebar in chloride contaminated mortar", Anti-Corrosion Methods and Materials, Vol. 63 No. 5, pp. 377-385. https://doi.org/10.1108/ACMM-12-2014-1473