Electro-chemical chloride extraction: Influence of C3A of the cement on treatment efficiency

The aim of this study was to clarify whether the C3A content of cement had a significant effect on electrochemical chloride extraction (ECE) treatment efficiency. It is known that a higher C3A content in a cement gives it superior chloride complexing ability resulting in the formation of an “insoluble” calcium chloro aluminate compound.ECE was applied using cylindrical specimens made from concrete containing two levels of C3A (4.3% and 9.05%). Specimens were 5 cm in diameter and 10 cm in height. Steel was placed in the axial direction with an embedded length of 7 cm. These specimens were immersed in an NaCl solution and dried in a stream of air at 40 °C for 10 months. The corrosion was monitored by half-cell potential and polarization resistance measurements. After steel depassivation, ECE was applied for 20, 30, 40 and 50 days using a constant current density of 1 A/m2 of steel. At the end of the treatment, the specimens were maintained at 20 °C and 70% RH in order to observe the evolution of the steel (electrochemical measurements).The results show that, after 30 days of treatment, the chloride content remained constant in the specimen. This was probably due to OH− ion formation on the steel. The OH− ions “contribute” to the current transport, decreasing the ECE efficiency. Concerning the C3A content, ECE efficiency was slightly affected by C3A because only a part of the bound chloride ions was released. From the point of view of corrosion, half-cell potential showed a shift in the positive direction, indicating little corrosion activity at 20 °C and 70% RH. However, polarization resistance measurements showed that 2 months post treatment corrosion rates were significant, although the corrosion rate decreased from 6 μA/cm2 to 2.5 μA/cm2.