Microstructure of concrete after electrochemical chloride extraction treatment

The mercury intrusion method and the scanning electron microscopic (SEM) method were used to study the influence of electrochemical chloride extraction treatment on the distribution and microstructures of ions in concrete. Samples were selected from the zone near steel reinforcement and the outer surfaces of concrete specimens with different water to cement ratios after electrochemical chloride extraction (ECE) treatment. Chloride ion, potassium ion and sodium ion content, pore structure and microstructure were tested on these samples. The results show that after the ECE treatment ion content near steel for chloride ions, potassium ions and sodium ions, are respectively 1/2, 5~10 times and 8~18 times their concentrations in the outer surface. Meanwhile, there were some discontinuous granular hydration products and a little decomposed hydration calcium silicate hydrate (CSH) gels. However, a great deal of potassium ions and sodium ions accumulated near the steel where there was much less concentration of chloride ions than in the outer surface of the concrete. After the ECE treatment, the concrete near the steel presented a higher porosity with more coarse pores and a weak microstructure. On the contrary, the outer surface concrete showed a compact microstructure with smaller pores and an intact hydration product network.