ELECTRO-OSMOTIC CHEMICAL TREATMENTS: EFFECTS OF Ca(2+) CONCENTRATION ON THE MECHANICAL STRENGTH AND pH OF KAOLIN

Electro-osmotic chemical treatment is an innovative method to improve the strength of soft clays for geotechnical engineering purposes; the effectiveness of the treatment may be related to treatment time, the concentration of the solutions injected, and to variation of pH in the clay. The objective of this study was to investigate the relationship between the above-mentioned factors and the improvement in strength when calcium chloride solution was used as an injection material. A series of tests was carried out by injecting different concentrations of calcium chloride solution into a kaolin suspension, for different treatment times, during electro-osmosis. After the tests, the pH, cone resistance, water content, and concentration of Ca(2+) in the kaolin at different locations were measured and analyzed. The results show that the concentration of Ca(2+) in the kaolin, the pH, and the strength were increased near the cathode with increases in concentration of CaCl(2) and treatment time. An insignificant increase in strength, due to ion exchange over the entire specimen, for short treatment times of 2 to 24 h, was observed because of a small increase in concentration of Ca(2+) and in pH. During long-term treatment (120 h), a considerable increase in concentration of Ca(2+) (137.0 mg/g) and pH (pH = 10) was observed near the cathode. This led to a pozzolanic reaction, which in turn caused a significant increase in the mechanical strength of the kaolin.