Mechanism of soil cementation by electroosmotic chemical treatment

• Ca-hydration products could be formed in a weak alkaline environment.
• Ca-hydration products could fill the soil void, causing the increase in strength.
• Ca-hydration products were further transformed into calcium silicate hydrates.

The injection of calcium chloride solution through the anode during electroosmosis has been shown to be effective in strengthening soft clay. The objective of this study was to investigate the mechanism responsible for this improvement using a kaolinite. Several types of samples were prepared, including a sample directly taken from the clay near the cathode after the completion of an electroosmotic chemical treatment test and samples of kaolinite mixed with different concentrations of calcium ion solutions and cured for various times. A mechanical strength test and chemical and mineralogical analyses were performed to examine the properties and compositions of the samples. Results showed that some crystalline products could be formed in an alkaline environment of pH around 10 or after a short treatment time. The products filled some of the clay voids, causing a moderate increase in clay strength. In a strongly alkaline environment, calcium silicate and/or aluminum hydrate would be formed with a longer curing time, leading to a substantial increase in clay strength. Therefore, raising the concentration of the injected calcium chloride solution, enlargement of the applied electric voltage and extension of treatment time could result in greater clay strength.