Abstract

Injection of CaCl2 and Na2SiO3 solutions into clay suspensions during electroosmosis often improves the cohesive strength of clays near the anode and cathode, whereas the cohesive strength of clays between the electrodes remains weak. Although the main improvement mechanism for the cohesive strength of clays near the cathode was demonstrated to be a pozzolanic reaction (formation of calcium silicate hydrate cement), the mechanism of improved cohesive strength near the anode is still not understood. The objective of the present study was to investigate the mechanism for the improvement of cohesive strength near the anode and, thus, make it possible to determine a way to enhance the range in improvement using kaolinite as the test clay. The test was performed by first injecting CaCl2 solution during electroosmosis until the optimum volume of CaCl2 was attained. This was followed by treatment with Na2SiO3 solution for different lengths of time. The results indicate that the anode region after treatment was acidic (pH = 4) because the electrolysis of water causes acidification near the anode. As Na2SiO3 solution was injected through the anode, the mechanism of cohesive strength improvement of the treated clay near the anode was attributed to the silicic acid polymerization effect provided by the Na2SiO3 solution. The silicic acid may link the clay particles together to form a gel network in a low pH environment. The clay gel network structure developed rigidity as the water content was reduced. In addition, as the volume of injected Na2SiO3 solution was increased, the cohesive strength near the anode also increased.

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