Role of clay-fluid molecular interactions on fluid flow and mechanical behavior of swelling clays

The usefulness of Na-montmorillonite in civil engineering and environmental applications such as sealant and liners in dams and landfills can be attributed to its small particle size, high swelling capacity and low permeability to water. In applications such as geosynthetic liners (GCL), it is expected that the clay will behave as a barrier to landfill leachates and other toxic substances. This study involves understanding the effect of dielectric constant on the clay-fluid molecular interaction of Na-montmorillonite using different solvents with varying dielectric constant values ranging from 110 to 2.4, and using XRD (x-ray diffraction analysis) and FTIR (Fourier transform infrared spectroscopy) as the characterization techniques. This study also investigates the effect of dielectric constant of the solvent on the macroscale flow and mechanical properties of Namontmorillonite. Since currently available permeameters do not produce accurate permeability test results for swelling clays, a new permeability device, which allows for accurate measurements of permeability, was designed and fabricated.;Study shows that the solvents with high dielectric constants make strong interaction with interlayer water as well as clay Si-O structure whereas solvents with low dielectric constants make only weak interaction with interlayer water or clay Si-O structure. It was also observed that, as compared to low dielectric solvents, high dielectric solvents take a longer period of time to enter into the interlayer completely. It is found that the molecular hydraulic property of Na-montmorillonite with water to be 3.22 x 10-9 cm/sec. Macroscale permeability experiments show that permeability of Na-montmorillonite is increased by six orders of magnitude when permeated with low dielectric constant solvents as compared to high polar water. Consolidation test results show that the time rate as well as total consolidation of Na-montmorillonite is significantly larger when the clay is saturated with low dielectric constant solvents. It was also observed that clay undergoes particle breakdown when saturated with water, altering the microstructure of the clay. Clay undergoes a decreasing degree of particle breakdown with decreasing dielectric constant value of the solvent. This study clearly shows the role of molecular interaction on the flow and mechanical properties of swelling clays.