Coupled Mechanical and Chemical Behavior of Bentonite Engineered with a Controlled Organic Phase

This experimental investigation quantified the physical and chemical behavior of two organoclays, synthesized using the quaternary ammonium organic cations hexadecyltrimethylammonium bromide (HDTMA) and benzyltriethylammonium chloride (BTEA). The organic cations were exchanged onto montmorillonite at increasing percentages of the clayʹs cation exchange capacity in order to increase the packing density of the organic cations on the clay surfaces. Increasing the organic content of the organoclays, and the cation packing density, decreased the specific gravity, N2-BET surface area, liquid limit in water, and clay compressibility in the consolidation test for both organoclays. However, the liquid limit in methanol and sorptive capacity for benzene increased for HDTMA organoclay but decreased for BTEA organoclay as the density of organic cation packing was increased. Additionally, the measured friction angle for HDTMA organoclay decreased, while the friction angle for BTEA organoclay increased as a function of increasing organic cation packing density. The creation of an organic phase on the soil created a hydrophobic, rather than hydrophilic, clay that demonstrated reduced interaction with water. The nature of the organic phase in the long chain HDTMA was a fluid-like phase that demonstrated partitioning uptake of organic compounds, and reduced (lubricating) frictional interaction in the direct shear test. In contrast, the organic phase in the BTEA clay formed an adsorptive phase that interacted specifically with organic compounds (that is, not through dissolution), and increased the frictional interaction as the organic cation packing density was increased.