Thixotropic Behavior of Compacted Clays

The variation in dynamic shear modulus with time was used to study both the rate and extent of thixotropic stiffening in compacted clays. The shear modulus was measured by the resonant column technique in which torsional oscillations of very low amplitude were applied to the base of a free-standing cylindrical sample. By means of this approach it was possible to consider the influence of a large number of variables including molding water content, clay mineralogy, and electrolyte concentration. The shear modulus reached its maximum value well dry of optimum and fell off rapidly on the wet side. Thixotropic stiffening occurred only on the wet side within a finite range of water contents. Both the rate and extent of thixotropic action was affected by electrolytes in the molding water. High concentrations of calcium chloride tended to suppress the range of water contents within which thixotropy occurred, whereas small amounts of dispersing agent had the opposite effect.