Bentonite dispersions: Transition from liquid-like to solid-like behavior and cracking

Cylindrical samples of 11-13. wt% aqueous bentonite dispersions with a range of resting times after preparation (0-72. h) were subject to axial squeezing and revealed a transition from a Bingham liquid-like behavior to solid-like behavior. The liquid-like behavior is characterized by viscous spreading arrested by the yield stress, whereas the solid-like behavior is characterized by stasis at lower loads followed by discontinuity of the displacement and cracking above some critical level of load. A mechanical response, dependent on resting time, implied irreversible aging as a result of slow swelling of the clay crystallites, i.e. the internal structure being built over time in the material at rest. Dispersions of 11. wt% and 12. wt% transitioned from liquid-like to solid-like behavior in a single experiment at a resting time of 24. h and 3. h, respectively. At higher concentrations (18-22. wt%) the material always behaves as a solid. The solid-like behavior is distinguished from the liquid-like behavior by the appearance of cracks. The additional bending and buckling experiments conducted with dispersions of 18-22. wt% revealed Young's moduli of 330-500. kPa, yield stresses of 9-15. kPa, cracking stresses of 15-25. kPa, and cracking strains of 8-10%. For all concentrations explored, a linear dependence of the yield stress on concentration was found. It is demonstrated for the first time using uniaxial compression that liquid bentonite dispersions at a concentration of 11-12. wt% reveal transition to a solid in a single experiment where they become capable of developing surfaces of discontinuity of the displacement.