Time-dependent rheological behavior of bentonite suspensions: An experimental study

The thixotropic behavior of bentonite suspensions was studied using different experimental procedures. It was found that the bentonite dispersions exhibit a time-dependent non-Newtonian behavior. In addition to the major factors affecting the rheological properties in the dispersion were the shearing value and duration, the rest time preceding the measurements and the structural state of the dispersion. The Herschel-Bulkley model was found to correlate well with the behavior of bentonite suspensions. The time evolution of the shear stress at constant shear rates was correlated by the Bird-Leider equation. In order to take into account structural evolution of the suspensions, the rheological law was modified by the introduction of the phenomenological model of Tin and Boger derived from Moore's kinetics evolution. It was observed that at short rest times and low shearing conditions, this model describes satisfactorily the time-dependent behavior of the bentonite suspensions. The behavior laws and kinetics evolution were established through the determination of structure destructuration and reorganization rates values. The structure parameters were found to be dependent on the clay concentration, providing evidence that the scale characteristic times of the buildup and breakdown processes are also concentration dependent. (c) 2005 The Society of Rheology.