Rheological characteristics and thixotropic behavior of four clay minerals belonging to different types of morphology and lattice structure were investigated.
Clay-water samples were prepared at about their liquid limits and the testing was accomplished by unconfined compression applied at different rates of deformation.
From the stress to strain rate relationships the yield value was determined as an intercept on the stress axis at zero rate of strain, and the slope gave the viscosity coefficient.
Regain of strength or thixotropic character of the samples was evaluated in terms of the viscosity and yield values at various periods of aging.
The influence of temperature on the aging process was studied using attapulgite at three temperatures, 21°C., 36°C., 51°C.
The activation energy of the process of aging for attapulgite was calculated using both viscosity coefficients and ultimate yields. The values were within experimental uncertainty for the two sets of data and it was thereby concluded that changes of these parameters were due to a single reaction. The activation energy was found to be 9.4 kcal mole−1, which suggests a physical rather than a chemical change.