(326f) Modeling of the Time-Dependent Rheological Behavior of Particulate Suspensions

Understanding the rheology, i.e. the flow properties, of particulate suspensions is important in many industrial applications, including coatings, paints, food, pharmaceuticals, and cements and where pumping, extrusion and or printing are involved. The rheology of these particulate systems depends on a number of physical and chemical properties of the particles and solution phase. Particulate suspensions, for example cement-based pastes, have been shown to display flow curves wherein shear stress is a function of how long the paste has been sheared, and thus exhibits time-dependent rheological behavior. Furthermore, such suspensions exhibit a transition from thixotropic to anti-thixotropic flow. In this work, a two-part mathematical model has been developed to explain the time-dependent rheological behavior of such suspensions. Carefully designed rheometric experiments including repetitive cyclical ramp up and ramp down flow protocols were performed on cement and silicon carbide pastes as model systems to obtain rheology data. The two-part model adequately captures the related time-dependencies, thixotropy and anti-thixotropy, as well as the transitions between the two. Parameters of the model were estimated, and physical explanations provided in the context of printing applications.