(564b) Comparative Study of the Time Dependent Rheological Behavior of Particulate Suspensions - Cement Paste and Silicon Carbide Paste

Understanding the rheology of particulate suspension is important in many industrial applications, including coatings, paints, food, pharmaceuticals, and cements and where pumping and extrusion are used, among others. For cement paste suspensions, it is rheology that is critical to its suitability for use in construction applications, including 3D printing. Rheology depends on a number of physical and chemical properties of the cement and the paste formed thereof. Furthermore, the way that the paste was processed matter, including how it was mixed and even the measuring conditions. Critically important is the need to separate the effects of these factors on the rheology of cement paste, which has been shown to depend not only on the shear history of the paste, but also on the age of the paste i.e., properties evolving with time, thus exhibiting time-dependent rheological behavior.

This work attempt to separate the contribution of one of the contributing chemical factors, hydration, from the overall evolution of time-dependent rheological behaviors in cement-based systems. The effect of shear history and apparent particle size distribution of two solids, a Type I-II hydraulic portland cement and non-hydraulic silicon carbide surrogate, was studied. The rheological behavior of their respective pastes in deionized water, 0.15% superplasticizer solution, and 0.15% ammonium polymethacrylate solution was determined and compared. Contrary to the earlier suggestions that the thixotropic to anti-thixotropic transition of cement paste might be due largely to hydration related structural buildup, these comparative results show that particle-association or flocculation-de-flocculation related structural changes might be equally as significant.