Paddle Mixer for Viscoplastic Materials and Pastes

A. Krupica and T. Jirout

Abstract
A modified paddle mixer suitable for the homogenization of viscoplastic fluids and pastes, such as contemporary concrete mixtures, was developed to enhance homogeneity of the product, a crucial step in ensuring desired mechanical properties. In addition to the improvement in flow characteristics, this study presents the basic dimensionless characteristics in regression form, along with the measurement of the Metzner–Otto constant. These characteristics are essential for the use of the paddle mixer as an onsite rheometer, enabling rapid and straightforward evaluation of the desired rheological properties of the prepared mixture. The performance of the paddle mixer was assessed through homogenization experiments and power input measurements at various rotation speeds. The paddle mixer displayed creeping flow behavior up to a Re value of 50. The geometry of the paddle mixer was modified to achieve homogeneity throughout the volume, significantly influencing mixing mainly in the axial region of the mixer. To compensate for the non-Newtonian behavior, the Metzner–Otto approach was employed. Under creeping flow conditions and for pastes displaying flow index above 0.5, the paddle mixer can be characterized by a Metzner-Otto constant of 54.

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Keywords
paddle mixer, concrete, Metzner–Otto, viscoplastic, non-Newtonian, paste