Spherical rheometer for determining the rheological parameters of fresh concrete

In-situ characterisation during the vibration process

This paper will introduce a new type of testing method based on a spherical viscometer for measuring the rheological parameters of fresh concrete. A steel sphere is drawn through fresh concrete at a constant speed and the stationary value arising for its resistance is measured. This measurement is repeated at varying speeds and the resistance forces measured, i.e. the shear stress occurring as a result of these, are correlated to each of the differing speeds or shear rates. By way of contrast to the more commonly used rotation viscometers, this measur- ing device also makes it possible to take measurements during the vibrations process. It has become apparent that rheological behaviour undergoes a fundamental change during the vibration process. “Dormant” concrete behaves in crude approximation according to Bingham’s law; vibrated concrete exhibits shear thinning behaviour which can be sufficiently well described using a power-law fluid model. In a non- vibrated state, the effects of structural shifts, whose cause could not be satisfactorily explained, can be noticed if the sphere is drawn at very low speeds. An attempt was made on the basis of data sets from vibrated/non-vibrated concretes to recalculate material parameters by describing them as power-law fluid.

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