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In-situ characterisation during the vibration process

Spherical rheometer for determining the rheological parameters of fresh concrete


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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CPi worldwide journals are trade journals for the concrete and precast concrete industry that are published in 12 different language editions in more than 170 countries. These trade journals, with their practical editorial reporting on research, production and applications, are specifically addressing the decision makers of the concrete and precast concrete industry.

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