Open Access

Abstract The component-specific quality of linings and prefabricated components made from refractory castables is largely determined by the processing properties during the placement of refractory castables. These are, in particular, the rheological properties, specifically the shear rate-de-pendent dynamic viscosity. Existing measurement methods for determining the shear rate-dependent dynamic viscosity of aggregate-containing suspensions such as refractory castables are prone to errors and inaccurate. From a scientific point of view, an exact determination of the shear rate-dependent dynamic viscosity as well as influencing variables on the rheological properties of refractory castables cannot be realized due to the lack of measurement methods. This leads to contradictory and unclassifiable statements on the influence of aggregate fractions on the rheological properties of refractory castables in the state of science and technology. From a technical point of view, this complicates the rheological optimization of refractory concretes. Within this work, a measuring method was developed with which the shear rate-dependent dynamic viscosity of aggregate-containing suspensions such as refractory castables can be determined precisely. The measurement method is based on a spherical viscometer for deter-mining the dynamic viscosity and the coupling with a CFD-FEM simulation to determine the actual prevailing shear rate. The determination of the dynamic viscosity is based on the determination of the pull-out speed at a defined pull-out force (force-controlled) according to Stokes' law. It was shown that the pull-out speed and the shear rate can be correlated linearly, which made it possible to redesign the measuring method in a shear rate-controlled manner. A check showed that the shear rate-dependent dynamic viscosity of aggregate-containing suspensions such as refractory castables could be determined just as accurately. The CFD-FEM simulation downstream of the test was no longer necessary. It was demonstrated that the shear rate-dependent dynamic viscosity of aggregate-containing suspensions increases with increasing mineral aggregate content. Furthermore, it was shown that the complex composition of refractory castables defines their rheological properties. Variations in the particle size distribution of the medium grain and the coarse grain can significantly influence the shear rate-dependent dynamic viscosity, but do not necessarily have to. This also depends on the particle size distribution of the slurry. Furthermore, the dynamic viscosity can be influenced to a different extent at different shear rates. An unpredictable influence of increasing shear rates on dynamic viscosity can therefore be observed. This complexity complicates the rheological optimization of refractory concretes. Nevertheless, it has been proven that a rheological optimization of refractory concretes, for example the suppression of dilatancy, can also be achieved by optimizing the particle size distribution of the mineral aggregates.