Charakterisierung und Modellierung des Fließverhaltens von selbstverdichtendem Beton

Within the framework of the present thesis, rheological and tribological investigations on self-compacting mortars (SCM) and self-compacting concretes (SCC) as well as numerical calculations applying the Computational Fluid Dynamics Code (CFD) FLUENT were performed. First, extensive investigations were conducted on the rheological behaviour of SCM. SCM show an optimised rheological behaviour when the grading curves are as close as possible to the ideal grading curve according to Funk & Dinger. The distance between the solid particles and the water demand, which is an indirect parameter for the particle distance, is directly related to the grain size distribution and to the grain shape. SCM consisting of mainly spherically shaped solid particles with a grading curve corresponding to the ideal grading curve according to Funk & Dinger feature more favourable rheological properties, i. e. they feature a higher flowability at the same water content. The “grading curve difference” was introduced as granulometric characteristic to quantify this rheological behaviour. It was calculated from the difference between the actual grading curve and the target grading curve.Since the water content and the distance caused by the water between the solid particles are the significant control parameters for the viscosity and the rheological behaviour (shear thinning, linear, shear thickening), a particle distance model was established to quantify this correlation. For SCM with a slump flow of 260 to 280 mm (testing with Haegermann cone), the established particle distance model shows a clear correlation between the water-induced particle distance of the solid particles and the relative viscosity. Moreover, this model indicates that, at particle distances smaller than 0.8 µm, a shear thickening and, at particle distances higher than 0.8 µm, a shear thinning behaviour of the examined self-compacting mortars is to be expected. At a particle distance of about 0.8 µm, the mortars show a Bingham flow behaviour. Within the framework of the tribological investigations, the friction between formwork surface and SCM or SCC, the so-called fluid-structure-interaction, was examined in order to understand the flow processes. For this purpose, a tribometer was developed and tests were performed on SCM and SCC. The investigations show a significant influence exerted by the surface roughness of the formwork surface on the friction. Another major influencing factor is the occurring fresh concrete pressure. As was to be expected, an almost proportional relation between the occurring fresh concrete pressure and the measured shear stress was verified. The third significant influencing parameter is the viscosity of the SCC. This became apparent in both, the tribometer tests as well as the L-box tests. Finally, a simple model was established which enables the determination of the occurring frictional forces of a formwork/concrete combination not only for SCC but also for vibrated concrete. In the end, it was examined if the CFD-Code FLUENT was suitable to simulate the flow processes of SCC. All in all, it was shown that the simulation of the flow processes of SCM as well as of SCC as single-phase fluid is presently only possible to a very limited extent when using the CFD-Code FLUENT. A transfer of the results to other geometries and the inverse determination of rheological characteristics is not possible. Beyond that, a shear stress to simulate the friction between SCC and formwork can be defined only in the direction of the axes of the coordinates so that it cannot be applied at spatial geometries like the slump flow test. In the tribometer tests it became obvious that the viscosity of the fluid in combination with the maximum grain size exert a significant influence on the flow velocity. Hence, the chosen approach of the single-phase fluid does not seem to be necessarily suitable for highly filled fluids, which becomes also apparent in the simulations using other geometries. In classical rheology, there are models to simulate two-phase fluids which must therefore now be expanded to higher percentages of solid particles. At that, a term must be incorporated into the model to describe the contact surface. The present thesis shows that the rheological properties of SCC can be specifically adjusted with the water content resulting from the water demand of the raw materials and the mixing water where the resulting particle distance is the main parameter. The water demand can be controlled by the granulometry of the total grading curve of the solid in the fluid. In this respect, this thesis furnishes essential information