Computational Fluid Dynamic Modelling of the Rotational Viscometer

Abstract

The use of fillers in a bituminous binder satisfies two main criteria: the improvement of the system’s mechanical properties and the utilisation of waste products with the associated environmental benefit. An increasing number of filler materials are being used, all with different gradations and specific gravities. It is important to the asphalt technologist to understand the effect the fillers have on the viscosity of the hot bitumen and to ensure even distribution of the filler particles within the mix. One of the instruments used to quantify the behaviour of hot bitumen and bitumen-filler mixtures is the rotational viscometer. Previous research has identified substantial changes in the viscosity with time of both the pure bitumen and the bitumen-filler mixture when measured by the rotational viscometer.
This study uses Computational Fluid Dynamics (CFD) to model behaviour of the bitumen and bitumen-filler in the viscometer. By means of complex rheological models, the pseudoplastic and thixotropic nature of the bitumen is identified and successfully modelled. In addition, the effect of filler drift is identified and modelled, indicating that the steady state equations used to calculate viscosity in the viscometer are invalid for such systems.