Abstract
Multi-phase materials are common in several fields of engineering and rheological measurements are intensively adopted for their development and quality control. Unfortunately, due to the complexity of these materials, accurate measurements can be challenging. This is the case of bitumen-rubber blends used in civil engineering as binders for several applications such as asphalt concrete for road pavements but recently also for roofing membranes. These materials can be considered as heterogeneous blends of fluid and particles with different densities. Due to this nature the two components tends to separate and this phenomenon can be enhanced with inappropriate design and mixing. This is the reason behind the need of efficient dispersion and distribution during their manufacturing and it also explains while real-time viscosity measurements could provide misleading results. To overcome this problem, in a previous research effort, a Dual Helical Impeller (DHI) for a Brookfield viscometer was specifically designed, calibrated and manufactured. The DHI showed to provide a more stable trend of measurements and these were identified as being “more realistic” when compared with those obtained with standard concentric cylinder testing geometries, over a wide range of viscosities. However, a fundamental understanding of the reasons behind this improvement is lacking and this paper aims at filling these gaps. Hence, in this study a tailored experimental programme resembling the bitumen-rubber system together with a bespoke Computational Fluid Dynamics (CFD) model are used to provide insights into DHI applicability to perform viscosity measurements with multiphase fluids as well as to validate its empirical calibration procedure. A qualitative comparison between the laboratory results and CFD simulations proved encouraging and this was enhanced with quantitative estimations of the mixing efficiency of both systems. The results proved that CFD model is capable of simulating these systems and the obtained simulations gave insights into the flow fields created by the DHI. It is now clear that DHI uses its inner screw to create a vertical dragging of particles within a fluid of lower density, while the outer screw transports the suspended particles down. This induced flow helps keeping the test sample less heterogeneous and this in turns allows recording more stable viscosity measurements.This work was supported by the Engineering and Physical Sciences Research Council (EPSRC) [grant number EP/M506588/1].
Highlights
Rheological properties and their measurement are of paramount importance for the development, performance and applications of products across a wide range of industries
This paper presents a Computational Fluid Dynamics (CFD) model able to reproduce the observations obtained from a laboratory investigation aimed at resembling a bitumen-rubber system during product development over a wide range of testing conditions
The authors used customised laboratory testing and computer simulations to gain a deeper understanding of the fundamental mechanisms behind the improved viscosity measurements obtained when using the Dual Helical Impeller (DHI) with rubberised bitumen
Summary
Rheological properties and their measurement are of paramount importance for the development, performance and applications of products across a wide range of industries. The use of bituminous binders modified with polymers is a common practice used to enhance the performance of road pavements and roofing membranes Measurements of their viscosity/rheology can be challenging due to the often heterogeneous structure of these complex systems, especially if these materials suffer from phase stratification within the time frame of typical viscosity measurements, as in the case of rubberized bitumen [7]. Due to the complexity of these materials, accurate measurements can be challenging This is the case of bitumen-rubber blends used in civil engineering as binders for several applications such as asphalt concrete for road pavements but recently for roofing membranes. Due to this nature the two components tends to separate and this phenomenon can be enhanced with inappropriate design and mixing This is the reason behind the need of efficient dispersion and distribution during their manufacturing and it explains while real-time viscosity measurements could provide misleading results. This induced flow helps keeping the test sample less heterogeneous and this in turns allows recording more stable viscosity measurements
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