Are we correctly measuring the rotational viscosity of heterogeneous bituminous binders?

Abstract

Modified bituminous binders allow asphalt technologists to design asphalt mixtures with superior performance. However, several recent studies highlighted that due to the complexity of these material, their characterisation can be challenging since common procedures used to characterise neat bitumen might not be adequate. For instance, during high temperature rotational viscosity testing of recycled tyre rubber modified binders (RTR-MB), a number of changes may occur to the sample leading to the here-defined sample stability which in turn provides misleading results. In this study the authors want to first provide a deeper understanding of this phenomenon by a numerical analysis using a bespoke Computational Fluid Dynamics (CFD) model to simulate the laboratory tests and use innovative visual aids to monitor the sample stability of heterogeneous bituminous binders during the rotational test. The numerical analysis was complemented by a laboratory campaign aiming at proving the occurring of sample stability during viscosity measurement of heterogeneous bituminous binders with a standard testing setup (SC-27). Furthermore, a dual helical ribbon (DHR) is here introduced as a solution to overcome the issue. Hence, laboratory tests were undertaken also with DHR and differences in viscosity measurements of neat bitumen, SBS-MB and RTR-MB were recorded. Results of this combined numerical and empirical approach proved that the standard setup for rotational viscosity measurements seems not be adequate for RTR-MB and depending on the level of modification and test temperatures, might not be best suited for SBS-MB either. The DHR seems to solve the issue and authors strongly recommend the adoption of this testing geometry to obtain more realistic high-temperature viscosity measurement of heterogeneous bituminous binders.

Keywords:

• sample stability
• dual helical ribbon
• modified bitumen
• CFD
• recycled tyre rubber
• rheology

Acknowledgements

The authors confirm contribution to the paper as follows: study conception and design: Davide Lo Presti, Gaspare Giancontieri, Data collection: Gaspare Giancontieri; Davide Lo Presti Numerical simulations: Gaspare Giancontieri; David Hargreaves Analysis and interpretation of results: Gaspare Giancontieri, David Hargreaves, Davide Lo Presti; Draft manuscript preparation: Gaspare Giancontieri, Davide Lo Presti. All authors reviewed the results and approved the final version of the manuscript.

Additional information

Funding

This investigation was initially supported by the Engineering and Physical Sciences Research Council (EPSRC) and it is now further developed within the SMARTI ETN project which has received funding from the European Union’s Horizon 2020 Programme under the Marie Curie-Skłodowska actions for research, technological development and demonstration, under grant number 721493 (http://smartietn.eu); Italian Ministry of University and Research [grant number MIUR dm n.372 08/05/18].