The impact of chaotic advection on the microstructure of polymer-modified bitumen

Owing to the high viscosity of the materials involved, mixing is often a critical step when processing polymer-modified bitumen (PMB), directly influencing the microstructure and the stability of final products. We provide experimental evidence suggesting that laminar chaotic advection may prove a valuable strategy for obtaining a homogeneous and finely interdispersed polymer-bitumen mixture in affordable time. As a case study, we investigate the mixing performance of a lab-scale flat-bottomed cylindrical vessel stirred by a radial impeller, either located symmetrically or eccentrically with respect to the vessel axis. The same geometries with a flat-disk impeller are also considered for comparison. The Mix- Norm is used in combination with image analysis as an objective measure of mixing performance. Results of mixing performance are independently validated by rheological tests. The experiments pinpoint kinematic chaos as the fundamental transport mechanism enhancing both the dispersion process and the microstructural quality of the resulting PMBs mixture.