Processing, rheology, and storage stability of recycled EVA/LDPE modified bitumen

The optimum processing conditions for the manufacture of polymer-modified bitumens (PMBs), as well as the rheological properties of the final polymer-bitumen blends, strongly depend on the characteristics of the mixing device used. The present work is focused on the comparison among the kinetics of the mixing process and the rheological properties and microstructural characteristics of PMBs manufactured in two different mixers. Thus, blends of 60/70 penetration grade bitumen and recycled EVA/LDPE were processed in both high and low-shear devices. Knowledge on the evolution of shear viscosity and microstructure with time, as well as on the mechanical properties of the final polymer-bitumen blends, was gained from rheological and modulated DSC tests, and optical microscopy. The results obtained demonstrate that processing in the high-shear device yields a significant decrease in the time needed for the polymer-bitumen blend to reach the final stage of the manufacturing process, as well as an important reduction in bitumen oxidation and enhanced properties in a wide range of in-service temperatures. However, polymer-bitumen blends manufactured in the high-shear device are not stable during its storage at high temperature.