On the Assessment and Optimisation of the Processing Conditions of Tyre-Rubber Modified Bitumen

The current study aims at understanding the effect of the variables associated with manufacturing rubberised bitumens in order to develop rubberised bitumen with superior mechanical properties and identify optimised processing conditions for its production. The experimental work covered extensive laboratory testing of several rubberised bitumen blends. The rubberised bitumen was manufactured using four paving grade bitumens (180/240, 160/220, 70/100, 80/100), three tyre rubber types (mechanical ground, waterjet powder, ambient ground powder), and various processing conditions (shear levels, temperatures, processing times). Characterisation of the manufactured blends included rotational viscosity, softening point, and Fraass breaking point. The findings derived from the experimental programme relate to optimised processing conditions for the tyre rubber blends. Overall, this research showed that simple, relatively quick, and inexpensive test methods can be used for comprehensive characterisation of recycled tyre rubber blends. Similarly, it was found that the properties of rubberised bitumen were highly factor dependent, including effects of the: source of base bitumen (physicochemical properties), source of rubber particles, and processing conditions (shear mixing, temperature, and time). The impact of rubber pre-treatment on the performance was found to be negligible for the studied combinations. Clear bitumen-specific effects were observed from the soft and hard bitumen types considered. Furthermore, temperature and shear processing conditions had the paramount effects on the level of bitumen modification. Optimised conditions for rubberised bitumen production suggested a range of temperature of 180–210 °C, up to 180 min for high shear, and up to 30 min for ultra-high shear.