Classification and selection of exhausted oils for rejuvenating bituminous blends

The use of rejuvenators (RJ) is critical to increasing the amount of recycled asphalt in new mixtures. However, their usage and classification have not achieved a consistent common practice. One of the properties that lacks a comprehensive investigation is their re-aging tendency. In this work, mineral oil from the automotive industry (MO), a waste domestic cooking vegetable oil (VO), and biodiesel (BD) produced from VO were tested as rejuvenators of a laboratory-aged unmodified binder. Infrared spectroscopy and thermogravimetric analysis were used to gather preliminary information on the single RJs. Then, their compatibility with the aged binder was tested at low and high temperature through contact angle and diffusion tests. Finally, their re-aging tendency was determined by using rheological parameters. The RJs showed adequate compatibility and diffusivity, being the VO slightly better than the others are. All the RJs provided a visible restoration of the initial binder properties. The main differences between the three oils are displayed during the second life cycle of the binder (simulated by aging the rejuvenated binders). In this case, the VO and MO do not provide any relevant concerns, while the BD tendency to evaporate slightly above 120 °C may represent a problem during the production and the paving of the mixture. VO and MO blends showed a good aging resistance and may provide a promising life cycle, with the VO being the recommended RJ.