Rheological and structural properties at high and low temperature of bitumen for warm recycling technology

The use of recycled bitumen (such as the Recycled Asphalt Pavement, RAP) in production of new pavements is becoming an important issue, owing to the potential economic and environmental benefits derivable from the replacement of virgin materials with recycled ones. Nevertheless, the properties of RAP negatively affect the final behavior of pavement, reducing, therefore, its practical use. With the aim of modifying RAP behavior, rejuvenating additives are often used; anyway, their effects have to be carefully studied, according to the properties of both RAP and virgin bitumen. In this work, simulated aged bitumens were used to test the effects of two rejuvenating agents; rheological fundamental tests in steady and dynamic condition were carried out in a wide range of temperature using both shear and extensional kinematic conditions with the aim of investigating material behavior and additive effects both at high and low temperature. Moreover, the bitumen microstructure was investigated with Nuclear Magnetic Resonance (NMR) to better understand the change in material behavior. The rheological characterization has shown itself able to evidence the changes caused by simulated long- and short-term aging. Moreover, the positive effects of additives were highlighted at both high and low temperature and the rheological results were confirmed by NMR characterization showing that the most promising agent is able to restore a structure, based on asphaltene and maltene phases, very similar to those of the short-term aged system and virgin material.