Bitumen aging occurs through volatilization, oxidation and supramolecular assembly variations involving drastic changes in the structure of the material. Due to the ageing process of bitumen and its corresponding increase in viscosity, the stiffness of asphalt pavement is increased during its lifetime. Chemically, the relative content between asphaltenes and maltenes in the bitumen shifts towards a lower maltene fraction. Therefore, addition of high amounts of Reclaimed Asphalt Pavement (RAP) in asphalt mixtures may negatively affect the quality and performance of the final mix design. Rejuvenating agents can assist in this process by decreasing the aged bitumen’s viscosity and restoring its original properties. An efficient rejuvenating agent favors there organization of the colloidal structure of the oxidized bitumen, thus recreating a supramolecular structure similar to fresh bitumen. Then, novel experimental approaches are needed to evaluate the efficiency of rejuvenators as well as the effect such additives have on aged bitumen properties. To achieve the aforementioned purpose, two advanced experimental approaches able to provide detailed information on bitumen microstructure are examined here. The essential concepts underlying the scattering and NMR techniques will be reviewed and the results of some recent applications of these methods in the evaluation of the effectiveness of the RAP rejuvenation will be synthetically illustrated.
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