Rheological Characterization and Performance Assessment of Asphalt Materials Containing Bio - Based Binders: Contribution to RILEM TC 323 - APD

The increasing need to reduce the environmental impact of road infrastructure and the dependence on petroleum-derived materials has encouraged the development of alternative binders obtained partly or entirely from renewable resources. In this context, bio-binders represent a promising option for reducing the use of conventional asphalt binders in asphalt pavements. However, their rheological behavior, response to aging, and performance characteristics may differ significantly from those of conventional asphalt binders and therefore require appropriate experimental characterization. This thesis investigates the potential of bio-binders as alternatives to conventional petroleum-based asphalt binders through the laboratory characterization and comparison of two conventional asphalt binders (named AB1 and AB2) and two bio-binders (named BB1 and BB2). The experimental study, developed within the framework of RILEM TC 323-APD TG2, combines DSR Amplitude Sweep and Frequency Sweep tests performed under unaged, RTFOT-aged, and extended-RTFOT-aged conditions. The analysis considers the Linear Viscoelastic Region (LVER), complex shear modulus, phase angle, damping factor, crossover frequency, and master-curve characteristics, together with rheological modeling. MSCR tests are additionally used to investigate permanent deformation and elastic recovery at high temperatures, while LAS tests and VECD analysis are applied to evaluate fatigue behavior. The experimental results reveal substantial differences among the materials investigated and, in particular, between the two bio-binders. BB1 exhibits comparatively low sensitivity to aging and a distinctive viscoelastic response characterized by multiple transitions between viscous and elastic dominated behavior. Its most significant advantage is observed in the MSCR tests, where it shows very low non-recoverable deformation and pronounced elastic recovery, indicating excellent resistance to permanent deformation under the investigated conditions. However, its LAS response indicates comparatively limited fatigue resistance. BB2 shows a substantially different behavior, with greater aging-induced stiffening and higher susceptibility to permanent deformation, but a more favorable fatigue response than BB1. A relative performance assessment combining aging resistance, rheological behavior, rutting resistance, and fatigue resistance further highlights trade-offs among the different performance characteristics. The results demonstrate that bio-binders cannot be considered a homogeneous material class and that their behavior strongly depends on their specific formulation. Overall, the study confirms that conventional rheological procedures can provide an effective basis for characterizing and comparing bio-binders. However, non-conventional responses may require the combined interpretation of several rheological indicators. The suitability of bio-binders for pavement applications should therefore be assessed through a balanced evaluation of their aging stability, viscoelastic behavior, resistance to permanent deformation and fatigue performance, rather than solely on the basis of their bio-based origin.