A multi-scale investigation of the fractional viscoelastic properties of rejuvenated recycled asphalt mixtures: experimental approach

This study investigates the viscoelastic properties of rejuvenated recycled asphalt mixtures containing 35%, 50%, and 65% RAP at the bitumen, asphalt mastic, and asphalt mixture scales using the 2S2P1D rheological model. Master curves of dynamic modulus and phase angle were constructed using time-temperature superposition, and Cole-Cole diagrams were employed to assess changes in viscoelastic behavior through variations in their shape, slope, and characteristic regions associated with elastic and viscous responses. The results show that aging significantly increases stiffness, viscosity, and relaxation time, while the incorporation of a triglyceride/fatty acid-based rejuvenator effectively restores the viscoelastic behavior of aged bitumen toward that of virgin bitumen. The rejuvenator induced a recovery of the glassy modulus, relaxation time, and 2S2P1D shape parameters across all investigated material scales, although the extent of recovery varied with the material scale. Scale-dependent variations in 2S2P1D parameters were observed from bitumen to asphalt mastic and asphalt mixture scales. Overall, the results provide a comprehensive multi-scale evaluation of rejuvenated recycled asphalt mixtures and support the effective use of rejuvenators in high-RAP asphalt mixtures. This work provides a systematic multi-scale quantification of rejuvenator effects using the 2S2P1D model, which can support the design of recycled asphalt mixtures.