Chemo‑mechanical assessment of ageing and performance trade‑offs in bio‑based rejuvenators for RAP‑rich binders

Abstract This study investigates the ageing behavior and performance trade‑offs of three bio‑based rejuvenators (namely, Anova, Sylvaroad, and Tall‑Oil Pitch (TOP)) in a 30% RAP binder system using a chemo‑mechanical framework combining Linear Amplitude Sweep (LAS), Multiple Stress Creep Recovery (MSCR) and Fourier Transform Infrared (FTIR). All binders were evaluated after short‑term ageing and again after PAV to capture long‑term oxidative evolution. The results show that rejuvenator chemistry strongly influences not only initial softening but, more critically, the long‑term oxidative pathway that governs fatigue and rutting performance. Anova and Sylvaroad improved unaged fatigue resistance, but their long‑term behavior was highly dosage‑dependent: 5% dosages retained favorable fatigue performance after ageing, whereas 10–15% led to excessive softening, higher post-ageing $$J_{{{\text{nr}}}}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>J</mml:mi> <mml:mtext>nr</mml:mtext> </mml:msub> </mml:math> , and reduced durability. TOP exhibited the lowest carbonyl and sulfoxide development and delivered the most stable post‑ageing rutting performance, though its stiffness limited fatigue life compared with optimally dosed Anova and Sylvaroad. The findings highlight that ageing susceptibility, not initial softening alone, must guide rejuvenator selection. Moreover, the chemo‑mechanical approach adopted in this study offers a practical tool for more informed decision‑making in RAP‑rich pavement design.