Evaluating the multi-scale performance and mechanical behavior of reclaimed asphalt pavement (RAP) mixtures incorporating waste-derived oils and vacuum bottom rejuvenators

Maximizing the utilization of reclaimed asphalt pavement (RAP) while maintaining long-term fatigue durability is essential for sustainable pavement infrastructure. To address this challenge, this study aims to establish a multi-scale framework for evaluating and optimizing rejuvenator performance in high-RAP mixtures. Accordingly, the efficacy of three distinct rejuvenators—Waste Engine Oil (WEO), Lubricant Oil (LU), and Vacuum Bottom (VB)—was investigated in restoring the chemical and mechanical properties of bitumens and mixtures incorporating 30%, 45%, and 60% RAP. Using a viscosity-matching approach, rejuvenator dosages were optimized to target virgin PG64-22 bitumen rheology. SARA analysis showed that LU and VB restored colloidal balance by reducing asphaltenes from 27.0% to 17.5–18.1% and restoring aromatics to 44.3–45.2%, whereas WEO provided only partial chemical recovery. Linear Amplitude Sweep (LAS) testing revealed that LU and VB extended bitumen fatigue life by 21% and 29% at 2.5% and 5.0% shear strains, respectively. At the mixture scale, 4-point bending fatigue resistance improved by 76–85% at 500 µɛ and by 34–40% at severe 700 µɛ for 60% RAP mixtures with LU and VB. Furthermore, moisture durability was increased, with R60LU reaching a superior Tensile Strength Ratio (TSR = 90.7%) compared to the control (80.7%). These quantitative findings demonstrate that chemical rejuvenation via LU or VB provides 60% RAP mixtures with comparable or superior laboratory fatigue and moisture resistance relative to the virgin mixture.