Aging sensitivity of recycled binder blends based on assessment of rheological, chemical, and nano-mechanical properties

Economic and sustainability factors drive the increased use of reclaimed asphalt pavement (RAP) in road construction. Recycling agents, or rejuvenators, enhance the rheological properties of aged RAP binders, thereby improving asphalt pavement performance. However, a comprehensive understanding of the impact of recycling agents on binder properties and aging characteristics remains critical. This study investigates these effects through an extensive characterisation of RAP binder blends, focusing on rheological, chemical, and nano-mechanical properties. Key findings reveal that higher RAP content correlates with elevated levels of carbonyl (C=O) and sulfoxide (S=O) bonds, indicating increased oxidative aging. The absorbance aging index (AAI), derived from the SAR-AD (Saturates, Aromatics, Resins, Asphaltene Determinator) test, effectively detected variations in chemical fractions due to laboratory aging and RAP content. Atomic Force Microscopy (AFM) further quantified changes in the DMT (Derjaguin, Muller, Toropov) modulus with increasing RAP proportions. The Aging Rate (AR) parameter was also used to evaluate the impact of RAP and recycling agents on aging. Recycling agents improved rheological properties and reduced polar associations within RAP binder blends but also heightened aging susceptibility. This research provides critical insights into the interplay between RAP, recycling agents, and aging, offering a foundation for optimising sustainable pavement solutions.