Physico-chemical characterization of bio-based additives for restoration of reclaimed asphalt binders

Recycling end-of-life asphalt is essential for sustainable pavement construction yet ageing-related chemical changes in asphalt binders increase viscosity and limit recyclability. Low-viscosity, biomass-derived additives are increasingly used to restore aged binder properties, but their chemical diversity and true bio-based content remain insufficiently understood. This study provides a detailed chemical categorization of 20 commercially available bio-additives and evaluates their suitability for asphalt recycling. Infrared spectroscopy enabled classification of the additives into six families (acids I and II, esters I and II, phenolics I and II) based on characteristic absorption patterns. Complementary one- and two-dimensional NMR analyses further distinguished structural features such as saturation levels, chain lengths, and aromatic/aliphatic composition. Radiocarbon (14C) analysis was applied to selected additives to verify their biogenic origin, revealing three groups: fully biogenic products, predominantly biogenic materials modified with fossil-derived components, and additives dominated by fossil carbon. This demonstrates the value of 14C measurements as a robust tool for certifying bio-based content. Several low-viscosity additives from the acid I, esters I/II, and phenolic I families were blended (5–10 %) with binders extracted from reclaimed asphalt pavement (RAP). Dynamic Shear Rheometry confirmed effective restoration of rheological properties across multiple combinations. Finally, FTIR- and NMR-based approaches for assessing oxidation state and quantifying additive content were evaluated, highlighting both their potential and method-specific limitations.Overall, this study delivers a practical chemical–rheological framework for classifying bio-additives, verifying their bio-based content, and providing tools for improved evaluation of aging state and bio-additive content, supporting the development of more sustainable asphalt materials.