Comprehensive review of aging phenomena in conventional and bio-based asphalt binders: Challenges and future directions

Aging plays a critical role in determining the durability and long-term performance of asphalt pavements, as it is influenced by both external factors (e.g., temperature, ultraviolet (UV) radiation, moisture, oxidative gases) and internal factors such as binder composition. Although laboratory simulations of aging are well established for conventional bituminous binders, limited attention has been paid to replicating and evaluating aging processes in bio-based binders. This review provides a comprehensive analysis of current laboratory techniques for simulating and assessing binder aging, with a focus on two key areas: aging simulation protocols and evaluation methodologies. The analysis shows that although several efforts have been made to incorporate external aging factors into lab simulations, significant challenges persist, especially in the case of bio-based binders, which are characterized by a high variability in composition and limited understanding of their aging behavior. Current evaluation approaches also exhibit limitations. Improvements are needed in the molecular-level analysis of oxidation (e.g., through more representative oxidation models in molecular dynamics simulations), in the separation and quantification of binder constituents, and in the application of advanced techniques such as fluorescence microscopy to better characterize polymer dispersion. To enhance the reliability of laboratory simulations, future research should aim to improve the correlation between laboratory and field aging, define robust aging indexes, and refine characterization methods. These advancements are particularly critical for bio-based binders, whose performance is highly sensitive to aging and for which standard test protocols are still underdeveloped. A deeper understanding of aging mechanisms in both polymer-modified and bio-based binders, along with improved analytical tools for assessing oxidative degradation and morphological changes, will be essential to support the development of sustainable, high-performance paving materials.