Macro- and meso-scale experimental study of encapsulated rejuvenators for self-healing asphalt system

Self-healing asphalt concrete (AC) presents an opportunity to increase the sustainability of pavements by increasing their life cycle. The last decade of research has led to significant breakthroughs in the development and application of self-healing capsules for asphalt concrete. However, optimally tuning the use of these materials still has not been achieved, in part due to the multitude of mechanisms at play. Unlike prior single-scale studies, this study establishes a multiscale laboratory framework to evaluate nine rejuvenator capsule types at four levels, including capsule, binder, fine aggregate matrix (FAM), and asphalt concrete (AC), to systematically link capsule rupture and chemical diffusion behavior with mixture-level fatigue and rutting responses. This cross-scale validation clarifies inconsistencies in earlier studies and provides a transferable pathway for capsule design from laboratory to future pavement application. With nine capsule designs, the study examines key capsule design factors, including shell thickness, healing agent type, healing agent concentration, and capsule content in the mix. The findings suggest that capsule properties are strongly influenced by the chemical composition of the healing agent, alginate shell concentration, and the capsule shell. Capsules containing bio-oil contributed to a softer mixture and facilitated a higher diffusion rate. To optimize healing efficiency, capsules with varying shell thicknesses and rejuvenator types could be deployed to prevent premature release and maximize the use of healing agents. Additionally, capsules with a higher rejuvenator content proved more effective in addressing severe damage, while a higher overall capsule content was better suited for mitigating widely distributed minor damage. The findings underscore that excessive capsule dosage or high oil to water (ow) ratios may lead to permanent deformation, but optimized formulations with moderate capsule contents ( ≤ 3%) and low ow ratios ( ≤ 1) can minimize rutting potential. Finally, encapsulated healing agent technology demonstrated the benefits of recurrent use over many loading repetitions and healing cycles, compared to solely adding rejuvenators to mixtures. Although the findings are limited to controlled laboratory conditions, the developed framework provides mechanistic insights and design guidance that can inform future field studies and pavement applications.