Sustainable self-nourishing and self-healing bitumen enabled by pH-responsive microcapsules containing recycled waste soybean cooking oil

This study introduces a paradigm shift in asphalt technology by developing a sustainable bitumen material with autonomous self-nourishing and self-healing capabilities. The innovation centers on pH-responsive microcapsules, engineered with a chitosan/sodium alginate (CS/SA) shell to encapsulate waste soybean cooking oil (WSCO). Unlike conventional passive shells, this intelligent design leverages the local acidification from bitumen oxidative aging as an intrinsic trigger. The microcapsules, fabricated via coaxial electrospray (20–50 μm, 91.5 % encapsulation efficiency), demonstrated excellent thermal stability (up to 250 °C) and mechanical robustness. They exhibited a remarkable pH-triggered release: cumulative WSCO release reached 78.3 % at pH 4.0 over 96 h, compared to only 12.5 % at pH 7.0. In bitumen, this dual functionality was conclusively validated. The self-nourishing action significantly mitigated aging, with 5.0 wt% microcapsules reducing the complex modulus increase after aging to just 43 % versus 1142 % for neat bitumen. Simultaneously, the self-healing efficiency reached 68.4 % with 4.0 wt% microcapsules, maintaining 58.9 % after five healing cycles. This synergistic proactive and reactive system, which effectively upcycles waste oil, offers a transformative solution for drastically prolonging pavement service life and enhancing the sustainability of infrastructure materials.