Material-designed self-healing microcapsules for controlled release in asphalt-based composites

Asphalt pavements develop fatigue cracks during long-term service, while conventional rehab methods are inefficient and costly. Due to its excellent self-healing enhancement performance, microcapsule technology has become a research hotspot. However, current research lacks systematic investigation into the stability of microcapsules during construction and service phases, as well as the accuracy of their release mechanisms. This research aims to prepare self-healing microcapsules tailored for asphalt mixture. Accordingly, it systematically executed a full-process material optimization, structural regulation, and performance validation. Firstly, gel-permeation chromatography (GPC) was used to select the optimal rejuvenator as the core material. Meanwhile, the melamine-urea-formaldehyde (MUF) shell was chosen based on the asphalt mixture matrix's elastic-modulus matching criterion. Subsequently, microcapsules were synthesized via in-situ polymerization. By adjusting the core-shell ratio and particle size, microcapsules with controllable diameter (5–150 µm), adjustable shell thickness (200–500 nm), and compatible elastic modulus with asphalt were fabricated. Then, scanning electron microscope (SEM), differential scanning calorimetry (DSC), and nanoindentation test revealed that the microcapsules exhibit excellent thermal stability (decomposition temperature 240–280 °C) and mechanical compatibility with asphalt. Finally, rutting tests, pull-out tests, and fluorescence microscopy (FM) revealed that MUF microcapsules (particle size <25 µm) showed 60.23 % survival during construction (23.6 % higher than melamine formaldehyde microcapsules). The service-phase loss rate remained below 3 %, and the self-healing completion of asphalt cracks takes 15 min. This research achieves the tri-functional integration of “survivability, triggerability, and restorability” for microcapsules within asphalt mixtures. Providing a reliable technological pathway to enhance asphalt pavement life-cycle performance.