Enhanced Self-Healing Process of Sustainable Asphalt Materials Containing Microcapsules

Abstract

Asphalt is a typical self-healing material, but the healing process is rather inefficient. Therefore, melamine–urea–formaldehyde (MUF) microcapsules containing rejuvenator were fabricated to enhance the self-healing ability of asphalt. Optical and scanning electronic microscopy (SEM) morphologies showed that the prepared microcapsules were intact, and the outer surface of the microcapsule was rough, with both observations were beneficial for the interaction between asphalt and microcapsules. Microcapsules were mixed with asphalt by a proportion of 3 wt %, and almost all the microcapsules were kept intact even when experiencing 160 °C high temperature and mechanical agitation. It is noted that microcapsules were distributed homogeneously, which were highly likely to release rejuvenator after meeting with microcracks. A ductility self-healing test, along with fluorescence microscopy observations, was conducted to demonstrate how MUF microcapsules performed in asphalt. The test found that microcapsules were broken by the fracture energy at the tip of the crack, and thus a rejuvenator channel among microcapsules and cracks was formed to let the rejuvenator capillary-flow into the crack before the closure of microcracks. The DSR (dynamic shear rheometer) fatigue–healing–fatigue test and direct tensile test were further carried out to evaluate the healing efficiency of asphalt binder containing different contents of microcapsules.