Understanding the final surface state of self-healing microcapsules containing rejuvenator in bituminous binder of asphalt

Self-healing microcapsules containing rejuvenator now is an environmental-friendly and energy saving commercial product for long-life asphalt pavement successfully applied in China. The results of basic research and practical application are very excellent, which makes it as an ideal way to extend the service life of the asphalt pavement. However, little knowledge is reported about the final state of broken microcapsules still existing in bitumen binder after a self-healing process, which causes users? doubts and concerns. The purpose of this work was to observe and determine the final state of microcapsules in bituminous binder of asphalt after completing a whole self-healing process. Scanning electron microscope (SEM) morphology showed that that microcapsules were dispersed in bituminous binders homogeneously. At the same time, transmission electron microscope (TEM) result indicated that the mixture of rejuvenator and bitumen was back-filled with empty microcapsules. FTIR-ART result also confirmed that the broken microcapsules were not empty holes in bitumen, but solid particles full of mixture substances of bitumen and rejuvenator. Broken shells in bitumen binder kept a stable state without particle aggregation. FT-IR analysis also proved bituminous molecules had moved into the broken rejuvenator under the diffusion power of concentration difference. Mechanical analysis also showed that broken shells in bitumen did not damage the original property of bitumen because the shell was full of substances. All the above results show that the final microcapsules are not holes, which do not destroy the mechanical property of bitumen binder of asphalt.