Experimental investigation and mechanism analysis of novel multi-self-healing behaviors of bitumen using microcapsules containing rejuvenator

• The multi-self-healing ability of microcapsule/bitumen composite was found.
• This ability connects with the interface energy of microcrack.
• Microcapsules can break at various periods.
• This ability is a continuous adjustment of microstructure of bitumen.

The aging problem of bitumen leads to pavement failure after years of usage. To improve its self-healing ability, it has been found that microencapsulated rejuvenator within bitumen may be an alternative approach. The aim of this paper is to investigate a novel multi-self-healing behavior of bitumen using microcapsules containing rejuvenator with different shell thickness and size distribution. The microcapsule sample was composed of three types of microcapsules with different mean size and shell thickness values. A modified beam on elastic foundation (BOEF) method was applied to investigate the mechanical properties of bitumen/microcapsule materials. The results show that these microcapsules were broken by microcracks under different conditions with a good normal distribution. The remaining microcapsules near the microcrack had the ability to leak rejuvenator later when another microcrack generated with even high crack tip strain. After loading–unloading cycles, the multi-self-healing ability of microcapsule/bitumen composite softened through of rejuvenator diffusion into bitumen. Properties of virgin and rejuvenated bitumen also confirmed that the aged bitumen had a multi-recovery ability due to the microcapsules containing rejuvenator. Both models of mechanical healing and physic–chemical healing were applied to analyze the mechanism of the multi-self-healing process. With a constant change and adjustment of microstructure, viscosity and thixotropy of bitumen, it possesses a healing ability numerous times over.

Load–strain curves of BOEF test under (a) 0 °C and (b) 25 °C for bitumen samples containing 2.0 wt.% microcapsule; self-healing cycles: ➀ first time, ➁ second time, ➂ third time, ➃ aged bitumen, and, ⑤ fourth time.Figure optionsDownload as PowerPoint slide