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Microencapsulated rejuvenator powder has been used to repair microcracks and improve self‐healing ability of aged bitumen. These microcapsules must retain their integrity in bitumen matrix with necessary special characters such as excellent mechanical properties, thermal stability, and compactability. Herein, novel self‐healing microcapsules containing bituminous rejuvenator with nano‐CaCO3/organic composite shells were developed by in situ polymerization using methanol‐modified melamine‐formaldehyde as organic shell material. The effect of nano‐CaCO3 particle contents on the mechanical properties, thermal stability, and compactability of microcapsules were examined utilizing nanoindentation, thermogravimetric analysis, and visible spectrophotometer. Nano‐CaCO3 particles had greatly enhanced the thermal stability and mechanical properties of the microcapsule because of the higher thermal resistance of nano‐inorganic/organic composite shells. These microcapsules could survive in melting bitumen without destruction. The release curves of microcapsules in ethyl alcohol, relationship between time and logarithmic residual weight of rejuvenator, showed that the nano‐CaCO3/organic composite shell structure led to a higher compactability of microcapsules. POLYM. COMPOS., 39:E1441–E1451, 2018. © 2017 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

SEM cross-section morphologies of hollow fibers in bitumen, (a) the interface morphology of several hollow fibers in bitumen, and (b) the enlarged interface morphology of hollow fibers in bitumen. • No debonding was found between the PVDF hollow fibers and the bitumen. • The content of hollow fibers affects the self-healing behaviors of bitumen. • The fiber orientation affects the self-healing efficiency. • The self-healing follows the time-temperature superposition principle. Smart microvascular self-healing bituminous composites are considered a promising approach to prolong pavement service life. The objective of this work was to investigate the microvascular self-healing capability of bituminous material by using hollow fibers with oily rejuvenator through a direct-tension mechanical experiment. The hollow fibers with oily rejuvenator were prepared using a wet-spinning approach by applying polyvinylidene fluoride material. The fixed-length hollow fibers with sealed ends were mixed in bitumen to form composite samples. Through a repetitive tensile method, the tension strength data were used to calculate the self-healing efficiency autonomously by considering crack closure and healing at various healing temperatures and times. The scanning-electron-microscope morphology showed that the polyvinylidene fluoride hollow fibers had a tight interfacial structure with bituminous material without debonding. X-ray computed tomography results indicated that the fibers were distributed homogeneously in bitumen. The fiber content and fiber orientation affected the self-healing capability of bituminous samples at 0 °C. To simplify the influence of the above two factors of the fibers, only one fiber was placed in bitumen samples parallel to the tension direction. With an increase in temperature from 0 to 30 °C, the self-healing capability of the bitumen samples increased dramatically. This phenomenon is attributed to the accelerated penetration speed of rejuvenator in the bitumen. An increase in time increased the self-healing capability of the bitumen samples. The rejuvenator may have sufficient time to leak from the hollow fibers and penetrate the bitumen. The results provide a guide to the microstructural design of the vascular fibers and the application of hollow fibers in self-healing asphalt pavement. [ABSTRACT FROM AUTHOR]

Graphical abstract SEM cross-section morphologies of hollow fibers/bitumen composites, (a) the original interface morphology of the bitumen sample, (b) the bitumen sample after one hundred thermal treatment cycles, one cycle including an increasing–decreasing temperature process in 1.5 h, every two cycles owing a time interval of 1.5 h, (c) an amplified interface morphology of a hollow fiber and bitumen after the thermal treatment. Highlights • The states of self-healing hollow fibers in bitumen were experimentally observed. • Hollow fibers survived in bitumen. • The break of hollow fibers was triggered by microcracks. • The outflow rejuvenator permeated through the micropores into aged bitumen. Abstract Hollow fiber containing rejuvenator is a promising smart material for vascular self-healing bituminous materials of pavement. The objective of this work was to experimentally observe the states of self-healing hollow fibers containing rejuvenator in pure bituminous material. Polyvinylidene fluoride (PVDF) hollow fibers containing oily rejuvenator were spun through single-wet-spinning method. The fixed-length hollow fibers with sealed ends were mixed in bitumen forming composite samples. The inter-surface and outer-surface microstructure of hollow fibers were observed by an environmental scan electron microscopy (ESEM). The micropores in fiber-shells were channels for rejuvenator to pass through. X-ray computed tomography (XCT) results indicated that these fibers distributed in bitumen with an integrality state. Three-dimensional reconstruction XCT (3D-XCT) images exhibited the details both of vertical and horizontal distribution of hollow fibers in bitumen. Thermogravimetic analysis (TGA) and a repeated thermal-cycle testament showed that the hollow fibers survived safely in bitumen. No debonding phenomenon was found between the fibers and bitumen. Oily rejuvenator released out of hollow fibers smoothly through the break point of hollow fiber/bitumen composite samples. The break images of hollow fibers in bitumen were also analyzed through 3D-XCT structures. At the same time, the movement tracks of oily rejuvenator out of hollow fibers were observed by a fluorescence microscopy. The rejuvenator permeated through the micropores on a hollow fiber into aged bitumen. These states mean that the self-healing can be triggered through the break points of hollow fibers as well as the self-rejuvenation when bitumen is aging. The above result is evidence that the hollow fibers containing rejuvenator will be a feasible approach to realize the self-healing and self-rejuvenating process of bitumen. [ABSTRACT FROM AUTHOR]

The aim of this work was to prepare and characterize a novel vascular self-nourishing and self-healing hollow fiber containing oily rejuvenator for aged bitumen. The hollow fibers containing oily rejuvenator were fabricated with micropores by a one-step wet-spinning method using polyvinylidene fluoride (PVDF) resin. Hollow fibers had been successfully prepared based on the test results of morphology, size and chemical structure. The hollow fibers had a good thermal stability with a decomposition temperature of 450 °C. The mechanical properties of fibers satisfied the requirements of use in bituminous materials. Because of the existence of micropores microstructure in fibers, the rejuvenator had the permeability out of fibers. The diffusion behaviors of rejuvenator were also measured by an attenuated total reflection flourier transformed infrared spectroscopy (FTIR-ATR) method. It was found that the diffusion coefficient greatly depended on the pore structure and temperature. A fitting model implied that the diffusion coefficient had a big deviation of Fick’s law and greatly influenced by the pore structure of hollow fibers. It is a guide to design and regulate the microstructure of hollow fibers with appropriate rejuvenator releasing behaviors. All above results implied that the existence of both self-nourishing and self-healing had been successfully proved in aged bitumen using hollow fibers containing oily rejuvenator. [ABSTRACT FROM AUTHOR]

The aging problem of bitumen leads to pavement failure after years of usage. Microcapsules containing rejuvenator is a promising chemical product applied to improve the self-healing ability of bitumen. The aim of this work was to fabricate and characterize the self-healing microcapsules containing bituminous rejuvenator with nano-inorganic/organic hybrid shells. The shell had a two-layer structure: the inside layer material was the cross-linked methanol modified melamine-formaldehyde (MMF) resin and the outside materials was composed of methanol modified MMF resin and nano-particles of calcium carbonate (nano-CaCO 3 ). The forming mechanism of the two-layer structure was described based on a twice-condensation process. Fourier transform infrared spectroscopy (FT-IR) and Energy Dispersive Spectroscopy (EDS) results confirmed the nano-inorganic/organic hybrid structure of shells. The ideal content of nano-CaCO 3 particles was optimized through the morphologies observation. The addition of nano-CaCO 3 particles did not greatly influence the mean size of microcapsules. On the contrary, the nano-CaCO 3 particles increased the shell thickness of microcapsules owing to the loosely composite structure of shells. Thermal stability tests showed that the microcapsules could survive in the bitumen with a temperature of 200 °C. Moreover, the microcapsules could resist a violent temperature change process without destruction attributing to the protection of nano-CaCO 3 particles. The nano-particles on microcapsules decreased the deformation possibility of shells tested by nanoindentation. [ABSTRACT FROM AUTHOR]