Abstract
This paper presents the synthesis and characterisation of biopolymeric capsules for asphalt self-healing. A sodium alginate biopolymer extracted from the cell wall of brown algae was used as the encapsulating material to contain Waste Cooking Oil (WCO) as a potential encapsulated rejuvenating agent for aged bitumen. Polynuclear capsules were synthesised by ionic gelation. The size, surface aspect and internal structure of the WCO capsules were evaluated using Optical and Scanning Electron Microscopy. The physical-chemical properties and thermal stability of the WCO capsules and their components were also evaluated. Moreover, the diffusion process and self-healing capability of the released WCO on cracked bitumen test samples were determined by image analysis through fluorescence microscopy. The main results of this study showed that the WCO capsules presented a suitable morphology to be mixed in asphalt mixtures. WCO capsules and their components presented mechanical and thermal stability and physical-chemical properties which suggest their feasibility for self-healing applications. It was proven that the encapsulated WCO can diffuse in the aged bitumen, reducing its viscosity and promoting the self-healing of microcracks.
Highlights
Self-healing by the action of encapsulated rejuvenating agents has been considered as a revolutionary technology for autonomous crack-healing of asphalt materials [1]
Statistical size analysis of 100 individual Waste Cooking Oil (WCO) capsules registered an average size from the alginate solution as proposed by McClements [22], and recently used by Concha of 1.649 mm (SD = 0.145 mm), with a spherical and uniform geometry (Figure 3a)
Statistical size analysis of 100 individual WCO capsules registered an average size of 1.649 mm (SD = 0.145 mm), with a spherical and uniform geometry (Figure 3a)
Summary
Self-healing by the action of encapsulated rejuvenating agents has been considered as a revolutionary technology for autonomous crack-healing of asphalt materials [1]. Cracking of asphalt materials mainly occurs due to the oxidation of the hydrocarbons in the bitumen by the action of operation and environmental agents [2]. When damage occurs in an asphalt material containing embedded encapsulated rejuvenators, cracks appear and eventually propagate until they reach and break or deform a capsule, releasing the contained rejuvenating agent. When the rejuvenating agent is released from inside the capsule (i.e., activation of polynuclear or core-shell capsules by deformation or break), the molecules of the released rejuvenator diffuse into the asphalt matrix and soften the aged bitumen, allowing the rejuvenated bitumen to flow through the open microcracks, facilitating the crack self-healing process [4].
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