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Healing Multiphysics of Asphalt Materials

Periodic Reporting for period 1 - HMAM (Healing Multiphysics of Asphalt Materials)

Reporting period: 2018-10-08 to 2020-10-07

Asphalt materials (AMs) are referred in this project to the bitumen-based construction materials including bitumen and asphalt mixtures such as mortar, mastic and concrete when mixed and compacted with mineral aggregates. Bitumen is an extremely complex compound material composed of thousands of different types of paraffinic, aromatic and naphthenic with varying saturations, polarities, function groups and heteroatoms. Complexity becomes serious for the AMs due to the inclusion of air voids, adhesion between bitumen and aggregates, and the microcrack growth in the mixture. A further layer of complexity is added by the healing nature of the AMs. It is observed that the AMs, when exposed to cracking damage caused by thermal, vehicle or other loadings, can heal the cracks and restore partially or fully their original set of properties depending on the loading rest period. The AMs’ healing leads to a recovery of the material’s physical, chemical and mechanical properties, which can defer the initiation and evolution of the material deteriorations and structural distresses and eventually result in an extension of the road service life. A road performance prediction without accurately modelling the healing process in the AMs will lead to a systematic error which could cause wrong decisions in material selections, road structural design or techno-economic analyses. Thus an increasing demand has been raised for a comprehensive understanding and accurate prediction of the AMs’ healing performance and the development of new materials and technologies for enhancing healing capacity and/or accelerating healing rate for AMs.

The objectives of this project included five acceptives: 1) training of the Fellow’s academic expertise, professional skills and inter-sectoral collaboration. 2) mechanism investigation of healing multiphysics of AMs. 3) modelling the circular dependences of healing multiphysics and computational performance prediction of AMs; 4) experimental development and evaluation of healing-capable AMs; 5) industrial application of healing evaluation framework and healing materials in new and recycled AMs. The project potential benefits were achieved by: 1) a better understanding of AMs’ healing mechanisms to accelerate the material suppliers’ innovation in developing highly healing-capable bitumen, asphalt and additives to be used in road infrastructures for service life extension; 2) an accurate performance prediction framework and evaluation protocol for healing-capable AMs to allow transport consultancy, construction contractors and highway agencies to optimize road design, construction and maintenance; 3) an implementation of healing modelling and materials in sustainable technologies, e.g. warm mix asphalt, reclaimed asphalt pavement, alterative renewable binders to enhance their field performance and ultimately reduce the greenhouse gas emissions and save natural resources like petroleum bitumen and mineral aggregates.
There are five work packages (WPs) undertaken through the project, which are elaborated as follows.

Month 1 - Month 24
WP1: Overall training-through-research. Extensive training activities were taken by the Fellow to enhance his expertise in multiphysics modelling and advanced material characterisation, in addition to project management, communication and networking skills developed through the project.
Main Outcome: A well-trained researcher with competitive academic knowledge and management skills.

Month 1 - Month 12
WP2: Investigation of multiphysics healing mechanisms of AMs. The Fellow focused on the circular dependent multiphysics for the healing mechanisms of an asphalt mixture. The models for interrelated multiphysics healing mechanism contain: 1) environmental physics including temperature profile dominated by oxygen distributions and oxidative aging kinetics; 2) chemical models for healing cracked surface by molecular interdiffusion and healing kinetics; 3) mechanical response model including material physical properties and mechanics-based constitutive modelling; and 4) microstructural morphology including models for asphalt film coating thickness, and in-film cracks.
Main Outcome: Two papers were published on academic journals. Two posts were presented at TRB Conference. Two papers were under review now.

Month 4 - Month 15
WP3: Development and validation of multiphysics healing models for AMs. The Fellow utilised the Comsol to convert the models for different physics developed in WP2 into weak-form partial differential equations and developed an asphalt pavement model considering healing. The model was validated using the extensive data from the literature.
Main Outcomes: A paper was prepared for submission.

Month 7 - Month 21
WP4: Experimental characterisation and healing evaluation protocol. The Fellow proposed a healing characterisation method based on crack length, and a healing prediction method to evaluate the developed healing agents. The Fellow found that low-density polyethylene and bio-oil pyrolysed from the organic fraction of municipal solid waste can promote the healing performance of the bitumen and asphalt.
Main Outcomes: Four paper were published on academic journals. A lecture is going to be presented at RILEM Conference.

Month 6 - Month 24
WP5: Industry applications and feedbacks.
The Fellow focused on implementing the multiphysics healing modelling framework on the industry AMs. Research network was induced through the industry placement in the industry partner institutions.
Main Outcomes: Organised three seminars and two workshops at the different organisations.
Overview: Through this project, the Fellow gained competitive academic knowledge and management skills, published six journal papers, and organised three seminars and two workshops to disseminate the research findings. In addition, there are two academic papers are under review, and one paper is prepared for submission.
Expected Results
The project led to several publishable scientific results (e.g. journal articles and conference proceedings), and applicable industry practices (e.g. performance framework and healing effectiveness evaluation protocol).

Research Impact on the Fellow
The research in this project helped the Fellow to reach his mid-term professional goal of attaining a leading and independent position in Academia. The training performed in this project extended the Fellow’s expertise from mechanics and experimentation to chemistry, and material science coupled with valuable professional skills such as project management, collaboration and communication.

Research Impact on the Whole Society
The results of the project were disseminated and published to the most extent via multiple communication platforms such as printed publications, conference presentations and so on, targeting a variety of potential users and partners including material companies, infrastructural designers, and researchers throughout Europe and the world.

Research Impact on the Local Community
The main host organised a series of outreach activities to encourage a great interest in science among university, school students and general public. The Fellow attended the host’s initiative of multimedia releases for publication on the University websites and Personal Research Website for public access. During the industry placement, the Fellow brought innovative ideas to the industry companies through workshops and seminars for collaboration.
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