Micro-Mechanical Interpretation of Moisture Induced Damage in Asphalt

The motorway and trunk road system in England has a total length of over 12,000 km and an asset value of £60bn. Extrapolating this to the whole of the UK road network of some 400,000 km and allowing for the much lower value per km of non-motorway/trunk roads gives a total highway asset worth some £600bn. Maintaining and rehabilitating this asset, while at the same time sustaining undisturbed traffic flows, has placed increased emphasis on the need for high-performance and increasingly more durable pavement materials. The majority of roads in the UK and throughout the world are constructed using asphalt mixtures with over 340 million tonnes being produced in Europe in 2007.

The most important factor influencing the durability of asphalt mixtures is the presence of water in the pavement structure and the detrimental effect that water has on the properties of the mixture. Moisture-induced damage is an extremely complicated mode of distress that leads to the loss of stiffness and structural strength of the asphalt and eventually to the costly failure of the road structure. An improved understanding of moisture-induced damage in asphalt and more moisture resistant materials could have a significant impact on road maintenance expenditure, particularly where rainfall is predicted to increase due to global warming.

In this project, for the first time, the micro-mechanical processes that result in moisture induced damage at meso- and macro-scale in asphaltic pavements, will be analysed in a comprehensive manner in which both cohesive and adhesive types of damage will be addressed and evaluated as a function of the physio-chemical characteristics of the components of the asphalt mix.

This project will involve the use of X-Ray CT to characterise the internal microstructure of the asphalt, the development of tools for the processing and conversion of these images into accurate 3D finite element meshes which will then be ised in a Finite Element simultion to investigate moisture damage in asphalt. A significant experimental programme will be required to determine the mechanical properties of the asphalt mixture components (and interfaces between the components) required by the FE analysis.

From the combined experimental and computational analyses it will become possible to reach unprecedented insight into the dominant parameters controlling moisture induced damage in asphaltic mixes. On the basis of the conclusions of the combined numerical-experimental studies, recommendations for practise shall be drafted focused on the improvement of the moisture resistance of typical asphalt mixtures and contributing thus to the sustainability of the UK road network.

The proposed work has strong potential to make a major impact in the understanding of the structure of particulate composites such as asphalt. This will apply to diverse applications and the highway construction market in particular.

By combining experimental and computer analyses, the work will provide an unprecedented insight into understanding moisture-induced damage of asphalt systems. This will facilitate new practice recommendations and innovation for the industry with a significant reduction in maintenance costs and greater sustainability. This will have a major impact on policy makers (at government and local level), industry (particularly material suppliers) and consultants.

Furthermore, the development of the approach to apply to particulate composite applications generally will open up the potential for many wider applications outside asphalt including aerospace (eg performance of composites), medical (eg bio-scaffolds) and food processing amongst others.

Impacts will be wide ranging as follows:

Broad economic impacts
Substantially reducing maintenance time and travel delays will have a major benefit to the economy in terms of cost reductions and time saved. An industry technological lead will enhance the competitiveness of the UK and our economic success in overseas markets. New highway material markets will create new jobs, both in the supplier industries (which may be different to the existing ones) and from new export markets for the UK economy.

Commercial sector and industry impacts
The pavement market is an enormous market with an estimated global demand for bitumen (for pavements alone) of 99.3 million tons in 2007. Whilst the projected growth for the next decades is not high, UK industry (such as binder and aggregate industries) and policy makers will most benefit by the development of innovative designs for new, moisture resistant, pavements with improved sustainability. Market opportunities are not just UK based but are worldwide as the innovation will provide an international technological lead. In other composite applications the underpinning knowledge can be similarly used to enhance competitiveness and the opening of new markets. Timescales for significant commercial impacts are likely to be in the 5-15 year timescale but substantial industry involvement is planned by the end of the project.

Impact on government and policy makers
Key government stakeholders, such as the Highways Agency, the Department for Transport and Local Authorities, will see significant potential impact from a substantial reduction of maintenance costs and travel times combined with the implementation of good sustainable practice. Interest could translate very quickly into active support for development in the highway and other markets market applications, either directly funded from industry or with TSB/EPSRC support.

Societal impacts
In the longer term impacts on society include a better quality of life from reduced travel times and a move to greater sustainability.

People impacts
The project will help train the multi-disciplinary staff necessary in industry when the technologies move over to a commercialisation phase.

Impact implementation plans
A range of pro-active measures will be implemented to ensure maximum impact including:

1. Industry and policy maker involvement throughout the programme
2. Dissemination activities, including workshops and seminars aimed at the construction market as well as potential broader applications
3. The development of an action plan to secure ongoing industry support and funding for promising areas
4. Monitoring the potential for new IP emerging from the work.
5. Use of Nottingham Asphalt Research Consortium (NARC) to promote the outputs of the work.