Many billions of EUROs are spent on road construction and maintenance each year, and road transport is the primary method of mobility for European people and goods. Transport constitutes about 10 % of the Gross National Product of the European Union and more than 80 % of the total transport of people and goods is provided by the road infrastructure. Investment in road construction and maintenance in Europe is therefore at a very high level and any improvements can have a significant effect on the overall cost benefit ratio.
In many countries premature break down of especially low volume asphalt roads is an accelerating problem. The origin is usually increasing traffic, higher axle loads and an increasing use of super single tires, but also distresses like rutting and cracking caused by heavy traffic under the influence of climate and thermal movements. Water in pavements and embankments plays a primarily role giving shorter service life of pavements and increasing the need of rehabilitation measures. A further problem that is becoming of more and more concern, is the possibility that the road is a source of contaminants that are having an undesirable effect on the hydrological environment. Two sources are possible: leaching of contaminants from the road construction materials and earthworks; contaminant in runoff from rainwater or snowmelt that flows over the top of the pavement and then soaks into the ground.
The resources for maintenance works are limited and often not sufficient to keep the roads in a proper condition. Much work therefore is needed to develop new cost effective maintenance methods. The activities within this COST Action face the problem of transport system efficiency, developing new knowledge about water movement in pavements and creating a more efficient methodology of road construction and rehabilitation.
The main objective of the Action is to increase the knowledge required for improving the highway performance and minimising the leaching of contaminants from roads and traffic.
Improvement of pavement performance will lead to less road closures, better use of the road network, longer service life and more effective transportation of goods and people.
The aim of the Action can further be divided into the following four secondary objectives:
- to identify water movement and moisture conditions in unbound pavement layers and subgrade for different types of road constructions in various climatic conditions,
- to investigate the relationship between the mechanical behaviour of materials/soils and their hydraulic conductivity and moisture condition,
- to implement finite element modelling based on laboratory analysis and field studies in order to simulate water movement and moisture conditions in road construction,
- to identify, investigate and control contaminants leaching from soils, natural aggregates and by-products.
Besides these technical objectives, the Action's results will contribute also to the environmental and road safety improvement.
The work has been organised in the following activities.
- State-of-the-art. Activities were carried out to do a Literature review on:
- observations and results obtained in laboratory experiments and field investigations;
- tests and use of models for prediction and design purposes.
The chief achievement is a nearly 400 page book published by Springer. A total of 13 chapters, plus annexes, have allowed the WATMOVE team to cover the topic matter in considerable detail so that students, researchers, practitioners and policy makers will all find sections of value to them. Summarising, the earlier chapters explain theory, the central chapters seek to apply that in more advanced ways and the final chapters describe the practical out-workings. Best practice is described both with respect to the latest modelling techniques and also with respect to in-situ application.
Early on in the study , the team identified, that heat flow is a very important driver of moisture content and moisture movement (for example, in connection with water movements causing frost heave).Therefore, particular and specific attention was given to this aspect. Also, regarding the movement of contaminants in the pavement construction, subgrade, embankments and adjacent earthworks, it was quickly realised that the water driving such seepage comes, largely, from run-off and will already be contaminated before it enters the pavement / embankment structure. The WATMOVE team therefore concluded that the book should also address contaminated water run-off, even though with the emphasis on percolating water in the substructure.
The main findings or achievements are the following.
- Conventional and modern test methods for determining water content are described, particularly those that are non-destructive and, therefore, may be used in-situ for control and monitoring purposes. Given the importance of suction, techniques for measuring this are also covered. There are a wide range of permeability tests available. Six are selected for detailed study and review and their appropriate application is described.
- Temperature highly affects pavement performance. High and low temperature not only affect viscosity of asphalt concrete but can also have very significant impact on moisture flow within pavements. At temperatures below 0°C the freezing of pavements drastically changes permeability and frost heave might occur forcing water to flow upwards to the freezing front.
- Heat transfer in soils involves convection, radiation, vapour diffusion and conduction. For pavements, conduction is the most important factor. During warm and sunny summer days though, it has been determined that natural convection should not be neglected.
- Frost susceptible soils always experience frost heave and
The study team has produced a book with an original concept. In fact, it brings together engineering theory, geological constraints, and best-practice into a book that covers scientific aspects, engineering principles and design solutions. Nonetheless, there is much more to be discovered and written. The subject concerning the movement of water in road layers and in the adjacent earthworks is far more complex and extensive than any member of the WATMOVE study team realised. Despite having produced a substantial book, it seems that, in many respects, the task of advancing the topic of sub-surface drainage is hardly started. Like many other subjects, once you begin to investigate them, you find that there are many aspects that are little understood and that no-one has ever tried to answer some of these questions. The book produced by WATMOVE has identified many areas that are, as yet, unresearched.