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Environmental balance, output and service life must be right
03. November 2011

The Swiss federal technical university EPFL in Lausanne (Switzerland) is undertaking intensive research into the asphalt mix of the future. Prof. André-Gilles Dumont and his team are searching for the crucial qualities of asphalt and developing visions for the roads we will build in the future.


Interview with asphalt expert Professor André-Gilles Dumont..

Ammann: The advantages of low-temperature asphalt are well-known, as is the principle of temperature reduction. Why are we seeing a variety of research projects concentrating on this forward-looking technology at this precise moment in time?

Professor André-Gilles Dumont: Professor André-Gilles Dumont: Low-temperature technologies were not priority issues in the past as our society had cheap energy at its disposal. Neither were CO2 emissions of particular interest. Today, we are facing new challenges, and low-temperature asphalts can provide an important contribution towards environmental protection. Environmental balance, output and service life must be right. After all, lower temperatures and therefore lower vapours promise to make an interesting contribution towards improving health and safety at the workplace. Asphalt manufacturers and road builders have developed promising production processes, to which a scientific approach will add substance.

You developed the basics for the Swiss research project “Low-Temperature Asphalt”. What aspects are the primary focus of current research?

Dumont: We have to produce asphalts at lower temperatures whose mechanical properties are at least equal to those of hot mix aggregates. One sub-project is looking specifically at the effects lower production temperatures have on asphalt plants. The project is investigating the retrofit equipment required for specific processes. A further project is assessing and evaluating the energy and environmental balance during production to estimate the benefits. The gain in service life is estimated on the basis of asphalt ageing. A global evaluation model will be made available to authorities and contractors; they will then be able to select the production process that is the most suitable for their particular purpose.


Where do you see the technical challenges and potential obstacles of the future?

Dumont: We are optimistic with regard to the development of these techniques. However, they still require further optimisation before they can represent an acceptable alternative to conventional methods. The risk lies clearly in the abundance of existing methods. There was a similar situation many years ago with the advance of polymer bitumen. At the time it was possible to test the performance of different techniques under real life conditions. This enabled the clear rejection of three unsuitable products.


What do you say to critics who doubt the quality and durability of low-temperature asphalt in comparison to conventional products?

Dumont: Experience to date does not yet allow us to guarantee good performance in the long term. It is therefore important to look very closely at new technologies. However, one could also extend the debate to include conventional hot aggregate mix, as it unfortunately often has an inadequate lifetime! 


How can your research department influence authorities and contractors to promote the break-through of low-temperature asphalt? ?

Dumont: Our contribution has to provide answers to the questions you are posing: Is durability equal to or better than that of conventional materials? Is the energy and environmental balance as promising as has been described? Authorities should integrate low-temperature asphalts in their calls for tender on the basis of the answers we provide. It must also be mentioned that a standard describing the family of low-temperature asphalts should be drawn up as soon as possible. The existence of a standard – even though it may not contain limit values – would boost the product’s profile and enhance its credibility. That would be a sales argument in negotiations with awarding authorities.


Does the same apply to hot mix aggregate with reclaimed asphalt?

Dumont: Knowledge of reclaimed asphalt was more than patchy at the time the first Swiss standards on recycled materials were drawn up. It was therefore decided that these mixes must have the same properties as new asphalts. This is not the case where high levels of reclaimed asphalt are used. The current level of knowledge seems to indicate a need for materials to be classified. We should promote a high ratio of reclaimed asphalt for the base layers and a low ratio for the top surfaces that are subject to the most wear and tear.
Using large quantities of reclaimed asphalt is a different topic to low-temperature asphalts: We will soon be faced with a mountain of asphalt chunks that we will have to recycle, sooner or later. We have no choice but to improve aggregate mixes with a proportion of reclaimed asphalt, and we also have to be willing to recycle our layers more than once. Let’s not forget that the largest – albeit aged – current source of bitumen lies in the roads themselves.


Ammann is one of the world’s pioneering implementers of ecological goals with regard to a more ecological road infrastructure and actively participates in associated projects. What contribution can university-based research make towards the goal of “green” roads?

Dumont: On the one hand we improve existing methods, as is already the case with low-temperature asphalts and reclaimed asphalt. On the other hand we are also willing to push into the field of innovation. International research projects give birth to new ideas, for instance roads with a very long lifetime (perpetual roads) or roads that are permanently open to traffic (forever open roads) and are able to “repair themselves”, among other things.


How does the realignment in politics and society at large with regard to nuclear power and the search for alternative energy sources affect the future production of asphalt mixtures?

Dumont: Every catastrophe brings with it an incentive to improve things and make them safer. The looming energy crisis will boost the imagination. But before we start looking for alternative sources we first need to reduce our energy requirements in the immediate short term. For example: we could store the sand on a large surface area protected by a roof that utilises solar energy; additionally, the natural and constant air flow would aerate the sand. The energy used to evaporate water from the sand represents a significant part of the overall energy needed to produce a tonne of asphalt. Recovering the energy that escapes through the chimney stack could also contribute to drying and tempering aggregate.


There are many approaches towards building future roads without using oil and bitumen. What are the most promising from today’s point of view?Dumont: Bitumen is actually a by-product of the oil refining process. There are not many uses for it other than road construction, and so it will remain the base material for many years to come. Improving the properties of bitumen by means of chemical processes and additives is desirable and occurs on a global level. However, further progress is still required with regard to stability against permanent deformation and crack formation.