Surfacing roads with a new asphalt mixture helps save a lot of fuel and consequently reduce the emissions of CO2. TNO and Strukton Civiel have succeeded in developing this innovative product. They did so on behalf of, and in close collaboration with, the province of Zuid-Holland. The aim is to cover as much of the 550-kilometre network of provincial roads with this layer of material as possible.
“Energy-saving innovations for the road network are a key part of the province’s energy agenda,” explains Mirza Milosevic of the ‘Dienst Beheer Infrastructuur’ (infrastructure management department) of the province of Zuid-Holland. One of the ideas was to use smarter materials during large-scale maintenance work that would reduce the rolling resistance of car tyres. Cars that move more smoothly over the road surface consume less fuel, which helps reduce CO2 emissions.
Reducing rolling resistance
The province asked TNO to investigate the technical feasibility. Strukton Civiel, meanwhile, was asked to develop a new method for measuring rolling resistance and to acquire knowledge of different types of asphalt mixtures and their effect on rolling resistance. “That request was exactly in keeping with our own initiatives for promoting sustainability in road construction,” explains scientific researcher Dr Frank Bijleveld of Strukton Civiel (the former Ooms Civiel). “We carry out advanced laboratory tests in order to be better able to predict performance in practice. We have been working in partnership with TNO for many years now, on innovations like SolaRoad, the road that converts sunlight into electricity.”
“It means a substantial benefit for the environment, but for more or less the same building costs without making any concessions to safety or quality”
Composition of asphalt
Senior road construction scientist Dr Steven Mookhoek of TNO says, “We have worked together from the very start. Every step we have taken has followed joint consultations, and always with the same goal in mind. Optimizing contact between tyres and road surface makes a really big difference, in terms of the quantities of CO2 emitted. That is because the composition of asphalt has a significant effect on rolling resistance, hence fuel consumption. We started off by conducting a study of the relevant literature. There are many readings available from Scandinavia in particular. We wanted to know exactly what properties the roads have that they had measured and how they perform in terms of rolling resistance.
Testing the mixtures
From the tests, it appeared that the texture of the asphalt is far and away the most decisive factor in terms of rolling resistance. The coarser the road surface, the more tyres become deformed and therefore the more energy they use. “At Strukton Civiel, we had a rough idea of the size of effect associated with each property, but TNO has now pinned this down very precisely,” says Bijleveld. “With that information, we were able to get to work in our laboratory in a much more targeted way. In the past, we have developed a device with the Delft University of Technology for testing the skid resistance and loss of stones of asphalt raveling. It is a kind of record player on which you allow tyres to ‘drive’ over discs with a range of surfaces. It serves to simulate the traffic that runs over road surfaces every day. Building roads using all kinds of mixtures in order to test them is hardly a realistic proposition. It would take a lot of time and money. Now, we were able to compare the results of our laboratory tests with real-world measurements taken in other countries. It meant the results were reliable.” The ideal composition developed by Strukton Civiel was eventually tested on a limited accessed road several hundred metres in length in the town of Hoorn. The intention was to validate the laboratory values in practice. For that, Strukton Civiel and TNO called upon the assistance of the Gdańsk University of Technology in Poland, which has a special measuring vehicle for testing rolling resistance on asphalt roads.
“The rolling resistance is ten percent lower than with the standard surface used extensively in Zuid-Holland, which amounts to fuel savings of two percent”
Less fuel, less CO2, less noise
The results exceeded the province’s expectations. It appears that the new surface sharply reduced the resistance between tyres and roads and therefore cuts fuel consumption. The rolling resistance was ten percent lower than with the standard surface used extensively in Zuid-Holland, which amounts to fuel savings of two percent. “That may not seem very much, but for the province, these figures are fantastic. For every kilometre of road, with an average traffic intensity of 15,000 vehicles per day, it represents a saving of at least 10,000 litres of fuel a year. And you can multiply that by 550 kilometres of provincial roads. The emissions of CO2 are lower too - also by two percent. To put it into perspective, for each kilometre the difference is the equivalent of the emissions of five households are year,” explains Milosevic. Bijleveld: “But that’s not all. In Hoorn, we and TNO tested several characteristics. For example, the new surface appears to have thirty percent more better skid resistance, and is therefore safer, and also produces 5.5 dB(A) less noise. The expected lifespan is similar.”
“It is a great innovation that has enabled us to show that altering the asphalt can lead to major energy savings”
As far as the province was concerned, the environmental benefits were the most important aim, but the fact that costs are the same without any concessions being made to other functional properties such as safety or quality have come as a pleasant surprise to Milosevic. “And thanks to the detailed readings, I can specify to companies, during tendering procedures, what we expect from them in terms of energy savings, noise reductions, and safety. They will have to show evidence that they can meet these requirements. TNO helps us to articulate accurately what the technical specifications are so that contractors know what they are faced with.”