A new study by a researcher working for Danish consultant Cowi has developed a technique for designing asphalt mixes that can help reduce CO₂ emissions from vehicles.

​A reduction of the pavement’s rolling resistance can reduce emissions as less fuel is needed to get the wheels moving. A recent PhD project has provided a new tool for optimising the asphalt mixture.

A quarter of the energy consumption in Denmark is related to road transportation; and a third of that energy is actually used to overcome the rolling resistance. Both money and CO₂ emissions can be saved by reducing the rolling resistance of the pavement, said Cowi.

The trick is to use smaller stones in the asphalt mixture, but without undermining the performance of the pavement. Huan Feng, pavement specialist at Cowi, gives part of the answer in his recent PhD project ”Modelling of asphalt mixture – A discrete element method (DEM) to study the viscoelastic behaviour of asphalt mixture.”

”The project focuses on establishing a scientific background for novel pavement types and asset management solutions that minimise the rolling resistance for cars and trucks, and eventually attains the goal of reducing CO₂ emission from the transportation sector,” he said.

The mathematical model he developed saves time compared to lab tests and has already been applied to a project by Vejdirektoratet, the Danish road authority. The results indicate that the fuel consumption can be reduced by 3-5 percent without undermining the road grip.

However, it will take further studies to determine fully on the viscoelastic behavior of the asphalt when changing the mix design, he pointed out. “A road consist of many layers and we have only focused on the top 3-4 centimetres, which is the strongest and most expensive part and it is the top layer that decides how it feels to drive on the road. But when you change the mixture in the top layer it also has an impact on the lower layers, and this impact needs to be investigated as well before any final conclusions can be made” he said.

Thomas Mejer, market director at Cowi Highways and Airports International, considers the new findings to be an important first step towards a more sustainable transportation sector. “There is a great need for new infrastructure not least in Africa where we have several projects,” he said. “We are aiming at the most sustainable solutions and reducing CO₂ emissions while maintaining high performance and durability are key components to achieve that. In other words, the mathematical modeling holds a great potential for optimizing the sustainability of new roads.”