On the road to bio-asphalt

Manufacturers use bitumen as a binding agent in asphalt. Bitumen is a product derived from crude oil. There are several disadvantages to this material: there is a shortage of bitumen, and its quality varies tremendously.

Sustainable alternative

Thus, Wageningen researchers started looking for a sustainable alternative to bitumen. They wanted an alternative that was an abundantly available natural resource that could serve as a binding agent for asphalt. The researchers chose lignin, a waste stream from the production of paper and cardboard. This natural adhesive offers the same structure and binding qualities as bitumen and can be produced in large quantities. Pulp and paper processing industries currently deploy lignin in low-value applications such as fuel for energy.

In 2015, a first test strip of 70 metres of lignin asphalt was laid in Zeeland. There are currently over 25 test roads with a lignin surface, from a bicycle lane on Wageningen Campus to a provincial road in Groningen. One road in Vlissingen even contains lignin in each of the layers of asphalt, partially mixed with recycled asphalt. The roads are constructed by partners in the construction industry, and Wageningen researchers regularly sample the asphalt to measure its durability. To date, these tests yield positive results: the roads are in excellent condition and meet all the requirements.

- Unfortunately, your cookie settings do not allow videos to be displayed. - check your settings

Far fewer emissions

The application of lignin causes a significant drop in CO2 emissions. According to lignin expert Richard Gosselink, who has been involved in the study from the start, CO2 emissions are slashed by 35-70% by replacing half of the bitumen. The greenhouse gas is sequestered in the road for a long time. Another major advantage is that lignin can be produced under much lower temperatures and thus requires far less energy to produce.

Lignin’s potential exceeds asphalt. In collaboration with the Dutch company Trespa, WUR worked on panels that could be used indoors, in which half of the toxic substance phenol was replaced with lignin. Trespa calculated that this reduced CO2 emissions by 30-50%. An increasing number of businesses are interested in commercial applications for this sustainable adhesive.

European highways

In the meantime, Richard Gosselink and his colleagues work on the large-scale application of lignin in asphalt. This could potentially make a huge difference. Approximately 12 million tonnes of bitumen are used in Europe per year. Using lignin in European highways would lead to a considerable reduction in CO2 emissions.

That stage has yet to be reached, but the first steps to get there have been taken. Rijkswaterstaat (the department of Public Works) is keenly interested in the developments. As soon as such large road owners acknowledge lignin asphalt as a worthy alternative, the developments are likely to accelerate. Thanks to Wageningen’s power of innovation, we are on the road to sustainable asphalt.