In the Netherlands there are now test roads and cycle paths that are paved with a bitumen-like product made from the natural binder lignin. These include a section of road on an industrial site—used daily by cars and heavy trucks, some minor roads, and a cycle path at Wageningen University & Research, which is in three sections, each produced using a different lignin-based bio-bitumen.

Every year the EU produces around 15 million tonnes of bitumen. Most of this is mixed with aggregates such as crushed rock, sand and gravel to create asphalt—the sticky bitumen binds it all together—to build roads. Around 90%t of all paved roads are surfaced with asphalt and in the EU more than 200 million tonnes of this composite material is produced annually. Bitumen is a very thick liquid form of crude oil. It does occur naturally, but the stuff used as a binder in asphalt is a by-product of oil refining.

Lignin is a structural polymer in plants and trees that is released as a waste product from a number of industrial processes. The Dutch demonstration projects use lignin from various sources, including different types of paper pulp production and a bio-refinery that produces cellulosic ethanol from straw. The bio-based asphalt binders were created by blending the different lignins from the various waste streams to achieve the required properties.

We already built eight demonstration roads in the Netherlands with this type of new binder, so 50% lignin, 50% bitumen. We now have four years’ experience with that and it looks very good.

—Dr. Richard Gosselink, from Wageningen Food & Biobased Research

Wageningen Food & Biobased Research is the coordinator for LignoCOST, a Pan-European Network on the Sustainable Valorization of Lignin. More than 200 participants from 38 countries are connected. The focus lies on sharing and creating knowledge that stimulates lignin valorization towards industrial applications. Dr. Gosselink is the Chair.

Gosselink says that on the demonstration roads, the material appears to be performing in a similar way to standard bitumen, “although we see that they have a slight noise reduction”. But he adds that they need to monitor the roads for the normal lifetime of asphalt, which is 10–15 years. “Normally after 10 years you would have some damage, which leads to some maintenance,” Gosselink explains.

To get beyond 50% bio-based they will need to chemically modify some of the lignin, Gosselink explains, but he is confident that 100% bio-based bitumen is possible.

The question is will it only be with lignin or do we also need other bio-based components alongside it.

—Dr. Gosselink