A 100-metre trial section in Zeeland is currently being used to test bio-asphalt. Half of the petroleum in the bitumen used in this asphalt to bind together the particles has been replaced with lignin. Should the woody substance prove itself on the road, bio-asphalt can expect to find a considerable market.
There is a huge demand for asphalt in the Netherlands for surfacing new roads and, in particular, repairing existing ones. An estimated ten million tonnes of asphalt is used a year, four to five per cent of which consists of bitumen. Bitumen is the final heavy fraction remaining after the refinery of petroleum and ensures that the grit particles and small pebbles in the asphalt stick together properly. Bitumen covers the particles like a film, as it were, and provides the road surface with the right structure and grip after it has been installed with asphalt equipment.
Scientists from Wageningen UR Food & Biobased Research in collaboration with the Dutch Asphalt Knowledge Centre (AKC) succeeded in upscaling the discovery from the lab scale to the demonstration in practice in only 18 months. This is very fast, and indicates the extent to which the use of lignin as a bitumen replacement appeals to the imagination. “The use of lignin is still more expensive but we expect the price will drop quickly if it can be applied on a larger scale,” says Richard Gosselink, coordinator of the Lignin Platform of Wageningen UR.
Around 400 to 500 thousand tonnes of bitumen is used each year. The scientists discovered lignin’s potential as a biobased replacement for the fossil bitumen in the laboratory in 2014. “We found that lignin has similar characteristics to bitumen,” Gosselink explains. Lignin is very sticky, can easily be processed and is also similar to bitumen with regards to UV stability and dimension stability. As a result of the latter, the asphalt surface hardly swells or shrinks at all in rain or sunshine, according to Gosselink.
Large amounts of lignin are available for an indefinite period. The substance that gives plants their firmness is released in the production of pulp in the paper industry, and is also a substantial residual stream in the production of second generation bio fuels (ethanol).
A test with one tonne of bio-asphalt had previously been carried out and, since July, some 25 tonnes have been used to cover the access roads to an industrial estate in Zeeland, not far from the H4A asphalt plant. Together with partners such as the Asphalt Knowledge Centre, Zeeland Seaport and the Province of Zeeland, H4A is very interested in the test results, which should prove the possibility of transitioning to the renewable biobased raw material lignin. Initially it was decided to use a 50/50 mixture with bitumen.
Less sound and less fuel
The test comprises three road segments of 70 metres each; one with low temperature asphalt, one with low temperature lignin asphalt, and finally a reference segment with traditional high temperature asphalt. The test trajectory is situated on a straight road without traffic lights to ensure equal conditions. “We will be studying whether lignin improves the rolling resistance of the asphalt,” Gosselink continues. “This would reduce the noise of the road and allow traffic to consume less fuel, which would mean additional savings in fossil fuels.” The test will last for a period of two years.
More market opportunities
The Biobased Infraproject in Zeeland is studying more biomass applications in infrastructure, such as biobased fibres in concrete elements, and the cultivation of biomass in road shoulders for bioplastics.
At Wageningen UR, Gosselink is also looking into other applications of lignin. In addition to high-quality uses such as vanilla and bio-aromatics for the chemical industry, Gosselink and his colleagues are studying the possibility of lignin as a fuel additive. “We are also studying the replacement of other bitumen products, for example in roofing or in tiles backings,” Richard Gosselink concludes. “The fast rise of bio-asphalt is one of the many opportunities to apply lignin and actually make a profit. This means that a common saying among business people ‘you can do everything with lignin except making money’ no longer applies.”