Stora Enso and the Swedish road and infrastructure operator Svevia are testing lignin in asphalt on Swedish roads. Lignin is used as the binding agent and can replace up to one half of the oil-based bitumen in asphalt.
Lignin is a polymer that provides rigidity and mechanical strength to wood. Derived as a sidestream of pulp manufacturing, lignin is a valuable material from the perspective of circular economy.
Asphalt consists of stone and bitumen, which is made of crude oil. Replacing bitumen with a bio-based material could lead to a dramatic reduction in the negative environmental effects of asphalt.
Mattias Andersson, asphalt production specialist at Svevia, says that so far, completely replacing bitumen in asphalt has not been successful.
’In the Netherlands lignin has been mixed in asphalt since 2015, but even they have only succeeded in partially replacing bitumen,’ says Andersson.
In Sweden, tests with lignin started last autumn. The first test stretch is a couple hundred metres of road between Sandbrink and Gnesta. Results to date are promising.
’The asphalt surface appears good and homogeneous. It’ll be interesting to see what winter does to it. We’ll be able to study that once the snow melts and the meltwater drains off,’ says Andersson. The effects of winter maintenance and sub-zero temperatures on the asphalt will also become visible.
Renewable and non-toxic, lignin may also find other uses as replacement for non-renewable materials. ’In future lignin could also be used to produce carbon fibre based from a renewable raw material, to replace petrol-based materials in cars and wind turbines, for example,’ says Heikki Lotti, Senior Business Development Specialist Lignin at Stora Enso, in an interview in the Paperi ja Puu magazine