PEAB Asphalt has laid a short section of road in Northern Sweden with asphalt containing lignin, an organic polymer found in plants and some algae. The lignin used in this trial has been extracted from softwood. Replacing some of the bitumen in a mix with a renewable material such as lignin would reduce consumption of bitumen and lessen the environmental impacts of road construction.
The trial is part of a bigger European-funded research programme, Rewofuel, to investigate the use of biofuel in sectors such as aviation and automotive. The €19.8 million programme kicked off in June 2018 and will run until the middle of 2021.
PEAB laid the 50m-long section of binding layer asphalt in early July on a municipal street in Sundsvall, which is around 400km north of Stockholm. Up to 10,000 vehicles/day use the road in an area which experiences severe weather conditions in winter, requiring studded tyres to deal with the snow and ice.
“This first field trial was important for us because it allowed us to see the effects of the lignin during normal production, whether it reacts to anything, how it smells,” explained Mats Wendel, innovation advisor for PEAB Asfalt, with is part of the PEAB construction and civil engineering group. Wendel reports that there was no difference in the production and workability of the asphalt, although it did smell slightly different, with some observers noticing the scent of wood.
Although PEAB has successfully replaced up to 25% of the bitumen with lignin in laboratory tests, the researchers decided to go for a more modest 10% replacement for the field trial. “That kept us within the national specification, which is based on the European one,” said Wendel. “We thought it was a good thing to stay safe for our first trial.”
Swedish chemical and cleantech company Sekab produced the lignin used in the asphalt trial. One of the biggest technical challenges for the researchers was how to mix the lignin, which is in powder form, into the bitumen.
The next step will be to carry out more trial paving sections, including laying surface courses which can be monitored for performance over time. Although studies suggest that asphalt containing lignin could perform better than asphalt with bitumen only, Wendel says that currently they can only say that the performance is just as good as a standard mix asphalt.
PEAB Asfalt has been aggressively pursuing carbon reduction goals across its business, working over the past five years to introduce biofuels at its asphalt plants in order to lower carbon emissions by almost 50%. “This year we will be using renewable fuels at all our stationary plants,” said Wendel. “If you can reduce carbon emissions by half using existing technology and still be competitive, then you can move on to start working on the other half.”
International and national carbon reduction commitments mean that highway authorities in Sweden are also keen to try new technologies and get involved in trials, said Wendel: “Road owners know that they have to be part of the change.”