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Lignin pilot projects in Canadian cities pave way for greener roads

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The northern Ontario City of Thunder Bay is looking to become the second Canadian municipality to pave its roads with the complex organic polymer lignin, an experimental “green asphalt” that is a forestry byproduct from the pulp making process.

Asphalt for roads is often manufactured by binding together aggregate with bitumen, a petroleum product. However, lignin is being piloted in some cities as a possible replacement for some of the bitumen used in the asphalt mix. Known as a “natural wood glue”, lignin binds together the cellulose fibres in plants, and may serve the same purpose in the production of asphalt pavement, according to not-for-profit trial leader FPInnovations.

Road paving with the lignin blend is already taking place at Thunder Bay’s solid waste and recycling facility, city officials announced.

“This is a wonderful opportunity for the City of Thunder Bay to take part in this new, innovative solution,” announced Kayla Dixon, Thunder Bay’s director of engineering and operations, in a statement. “If this product is successful and meets the city’s asphalt performance specifications, there would be many long-term economic and environmental benefits in utilizing the lignin-based asphalt,” she added.

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In 2019, FPInnovations and Resolute Forest Products Inc. commissioned a thermomechanical pulp bio-refinery in Thunder Bay. The pilot plant produces lignin for use in innovative products such as the lignin-based asphalt used for the Thunder Bay trial.

While lignin’s environmentally-friendly advantage over mixing bitumen is clear, FPInnovations suggests that how it performs in extreme cold weather is not. The product has had success through milder winters in Europe, but it is part of the reason why the new trial is underway in Thunder Bay, and why lignin-based asphalt was laid in Alberta’s Sturgeon County over summer 2021.

“We know how important well-constructed and durable roads are in Sturgeon County,” announced Mayor Alanna Hnatiw in a statement. “I know that our traffic and the Sturgeon winter will make for a worthy test of the viability of lignin as a road-building material.  We are pleased to be part of this pilot project and look forward to seeing the potential impact of this new technology,” she added.

Tests in Europe have confirmed the feasibility of using lignin as a partial replacement for bitumen, with lignin substitution rates as high as 50%.

In a preliminary study performed in Alberta, assuming it is feasible to substitute 5% to 10% of the bitumen in a typical asphalt mixture with lignin, results showed that emissions of up to 16,000 to 31,000 tonnes of CO2 equivalent per year could be avoided. On a national scale, this translates into a reduction of GHG emissions in the order of 117,000 to 260,000 tonnes of CO2 eq. per year. This is equivalent to removing up to 56,171 cars from the road each year.

FPInnovations also notes that the overall bitumen market in Canada for asphalt is currently estimated at about 4 million tonnes per year, so adapting asphalt production processes to include the integration of lignin could prove challenging.

“Finding the right percentage of lignin to substitute for bitumen while improving asphalt performance attributes such as fatigue strength, rutting resistance, pull-out resistance, resistance to crack degradation, noise (tire-to-road contact), and load-bearing capacity will be key to the project’s success,” said Allan Bradley, lead researcher in FPInnovations’ transportation and infrastructure group. “Additional lab testing will also focus on verifying how lignin can affect asphalt thermal cracking performance, a critical property to improve in our climate.”

Over the coming months, an accelerated pavement testing program will be conducted in a high-tech full-scale simulator at Université Laval’s i3C Chair.

Pilot projects are also under discussion in Edmonton and within the provinces of Quebec and British Columbia.

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