In recent years, environmental considerations related to the use of petroleum-based products have led many around the world to evaluate greener options for reducing the carbon footprint of asphalted roads.
In addition, pavement degradation, accelerated by higher traffic and increasing cycles of freeze and thaws due to climate change, has a direct impact on municipalities and transportation departments that have seen their costs increase. Asphalt for roads is manufactured by binding together aggregate with bitumen, a petroleum product. However, lignin, a natural by-product of the pulp making process, is being hailed as a possible replacement for some of the bitumen used in the asphalt mix. Known as the “natural wood glue”, lignin binds together the cellulose ﬁbres in plants, and it is believed it can serve the same purpose in the production of asphalt pavement.
In Canada, the overall bitumen market for asphalt is currently estimated at about 4M tonnes per year and, with nearly 40% of the road network paved—representing hundreds of thousands of kilometers—this number is expected to increase with growth in road paving and maintenance activities. However, there are two major challenges to replacing a well-established and understood product such as bitumen with lignin.
First: It is not fully understood how asphalt made with a mixture of bitumen and lignin will react in cold weather. Partially replacing bitumen with lignin as the binder in asphalt was only tested under Europe’s milder winter conditions, meaning that using lignin-based asphalt products in Canada’s harsher weather conditions requires both local lab testing and pilot demonstration tracks.
Second: There remains the question of adapting asphalt production processes to include the integration of lignin. FPInnovations saw the potential and undertook the challenge.
To confirm the feasibility of using lignin-modified asphalt pavement under Canadian conditions and to address the process issues, FPInnovations chose to work alongside players from the entire asphalt value chain, from governments and universities to process specialists and lignin and asphalt producers.
Early results have been promising, according to Allan Bradley, Lead Researcher in FPInnovations’ Transportation and Infrastructure group. “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. Additional lab testing will also focus on verifying how lignin can affect asphalt thermal cracking performance, a critical property to improve in our climate.”
While acceptable performance characteristics will be necessary to ensure the final product is certified by municipal and provincial governments, the real challenge to market penetration of this new bioproduct will be in creating an economic asphalt production process that integrates lignin. To that end, FPInnovations has initiated discussions with asphalt producers, key players in resolving this challenge. Their experience and know-how on the workability of asphalt products is expected to offer a better understanding of its production at scale.
“We are very happy to be part of this project and to contribute our knowledge,” said Mr. Fred Hakala, General Manager of Pioneer Construction, field test partner in Thunder Bay, ON. “Tests must demonstrate that the product obtained from the substitution of bitumen with lignin will offer equivalent, if not superior qualities to the existing products, but the economic impact must also be clearly evaluated, for both asphalt producers and customers.”
From laboratory to testbed
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. The simulator will assess, in just a few short weeks, the effect of years of repeated heavy traffic loads on lignin-modified asphalt pavement. This coming Fall, upon receipt of conclusive results from the lab and simulator testing, the first pilot demonstrations of lignin-modified asphalt pavement in Canada will take place in Sturgeon County, AB, and Thunder Bay, ON. “We are excited to participate in a project bringing sustainable products to the marketplace,” confirmed Richard Hart, General Manager at Park Paving, field test partner in Sturgeon County, AB. “Our climate requires specialized materials to withstand the many freeze/thaw cycles, and the quality of asphalt cannot be compromised as a result of bitumen substitution. The final product must meet or exceed current specifications as well as provide a positive economic impact for the rate payer.”
The city of Edmonton, AB, is also evaluating the possibility of conducting a pilot test and discussions are currently underway with the provinces of Québec (Ministère du Transport du Québec) and British Columbia (different municipalities) to perform demonstration projects in their jurisdictions. “These upcoming field trials are intended to find the optimal mix formulation that achieves performance improvements while minimizing negative impacts, using compounds that will keep the final product competitively priced”, adds Bradley.
Assuming a formulation with 5-10% of the bitumen replaced by lignin, and a 20% market penetration of the new enviro-friendly product, a potential yearly demand for lignin of 40,000 to 80,000 tonnes would be created and a new market opened for high-value lignin from Canadian kraft pulp mills.
In Canada, West Fraser’s pulp and paper plant in Hinton, AB, already produces renewable, consistent, and sustainably-produced lignin using the LignoForce SystemTM, a process jointly developed by FPInnovations and NORAM Engineering. “We are thrilled to see the preliminary results from field trials using the lignin produced by our plant,” said Rod Albers, Manager for Energy and Bioproduct Development for West Fraser. “This is an important step towards achieving an efficient product made from natural, renewable material derived from Canadian forest fibre that performs in the challenging weather conditions roads experience.”
FPInnovations’ Environment and Sustainability group analysed the potential environmental benefits of using lignin in asphalt. In a preliminary study performed for the province of Alberta, assuming it is feasible to substitute5 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.
As Canada’s road network continues to grow, the use of greener and more economic options, such as lignin, would benefit many.