Climate change is a growing threat to the world’s population. Discussions at the recent COP26 Conference in Glasgow, Scotland, concluded with a goal of Net Zero by 2050, a statement that reiterates the importance of finding solutions to reduce GHG emissions.
The urgency of action along with the abundance of available forest resources in Canada are leading organizations like FPInnovations to implement new products and solutions. One such solution is lignin-modified asphalt, a green technology that could improve road performance while creating value from an abundantly available forest residue.
Effects of warming on road infrastructures
A recent report from the Government of Canada stated that the country’s climate is warming twice as fast as the global average. In parallel, a growing number of sources describe the impact of warming on road infrastructure.
In a report presented to Infrastructure Canada (1), National Research Council of Canada revealed the impact of climate change and extreme weather events on the flexible pavement structural behaviour and how that severely shortened the road design life, therefore it is important to consider the impact of projected temperature on material selection instead of current use of historical. This brings us to the importance of studying the climate change impact on asphalt selection and it necessitates the development of NRC Climate Adaptation and Asphalt Selection Tool (CAAST). Rutting, namely, is more likely to occur as temperature increases. The low asphalt concrete stiffness associated with high temperatures (above normal operating temperatures) reduces the material’s ability to function properly as a surface layer responsible for distributing surface loads and minimizes the effectiveness of lower layers. The unprecedented high stresses caused by low asphalt stiffness are alarming and are expected to affect the performance of the backfill layers below the asphalt concrete layer. As Canada has thousands of kilometers of flexible pavement, it is becoming critical to implement viable options to address the effects of climate change on road infrastructure.
Reducing environmental footprint of roads
In recent months, FPInnovations launched a project aimed at substituting part of the bitumen used in asphalt pavement with lignin, a natural glue in wood from Canadian forests (read our previous article on this topic). To ensure that the new asphalt product is rapidly adopted by road owners, it was important that asphalt economics, workability, and performance were not sacrificed in the drive to enhance its green properties. To this end, École de technologie supérieure is guiding the formation of the asphalt mixture through extensive testing.
The environmental impact of lignin-modified asphalt mixtures was initially quantified in preliminary studies performed by FPInnovations’ Environment and Sustainability group. These studies helped determine the potential advantage in terms of GHG emissions reduction of substituting lignin for bitumen.
Road demonstrations were completed in three cities location across Canada during Summer 2021 and will be used to validate the preliminary data. The demonstrations will help validate the use of lignin-based asphalt under a range of climatic conditions and paving applications, in addition to providing real-life data to evaluate GHG emission reductions and construction costs, mixing methodology, and workability of lignin-dosed asphalt mixtures. Furthermore, they will help introduce the technology more widely in proximity to different Canadian lignin producers.
Going further with greener roads
Following the initial phase of laboratory testing to validate the potential of lignin-based asphalt as a replacement for conventional pavements commonly used in Canada, three full-scale asphalt demonstration sections were constructed in different Canadian cities. Two methods of mixing in the lignin were trialed—called ‘wet’ and ‘dry’ processes based on when the lignin is added to the asphalt mix. Each demo site also featured side-by-side comparisons of lignin-dosed asphalt mixtures and conventional asphalt mixtures.
For all three sites, monitoring will last several years to assess the performance of the lignin-modified pavements under different climatic variations; in addition, the paved boulevard in Québec City will be subject to both high traffic volumes and frequent winter road maintenance.
Full-scale trafficking test at Université Laval
Starting this October with construction of a fully instrumented lignin-modified pavement, a full-scale trafficking test will be conducted by Université Laval with its high-tech, heavy vehicle simulator. Below images show the instrumentation placed immediately below the asphalt layer and the test section paving process. The test pavement comprised 3 m of conventional Québec City pavement and 3 m of the same pavement structure but with some kraft lignin substituted for bitumen [i.e., 60 mm of ESG10 (10% lignin) over 80 mm of GB20 (20% lignin)]. This test will assess, in just a few short weeks, the effect of years of repeated heavy traffic loads on the rutting performance of lignin-modified asphalt pavement.
Work continues …
The project shows promising results so far, thanks to the commitment and motivation of the many partners who took part in the demonstrations. All partners are committed to the development of new products and solutions that will allow for greener and more economical roads, while remaining safe.
For FPInnovations and its research partners, work continues. The next months will bring additional results and data that will help to improve the technology.
It is to be hoped that the demonstrations at the three existing sites, as well as in cities that have expressed a desire for their own demonstrations, will help stimulate public and government interest. Their endorsement is critical to the development of new, greener technologies that will help Canada to adapt more effectively to climate change. One road at a time.
(1) Omran Maadani and Mohammad Shafiee, 2021. Impact of Climate Change and Extreme Weather Events on Flexible Road Performance – sensitivity Study. National Research Council Canada, March 31, 2021.