Coming Soon: Plant-Based Roads

Plant-Derived Material Can Make Our Roads Carbon-Negative

Credit: Pexels

With all the attention focused on shifting from fossil fuels to renewables, there has been less emphasis on the hundreds of other products made from petroleum and finding substitutes for them. Some of the more common commodities are plastics, shoes, lubricants, paints, sports equipment, synthetic fibers for clothing, and building materials, including roofing.

One ubiquitous product is bitumen, a fossil-fuel-derived binder that holds asphalt aggregate together. A company in Norway is recycling old, damaged roads by using a plant-based binder instead of bitumen. Currently, it has applied this process only to repairing roads. Because Norway is far north, its roads suffer from repeated freeze-thaw cycles. The non-petroleum bioasphaltic binder it employs is lignin — a wood-based material essential to creating structure for trees and plants. The company utilizes a machine called the Carbon Crusher to grind up the top layer of damaged roads before applying the lignin to rebind the ground-up aggregate into a new, durable top layer. 

Approximately 18 billion tons of asphalt make up U.S. roads. All these roads need to be maintained. Asphalt is energy- and resource-intensive, contributing substantially to climate change. Lignin, one of the most abundant natural polymers, is an ideal substitute for crude oil bitumen. Because trees capture CO2 as they grow, using lignin on roads sequesters carbon. This significantly shrinks the carbon impact, especially for road repair. When the road aggregate is recycled, as in Norway, the use of new material is avoided and their associated carbon emissions from production and transportation, often making the entire process carbon-negative.

The process of rehabilitating roads with lignin is faster, cheaper, and more durable than what has been the case with standard bitumen repairs. The biggest plus, however, is its environmental benefits. In Norway, they are finding that lignin is more flexible than bitumen, allowing the repaired surfaces to adapt better to the harsh weather, preventing cracks and making the repairs last longer.

Sweden and the Netherlands are also repairing roads with lignin. The process is starting to be applied to building new roads, but with fewer environmental advantages. The ultimate aim, however, is to stop building new roads — which incentivizes more driving — and focus on better care of existing highways.

It is critical that substitute products, processes, and technologies be found for the myriad of common petroleum-based products that dominate our modern life. What is now underway for asphalt is an instructive model.


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