By Martino De Mori

Europe is electrifying its vehicles while the roads beneath them remain almost entirely fossil-dependent. A pilot scheme in northern Spain shows that bio-based binders can cut bitumen's carbon footprint by up to 75%. But can Europe source these materials without depleting the ecosystems that supply them? "In the bioeconomy, the limit is the forest," warns Martin Pigeon of Fern.

On the N-623 in Revilla de Camargo, northern Spain, traffic flows as it always has. Cars and trucks roll over asphalt indistinguishable from any other European road. Drivers have no reason to suspect that a 60-metre stretch along this 150-kilometre route linking Burgos to Santander contains a binder partly sourced from biological materials. Small in scale, that segment raises larger questions about Europe’s path to decarbonising infrastructure. The transport transition has focused on vehicles; the infrastructure beneath them is a different story. Asphalt — the continent's dominant paving material — depends on bitumen, a product of crude oil refining, and road construction has barely entered the decarbonisation debate. The carbon released as bitumen oxidises in place is relatively minor; its upstream footprint is not. According to Eurobitume's Life Cycle Assessment 4.0 (2025), crude oil extraction accounts for around 70% of refined bitumen's global warming potential, with refining and transport adding a further 22%. The deeper question is whether there is an exit — not from this road, but from the fossil dependency embedded in the roads themselves.

"You need to start from what the forest has to offer," says Martin Pigeon, Researcher and campaigner at the Brussels-based NGO Fern — and that starting point, he warns, is already under pressure. Road vehicles dominate a network extending more than five million kilometres, making transport responsible for roughly a quarter of EU greenhouse gas emissions. Yet European forests — the resource base that bio-based alternatives depend on — are not in good shape. "Logging levels are excessive, and the climate crisis and biodiversity collapse are already impacting forest very severely." Data under the EU's LULUCF framework shows that their carbon sink capacity has declined in recent years. Pigeon warns against assuming that bio-based materials can simply replace fossil ones at scale. "The problem with fossil fuels is that they put us in a mindset in which the sky is the limit. In the bioeconomy, the limit is the forest." Roughly half of all harvested wood in Europe is currently burned for energy. "We can do better than that," he adds — but only if overall extraction remains within sustainable bounds.

This tension is precisely why bio-based binders are now being tested as alternatives to fossil-derived bitumen. The pilot section on the N-623 was built as part of the EU-funded LIAISON project, which explores innovative materials to reduce the environmental footprint of transport infrastructure. Here, conventional penetration-grade bitumen gave way to a new kind of bio-based binder. According to Irune Indacoechea, Researcher at the Universidad de Cantabria, three types of bio-binders were initially evaluated. “Two were lignin-based, while a third consisted of two distinct phases: an asphaltene-like phase and a maltene-like phase.” Laboratory testing showed limits in extensive lignin substitution. “An extensive use of this material leads to a reduction in the mixture mechanical performance,” she explains, as lignin mirrors are only part of the chemical structure of bitumen. The selected binder, containing 40% bio-based content, fully replaces conventional bitumen while maintaining performance. “It performed well in terms of water sensitivity, resistance to permanent deformation, stiffness and fatigue,” Indacoechea notes. Operationally, the transition is manageable, though production adjustments are required and long-term durability remains under observation. “The laying and compaction of the bio-asphalt do not appear to differ from those of traditional mixtures.” From a climate perspective, she estimates that the bio-binder cuts approximately 1,200 kg of CO₂-equivalent per tonne of binder — translating into around 75% lower carbon footprint at mixture scale. Part of the CO₂ absorbed by biomass during growth remains stored in the binder.

Beyond the Spanish pilot, however, the broader strategic question concerns deployment and resource allocation. Martin Junginger, Full Professor of Bio-Based Economy at Utrecht University, cautions against premature conclusions. “Earlier Dutch demonstrations of our research, including CHAPLIN-XL lignin-road in Vlissingen, showed that bio-based roads performed very well in the short term,” he recalls. On scaleability, the constraints are real: "Lignin can substitute bitumen up to roughly 50%, not 100%." Supply could be substantial — European pulp and paper mills generate large lignin volumes as a byproduct, currently burned for energy. But the risk is clear, he warns: "If the replacement energy comes from natural gas, we risk shifting the problem rather than solving it."

Here, Junginger's systemic view meets Pigeon's ecological realism. Redirecting biomass from energy to longer-lived materials may improve efficiency — but only if harvesting remains within sustainable bounds. Junginger notes that "if higher demand for woody biomass leads to afforestation, that can increase carbon sequestration, but new forests must be species-rich and climate-resilient." Circularity, for Junginger, offers the most concrete avenue. "Rejuvenating recycled bitumen with bio-based binders allows both fossil reduction and material circularity." But substitution must remain bounded — Pigeon is unambiguous: "There aren't enough plants on the planet to displace the fossil fuel economy one for one. We need to think better."

The 60-metre stretch on the N-623 is therefore more than a technical trial. It marks the convergence between engineering feasibility and ecological constraint, deepening a debate that extends far beyond this particular road. How should Europe allocate its finite biomass resources? Can infrastructure decarbonisation proceed without pushing pressure onto forests already under strain?