Bitumen on the Road to Sustainability and Innovation

According to WPB, the familiar black asphalt under our tires — held together by bitumen — faces a future crossroads. As the world steadily moves away from fossil fuels, industries must confront a pressing challenge: how to maintain and build roads without relying on petroleum-derived materials. Bitumen, once a residual waste from oil refining, has evolved into an indispensable product in road construction. Yet, the need for sustainable, climate-friendly solutions is driving innovation across the sector.

Bitumen’s role is both essential and problematic. Each ton of asphalt contains around 50 kilograms of bitumen, which acts as the binder holding the aggregate together. One of its advantages is that it can be re-melted at temperatures above 150°C, making recycling theoretically easier than with cement-based materials. But the material has a hidden weakness: over time, it ages. Under the effects of sunlight, air, and high temperatures, some of bitumen’s thousands of chemical components evaporate or transform, leaving it brittle and less effective at bonding the asphalt mix.

This aging means that when old road material is reused, it must be supplemented with fresh bitumen or special rejuvenators designed to restore flexibility and adhesion. The market already offers numerous rejuvenating products, some derived from renewable raw materials, opening the door to more sustainable recycling practices.

In countries like Switzerland, where roads are more often rehabilitated than newly built, recycling has become an attractive path forward. Asphalt researcher Martins Zaumanis from Empa in Dübendorf points out that significant recycling potential lies hidden in existing road surfaces — but it’s not fully tapped. Currently, recycling is common in the lower layers of a road, yet the top layers, which face the most wear, still mostly rely on virgin materials.

Promising experiments are already underway. For example, a test section in Uster, near Zurich, was constructed with a surface layer containing nearly one-third reclaimed asphalt. Meanwhile, on the Lukmanier Pass, connecting the regions of Graubünden and Ticino, researchers pushed the recycling rate in the lower layers up to 85%, using tall oil (a byproduct of the paper industry) as a rejuvenator. These high-recycling pavements, despite facing heavy traffic and harsh weather, are reportedly performing as well or even better than conventional roads.

Environmental impact is a central concern. Producing asphalt releases significant CO2 — about 50 kilograms per ton — mainly due to the extraction and heating of bitumen and aggregates. Extending the lifespan of roads thus plays a crucial role in reducing the overall carbon footprint. Chemist Hinrich Grothe from the Technical University of Vienna is investigating how bitumen’s aging process itself contributes to emissions. Using a combination of spectroscopic analysis and mechanical tests, Grothe’s team aims to reveal how chemical changes alter the material’s properties over time.

The search for sustainable alternatives has also led to major collaborative projects. One such effort, the Nobit project (short for “No Bitumen”), has secured over €700,000 in funding. Led by asphalt expert Michael Wistuba from the Technical University of Braunschweig, the initiative aims to develop systematic testing methods and design strategies for creating high-performance asphalts from recycled and plant-based materials. From 2026 onward, test sections — ideally at least one kilometer long — will be laid, potentially on highways, to trial these innovative mixes.

Several bio-based additives are under examination. Among them are modified vegetable oils from Cargill, plant resins from the plastics company Kraton, and rejuvenators made from the caustic liquid found in cashew nut shells, supplied by the Dutch company Ventraco. While some of these products have already gained attention — such as the “biobitumen” offered by German startup B2Square, which integrates cashew-shell derivatives — questions remain regarding the sourcing of fossil components in these mixtures and whether the label “bio” truly applies.

Meanwhile, researchers and engineers in Basel are exploring yet another approach: incorporating biochar — a carbon-rich material similar to charcoal — into asphalt. Produced from green waste at high temperatures under low-oxygen conditions, biochar offers a way to lock carbon dioxide directly into road surfaces. For every ton of biochar-infused asphalt, approximately 50 kilograms of CO2 can be sequestered. Early tests also suggest performance benefits, with improved resistance to rutting compared to conventional asphalt.

Although these biochar-enhanced mixes have so far only been applied to the thicker, less stressed lower asphalt layers, the potential remains significant. Pilot installations are currently being monitored both in quiet residential streets and on heavily used truck routes in the Basel region. Even neighboring areas have launched their own trials.

The long-term results of these pilot projects will be crucial. Only with time and real-world data can the road construction sector determine whether these innovations will allow roads to shift from being climate burdens to becoming active contributors to climate solutions. By combining advanced recycling, bio-based additives, and carbon-sequestering technologies, the industry may be paving the way — quite literally — toward a more sustainable and resilient infrastructure future.

By WPB

Bitumen, Road, Pavement