Waste incineration bottom ash as a sustainable alternative – Øresund Motorway expansion

A focus on sustainability and innovative use of materials

If you drive along the stretch between the Amager Motorway and the airport, you can’t miss the major roadworks underway. The existing motorway is being widened with an additional lane along its busiest section, including the junctions towards the Amager Motorway and central Copenhagen. Nearly 100,000 motorists use this stretch every day.

Different materials are being used along this stretch, and for good reason. Traditional sand and gravel are extracted from quarries, and their use is not particularly sustainable due to the resources required for extraction. Incinerator bottom ash, by contrast, is a by-product of waste incineration—the material left after waste is burned—and can be recycled as a more sustainable alternative.

The incinerator bottom ash is stored in stockpiles, where it absorbs CO₂ and binds heavy metals as it cools. It is then sorted into different particle sizes, allowing it to be graded to match the particle-size distributions of conventional sub-base aggregate and capping sand. This makes it both a more sustainable and a practical material.

The new guidelines on the use of incinerator bottom ash, published in 2024, now allow it to be used on motorways and in the unbound base course.

Better infrastructure and sustainable road construction

Working with SWECO, SYSTRA established that incinerator bottom ash aggregate can be used in the construction of the Øresund Motorway. Its expansion will therefore be the first motorway project in Denmark to use this sustainable material.

The use of incinerator bottom ash must, of course, comply with environmental regulations. For example, the material must not be placed too close to drinking water wells or protected natural areas. These requirements have been met on the project, meaning the motorway expansion can improve infrastructure while also contributing to more sustainable road construction in Denmark.

To prevent long-term impacts on the surrounding environment, a membrane is installed around the embankment. This helps ensure that water cannot seep through the incinerator bottom ash in areas where there is no impermeable layer above it, reducing the risk of unwanted leaching of potentially harmful heavy metals over time.

During construction, detailed procedures also govern how the material is handled and placed. For example, the stockpile used at each location is recorded, providing traceability and oversight for this relatively new road construction material.

By making incinerator bottom ash a key component of the road structure, we are taking an important step towards more sustainable infrastructure. It is not only a sustainable choice but also a practical one: the material offers good strength properties and reduces its carbon footprint during maturation. We are proud to be among the first to implement this technology in a Danish motorway project, and look forward to continuing our work to create the greener roads of the future.

Gustav Brandt-Pedersen, Consultant in the Roads & Planning Department at SYSTRA Denmark

As an added benefit, there is a site in Ørestad where incinerator bottom ash is stockpiled. This means the material does not need to be transported over long distances, further reducing its carbon footprint.