Circular roads

22 April 2022

Every day, millions of people use asphalt pavements to travel from A to B. But have they ever wondered how the production of asphalt paving works? And is asphalt a sustainable material?

As we deplete our resources and become increasingly concerned with preserving the environment, road construction and maintenance is another sector where cities could find more sustainable solutions. One way they do that, is through green public procurement practices – where Europe’s public authorities use their purchasing power to choose environmentally friendly goods, services and works.

Flexible procurement

Public authorities are responsible for building new public road networks and maintaining existing ones, which means that their purchasing power could make a real difference, especially if they join forces triggering an economy of scale. In starting a conversation with market operators, public authorities can make the most of innovative solutions to reduce energy and raw material demand for asphalt production and paving, therefore making the process more sustainable.

Part of this conversation can occur at the procurement stage. For example, Rotterdam is taking a performance-based approach to its future procurement for asphalt maintenance and construction, explains Léon Dijk, Environmental Specialist and Sustainable Public Procurement Advisor at the municipality of Rotterdam. In a performance-based procurement, the contracting authority – the city or public buyer – doesn’t detail what needs to be delivered, nor how.

This means that suppliers have more flexibility and can propose different solutions, as long as they can prove that they meet the required quality standards. The key to this approach is defining a set of indicators and predefined assessment methodologies to evaluate the environmental impact and durability of the solutions suggested.

In comparison, the traditional prescriptive approach defines specific means to accomplish a better environmental performance; for example, the type of low impact asphalt or the minimum percentage of recycled asphalt. This may require contractors to adapt their production processes and may de facto pass by new innovative solutions.

More recycling, less emissions

Partners from the poroject talk while standing on the Asphalt Facility premise
Members of the Working Group on circular construction in Rotterdam

Some of the solutions to improve the overall efficiency of road infrastructure during the construction, maintenance and end-of-life phases were presented in Rotterdam to members of the Working Group on circular construction – one of the working groups under the European Commission’s Big Buyers initiative. They included applying energy-efficient production methods, such as indirect heating and the use of reclaimed asphalt.

For example, indirect heating – compared to traditional direct drum heating – limits heat loss, reducing the amount of fuel needed and thus lowering emissions. KWS, the owner of  Asfaltcentrale Rotterdam – an asphalt production plant – claims that “indirect heating damages the old asphalt less and results in fewer emissions of harmful materials. Compared to traditional asphalt construction, the production of this asphalt cuts CO₂ emissions by 75%.”

In addition to lower production temperatures, Asfaltcentrale Rotterdam creates asphalt mixtures in a more environmentally-friendly fashion through high rates of reclaimed asphalt. This latter comes from removed or reprocessed pavement materials containing asphalt and aggregates, which – when adequately crushed and screened – consist of high-quality, well-graded aggregates coated with asphalt cement that are mostly recycled and reused for pavement. Rotterdam’s Highly Ecologic Recycling Asphalt System (HERA) technology allows old asphalt to be reused five times more often and to lower emissions of harmful gases.

Sustainable solutions should also take into account the carbon footprint of transportation – this includes carrying raw materials to the production plant and transporting asphalt from the plant to the construction area. An increase in recycled materials decreases the need to transport raw materials to the plant, lowering the overall carbon footprint.

Open questions

Rotterdam’s solution shows that asphalt production facilities can do more than is typically asked in public tenders. “Treat your roads as a waste project and think about the future,” says Pascal Kregting from the Koninklijke Bouwend Nederland, an association of construction and infrastructure companies that connects and supports construction and infrastructure firms in the Netherlands.

In addition, the rise in energy costs presents a significant challenge for asphalt makers. The fossil fuels price increase, in particular, may motivate producers to switch to circular materials to remain profitable. Most facilities in the Netherlands can already increase the share of recycled materials in asphalt to 40-50%, much more than current national regulations.

Could raising the percentage of recycled materials impact asphalt’s durability? As recycled asphalt is a relatively new solution, there are still questions about its longevity. For example: will roads built with recycled asphalt require more maintenance? If so, this could impact the overall sustainability of this particular solutions. Producers, however, claim that asphalt’s endurance can be checked with proper tests performed 12-24 months after completing the works.

Some questions remain, but members of the Working Group on circular construction have glanced at a future where our roads look a little more circular, and are thinking about how to build on it.

The Working Group on circular construction is one of four working groups established under the European Commission’s Big Buyers for Climate and Environment initiative, coordinated jointly by ICLEI and Eurocities. The initiative aims to promote innovation through linking public buyers with market actors and identifying where joint actions, dialogue and international cooperation among public buyers across Europe can successfully trigger a positive impact on the market.

Eurocities leads this group, bringing together municipalities, road authorities and market actors from all over Europe whose aim is to change existing road construction methods favouring more sustainable practices through procurement. Its participants include both local governments, such as the municipalities of Lisbon, Vienna, Haarlem and Rotterdam, and national entities like the Danish Road Authority.


Wilma Dragonetti Eurocities Writer