Man with temperature in front of material mixture

August 2026 | Reading duration: 6 min

Warm mix asphalt – how challenges turn into opportunities

The new standard for road construction

The change has been decided: As of 1 January 2027, warm mix asphalt (WMA) will become the new mandatory standard construction method in Germany. The leading driver of this development is the German Asphalt Association (DAV) with a clear focus on protecting employees – in particular in the areas of paving and compaction. This shifts the focus not only on the job sites, but already on the point of production: Asphalt mixing plants become the crucial factor for successful use of WMA.

A new challenge, from the mixing plant to compaction

While conventional hot mix asphalt (HMA) is still produced at 140 to 180 °C, 110 to 130 °C are sufficient for WMA. It is therefore also referred to as low-temperature asphalt (LTA). The result: less energy input, less CO₂ emissions , less harmful PAH vapours and, last but not least, improved health and safety. But, on the flip side, lower temperatures mean higher viscosity, which presents a real technical challenge. Bitumen becomes tough and is harder to process, but good-quality asphalt requires the contained aggregate to be evenly covered with bitumen. And that is exactly where it becomes clear what modern plant technology has to provide in the future.

Viscosity

The viscosity of bitumen is the inner flow resistance of the material and therefore its temperature-dependent flowability. Bitumen has a highly thermoviscuous property: As the temperature increases, viscosity decreases significantly, making the material softer and more malleable, while at low temperatures it strongly increases and has a brittle property. The consequences: Viscosity crucially influences the individual steps of asphalt production and during subsequent use. Bitumen can be pumped and mixed into ready-to-use paving material only if it is at the ideal temperature. The subsequent processing therefore has to take place within a short time window to ensure the long-term paving quality of the roads and surfaces.

To meet the challenges of tomorrow, Benninghoven uses technological solutions that focus on improving health and safety, reducing the energy input, achieving more efficient processes and measurably reducing emissions.

Technological solutions for asphalt mixing plants

Different technical solutions are available today for producing WMA in a reliable process. This includes, in particular, adding foam bitumen as well as solid or liquid additives that have a specific impact on the processing properties of the bitumen to allow production at reduced temperatures.

Foam bitumen

When hot bitumen is mixed with water, it foams up to many times its original volume, which temporarily changes the viscosity.

Solid additives

The powder/granulate feed system and the multivariable feed system are the technical solutions from Benninghoven for adding solid additives.

Liquid additives

For adding liquid additives, Benninghoven offers the liquid additive dosing system with up to 2 IBCs and 2 pumps that are resistant to chemicals and high temperatures.

Foam bitumen

Just add water

During asphalt production, the challenge is to evenly wet and coat the aggregate with bitumen at low temperatures while ensuring the correct processing characteristics. The foam bitumen technology offers a solution to this problem.

The targeted addition of a defined water quantity briefly foams up the bitumen, significantly increasing its volume. This temporarily lowers the viscosity, which in turn improves the wetting of the heated aggregate. For this procedure, the aggregate has to be heated to a much lower temperature. The use of foam bitumen therefore enables even mixing without any additional chemical additives while reducing the mixing temperatures.

Using water also has two other advantages: There is no need for additional storage of chemical additives. And when the asphalt has to be removed later on, there is no need to worry about potential emissions released during reheating for reuse.

The Benninghoven foam bitumen module can be retrofitted to existing plants easily and quickly. The clever “Plug & Work” solution enables smooth integration – completely independently of the plant manufacturer.

Plug & Work for maximum efficiency –
easy retrofit of a foam bitumen module

“Our foam bitumen module offers a solution that is specifically based on the requirements of existing plants, regardless of whether this plant is from Benninghoven or from a different supplier. With the Plug & Work principle, plant owners can retrofit this technology quickly and with minimum effort. Smooth integration is particularly important to us. That is why our plants come with pre-planned interfaces for connecting without faults. The system remains independent, requiring no intervention in the existing control system,” explains Ertugrul Aksakal, Development Engineer for Research and Process Engineering at Benninghoven.

Solid additives

Flexible dosing

The controlled addition of solid additives in WMA production opens up another opportunity, in particular when it comes to dosing accuracy and process reliability. Benninghoven offers solutions for this at several levels

How it works: Small quantities are transported upwards through a granulate feed system and into the weighing and mixing section by means of air flow and are added directly into the mixer. The patented RAP feed system is another option that enables precision dosing using weighing technology. For this process, the material is fed via an elevator or inclined conveyor and can be integrated into existing plants.

Liquid additives

Precise and reliable

Another option is to add liquid additives into the process. Two feed pumps ensure accurate dosing into the bitumen weigh hopper or directly into the mixer

“In the context of the NTA change, Benninghoven offers a particularly practical and yet future-oriented approach: Users benefit from technological solutions that are already designed for the future regulatory requirements for WMA. But with the flexible Retrofit solutions, it is also possible to retrofit almost any existing asphalt mixing plant efficiently. Thanks to the “Plug & Work” principle, integration can be completed within a very short time and without complex modifications,” explains Aksakal.

Diagram with exponential curve shows how PAC emissions can be reduced if the asphalt production temperature is lowered.

Lowering the temperature by up to 30 °C during asphalt production offers a significant savings potential. For a daily production of 2,000 tonnes of asphalt, large quantities of energy and resources can be saved every day. In the example with 2,000 tonnes of asphalt, around 18,000 kWh less energy is required for heating, which is equivalent to more than 9 kWh per tonne of finished asphalt. The consumption of heating oil is reduced by 1,800 litres per day, which equates to around 0.9 litres per tonne of asphalt. The lower temperature also significantly reduces the PAC emissions (polycyclic aromatic hydrocarbons): by an impressive 87.5%.

In addition to the reduced energy consumption, the following applies: 1 kg less CO₂ is emitted for every 10 °C of temperature reduction. For the calculation shown above, that means: If the temperature is lowered by 30° C, 6,000 kg of CO₂ can be saved for a daily production of 2,000 t of asphalt.

These number illustrate impressively how optimised temperature control in asphalt production can save energy, raw materials, emissions and CO₂ – a crucial contribution to more efficient and sustainable road construction.

What other savings potentials are available for emissions in road rehabilitation? Click here to learn more.

Tolles Produkt

“With a targeted temperature reduction of 30 °C, we can achieve energy savings of up to 10% while lowering CO₂ emissions and without compromising on the mixture quality. In addition to this, the lower temperature can reduce wear on the plant. And last but not least, less fumes means improved health and safety during paving.”

Ertugrul Aksakal, Development Engineer for Research and Process Engineering at Benninghoven

Warm mix asphalt with the Wirtgen Group – one brand family, one perfectly coordinated process

Other challenges connected to the use of WMA occur during paving at the construction site. During paving as well as compaction, construction companies have to adapt processes and leave the beaten track. Vögele and Hamm offer comprehensive solutions to enable smooth and efficient use. Learn more in the next parts of our series of articles on WMA.