Man checking mix temperature

August 2026 | Reading time: 6 min

Warm mix asphalt – how challenges are turned into opportunities

The new standard for road construction

The decision has already been made: From January 1, 2027, warm mix asphalt (WMA) will become the mandatory type for road construction in Germany. The German Asphalt Association has been largely responsible for this development, which it has promoted with the safety of workers in mind – especially those involved in paving and compaction. Apart from the construction site, another clear point of focus is asphalt production, as the asphalt mixing plant will become a key factor in the successful adoption of WMA.

A new challenge – from the mixing plant to asphalt compaction

While conventional hot-mixed asphalt is produced at temperatures ranging from 140 to 180 °C, warm mix asphalt needs no more than 110 to 130 °C. WMA is therefore often also referred to as reduced- or low-temperature asphalt. The end result is reduced energy consumption, fewer carbon emissions , less hazardous PAH vapors, and – last but by no means least – improved worker safety. A lower temperature means a higher viscosity creating a real technical hurdle: bitumen thickens up and becomes harder to work with. Yet a high-quality grade of asphalt is only achieved if all of the aggregate it contains is evenly coated with bitumen. And this is the exact problem that modern plant technology needs to address.

Viscosity

The viscosity of bitumen describes the material’s internal flow resistance and therefore its temperature-dependent ability to flow. Bitumen’s viscosity reacts strongly to thermal changes: As the temperature rises, the viscosity decreases significantly making the material softer and easier to shape. At lower temperatures, the viscosity increases and becomes brittle. As a result, viscosity is a key factor for the individual steps involved in both asphalt production and its later use on the construction site. Bitumen must be at an ideal temperature before it can be pumped or mixed and processed into a material ready for placement. This subsequent processing step must therefore be completed within a short window of time to ensure long-lasting paving quality for roads and paved surfaces.

To ensure tomorrow’s challenges can be prepared for today, Benninghoven employs technological solutions that target improvements in occupational safety, reduces energy consumption, increases efficiency in process flows, and provides a measurable decrease in carbon emissions.

Technological solution strategies for asphalt mixing plants

To achieve process reliability with warm mix asphalt, a range of technical approaches are now available. Alongside the addition of foamed bitumen, solid or liquid additives can also be used: these influence the behavior of bitumen during processing and therefore enable the production of asphalt at lower temperatures.

Foamed bitumen

When hot bitumen is mixed with water, the bitumen foams to several times its original volume, temporarily changing its viscosity.

Solid additives

Benninghoven offers several technical solutions for solid additives, including its powder/granulate dosing system and multi-variable feed system.

Liquid additives

For liquid additives, Benninghoven offers the technical solution of a liquid additive feed system that consists of one or two IBCs and two pumps, all of which feature good chemical and thermal stability.

Foamed bitumen

Only requires the addition of water

During warm mix asphalt production, the challenge is to ensure the uniform wetting and coating of aggregate by bitumen at a low temperature while keeping bitumen in a physical state that can easily be processed. The use of foamed bitumen is one solution to this problem.

The targeted addition of a defined quantity of water temporarily foams hot bitumen and significantly increases its volume. This temporarily reduces its viscosity, which accordingly improves the wetting of the preheated aggregate. Thanks to this procedure, the aggregate preheating step can be completed at a much lower temperature. As a result, the use of foamed bitumen achieves uniform mixing without the need for chemical additives while also helping to reduce the mixing temperature.

Foamed bitumen only requires water, which also offers two other benefits. First, there is no need to store chemical additives on site. Second, there is no danger of any emissions being produced by the repeat heating of the asphalt if the pavement is removed at a later stage and used as reclaimed asphalt.

The foamed bitumen module from Benninghoven is a quick and easy retrofit for existing asphalt mixing plants. Thanks to the company’s “Plug & Work” approach, integration is straightforward for any plant – regardless of the manufacturer.

Plug & Work for maximum efficiency –
the foamed bitumen module is an easy retrofit

“Our foamed bitumen module is a solution that we have deliberately oriented towards the requirements of existing mixing plants. This existing facility can be a Benninghoven plant or it can be a plant from another manufacturer. Thanks to our ‘Plug & Work’ principle, plant owners can retrofit the technology quickly and with minimal effort. We were also keen to ensure that retrofits don’t introduce any new problems. This is why our own plants are already designed with interfaces to ensure straightforward integration. The new system stays fully autonomous – so no intervention is required in the existing control system,” explains Ertugrul Aksakal, Design Engineer, Benninghoven Research and Process Engineering.

Solid additives

Flexible dosing

Another option for WMA production is offered by the controlled feeding of solid additives – especially if dosing accuracy and process reliability are important. Benninghoven offers two solutions to suit different process volumes.

The first solution uses an air-powered granulate feed system that conveys small quantities of additive into the weighing/mixing section and so directly into the mixer. The second solution is the company’s patented multivariable RAP feed system, which enables high-precision dosing via the weighing system. In this case, the material can be fed either via an elevator or inclined conveyor, and can be integrated into existing plants.

Liquid additives

Precise and reliable

Another option is the incorporation of liquid additives into the process. Two feed pumps are used to ensure precise dosing into the bitumen scale or alternatively directly into the mixer.

“For those transitioning to WMA, Benninghoven has enabled a really pragmatic approach that’s likewise future-proof: Users benefit from technological solutions that have already been designed to meet the forthcoming regulatory requirements for warm mix asphalt. And, thanks to the flexible approach to Retrofits, almost any existing asphalt mixing plant can be upgraded efficiently. Our ‘Plug & Work’ principle also ensures a fast turnaround for integration and avoids time-consuming conversions,” Aksakal explains.

A graph plotting an exponential curve shows how PAH emissions can be cut by reducing the temperature at which asphalt is produced.

Lowering the temperature of asphalt by up to 30 °C during the manufacturing process offers significant potential savings for asphalt producers. For a daily production volume of 2,000 metric tons of asphalt, this translates into major reductions in energy and resource usage. The energy need to heat this volume of 2,000 metric tons of asphalt would be cut by around 18,000 kWh, for example – equivalent to more than 9 kWh per metric ton of finished asphalt. Heating oil consumption is also reduced by 1,800 liters per day, or around 0.9 liters per metric ton of asphalt. The lower temperature also significantly reduces emissions of PAHs (polycyclic aromatic hydrocarbons). By no less than 87.5%.

Alongside the obvious savings on energy consumption, Carbon emissions are cut by 1 kg for every 10 °C drop in temperature. Returning to the above calculation, a 30 °C reduction in temperature would cut carbon emissions by 6,000 kg for a daily production volume of 2000 t of asphalt.

These figures impressively illustrate how optimized temperature management in asphalt production can achieve savings in energy, raw materials, and (carbon) emissions, making a decisive contribution to more efficient and more sustainable road construction.

What else can be done to reduce emissions in the road rehabilitation process chain? Click here to learn more.

Tolles Produkt

“Reducing the temperature by the target amount of 30 °C can achieve energy savings of up to 10%. This simultaneously cuts carbon emissions without compromising on the quality of the mix. What’s more, the lower temperature can also reduce general wear and tear on the plant. Last but not least: fewer vapor emissions also improve worker safety during asphalt paving.

Ertugrul Aksakal, Design Engineer, Benninghoven Research and Process Engineering

Warm mix asphalt in the Wirtgen Group – one brand family, one well-coordinated process

Other challenges from the use of warm mix asphalt are encountered during paving work on the construction site. Construction companies will need to abandon traditional methods and adjust their processes for both paving and compaction. Vögele and Hamm offer an extensive range of solutions to ensure the respective work is both easy and efficient. Find out more about these solutions in the next instalments of our series of articles on warm mix asphalt.