From hot to warm

A modern trend: reduced-temperature asphalt

Making asphalt is usually “hot stuff”, since mixing normally takes place at around 160 °C. This process requires a lot of energy, which is both expensive and polluting. An alternative to conventional asphalt production is reduced-temperature asphalt, also known as low-temperature asphalt, warm asphalt or “warm mix”.

The production of reduced-temperature asphalt is not in itself a new invention, with the process having been trialed as far back as the 1990s. Today, however, where carbon footprints, resource conservation and reducing energy input have all come to the attention of highway departments, reduced-temperature asphalt is enjoying a renaissance. As a company that keeps its eye on sustainability, Benninghoven responded to this trend quickly by developing optimized technological solutions to provide the market with reduced-temperature asphalt capable of meeting high quality standards.

Reduced-temperature asphalt is asphalt that can be manufactured and processed at a lower temperature without negatively affecting its properties.

A groundbreaking step

Although the temperatures used for mastic asphalt production have already been lowered for reasons of work safety (since 2008: from 250 °C to 230 °C), reduced-temperature rolled asphalt has not yet become established in Germany – in contrast to the USA and other European countries, where up to 40% reduced-temperature asphalt is now commonly installed. Benninghoven offers several impressive solutions in this area. Asphalt mixing plants from Benninghoven are in use all over the world, offering impressive proof that high-quality asphaltic mixture, cost-effectiveness, and compliance with climate, health, and safety regulations are not a contradiction in terms.

At a glance

What is reduced-temperature asphalt?

As typically used, the term refers to asphaltic mixtures that are produced at temperatures between 110 °C and 130 °C. In contrast, hot asphalts are typically manufactured at between 140 °C and 180 °C – and typically with bitumen at 160 °C as the binder. A key benefit: The production and processing of reduced-temperature asphaltic mixtures is essentially possible using conventional methods.

Good reasons for reduced-temperature asphalt

20 °C to 40 °C lower makes a decisive difference

Environmental protection and conservation of resources

Huge energy-saving potential

In its asphalt guidance published on the topic of reduced-temperature asphalts, the German Asphalt Association (Deutscher Asphaltverband e.V.) notes that a temperature reduction of 30 °C can achieve significant savings in terms of energy, resources and the emissions footprint.

Example: daily production of 2,000 t of asphalt

(Deutscher Asphaltverband e.V., Asphalt Guideline, Reduced-Temperature Asphalts)

Occupational health and safety

Improved working conditions for production and laying

Fumes and aerosols are released during the hot processing of bitumen. Even relatively small reductions in temperature can significantly reduce the volume of fumes and aerosols, and protect personnel not only during production but also transportation and laying. Thermal loads are also reduced simultaneously.

Keeping below operational exposure limits

Reduced-temperature asphalt makes a significant contribution to keeping below the legal occupational exposure limit for bitumen of 1.5 mg/m³ (from 2024 onwards).

What it’s all about: reducing bitumen viscosity

Bitumen is only capable of wetting and enveloping the aggregates in the mixer at a temperature of roughly 140 °C – below this, the bitumen is too viscous. So, to lower the temperature during asphalt production, the bitumen viscosity needs to be temporarily reduced. This is achieved by adding water (foam bitumen) or a number of other additives.

As the hot bitumen is mixed with water, the steam that is produced expands rapidly: the bitumen then foams up and its volume increases by several orders of magnitude. This enlarged surface area ensures better wetting of the aggregates in the mixer. As a result, aggregates can be enveloped properly even at lower temperatures. Another option for reducing bitumen viscosity is to add solid or liquid additives.

A significant drop in energy

A comparison of the various temperatures involved in producing hot asphalt, reduced-temperature asphalt and cold asphalt shows that the use of foam bitumen is capable of lowering temperatures by up to 40 °C, while still ensuring high-quality asphaltic mixtures at temperatures ranging from 110 °C to 130 °C. At the same time, energy consumption and CO₂ emissions are significantly reduced.

The fastest route to reduced-temperature asphalt

Our solutions for you

Solution 1: An easy retrofit: Benninghoven’s foam bitumen module

Technical feasibility is simpler than you might think for operators of asphalt mixing plants. The weighing/mixing section is simply expanded to include Benninghoven’s foam bitumen module, which consists of a bitumen pump, an expansion chamber, piping, an input nozzle bar and water dosing device, and can be retrofitted easily to existing plants as part of Benninghoven’s “Plug & Work” principle.

Plug & Work

Thanks to pre-installed interfaces, the foam bitumen module simply connects to the mixer box and the bitumen weighing hopper.

Conserves materials

The reduced thermal load has a positive effect on components and results in less wear on the asphalt mixing plant. At the same time, the lower production temperature also reduces the effects of thermal ageing on the binder.

Water – a readily available input

Typically, the water required for the foam bitumen module will be on hand at any asphalt mixing plant. As an input material, water is both inexpensive and non-hazardous.

“Foam bitumen is the perfect solution for our production of reduced-temperature asphalt. Benninghoven has plenty of experience in the field and can even integrate its systems into existing plant.”

Matthias Lenarz, Bitumen Team Leader

Solution 2: Use of additives in the mixer itself

Small quantities of solid additives are added by means of a powder or granulate dosing system. The adhesive system can also be used to add one or two liquid additives to the process.