Ammann’s Sustainable Asphalt Production - What’s New & What’s Next

Dr. Hans-Friedrich Peters, Executive Vice President of Ammann’s Plants Division provides an in-depth look at how asphalt production has become more sustainable – and a glimpse of what’s on the horizon.

“Green” road building always refers to the use of recycled asphalt (RAP); can these recycled materials perform as well as the mix made from virgin aggregates?
Yes, “Green” road building does refer to RAP – and it should. The biggest reductions in indirect CO₂ emissions result from the implementation of RAP. We should not categorise RAP as waste material; it is a perfectly fine substitute for virgin materials. The aggregates in reclaimed asphalt show little aging and are mechanically and geometrically within the quality ranges of new material.

Bitumen holds up well too. Its aging is limited and can be compensated by using small amounts of new bitumen. When utilising RAP, you’re saving on both aggregate and bitumen costs – while reducing emissions, initially and over the lifetime of a road.

Our technology allows the use of RAP percentages up to 100%. In reality, the percentage is usually much less, based on the amount of RAP that is available, and the recipes defined by the authorities.

Are countries increasingly adopting recycling?
Sustainability has been part of the roadbuilding conversation for decades. Improvements that make the methods and machines more environmentally friendly continue to gain momentum. Industry leaders increasingly see green practices as not only a way to better the world, but as a tactic to improve profitability too.

Many countries that did not initially adopt recycling are now moving ahead rather quickly. China is an example of this. The country is leveraging some of Ammann’s most advanced recycling plants and creating mix with extremely high percentages of RAP.

The earlier adopters are now recycling even more. That can result from governments lifting restrictions, but increasingly it’s because the asphalt producers see the value of RAP.

Whatever the motivations, the global community is benefitting. From an environmental perspective, all parties involved should increase their efforts to expand the percentage of RAP being used for new pavements.

How do Ammann plants heat the 100% RAP mix without damaging the bitumen?
The challenge with RAP is the heating of the materials. Hot temperatures damage bitumen. In some processes, virgin aggregate is heated, which mixes with the RAP to raise its temperature. But when making mix with 100% RAP, there is no virgin aggregate – and therefore no secondary heat source.

On the high end of RAP utilisation is the Ammann ABP HRT (High Recycling Technology) Asphalt-Mixing Plant. As stated, it can produce mix with up to 100% RAP. No virgin aggregate is required.

There is considerable technology and innovation involved in the HRT concept, in particular, the RAH100 counterflow drying process technology. Essential to the RAH100 is its gentle heating process. During the warm mix process, the dryer heats materials between temperatures of 100ºC and 130ºC. It also makes asphalt at 140ºC to 160ºC - if a more traditional mix is desired.

The heating is usually where the complications with RAP material arise. RAP must reach its target temperature, but the valuable bitumen will be damaged if the material is heated too quickly. The RAH100 eliminates that concern. It consists of two connected sections. One is a hot gas generator that contains a burner and forces air toward the second section, which is a counterflow dryer.

The RAP enters at the far end of the counterflow dryer section and moves toward the heat chamber. At the end of the counterflow dryer, RAP is transported to an accompanying silo. The heated RAP mix leaves the dryer before the temperature becomes excessive, so it never reaches the critical temperature where the bitumen is damaged.

One quick point about the ABP HRT: it’s an extremely advanced plant – I would say it’s clearly the industry leader. Yet Ammann always strives for further improvement, so this system, created more than a decade ago, is constantly improved. That includes the hot gas generator, which has been upgraded on multiple occasions.

In the ABP HRT plant, the recycling system is placed above the mixer; what is the purpose of this design?
The plant is designed around the incorporation of large percentages of RAP. What you see is a nod to the fact that the HRT plant has elevated RAP from a supporting role to the lead actor.

As you stated, the most striking difference is that the ABP HRT’s entire recycling system is arranged vertically, in direct line above the mixer. This allows materials to be dropped instead of conveyed, which minimises wear and optimises transport of the hot RAP. The HRT approach also means that there is enough room in the plant’s tower for additive feed components and for carrying out inspection and maintenance work.

Today the HRT concept is the smartest operational method for handling the specific properties of RAP.


Though making a mix that consists of 100% RAP is impressive, yet many mix makers will utilise lesser amounts of RAP. What are the solutions for these customers?
Many of our customers fall into this category, and we most assuredly have products for them. There are varied heating processes that depend on the amount of recyclables. The RAH60 is a parallel flow dryer where up to 60% hot recycled materials can be fed. The RAH50 is a middle-ring dryer that incorporates up to 40% hot recycled materials.

Recycling can occur at Ammann plants without these specific dryers. Up to 30% cold recycled material can go directly into the mixer, meaning almost every Ammann plant is capable of utilising that amount of RAP.

Are there more opportunities for making further reductions in emissions?
The newest opportunity for further reduction is with regard to volatile organic compounds (VOCs). These compounds must be diminished in the clean gas stream to cut the total carbon value.

We continually work to reduce CO₂ emissions. This can be accomplished by actively cooling the drum, increasing drying efficiency and utilising energy sources such as biofuels and wood dust. Ammann technology can diminish CO₂ by 10% or even considerably more, depending on the age of the plant and the technology chosen.

There are other somewhat hidden opportunities to trim CO₂ emissions, including the bitumen tank farm. A traditional farm consists of horizontal tanks heated with thermal oil. Changing to an electrically heated, vertical tank farm results in considerable advantages. There is no oil consumption and therefore no emissions. Electric heating is cost-effective, too. In fact, electrically heated bitumen tanks have become standard in all of Europe and other parts of the world.

There are also other emissions like dust and odour. Their level of importance and the maximum values being allowed differs greatly from country to country and area to area. Our technology allows the lowest values for all of them (e.g. < 10mg/m³ of dust) without causing any restrictions on the plant operations.

Low temperature asphalt (LTA) is another opportunity that is becoming more prevalent. While conventional asphalt is produced at around 170°C, the low temperature processes of today allow production temperatures of around 100°C. Lowering the manufacturing temperature eases energy needs, and therefore emissions, too. LTA impacts the entire production process – including drying, mixing sequences and recycling. Ammann has focused our research and development on the complete manufacturing process for LTA.

Why are plants sometimes located in residential and commercial areas and what can be done to limit the noise they generate?
A shortage of industrial land means that asphalt plants increasingly must be located closer to residential areas. Local governments can have very strict standards when it comes to noise, so we have to make the plants as quiet as possible.

Ammann has been very proactive on this front. We offer varied sound-suppression packages to meet our customers’ specific needs. Some customers need to lower sound a bit, while others have to take more substantial measures. The efforts start with equipping burners with variable speed motor drives, which are much more quiet, and stack silencers, which control exhaust noise.

We offer more and more sound-suppression options, all the way to cladding the entire plant. That cladding, by the way, makes the plants look like commercial buildings. They are beautiful facilities that fit nicely in urban office parks. Passers-by would never guess there is an asphalt-mixing plant inside.

Can anything further be done to limit the dust that results from these plants?
The conversation about dust emissions starts with the baghouse. Ammann Asphalt-Mixing Plants remove dust through a highly efficient baghouse filter. It actually lowers exhaust dust to less than 10 mg/m³, which is an exemplary benchmark. We are currently working on reducing this value significantly again to < 5mg/m³.

People often focus solely on the dust resulting from the mix-making process, and what comes out of the chimney. They forget that all the logistical operations around an asphalt-mixing plant, and around equipment like trucks and wheel loaders, are creating much more dust than the plant itself. Fortunately, countries like China and some areas in Europe are increasingly considering these other sources.

Ammann and our customers have together developed solutions to further limit dust. We focus on dust reduction points for further improvement. Taking measures at the cold feeder, load-out, skip hood, overflow silo, filler loading area, screen, belts, and transfer points make a big difference. This is in addition to the efforts provided through the baghouse.

To summarise the current state of emissions, I would say that the main focus is on trimming CO₂, VOCs and NOx in the combustion process and on reducing the residual dust content after the baghouse. There are also markets in which, for example, the integration of pre-dosing into the dedusting process is also being promoted.

What about local governmental requirements on CO₂, sound and dust emissions, and the odour emitted by plants placed in residential or commercial areas?
Overall, the requirements are becoming stricter – but they are extremely different from one country to another. We are eager to comply with all the regulations because it’s the law and because we want to be good neighbours too. This means a lot more than shrinking carbon and VOC emissions: it includes muffling sound, which we just discussed, as well as dust and odour.

With regard to odour, bitumen fumes are the primary source of odour. Ammann offers different solutions to contain the fumes and the odour that can result. As with dust, we have reduction points – in this case the bitumen tanks, the skip and load-out levels and the stack.


What is your observation of alternative energy sources, including biofuels?
The use of these new fuels is another meaningful win on the green front. We are taking renewable energy sources, or, in some cases, converting a waste product into fuel. This conserves natural resources and puts less pressure on landfills.

Ammann biofuel burners can also utilize the more traditional fuels such as natural gas, LPG, light and heavy oil and kerosene. This alleviates the concerns of customers who are hesitant to rely solely on newer fuels.

On the renewable front, we are very high on the wood dust burner, which transforms wood dust (a material that is available from local sources), into a renewable fuel. What makes this dust burner even more exceptional is its carbon neutrality. The carbon dioxide released when burning wood is offset by the fact that the tree consumed that amount of carbon dioxide during its life. Therefore, this part of the emissions is carbon-neutral. The burner has proven effective and is utilized on a number of Ammann Asphalt-Mixing Plants. It can be retrofitted on existing plants as well.

Biofuels of course are another initiative; they support climate protection and reduce dependency on mineral oil. Examples of these fuels are rapeseed and sugar cane. Tall oil, which is a waste product of cellulose sulphate production, can be used too.

We expect that in the near future other fuel types such as hydrogen will significantly reduce gas emission values. These fuels will also be much more important in our industry. Ammann is already working on solutions to be prepared for this.

How can an asphalt producer change to a more green operation while utilising his existing plant?
Asphalt producers might be surprised by how much they can accomplish with their existing plant. A very easy first step is to upgrade the control system. A modern control system can have a significant impact on efficiency, and that cuts across many parts of the process. Improved efficiency will lessen fuel usage, emissions, and material waste.

Training is another immediate step that can be taken. The best plant and control system in the world will underperform if the operator is unable to leverage the built-in value. Another option is a more comprehensive retrofit. It still costs a fraction of the price of a new plant and is compatible with products made by Ammann and other manufacturers. A retrofit has a host of options, including recycling solutions. A retrofit enables the use of foam bitumen, waxes, and other additives. Special bitumen and alternative mixing cycles can be utilised as well.

Again, the plant owner can determine the level of the commitment. Many retrofit customers incorporate a new dryer, which optimises heat transfer – and of course reduces emissions – and enables the employment of an expanded range of materials, including RAP. A retrofit can include environmental upgrades to the bitumen tank and baghouse. It can incorporate noise reduction solutions, too. A host of technological improvements can be made – including revamped burners, mixers, and the control system.