The future of sustainable asphalt


Q&A with Dr. Hans-Friedrich Peters, executive vice president of Ammann’s plants division

The roadbuilding industry has paid attention to issues of sustainability for decades. However, environmentally friendly improvements in asphalt and roadbuilding machines continue to gain momentum. 

For the industry, sustainable approaches not only reduce the impact on the environment, they are also able to improve profitability. 

At the forefront of sustainability efforts is Dr. Hans-Friedrich Peters, executive vice president of Ammann’s plants division. Peters recently provided an in-depth look at how asphalt production has become more sustainable, as well as a glimpse at what’s to come.

Q: Can recycled asphalt materials really perform as well as mix made from virgin aggregate?

A: The biggest reductions in indirect carbon dioxide emissions result from the implementation of RAP.

We should not categorize 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 utilizing RAP, you’re saving on both aggregate and bitumen costs – while reducing emissions, initially and over the lifetime of a road.

Dr. Hans-Friedrich Peters

Q: Are countries increasingly adopting recycling, or have we hit a bit of a plateau? 

A: 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.

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

Q: Making mix that theoretically consists of 100 per cent RAP is impressive. Yet many mix makers will utilize less amounts of RAP. What are the solutions for these customers?

A: 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 per cent hot recycled materials can be fed. The RAH50 is a middle-ring dryer that incorporates up to 40 per cent hot recycled materials.

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

Q: At some point, it would seem that manufacturers such as Ammann could only make so much progress on emissions. Are there opportunities for further reductions?

A: There are. The newest is in 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 carbon dioxide emissions. This can be accomplished by actively cooling the drum, increasing drying efficiency and utilizing energy sources such as biofuels and wood dust. Ammann technology can diminish carbon dioxide by 10 per cent or even considerably more, depending on the age of the plant and the technology chosen.

There are other somewhat hidden opportunities to trim carbon dioxide 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 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.

Q: Why are plants located in residential or commercial areas, and what can be done to limit the noise?

A: 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 quieter, 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. Passersby would never guess there is an asphalt-mixing plant inside.

Q: Dust emissions are becoming a bigger issue as plants must often be located in sensitive areas. Can anything further be done to limit the dust that results from these plants?

A: 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 per cubic metre, which is an exemplary benchmark. We are currently working on reducing this value significantly again, to 5 mg per cubic metre.

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 also 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 makes a big difference. That’s in addition to the efforts provided through the baghouse.

To summarize the current state of emissions, I would say 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 de-dusting process is also being promoted.

Q: Are local governmental requirements becoming stricter in general? 

A: Overall yes, the requirements are becoming stricter – but they are extremely different from one country to the next.

We are eager to comply with all the regulations because it’s the law and because we want to be good neighbours, too. That means a lot more than shrinking carbon and VOC emissions. It also includes muffling sound, which we just discussed, as well as dust and odour.

In regards 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.

Q: There is a great deal of talk about alternative energy sources, including biofuels. But should mix producers be hesitant to commit to such fuels, as they are somewhat unproven and their availability might not be as consistent as traditional sources?

A: Ammann biofuel burners can also utilize 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.

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.

On the renewable front, we are very high on the wood dust burner. The burner 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 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 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.

Q: How can an asphalt producer begin to make the change to a more green operation, while utilizing their existing plant?

A: 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. And the as1 is the best in the business at doing exactly that.

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 you can choose from, including recycling solutions. A retrofit enables the use of foam bitumen, waxes and other additives. Special bitumen and alternative mixing cycles can be utilized as well.

Again, the plant owner can determine the level of the commitment. Many retrofit customers incorporate a new dryer, which optimizes 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.