Now is the time to make a change! On the topic of “Sustainable use of asphalt as a building material”, we invite Dr. Carsten Karcher (Secretary General of the European Asphalt Association) for an interview.

infraTest: Welcome, Dr Karcher. Thank you very much for taking the time for our interview. As Secretary General of EAPA, you certainly have a lot to do. What are your main tasks?

Karcher: I move around the Brussels scene and collect information on regulations, legislation, initiatives and relevant asphalt information from member companies and countries. I then prepare and disseminate this to the members of the association. I moderate and represent the interests of the asphalt association, trying to harmonise different objectives.

infraTest: An exciting but also demanding field of activity. What insights have you been able to draw from your work regarding the sustainability of asphalt as a building material?

Karcher: Sustainability is a frequently discussed and highly topical issue. That makes it very complex, because there is a lack of a uniform understanding of this term. Asphalt is 100 % recyclable. This makes us fundamentally very sustainable. This understanding has been around for about 35 years. In addition, there are new developments, issues regarding CO2 emissions and the overall CO2 balance, resource conservation and environmental protection. The question is always: Where can we save what?
This would be possible, for example, in the area of asphalt production, asphalt transport or asphalt paving. But we also have to look at the vehicles that drive on the asphalt and emit CO2. It is a question of fuel consumption, rolling resistance and thus CO2 consumption. Roads that are well maintained and level reduce rolling resistance and thus CO2 emissions.
Sustainability is therefore very broad: What raw materials are used, how far are the delivery routes, how much energy is used to produce the asphalt (keyword low-temperature asphalt)? Is the asphalt paved with equipment that is operated electronically or with renewable energies? How durable is the asphalt? All these factors are highly relevant. Finally, it is important to consider how much energy is required by the rolling traffic on this road.

infraTest: Where do you see the greatest potential for implementing the idea of sustainability in relation to asphalt?

Karcher: By far the greatest potential can be seen during the use phases of roads. 95-98 % of energy is consumed during the use phase. Not for maintenance, but for the traffic that rolls over it. It is questionable to what extent this can be attributed to the building material. But this is also part of the life cycle of asphalt. The production of the building material is thus almost subordinate. Nevertheless, there are great opportunities here as well. We, in the European Asphalt Association, regularly collect data on the “Asphalt in Figures”. In the course of this, we determine the average, country-specific CO2 emissions for one tonne of asphalt and how these are changing. Further potential savings can be made through recycling, lower temperatures, other construction materials, various logistical aspects and transport routes. In this way, the asphalt industry could already achieve the 50% and 55% emission reductions that the European Commission has announced as targets for 2050.

infraTest: The absolute buzzword of the industry is low-temperature asphalt. Do you think we need to push this aspect further in terms of sustainability or are there other areas where we could achieve faster success?

Karcher: The asphalt industry reuses a lot of asphalt, so we were already implementing the sustainability idea before the discussions. Currently, I would say the biggest potential is in the fuels for the asphalt mixing plants. It has to be checked how sustainable these are, as they are included in the CO2 balance per tonne of asphalt. Possible new options are biofuels.
But low-temperature asphalt also plays a role because it can save energy. Low-temperature asphalt has several aspects, however, and that is not only the CO2 emission. It is also the application possibilities of this building material. Faster cooling, faster opening to traffic and faster implementation of maintenance measures. Lowering the paving temperature of asphalt by 10 K reduces emissions by 50% and thus the fumes that escape from the hot asphalt.

infraTest: Low-temperature asphalt sounds almost like a miracle cure. Does it also have disadvantages?

Karcher: Low-temperature asphalt is normal asphalt produced with a different process. These different production methods mean that predominantly less energy is needed for paving. However, boundary conditions must be taken into account: For sufficient compaction, the asphalt must not cool down too much. Experience is needed for this special handling. But the information we have from other countries shows no disadvantages, and in other European countries up to 40% low-temperature asphalt is being laid. In Germany, some people believe that the durability of low-temperature asphalt suffers. However, other countries cannot confirm this. Therefore, it can be assumed that this construction material, if used correctly, is a further development of asphalt as we currently know it.

infraTest: So why did it take so long to develop the manufacturing process for this asphalt? Was there no need?

Karcher: In my opinion, there was no need and no pressure. It was not about saving energy or reducing emissions, nor was it about earlier traffic clearance. Low-temperature asphalt was developed in Germany and Scandinavia about 20 years ago and then disappeared into a drawer. It was only after a scanning tour by the Americans in Germany in 2007 that this concept became more popular. In retrospect, the developing engineers were 20 years too early.
It is now the same as it was back then with Stone Mastic Asphalt, which was considered a special
construction method for 20 years before it was included in the “proper” set of regulations. It’s the same now with low-temperature asphalt. We Germans just need a little longer in this respect.

infraTest: Is every asphalt mixing plant currently capable of producing low-temperature asphalt or does a changeover have to take place first?

Karcher: That is a question I cannot answer completely. It depends on the machine technology. It is possible to produce low-temperature asphalt with foamed bitumen. This is a water vapour bitumen mixture that reduces the viscosity. Alternatively, the use of additives is an option, which must be dosed accordingly. But conversions are not a hindrance. Low-temperature asphalt is not exotic. Asphalt mixing plant manufacturers have the necessary technology.

infraTest: Previously, you identified the use phase as an important starting point with regard to the idea of sustainability. In your opinion, which measure should be pursued in second place?

Karcher: That is the topic of circular economy. That means that every tonne of asphalt remains a tonne of asphalt in the future and is used again in the exact layer from which it was taken (reuse).  So it remains asphalt in any case and not a subordinate product. Because that would be recycling. Therein lies the advantage of asphalt. When properly taken from the road and processed, it produces an almost 100 per cent replica of the original material. Sometimes rejuvenators have to be added because the material is subject to ageing. If at some point no more additional roads are built, but only existing ones are reprocessed, then the asphalt will be reinstalled at this or another point in the cycle. This means we will not need new bitumen and aggregates once saturation of our infrastructure is reached. This reinforces the circular economy phenomenon. Nothing is thrown away and replaced with something new.
This is also in line with the waste hierarchy, according to which waste is first avoided. If waste cannot be avoided, the product is to be repaired. In this case, asphalt would be rehabilitated or preserved. If this is not possible, at least parts of this product should be used in a similar new product (i.e. asphalt reuse). If this is not possible, the building material contained should be used in a recycling process. Asphalt is therefore to be used in another road construction product as black stone.

infraTest: Thank you very much for this comprehensive assessment. What is your next project? The E&E Congress will take place in a few months. Are you already looking forward to it?

Karcher: Yes, tremendously! I’m happy when it finally starts. You can’t imagine how much work and heart and soul has gone into this project. Because after the postponement due to the pandemic, we changed the format to a virtual congress. I am most curious to see how our event will be received. So far, over 500 participants have already registered and we have a full virtual exhibition. Both in terms of exhibitors and lectures. We’ve invited top-notch speakers again and have informative booths that set new standards with innovative and smart technology. But our highlight are the live sessions. There will also be live Q&A after the presentations, so everyone is welcome to interact with us. At our E&E Congress, virtual visitors are not just passive participants. Take an active part and immerse yourself in a new world. I look forward to welcoming you online from 15 to 17 June!