Wishes for our road surface

Asphalt. We drive over it every day in our cars or on our bikes; so, above all, it must be comfortable and quiet. But are our road surfaces also capable of more? For instance, improving the environment and supplying us with energy? Or reducing traffic jams? We put these questions to our own asphalt guru, Gerbert van Bochove.

October 16, 2017

The man allowing us to explore the future of asphalt is an old hand in the business. Gerbert van Bochove has been working on road surfaces since the 1980s. After completing his degree in Civil Engineering at the Delft University of Technology, he joined the Research & Development department of Bitumarin, a company that focussed on hydraulic engineering structures based on bituminous materials. This subsidiary of Heijmans was discontinued once the Delta Works were completed.

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Gerbert next to a road featuring Recoflex. This newly developed asphalt features plastic fibres, which make the asphalt more flexible. This means a single layer of asphalt will suffice and roadworks will require less time

Gerbert enjoys studying bitumen, sand and gravel, and exploring the capabilities of this combination. Together with a team of technologists and advisers, he has pioneered many asphalt innovations, including GreenwayLE, Air Jet Sealing, Recoflex and self-healing asphalt. His greatest discovery: double-layered porous asphalt (ZOAB).

Circularity close by

One of society's main requirements for urbanised areas involves reducing the use of (raw) materials. This calls for more recycling. According Gerbert, the good news is that circular road surfacing is close by. ‘Our existing asphalt is the source for the new asphalt. New asphalt for substrates and intermediate layers contains a minimum of 60% recycled asphalt, and we’re working towards 70%.’

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A legacy of last century’s oil crisis, when the Netherlands was forced to be economical with raw materials. Now socially responsible. Only the upper layer of the asphalt still contains a lot of new materials, while these layers are actually first to be replaced. Porous asphalt cannot contain any recycled old asphalt whatsoever. But this is something Heijmans is working on. We have already received the first official approvals for our new procedure from the Rijkswaterstaat. This has put us in a unique position and, contrary to standard regulations, means we can recycle porous asphalt."

Check out our self-healing asphalt

Botox for road surfaces

Asphalt with a longer lifespan is also good news for Dutch residents. Less maintenance means fewer traffic jams due to roadworks. Gerbert: ‘Double-layered porous asphalt will now last nine and thirteen years on inside and outside lanes respectively, without maintenance. And this could easily be extended via, for example, preventive maintenance using rejuvenation agents’. That's why Heijmans launched Air Jet Sealing six years ago: the ‘beauty cream’ for porous asphalt. Jet engines are used to blast rejuvenation cream into the road surface to give the porous asphalt layer an internal upgrade.

Bitumen is an important constituent of asphalt; it is a residual product from oil refineries, which holds the sand and crushed stone together. However, bitumen supplies are likely to run out because refineries are increasingly retaining bitumen for higher-quality products like fuels and oil. Bitumen is thus becoming increasingly valuable - another reason to increase recycling. Replacement using materials with a different basis, like bio-based binding agents, is also being explored.

The proof of the pudding is in the eating. That's why I like clients who are open to experiments

Although Gerbert does not think the bitumen supply will run out, he and his colleagues are working hard to rejuvenate old bitumen. ‘Bitumen in old asphalt is crumbly and stiff; it loses its elasticity. We recently developed a process where we mix asphalt with aged polymer bitumen; this is the highest quality means of recycling.’

Inventiveness and space creation

Gerbert should not be seen as some kind of sorcerer, slaving away over a cauldron in an effort to find the best recipe for a magic potion. ‘Often you’ll come up with ideas by sparring with one another, not just sitting in your lab. That’s why I enjoy talking and discussing with other asphalt experts, which always produces solutions.’

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This is why we regularly collaborate with the Rijkswaterstaat. ‘As a contractor, we serve as an intermediary between theory and practice. We must be able to try out innovations once lab tests have been completed. Test sections on real motorways are thus extremely important to us, and the Rijkswaterstaat is instrumental in facilitating this.’

Quiet as a mouse

Even though Gerbert and his colleagues simulate all manner of realistic situations in their asphalt lab, clients prefer to have results from experiments performed ‘in real life’. Gerbert: ‘The proof of the pudding is in the eating. That's why I like clients who are open to experiments. You’ll even find them at local authorities, like in Ede, where we were allowed to lay Recoflex on various unsurfaced roads. The best ones are asphalt enthusiasts like me, who organize tenders so innovations can be validated. That’s when we often get results.’

Noise nuisance is one of the biggest sources of irritation among the Dutch population. Quieter asphalt is becoming increasingly important, partly because cities are getting closer to motorways. The fact that double-layered porous asphalt is twice as quiet as single-layered porous asphalt is remarkable progress, but Gerbert believes we still have some way to go.

‘People perceive abnormal noise to be a nuisance, like when one drives over expansion joints. We have found an answer to this issue: the Brainjoint. Results of the Stille Duurzame Voegovergangen (‘Silent Sustainable Expansion Joints’) contest, organized by Rijkswaterstaat. This shows how one innovation - double-layered porous asphalt - can encourage another.’

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Sustainability is a criterion in a more and more tenders. By 2030, our road network must actually be energy-neutral. Heijmans has responded to this deadline with Greenway LE, low-temperature asphalt. Gerbert: ‘But asphalt with lower rolling resistance is another option, and will help to reduce fuel consumption in cars. If asphalt is more even and more porous, it becomes easier to expel compressed air in the contact area between tyres and road surface.’ 

Gerbert and his colleagues are currently working on an ultra-quiet asphalt, which will help to further reduce noise thanks to the rubber in the road surface. In the end, cars will make almost no noise whatsoever. Thus plenty of benefits for the environment. The only thing asphalt cannot do at this moment in time is absorb particulate matter. Gerbert: ‘There’s too much of it in the air relative to the available road surface.’

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In order to test porous asphalt, Gerbert performs a test using a special tube. This reveals how quickly water drains off.

Robot on rollers

Despite his passion for producing and laying asphalt, Gerbert expects these processes to change. Digitization will also offer advantages in the asphalt supply chain. ‘In the past, you often had to rely on experience and gut instinct, but automated controls can now do a much more accurate job.’

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Innovation requires knowledge and insight into how materials and products work, as well as knowledge of practical situations and the ‘market’. Gerbert has been transferring his knowledge to several colleagues for quite some time. ‘Not just technical knowledge, but also the mentality needed to innovate. Having the courage to go against the grain.’


Self-driving cars and motorways that generate energy - Gerbert hopes to experience all such innovations. ‘In Den Bosch, buses are already able to charge themselves via induction whilst stopping’, he says enthusiastically. It will not be long now. At present, everything situated on, over and next to the road is still an important source of information for motorists, but signs and markings will disappear.

Gerbert continues his musings: ‘Eventually, all road traffic will be controlled by one big automated, monitored system. Software will direct you to your destination. If we can build that, plus a road surface on which you can charge electric vehicles, then we’ll end up being a transport provider rather than a road authority or contractor.’