Five questions for Koos Jol

‘I’m always looking for innovation’

Every day, experts invest a lot of energy in the material that we drive over without a second thought. Asphalt is continuously being improved and updated, including in Heijmans’ asphalt lab. Project Advisor Koos Jol introduces us to his world.

October 17, 2017

How do you come up with a new asphalt mix?

‘If we’re developing a new mix, we look at the functional requirements and lifespan of the intended mix. As soon as we know what properties the mix must offer, we get together with our team of experts and examine the options. When it comes to innovations, and new mixes beyond the framework of the standard RAW provisions, we involve Rijkswaterstaat in the development process. Everyone thus works together to supply a decent product.’

‘Sustainability is an important motive. Heijmans is encountering more and more DBFM contracts, where we are responsible for the long-term maintenance of (motorway) roads. For example, we are responsible for maintaining the A12 Veenendaal – Ede – Grijsoord for 16 years. And this responsibility extends to 25 years for 3Angle: A27/A1 Utrecht – Eemnes – Amersfoort. During this period, asphalt quality must be sustained and lifespan plays a decisive role. Heijmans cannot afford to be confronted by unexpected damage.’

Were you involved in the invention of porous asphalt?

‘No, that was before my time. However, I was involved in recycling double-layered porous asphalt. It features a substrate of coarse grit and a thinner top layer of fine grit. This enables us to drastically reduce noise and ensure good water drainage.’

‘Heijmans is a strong player in the field of asphalt recycling. A number of extra steps are needed before double-layered porous asphalt can be recycled. The asphalt contains bitumen as a binding agent. Bitumen starts to become more brittle once asphalt has been in place for a while: harder and of lesser quality. This is particularly the case with porous surfacing, like double-layered porous asphalt. The state of the current mix thus needs to be examined prior to recycling.

Heijmans has developed a process for rejuvenating the bitumen in old asphalt, which makes sure properties are restored to those of new bitumen. This process has proven itself when developing Greenway LE (low-temperature asphalt) and is now used for recycling double-layered porous asphalt.’

What does the research entail?

‘We collect milled material in order to study old asphalt; what is the composition of the mix; what is the condition of the bitumen; and what is needed to improve the properties so it becomes suitable for re-use. We conduct this research in our own laboratory. Once a suitable composition for reusing asphalt has been ascertained, we chart the risks.’

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Old milled material is examined in the lab

‘The age of bitumen, weather conditions and traffic load determine the impact on asphalt quality. Wear is one problem with double-layered porous asphalt - asphalt stones get knocked and come loose. In addition, Rijkswaterstaat has submitted a standard study into frost. One of the questions was how the asphalt responds to repetitive freezing and thawing.

These studies are normally performed in our lab, but are also carried out by organizations like TNO. Ultimately you’re working on a finished product for a test section. This is a section of (existing) road where we’ll test the asphalt for a variety of factors, like large-scale production and processing. We’ll also test the technical and functional properties of the asphalt. If the study is successful, we'll receive clearance from Rijkswaterstaat. The mix will then become a standard product.’

Does your heart beat faster when you see a fresh section of asphalt?

‘I look at roads in a different way. I’m always on the lookout for cracks, ruts and potholes. I look at the cause, where there’s room for improvement or how we could have prevented the problem. My wife does get fed up with it once in a while. Apparently, I can sound like an old record sometimes. Oh well, it’s all part of the job I guess. As an asphalt expert I’m always looking for better asphalt.’

Speaking of innovation, what are your thoughts on future-proof asphalt?

‘Nowadays asphalt needs to last longer and longer and recycling is becoming increasingly important. After all, this saves money and is good for the environment. Another development is automated driving. The self-driving car will have consequences for asphalt. Loads will become more even because cars will brake less often or less abruptly. A potential disadvantage is that everyone could end up driving in the centre of the lane, thus increasing load in that area. This would increase the risk of rutting and wear. So, in due course, we’ll be lumbered with the task of finding a solution for this issue. That's what makes my work so challenging.’