Wherever you look in the Netherlands, there is a good chance that you will see a piece of asphalt somewhere. Our country is full of them. You will find no less than 140,000 kilometers of cycling and hiking trails, regional and motorways in the Netherlands, most of which is asphalted. We drive over it en masse every day with buses, trucks, bicycles and cars. Asphalt is as common in the Netherlands as the cheese slicer, licorice and stamppot.
Asphalt is best suited to drive over in the Netherlands, because it has little problems with subsidence.
Asphalt works well in the Netherlands. We have many soft surfaces and the material bends a bit (see box), so that it does not sag or tear. In addition, it produces relatively little noise. Also handy in the densely built-up Netherlands. Still, things can be improved and changes are on the way. Asphalt researchers have their eyes on the future and are working on innovations. NEMO Kennislink speaks with experts Sandra Erkens (TU Delft) and André Doree (University of Twente) to discuss how it will develop further in the coming decades. They expect that asphalt will be made more sustainable and that more technical gadgets will be incorporated into it.
The first steps in that direction can already be seen. It is even possible to drive on the asphalt of the future. Different pieces are already being tested in the open air at various places in the Netherlands. The world’s first bio-asphalt is located in Vlissingen. But also in Anna Paulowna, Utrecht, Alkmaar and Rotterdam you will already find greener variants of asphalt.
In the current method of making asphalt, sand, stone and a third substance (currently bitumen) are mixed. If you heat this up, it mixes well and, more importantly, you can spread it on the road. “It’s a bit like chocolate. When it is warm, it softens and you spread it more easily and spread it on the road that way. When it has cooled down, it becomes stiff and tough and you can drive over it by car ”, says Erkens.
More sustainability is mainly feasible by replacing the bitumen. This is a residual flow from the oil industry and is therefore reused in asphalt. “But it is very annoying for road builders that they do not know exactly what the bitumen contains,” says André Doree, professor at the University of Twente and an expert in the renewal of road construction. “Oil companies are rather vague about it. This makes it sometimes difficult to determine the perfect composition. Moreover, bitumen naturally remains a fossil product, because it is made from oil. ”
All kinds of sustainability initiatives are therefore aimed at no longer using bitumen. Bitumen consist of both long and short molecules. The long variants are replaced by lignin in tests. These are also large molecules ”, says Sandra Erkens, professor of applied road engineering at TU Delft. Lignin, a by-product of paper production, was used for the test in Vlissingen. “But you can also think of other sticky substances, such as algae oil or resins and remnants of organic waste. It is good that this is being researched, but it is still unclear, as always with new developments, how successful this will be. ”
Asphalt as the champion of the street
The Netherlands is a delta area with soft surfaces that deform a lot over the years. The great quality of asphalt is that it can handle that well. It bends a bit with those settings without breaking. This is not possible with concrete. Is the bottom subsiding? Then a part of the concrete sinks and breaks. Stones are uncomfortable to drive over at high speeds and produce a lot of noise. “Asphalt is a bit like chewing gum. When it is warm, you can deform it and it is soft. When cooled, it becomes tougher and stiffer. That works well for laying, repairing and bending a bit with subsidence, ”says Erkens. In addition, asphalt is less noisy than concrete and stones. In the densely built-up Netherlands, this makes the material the champion of the street.
Mattress with a topper
Another option is to mix the bitumen with so-called epoxy, a plastic that you can make biologically. “Epoxy can be compared to two-component glue, which you can buy at the hardware store. If you add epoxy to the asphalt mixture during production, it will become very hard. The idea is that the asphalt will last longer and be damaged less quickly. That is also more sustainable ”, says Erkens.
Researchers want the new ways of making asphalt to be easy to fit into the current method of manufacturing it. The reason for this is that it is so cheaper, but also because asphalt is already largely reused. “Asphalt consists of several layers,” says Doree. “The bottom layer is very strong and can often remain. You have to replace the top layer more often due to wear. ” You can think of a mattress with a topper on it. The large mattress is the firm underlay. The piece of asphalt that you drive over is the topper, on which you lie softly dreaming away in your bed.
Is the asphalt due for replacement? Then only the top piece, ie the topper, is scraped off and reused. Workers mill away the top part. That goes per layer, like you cut a cheese. This then goes back into the boiler and you make a new mix of it so that strong asphalt is produced. In this way, the 140,000 kilometers of asphalt that is already in the Netherlands is a nice stock to reuse later. “This approach to recycling originated around the oil crisis in the last century. Because reusing asphalt means that you need less new stones and bitumen, it is economically attractive for road builders, ”says Erkens.
Major innovations are therefore in fairly small adjustments. That also applies to more technology in the way. Now the asphalt is only to be ripped over. You may be able to communicate with it in the future. Scientists are investigating how to make the road surface smart. For example by adding sensors. This illuminates the road surface, for example to indicate which way vehicles should go. It is even more likely that the road surface will be driven by intelligent, (partly) autonomous cars. They communicate with each other, but also with the road. This way they share information about where they are and prevent collisions.
But how do you get these kinds of small sensors in the road surface? TU Delft and University of Twente are investigating this together. For example, by mixing RFiD tags into the asphalt. “But this is not that easy. The mixture becomes very hot, about one hundred and fifty to two hundred degrees Celsius, and then it is also driven over with heavy rollers after spreading. These are not pleasant conditions for electronics. It is a form of violence that they cannot handle well. Yet you will have to adapt this type of technology to the current way of making asphalt, because you want to fit it in and not change everything for it, ”says Erkens.
An artistic representation of electric charging while driving, created by Studio Roosegaarde. Pavol Bauer of TU Delft is researching this.
Another problem is that you often no longer know where the sensors are exactly. “A truck tips the smart asphalt into a spreading machine and puts it on the road. There is a good chance that you will no longer know where the sensors are. And there is also a considerable risk that they are broken, ”says Doree. “We have to solve that before we can use it.”
Loops and charging systems in the road surface also seem to have a future – NEMO Kennislink has already written extensively about this. In doing so, you install electronics in the asphalt that charges electric cars while they are driving. It’s the wet dream of many electric riders. After all, it is then possible to drive much further. The battery is then continuously charged while on the road via so-called inductive charging. Just like your electric toothbrush is being charged. But it is not that easy to install them in the asphalt, says Erkens. “Those loops come close to the top. There they cause stress concentrations and this causes damage to the road surface. Compare it with tram rails in cities. There too you have two different stiffnesses next to each other: every time a tram passes over it, it pulls apart. It is not useful for the life of asphalt. We still have to find a solution for that. ”
Source: Kennislink by www.nemokennislink.nl.
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