Cities are beautiful and have tremendous potential for constant change. Have a look to the biggest cities around the world – nothing remains the same. A new shop here. A bar closes there – another hip bar opens up. People move from one city to another through an increase in mobility; so on and so forth. One of the most important materials in cities is asphalt, without which we would not be able to move from A to B. Well, you could fly, but from where would your flight take off?
Erik Schlangen, a civil engineer and pioneer of experimental micro mechanics who focuses on making industrial materials more durable, shares the opinion that asphalt is a very nice material to drive on. However, with one reservation: on rainy days – when lots of water soaks into the material. If you are riding a bicycle and do not pass cars as quickly as you can on one of these days, you will not be happy with what happens next. Also, you are already likely familiar with the fact that asphalt is very noisy.
Talking about “splash-free roads” …
So how can we solve these problems and create a better living city? Erik Schlangen states that one solution is to make roads out of porous asphalt. Porous asphalt, the material used in most highways in the Netherlands, allows water to flow through it and lets rainwater dissipate outwards, thus creating a “splash-free” road to drive on. Another great side effect is the noise attenuation due to the hollow properties of the material.
Unfortunately, one disadvantage of porous asphalt is raveling. What is that you might ask?! Raveling is when the stones that the asphalt is comprised of wear away, one after another, until there is nothing left to drive on. With light raveling, these loose stones present a potential danger to your windshield; after severe raveling, potholes form. Take a look at a slide from Erik Schlangen’s TED talk. As you can see, porous asphalt has only a small amount of bitumen binder between the larger aggregate stones to hold them together. Through weathering, UV light, and oxidation, the bitumen contracts, forms micro-cracks, and delaminates from the aggregates. While driving on the road, the aggregates wear away.
… and other “groundbreaking” inventions
But don’t fret – there is a solution. Erik Schlangen and his team toyed with the idea of self-healing asphalt. To repair porous asphalt and prevent raveling, they took steel wool, typically used for cleaning pans, cut it into very small pieces, and mixed it with the bitumen. Then they used an induction machine to heat up the steel, which in turn melts the bitumen which then flows into the micro-cracks in the asphalt. After doing so, the aggregate stones reattach to the surface and return the asphalt to its save driving condition. Of course, this procedure needs to be repeated to maintain the surface’s integrity.
Excited by the prospects of Schlangen’s work, the Dutch government donated a piece of a highway to Schlangen and his team where they could further test the promising material. In the video below, Schlangen shows the test track that should last for several years without significant wear. If the asphalt is “healed” every four years, it can effectively double the surface’s life and, in turn, save a lot of money in infrastructure expenditures.
If you are still skeptical about Schlangen’s work, have a look at his TED talk below and watch your doubts melt away.
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