Erik Schlangen, an engineering professor at Delft University of Technology, however, has invented a self-healing type of asphalt that has a lifespan double that of the traditional porous variety.
Schlangen explains, “Though porous asphalt has very good properties it also leads to durability problems. For example, as there are a lot of pores inside you get much faster oxidation than with usual asphalt and then the bitumen becomes very brittle due to this oxidation and cracks easily. You get these small micro cracks in the bitumen and so, when a car drives over the road, the stones at the surface come off.”
The wool heats up and melts the bitumen around it, closing the micro cracks
If untreated these small cracks will grow and grow until they become large potholes that can damage vehicles and cause serious accidents. A porous asphalt road will last about 8 years before the top layer will need to be replaced. Schlangen’s answer to this problem was, rather strangely, to add steel to the bitumen mix.
He says, “We add a very small amount of steel wool fibres , less than one percent of the volume, and then apply an induction plate to heat up the steel wool. When the wool heats up it melts the bitumen around it and closes the micro cracks.”
This means that every couple of years as the cracks start to appear, you could apply induction heat to the roads and they would heal themselves. Schlangen says, “You have to do that before they turn into potholes. You go on the road with an induction machine, it can be on a truck say and you drive over it, it heats up the wool and melts the bitumen and then the stones are fixed again.”
They have already trialled this on roads and it appears to be working well. He says, “We’ve tested a 400 meter section of road in the southern Netherlands that we laid down two years ago. There we applied induction heat and it works perfectly. We took a lot of samples from the road and aged them in the lab by putting them in the oven and spraying them with water etc and then applied induction heat and the tests have proved that we can double the surface life of asphalt, maybe even more.”
Although this steel infused asphalt costs more than the traditional kind, in the long run money will be saved.
Schlangen says “The cost of material is increased somewhat because you have to add steel fibres but that’s not more than a 25% increase of the cost of the material and then there is the induction machine – you need some investment to build that and you have to drive over the roads with it. However, if you have double the surface life of your road, and no maintenance in between except driving over it with an induction machine, that saves a lot of money – the government will be able to make new savings this way.”
Check out the TED talk below which shows Schlangen putting his self-healing asphalt to the test: