Cracks in asphalt are a common sight, but a pain to repair. It is expensive and because the roads need to be closed down for construction, traffic jams occur. Researchers at ETH Zurich and EMPA in Switzerland are working on a solution by creating pothole proof, self-healing asphalt, which can be mended using a magnet field.

Bitumen is a sticky, viscous black binder used in road construction, made from petroleum. The bitumen is mixed with aggregate particles for the use of road construction, but slowly crumbles down due to wear and tear, differences in temperature and chemical substances. The cracks that develop are first microscopic, but eventually grow under the weight of traffic.

To make the self-healing asphalt, the binder is mixed with iron oxide nanoparticles. When these particles are exposed to a magnetic field, they heat up. This heat is transferred to the bitumen, softening it and thereby closing the cracks.

To be completely self-healing, roads must be constructed entirely using the nanoparticle mixture, but existing potholes can be mended with the new material.

A few years ago, there was a similar project, but instead of nanoparticles, steel wool fibres were used. However, the main problem with this was that the fibres took too long to heat up, which would mean that it would take several minutes to fix half a metre of road.

The iron oxide nanoparticles used in the current project heat up much quicker, eliminating this problem. In addition, iron oxide particle are not harmful for human health, though because they are strongly bound with the bitumen, it is unlikely they could escape in the first place.

Because of the constant road-stress, the surface has to be treated annually. The researchers envision that this could be done using maintenance vehicles equipped with giant magnetic coils, to quickly kick-start the healing process.

Photos: Reuters / EMPA