Knitting a road with stones and string

Greener road-building

SINCE THE Romans began doing it with great panache more than 2,000 years ago, road-building has been a sweaty, grubby business, involving heaving great quantities of rocks and stones into place and, in more recent times, covering the surface with asphalt or concrete. Now a group of Swiss researchers think they have come up with a more elegant solution. Strange as it may seem, this involves knitting.

Martin Arraigada and Saeed Abbasion of the Swiss Federal Laboratories for Materials Science and Technology use a robotic arm to lay out string in a series of elaborate patterns. As the knitting takes shape, layers of stones are added and tamped down. The string entangles the stones, keeping them in place. The result is a structure that is surprisingly stable and strong. In one experiment a section of pavement put together in this way withstood a load of half a tonne. The encapsulated stones hardly moved at all.

Roads and pavements are usually made from layers of different grades of sand, gravel and stones. Once these are in place the surface is treated with an aggregate that is sealed and…