BLIZZARD-bound motorists won't have to wait for a salting truck or snow plough to clear the way if a "self-heating" road takes off.
While salting disperses ice and snow, the salty run-off corrodes the steel rods that reinforce roads and bridge decks, and also damages vehicles. With the US government striving to improve its road infrastructure after a fatal bridge collapse in Minnesota in 2007, new methods to clear snow without damaging structures are being sought.
One such method, being developed by Christiana Chang at the University of Houston, Texas, and colleagues is to incorporate electric heating elements into concrete roads or bridge decks. When cold weather is forecast, the element can be fired up to heat the road and prevent ice forming.
There are various methods to make a slab of concrete that can be heated electrically. One way is to pepper the mix with an electrically resistive material that will convert electric current into heat, like the element of a kettle.
To start with, the team tried this approach, using fly ash, a waste product of burning coal in power stations, as the element, followed by steel shavings. Both options had the desired effect.
Then they tried an alternative method, using sheets of carbon nanofibres to heat the concrete, and found it was much faster.
Nanofibres comprise lengths of cone-shaped nanotubes nested "like paper cups stacked on top of each other", says Chang. She bonded multiple layers of nanofibre-embedded paper beneath a chunk of road concrete that was 10 centimetres thick and 25 square centimetres in area. It warmed from -10 °C to 0 °C in 2 hours while consuming just 6 watts of electrical power (Smart Materials and Structures, DOI: 10.1088/0964-1726/18/12/127001). Heating the block slowly reduced power consumption.
"It's an interesting technique, but scaling it up to cover whole roads will require enormous power," says Derek Carder, an engineer with the Transport Research Laboratory (TRL) in Wokingham, UK. Indeed, overly high power use was a problem for a self-heating road trialled by TRL itself in 2007, he says.
In a process called interseasonal heat transfer, TRL's system stored summer heat in water kept in insulated reservoirs. In cold weather, this warm water was pumped through a grid of pipes beneath the road to prevent icing. But the pumps proved too power-hungry. "Ideas like these don't seem viable for whole roads, but they may work for known cold spots or bridge decks," Carder says.
The Houston team, however, say that their method is less complex and that as sheets of paper embedded with nanofibres are already used to make electronic components, they are readily available and cheap. They add that savings made on salting and snowplough labour could make their low-maintenance design viable.
Source : www.newscientist.com
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