Quirks & Quarks·New
Bob McDonald’s blog: Researchers in China have developed a technology for an asphalt additive that can slowly release salt on-demand over the life of the road.
Bob McDonald’s blog: Asphalt can be engineered with slow-release salt incorporated in it
Bob McDonald · CBC Radio
Canadians are all too familiar with icy roads and treacherous driving conditions, especially before the snow plows, gritters and salters arrive. But scientists in China have developed a novel additive for asphalt containing embedded salt that enables the road to melt ice on its own.
The most common material used to melt road ice is rock salt — plain old sodium chloride. In Canada, more than five million tons of salt are spread on roads every year.
While it is effective at clearing roads of snow and ice, salt has negative effects on roadside vegetation, soil, birds and freshwater ecosystems. Salt-laden runoff water is briny, making it difficult for aquatic life, and it can contaminate groundwater.
On top of that, there is the corrosive effect of salt on vehicles and roadways themselves.
Alternatives to road salt, such as calcium chloride, magnesium chloride or other chemicals, have been used, but many still have environmental effects. And of course, there’s a cost to all that salt and the machinery and labour to apply it.
Another option, developed over decades and used in some areas, is to incorporate salt into the asphalt mix when the road is laid or resurfaced. This salt is then released when the road is icy – the road essentially salts itself as needed.
It’s a clever idea that’s much more complicated than it seems. The salt needs to be mixed with additives to make it release only at appropriate temperatures, at an appropriate rate, and not leave voids in the road-bed that would weaken it and cause the pavement to break down.
Researchers in China reporting in the American Chemical Society journal ACS Omega have released their study of the latest, improved iteration of this idea.
They started with a sodium acetate salt – rather than a traditional chloride salt – which is less corrosive, making it kinder to the vehicles and road infrastructure. They encapsulate it in small polymer spheres that are incorporated into asphalt while it is being made.
The researchers designed the polymer capsules with tiny channels that release salt at a very slow rate, so they estimate a roadway could remain ice resistant for at least eight years.
The salt is slowly released onto the surface of the road over time to act as a melting agent that is present before the snow falls. In a real world test, a ramp on a Beijing expressway was covered with a five-centimetre deep layer of treated asphalt and did not accumulate snow as readily as untreated ramps.
They also found that if snow and ice accumulate during a heavy storm, a water layer forms between the ice and the road surface that makes it easier to break the ice up, even by regular traffic.
An ice-melting road would require less plowing, which translates into lower maintenance costs and less wear-and-tear on the pavement.
In an attempt to keep the cost of the new material down, the salt was made from industrial biomass by-products, and mixed with waste slag from steel manufacturing to provide a mechanical structure that can withstand the pounding of vehicles.
According to the RCMP statistics from 2017, nearly one-third of all vehicle accidents in Canada involve wet, snowy or icy roads, while insurance companies report a nearly 50 per cent increase in claims during December and January.
While this self-salting technology is still in the experimental stage, someday, ice-melting roads could contribute to enhancing road safety — especially in this country, where driving on ice is an annual necessity.
ABOUT THE AUTHOR
Bob McDonald is the host of CBC Radio’s award-winning weekly science program, Quirks & Quarks. He is also a science commentator for CBC News Network and CBC-TV’s The National. He has received 12 honorary degrees and is an Officer of the Order of Canada.