Ice on roads isn't a good thing, but neither are the eco-unfriendly chloride-based salts used to melt it. Scientists have developed a greener and more effective alternative, however, that could be mixed right into the asphalt and remain active for years.
The chloride-based ice-melting salts which are currently spread on roads can harm the environment when they run off the asphalt and into nearby waterways.
They may also degrade the very roads that they're de-icing, plus they cause cars to rust and they have to be applied repeatedly throughout the winter. Even then, once a fresh layer of ice forms on the asphalt, drivers are stuck with it until the salt-spreading trucks arrive again.
Scientists from China's Hebei University of Science and Technology (and other institutions) set out to address those shortcomings, starting out by developing a chloride-free acetate-based salt. Such salts are considerably less environmentally harmful than chlorides, they're less corrosive to steel and other materials, plus they work at lower temperatures.
The researchers proceeded to mix the salt with a surfactant, silicon dioxide, sodium bicarbonate and blast furnace slag (which has also been used in salt-proof concrete), resulting in a fine powder. Particles of that powder were then coated with a polymer solution, producing microcapsules. Finally, the scientists replaced some of the mineral filler in a conventional asphalt mixture with those capsules.
When the special asphalt was tested on the off-ramp of a highway, it was found not only to continuously melt the snow that fell upon it, but also to lower the freezing point of water from O ºC (32 ºF) down to -21 ºC (-6 ºF). What's more, based on lab tests, the researchers estimate that a 5-cm (2-in)-thick slab of the pavement would continue to release its salt capsules for seven to eight years, keeping the road clear that whole time.
A paper on the study was recently published in the journal ACS Omega.
Source: American Chemical Society
