Phase-change materials — or PCMs — show up in the research literature from time to time.
They're intriguing things: materials that release latent heat as the material changes between its liquid and solid state. Many different materials have been used in different ways.
One suggestion, which got a brief burst of publicity a decade or more ago, was to embed capsules of PCMs in gypsum board to help stabilize interior temperatures in conjunction with a building's HVAC system.
I don't know what became of the idea. I've done a couple of quick searches without turning up any evidence that it ever developed into a commercial product.
Now PCMs are back in the news, this time by researchers from three American universities including Drexel U in Philadelphia. They have come up with a system that could create roads that de-ice themselves during winter storms. All they had to do was add a little paraffin wax to the road's concrete mix.
Put that way, it sounds trivial, but it's not. After more work is done, researchers may have a product that could be used at airports to keep runways free from ice and snow. It could be used on expressway ramps.
There could be many applications in the parts of North America where snow and ice can cause problems.
The research team involved people from Purdue University and Oregon State. The team leader was Yaghoob Farnam, of Drexel. The team was among the first to show that using PCMs as an environmentally friendly alternative to salt can be just as effective as the standard salting, scraping and plowing.
"Phase-change materials can be incorporated into concrete using porous lightweight aggregate or embedded pipes, and when the PCM transforms from liquid to solid during cooling events, it can release thermal heat that can be used to melt ice and snow," Farnam says. "By inhibiting the formation of ice and snow on the pavement or bridge surface, the use of PCM may reduce or eliminate the need for de-icing chemicals or salts, snowplowing or both — saving money and positively influencing the environmental impact of such operations."
The paraffin oil the team used is the same ingredient that is found in candles, wax polishes, cosmetics and waterproofing compounds.
Like all PCMs, it releases thermal energy when it changes its physical state, which means that as the temperature drops and the oil begins to solidify, it releases energy as latent heat. That in turn means that the oil can be tailored to embed de-icing capabilities in a road surface so that it becomes thermally active during snowstorms.
During the research, the team created a set of concrete slabs. One had paraffin-filled pipes embedded in it and one had porous lightweight aggregate infused with paraffin. The third was a reference slab without paraffin. Each was sealed in an insulated container and then covered with about five inches of "snow" manufactured in the lab.
With each container held just above the freezing mark, both the paraffin-treated slabs melted the snow within 25 hours, all the snow on the reference slab remained frozen. Thawing was a little faster on the slab with the paraffin-filled tubes. But in the group's second experiment, in which the ambient air temperature in each container was lowered to freezing before the snow was added, the paraffin-treated aggregate was more effective than the embedded pipes.
Farnam says the team believes that infusing lightweight aggregate paraffin is the method that shows the most promise. But he warns that additional research is necessary.
That would enable researchers to gain a better understanding of other factors such as ways in which the paraffin might influence things like the durability of the concrete pavement, skid resistance and long-term stability.
With winter approaching, I have just laid in a bag of de-icing salt. So I'd be curious to know how concrete infused with paraffin would perform on my front walk.
Korky Koroluk is an Ottawa-based freelance writer. Send comments to firstname.lastname@example.org.