Dropping temperatures and the prospect of snow looming in the forecast have Philadelphians crunching through layers of road salt that keep ice and snow from settling on sidewalks and streets.
But what if a sidewalk could melt ice on its own?
That’s the goal of a three-year-long project at Drexel University to develop self-heating concrete, which can keep streets safe from icy conditions while avoiding the environmental and cost concerns associated with traditional road salt.
Salting a city’s streets requires lots of man power and can damage roadways and contaminate the soil around them, said Amir Farnam, an associate engineering professor who leads Drexel’s Advanced Infrastructure Materials Lab.
“We wanted to create an alternative solution,” he said.
Farnam’s team developed two types of concrete that use paraffin wax, a petroleum-based oil used in candles and crayons. Then they placed several slabs in a university courtyard and let nature take its course.
Although each performed better in different weather conditions, both types were able to melt snow on their own.
Researchers captured proof during a February 2022 snowstorm, recording video footage that showed a slab of normal concrete blanketed in white. But its self-heating counterparts kept the flurries off for days.
The concept utilizes the unique properties of materials known as phase-change materials.
In warm, sunny conditions, a phase-change material like paraffin will liquefy. But in cold conditions, it will slowly harden into a solid. As it solidifies, it gives off heat.
“It’s kind of like a battery — paraffins recharge when there’s sun and heat, turning into their liquid phase,” Farnam said. “And when snow or rain or a cold event comes, they start [solidifying] and releasing heat.”
Farnam’s team experimented with two methods of mixing concrete with paraffin. Both have useful applications depending on weather conditions, he said. “Depending on the weather, one would outperform the other one,” he said.
One method involves placing paraffin inside capsules, then mixing the capsules into concrete. This method helps melt snow quickly, but it was effective across only a short range of temperatures.
In another method, Farnam’s team infused pebbles and stone fragments with paraffin, then combined those pebbles with a standard concrete mix.
The concrete with pebbles treated with paraffin released heat over a longer period of time, so it wasn’t as good at quickly melting snow. But it was effective across a wide range of temperatures, he said. For example, Farnam said, it could prove useful for detaching ice from the surface of a road so it can be plowed away.
Philadelphia shouldn’t retire its snowplows and salting teams just yet, Farnam said. In a 10-day cold snap, for example, paraffin will release heat as temperatures drop and then stay solid until they rise again.
“If you’re designing for Philly, it’s not going to be working 100% of the time,” he said.
But the Drexel team’s self-heating concrete worked effectively more than 50% of the time during snowy conditions in Philadelphia between 2021 and 2024, he said. During that time, the temperature dropped below freezing 32 times and the city saw more than an inch of snow five times, according to a Drexel article on the experiment.
Self-heating concrete is more resilient to the cycles of freezing and thawing that create potholes and damage roads, Farnam said. And the technology can help cities use less salt.
“You want to do a combination of, maybe, salt and this technology,” Farnam said. “Even a 50% reduction in salt use in 10 to 15 years of a road’s service life — that’s enormous,” Farnam said. “You save costs, energy, and you can extend the service life. Instead of a road that lasts 10 years, you could have 20 years.”
It remains to be seen whether cities or developers will adopt the technology.
Farnam, who has a patent pending for the concrete developed at Drexel, said his most recent research was funded by a company interested in selling self-heating concrete.
And a decade ago, when he was researching these materials as a Ph.D. student, he and his adviser fielded some interest from the Federal Aviation Administration, which was looking into ways to better de-ice runways.
“The upfront cost is going to be high — twofold or threefold [the cost of traditional concrete], so it would be really hard to convince a Department of Transportation to implement it,” Farnam said.
But, ultimately, he said, self-heating concrete could lower costs for maintenance and replacement of roads. “You could save a lot of taxpayers money,” he said.
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