What if the pavement could melt snow by itself?
That is the promise behind new research by scientists including a Drexel University engineer, who fashioned slabs of concrete that contained an unusual ingredient: paraffin oil.
The concrete looks and feels just like the regular kind, as the oil is not on the surface. Instead, the oil is impregnated into the porous "aggregate" stones that are used as filler within the pavement.
In laboratory experiments, shaved ice melted faster on top of this special-recipe concrete than on the regular kind. The reason? The oil had a freezing point of about 40 degrees Fahrenheit — 8 degrees warmer than the freezing temperature of ice and snow.
As the mercury drops and the oil is in the process of solidifying, heat is drawn away from it to the snow and ice on the surface, said Yaghoob Farnam, a Drexel assistant professor of civil, architectural, and environmental engineering.
"When it freezes, heat is coming out of it," Farnam said. "It will gradually move to the top surface."
The paraffin oil is known as a phase-change material, referring to the changes between its liquid and solid phases. Similar materials have been used to insulate homes, but those paraffins have much higher freezing points, and are wax-like solids around room temperature. The waxy material acts as a sort of buffer inside the wall of a house, drawing heat away from the interior when it melts on a hot day, and releasing it back inside the house when it solidifies on a cooler day.
At Widener University, such materials also are being tested in prosthetic limbs, drawing heat away from the joint so as to reduce perspiration, sores, and blisters.
"Same concept, but different targets," Farnam said.
The Drexel engineer collaborated on the snow-melt research with colleagues from Oregon State and Purdue Universities. Their findings were published in the journal Cement and Concrete Composites.
Farnam and his colleagues now want to test this enhanced concrete outdoors, with sophisticated thermal sensors embedded in the pavement and video cameras to capture the battle between engineering and winter.
They also would like to develop a phase-change material with a slightly lower freezing point — at a more effective sweet spot just above the freezing point of snow and ice. Different materials might work better in various parts of the country, depending on the local climate.
Laboratory results suggest that this enhanced concrete could melt snow over the course of a day or so, taking care of as much as several inches' worth. But once the paraffin oil has frozen, its snow-melting powers wear off — until the weather warms up a bit and the process can occur once again.
Still, the researchers hope their concrete could reduce the need for plowing, shoveling, and spreading rock salt — a material that harms the environment.
The climate of the Delaware Valley seems especially well suited to the concept, Farnam said.
"We believe that based on modeling, in areas like Philly, it's perfect," he said. "We do have very nice heating and cooling cycles."