Rock Doc

As you watch the falling snow, do you marvel at the beauty of the scene or immediately dread driving to work on icy pavement?

Most of our nation’s roads get at least some snow most years, and that means clearing snow and ice from pavement is big business. For highways alone, agencies in the U.S. spend $2.3 billion each season trying to remove snow and ice. And billions more are spent by local governments battling Mother Nature on city streets and county roads.

A traditional way of addressing roadway snow and ice is by spreading salt. In my home state of Washington, workers use about 4 tons of salt in each lane of a mile’s worth of pavement each year. In Minnesota the figure is 9 tons per lane per mile, and in New York it’s a whopping 12 tons.

“That reflects the fact salt is cheap in New York -- and they have high traffic volume as well as lots of snow in places like around the Great Lakes,” said Professor Xianming Shi. Shi is a civil engineer at Washington State University. He researches new and better ways to melt ice on pavement or even prevent it from accumulating in the first place.

The problem with road salt is that it doesn’t vanish with the snow. Instead, via snowmelt, it trickles into groundwater and pollutes local streams and well water. The Environmental Protection Agency recently reported high levels of sodium and chloride, the ingredients of common table salt, in East Coast groundwater. The runoff from roadway salt threatens drinking water supplies, Shi told me.

For a number of years there have been some greener alternatives to spreading salt on roads. Any substance that lowers the freezing point of water can be helpful. One alternative substance that’s well established is a waste product from sugar beet refining.

“That’s a well-known, patented technology,” Shi said.

Shi and his research team are looking at local wastes that can be upcycled for winter roadway operations. These materials range from residue from wine production to materials from flower growers and the biodiesel industry.

Another goal of the work is to find substances that are less corrosive but achieve the same level of pavement friction.

“Magnesium chloride is sometimes sprayed on roads to combat ice,” Shi said. “But magnesium exchanges with calcium in concrete at depth.”

That exchange weakens the concrete, a bit like an elderly person losing bone mass. Overall, the strength of the concrete can be reduced by up to 50 percent.

“So we need to design concrete to better withstand exposure to magnesium chloride,” Shi told me.

It would be wonderful, of course, if pavement resisted the accumulation of ice. The texture of pavement can be manipulated to some extent to resist ice buildup. Nano- and micro-sized particles can be added to concrete to weaken its bond to ice or compacted snow.

“It’s more costly,” Shi said. “Still, it can be useful in some places, like in mountain passes.”

There’s some good research in progress at WSU. But while waiting for further developments, don’t throw out your back as you shovel.

Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. This column is a service of the College of Agricultural, Human, and Natural Resource Sciences at Washington State University.