The science of de-icing roads

GRAND RAPIDS, Mich. (WOOD) - What do you get when you combine liquid calcium chloride and salt? Drivable roads.

County road commissions rely on salt to clear the roads during the winter months. But salt has its limits.

When road crews go out during storms, the object is not always to melt the ice but rather to break the bond between it and the road surface. When the salt is dry, it does nothing.

But when it gets wet, it makes a brine -- and that's what starts cutting the ice. The salt truck drivers use a wetting agent -- liquid calcium chloride -- added to the salt.

Since the salt at this point is a prewet solid it begins working much sooner. If operators spread dry salt on the roads, they'd have to rely on melting snow to start that process.

It isn't entirely true that salt stops working at a certain temperature. Salt works, but so much more is needed at lower temperatures it doesn't make sense to keep dumping it on.

"Once you get below 20 degrees you have to start looking. Is it rush hour? Can we afford to put it down to get people throuh rush hour?Is it during the middle of the day when we have some sunlight ? What is the windchill? That windchill will refreeze just like your skin," said Jerry Byrne of the Kent County Road Commission. "All of those things come into play. So we can't afford it economically, the infrastructure can't afford 2000 pounds (of salt) a mile, the environment can't afford it and your car can't afford it."

Salt also hastens the thaw-refreeze process. That means salt today, potholes tomorrow. And no matter what temperature it is when the salt is applied, it doesn't work immediately.