Keeping Minnesota roads clear in the winter is a large order. Traditionally, road maintenance crews have relied heavily on salt, but recent shifts in understanding have led researchers to realize that salt comes at a cost.
“There are multiple aspects to this chloride issue that we need to tackle,” said Andy Erickson, research associate at the St. Anthony Falls Laboratory at the University of Minnesota and a presenter at the Road Salt Symposium in October 2019. “There are high costs to the environment and to our infrastructure.”
Fortunately, the U of M has been working on the problem. At the gathering, Erickson outlined some of the more promising practices that he and others at the U have been developing.
Alternative chemicals
Every deicing chemical has its pros and cons. Potassium acetate, for example, has been used by MnDOT for deicing bridges in certain parts of the state, and it works at colder temperatures than chloride. It’s less corrosive to most metals, but it does cost more and has greater impacts on galvanized steel. It also has some environmental impacts of its own; they’re just different, and the impacts have yet to be fully studied, Erickson said.
Propylene glycol is less corrosive to metals than salt and causes less environmental and infrastructure damage, but it also costs more and seems to have a negative effect on asphalt and concrete.
Alternative chemicals, in general, show a lot of promise, but their advantages and disadvantages need to be studied and weighed carefully before committing, he explained.
Sand and heat
Chloride and other chemicals aren’t the only way to break the bond between pavement and ice: U of M researchers have looked into creating hydrophobic coatings that prevent ice from sticking to pavement in the first place. They’ve also considered the possibility of conductive, heated pavements and microwaving roads.
Sand also has a lot of potential, especially if heated before application to prevent bouncing. “If you heat the sand,” Erickson said, “as soon as it hits any type of ice, it melts and then freezes into the ice, and makes the ice effectively sandpaper.”
This mitigates the need to fully clear the roads and has been shown to reduce sand usage by 50 percent or more in some cases.
Stormwater
Simple changes in storm drainage infrastructure could also have a large impact. Stormwater ponds, for example, already collect salt in street-level runoff.
“So why couldn’t we use those ponds to capture salt in the spring snowmelt, pump that out so that it’s no longer in the system?” Erickson said. “That’s using existing infrastructure to address a problem.”
Disconnecting infiltration connections between surface and groundwater sources during the spring melt would be key: If the chloride-heavy water could be held long enough to remove the salt, a lot of chloride could be kept out of wells and rivers.
“I don’t need to summarize and tell you chloride is an issue,” Erickson concluded. “But we have some solutions already here today and some very interesting ideas coming very soon in the future.”
—Sophia Koch, LTAP freelancer
