MINNEAPOLIS (WCCO) — They may be the only bad thing about the dawn of spring. Potholes are busting out all over Minnesota. But why are potholes so hard to fix?
“They’re terrible, they ruin our cars and they don’t do anything about them,” said one Minneapolis motorist.
“I almost fell into one on the way to work this morning,” laughed another man.
But even though the city of Minneapolis, for example, has dumped 200 tons of so-called “cold mix” into potholes so far this winter, the city knows that the cold mix is a temporary solution.
So, why is a permanent solution so elusive?
“The hard process is getting the patch to stay in place,” said Steve Johnson, vice president of Cimline Sales, the parent company of DuraPatcher which is a newer pothole patching system that uses spray injection to shoot the mix into a pothole.
“This is a permanent repair and the advantage is, it fills from the bottom up, so there’s no compaction required,” said Johnson.
Cold mix doesn’t stick very well to the inside of a pothole and so the mix ends up pouring out of the hole. But cities can’t get the regular, heated asphalt they use to build roads during the winter.
“The asphalt plants typically shut down from October till March or April, so the hot mix isn’t available. At that point, you can only go with what’s called a cold mix,” said Johnson.
It’s a point Minneapolis Mayor R.T. Rybak echoed on his blog, writing: “it’s a quick, temporary fix that doesn’t last as long as hot asphalt but makes streets passable until we can repair them permanently.”
Whenever any water infiltrates the loose connection that the cold mix has formed, it can freeze, then expand and then push that cold mix out again.
The DuraPatcher is a pressure system that combines a liquid mix of asphalt, water and soap with a rock aggregate.
The first step involves using low pressure air to blow out the junk and water in a pothole. Next, the emulsion is sprayed on the surface.
“That gives the patch something to bond to,” said Johnson.
Then out comes the rock.
“The rock is actually coated as it’s sprayed into the patch. That covers all the surfaces and allows it to bond to the road and to itself,” he explained.
Finally, a layer of dry rock is sprayed, so cars can drive on the patch immediately.
“We can come back in a year and this patch will still be here,” said Johnson.
According to the company, the cost of the materials (rock and emulsion) is about half the price of the “cold mix” road crews use today.
Plus this system fills potholes much quicker than a traditional road crew.
However, there is an upfront cost of at least $60,000 to buy the DuraPatcher equipment.
“There’s no comparison to dry mix,” said Lynn Nardinger, Deputy Director of Public Works for the City of Red Wing. “The cold mix never stays in.”
Red Wing has used the system for several years and, according to Nardinger, “it’s well worth it.”