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Michigan road crews patch 500,000 potholes a year and "hope for the best"

How a pothole forms gif animation
Paula Friedrich
Michigan Radio
A crash course in pothole formation

After Proposal  1 was voted down earlier this month, the messagefrom voters seemed to be that they wanted a bill that simply addressed road funding. No extra politics, special interests or provisions.

So what happens when you strip away the politics of road repair? What goes into the actual, well, road repair?

Take a pothole. The Michigan Department of Transportation deals with up to 500,000 potholes a year.

How does it form? 

As a concrete road gets older, it starts cracking. When it rains, water falls through the cracks and soaks into the soil beneath the concrete. Michigan winter rolls in, and the water freezes and expands, pushing the concrete up and out. Come spring, the ice melts away, but the concrete stays domed. This gets repeated a couple of times as May temperatures fluctuate and play with our collective hearts.

Drawing of a pothole forming.
Credit Paula Friedrich / Michigan Radio
Michigan Radio

Eventually, a car will drive over the road and, since the hollowed out space can’t support the car's weight, the road cracks.

A pothole is born.

How does it get fixed now?

That depends on a few things, said MDOT’s Director of Operations Field Services Mark Geib.

More likely than not, a pothole gets fixed with what’s called a cold patch. Sort of like at the dentist, the hole is cleaned and then plugged with bituminous-coated asphalt, a material chosen for its quick-hardening properties. That way, repairs don't have to stop traffic for too long.

“You see the maintenance forces out there shoveling the material into a pothole and then backing away and tamping it just quickly and then getting out of the way and letting traffic run on it right away,” said Geib.

Cold patches are just short term fixes. Over time, as cars continue to drive over the patched pothole, the bituminous-coated asphalt wears down again.

Potholes are one problem you can report with the GRCity 311 app.
Credit Chelsea Oakes / Creative Commons
Creative Commons
Potholes are one problem you can report with the GRCity 311 app.

If at all possible, longer-term fixes are preferred, Geib said.  That might mean using hot mix asphalt (the epoxy glue to the cold patch's glue stick) or cutting a chunk out of the road and replacing it entirely. However, that takes time, something that's hard to come by in high-traffic areas.

Better fixes also cost more, and with transportation funding up in the air, Geib said, they're also rarer.

“Our budgets are so tight now that a lot of times we just have to put in something that will last for a few months and hope for the best,” he said.

MDOT currently spends around $10 million a year filling potholes, Geib said. That's about $1,000 per mile of road in MDOT's network, annually.

“If we had better roads, that would be money that we could just put back into building roads right the first time,” he said.

Getting to better roads

Emily Herbert is a graduate research assistant in University of Michigan professor Victor Li's lab. She's been helping Li continue to develop "self-healing concrete."

The self-healing concrete could work to prevent potholes, Herbert said. When it starts to break, the cracks are tiny -- almost invisible to the naked eye -- and when they're exposed to water and air, a chemical reaction within the concrete creates a healing product that fills the cracks. The material also has almost metal-like qualities, Herbert says, that allow it to literally bend under weight. 

This science-fiction sounding thing also costs a lot more than regular concrete. Herbert estimated the up-front costs are likely two to three times higher, but noted that the self-healing concrete could potentially save up to 50% of long-term repair costs.

Geib said there are a number of futuristic materials like the self-healing concrete that are being developed. MDOT is always evaluating new materials, and coordinating with other states to hear what they've tested, but without extra funding, there's not much room to invest in materials with high initial costs when there are still potholes that need to be patched. 

- Paula Friedrich, Michigan Radio Newsroom

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