The temperature hit a record-breaking 101 degrees last Monday, and metro area highways and freeways crumbled under the heat.
On that day alone, Minnesota Department of Transportation (MnDOT) crews responded to more than a dozen simultaneous road explosions in the Twin Cities as the extreme heat caused concrete to heave, crack and buckle.
A trio of pavement failures brought traffic to a near standstill on southbound Interstate 35W between County Road 23 and Sunset Avenue in Lino Lakes. Concrete also buckled Monday afternoon and evening on I-694 near Lexington Avenue in Shoreview and on Cedar Avenue near the I-35E interchange in Eagan and downstream at Palomino Drive in Apple Valley.
Numerous road buckles have happened over the past week in greater Minnesota, too. On northbound I-35 near Rush City, it was so bad that drivers were told to avoid the area.
"It is the season," said Anne Meyer, a MnDOT spokeswoman. "When temperatures heat up for extended periods of time, we see this."
Concrete roads are built to endure a wide range of extremes — from very hot to very cold — and are cut into sections to allow space for the pavement to expand and contract. In most conditions, that space is sufficient.
Road buckles are slow in forming, sort of like potholes. The sun warms the concrete, and the hotter it gets, the more it expands, Meyer said.
Dust, dirt and sand fall in the cracks over time and eat away at the space that pavement needs to expand. When road temperatures exceed the ambient temperature, the concrete doesn't have enough room to move. That is exacerbated by vehicles driving over the compromised pavement until it finally breaks, pops and heaves, Meyer said.
Road buckles can happen anywhere but are most likely to happen in places where concrete is old or weakened, like on I-35W in Lino Lakes where there had been a previous explosion.
They are less likely to happen on asphalt roads, which are more flexible than concrete. But high heat can cause a bump similar to a frost heave to form, making them equally dangerous.
Regardless of the deformity, "don't drive over them," Meyer said, noting buckled roads can cause significant damage to vehicles. At the very least, motorists encountering them should slow down and change lanes if possible. And they should call 911 to report them.
MnDOT classifies pavement malfunctions as a road emergency, and they are given "a top priority," Meyer said. Crews are dispatched immediately, she said.
For big jobs such as on I-35W, MnDOT uses a milling machine to cut a trench-like path across the traffic lane. Crews cut out the bad concrete and clear away dirt and grime, then fill the groove with a hot asphalt mix and smooth it out.
It's a "quick-fix, Band-Aid fix" said MnDOT spokesman Kent Barnard. But the goal is to get the road drivable as soon as possible, he said.