Today's extreme heat and high humidity has the Minnesota Department of Transportation on alert for road explosions.

When temperatures soar into the 90s as they will in the metro area and across a large swath of Minnesota, concrete surfaces heat up and expand. The problem is that the concrete has no where to go but up, said Cliff Gergen, superintendent of MnDOT's Smooth Roads maintenance program.

"We have joints every 20 feet. The concrete expands and when it moves they all get tight," he said. "With the moisture under the road, the heat just cooks it and it takes the easiest path. It gets hot and lifts the road."

The greatest risk for pavement failure is at weak spots on concrete roads or freeways that are 10 years or older. Roads such as I-394 that have an asphalt layer over the concrete have the potential to blow, too. Newer roads are sealed tighter and less prone to heat-related stress.

MnDOT is prepared to respond to a situation should one happen, Gergen said. He said crews out working on other projects will be diverted to fix any road buckles. Crews make temporary fixes "to get the road open," Gergen said.  A permanent fix is made at a later time.

Although none have been reported yet, Gergen said he expects that to happen Monday.

This coolish summer of 2014 has kept the number of road explosion lower than in past years.

"It depends on the year," he said, noting that in 2011 there were 20 road blows during the three-week state government shut down.  But "we've had a couple of them already this year."

How pavement buckles

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