Old roads hit hardest by heat wave

Road crews scrambled to repair 60 cases of heat-related pavement failure last week in the metro area and around Mankato and Rochester, according to transportation officials.

While pavement buckling isn't uncommon during the hottest days of summer, the number of failures during last week's short, intense heat wave was larger than usual. The Twin Cities region alone had 28 instances of it on Monday and 18 on Tuesday.

"We had sort of a bad situation," said Maureen Jensen, road research manager for the Minnesota Department of Transportation. "We had a very wet spring, [a] rapid temperature change and our pavements are continuing to age, so we saw more blowups on pavements that are older."

Matt Zeller, executive director of the Concrete Paving Association of Minnesota, said older roads are more susceptible to heat-buckling because they have fewer expansion joints -- the half-inch separations between concrete sections. He said new highways have them every 15 feet, while older highways have them every 27 feet or more.

The more joints, the more room sections have to expand without butting against each other and buckling, Zeller said.

University of Minnesota civil engineering Prof. Mihai Marasteanu, who has researched how low temperatures affect pavement cracking resistance, said another problem is the failure of the caulking or sealants used to keep moisture and debris out of the joints.

Marasteanu explained that "joints are the weakest link in the system," and if sand and debris fill them, the sections don't have room to expand. They can push against each other and can rise 4 inches or more.

MnDOT's Jensen said that she and her colleagues continue to look for ways to make concrete pavements less permeable and make joints function better at a testing facility in Albertville, Minn. She said the best way to reduce failures is to keep joints clean and make sure the sealants are working properly.

Zeller said the ideal solution would be replacing older roads. However, costs for building a new highway can be about "one million a mile," and he noted that properly cleaning all of the joints would also be cost-prohibitive.

"Dealing with a few blowups is a fairly easy way to deal with the old designs," said Zeller.