Extreme heat has caused roads to buckle — why does this happen?

Much of the United States has been under a heat wave that has millions sweltering. In some states, such as Missouri, Arkansas and Delaware, roads have started buckling because of the extreme temperatures.

Instances like this are “not very common, because if you’ve designed and built the road correctly, this shouldn’t happen,” Amit Bhasin, director of the Center for Transportation Research at The University of Texas at Austin, told NPR.

“But it does happen once in a while,” Bhasin added.

NPR noted that a “vast majority” of roads in the U.S. are asphalt, which can soften or rut when it gets too hot. Most of the road bucklings reported, though, have been on concrete roads, NPR wrote.

Why do roads buckle in the heat?

Materials like concrete expand in the heat as a result of thermal expansion, defined by the California Institute of Technology as when a material’s atoms vibrate more as the temperature increases, making them push away from neighboring atoms.

The Nebraska Department of Transportation said a pavement “blow-up” can happen when a roadway’s surface expands at a crack or joint where moisture seeps in because of thermal expansion. This crack makes the pavement weak, which makes it buckle or “warp.”

This usually starts with a slight spalling in the crack, NDOT said. Either the condition gradually gets worse, or a “blow-up” happens instantly.

“If your concrete is not designed to handle a certain temperature or… suddenly you have this extraordinary heat wave and it expands more than what the joint allows it to, then it’s got no place to go,” Bhasin said to NPR. . “Then what it’s going to do is start pushing against the concrete panel from the other side of the joint and start moving into each other and cause breaking.”

NDOT says motorists should pay attention to pavement surfaces when driving in above 90-degree heat, and use caution or reduce speeds when getting to these areas.