For U.S. motorists in any parts of the million-square-mile area under the heat dome of 2011 – with temperatures in the 90s and 100s (Fahrenheit), and heat indices 20 and 30 points higher in some places – there’s more to worry about than engine coolant and functioning air conditioners. Add exploding potholes to the list.
Actually, it’s pavement that is exploding, leaving potholes in its wake. This largely occurs with asphalt roads. Where concrete slabs are used in highway construction, the danger is buckling, as when one-ton chunks of concrete push upward due to the expansion effect of heat, creating dangerous steps and ramps in the roads.
Cable network CNN reports there are 141 million people living in the areas affected by the heat wave, which stretches from southeastern California and Arizona, across Texas and the Gulf states, up across the eastern seaboard to New York and Boston, as well as through the Plains states on up through the Dakotas, Wisconsin, Illinois and Michigan. Triple digit temperatures were felt on Wednesday, July 20 in Las Vegas, Phoenix, Blythe (California), Wichita, Topeka and Lawrence (Kansas), Wichita Falls (Texas), Omaha, Oklahoma City, Tulsa, Fort Smith (Arkansas), Columbia (South Carolina) and Chicago. Cities edging close to that with temperatures in the high 90s were St. Louis (99 degrees), Kansas City (96 degrees), Dallas (96 degrees), Detroit (95 degrees) and Minneapolis (96 degrees).
In Iowa, the cities of Cedar Rapids (97 degrees), Des Moines (97 degrees) and Waterloo (97 degrees) are just about as bad off as in neighboring states. But high temperatures did not slow intrepid news reporters in those cities, as well as Chicago and Minneapolis, from identifying the phenomenon of exploding and buckling pavement. Culled from the media in several cities we see the following:
From the Quad Cities Times: “Drivers traveling in Iowa should be aware that the mercury might not be the only thing to rise during the sweltering summer heat. Pavement blowups occur when thermal expansion forces the pavement to buckle and shatter. A number of such incidents have been occurring this week. ‘The wet weather in parts of the state combined with the extreme heat is a recipe for pavement blow ups,’ says John Selmer, director of the Iowa Department of Transportation’s (DOT) Statewide Operations Bureau.”
From the Des Moines Register: “Extreme heat caused road buckling at the intersection of First Street and Ankeny Boulevard on Tuesday. City officials have temporarily fixed the problems to keep traffic moving. Heat pushed up the concrete and part of a steel storm sewer grate. A cold patch was applied to the hole. In eastern Iowa, repairs are underway on a stretch of Interstate 380 after sizzling temperatures caused the pavement to buckle. The ‘blowup’ happened Monday night in the northbound lanes about a mile south of the Swisher exit, between Iowa City and Cedar Rapids.”
But this is nothing new, not even for the Summer of 2011. Already in early June, pavement problems due to heat were reported in Watertown, Wisconsin.
From the Watertown Daily Times: “The high-rising temperatures Tuesday caused several area roads to buckle and blow up. High temperature records were set throughout the state Tuesday as Watertown recorded a high of 94 and in Milwaukee the mercury reached 97 degrees. When the temperatures rise, such as they did on Tuesday, highway concrete expands, according to Randy Franks, supervisor at the Dodge County Highway Department. When there is no place to go the concrete cracks and blows up, he said.”
Watertown’s street superintendent Rick Schultz explains that crews use a milling machine and skid steer to grind cracking pavement, sometimes completely repairing joints underneath the road. When they need to mill down to the sub-base of an asphalt road, the section of pavement is cut out completely and reconstructed. Seal coating, itself a method used to preserve aging pavement, sometimes “bleeds” under very hot conditions, which is then addressed with aglime (crushed limestone or dolomite) to stem loss of the seal.
From CBS affiliate WCCO-TV (Minneapolis): Sections of I-94 in the Twin Cities area were closed due buckling pavement.
From WBBM-TV (Chicago): The station is warning viewers that portions of Lake Shore Drive buckled in 2010, when temperatures were not as high. “[Concrete] pavement buckling is different from a frost heave, which happens in cold weather. In a frost heave, water gets under the pavement, which expands and blows up when the water turns to ice. But in a pavement buckle, a crack or joint running across the center line of a roadway fills with material that doesn’t compress or tamp down, and thermal expansion causes forces strong enough to blow the pavement out.” Brian Steele, spokesperson for the Chicago Department of Transportation, compares buckling to what happens in an earthquake. About 100,000 cars travel on Lake Shore Drive every day.
Heat damaged pavement is nothing new, and helps explain why tropical and semi-tropical cities such as Miami, Los Angeles and Honolulu have their own deteriorating pavement issues (i.e., potholes) to deal with. The cause is moisture under the pavement heating up and expanding, not unlike with a pressure cooker blowing its lid. Moisture in freeze-thaw conditions – factors more familiar in the upper Midwest, typically in late winter and early spring – break pavement and create potholes as moisture expands and contracts inside and under pavement cracks.