The Oklahoma Department of Transportation reports success from using an asphalt mixture that prevents cracking, what some call “self-healing” asphalt.
ODOT used a crack attenuating mixture (CAM) on a repaving project in 2012 on I-40 in Caddo County. Eleven years later, the 2-mile section has an International Roughness Index that averages 50 inches per mile, “which is smooth enough to result in ride quality bonuses for new construction in some states,” according to the Federal Highway Administration. A good IRI is considered to be less than 95 inches per mile.
“CAM’s flexibility can help prevent a crack from coming up through to the surface,” says Oklahoma Asphalt Paving Association Executive Director Larry Patrick.
CAM was used in combination with ODOT’s highly modified asphalt binder as an intermediate layer on the I-40 project. That project has been nominated for a Perpetual Pavement by Conversion Award from the Asphalt Pavement Alliance.
Since the original I-40 project, ODOT has used CAM on roadways ranging from interstates to county roads throughout the state. "It has proven to be a practical, effective and economical approach to delaying or preventing reflection cracking," FHWA says.
ODOT recently awarded a contract for milling and repaving an adjacent 7-mile stretch of I-40 in Canadian County in which CAM will be used. The project involves milling 7 inches of existing asphalt, placing a CAM layer and then Superpave and stone matrix asphalt on top. The $24 million project is expected to start in summer and provide good pavement for 15 years.
“We’re super-excited about it, because right now, we must go out there daily to make repairs,” says ODOT District Engineer Trenton. “We have to close down a lane, mill out a section, add new asphalt, and then 5 feet ahead of that, do it again. This project will give us good pavement that we’re not out there every day trying to maintain.”
CAM was originally designed by the Texas Department of Transportation in 2007 and has been used extensively in Houston and Dallas areas on top of old concrete pavements. It has been used as an interlayer between existing pavement and a thin asphalt layer, but it has also been placed as a .5- to 1-inch surface course, proving to be rut and skid resistant, according to FHWA.
