From Thin Air to Thin Concrete

Ultra-thin whitetopping technology has been used successfully since 1992 in hundreds of applications across the U.S. The technology involves applying 2 to 4 in. of concrete over distressed asphalt pavement, of which a like amount has been milled. And while the technology has been used on roadways and airport applications before, one forward-thinking group of people has used this technology on an airport runway.

The Savannah-Hardin County Airport in Savannah, Tenn., received a 4-in. concrete overlay on its existing asphalt runway, making it the nation’s first ultra-thin whitetopping on a general aviation runway.

The Savannah-Hardin County Airport Authority teamed up with the Tennessee Aeronautics Division, design firm Barge Waggoner Sumner & Cannon Inc. (BWSC) and paving contractor Southern Roadbuilders Concrete Paving Division of APAC—Georgia, on this landmark project.

According to Tony Manci, vice president of BWSC, the 38-year-old, 5,000-ft-long asphalt runway was structurally sound. Its cracks had been filled with rubber asphalt, but over time the cracks were increasing in number and size. After extensive research into the structural integrity of the existing runway, BWSC determined the 3 in. of asphalt and the stone base were structurally sound. In addition to visual inspection, BWSC tested the subgrade, ran a pavement condition survey and used non-destructive methods to determine the structural strength.

"We found the integrity was good; the surface had problems," Manci said. "We designed the pavement based on the strength of the existing asphalt structure."

Manci felt that the cracks in the asphalt runway were so severe that they would reflect through a new asphalt overlay. That left two main options—to reconstruct the runway totally with asphalt or to put down a thin concrete overlay on the existing runway.

"We found UTW was more expensive than a standard asphalt overlay, but less costly than total reconstruction," Manci said.

He was quick to point out that initial cost was not the only factor in the decision.

Manci expects 25 years of service from the new runway. He based this determination on the numerous successful UTW projects constructed by the Tennessee DOT throughout the state, mostly intersections. "The trucks at those intersections are heavier than the airplanes using the new runway," he added.

The contractor milled off 1/4 in. of the existing runway to improve the bond between the old asphalt and the new 4 in. of concrete. According to Dennis Ramsey, vice president of concrete paving for Southern Road Builders, the contractor placed 7,000 to 8,000 sq yd per day.

Manci was impressed with the speed of construction of the UTW runway. The whitetopping of the runway only was initially scheduled for 40 days. The airport later added the taxiway connectors and the apron to the job. Even with the additional work, the contractor finished ahead of schedule. At day 32, the paving was finished.

BWSC is monitoring the performance of the UTW. The strain gauges placed in the concrete will show the significance of the bond between the concrete and asphalt. "That bond is critical," Manci said.

The designers also varied some factors to determine optimum design and construction methods. They changed the standard 4-ft x 4-ft joint spacing to 3 ft x 4 ft in some sections. For the majority of the project, they left the cracks in the existing asphalt alone; in one section, they repaired them with a sand slurry mix.

"We want to see if there’s any difference in performance," Manci said.

If you’re interested in learning more about this technology, visit ACPA’s website (www.pavement.com). For general information about UTW, order "Ultra-Thin Whitetopping—Today’s Choice" (PL948P) from the ACPA publications catalog by calling 800/868-6733. A video highlighting this project also is available in VHS and CD-ROM versions. Request "Ultra-Thin Whitetopping for Airfields" (VHS version is VC521P; CD-ROM version is CD016P).