Feature

September/October 2009

The Right Mix

New main runway at Edwards Air Force Base built usinghigh-strength concrete mix

By Tom Nicholson

(Photo Courtesy of CH2M-Hill Inc.)

It took the right mix of capabilities—and concrete—to deliver a mission-critical runway for the U.S. Air Force.

In a first for the Air Force, a joint-venture design-build team completed construction in October 2008 of a 300-ft-wide, 15,000-ft-long runway at Edwards Air Force Base in California. The $200-million project added a runway to a facility capable of handling any aircraft, including space shuttles.

Edwards is home to the Air Force Flight Test Center, and the runway is used to test military aircraft. To do that, the runway had to be capable of landing 800,000-lb aircraft with tire pressures of more than 400 psi.

It took the team of Denver-based CH2M Hill; Centennial, Colo.-based Interstate Highway Construction (Colorado Contractors Association); and the U.S. Army Corps of Engineers about two years to complete. Full flight operations resumed in December, and there already have been two space-shuttle landings.

The project was handled in two phases, which included the five-month demolition of an existing runway, construction of a 13,000-ft temporary runway and, finally, construction of the main runway.

“Operations were still ongoing, which made speed important,” says John W. Stephens, U.S. Army Corps of Engineers project manager. The design-build project was broken into two phases for the temporary runway and three phases for the main runway. “We wanted complete sets of drawings for each package,” Stephens says.

The team integrated each firm’s specialties, says David Bird, project manager for CH2M-Hill, which handled the design work. “We combined in this joint venture as a powerful team,” he says. “We brought experience in design, project management, consulting and full-service capabilities and integrated it with a powerful field contingent at IHC.”

Crews removed nearly half a million cu yd of concrete from an old runway demolished at the start of the project. (Photo Courtesy of CH2M-Hill Inc.)

Ken Schaeffer, IHC president, says the joint venture “worked closely and cooperatively” throughout the project. Bird adds, “We see the benefits of this alignment and are seeking more aviation projects.”

To demolish the existing runway, the team removed 445,000 cu yd of concrete in nine weeks, then constructed a 12,000- ft by 200-ft temporary runway with taxiways and parking pads. Workers used 4-in.-thick asphalt on a 10-in. aggregate base.

The team prepared 36 trial mixes of concrete to find the right formula for the specified performance requirements for slip-form paving, Bird says. But because of the remote site, transporting rock, sand, water and cement was difficult, he adds.

“We had to perform a materials study and go to different quarries throughout the region,” Bird says. “We found the properties of each material changed with every quarry we went to within a 70-mile radius.” To solve the problem, the team “entered into our own quarrying operations to get the right mix for the concrete,” he adds. “We got access to a quarry and mined it, and we crushed the stone ourselves.”

They perfected a mix of aggregates before pouring a total of 33 miles of concrete for the new runway. (Photos Courtesy of CH2M-Hill Inc.)

It took 120 days to determine the optimum concrete mix. “We broke beams at stress loads of three to 90 days, and then repeated that with each mix,” says Dean Rue, CH2M Hill project manager. “The exact mix is classified, but it is capable of handling between 650 psi and 700 psi.” In all, the team placed 28 miles of concrete, 33 ft wide and 16 in. to 20 in. thick, Stephens says.

Unstable soil tossed a wrench into the works. In constructing the base for the runway, “We ran into all kinds of problems with soils,” Bird says. The site is near a dry lake bed with varied soils and too much moisture content.

“We had to develop processes to confront them,” Bird says. “We formed ‘tiger teams’—small groups from all sides—assigned to develop a solution for each problem. It worked well, and it has become a process we use going forward.”