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The dump trucks full of concrete roll from 6 a.m. until 6 p.m. so aircraft can roll around the clock into and out of the world's busiest air cargo hub at Memphis International Airport.
The trucks haul about 200 loads daily for the Tennessee Division of APAC Inc. as it extends Taxiway Yankee-South by 7,200 ft.
"The taxiway is needed primarily for FedEx traffic," said Joseph Polk, manager of construction administration for the Memphis-Shelby County Airport Authority.
The air cargo giant is not the only user. UPS and DHL also have air cargo operations in Memphis and nine commercial airlines were part of the 393,690 takeoffs and landings in 2004.
The $27 million project is Phase Two of the taxiway extension, which includes the taxiway itself, a threshold to the adjoining runway, access ramps to a new air cargo facility and a new Tennessee Air National Guard terminal, and concrete paving for the airport's aircraft rescue and fire-fighting center.
The job started in August 2004 and is on schedule for completion late this month.
Within that timeframe, APAC faced a smaller window to build a threshold approach to the 11,120-ft. 18C-36C runway, which was reduced temporarily to about 9,000 ft.
"It took hard work and scheduling" to make the 45-day deadline, said Mike Morganthaler, project manager. Also helping was some "extremely good weather."
"We worked seven days a week, daylight until dark," he added.
The taxiway itself starts with 6 in. of soil cement, then a 10-in. layer of cement-treated base (CTB), 4 in. of open-graded asphalt and a 19-in. layer of concrete.
The project will consume 75,115 cu. yds. of concrete, 170,000 tons of CTB and 61,700 tons of asphalt.
Site preparation had been done during an earlier contract that involved moving 1 million cu. yds. of dirt to build up the taxiway surface by about 15 ft.
Drainage included installation of about 1,500 ft. of concrete pipe, ranging from 18 in. to 36 in., and one double box culvert measuring 6 by 8 ft. that runs about 250 ft. over a creek.
The 100-ft.-wide taxiway is larger than the normal 75-ft. strips to allow for the larger wingspans on some of the planes that will use it. FedEx has orders for 10 Airbus A380s, with a 262-ft. wingspan, and the Tennessee Air National Guard (TANG) is converting its fleet to nine C-5As, with a wingspan of 223 ft.
Paving is done in four 25-ft. "strips" in a method that resembles automation. The dump trucks arrive with a load of concrete, dump it out to a placer that pushes it evenly across the 25-ft. width. The paver follows, "drumming" air out, then leveling and smoothing the surface.
The paver vibrates at 7,000 to 8,000 revolutions per minute, said Bob Brady, APAC's paving foreman.
"We work 30 minutes from plant to smooth," while meeting American Society for Testing and Materials (ASTM) standards, he said.
His crews lay about 1,500 ft. of 19-in. concrete a day. The pace slows in some areas, like the ramp to the National Guard terminal, where the concrete is 24 in. deep.
The paver slip-forms the concrete, meaning no wooden forms are used because the water content of the concrete is low enough that it will form in place.
"We try to run a 1.25-in. slump," Morganthaler said.
The cone test for slump is one of two done on the concrete at random intervals daily, he said.
The other is a strength test to ensure meeting a 650-psi flexural strength standard. The concrete is poured in a mold, then soaked and broken at three, seven and 28 days, Morganthaler said.
The concrete has to reach 650 psi in 28 days, but he said, "We can haul on it at 500 (psi) and pave on it at 450."
"The more cement, the less water, the stronger it is," he said.
The concrete goes down over a maze of structural and electrical subsystems. One is its own strengthening underlay. Racks of 1.75-in. steel dowels are placed at intervals where expansion cracks will be cut and neoprene seals inserted. Another series of 18-in. dowels is inserted between each of the four 25-ft. taxiway "strips." The dowels aid in load transfer between the sections, Morganthaler said.
The concrete also covers the electrical system that serves the taxiway lights, which must lie flat along the surface.
"The fixtures have to be within a tight tolerance," said Jim Zerby, president of Hypower Inc., the Ft. Lauderdale, Fla.-based company that is installing the lighting system.
"They cannot stick up above the concrete (more than) 1-1/16 in.," he said.
Hypower installs a "base can," actually a junction box, in carefully measured spots before the concrete is poured.
After it dries, workers come back and drill 4-in. "pilot" cores to locate the center of each junction box, then mark the outer edges where they will drill a 13-in. cut for the light housing.
The FAA issues most of the lighting specifications and some airports have added to them.
The Memphis airport has "its own requirements. They have improved a lot on the FAA," Zerby said.
The lines are 5,000 volts to handle the power drop over the distance, which can run for miles up and down a runway or taxiway, he said. The temporary runway shortening meant runway markings had to be erased, new ones painted on and those erased when the runway went back to full use.
Crews from Hi-Lite Markings Inc. of Adams Center, N.Y., use a high-pressure sprayer that shoots needles of water to remove the old paint.
The water-based paint "turns into powder," said Mike Church, project supervisor. An oil base or epoxy paint would flake off with wear, creating a hazard for jet engines.
The company's truck lays down a coat of paint and the small glass pellets, which reflect light at night. It returns with a coat of black to outline. A typical runway paint job can be finished in about eight hours, Church said, but three days are needed to remove it.
The paint job lasts about two years in southern states but must be re-done annually in northern states where snoplows are in use, he said.
APAC set up a concrete plant on airport land, hauling in No. 4 and No. 7 stone, sand and cement to mix on a ready-to-use basis, producing 2,000 to 2,500 cu. yds. daily.
A 350-ft. well providing 64-degree water helps keep the concrete temperature low during Memphis' regular 90 degree-plus summer days, Morganthaler said.
Some of it is chilled to 40 degrees, then added to the 64-degree water to mix the concrete, an effort to keep it below 90 degrees to counter drying problems, he said.
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