Sinking down

Contractor digs deep to re-build New Orleans runway

By Sam Barnes

Nearly 45 in. of asphalt had been piled on top of New Orleans International Airport's Runway 1-19 by the time Boh Bros. Construction LLC began the runway's reconstruction last spring.

Over the years, the heavily used north-south runway had been sinking, and placing more asphalt to bring it back to grade had become a quick fix.

"On the northern end of the runway, where the planes touch down, there were numerous layers of asphalt," said Roy Mouledous, jobsite superintendent with the New Orleans-based contractor. "And that was on top of a layer of sand and a second runway built 30 years ago.

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"In effect, there were two complete runways stacked on top of each other, both sinking into the ground."

And with each new lift of asphalt, the sinking worsened.

The current $25 million project should solve the problem, with the existing top runway completely replaced with a super-thick slab of concrete reaching 16 in. on top of sand and limestone. And leaving the oldest runway slab in place should further slow future sinking.

When work began last spring, the 1.5-million-sq.-ft. project was divvied up into three phases, stretching from south to north for 7,000 ft.

Work on the middle, 1,200-ft.-long phase two section began first because it intersected the airport's east-west runway.

"We were approaching June and the airport needed us to get that section done fast," Mouledous said. "The air is lighter in the summer and the planes need more runway to achieve lift. Having a shorter east-west runway meant the airlines had to lighten their loads to achieve the required threshold, and they don't like to do that."

The crew had a 20-day window to perform the entire phase.

"We had to mill the old runway, break up the concrete, excavate it, put the sand and stone in, pave it, then get out," Mouledous added. "They were flying right over us during that period of time."

Once phase two was completed, crews began milling the 600-ft.-long, phase one section at the southern end of the runway near the airport terminal. Midwest Asphalt Corp. of Gainesville, Texas, performed the milling for all three phases, often working 16 hours a day.

The phase three section is the longest at 5,200 ft., and was completed in early October.

"They (Midwest Asphalt) had five machines going continuously, milling to depths ranging from 9 in. to 45 in.," Mouledous said. "One very large area had depths of 30 in." The machines typically made several passes during the process, milling 2 to 3 in. per pass.

Antigo Construction Inc. of Antigo, Wis., then broke the 10-in.-thick concrete runway slab beneath the asphalt with guillotine hammers, excavated and hauled the concrete for crushing and recycling.

For the new runway pavement, the Boh Bros. crew placed 1 ft. of sand, a layer of geotextile fabric and 8 in. of limestone. The limestone was graded using "stakeless grading," which relies upon Global Positioning Systems technology. The grading method helped the contractor achieve more accurate machine and blade positioning in real-time, thus reducing both time and cost of construction.

"Once they compacted it and got it to grade, we came in with the paving crew and started placing concrete," said paving superintendent Ken Bordelon.

An on-site batch plant operated by Lafarge Corp. of Metairie supplied 750 psi flexural strength concrete for the paving operation. About 100,000 cu. yds. of concrete were ultimately placed for two lifts of concrete totaling 16 in. deep.

Bordelon said a large paving train helped maintain a continuous paving operation.

"The concrete, after being delivered by truck to the paving site, was dumped into a belt spreader that distributed the concrete in an 11-in.-thick lift," he said. A strong wire mesh was placed on top of the first lift, followed by 5 in. of additional concrete placed by a slip-form paver.

"We set a goal of about 1,800 cu. yds. of concrete a day, and most of the time we achieved that," Bordelon added. "We split the pours into equal increments determined by the capacity of the batch plant and how many trucks we could run." A crew of 13 people was needed during the paving.

A little creativity was required when the contractor had to build a new crossover connecting the north-south runway with a parallel taxiway. Since the crossover had to be built in an undeveloped area, the project engineer decided that foam blocks would provide the best pavement foundation.

"That's virgin ground that had never been built on, so the new pavement would have sunk at a faster rate than the paved areas it connected to," said project engineer W. O. Johnson of W. O. Johnson & Associates Inc. of New Orleans. To compensate for that, the engineer specified 4 ft. of foam block, 4 in. of concrete, 16 in. of sand and 8 in. of limestone, all topped with 16 in. of concrete.

A holding bay area on the northernmost end of the runway required similar foam block construction. Phylway Construction Co. of Thibodaux performed all of the excavation and placement of the foam blocks.

While they were waiting on the concrete to be poured on top of the blocks, Phylway put concrete barricades along the perimeter to keep the blocks from floating during a rainstorm.

Other work required the milling and asphalt overlay of two jet engine "blast pads" at the northern and southern ends of the site.

Roy Williams, director of aviation at the airport, said two grants totaling $10.2 million were provided by the Federal Aviation Administration to help fund the project.

"It has been over 20 years since this runway was last rehabilitated," Williams added. "The New Orleans Aviation Board made the decision that patching and filling the runway was not enough. For the long-term benefit of the airport, the airlines and the communities surrounding the airport, we decided to go forward with a complete rehabilitation."

About $6.3 million of the grant for the runway rehabilitation project came from discretionary funds.

"This is especially significant when much of the discretionary funding this year is being devoted to security projects," Williams said. Another $2.4 million came from entitlement funds that are derived from a formula based on the level of passenger activity at a facility. Also included in the grant is $1.5 million for a noise mitigation program. These funds are to continue an ongoing sound insulation program.

To date, the airport has received a total of $20 million in grants for the rehabilitation project.

Useful Resources

For more about future projects and initiative of the Federal Aviation Administration, go to: http://www.faa.gov/AboutFAA/FlightPlan.cfm