The sun goes down at Hartsfield-Jackson Atlanta International Airport as Archer Western slipforms another 25 ft. (7.6 m) wide paving pass for the airport’s new apron.
The new Maynard H. Jackson Jr. International Terminal at Hartsfield-Jackson Atlanta International Airport just opened for business. The new 1.2 million sq. ft. (111,484 sq m) terminal features 12 gates, eight security checkpoints, separate levels for arrivals and departures, as well as a 178,000 sq. yd. (148,831 sq m) concrete apron for the international airplanes to park when arriving at the new gates.
Archer Western won the contract to slipform the terminal’s new concrete apron, replace the existing Taxiway D, as well as other utilities and embankment work. They brought in one of their GOMACO paving trains, a PS-2600 placer/spreader, a two-track GHP-2800 paver, and a T/C-600 texture/cure machine. A GSI (GOMACO Smoothness Indicator) machine, as required for all concrete paving projects at the Hartsfield-Jackson Atlanta International Airport, follows the paving train. A GOMACO 9500 placer was also used for hand pours on the apron.
The design of the apron dictated short paving runs, which limited daily slipform production. A 0.5 percent fall, to keep water from ponding on the apron, also was a difficult aspect of the project.
“Maintaining the 0.5 percent fall and keeping water from ponding on the new apron was one of the more difficult challenges,” Justin Cooper, assistant project manager of Archer Western, said. “That is super flat and not a lot of room to play with. With the GSI, we were able to check the overall smoothness constantly and make sure our setup was right on.”
The new apron was slipformed on top of a 9 in. (22.9 cm) thick soil-cement subbase. The concrete for the project was produced on site by a mobile batch plant. It was a standard P501 concrete with a low slump of 0.75 in. (1.9 cm). Approximately 15 trucks hauled 10 cu. yd. (7.6 cu m) loads of concrete to the GOMACO paving train.
“We used the PS-2600 on the project for the ride quality it gives us,” Cooper said. “We had good ride numbers using this really stiff mix. The PS-2600 really helped out and provided the initial knockdown of the concrete, which helped provide a nice smooth finish behind the GHP-2800 paver.”
The GOMACO two-track GHP-2800 slipformed the apron in paving passes 25 ft. (7.6 m) wide and 20 in. (50.8 cm) thick. Dowel baskets were placed on grade every 25 ft. (7.6 m), with some areas of welded wire reinforcing depending on the shape of the slab.
“We had very little finishing work behind the paver and found the more we worked with the slab, the worse the numbers typically were,” Cooper said. “The straightedging to adjacent lanes was important to ensure ponding water would not be held on the relatively flat apron.”
Archer Western’s daily paving production was limited by the layout of the project. The GOMACO 9500 placer was used in several areas for hand pours around embankment utilities, fuel pits, underdrains and other various utilities. They also had to work around other contractors who were building the new terminal. Average slipform paving production was 1,500 cu. yds. (1,147 cu m) per day. Their best production day reached 2,000 cu. yds. (1,529 cu m).
“The way the project was set up, the lanes weren’t long enough to have a really good day,” Cooper explained. “We did have some 1800 and 1900 cu. yd. days, but mostly we could only go as far as the lanes would take us.”
Finishing work behind the paver was kept to a minimum. They applied a burlap drag by hand and then used the GOMACO T/C-600 texture/cure machine to apply a white spray cure.
All of the new pavement was profiled by Archer Western’s GSI machine. The airport specification states that as soon as the concrete has hardened sufficiently, and within 24 hours of placement, the contractor will test the pavement surface.
Seven GSI units were mounted on the GSI machine, as required by the airport’s specification. The individual GSI units trace a line 12 in. (30.5 cm), 4 ft. (1.2 m), and 8 ft. (2.4 m) off the joint line on each side, and also along the centerline of each 25 ft. (7.6 m) wide paving pass.
The airport also requires Archer Western to use a 16 ft. (4.9 m) rolling straightedge to check the new pavement. Surface deviations exceeding 0.25 in. (.6 cm) in 16 ft. (4.9 m) in any direction require correction. Any deviation over 0.5 in. (1.3 cm) must be removed and replaced.
“On road projects we just run the sensors in the wheel paths, but since this is an airport project, the GSI is checking the entire width of the slab with seven sensors,” Cooper said. “We have 20 in. thick concrete edges, some up to 25 in. for thickened edges and they had to be constantly monitored. That was pretty challenging, but we were able to achieve the necessary smoothness.”
The new terminal just opened to rave reviews from airport personnel and travelers. Archer Western was able to overcome some tough challenges and deliver an exceptionally smooth and flat apron at the Hartsfield-Jackson Atlanta International Airport.
“It was definitely challenging, to say the least,” Cooper said. “We completed on time and delivered the project within spec. The airport in Atlanta is big on concrete paving and they make sure that we deliver the highest quality paving in the country at the airport.”
This article was reprinted with permission from GOMACO World Magazine Volume 40, Number 1.