GOMACO World Index --- GOMACO World 40.1 - June 2012
The new Maynard H. Jackson Jr. International Terminal at Hartsfield-Jackson Atlanta International Airport just opened for business. The new 1.2 million square foot (111,484 m2) terminal features 12 gates, eight security checkpoints, separate levels for arrivals and departures, as well as a 178,000 square yard (148,831 m2) 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, was also 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 for 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 nine inch (229 mm) 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 inch (19 mm). Approximately 15 trucks hauled 10 cubic yard (7.6 m3) 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 feet (7.6 m) wide and 20 inches (508 mm) thick. Dowel baskets were placed on grade every 25 feet (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."
The sun goes down at Hartsfield-Jackson Atlanta International Airport as Archer Western slipforms another 25 foot (7.6 m) wide paving pass for the airport's new 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 1500 cubic yards (1147 m3) per day. Their best production day reached 2000 cubic yards (1529 m3).
"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 cubic yard (1376 and 1453 m3) 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. The GSI is set up as a California profilograph. The roughness index value cannot exceed 10 inches per mile (158 mm/km) for each 500 linear foot (152.4 m) section based on a two-tenths blanking band.
Seven GSI units were mounted on the GSI machine, as required by the airport's specification. The individual GSI units trace a line 12 inches (305 mm), four feet (1.2 m), and eight feet (2.4 m) off the joint line on each side, and also along the centerline of each 25 foot (7.6 m) wide paving pass.
The airport also requires Archer Western to use a 16 foot (4.9 m) rolling straightedge to check the new pavement. Surface deviations exceeding 0.25 inch (6 mm) in 16 feet (4.9 m) in any direction require correction. Any deviation over 0.5 inch (13 mm) 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 inch (508 mm) thick concrete edges, some up to 25 inches (635 mm) 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."