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Paving of airport runways, taxiways, and aprons has provided a strong market for portland cement concrete in recent years, as commercial and military airports upgrade their ground facilities to keep up with increasing air traffic. In 1992, 25 million flights took off or landed at the nation's 100 largest airports. By 2005, the Federal Aviation Administration projects that number to increase by almost 38% to 34.5 million. Demand for concrete is greatest at these large facilities, because concrete provides the substantial pavement strength required to withstand the impact of airplanes such as the 747, which can weigh more than 850,000 lb (382,000 kg.) when fully loaded.

Some 1.1 million metric tons of portland cement were used in the United States for airport pavement projects in 1995, up 22% from a decade earlier, when 895,000 metric tons were used. Since there has been little demand for construction of new airports in the United States for some time—the Denver International Airport being a notable exception—most of this cement is going into concrete needed for existing airport pavements or adding new runways to existing airports. Engineers and contractors are taking advantage of fast-track technology to upgrade ground facilities with minimal traffic disruption, and continue to hone design techniques to achieve maximum pavement life.

The first United States airport runway was built in 1928 in Dearborn, Michigan, by the Ford Motor Company for a Ford-manufactured plane called the Silver Goose. This and other early runways used variable pavement thicknesses similar to those of early highways: concrete 8 or 9 in. (20 or 22.5 cm) deep at the edges and 6 or 7 in. (15 or 17.5 cm) thick at the center. Until World War II, engineers designed these concrete pavements based on the anticipated loads imposed by refueling trucks carrying gasoline to the airplanes, rather than the airplanes themselves, because the trucks imposed a more critical wheel load. Concrete pavement markets span from driveways and parking lots to mainline interstate highways.

In 1942, at the beginning of World War II, 93 million sq yd (74 million sq m) of airfield pavement was placed in the United States as the country mobilized to get planes airborne. At that time, 6 in. (15 cm) deep concrete pavements were the norm, but heavier airplanes created the need to increase concrete runway pavement depth to 12 in. (30 cm) thick. Eventually, engineers specified runway pavements as thick as 24 in. (60 cm) to accommodate heavy loads imposed by larger aircraft. The addition of more wheels to these airplanes, which better distributed the loads on the pavement, reduced the pavement depth required to 12 in. (30 cm) in the late 1940s.

Today, specifications for airport concrete pavement vary depending on subgrade conditions, expected loading, and anticipated pavement life-span. New concrete runways at non-hub airports generally range in thickness from 9 to 12 in. (22.5 to 30 cm), while runways at hub airports often are constructed 15 to 18 in. (37.5 to 45 cm) thick to withstand larger and more frequent loading.

Durability an Issue
In an effort to create more cost-effective, longer lasting airport pavements, the Federal Aviation Administration continues to investigate the durability of alternative pavement designs. One such study is underway in Illinois at the Greater Rockford Airport, where researchers are examining a taxiway paved under three different specifications. Because pavements usually deteriorate first at their joints, investigators are studying a section of unjointed, 1,200 ft (360 m) long concrete made with shrinkage compensating cement (Type K) that expands during the concrete's early curing to counteract the expected shrinkage that causes cracking. In addition, the unjointed pavement includes steel reinforcing fibers and is reinforced with prestressed steel to improve its tensile strength. The pavement section is only 7 in. (17.5 cm) thick.

Researchers will compare this unjointed pavement with a 10 in.(25 cm) thick pavement section that also contains Type K cement and steel reinforcing fibers, but no prestressed steel reinforcing. Contractors placed this pavement with joints spaced from 85 to 200 ft (25.5 to 60 m) apart. The third pavement section is a control section, consisting of conventional, 15 in. (37.5 cm) thick concrete pavement containing joints spaced 20 ft (6 m) apart. Paving engineers expect results of the study to influence future airport pavement design. Engineers anticipate at least 40 years of service—twice the number of service years airport pavements are usually designed to meet—from pavements constructed at the $4.2 billion Denver International Airport, opened in early 1995 after 5-1/2 years of construction. Contractors placed 2.5 million cu yd of concrete to create five 12,000 ft (3,600 m) long runways, plus taxiways and aprons. To ensure pavement durability, designers carefully compensated for Denver's expansive soil, which tends to swell and move, by excavating the site. Contractors then laid down 6 ft (1.8 m) of compacted, non-expansive soil; a 12 in. (30 cm) deep subgrade layer of rototilled, lime-treated soil; and an 8 in. (20 cm) thick cement-treated base before pouring 17 in. (42.5 cm) of concrete paving.

At many airports today, fast-track technology plays an important role in the rehabilitation of existing pavements because airport officials cannot close runways and taxiways without severely impacting operations. At the Seattle-Tacoma International Airport in Washington, for example, engineers created a complex slab replacement schedule for a 1994 rehabilitation project that allowed contractors to rebuild the runway at night and reopen it to airplane traffic each morning. Contractors demolished two pavement slabs each night and replaced them with temporary, precast panels. Each subsequent night, the temporary panels were removed, and new slabs of high-early-strength concrete were cast in place. At the same time, workers demolished two additional existing slabs and replaced them with the temporary precast panels. In this manner, contractors replaced 73 concrete runway slabs with minimal disruption.