A Boeing 747 jumbo jet can weigh more than 800,000 pounds at full capacity and have a takeoff speed of 180 miles per hour. Now imagine the full-force of 350 aircrafts hitting one runway, every day. Runway construction specifications have to be strictly adhered to and the contractor has to pave with surgical precision within the allotted time.
So when Tilcon Connecticut Inc - a leading asphalt producer and contractor in New England - was given the state contract of repaving Runway 6-24 at Bradley International Airport in Hartford, Connecticut, it knew it had its work cut-out. But with the help of a Volvo PF6110 tracked paver and two Volvo DD138HFA and DD118HF compactors, it rose to the challenge.
"Runway 6-24 is the main runway at Bradley," says Richard Birge, manager of construction for Tilcon, "But it had to be shut down for three consecutive weekends while we milled and paved - it was imperative that we kept to the schedule."
Bradley airport is managed by ConnDOT and services more than six million passengers annually. The Federal Aviation Administration (FAA) recommends rehabilitation of airport runways every 20 years and funded this $17 million project, which entailed not only resurfacing but upgrading the main water line and installing new lighting along the runway.
Like all state highway jobs, if Tilcon missed the completion date ConnDOT would impose fines. So milling and paving crews were scheduled around the clock with up to eight teams working 12-hour shifts.
"There were no rain dates in the schedule," explains Richard. "If it rained a lot, we had to change the hours worked. At times we were operating 24 hours a day."
The FAA stipulated that Tilcon had to mill the 2,896 metre (9,500 foot) long, 76m (250ft) wide, runway with a four-inch-thick mat using 62,900 tons of approved hot mix asphalt. But because Tilcon's asphalt plant is 24 miles (39 kilometres) away from the airport, it had to use a convoy of 30 trucks running back and forth, day and night, to transport 1,800 tons of the material per shift.
The FAA also stated that each paving strip had to be 6m (20ft) wide. But Tilcon decided to pave in 8m (25 ft) strips instead, to maximise efficiency.
The company chose a Volvo PF6110 tracked paver with an Omni 318 screed. The screed has a standard paving width of 5m (18 ft) so Volvo installed four 30cm (1ft) extensions on each side to increase the width.
According to Larry Spring, road paving specialist for Volvo Construction Equipment, the Omni 318 screed provides optimum density, especially at the joints, to achieve the tight specifications and traction.
Before paving could begin, the compaction density and quality of the asphalt had to be trialled in test strips - which were inspected by ConnDOT and the FAA. Tilcon spent four days becoming familiar with the paver with the help of Volvo's dealer Tyler Equipment, which had representatives on hand to provide support and training.
Compaction density requirements are also very stringent for airport paving jobs. Highway contracts usually require 92% compaction density; however, the FAA demands 96.3%. The Volvo DD118HF and DD138HFA double drum asphalt compactors were selected for the job because they feature eight amplitude setting, allowing the specified amount of force to be applied, preventing over-compaction. Two DD138HFAs ran behind the paver in an echelon formation for the initial breakdown compaction, then the DD118HF followed for the finishing.
"Over-compaction will break down the stone in the mix design," explains Larry. "If this happens you lose the stability and strength of the pavement required to handle the airplanes."
ConnDOT performed routine inspections during the compaction and five-inch core samples were taken for density tests to be performed at its laboratory before the runway could be used.
Runway 6-24 opened on June 23, 2009 and Connecticut Governor M. Jodi Rell hailed the success of the project, stating it was "On time and under budget." Tilcon has since repaved Runway 15-33 at Bradley, which was a smaller project than Runway 6-24. Tilcon has nine paving crews and assumes a majority of state contracts, such as highway road building and repair. It also produces crushed stone and ready-mixed concrete.
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