The main terminal apron at Tucson International Airport received a much-needed facelift, 52 years after the original concrete ramp was placed. The three-phase project included placing 147,000 square yards of portland cement concrete pavement (PCCP) in 16-, 9-, and 6 ½-inch thicknesses. It also covered demolition and a wide range of upgrades. The $36 million, 22-month project was scheduled to be completed in July.
Because the airport had to stay open through construction, the project was divided into 10 work zones so that no more than two airline gates would be taken out of service at any time. Granite Construction, the general contractor, used metal paving forms with built-in dowel holders to maintain productivity and meet tight tolerances on the project.
Holding close tolerances was a priority. Project superintendent Aaron Tipton says, “We placed 20-foot lanes to meet tight tolerances. The corners of every 20x20-foot panel had to meet plan elevations to specs within four hundredths.”
To hold these tolerances, Granite selected steel paving forms from Metal Forms Corporation (MFC) of Milwaukee. The contractor used 571 DUAL Paving Forms in five different sizes, totaling more than 5,700 lineal feet. All were 10 feet long and designed so they can be used for two different pavement depths.
Several sizes of forms were used because pavement thickness varied depending on the loading each area must accommodate. Areas that support aircraft traffic are 16 inches thick, while those closer to the terminal that only see light vehicle traffic are 9 inches thick. Next to the building, where loading is the lightest, the pavement has to be only 6-1/2 inches thick. Manholes, electrical boxes, fuel hydrant systems, and other services generally are in the 16-inch-thick areas.
The forms were set in multiple 20-foot-wide lanes so the paver can ride atop them and pave every other lane. Transit mixers delivered concrete from both sides alongside the forms. After the forms were pulled, the machine traveled on the new concrete to pave the lanes in between.
The project required a high degree of planning and coordination to minimize impact on airport operations, yet maximize productivity and efficiency. “We started in work zones one and 10, on opposite sides of the terminal,” says Tipton. “The project was phased in a manner that allowed our crews to reconstruct pavements at two gates on each concourse simultaneously. This allowed our grading crews to work on work zone one and shift to the opposite work zone while we were setting forms on this side.” This helped balance labor needs and kept employees’ hours steady while also making it easier to manage equipment utilization.
Once grading was complete and the forms were set, a crew placed as many as 800 cubic yards on a typical day. Project engineer Bill Carney says the project used a standard 650 psi flexural mix (FAA P-501 Specification) to handle the aircraft loading and traffic. Joints are doweled, but rebar mats were not used except for specific areas that need rebar, such as around manholes and irregularly shaped areas. “That makes more effective use of the concrete’s flexural properties,” he says.
Finishing for the 16-inch areas was done with a self-propelled triple roller tube paver that includes a gang vibration system. Granite extended the machine’s rollers about 2 feet on each side to prevent spalling by spreading the weight past the edge of the new concrete when paving the intermediate lanes. A paver also is used for the 9-inch areas, but a concrete pump, standard roller screed, and hand finishing were used for the 6-1/2-inch portions, as well as for hydrant pits, electrical boxes, and other service areas.
Dowel bars along both sides tie the lanes together. MFC provided dowel bar supports to hold the dowel bars level and ensure that they were aligned properly. Grommets, placed in the face of the forms and combined with the dowel bar braces, secured the bars in place during placing. The FAA doesn’t allow the use of mechanically placed dowels, as is often done with large paving machines.
“Using the forms with holes and grommets to hold the dowels in place allowed us to get them set right where we need them prior to pouring,” says Carney. “Placing the dowels before the pour relieved us of having to drill into the placed concrete.” He also points out that using form-set dowels saved as much as $500,000, compared to drilling and setting the dowels with epoxy after placing. It is much faster than drilling and provides scheduling benefits.
Because the aggregate base consists of recycled pavement that was crushed and screened to 1-1/2 inches, Granite added screw jacks and turnbuckles to help align the forms to meet the tight 0.04-foot pavement specification without using shims. Tabs also allowed the forms to be bolted together at the joints and provided a more rigid connection.
Form stakes are driven using a jackhammer and a special end fitting. To facilitate pulling the forms straight back when the concrete was cured, Granite devised an attachment for a mini-excavator. Carney says, “We couldn’t use a forklift because there wasn’t enough room to maneuver with the length of the panels. We made an attachment that just slips underneath the form, and we can pull it straight back, turn the mini-excavator around and place the form at 90 degrees.” A forklift can then come down the lane and pick up the forms.
The collaboration between Granite Construction and MFC saved time and the new apron will be of service to the airport for decades to come.