Central Wisconsin Airport Takes First Step in Decoupling Runways

The $14 million runway reconstruction that Central Wisconsin Airport (CWA) completed last fall not only rebuilt its 53-year-old runway. The project also sets the stage for another airfield project that will improve safety and help ensure future viability of the airport.

Runway 17-35 dates back to 1974, five years after CWA was originally constructed and opened. The surface had been rehabbed over the years, but there was still some original pavement in place, and, overall, the runway had reached the end of its useful life.

Assistant Airport Director Mark Cihlar notes that differential frost heave is a primary challenge for pavement at CWA because the airfield has very frost-susceptible soils with widely varying depths of bedrock. Several rehabilitation projects had addressed pavements that were affected by the frost heave, but it was time to perform a full-depth reconstruction and address the underlying issue.

Planning for the reconstruction began in 2016, when CWA engaged consulting firm Mead & Hunt to complete an Airport Master Plan. The airport has two runways (17-35 and 8-26) that form a “T,” with a safety hotspot where they intersect because of the closely aligned thresholds. “Basically, the FAA acknowledged that we needed to reconstruct Runway 17-35, but they wanted to see the runway intersection decoupled first,” Cihlar explains.

This led the airport into a five-year planning effort about runway decoupling. Throughout that time, the team identified at least 12 alternatives before determining the ideal solution for the project.

Maintaining the existing runway length (6,500 feet) was one of the primary objectives. “There was a lot of community feedback, and they really questioned why we were looking at this,” Cihlar recalls. “But once FAA safety concerns were explained, we had the community’s support as long as it did not reduce the utility of the airport.”

Initially, the assumed solution was to shift Runway 17-35 to the south. But it soon became apparent that moving 17-35 would create operational issues. Instead, the preferred solution that emerged was shifting Runway 8-26 to the east and reconstructing Runway 17-35 in its existing location. This means that 17-35 will be CWA’s only runway available during much of the Runway 8-26 shift project. In order for that to happen, the FAA had to designate 17-35 as a secondary commercial service runway. “Once we received that, everything fell into place,” Cihlar recalls.

“The FAA suggested reducing it down to a general aviation-only crosswind runway, but it met the requirements for a secondary runway because of its significant use in the region,” he adds. “Getting it designated as a secondary runway and being able to maintain it was the crucial hurdle for us to overcome. It’s going to help support the long-term viability of the airport.”

Trierweiler Construction & Supply Company won the construction contract in September 2020 and kicked off work in February 2021. The project included:

• runway longitudinal grade adjustments,
• connector taxiway reconstruction,
• grading the runway safety area,
• upgrading navigational aids,
• rehabilitating parallel taxiway pavement,
• installing new runway and taxiway LED edge lighting,
• replacing lighting controls in the tower, and
• electrical vault improvements.           

Phasing Considerations

Engineering firm Becher-Hoppe worked with the airport and users to develop a seven-phase construction safety plan to minimize impact to airfield traffic. In order to support operations, it was critical to keep Runway 8-26 open as much as possible during construction—not only for its length (7,648 feet), but also for its navigational aids.

Runway 17-35 was shut down for the duration of its reconstruction, but the northern section remained available for taxiing to ensure use of the full length of Runway 8-26. There were also limited overnight closures of the entire airport to install the displaced threshold on 8-26.

Implementing the displaced threshold on Runway 8 required a lot of coordination. Crews placed temporary signage and installed new pavement markings and lighting to reflect the temporary change.

During the first phase of work, a temporary fence was installed to separate the project from the airport operations area, both as a security measure and to mitigate potential runway incursions. An east-west fence separated construction personnel on the south end of the runway from the airport operations area.

During intersection work, that 6,500-foot temporary fence was relocated to remove the entire intersection from the aircraft operating area because crews would be working within 10 feet of the displaced threshold safety area. “That was really effective in streamlining and making the project easier from both a security and a traffic control standpoint,” Cihlar notes.

The runway and taxiway were outfitted with new LED lights, funded by an Airport Improvement Program grant. At the same time, the airport updated all of its navigational aids for 17-35, adjusted the elevation of Runway 17’s precision approach pathway indicator and installed a new precision approach pathway indicator on Runway 35.

Solutions for Unique Soil

With Runway 17-35 requiring a full-depth reconstruction, project engineers had their hands full. Karl Kemper, president and project engineer with Becher-Hoppe, describes the soils at CWA as “very challenging and highly variable.” Frost susceptibility, variable ground water levels and shallow bedrock posed compounding challenges for the project, he adds.

Airport officials have been aware of their frost-susceptible soils almost as long as CWA has been open. In the early 1980s, pavement was failing much earlier than expected, and the airport developed a subbase pavement section that would address the issue. Wisconsin Department of Transportation, FAA and U.S. Army Corps of Engineers were key partners in that effort.

The design they developed is a layered subbase of crushed rock topped with a layer of concrete. The subbase contains 3 feet of large 12-inch-minus stone, followed by a layer of 3-inch-minus stone, and a 1-inch-minus stone layer on top of that. “The idea is to have an open and free-draining subbase to get all of the water out, that’s also sturdy to help bridge over any low-strength underlying soils,” Kemper explains.

A portion of Taxiway B constructed with that subbase in 1985 is still holding up very well, so the airport has used the same strategy on other pavement sections, including when Runway 8-26 was reconstructed in 2004. The special subbase was part of the plan for Runway 17-35. However, FAA did not have a standard materials specification for the crushed rock, so CWA officials and Becher-Hoppe worked with agency on a modification of standards for the subbase.

“Because it wasn’t a standard material, it took a little bit of work getting there, but we finally were able to get approval to use that crushed rock and to include recycled existing concrete from the site,” says Kemper. A crusher was set up on-site to process the reclaimed concrete. Reusing it reduced the amount of material that needed to be hauled in for the project.

Under drains were constructed along each runway edge to drain the subbase. Shallow bedrock ledges were blasted and excavated to provide a base layer of even thickness to support the pavement layer.

Another challenge CWA faced was alkali-silica reaction, commonly referred to as ASR. Aggregates sourced locally are susceptible to the condition, so Type F fly ash was used in the concrete mix to mitigate the ASR. This poses a secondary problem, however, because Type F fly ash is known to slow the curing time of concrete. During quality assurance testing at CWA, the 28-day breaks on the concrete did, in fact, come up short on strength. But samples taken at 90 days far exceeded the 28-day requirement.

Originally, the pavement design for Runway 17-35 called for the crushed rock subbase, then 5 inches of cement-treated permeable base course with 10 inches of concrete on top. But the contractor offered a no-cost change order, which was approved by FAA, to pave a single-pass 15 inches of concrete (instead of 10) in lieu of paving the cement-treated permeable base.

The project team also applied a major lesson learned from previous work on Runway 8-26. Cihlar reports that its pavement has held up “beautifully,” but the centerline joint on the crown of the runway has posed some challenges. Winter operations crews try to avoid riding the snowplow on the joint, but it’s sometimes unavoidable, particularly in low-visibility conditions. When a snowplow does run over the joint, it damages the plow blade and center joint. “That center joint is really the one area of pavement where we know in the next 10 years, we’re going to have to do a rehab,” says Cihlar.

To avoid the possibility of similar damage on Runway 17-35, CWA modified the design to offset the centerline joint from the crown. Trierweiler Construction fabricated a custom screed for the slip form paver to form the crown breakpoint in the slab. Special tools were made for finishing and checking the offset centerline joint as well. By using two stringless pavers for mainline paving, setup time was reduced for 24- and 26-foot slab widths needed for the offset crown. “Now, if plows accidentally get on the crown, it’s still hard on our plows and on the crown of the pavement, but it won’t be the joint of the pavement,” notes Cihlar.

Next Up

When Runway 8-26 is shifted to its new location, CWA will have the desired separation between its two runways. After pavement for the east end is in place, a displaced threshold will be installed, and the airport will temporarily close down Runway 17-35, remove pavement on the west end and add a new connecting taxiway. The project, which is scheduled to begin next year, will also replace a MALSR system that has been unmaintained by FAA and out of service for over eight years, relocate the glideslope and localizer, and add new runway and taxiway lights. The parallel taxiway will be shifted north to achieve the standard 400-foot separation.

CWA anticipates an Airport Improvement Program discretionary grant and supplemental funding for the project in fiscal year 2022.

Like other airports, CWA was significantly hampered by COVID-19.  Before the pandemic, it was on track for 160,000 enplanements in 2020 with 13 flights per day. “We’re hopeful that next year we can attract a low-cost carrier,” Cihlar says. “Having this runway during the decoupling project is going to help us sustain our operations.”

CWA is seeing tremendous growth in corporate aviation. Prior to COVID, the airport served one or two transient corporate jets per week. Currently, it receives upwards of three per day. “Plus, we’ve had a lot of corporate hangar development,” Cihlar adds. An area of the airport that had remained undeveloped for 30 years now has three new hangars. In the last three years, CWA gained a medivac facility, a new corporate tenant and an existing tenant built a new hangar. “It’s some great development on the airport,” Cihlar remarks.