Many airport operators feel they have limited options when it comes to airfield pavements. As vital concrete and asphalt assets age and deteriorate, they repair areas as needed and wait for the field's pavement condition index to dictate a replacement project. When that day comes and goes, a new version of the same cycle begins again.
That's not the approach at Lambert-St. Louis International (STL). Officials there determined that if they strategically use all available tools, they can stretch the anticipated peak in capital improvement investments and flatten the airport's spending curve into a more manageable and consistent annual capital improvement program. Breaking out of the standard repair-replace cycle is projected to save STL $23 million in coming years.
Project: Airfield Pavement Preservation
Location: Lambert-St. Louis Int'l
Recent Project: Runway 12R-30L
Strategy: Reconstruct 1/3 of runway & aggressively repair remaining 2/3, with scheduled periods of standard maintenance & additional aggressive repairs for next 20 yrs
Cost of Recent Reconstruction/Repairs: $16 million
Construction Timeline: 6 months
Anticipated Future Savings: $23 million (present worth value)
Engineering Consultant: Crawford, Murphy & Tilly
Construction Management: Kwame/Green Joint Venture
Contractor: The Harper Co.
Topographic Surveys: David Mason
Topographic Surveys & Design Assistance: EDSI
Geotechnical Investigation & Design Assistance: TSI
Pavement Testing & Analysis: Engineering and Research Int'l
"We took control of our pavement assets," says Jerry Beckmann, deputy airport director of Planning and Development at the St. Louis Airport Authority. "And by doing so, what could have been a funding mountain was reduced to basically a speed bump."
STL has succeeded in extending the service life of runways and some taxiways 10 to 15 years, while also improving the overall pavement condition index of its airfield system. Notably, it accomplished this without dramatic increases in annual funding levels
Since 2000, STL has spent between $8 million and $12 million per year rehabilitating or reconstructing their existing pavements on airside capital construction, and officials expect outlays to remain similarly consistent for the foreseeable future. (The annual outlay excludes the recent Runway 11-29 complex expansion.)
Personnel from Crawford, Murphy & Tilly, the airport's engineering consultant, note that the impressive results at STL underscore the value of its long-term collaborative approach to airfield pavement management and strategic use of repair methods. They also attribute the successes to officials making decisions driven by detailed data and viewing individual projects in the context of an overall capital program and its funding limitations.
Ty Sander, the company's project manager at STL, recalls seeing huge challenges on the horizon for the airport about 15 years ago. "But we were determined to develop a new game plan to address it," he adds.
"When it comes to pavement projects, a great deal of value can be gained in the decision-making process when you dig down into the details at a micro level, but never lose sight of the overall capital program and your funding limitations," explains Sander.
With a runway and taxiway system largely constructed between 1978 and 1983, time and money were both issues for STL. When Crawford, Murphy & Tilly began assessing the situation with STL, the airport's pavement management system indicated that a majority of the airfield pavements were on a trajectory to require major reconstruction near 2015. Airport officials, however, knew that the prevailing economic and operational realities of the 21st century would never allow for the massive construction projects that occurred there in the early 1980s.
STL focuses on balancing reconstruction with extending pavement service life through a holistic management and design approach that emphasizes strategic rehabilitation, explains Sander. The approach has proved highly successful in stretching the effective lifespan of individual pavement components, he elaborates.
Its long-term game plan was demonstrated most recently on the airport's main runway, 12R-30L. Based on pavement condition index values, a solid case could have been made for a wholesale replacement of the runway - a position viewed as an acceptable option by the FAA at the time, relates Sander. While an $80 million project to replace Runway 12R-30L would have undoubtedly succeeded, it would have also compromised STL's ability to adequately address other pavement and capital needs in a timely manner, he explains.
When approaching the FAA about the project, STL took a tactic the agency doesn't often encounter. Rather than proposing an expansion of the project scope that required more funds, officials suggested a less-is-more approach for Runway 12R-30L. Their logic? Spending less on that particular project would leave more resources available for other airfield pavement needs.
"Our philosophy is to look for ways to maximize the use of the good pavements that are out there - with a little more detailed value engineering up front, which can pay big dividends in overall life-cycle costs," Sander explains. "That process begins with making sure we know all aspects of the pavements condition and performance."
A "strategic rehabilitation approach" requires additional pavement testing and evaluation, he emphasizes. New data about STL's main runway was tied into archived information from previous pavement management studies. Together, it revealed that for a majority of the runway, the underlying structure of the pavement could last another 20 years. A vital part of the plan was managing surface distress on 12R-30L (and associated potential for debris that could create foreign object damage to aircraft) without depleting significant maintenance resources.
Subcontractor Engineering and Research International was hired to create and execute a testing regime to determine the amount of load transfer. Personnel used ground-penetrating radar to assess the different layers beneath the pavement. A finite element analysis determined the overall structural capacity of the pavement and modeled anticipated airfield traffic for the next 20 years.
"Through these 'ou-of-the-box' processes, we were able to get a much more precise understanding of where attention would need to be focused," Sander notes.
The end result was a design that reconstructed only the western third of the runway and employed a range of concrete pavement repair techniques for the eastern two-thirds. A life cycle cost analysis of a 20-year strategy yielded a present worth value cost savings of $23 million. The plan called for an aggressive concrete repair program the first year, normal maintenance in years two through 10, another aggressive pavement repair cycle during the 11th year, and normal maintenance in years 12 to 20.
Crawford, Murphy & Tilly personnel tapped into "vast amounts of data" about STL's airfield to execute the strategy. The airport's ongoing pavement management program and 15 years of pavement concrete index updates provided the team with invaluable historical resources that would otherwise have been difficult to collect, notes Sander. The format and metrics of the archived data were so uniform that the team could essentially compare apples to apples through different snapshots in time, he reports.
"The airport's maintenance staff have been an invaluable source of insight for us," adds Sander. "If you want to really understand how a pavement is performing, spend some time with the people who are out there every day working on it."
On-the-ground intelligence and historical data about the condition of specific sections of pavement allowed engineers to depart from the traditional default of full-scale replacement. Instead, they were able to focus on maintaining as much of STL's good pavement as possible.
The new mindset evolved organically, says Sander. A major transition during the 1990s and early 2000s left the airport scrambling to increase capacity with a new third runway. When the airport's primary airline tenant cut its flights almost in half as the runway program was being completed, the picture changed dramatically.
As project funding became scarcer, airport leadership challenged its design team to be more cost-effective and to instill consistency in STL's annual capital improvement program. The strategic rehabilitation program that was developed in response has been so successful that other airports are considering similar modifications to their own approaches, notes Sander.
STL is applying the savings from its shortened runway repair schedule to taxiway rehabilitation work - projects that would have otherwise been put on hold. Ultimately, delaying taxiway work would have required the airport to spend additional maintenance resources to support ongoing flight operations.
"The key to all of this is making sure that the design strategy for pavement repair concentrates resources where they make the most sense," explains Beckmann. "That's how you make this successful."
With 630 acres of airfield pavement to maintain, STL must reconstruct a certain portion of its concrete to make its investment last for 30 to 40 years and avoid an inevitable backlog of repairs, he elaborates. Strategic rehabilitation targets improvement for pavements that are within five to 15 years of the end of their service life. At that age, they are still in reasonably good shape but beginning to deteriorate at a faster rate, Sander notes. Such pavements can have their service lives extended for an additional 10 to 20 years, he adds.
Peace of Mind
A 10-year review of performance on the airport's north runway, where the strategic rehabilitation approach was applied in 2004, demonstrates that pushing major reconstruction back five to 10 years can yield surprising efficiencies without dramatically impacting maintenance costs. In that case, STL opted to limit full reconstruction to the center 50 feet of the 150-foot wide runway and performed lighter repairs to the outer panels, each also 50 feet wide. (For information about a similar partial replacement project at Hartsfield-Jackson Atlanta International, visit AirportImprovement.com.)
The outer panels have held up well, reports Sander. So rather than reconstructing them, STL is planning a second strategic rehabilitation that will address less than 10% of the overall pavement at a fraction of the cost of a full replacement. As before, contractors will fully or partially replace some panels, then seal and/or repair additional cracks and spalls as needed.
"Our goal here is to extend the service life of the full runway at least another 10 years," Sander comments. "And that's completely feasible. We've demonstrated that."
STL's previous success with strategic rehabilitation provides a reassuring effect. By proactively integrating methods that extend the lifespan of airfield pavements, airport officials can maintain control over infrastructure deterioration and achieve a more balanced capital improvement program, explains Sander. It also allows them to get ahead of the curve and develop more accurate schedules for projected needs.
"When it comes to pavements, we no longer feel like we're just putting out one fire after another," Beckmann relates.
Sander points to STL's experiences as proof positive that airports do not need to dedicate disproportionate amounts of funding to declining airfield pavements. Even though they are complex systems with too many variables for precise project forecasting, maintaining them in a cost-efficient manner is not unmanageable, he emphasizes.
"You have to work with all of the tools that are available to you and you have to be willing to take that deep-dive, big-picture approach," Sander advises. "If you do that, then there's no reason you can't ensure the safety and pavement of your pavements well into the future."