Manassas Apron Project Reaps Rewards from Reclamation Efforts

Author: 
Nicole Nelson
Published in: 
September
2011

When Manassas Regional Airport completed the final phase of its nearly $11 million East Apron Rehabilitation and Expansion Program last fall, airport officials felt like they received a "two-fer." Recycling existing pavement saved both time and money.

Airport director Juan Rivera credits Campbell & Paris




factsfigures

Project: East Apron Rehabilitation & Expansion, Phase III

Location: Manassas (VA) Regional Airport

Cost: $3.163 million

Funding: ARRA stimulus grant

Design Engineer: Campbell & Paris Engineers

Prime Contractor: Chemung Contracting Corp.

Timeline: Aug. 2009 - Sept. 2010

Engineers (C&PE) with devising and executing the plan to use asphalt millings from the existing cement-treated base course to create a strong foundation for the final rehab. The time saved by using on-site materials minimized ramp closure - an especially important benefit for Virginia's busiest general aviation airport.

Modifications to Standards

While traditional rehabilitation projects involve full-depth pavement demolition and removal, C&PE opted for more current recycling strategies - in particular, using reclaimed asphalt pavement (RAP), explains Mark McGuire, P.E., senior vice president, C&PE.

The approach required the firm to write a new specification for the use of RAP material as a base course for the apron shoulder expansion and to modify the FAA P-304 specification for the mixed-in-place cement-treated aggregate base course. Both aspects required FAA approval prior to bidding.

"Overall, we simply specified a gradation for the RAP material similar to the FAA P-209 standard for aggregate base course," McGuire explains, noting that C&PE tried to keep the specifications for the RAP and mixed-in-place cement-treated aggregate as close to existing specifications and as simple as possible. "This let the contractors know during bidding that they would need to perform an extra step during construction, to work with the milled asphalt material to achieve a gradation acceptable for its use as a base course under the apron and shoulder expansion. The modifications to the FAA P-304 cement-treated aggregate specification were a little more complex, but in general, development of the mix design, methods for mixing and achieving compaction, and testing were modified to suit this type of project."

Terry Page, manager of the FAA Washington Airports District Office, says the innovative method not only made the project more environmentally friendly, but also more efficient. By reclaiming and reusing the pavement, crews didn't expose the subgrade to the elements, which consequently incurs delays, explains Page.

Timeline Constraints

C&PE built the project schedule around funding and the need to develop mix samples.

"The mix design process is typically a 30-day time period, so we needed to take that into account when developing the number of contract days for the construction schedule," McGuire recalls. "We ended up starting the project in late fall due to the funding cycle, and we took advantage of that period by specifying an initial paperwork milestone for all submittals, the construction schedule and quality control plan requirements during the winter months."

Chemung collected the materials and developed its mix design during this period, as construction was not set to start until the following spring. The final phase of the project was also dictated by the availability of American Recovery and Reinvestment Act (ARRA) funds via the FAA, which covered the entire project cost.

"We always want to start construction as soon as possible so contractors don't have to hold prices for a prolonged duration," McGuire relates. "While not ideal, we were able to let contractors know during the bid process that construction wouldn't begin for almost nine months after receipt of bids, and at least let them prepare their bids accordingly."

Respect for Weather

The airport's flood plain and wet soils weighed heavily in the ultimate decision to recycle the base course in place.

As engineer of record for the initial apron construction 20 years prior, C&PE's H.D. Campbell Jr. was familiar with the existing cement-treated aggregate material and saturated underlying soils.

"We knew some of our methods might be considered unconventional, but exposing the existing subgrade during construction was our least desirable option," Campbell explains.

"We've done quite a bit of work at the airport over the past 30 years and were aware of the continuously wet soil conditions," McGuire adds, noting that the paved apron areas are about five feet above the 100-year flood plain elevation. "Excessive drying operations during construction were likely if we exposed the subgrade soils to the elements with a full-depth demolition and removal strategy. We wanted to avoid those issues and reclaiming the in-place cement-treated aggregate helped us avoid quite a bit of drama."

A concrete channel was placed directly adjacent to the shoulder expansion to capture runoff from the apron, explains McGuire. Prior to that, the runoff exited directly into a grass area that contributed to prominent wet soil conditions and pavement failures in adjacent areas. These problems have since been alleviated with the use of the concrete drainage channel that also allowed the use of RAP material in lieu of crushed aggregate under the concrete.

In total, about 66,800 square yards of existing cement-treated aggregate material was reclaimed from an average depth of 10 inches. About 18,558 cubic yards of material consequently didn't need to be hauled off site or replaced.

"That is where we realized the big cost savings and green impact," McGuire relates. In addition, the contractor only used three pieces of construction equipment: a truck to offload and spread the cement, a road reclaimer to perform the mix-in-place operations and a vibratory drum roller to compact the reclaimed material.

"Overall, the project went well," Rivera summarizes. "The technique we used with the third phase not only helped us stay on schedule, but it had the recycling aspects. We were able to create a situation where we were able to work throughout the summer without long delays due to weather."

Subcategory: 
Runway/Ramp

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