Case Study
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December
2003
WAUKESHA COUNTY AIRPORT / CRITES FIELD WAUKESHA, WI
Full Depth Reclamation [FDR] - A Rehabilitation Option for
Deteriorated Hot Mix Asphalt [HMA] Pavements
Crites Field
Crites Field, the local and historic name for the Waukesha County regional airport, has been
growing in both air traffic and in importance to the Waukesha County community in general.
In the past several years, take-offs and landings have increased to over 100,000 per year.
The main runway, now a Portland cement concrete pavement, was reconstructed a few years
ago, but the auxiliary runway [18/36], an old asphalt pavement, had deteriorated. It needed
rehabilitation. The 3,600 foot runway was originally constructed on fill with a three inch hot
mix asphalt [HMA] surface over only about eight inches of crushed aggregate base course.
The surface was badly cracked and very rough for an airport runway, not suitable even for an
auxiliary facility.
Design Options
In concert with the Wisconsin Department of Transportation Bureau of Aeronautics [BOA],
Mead & Hunt, Inc., a consulting firm specializing in airport design and construction,
developed two alternatives for the pavement reconstruction phase of this project. They
included either removing the existing pavement, reconstructing the sub-grade, installing a
geo-textile fabric, replacing the base and repaving or pulverizing / recycling the existing
pavement in place, stabilizing / strengthening the material with class 'C' fly ash and repaving
with four inches of new HMA pavement. The second alternative known as full depth
reclamation [FDR] is rapidly becoming the HMA rehabilitation option of choice for many
jurisdictions. Evaluating the bids, the FDR option was lower by over 25% compared to the
more traditional construction method. After significant discussion and evaluation of the
options, the BOA and Mead & Hunt's engineering staff recommended FDR based on the
economic advantage and the anticipated saving of construction time. The airport manager,
Keith Markano, supported selection of the FDR option, even though he had no prior
experience with the process.
Mr. Markano conferred with the Waukesha County highway department, which recently used
the FDR method successfully on several of their rehabilitation projects. The response was
positive, making it more comfortable for him to approve the option.
Waukesha County has reconstructed several miles of trunk highways using FDR, some of
which have been the basis for ongoing performance studies. One section in particular has
been evaluated in each of the past five years using a falling weight deflectometer [FWD] to
evaluate both pavement and base performance. Surface performance has been very good and
base performance has been so good, it lead engineers to support increasing the structural
number used in HMA pavement design.
Geotechnical Recommendations
To assure that the pulverized asphalt pavement [PAP] material was treated with proper
concentrations of class 'C' fly ash, Soils & Engineering Services [SES] was engaged to
perform lab tests on the pulverized material. Several PAP material samples were taken to the
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lab where moisture / density relationships were determined using procedure ASTM - D 1557.
Optimum density was determined to be 137.7 pcf at a moisture content of 6.4%. Several
Proctor points were evaluated with varying concentrations of fly ash. The recommended
application of fly ash was 110 Ibs. per square yard or about 8% by weight. This rate is very
typical for stabilizing PAP where the range is 7 - 11% fly ash and in the range of 6 - 8.5%
moisture. Other materials on site were tested as well to assure performance during and after
construction. Mead & Hunt engineers, the airport manager and the contractors met on a
regular basis to share information, determine schedules and keep the project on track.
Construction Process
Full Depth Reclamation follows a well defined
series of operations. First the existing FDVIA
pavement is pulverized, usually to a depth of 12
inches. The FDVIA and aggregate base course
materials below it are reduced to a combination
of materials that are in effect a high grade new
base course. Gradation is similar to that of a
conventional crushed stone. The materials are
relatively loose and need to be compacted, and
re-graded to meet design requirements. Water is
usually added to assure proper density. Next,
the fly ash is distributed on the new surface with the vane feeders mentioned earlier. The
vane feeders are calibrated to spread fly ash on the surface at the specified design rate.
Next the materials are mixed with a pulverizer to produce a homogeneous mixture of PAP
and fly ash. Generally, the depth of treated material is 8 - 9 inches. Since moisture content of
the mixture is crucial, a water truck is connected to the pulverizer and water is injected
directly into the mixing chamber. Constant monitoring of the moisture content is required.
Once the materials are mixed and blended, a vibratory pad-foot roller makes several passes
over the material. It is essential that the vibratory roller follow the mixing operations as
closely as practicable. In most cases, there is no delay between the mixing and the
compaction. Delays will result in reduced performance of the new base material.
Next the newly blended material is graded to meet geometric requirements for cross slope,
profile and curvature, if any. After that it is rolled once again with a roller, this time a smooth
drum roller operating in static mode. This is important because once the fly ash and water are
mixed with the PAP and compacted, the process of hydration begins. It continues throughout
the grading process and to apply additional vibratory loads would interfere with the hydration
process. Final rolling simply seals the surface of the strengthened material and provides a
smooth, uniform surface for the new HMA pavement. In some cases, several days may pass
between the fly ash stabilizing and construction of the new HMA surface. It is common to
fog the finished surface with water to enhance hydration and to control dusting as the
materials dry.
One advantage the FDR construction option provides is that after initial compaction and
preliminary grading is complete, traffic, both construction and vehicular can traverse the
work site. Other construction operations can be completed simultaneously and delivery
vehicles are not impeded.
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Contractors
The prime contractor on the project was Super Excavators, Inc a regional grading and
underground contractor headquartered in Menomonee Falls, WI. Payne & Dolan, Inc of
Waukesha was the subcontractor responsible for the pulverizing, fly ash stabilizing and final
HMA paving. Lafarge North America was the fly ash supplier and We Energies, a regional
electric utility company produced the class 'C' fly ash at its Oak Creek Power Plant.
Payne & Dolan has been involved in the FDR process for many years in the area. Their
equipment operators, foremen and project managers are very experienced and over time have
become knowledgeable in the process, being able to sense performance of the mixed
materials by the way in which the equipment behaves. Moisture content is crucial and the
operators watch the mixture constantly.
Fly ash transportation from the power plant to the project site was provided by Hribar
trucking. Hribar also operated the vane feeders used to distribute the fly ash on the PAP
surface. The vane feeders are owned by Lafarge and are typically provided as part of the fly
ash delivered to the project site. Because the completion schedule for this project was
ambitious, two vane feeders were provided. By using two units, there was no time lost
transferring fly ash from the tank trucks to the vane feeders. Payne & Dolan equipment was
in service continuously pulverizing and blending fly ash with the PAP.
Quality Assurance
Throughout the project, Mead & Hunt engineers were on site to provide guidance to the
contractors. Their technicians did all the necessary staking to provide the contractor
information for final grades. In airport construction, grade tolerances are very important. And
because construction progress was very fast, the technicians needed to move quickly to stay
ahead of the hydration process.
The geotechnical consultant, SES, was on site throughout the project to monitor density and
moisture content of the new material. The compaction recommended by SES for the PAP
was 95%. In over 80 test sites, all met or exceeded the minimum design requirement. Many
were in the upper ranges of compliance and several were at 100%. Moisture tests were all in
the range of 6 - 9%, all in compliance with recommendations and certainly acceptable for
performance. During the course of the project, heavy rain fell several times on the new base.
Even with that, performance surpassed minimum requirements. The new surface shed rain as
designed and continued to gain strength through hydration.
During construction of the new HMA lower course, SES monitored densities as well. With
the new firm base, in all cases, design density was exceeded, a testimonial to performance of
FDR material.
Environmental Considerations
The FDR project on Crites Field was completed in a very timely way. Weather did not
interfere with progress and there were significant environmental advantages. The existing
pavement [both HMA and base course] components were pulverized and re-used completely.
No material was hauled off site and no additional natural materials were brought in. Trucking
costs were minimized and over 2,000 tons of class 'C' fly ash from the utility company was
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used in a beneficial application. The fly ash used in this project was not cement replacement
quality [for use in concrete] and may have otherwise been sent to a disposal site.
During construction, representatives from the
Wisconsin Department of Natural Resources,
the USEPA and the utility company were on
site to observe the progress on the project.
There was uniform agreement that the work
was done in compliance with standing
regulations [Wisconsin administrative code NR
538] and policies of the utility itself. Wisconsin
Department of Transportation specification
policies and procedures were followed as well.
The vane feeders used to spread the fly ash on
the PAP surface are designed to control the application rate, but also are very effective in
minimizing or eliminating fugitive dust. The representatives also agreed that projects that
utilize the FDR option will continue to become more attractive. With the price of asphalt
continuing to increase, this alternative will find its way into the construction industry.
Economic Considerations
Full Depth Reclamation utilizes existing materials which were paid for during initial
construction and class 'C' fly ash. The typical cost for the FDR process, including
pulverizing, spreading fly ash, mixing, watering, compacting and grading to paving grade is
approximately $4.50 per square yard, complete and ready to pave. On this project the cost of
traditional construction was estimated at $200,000. The final cost of the FDR option saved
the taxpayers of the state and county over $50,000. In addition, selecting this option saved
substantial construction time.
Over 30,000 square yards of material were pulverized and stabilized with fly ash in only six
days. It allowed the project to move forward very quickly with no delays caused by rainy
weather. And while cost is somewhat difficult to estimate, air traffic interruption due to
construction was held to a minimum.
Conclusions
In discussing the project with the airport
manager, Mr. Markano, he expressed his
pleasure and satisfaction with the choice. He
had the support of the Waukesha County
Executive and his staff. His satisfaction and the
satisfaction of his customers, the pilots and
passengers that use the facility are very
important. One feature of the FDR process he
was pleased with is very short construction
time.
This was the first major project of this type for the Bureau of Aeronautics and the engineer,
Mead & Hunt. Both expressed satisfaction with the performance of the FDR process and the
cost advantages it exhibited. They learned many of the details of construction, materials and
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procedures. It appears that as work on other general aviation airports in the state becomes
necessary, this option will begin to become the primary design option. It already has in many
county highway agencies.
The contractors are pleased with the results this project produced as well. Payne & Dolan,
who has done a number of similar projects, gained additional experience with the close
tolerances required by FAA specifications. The use of more than one vane feeder truly
helped expedite the work. Most agree that the advantage FDR provides by eliminating the
concern for rain events during the course of the work can be a real asset.
This report was prepared by James R. Rosenmerkel, P.E., engineering consultant to Lafarge North America.
He spent many hours in the field with the contractors, utility representatives, engineers and regulators
providing guidance and advice. Design details were provided by the various parties and are reported as
received. Additional information is available atjbrosie@sbcglobal.net or at 262-547-2585.
Submitted By:
James R. Rosenmerkel, P.E.
CĄ
COAL COMBUSTION
PRODUCTS PARTNERSHIP
This coal ash utilization case study is a selection of the Coal Combustion Product Partner ship. For
more information, consult the C2P2 web site at http://www.epa.gov/epaoswer/osw/conserve/c2p2/
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