Rehabilitating Asphalt Highways:
Coal Fly Ash Used on Ohio Full Depth Reclamation Projects
Case Study
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December
2007
Much of the almost two million miles of asphalt roadways in the United States are severely distressed
and in need of repair or replacement. Over the last few decades increasing traffic demands combined with
decreasing funding for repairs, environmental concerns and an emphasis on safe, efficient transportation
systems have stimulated research and field demonstration projects to explore methods to reuse and recycle
pavement materials.
In response to this need, the Department of Civil and Environmental Engineering and Geodetic Science
at Ohio State University (OSU) has partnered with the two fastest growing counties in Ohio (Delaware
and Warren) to construct and monitor two pavement sections in which failing asphalt pavements were
recycled in 2006 using Ohio coal-generated Class F fly ash as a cementing agent in a full depth reclamation
(FDR) process.
"The value of this technology and demonstration project to the contractor is at a minimum two-fold,"
says Chris Anspaugh, construction manager, Base Construction. "With the price of cementitous additives
continuing to rise in price due to the substantial energy costs involved in producing them it would be of
value to the contractor, from a competitive standpoint, to have alternative products available that will
achieve the same end results.
"Secondly, the contractor needs testing data available that can be submitted to the owner to assure them that
the product will perform as we are claiming," he continues. "This research will go a long way in providing
that information." This project will demonstrate that when non-concrete quality fly ash in combination with
lime or lime kiln dust are properly incorporated into FDR reconstruction of a flexible pavement, the use
of fly ash can be economically attractive while offering increased structural and service performance, and
should not lead to a degradation of environmental quality.
On this FDR research preservation project, the complete depth of the flexible pavement section consisting
of the asphalt layer, base, subbase and a pre-determined amount of the underlying existing subgrade soil
were uniformly pulverized, blended with chemical additives (Class F fly ash in combination with lime or
lime kiln dust), and compacted to construct a new stabilized base course.
An asphalt overlay was then placed over the stabilized base. Class F fly ash in itself is not self-cementing.
It needs additional lime to undergo a cementitous reaction. It's important to note that fly ash, when used in
combination with lime or lime kiln dust, performs two important functions in FDR work:
l.Fly ash provides the silica
and alumina needed for
cementitous reaction with
lime to increase the strength,
stiffness, and durability of
the stabilized base layer
2. Fly ash acts as a mineral
filler to fill the voids in
the granular pulverized
pavement mix, reducing the
permeability of the FDR
stabilized base layer.
Material before mixing (left) and after mixing (right). Note the fly ash on the left side.
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Case Study
18
Rehabilitating Asphalt Highways: Coal Fly Ash Used on Ohio Full Depth Reclamation Projects
Construction Projects
Delaware County (just north of Columbus) is the fastest growing county in Ohio. In collaboration with
the Delaware County Engineer's Office, Section Line Road between State Route 42 and Home Road was
selected for FDR reconstruction in 2006.
The pavement sampling and
design was carried out by EDP
Consultants under the supervision
of OSU. A total of nine sections
were constructed using the
following six mixes:
4 percent lime with 6 percent
fly ash, 8-inch stabilization
depth (0.7 mile)
5 percent lime kiln dust
with 5 percent fly ash, 8-inch
stabilization depth (0.6 mile)
Compaction of the FDR base layer in Delaware County
3 percent lime kiln dust with
1.4 gallons per square yard emulsion, 8-inch stabilization depth (0.7 mile)
5 percent cement, 12-inch stabilization depth (0.8 mile)
2 percent cement with 1.6 gallons per square yard emulsion, 8-inch stabilization depth (0.3 mile)
5-inch mill and fill (two 0.1-mile sections at the north and south ends of the project, and a 0.7-mile as
well as 0.1-mile sections near the middle of the project).
The FDR rehabilitation of the Section Line Road was completed in five phases. Milling removed 5 inches of
the existing pavement asphalt surface, followed by pre-pulverization of the remaining pavement materials
to specified depths. The third phase involved treating the pulverized pavement materials with the six
admixtures outlined above. Water was then added to the mix and it was compacted immediately. The last
phase involved resurfacing the pavement with 5 inches of hot mix asphalt.
In Warren County, just South
of Cincinnati, failing pavement
was sampled and an appropriate
mix design was carried out by
EDP Consultants again under the
supervision of OSU. Two sections
were constructed as follows:
4 percent lime with 6 percent
fly ash, 12-inch stabilization
depth (0.32 mile)
5 inch mill and fill (0.08 mile)
The five-phase FDR rehabilitation Asphalt placed over treated pavement base materials
included milling and removal of 4
inches of the existing pavement asphalt surface. Secondly the remaining pavement materials were pre-
pulverized to a depth of 12 inches. The third phase involved treating the pulverized pavement materials with
lime at an application rate of 4 percent and allowing the material to mellow for a 24-hour period.
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Rehabilitating Asphalt Highways: Coal Fly Ash Used on Ohio Full Depth Reclamation Projects
Case Study
18
After the mellow period, 6 percent fly ash from Zimmer power plant of Duke Energy was blended into the
mix to a depth of 12 inches. Water was added to the mix and it was compacted immediately. The last phase
involved resurfacing the pavement with 4 inches of hot mix asphalt.
Pavement instrumentation and monitoring
During construction, the Delaware and Warren pavement sections were fitted with the following structural
and environmental monitoring devices:
Strain gauges at bottom of asphalt layer
Pressure cells at bottom of stabilized base layer
Pore pressure devices at bottom of stabilized base layer
Linear Variable Displacement Transducers (LVDT) for measuring vertical deflections of pavement
Lysimeters installed within the stabilized base to monitor leachate quality.
Data collection from the above
monitoring devices is being carried
out on a quarterly basis.
Falling Weight Deflectometer
(FWD) tests (to measure pavement
load deflection behavior, resilient
modulus of pavement layers and
subgrade soil, and base structural
layer coefficient) are being carried
out by the Ohio Department of
Transportation. The FWD tests
carried out on the pavement before
and immediately after completion
of rehabilitation show that FDR
of the pavements with fly ash (and
lime or lime kiln dust) increased
the elastic modulus of the base
layer. The fly ash sections exhibited
elastic moduli of base layers similar
to cement and cement plus emulsion sections. FWD tests will continue to be carried out twice a year to
determine the longer term elastic moduli of the various sections constructed in this project.
Objective and Goals
The overall objective of this work is to demonstrate the effective use of Class F fly ash in combination
with lime or lime kiln dust in the FDR of asphalt pavements. This is done by establishing field-verified
relationships for the service performance and structural and environmental behavior of FDR pavements
constructed using lime-activated fly ash.
There are four interrelated activities. In the first, laboratory studies specifically designed to investigate
the physical, chemical, and engineering properties of fly ash FDR mixes were conducted. This allowed
the research team to determine the optimal material mixes that were implemented in the two pavement
preservation projects. In the second activity, the two highway pavements that were constructed and
instrumented in 2006 will be monitored for two years. This is to obtain robust field results on the structural,
service, and environmental performance of field-constructed FDR bases. In the third activity, existing flexible
The OSU pavement instrumentation is installed at the bottom of the FDR layer (left to
right) pressure cell, porepressure device andLVDTbase inDelaware County.
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Rehabilitating Asphalt Highways: Coal Fly Ash Used on Ohio Full Depth Reclamation Projects
Case Study
18
pavements constructed in Ohio using FDR will be investigated to allow for evaluation of the performance
of existing projects for which no performance data has been collected to date. Lastly, the existing outreach
and technology transfer efforts of the Coal Combustion Products (CCP) Extension Program at OSU will be
focused on county, state, and federal transportation officials and other end users of the technology.
"Class F Fly ash can be a valuable cementing ingredient when used with lime, which was first recognized
by the Roman Civilization 2000 years ago and proven with time since then. The lime industry believes in
the important opportunity in road construction to promote the synergisticism and pozzolanic reaction of
lime and coal fly ash" said Joel Beeghly, Senior Technical Specialist with Carmeuse Lime Company.
Environmental Benefits
In addition, to demonstrating the technology itself, these projects address a very important environmental
issue, says Professor William Wolfe of OSU's Department of Civil and Environmental Engineering and
Geodetic Science. "Since the production of one ton of cement produces about one ton of carbon dioxide,
which is then released into the atmosphere," he says, "the widespread replacement of cement with fly ash in
roadway reconstruction will result in significant reductions in the generation of this greenhouse gas."
This three-year project at OSU, totaling over $2 million, is funded primarily by the Ohio Coal Development
Office of the Ohio Air Quality Development Authority with additional support from the Delaware and
Warren County Engineers Offices, Base Construction, Carmeuse NA, Mintek Resources, Fly Ash Direct,
Headwater Resources, and others.
"Last year, two counties in Ohio used Ohio coal-generated fly ash in reclaiming failed asphalt pavements,"
says Mark Shanahan, executive director of the Ohio Air Quality Development Authority, which manages
the Ohio Coal Development Office. "This resulted in more durable highway infrastructure and promoted
the recycling of pavement materials and coal combustion byproducts, both of which would otherwise have
been landfilled."
Greg Samios, proj ect manager of EDP Consultants Inc. adds, "The unique opportunity of a comparative mix
design study has enabled EDP Consultants to increase our knowledge and understanding of how different
chemical additives may benefit the recycling industry."
Submitted By:
Tarunjit S. Butalia, Ph.D., PE.
Research Scientist & Coal Combustion Products Coordinator
Department of Civil and Environmental Engineering and Geodetic Science
The Ohio State University
470 Hitchcock Hall, 2070 Neil Avenue, Columbus, Ohio 43210-1275
Tel: (614) 688-3408 (Work), Fax: (614) 292-3780
Email: butalia.l@osu.edu
CCPOhio Web Page: http://ccpohio.eng.ohio-state.edu
About the author: Dr. Tarunjit S. Butalia, RE., is a research scientist and coal combustion products coordinator for the CCP Extension Program
at the Department of Civil and Environmental Engineering and Geodetic Science at The Ohio State University.
This article (in an expanded form) appeared in the February 2007 issue of Asphalt Contractor and can be accessed from the following link
http://www.forconstructionpros.com/print/Asphalt-Contractor/Features/Rehabilitating-Asphalt-Highways/2FCP4421:
COAL COMBUSTION
PRODUCTS PARTNERSHIP
This coal ash utilization case study is a selection of the Coal Combustion Product Partnership. For
more information, consult C2P2 web site at http://www.epa.gov/epaoswer/osw/conserve/c2p2/
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