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Recent Projects >Franklin County Highway
84
County Highway 84 in Franklin County, Alabama
 A
severely deteriorated roadway in northwestern Alabama was recently
rehabilitated through the Full-Depth Recycling (FDR) process. Mr.
David Palmer, County Engineer, Franklin County Highway Department
had one particular roadway that had become a maintenance headache
for his agency and had been searching for new ways to create a more
durable roadway that could support his County's increasing traffic
loads. Mr. Palmer met with individuals from the Portland Cement
Association, the American Concrete Pavement Association, and National
Cement Company of Alabama to hear about FDR and what it could mean
for his roadways. Upon hearing the positive news of both durability
and economy using FDR, Mr. Palmer agreed to the process and a 1.7-mile
stretch of Franklin County Highway 84 just north of Cedar Lake became
the first known FDR project in the state of Alabama incorporating
portland cement.
 Samples
of the deteriorated bituminous surfacing and underlying base materials
were collected from numerous locations along the roadway to a depth
of eight inches - the depth of the proposed FDR base. These samples
were sent to a geotechnical testing laboratory where they were evaluated
for suitability in the FDR process. In addition to establishing
the maximum dry density and optimum moisture content for the roadway
material, a Mix Design was prepared that determined that five percent
portland cement blended with the existing roadway material would
result in a new homogenous base material with a minimum unconfined
compressive strength of 350 pounds per square inch - a strength
more than capable of supporting the traffic on this roadway.
 With
all the necessary preliminary sampling and testing completed, roadway
construction activities began on September 18, 2002. The cement
was delivered to the project in bulk tankers where it was applied
directly on top of the roadway at an application rate of approximately
37 pounds per square yard - a rate that equated to the five percent
as determined during the Mix Design process. Through one pass of
a Caterpillar RR-250 reclaimer, the existing roadway and underlying
soils were pulverized and blended together with the portland cement.
Water trucks applied water to this blended material, bringing it
to its required optimum moisture. One additional pass with the reclaimer
resulted in a homogenous roadway base material.
The roadway was shaped to the appropriate line, grade, and cross-sections
using a Caterpillar 12H motor grader and then compacted using a
Caterpillar CP563C vibratory sheepsfoot roller and a Caterpillar
CS563C vibratory smooth drum roller. A nuclear density gauge was
used at numerous locations throughout the project to ensure that
a minimum density of 96% (as determined during the laboratory evaluation)
was successfully obtained. The roadway was then kept continuously
moist through repeated applications of water by the water truck
to ensure that the cement-stabilized roadway cured properly and
attained its desired strength. The final step in the construction
process was the later application of a double bituminous surface
treatment.
As in the case of Franklin County Highway 84, portland cement is
the key to reconstructing flexible pavements that have failed. The
incorporation of portland cement with the old base course material,
often including the old asphalt surface, provides a practical, cost-effective
means of strengthening worn-out pavements. The cement binds the
particles together to form a stabilized base material capable of
withstanding moisture infiltration and degradation. It increases
the strength of the base without the need for removing the old material
and hauling in large quantities of expensive new base materials.
The success of the Franklin County project is paving the way for
greater acceptance of FDR in Alabama as an economical process for
long-term road rehabilitation. In fact, an FDR project was constructed
in a Trussville, Alabama subdivision in Jefferson County in April
of this year and the Alabama Department of Transportation is currently
in the process of finalizing their plans for their first FDR project
to be let later this summer. |