This project on the heavily
trafficked Interstate in Arizona's high country is probably one
of major success stories of Asphalt-Rubber in cold climates.
Flagstaff, a university town in northern Arizona with an elevation
of 7,000 feet, is nestled at the base of the San Francisco Peaks,
Arizona's highest point at 12,633 feet. A popular skiing destination,
the area averages 108.8 inches of snow and 28 inches of rainfall
on annual basis presenting a challenge to the Arizona Department
of Transportation maintenance crew in keeping Interstates and
other key State Highways such as 89 and 180, gateways to Utah
and the Grand Canyon respectively, open for travel. To deal with
the extreme weather and the punishment of the snow plows, pavements
have to be tough in this area. The I-40 project built in 1990
has proved Asphalt-Rubber is a paving material that can meet
the challenge of any climate.
The following is a summarization of a 1999 Arizona
Department of Transportation paper, Flagstaff I-40 Asphalt-Rubber
Overlay-Nine Years of success" presented at the 78th Annual
Meeting of the ransportation Research Board, by author George
B.Way, P.E., Pavement Design Engineer. Copies of this report
can be downloaded from the RPA website www.rubberpavements.org
In 1990, the Arizona Department of Transportation
designed and constructed a large scale Asphalt-Rubber (AR) test
project in Flagstaff, Arizona on the very heavily trafficked
Interstate 40. The 1999 traffic exceeded 20,000 vehicles per
day with 35% large trucks.
The purpose of the test project was to determine
whether a relatively thin overlay with AR could reduce reflective
cracking. Asphalt-Rubber is a mixture of 80% hot paving grade
asphalt and 20% ground tire rubber. |
This mixture is also commonly referred to as the Asphalt-Rubber
wet process or McDonald process.
The overlay project was built on top of a very badly
cracked concrete pavement, constructed in 1969 and exhibiting
signs of failure by 1974. ADOT maintenance spent approximately
$80,000 per year trying to hold the pavement together. By 1988
reconstruction, at a cost estimated to be at least $30 million,
appeared to be the only option.
However, due to money and time constraints, which
were estimated to take four years, the project could not be reconstructed.
Various overlay strategies were considered, including many different
overlay thicknesses, use of a fabric interlayer, asphalt-rubber
interlayer, various mixes, edge drains and cracking and seating.
Each alternative was discussed and reviewed at the central and
district offices. In addition the project was I-40 led to the
construction of five projects also selected as a Strategic
Highway
A German delegation visit to the I-40 led to the construction
of five projects in Germany in 2002/2003 |
Research (SHRP) Specific Pavement Studies (SPS-6) to test various
overlay and rehabilitation strategies on concrete
pavement. ADOT selected an Asphalt-Rubber binder to test whether
a relatively thin pavement overlay could control reflective cracking.
The design section included edge drains, crack and seat the concrete
Pavement, a five inch overlay consisting of a three inch conventional
dense hot mix asphalt, a two inch gap graded asphalt-rubber mix
(AR-AC) with a 6.5% binder and a one-half inch AR OGFC with a
9% binder content. The design was for ten years, but all involved
in the project considered it would last six years given the thin
overlay design and the poor condition of the concrete.
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The Asphalt-Rubber overlay has performed beyond
the original expectations. After nine years of service the overlay
is virtually crack free, with good ride, virtually no rutting
or maintenance and good skid resistance. The benefits of using
Asphalt-Rubber on this project represents about $18 million dollars
in construction savings and four years less construction time.
The SHRP SPS-6 section of 4"conventional HMA compared
to 2" AR in 1998, placed in 1990 |
The Strategic Highway Research Program SPS-6 test sections
built in conjunction with the project further illustrate the
very good performance performance of the Asphalt-Rubber. Results
of this roject have led to widespread use of Asphalt-Rubber hot
mixes throughout Arizona. The project has drawn visitors from
all over the world and has resulted in projects in Alberta, Canada
(15 projects); Korea; Germany, Spain, Austria; Portugal and Taiwan.
In the U.S., the states of Nebraska, Tennessee, and New Mexico
have placed projects using the ADOT AR AC and AR OGFC strategy.
The state of Colorado, based on the cold weather performance
in
northern Arizona placed an Asphalt-Rubber Chip Seal in June 2003.
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