980760 “Stone Matrix Asphalt: The Wisconsin Experience”
Abstract: In 1991, the Wisconsin Department of Transportation and the
asphalt paving industry in the state decided to construct a trial installation
of an asphalt paving technology that had piqued the interest of a group of
professionals that had recently toured Europe. The success of that initial trial
was the basis of the decision to conduct a thorough evaluation of Stone Matrix
Asphalt (SMA). Subsequently, six projects were constructed at various locations
around the state. Each project contained six test sections utilizing various
fiber and polymer modified SMA mixes. Besides evaluating the various types of
SMA's, this research effort also contained elements in it to allow evaluation of
the impact of aggregate size and aggregate hardness on the effectiveness of the
SMA mixes. These projects were constructed over a period of three years, with
the last one constructed in 1994. All of the projects were evaluated from the
standpoint of the ease of construction and performance. While the ease of
construction was to be evaluated mostly on a subjective basis, the performance
measures were established to be objective and measurable. The performance
measures were: amount of cracking; friction characteristics; overall pavement
distress; amount of rutting; noise impacts; and ride. Conclusions:
Although the data collected so far is limited, it is pointing to an asphalt
pavement that resists cracking and rutting, while providing a good ride and
excellent frictional qualities. The study is far from complete at this time,
since the newest test sections were constructed in 1994, and their evaluation
will not be completed until 1999. However, from the data available, it appears
that the SMA pavements are performing better than the standard AC pavement in
all respects and show definite promise in being a durable and long lasting
asphalt pavement.
Robert B. Schmiedlin, Wisconsin Department of
Transportation, 3502 Kinsman Blvd., Madison, WI 53704. Tel: (608) 246-7950 Fax:
(608) 246-4669. e-mail: rschmie1@mail.state.wi.us
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980968 “Georgia DOT’s Experience with Microsurfacing”
Abstract: Microsurface mix, or microsurfacing, can be used for sealing
and providing a friction surface for cracked and deteriorated surface mixes.
This mix, essentially consisting of 9.5 mm (3/8 in.) screenings bonded by a
polymer-modified asphalt emulsion, is economical and can be placed very swiftly.
Microsurfacing is also aesthetically pleasing because of its resemblance to hot
mix asphalt. In 1990-91, Georgia DOT (GDOT) successfully used microsurfacing in
a test section on I-75 in Henry County which had high traffic volumes and a
heavy truck concentration. Two varieties of the mix were used, and both showed
little deterioration after two years. In 1996, GDOT opted to use microsurfacing
for a 9.2 km (5.7 mile) section of I-285 in Atlanta between Conley Rd. and Old
National Hwy. This 92 lane-km (57 lane-mile) project was initiated to address
the raveling and cracking in the section and improve its appearance prior to the
1996 summer Olympics. The I-285 project began in late May, 1996, and was
completed in one month. Conclusions: The micro-surfacing used on I-285
has performed quite well since the project completion. No additional problems
have been encountered with raveling or load cracking. The mix has provided
excellent smoothness and good friction, with a minimal increase in pavement
noise levels. Microsurfacing may be suitable for use on cracked pavements in
lieu of more conventional rehabilitation methods such as crack sealing,
leveling, and double surface treatments. Microsurfacing provides a convenient,
economical way of addressing pavement distress such as raveling and cracking.
The use of plant mix resurfacing can be delayed for some time if micro-surfacing
is utilized.
Donald E. Watson, David Jared, Georgia Department of
Transportation, Office of Materials and Research, 15 Kennedy Drive, Forest Park,
Georgia 30050. Tel: (404) 363-7521 Fax (404) 363-7684. e-mail: watson_d@dot.state.ga.us
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980970 “Georgia DOT’s Progress in Open-Graded Friction Course
Development”
Abstract: In order to improve the safety of motorists on Georgia
highways, the Georgia Department of Transportation (GDOT) has continued to use
the most advanced and effective pavements available, including the open-graded
friction course (OGFC). Since OGFCs were conceived in the 1950's and 1960's,
GDOT has used these mixes as thin porous wearing layers primarily on interstate
highways. In the past, GDOT encountered problems with OGFC use, including
asphalt cement (AC) draindown, rapid oxidation, raveling, and stripping of
underlying layers. Consequently, GDOT placed a moratorium on OGFC use in 1982.
Since that time, however, several modifications have been made to improve the
performance of OGFC mixes. Hydrated lime is added as an anti-stripping agent to
OGFC and to all other mixes used on the Georgia state route system, including
dense-graded mixes which underlie OGFC. Fibers are added to eliminate AC
drain-down. Polymer-modified AC is added to improve the durability of the
pavement by reducing problems associated with premature oxidation and raveling.
Production temperatures are increased to more thoroughly dry aggregate
components and thus improve AC adhesion. Finally, coarser gradations and thicker
layers are used to improve permeability. Conclusions: With the
modifications made to these mixes in the last few years, significant
improvements in mix performance have already been noted. The benefits of using
the modified OGFC and PEM mixes far outweigh the difficulties that may be
encountered during production and placement. The improved permeability of the
mix results in reduced potential for hydroplaning, reduction of splash and
spray, improved friction, better nighttime visibility, and better visibility of
traffic striping. Agencies which have used this mix in the past and experienced
problems similar to those experienced by GDOT should consider the possibility of
using this modified OGFC on high-volume traffic facilities.
Donald E. Watson,
Andrew Johnson, David Jared, Georgia Department of Transportation, Office of
Materials and Research, 15 Kennedy Drive, Forest Park, Georgia 30050. Tel. (404)
363-7521 Fax (404) 363-7684. e-mail: watson_d@dot.state.ga.us