Superpave gyratory compactor is a transportable device whose primary
function is to fabricate test specimens by stimulating the effect of
traffic on an asphalt pavement. The specimens fabricated with the gyratory
compactor are used to determine the volumetric properties (air voids,
voids in the mineral aggregate, and voids filled with asphalt) of Superpave
mixes. Those properties, measured in the laboratory, indicate how well
the mix will perform in the field. The gyratory compactor is also well-suited
for quality control/quality assurance, as it can be set up at the job
site to verify that the delivered asphalt mix meets the job mix volumetric
mixes to simulate construction compaction and traffic loads, the Superpave
gyratory compactor provides specimens that are much more representative
of actual in-service pavements. The level or amount of compaction is
dependent on the environmental conditions and traffic levels expected
at the job site.
a mix with a high degree of internal friction and thus a high shear
strength, the Superpave mix design procedures include requirements for
aggregate angularity and gradation. The design goal: a strong stone
skeleton that will resist rutting, yet include enough asphalt and voids
to improve the durability of the mix.
system includes mix analysis procedures that predict how well a mix
will perform in the field. These procedures are intended to provide
additional information on asphalt mixes that will be placed in pavements
with very high traffic volumes and loads. Two new, sophisticated pieces
of laboratory equipment-the Superpave shear tester and the indirect
tensile tester-are used to measure specific engineering properties of
the laboratory-compacted asphalt mix. The test results are then entered
into software models that predict how many equivalent single-axle loads
the pavement will carry, or how much time will elapse, before a certain
level of rutting, fatigue cracking, or low-temperature cracking develops.
procedures for the Superpave shear tester and the indirect tensile tester
are currently being refined to ensure that the procedures are sound
and that results are repeatable. The performance prediction models are
also undergoing evaluation and validation and will be refined as necessary.
it Happen - Partners in Implementation
to the all-new Superpave system is a big task, necessitating careful
planning and coordination among all the partners in the highway industry.
that the switch to the Superpave system would be well planned and coordinated,
the Federal Highway Administration (FHWA) established a national Asphalt
Technical Working Group (TWG). Composed of representatives from highway
agencies, suppliers, contractors, academia, and FHWA, the Asphalt TWG
provides advice on how best to encourage the adoption of the Superpave
system within the highway industry. Assisting the Asphalt TWG are several
expert task groups composed of specialists in pertinent subject areas,
such as binders, asphalt mixes, and pavement modeling.
asphalt user-producer groups also play a key role in the Superpave implementation
effort. Made up of highway agencies and companies that use and produce
asphalt binders, the user-producer groups have outlined a sensible,
planned strategy for adopting the Superpave system on a regional basis.
They also provide a forum for discussing common concerns and arriving
at workable solutions.
the Superpave system and equipment closer to the users, five Superpave
regional centers have been established. Under an FHWA program they will
conduct a thorough and coordinated shakedown of the procedures used
with the Superpave shear test and indirect tensile test. The centers,
operated jointly by universities and State departments of transportation,
will also provided training on a regional basis.
Up To Speed
State highway agencies and contractors become proficient with the new
Superpave procedures and devices, FHWA sponsors training courses in
the use of the binder test equipment and mix equipment. The hands-on
training is conducted at the National Asphalt Training Center, which
FHWA established at the Asphalt Institute in Lexington, Kentucky.
the first 18 months of Superpave training, the center held 30 courses
in the Superpave binder and mix procedures and trained approximately
600 engineers and technicians. FHWA recently selected the Asphalt Institute
to conduct the second phase of Superpave training. This phase will continue
for the more advanced mix analysis equipment. Training and assistance
will be taken directly to the users and the regional centers.
under an FHWA contract, the University of Maryland and its project team
are evaluating, validating, and refining the software and pavement performance
models that form the core of the Superpave mix analysis and performance
prediction procedures. Once the Superpave software is ready for release,
the university will provide technical assistance and training workshops.
training is conducted in the laboratory. FHWA's mobile asphalt laboratory
brings technical assistance and training in the Superpave system directly
to highway agencies and contractors at job sites around the country.
TWG has set a target date of 1997 for nationwide implementation of the
Superpave binder specification and 2000 for nationwide adoption of the
Superpave volumetric mix design procedures. Most State highway agencies
and many contractors already have the necessary binder test equipment
and the Superpave gyratory compactor. Some States are already building
Superpave pavements, and other projects are in the pipeline.
system will mean major changes in the way we design asphalt mixes. It
requires significant investments in equipment and training. But the
extensive testing and validation conducted to date on the Superpave
system indicate that Superpave pavements will last longer. Longer lasting
pavements will mean lower maintenance costs and fewer highway work zones.
And that means better roads ahead.