980223 “Critical Review of VMA Requirements in Superpave”
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980590 “Comparison of Superpave and Marshall Mixtures for
Low-Volume Roads/Shoulders”
Abstract: Superpave and Marshall mix designs were done using local
aggregates to study the suitability of the Superpave mix design as compared to
the Marshall mix design for low volume roads, especially shoulders. Three
different locally available aggregates, crushed lime stone and coarse and fine
river sands, were used in this study. Five different blends with varying
proportions of coarse and fine river sands were selected. Mix samples were
compacted in the Superpave gyratory compactor with applicable number of
gyrations as well as with the Marshall hammer using fifty blows per face. Bulk
densities of the compacted samples and maximum specific gravities of loose
samples were also measured for each blend. Conclusions: The results
showed that 1) Superpave mix design for low-volume roads/shoulders results in
lower estimated asphalt content compared to the Marshall method. 2)The required
asphalt content increases as the proportion of coarse river sand increases in
the mix. 3) Superpave requirements for the Voids Filled with Asphalt (VFA) for
low volume traffic, i.e., less then 0.3 million ESALs, appeared to be too high.
High asphalt film thicknesses were computed for the mixtures which did not meet
the Superpave VFA requirements. 4) Lowering the design number of gyrations
(Ndes) for compaction of samples would result in increased asphalt requirement
for the Superpave mixture with a given gradation.
Affan Habib, Soil &
Materials Engineers, Inc., 43980 Plymouth Oaks Blvd., Plymouth, MI 48170. Tel:
(313) 454 – 9900 Fax: (313) 454 –0629. e-mail: affan@ksu.edu. Mustaque Hossain, Rajesh Kaldate,
Department of Civil Engineering, Kansas State University, Manhattan, KS 66506.
Tel: (785) 532 – 1576 Fax: (785) 532-7717. e-mail: mustak@ksu.edu, Glenn A. Fager, Kansas
Department of Transportation, Bureau of Materials & Research, 2300 Van
Buren, Topeka, KS 66611. Tel: (913) 296 – 3008 Fax: (913) 296- 2526. e-mail: glenn@dtmrc.wpo.state.ks.us
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980714 “Calculating Air Voids at a Specified Number of
Gyrations in the Superpave Gyratory Compactor”
Abstract: The Superpave volumetric mix design is based on compaction of
mixtures to Nmax revolutions, yielding approximately 2 percent air voids, and
then back-calculating the properties of the mixture at Ndesign revolutions.
Ndesign revolutions is the specified number of revolutions at which the sample
should achieve 4 percent air voids. It has been shown, both in mixture design
and in field quality control testing, that this back-calculation procedure is
not always accurate for determining the number of gyrations that give 4 percent
air voids in the compacted sample. This paper examined the current
back-calculation procedure and shows the observed inaccuracy in the current
method in both the quality control/quality assurance (QC/QA) and the mixture
design procedures. It also examined an alternative method that has shown to be
more accurate in predicting the number of gyrations at which a mixture reaches a
given air void level. Conclusion: The current Superpave procedure for
back-calculating air voids at a set number of gyrations can be inaccurate for
some aggregates and gradations. By using the best fit slope of the compaction
curve up to the “locking point,” it is possible to more accurately predict the
number of gyrations which will give 4 percent air voids. Mixtures with smaller
nominal maximum size give more consistent results in the prediction of number of
gyrations to achieve 4 percent air voids. Due to the characteristics of gyratory
compaction, mixtures with a larger nominal maximum size do not show the same
accuracy as smaller sized gradations in the prediction of number of gyrations to
achieve 4 percent air voids. The proposed method for determining the number of
gyrations to achieve 4 percent air voids shows to be more accurate than the
Superpave method. The proposed method determines the slope of the compaction
curve, which is speculated as a mixture property. Every point in the compaction
curve is not necessary for proper characterization of the mixture as long a
consistent representative sampling of the data is used.
William R. Vavrik,
University of Illinois at Urbana-Champaign, 1611 Titan Drive, Rantoul, Illinois
61866. Tel: 217-893-0406 Fax: 217-893-0601. e-mail: w-vavri@uiuc.edu. Samuel H. Carpenter,
University of Illinois at Urbana-Champaign, 205 N. Mathews Ave., MC-250, Urbana,
Illinois 61801. Tel: 217-333-4188 Fax: 217-333-1924. e-mail: scarpent@uiuc.edu.
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980928 “Contribution of fine Aggregate Angularity and Particle
Shape to Superpave Mixture Performance”
Abstract: The Superpave system currently is being implemented by state
highway agencies. Many states have already implemented the asphalt binder
specification during 1997. The volumetric mix design system, however, is being
actively implemented. As states consider specification changes necessitated by
Superpave implementation, some questions are being raised. Fine aggregate
angularity (FAA) requirements, one of the aggregate consensus properties, has
generated considerable debate in some areas of the country. Adopting an FAA
requirement of 45% for high traffic pavements has changed the number of sources
available for asphalt mixtures. Superpave also provides a limit on flat and
elongated particles. The aggregate properties requirement have increased
interest regarding the basis of the specification and the values specified. This
paper contains results of a limited cooperative study by industry and agency to
evaluate the role of fine aggregate angularity and particle shape on asphalt
mixture properties. Conclusions: The coarse Superpave gradation selected
for this study appears to have de-emphasized the role of fine aggregate in the
mixture response to rutting. Rate of rutting, and rut depths measured on the
Asphalt Pavement Analyzer did not correlate with fine aggregate angularity. All
mixtures had similar phase angles at high frequency loading. Complex modulus of
the mixtures as tested on the Superpave Shear Tester did not vary with different
fine aggregate angularity. Based on the results of this limited study, crushed
stone aggregates containing flat and elongated particles based on a maximum to
minimum dimension ratio of 3:1 do not negatively effect the volumetric
properties of Superpave asphalt mixtures.
Gerald A. Huber, Heritage Research
Group. Tel: (317) 390-3141 Fax: (317) 486-5095. e-mail: gerald.huber@heritage-enviro.com.
J. Chris Jones, Paul E. Messersmith, Superfos Construction U.S., N. Mike
Jackson, University of Tennessee at Knoxville
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980944 “The Relation Between Pavement Temperature and Weather
Data: A Wisconsin Field Study To Verify the Superpave Algorithm”
Abstract: Six test sections were constructed on USH 53 in Trempealeau
County, Wisconsin using different PG graded asphalt binders to validate the
Superpave pavement temperature algorithm and the binder specification limits.
This paper includes details of the instrumentation systems used and the analysis
of the data collected during the first 22 months of the project. The analysis
was focused on development of a statistical model for estimation of low and high
pavement temperatures from meteorological data. The model was compared to the
Superpave recommended model and to the more recent model recommended by LTPP
program. Conclusions: The temperature data analysis indicates that there
is a strong agreement between the new model and the LTPP model for the
estimation of low pavement design temperature. The analysis, however, indicates
that the LTPP model and the Superpave model underestimate the high pavement
design temperature at air temperatures higher than 30(C. The temperature data
analyses also indicate that there are significant differences between the
standard deviation of air temperatures and the standard deviation of the
pavement temperatures. These differences raises some questions about the
accuracy of the reliability estimates used in the current Superpave
recommendations.
Peter J. Bosscher, Hussain U. Bahia, Suwitho Thomas, Jeffrey
S. Russell, Dept. of Civil & Environ. Engineering, University of Wisconsin,
Madison, WI 53706. Tel: (608) 262-7245 Fax: (608) 262-5199. e-mail: bosscher@engr.wisc.edu.
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981074 “An Evaluation of Superpave Gyratory Compaction of Hot
Mix Asphalt”
Abstract: Superpave recommends that aggregate gradations for Hot Mix
Asphalt (HMA) pass outside the restricted zone in order to provide adequate VMA
and to avoid excessive use of rounded sands which leads to reduced rutting
resistance. This study was carried out to evaluate the effect of restricted zone
on volumetric properties of mixes consisting of all crushed, and all crushed and
partially uncrushed materials. Mix designs were conducted with the Superpave
gyratory compactor for two types of aggregate blends: one with all crushed
granite and another with crushed granite and 20 percent natural sand. Three
gradations for each type of aggregate blend consisted of gradations passing
above, through, and below the restricted zone. A part of this study was carried
out to compare the correction factors obtained at different gyration levels
during compaction of HMA, and to evaluate the change in correction factors with
gyration levels. Conclusions: For a given aggregate blend, gradations
below or above the restricted zone provided higher VMA than mixes through the
restricted zone. Mixes with crushed aggregate provided higher VMA than mixes
with partially crushed aggregate. The mixes with gradations below the restricted
zone had the highest voids at Ninitial, whereas the mixes with gradations above
the restricted zone had the lowest voids at Ninitial. For all crushed mixes, the
mixes with gradation above the restricted zone had the highest voids at
Nmaximum, and the mixes with gradations below the restricted zone had the lowest
voids at Nmaximum. None of the mixes containing natural sand met all the
requirements for volumetric and gyratory properties. The mixtures for all
crushed material met all requirements when passing through the restricted zone
and below the restricted zone. The correction factor was found to decrease and
become close to constant at higher gyration levels. At lower gyrations,
densities were found to be greater than that obtained by back calculation from
the density at Nmaximum. The coarse textured mixture had a larger difference
between the back calculated and actual air voids.
Rajib B. Mallick, Shane
Buchanan, E. R. Brown, Mike Huner, National Center for Asphalt Technology. Tel:
(334) 844-6259 Fax: (334) 844-4485. e-mail: rajibb@eng.auburn.edu.
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981218 “Kentucky’s Experience with Superpave Binder
Specifications”
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981281 “Reference Standards for Use with the Indirect Tension
Test”
Abstract: The purpose of this paper is to describe the fabrication,
calibration, and use of high-density polyethylene (HDPE) reference standards for
the indirect tension (IDT) creep test. The IDT creep test was developed during
the Strategic highway research program, and is one of the standard Superpave
mixture tests now under further development and implementation. The use of
reference standards in conjunction with the IDT test will help to achieve rapid
and effective implementation of this promising test method. An IDT reference
standard is useful in three ways: it serves as a final step in a thorough
calibration of the IDT system; it allows rapid verification of the IDT test
system in between calibrations; and it serves as a useful tool for training
engineers and technicians in proper execution of the test. In this study, HDPE
specimens were calibrated using the IDT creep test. During this calibration,
statistical methods were used to verify that the HDPE was homogenous, linear,
and isotropic. The calibration was then confirmed using companion specimens of
the HDPE machined for testing using the bending beam rheometer (BBR).
Conclusions: High density polyethylene (HDPE) is reasonably homogenous,
isotropic, and linear, and is thus suited for use in producing reference
standards for the indirect tension (IDT) creep test. The creep compliance of
HDPE is similar to that of typical hot-mix asphalt concrete at 0 °C, which is
nearly ideal for use as an IDT reference standard. IDT reference standards
produced from HDPE can be calibrated through replicate measurements on a
recently calibrated IDT device operated by an experienced technician or
engineer. The calibrated values of creep compliance or modulus, and m-value, can
be initially verified and periodically checked with companion specimens machined
for use with the bending beam rheometer. The proposed IDT reference standards
can be used as a final step in thorough, regularly scheduled calibrations; to
periodically verify proper operation of the IDT in between scheduled
calibrations; and as an aid in training technicians and engineers in proper
technique in performing the IDT creep test.
Donald W. Christensen, Yusuf A.
Mehta, The Pennsylvania State University, Research Office Building, University
Park, PA 16802. Tel: (814) 863-1903 Fax: (814) 865-3039. e-mail: dwc1@psu.edu.
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981285 “Superpave Field Implementation: Florida’s Early
Experience”
Abstract: Over the past 10-15 years, Interstate pavements in north
Florida have experienced a significant number of failures, primarily due to
rutting. It was believed that the present fine graded, 50-blow Marshall designed
mixes were inadequate to withstand current loading conditions. The newly
developed Superpave system represented an opportunity to address a number of
Florida’s asphalt pavement problems. Thus, the Florida Department of
Transportation (FDOT) made a concerted effort to implement Superpave technology
in 1996. During this period, a total of eight projects were changed from the
traditional Marshall mix designs to Superpave. Conclusions: This paper
documents some of Florida’s early experiences with the field implementation of
Superpave (including issues of compaction, the relationship between lift
thickness and compactibility, water permeability and density requirements, as
well as general and specific comparisons of the coarse-graded Superpave mixes
and the fine-graded Marshall mixes). As an AASHTO Lead State in Superpave
Implementation, Florida is a very strong advocate of the Superpave system, and
believes this new technology will address most, if not all of the pavement
problems encountered in Florida. As such, any problems that are encountered with
its implementation need to be quickly resolved with the understanding that
complete implementation will lead to a longer-lasting and safer highway system
in the State of Florida and the rest of the nation.
James A. Musselman,
Bouzid Choubane, Gale C. Page, Patrick B. Upshaw, Florida Dept. of
Transportation, State Materials Office, 2006 N.E. Waldo Road, Gainesville, FL
32609. Tel: (352) 337-3100 Fax: (352) 334-1649.
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