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FY 2012 Research Problem Statement
ODOT Research Section
200 Hawthorne Ave. SE
Suite B-240Salem OR 97301-5192
Phone (503) 986-2700
Fax (503) 986-2844
I. TITLE
12-048 Develop a Performance Based Aggregate Gradation Design
Method for Oregon State
II. PROBLEMFor dense-graded asphalt concrete mixtures, around 85
percent of the volume is made up of aggregates. The aggregate
structure and characteristics, particularly aggregate gradation,
shape (angularity), and coarse aggregate surface texture,
have been found to have great impact on the strength, stability,
rutting resistance, and fatigue performance of an asphalt
mixture. Although important, there is relatively less research
in this area; especially lack of study on identifying a clear
relationship between aggregate properties (gradation and
morphology properties) and performance.
Current Superpave mix design relies on a trial-and-error method
to design aggregate blends conforming
Superpave control points requirements. This approach is time
consuming and will sometimes produce mixtures that may
not perform well in the field. Oregon State uses a similar
approach of gradation analysis that is following the 0.45 power
maximum density line but with some deviations to allow adequate
Voids in Mineral Aggregate (VMA) [Thompson 2006].
Even the volumetric properties are all satisfied, the designers
are not sure the quality of the mix in the field.
Some recent researches have tried to improve the gradation
design and enhance understanding about aggregate
component. For example, the Baileys Method [Vavrick et al. 2002]
analyzes the aggregate gradation based on packing
characteristics of aggregates; the Power Law Method [Ruth 2000]
describes a gradation curve based on a power
regression equation; and the NCHRP 9-33 new Superpave Mix Design
manual suggests adjusting gradations using a
continuous density line which describes the percent of deviation
from the maximum density line. However, all these
methods cannot link the gradation to mix performance and still
rely on a trial-and-error process. In a study done for
Oregon asphalt mixtures, Thompson [2006] reported the use of
Baileys method may lead to extremely fine mixes not
common in Oregon. This study also suggested besides the several
sieve sizes recommended by Baileys method, more
sizes should be included for the gradation evaluation.
Therefore, in order to improve the quality of the mixtures,
enhance the pavement resistance to premature failure,
and improve the pavement durability and sustainability for
Oregon State, it is necessary to develop a more rationalized
gradation design method which can provide a linkage between the
gradation properties and mechanical performance. The
designer should be able to use this tool to design high quality
mixes with more efficiency.
III. PROPOSED RESEARCH, DEVELOPMENT, OR TECHNICAL TRANSFER
ACTIVITYThe proposed study aims to develop a systematic but
practical tool for ODOT to select and optimize the aggregate
gradations for dense-graded asphalt mixtures, to reach expected
field performance. The design tool will target to develop
gradations that have good compactibility, rutting resistance,
dynamic modulus (stress-strain relationship), and cracking
resistance, all of which are greatly affected by the packing and
interlocking characteristics of an aggregate skeleton.
Similar concept can be used to develop gradation design
guidelines for gap-graded or other types of mixes.
The proposed research will be a work combining theoretical
packing theory analysis, experimental testing to
generate and validate the relationship between gradation,
volumetric properties, and mechanical performance, an image-
aided discrete element modeling (DEM) to simulate various
contact models and validate gradation parameters, and field
data validation. This research approach is considered reasonable
and very promising based on the findings from the PIs
current project, Design Choice of Aggregate Gradation for Hot
Mix Asphalt Mixtures. Specifically, this study can be
conducted in four steps:
1. Develop a direct linkage between gradation and volumetric
properties (VMA) for Oregon mixes based on packingtheories and DEM
simulations. This provides a simple way to estimate volumetric
properties of mix without the
need of running volumetric testing, which can also be used for
optimizing gradations.
2. Develop correlations between volumetric properties and
mechanical performance (compactibility, rut resistance,dynamic
modulus, and fatigue resistance) based on performance models and
DEM simulation.
3. Identify the effect of aggregate gradation and morphological
properties (shape and angularity) on performance. Agradation design
tool will be developed for assisting on adjusting gradations to
achieve target performance.
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4. Evaluate and validate the effectiveness of the developed
design tool according to existing Oregon mixtures andtheir field
performance.
IV. POTENTIAL BENEFITSThe expected benefits and impact to ODOT
could be in the following:
1. This study will help ODOT to design better performing asphalt
mixtures. The practical tools proposed willimprove the efficiency
of developing aggregate blending that not only satisfies the
volumetric properties, but also
can lead to expected field performance (compactibility, rutting
resistance, dynamic modulus, and cracking
resistance). This is especially useful when new type of mixtures
for example, high-RAP, mixtures using recycled
concrete, and new aggregate types, are to be used.
2. This study will help ODOT to evaluate existing asphalt
mixtures in the pavement and identify the causes ofpavement
premature failure from the materials point of view. It is
hypothesized inappropriate aggregate
structures and packing may have problems such as hard to
compact, low stability and durability, therefore, lead to
premature failure of pavements.
3. This study will help determine and optimize asphalt content
at the early stage of the mix design to save cost. Byadjusting
aggregate gradations using the developed tools and methods, the
designer will be able to reasonably
reduce the amount of asphalt required while still maintain
satisfactory performance in the field.
4. Ultimately, this study will benefit ODOT by improving the
quality of the asphalt pavements, extend pavementservice life,
making the pavement mix design more rational, and result in cost
and energy savings by improving
the durability and reliability of pavement structures.
Consequently, the pavement becomes more sustainable.
V. IMPLEMENTATIONThis study will produce a detailed guidelines
of aggregate gradation design and an easy-to-use excel spreadsheet
designtool that material engineers at ODOT or other mix designers
in Oregon State can use. The methodology used in this study
can also be disseminated to other states as long as it is
calibrated based on their local materials.
VI. LIST OF REFERENCES (optional)Existing researches and
references related to the aggregate gradation design mainly include
four approaches:
1. Baileys method. There are a number of references in this
area. This reference is one of the important ones. Vavrik, W. R.,
Huber, G., Pine, W. J., Carpenter, S. H., and Bailey, R. (2002).
"Bailey Method for Gradation
Selection in Hot-Mix Asphalt Mixture Design." Transportation
Research E-Circular, Report No: E-C044.
2. Power Law method. Ruth, B. E. (2000), Development of
Tentative Guidelines for the Selection of Aggregate Gradations for
Hot-Mix
Asphalt. Proceedings, Association of Asphalt Paving
Technologists.
3. NCHRP 9-33 project report guideline Donald Christensen, et
al. A Mix Design Manual for Hot-Mix Asphalt, NCHRP 9-33 Report,
2009.
4. Our ongoing research on aggregate packing characteristics
Shen, S. and H. Yu (in press). Analysis of Aggregate Gradation and
Packing for Easy Estimation of HMA Voids in
Mineral Aggregate. ASCE Journal of Materials in Civil
Engineering.
Shen, S, Yu H. (2010). Characterize packing of aggregate
particles for paving materials: Particle size impact.Journal of
Construction and Build Materials.
http://dx.doi.org/10.1016/j.conbuildmat.2010.09.008
Yu, H. and S. Shen (2011). Simulation of Simple Performance Test
of Hot Mix Asphalt Mixture Using ThreeDimensional Discrete Element
Method. The 89th Transportation Research Board (TRB) Annual
Meeting, DVD
Compendium, January 23-27, 2011.
VII. CONTACT INFORMATION
Your name: ____Shihui Shen____ Person Responsible for
Implementation:Affiliation: Washington State University
Affiliation:
Telephone: 509-3357455 Telephone:
Email: [email protected] Email:
http://dx.doi.org/10.1016/j.conbuildmat.2010.09.008http://dx.doi.org/10.1016/j.conbuildmat.2010.09.008http://dx.doi.org/10.1016/j.conbuildmat.2010.09.008
