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Indiana Mineral Aggregates AssociationIndiana Mineral Aggregates AssociationIndiana Mineral Aggregates AssociationIndiana Mineral Aggregates Association
Aggregate Blending
for Friction Resistance
Indiana Mineral Aggregates AssociationIndiana Mineral Aggregates AssociationIndiana Mineral Aggregates AssociationIndiana Mineral Aggregates Association
Winter WorkshopsWinter WorkshopsWinter WorkshopsWinter Workshops
February 9, 2012February 9, 2012February 9, 2012February 9, 2012
Rebecca S. McDaniel, PE, PhDRebecca S. McDaniel, PE, PhDRebecca S. McDaniel, PE, PhDRebecca S. McDaniel, PE, PhD
Technical DirectorTechnical DirectorTechnical DirectorTechnical Director
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FrictionFrictionFrictionFriction----Related Projects at NCSC Related Projects at NCSC Related Projects at NCSC Related Projects at NCSC
� Identification of Laboratory Technique to Identification of Laboratory Technique to Identification of Laboratory Technique to Identification of Laboratory Technique to Optimize Superpave HMA Surface Friction Optimize Superpave HMA Surface Friction Optimize Superpave HMA Surface Friction Optimize Superpave HMA Surface Friction Characteristics Characteristics Characteristics Characteristics (completed)
� Evaluation of Recycled Asphalt Pavement Evaluation of Recycled Asphalt Pavement Evaluation of Recycled Asphalt Pavement Evaluation of Recycled Asphalt Pavement for Surface Mixturesfor Surface Mixturesfor Surface Mixturesfor Surface Mixtures (draft final report in review)
� Maximizing the Use of Local Materials in Maximizing the Use of Local Materials in Maximizing the Use of Local Materials in Maximizing the Use of Local Materials in HMA Surfaces HMA Surfaces HMA Surfaces HMA Surfaces (draft final report submitted)
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Goals for Required Lab MethodGoals for Required Lab MethodGoals for Required Lab MethodGoals for Required Lab Method
� Test friction and texture
� Accelerate polishing
� Test asphalt mixtures, not aggregates only
Ideal to be able to test in lab and field� Ideal to be able to test in lab and field
� Led to identification of Dynamic Friction
Tester and Circular Track Meter
� Needed a polisher to match
� Idea from NCAT, refined by NCSC
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BackgroundBackgroundBackgroundBackground� Pavement friction is function of microtexture
and macrotexture.
� Microtexture – provided by aggregate surface
� Macrotexture – determined by overall properties of
the pavement surface (NMAS and gradation of the pavement surface (NMAS and gradation of
aggregates, binder content, etc.)
� Friction at the tire-pavement interface is
caused by:
� Adhesion – between tire and surface (microtexture)
� Hysteresis - deformation of tire around surface
irregularities (macrotexture)
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Designing for Pavement FrictionDesigning for Pavement FrictionDesigning for Pavement FrictionDesigning for Pavement Friction
� Most states specify allowable surface aggregates by
type based on historical usage and aggregateaggregateaggregateaggregate tests.
� Useful, but do not consider macrotexture.
� Need mixture test and specifications.
� Widely available aggregates are carbonates.
� Tend to polish
� Polish resistant aggregates are not readily available
and must be hauled in -- $$$.
� Coarser mix texture may reduce the need for high
microtexture aggregates.
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Dynamic Friction Tester (DFT)Dynamic Friction Tester (DFT)Dynamic Friction Tester (DFT)Dynamic Friction Tester (DFT)
(a)
DFT – dynamic friction at 20 km/h (DF20)
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Circular Track Meter (CTM)Circular Track Meter (CTM)Circular Track Meter (CTM)Circular Track Meter (CTM)
(b)
CTM – Mean Profile Depth, mm
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International Friction IndexInternational Friction IndexInternational Friction IndexInternational Friction Index
IFI (F60, Sp)
SpeDFF
40
20732.0081.060
−
+=
MPDS p 7.892.14 += MPDS p 7.892.14 +=
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Circular Track Circular Track Circular Track Circular Track
Polishing MachinePolishing MachinePolishing MachinePolishing Machine
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(a) (b)
(c) (d)
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Texture and Friction (DF20)Texture and Friction (DF20)Texture and Friction (DF20)Texture and Friction (DF20)
0.9
1.2
0 50 100 150
MP
D, m
m 0.7
0.9
MPD
(a)
0.3
0.6
0.9
MP
D, m
m
0.3
0.5
0.7
DF 2
0
DF20
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IFI (F60)IFI (F60)IFI (F60)IFI (F60)
0.4
0.5
0.6
F60
(b)
0.2
0.3
0.4
0 50 100 150
no. wheel passes, 10^3
F60
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Identification of Laboratory Techniques Identification of Laboratory Techniques Identification of Laboratory Techniques Identification of Laboratory Techniques
to Optimize Superpave HMA Surface to Optimize Superpave HMA Surface to Optimize Superpave HMA Surface to Optimize Superpave HMA Surface
Friction CharacteristicsFriction CharacteristicsFriction CharacteristicsFriction Characteristics
�Assess/optimize combined micro- and macrotexture
�Develop/modify lab device (and tests) to polish HMA
�Evaluate influence of mix composition on friction
�Develop model for friction prediction
�Funded by Indiana and Iowa DOTs
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Experimental Experimental Experimental Experimental
DesignDesignDesignDesign
� 3 Gradations – Fine, Coarse, S-shaped
0
20
40
60
80
100
Sieve size, mm
Cum
ulat
ive
% P
assi
ng
0.075 1.180.60.3 19 12.59.52.36 25
Fine gradation, F
S-shaped gradation, S
Coarse gradation, C
� 3 Gradations – Fine, Coarse, S-shaped
� 2 Aggregate Sizes – 9.5 mm and 19 mm
� 2 Friction Aggregates – steel slag and quartzite
� 3 “Soft” Aggregates – hard and soft limestones, and dolomite
� 4 Friction Agg Contents – 10, 20, 40, 70%
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Key FindingsKey FindingsKey FindingsKey Findings
� Steel slag slightly more polish resistant than quartzite.
� Mixes with soft limestone polished more than hard
limestone or dolomite.
� Increasing friction aggregate content improved � Increasing friction aggregate content improved
polishing resistance.
� Friction aggregate content should be at least 20%.
� Larger NMAS mixes have higher friction.
� Fineness modulus of the aggregate blend appears to
correlate with pavement macrotexture.
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Key FindingsKey FindingsKey FindingsKey Findings
� S-Shaped gradation generally resulted in higher
macrotexture.
� Frictional properties can be improved by using polish
resistant aggregate blends or by increasing resistant aggregate blends or by increasing
macrotexture (FM).
� A model for describing the change in friction
parameters under traffic/ polishing was developed.
� The lab procedures are very promising tools.
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Polishing ModelPolishing ModelPolishing ModelPolishing Model
I III II
y2 y1
Friction Stabilization ZoneDecreasing Friction ZoneInitial Pavement Life Zone
x, log no. of passes
F60
x0 x1
y3
y2 y1
a4
Calculate F60 (IFI Value) per E1960. See AAPT 2009, Kowalski et al.
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Evaluation of Recycled Asphalt Evaluation of Recycled Asphalt Evaluation of Recycled Asphalt Evaluation of Recycled Asphalt
Pavement for Surface MixturesPavement for Surface MixturesPavement for Surface MixturesPavement for Surface Mixtures
�RAP not used to full extent in surfaces
Unknown aggregates� Unknown aggregates
� Determine threshold level of RAP that has minimal
effect or method to test aggregates in the RAP
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Experimental Design
� Mix Type – HMA and SMA
� Lab Fabricated “Worst Case” RAP
� RAP Content – 0, 15, 25, 40%
� Friction Aggregate – Steel Slag and ACBF Slag
�Field testing of 8 existing surfaces (15-25% RAP)
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Use of the Model
0.30
0.40
0.50
F60
@ X
1
DGA
SMA
0.30
0 10 20 30 40% (by weight) of RAP
-0.040
-0.030
-0.020
-0.010
0 10 20 30 40
polis
hing
rat
e, a
4
% (by weight) of RAP
DGA
SMA
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PreliminaryPreliminaryPreliminaryPreliminary Findings and RecommendationsFindings and RecommendationsFindings and RecommendationsFindings and Recommendations
� Report not officially accepted yet.
� Adding small quantities of poor quality RAP had little
effect on friction.
� Adding higher amounts of RAP had an effect on
friction.friction.
� When blended with high quality friction aggregates,
performance was still acceptable at 25% RAP.
� Adding more RAP without changing binder grade
increased critical cracking temperature.
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PreliminaryPreliminaryPreliminaryPreliminary Findings and RecommendationsFindings and RecommendationsFindings and RecommendationsFindings and Recommendations
� Field friction testing suggests 15% RAP is acceptable
and higher RAP contents are possible for medium
volume roadways.
� Recommended limit of 20% RAP by binder Recommended limit of 20% RAP by binder
replacement for Category 3 and 4 roadways.
� Further field testing for Category 5.
� On case by case basis, consider higher RAP contents
when RAP aggregates can be known.
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DisclaimerDisclaimerDisclaimerDisclaimer
� The views
expressed here
are those of the
presenter and do presenter and do
not represent the
views of the
sponsor!
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Maximizing the Use of Local Maximizing the Use of Local Maximizing the Use of Local Maximizing the Use of Local
Materials in HMA SurfacesMaterials in HMA SurfacesMaterials in HMA SurfacesMaterials in HMA Surfaces
Objective – explore opportunities to allow the use of
more local materials in HMA in place of “imported” fine more local materials in HMA in place of “imported” fine
and coarse aggregates
Draft final report will be submitted this afternoon.
Very preliminary results.
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� Local coarse aggregate content – up to 40%
blended with the same 3 high quality aggs
� Local fine aggregate content – up to 20%
Experimental DesignExperimental DesignExperimental DesignExperimental Design
(with steel slag, ACBF slag and sandstone CA)
� HMA and SMA mixes
OMM selected aggregates for testing.
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PreliminaryPreliminaryPreliminaryPreliminary FindingsFindingsFindingsFindings
� Adding polish susceptible agg caused
decrease in surface friction in HMA and SMA.
� But friction was still acceptable at up to
around 20% local agg.around 20% local agg.
� Fine aggregate data was somewhat erratic.
� Appears fine agg up to 20% was small
negative effect on friction.
� Other considerations besides friction.
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Substituting local agg for steel slag could save:
� $1.50 to 2 per ton of hot mix (fine aggregate)
� $3 to 4 per ton of hot mix (coarse agg)
Potential Cost SavingsPotential Cost SavingsPotential Cost SavingsPotential Cost Savings
� $3 to 4 per ton of hot mix (coarse agg)
� $4.50 to 6 per ton of hot mix (both)
� Up to 10% of cost of mix
� $3000 to 4000 per lane mile of surface mix
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DisclaimerDisclaimerDisclaimerDisclaimer
� The views
expressed here
are those of the
presenter and do
not represent the not represent the
views of the
sponsor!
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� North Central Asphalt User Producer Group
Technical Conference
� Hyatt Regency, Indianapolis
� February 15-16, 2012
Upcoming Event!
� February 15-16, 2012
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NCAUPG Technical Conference
Hyatt Regency, Indianapolis
February 15-16, 2012
Questions???
Rebecca McDanielRebecca McDanielRebecca McDanielRebecca McDaniel
[email protected]@[email protected]@purdue.edu
765/463765/463765/463765/463----2317 x 2262317 x 2262317 x 2262317 x 226
https://engineering.purdue.edu/NCSChttps://engineering.purdue.edu/NCSChttps://engineering.purdue.edu/NCSChttps://engineering.purdue.edu/NCSC