Superior Performing Asphalt
Pavements
 Performance based design system
testing and design procedures simulate closer to
the actual loading and climatic conditions
performance graded asphalt binders
aggregate specifications
hot mix asphalt design and analysis system
Level 1 material selection and volumetric design
Level 2 Level 1 design + performance testing
Level 3 Level 1 design + more performance testing
Enhanced mix performance
Permanent deformation
Fatigue Cracking
and
temperature cracking
ENCI
579 Low
8
1
Superpave
 SHRP established 1987 - 5 yrs.
 Binder specs in use by 100% of US, Ont., Quebec
in Canada
 Level 1 Mix design - partial use
 Still to come
simple performance tests
performance prediction models
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2
Superpave Mixture Design
Key features are laboratory compaction and
performance testing
Laboratory compaction
Superpave gyratory compactor (SGC)
compacts test specimens to simulate actual
pavement and loading conditions
provides information about the compactability of a
particular mixture
design mixtures that do not exhibit tender mix
behavior and do not densify to low air voids under
traffic
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3
Superpave Mixture Design
 Performance testing and performance prediction models
detailed predictions of actual pavement performance in
terms of ESAL’s
Superpave Shear tester (been replaced by triaxial)
Indirect Tensile tester
 Short term aging protocol
performance of HMA immediately after construction
is influenced by mix properties from hot mixing and
compaction
oven aged mix at 135 C 4 hours to simulate delays
that can occur during construction
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Superpave Mixture Design
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5
Level 1 Mix Design
 Volumetric mix design
 Select asphalt and aggregate materials
 develop several aggregate trial blends (3) that
meet Superpave aggregate specs
 blend asphalt, compact, analyze
 use best blend with several asphalt contents to
determine the design asphalt content at 4% air
voids and compare to other criteria
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Gyratory Compactor
 Better simulates field compaction than hammer
 Compacts specimen but also measures density
during compaction
 Measures compactibility so tender mixes are
identifies
 Larger size aggregate blends can be used (50 mm
max size) because of larger mold sizes
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 Amount of compaction depends on traffic and climate
 Ndes is the design number of gyrations used for volumetric
properties
 Nmax < 98%, Nini < 89% of max. density - used to indicate
compactibility
 Log Nmax = 1.1 Log Ndes
 Log Nini = .45 Log Ndes
Trial Blends
 The available aggregate stockpiles are combined in varying
percentages, 3 blends are usually considered
 Aggregate properties are determined (either on blends or
estimated from individual aggregates)
 Compact each blend and estimate volumetric properties
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Trial Blends
 For each aggregate trial blend:
 Asphalt binder grade selected
 Mixing temperature (non modified)
viscosity .15 - .19 Pa-s (150 – 190 mm2/s)
 Compaction temperature
viscosity = 0.25 - .31 Pa-s (250 – 310 mm2/s)
 Prepare aggregates
2 specimens for each trial blend : 2 x 4700g for compaction
1 approx. 2000g for max density (uncompacted mix)
1 x 3700 g for moisture sensitivity
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Trial Blends
 Heat, mix with asphalt and short term age for 4
hours at 135°C representing possible delays in the
field
 Compact specimens for Nmax gyrations, recording
height
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Data Analysis
 Measure density at Nmax, using volume of cylinder
calculate estimated density at Nmax, Nini, Ndes
 Errors in estimated densities due to surface
irregularities of briquette are corrected using ratio of
measured to estimated density at Nmax
 Measure Max. theoretical density of the
uncompacted mix
 Calculate air voids, VMA, VFA at Ndes
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Data Analysis
 When you calculate your air voids you want to be at
4%………..
 Estimate asphalt content at 4% using
Pb,est = Pbi - (.4x(4-AV%))
 Calculate corrected values of design VMA and VFA
for 4% air voids using
VMAest = VMAinitial+C x (4-AV%) where C
= .1 if AV% < 4% or .2 if AV% > 4%
VFAest = ( VMAest- 4) / VMAest
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Blend Selection
 Check blend properties against design criteria
VMA VFA meets table 6-14,6-15 in text
Nini < 89%, Nmax < 98% of max density
passes moisture sensitivity (T283)
80 % minimum indirect tensile strength
dust content (% passing 0.075 mm sieve divided by effective
asphalt content) between .6 and 1.2
 Choose best blend - new samples ( 2 compaction 2 max
density) are made and checked
Pb @ 4% AV
one at 0.5% less
2 more at 0.5% and 1% higher
volumetric properties calculated at each a/c content
579 8 other criteria checked
a/c content at 4 %ENCI
chosen
15
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Level 2 & 3 Design
 Performance tests for permanent deformation fatigue
cracking and low temperature cracking
Superpave Shear Tester (SST) (been replaced by triaxial)
Indirect Tensile Tester (IDT)
 Lab testing has not yet been validated with field results and is
still in experimental stage
 Current expectations are that Level 2 & 3 will be combined
into one and Level 1 will include an additional simplified
stability test
 At present research - triaxial testing for rutting and fatigue
and indirect tension test for thermal cracking - presently being
evaluated
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Example - Level 1
 Interstate 43 in Milwaukie, Wisconsin
 Nominal max aggregate size = 19mm
 Design ESALs = 18,000,000
this would actually require a level 3 design
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 Select a PG 58-34
mix temp = 165 to 172°C
compaction temp = 151 to 157°C
 5 stockpiles - measure bulk and apparent specific gravities
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 Measure 4 consensus properties
can measure blends but will use individual in this case to
estimate blend properties which has an advantage in choosing
blends
final design blends must meet criteria not individual stockpiles
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 3 blends are produced
1 - Intermediate, 2 - Coarse, 3 - Fine
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 Blends are checked against gradation requirements and
for consensus properties - all 3 pass
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 Trial asphalt content
absorption water calculated from bulk and apparent specific
gravities of aggregate blends
Absorption water % = 100 (1/Gsb-1/Gsa)
Blend 1 = .9% water absorption
Blend 2 = 1.0%, Blend 3 = .9%
 From table 6-12 in text, initial binder content is 4.4% for all 3
blends
 Two samples of each blend are compacted using Nini = 8,
Ndes = 109, Nmax = 174 (from design table table 6-13 text)
 Maximum and bulk specific gravities (RD) (Gmm, Gmb) are
measured and compactor data obtained
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Trial Blend 1
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Trial Blend 1
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Trial Blend 2
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Trial Blend 2
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Trial Blend 3
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Trial Blend 3
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• The % max density at Nini , Ndes, Nmax is calculated from an
average of the two samples of each blend
 Calculated air voids and VMA at Ndes
AV = 100 - %Gmm
1 = 100-96.2 = 3.8%, 2 = 4.3%, 3=4.8%
%VMA = 100 - (%Gmm x Gmm x (1 - Pbi))/Gsb
1 = 100-(96.2x2.563x.956)/2.699 = 12.7%
2 = 13.0%
3 = 13.5%
 Estimate properties @ 4% air voids
 Pb,est = Pbi - (.4 x(4-AV))
1 = 4.4-(.4x(4-3.8)) = 4.3%
2 = 4.5%
3 = 4.7%
 VMAest = VMAinitial + C x (4 - AV)
1 = 12.7 + (.1 x (4.0 - 3.8)) = 12.7%
2 = 13.0 + (.2 x (4.0 - 4.3)) = 13.0%
3 = 13.5 + (.2 x (4.0 - 4.8)) = 13.4%
 %VFAest = 100x (VMAest - 4)/VMAest
1 = 100 x (12.7 - 4.0)/12.7 = 68.5%
2 = 69.2%
3 = 70.1%
ENCI 579 8
31
 Estimate properties at 4% Air Voids
 %Gmm,est @ Nini = % Gmm,trial - (4-Av,trial)
1 = 87.1-(4-3.8) = 86.9%
2 = 85.9%
3 = 87.1%
 Similarly for Nmax
1 = 97.4%
2 = 97.7%
3 = 97.3%
 Results for 4% air voids for 3 blends:
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34
 Dust ration = P0.75/Pbe,est
1 = 3.1/3.6 = .86
2 = 2.9/3.7 = .78
3 = 3.5/4.0 = .88
All pass with values between .6 and 1.2
 Blend 1 fails VMA, blend 2 just meets VMA, therefore select
blend 3
 If no blends were acceptable start over with new stockpile
ratios
 Evaluate blend 3 as before by mixing 2 specimens with 4.2%,
4.7%, 5.2% and 5.7% AC contents
 Note: this time aggregate consensus properties must be
measured on the blends and not calculated from stockpile
values
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Calculating mix volumetric properties (not
estimating) for the final blend use:
 Calculated air voids, VMA, VFA at Ndes
%AV = 100 - %Gmm
%VMA = 100 - (%Gmm x Gmm x (1 - Pbi))/Gsb
%VFA = 100 x ((VMA - AV)/VMA)
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 Blend is tested for moisture sensitivity and has tensile
strength ratio of 82.6% which exceed the 80% minimum
requirement
 This blend meets all required design criteria and is approved
for use!
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44