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HMA Superpave Mix Design 1
Superpave Mix Design
Senior/GraduateHMA Course
HMA Superpave Mix Design 2
MIXTURE DESIGN
HMA Superpave Mix Design 3
HMA Mix Design• Objective:
• Develop an economical blend of aggregates and asphalt binder that meet design and functional requirements
• Historical mix design methods
• Marshall
• Hveem
• New
• Superpave gyratory
HMA Superpave Mix Design 4
Requirements in Common
• Sufficient asphalt binder to ensure a durable pavement
• Sufficient stability under traffic loads
• Sufficient air voids
• Upper limit to prevent excessive environmental damage
• Lower limit to allow room for initial densification due to traffic
• Sufficient workability
HMA Superpave Mix Design 5
• Simulate field densification• traffic• climate
• Accommodate large aggregates• Measure compactability• Conducive to QC
Goals of Compaction Method
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AASHTO T 312 Gyratory Compaction
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• Basis• Texas equipment• French operational
characteristics• 150 mm <5.9”> diameter
• up to 37.5 mm nominal size• Height Recordation
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Superpave Gyratory Compactor
HMA Superpave Mix Design 8
reactionframe
rotatingbase
loadingram
control and dataacquisition panel
mold
heightmeasurement
tilt bar
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150 mm diameter mold
ram pressure600 kPa
1.25 degrees30 gyrationsper minute
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Ndesign Table
Compaction Level
Traffic Level Ninitial Ndesign Nmaximum
Gyrations %Gmm
< 0.3 6 < 91.5 50 75
0.3 to < 3.0 7 < 90.5 75 115
3.0 to < 30.0 8 < 89.0 100 160
> 30.0 9 < 89.0 125 205
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General Notes to Revised Table
• Traffic Level is Based Upon 20 Year Pavement Design Life
• Slow / Standing Traffic : Increase Ndesign
by 1 Level.
HMA Superpave Mix Design 12
Superpave Gyratory Compaction
• Select mixing and compaction temperature based on asphalt binder properties
• Select number of gyrations to use based on design traffic level
HMA Superpave Mix Design 13
4 Steps of Superpave Mix Design
1. Materials Selection 2. Design Aggregate Structure
3. Design Binder Content 4. Moisture Sensitivity
TSR
HMA Superpave Mix Design 14
Step 1: Materials Selection
• Materials Selection consists of:
• Choosing the correct asphalt binder
• Choosing the aggregates that meet the quality requirements for the mix
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Superpave Asphalt Binder Specification
The grading system is based on Climate
PG 64 - 22
Performance Grade
Average 7-day max pavement temperature
Min pavement temperature
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Aggregate Consensus Properties
Coarse Aggregate Angularity
Fine Aggregate Angularity
Traffic Level
< 100 mm > 100 mm < 100 mm > 100 mm
< 0.3 75 / --- 50 / --- 40 40
0.3 to < 3.0 85 / 80 60 / --- 45 40
3.0 to < 30.0 95 / 90 80 / 75 45 40
> 30.0 100 / 100 100 / 100 45 45
HMA Superpave Mix Design 17
Aggregate Properties
1 3 5
Traffic LevelSand
Equivalent, %Flat and
Elongated, %
< 0.3 40 ---
0.3 to < 3.0 45 10
3.0 to < 10.0 45 10
10 to < 30.0 45 10
> 30.0 50 10
HMA Superpave Mix Design 18
Steps of Superpave HMA Mix Design
1. Materials Selection1. Materials Selection 2. Design Aggregate Structure2. Design Aggregate Structure
3. Design Binder Content3. Design Binder Content 4. Moisture Sensitivity4. Moisture Sensitivity
TSRTSR
HMA Superpave Mix Design 19
Step 2: Aggregate Gradation
• Establish trial aggregate blends
• 3 suggested
• evaluate combined aggregate properties
• Estimate optimum asphalt binder content
• Manufacture and compact trial blends
• Evaluate the trial blends
• Select the most promising blend
HMA Superpave Mix Design 20
Establish Trial Blends
• Develop three gradations based on
• Stockpile gradation information
• Gradation specification
• Optimize use of materials in the most economical blends
• Estimate properties of combined stockpiles
HMA Superpave Mix Design 21
Establish trial asphalt binder content
• Superpave Method
• Engineering judgement method
HMA Superpave Mix Design 22
Trial Asphalt Binder Content
• Use known or estimated values for
• Effective aggregate specific gravity, Gse
• Asphalt binder absorbed, Vba
• Calculate the effective binder content, Vbe
HMA Superpave Mix Design 23
Trial Asphalt Binder Content
• Calculate the initial asphalt binder content:
• Where:
Pbi = 100 Gb (Vbe + Vba)
(Gb (Vbe + Vba)) + Ws
Ws = Ps (1 – Va)
(Pb / Gb) + (Ps Gs)
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Next steps
• Sample preparation
• Select mixing and compaction temperatures
• Preheat aggregates and asphalt
• Mix components
• Compact specimens
• Extrude and determine volumetrics
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Place pre-heated aggregate in bowl and add hot asphalt
Mixing
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Mixing
Place bowl on mixer and mix until aggregate is well-coated
HMA Superpave Mix Design 27
Short Term Aging
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Short Term Aging Important
• Allows time for aggregate to absorb asphalt binder
• Helps minimize variability in volumetric calculations
• Most terms dependent upon volumes which change with changes in the amount (volume) of absorbed asphalt binder
HMA Superpave Mix Design 29
Determine the sample mass
• Estimate an asphalt binder content
• Mix up a sample & determine Gmm
• Calculate the bulk gravity needed to achieve 4 % air voids (Va)
• Calculate the weight for a pill with a height of 150 mm
Sample Mass
h d
d 2 hx
4 * 0.001 cm3/mm3Sample Volume = Vmx =
Where: Vmx = volume of specimen in mold)d = diameter of mold (150 mm)hx = height of specimen in mold
Sample mass = (Est. Gmb) (Sample Volume)
HMA Superpave Mix Design 31
d 2 hx
4 * 0.001 cm3/mm3Sample Volume = Vmx =
d 2
4 * 0.001 cm3/mm3 = 3.1416 * 150* 150 * 0.0001
4
= 17.671
Sample Mass Example Calc.
HMA Superpave Mix Design 32
Overview of Compaction Procedure
• Initialize Compactor• verify/set ram pressure at 600 kPa
• verify/set number of gyrations for Ndes
• Fill Gyratory Mold With HMA• paper disk on bottom• one lift of HMA• slightly round top of HMA• paper disk on top
• Load Mold into Gyratory Compactor
HMA Superpave Mix Design 33
After aging, take mix and preheated mold from oven. Place paper in bottom of mold.
Compaction
HMA Superpave Mix Design 34
Place mix in mold
Compaction
HMA Superpave Mix Design 35
Place another paper disc on top
of the mix
Compaction
HMA Superpave Mix Design 36
Slide mold into the compactor
Compaction
HMA Superpave Mix Design 37
Overview of Compaction Procedure (cont.)
• Start Test (the following occurs automatically):
• ram lowers
• angle is applied
• compaction occurs
• ram raises
• Extrude Specimen
• Allow Specimen to Cool
• Determine Bulk Specific Gravity
HMA Superpave Mix Design 38
Start compactor
Compaction
HMA Superpave Mix Design 39
Extrude sample and remove paper
from both sides while still warm
Compaction
HMA Superpave Mix Design 40
% Gmm
Log Gyrations
10 100 1000
Nini
Ndes
Nmax
Three Points on SGC Curve
HMA Superpave Mix Design 41
Estimate Aggregate Blend Properties(Example)
Property Criteria Trial Blend 1 2 3
Ninitial, % < 89.0 87.1 85.6 86.3Ndesign, % 96.0 97.6 97.4 96.5Nmax, % < 98.0 96.2 95.7 95.2Air Voids, % 4 4.4 4.4 4.4VMA, % 13 12.7 13.0 13.5
HMA Superpave Mix Design 42
4 Steps of Superpave Mix Design
1. Materials Selection 2. Design Aggregate Structure
3. Design Binder Content 4. Moisture Sensitivity
TSR
HMA Superpave Mix Design 43
General Guidance
• Compact the trial mixtures in accordance with AASHTO T 312 which now requires specimens be compacted to the design number of gyrations
• When doing a mix design when you compact a pair of samples to Nmaximum and check them to see if the Nmaximum value of 98% is exceeded.
HMA Superpave Mix Design 44
% Gmm
Log GyrationsLog Gyrations
10 100 1000
increasingincreasingbinderbinder
Design Asphalt Binder Content
HMA Superpave Mix Design 45
Superpave Mixture Requirements
• Mixture Volumetrics
• Air Voids (Va)
• Mixture Density Characteristics• Voids in the Mineral Aggregate (VMA)• Voids Filled with Asphalt (VFA)
• Dust Proportion
• Moisture Sensitivity
HMA Superpave Mix Design 46
Mix VMA Requirements Voids in the Mineral Aggregate
Table 334-9
9.5 mm 15.0 12.5 mm 14.0 19.0 mm 13.0
Mix typeMinimum VMA, %
% asphalt binder
VMA
HMA Superpave Mix Design 47
Mix VFA RequirementsVoids Filled with Asphalt
VFA
A 70 – 80B 65 – 78C 65 – 75D 65 – 75E 65 - 75
Traffic Level Design VFA, %
% asphalt binder
HMA Superpave Mix Design 48
Mix Requirement for Dust Proportion
1001009283654836221594
% weight of - 0.075 material
% weight of effective asphalt binder
0.6 < < 1.6
HMA Superpave Mix Design 49
DP
VMA
% asphalt binder
VFA
%Gmm at Nini
%Gmm at NmaxVa
Selection of Design Asphalt Binder ContentSelection of Design Asphalt Binder Content
% asphalt binder
% asphalt binder
% asphalt binder
% asphalt binder% asphalt binder
HMA Superpave Mix Design 50
Classroom Example
• Using the data on the next sheet, determine:
• The design asphalt binder content
• The VMA at the design asphalt binder
• The VFA at the design asphalt binder
• The dust to asphalt ratio
HMA Superpave Mix Design 51
Classroom Example
Pba = 0.4 % & the percent of minus 200 is 6%
% AC Va VMA
4.5 5.5 15.1
5.0 4.5 15.0
5.5 3.3 14.9
6.0 2.4 15.0
HMA Superpave Mix Design 52
94.0
94.5
95.0
95.5
96.0
96.5
97.0
97.5
98.0
4.0 4.5 5.0 5.5 6.0 6.5
% Asphalt Binder
%G
mm @
Nde
s
HMA Superpave Mix Design 53
14.7
14.8
14.9
15.1
15.2
15.3
4.0 4.5 5.0 5.5 6.0 6.5
% Asphalt Binder
% V
MA
HMA Superpave Mix Design 54
63
67
72
76
81
85
4.0 4.5 5.0 5.5 6.0 6.5
% Asphalt Binder
% V
FA
HMA Superpave Mix Design 55
4 Steps of Superpave Mix Design
1. Materials Selection 2. Design Aggregate Structure
3. Design Binder Content 4. Moisture Sensitivity
TSR
HMA Superpave Mix Design 56
DEFINITION
Stripping is the breaking of the adhesive bond between the aggregate surface and the
asphalt binder
HMA Superpave Mix Design 57
Stripping potential is controlled by
• Asphalt binder properties
• Aggregate properties
• Mixture characteristics
• Climate
• Traffic
• Construction practices
HMA Superpave Mix Design 58
Surface Chemistry
• Hydrophilic - “water loving”
• Those with high silica content
• Granites
• Hydrophobic - “water hating”
• Those with high carbon content
• Limestones
• But - it depends
HMA Superpave Mix Design 59
ANTISTRIP ADDITIVESSurface Active Agents
• Generally they are chemical compounds containing amines
• Amines are basic compounds derived from ammonia
• Heat stability can be a problem• Dosage rate is generally 0.5 % (but it depends)• Can change the properties of the asphalt cement
- generally soften
HMA Superpave Mix Design 60
ANTISTRIP ADDITIVESLime
• Hydrated lime - Ca(OH)
• AASHTO Specification -
• The result is a bonding of the calcium with the silicates in the aggregate
• Or an interaction or modification of the acidic portions of the asphalt
• Dosage rate is generally 1 to 1.5%
HMA Superpave Mix Design 61
• Six specimens are made at optimum asphalt binder content
• VTM is 7.0 + 0.5 % for all other mixes
• Three specimens are vacuum saturated
• 90 % saturation minimum
• One freeze-thaw cycle
• Determine the indirect tensile strength of for all six of the specimens
• Determine the percent retained strength
T-283 Procedure
HMA Superpave Mix Design 62
Treatment with admixtures
• Liquid antistrip
• Asphalt binder is heated to 325 F
• Add liquid antistrip
• Stir for 2 minutes
• Lime
• Dry mixed to the hot aggregate or damp aggregate immediately before the asphalt binder is added and mixed (the process used should match that being used in the field).
HMA Superpave Mix Design 63
Vacuum Saturation
• Place the specimen in vacuum chamber covering with at least one-inch of water
• Drop the pressure by 26 inches of mercury for 30 minutes
• Tap the chamber to dislodge trapped bubbles
• Release the vacuum and leave in water for 30 minutes.
HMA Superpave Mix Design 64
Vacuum saturation
• After 30 minutes determine the percent saturation
% Saturation = {(100) (D-A)}
{(C-B)(E)}
A: Dry wt
B: Wt in water before saturation
C: SSD wt. Before vacuum
D: SSD wt. After vacuum
E: Percent air voids in specimen
HMA Superpave Mix Design 65
Vacuum Saturation
HMA Superpave Mix Design 66
Heating Pills in Hot Water Bath
HMA Superpave Mix Design 67
Specimens placed in chamber at 25 C
HMA Superpave Mix Design 68
Applying Load
HMA Superpave Mix Design 69
INDIRECT TENSILE STRENGTH
S = 2p/ h DS – strength
P = load
H = width of specimen
D = the diameter
Dry Tensile Strength(average)
Wet Tensile Strength(average)
TSR = x 100 80 %Wet
Dry
Deformation Rate: 51 mm / min @ 25 oC
Moisture SensitivityAASHTO T 283 Test Procedure
HMA Superpave Mix Design 71
QUESTIONS ?