SuperPaveFed PDF
SuperPaveFed PDF
SuperPaveFed PDF
Version 6.2
SUPERPAVE
Superpave
Asphalt Mixture Design
Workshop
Developed by the Asphalt Team
Thomas Harman (202) 493-3072
Federal Highway Administration, HRDI-11
6300 Georgetown Pike, McLean, VA 22101
John D'Angelo (202) 366-0121
John Bukowski (202) 366-1287
Federal Highway Administration, HIPT
400 Seventh Street, S. W., Washington, DC 20590
In conjunction with
Charles Paugh
Carl Gordon
With excerpts from
Field Management of Asphalt Mixes - Summary of Simulation Studies,
FHWA National Asphalt Training Center Training Manuals,
Asphalt Institute MS & SP Series, &
Superpave Lead States Guidelines.
SUPERPAVE
This workshop is intended to demonstrate the Superpave asphalt mixture design system
developed by the Strategic Highway Research Program (SHRP), along with the application
of certain innovative concepts in field management of asphalt mixes. This workshop
includes the latest recommendations of the Superpave Lead States and the Mixture, Binder,
& Aggregate Expert Task Groups.
SUPERPAVE
TABLE OF CONTENTS
FOREWORD ...................................................................................................................................1
INTRODUCTION ...........................................................................................................................1
Background of SHRP...........................................................................................................1
SHRP Implementation .........................................................................................................2
SUPERPAVE OVERVIEW ............................................................................................................3
Simulation Background .......................................................................................................5
SELECTION OF MATERIALS......................................................................................................6
Binder Tests Required for Mixture Design........................................................................15
Aggregate Selection ...........................................................................................................19
CONSENSUS PROPERTY STANDARDS......................................................................20
Coarse Aggregate Angularity (ASTM D 5821).....................................................20
Uncompacted Void Content of Fine Aggregate (AASHTO TP33) .......................21
Flat or Elongated Particles in Coarse Aggregate (ASTM D 4791) .......................21
Sand Equivalent Test (AASHTO T 176) ...............................................................22
SOURCE PROPERTY STANDARDS .............................................................................31
L.A. Abrasion (AASHTO T 96) ............................................................................31
Sulfate Soundness (AASHTO T 104)....................................................................31
Clay Lumps and Friable Particles (AASHTO T 112)............................................32
SELECTION OF A DESIGN AGGREGATE STRUCTURE ......................................................33
SELECTION OF THE DESIGN ASPHALT BINDER CONTENT.............................................63
EVALUATION OF MOISTURE SENSITIVITY AASHTO T-283............................................67
APPENDICES ...............................................................................................................................68
PROJECT SUMMARY .....................................................................................................69
MIXING AND COMPACTION TEMPERATURE DETERMINATION .......................74
SUPERPAVE
LIST OF TABLES
Original: MP-2, Table 1 - Binder Selection on the Basis of Traffic Speed and Traffic Level........9
Current 01: MP-2, Table 1 - Binder Selection on the Basis of Traffic Speed and Traffic Level.10
Table: Superpave Performance Grades (PG)................................................................................11
Table: Binder Specification Test Results......................................................................................13
Table: Aggregate Stockpiles.........................................................................................................19
Table: Aggregate Tests .................................................................................................................20
Original: MP-2, Table 4 - Coarse Aggregate Angularity Criteria (ASTM DX) ...........................23
Original: MP-2, Table 5 - Uncompacted Void Content of Fine Aggregate Criteria (TP33).........23
Current 01: MP-2, Table 4 - Superpave Aggregate Consensus Property Requirements..............25
Table: Simulation Study Test Results (ASTM D 5821), CAA.....................................................26
Table: Simulation Study Test Results (AASHTO TP 33), FAA ..................................................26
Table: Simulation Study Test Results (ASTM D 4791), F&E .....................................................27
Table: Simulation Study Test Results (AASHTO T 176), SE......................................................27
Table: Superpave Aggregate Gradation Requirements .................................................................35
Table: Develop Trial Blends.........................................................................................................36
Table: Summary of Trial Blend Percentages ................................................................................39
Table: Summary of Actual Stockpile and Estimated Blend Properties ........................................39
Table: Estimated Effective Specific Gravities..............................................................................41
Table: Estimated Volume of Absorbed Binder.............................................................................41
Table: Estimated Weight of Aggregate and Percent of Binder ....................................................42
Table: Required Tests ...................................................................................................................43
Original: PP-28, Table 2 - Gyratory Compaction Criteria.............................................................46
Current 01: PP-28, Table 1 - Superpave Gyratory Compaction Effort ........................................47
Original: PP-28, Table 3 - Summary of Volumetric Design Criteria ............................................48
Current 99: PP-35, Table 2 - Superpave Volumetric Mixture Design Requirements ..................49
Original: PP-35, Table 4 - Selection of a Design Aggregate Structure (Example) .......................50
Current 99: PP-28, Table 4 - Selection of a Design Aggregate Structure (Example) .................51
Table: Summary of Project Volumetric Criteria............................................................................52
Table: Trial Blend No. 1: Specimen Compaction & Height Data .................................................55
Table: Trial Blend No. 1 Compaction Results...............................................................................55
Table: Trial Blend No. 1 Compaction Results...............................................................................57
Table: Summary Superpave Gyratory Compaction Results .........................................................59
Table: Summary of Estimated Properties at 4 % Va ......................................................................61
Table: Required Tests ...................................................................................................................63
Table: Compaction Test Results ...................................................................................................64
Table: Volumetric Test Results at Ndesign .....................................................................................65
Table: Summary of Design Mixture Properties at 5.4 % AC (Pb ) ...............................................65
Table: AASHTO T 283 Results....................................................................................................67
SUPERPAVE
LIST OF FIGURES
Figure:
Figure:
Figure:
Figure:
Figure:
Figure:
Figure:
SUPERPAVE
SUPERPAVE
Workbook: Introduction
Page 1
FOREWORD
The focus of this workbook is to provide engineers and technicians with a detailed
example of Superpave Volumetric asphalt mixture design.
INTRODUCTION
a.
Background of SHRP
The Strategic Highway Research Program (SHRP) was established by Congress
in 1987 as a five-year, $150 million dollars, product driven, research program to
improve the quality, efficiency, performance, and productivity of our nation's
highways and to make them safer for motorists and highway workers. It was
developed in partnership with States, American Association of State Highway
and Transportation Officials (AASHTO), Transportation Research Board (TRB),
Industry, and Federal Highway Administration (FHWA). SHRP research focused
on asphalt (liquids and mixtures), concrete & structures, highway operations, and
long-term pavement performance (LTPP).
SUPERPAVE
Workbook: Introduction
b.
Page 2
SHRP Implementation
As a follow-up program to SHRP, Congress authorized $108 million over six
years as part of the Intermodal Surface Transportation Efficiency Act (ISTEA) of
1991, to establish programs to implement SHRP products and to continue SHRP's
LTPP program. The FHWA was given the responsibility of directing the
implementation efforts to facilitate the application of the research findings.
Several concurrent efforts were undertaken including:
1)
Asphalt Technical Working Group (TWG)
2)
Expert Task Groups:
a)
Asphalt Binder
b)
Asphalt Mixture
c)
Superpave Models - Now part of NCHRP 9-19
3)
Pooled Fund Equipment Buys - Nearly Completed
4)
National Asphalt Training Center - Completed
5)
Mobile Superpave Laboratories
6)
Equipment Loan Program - Completed
7)
Expert Technical Assistance
8)
Superpave Regional Centers
9)
Superpave Models Contract - Now NCHRP 9-19
10)
Superpave Lead States
In 1998, Congress enacted the Transportation Equity Act for the 21st Century
(TEA21). Although TEA21 encourages the continued implementation of SHRP
technologies, no specific funding is provided. To address this shortfall in funding
the FHWA, AASHTO, TRB, and NCHRP approached the States to fund critical
Superpave activities with NCHRP funding. The Asphalt TWG has been replace
by the TRB Superpave Committee. The ETGs have also been transferred to TRB
for management. FHWA will continue to provide expert technical assistance.
SUPERPAVE
Workbook: Introduction
Page 3
SUPERPAVE OVERVIEW
The final product of the SHRP asphalt program area is Superpave. Superpave is an acronym
which stands for:
1.
2.
3.
4.
Selection of Materials,
Selection of a Design Aggregate Structure,
Selection of the Design Asphalt Binder Content, and
Evaluation of Moisture Sensitivity of the Design
Mixture.
Criteria for materials selection and compaction are a function of three factors:
a.
b.
c.
Environment,
Traffic, and
Pavement Structure.
Binder selection is based on environmental data, traffic level and traffic speed. Aggregate
selection is based upon layer location, traffic level, and traffic speed.
Selection of the design aggregate structure (design blend) consists of determining the aggregate
stockpile proportions and corresponding combined gradations of the mix design. The design
aggregate structure, when blended at the optimum asphalt binder content, should yield
acceptable volumetric properties based on the established criteria.
Selection of the design (optimum) asphalt binder content consists of varying the amount of
asphalt binder in the design aggregate structure to obtain acceptable volumetric properties when
compared to the established mixture criteria. It also provides a feel for the sensitivity of the
design properties to changes in the asphalt binder content during production.
Evaluation of moisture sensitivity consists of testing the design mixture by AASHTO T-283, or
other State specified method, to determine if the mixture will be susceptible to moisture damage.
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Simulation Background
a.
b.
c.
The posted traffic speed for the design section is 80 kilometers per hour, kph (50
mph). The estimated actual average speed for this section, accounting for speeding
and rush hour, is 72 kph (45 mph).
d.
The mix is a surface course (such that the top of this pavement layer from the
surface is less than 100 millimeters).
The project location in conjunction with the Weather Database will provide the minimum
pavement temperature, the maximum pavement temperature, and the maximum air
temperature. The estimated traffic and project temperature data, in combination with the
layer location will establish the material and compaction criteria.
Update:
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Workbook: Step 1- Selection of Materials
Page 5
SELECTION OF MATERIALS
The performance grade (PG) binder required for the project is based on environmental data,
traffic level and traffic speed. The environmental data is obtained by converting historic air
temperatures to pavement temperatures. The SHRP researchers developed algorithms to convert
high and low air temperatures to pavement temperature:
(2)
(1)
(3)
(4)
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The Lead States have recommended the adoption of the FHWA Long-Term Pavement
Performance (LTPP) Programs new algorithms based upon the following rationale:
Lead States Rationale
The current SHRP low-pavement-temperature algorithm does not correctly determine the low
pavement temperature from the air temperature. The FHWA LTPP program has developed a
new low-pavement-temperature algorithm from their weather stations at over 30 sites all over
North America. The Binder Expert Task Group feels the LTPP algorithm is far more accurate
and should be used in all AASHTO documents. Data supporting the LTPP algorithm is
presented in LTPP Seasonal Asphalt Concrete Pavement Temperature Models, FHWA-RD-97103, September, 1998.
The LTPP proposed algorithms are as follows:
LTPP High-Temperature Model with Reliability
T(pav) = 54.32+0.78 T(air) -0.0025 Lat -15.14 log10(H + 25)+ z (9 +0.61 air)
where: T(pav) =
T(air) =
Lat =
H=
air =
z=
(5)
(6)
A complete report documenting the research is available entitled, LTPP Seasonal Asphalt
Concrete (AC) Pavement Temperature Models. Publication No. FHWA-RD-97-103, September
1998.
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Workbook: Step 1- Selection of Materials
Page 7
The average 7-day maximum pavement temperature (Tmax) and the minimum pavement
temperature (Tmin) define the binder laboratory test temperatures. A factor of safety can be
incorporated into the performance grading system based on temperature reliability. The 50 %
reliability temperatures represent the straight average of the weather data. The 98 % reliability
temperatures are determined based on the standard deviations of the low (Low Temp ) and high
(High Temp) temperature data. From statistics, 98 % reliability is two standard deviations from the
average value, such that:
Low Temperature
High Temperature
Mean 52 degrees
STD 3 degrees
STD 2 degrees
Mean
Mean
Normal
Distribution
-3
-2
-1
+1
+2
-18
+3
-3
-22
-22
84%
-24
-28
97.5%
-27
+1
+2
+3
52
50%
Grades
54
58
84%
56
58
97.5%
-28
99.8%
-1
52
50%
-21
-2
58
99.8%
58
Page 12
SUPERPAVE
Workbook: Step 1- Selection of Materials
Page 8
Traffic level and speed are also considered in selecting the project performance grade (PG) binder
either through reliability or grade bumping. A table is provided in AASHTO MP-2, Standard
Specification for Superpave Volumetric Mix Design, to provide the designer with guidance on
grade selection. The Lead States proposed a new table to better clarify the intent of grade
bumping.
Original: MP-2, Table 1 - Binder Selection on the Basis of Traffic Speed and Traffic Level
TRAFFIC LOADING
Standing (< 20 km/h)
> 3 x 107
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Workbook: Step 1- Selection of Materials
Page 9
Current 03: MP-2, Table 1 - Binder Selection on the Basis of Traffic Speed and Traffic Level
c
d
e
f
Increase the high temperature grade by the number of grade equivalents indicated (one grade is equivalent to
6C). Use the low temperature grade as determined in Section 5.
The anticipated project traffic level expected on the design lane over a 20 year period. Regardless of the actual
design life of the roadway, determine the design ESALs for 20 years.
Standing Traffic - where the average traffic speed is less than 20 km/h.
Slow Traffic - where the average traffic speed ranges from 20 to 70 km/h.
Standard Traffic - where the average traffic speed is greater than 70 km/h.
Consideration should be given to increasing the high temperature grade by one grade equivalent.
Note 4 - Practically, PG binders stiffer than PG 82-xx should be avoided. In cases where the required
adjustment to the high temperature binder grade would result in a grade higher than a PG 82,
consideration should be given to specifying a PG 82-xx and increasing the design ESALs by one level
(e.g., 10 to <30 million increased to > 30 million).
Authors Note
The designer should use either reliability or the above table to address high traffic levels and
slower traffic speeds. Both methods can effectively bump the performance grade such that
the appropriate binder is used. However, using them in combination will result in an
unnecessarily stiff binder, which in turn may cause problems during production and lay down.
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Workbook: Step 1- Selection of Materials
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Performance grades are delineated by 6C increments. The following table shows the Superpave
performance grade temperatures. A few State highway agencies have chosen to specify
alternative performance grades. In Georgia, for example, the department of transportation
specifies a PG 67-22. This ensures the DOT of receiving an asphalt binder similar to what they
have used historically, AC-30. Although highway agencies are not encouraged to alter the
Superpave performance grades, Georgia is still receiving a performance grade asphalt. Binders
provided to meet their modified specification still have to meet the Superpave test criteria, just at
different temperatures.
52C
58C
64C
70C
76C
76+ n6
-28C
-28-n6
-4C
-10C
-16C
-22C
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For Hot Mix, USA, the following data is obtained from the project location and historical
temperature data:
a.
Latitude is 41.1 degrees,
b.
7-day average maximum air temperature is 33.0C with a of 2C, and
c.
1-day average minimum air temperature is -21.0C with a of 3C.
From this data the high and low pavement temperature are determined at a depth of 20 mm:
SHRP Algorithms
High pavement temperature
Low pavement temperature
PG 58-22 at 50% reliability
PG 58-28 at 98% reliability
LTPP Algorithms
53.2C
-21.0C
50.8C
-14.7C
Q. For the pavement high temperature calculations, which algorithm produces the highest
value?
a. SHRP, or
b. LTPP.
Q. For the pavement low temperature calculations, which algorithm produces the lowest value?
a. SHRP, or
b. LTPP.
Q. Does this make the new LTPP algorithms more or less conservative?
a. More, or
b. Less.
Q. Does the project traffic level of 6.3 million ESALs warrant an increase in the high
temperature performance grade?
a. Yes, or
b. No.
Q. Does the estimated, actual, average speed of 72 kph warrant an increase in the high
temperature performance grade?
a. Yes, or
b. No.
For Hot Mix, USA, the 50 % reliability LTPP performance grade is a PG 52-16. The project
traffic level and speed do not require grade bumping. However, the traffic speed is just above
SUPERPAVE
Workbook: Step 1- Selection of Materials
Page 12
the threshold for grade bumping and historically in this area pavements have shown
susceptibility to low-temperature cracking. Such that, the agency shall require a PG 58-22.
Binder Selection
The project asphalt binder is tested for specification compliance to the Superpave PG system.
Project Binder:
Binder Source:
PG 58-22
Asphalt is Us
Property
Flash Point
Results
Original Binder
n/a
310C
Criteria
> 230C
Rotational Viscometer
135C
0.364 Pa-s
< 3 Pa-s
Rotational Viscometer
165C
0.100 Pa-s
n/a
1.7 kPa
Mass Loss
2.8 kPa
-12C
< 1.0 %
> 2.2 kPa
< 5 MPa
280 MPa
0.334
> 0.300
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Workbook: Step 1- Selection of Materials
Page 13
Thermal Stress
Curve From BBR
Tcritical
Temperature
Stress
Role of DTT
and BBR
______________
Thermal stress
curve (dotted line)
is computed from
BBR data. Failure
Strength is measured
using the DTT. Where
they meet, determines
critical cracking
temperature, Tc.
Stress
Strength
Reserve
Strength
Low m
High m
Temperature
SUPERPAVE
Workbook: Step 1- Selection of Materials
Page 14
= Y cSt or
X Pa-s *
1000
(CF * Gb)
= Y cSt
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Workbook: Step 1- Selection of Materials
Page 15
Q.
What are the equal-viscous mixing and compaction ranges for this asphalt binder?
A.
First the temperature correction factors for Gb are calculated at the two test temperatures:
CF135C = -.0006(135C) + 1.0135 = 0.933
CF160C = -.0006(160C) + 1.0135 = 0.918
364 cP
(0.933 * 1.030)
= 379 centiStokes
Viscosity at 160C =
100 cP
(0.918 * 1.030)
= 106 centiStokes
This data is now analyzed graphically based on the Log-Log(base 10) of the viscosity in centiStokes
plotted against the Log(base 10) of the temperature in degrees Kelvin (273 + C), see figure. From
the graph the following temperature data is determined:
Range
Mixing
Compaction
Temperature, _C
148C to ____?
138C to 142C
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Workbook: Step 1- Selection of Materials
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0.40310
290
270
Compaction Range
0.38250
230
210
0.36190
Mixing Range
170
0.34150
140
130
0.32120
110
0.30100
90
0.2880 120
125
2.60
130
135
140 2.62
145
150
155
160 2.64
165
170
175
180 2.66
185 190
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Workbook: Step 1- Selection of Materials
Page 17
Summary of Results
Mixing Temperature Range
148C to 152C
138C to 142C
Note: This relationship does not work for all modified asphalt binders.
Note: See the Appendix for the mathematics required to perform the mixing and compaction
temperature range determinations.
Note: The conversion from centipoise to centiStokes is important, however it is not required.
Determining mixing and compaction temperatures based upon 150 to 190 centipoise and
250 to 310 centipoise ranges, respectively, will only effect the results by 1 to 2C.
SUPERPAVE
Workbook: Step 1- Selection of Materials
Page 18
Aggregate Selection
Superpave utilizes a completely new system for testing, specifying, and selecting asphalt
binders. While no new aggregate tests were developed, current methods of selecting and
specifying aggregates were refined and incorporated into the Superpave design system.
Superpave asphalt mixture requirements were established from currently used criteria.
For this simulated project, four (4) stockpiles of materials consisting of two (2) coarse materials
and two (2) fine materials are employed. Representative samples of the materials are obtained,
and washed sieve analysis is performed for each aggregate. The gradation results are shown in
the Aggregate Blending Section.
The specific gravities (bulk Gsb and apparent Gsa ) are determined for each aggregate. The
specific gravities are used in trial binder content and Voids in Mineral Aggregate (VMA)
calculations.
Table: Aggregate Stockpiles
Aggregate Stockpile
Coarse Aggregate
Intermediate Aggregate
Manufactured Fines
Natural Fines
Bulk, Gsb
2.567
2.587
2.501
2.598
Apparent, Gsa
2.680
2.724
2.650
2.673
In addition to sieve analysis and specific gravity determinations, Superpave requires certain
consensus and source aggregate tests be performed to assure that the combined aggregates
selected for the mix design are acceptable. The consensus property criteria are fixed in the
Superpave design system; these are minimum requirements, which should be adhered to
regardless of geographic location. The source property criteria are specified by the State
highway agency. Superpave recommends three source property tests, which should be included
in the aggregate selection process.
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Page 19
Source Properties
(Set by SHA)
Resistance to Abrasion (T 96)
Soundness (T 104)
Clay Lumps & Friable Particles (T 112)
Superpave requires the consensus and source properties be determined for the design aggregate
blend. The aggregate criteria are based on combined aggregates rather than individual aggregate
components. However, it is recommended the tests be performed on the individual aggregates
until historical results are accumulated and also to allow for the blending of the aggregates in the
mix design.
Authors Note
An aggregate which does not individually comply with the criteria is not eliminated from the
aggregate blend. However, its percentage of use in the total aggregate blend is limited.
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Workbook: Step 1- Selection of Materials
Page 20
W
( V - Gsb)
Uncompacted Voids, U =
* 1
100
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Fixed post
(B)
swinging arm
fixed post
(A)
*
* 100
sand reading
sedimented
aggregate
SR - sand reading
CR - clay reading
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The criteria for the consensus property standards as outlined in AASHTO MP-2 is as follows:
MP-2 Table 5 - Coarse Aggregate Angularity Criteria (D 5821).
MP-2 Table 5 - Fine Aggregate Angularity Criteria (T304, Method A).
MP-2 Table5 - Sand Equivalent Minimum Criteria ( T176).
MP-2 Section for Flat and Elongated Particles 6.5 The aggregate shall meet the flat and elongated requirements specified in Table 5 measured
according to D4791, with the exception that the material passing the 9.5-mm sieve and retained
on the 4.75-mm sieve shall be included. The aggregate shall be measured using the ratio of 5:1,
comparing the length (longest dimension) to the thickness (smallest dimension) of the aggregate
particles.
6.6 When RAP is used in the mixture, the RAP aggregate shall be extracted using a solvent extraction
(T164) or ignition oven (T308) as specified by the agency. The RAP aggregate shall be included
in determinations of gradation, coarse aggregate angularity, fine aggregate angularity, and flat and
elongated requirements. The sand equivalent requirements shall be waived for the RAP aggregate
but shall apply to the remainder of the aggregate blend.
Current 03: MP-2, Table 5 - Superpave Aggregate Consensus Property Requirements
Design ESALsa
(Million)
< 0.3
0.3 to < 3
3 to < 10
10 < 30
> 30
a
Fractured Faces,
Coarse Aggregatec
Percent Minimum
Depth from Surface
< 100 mm
> 100 mm
55/-/75/50/85/80b
60/95/90
80/75
100/100
100/100
Sand
Equivalent
Percent,
Minimum
Flat and
Elongatedc
Percent,
Maximum
40
40
45
45
50
10
10
10
10
The anticipated project traffic level expected on the design lane over a 20-year period. Regardless of the actual
design life of the roadway, determine the design ESALs for 20 years.
85/80 denotes that 85 percent of the coarse aggregate has one fractured face and 80 percent has two or more
fractured faces.
This criterion does not apply to 4.75-mm nominal maximum size mixtures.
Note 7- If less than 25 percent of a construction lift is within 100 mm of the surface, the lift may be considered to
be below 100 mm for mixture design purposes.
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1+ Fractured
99 %
80 %
Criterion
__ % min
2+ Fractured
97 %
60 %
Criterion
__ % min
This test is commonly only performed on the coarse aggregates during the initial screening of
materials, even though the fine aggregate stockpiles may contain a small percentage retained on
the 4.75 millimeter sieve. This test should also be run on the plus 4.75 millimeter material of the
final design aggregate blend.
Q.
Based on the Current 03 table, what is the criterion for this surface mixture with an
estimated traffic of 6,300,000 ESALs, (fill in the above table)?
Do both stockpiles meet the criteria, (Y/N)? If the answer is no, what does this mean?
(1)
Stockpile cannot be used. or
(2)
Percentage of stockpile in blend is limited.
Q.
% Air Voids
48
42
Criterion
> __
Based on the Current 01 table, what is the criterion for this surface mixture with an
estimated traffic of 6,300,000 ESALs, (fill in the above table)?
Do both stockpiles meet the criteria, (Y/N)? If the answer is "no," what does this mean?
a.
Stockpile cannot be used. or
b.
Percentage of stockpile in blend is limited.
Authors Note
Fine aggregates with higher angularity may aid in the development of higher voids in mineral
aggregate (VMA).
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Q.
% Elongated
9%
2%
Criterion
__ %
Based on the Current 01 table, what is the criterion for this surface mixture with an
estimated traffic of 6,300,000 ESALs, (fill in the above table)?
Do both stockpiles meet the criteria, (Y/N)? If the answer is "no," what does this mean?
a.
Stockpile cannot be used. or
b.
Percentage of stockpile in blend is limited.
Sand Equivalent
51 %
39 %
45%
Criterion
__ %
Q. Based on the Current 01 table, what is the criterion for this surface mixture with an
estimated traffic of 6,300,000 ESALs, (fill in the above table)?
Do both stockpiles meet the criteria, (Y/N)? If the answer is "no," what does this mean?
a. Stockpile cannot be used. or
b. Percentage of stockpile in blend is limited.
Q. For this project, did any of the criteria change from using the Current 01 table versus
the original standards in AASHTO MP-2?
Consensus Standard
CAA
FAA
F&E
SE
Original Criteria
85 / 80
45
10
45
Current 01 Criteria
85 / 80
45
10
45
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Coarse Aggregate Angularity - Previous references in SHRP reports and elsewhere to the
Pennsylvania Department of Transportation Test Method No. 621 for determining coarse
aggregate angularity have been revised in AASHTO MP2, Standard Specification for
Superpave Volumetric Mix Design to reference ASTM D5821, Standard Test Method for
Determining the Percentage of Fractured Particles in Coarse Aggregate, to more critically
discriminate between aggregates.
Fine Aggregate Angularity - Fine aggregate angularity should be determined in accordance
with AASHTO TP-33, Uncompacted Void Content of Fine Aggregate, method A. The Lead
States recommend the current Superpave fine aggregate angularity requirement of 45 at greaterthan 3 million ESALs and 40 at less-than 3 million ESALs be specified. It should be noted that
the aggregates bulk specific gravity is a critical factor in the determination of the fine aggregate
angularity, therefore, this value should be determined on a frequency appropriate for the
variability of the source.
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Workbook: Step 1- Selection of Materials
Page 26
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Workbook: Step 1- Selection of Materials
Page 27
25
20
15
5:1 Ratio
3:1 Ratio
10
5
0
1 2 3 4
5 6 7 8
9 10 11 12
13 14 15 16
17 18 19 20
21 22 23 24
25 26 27
Stockpile
100
80
60
3:1 Ratio
5:1 Ratio
40
20
0
5
10
15
20
25
Criteria (Maximum)
30
It is recommended each specifying agency should perform a market analysis to access the impact
of specifying a 3:1 source property standard.
SUPERPAVE
Workbook: Step 1- Selection of Materials
Page 28
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Workbook: Step 1- Selection of Materials
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Workbook: Step 1- Selection of Materials
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To select the design aggregate structure, trial blends are established by mathematically
combining the gradations of the individual materials into a single blend. The blend is then
compared to the specification requirements for the appropriate sieves. Gradation control is based
on four control sieves: the maximum sieve, the nominal maximum sieve, the 2.36 mm sieve, and
the 0.075 mm sieve. Definitions:
Nominal Maximum Sieve Size: One standard sieve size larger than the first sieve to retain
more than 10 percent.
Maximum Sieve Size: One standard sieve size larger than the nominal maximum size.
The 0.45 power maximum density line is draw from the origin to 100 percent passing the
maximum size.
Standard
Sieves
50.0 mm
37.5 mm
25.0 mm
19.0 mm
12.5 mm
9.50 mm
4.75 mm
2.36 mm
1.18 mm
0.60 mm
0.30 mm
0.15 mm
0.075 mm
SUPERPAVE
Workbook: Step 2- Selection of a Design Aggregate Structure
Q.
Page 31
English
Sieves
A.
Standard
Sieves
(1)
No. 100
(A)
50.0 mm
(2)
No. 4
(B)
37.5 mm
(3)
1/4 inch
( C)
25.0 mm
(4)
1 inch
(D)
19.0 mm
(5)
No. 200
(E)
12.5 mm
(6)
No. 80
(F)
9.50 mm
(7)
No. 50
(G)
4.75 mm
(8)
inch
(H)
2.36 mm
(9)
No. 16
(I)
1.18 mm
(10)
No. 20
(J)
0.60 mm
(11)
No. 40
(K)
0.30 mm
(L)
0.15 mm
(M)
0.075 mm
(1)L, (2)G, (3)*, (4)C, (5)M, (6)*, (7)K, (8)E, (9)I, (10)*, (11)*
* - English sieve is not part of the Standard sieve stack.
SUPERPAVE
Workbook: Step 1- Selection of Materials
Page 32
There is also a recommended "restricted zone." The restricted zone is an area on either side of
the maximum density line generally starting at the 2.36 millimeter sieve and extending to the
0.300 millimeter sieve. The minimum and maximum values required for the control sieves
change (as does the restricted zone) as the nominal size of the blend changes. The following
table defines the control points and recommended restricted zones for different nominal
maximum sieve sizes.
9.5 mm
50.0
37.5
25.0
19.0
12.0
9.50
2.36
0.075
Sieve
4.75
2.36
1.18
0.60
0.30
100
90 - 100
32 - 67
2.0 - 10.0
47.2
31.6 - 37.6
23.5 - 27.5
18.7
100
90 - 100
100
90 - 100
100
90 - 100
28 - 58
23 - 49
19 - 45
2.0 - 10.0
2.0 - 8.0
1.0 - 7.0
Recommended Restricted Zone
39.5
39.1
34.6
26.8 - 30 8
25.6 - 31.6
22.3 - 28.3
18.1 - 24.1
19.1 - 23.1
16.7 - 20.7
13.6 - 17.6
15.5
13.7
11.4
37.5 mm
100
90 - 100
15 - 41
0.0 - 6.0
34.7
23.3 - 27.3
15.5 - 21.5
11.7 - 15.7
10.0
All trial blend gradations (washed in accordance to AASHTO T-11) must pass between the
control points established. In addition, they should be outside of the area bounded by the limits
set for the restricted zone.
SUPERPAVE
Workbook: Step 2- Selection of a Design Aggregate Structure
Page 33
Typically the State highway agency will specify the nominal maximum size required for the
pavement layer. For our simulation study, the specified size is 19.0 mm. It is recommended that
three trial blends be initially developed.
Table: Develop Trial Blends
Aggregates
Coarse
Agg.
Sieve
37.5 mm
25.0 mm
19.0 mm
12.5 mm
9.5 mm
4.75 mm
2.36 mm
1.18 mm
0.60 mm
0.30 mm
0.15 mm
0.075 mm
100.0
100.0
92.0
50.0
14.0
3.0
2.0
2.0
2.0
2.0
2.0
2.0
Intr.
Agg.
Man.
Fines
Stockpile Gradations
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
100.0
95.0
100.0
25.0
6.0
87.0
4.0
65.0
42.0
4.0
18.0
3.0
6.0
3.0
2.8
3.7
Natrl.
Fines
100.0
100.0
100.0
100.0
100.0
100.0
93.0
64.0
48.0
32.0
18.0
10.0
Trial
No. 1
46%
24%
15%
15%
No. 1
100.0
100.0
96.3
77.0
59.2
37.4
29.4
21.2
15.4
9.1
5.2
3.6
Trial
No. 2
51%
25%
15%
9%
No. 2
100.0
100.0
95.9
74.5
54.9
31.8
23.9
17.5
12.6
7.4
4.3
3.2
Trial
No. 3
25%
24%
23%
28%
No. 3
100.0
100.0
98.0
87.5
77.3
57.8
48.0
34.3
24.6
14.3
7.6
5.8
Nominal Maximum Sieve Size: One standard sieve size larger than the first
sieve to retain more than 10 percent. The first sieve to retain more than 10
percent for all blends is the 12.5 millimeter. On sieve larger is the 19.0
millimeter. Such that the nominal maximum sieve size is the 19.0 millimeter.
Maximum Sieve Size: One standard sieve size larger than the nominal
maximum size. Such that the 25.0 millimeter is the maximum sieve size.
SUPERPAVE
Workbook: Step 1- Selection of Materials
Page 34
Restricted Zone????
Figure: Trial Blends 0.45 Power Chart
100
Control
Points
Restricted
Zone
Max Density
Percent Passing
80
60
40
Trial No. 1
Trial No. 2
Trial No. 3
20
0
0.5
1.5
2.5
3.5
4.5
SUPERPAVE
Workbook: Step 2- Selection of a Design Aggregate Structure
Page 35
Once the trial blends are established, preliminary determinations of the blended aggregate
properties can be determined. This can be estimated mathematically from the individual
aggregate properties using the blend percentages. The combined aggregate bulk and apparent
specific gravities are determined using the law of partial fractions. (If the individual properties
were not previously determined, the consensus and source properties standards need to be
determined for the design aggregate blend.) Example:
Stockpile
Trial
Blend #1
Percentage
46 %
24 %
15 %
15 %
Coarse Aggregate
Intermediate Agg
Manufactured Fines
Natural Fines
Percent of plus
4.75 mm
Material
97 %
75 %
0%
0%
Test Results
Coarse
Angularity
99/97
80/60
n/a
n/a
Test Results
Bulk Sp.Gv.
Gsb
2.567
2.587
2.501
2.598
(99
CAA1
CAA1+
97 * 46 + 80 * 75
(97
CAA1+
C11 , C12 ,C1n
P4751 , P4752 ,...P475n
P1 , P2 ,...Pn
46 + 75
24)
24)
= 94
where:
Gsb
= bulk specific gravity for the total aggregate blend
P1 , P2 ,...Pn = percentage by weight of aggregates, 1, 2,...n
G1 , G2 ,...Gn = bulk specific gravity of aggregates, 1, 2,...n
SUPERPAVE
Workbook: Step 1- Selection of Materials
Page 36
Stockpile Percentages
Stockpile A
Coarse
46
51
25
No. 1
No. 2
No. 3
Consensus Test
Coarse Agg Ang, +4.75
Fine Agg Ang, -2.36
Flat/Elongated, +9.5
Sand Equivalent, - 4.75
97
2
86
3
Stockpile B
Stockpile C
Intermediate
Manuf. Fines
24
15
25
15
24
23
Consensus Property Percentages
75
0
6
87
0
>5<
25
100
Stockpile D
Natural Fines
15
9
28
0
93
0
100
Criteria
CAA
85/80min
FAA
45 min
F&E
10 max
SE
45 min
Bulk Sp.Gv., Gsb
Apparent Sp.Gv., Gsa
Q.
Calculated Values
Stockpile
A
Stockpile
B
Stockpile
C
Stockpile
D
99/97
n/a
9
n/a
2.567
2.680
80/60
n/a
2
45
2.587
2.724
n/a
48
n/a
51
2.501
2.650
n/a
42
n/a
39
2.598
2.673
Trial
Blend
No.1
94/86
45
9
45
2.566
2.685
Trial
Blend
No. 2
94/87
46
9
46
2.565
2.686
Trial
Blend
No. 3
91/____?
45
9
_____?
2.565
2.681
SE
A.
SE
SUPERPAVE
Workbook: Step 2- Selection of a Design Aggregate Structure
Page 37
SUPERPAVE
Workbook: Step 1- Selection of Materials
Page 38
Gse
2.637
2.637
2.635
Step 2:Estimate the volume of asphalt binder (Vba ) absorbed into the aggregate:
Vba
Va
Pb
Ps
Gb
=
=
=
=
=
Vba
0.0233
0.0239
0.0232
Step 3:Estimate the volume of effective binder (Vbe ) of the trial blends:
Vbe = 0.176 - 0.0675 * Logarithmnatural (Sn)
where:
Sn
Vbe
SUPERPAVE
Workbook: Step 2- Selection of a Design Aggregate Structure
Page 39
Vbe
0.061
0.070
0.082
0.090
0.102
0.110
0.130
Step 4:Estimate initial trial asphalt binder (Pbi ) content for the trial blends:
Ps * (1 - Va )
Ws = ____________
(Pb/Gb + Ps/Gse )
Pbi =
Gb * (Vbe + Vba )
__________________ * 100
(Gb *(Vbe + Vba )) + Ws
Ws
Pbi
= weight of aggregate
= percent (by weight of mix) of binder
where:
0.95 * (1 - 0.04)
Trial Blend No. 1; Ws = _______________________ = 2.231
(0.05/1.030 + 0.95/2.637)
1.030 * (0.090 + 0.0233)
Trial Blend No. 1; Pbi = _____________________________ * 100 = 4.95 %
(1.030 * (0.090 + 0.0233)) + 2.231
Ws
2.231
2.231
2.229
Pbi
4.95 %
4.98 %
4.95 %
SUPERPAVE
Workbook: Step 1- Selection of Materials
Page 40
The estimated percent of binder determined by the equations can not replace experience.
Local aggregate and binders when combined will almost always require a slightly different
optimum asphalt content. Your experience with Superpave mixtures should always govern
over these calculated estimates.
Next: Evaluate Trial Blends at Estimated Asphalt Binder Contents
Table: Required Tests
Trial Blend
Number 1
Number 2
Number 3
Total (55,200 g)
Superpave
Gyratory Compactor
Specimens
3 Specimens
4800 g/ea
3 Specimens
3 Specimens
9 Specimens (43,200 g)
Rice, Gmm
Max Specific Gravity
(T 209)
2 Tests
2000 g/ea
2 Tests
2 Tests
6 Tests (12,000 g)
A minimum of two specimens (FHWA recommends three) for each trial blend are
compacted using the Superpave gyratory compactor. A mixture weight of 4800 grams is
usually sufficient for the compacted specimens. Two specimens are also prepared for
determination of the mixture's maximum theoretical specific gravity, (Gmm ). A mixture
weight of 2000 grams is usually sufficient for the specimens used to determine Gmm.
Excerpt, AASHTO T 209:
Nominal Maximum
Size of Aggregate
(mm)
25.0
19.0
12.5
9.5
4.75
Minimum Mass
of Sample
(kg)
2.5
2.0
1.5
1.0
0.5
Authors Note
Nominal maximum size of aggregate for the above table is based on AASHTO definition not
Superpave. Such that the nominal maximum size is the smallest sieve size through which the
entire amount of aggregate is permitted to pass. How does this relate to Superpave?
SUPERPAVE
Workbook: Step 2- Selection of a Design Aggregate Structure
Page 41
Aging
Specimens are mixed at the appropriate mixing temperature based on the temperature-viscosity
relationship. The specimens are short-term aged. The original procedure required 4 hours of
short term aging in a forced-draft oven at 135C. The mix is spread to a density of 21 to 22
kilograms per square meter (kg/m) of pan (approximately 10 mm thick). The specimens are
hand mixed every hour. The Lead States propose an alternate procedure, based on the following
rationale:
Lead States Rationale
NCHRP 9-9, Evaluation of the Superpave Gyratory Compaction Procedure, research
performed by NCAT has shown there is not a practical difference for non-absorptive
aggregates in mixture volumetric properties when 2- or 4-hour conditioning is performed. This
research confirmed previous findings of the Mixture Expert Task Group. Additionally, NCAT
evaluated the difference in a mixtures volumetric properties when aging is performed at the
mixtures compaction temperature and aging at 135C. While differences were noted, it was
determined that these differences were inconsequential from an engineering perspective.
However, additional research sited by the FHWA indicates there is a difference in the
resulting mechanical properties of mixtures conditioned for 2 versus 4 hours. Adopting a
specific 2-hour mixture conditioning period for the volumetric mixture design procedure at the
mixtures compaction temperature will expedite mixture design development. The existing
short and long aging procedures are maintained for use when mechanical property testing of
the mixture will be performed.
Summary of Practice
Original: For short term aging a mixture of aggregate and asphalt binder is aged in a forceddraft oven for 4 hours at 135C. For long term aging a compacted mixture of
aggregate and asphalt binder is aged in a forced-draft oven for 5 days at 85C.
Current 99: For mixture conditioning for volumetric mixture design, a mixture of aggregate and
asphalt binder is conditioned in a forced-draft oven for 2 hours at the mixtures
specified compaction temperature.
For short-term mixture conditioning for mechanical property testing, a mixture of
aggregate and asphalt binder is aged in a forced-draft oven for 4 hours at 135C.
For long-term mixture conditioning for mechanical property testing, a compacted
mixture of aggregate and asphalt binder is aged in a forced-draft oven for 5 days at
85C.
SUPERPAVE
Workbook: Step 1- Selection of Materials
Page 42
Compaction
History Lesson
The Superpave system, developed under SHRP, employs gyratory compaction to fabricate
asphalt mixture specimens. The level of compaction in the SGC is based upon the design
traffic and the average 7-day maximum air temperature. The design traffic is the projected,
single lane, traffic volume over 20 years - expressed in ESALs. AASHTO MP-2 provides a
table for selection of specimen compaction levels. The table has seven traffic categories and
four ranges of temperatures, constituting a total matrix of twenty-eight (28) different
compaction levels.
The compaction table is based on research conducted under the SHRP contract by the Asphalt
Institute, (AI). The researchers evaluated 9, in-service, general pavement studies, (GPS), from
across the United States, using a prototype gyratory compactor. All of the GPS sites were
performing well after several years of service. The sites were cored and volumetrics were
determined. Aggregates were then recovered and recombined with a standard asphalt binder
(AC-20) and compacted in a prototype SGC. The compaction efforts required to produce four
percent air voids were determined. This effort was then equated to traffic level and site
environmental data resulting in the table of compaction levels.
NCHRP 9-9 entitled, Refinement of the Superpave Gyratory Compaction Procedure,
conducted by NCAT, evaluated the sensitivity of the compaction levels. The principal
investigator, Dr. E. Ray Brown, and his team investigated whether there is any significant
volumetric property differences between mixtures compacted at the various compaction levels.
A parallel effort conducted by the FHWA Mixture ETG, investigated the validity of the
number of gyrations used to design asphalt mixtures. This effort, designated, N-design II,
was conducted through the AI in partnership with Heritage Research Group. The principal
researchers included Mike Anderson (AI), Gerry Huber (Heritage), Bob McGennis (South
Central Superpave Regional Center), and Rich May (previously with AI, now with Koch
Materials). The researchers were provided with samples and data from several State Highway
Agencies, FHWA Turner Fairbank Highway Research Center, and FHWA Performance
Related Specifications Test Track, (WesTrack).
The NCHRP 9-9 research effort developed a simplified, compaction matrix. As did the
research N-design II effort. During the Mix ETG meeting held September 22 and 23, 1998 in
Baltimore, Maryland, the expert task group reviewed the findings of both research efforts. On
September 24, 1998, the Superpave Lead States met and concurred with the efforts of the Mix
ETG. These efforts resulted in the development of a proposed new compaction matrix. The
proposed new compaction table has been forwarded by the Mix ETG to AASHTO for
balloting and possible inclusion in the standards.
SUPERPAVE
Workbook: Step 2- Selection of a Design Aggregate Structure
Page 43
The Superpave compaction criteria are based on three points during the compaction effort: an
initial (Nini ), design (Ndes ), and maximum (Nmax ) number of gyrations. Limiting criteria based
on the percent of Gmm has also been established for the initial, design, and maximum number of
gyrations. The following is the original and current 99 tables for compaction effort according to
AASHTO PP-28, Standard Practice for Designing Superpave HMA.
Original: PP-28, Table 2 - Gyratory Compaction Criteria
Estimated
Traffic
million
< 0.3
0.3 to < 1
1.0 to < 3
3.0 to <
10
10 to < 30
30 to <
100
> 100
Ni
7
7
7
8
<39C
Nd
68
76
86
96
Nm
104
117
134
152
39 C - 40 C
Ni
Nd
Nm
7
74
114
7
83
129
8
95
150
8
106 169
41C - 42C
Ni
Nd
Nm
7
78
121
7
88
138
8
100 158
8
113 181
41C - 44C
Ni
Nd
Nm
7
82
127
8
93
146
8
105 167
9
119 192
8
9
109
126
174
204
9
9
121
139
195
228
9
9
128
146
208
240
9
10
135
153
220
253
142
233
10
158
262
10
165
275
10
172
288
SUPERPAVE
Workbook: Step 1- Selection of Materials
Page 44
Compaction Parameters
< 0.3
Ninitial
6
Ndesign
50
Nmax
75
0.3 to < 3
75
115
3 to < 30
100
160
>30
125
205
(1)
Design ESALs are the anticipated project traffic level expected on the design lane over a 20-year period. Regardless of
the actual design life of the roadway, determine the design ESALs for 20 years, and choose the appropriate Ndesign level.
1.
Typical Roadway Applications as defined by A Policy on Geometric Design of Highway and Streets, 1994, AASHTO.
Note 17 --
When specified by the agency and the top of the design layer is 100 mm from the pavement surface and the
estimated design traffic level 0.3 million ESALs, decrease the estimated design traffic level by one, unless the
mixture will be exposed to significant main line and construction traffic prior to being overlaid. If less than 25% of the
layer is within 100 mm of the surface, the layer may be considered to be below 100 mm for mixture design purposes.
Note 18 When the design ESALs are between 3 to < 10 million ESALs the agency may, at their discretion, specify Ninitial at 7,
Ndesign at 75, and Nmax at 115, based on local experience.
The volumetric criteria for the original and current 99 compaction effort is as follows:
Volumetric Property
Superpave Criteria
4 percent
VMA at Ndesign
% Gmm @ at Nini
<89.0
% Gmm @ Ndesign
96.0
% Gmm @ Nmax
< 98.0
Design ESALs1
Required Density
(million)
Voids Filled
With
Dust-to-Binder
Ratio
Asphalt
(Percent)
Nominal Maximum Aggregate Size, mm
Ninitial
Ndesign
Nmax
37.5
25.0
19.0
12.5
9.5
11.0
12.0
13.0
14.0
15.0
70 - 80 3,4
< 0.3
91.5
0.3 to < 3
90.5
65 - 784
3 to < 10
89.0
65 - 752,4
96.0
98.0
0.6 - 1.2
10 to < 30
30
1.
2.
Design ESALs are the anticipated project traffic level expected on the design lane over a 20-year period. Regardless of the actual design life of the
roadway, determine the design ESALs for 20 years, and choose the appropriate Ndesign level.
For 9.5-mm nominal maximum size mixtures, the specified VFA range shall be 73% to 76% for design traffic levels 3 million ESALs.
1. For 25.0-mm nominal maximum size mixtures, the specified lower limit of the VFA shall be 67% for design traffic levels < 0.3 million ESALs.
2. For 37.5-mm nominal maximum size mixtures, the specified lower limit of the VFA shall be 64% for all design traffic levels.
Note 19 -- If the aggregate gradation passes beneath the boundaries of the aggregate restricted zone specified in Table 3, consideration should be given
to increasing the dust-to-binder ratio criteria from 0.6 - 1.2 to 0.8 - 1.6.
Volumetric Property
Criteria
4.4
4.4
4.4
%Gmmini (trial)
88.1
86.5
87.1
%Gmm (trial)
95.9
95.3
94.7
%Gmmmax
97.6
97.3
96.4
Va at Ndes
4.1
4.7
5.3
VMAtrial
12.9
13.4
13.9
4.0
-0.1
-0.7
-1.3
Pb
0.0
0.3
0.5
VMA
0.0
-0.1
-0.3
4.4
4.7
4.9
VMA (des)
12.9
13.3
13.6
> 13.0
%Gmmini (des)
88.2
87.2
88.4
< 89.0
%Gmmmax (des)
97.7
98.0
97.7
< 98.0
Notes:
The top portion of this table presents measured compaction densities and volumetric properties for specimens prepared for
each trial aggregate gradation at the initial trial asphalt content.
None of the specimens had an air void content of exactly 4.0 percent. Therefore, the procedures described in Section 9 must
be applied to: 1) estimate the design asphalt content at which Va = 4 percent, and 2) obtain adjusted VMA and compaction
density values at this estimated asphalt content.
The middle portion of this table presents the change in asphalt content (
content (Va) is adjusted to 4.0 percent for each trial aggregate gradation.
A comparison of the VMA and densities at the estimated design asphalt content to the criteria in the last column shows that
trial gradation #1 does not have sufficient VMA (12.9 % versus a requirement of > 13.0 %). Trial gradation #2 exceeds the
criterion for density at maximum gyrations (98.0 versus a requirement of < 98.0 %). Trial gradation #3 meets the
requirements for density and VMA and in this example is selected as the design aggregate structure.
Volumetric Property
Criteria
4.4
4.4
4.4
%Gmminitial (trial)
88.1
88.8
87.1
%Gmmdesign (trial)
95.9
95.3
94.7
Va at Ndesign
4.1
4.7
5.3
VMAtrial
12.9
13.4
13.9
4.0
-0.1
-0.7
-1.3
Pb
0.0
0.3
0.5
VMA
0.0
-0.1
-0.3
4.4
4.7
4.9
VMA (design)
12.9
13.3
13.6
%Gmminitial (design)
88.2
89.5
88.4
> 13.0
ESALs
Criteria,
%Gmm
<0.3 x 106
<91.5
0.3 - 3 x 10
<90.5
> 3 x 106
< 89.0
Notes:
The top portion of this table presents measured compaction densities and volumetric properties for specimens prepared for each trial aggregate
gradation at the initial trial asphalt content.
None of the specimens had an air void content of exactly 4.0 percent. Therefore, the procedures described in Section 9 must be applied to: 1)
estimate the design asphalt content at which Va = 4.0 percent, and 2) obtain adjusted VMA and density values at this estimated asphalt content.
The middle portion of this table presents the change in asphalt content (
content (Va) is adjusted to 4.0 percent for each trial aggregate gradation.
A comparison of the VMA and densities at the estimated design asphalt content to the criteria in the last column shows that trial gradation #1
does not have sufficient VMA (12.9% versus a requirement of 13.0%). Trial gradation #2 exceeds the criterion for density at Ninitial
gyrations (89.5 versus a requirement of < 89.0 %). Trial gradation #3 meets the requirements for density and VMA and, in this example, is
selected as the design aggregate structure.
For Hot Mix, USA, the estimated, 20-year, design traffic is 6,300,000 ESALs. The traffic level falls in the 3 to less than 30 million
ESAL range. The project is a State route, which falls in the typical roadway application defined in the current 99 table above. Such
that, from the table the initial, design, and maximum number of gyrations are 8, 100, and 160, respectively. The following table
summarizes the volumetric criteria for the project:
Volumetric Property
N ini
%Gmm at Nini
N ini
%Gmm at Ndesign
N max
%Gmm at Nmax
Volumetric Criteria
8 gyrations
89 %
100 gyrations
= 96 % (4% air voids)
160 gyrations
98 %
13.0 minimum
65 - 75 percent
Dust-to-Binder Ratio
0.6 - 1.2
For the evaluation of the trial blends, specimens are compacted to the design number of gyrations, with the specimen height collected
during the compaction process. Since the specimen mass and cross section are constant throughout compaction, the density can be
continually calculated based on the height.
After compaction is complete, the specimen is extruded and the bulk specific gravity is determined (Gmb ) by AASHTO T 166. The
Gmm of each blend is also determined by AASHTO T-209. From this, the design percent of maximum theoretical specific gravity
(%Gmm des) can be calculated. Such that, from the compaction height data (hx ), the %Gmm per gyration can be determined as follows:
Initial:
% Gmm
95
90
85
80
10
20
50
100
Log(Number of Gyrations)
200
500
1,000
For each option blend, three gyratory specimens are compacted (AASHTO TP 4) in the Superpave gyratory compactor to Ndes and two
maximum theoretical specific gravities are determined (AASHTO T 209) (Gmm ). The gyratory specimens are extruded from the
molds and bulk specific gravities are determined (Gmb ).
Specimen 1:
Gmb
= 2.351
Specimen 2:
Gmb
= 2.348
Specimen 3:
Gmb
= 2.353
The percent of maximum theoretical specific gravity at Ndes (% Gmm des) is calculated as follows:
Q.
Specimen 2:
Specimen 3:
Trial Blend
Height
Height
Height
No. 1
Nini=8
Ndes=100
Nmax=160
Specimen 1
129.6 mm
117.4 mm
Specimen 2
129.8 mm
117.4 mm
Specimen 3
129.9 mm
117.8 mm
%Gmm des
95.0 %
n/a
94.9 %
95.1 %
As stated above, the initial %Gmm is calculated based on the height ratios multiplied by the design %Gmm. Such that:
Specimen 1:
Q.
Specimen 2:
%Gmm ini
Specimen 3:
%Gmm ini
%Gmm ini
%Gmm des
%Gmm max
Nini=8
Ndes=100
Nmax=160
86.1 %
95.0 %
__._ %
94.9 %
__._ %
95.1 %
n/a
Graph the results on the Superpave Gyratory Compaction Chart provided (See next page).
% of Gmm
93
92
91
90
89
88
87
86
85
84
83
82
81
80
1
10
20
50
Log(Number of Gyrations)
100
200
500
1,000
%Gmm ini
%Gmm des
%Gmm max
Nini=8
Ndes=100
Nmax=160
86.1 %
95.0 %
85.9 %
94.9 %
86.3 %
95.1 %
Specimen
n/a
% Gmm
100
Specimen 1
Specimen 2
Specimen 3
N initial
N design
90
80
1
10
100
Log(Nummber of Gyrations)
Q.
For a design target of 4.0 % voids in total mix at Ndes , is the asphalt binder content high
or low?
Big Q.
Should asphalt binder content be the main criteria for mixture design, Y or N?
Nini - "Tenderness Check" Nini represents the mix during construction. Mixes that
compact too quickly in the gyratory may have tenderness problems during construction.
Ndesign - "Volumetric Check" Ndesign represents the mix after construction and trafficking.
Mix volumetrics, (Va , VMA, VFA), are compared to empirically based criteria.
Nmax - "Rutting Check" Mixes that commonly rut have been compacted below 2 % voids
under traffic. Mixes that compact below 2 % voids in the gyratory may have rutting
problems. (Applied only at the end of design procedure.)
All three trial blends are compacted and the volumetric properties are determined. It is important
to recognize that the trial blends are compacted at an estimated asphalt binder content. Under
Superpave the design (optimum) asphalt binder content provides a mixture with four percent (4.0
%) voids in total mix (VTM or Va ) at the design number of gyrations (Ndesign ); in addition to
satisfying all other criteria. Only one of the trial blends at Ndesign yielded four percent (4.0 %) Va
. All this means is that the estimated trial asphalt contents were not exact. This will almost
always be the case.
Trial
Blend
% AC
%Gmm ini
%Gmm des
Va
VMA
Nini = 8
Ndes = 100
Ndes = 100
Ndes = 100
5.0
86.1
95.0
5.0
14.0
5.0
86.5
96.0
4.0
13.0
5.0
89.6
95.5
4.5
13.5
% Gmm
100
Trial Blend 1
Trial Blend 2
Trial Blend 3
N initial
N design
90
80
1
10
Log(Nummber of Gyrations)
100
Superpave provides a procedure for adjusting the volumetric results to reflect a four percent (4.0
%) void content at Ndes . Upon completing the adjustments, the trial blends are then
analyzed based on the established criteria.
The aggregate gradation governs the slope of the gyratory compaction curve (rate of compaction). In looking at the
above compaction curves, it can be seen that the three trial blends produce different compaction rates. Because of
this relationship, the blends' properties can be estimated.
1)
2)
C = 0.2
3)
Estimated voids filled with asphalt (VFA) at Ndes, at 4.0 % Va, VFAest
4)
Trial Blend No. 1; Est %Gmm ini = 86.1 - (4.0 - 5.0) = 87.1 %
5)
Trial Blend No. 1; Est %Gmm max = 96.1 - (4.0 - 5.0) = 97.1 %
6)
Note:
The F / Pbe ratio under Superpave is based on the effective asphalt binder content, not the total. This is
sometimes referred to as the dust proportion.
VMA
VFA
F / Pbe
%Gmm ini
Pb
at Ndes
at Ndes
Ratio
No. 1
5.4 %
13.8 %
71 %
0.82
87.1 %
No. 2
5.0 %
13.0 %
69 %
0.81
86.5 %
No. 3
5.2 %
13.4 %
70 %
1.15
90.1 %
Criteria
n/a
13.0 %
65 - 75 %
0.6 - 1.2
89.0 %
minimum
range
range
maximum
Selecting the Design aggregate structure is the most difficult step. The estimated trial blends'
properties are evaluated against the criteria:
However: VMA just meets the minimum requirement and the %Gmm max is just
under the maximum criterion - during production it may be difficult to stay within
the compaction criteria.
Select
Trial Blend
Number 1!
Q.
What if all three initial Trial Blends meet the design requirements. How would the
Design Aggregate Structure be selected?
A.$
Economics $
SELECTION OF THE
Once the design aggregate structure is selected, Trial Blend No. 1 in this case, specimens are
compacted at varying asphalt binder contents. The mixture properties are then evaluated to
determine a design asphalt binder content. Superpave requires a minimum of two specimens
compacted at each of the following asphalt contents, (FHWA recommends three specimens
compacted at each asphalt binder content):
For Trial Blend No. 1, the asphalt binder contents for the mix design are 4.9%, 5.4%, 5.9%, and
6.4%. Two specimens are also prepared at each asphalt binder content for determination of
maximum theoretical specific gravities (Gmm ).
Batch Asphalt
Superpave Gyratory
Rice, Gmm
Binder Content
Compactor
(T 209)
5.4% Target*
3 Specimens
2 Tests
5.9%(+%)
3 Specimens
2 Tests
6.4%(+1%)
3 Specimens
2 Tests
4.9%(-%)
Total (73,600
57,600 g
16,000 g
g)
Lead States
Based upon the recommendations of NCHRP 9-9,
compact the design aggregate blend only to Ndes .
Authors Note
Based on the calculations, 5.4 % is the estimated optimum asphalt content and should be the
target asphalt content for binder content selection. From a practical standpoint the results
from the design aggregate structure selection can used to reduce the batching of all four binder
contents.
% Gmm
100
6.40%
5.90%
5.40%
4.90%
N initial
N design
90
80
1
10
Log(Nummber of Gyrations)
100
Note: Each compaction curve represents the average of three compacted specimens.
%Gmm ini
%Gmm des
4.9 %
85.8 %
94.8 %
5.4 %
87.1 %
96.0 %
5.9 %
88.3 %
97.3 %
6.4 %
89.6 %
98.5 %
89.0 %
= 96.0 %
Asphalt
Content
Criteria
Va
VMA
VFA
4.9 %
5.2 %
14.2 %
62.7 %
5.4 %
4.0 %
13.5 %
70.4 %
5.9 %
2.7 %
12.8 %
78.1 %
6.4 %
1.5 %
12.2 %
87.7 %
4.0 %
13.0%
65-75
Asphalt
Content
Criteria
Similar to the Marshall mix design procedure, the volumetric properties are plotted versus
asphalt content. This provides a graphical means of determining the design asphalt binder
content (see Figures). The design asphalt binder content is established as 4.0 % air voids (Va )
at Ndes of 100 gyrations. In this simulation, the design asphalt binder content is 5.4 %. All other
mixture properties are checked at the design asphalt binder content to verify that they meet the
criteria. The design values for the 19.0 mm nominal mixture (Trial Blend No. 1) are indicated
below:
Mix Property
Results
Criteria
Va at Ndes
4.0 %
4.0 %
VMA at Ndes
13.5 %
13.0 % Min
VFA at Ndes
70 %
65 - 75 %
F / Pbe Ratio
0.87
0.6 - 1.2
%Gmm ini
86.9 %
89 %
%Gmm max
n/a
98 %
Va
6.0
5.0
15.0
VMA at Ndes
Va at Ndes
VMA
16.0
4.0
3.0
14.0
13.0
12.0
2.0
11.0
1.0
4.5
5.5
4.5
VFA
90.0
1.4
DUST-TO-BINDER
85.0
VFA at Ndes
10.0
6.5
80.0
75.0
70.0
65.0
5.5
F/Pbe
6.5
1.2
1.0
0.8
0.6
60.0
4.5
5.5
Asphalt Binder Content
6.5
0.4
Asphalt Binder Content
The design aggregate structure at the optimum asphalt content is now checked at the maximum
number of gyrations (Nmax ). As stated above, the compacted mixture should retain a minimum
of 2 percent air voids, (maximum of 98 % Gmm ), at Nmax. For this project the following is
determined:
If the mix failed to meet the criterion, this indicates that a pavement made of this mix may be
susceptible to rutting. The aggregate gradation should be adjusted accordingly. Different
stockpile material may be required.
_ EVALUATION OF
MOISTURE SENSITIVITY AASHTO T-283
The final step in the volumetric mix design process is to evaluate the moisture sensitivity of the
design mixture. This step is accomplished by performing AASHTO T 283 on the design
aggregate blend at the design asphalt binder content. Specimens are compacted to approximately
7.0% (1.0%) air voids. One subset of three specimens is considered the control/unconditioned
subset. The other subset of three specimens is the conditioned subset. The conditioned subset is
subjected to partial vacuum saturation followed by an optional freeze cycle, followed by a 24
hour heating cycle at 60_C. All specimens are tested to determine their indirect tensile strengths.
The moisture sensitivity is determined as a ratio of the tensile strengths of the conditioned subset
divided by the tensile strengths of the control subset. The table below indicates the moisture
sensitivity data for the mixture at the design asphalt binder content.
Samples
Superpave Gyratory
Indirect Tensile
Compactor
Strength
Un-conditioned
3 Specimens compacted
Specimens (Dry)
to 7 % Va (14,400 g)
Conditioned
3 Specimens compacted
Specimens (Wet)
to 7 % Va (14,400 g)
872 k Pa
721 k Pa
% TSR
82.7 % (Ok)
Superpave Criteria
80.0 % Min
The minimum criteria for tensile strength ratio is 80.0 %. The design blend (82.7 %) meets the
minimum requirement. At this point, Superpave Volumetric Mixture Design is complete.
Authors Note
The criteria for TRS is based on experience gained from analysis 4 inch Marshall specimens.
There is an ongoing debate concerning the use of 150 mm (6 inch) SGC specimens in the
AASHTO T -283 procedure. Most designers are using T-283 with SGC specimens. However,
others are using 4 inch specimens, while others are using the SGC specimens with 100%
saturation, while still others are using other test procedures. The use of AASHTO T-283 is
not required to design a Superpave mix. However, some method of moisture sensitivity
should be employed.
APPENDICES
PROJECT SUMMARY
RAP Guidelines, on CD
Appendix
PROJECT SUMMARY
Each year, millions of tons of asphalt mix are produced and placed on our Nation's
highways. Some of these asphalt mixes, which meet the state highway agencies design
requirements, are still displaying premature pavement distress in the form of stripping,
bleeding, rutting, cracking, and raveling. These distresses lead to poor ride, skid
problems, increased maintenance cost and an accelerated need for rehabilitation. To
address these problem mixes, engineers and contractors are placing additional emphasis
on improved field management of asphalt mixes.
To assure that asphalt mixes will perform as required, various quality control systems are
employed. Historically, monitoring of asphalt and aggregate proportions has been used
to measure and control the quality of the mix. However, mixes produced with the
required asphalt binder content and aggregate gradation have not always performed as
intended. A change occurs in the fundamental make up of mixes from design to
construction. This is because the design mixing bowl does not duplicate what happens in
the contractor's plant. Incorporation of volumetric mix design properties into field
quality control and quality assurance systems can help identify mix-related problems
before tons of material are placed on the roadway. These properties include Voids in
Total Mix (Va ), Voids in Mineral Aggregate (VMA), and Voids Filled with Asphalt
(VFA). When these properties are determined and monitored in the field, on plant
produced mix, engineers have the information necessary to identify problems and make
effective changes to the mix.
To demonstrate the concept of volumetric properties for field quality control and other
innovations, the Federal Highway has developed demonstration project number 90 (DP
90), "Superpave Asphalt Mix Design and Field Management." The project centers
around two (2) fully equipped mobile asphalt laboratories. The laboratories are 14.3
meters by 2.6 meters and weigh approximately seventeen (17) metric tonnes each. For a
simulation study, one of the laboratories is brought onto an active paving project site of
requesting state highway agencies (SHAs). Once set up, the laboratory personnel
perform the latest testing procedures on field-produced mixes in simulation studies.
Also, the latest computer software packages on asphalt mix design and pavement
construction are demonstrated. Additionally, the project personnel provide technical
assistance to SHAs desiring to evaluate equipment and techniques.
Appendix
As part of the latest techniques, the Strategic Highway Research Program (SHRP)
Superpave system is demonstrated in the mobile laboratories. The asphalt portion of
SHRP was a $ 50 million dollar, 5 year effort to develop new performance related tests
and specifications for asphalt binders and mixtures. Pieces of the SHRP asphalt test
equipment that are adaptable to field use are integrated into the field management
concept. These include Superpave computer software, Superpave gyratory compactor,
rotational viscometer, dynamic shear rheometer (DSR), and the modified Maximum
Specific Gravity (Rice) test.
Module I -
Module II -
Module III -
Workshop Activities
STANDARD TESTS
Aggregates:
AASHTO T 2
Sampling Aggregates
AASHTO T 11
AASHTO T 27
Appendix
AASHTO T 30
AASHTO T 84
AASHTO T 85
AASHTO T 176 Plastic Fines in Graded Aggregates and Soils by Use of the Sand
Equivalent Test
AASHTO T 248 Reducing Field Samples of Aggregate to Testing Size
AASHTO TP 33 Uncompacted Void Content of Fine Aggregate
(Fine Aggregate Angularity)
ASTM D 5861
Asphalt Binder:
AASHTO T 40
AASHTO T 49
Asphalt Mixes:
Appendix
AASHTO T 168 Sampling Bituminous Paving Mixtures
AASHTO T 195 Determining Degree of Particle Coating of Bituminous-Aggregate
Mixtures
AASHTO T 164 Quantitative Extraction of Bitumen from Bituminous Paving Mixtures,
Methods A and E, Centrifuge and Vacuum Extraction
AASHTO T 209 Maximum Specific Gravity of Bituminous Paving Mixtures, Rice
Method (ASTM D 2041) with Supplemental Dry-Back Procedure
AASHTO T 245 Resistance to Plastic Flow of Bituminous Mixtures Using Marshall
Apparatus (ASTM D 1559)
AASHTO T 269 Percent Air Voids in Compacted Bituminous Paving Mixtures (ASTM
D 3203)
AASHTO T 283 Resistance of Compacted Bituminous Mixture to Moisture Induced
Damage (TSR)
AASHTO TP 4 Determining the Density of Hot Mix Asphalt (HMA) Specimens by
Means of the Superpave Gyratory Compactor
ASTM D 4125
AASHTO PP 2
ASTM D 2950
VA SS 304
Simulation Studies
Appendix
As an integral aspect of the Demonstration Project, the Mobile Asphalt Laboratories perform a
complete regimen of testing over the course of 4-6 weeks at active asphalt mix plants. Two
simulation studies are conducted. Test results and reports are issued to the State Highway
Agency and the contractor upon completion.
Simulations
The series of tests, the sequence, etc., will include plant produced mix samples as well as
stockpile aggregates and asphalt binder samples. Properties such as voids in mineral
aggregate (VMA), voids in total mix (Va ), voids filled with asphalt (VFA), fines to
effective asphalt ratio (F / Pbe ), etc., in conjunction with gradations and extractions,
should give the field personnel adequate data to fully evaluate the properties of mix being
produced and, if necessary, make appropriate adjustments. The goal is to show the SHA
and the contractor how valuable this early, complete set of plant-produced mix design
tests can be in assuring quality mixes.
The Second Simulation calls for the running of Acceptance testing. A combination of
volumetrics and field densities will be used to determine acceptance. The speed and
accuracy in conducting Volumetric property tests have been enhanced by the automation
of the devices. The slowness and the waste product of running extractions are forcing
materials engineers to look for cleaner, safer tests. The use of the nuclear asphalt content
gauge may be able to help reduce the number of extraction tests necessary.
Appendix
Reporting
Quality Level Analysis: Upon completion of the field tests, a statistical analysis of
the test results will be produced, compared with the acceptance factors, documented,
and distributed to the SHA and the contractor.
Module II:Superpave
At the conclusion of the Strategic Highway Research Program (SHRP), the Federal Highway
Administration (FHWA) was given the responsibility of implementing the research findings, one
of which is the Superpave Asphalt Mixture Design and Analysis System. The mobile laboratory
will conduct a Superpave mix design using the materials available at the simulation project site
of the host state. The compactor used for this design procedure is a Superpave Gyratory
Compactor. Proper use, specimen manufacture, and data analysis will be demonstrated.
Module III:Workshop
Activities
A classroom workshop has been developed to bring together engineers and senior lab technicians
for an introduction to the void properties quality control and quality assurance program. The 1
day workshop will address the requirements necessary to institute a successful program. The
field management of asphalt mixes, to be effective, is a blend of design, production, acceptance,
and performance. During the workshops each of the elements is reviewed.
Appendix
Project Leader
(202) 366-0121
Appendix
Variables:
_ = viscosity, in centiStokes
u = Log10(Log10(_))
T = temperature, in Kelvin
t = Log10(T)
m = slope of the line
b = Y axis intercept (Log-Log(Viscosity))
Data: _1 = 379 centiStokes, viscosity at first test temperature T1 = 135_ + 273_ = 408_K
u1 = Log10(Log10(_1 )) = 0.4114
t1 = Log10(T1 ) = 2.611
Calculations:
tx = (ux - b)/m,
Appendix
where ux = Log10(Log10(150, 190, 250, & 310)) = 0.3377, 0.3577, 0.3798, & 0.3964
Tx = 10tx
Mixing:
425.9_K (153_C) to
421.0_K (148_C)