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APPENDIX C
Draft AASHTO Standard for Steady Shear Flow
and Phase Angle Methods
Note: These draft specifications have been modified for the purpose of inclusion in this report.
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Standard Method of Test for
Determining the Laboratory Mixing &
Compaction Temperature of Asphalt
Binder Using a Dynamic Shear
Rheometer (DSR)
Steady Shear Flow Method
AASHTO Designation: X XXX-XX
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Standard Method of Test for
Determining the Laboratory Mixing & Compaction
Temperature of Asphalt Binder Using a Dynamic Shear
Rheometer (DSR)
Steady Shear Flow Method
AASHTO Designation: X XXX-XX
SCOPE
This test method covers the determination of laboratory mixing and compaction
temperatures using a steady shear flow test. The steady shear flow test is
conducted using the Dynamic Shear Rheometer (DSR) utilizing the rheometers
capability to function in constant rotation in one direction.
The values stated in SI units are to be regarded as the standard.
This standard does not purport to address all of the safety concerns, if any, associated
with its use. It is the responsibility of the user of this standard to establish
appropriate safety and health practices and determine the applicability of
regulatory limitations prior to use.
REFERENCED DOCUMENTS
2.1 AASHTO Standards
· M320, PERFORMANCE GRADED ASPHALT BINDER
· T315, DETERMINING THE RHEOLOGICAL PROPERTIES OF
ASPHALT BINDER USING A DYNAMIC SHEAR RHEOMETER (DSR)
2.2. ASTM Standard
· D8, TERMINOLOGY RELATING TO MATERIALS FOR ROADS AND
PAVEMENTS
· D2493,VISCOSITY-TEMPERATURE CHART FOR ASPHALTS
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3. TERMINOLOGY
3.1 Definitions:
3.1.1 Definitions of terms used in this practice may be found in ASTM D8,
determined from common English usage, or combinations of both.
4. SUMMARY OF TEST METHOD
4.1. A sample of unaged asphalt binder is tested in the DSR using the 25-mm plate
geometry with a 0.5-mm gap setting. The sample is tested in flow mode over a
range of shear stresses from 0 to 500 Pa at 3 temperatures (76, 82, 88C).
4.2. After testing is completed, the viscosity values at 500 Pa are plotted versus
temperature on a log-log scale. From the plot, mixing and compaction
temperatures are determined based upon specified viscosity ranges.
5. SIGNIFICANCE AND USE
5.1 This test method is designed to determine the laboratory mixing and compaction
temperatures for modified and unmodified asphalt binders.
6. PROCEDURE
6.1. Sample Preparation The sample for the Steady Shear Flow test is prepared the
same as samples for T 315 using the 25-mm plates with the following exceptions
as noted in 6.1.1. The temperature control will also follow T 315 requirements.
6.1.1 The test gap for the Steady Shear Flow test will be 0.5 mm. An additional
0.025- mm gap will be added before trimming to allow for creation of the bulge.
6.2. Set the DSR software to perform a steady shear flow test from 50 to 500 Pa,
collecting 5 data points for viscosity per log decade.
6.2.1 A 12 second data-sampling period should be used.
6.2.2 Steady state conditions will be met when 3 consecutive viscosity readings vary
less than 2%. A maximum test time for each stress level of 12 minutes should
be set to ensure that tests won't last interminably.
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6.3. After testing is completed, increase temperature by 6°C and repeat steps 6.1 6.3
until the number of desired test temperatures has been reached.
7. HAZARDS
7.1. Use standard laboratory safety procedures in handling the hot asphalt
binder when preparing specimens for this test method.
8. CALCULATION
8.1. Using the results obtained in Section 6, create a log-log plot of Viscosity (Pa-S) at
500 Pa versus Temperature (°C). Information on the construction of viscosity
temperature charts can be found in ASTM D2493.
8.2. Construct a line through the 3 data points on the plot created in section
8.1. Extend the line as necessary to cross mixing and compaction target
viscosity ranges.
8.3. Using target ranges of 0.15 to 0.19 Pa-S for mixing and 0.32 0.38 Pa-S
for compaction, determine the mixing and compaction temperature ranges
either visually or using a computer graphing program.
9. REPORT
9.1 Report the following information:
9.1.1 Sample identification;
9.1.2. Test Temperatures, nearest 0.1 °C;
9.1.3. Viscosity at 500 Pa for each test temperature, cP;
9.1.4. Mixing temperature range, nearest °C;
9.1.5. Compaction temperature range, nearest °C;
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10. PRECISION AND BIAS
10.1. Precision The research required to develop precision estimates has not
been conducted.
10.2. Bias The research required to establish the bias has not been
conducted.
11. KEYWORDS
11.1. Steady Shear Flow; laboratory mixing temperature; laboratory compaction
temperature, Dynamic Shear Rheometer (DSR); modified asphalt binder, target
viscosity range.
APPENDIX
X.1. SAMPLE CALCULATIONS
X1.1. Table X1.1 shows a set of test results at 3 temperatures:
Table X1.1 Steady Shear Flow Test Results
Test Temperature, °C Viscosity at 500 Pa, Pa-S
76.0 34.1
82.0 18.8
88.0 10.7
X.1.2. Figure X1.1 shows the data in Table X1.1 plotted on a log-log
Temperature - Viscosity chart:
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500
100
10
Viscosity, Pa-s
1 Compaction Range
0.1 Mixing Range
52 58 64 70 76 82 88 100 120 135 150 165 180 200
Temperature, C
Figure X1.1 Test Data Plot Showing Viscosity at 500 Pa and 3 Test
Temperatures
X.1.3 Using a compaction temperature range of 0.32 0.38 Pa-S, the laboratory
compaction temperature of this asphalt binder will be 137 140°C.
X.1.4. Using a mixing temperature range of 0.15 0.19 Pa-S, the laboratory
mixing temperature of this asphalt binder will be 152 157°C.
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Standard Method of Test for
Determining the Laboratory
Mixing & Compaction
Temperature of Asphalt Binder
Using a Dynamic Shear
Rheometer (DSR).
The Phase Angle Method.
AASHTO Designation: X XXX-XX
American Association of State Highway and Transportation Officials
444 North Capitol Street N.W., Suite 249
Washington, D.C. 20001
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Standard Method of Test for
Determining the Laboratory Mixing &
Compaction Temperature of Asphalt Binder
Using a Dynamic Shear Rheometer (DSR)
The Phase Angle Method
AASHTO Designation: X XXX-XX
________________________________________________
SCOPE
This test method covers the determination of the dynamic shear modulus and phase
angle of asphalt binder when tested in dynamic (oscillatory) shear using
parallel plate test geometry. It is applicable to asphalt binders having
dynamic shear modulus values in the range from 50 Pa to 10 MPa. This
range in modulus is typically obtained between 40°C and 150°C at an
angular frequency of 0.1 to 100 rad/s. This test method is intended for
determining the linear viscoelastic properties of asphalt binders over a range
of both frequency & temperature in order to determine a reasonable master
curve of the visco-elastic properties of asphalt binder. This master curve will
be used to determine the appropriate laboratory mixing & compaction
temperatures.
This standard is appropriate for unaged material or material aged in accordance
with T 240
and R 28.
Particulate material in the asphalt binder is limited to particles with longest
dimensions less
than 250µm.
This standard may involve hazardous materials, operations, and equipment. This
standard does not purport to address all of the safety problems associated with
its use. It is the responsibility of the user of this procedure to establish
appropriate safety and health practices and to determine the applicability of
regulatory limitations prior to use.
____________________________________________________________________
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REFERENCED DOCUMENTS
AASHTO Standards:
· M 320, Performance-Graded Asphalt Binder
· R 28, Accelerated Aging of Asphalt Binder Using a Pressurized Aging
Vessel (PAV)
· R 29, Grading or Verifying the Performance Grade of an Asphalt
Binder
· T 40, Sampling Bituminous Materials
· T 240, Effect of Heat and Air on a Moving Film of Asphalt (Rolling
Thin-Film Oven Test)
ASTM Standards:
· C 670, Practice for Preparing Precision and Bias Statements for Test
Methods for Construction Materials
· E 1, Specification for ASTM Thermometers
· E 77, Standard Test Method for Inspection and Verification of
Thermometers
· E 563, Standard Practice for Preparation and Use of an Ice-Point Bath
as a Reference Temperature
· E 644, Standard Test Methods for Testing Industrial Resistance
Thermometers
· D 2170, Standard Test Method for Kinematic Viscosity of Asphalts
(Bitumens)
· D 2171, Standard Test Method for Viscosity of Asphalts by Vacuum
Capillary Viscometer
Deutsche Industrie Norm (DIN) Standards:
· 43760, Standard for Calibrations of Thermocouples
National Cooperative Highway Research Program Report:
·
NCHRP Report xxx, Procedure for Determining Mixing and
Compaction Temperatures of Asphalt Binders in Hot Mix
Asphalt
_______________________________________________________________________
TERMINOLOGY
Definitions:
asphalt binder--an asphalt-based cement that is produced from petroleum residue either
with or without the addition of non-particulate organic modifiers.
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Descriptions of Terms Specific to This Standard:
annealing--heating the binder until it is sufficiently fluid to remove the effects of steric
hardening.
complex shear modulus (G*)--ratio calculated by dividing the absolute value of the
peak-to-peak shear stress, , by the absolute value of the peak-to-peak shear
strain, .
calibration--process of checking the accuracy and precision of a device using NIST-
traceable standards and making adjustments to the device where necessary to
correct its operation or precision and accuracy.
dummy test specimen--a specimen formed between the dynamic shear rheometer (DSR)
test plates from asphalt binder or other polymer to measure the temperature of
the asphalt binder held between the plates. The dummy test specimen is used
solely to determine temperature corrections.
loading cycle--a unit cycle of time for which the test sample is loaded at a selected
frequency and stress or strain level.
phase angle ()--the angle in radians between a sinusoidally applied strain and the
resultant sinusoidal stress in a controlled-strain testing mode, or between the
applied stress and the resultant strain in a controlled-stress testing mode.
loss shear modulus (G´´)--the complex shear modulus multiplied by the sine of the phase
angle expressed in degrees. It represents the component of the complex modulus
that is a measure of the energy lost (dissipated during a loading cycle).
storage shear modulus (G´)--the complex shear modulus multiplied by the cosine of the
phase angle expressed in degrees. It represents the in-phase component of the
complex modulus that is a measure of the energy stored during a loading cycle.
parallel plate geometry--refers to a testing geometry in which the test sample is
sandwiched between two relatively rigid parallel plates and subjected to
oscillatory shear.
oscillatory shear--refers to a type of loading in which a shear stress or shear strain is
applied to a test sample in an oscillatory manner such that the shear stress or
strain varies in amplitude about zero in a sinusoidal manner.
linear viscoelastic--within the context of this specification refers to a region of behavior
in which the dynamic shear modulus is independent of shear stress or strain.
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X11. DETERMINATION OF TIME TO THERMAL
EQUILIBRIUM
X11.1.1 Reason for Determining Time Required to Obtain Thermal Equilibrium:
X11.1.2 After the test specimen has been mounted in the DSR, it takes some time for the asphalt
binder between the test plates to reach thermal equilibrium. Because of thermal gradients
within the test plates and test specimen, it may take longer for the test specimen to come
to thermal equilibrium than the time indicated by the DSR thermometer. Therefore, it is
necessary to experimentally determine the time required for the test specimen to reach
thermal equilibrium.
X11.1.3. The time required to obtain thermal equilibrium varies for different
rheometers. Factors that affect the time required for thermal equilibrium
include:
X11.1.4. Design of the rheometer and whether air or liquid is used as a heating-cooling medium;
water has roughly 25 times more thermal conductivity to that of air. Air conductivity is
improved by increasing the velocity of air flow.
X11.1.5. Difference between ambient temperature and the test temperature,
different when testing below room temperature, and above room
temperature,
X11.1.6. Difference in temperature between the trimming and test temperature, and
X11.1.7. Plate size, different for the 8-mm and 25-mm plate.
X11.2. It is not possible to specify a single time as the time required to obtain thermal
equilibrium. For example, thermal equilibrium of the asphalt sample is reached much
quicker with liquid-controlled rheometers than with air-cooled rheometer. This requires
that the time to thermal equilibrium be established for individual rheometers, typical
trimming and testing temperatures, and testing conditions.
________________________________________________________________________
X12. METHOD TO DETERMINE THE TIME REQUIRED TO
OBTAIN THERMAL EQUILIBRIUM FOR BOTH THE
DSR & THE SAMPLE
X12.1.1. The time to reach thermal equilibrium is the time required to reach a constant modulus
regardless of heating to that temperature or cooling down to that temperature. Typically,
this time will be greater than the time for the DSR reports on its display reading for
temperature to be stable. The asphalt sample heats and cools much slower then the
response of the environmental chamber. Thus, it is important to determine the precise
time required for a DSR to achieve thermal equilibrium for the asphalt sample.
X12.2. As a guide, safe values which can be used with most modern are as follows. Rheometers
using a total fluid immersion principle of the sample in water will require a minimum of
3 minutes from the time the chamber stabilizes within ±0.1°C. A forced gas oven will
require a minimum of 60 minutes from the time the chamber stabilizes within ±0.1°C.
Refer to the manufacturer for specific help to determine the required time to stabilize the
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sample for accurate asphalt measurements for specific DSR model. Dry directly heated
plates or oven chambers employing radiant heating or not pre-conditioned gas may take
significantly longer then 60 minutes to achieve thermal equilibrium on the asphalt sample
with acceptable thermal gradients.
X12.3. The following procedure can be used to determine the appropriate time
required to achieve sample thermal equilibrium for a specific DSR.
X12.3.1 A reliable estimate of the time required for thermal equilibrium can be obtained by
monitoring the DSR temperature and the complex modulus of a sample mounted between
the test plates. Because the modulus is highly sensitive to temperature, it is an excellent
indicator of thermal equilibrium. The following procedure is recommended for
establishing the time to thermal equilibrium:
X12.3.2. Mount a binder sample in the DSR and trim in the usual manner. Create a
bulge and bring the test chamber or fluid to the test temperature.
X12.3.3. Operate the DSR in a continuous mode at 10 rad/s using an unmodified asphalt binder
sample--one that does not change modulus with repeated shearing. If testing at grade
temperature use 10% strain. If testing at other then grade temperature, use the smallest
strain value that gives good measurement resolution.
X12.3.4. Perform a series of temperature steps, each held for at least 2000 seconds, while
recording the modulus at 30 s time intervals. These steps should approach the nominal
temperature from heating and cooling in order to identify any thermal hysteresis within
the sample. Results should be displayed on a plot of the modulus versus time (Figure
X12.1). As the example in Figure X12.1, the temperature profile was 70°C, 76°C, 70°C,
64°C, 70°C, 76°C, 70°C. Results as shown in Figure X12.1. can be graphed as an
overlay of G* to permit the comparison of the 70°C results of modulus as shown in
(Figure X12.2). Where the G* data for 70°C overlay defines the instrument's time to
reach thermal equilibrium. In this example, the time to thermal equilibrium is reported as
0.6k seconds (600 seconds).
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Figure X12.1--Results of the test to determine a DSR's temperature performance
Figure X12.2--Comparison of Modulus at 70C; Thermal equilibrium reached where the center G* values
agree (at about 500sec in this example)
X12.3.5. By approaching the nominal temperature from both heating and cooling, enables the
identification of actual Thermal Equilibrium from the effects of apparent thermal
hysterisis. Thermal hysteresis is the effect of the inefficient thermal conductivity of the
environmental chamber in which the sample core or sample edge contains greater then
the required ±0.1°C thermal gradient over the time permitted to achieve thermal
equilibrium The appearance of thermal equilibrium may be mistaken for the slow
response of the asphalt to change temperature as asphalt is a poor thermal conductor.
This effect is obvious in Figure X12.3. Given longer time to achieve thermal
equilibrium the amount of thermal hysteresis should reduce.
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Figure X12.3--Identifying Thermal Hysteresis; G* does not recover post.
X12.3.6. Once the DSR's time to thermal equilibrium has been identified, a small
buffer time of 2 minutes should be added as a conditioning period to the
testing programmed time for equilibrium. From the example of Figure
X12.3., where the DSR's time to thermal equilibrium is 600 seconds (DSR
TE), and the additional conditioning buffer of 120 seconds gives the total
time to use for testing as 720 seconds. Testing thermal equilibrium
(Sample TE would be 720 seconds (12min), as shown in (Figure X12.4.).
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Figure X12.4--Identifying the Sample time for Thermal Equilibrium
X12.4. Because the time required to reach thermal equilibrium can vary with the test temperature
and testing conditions, the time to thermal equilibrium should be established separately
for any new testing protocol. Once the time to thermal equilibrium has been established,
it does not have to be repeated unless the test conditions change.
________________________________________________________________________
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X13. EXAMPLE OF FREQUENCY SWEEP ISOTHERMS
X13.1 Graph of G* and phase angle for each of the individual frequency sweeps at each
temperature on a single graph (Figure X13.1)
Figure X13.1-Graph of frequency sweeps for each temperature.
X14. EXAMPLE OF MASTER CURVE AT 80°C AND
DETERMINATION OF FREQUENCY WHERE THE PHASE
ANGLE IS EQUAL TO 86 DEGREES.
X14.1. Display of Isotherms (Figure X14.1) The example in Figure X14.1 shows 4 sets of
isotherms for an asphalt binder.
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Figure X14.1- Graph of Isotherms.
X14.2. Performing the Time Temperature Superposition model to the data using a reference
temperature of 80°C would produce the master curve shown in Figure X14.2.
Figure X14.2.- Master Curve created to an 80°C reference from isotherms.
X14.3. From the master curve, identify the phase angle of 86 degrees and determine the
frequency at which it occurs (Figure X14.3). Most modern DSRs provide features within
their software in which enables the operator the ability to identify specific points from the
graph or table. In the event the exact value is not provided, interpolate between the two
nearest points bracketing the 86 degree value. The exactness required for the reporting of
frequency in this process is ±10%. Small errors in reporting have little to no effect on the
final determination of both mixing & compaction temperature.
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Figure X14.3- Determination of Frequency at a phase angle of 86 degrees from the master curve
_______________________________________________________________________
X15. VERIFICATION OF MASTER CURVE WORKING DATA BY
USING BLACK SPACE DIAGRAM
X15.1 A good example of a Black Space diagram where there is shown a continuous curve
exhibited in the results (Figure X15.1). This is where there are not obvious
discontinuities.
FIGURE X15.1- Good example of Black Space diagram
X15.2. A poor example of a Black Space diagram, where there are obvious discontinuities in the
results (Figure X15.2). In the case of a poor Black Space, the data should be retested
with particular attention to ensuring all the data are collected in the linear visco-elastic
region by ensuring the correct strains are applied properly to all frequencies and that the
temperatures are correct for each frequency tested. (Figure X15.2)
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FIGURE X15.2- Poor example of Black Space diagram
X16. DETERMINATION OF LABORATORY MIXING
TEMPERATURE
X16.1. Use the following equation to determine laboratory compaction
temperature in ºF.
Mixing Temperature (ºF) = 325-0.0135 (X16)
Where = the frequency in rad/s for the phase angle of 86 degrees as reported from the
master curve. 12.2.4
________________________________________________________________________
X17. DETERMINATION OF LABORATORY COMPACTION
TEMPERATURE
X17.1. Use the following equation to determine laboratory compaction
temperature in ºF.
Compaction Temperature (ºF) = 300-0.012 (X17)
Where = the frequency in rad/s for the phase angle of 86 degrees as
reported from the master curve. 12.2.4
________________________________________________________________________
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X18. SAMPLE REPORT
Header Information:
Item Data Group 1 Item Data Group 2
Operator's Name: 24 Alpha-Numeric Date of Test (dd/mm/yy): __/__/__
18 Alpha Time of Test (hr:min): __:__
Test Specimen ID No.:
DSR Manufacturer: 12 Alpha-Numeric
Project ID No.: 12 Alpha-Numeric
File Name: 12 Alpha-Numeric DSR Model: 12 Alpha-Numeric
DSR Serial Number Or
Sample Grade: 18 Alpha-Numeric
12 Alpha-Numeric Other Identifying ID No.:
Frequency, rad/s for
Phase Angle of 86
0.000 Software Version: 12 Alpha-Numeric
degrees
at a temperature of 80°C
Mix Temperature, °F 000
Compaction
000
Temperature, F
________________________________________________________________________
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X19. REFERENCES
X19.1. Anderson, D. A. and M. Marasteanu. "Manual of Practice for Testing
Asphalt Binders in Accordance with the Superpave PG Grading System."
The Pennsylvania Transportation Institute, The Pennsylvania State
University, PTI 2K07, November 1999 (Revised February 2002).
X19.2. Wadsworth, H., ed. Handbook of Statistical Methods for Engineers and
Scientists. McGraw-Hill, New York, NY, 1990.
X19.3. Anderson, D. A., C. E. Antle, K. Knechtel, and Y. Liu. Interlaboratory
Test Program to Determine the Inter- and Intra-Laboratory Variability of
the SHRP Asphalt Binder Tests. FHWA, 1997.
X19.4. Cox, W. P. and E. H. Merz. Correlation of Dynamic and Steady Flow
Viscosities, Journal of Polymer Science, Volume 28, 1958, pp. 619622.
X19.5. West, R. Procedure for Determining Mixing and Compaction
Temperatures of Asphalt Binders in Hot Mix Asphalt, NCHRP Report
XXX, 2008.
