AASHTO T315-12 Standard Method of Test For Determining The Rheological Properties of Asphalt Binder Using A Dynamic Shear Rheometer (DSR) - Light

13/2/2015 Standard Method of Test for Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR)
Standard Method of Test for Determining the Rheological Properties of
Asphalt Binder Using a Dynamic Shear Rheometer (DSR)
AASHTO Designation: T 315121
1. SCOPE
1.1. 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 100 Pa to 10 MPa. This range in modulus is
typically obtained between 6 and 88°C at an angular frequency of 10 rad/s. This test method is intended for
determining the linear viscoelastic properties of asphalt binders as required for specification testing and is not
intended as a comprehensive procedure for the full characterization of the viscoelastic properties of asphalt
binder.
1.2. This standard is appropriate for unaged material or material aged in accordance with T 240 and R 28.
1.3. Particulate material in the asphalt binder is limited to particles with longest dimensions less than 250 μm.
1.4. This standard may involve hazardous materials, operations, and equipment. This standard does not purport to
address all of the safety concerns 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.
2. REFERENCED DOCUMENTS
2.1. AASHTO Standards:
M 320, PerformanceGraded Asphalt Binder
R 28, Accelerated Aging of Asphalt Binder Using a Pressurized Aging Vessel (PAV)
R 29, Grading or Verifying the Performance Grade (PG) of an Asphalt Binder
T 40, Sampling Bituminous Materials
T 240, Effect of Heat and Air on a Moving Film of Asphalt Binder (Rolling ThinFilm Oven Test)
T 314, Determining the Fracture Properties of Asphalt Binder in Direct Tension (DT)
2.2. ASTM Standards:
C 670, Standard Practice for Preparing Precision and Bias Statements for Test Methods for Construction
Materials
D 2170/D 2170M, Standard Test Method for Kinematic Viscosity of Asphalts (Bitumens)
D 2171/D 2171M, Standard Test Method for Viscosity of Asphalts by Vacuum Capillary Viscometer
E 1, Standard Specification for ASTM LiquidinGlass Thermometers
E 77, Standard Test Method for Inspection and Verification of Thermometers
E 563, Standard Practice for Preparation and Use of an IcePoint Bath as a Reference Temperature
E 644, Standard Test Methods for Testing Industrial Resistance Thermometers
2.3. Deutsche Industrie Norm (DIN) Standard:
43760, Industrial Platinum Resistance Thermometers and Platinum Temperature Sensors
3. TERMINOLOGY
3.1. Definitions:
http://hm.digital.transportation.org/HM/34/HM34/Part_II_Tests/Bituminous_Materials/t_024.aspx#t_0241?mode=print 1/33
3.1.1. asphalt binder—an asphaltbased cement that is produced from petroleum residue either with or without the
addition of nonparticulate organic modifiers.
3.2. Descriptions of Terms Specific to This Standard:
3.2.1. annealing—heating the binder until it is sufficiently fluid to remove the effects of steric hardening.
3.2.2. calibration—process of checking the accuracy and precision of a device using NISTtraceable standards and
making adjustments to the device where necessary to correct its operation or precision and accuracy.
3.2.3. complex shear modulus (G*)—ratio calculated by dividing the absolute value of the peaktopeak shear
stress, τ, by the absolute value of the peaktopeak shear strain, γ.
3.2.4. 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.
3.2.5. 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.
3.2.6. loading cycle—a unit cycle of time for which the test sample is loaded at a selected frequency and stress or
strain level.
3.2.7. 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).
3.2.8. molecular association—a process where associations occur between asphalt binder molecules during storage
at ambient temperature. Often called steric hardening in the asphalt literature, molecular associations can
increase the dynamic shear modulus of asphalt binders. The amount of molecular association is asphalt
specific and may be significant even after a few hours of storage.
3.2.9. 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 by about zero in a sinusoidal
manner.
3.2.10. 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.
3.2.11. phase angle (δ)—the angle in radians between a sinusoidally applied strain and the resultant sinusoidal stress
in a controlledstrain testing mode, or between the applied stress and the resultant strain in a controlled
stress testing mode.
3.2.12. portable thermometer—an electronic device that consists of a temperature detector (probe containing a
thermocouple or resistive element), required electronic circuitry, and readout system.
3.2.13. reference thermometer—a NIST–traceable liquidinglass or electronic thermometer that is used as a
laboratory standard.
3.2.14. steric hardening—see molecular association.
3.2.15. storage shear modulus (G′ )—the complex shear modulus multiplied by the cosine of the phase angle
expressed in degrees. It represents the inphase component of the complex modulus that is a measure of the
energy stored during a loading cycle.
3.2.16. temperature correction—difference in temperature between the temperature indicated by the DSR and the
test specimen as measured by the portable thermometer inserted between the test plates.
3.2.17. thermal equilibrium—is reached when the temperature of the test specimen mounted between the test plates
is constant with time.
3.2.18. verification—process of checking the accuracy of a device or its components against an internal laboratory
standard. It is usually performed within the operating laboratory.
4. SUMMARY OF TEST METHOD
4.1. This standard contains the procedure used to measure the complex shear modulus (G*) and phase angle (δ)
of asphalt binders using a dynamic shear rheometer and parallel plate test geometry.
4.2. The standard is suitable for use when the dynamic shear modulus varies between 100 Pa and 10 MPa. This
range in modulus is typically obtained between 6 and 88°C at an angular frequency of 10 rad/s, dependent
upon the grade, test temperature, and conditioning (aging) of the asphalt binder.
4.3. Test specimens 1 mm thick by 25 mm in diameter or 2 mm thick by 8 mm in diameter are formed between
parallel metal plates. During testing, one of the parallel plates is oscillated with respect to the other at
preselected frequencies and rotational deformation amplitudes (strain control) (or torque amplitudes (stress
control)). The required stress or strain amplitude depends upon the value of the complex shear modulus of
the asphalt binder being tested. The required amplitudes have been selected to ensure that the
measurements are within the region of linear behavior.
4.4. The test specimen is maintained at the test temperature to within ±0.1°C by positive heating and cooling of
the upper and lower plates or by enclosing the upper and lower plates in a thermally controlled environment
or test chamber.
4.5. Oscillatory loading frequencies using this standard can range from 1 to 100 rad/s using a sinusoidal
waveform. Specification testing is performed at a test frequency of 10 rad/s. The complex modulus (G*) and
phase angle (δ) are calculated automatically as part of the operation of the rheometer using proprietary
computer software supplied by the equipment manufacturer.
5. SIGNIFICANCE AND USE
5.1. The test temperature for this test is related to the temperature experienced by the pavement in the
geographical area for which the asphalt binder is intended to be used.
5.2. The complex shear modulus is an indicator of the stiffness or resistance of asphalt binder to deformation
under load. The complex shear modulus and the phase angle define the resistance to shear deformation of
the asphalt binder in the linear viscoelastic region.
5.3. The complex modulus and the phase angle are used to calculate performancerelated criteria in accordance
with M 320.
6. APPARATUS
6.1. Dynamic Shear Rheometer (DSR) Test System—Consisting of parallel metal plates, an environmental
chamber, a loading device, and a control and data acquisition system.
6.1.1. Test Plates—Stainless steel or aluminum plates with smooth ground surfaces. One 8.00 ± 0.02 mm in
diameter and one 25.00 ± 0.05 mm in diameter (Figure 1). The base plate in some rheometers is a flat plate.
A raised portion, a minimum of 1.50 mm high, with the same radius as the upper plate is required. The raised
portion makes it easier to trim the specimen and may improve test repeatability.
Note 1—To obtain correct data, the upper and lower plates should be concentric with each other. At present
there is no suitable procedure for the user to check the concentricity except to visually observe whether or
not the upper and lower plates are centered with respect to each other. The moveable plate should rotate
without any observable horizontal or vertical wobble. This operation may be checked visually or with a dial
gauge held in contact with the edge of the moveable plate while it is being rotated. There are two values that
determine the operating behavior of a measuring system: centricity (horizontal wobble) and runout (vertical
wobble). Typically, wobble can be detected if it is greater than ±0.02 mm. For a new system, a wobble of
±0.01 mm is typical. If the wobble grows to more than ±0.02 mm with use, it is recommended that the
instrument be serviced by the manufacturer.
Figure 1—Plate Dimensions
6.1.2. Environmental Chamber—For controlling the test temperature, by heating or cooling (in steps or ramps), to
maintain a constant specimen environment. The medium for heating and cooling the specimen in the
environmental chamber shall not affect asphalt binder properties. The temperature in the chamber may be
controlled by the circulation of fluid such as water, conditioned gas such as nitrogen, or by a suitable
arrangement of solidstate Peltier elements surrounding the sample. When forced air is used, a suitable drier
must be included to prevent condensation of moisture on the plates and fixtures and, if operating below
freezing temperatures, the formation of ice. The environmental chamber and the temperature controller shall
control the temperature of the specimen, including thermal gradients within the sample, to an accuracy of
±0.1°C. The chamber shall completely enclose the top and the bottom plates to minimize thermal gradients.
Note 2—A circulating bath unit, separate from the DSR, that pumps the bath fluid through the test chamber
may be required if a fluid medium is used. The flow rate of the bath media should not be modified once the
temperature settings have been adjusted to the desired value. Media lines should be periodically inspected
and cleaned or replaced if necessary to remove obstructions
6.1.2.1. Temperature Controller—Capable of maintaining specimen temperatures within ±0.1°C for test temperatures
ranging from 3 to 88°C.
6.1.2.2. Internal Temperature Detector for the DSR—A platinum resistance thermometer (PRT) mounted within the
environmental chamber as an integral part of the DSR and in close proximity to the fixed plate, with a range
of 3 to 88°C, and with a resolution of 0.1°C (see Note 3). This thermometer shall be used to control the
temperature of the test specimen between the plates and shall provide a continuous readout of temperature
during the mounting, conditioning, and testing of the specimen. The PRT shall be calibrated as an integral unit
with its respective meter or electronic circuitry.
Note 3—PTRs meeting DIN Standard 43760 (Class A) or equal are recommended for this purpose.
6.1.3. Loading Device—Capable of applying a sinusoidal oscillatory load to the specimen at a frequency of 10.0 ±
0.1 rad/s. If frequencies other than 10 rad/s are used, the frequency shall be accurate to 1 percent. The
loading device shall be capable of providing either a stresscontrolled or straincontrolled load. If the load is
strain controlled, the loading device shall apply a cyclic torque sufficient to cause an angular rotational strain
accurate to within 100 μ rad of the strain specified. If the load is stress controlled, the loading device shall
apply a cyclic torque accurate to within 10 mN·m of the torque specified. Total system compliance at 100 N·m
of torque shall be less than 2 mrad/N·m. The manufacturer of the device shall certify that the frequency,
stress, and strain are controlled and measured with an accuracy of one percent or less in the range of this
measurement.
6.1.4. Control and Data Acquisition System—Capable of providing a record of temperature, frequency, deflection
angle, and torque. Devices used to measure these quantities shall meet the accuracy requirements specified
in Table 1. In addition, the system shall calculate and record the shear stress, shear strain, complex shear
modulus (G*), and phase angle (δ). The system shall measure and record G*, in the range of 100 Pa to 10
MPa, to an accuracy of 1.0 percent or less, and the phase angle, in the range of 0 to 90 degrees, to an
accuracy of 0.1 degree.
Table 1—Control and Data Acquisition System Requirements
6.2. Specimen Mold (Optional)—The overall dimensions of the silicone rubber mold for forming asphalt binder test
specimens may vary but the thickness shall be greater than 5 mm. If the mold is a single sample mold, the
following dimensions have been found suitable: For a 25mm test plate with a 1mm gap, a mold cavity
approximately 18 mm in diameter and 2.0 mm deep. For an 8mm test plate with a 2mm gap, a mold cavity
approximately 8 mm in diameter and 2.5 mm deep.
6.3. Specimen Trimmer—With a straightedge at least 4 mm wide.
6.4. Wiping Material—Clean cloth, paper towels, cotton swabs, or other suitable material as required for wiping
the plates.
6.5. Cleaning Solvents—Mineral oil, citrusbased solvents, mineral spirits, toluene, or similar solvent as required
for cleaning the plates. Acetone for removing the solvent residue from the surfaces of the plates is also
necessary.
6.6. Reference Thermometer—Either NIST–traceable liquidinglass thermometer(s) or NIST–traceable electronic
thermometric device(s). This temperature standard shall be used to standardize the portable thermometer
(Section 9.3).
6.6.1. LiquidinGlass Thermometer—NISTtraceable thermometer(s) with a suitable range and subdivisions of
0.1°C. The thermometer(s) shall be a partial immersion thermometer(s) within an ice point and standardized
in accordance with ASTM E 563.
6.6.1.1. Optical Viewing Device (Optional)—For use with liquidinglass thermometers that enhances readability and
minimizes parallax when reading the liquidinglass reference thermometer.
6.6.2. Electronic Thermometer—Incorporating a resistive detector (Note 3) with an accuracy of ±0.05°C and a
resolution of 0.01°C. The electronic thermometer shall be standardized at least once per year using a NIST–
traceable reference standard in accordance with ASTM E 77.
6.7. Portable Thermometer—A standardized portable thermometer consisting of a resistive detector, associated
electronic circuitry, and digital readout. The thickness of the detector shall be no greater than 2.0 mm such
that it can be inserted between the test plates. The reference thermometer (see Section 6.6) may be used for
this purpose if its detector fits within the dummy specimen as required by Section 9.4.1 or 9.4.2.
7. HAZARDS
7.1. Standard laboratory caution should be used in handling the hot asphalt binder when preparing test specimens.
8. PREPARATION OF APPARATUS
8.1. Prepare the apparatus for testing in accordance with the manufacturer’s recommendations. Specific
requirements will vary for different DSR models and manufacturers.
8.2. Inspect the surfaces of the test plates and discard any plates with jagged or rounded edges or deep
scratches. Clean any asphalt binder residue from the plates with an organic solvent such as mineral oil,
mineral spirits, a citrusbased solvent, or toluene. Remove any remaining solvent residue by wiping the
surface of the plates with a cotton swab or a soft cloth dampened with acetone. If necessary, use a dry cotton
swab or soft cloth to ensure that no moisture condenses on the plates.
8.3. Mount the cleaned and inspected test plates on the test fixtures and tighten firmly.
8.4. Select the testing temperature according to the grade of the asphalt binder or according to the preselected
testing schedule (see Note 4). Allow the DSR to reach a stabilized temperature within ±0.1°C of the test
temperature.
Note 4—M 320 and R 29 provide guidance on the selection of test temperatures.
8.5. With the test plates at the test temperature or the middle of the expected testing range, establish the zero
gap level (1) by manually spinning the moveable plate, and while the moveable plate is spinning, close the
gap until the removable plate touches the fixed plate (the zero gap is reached when the plate stops spinning
completely), or (2) for rheometers with normal force transducers, by closing the gap and observing the
normal force and after establishing contact between the plates, setting the zero gap at approximately zero
normal force.
Note 5—The frame, detectors, and fixtures in the DSR change dimension with temperature causing the zero
gap to change with changes in temperature. Adjustments in the gap are not necessary when measurements
are made over a limited range of temperatures. The gap should be set at the test temperature or, when tests
are to be conducted over a range of temperatures, the gap should be set at the middle of the expected range
of test temperatures. For most instruments, no gap adjustment is needed as long as the test temperature is
within ±12°C of the temperature at which the gap is set. If the instrument has thermal gap compensation, the
gap may be set at the first test temperature instead of the middle of the range of test temperatures.
8.6. Once the zero gap is established as per Section 8.5, move the plates apart to approximately the test gap and
preheat the plates. Preheating the plates promotes adhesion between the asphalt binder and the plates,
especially at the intermediate grading temperatures.
8.7. To preheat 25mm plates, bring the test plates to the test temperature or the lowest test temperature if
testing is to be conducted at more than one temperature. To preheat 8mm plates, bring the plates to
between 34 and 46°C. Move the plates apart and establish a gap setting of 1.05 mm (for 25mm diameter
test specimens) or 2.10 mm (for 8mm diameter test specimens).
Note 6—In order to obtain adequate adhesion between the asphalt binder and the test plates, the plates
must be preheated. Preheating is especially critical when the silicone mold is used to prepare the asphalt
binder for transfer to the test plates and when the testing is conducted with the 8mm plates. When the direct
placement method is used, as long as the test plates are immediately brought in contact with the asphalt
binder, the heat carried with the asphalt binder improves adhesion. The preheating temperature needed for
proper adhesion will depend on the grade and nature of the asphalt binder and the test temperature (8mm or
25mm plates). For some of the stiffer binder grades, especially those with high levels of modification, heating
the plates to 46°C may not be sufficient to ensure proper adhesion of the asphalt binder to the test plates,
especially if the silicone mold is used and the testing is conducted with 8mm plates. For highly modified
asphalt binders only, higher preheat temperatures may be used.
9. VERIFICATION AND CALIBRATION
9.1. Verify the DSR and its components at least every 6 months and when the DSR or plates are newly installed,
when the DSR is moved to a new location, or when the accuracy of the DSR or any of its components is
suspect. Four items require verification—the test plate diameter, DSR torque transducer, portable
thermometer, and DSR test specimen temperature. Verify the DSR temperature transducer before verifying
the torque transducer.
9.2. Verification of Plate Diameter—Measure the diameters to the nearest 0.01 mm. Maintain a log of the
measured diameters as part of the laboratory quality control program so that the measurements are clearly
identified with the specific plates. Enter the actual measured dimensions into the DSR software for use in
calculations. If the top and bottom plates differ in diameter, enter the smaller of the two measured diameters.
Note 7—An error of ±0.05 mm in the diameter of the plate results in a 0.8 percent error in the complex
modulus for the 25mm plate. For the 8mm plate, errors in diameter of ±0.01, ±0.02, and ±0.05 mm give
respective errors in complex modulus of 0.5, 1.0, and 2.5 percent (see Figure 2).
Figure 2—Effect of Error in Gap or Plate Diameter
9.3. Verification of Portable Thermometer—Verify the portable thermometer (used to measure the temperature
between the test plates), using the laboratory reference thermometer. A portable thermometer shall be
considered the combination of the meter (readout device) and the thermistor (temperature probe) as a single
unit, and must be verified as such. If the reference thermometer (Section 6.6) is also used as a portable
thermometer to measure the temperature between the test plates, it shall meet the requirements of Section
6.7.
9.3.1. Recommended Verification Procedure—Bring the reference thermometer into intimate contact with the
detector from the portable thermometer and place them in a thermostatically controlled and stirred water
bath (Note 8). Ensure that deionized water is used to prevent electrical conduction from occurring between
the electrodes of the resistive temperature sensitive element. If deionized water is not available, encase the
reference thermometer and detector of the portable thermometer in a waterproof plastic bag prior to
placement in the bath. Obtain measurements at intervals of approximately 6°C over the range of test
temperatures allowing the bath to reach thermal equilibrium at each temperature. If the readings of the
portable thermometer and the reference thermometer differ by 0.1°C or more, record the difference at each
temperature as a temperature correction, and maintain the corrections in a log as part of the laboratory
quality control program.
Note 8—A recommended procedure for the hightemperature range is to use a stirred water bath that is
controlled within ±0.1°C such as the viscosity bath used for ASTM D 2170/D 2170M or D 2171/D 2171M. For
a lowtemperature bath, an ice bath or controlledtemperature bath may be used. Bring the probe from the
portable thermometer into contact with the reference thermometer, and hold the assembly in intimate
contact. A rubber band works well for this purpose. Immerse the assembly in the water bath, and bring the
water bath to thermal equilibrium. Record the temperature on each device when thermal equilibrium is
reached.
Note 9—If the readings from the two devices differ by 0.5°C or more, the calibration or operation of the
portable thermometer may be suspect, and it may need to be recalibrated or replaced. A continuing change in
the temperature corrections with time may also make the portable thermometer suspect.
9.4. Test Specimen Temperature Correction—Thermal gradients within the rheometer can cause differences
between the temperature of the test specimen and the temperature indicated by the DSR thermometer (also
used to control the temperature of the DSR). The DSR thermometer shall be checked at an interval no greater
than six months. When these differences are 0.1°C or greater, determine a temperature correction by using a
thermal detector mounted in a silicone rubber wafer (Section 9.4.1) or by placing asphalt binder (dummy
sample) between the plates and inserting the detector of the portable thermometer into the asphalt binder
(Section 9.4.2).
9.4.1. Method Using Silicone Rubber Wafer—For the entire range of test temperatures, place the wafer between the
25mm test plates, and close the gap to bring the wafer into contact with the upper and lower plate so that
the silicone rubber makes complete contact with the surfaces of the upper and lower plates. If needed, apply
a thin layer of petroleum grease or antiseize compound (see Note 10) to completely fill any void space
between the silicone rubber and the plates. Complete contact is needed to ensure proper heat transfer across
the plates and silicone rubber wafer. Determine any needed temperature correction as per Section 9.4.3.
Note 10—Antiseize compound available by that name at hardware and auto supply stores is much less apt
to contaminate the circulating water than petroleum grease.
Note 11—The thickness of the silicone wafer should be measured with calipers to identify the actual
thickness. The thickness can be used to set the gap for temperature.
9.4.2. Method Using Dummy Test Specimen—The dummy test specimen shall be formed from asphalt binder or
other polymer that can be readily formed between the plates. Mount the dummy test specimen between the
test plates, and insert the detector (probe) of the portable thermometer into the dummy test specimen. Close
the gap to the test gap (1 mm for 25mm plates and 2 mm for 8mm plates) keeping the detector centered
vertically and radially in the dummy test specimen. Heat the plates as needed to allow the dummy test
specimen to completely fill the gap between the test plates. It is not necessary to trim the dummy test
specimen but avoid excessive material around the edges of the plates. Determine any needed temperature
correction as per Section 9.4.3.
Note 12—Silly putty can leave a residue of silicone oil on the surfaces of the plates, and for this reason, its
use as a dummy specimen is not recommended.
9.4.3. Determination of Temperature Correction—Obtain simultaneous temperature measurements with the DSR
thermometer and the portable thermometer at 6°C increments to cover the range of test temperatures. At
each temperature increment, after thermal equilibrium has been reached, record the temperature indicated
by the portable thermometer and the DSR thermometer to the nearest 0.1°C. Temperature equilibrium is
reached when the temperature indicated by both the DSR thermometer and the portable thermometer do not
vary by more than 0.1°C over a 5min period. Obtain additional measurements to include the entire
temperature range that will be used for measuring the dynamic shear modulus.
9.4.4. Plot Correction Versus Specimen Temperature—Using the data obtained in Section 9.4, prepare a plot of the
difference between the two temperature measurements versus the temperature measured with the portable
thermometer (Figure 3). This difference is the temperature correction that must be applied to the DSR
temperature controller to obtain the desired temperature in the test specimen between the test plates. Report
the temperature correction at the respective test temperature from the plot and report the test temperature
between the plates as the test temperature. Alternatively, the instrument software may be written to
incorporate these temperature corrections.
Note 13—The difference between the two temperature measurements may not be a constant for a given
rheometer but may vary with differences between the test temperature and the ambient laboratory
temperature as well as with fluctuations in ambient temperature. The difference between the two
temperature measurements is caused in part by thermal gradients in the test specimen and fixtures.
Figure 3—Determination of Temperature Correction
9.5. Verification of DSR—Verify the accuracy of the torque transducer and angular displacement transducer.
Note 14—A newly installed or reconditioned instrument should be verified on a weekly basis using the
procedures in Section 9.5 until acceptable verification has been demonstrated. Maintaining the data in the
form of a control chart where the verification measurements are plotted versus calendar date is
recommended (see Appendix X2).
9.5.1. Verification of Torque Transducer—Verify the calibration of the torque transducer a minimum of once every
six months using a reference fluid or manufacturersupplied fixtures when the calibration of the torque
transducer is suspect or when the dynamic viscosity, as measured for the reference fluid, indicates that the
torque transducer is not in calibration.
9.5.1.1. Verification of Torque Transducer with Reference Fluid—The complex viscosity measured with the DSR shall
be within 3 percent of the capillary viscosity as reported by the manufacturer of the reference fluid;
otherwise, the calibration of the torque transducer shall be considered suspect. Calculate the complex
viscosity as the complex modulus, G*, divided by the angular frequency in rad/s. Recommended practice for
using the reference fluid is given in Appendix X3.
(1)
where:
ηa = the standard capillary viscosity as reported by the supplier of the reference fluid; and
ηb = the measured viscosity as calculated from the complex modulus, G*, divided by the angular
frequency in rad/s.
Note 15—A suitable reference fluid is available from Cannon Instrument Company as Viscosity Standard
Number N2700000SP. The viscosity of the standard is reported in mPa·s. Convert the viscosity measurements
to mPa·s before calculating the percent variance.
9.5.1.2. Verification of Torque Transducer with Fixtures—Verify the calibration of the torque transducer using the
manufacturersupplied fixtures in accordance with the instructions supplied by the manufacturer. Suitable
manufacturersupplied fixtures are not widely available. If suitable fixtures are not available, this requirement
shall be waived.
9.5.2. Verification of Angular Displacement Transducer—If manufacturersupplied fixtures are available, verify the
calibration every six months or when the calibration of the DSR is suspect. If suitable fixtures are not
available, this requirement shall be waived.
9.5.3. If the DSR cannot be successfully verified according to Section 9.5, it shall not be used for testing in
accordance with this standard until it has been successfully calibrated by the manufacturer or other qualified
service personnel.
10. PREPARING SAMPLES AND TEST SPECIMENS
10.1. Preparing Test Samples—If unaged binder is to be tested, obtain test samples according to T 40.
10.1.1. Degassing Prior to Testing—If the asphalt binder is also being tested according to T 314 (DT) and has been
conditioned according to T 240 (RTFO) and R 28 (PAV), degas the asphalt binder as described in R 28 prior to
testing. Otherwise, degassing of the asphalt binder sample is not required.
10.1.2. Anneal the asphalt binder from which the test specimen is obtained by heating until sufficiently fluid to pour
the required specimens. Annealing prior to testing removes reversible molecular associations (steric
hardening) that occur during normal storage at ambient temperature. Avoid heating the binder samples above
a temperature of 163°C; however, with some modified or heavily aged asphalt binders, pouring temperatures
above 163°C may be required. Loosely cover the sample, and stir it occasionally during the heating process
to ensure homogeneity and to remove air bubbles. Minimize the heating temperature and time to avoid
hardening the sample.
Note 16—For neat asphalt binders, minimum pouring temperatures that produce a consistency equivalent to
that of SAE 10W30 motor oil (readily pours but not overly fluid) at room temperature are recommended.
Note 17—For PAV aged samples, asphalt binder may be placed in a vacuum oven set at a maximum of
175°C for 40 min. Due to the poor heat transfer in the vacuum oven, the asphalt binder will not be
overheated.
10.1.3. Cold material from storage containers must be annealed prior to usage. Structure developed during storage
can result in overestimating the modulus by as much as 50 percent.
10.2. Preparing Test Specimens—Zero the gap as specified in Section 8. Carefully clean and dry the surfaces of the
test plates so that the specimen will adhere to both plates uniformly and strongly. Heat the chamber to 34 to
46°C when using the 8mm specimens. Heat the chamber to the test temperature or the beginning of the
range (Note 6) when using 25mm specimens. This requirement is to preheat the upper and lower plates to
allow specimen adhesion to both plates. Prepare a test specimen using one of the methods specified in
Section 10.3.1, 10.3.2, or 10.3.3.
10.3. Transfer asphalt binder to one of the test plates through pouring (Section 10.3.1), direct transfer (Section
10.3.2), or by use of a silicone mold (Section 10.3.3). Use a sufficient amount of asphalt binder so that
trimming is required.
Note 18—Direct transfer and pouring are the preferred methods because the test results are less likely to be
influenced by steric hardening than with the silicone mold method. Direct transfer and direct pouring result in
higher asphalt binder temperatures when the plates and asphalt binder are brought into contact, thereby
improving adhesion. For this reason, it is also important to bring the asphalt binder and plates into contact
promptly after pouring or direct transfer.
10.3.1. Pouring—Only when using rheometers that are designed for removal of the plates without affecting the zero
setting, remove the removable plate and, while holding the sample container approximately 15 mm above the
test plate surface, pour the asphalt binder in the center of the upper test plate continuously until it covers the
entire plate except for an approximate 2mm wide strip at the perimeter (Note 19). Wait only long enough for
the specimen to stiffen, to prevent movement, and then mount the test plate in the rheometer for testing.
Note 19—An eye dropper or syringe may be used to transfer the hot asphalt binder to the plate.
10.3.2. Direct Transfer—Transfer the hot asphalt binder to one of the plates using a glass or metal rod, spatula, or
similar tool. Immediately after transferring the hot asphalt binder to one of the plates, proceed to Section 10.4
to trim the specimen and form the bulge.
Note 20—A small, narrow stainless steel spatula of the type used to weigh powders on an analytical balance
has been found suitable for transferring the asphalt hot binder. When using a rod, form the test specimen with
a twisting motion, using a mass of sufficient size. The twisting motion seems to keep the mass on the rod in
control. A 4 to 5mm diameter rod is suitable. The glass rod technique is especially useful for the 8mm
plate.
10.3.3. Silicone Mold—Pour the hot asphalt binder into a silicone rubber mold that will form a pellet having dimensions
as required in Section 6.2. Allow the silicone rubber mold to cool to room temperature. The molds shall be
covered while cooling to eliminate contamination. The specimen may be mounted to either the upper or lower
plate. To mount the specimen to the lower plate, remove the specimen from the mold and center the pellet on
the lower plate of the DSR. To mount the specimen to the upper plate, center the specimen on the upper plate
while it is still in the silicone rubber mold. Gently press the specimen to the upper plate and then carefully
remove the silicone rubber mold leaving the specimen adhered to the upper plate. Complete all testing within
4 h of pouring the specimen into the silicone rubber mold.
10.3.3.1. The filled mold should be cooled at room temperature by placing the mold on a flat laboratory bench surface
without chilling. Cooling to temperatures below room temperature results in an unknown thermal history that
may affect the measured values of modulus and phase angle. Cooling may also result in the formation of
moisture on the surface of the specimen that will interfere with adhesion of the specimen to the plates.
Note 21—Solvents should not be used to clean the silicone rubber molds. Wipe the molds with a clean cloth
to remove any asphalt binder residue. With use, the molds will become stained from the asphalt binder,
making it difficult to remove the binder from the mold. If sticking becomes a problem, discard the mold.
Note 22—Some binder grades cannot be removed from the silicone mold without cooling. Materials such as
PG 5234, PG 4634, and some PG 5834 grades do not lend themselves to being removed from the mold at
ambient temperatures. If the binder specimen cannot be removed from the mold without cooling, the direct
transfer or pouring method may be used, or the filled mold may be chilled in a freezer or refrigerator for a
maximum of 10 min to facilitate demolding the specimen.
10.4. Trimming Test Specimen—Immediately after the specimen has been placed on one of the test plates as
described above, move the test plates together until the gap between the plates equals the testing gap plus
the gap closure required to create the bulge. (See Section 10.5 for gap closure required to create the bulge.)
Trim excess binder by moving a heated trimming tool around the edges of the plates so that the asphalt
binder is flush with the outer diameter of the plates.
Note 23—The trimming tool should be at a temperature that is sufficiently hot as to allow trimming but not
excessively hot as to burn the edge of the specimen. The trimming tool should also not be excessively cool as
to snag or damage the edge of the test specimen.
Note 24—The gap should be set at the starting test temperature (Section 11.1.1) or at the middle of the
expected range of test temperatures (Section 11.1.2). See Note 5 for guidance on setting the gap. Typically,
reliable test results may be obtained with a single sample using temperatures within 12°C of the temperature
at which the gap is set.
10.5. Creating Bulge—Immediately after the trimming is complete, decrease the gap by the amount required to
form a slight bulge at the outside face of the test specimen. The gap required to create a bulge is rheometer
specific and depends upon factors such as the design of the rheometer and the difference between the
trimming temperature and test temperature. Recommended closure values for creating the gap are 0.05 mm
for the 25mm plate and 0.10 mm for the 8mm plate. A recommended practice for verifying the gap closure
required to produce an appropriate bulge is given in Appendixes X8, X9, and X10.
Note 25—The complex modulus is calculated with the assumption that the specimen diameter is equal to the
plate diameter. If the asphalt binder forms a concave surface at its outer edges, this assumption will not be
valid and the modulus will be underestimated. The calculated modulus is based upon the radius of the plate
raised to the fourth power. A slight bulge equal to approximately onequarter of the gap is recommended. A
procedure for determining the closure required to form an acceptable gap is given in Appendixes X8, X9, and
X10.
11. PROCEDURE
11.1. Bring the specimen to the test temperature ±0.1°C. See Note 4.
Note 26—The gap should be set at the starting test temperature (Section 11.1.1) or at the middle of the
expected range of test temperatures (Section 11.1.2). See Note 5 for guidance on setting the gap. Typically,
reliable test results may be obtained with a single sample, in an 8mm to 25mm plate, using temperatures
within 12°C of the temperature at which the gap is set.
11.1.1. When testing a binder for compliance with M 320, select the test temperature from the appropriate table in M
320.
11.1.2. When conducting a temperature sweep, start at a midrange test temperature and increase or decrease the
test temperature to cover the desired range of test temperatures. (See Sections 6 and 7 in R 29.)
11.2. Set the temperature controller to the desired test temperature, including any offset as required by Section
9.4.4. Allow the temperature indicated by the RTD to come to the desired temperature. The test shall be
started only after the temperature has remained at the desired temperature ±0.1°C for at least 10 min.
Note 27—It is impossible to specify a single equilibration time that is valid for DSRs produced by different
manufacturers. The design (fluid bath or air oven) of the environmental control system and the starting
temperature will dictate the time required to reach the test temperature. The method for determining the
correct thermal equilibrium time is described in Appendix X12.
11.3. Strain Control Mode—When operating in a straincontrolled mode, determine the strain value according to the
value of the complex modulus. Control the strain within 20 percent of the target value calculated by Equation
2.
(2)
where:
γ = shear strain in percent, and
G* = complex modulus in kPa.
11.3.1. When testing specimens for compliance with M 320, select an appropriate strain value from Table 2. Software
is available with the dynamic shear rheometers that will control the strain automatically without control by the
operator.
Table 2—Target Strain Values
11.4. Stress Control Mode—When operating in a stresscontrolled mode, determine the stress level according to the
value of the complex modulus. Control the stress within 20 percent of the target value calculated by Equation
3.
(3)
where:
τ = shear stress in kPa, and
G* = complex modulus in kPa.
11.4.1. When testing specimens for compliance with M 320, select an appropriate stress level from Table 3. Software
is available with the dynamic shear rheometers that will control the stress level automatically without control
by the operator.
Table 3—Target Stress Levels
11.5. When the temperature has equilibrated, condition the specimen by applying the required strain for a
recommended 10 cycles or a required range of 8 to 16 cycles at a frequency of 10 rad/s (see Note 28).
Obtain a test measurement by recording data for an additional recommended 10 cycles or a range of 8 to 16
cycles. Reduce the data obtained for the second set of cycles to produce a value for the complex modulus and
phase angle. Typically a Fast Fourier Transform (FFT) is used to reduce the data. Multiple measurements
may be obtained to verify that the sample is properly prepared. Disbonding between the plates and the binder
or fracture in the sample can result in a decrease in the modulus with repeat measurements. Some asphalt
binders may exhibit a reduced modulus with continued application of shear stresses (multiple measurements).
The data acquisition system automatically acquires and reduces the data when properly activated. When
conducting tests at more than one frequency, start testing at the lowest frequency and increase to the highest
frequency.
Note 28—The standard frequency of 10 rad/s is used when testing binder for compliance with M 320.
11.6. The data acquisition system specified in Section 6.1.4 automatically calculates G* and δ from test data
acquired when properly activated.
11.7. Initiate the testing immediately after preparing and trimming the specimen. The testing at subsequent
temperatures should be done as quickly as possible to minimize the effect of molecular associations (steric
hardening) that can cause an increase in modulus if the specimen is held in the rheometer for a prolonged
period of time. When testing at multiple temperatures all testing should be completed within 4 h.
12. INTERPRETATION OF RESULTS
12.1. The dynamic modulus and phase angle depend upon the magnitude of the shear strain; the modulus and
phase angle for both unmodified and modified asphalt binder decrease with increasing shear strain as shown
in Figure 4. A plot such as that shown in Figure 4 can be generated by gradually increasing the load or strain
amplitude, thereby producing a strain sweep. It is not necessary to generate such sweeps during normal
specification testing; however, such plots are useful for verifying the limits of the linear region.
Figure 4—Example of Strain Sweep
12.2. A linear region may be defined at small strains where the modulus is relatively independent of shear strain.
This region will vary with the magnitude of the complex modulus. The linear region is defined as the range in
strains where the complex modulus is 95 percent or more of the zerostrain value.
12.3. The shear stress varies linearly from zero at the center of the plates to a maximum at the extremities of the
plate perimeter. The shear stress is calculated from the applied or measured torque, measured or applied
strain, and the geometry of the test specimen.
13. REPORT
13.1. A sample report format is given in Appendix X13. Provide a complete identification and description of the
material tested including name, grade, and source.
13.2. Describe the instrument used for the test including the model number.
13.3. The strain and stress levels specified in Tables 2 and 3 have been selected to ensure a common reference
point that has been shown to be within the linear region for neat and modified asphalt binders. Some systems
may not be linear within this region. When this situation is observed, report the modulus at the recommended
stress or strain levels but also report that the test conditions were outside the linear region.
13.4. For each test, report the following:
13.4.1. Test plate diameter, nearest 0.1 mm, and test gap, nearest 1 μm;
13.4.2. Test temperature, nearest 0.1°C;
13.4.3. Test frequency, nearest 0.1 rad/s;
13.4.4. Strain amplitude, nearest 0.01 percent, or torque, nearest mN·m;
13.4.5. Complex modulus (G*) for the 10 measurements, kPa to three significant figures;
13.4.6. Phase angle (δ) for the second 10 cycles, nearest 0.1 degrees; and
13.4.7. G*/sinδ, nearest 0.01 kPa, or G*sinδ, nearest whole number.
14. PRECISION AND BIAS
14.1. Precision—Criteria for judging the acceptability of dynamic shear results obtained by this method are given in
Table 4.
14.1.1. SingleOperator Precision (Repeatability)—The figures in Column 2 of Table 4 are the coefficients of variation
that have been found to be appropriate for the conditions of test described in Column 1. Two results obtained
in the same laboratory, by the same operator using the same equipment, in the shortest practical period of
time, should not be considered suspect unless the difference in the two results, expressed as a percent of
their mean, exceeds the values given in Table 4, Column 3.
14.1.2. Multilaboratory Precision (Reproducibility)—The figures in Column 2 of Table 4 are the coefficients of variation
that have been found to be appropriate for the conditions of test described in Column 1. Two results
submitted by two different operators testing the same material in different laboratories shall not be
considered suspect unless the difference in the two results, expressed as a percent of their mean, exceeds
the values given in Table 4, Column 3.
Table 4—Precision Estimates
Note 29—The precision estimates given in Table 4 are based on the analysis of test results from eight pairs
of AMRL proficiency samples. The data analyzed consisted of results from 185 to 208 laboratories for each of
the eight pairs of samples. The analysis included five binder grades: PG 5234, PG 6416, PG 6422, PG 70
22, and PG 7622 (SBS modified). Average original binder results for G*/sinδ ranged from 1.067 kPa to 2.342
kPa. Average RTFO residue results for G*/sinδ ranged from 2.274 kPa to 7.733 kPa. Average PAV residue
results for G*·sinδ averaged from 1100 kPa to 4557 kPa. The details of this analysis are in the final report for
NCHRP Project No. 926, Phase 3.
Note 30—As an example, two tests conducted on the same PAV residue yield results of 1200 kPa and 1300
kPa, respectively. The average of these two measurements is 1250 kPa. The acceptable range of results is
then 13.8 percent of 1250 kPa or 173 kPa. As the difference between 1200 kPa and 1300 kPa is less than 173
kPa, the results are within the acceptable range.
14.2. Bias—No information can be presented on the bias of the procedure because no material having an accepted
reference value is available.
15. KEYWORDS
15.1. Dynamic shear rheometer; DSR; complex modulus; asphalt binder.
APPENDIXES
(Nonmandatory Information)
X1. TESTING FOR LINEARITY
X1.1. Scope:
X1.1.1. This procedure is used to determine whether an unaged asphalt binder exhibits linear or nonlinear behavior at
the upper grading temperature, e.g., 52, 58, 64, 70, 76, or 82°C. The determination is based on the change in
complex shear modulus at 10 rad/s when the strain is increased from 2 to 12 percent.
X1.2. Procedure:
X1.2.1. Verify the DSR and its components in accordance with Section 9 of this standard.
X1.2.2. Prepare the DSR in accordance with Section 10 of this standard.
X1.2.3. Prepare a test specimen for testing with 25mm plates as per Section 11 of this standard. Select the test
temperature as the upper grading temperature for the binder in question.
X1.2.4. Determine the complex shear modulus at 2 and 12 percent strain following the test procedure described in
Section 12 except as noted below. Always start with the lowest strain and proceed to the next larger strain.
X1.3. Strain Controlled Rheometers—If the software provided with the DSR will automatically conduct tests at
multiple strains, program the DSR to obtain the complex shear modulus at strains of 2, 4, 6, 8, 10, and 12
percent. If this automatic feature is not available, test by manually selecting strains of 2, 4, 6, 8, 10, and 12
percent strain.
X1.4. For stresscontrolled rheometers, compute the starting stress based on the complex shear modulus, G*, and
shear stress, τ, as determined at the upper grading temperature during the grading of the binder. At this
temperature the complex modulus, G*, will be greater than or equal to 1.00 kPa and the shear stress, τ, will
be between 0.090 and 0.150 kPa (see Table 2). Calculate the starting stress as τ /6.00 kPa. Increase the
stress in five increments of τ /6.00 kPa.
Note X1—Sample calculation: Assume a PG 6422 asphalt binder with G* = 1.29 kPa at 64°C and τ = 0.135
kPa. The starting stress will be 1.35kPa/6 = 0.225 kPa. Test at 0.225, 0.450, 0.675, 0.900, 1.13, and 1.35
kPa, starting with 0.225 kPa.
X1.5. Plot of Complex Modulus Versus Strain—Prepare a plot of complex shear modulus versus percent strain as
shown in Figure 4. From the plot, determine the complex shear modulus at 2 and 12 percent strain.
X1.6. Calculations:
X1.6.1. Calculate the modulus ratio as the complex shear modulus at 12 percent strain divided by the complex shear
modulus at 2 percent strain.
X1.7. Report:
X1.7.1. Report the following:
X1.7.1.1. Complex shear modulus (G*) to three significant figures;
X1.7.1.2. Strain, nearest 0.1 percent;
X1.7.1.3. Frequency, nearest 0.1 rad/s; and
X1.7.1.4. The ratio calculated by dividing the modulus at 12 percent strain by the modulus at 2 percent strain.
X1.8. Data Interpretation:
X1.8.1. The measurement was performed in the nonlinear range of the material if the modulus ratio as calculated in
Section X1.11 is <0.900 and linear if ≥0.900. If the measurement was performed in the nonlinear range of
the material, the results obtained under this standard will be considered as invalid for grading a binder
according to M 320.
X2. CONTROL CHART
X2.1. Control Charts:
X2.1.1. Control charts are commonly used by various industries, including the highway construction industry, to
control the quality of products. Control charts provide a means for organizing, maintaining, and interpreting
test data. As such, control charts are an excellent means for organizing, maintaining, and interpreting DSR
verification test data. Formal procedures based on statistical principles are used to develop control charts and
the decision processes that are part of statistical quality control.
A quality control chart is simply a graphical representation of test data versus time. By plotting laboratory
measured values for the reference fluid in a control chart format, it is easy to see when:
The measurements are well controlled and both the device and the operator are performing properly.
The measurements are becoming more variable with time, possibly indicating a problem with the test
equipment or the operator.
The laboratory measurements for the fluid are, on the average above or below the target (reference fluid)
value.
Many excellent software programs are available for generating and maintaining control charts. Some
computerbased statistical analysis packages contain procedures that can be used to generate control charts.
Spreadsheets such as Microsoft’s Excel can also be used to generate control charts and, of course, control
charts can be generated manually. (See Table X3.1 as an example.)
X2.2. Care in Selecting Data:
X2.2.1. Data used to generate control charts should be obtained with care. The idea of randomness is important but
need not become unnecessarily complicated. An example will show why a random sample is needed; a
laboratory always measures the reference fluid at the start of the shift or workday. These measurements
could be biased by startup errors such as a lack of temperature stability when the device is first turned on.
The random sample ensures that the measurement is representative of the process or the material being
tested. Said another way, a random sample has an equal chance of being drawn as any other sample. A
measurement or sample always taken at the start or end of the day, or just before coffee break, does not
have this chance.
X3. EXAMPLE
X3.1. The power of the control chart is illustrated in Table X3.1 using the verification data obtained for the DSR.
Other DSR verification data suitable for a quality control chart presentation include measurements for
determining the temperature correction, calibrating the electronic thermometer, and maintaining data from
internally generated asphalt binder reference samples. For this example, the reported viscosity for the
reference fluid is 271 Pa·s; hence, the calculated value for G* is 2.71 kPa. This value for G* is labeled as “G*
from Reference Fluid” in Figure X3.1. The laboratory should obtain this value on average if there is no
laboratory bias.
Table X3.1—Sample Test Data
X3.2. Comparison of 22Week Laboratory Average for G* with Value Calculated from Reference Fluid:
X3.2.1. The 22week average of the laboratory measurements is labeled as “22Week Laboratory Average” in Figure
X3.1. Over the 22 weeks for which measurements were made, the average was 2.73 kPa. This value
compares favorably with the calculated reference value, 2.71 kPa, differing on the average by only 0.7
percent. There appears to be little laboratory bias in this data.
X3.3. Comparison of CV of Laboratory Measurements with Round Robin CV:
X3.3.1. From a previous round robin study, the within laboratory standard deviation (d1s) for the fluid was reported
as 0.045 (CV = 1.67 percent). The 22week standard deviation for the measured values of G* is 0.051 CV =
1.86 percent), as compared to 0.045 (CV =1.67 percent) reported from the round robin. However, it should
be pointed out that the 22week CV, 1.86 percent, also includes daytoday variability, a component of
variability not included in the roundrobin d1s value. Based on this information the variability of the laboratory
measurements are acceptable.
X3.4. Variability of Measured Values:
X3.4.1. In Figure X3.1, the value of G* calculated from the reference fluid is shown as a solid line. Also shown are
two dotted lines that represent the G* calculated from the reference fluid ±2 d1s where d1s is the value from
the round robin. The calculated reference value for the fluid is 2.71 kPa, and the standard deviation is 0.045.
Thus, a deviation of 2 d1s gives values of:
(X3.1)
If the laboratory procedures are under control, the equipment is properly calibrated, and there is no
laboratory bias, 95 percent of the measurements should fall within the limits 2.62 kPa and 2.80 kPa.
Laboratory measurements outside this range are suspect, and the cause of the outlier should be investigated.
The outlier may be the result of either testing variability or laboratory bias. The measurement from Week 10
in Figure X3.1 falls outside the ±2 d1s limits and is cause for concern such that testing procedures and
verification should be investigated.
If a measurement deviates from the target, in this case G* from the reference fluid, by more than ±3 d1s,
corrective action should be initiated. The ±3 d1s limits 99.7 percent of the measured values if the laboratory
procedures are under control and the equipment is properly calibrated.
X3.5. Trends in Measured Value:
X3.5.1. The control chart can also be used to identify unwanted trends in the data. For example, from Weeks 1 to 5,
a steady decrease in the measured value is observed. This is cause for concern and the reason for the trend
should be investigated. More sophisticated rules for analyzing trends in control charts can be found
elsewhere.
Figure X3.1—Control Chart
X4. USE OF REFERENCE FLUID
X4.1. Source of Reference Fluid:
X4.2. An organic polymer produced by Cannon Instrument Company as Viscosity Standard N2700000SP has been
found suitable as reference fluid for verifying the calibration of the DSR. The viscosity of the fluid, as
determined from NIST–traceable capillary viscosity measurements, is approximately 270 Pa·s at 64°C.
However, the viscosity of the fluid varies from one lot to the next. The lotspecific viscosity is printed on the
label of the bottle.
X5. CAUTIONS IN USING REFERENCE FLUID
X5.1. Some items of caution when using the reference fluid are:
The fluid cannot be used to verify the accuracy of the phase angle measurement.
The fluid must not be heated as heating can degrade the fluid, causing a change in its viscosity.
The fluid should be used for verification only after the DSR temperature measurements are verified.
The fluid cannot be used to calibrate the torque transducer. The manufacturer or other qualified service
personnel using a calibration device designed specifically for the rheometer should perform the calibration.
These calibration devices are typically not available in operating laboratories.
When tested at 10 rad/s, the reference fluid should be used only at 64°C and above. At lower temperatures,
the fluid is viscoelastic; hence, the viscosity, η, reported on the certificate by Cannon will not match the
complex viscosity η* = G*/10 rad/s determined from the measurement.
Bubbles in the fluid will have a dramatic effect on the measured value of G*. The fluid in the bottle should
be free of bubbles and care must be taken not to introduce bubbles when preparing test specimens.
Recommended procedures for preparing test specimens are given in Appendix X6.
X6. CALCULATION OF G* FROM STEADYSTATE VISCOSITY MEASUREMENTS
X6.1. Among the different methods for converting between dynamic and steadystate viscosity of polymers, the
most popular and most successful is the socalled CoxMerz empirical rule. The rule leads, in simplified terms,
to the following approximation.
(X6.1)
where:
G* = the complex modulus;
ω = the angular frequency in radians/s; and
η = the shear rate independent capillary viscosity as reported by the supplier of the reference fluid.
For this rule to apply the measurements must be in the viscous region where the phase angle approaches 90
degrees. The value of the complex modulus is then simply 10 times the value of the capillary viscosity. For
example, if the capillary viscosity is 270,000 mPa·s the complex modulus is:
(X6.2)
The reference fluid behaves as a viscous fluid at 64°C and above and provides very accurate estimates of G*
above 64°C. At temperatures below 58°C the fluid gives incorrect values for G* with the error increasing as
the temperature departs from 64°C. At 64°C and above G* divided by the frequency in radians per second
should be no more than 3 percent different than the viscosity printed on the bottle label. If this is the case,
then the torque calibration should be considered suspect.
X7. METHODS FOR TRANSFERRING THE FLUID TO THE TEST PLATES
X7.1. Three different methods are recommended for transferring the fluid to the test plates:
X7.2. The glass rod method (Section X7.1), the spatula method (Section C4.3), and a direct method where a
removable test plate is held in direct contact with the fluid in the bottle (Section C4.4).
X7.3. Glass Rod Method (Figure X7.1):
X7.3.1. In this method, a glass rod is inserted into the fluid and rotated (Step 1) while in the fluid. Continue rotating
the rod, and pull it slowly from the fluid (Step 2) carrying a small mass of the fluid with the rod. Touch the
mass to the plate (Step 3) to transfer the fluid to the plate. See Figure X7.1.
Figure X7.1—Using a Glass Rod to Place the Reference Fluid on the Plate
X7.4. Spatula Method (Figure X7.2):
X7.5. When carefully used, a spatula may be used to transfer the fluid. Special care must be taken not to trap air as
the material is scooped from the bottle (Step 1). Smear the mass on the spatula onto the plate (Step 2) and
cut the mass from the spatula by drawing the spatula across the edge of the plate (Step 3). This method
appears to be the most difficult to implement and is the least recommended of the three methods.
Figure X7.2—Using a Spatula to Place the Reference Fluid on the Plate
X7.6. Direct Touch Method (Figure X7.3)—If the rheometer is equipped with plates that may be removed and
reinstalled without affecting the gap reference, remove one of the plates and touch the surface of the plate to
the surface of the fluid in the bottle (Step 1). Pull the plate from the bottle, bringing a mass of the fluid along
with the plate (Step 2). Invert the plate and allow the fluid to flow out into a mushroom shape (Step 3).
Figure X7.3—Direct Touch Method to Place the Reference Fluid on the Plate
Proceed immediately to Section 10.5 to trim the reference fluid specimen and form the bulge.
Proceed with testing the reference fluid specimen as described in Section 11.
X8. SELECTION OF GAP CLOSURE TO OBTAIN BULGE
X8.1. Need for Accurate Measurement of Specimen Diameter:
X8.2. The accuracy of the DSR measurements depends upon an accurate measurement of the diameter of the test
specimen. The diameter of the test specimen is assumed to be equal to the diameter of the test plates. For
this reason, the trimming of excess binder and the final closure of the gap to produce a slight bulge in the test
specimen are critical steps in the DSR test procedure. When the gap is closed to its final dimension, the bulge
must be of sufficient size to compensate for any shrinkage in the binder and consequently avoiding a concave
surface as shown in Figure X8.1. The diameter of the test specimen in Figure X8.1 approaches d, rather than
d′, the diameter of the plate. The modulus, G*, is calculated according to the following equation:
(X8.1)
where:
G* = complex modulus;
τ = torque applied to test specimen;
h = thickness of test specimen;
Θ = angular rotation, radians; and
r = radius of test plate.
Figure X8.1—Concave Surface Resulting from Insufficient Closure after Trimming
Figure X8.2—Proper Bulge
X8.3. According to Equation X8.1, the modulus depends upon the radius (or diameter) raised to the fourth power.
Therefore, a small concavity in the outer surface of the test specimen, as shown in Figure X8.1, will have a
large effect on the measured modulus because the actual specimen diameter will be less than the plate
diameter. For a given amount of concavity, the effect on the measured modulus is greater for the 8mm plate
than the 25mm plate. A more desirable result is a slight bulge as illustrated in Figure X8.2. Shear stresses
are not transferred directly from the plate to the overhanging binder; therefore, the effect of a slight bulge on
the measured modulus is much less than a slight concavity. It should be noted that errors in the diameter of
the test specimen do not affect the measured values of the phase angle.
X9. RECOMMENDED GAP CLOSURE VALUES
X9.1. Recommended values for the gap closure required to form a bulge at the test temperature similar to the bulge
illustrated in Figure X8.2 are given in Section 10.5 as 50 µm and 100 µm for the 25mm and 8mm plates,
respectively. Although these values may be appropriate for many rheometers, they may not be appropriate
for all rheometers. The applicability of these values to a specific rheometer may be determined by preparing
a test specimen using the recommended closure and observing the shape of the bulge after the final closure
of the gap and after the test specimen is at the test temperature. If the recommended closure values do not
give an appropriate bulge, the recommended closure values should be adjusted as appropriate.
Proper and improper bulges are shown in Figures X10.1 through X10.3. A magnifying glass is useful for
examining the shape of the bulge. Regardless of the closure required to produce a desirable bulge, the actual
gap should be used in the calculations.
X10. FACTORS AFFECTING BULGE DEVELOPMENT
X10.1. A number of factors can affect the bulge formed at the test temperature. These include:
The amount of closure used to create the bulge.
The difference in temperature between the trimming temperature, the temperature at which the bulge is
created, and the test temperature.
Thermal expansioncontraction characteristics of the rheometer.
Thermal contraction and expansion of the asphalt binder.
A concave surface is more likely to form at the intermediate temperatures, than at the upper test
temperatures (8mm plate rather than the 25mm plate). In fact, at the higher test temperatures excessive
material can be squeezed from the plates as shown in Figure X10.3. This situation should also be avoided and
may require gap closures somewhat less than the recommended values.
Figure X10.1—Good Bulge Size
Figure X10.2—Concave Bulge
Figure X10.3—Oversized Bulge
X11. DETERMINATION OF TIME TO THERMAL EQUILIBRIUM
X11.1. Reason for Determining Time Required to Obtain Thermal Equilibrium:
X11.1.1. 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.
X11.1.2. The time required to obtain thermal equilibrium varies for different rheometers. Factors that affect the time
required for thermal equilibrium include:
X11.1.3. Design of the rheometer and whether air or liquid is used as a heating/cooling medium;
X11.1.4. Difference between ambient temperature and the test temperature, different when testing below room
temperature, and above room temperature;
X11.1.5. Difference in temperature between the trimming and test temperature; and
X11.1.6. Plate size, different for the 8mm and 25mm plate.
X11.2. It is not possible to specify a single time as the time required to obtain thermal equilibrium. For example,
thermal equilibrium is reached much quicker with liquidcontrolled rheometers than with aircooled
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
X12.1. 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:
X12.2. 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. Operate the rheometer in a continuous mode at 10 rad/s using an unmodified asphalt binder—one that does
not change modulus with repeated shearing. Use the smallest strain value that gives good measurement
resolution.
X12.4. Record the modulus at 30s time intervals, and plot the modulus versus time (Figure X12.1).
Figure X12.1—Determining Thermal Equilibrium Time
X12.5. The time to reach thermal equilibrium is the time required to reach a constant modulus. Typically, this time
will be greater than the time required to reach a constant reading on the DSR thermometer.
X12.6. Because the time required to reach thermal equilibrium will vary with the test temperature and testing
conditions, the time to thermal equilibrium should be established separately for both intermediate and high
temperature measurements. Once the time to thermal equilibrium has been established, it does not have to
be repeated unless the test conditions change.
X13. SAMPLE REPORT
Header Information:
Test Results for Grading (Use separate column for each test temperature):
Test Results for Linearity Determination:
X14. REFERENCES
X14.1. 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).
X14.2. Anderson, D. A., C. E. Antle, K. Knechtel, and Y. Liu. Interlaboratory Test Program to Determine the Inter
and IntraLaboratory Variability of the SHRP Asphalt Binder Tests. FHWA, 1997.
X14.3. Cox, W. P. and E. H. Merz. Correlation of Dynamic and Steady Flow Viscosities, Journal of Polymer Science,
Vol. 28, 1958, pp. 619–622.
X14.4. Wadsworth, H., ed. Handbook of Statistical Methods for Engineers and Scientists. McGrawHill, New York, NY,
1990.
1
Formerly AASHTO Provisional Standard TP 5. First published as a full standard in 2002.

AASHTO T315-12 Standard Method of Test For Determining The Rheological Properties of Asphalt Binder Using A Dynamic Shear Rheometer (DSR) - Light

Uploaded by

Copyright:

Available Formats

AASHTO T315-12 Standard Method of Test For Determining The Rheological Properties of Asphalt Binder Using A Dynamic Shear Rheometer (DSR) - Light

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

AASHTO T315-12 Standard Method of Test For Determining The Rheological Properties of Asphalt Binder Using A Dynamic Shear Rheometer (DSR) - Light

Uploaded by

Copyright:

Available Formats

13/2/2015 Standard Method of Test for Determining the Rheological Properties of Asphalt Binder Using a Dynamic Shear Rheometer (DSR)

You might also like