ASTM D6648-08(2016)
(Test Method)Standard Test Method for Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR)
Standard Test Method for Determining the Flexural Creep Stiffness of Asphalt Binder Using the Bending Beam Rheometer (BBR)
SIGNIFICANCE AND USE
5.1 The temperatures for this test are based upon the winter temperature experienced by the pavement in the geographical area for which the asphalt binder is intended.
5.2 The flexural creep stiffness or flexural creep compliance, determined from this test, describes the low-temperature stress-strain-time response of asphalt binder at the test temperature within the range of linear viscoelastic response.
5.3 The low-temperature thermal cracking performance of asphalt pavements is related to the creep stiffness and the m-value of the asphalt binder contained in the mix.
5.4 The creep stiffness and the m-value are used as performance-based specification criteria for asphalt binders in accordance with Specification D6373.
SCOPE
1.1 This test method covers the determination of the flexural-creep stiffness or compliance and m-value of asphalt binders by means of a bending beam rheometer. It is applicable to material having flexural-creep stiffness values in the range of 20 MPa to 1 GPa (creep compliance values in the range of 50 nPa–1 to 1 nPa–1) and can be used with unaged material or with materials aged using aging procedures such as Test Method D2872 or Practice D6521. The test apparatus may be operated within the temperature range from –36°C to 0°C.
1.2 Test results are not valid for test specimens that deflect more than 4 mm or less than 0.08 mm when tested in accordance with this test method.
1.3 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.
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D6648 − 08 (Reapproved 2016)
Standard Test Method for
Determining the Flexural Creep Stiffness of Asphalt Binder
Using the Bending Beam Rheometer (BBR)
This standard is issued under the fixed designation D6648; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope E77 Test Method for Inspection and Verification of Ther-
2 mometers
1.1 This test method covers the determination of the
2.2 DIN Standard:
flexural-creep stiffness or compliance and m-value of asphalt
binders by means of a bending beam rheometer. It is applicable
tomaterialhavingflexural-creepstiffnessvaluesintherangeof
3. Terminology
20 MPa to 1 GPa (creep compliance values in the range of 50
–1 –1
nPa to 1 nPa ) and can be used with unaged material or with 3.1 Definitions:
materials aged using aging procedures such as Test Method
3.1.1 asphalt binder, n—an asphalt-based cement that is
D2872 or Practice D6521. The test apparatus may be operated produced from petroleum residue either with or without the
within the temperature range from –36°C to 0°C.
addition of modifiers.
3.1.2 physical hardening, n—a time-dependent, reversible
1.2 Test results are not valid for test specimens that deflect
stiffening of asphalt binder that typically occurs when the
more than 4 mm or less than 0.08 mm when tested in
binder is stored below room temperature.
accordance with this test method.
1.3 This standard does not purport to address all of the 3.2 Definitions of Terms Specific to This Standard:
safety concerns, if any, associated with its use. It is the 3.2.1 contact load, n—the load, P , required to maintain
c
responsibility of the user of this standard to establish appro- positive contact between the test specimen, supports, and the
priate safety and health practices and determine the applica- loading shaft; 35 6 10 mN.
bility of regulatory limitations prior to use.
3.2.2 flexural creep compliance, D(t), n—the ratio obtained
by dividing the maximum bending strain (see Eq X1.5)ina
2. Referenced Documents
beam by the maximum bending stress (Eq X1.4). The flexural
2.1 ASTM Standards:
creep stiffness is the inverse of the flexural creep compliance.
C802 Practice for Conducting an Interlaboratory Test Pro-
3.2.3 flexural creep stiffness, S (t), n—the creep stiffness
e
gram to Determine the Precision of Test Methods for
obtained by fitting a second order polynomial to the logarithm
Construction Materials
of the measured stiffness at 8.0, 15.0, 30.0 60.0, 120.0, and
D140 Practice for Sampling Bituminous Materials
240.0 s and the logarithm of time (see Eq 5, section 14.4).
D2872 Test Method for Effect of Heat andAir on a Moving
3.2.4 measured flexural creep stiffness, S (t), n—the ratio
m
Film of Asphalt (Rolling Thin-Film Oven Test)
(see Eq 3, section 14.2) obtained by dividing the measured
D6521 Practice for Accelerated Aging of Asphalt Binder
maximum bending stress (see X1.4) by the measured maxi-
Using a Pressurized Aging Vessel (PAV)
mum bending strain (see Eq X1.5). Flexural creep stiffness has
D6373 Specification for Performance Graded Asphalt
been used historically in asphalt technology while creep
Binder
compliance is commonly used in studies of viscoelasticity.
3.2.5 m-value, n—the absolute value of the slope of the
logarithm of the stiffness curve versus the logarithm of time
This test method is under the jurisdiction of ASTM Committee D04 on Road
and Paving Materials and is the direct responsibility of Subcommittee D04.44 on
(see Eq 6, section 14.5).
Rheological Tests.
3.2.6 test load, n—the load, P, of 240-s duration used to
Current edition approved Oct. 1, 2016. Published October 2016. Originally
t
approved in 2001. Last previous edition approved in 2008 as D6648 – 08. DOI:
determine the stiffness of the asphalt binder being tested; 980
10.1520/D6648-08R16.
6 50 mN.
This standard is based on SHRP Product 1002.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on Deutsches Institut fuer Normung (German Standards Institute), Beuth Verlag
the ASTM website. GmbH, Burggrafenstrasse 6, 1000 Berlin 30, Germany.
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D6648 − 08 (2016)
3.2.7 zero load cell reading—the load indicated by the data 5.4 The creep stiffness and the m-value are used as
acquisition system when the shaft is free floating in the bath performance-based specification criteria for asphalt binders in
and at the position that occurs when first making contact with accordance with Specification D6373.
a test specimen.
6. Interferences
4. Summary of Test Method
6.1 Measurements for which the mid-point deflections of
4.1 The bending beam rheometer is used to measure the
the test specimen is greater than 4.0 mm are suspect. Strains in
mid-point deflection of a simply supported prismatic beam of
excess of this value may exceed the linear response of asphalt
asphalt binder subjected to a constant load applied to its
binders.
mid-point. The device operates only in the loading mode;
6.2 Measurements for which the mid-point deflections of
recovery measurements cannot be obtained with the bending
the test specimen are less than 0.08 mm are suspect. When the
beam rheometer.
mid-point deflection is less than 0.08 mm, the test system
4.2 A prismatic test specimen is placed in the controlled
resolution may not be sufficient to produce reliable test results.
temperature fluid bath and loaded with a constant test load for
240.0 s. The test load (980 6 50 mN) and the mid-point
7. Apparatus
deflection of the test specimen are monitored versus time using
7.1 A bending beam rheometer (BBR) test system consist-
a computerized data acquisition system.
ing of the following: (1) a loading frame with test specimen
4.3 The maximum bending stress at the midpoint of the test
supports, (2) a controlled temperature liquid bath which
specimen is calculated from the dimensions of the test
maintains the test specimen at the test temperature and pro-
specimen, the distance between the supports, and the load
vides a buoyant force to counterbalance the force resulting
appliedtothetestspecimenforloadingtimesof8.0,15.0,30.0,
from the mass of the test specimen, (3) a computer-controlled
60.0, 120.0, and 240.0 s. The maximum bending strain in the
data acquisition system, (4) test specimen molds, and (5) items
test specimen is calculated from the dimensions of the test
for verifying and calibrating the system.
specimen and the deflection for the same loading times. The
7.2 Loading Frame—A frame consisting of a set of sample
stiffness of the test specimen for the specific loading times is
supports, a blunt-nosed shaft to apply the load to the midpoint
calculated by dividing the maximum bending stress by the
of the test specimen, a load cell mounted in line with the
maximum bending strain.
loading shaft, a means for zeroing the load applied to the test
specimen, a means for applying a constant load to the test
5. Significance and Use
specimen and a deflection measuring transducer attached to the
5.1 The temperatures for this test are based upon the winter
loading shaft. A schematic of the device is shown in Fig. 1.
temperature experienced by the pavement in the geographical
7.3 Loading System—A loading system that is capable of
area for which the asphalt binder is intended.
applyingacontactloadof35 610mNtothetestspecimenand
5.2 Theflexuralcreepstiffnessorflexuralcreepcompliance,
maintaining a test load of 980 6 50 mN within 610 mN.
determinedfromthistest,describesthelow-temperaturestress-
7.3.1 Loading System Requirements—The rise time for the
strain-time response of asphalt binder at the test temperature
test load shall be less than 0.5 s. The rise time is the time
within the range of linear viscoelastic response.
required for the load to rise from the 35 6 10 mN contact load
5.3 The low-temperature thermal cracking performance of to the 980 6 50 mN test load. During the rise time the system
asphalt pavements is related to the creep stiffness and the shall dampen the test load to 980 6 50 mN. Between 0.5 and
m-value of the asphalt binder contained in the mix. 5.0 s, the test load shall be within 650 mN of the average test
FIG. 1 Schematic of Test Device
D6648 − 08 (2016)
verified as per section 11.5. A platinum resistance thermometric device
load, and thereafter shall be within 610 mN of the average test
meeting DIN Standard 43760 (ClassA) is recommended for this purpose.
load. Details of the loading pattern are shown in Fig. 2.
7.3.2 Loading Shaft—Aloading shaft continuous and in line 7.5 Controlled-Temperature Fluid Bath—A controlled-
with the load cell and deflection measuring transducer with a temperature liquid bath capable of maintaining the temperature
spherically shaped end 6.3 6 0.3 mm in radius. at all points in the bath to within 60.1°C of the test tempera-
7.3.3 Load Cell—A load cell to measure the contact load ture in the range of –36°C to 0°C. Placing a test specimen in
and the test load. It shall have a minimum capacity of no less the bath may cause the bath temperature to fluctuate 60.2°C
than 2.00 N and a resolution of at least 2.5 mN. It shall be from the target test temperature. Consequently bath fluctua-
mounted in line with the loading shaft and above the fluid level tions of 60.2°C during iso-thermal conditioning shall be
in the controlled temperature bath. allowed.
7.3.4 Linear Variable Differential Transducer (LVDT)—A 7.5.1 Bath Agitator—A bath agitator for maintaining the
linearvariabledifferentialtransducerorothersuitabledeviceto required temperature homogeneity with agitation intensity
measure the deflection of the test specimen. It shall have a such that the fluid currents do not disturb the testing process
linearrangeofatleast6mm,andbecapableofresolvinglinear and mechanical noise caused by vibrations is less than the
movement of 2.5 µm. It shall be mounted axially with and resolution specified in 7.3.3 and 7.3.4.
above the loading shaft.
7.5.2 Circulating Bath (Optional)—Acirculating bath sepa-
7.3.5 Sample Supports—Two stainless steel or other non-
rate from the test frame, which pumps the bath fluid through
corrosive metal supports with a 3.0 6 0.3 mm contact radius
the test bath. If used, vibrations from the circulating system
and spaced 102 6 1.0 mm apart. The spacing of the supports shall be isolated from the bath test chamber so that mechanical
shallbemeasuredto 60.3mmandthemeasuredvalueshallbe
noise is less than the resolution specified in 7.3.3 and 7.3.4.
used in the calculations in Section 14. The supports shall be
7.6 Data Acquisition and Control Components—A data
dimensionedtoensurethatthetestspecimenremainsincontact
acquisition system that resolves loads to the nearest 2.5 mN,
with the radiused portion of the support during the entire test.
test specimen deflection to the nearest 2.5 µm, and bath fluid
See Fig. 3.
temperature to the nearest 0.1°C. The data acquisition system
7.3.5.1 The width of the test specimen support that contacts
shall sense the point in time when the signal to switch from the
the test specimen shall be 9.50 6 0.25 mm. See Fig. 3.
contactloadtothetestloadisactivated.Thistimeshallbeused
7.3.5.2 Avertical alignment pin 2 to 4 mm in diameter shall
as the zero loading time for the test load and deflection signals.
be provided at the back of each support to align the test
Using this time as the reference for zero time, the data
specimen on the supports. The front face of the pins shall be
acquisition system shall provide a record of subsequent load
6.75 6 0.25 mm from the middle of the support. See Fig. 3.
and deflection measurements at 8.0, 15.0, 30.0, 60.0, 120.0,
7.4 BBR Thermometric Device—A calibrated thermometric and 240.0 s.
device integral to the BBR and capable of measuring the
7.6.1 Filtering of Acquired Load and Deflection Signals—
temperatureto0.1°Covertherangefrom–36°Cto0°Cwithits
The load and deflection signals shall be filtered with a low pass
thermalsensor(probe)mountedwithin50mmofthegeometric
analog or digital (or both) filter that removes components with
center of the test specimen.
frequencies greater than 4 Hz from the load and deflection
signals. Filtering may be accomplished by averaging five or
NOTE 1—The required temperature measurement can be accomplished
more digital signals equally spaced in time about the time at
with an appropriately calibrated thermometric device (platinum resistance
or thermistor based). Calibration of the thermometric device can be whichthesignalisreported.Theaveragingshallbeoveratime
FIG. 2 Definition of Loading Pattern
D6648 − 08 (2016)
FIG. 3 Schematic of Specimen Supports
period less than or equal to 60.2 s of the reporting time. For 7.8.2 Stainless Steel (Thin) Beam for Overall System
example, the load and deflection signals at 8.0 s may be the Check—One stainless steel beam 1.0 to 1.6 mm thick by 12.7
average of signals at 7.8, 7.9, 8.0, 8.1, 8.2 s. 6 0.1 mm wide by 127 6 5 mm long with an elastic modulus
reported to three significant figures by the manufacturer of the
7.7 Test Specimen Molds—Test specimen molds with inte-
BBR. The manufacturer of the BBR shall measure and report
rior dimensions of 6.35 6 0.05 mm wide by 12.70 6 0.05 mm
thethicknessofthisbeamtothenearest0.01mmandthewidth
deep by 127 6 5 mm long fabricated from aluminum or
to the nearest 0.05 mm. The dimensions of the beam shall be
stainless steel as shown in Fig. 4, or from silicone rubber as
used to calculate the modulus of the beam during the overall
shown in Fig. 5.
system check (see section 11.3).
7.7.1 The thickness of the two spacers used for each mold
7.8.3 Standard Masses—Standard masses for verification
(small end pieces used in the metal molds) shall be measured
and calibration as follows:
with a micrometer and shall meet the requirements of Section
7.8.3.1 Verification of Load Cell Calibration—One or more
7.7. The measurements shall be recorded as part of the
masses totaling 100.0 6 0.2 g and two masses of 2.0 6 0.2 g
laboratory quality control program.
each for verifying the calibration of the load cell (see section
7.8 Items for Calibration or Verificati
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