ASTM D7460-08
(Test Method)Standard Test Method for Determining Fatigue Failure of Compacted Asphalt Concrete Subjected to Repeated Flexural Bending
Standard Test Method for Determining Fatigue Failure of Compacted Asphalt Concrete Subjected to Repeated Flexural Bending
SIGNIFICANCE AND USE
The laboratory fatigue life determined by this standard for beam specimens have been used to estimate the fatigue life of asphalt concrete pavement layers under repeated traffic loading. Although the field performance of asphalt concrete is impacted by many factors (traffic variation, speed, and wander; climate variation; rest periods between loads; aging; etc.), it has been more accurately predicted when laboratory properties are known along with an estimate of the strain level induced at the layer depth by the traffic wheel load traveling over the pavement.
Note 1—The quality of the results produced by this standard are dependent on the competence of the personnel performing the procedure and the capability, calibration, and maintenance of the equipment used. Agencies that meet the criteria of Specification D 3666 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Specification D 3666 alone does not completely assure reliable results. Reliable results depend on many factors; following the suggestions of Specification D 3666 or some similar acceptable guideline provides a means of evaluating and controlling some of those factors.
SCOPE
1.1 This test method provides procedures for determining a unique failure point for estimating the fatigue life of 380 mm (14.96 in.) long by 50 mm (1.97 in.) thick by 63 mm (2.48 in.) wide asphalt concrete beam specimens sawed from laboratory or field compacted asphalt concrete, which are subjected to repeated flexural bending.
1.2 The between-laboratory reproducibility of this test method is being determined and will be available on or before June 2013. Therefore, this test method should not be used for acceptance or rejection of a material for purchasing purposes.
1.3 The text of this standard references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.
1.4 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)
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Designation:D7460–08
Standard Test Method for
Determining Fatigue Failure of Compacted Asphalt Concrete
Subjected to Repeated Flexural Bending
This standard is issued under the fixed designation D7460; 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 D5361 Practice for Sampling Compacted Bituminous Mix-
tures for Laboratory Testing
1.1 This test method provides procedures for determining a
E29 Practice for Using Significant Digits in Test Data to
unique failure point for estimating the fatigue life of 380 mm
Determine Conformance with Specifications
(14.96 in.) long by 50 mm (1.97 in.) thick by 63 mm (2.48 in.)
2.2 AASHTO Standards:
wide asphalt concrete beam specimens sawed from laboratory
T 321 Standard Method of Test for Determining the Fatigue
or field compacted asphalt concrete, which are subjected to
Life of Compacted Hot-MixAsphalt (HMA) Subjected to
repeated flexural bending.
Repeated Flexural Bending
1.2 The between-laboratory reproducibility of this test
PP 3 Preparing Hot-Mix Asphalt (HMA) Specimens by
method is being determined and will be available on or before
Means of the Rolling Wheel Compactor
June 2013. Therefore, this test method should not be used for
R30 Standard Practice for Mixture Conditioning of Hot-
acceptance or rejection of a material for purchasing purposes.
Mix Asphalt (HMA)
1.3 The text of this standard references notes and footnotes
which provide explanatory material. These notes and footnotes
3. Terminology
(excluding those in tables and figures) shall not be considered
3.1 Definitions:
as requirements of the standard.
3.1.1 beam modulus—Flexural Beam Stiffness, as deter-
1.4 This standard does not purport to address all of the
mined in 10.1.3.
safety concerns, if any, associated with its use. It is the
3.1.2 failure point—the number of cycles to failure, N,
f
responsibility of the user of this standard to establish appro-
which corresponds to the maximum or peak Normalized
priate safety and health practices and determine the applica-
Modulus 3 Cycles (Fig. 13) when plotted versus Number of
bility of regulatory limitations prior to use.
Cycles.
2. Referenced Documents 3.1.3 initial beam modulus—Flexural Beam Stiffness deter-
mined at approximately 50 load cycles.
2.1 ASTM Standards:
3.1.4 normalized modulus 3 cycles—see Rowe and Boul-
D75 Practice for Sampling Aggregates
din (1):
D140 Practice for Sampling Bituminous Materials
D979 Practice for Sampling Bituminous Paving Mixtures
~Beam Stiffness 3 Cycle Number!
D2041 Test Method for Theoretical Maximum Specific ~Initial Beam Modulus 3 Cycle of Initial Beam Modulus!
Gravity and Density of Bituminous Paving Mixtures
4. Summary of Test Method
D3203 Test Method for Percent Air Voids in Compacted
Dense and Open Bituminous Paving Mixtures 4.1 The four-point flexural bending test method is con-
D3549 Test Method for Thickness or Height of Compacted ducted on compacted beam specimens to evaluate the fatigue
Bituminous Paving Mixture Specimens properties of an asphalt concrete mixture. A cyclic haversine
D3666 Specification for Minimum Requirements forAgen- (displaced sine wave with full amplitude on tension side of
cies Testing and Inspecting Road and Paving Materials zero) displacement is applied at the central H-frame third
pointsofabeamspecimen,whiletheouterthirdpointsareheld
in an articulating fixed position. The frequency rate ranges
from 5 to 10 Hz. This produces a constant bending moment
This test method is under the jurisdiction of ASTM Committee D04 on Road
and Paving Materials and is the direct responsibility of Subcommittee D04.26 on
Fundamental/Mechanistic Tests.
Current edition approved July 1, 2008. Published July 2008. DOI: 10.1520/
D7460-08. Available from American Association of State Highway and Transportation
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Officials (AASHTO), 444 N. Capitol St., NW, Suite 249, Washington, DC 20001,
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM http://www.transportation.org.
Standards volume information, refer to the standard’s Document Summary page on The boldface numbers in parentheses refer to the list of references at the end of
the ASTM website. this standard.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D7460–08
over the center third (L/3) span (118.5 to 119 mm (4.66 to 4.69 ment (and resulting strain) during each load cycle. The loading
in.)) between the H-frame contact points on the beam speci- device shall be capable of (1) providing cyclic haversine
men. The level of desired strain is pre-calculated and an input (= SIN (degrees/2))loadingatafrequencyrangeof5to10Hz,
for the displacement control. The deflection at the mid-length (2) subjecting specimens to 4-point bending with free rotation
position (L/2) of a beam specimen is regulated by the closed and horizontal translation at all load and reaction points, and
loop control system. (3) forcing the specimen back to its original position (that is,
zero deflection) at the end of each loading cycle. Fig. 1
5. Significance and Use
illustrates the haversine waveform. Figs. 2 and 3 show the
5.1 The laboratory fatigue life determined by this standard movements of the Cox and IPC loading devices, respectively;
for beam specimens have been used to estimate the fatigue life
the Cox device loads in a downward direction and the IPC
of asphalt concrete pavement layers under repeated traffic loads in an upward direction. The early version of the IPC
loading. Although the field performance of asphalt concrete is
device does not have free translation at the inner clamps;
impacted by many factors (traffic variation, speed, and wander; however, the newer model allows free rotation and translation
climate variation; rest periods between loads; aging; etc.), it
at all four clamps.
has been more accurately predicted when laboratory properties 6.1.2 Environmental Chamber (Temperature Control
are known along with an estimate of the strain level induced at System)—The environmental chamber shall enclose the entire
the layer depth by the traffic wheel load traveling over the specimen and maintain the specimen at the desired test
pavement. temperature.Thetemperatureshallbewithin 60.5°C(60.9°F)
throughout the conditioning and testing times.An environmen-
NOTE 1—The quality of the results produced by this standard are
tal chamber is not required if the temperature of the surround-
dependent on the competence of the personnel performing the procedure
ing environment can be maintained within the specified limits.
and the capability, calibration, and maintenance of the equipment used.
6.1.3 Control and Data Acquisition System—During each
Agencies that meet the criteria of Specification D3666 are generally
considered capable of competent and objective testing/sampling/
load cycle the control and data acquisition system shall be
inspection/etc. Users of this standard are cautioned that compliance with
capable of measuring the displacement of the beam specimen,
Specification D3666 alone does not completely assure reliable results.
and adjusting the load applied by the loading device such that
Reliable results depend on many factors; following the suggestions of
the specimen experiences a constant level of displacement on
Specification D3666 or some similar acceptable guideline provides a
each load cycle. In addition, it shall be capable of recording
means of evaluating and controlling some of those factors.
load cycles, applied loads, beam displacements, and tempera-
6. Apparatus
ture while computing and recording the maximum tensile
stress, maximum tensile strain, phase angle, and stiffness at
6.1 Test System—The test system shall consist of a load
load cycle intervals specified by the user.
frame,anenvironmentalchamber(temperaturecontrolsystem)
6.2 Miscellaneous Apparatus and Materials—For the Cox
and a closed loop control and data acquisition system. The test
device, an aluminum, wedge-shaped target for connecting the
system shall meet the minimum requirements specified in
displacement sensor to the neutral axis of the specimen and
Table1.Thisstandardspecificallydescribesthesystemsoftwo
cyanoacrylate(superglue)orequivalentisneededforattaching
primary suppliers (Cox and Sons, Inc. [Cox] and Industrial
the target to the specimen. With both the Cox and the IPC
Process Controls, Ltd. [IPC]); however, other similar equip-
equipment, an alignment fixture and a solid aluminum beam
ment could also be used.
are needed for setting the proper clamp spacing and a saw
6.1.1 Loading Device—The test system shall include a
suitable for cutting the beams with parallel faces to the proper
closed-loop, computer controlled loading component which,
tolerance.
during each load cycle in response to commands from the data
processing and control component, adjusts and applies a load
7. Hazards
suchthatthespecimenexperiencesaconstantlevelofdisplace-
7.1 Observe standard laboratory safety precautions when
preparing and testing asphalt concrete specimens.
TABLE 1 Test System Minimum Requirements
Load Measurement and Control Range: 0 to 5 kN (0 to 1124 lbf)
8. Sampling and Test Specimen Preparation
Resolution: 2.5 N (0.56 lbf)
8.1 Laboratory-Mixed and Compacted Specimens—Sample
Accuracy: 5 N (1 lbf)
asphalt binder in accordance with Practice D140 and sample
Displacement Measurement and Control Range: 0 to 5 mm (0 to 0.2 in.)
aggregate in accordance with Practice D75. If a complete
Resolution: 2.5 µm (9.8 3 10 in.)
Accuracy: 5 µm (2.0 3 10 in.) fatigue curve is desired, prepare nine replicate asphalt concrete
beam specimens, from slab(s) or beam(s) compacted in accor-
Frequency Measurement and Control Range: 5 to 10 Hz
dance with AASHTO PP 3. Otherwise, prepare as many
Resolution: 0.005 Hz
specimens as desired for individual beam test results. Labora-
Accuracy: 0.01 Hz
tory prepared mixtures are typically conditioned with a short-
Temperature Measurement and Control Resolution: 60.25°C (60.45°F)
term aging process, such as defined in AASHTOR30. Test at
Accuracy: 60.5°C (60.9°F)
least six replicate asphalt concrete beam specimens at different
Displacement Sensor Linear Variable Differential
strain levels in order to develop a fatigue curve, as shown in
Transducer (LVDT), Extensometer,
Fig.4.Theextraspecimensmayalsobetestedasdesired,ifthe
or similar device
data appears to include an outlier, or if a beam failure occurs
D7460–08
FIG. 1 Illustration of Haversine Wave Form Relative to Sine Wave
FIG. 2 Load and Freedom Characteristics of Fatigue Test Apparatus (Cox)
D7460–08
NOTE 1—Early model shown; the newer model allows free rotation and translation at all four clamps.
FIG. 3 Load and Freedom Characteristics of IPC Fatigue Test Apparatus
NOTE—Strain levels should be adjusted for the material.
FIG. 4 Example Fatigue Curve
D7460–08
directlyataclamp.Alinearrelationshiponalog-logplotexists alltheclampswillbealigned.Ifthetopandbottomsidesofthe
between N and the level of strain (µ´, microstrain = strain 3 beam test specimen are not parallel, it should not be an issue
f
10 ). with the clamping. The saw cuts are typically straight on all
sides of the beam even if these are not parallel to each other;
NOTE 2—The type of compaction device (linear kneading, rolling
the top clamps will compensate for the lack of parallelism,
wheel, vibratory) may influence the test results, relative to representing
since the clamps are all independent of each other. The Cox
actual construction.
fixture is designed to use the 3.175 mm ( ⁄8 in.) tensile bar
NOTE 3—Normally test specimens are compacted using a standard
compactive effort. However, the standard compactive effort may not
coupler for facilitating 360° movement without creating an
reproduce the air voids of roadway specimens measured according to Test
eccentricmoment,asshowninFig.5.Thetwospent3.175mm
Method D3203. If specimens are to be compacted to a target air void
( ⁄8 in.) tensile bars pictured on the right-hand side of Fig. 5
content, the compactive effort should be determined experimentally.
show the deformation that can occur due to years of fatigue
8.2 Plant-Mixed, Laboratory Compacted Specimens—
testing; any shortening of the shaft changes the stroke location.
Obtain asphalt concrete samples in accordance with Practice
If the fixture uses this type of coupler, this initial sensor
D979. If a complete fatigue curve is desired, prepare nine
location should be checked after every seven testing days to
replicate asphalt concrete beam specimens, from slab(s) or
evaluate the condition of the coupler. If the fixture is hard
beam(s) compacted in accordance with AASHTO PP 3. Oth-
coupled, as with the IPC device, this alignment check can be
erwise, prepare as many specimens as desired for individual
performed less frequently.
beam test results. See Notes 2 and 3. Test at least six replicate
9.2 Specimen Measurement—Measure the height and width
-4
asphalt concrete beam specimens at different strain levels in
of the specimen to the nearest 0.01 mm (3.94 3 10 in.) at
order to develop a fatigue curve, as shown in Fig. 4. The extra
three or more different points along the middle 100 mm (3.94
specimens may also be tested as desired, if the data appears to
in.) of the specimen length in accordance with applicable
include an outlier, or if a beam failure occurs directly at a
sections of Test Method D3549, Determine the average of the
clamp.
measurements for each dimension and record the averages to
8.3 Roadway Specimens—Obtain compacted asphalt con-
the nearest 0.1 mm (0.004 in).
crete samples from the roadway in accordance with Practice
9.3 Attaching the Target to the Neutral Axis of Specimen
D5361.
(Required with the Cox Fixture)—Locate the center of a
8.4 Specimen Trimming—Saw at least 6 mm from all sides
specimen on one of its 50 mm (1.97 in.) high lengthwise sides
of each compacted specimen to provide smooth, parallel
(i.e., mid-height and mid-length of the beam). Apply cy-
(saw-cut) surfaces for mounting the measurement gages. The
anoacrylate (super glue) or equivalent in a circle around this
final required dimensions of the test specimen, after sawing,
point and place the target on the glue such that the top of the
are 380 6 6 mm (14.96 6 0.24 in.) in length, 50 6 2 mm (1.96
target is a
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