ASTM D8458-22

Standard Test Method for Evaluation of Fatigue Performance of Asphalt Mixtures Using the Three-Point Bending Cylinder (3PBC) Test

SIGNIFICANCE AND USE
5.1 This test method can be utilized to determine the fatigue resistance of asphalt mixtures. The test method is generally valid for specimens that are tested at intermediate temperatures. The three-point bending cylinder test samples are obtained by coring a 68 mm diameter cylinder from the center of a 150 mm diameter gyratory compacted sample, or horizontal coring from field cores or slabs cut from field sections. After coring, the sample is ready for testing and no further sample preparations steps are required. The two ends of the 68 mm diameter three-point bending cylinder sample do not need to be sliced.  
5.2 The Timoshenko beam theory is used to calculate the reduction in dynamic modulus for each loading cycle. The test can be used to investigate the fatigue behavior of asphalt mixtures at various strain levels, temperatures, and frequencies. The results can be used to compare the fatigue life (Nf) for different asphalt mixtures. The Nf value can be calculated as the 50 % reduction in dynamic modulus. The Nf value is an indicator of fatigue performance of asphalt mixtures containing various mix design properties, asphalt binder types and modifications, gradations, and recycled materials. Typically, a higher Nf value indicates better fatigue performance. The Nf value may be used to identify crack-prone mixtures in performance-based mix design or in construction acceptance procedures, or both.
Note 1: The quality of the results produced by this test method 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 D3666 are generally considered capable of competent and objective testing, sampling, inspection, etc. Users of this test method are cautioned that compliance with Specification D3666 alone does not completely ensure reliable results. Reliable results may depend on many factors; following the suggestions of Specifi...
SCOPE
1.1 This test method provides a procedure to determine the fatigue life (number of cycles to failure, Nf) of asphalt mixtures, and also the reduction in dynamic modulus (|E*|) with loading cycles, using cylindrical samples subjected to three-point cyclic bending. The results obtained from this test can be used to calibrate Viscoelastic Continuum Damage (VECD) models to obtain a damage characteristic curve, which in turn can be used to obtain fatigue lives (Nf) at a variety of temperatures, strain levels, and frequencies (a separate standard practice is being drafted for this procedure). Even though this test method is intended primarily for displacement (strain) controlled fatigue testing, certain sections may provide useful information for force-controlled tests.  
1.2 The test method describes the testing apparatus, instrumentation, specimen fabrication, and analysis procedures required to determine the number of cycles to failure of asphalt concrete.  
1.3 The text of this test method 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 test method.  
1.4 Units—The values stated in SI units are to be regarded as the standard. No other units of measurement are included in this standard.  
1.5 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 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 (T...

General Information

• Status: Published
• Publication Date: 14-Dec-2022
• ICS: 93.080.20 - Road construction materials
• Technical Committee: D04 - Road and Paving Materials
• Drafting Committee: D04.26 - Fundamental/Mechanistic Tests

Relations

• Refers: ASTM D8-19 - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 01-Aug-2019
• Refers: ASTM D8-18c - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 15-Dec-2018
• Refers: ASTM D8-18b - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 15-Aug-2018
• Refers: ASTM D8-18a - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 01-Jul-2018
• Refers: ASTM D8-18 - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 01-Feb-2018
• Refers: ASTM D3549/D3549M-17 - Standard Test Method for Thickness or Height of Compacted Asphalt Mixture Specimens
• Effective Date: 01-Oct-2017
• Refers: ASTM D8-17c - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 15-Jul-2017
• Refers: ASTM D8-17b - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 15-Jun-2017
• Refers: ASTM D8-17a - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 01-May-2017
• Refers: ASTM D8-17 - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 01-Mar-2017
• Refers: ASTM D8-16b - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 01-Dec-2016
• Refers: ASTM D3666-16 - Standard Specification for Minimum Requirements for Agencies Testing and Inspecting Road and Paving Materials
• Effective Date: 01-Oct-2016
• Refers: ASTM D8-16a - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 15-Sep-2016
• Refers: ASTM D8-16 - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 01-Sep-2016
• Refers: ASTM D8-15 - Standard Terminology Relating to Materials for Roads and Pavements
• Effective Date: 01-Sep-2015

Overview

ASTM D8458-22 is the standard test method for evaluating the fatigue performance of asphalt mixtures using the Three-Point Bending Cylinder (3PBC) test. Developed by ASTM, this international standard describes a reliable laboratory procedure for determining the fatigue life (Nf) and reduction in dynamic modulus (|E*|) of asphalt mixtures. The standard helps practitioners assess the fatigue resistance of asphalt concrete, a critical property in the durability and performance of pavements subject to repeated traffic loading. By using specimens prepared from laboratory-compacted, plant-mixed, or field-cored asphalt samples, ASTM D8458-22 enables comparison between different mixtures and supports the development and evaluation of high-performance, crack-resistant pavements.

Key Topics

• Fatigue Life Determination: Defines methods for measuring the number of cycles to failure (Nf) under repeated cyclic loading, providing a quantitative indicator of a mixture’s fatigue resistance.
• Dynamic Modulus Reduction: Evaluates the decrease in dynamic modulus (|E*|) of asphalt specimens during testing, which is essential for understanding damage accumulation.
• Test Apparatus and Sample Preparation: Specifies equipment requirements including the three-point bending cylinder fixture, environmental chamber for temperature control, and instrumentation such as load frames, displacement sensors, and data acquisition systems. Important details include sample coring, specimen dimensions (68 mm diameter), and minimal sample preparation.
• Timoshenko Beam Theory: Utilizes this theory for calculating dynamic modulus and interpreting test data, accommodating both bending and shear deformations typical in asphalt specimens.
• Measurement Conditions: Test procedures are valid for intermediate temperatures and allow adjustment for different strain levels, temperatures, and frequencies, offering flexibility for performance-based evaluations.
• Performance Indicators: Provides reporting formats for key results such as initial dynamic modulus, applied loads, tensile stress/strain, and cycles to failure for consistent quality assessment.

Applications

• Mix Design Optimization: Use test results to compare fatigue performance for various asphalt mixture designs, binder types, aggregate gradations, and levels of recycled content.
• Quality Control and Acceptance: Integrate Nf values and modulus reduction measures into performance-based specifications for construction acceptance and ongoing pavement quality assurance.
• Crack-Prone Mixture Identification: Employ fatigue life results to detect mixtures susceptible to early cracking, enabling preemptive modifications in mix design or construction practices.
• Support for VECD Modeling: Provides data for calibrating Viscoelastic Continuum Damage (VECD) models, which are vital for advanced mechanistic-empirical pavement design and durability forecasting.
• Laboratory and Field Assessment: Accommodates both laboratory-mixed and field-cored specimens, supporting research as well as real-world pavement evaluation and forensics.

Related Standards

• ASTM D8: Terminology relating to roads and paving materials.
• ASTM D979/D979M: Practice for sampling asphalt mixtures.
• ASTM D3549/D3549M: Test method for thickness or height of asphalt mixture specimens.
• ASTM D3666: Specification for minimum requirements for agencies testing and inspecting road and paving materials.
• ASTM D5361/D5361M: Practice for sampling compacted asphalt mixtures for laboratory testing.
• ASTM D6373: Specification for performance-graded asphalt binder.
• AASHTO R30: Practice for mixture conditioning of hot mix asphalt.
• AASHTO T 378: Method for determining the dynamic modulus and flow number for asphalt mixtures.
• AASHTO M320/M332: Specifications for performance-graded asphalt binder, including those using multiple stress creep recovery.

By following ASTM D8458-22, professionals in the paving industry can enhance the reliability of asphalt pavement designs, improve material selection, and ensure road longevity through scientifically validated fatigue testing protocols.

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: D8458 − 22
Standard Test Method for
Evaluation of Fatigue Performance of Asphalt Mixtures
Using the Three-Point Bending Cylinder (3PBC) Test
This standard is issued under the fixed designation D8458; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 This test method provides a procedure to determine the 2.1 ASTM Standards:
fatigue life (number of cycles to failure, N) of asphalt D8Terminology Relating to Materials for Roads and Pave-
f
mixtures, and also the reduction in dynamic modulus (|E*|) ments
with loading cycles, using cylindrical samples subjected to D979/D979MPractice for Sampling Asphalt Mixtures
three-point cyclic bending. The results obtained from this test D3549/D3549MTest Method for Thickness or Height of
can be used to calibrate Viscoelastic Continuum Damage Compacted Asphalt Mixture Specimens
(VECD)modelstoobtainadamagecharacteristiccurve,which D3666Specification for Minimum Requirements for Agen-
in turn can be used to obtain fatigue lives (N) at a variety of cies Testing and Inspecting Road and Paving Materials
f
temperatures, strain levels, and frequencies (a separate stan- D5361/D5361MPractice for Sampling Compacted Asphalt
dard practice is being drafted for this procedure). Even though Mixtures for Laboratory Testing
this test method is intended primarily for displacement (strain) D6373 Specification for Performance-Graded Asphalt
controlled fatigue testing, certain sections may provide useful Binder
information for force-controlled tests.
2.2 AASHTO Standards:
R30Practice for Mixture Conditioning of Hot MixAsphalt
1.2 The test method describes the testing apparatus,
(HMA)
instrumentation,specimenfabrication,andanalysisprocedures
R83Preparation of Cylindrical Performance Test Speci-
requiredtodeterminethenumberofcyclestofailureofasphalt
mens Using the Superpave Gyratory Compactor (SGC)
concrete.
T 378Standard Method of Test for Determining the Dy-
1.3 The text of this test method references notes and
namic Modulus and Flow Number for Asphalt Mixtures
footnotes which provide explanatory material.These notes and
Using the Asphalt Mixture Performance Tester (AMPT)
footnotes (excluding those in tables and figures) shall not be
M 320Standard Specification for Performance-Graded As-
considered as requirements of the test method.
phalt Binder
1.4 Units—The values stated in SI units are to be regarded
M 332Standard Specification for Performance-Graded As-
as the standard. No other units of measurement are included in
phalt Binder Using Multiple Stress Creep Recovery
this standard.
(MSCR) Test
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 3. Terminology
responsibility of the user of this standard to establish appro-
3.1 Definitions:
priate safety, health, and environmental practices and deter-
3.1.1 dynamic modulus, |E*|—theamplitudeofthecomplex
mine the applicability of regulatory limitations prior to use.
modulus that defines the relationship between the stress and
1.6 This international standard was developed in accor-
strain of viscoelastic materials. The |E*| is simply the peak-to-
dance with internationally recognized principles on standard-
peak stress divided by peak-to-peak strain in a cyclic test run
ization established in the Decision on Principles for the
at a constant frequency.
Development of International Standards, Guides and Recom-
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
This test method is under the jurisdiction of ASTM Committee D04 on Road Standards volume information, refer to the standard’s Document Summary page on
and Paving Materials and is the direct responsibility of Subcommittee D04.26 on the ASTM website.
Fundamental/Mechanistic Tests. Available from American Association of State Highway and Transportation
Current edition approved Dec. 15, 2022. Published January 2023. DOI: 10.1520/ Officials (AASHTO), 444 N. Capitol St., NW, Suite 249, Washington, DC 20001,
D8458-22. http://www.transportation.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D8458 − 22
results. Reliable results may depend on many factors; following the
3.1.2 initial dynamic modulus, |E*| —initial undamaged
suggestions of Specification D3666 or some similar acceptable guideline
dynamic modulus determined at approximately 50 load cycles.
provides a means of evaluating and controlling some of those factors.
3.1.3 Poisson’s ratio—the ratio of transverse to longitudinal
strains of a loaded specimen.
6. Apparatus
3.1.4 Timoshenko beam theory—the theory which considers
6.1 Test System—The test system consists of a three-point
the bending and shear effects when subjected to loading, and
bending cylinder test setup, a load frame capable of providing
commonly used in low aspect ratio beams (that is, when
cyclic load and displacement, an environmental chamber
length-to-diameter ratio of a beam is <6).
(temperature control system), and closed-loop control and data
3.2 Fordefinitionsofothertermsusedinthisstandard,refer
acquisition system. Fig. 1 illustrates the details of the three-
to Terminology D8.
point bending cylinder setup. The side clamps shall hold the
asphalt sample fixed with no sliding, rotation, or combination
4. Summary of Test Method
thereof. High-strength steel shall be used in the production of
4.1 A cylindrical specimen is clamped using C-shaped
the fixture. The test system’s minimum requirements are
clamps in a three-point bending setup and subjected to sinu-
specified in Table 1.
soidal actuator displacement-controlled loading with zero
6.2 Three-Point Bending Cylinder (3PBC) Test Fixture—
mean. While the loading is applied at the central clamp, the
The test fixture is composed of a 175 mm solid base, two fixed
side clamps hold the sample in a fixed position. The actuator
95 mm end supports used to clamp the sample, and a 95 mm
displacement is set such that the initial strain ranges from 200
–6 central clamp for application of cyclic (zero-mean) vertical
to 800 × 10 mm/mm. The recommended loading frequency
load. Supports and loading clamps are composed of two
rate is from 5 Hz to 10Hz. The load and deflection at the
C-shaped pieces, which are screwed together to hold the
central clamp are measured during the entire duration of the
asphaltsampleinplace.ThelowerC-shapedpiecesarewelded
test to be later analyzed by Timoshenko beam theory formu-
tothebaseplate.Thedistancebetweentwosupportsis125mm
lations to calculate the change in dynamic modulus (|E*|) per
andtheinnerdiametersofclampsare68mmeach.Topbarsare
loading cycle.
placedonsideclampstopreventanypotentialdeflectionofthe
side clamps (see Fig. 1). All the parts (except the LVDT
5. Significance and Use
holders) are made of high-strength steel to prevent any
5.1 Thistestmethodcanbeutilizedtodeterminethefatigue
undesirable deformation during the test. It is noted that
resistance of asphalt mixtures. The test method is generally
dimensional tolerances shown in Fig. 1 are mandatory.
valid for specimens that are tested at intermediate tempera-
tures. The three-point bending cylinder test samples are ob- 6.3 Loading Device—The test system includes a closed-
tained by coring a 68 mm diameter cylinder from the center of
loop, computer-controlled loading component which, during
a 150 mm diameter gyratory compacted sample, or horizontal each load cycle in response to commands from the data
coring from field cores or slabs cut from field sections. After
processing and control component, adjusts and applies a load
coring, the sample is ready for testing and no further sample suchthatthespecimenexperiencesaconstantlevelofdisplace-
preparations steps are required. The two ends of the 68 mm
ment during each loading cycle. The loading device should be
diameterthree-pointbendingcylindersampledonotneedtobe capable of providing peak-peak sinusoidal loading with zero
sliced.
mean at a frequency range of 5 Hz to 10 Hz. Fig. 2(a) and Fig.
2(b) show the three-point bending cylinder setup with a
5.2 The Timoshenko beam theory is used to calculate the
mounted specimen in a material testing system and asphalt
reduction in dynamic modulus for each loading cycle. The test
mixture performance tester, respectively.
can be used to investigate the fatigue behavior of asphalt
mixtures at various strain levels, temperatures, and frequen-
6.4 Environmental Chamber (Temperature Control
cies.Theresultscanbeusedtocomparethefatiguelife(N)for
f System)—The environmental chamber shall enclose the entire
different asphalt mixtures. The N value can be calculated as
f specimen and the fixture and maintain the specimen at the
the 50% reduction in dynamic modulus. The N value is an
f desired test temperature within 60.5°C throughout the condi-
indicatoroffatigueperformanceofasphaltmixturescontaining
tioning and testing times. An environmental chamber is not
various mix design properties, asphalt binder types and
requiredifthetemperatureofthesurroundingenvironmentcan
modifications, gradations, and recycled materials. Typically, a
be maintained within the specified limits.
higher N value indicates better fatigue performance. The N
f f
6.4.1 Control and Data Acquisition System—During each
value may be used to identify crack-prone mixtures in
load cycle, the control and data acquisition system shall be
performance-based mix design or in construction acceptance
capable of measuring the displacement of the beam specimen,
procedures, or both.
and adjusting the load applied by the loading device such that
NOTE 1—The quality of the results produced by this test method are the specimen experiences a constant level of displacement on
dependent on the competence of the personnel performing the procedure
each load cycle. In addition, it shall be capable of recording
and the capability, calibration, and maintenance of the equipment used.
load cycles, applied loads, beam displacements, and tempera-
Agencies that meet the criteria of Specification D3666 are generally
ture while computing and recording the maximum tensile
considered capable of competent and objective testing, sampling,
stress, maximum tensile strain, phase angle, and dynamic
inspection, etc. Users of this test method are cautioned that compliance
with Specification D3666 alone does not completely ensure reliable modulus at load cycle intervals specified by the user.
D8458 − 22
FIG. 1 General Schematic View of the Three-Point Bending Cylinder Test Setup with a Loaded Specimen: (a) Elevation View; (b) Side
View; and (c) Plan View
6.5 Deformation Measurements—Mid-span deformation same LVDT type can be used to perform dynamic modulus
shall be measured using sensors mounted on two sides of the
tests according to AASHTO T 378.
central clamp as shown in Fig. 2.Also, it is encouraged to use
6.6 Caliper or ruler accurate to 60.05mm for specimen
a lateral LVDT to monitor the lateral movement of the side
diameter measurement.
clamps, if applicable. Spring-loaded linear variable differential
transducers (LVDTs) are recommended but not specified. The
D8458 − 22
FIG. 1 General Schematic View of the Three-Point Bending Cylinder Test Setup with a Loaded Specimen: (a) Elevation View; (b) Side
View; and (c) Plan View (continued)
6.7 The temperature measurements shall be performed us- 8.2 If the testing is run for the purpose of ranking multiple
ing a calibrated digital thermometer with a tolerance range of
asphalt mixtures, a minimum of two replicates per testing
no more than 60.2°C.
condition is recommended. If a complete fatigue curve is
needed for use in the viscoelastic continuum damage (VECD)
6.8 Data Quality—Accept only test data meeting the data
analysis, a minimum of four replicates are recommended,
quality statistics given in Table 2. Calculation steps and all the
where two replicates will be tested at one temperature and the
formulations for these data quality statistics are provided in
other two will be tested at another temperature. Otherwise,
Annex A2.
prepare as many samples as required.
7. Hazards
8.3 Laboratory-Mixed and Laboratory Compacted (LMLC)
7.1 Observe standard laboratory safety precautions when
Specimens—The3PBCspecimenshallhaveadiameterof68 6
preparing and testing asphalt concrete specimens.
0.5 mm and a minimum length of 150 mm. LMLC specimens
shall be short-term conditioned before the compaction as
8. Sampling and Test Specimen Preparation
defined inAASHTO R30. Prepare the asphalt concrete speci-
mens in general accordance with AASHTO R 83 (it takes
8.1 The three-point bending cylinder test may be conducted
approximately 16h for the specimens to be fully cooled down
on laboratory-prepared test specimens and/or field cores with
NMAS less than or equal to 19 mm. to room temperature). Then, core the compacted sample to
D8458 − 22
FIG. 1 General Schematic View of the Three-Point Bending Cylinder Test Setup with a Loaded Specimen: (a) Elevation View; (b) Side
View; and (c) Plan View (continued)
TABLE 1 Test System Minimum Requirements
Measurement Range Accuracy Resolution
Load measurement and control 0 to 5 kN 5 N #0.0012 kN
Displacement measurement and control 0 to 5 mm 5 µm 0.0025 mm
Frequency measurement and control 5 to 10 Hz 0.01 Hz Not specified
Temperature measurement and control 5 to 35 °C ±0.5 °C Not specified
Minimum number of data samples for each cycle 40 N/A Not specified
obtain 68 mm diameter samples with an air void level of the PMLC specimens shall not be short-term aged and prepared in
operator’s choice (for example, 7 % 6 0.5 %). Cored samples general accordance with AASHTO R83. The gyratory speci-
can also be rapidly dried by automatic drying machines (for menwillthenbecoredtoobtain68mmdiametersampleswith
example, CoreDry). In this process, a 3PBC sample can be an air void level of the operator’s choice (for example, 7 % 6
tested within an hour of conditioning. Otherwise, traditional 0.5 %). Cored samples can also be rapidly dried by automatic
drying using a fan can be used which needs 24 to 48h of drying machines (for example, CoreDry). In this process, a
conditioning prior testing. 3PBC sample can be tested within an hour of conditioning.
Otherwise, traditional drying using a fan can be used which
8.4 Plant-Mixed, Laboratory Compacted (PMLC)
needs 24 to 48h of conditioning prior testing.
Specimens—Obtain asphalt concrete samples in accordance
with Practice D979/D979M. The 3PBC specimen shall have a 8.5 Field-Cored Specimens—Obtain compacted asphalt
diameter of 68 6 0.5 mm and a minimum length of 150 mm. concretesamplesfromtheroadwayingeneralaccordancewith
D8458 − 22
FIG. 2 Three-Point Bending Cylinder Test Setup with a Loaded Specimen in the (a) Material Testing System (MTS) and (b) Asphalt
Mixture Performance Tester (AMPT)
TABLE 2 Test System Limits for Data Quality Indicators
Indicator Symbol Equation Limit
Standard error of the applied load se(P) Eq A2.9 #10 %
Average standard error of the measured displacements se(δ) Eq A2.21 #10 %
Uniformity coefficient for the displacement measurements U Eq A2.22 #30 %
δ
Uniformity coefficient for the phase angle measurements U Eq A2.23 #3 degrees
θ
Practice D5361/D5361M. The 3PBC specimen shall be cored 8.6 Measurement of Specimen Dimensions—Measure the
horizontally (perpendicular to the direction of traffic) and shall height and diameter of the specimen to the nearest 0.1 mm at
have a diameter of 68 6 0.5 mm and a minimum length of
three different points at 120° apart in accordance with appli-
150mm. Field coring is only applicable to asphalt concrete
cable sections of Test Method D3549/D3549M, determine the
layers thicker than 75 mm. Do not use this method if a
average of the measurements for each dimension, and record
homogeneous asphalt concrete layer with thickness greater
the averages to the nearest 0.1 mm.
than 75 mm does not exist in the field.
D8458 − 22
8.7 Specimen Preconditioning—Place the specimen in an movement of the side clamps, if applicable. Finally, the top
environmental chamber at a target test temperature 6 1.0°C bars are placed to prevent any potential deflection of the side
clamps.
for a minimum of 2h prior to beginning the test. Exact
conditioning time should be determined by using a thermo-
8.11 Set the displacement amplitude based on the desired
couple placed at the center of a dummy sample and recording
strainratebymanuallyadjustingthesensorandtheparameters
the time required to reach the target temperature.
in the test control software. Select the desired initial strain (for
–6
example, 200 to 800 × 10 mm/mm) and loading frequency
8.8 Testing Temperatures—Recommended test temperature
(for example, 5 Hz) and the load cycle intervals at which test
is the PG ITdefined in Specification D6373,AASHTO M 320,
results are to be recorded and computed. Use the following
or AASHTO M 332 and provided in the following equation:
equation to compute the target displacement based on the
PH 1PG
HT LT desired strain at the bottom of the 3PBC sample in the
T 5 PG 5 14 (1)
1 IT
mid-span:
where: πd
δ 5 K ε (3)
~ !
z y
max
4L
T = first testing temperature (°C),
PG = intermediate performance grade temperature (°C),
IT
8.11.1 The parameters of Eq 3 are defined in Section 9, and
PH = climatic high-performance grade temperature (°C),
HT
therefore are not repeated here for brevity.
and
PG = climatic low-performance grade temperature (°C). 8.12 Within the load cycles to be recorded, include an
LT
interval near the point of five cycles. Average the specimen
NOTE 2—If the data will be analyzed using the simplified viscoelastic
continuum damage theory (VECD), test should be repeated at another dynamicmodulusatthefifthloadcycle;thisdynamicmodulus
temperature.Thisisneededtodetermineifthepseudostiffness(C)versus
is the recommended estimate of the initial beam dynamic
damageparameter(S)relationshipisunique,regardlessofthetemperature
modulus.
of testing. Recommended second testing temperature is 10°C lower than
8.13 Select a displacement level (st
...