1、Designation: D7460 10Standard Test Method forDetermining Fatigue Failure of Compacted Asphalt ConcreteSubjected to Repeated Flexural Bending1This standard is issued under the fixed designation D7460; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method provides procedures for determining aunique failure point for estimating
3、 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 laboratoryor field compacted asphalt concrete, which are subjected torepeated flexural bending.1.2 The between-laboratory reproducibility of this testmethod is bei
4、ng determined and will be available on or beforeJune 2013. Therefore, this test method should not be used foracceptance or rejection of a material for purchasing purposes.1.3 The text of this standard references notes and footnoteswhich provide explanatory material. These notes and footnotes(excludi
5、ng those in tables and figures) shall not be consideredas requirements of the standard.1.4 UnitsThe values stated in SI units are to be regardedas standard. Other units of measurement included in thisstandard are for information only.1.5 This standard does not purport to address all of thesafety con
6、cerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D75 Practice for Sampling AggregatesD1
7、40 Practice for Sampling Bituminous MaterialsD979 Practice for Sampling Bituminous Paving MixturesD2041 Test Method for Theoretical Maximum SpecificGravity and Density of Bituminous Paving MixturesD3203 Test Method for Percent Air Voids in CompactedDense and Open Bituminous Paving MixturesD3549 Test
8、 Method for Thickness or Height of CompactedBituminous Paving Mixture SpecimensD3666 Specification for Minimum Requirements for Agen-cies Testing and Inspecting Road and Paving MaterialsD5361 Practice for Sampling Compacted Bituminous Mix-tures for Laboratory TestingE29 Practice for Using Significan
9、t Digits in Test Data toDetermine Conformance with Specifications2.2 AASHTO Standards:3T 321 Standard Method of Test for Determining the FatigueLife of Compacted Hot-Mix Asphalt (HMA) Subjected toRepeated Flexural BendingPP 3 Preparing Hot-Mix Asphalt (HMA) Specimens byMeans of the Rolling Wheel Com
10、pactorR30Standard Practice for Mixture Conditioning of Hot-Mix Asphalt (HMA)3. Terminology3.1 Definitions:3.1.1 beam modulusFlexural Beam Stiffness, as deter-mined in 10.1.3.3.1.2 failure pointthe number of cycles to failure, Nf,which corresponds to the maximum or peak NormalizedModulus 3 Cycles (Fi
11、g. 13) when plotted versus Number ofCycles.3.1.3 initial beam modulusFlexural Beam Stiffness deter-mined at approximately 50 load cycles.3.1.4 normalized modulus 3 cyclessee Rowe and Boul-din (1):4Beam Stiffness 3 Cycle Number!Initial Beam Modulus 3 Cycle of Initial Beam Modulus!4. Summary of Test M
12、ethod4.1 The four-point flexural bending test method is con-ducted on compacted beam specimens to evaluate the fatigueproperties of an asphalt concrete mixture. A cyclic haversine(displaced sine wave with full amplitude on tension side of1This test method is under the jurisdiction of ASTM Committee
13、D04 on Roadand Paving Materials and is the direct responsibility of Subcommittee D04.26 onFundamental/Mechanistic Tests.Current edition approved June 1, 2010. Published July 2010. Originally approvedin 2008. Last previous edition approved in 2008 as D764008. DOI: 10.1520/D7460-10.2For referenced AST
14、M standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American Association of State Highway and TransportationOfficial
15、s (AASHTO), 444 N. Capitol St., NW, Suite 249, Washington, DC 20001,http:/www.transportation.org.4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United
16、 States.zero) displacement is applied at the central H-frame thirdpoints of a beam specimen, while the outer third points are heldin an articulating fixed position. The frequency rate rangesfrom 5 to 10 Hz. This produces a constant bending momentover the center third (L/3) span (118.5 to 119 mm (4.6
17、6 to 4.69in.) between the H-frame contact points on the beam speci-men. The level of desired strain is pre-calculated and an inputfor the displacement control. The deflection at the mid-lengthposition (L/2) of a beam specimen is regulated by the closedloop control system.5. Significance and Use5.1 T
18、he laboratory fatigue life determined by this standardfor beam specimens have been used to estimate the fatigue lifeof asphalt concrete pavement layers under repeated trafficloading. Although the field performance of asphalt concrete isimpacted by many factors (traffic variation, speed, and wander;c
19、limate variation; rest periods between loads; aging; etc.), ithas been more accurately predicted when laboratory propertiesare known along with an estimate of the strain level induced atthe layer depth by the traffic wheel load traveling over thepavement.NOTE 1The quality of the results produced by
20、this standard aredependent on the competence of the personnel performing the procedureand the capability, calibration, and maintenance of the equipment used.Agencies that meet the criteria of Specification D3666 are generallyconsidered capable of competent and objective testing/sampling/inspection/e
21、tc. Users of this standard are cautioned that compliance withSpecification D3666 alone does not completely assure reliable results.Reliable results depend on many factors; following the suggestions ofSpecification D3666 or some similar acceptable guideline provides ameans of evaluating and controlli
22、ng some of those factors.6. Apparatus6.1 Test SystemThe test system shall consist of a loadframe, an environmental chamber (temperature control system)and a closed loop control and data acquisition system. The testsystem shall meet the minimum requirements specified inTable 1. This standard specific
23、ally describes the systems of twoprimary suppliers (Cox and Sons, Inc. Cox and IndustrialProcess Controls, Ltd. IPC); however, other similar equip-ment could also be used.6.1.1 Loading DeviceThe test system shall include aclosed-loop, computer controlled loading component which,during each load cycl
24、e in response to commands from the dataprocessing and control component, adjusts and applies a loadsuch that the specimen experiences a constant level of displace-ment (and resulting strain) during each load cycle. The loadingdevice shall be capable of (1) providing cyclic haversine(= SIN2(degrees/2
25、) loading at a frequency range of 5 to 10 Hz,(2) subjecting specimens to 4-point bending with free rotationand horizontal translation at all load and reaction points, and(3) forcing the specimen back to its original position (that is,zero deflection) at the end of each loading cycle. Fig. 1illustrat
26、es the haversine waveform. Figs. 2 and 3 show themovements of the Cox and IPC loading devices, respectively;the Cox device loads in a downward direction and the IPCloads in an upward direction. The early version of the IPCdevice does not have free translation at the inner clamps;however, the newer m
27、odel allows free rotation and translationat all four clamps.6.1.2 Environmental Chamber (Temperature ControlSystem)The environmental chamber shall enclose the entirespecimen and maintain the specimen at the desired testtemperature. The temperature shall be within 60.5C (60.9F)throughout the conditio
28、ning and testing times. An environmen-tal chamber is not required if the temperature of the surround-ing environment can be maintained within the specified limits.6.1.3 Control and Data Acquisition SystemDuring eachload cycle the control and data acquisition system shall becapable of measuring the d
29、isplacement of the beam specimen,and adjusting the load applied by the loading device such thatthe specimen experiences a constant level of displacement oneach load cycle. In addition, it shall be capable of recordingload cycles, applied loads, beam displacements, and tempera-ture while computing an
30、d recording the maximum tensilestress, maximum tensile strain, phase angle, and stiffness atload cycle intervals specified by the user.6.2 Miscellaneous Apparatus and MaterialsFor the Coxdevice, an aluminum, wedge-shaped target for connecting thedisplacement sensor to the neutral axis of the specime
31、n andcyanoacrylate (super glue) or equivalent is needed for attachingthe target to the specimen. With both the Cox and the IPCequipment, an alignment fixture and a solid aluminum beamare needed for setting the proper clamp spacing and a sawsuitable for cutting the beams with parallel faces to the pr
32、opertolerance.7. Hazards7.1 Observe standard laboratory safety precautions whenpreparing and testing asphalt concrete specimens.8. Sampling and Test Specimen Preparation8.1 Laboratory-Mixed and Compacted SpecimensSampleasphalt binder in accordance with Practice D140 and sampleaggregate in accordance
33、 with Practice D75. If a completefatigue curve is desired, prepare nine replicate asphalt concretebeam specimens, from slab(s) or beam(s) compacted in accor-dance with AASHTO PP 3. Otherwise, prepare as manyTABLE 1 Test System Minimum RequirementsLoad Measurement and Control Range: 0 to 5 kN (0 to 1
34、124 lbf)Resolution: 2.5 N (0.56 lbf)Accuracy: 5 N (1 lbf)Displacement Measurement and Control Range: 0 to 5 mm (0 to 0.2 in.)Resolution: 2.5 m (9.8 3 105in.)Accuracy: 5 m (2.0 3 104in.)Frequency Measurement and Control Range: 5 to 10 HzResolution: 0.005 HzAccuracy: 0.01 HzTemperature Measurement and
35、 Control Resolution: 60.25C (60.45F)Accuracy: 60.5C (60.9F)Displacement Sensor Linear Variable DifferentialTransducer (LVDT), Extensometer,or similar deviceD7460 102FIG. 1 Illustration of Haversine Wave Form Relative to Sine WaveFIG. 2 Load and Freedom Characteristics of Fatigue Test Apparatus (Cox)
36、D7460 103specimens as desired for individual beam test results. Labora-tory prepared mixtures are typically conditioned with a short-term aging process, such as defined in AASHTO R30. Test atleast six replicate asphalt concrete beam specimens at differentstrain levels in order to develop a fatigue c
37、urve, as shown inFig. 4. The extra specimens may also be tested as desired, if thedata appears to include an outlier, or if a beam failure occursdirectly at a clamp.Alinear relationship on a log-log plot existsbetween Nfand the level of strain (, microstrain = strain 3106).NOTE 2The type of compacti
38、on device (linear kneading, rollingwheel, vibratory) may influence the test results, relative to representingactual construction.NOTE 3Normally test specimens are compacted using a standardcompactive effort. However, the standard compactive effort may notreproduce the air voids of roadway specimens
39、measured according to TestMethod D3203. If specimens are to be compacted to a target air voidcontent, the compactive effort should be determined experimentally.8.2 Plant-Mixed, Laboratory Compacted SpecimensObtain asphalt concrete samples in accordance with PracticeD979. If a complete fatigue curve
40、is desired, prepare ninereplicate asphalt concrete beam specimens, from slab(s) orbeam(s) compacted in accordance with AASHTO PP 3. Oth-erwise, prepare as many specimens as desired for individualbeam test results. See Notes 2 and 3. Test at least six replicateasphalt concrete beam specimens at diffe
41、rent strain levels inorder to develop a fatigue curve, as shown in Fig. 4. The extraspecimens may also be tested as desired, if the data appears toinclude an outlier, or if a beam failure occurs directly at aclamp.8.3 Roadway SpecimensObtain compacted asphalt con-crete samples from the roadway in ac
42、cordance with PracticeD5361.8.4 Specimen TrimmingSaw at least 6 mm from all sidesof each compacted specimen to provide smooth, parallel(saw-cut) surfaces for mounting the measurement gages. Thefinal required dimensions of the test specimen, after sawing,are 380 6 6 mm (14.96 6 0.24 in.) in length, 5
43、0 6 2 mm (1.966 0.08 in.) in height, and 63 6 2 mm (2.48 6 0.08 in.) inwidth. To minimize specimen variability, it is recommendedthat the beams be immediately labeled to ensure consistentorientation (top and sides) during testing, relative to thecompaction process.NOTE 1Early model shown; the newer
44、model allows free rotation and translation at all four clamps.FIG. 3 Load and Freedom Characteristics of IPC Fatigue Test ApparatusD7460 1048.5 Specimen StorageThe specimens should be stored ona 12.7 mm (12 in.) steel plate with a flatness of 0.127 mm(0.005 in.) across the surface of the plate from
45、end to end. Thisflat surface keeps the beam specimens from being pre-strainedbefore testing. Limit stacking of specimens to two high onstorage racks.9. Procedure9.1 Fixture AlignmentA solid aluminum beam, havingdimensions specified in 8.4 with tolerances to a flatness of0.051 mm (0.002 in.) across t
46、he length of the aluminum beam(measured using a straight edge and feeler gauges), is used toensure proper alignment of the beam fixture prior to testing.Insert the aluminum beam into the fixture, clamping the sideclamps on the outside frame first. Clamp the top clamps on theoutside frames followed b
47、y the top clamps on the insideframes. Place the actuator in load control and remove the load.Verify that the clamps are fully seated on the aluminum beam.On the Cox frame, apply the side clamps to the inside frames.After returning to displacement control, adjust the load to thepositive side of zero;
48、 make a note of the actuator displacementsensor location and start cycling from this position. Once thiszero load position is located and used as a guide, the bottom ofall the clamps will be aligned. If the top and bottom sides of thebeam test specimen are not parallel, it should not be an issuewith
49、 the clamping. The saw cuts are typically straight on allsides of the beam even if these are not parallel to each other;the top clamps will compensate for the lack of parallelism,since the clamps are all independent of each other. The Coxfixture is designed to use the 3.175 mm (18 in.) tensile barcoupler for facilitating 360 movement without creating aneccentric moment, as shown in Fig. 5. The two spent 3.175 mm(18 in.) tensile bars pictured on the right-hand side of Fig. 5show the deformation that can occur due to years of fatiguetestin
