1、Designation: D8237 18Standard Test Method forDetermining Fatigue Failure of Asphalt-Aggregate MixturesWith the Four-Point Beam Fatigue Device1This standard is issued under the fixed designation D8237; the number immediately following the designation indicates the year oforiginal adoption or, in the
2、case 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 a procedure for determining afatigue curve that is developed u
3、sing three or more strainlevels. The resulting data can be used in the fatigue models formechanistic-empirical pavement design (that is, PavementME). Failure points are determined for estimating the fatiguelife of 380 mm long by 50 mm thick by 63 mm in breadth(width) asphalt mixture beam (rectangula
4、r prism) specimenssawed from laboratory or field-compacted asphalt mixture,which are subjected to repeated flexural bending.1.2 The largest nominal maximum aggregate size (NMAS)recommended for beams 50 mm thick is 19 mm. Beams madewith an NMAS greater than 19 mm might significantly inter-fere with t
5、he material response, thereby affecting the repeat-ability of the test.1.3 The text of this standard references notes and footnoteswhich provide explanatory material. These notes and footnotes(excluding those in tables and figures) shall not be consideredas requirements of the standard.1.4 UnitsThe
6、values stated in SI units are to be regardedas standard. No other units of measurement are included in thisstandard, with the exception of degrees () where angle isspecified in accordance with IEEE/ASTM SI 10.1.5 This standard does not purport to address all of thesafety concerns, if any, associated
7、 with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accor-dance with internationally recogniz
8、ed principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D8 Terminology Relating
9、to Materials for Roads and Pave-mentsD75/D75M Practice for Sampling AggregatesD140/D140M Practice for Sampling Asphalt MaterialsD979/D979M Practice for Sampling Bituminous PavingMixturesD2041/D2041M Test Method for Theoretical MaximumSpecific Gravity and Density of Bituminous Paving Mix-turesD2726/D
10、2726M Test Method for Bulk Specific Gravity andDensity of Non-Absorptive Compacted Asphalt MixturesD3203/D3203M Test Method for Percent Air Voids in Com-pacted Asphalt MixturesD3549/D3549M Test Method for Thickness or Height ofCompacted Asphalt Mixture SpecimensD3666 Specification for Minimum Requir
11、ements for Agen-cies Testing and Inspecting Road and Paving MaterialsD5361/D5361M Practice for Sampling Compacted AsphaltMixtures for Laboratory TestingD7981 Practice for Compaction of Prismatic Asphalt Speci-mens by Means of the Shear Box CompactorD8079 Practice for Preparation of Compacted Slab As
12、phaltMix Samples Using a Segmented Rolling CompactorE4 Practices for Force Verification of Testing MachinesE29 Practice for Using Significant Digits in Test Data toDetermine Conformance with SpecificationsE2309/E2309M Practices for Verification of DisplacementMeasuring Systems and Devices Used in Ma
13、terial TestingMachines1This test method is under the jurisdiction of ASTM Committee D04 on Roadand Paving Materials and is the direct responsibility of Subcommittee D04.26 onFundamental/Mechanistic Tests.Current edition approved Dec. 1, 2018. Published December 2018. Originallyapproved in 2018. DOI:
14、 10.1520/D8237-18.2For referenced ASTM 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.Copyright ASTM International, 100 Barr Harb
15、or Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendati
16、ons issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1IEEE/ASTM SI 10 American National Standard for MetricPractice2.2 AASHTO Standard:3R30Standard Practice for Mixture Conditioning of Hot-MixAsphalt (HMA)3. Terminology3.1 Definitions of Terms Specific to This Stand
17、ard:3.1.1 p-p,npeak-to-peak stress amplitude at load cycle i.3.1.2 t,nmaximum tensile stress at the fiber of the beam.3.1.3 p-p,npeak-to-peak tensile strain at load cycle i.3.1.4 t,nmaximum tensile strain at the bottom fiber ofthe beam.3.1.5 p-p,npeak-to-peak displacement as determined inFig. 1.3.1.
18、6 S, nflexural beam stiffness, which is the stressdivided by the strain.3.1.7 Si,nthe initial beam stiffness determined at 50 loadcycles.3.1.8 failure point, nthe number of cycles to failure, Nf,which corresponds to the maximum or peak normalized beamstiffness normalized cycles when plotted versus n
19、umber ofcycles (9.9).3.1.9 normalized stiffness normalized cycles, nseeRowe and Bouldin (1).43.2 For definitions of other terms used in this standard, referto Terminology D8.4. Summary of Test Method4.1 The four-point flexural bending test method is con-ducted on compacted beam specimens to evaluate
20、 the fatigueproperties of viscoelastic asphalt mixtures using a fixed refer-ence point bending beam fixture. A cyclic sinusoidal loadingpattern is initiated having no rest periods from the startlocation. A fully executed peak-to-peak displacement (p-p)atthe articulating H-frame third points of the b
21、eam is induced.The outer third points are held in an articulating fixed positionabout the neutral axis of the beam. The frequency rate has adefault frequency of 10 Hertz (Hz) and a test temperature of20 C. This produces a constant bending moment over thecenter third (L/3, length between outside clam
22、ps divided by 3)span of 119 mm 6 0.5 mm (distance may vary betweenmanufacturers; check with manufacturers specifications) be-tween the H-frame contact points on the beam specimen. Thelevel of desired strain is pre-calculated and an input value forthe equipment peak-to-peak deflection. The peak-to-pe
23、ak de-flection at mid-length position (L/2, length between outsideframes divided by 2) of a beam specimen is regulated by theclosed-loop control system measured from the mid-heightposition (neutral axis). The peak-to-peak deflection is mea-sured relative to a fixed reference point located at the out
24、erarticulating fixed position.NOTE 1Caution should be applied when using frequencies above10 Hz, Pronk (2).5. Significance and Use5.1 The laboratory fatigue life determined by this standardfor beam specimens has been used to estimate the fatigue life3Available from American Association of State High
25、way and TransportationOfficials (AASHTO), 444 N. Capitol St., NW, Suite 249, Washington, DC 20001,http:/www.transportation.org.4The boldface numbers in parentheses refer to a list of references at the end ofthis standard.FIG. 1 Illustration of Actuator Response of Repeated Sinusoidal Peak-to-Peak De
26、fectionD8237 182of asphalt mixture pavement layers under repeated trafficloading. Although the field performance of asphalt mixtures isimpacted by many factors (traffic variation, loading rate, andwander; climate variation; rest periods between loads; aging;etc.), it has been more accurately predict
27、ed when laboratoryproperties are known along with an estimate of the strain levelinduced at the layer depth by the traffic wheel load travelingover the pavement.NOTE 2The quality of the results produced by this standard aredependent on the competence of the personnel performing the procedureand the
28、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, etc. Users of this standard are cautioned that compliance withSpecification D3666 alone does
29、not completely ensure reliable results.Reliable results depend on many factors; following the suggestions ofSpecification D3666 or some similar acceptable guideline provides ameans of evaluating and controlling some of those factors.6. Apparatus6.1 Test SystemThe test system shall consist of a loadf
30、rame, an environmental chamber (temperature controlsystem), and a closed-loop control and data acquisition system.The test system shall include a closed-loop, computer-controlled loading component which, during each load cycle inresponse to commands from the data processing and controlcomponent, adj
31、usts and applies a load such that the specimenexperiences a constant level of controlled maximum deflection(and resulting strain) during each load cycle. The test systemshall meet the minimum requirements specified in Table 1.NOTE 3Test system unit calibrations are performed in mm fordisplacement an
32、d kN for load measurements (Practices E4 and E2309/E2309M). Unit conversions will need to be made when applying tocalculations in Section 10.6.1.1 Loading DeviceThe loading device shall be capableof: (1) providing repeated sinusoidal loading at a frequencyrange of 5 to 25 Hz, and (2) subjecting spec
33、imens to four-pointbending with free rotation and horizontal translation at allclamped load and reaction points as shown in Figs. 2 and 3.Floating reference point bending beam fixtures are not recog-nized by this standard.NOTE 4The fundamental equations are more viable with dual con-trolling displac
34、ement sensors. The on-specimen displacement sensorcontrols the peak-to-peak displacement for the waveform loading of themaximum deflection value at the L/2 location, and the frame-mounteddisplacement sensor controls the H-frame point of origin location. Aneven better approach is the use of four disp
35、lacement sensors. Two dualcontrolling sensors, as listed previously in this note, and two recording theL/6 and 5L/6 locations to better understand the deflections between eachof the frames.6.1.2 Environmental Chamber (Temperature ControlSystem)The environmental chamber shall enclose the entirespecim
36、en and maintain the specimen at the default test tem-perature of 20 C. The temperature shall be within 60.5 Cthroughout the conditioning and testing times.NOTE 5Replacing an incandescent, florescent, or halogen light bulbwith light emitting diode (LED) for your environmental chamber reducesthe heat
37、signature and improves the chambers ability to control within60.5 C. Globe-style bulb design improves illumination of fixture andinside of chamber.6.1.3 Control and Data Acquisition SystemDuring eachload cycle, the control and data acquisition system shall becapable of measuring the peak-to-peak dis
38、placement of thebeam specimen, and adjusting the load applied by the loadingdevice such that the specimen experiences a constant level ofdisplacement on each load cycle. In addition, it shall be capableof recording load cycles, applied loads, beam displacements,and temperature. Minimum data capture
39、rate and samplingintervals are listed in Table 2. The minimum number of datasamples for each load cycle is 200.6.2 Miscellaneous Apparatus and MaterialsMeans or toolfor targeting the displacement sensor to the neutral axis of thespecimen and proper glue (cyanoacrylate) are required forattaching the
40、target to the specimen. A saw suitable for cuttingthe beams with parallel faces to the proper dimensions of380 mm 6 3 mm in length, 50 mm 6 2 mm in height, and63 mm 6 2 mm in breadth (width). A clamp alignment gaugeis required for setting the proper clamp spacing between theframes, ensuring parallel
41、ism and perpendicularity. A rigidmaterial beam having the dimensions specified in 6.2 andtolerance of 0.254 mm across the beam (measured using astraightedge and feeler gauge) will be the required beam gaugefor setting the proper clamping height. Yearly verification isrequired for the beam gauge to b
42、e in compliance.NOTE 6Hard, high-strength 7075 aluminum is found to be adequatefor the beam gauge. The aluminum bar off the shelf will require being cutto a length of 380 mm (McMaster Carr Item #9055K31).7. Hazards7.1 Observe standard laboratory safety precautions whenpreparing and testing asphalt m
43、ixture specimens.8. Sampling and Test Specimen Preparation8.1 Laboratory-Mixed and Compacted SpecimensSampleasphalt binder in accordance with Practice D140/D140M, andsample aggregate in accordance with Practice D75/D75M.Ifacomplete fatigue curve is desired, prepare six to nine replicateasphalt mixtu
44、re beam specimens, compacted in accordancewith Practice D7981 or D8079, or activeAASHTO compactionstandards for slab(s) or beam(s). Otherwise, prepare as manyspecimens as desired for individual beam test results.TABLE 1 Test System Minimum RequirementsLoad Measurement and Control Range: 5 kNResoluti
45、on: 0.005 NAccuracy: 0.01 NDisplacement Measurement and Control Range: 2.5 mmResolution: 2.5 mAccuracy: 5 mFrequency Measurement and Control Range: 5 to 25 HzResolution: 0.005 HzAccuracy: 0.01 HzTemperature Measurement and Control Range: 5 to 25 CResolution: 0.25 CAccuracy: 0.5 CDisplacement Sensor
46、Linear variable differentialtransducer (LVDT), extensometer,or similar deviceD8237 183Laboratory-prepared mixtures are conditioned with a short-term oven aging (STOA) process, such as defined in Section7.2 of AASHTO R 30 (condition loose mixture for 4 h at135 C). Determine the theoretical maximum sp
47、ecific gravityin accordance with Test Method D2041/D2041M. Determinethe bulk specific gravity in accordance with Test MethodD2726/D2726M. Calculate the percent air voids in accordancewith Test Method D3203/D3203M. Test at least six replicateFIG. 2 Specimen Articulation and DimensioningFIG. 3 Load Ch
48、aracteristics of Fatigue Test Apparatus Illustrated as Pure Sine WaveD8237 184asphalt mixture beam specimens at different 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 failu
49、re occurs directly at aclamp.Alinear relationship on a log-log plot exists between Nfand the level of tensile strain (, microstrain = strain 106).NOTE 7AASHTO R 30 also contains additional information onlong-term oven aging (LTOA) of compacted specimens for five days at85 C. In addition, new research in Braham et al. (3) and NCHRP Report871 (4) provides information on long-term aging loose mixture.NOTE 8The type of compaction device (linear kneading, rollingwheel, vibratory) may influence the test results relative to represe
