1、Designation: D 6648 08Standard Test Method forDetermining the Flexural Creep Stiffness of Asphalt BinderUsing the Bending Beam Rheometer (BBR)1This standard is issued under the fixed designation D 6648; the number immediately following the designation indicates the year oforiginal adoption or, in th
2、e case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope21.1 This test method covers the determination of theflexural-creep stiffness or complian
3、ce and m-value of asphaltbinders by means of a bending beam rheometer. It is applicableto material having flexural-creep stiffness values in the range of20 MPa to 1 GPa (creep compliance values in the range of 50nPa1to 1 nPa1) and can be used with unaged material or withmaterials aged using aging pr
4、ocedures such as Test MethodD 2872 or Practice D 6521. The test apparatus may be operatedwithin the temperature range from 36C to 0C.1.2 Test results are not valid for test specimens that deflectmore than 4 mm or less than 0.08 mm when tested inaccordance with this test method.1.3 This standard does
5、 not purport to address all of thesafety concerns, 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 Stand
6、ards:3C 802 Practice for Conducting an Interlaboratory Test Pro-gram to Determine the Precision of Test Methods forConstruction MaterialsD 140 Practice for Sampling Bituminous MaterialsD 2872 Test Method for Effect of Heat andAir on a MovingFilm of Asphalt (Rolling Thin-Film Oven Test)D 6521 Practic
7、e for Accelerated Aging of Asphalt BinderUsing a Pressurized Aging Vessel (PAV)D 6373 Specification for Performance Graded AsphaltBinderE77 Test Method for Inspection and Verification of Ther-mometers2.2 DIN Standard:4437603. Terminology3.1 Definitions:3.1.1 asphalt binder, nan asphalt-based cement
8、that isproduced from petroleum residue either with or without theaddition of modifiers.3.1.2 physical hardening, na time-dependent, reversiblestiffening of asphalt binder that typically occurs when thebinder is stored below room temperature.3.2 Definitions of Terms Specific to This Standard:3.2.1 co
9、ntact load, nthe load, Pc, required to maintainpositive contact between the test specimen, supports, and theloading shaft; 35 6 10 mN.3.2.2 flexural creep compliance, D(t), nthe ratio obtainedby dividing the maximum bending strain (see Eq X1.5) in abeam by the maximum bending stress (Eq X1.4). The f
10、lexuralcreep stiffness is the inverse of the flexural creep compliance.3.2.3 flexural creep stiffness, Se(t), nthe creep stiffnessobtained by fitting a second order polynomial to the logarithmof the measured stiffness at 8.0, 15.0, 30.0 60.0, 120.0, and240.0 s and the logarithm of time (see Eq 5, se
11、ction 14.4).3.2.4 measured flexural creep stiffness, Sm(t), nthe ratio(see Eq 3, section 14.2) obtained by dividing the measuredmaximum bending stress (see X1.4) by the measured maxi-mum bending strain (see Eq X1.5). Flexural creep stiffness hasbeen used historically in asphalt technology while cree
12、pcompliance is commonly used in studies of viscoelasticity.3.2.5 m-value, nthe absolute value of the slope of thelogarithm of the stiffness curve versus the logarithm of time(see Eq 6, section 14.5).3.2.6 test load, nthe load, Pt, of 240-s duration used todetermine the stiffness of the asphalt binde
13、r being tested; 9806 50 mN.3.2.7 zero load cell readingthe load indicated by the dataacquisition system when the shaft is free floating in the bathand at the position that occurs when first making contact witha test specimen.1This test method is under the jurisdiction of ASTM Committee D04 on Roadan
14、d Paving Materials and is the direct responsibility of Subcommittee D04.44 onRheological Tests.Current edition approved Jan. 15, 2008. Published February 2008. Originallyapproved in 2001. Last previous edition approved in 2001 as D 6648 01.2This standard is based on SHRP Product 1002.3For referenced
15、 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.4Deutsches Institut fuer Normung (German Standards Institute), Beuth VerlagG
16、mbH, Burggrafenstrasse 6, 1000 Berlin 30, Germany.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Summary of Test Method4.1 The bending beam rheometer is used to measure themid-point deflection of a simply supported prismatic beam
17、 ofasphalt binder subjected to a constant load applied to itsmid-point. The device operates only in the loading mode;recovery measurements cannot be obtained with the bendingbeam rheometer.4.2 A prismatic test specimen is placed in the controlledtemperature fluid bath and loaded with a constant test
18、 load for240.0 s. The test load (980 6 50 mN) and the mid-pointdeflection of the test specimen are monitored versus time usinga computerized data acquisition system.4.3 The maximum bending stress at the midpoint of the testspecimen is calculated from the dimensions of the test speci-men, the distanc
19、e between the supports, and the load applied tothe test specimen for loading times of 8.0, 15.0, 30.0, 60.0,120.0, and 240.0 s. The maximum bending strain in the testspecimen is calculated from the dimensions of the test speci-men and the deflection for the same loading times. The stiffnessof the te
20、st specimen for the specific loading times is calculatedby dividing the maximum bending stress by the maximumbending strain.5. Significance and Use5.1 The temperatures for this test are based upon the wintertemperature experienced by the pavement in the geographicalarea for which the asphalt binder
21、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 temperaturewithin the range of linear viscoelastic response.5.3 The low-temperature thermal cracking performanc
22、e ofasphalt pavements is related to the creep stiffness and them-value of the asphalt binder contained in the mix.5.4 The creep stiffness and the m-value are used asperformance-based specification criteria for asphalt binders inaccordance with Specification D 6373.6. Interferences6.1 Measurements fo
23、r which the mid-point deflections ofthe test specimen is greater than 4.0 mm are suspect. Strains inexcess of this value may exceed the linear response of asphaltbinders.6.2 Measurements for which the mid-point deflections ofthe test specimen are less than 0.08 mm are suspect. When themid-point defl
24、ection is less than 0.08 mm, the test systemresolution may not be sufficient to produce reliable test results.7. Apparatus7.1 A bending beam rheometer (BBR) test system consist-ing of the following: (1) a loading frame with test specimensupports, (2) a controlled temperature liquid bath whichmaintai
25、ns the test specimen at the test temperature and pro-vides a buoyant force to counterbalance the force resultingfrom the mass of the test specimen, (3) a computer-controlleddata acquisition system, (4) test specimen molds, and (5) itemsfor verifying and calibrating the system.7.2 Loading FrameA fram
26、e consisting of a set of samplesupports, a blunt-nosed shaft to apply the load to the midpointof the test specimen, a load cell mounted in line with theloading shaft, a means for zeroing the load applied to the testspecimen, a means for applying a constant load to the testspecimen and a deflection m
27、easuring transducer attached to theloading shaft. A schematic of the device is shown in Fig. 1.7.3 Loading SystemA loading system that is capable ofapplying a contact load of 35 6 10 mN to the test specimen andmaintaining a test load of 980 6 50 mN within 6 10 mN.7.3.1 Loading System RequirementsThe
28、 rise time for thetest load shall be less than 0.5 s. The rise time is the timerequired for the load to rise from the 35 6 10 mN contact loadto the 980 6 50 mN test load. During the rise time the systemshall dampen the test load to 980 6 50 mN. Between 0.5 and5.0 s, the test load shall be within 6 5
29、0 mN of the average testload, and thereafter shall be within 6 10 mN of the average testload. Details of the loading pattern are shown in Fig. 2.FIG. 1 Schematic of Test DeviceD66480827.3.2 Loading ShaftAloading shaft continuous and in linewith the load cell and deflection measuring transducer with
30、aspherically shaped end 6.3 6 0.3 mm in radius.7.3.3 Load CellA load cell to measure the contact loadand the test load. It shall have a minimum capacity of no lessthan 2.00 N and a resolution of at least 2.5 mN. It shall bemounted in line with the loading shaft and above the fluid levelin the contro
31、lled temperature bath.7.3.4 Linear Variable Differential Transducer (LVDT)Alinear variable differential transducer or other suitable device tomeasure the deflection of the test specimen. It shall have alinear range of at least 6 mm, and be capable of resolving linearmovement of 2.5 m. It shall be mo
32、unted axially with andabove the loading shaft.7.3.5 Sample SupportsTwo stainless steel or other non-corrosive metal supports with a 3.0 6 0.3 mm contact radiusand spaced 102 6 1.0 mm apart. The spacing of the supportsshall be measured to 6 0.3 mm and the measured value shallbe used in the calculatio
33、ns in Section 14. The supports shall bedimensioned to ensure that the test specimen remains in contactwith the radiused portion of the support during the entire test.See Fig. 3.7.3.5.1 The width of the test specimen support that contactsthe test specimen shall be 9.50 6 0.25 mm. See Fig. 3.7.3.5.2 A
34、 vertical alignment pin 2 to 4 mm in diameter shallbe provided at the back of each support to align the testspecimen on the supports. The front face of the pins shall be6.75 6 0.25 mm from the middle of the support. See Fig. 3.7.4 BBR Thermometric DeviceA calibrated thermometricdevice integral to th
35、e BBR and capable of measuring thetemperature to 0.1C over the range from 36C to 0C with itsthermal sensor (probe) mounted within 50 mm of the geometriccenter of the test specimen.NOTE 1The required temperature measurement can be accomplishedwith an appropriately calibrated thermometric device (plat
36、inum resistanceor thermistor based). Calibration of the thermometric device can beverified as per section 11.5. A platinum resistance thermometric devicemeeting DIN Standard 43760 (Class A) is recommended for this purpose.7.5 Controlled-Temperature Fluid BathA controlled-temperature liquid bath capa
37、ble of maintaining the temperatureat all points in the bath to within 6 0.1C of the testtemperature in the range of 36C to 0C. Placing a testspecimen in the bath may cause the bath temperature tofluctuate 6 0.2C from the target test temperature. Conse-quently bath fluctuations of 6 0.2C during iso-t
38、hermal con-ditioning shall be allowed.7.5.1 Bath AgitatorA bath agitator for maintaining therequired temperature homogeneity with agitation intensityFIG. 2 Definition of Loading PatternFIG. 3 Schematic of Specimen SupportsD6648083such that the fluid currents do not disturb the testing processand mec
39、hanical noise caused by vibrations is less than theresolution specified in 7.3.3 and 7.3.4.7.5.2 Circulating Bath (Optional)A circulating bath sepa-rate from the test frame, which pumps the bath fluid throughthe test bath. If used, vibrations from the circulating systemshall be isolated from the bat
40、h test chamber so that mechanicalnoise is less than the resolution specified in 7.3.3 and 7.3.4.7.6 Data Acquisition and Control ComponentsA dataacquisition system that resolves loads to the nearest 2.5 mN,test specimen deflection to the nearest 2.5 m, and bath fluidtemperature to the nearest 0.1C.
41、The data acquisition systemshall sense the point in time when the signal to switch from thecontact load to the test load is activated. This time shall be usedas the zero loading time for the test load and deflection signals.Using this time as the reference for zero time, the dataacquisition system s
42、hall provide a record of subsequent loadand deflection measurements at 8.0, 15.0, 30.0, 60.0, 120.0,and 240.0 s.7.6.1 Filtering of Acquired Load and Deflection SignalsThe load and deflection signals shall be filtered with a low passanalog or digital (or both) filter that removes components withfrequ
43、encies greater than 4 Hz from the load and deflectionsignals. Filtering may be accomplished by averaging five ormore digital signals equally spaced in time about the time atwhich the signal is reported. The averaging shall be over a timeperiod less than or equal to 60.2 s of the reporting time. Fore
44、xample, the load and deflection signals at 8.0 s may be theaverage of signals at 7.8, 7.9, 8.0, 8.1, 8.2 s.7.7 Test Specimen MoldsTest specimen molds with inte-rior dimensions of 6.35 6 0.05 mm wide by 12.70 6 0.05 mmdeep by 127 6 5 mm long fabricated from aluminum orstainless steel as shown in Fig.
45、 4, or from silicone rubber asshown in Fig. 5.7.7.1 The thickness of the two spacers used for each mold(small end pieces used in the metal molds) shall be measuredwith a micrometer and shall meet the requirements of Section7.7. The measurements shall be recorded as part of thelaboratory quality cont
46、rol program.7.8 Items for Calibration or VerificationThe followingitems are required to verify and calibrate the BBR.7.8.1 Stainless Steel (Thick) Beam for Compliance Mea-surement and Load Cell CalibrationsOne stainless steelbeam 6.4 6 0.3 mm thick by 12.7 6 0.3 mm wide by 127 65 mm long for measuri
47、ng system compliance and calibratingload cell. When this beam is used to measure the thickness oftest specimens as per section 13.2, the thickness of this beamshall be measured to the nearest 0.01 mm. This measurementshall be used in the calculation of the thickness of the testspecimens when using t
48、he equations in section 13.2.3.1.7.8.2 Stainless Steel (Thin) Beam for Overall SystemCheckOne stainless steel beam 1.0 to 1.6 mm thick by 12.76 0.1 mm wide by 127 6 5 mm long with an elastic modulusreported to three significant figures by the manufacturer of theBBR. The manufacturer of the BBR shall
49、 measure and reportthe thickness of this beam to the nearest 0.01 mm and the widthto the nearest 0.05 mm. The dimensions of the beam shall beused to calculate the modulus of the beam during the overallsystem check (see section 11.3).7.8.3 Standard MassesStandard masses for verificationand calibration as follows:7.8.3.1 Verification of Load Cell CalibrationOne or moremasses totaling 100.0 6 0.2 g and two masses of 2.0 6 0.2 geach for verifying the calibration of the load cell (see section11.3).7.8.3.2 Calibration of Load CellFour masses
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