1、Designation: D 6648 01Standard 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 50nPa-1to 1 nPa-1) and can be used with unaged material or withmaterials aged using aging
4、procedures such as Test MethodD 2872, Test Method D 1754, or Practice D 6521. The testapparatus may be operated within 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
5、.1.3 This standard does 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
6、Documents2.1 ASTM Standards:C 802 Practice for Conducting an Interlaboratory Test Pro-gram to Determine the Precision of Test Methods forConstruction Materials3D 140 Practice for Sampling Bituminous Materials4D 1754 Test Method for Effect of Heat and Air on AsphalticMaterials (Thin-Film Oven Test)4D
7、 2872 Test Method for Effect of Heat and Air on a MovingFilm of Asphalt (Rolling Thin-Film Oven Test)4D 6521 Practice for Accelerated Aging of Asphalt BinderUsing a Pressurized Aging Vessel (PAV)4E 77 Test Method for Inspection and Verification of Ther-mometers52.2 AASHTO Standard:AASHTO MP1 Standar
8、d Specification for PerformanceGraded Binder62.3 DIN Standard:7437603. Terminology3.1 Definitions:3.1.1 asphalt binder, nan asphalt-based cement that isproduced from petroleum residue either with or without theaddition of modifiers.3.1.2 physical hardening, na time-dependent, reversiblestiffening of
9、 asphalt binder that typically occurs when thebinder is stored below room temperature.3.2 Definitions of Terms Specific to This Standard:3.2.1 contact 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
10、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 flexuralcreep stiffness is the inverse of the flexural creep compliance.3.2.3 flexural creep stiffness, S(t), nthe creep stiffnessobtained by fitting a seco
11、nd 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 4, section 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
12、X1.4) by the measured maxi-mum bending strain (see Eq X1.5). Flexural creep stiffness hasbeen used historically in asphalt technology while creepcompliance 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
13、 logarithm of time(see Eq 5, section 14.5).3.2.6 test load, nthe load, Pt, of 240-s duration used todetermine the stiffness of the asphalt binder being tested; 9806 50 mN.4. Summary of Test Method4.1 The bending beam rheometer is used to measure the1This test method is under the jurisdiction of ASTM
14、 Committee D04 on Roadand Paving Materials and is the direct responsibility of Subcommittee D04.44 onRheological Tests.Current edition approved June 10, 2001. Published August 2001.2This standard is based on SHRP Product 1002 and AASHTO TPI.3Annual Book of ASTM Standards, Vol 04.02.4Annual Book of A
15、STM Standards, Vol 04.03.5Annual Book of ASTM Standards, Vol 14.03.6Available from the American Association of State Highway and TransportationOfficials, 444 N. Capitol St. NW, Washington, DC 20001.7Deutsches Institut fuer Normung (German Standards Institute), Beuth VerlagGmbH, Burggrafenstrasse 6,
16、1000 Berlin 30, Germany.1Copyright ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.mid-point deflection of a simply supported prismatic beam ofasphalt binder subjected to a constant load applied to themid-point of the test specimen. The device operates only in theloading
17、 mode; recovery measurements cannot be obtained withthe bending beam rheometer.4.2 A prismatic test specimen is placed in the controlledtemperature fluid bath and loaded with a constant test load for240.0 s. The test load (980 6 50 mN) and the mid-pointdeflection of the test specimen are monitored v
18、ersus 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 span length, and the load applied to the test specimenfor loading times of 8.0, 15.0, 30.0, 60.0, 120.0, and 240.0 s.
19、The maximum bending strain in the test specimen is calculatedfrom the dimensions of the test specimen and the deflection forthe same loading times. The stiffness of the test specimen forthe specific loading times is calculated by dividing the maxi-mum bending stress by the maximum strain.5. Signific
20、ance and Use5.1 The temperatures for this test are related to the wintertemperature experienced by the pavement in the geographicalarea for which the asphalt binder is intended.5.2 The flexural creep stiffness or flexural creep compliance,determined from this test, describes the low-temperature stre
21、ss-strain-time response of asphalt binder at the test temperaturewithin the range of linear viscoelastic response.5.3 The low-temperature thermal cracking performance ofasphalt pavements is related to the creep stiffness and them-value of the asphalt binder contained in the mix.5.4 The creep stiffne
22、ss and the m-value are used asperformance-based specification criteria for asphalt binders inaccordance with AASHTO Method of Practice MP1.6. Interferences6.1 Measurements for which the mid-point deflection of thetest specimen is greater than 4.0 mm are suspect. Strains inexcess of this value may ex
23、ceed the linear response of asphaltbinders.6.2 Measurements for which the mid-point deflection of thetest specimen is less than 0.08 mm are suspect. When themid-point deflection is less than 0.08 mm, the test systemresolution may not be sufficient to produce reliable test results.7. Apparatus7.1 A b
24、ending beam rheometer (BBR) test system consist-ing of the following: (1) a loading frame with test specimensupports, (2) a controlled temperature liquid bate which main-tains the test specimen at the test temperature and provides abuoyant force to counterbalance the force resulting from themass of
25、the test specimen, (3) a computer-controlled dataacquisition system, (4) test specimen molds, and (5) items forverifying and calibrating the system.7.2 Loading FrameA frame consisting of a set of samplesupports, a blunt-nosed shaft to apply the load to the midpointof the test specimen, a load cell m
26、ounted 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 measuring transducer attached to theloading shaft. A schematic of the device is shown in Fig. 1.7.3 Loading SystemA loading system
27、 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 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
28、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 50 mN of the average testload, and thereafter shall be within 6 10 mN of the average testload. Details of the loading pattern are
29、shown in Fig. 2.7.3.2 Loading ShaftA loading shaft continuous and in linewith the load cell and deflection measuring transducer with 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
30、 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 controlled temperature bath.7.3.4 Linear Variable Differential Transducer (LVDT)Alinear variable differential transducer or other suitable device tomeasure the deflection of
31、 the test specimen. It shall have alinear range of at least 6 mm, and be capable of resolving linearFIG. 1 Schematic of Test DeviceD 66482movement of 2.5 m. It shall be mounted axially with andabove the loading shaft.7.3.5 Sample SupportsTwo stainless steel or other non-corrosive metal supports with
32、 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 calculations in Section 14. The supports shall bedimensioned to ensure that the test specimen remains in contactwith the radiused portion o
33、f the support during the entire test.See Fig. 3.7.3.5.1 The width of the test specimen support in contactwith the test specimen shall be 9.50 6 0.25 mm. See Fig. 3.7.3.5.2 A vertical alignment pin 2 to 4 mm in diameter shallbe provided at the back of each support to align the testspecimen on the sup
34、ports. The front face of the pins shall be6.75 6 0.25 mm from the middle of the support. See Fig. 3.7.4 Temperature TransducerA calibrated temperaturetransducer capable of measuring the temperature to 0.1C overthe range from -36C to 0C and mounted within 50 mm of thegeometric center of the test spec
35、imen.NOTE 1The required temperature measurement can be accomplishedwith an appropriately calibrated platinum resistance thermometer (PRT) ora thermistor. Calibration of the PRT or thermistor can be verified as persection 11.5. A platinum resistance thermometer meeting DIN Standard43760 (Class A) is
36、recommended for this purpose.7.5 Controlled-Temperature Fluid BathA controlled-temperature liquid bath capable 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
37、 tofluctuate 6 0.2C from the target test temperature. Conse-quently bath fluctuations of 6 0.2C during iso-thermal con-ditioning shall be allowed.7.5.1 Bath AgitatorA bath agitator for maintaining therequired temperature homogeneity with agitation intensitysuch that the fluid currents do not disturb
38、 the testing processand mechanical 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 unitseparate from the test frame, which pumps the bath fluidthrough the test bath. If used, vibrations from the circulatingsystem
39、shall be isolated from the bath test chamber so thatmechanical noise is less than the resolution specified in 7.3.3and 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 fluidtemp
40、erature to the nearest 0.1C. The data acquisition systemshall sense the point in time when the signal to switch from theFIG. 2 Definition of Loading PatternFIG. 3 Schematic of Specimen SupportsD 66483contact load to the test load is activated. This time shall be usedas the zero loading time for the
41、test load and deflection signals.Using this time as the reference for zero time, the dataacquisition system shall 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
42、signals shall be filtered with a low passanalog and/or digital filter that removes components withfrequencies 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 repo
43、rted. The averaging shall be over a timeperiod less than or equal to 6 0.2 s of the reporting time. Forexample, 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 wi
44、de by 12.70 6 0.05 mmdeep by 127 6 5 mm long fabricated from aluminum orstainless steel as shown in Fig. 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 not v
45、ary from each other inthickness by more than 0.05 mm.NOTE 2Small errors in the thickness of the test specimen can have alarge effect on the calculated modulus because the calculated modulus isa function of the thickness, h, raised to the third power. (see Eq X1.3).7.8 Items for Calibration or Verifi
46、cationThe 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 measuring system compliance and calibratingload cell.
47、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 the equations in section 13.2.3.1.7.8.2 Stainles
48、s 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 measure and reportthe thickness of this beam t
49、o 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 each ofknown mass 6 0.2 g, and equally spaced in mass over
