1、Designation: D6816 11 (Reapproved 2016)Standard Practice forDetermining Low-Temperature Performance Grade (PG) ofAsphalt Binders1This standard is issued under the fixed designation D6816; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revis
2、ion, 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 practice covers the calculation of low-temperatureproperties of asphalt binders using data from
3、the bending beamrheometer (see Test Method D6648) (BBR) and the directtension tester (see Test Method D6723) (DTT). It can be usedon data from unaged material or from material aged using TestMethod D2872 (RTFOT), Practice D6521 (PAV), or TestMethod D2872 (RTFOT) and Practice D6521 (PAV). It can beus
4、ed on data generated within the temperature range from+6 C to 36 C.This practice generates data suitable for use inbinder specifications such as Specification D6373.1.2 This practice is only valid for data on materials that fallwithin the scope of suitability for both Test Method D6648 andTest Metho
5、d D6723.1.3 This practice can be used to determine the following:1.3.1 Critical cracking temperature of an asphalt binder, and1.3.2 Whether or not the failure stress exceeds the thermalstress in a binder at a given temperature.1.4 This practice determines the critical cracking tempera-ture for a typ
6、ical asphalt binder based on the determination ofthe temperature where the asphalt binders strength equals itsthermal stress as calculated by this practice.The temperature sodetermined is intended to yield a low temperature PG Grade ofthe sample being tested. The low temperature PG grade isintended
7、for use in purchase specifications and is not intendedto be a performance prediction of the HMA (Hot Mix Asphalt)in which the asphalt binder is used.1.5 The development of this standard was based on SI units.In cases where units have been omitted, SI units are implied.1.6 This standard may involve h
8、azardous materials,operations, and equipment. This standard does not purport toaddress all of the safety concerns, if any, associated with itsuse. It is the responsibility of the user of this standard toestablish appropriate safety and health practices and deter-mine the applicability of regulatory
9、limitations prior to use.NOTE 1The algorithms contained in this standard require implemen-tation by a person trained in the subject of numerical methods andviscoelasticity. However, due to the complexity of the calculations theymust, of necessity, be performed on a computer. Software to perform thec
10、alculation may be written, purchased as a spreadsheet, or as a stand-aloneprogram.22. Referenced Documents2.1 ASTM Standards:3C670 Practice for Preparing Precision and Bias Statementsfor Test Methods for Construction MaterialsD8 Terminology Relating to Materials for Roads and Pave-mentsD2872 Test Me
11、thod for Effect of Heat and Air on a MovingFilm of Asphalt (Rolling Thin-Film Oven Test)D6373 Specification for Performance Graded AsphaltBinderD6521 Practice for Accelerated Aging of Asphalt BinderUsing a Pressurized Aging Vessel (PAV)D6648 Test Method for Determining the Flexural CreepStiffness of
12、 Asphalt Binder Using the Bending BeamRheometer (BBR)D6723 Test Method for Determining the Fracture Propertiesof Asphalt Binder in Direct Tension (DT)3. Terminology3.1 DefinitionsFor definitions of general terms used in thisstandard, refer to Terminology D8.3.2 Definitions of Terms Specific to This
13、Standard:3.2.1 Arrhenius parameter, a1,nthis is the constant coef-ficient in the Arrhenius model for shift factors: ln(aT)=a1(1/T) (1/Tref).3.2.2 coeffcient of linear thermal expansion, ,nthefractional change in size in one dimension associated with atemperature increase of 1 C.1This practice is und
14、er the jurisdiction of ASTM Committee D04 on Road andPaving Materials and is the direct responsibility of Subcommittee D04.44 onRheological Tests.Current edition approved Dec. 15, 2016. Published December 2016. Originallyapproved in 2002. Last previous edition approved in 2011 as D6816 11. DOI:10.15
15、20/D6816-11R16.2The sole source of supply of the software package TSAR known to thecommittee at this time is Abatech, Incorporated. If you are aware of alternativesuppliers, please provide this information to ASTM International Headquarters.Your comments will receive careful consideration at a meeti
16、ng of the responsibletechnical committee1, which you may attend.3For 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 websi
17、te.Copyright ASTM International, 100 Barr Harbor 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 In
18、ternational Standards, Guides and Recommendations issued by the World Trade Organiziation Technical Barriers to Trade (TBT) Committee.13.2.3 creep compliance, D(T,t), nthe reciprocal of thestiffness of a material, 1/S(T,t), at temperature T and time t,which may also be expressed using reduced time,
19、,asD(Tref,).3.2.4 critical cracking temperature, Tcr,nthe temperature,estimated using this practice, at which the induced thermalstress in a material exceeds its fracture stress; the criticalcracking temperature is a “single event cracking” limit predic-tion which does not include the effect of low
20、temperaturethermal fatigue.3.2.5 failure stress, f,nthe tensile stress value at the pointof failure obtained from Test Method D6723.3.2.6 glassy modulus, nthe modulus at which the binderexhibits glass-like behavior, which is assumed to be equal to3109Pa.3.2.7 induced thermal stress, th,nthe stress i
21、nduced in amaterial by cooling it while it is restrained so that it cannotcontract.3.2.8 master curve, na composite curve at a single refer-ence temperature, Tref, which can be constructed by shifting,along the log time or log frequency axis, a series of overlap-ping modulus data curves at various t
22、est temperatures; themodulus data curve at the reference temperature is not shifted;the shifted smooth curve is called the master curve at thereference temperature.3.2.9 pavement constant, C, na constant factor that servesas a damage transfer function to convert the thermal stressescalculated from l
23、aboratory data to the thermal stresses gener-ated in the pavement. The damage transfer function is neededto account for the differences in the strain rates experienced bythe distribution of binder films in the pavement and the bulkstrain rate used in the Test Method D6723 DTT test. Fulldetails on th
24、e determination of the pavement constant may befound in Refs (1)4and (2), copies of which are on file atASTMInternational. After extensive analysis, the most appropriatepavement constant was determined to be 18. The pavementconstant of 18 is based on the most current available pavementperformance da
25、ta. The Federal Highway Administration(FHWA) and the Transportation Research Board (TRB) BinderExpert Task Group (ETG) continue to collect and analyze fieldperformance data. In the future, based on these analyses, thepavement constant will be adjusted as appropriate. The pave-ment constant is an emp
26、irical factor required to relate binderthermal stress to the pavement thermal stress.NOTE 2Research suggests that changing the pavement constant from16 to 24 results ina2to4Cchange in the critical cracking temperature,which is less than one low temperature grade interval (6 C).3.2.10 reduced time, ,
27、nthe computed loading time at thereference temperature, Tref, equivalent to actual loading attemperature T, which is determined by dividing actual loadingtime, t, at temperature T, by the shift factor, aT, = t/aT.3.2.11 reference temperature, Tref,nthe temperature atwhich the master curve is constru
28、cted.3.2.12 relaxation modulus, E(T,t), nthe modulus of amaterial determined using a strain-controlled (relaxation) ex-periment at temperature T and time t, which may also beexpressed using reduced time as E(Tref,).3.2.13 shift factor, aT,nthe shift in the time or frequencydomain associated with a s
29、hift from temperature T to thereference, Tref.3.2.14 stiffness modulus, S(T,t), nthe modulus (stress/strain) of a material at temperature T and time t, which mayalso be expressed using reduced time as S(Tref,).3.2.15 specification temperature, Tspec,nthe specifiedlow-temperature grade of the binder
30、being verified.4. Summary of Practice4.1 This practice describes the procedure used to calculatethe relaxation modulus master curve and subsequently thethermally induced stress curve for an asphalt binder from datagenerated on the BBR.4.2 The stiffness master curve is calculated from the stiff-ness
31、versus time data measured in the BBR at two tempera-tures. The fitting procedure follows Christensen-Anderson-Marasteanu (CAM) rheological model for asphalt binder. Thestiffness master curve is then converted to the creep compli-ance curve by taking its inverse.4.3 The creep compliance is converted
32、to relaxation modu-lus using the Hopkins and Hamming method (3), which is fittedto the CAM model. The Hopkins and Hamming method is anumerical solution of the convolution integral.4.4 The thermally induced stress is calculated by numeri-cally solving the convolution integral.4.5 The thermal stress c
33、alculations are based on Boltz-manns Superposition Principle for linear viscoelastic materi-als. The calculated thermally induced stress is then multipliedby the Pavement Constant to predict the thermal stress pro-duced in the hot-mix asphalt pavement. A value of 18 (eigh-teen) is used for the Pavem
34、ent Constant.4.6 The calculated thermal stress is then compared to thefailure stress from DTT to determine the critical crackingtemperature of the pavement.5. Significance and Use5.1 Estimated critical cracking temperature, as determinedby this practice, is a criterion for specifying the low-tempera
35、ture properties of asphalt binder in accordance withSpecification D6373.5.2 This practice is designed to identify the temperatureregion where the induced thermal stress in a typical HMAsubjected to rapid cooling (1 Ch) exceeds the fracture stressof the HMA.5.3 For evaluating an asphalt binder for co
36、nformance toSpecification D6373, the test temperature for the BBR andDTT data is selected from Table 1 of Specification D6373according to the grade of asphalt binder.NOTE 3Other rates of elongation and test temperatures may be usedto test asphalt binders for research purposes.4The boldface numbers i
37、n parentheses refer to the list of references at the end ofthis standard.D6816 11 (2016)26. Methodology and Required Data6.1 This practice uses data from both BBR and DTTmeasurements on an asphalt binder.6.1.1 The DTT data required is stress at failure obtained bytesting at a strain rate of 3 %min.
38、For continuous grade andPG grade determination, DTT results are required at a mini-mum of two test temperatures. The DTT tests shall beconducted at Specification D6373 specification test tempera-tures at the 6 C increments that represent the low temperaturebinder grade. For pass-fail determination,
39、DTT results arerequired at a single temperature that is the low temperaturegrade plus 10 C.6.1.2 Two BBR data sets at two different temperatures arerequired with deflection measurements at 8, 15, 30, 60, 120,and 240 s. The BBR test temperatures T and T minus 6 C(T 6) are selected such that S(T, 60)
40、300 MPa. T shall be one of the Specification D6373specification test temperatures at the 6 C increments thatrepresent the low temperature binder grade.7. Calculations7.1 Calculation of the Stiffness Master Curve:7.1.1 BBR Compliance DataD(T, t) = compliance at timet and temperature T D(T, 8), D(T, 1
41、5), D(T, 30), D(T, 60),D(T, 120), D(T, 240), D(T 6, 8), D(T 6, 15), D(T 6, 30),D(T 6, 60), D(T 6, 120), D(T 6, 240).7.1.2 BBR Stiffness Data is calculated as S(T, t)=1/D(T, t)7.1.3 Let the shift factor at the reference temperature aT=1.Determine aT 6, the shift factor for the data at temperatureT 6
42、C, numerically using Gordon and Shaws method toproduce master curves. The reference temperature shall be thehigher of the two test temperatures. The linear coefficient ofthermal expansion, above and below the glass transitiontemperature, shall be 0.00017 m/m/C. The glass transitiontemperature is tak
43、en as 20 C.NOTE 4This procedure is described in Gordon and Shaw (4)themaster curve procedure is the SHIFTT routine found in Chapter 5. Thevalue of 20 C is used for the glass transition temperature but has noeffect on the calculation as the linear expansion coefficient is assumed tobe the same either
44、 side of this temperature. Although a constant value ofthe linear coefficient of thermal expansion alpha is assumed, asphaltbinders may have variable values of alpha. The alpha for mixes, however,has been shown by various researchers to be approximately constant anddoes not vary with asphalt binders
45、.7.1.4 From aT-6calculate the Arrhenius parameter from thefollowing equations:lnaT26! 5 a1S1Tref2 6!21TrefD(1)a15lnaT26!S1Tref2 6! 21TrefD(2)NOTE 5The Gordon/Shaw method uses a shift factor (aT) in the formof a base 10 log (log10). However, this specification is based on the naturallog (ln or loge).
46、7.1.5 Reduced time, , for data at temperature T, is deter-mined by integrating the reciprocal of the shift factor withrespect to time in the following equation:t! 5 *0t dtaT(3)When T is constant with time, this reduces to the followingequation:t! 5taT(4)7.1.6 For all 12 values S(T,t) obtained then b
47、ecomesS(Tref,) with time being replaced by reduced time.7.1.7 The values are fitted to the Christensen-Anderson-Marasteanu (CAM) (5) model for asphalt master curves in thefollowing equation:STref,! 5 SglassyF11SDG2/(5)where:Sglassy= the assumed glassy modulus for the binder: Sglassy=3109Pa.7.1.8 Fit
48、 the resulting master curve data to this equationusing a nonlinear least squares fitting method to achieve a rootmean square error, rms(%), of less than or equal to 1.25 %.Appendix X1 contains an example calculation of this errorcriterion.7.2 Convert Stiffness Master Curve to Tensile RelaxationModul
49、us Master Curve:7.2.1 Use Hopkins and Hammings method to convert creepcompliance values D(Tref,)=1S(Tref,) to relaxation modulusE(Tref,).NOTE 6This procedure is described in Ref (3).7.2.2 The glassy modulus value of 3 109Pa shall beadopted in the analysis for S(Tref,1108s) = E(Tref,1108s). Calculate relaxation modulus data points using the follow-ing iterative formula from t =1108to t =1107s withintervals of 4 points per decade1.000, 1.778, 3.162 and 5.623(100.0,100.2
