1、Designation: D6723 12Standard Test Method forDetermining the Fracture Properties of Asphalt Binder inDirect Tension (DT)1This standard is issued under the fixed designation D6723; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the
2、 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 covers the determination of the failurestrain and failure stress of asphalt binders by means
3、 of a directtension test. It can be used with unaged material or withmaterial aged using Test Method D2872 (RTFOT), PracticeD6521 (PAV), orAASHTO T 240 (RTFOT) andAASHTO PP1(PAV). The test apparatus is designed for testing within thetemperature range from +6 to -36C.1.2 This test method is limited t
4、o asphalt binders containingparticulate material having dimensions less than 250 m.1.3 The values stated in SI units are to be regarded as thestandard.1.4 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
5、 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:2C670 Practice for Preparing Precision and Bias Statementsfor Test Methods for Construction MaterialsD8 Terminology Relati
6、ng to Materials for Roads and Pave-mentsD140 Practice for Sampling Bituminous MaterialsD2872 Test Method 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 BinderUs
7、ing a Pressurized Aging Vessel (PAV)E1 Specification for ASTM Liquid-in-Glass ThermometersE4 Practices for Force Verification of Testing MachinesE77 Test Method for Inspection and Verification of Ther-mometersE83 Practice for Verification and Classification of Exten-someter SystemsE220 Test Method f
8、or Calibration of Thermocouples ByComparison TechniquesE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method2.2 Deutche Industrie Norm (DIN) Standard:43760 Standard for Calibrating Thermocouples32.3 AASHTO Standards:T 2404PPI (PAV)43. Terminology3.1 Definit
9、ionsFor definitions of general terms used inthis standard, refer to Terminology D8.3.2 Definitions of Terms Specific to This Standard:3.2.1 brittle, adjtype of failure in a direct tension testwhere the stress-strain curve is essentially linear up to the pointof failure and the failure is by sudden r
10、upture of the testspecimen without appreciable reduction in cross-section of thespecimen.3.2.2 brittle-ductile, adjtype of failure in a direct tensiontest where the stress-strain curve is curvilinear and the failureis by sudden rupture of the test specimen. Limited reduction incross-section of the s
11、pecimen occurs before rupture.3.2.3 ductile, adjtype of failure in a direct tension testwhere the specimen does not rupture but fails by flow at largestrains.3.2.4 effective gage length, nfor specimens used in thistest, the effective gauge length, Le, has been determined to be33.8 mm. This is an eff
12、ective gauge length that represents theportion of the specimen that contributes to the majority of thestrain.3.2.5 failure, npoint at which the tensile load reaches amaximum value as the test specimen is pulled at a constant rateof elongation.1This test method is under the jurisdiction of ASTM Commi
13、ttee D04 on Roadand Paving Materials and is the direct responsibility of Subcommittee D04.44 onRheological Tests.Current edition approved Feb. 1, 2012. Published April 2012. Originallypublished as D6723 01. Last previous edition D6723 02. DOI: 10.1520/D6723-12.2For referenced ASTM standards, visit t
14、he 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.3Deutsches Institut fur Normung e.V. (German Standards Institute), BeuthVerlag GmbH, Burggrafenstras
15、se 6, 10787, Berlin Germany.4Available from the American State Highway and Transportation Officials, 444N. Capitol Street, N.W., Washington, DC 20001.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.6 failure strain, nthe tensile
16、strain corresponding tothe failure stress.3.2.7 failure stress, nthe tensile stress on the test speci-men when the load reaches a maximum value during the testmethod specified in this standard.3.2.8 gage section, nthe central portion of the specimenwhere the cross-section does not change with length
17、. For thegeometry used in this test method, the gage section is 18 mmin length (see Fig. 1).3.2.9 tensile strain, naxial strain resulting from the appli-cation of a tensile load and calculated as the change in lengthof the effective gage length caused by the application of thetensile load divided by
18、 the original unloaded effective gagelength.3.2.10 tensile stress, naxial stress resulting from theapplication of a tensile load and calculated as the tensile loaddivided by the original area of cross-section of the specimen.4. Summary of Test Method4.1 This test method describes the procedure used
19、to mea-sure the stress at failure and strain at failure in an asphalt bindertest specimen pulled at a constant rate of elongation. Testspecimens are prepared by pouring hot asphalt binder into asuitable mold. Two plastic end tabs are used to bond the asphaltbinder during the test and to transfer the
20、 tensile load from thetest machine to the asphalt binder.4.2 This test method was developed for asphalt binders attemperatures where they exhibit brittle or brittle-ductile failure.A brittle or brittle-ductile failure will result in a fracture of thetest specimen as opposed to a ductile failure in w
21、hich thespecimen simply stretches without fracturing. The test methodis not applicable at temperatures where failure is by ductileflow.4.3 A displacement transducer is used to measure theelongation of the test specimen as it is pulled in tension at aconstant rate of 1.00 mm/min. The load developed d
22、uring thetest is monitored and the tensile strain and stress in the testspecimen when the load reaches a maximum are reported as thefailure strain and failure stress, respectively.5. Significance and Use5.1 Stress at failure is used in a mechanistic pavementcracking model to compute critical crackin
23、g temperature. Theprocedure to compute critical cracking temperature is de-scribed in Practice D6521. The critical cracking temperature isthen used in specifying the low temperature grade of asphaltbinder in accordance with Specification D6373.5.2 The test method is designed to measure the strength
24、ofthe asphalt binder at the critical cracking temperature. Theasphalt binder has limited ability to resist stress withoutcracking. In the asphalt binder Specification D6373, failurestress is used to determine the critical cracking temperature.5.3 For evaluating an asphalt binder for conformance toSp
25、ecification D6373, the elongation rate of the gage section is1.0 mm/min and the test temperature is selected from Tablenumber 1 of Specification D6373 according to the grade ofasphalt binder. Other rates of elongation and test temperaturesmay be used to test asphalt binders.6. Apparatus6.1 Direct Te
26、nsion Test SystemAdirect tension test systemconsisting of (1) a closed feed-back loop displacement-controlled tensile loading machine, (2) a specimen grippingsystem, (3) either a fluid bath or an insulated chamber forreliable, accurate and uniform temperature control duringtesting and conditioning o
27、f specimen, (4) real-time load mea-suring and recording devices, (5) real-time elongation measur-ing and recording devices, (6) a real-time temperature detec-tion and recording device, and (7) real-time data acquisitionand display devices. The system shall have an electro-mechanical or servo-hydraul
28、ic loading unit capable of applyingand measuring tension and compression forces of at least 500N and actuator travel of 20 mm. The system stiffness shall beat least 3 MN/m including the load cell and the loading pins.The unit shall have a transducer to measure and control gripseparation and provide
29、a feedback for strain control with adisplacement resolution of 1.0 m. The system shall be capableof closed loop elongation rate control accurate to at least 1 %of the commanded specimen elongation rate using feedbackfrom a displacement transducer mounted between the loadingpins or a non-contact exte
30、nsometer measuring the elongation ofthe specimen.6.1.1 Tensile Loading Machine Equipped With TemperatureControlA tensile loading machine with a controlled-displacement loading frame capable of producing at least a500.00 N load is required. The loading frame shall be tablemounted. The gripping system
31、 (loading pins and platens) shallbe completely submerged under the cooling fluid if a fluidbased system is used. The gripping system shall be a minimumof 25 mm under the cooling fluid surface. Loading shall beaccomplished by pulling directly in tension in the plane of thespecimen. The distance betwe
32、en the load frames loadingpoints (between loading pins) shall accommodate specimenswith total length (including the end tabs) of at least 100.0 mm,(see Fig. 1). If an air cooled system is used, the testing frameshall be equipped with two standards (columns) with sufficientclear space between the sta
33、ndards so that an insulated tempera-ture control chamber can be placed between the standards.6.1.2 Specimen Gripping SystemThe gripping systemmust produce a self-aligning uniaxial test load and accept theend tabs described in 6.1.2.1 and be designed so that testspecimens can be easily mounted in the
34、 machine. The systemshall include two grips. Each grip shall include a specially-shaped pin that is mounted rigidly to the loading platens of thetesting machine. Fig. 2 shows a typical grip and loading pinassembly. One grip shall be fixed and remain stationary duringthe test while the other grip is
35、displaced at the desiredelongation rate.6.1.2.1 Specimen End TabsEnd tabs made from PhenolicG-10 material having the dimensions specified in Figs. 3-5shall be bonded to both ends of the test specimen to transfer thetensile load to the asphalt binder. The end tabs shall bemachined from standard G-10
36、Phenolic sheet. Each end tabshall contain a precisely machined hole lined with a 304stainless steel ring. The diameter of the lined hole shall be10.00 6 0.05 mm. Gripping of the specimen is accomplishedthrough the bond (adhesion) between the asphalt binder testD6723 122FIG. 1 Superpave Direct Tensio
37、n Specimen GeometryD6723123FIG. 2 Loading Pin and Grip Assembly for the Superpave Direct Tension TestD6723124FIG. 3 Superpave End Insert for Direct Tension Test (See Fig. 4 for the Metal Ring Dimensions to be Press Fitted into this End Insert)D6723125FIG. 4 Superpave End Insert Metal Ring for Direct
38、 Tension TestD6723126FIG. 5 Superpave Direct Tension Specimen MoldD6723127specimen and the end tab. Each end tab shall be mounted on aspecially shaped pin that is part of the gripping system. Thespecimen shall be mounted on the grips by positioning the endtabs in the test machine such that the end t
39、abs fit onto the pinsand are indexed against the face of the grips. Matching thecoefficient of thermal expansion of the asphalt binder and theend tabs is necessary to reduce thermal shrinkage stresses at theinterface that otherwise cause bond failures.6.1.3 Test Chamber for Temperature Control and T
40、estingThe temperature control chamber shall have sufficient space forstoring at least eight (8) specimens. The temperature controlrange for the cooling chamber, without asphalt binder speci-mens, at all points within the bath, shall be from +6C to -36Cwith temperature stability as a minimum of 60.1C
41、. Placing aroom temperature specimen in the cold chamber is allowed tocause the chamber temperature between the grips to fluctuate60.2C from the target test temperature during testing andisothermal conditioning of the specimen. However, duringtesting the temperature gradient between the grips shall
42、notexceed 60.1C. The temperature measurement shall be accom-plished with a calibrated Platinum Resistance TemperatureDetector (PRTD) located in the chamber in proximity of testarea (NIST Traceable, calibrated at 8 temperatures in the range+6C to -36C). If an air based cooling system is usedmechanica
43、l cooling or liquid nitrogen may be used to cool thechamber. It shall have a dehumidifying system with a capacitysuch that the formation of frost on the interior of the chamber,the test specimen, or any of the test fixtures is eliminated. Thechamber shall be capable of storing a minimum of eight tes
44、tspecimens on a rack which is thermally isolated from the wallsand floors of the chamber such that heat conducted from thewalls and floors of the chamber does not affect the temperatureof the stored specimens. If an air based cooling system is used,the chamber shall be fitted with a front-opening do
45、or formaintenance and standardization purposes and an access portthat allows for insertion of the operators hand and forearm toposition test specimens on the storage shelf for conditioningand to position test specimens on the grips for testing. Theaccess port shall be designed so that changes in cha
46、mbertemperature are 60.2C during an operation in which theoperators hand or forearm is inserted into or removed from thechamber. Visual access to the interior of the test chamber shallbe provided to permit proper mounting of test specimens andtest monitoring. Use of the laser requires optical glass
47、windowson two sides of the temperature chamber so that a beam of laserlight can be passed through the chamber without distorting thelaser beam.NOTE 1The required temperature measurement can be accomplishedwith an appropriately calibrated platinum resistance thermometer (PRT) ora thermistor. Calibrat
48、ion of the PRT or thermistor can be verified as per10.1.3. The platinum resistance thermometer meeting DIN Standard43760 (Class A) is recommended for this purpose.6.1.4 If fluid is used as a cooling medium, a suitable fluidfor temperature control and testing has been found to be anaqueous mixture of
49、 42 % potassium acetate powder and 58 %deionized water by weight. Alcohols have been found toembrittle asphalt binders (that is, affect failure properties inpresence of stress) and, therefore, shall not be used as amedium for temperature control and failure testing of asphaltbinder specimen.NOTE 2Potassium acetate is commercially available in the form of adeicing fluid mixture composed of approximately 50 % potassium acetateand 50 % deionized water. If this commercial fluid mixture is purchasedthe required 42 to 58 % potassium acetate to deioni
