1、Designation: D 6521 08Standard Practice forAccelerated Aging of Asphalt Binder Using a PressurizedAging Vessel (PAV)1This standard is issued under the fixed designation D 6521; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the ye
2、ar 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. Scope1.1 This practice covers the accelerated aging (oxidation) ofasphalt binders by means of pressurized air and elevat
3、edtemperature. This is intended to simulate the changes inrheology which occur in asphalt binders during in-serviceoxidative aging but may not accurately simulate the relativerates of aging. It is normally intended for use with residue fromTest Method D 2872 (RTFOT), which is designed to simulatepla
4、nt aging.NOTE 1Modified asphalt binders may phase separate or form skinsduring oven conditioning in Test Method D 2872 (RTFOT); the resultsfrom subsequent testing of this residue may not be representative ofmodified asphalts short-term aged under field conditions. Phase separa-tion, or formation of
5、skins, or both can also occur during PAV condition-ing. Therefore, the practice may not be suitable for some modifiedasphalts.NOTE 2PAV conditioning has not been validated for materials con-taining particulate materials.1.2 The aging of asphalt binders during service is affectedby ambient temperatur
6、e and by mixture-associated variables,such as the volumetric proportions of the mix, the permeabilityof the mix, properties of the aggregates, and possibly otherfactors. This conditioning process is intended to provide anevaluation of the relative resistance of different asphalt bindersto oxidative
7、aging at selected elevated aging temperatures andpressures, but cannot account for mixture variables or providethe relative resistance to aging at in-service conditions.1.3 The values stated in SI units are to be regarded as thestandard. Values in parentheses in inch-pound units are pro-vided for in
8、formational purposes only.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 standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations pr
9、ior to use.2. Referenced Documents2.1 ASTM Standards:2D8 Terminology Relating to Materials for Roads and Pave-mentsD 2872 Test Method for Effect of Heat andAir on a MovingFilm of Asphalt (Rolling Thin-Film Oven Test)D 4753 Guide for Evaluating, Selecting, and SpecifyingBalances and Standard Masses f
10、or Use in Soil, Rock, andConstruction Materials TestingD 6373 Specification for Performance Graded AsphaltBinderE 1137/E 1137M Specification for Industrial Platinum Re-sistance Thermometers2.2 AASHTO Standards:3M 320 Specification for Performance-Graded AsphaltBinder2.3 CGA Standards:4CGA G-7.11997
11、Commodity Specification for Air, FourthEdition3. Terminology3.1 Definitions:3.1.1 Definitions of terms used in this practice may be foundin Terminology D8, determined from common English usage,or combinations of both.4. Summary of Practice4.1 Asphalt binder is normally first conditioned using TestMe
12、thod D 2872 (RTFOT). Residue from the RTFOT is thenplaced in standard stainless steel pans and aged at the specifiedconditioning temperature for 20 h in a vessel pressurized with1This practice is under the jurisdiction of ASTM Committee D04 on Road andPaving Materials and is the direct responsibilit
13、y of Subcommittee D04.46 onDurability and Distillation Tests.Current edition approved Jan. 1, 2008. Published January 2008. Originallyapproved in 2000. Last previous edition approved in 2005 as D 6521 05.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Se
14、rvice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American Association of State Highway and TransportationOfficials (AASHTO), 444 N. Capitol St., NW, Suite 249, Washington, DC 20001,http:/www
15、.transportation.org.4Available from Compressed Gas Association (CGA), 4221 Walney Rd., 5thFloor, Chantilly, VA 20151-2923, http:/.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.air to 2.10 MPa. The conditioning temperature is select
16、edaccording to the grade of asphalt binder. The residue is thenvacuum degassed.5. Significance and Use5.1 This practice is designed to simulate the in-serviceoxidative aging that occurs in asphalt binders during pavementservice. Residue from this conditioning practice may be used toestimate the phys
17、ical or chemical properties of asphalt bindersafter several years of in-service aging in the field.5.2 Binders conditioned using this practice are normallyused to determine specification properties in accordance withSpecification D 6373 or AASHTO M 320.5.3 For asphalt binders of different grades or
18、from differentsources, there is no unique correlation between the time andtemperature in this conditioning practice and in-service pave-ment age and temperature. Therefore, for a given set ofin-service climatic conditions, it is not possible to select asingle PAV conditioning time, temperature and p
19、ressure thatwill predict the properties or the relative rankings of theproperties of asphalt binders after a specific set of in-serviceexposure conditions.5.4 The relative degree of hardening of different asphaltbinders varies with conditioning temperatures and pressures inthe PAV. Therefore, two as
20、phalt binders may age at a similarrate at one condition of temperature and pressure, but agedifferently at another condition. Hence, the relative rates ofaging for a set of asphalts at PAV conditions may differsignificantly from the actual in-service relative rates at lowerpavement temperatures and
21、ambient pressures.6. Apparatus6.1 An equipment system consisting of a pressure vessel,ovens, pressure-controlling devices, temperature-controllingdevices, pressure and temperature measuring devices, and atemperature and pressure recording system (see Fig. 1).6.1.1 Pressure VesselA stainless steel pr
22、essure vesseldesigned to operate at 2.1 6 0.1 MPa between 90 and 110Cwith interior dimensions adequate to hold ten PAV pans and apan holder. The pan holder shall be capable of holding ten PAVstainless steel pans in a horizontal (level) position, such that theasphalt binder film thickness is reasonab
23、ly uniform. The holdershall be designed for easy insertion and removal from thevessel when the holder, pans, and asphalt binder are at theconditioning temperature. A schematic showing a possibleconfiguration of the vessel, pan holder and pans, and specifyingdimensional requirements is shown in Fig.
24、2.NOTE 3The vessel may be a separate unit to be placed in a forceddraft oven for conditioning the asphalt binders or an integral part of thetemperature control system (for example, by direct heating of the vessel orby surrounding the vessel with a permanently affixed heating unit, forcedair oven, or
25、 liquid bath). For practical purposes, it is recommended that theFIG. 1 Schematic of PAV Test SystemD6521082vessel have the dimensions of 250 mm in diameter and 265 mm in height.6.1.2 Pressure and Temperature Controlling Devices:6.1.2.1 A pressure relief valve that prevents pressure in thevessel fro
26、m exceeding the design pressure of the vessel, but inno case exceeding 2.5 MPa during the conditioning procedure.6.1.2.2 A pressure regulator or regulating system capable ofcontrolling the pressure within the vessel to 60.02 MPa, andwith a capacity adequate to reduce the pressure from the sourceof c
27、ompressed air, so that the pressure within the loadedpressure vessel is maintained at 2.1 6 0.1 MPa gauge (relative)pressure during the conditioning process.6.1.2.3 A slow-release bleed valve or pressure controllerthat allows the pressure in the vessel at the completion of theconditioning procedure
28、to be reduced from 2.1 MPa to localatmospheric pressure within 8 to 15 min.6.1.3 Temperature Controlling DeviceA digital tempera-ture control device as described in 6.1.4.1 or 6.1.4.2 formaintaining the temperature during the conditioning procedurewithin the pressure vessel at the conditioning tempe
29、rature60.5C.6.1.3.1 A heating device (forced-draft oven or fluid bath)capable of restoring the conditioning temperature within thevessel after loading the pans and the pan holder and prior topressurizing the vessel within2hofplacing the loaded vesselin the heating device. The device shall be capable
30、 of maintain-ing the temperature within the pressure vessel at the condition-ing temperature 60.5C. If an oven is used, the oven shall havesufficiently large interior dimensions to allow forced air tofreely circulate within the oven and around the pressure vesselwhen the vessel is placed in the oven
31、. The oven shall containa stand or shelf that supports the loaded pressure vessel in alevel position above the lower surface of the oven.6.1.3.2 A pressure vessel with an integral temperature con-trol system that is capable of restoring the pre-conditioningtemperature, as determined in 9.3, within t
32、he vessel afterloading the pans and the pan holder, prior to pressurizing thevessel within 2 hours of placing the loaded vessel in the heatingdevice, and maintaining the temperature within the pressurevessel at the conditioning temperature 60.5C.NOTE 4Preheating the pressure vessel may be necessary
33、to achievethe conditioning temperature within the required 2-h period.6.1.4 Temperature and Pressure Measuring Devices:6.1.4.1 A platinum resistive thermometric device (RTD)accurate to the nearest 0.1C and manufactured in accordancewith Specification E 1137/E 1137M (IEC 751), or equal, formeasuring
34、temperature inside the pressure vessel. The RTDshall be calibrated as an integral unit with its respective metreor electronic circuitry.6.1.4.2 Temperature Recording DeviceA strip chart re-corder or other data acquisition system capable of recordingtemperature throughout the conditioning process to
35、within60.1C at a minimum interval of once per minute. As analternative, an electronic device capable of reporting onlymaximum and minimum temperatures (accurate to 60.1C)may be used.6.1.4.3 A pressure gauge capable of measuring the pressurein the pressure vessel to within 60.02 MPa during theconditi
36、oning process.6.2 Stainless Steel PansCylindrical pans, each 140 6 1mm (5.5 6 0.04 in.) in inside diameter and 9.5 6 1.5 mm (3/8NOTE 1Distance “a” controls the levelness of the pan. The assembly shall be supported at three or more support points. The distance “a”, measuredfrom each assembly support
37、point to the bottom of the pan (top of shelf or pan support point), shall be controlled to 60.05 mm.NOTE 2Distances b1and b2shall be such that any active portion of the temperature transducer is $10 mm from any adjacent surface.NOTE 3Distance “c” shall be $12 mm.FIG. 2 Schematic Showing Location of
38、Pans and RTD Within PAVD65210836 1/16 in.) deep, with a flat bottom. Pans shall be manufac-tured of stainless steel and shall have a metal thickness ofapproximately 0.6 mm (0.024 in.).NOTE 5Stainless steel pans rather than aluminum pans are requiredfor use in the PAV because they provide a safer env
39、ironment forhydrocarbons under elevated temperatures and pressures and they are notas easily warped or bent.NOTE 6Pans have a tendency to become warped or bent with use.Although tests show that a slight degree of warping does not significantlyaffect the results, frequent inspection to eliminate warp
40、ed or damagedpans is advisable. The indicated metal thickness has been found to provideadequate rigidity.6.3 BalanceA balance that is in accordance with GuideD 4753, Class G2.6.4 Vacuum OvenA vacuum oven capable of maintainingtemperature up to 180C with an accuracy of 65C and 15 61.0 kPa absolute pr
41、essure shall be used (see Note 7).6.4.1 Temperature and Vacuum Measuring Devices:6.4.1.1 Temperature Measuring DeviceA temperaturesensor capable of measuring the vacuum oven chamber tem-perature to within 65C.6.4.1.2 Vacuum Measuring DeviceA vacuum gauge, ab-solute pressure gauge or digital vacuum m
42、easuring systemcapable of measuring the absolute pressure in the chamber towithin 60.5 kPa (61.0 in. Hg).6.5 Vacuum SystemA vacuum system capable of generat-ing and maintaining pressure below 15 kPa absolute. Suitablevacuum systems include a vacuum pump, an air aspirator, or ahouse vacuum system.NOT
43、E 7A vacuum gauge provides the difference in pressure betweenambient atmospheric pressure and the absolute pressure within thevacuum oven. At sea level, where the atmospheric pressure is equal to101.3 kPa (29.9 in. Hg), and with an absolute pressure inside the ovenequal to 15.0 kPa (4.4 in. Hg), the
44、 vacuum gauge will read 86.3 kPa (25.5in. Hg). At an altitude of 1000 m (3281 ft) where the ambient atmosphericpressure is 89.7 kPa (26.5 in. Hg), the vacuum gauge reading will be 26.5in. Hg minus 4.4 in. Hg or 22.1 in. Hg. A temperature-corrected altitudeconversion for relative pressure gauge indic
45、ation is to subtract 0.85 in. Hgfor each 250 m of altitude (subtract 0.52 in. Hg for each 500 ft of altitude).6.6 OvenAn oven capable of maintaining a temperatureof 168 6 5C, readable to 1C.7. Materials7.1 Commercial bottled air meeting at least the minimumrequirements of the CGA for Grade D air, an
46、d having amaximum dew point to -40C.NOTE 8In North America, CGA Grade D air is commonly referred toas OSHA breathing air. CGA Publication G-7.11997 defines Grade D airas containing 19.523.5 % oxygen, balance being predominantly nitrogen.Carbon dioxide (CO2) is limited to 1000 ppm (v/v), carbon monox
47、ide islimited to 10 ppm and oil (condensed) to 5 mg/m3at NTP.8. Hazards8.1 Use standard laboratory safety procedures in handlingthe hot asphalt binder when preparing and conditioning speci-mens and removing the residue from the pressure vessel. Usespecial precaution when lifting the pressure vessel.
48、9. Calibration and Standardization9.1 Temperature Sensors9.1.1 PAV Thermometric DeviceVerify the calibration ofthe thermometric device to within 60.1C at least every sixmonths using a calibrated thermometric device traceable to anational standard. Verification shall be performed near thetemperature
49、of use within a range of 90.0 to 110.0C.NOTE 9The sensors for the thermometric devices in commerciallymanufactured PAV vessels cannot, or to avoid damage to the sensors andfittings, should not be removed for verification. A suitable verificationtechnique is to 1) bring the probe of the calibrated thermometric deviceinto intimate contact with the sensor mounted in the PAV vessel, 2) placethe cover over the vessel, allowing the leads for the thermometric deviceto exit the vessel under the cover without securing the cover, 3) allo
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