ASTM D6521-00

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
Designation:D6521–00
Standard Practice for
Accelerated Aging of Asphalt Binder Using a Pressurized
Aging Vessel (PAV)
This standard is issued under the fixed designation D 6521; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope D 8 Terminology Relating to Materials for Roads and Pave-
ments
1.1 This practice covers the accelerated aging (oxidation) of
D 1754 Test Method for Effect of Heat and Air on Asphalt
asphalt binders by means of pressurized air and elevated
Materials (Thin-Film Oven Test)
temperature. This is intended to simulate the type of changes
D 2872 Test Method for Effect of Heat and Air on Rolling
which occur in asphalt binders during in-service oxidative
Film of Asphalt (Rolling Thin-Film Oven Test)
aging but may not accurately simulate the relative rates of
D 4753 Specification for Evaluating, Selecting and Speci-
aging. It is intended for use with residue from Test Method
fying Balances and Scales for Use in Soil, Rock and
D 2872 (RTFOT) which is designed to simulate plant aging.
Construction Materials Testing
NOTE 1—Modified asphalt binders may phase separate or form skins
E 220 Test Method for Calibration of Thermocouples by
during oven conditioning in Test Method D 2872 (RTFOT); the results
Comparison Techniques
from subsequent testing of this residue may not be representative of
E 1137 Specification for Industrial Platinum Resistance
modified asphalts short-term aged under field conditions. Phase separa-
Thermometers
tion, or formation of skins, or both can also occur during PAV aging.
2.2 AASHTO Standards:
Therefore, the practice may not be suitable for some modified asphalts.
NOTE 2—PAV has not been validated for materials containing particu-
MP1 Provisional Standard Specification for Performance-
late materials.
Graded Asphalt Binder
1.2 The aging of asphalt binders during service is affected
3. Terminology
by ambient temperature and air pressure and by mixture-
3.1 Definitions:
associated variables such as the volumetric proportions of the
3.1.1 Definitionsoftermsusedinthispracticemaybefound
mix, the permeability of the mix, properties of the aggregates,
in Terminology D 8 determined from common English usage,
and possibly other factors. This conditioning process is in-
or combinations of both.
tended to provide an evaluation of the relative resistance of
different asphalt binders to oxidative aging at selected elevated
4. Summary of Practice
aging temperatures and pressures but cannot account for
4.1 Asphalt binder is first aged using Test Method D 2872
mixture variables or provide the relative resistance to aging at
(RTFOT). A specified thickness of residue from the RTFOT is
in-service conditions.
then placed in standard TFOT stainless steel pans and aged at
1.3 The values stated in SI units are to be regarded as the
the specified aging temperature for 20 h in a vessel pressurized
standard.
with air to 2.10 MPa. Aging temperature is selected according
1.4 This standard does not purport to address all of the
to the grade of this asphalt binder. The residue is then vacuum
safety concerns, if any, associated with its use. It is the
degassed.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
5. Significance and Use
bility of regulatory limitations prior to use.
5.1 This method is designed to simulate the type of in-
2. Referenced Documents
service oxidative aging that occurs in asphalt binders during
2.1 ASTM Standards:
Annual Book of ASTM Standards, Vol 04.03.
1 3
This practice is under the jurisdiction of ASTM Committee D04 on Road and Annual Book of ASTM Standards, Vol 04.08.
Paving Materials and is the direct responsibility of Subcommittee D04.46 on Annual Book of ASTM Standards, Vol 14.03.
Durability and Distillation Test. Available fromAASHTO, National Institute of Std. &Tech., Gaithersburg, MD
Current edition approved Jan. 10, 2000. Published April 2000. 20899.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
D6521
pavement service. Residue from this conditioning practice may a set of asphalts at PAV conditions may differ significantly
be used to estimate the physical or chemical properties of from the actual in-service relative rates at lower temperatures
asphalt binders after several years of in-service aging in the and pressures.
field.
6. Apparatus
5.2 Binders aged using this standard are used to determine
specification properties in accordance AASHTO MP1. The 6.1 An equipment system consisting of a pressure vessel,
binder is aged using the RTFOT test prior to this conditioning pressure controlling devices, temperature controlling devices,
pressureandtemperaturemeasuringdevices,andatemperature
step. Unaged asphalt binders, RTFOT residues, and PAV
and pressure recording system (see Fig. 1).
residues are used to determine specification properties in
6.1.1 Pressure Vessel—A stainless steel pressure vessel
accordance with MP1.
designed to operate at 2.1 6 0.1 MPa between 90 and 110°C
5.3 For asphalt binders of different grades or from different
with interior dimensions adequate to hold ten TFOT pans and
sources, there is no unique correlation between the aging time
a pan holder. The pressure vessel shall contain a pan holder
and temperature in this conditioning practice and in-service
capableofholdingtenTFOTstainlesssteelpansinahorizontal
pavement age and temperature. Therefore, for a given set of
(level) position such that the asphalt binder film thickness is
in-service climatic conditions, it is not possible to select a
reasonably uniform. The holder shall be designed for easy
single PAV aging time and elevated temperature and pressure
insertion and removal from the vessel when the holder, pans,
that will predict the properties or the relative rankings of the
and asphalt binder are at the aging temperature. A schematic
properties of all asphalt binders after a specific set of in-service
showing a possible configuration of the vessel, pan holder and
exposure conditions.
pans and specifying dimensional requirements is shown in Fig.
5.4 The relative degree of hardening of different asphalt
2.
binders varies with aging temperatures and pressures in the
NOTE 3—The vessel may be a separate unit to be placed in a forced
PAV. Therefore, two asphalt binders may age at a similar rate
draft oven for conditioning the asphalt binders or an integral part of the
at one condition of temperature and pressure, but age differ-
temperature control system (for example, by direct heating of the vessel or
entlyatanothercondition.Hence,therelativeratesofagingfor by surrounding the vessel with a permanently affixed heating unit, forced
FIG. 1 Schematic of PAV Test System
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
D6521
NOTE 1—Distance “a” controls the levelness of the pan. The assembly shall be supported at three or more support points. The distance “a”, measured
from each assembly support point to the bottom of the pan (top of shelf or pan support point), shall be controlled to 6 0.05 mm.
NOTE 2—Distances b and b shall be such that any active portion of the temperature transducer is$ 10 mm from any adjacent surface.
1 2
NOTE 3—Distance “c” shall be$ 12 mm.
FIG. 2 Schematic Showing Location of Pans and RTD Within PAV
airoven,orliquidbath).Forpracticalpurposes,itisrecommendedthatthe
in the oven. The oven shall contain a stand or shelf which
vessel has the dimensions of 250 mm in diameter and 265 mm in height.
supports the loaded pressure vessel in a level position above
Research has shown that the volume of the vessel is not an important
the lower surface of the oven.
factor in hardening due to aging.
6.1.3.2 A pressure vessel with integral temperature control
6.1.2 Pressure and Temperature Controlling Devices:
system that is capable of restoring the pre-aging temperature,
6.1.2.1 A pressure relief valve that prevents pressure in the
as determined in 9.3, within the vessel after loading the pans
vessel from exceeding the design pressure of the vessel, but in
and the pan holder and prior to pressurizing the vessel within
no case exceeding 2.5 MPa during the aging procedure.
2 hours of placing the loaded vessel in the heating device and
6.1.2.2 Apressure regulator or regulating system capable of
maintaining the temperature within the pressure vessel at the
controlling the pressure within the vessel to 6 0.02 MPa, and
aging temperature 6 0.5°C.
withacapacityadequatetoreducethepressurefromthesource
NOTE 4—Preheating the pressure vessel may be necessary to achieve
of compressed air so that the pressure within the loaded
the aging temperature within the required 2 h period.
pressure vessel is maintained at 2.16 0.1 MPa gage (relative)
6.1.4 Temperature and Pressure Measuring Devices:
pressure during the aging process.
6.1.4.1 A platinum RTD accurate to the nearest 0.1°C and
6.1.2.3 A slow release bleed valve that allows the pressure
meeting Specification E 1137 (IEC 751), or equal, for measur-
in the vessel at the completion of the conditioning procedure to
ing temperature inside the pressure vessel. The RTD shall be
be reduced from 2.1 MPa to local atmospheric pressure within
calibrated as an integral unit with its respective meter or
8 to 15 min.
electronic circuitry.
6.1.3 Temperature Controlling Devices—Adigital tempera-
6.1.4.2 Temperature Recording Device—A strip chart re-
ture control device as described in 6.1.3.1 or 6.1.3.2 for
corder or other data acquisition system capable of recording
maintaining the temperature during the aging procedure within
temperature throughout the aging process to 0.1°C. As an
the pressure vessel at the aging temperature 6 0.5°C.
alternative, an electronic device capable of reporting only
6.1.3.1 A heating device (forced-draft oven or fluid bath)
maximum and minimum temperatures (accurate to 6 0.1°C)
capable of restoring the aging temperature within the vessel
may be used.
after loading the pans and the pan holder and prior to
6.1.4.3 A pressure gage capable of measuring the pressure
pressurizing the vessel within2hof placing the loaded vessel
in the pressure vessel to within 60.02 MPa during the aging
in the heating device and maintaining the temperature within
process.
the pressure vessel at the aging temperature 6 0.5°C. If an
6.2 Stainless Steel Pans—Ten standard stainless steelTFOT
oven is used, the oven shall have sufficiently large interior
pans meeting the requirements of Test Method D 1754.
dimensions to allow forced air to freely circulate within the
oven and around the pressure vessel when the vessel is placed NOTE 5—Stainless steel pans are required for use in the PAV because
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn. Contact ASTM
International (www.astm.org) for the latest information.
D6521
they provide a safer environment for hydrocarbons under elevated
temperature at which to apply pressure to the vessel for
temperatures and pressures.
performing the aging procedure. This information will be
useful in 10.9.
6.3 Balance—A balance conforming to the requirements of
Specification D 4753, Class G2.
10. Procedure
6.4 Vacuum Oven—A vacuum oven capable of maintaining
10.1 Condition the asphalt binder in accordance with Test
temperature up to 180°C with an accuracy of 6 5°C and
Method D 2872 (RTFOT).
vacuum of 15 6 1.0 kPa absolute shall be used. The pressure
10.2 Combine the hot residue from the RTFOT bottles into
vessel itself may be used in lieu of a vacuum oven if it is
a single container, stir to blend, then transfer to TFOT pans in
capable of maintaining a temperature of 180°C and a vacuum
accordance with 10.4 for PAV conditioning or allow the hot
of 15.0 kPa.
residue in the container to cool to room temperature and cover
6.5 Vacuum System—A vacuum system capable of generat-
and store at room temperature for PAV conditioning at a later
ing and maintaining pressure below 15 kPa absolute. Suitable
date. If conditioned asphalt binder is allowed to cool to room
vacuum systems include a vacuum pump, an air aspirator, or a
temperature, heat it until it is sufficiently fluid to pour and stir
house vacuum system.
it before pouring it into the TFOT pans.
7. Materials 10.3 Place the pan holder inside the pressure vessel. If an
oven is used, place the pressure vessel inside the oven, select
7.1 Commercial bottled air or equivalent.
an aging temperature, and preheat the pressure vessel to the
aging temperature selected. If an integrated temperature con-
8. Hazards
trol pressure vessel is used, one should select an aging
8.1 Use standard laboratory safety procedures in handling
temperature and follow the manufacturer’s instructions for
the hot asphalt binder when preparing aging specimens and
preheating the pressure vessel.
removing the residue from the pressure vessel. Use special
precaution when lifting the pressure vessel. NOTE 8—If conditioning asphalt binders for conformance to AASHTO
MP1, select the appropriate aging temperature from Table 1 of MP1.
NOTE 9—For vessels placed in an oven, preheating the vessel 10 to
9. Calibration and Standardization
15°C above the aging temperature can be used to reduce the drop in PAV
9.1 Temperature Detector—Verify the calibration of the
temperature during the loading process and minimize the time required to
RTD and its respective meter or electronic circuitry to 0.1°C at
stabilize the system, after loading, to attain the required temperature.
least every six months using a calibrated temperature indicator
NOTE 10—Aging temperature in the PAV is selected to account for
traceable to a national standard. different climatic regions.Temperatures in excess of approximately 115°C
can change the chemistry of asphalt binders using an accelerated aging
NOTE 6—The RTD or thermistor and its meter may be calibrated by the
practice and should be avoided.
manufacturer or a commercial vendor. One suggested method is to
10.4 Place the TFOT pan on a balance and add 50 6 0.5 g
perform the following steps: (1) Select a partial immersion mercury-in-
glass thermometer with an appropriate ran
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