1、Standard Practice for Accelerated Aging of Asphalt Binder Using a Pressurized Aging Vessel (PAV) AASHTO Designation: R 28-12 American Association of State Highway and Transportation Officials 444 North Capitol Street N.W., Suite 249 Washington, D.C. 20001 TS-2b R 28-1 AASHTO Standard Practice for Ac
2、celerated Aging of Asphalt Binder Using a Pressurized Aging Vessel (PAV) AASHTO Designation: R 28-12 1. SCOPE 1.1. This standard practice covers the accelerated aging (oxidation) of asphalt binders by means of pressurized air and elevated temperature. The practice is intended to simulate in-service
3、oxidative aging of asphalt binders and is intended for use with residue from T 240 (RTFOT). 1.2. The aging of asphalt binders during service is affected by mixture-associated variables such as the volumetric proportions of the mix, permeability of the mix, properties of the aggregates, and possibly
4、other factors. This practice is intended to provide an evaluation of the relative resistance of different asphalt binders to oxidative aging at selected temperatures and cannot account for mixture variables. 1.3. This standard practice may involve hazardous materials, operations, and equipment. This
5、 standard does not purport to address all of the safety concerns associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations prior to use. 2. REFERENCED DOCUMENTS 2.1.
6、 AASHTO Standards: M 231, Weighing Devices Used in the Testing of Materials M 320, Performance-Graded Asphalt Binder T 240, Effect of Heat and Air on a Moving Film of Asphalt Binder (Rolling Thin-Film Oven Test) 2.2. ASTM Standard: E220, Standard Test Method for Calibration of Thermocouples By Compa
7、rison Techniques 2.3. Deutsche Industrie Norm (DIN) Standard: 43760, Standard for Calibrating Thermocouples 3. TERMINOLOGY 3.1. Definitions: 3.1.1. asphalt binderan asphalt-based cement that is produced from petroleum residue either with or without the addition of nonparticulate organic modifiers. 3
8、.1.2. in-servicerefers to aging of the asphalt binder that occurs in the pavement as a result of the combined effects of time, traffic, and the environment. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable la
9、w.TS-2b R 28-2 AASHTO 4. SUMMARY OF PRACTICE 4.1. Asphalt binder is first aged using T 240 (RTFOT). A specified thickness of residue, from the RTFOT, is then placed in stainless steel pans and aged at the specified aging temperature for 20 h in a vessel pressurized with air to 2.10 MPa. The aging te
10、mperature is selected according to the grade of the asphalt binder. At the completion of the PAV process, the asphalt binder residue is then vacuum degassed. 5. SIGNIFICANCE AND USE 5.1. This practice is designed to simulate the in-service oxidative aging that occurs in asphalt binders during paveme
11、nt service. Residue from this practice may be used to estimate the physical or chemical properties of asphalt binders after 5 to 10 years of in-service aging in the field. 5.2. Asphalt binders aged using R 28 are used to determine specification properties in accordance with M 320. The asphalt binder
12、 is aged with the RTFO test prior to this conditioning step. Tank asphalt binders, as well as RTFOT and residue from this practice, are used to determine specification properties in accordance with M 320. 5.3. For asphalt binders of different grades or from different sources, there is no unique corr
13、elation between the aging time and temperature in this practice and in-service pavement age and temperature. Therefore, for a given set of in-service climatic conditions, it is not possible to select a single PAV aging time and temperature that will predict the properties of all asphalt binders afte
14、r a specific set of in-service exposure conditions. 5.4. The relative degree of hardening of different asphalt binders varies at different aging temperatures in the PAV. Therefore, two asphalt binders may age similarly at one temperature, but age differently at another temperature. 6. APPARATUS 6.1.
15、 A test system consists of a pressure vessel, pressure-controlling devices, temperature-controlling devices, pressure- and temperature-measuring devices, and a temperature-recording device (Figure 1). 6.1.1. Pressure VesselA stainless steel pressure vessel designed to operate at 2.1 0.1 MPa between
16、90 and 110C with interior dimensions adequate to hold ten stainless steel pans and a pan holder. The pressure vessel shall contain a pan holder capable of holding ten stainless steel pans in a horizontal (level) position such that the asphalt binder film thickness in the bottom of the pans does not
17、vary by more than 0.5 mm across any diameter of the pan. The holder shall be designed for easy insertion and removal from the vessel when the holder, pans, and asphalt binder are at the test temperature. A schematic showing the vessel, pan holder and pans, and specifying the dimensional requirements
18、 is shown in Figure 2. Note 1The vessel may be a separate unit to be placed in a forced draft oven for conditioning the asphalt binders or an integral part of the temperature control system (for example, by direct heating of the vessel or by surrounding the vessel with a permanently affixed heating
19、unit, forced air oven, or liquid bath). 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b R 28-3 AASHTO Figure 1Schematic of Typical PAV Test System Compressed Air CylinderPressure VesselTemperature
20、ControlNeedle ValveRupture DiskPressure GaugePressureRegulatorBleed ValveNeedle ValvePressure ReleaseValveNeedle ValveQuick DisconnectRTDPAV 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b R 28-4 A
21、ASHTO Notes: 1. Distance “a” controls the levelness of the pans. 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 0.05 mm. Provisions shall
22、 be made to ensure that the bottom of the vessel is leveled so that the thickness of the binder in the pan varies by no more than 0.05 mm across the diameter of any pan. 2. Distance “b” shall be such that any active portion of the temperature transducer is 10 mm from the top surface of the vessel. 3
23、. Distance “c” shall be 12 mm. Figure 2Schematic Showing Location of Pans and RTD within Representative PAV 6.1.2. Pressure-Controlling Devices: 6.1.2.1. A pressure release valve that prevents pressure in the vessel from exceeding 2.2 MPa during the aging procedure. 6.1.2.2. A pressure regulator cap
24、able of controlling the pressure within the vessel to 1 percent, and with a capacity adequate to reduce the pressure from the source of compressed air so that the pressure within the loaded pressure vessel is maintained at 2.1 0.1 MPa during the practice. 6.1.2.3. A slow release bleed valve that all
25、ows the pressure in the vessel at the completion of the conditioning procedure to be reduced at an approximately linear rate from 2.1 MPa to local atmospheric pressure within 9 1 min. 6.1.3. Temperature-Controlling DevicesA temperature control device as described in Section 6.1.3.1 or Section 6.1.3.
26、2 for maintaining the temperature during the aging procedure at all points within the pressure vessel at the aging temperature 0.5C and a digital proportional controller for maintaining the specified temperature control. 6.1.3.1. A forced-draft oven or fluid bath capable of (1) bringing the loaded u
27、npressurized vessel to the desired conditioning temperature 0.5C, as recorded by the Resistance Thermal Detector (RTD) inside the vessel within 2 h, and (2) maintaining the temperature at all points within the pressure Wall Clearance 10 mmProvide at least5-mm clearance tonearest surface10 TFOT pans
28、supportedon shelf or standards.Entire assembly shall beremovable as anintegral unit.Assembly support pointAssembly to includepans and supportsTo temperature transducer andtemperature readout10 mm from topof asphalt binderacb 2015 by the American Association of State Highway and Transportation Offici
29、als.All rights reserved. Duplication is a violation of applicable law.TS-2b R 28-5 AASHTO vessel at the aging temperature 0.5C. The oven shall have sufficiently large interior dimensions to allow forced air to freely circulate within the oven and around the pressure vessel when the vessel is placed
30、in the oven. The oven shall contain a stand or shelf that supports the loaded pressure vessel in a level position above the lower surface of the oven (i.e., maintains the film thickness in the aging pans within the specified tolerance). 6.1.3.2. A pressure vessel with integral temperature control sy
31、stem that is capable of (1) bringing the loaded pressure vessel to the desired conditioning temperature 0.5C within 2 h, as recorded by the RTD inside the loaded pressure vessel, and (2) maintaining the temperature at all points within the pressure vessel at the aging temperature 0.5C. 6.1.4. Temper
32、ature- and Pressure-Measuring Devices: 6.1.4.1. A platinum RTD accurate to the nearest 0.1C and meeting DIN Standard 43760 (Class A), or equal, for measuring temperature inside the pressure vessel. The RTD shall be calibrated as an integral unit with its respective meter or electronic circuitry. Not
33、e 2The RTD or thermistor and its meter may be calibrated by the manufacturer or a commercial vendor. Verification can be obtained by comparing the output from the RTD with an NIST traceable ASTM 94C mercury-in-glass thermometer in accordance with ASTM E220. A stirred fluid bath is suitable for calib
34、rating the thermal detector. Select a partial immersion mercury-in-glass thermometer with an appropriate range and place the thermal detector and the thermometer in the stirred water bath. Fasten the detector to the glass thermometer with a rubber band or rubber O-ring. Allow the bath, detector, and
35、 thermometer to come to thermal equilibrium and record the temperature of the glass thermometer and the readout from the thermal detector. The temperature in the bath shall not change by more than 0.1C/min during the calibration process. 6.1.4.2. Temperature-Recording DeviceA strip chart recorder or
36、 other data acquisition system capable of recording temperature throughout the test to 0.1C. As an alternative, an electronic device capable of reporting maximum and minimum temperatures (accurate to 0.1C) may be used. 6.1.4.3. A pressure gauge capable of measuring the pressure in the pressure vesse
37、l to within 1 percent during the test. 6.2. Stainless Steel PansTen standard stainless steel pans with an inside diameter of 140 mm (51/2in.) and 9.5 mm (3/8in.) deep with a flat bottom. Pans shall be made of stainless steel and should have a metal thickness of approximately 0.635 mm (0.025 in.). 6.
38、3. BalanceA balance conforming to the requirements of M 231, Class G 2. 6.4. Vacuum OvenA vacuum oven capable of maintaining a temperature up to 180C with an accuracy of 5.0C and a vacuum of 1.0 kPa absolute. 6.5. Vacuum SystemA vacuum system capable of generating and maintaining pressures below 15
39、kPa absolute. Suitable vacuum systems include a vacuum pump, air aspirator, or house vacuum system. 7. MATERIALS 7.1. Commercial bottled air or equivalent. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law
40、.TS-2b R 28-6 AASHTO 8. HAZARDS 8.1. Use standard laboratory safety procedures in handling the hot asphalt binder when preparing test specimens and removing the residue from the pressure vessel. Use special precaution when lifting the pressure vessel. 9. CALIBRATION AND STANDARDIZATION 9.1. Temperat
41、ure DetectorVerify the calibration of the RTD to 0.1C at least every 6 months using a calibrated thermometer. 9.2. Pressure GaugeStandardize the pressure gauge to an accuracy of 1 percent at least every 6 months. Note 3The pressure gauge is usually calibrated by the manufacturer or a commercial cali
42、bration service. Verification of the continued stability of the pressure gauge within the specified requirements should be done periodically by checking against another certified pressure measurement device. 9.3. To determine the optimum temperature at which to apply pressure to the pressure vessel,
43、 several tests should be made. With the vessel loaded with pan rack and empty pans, increase the temperature to aging temperature. When the temperature inside the pressure vessel is within 10C of the aging temperature, apply an air pressure of 2.1 0.1 MPa. Record the temperature increase when the pr
44、essure is applied. Perform the procedure at least three times and use the average temperature increase to establish the temperature at which to apply pressure to the vessel for performing the aging procedure. 10. PROCEDURE 10.1. Condition the asphalt binder in accordance with T 240 (RTFOT). 10.2. Af
45、ter combining the RTFOT residue into a single container and blending as specified in T 240; (1) pour the hot residue directly into the stainless steel pans for immediate conditioning in the PAV, or (2) pour the residue into the stainless steel pans, cover and set aside for conditioning at a later ti
46、me, or (3) allow the residue to cool in the single container for conditioning at a later time. If the residue is allowed to cool in the pans, reheat the pans and residue to the conditioning temperature. If the residue is stored in a single container, heat the residue, stir gently, and pour the heate
47、d residue into the pans. 10.3. Place the pan holder inside the pressure vessel. If an oven is used, place the pressure vessel inside the oven. If an integrated temperature control pressure vessel is used, turn on the heater. Select an aging temperature and preheat the pressure vessel to the aging te
48、mperature selected. Note 4If conditioning asphalt binders for conformance to M 320, select the appropriate aging temperature from Table 1 of M 320. Note 5Preheating the vessel 10 to 15C above the conditioning temperature can be used to reduce the drop in PAV temperature during the loading process an
49、d minimize the time required to stabilize the system, after loading, to attain the required temperature. Note 6Aging temperature in the PAV is selected to account for different climatic regions. Temperatures in excess of approximately 115C can change the chemistry of asphalt binders aged in accelerated tests and should be avoided. 2015 by the American Association of State Highway and Transportation Officials.All rights reserved. Duplication is a violation of applicable law.TS-2b R 28-7 AASHTO 10.4. Place the stainless
