AASHTO R 28:12(2016) Standard Practice for Accelerated Aging of Asphalt Binder Using a Pressurized Aging Vessel (PAV).
4. SUMMARY OF PRACTICE
4.1. Asphalt hinder is tirst aged using T 24(1 (RTFIJ[). A specilied thickness 01 residue, trom 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 temperature is selected according to the grade of the asphalt hinder. At the completion of the PAV process. the asphalt hinder 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 pavement 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 is aged with he RTFO test prior to this conditioning step. Tank asphalt hinders, 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 correlation
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 hinders after
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.
6.1. 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 Vessel—A stainless steel pressure vessel designed to operate at 2.1 ± 0.1 MPa between
90 and 110°C 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 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 hinder are at the test temperature. A schematic showing the vessel, pan holder and pans. and specifying the dimensional requirements is shown in Figure 2.AASHTO R 28 pdf download.