ASTM D6521-08

This practice is designed to simulate the in-service oxidative aging that occurs in asphalt binders during pavement service. Residue from this conditioning practice may be used to estimate the physical or chemical properties of asphalt binders after several years of in-service aging in the field.

Binders conditioned using this practice are normally used to determine specification properties in accordance with Specification D 6373 or AASHTO M 320.

For asphalt binders of different grades or from different sources, there is no unique correlation between the time and temperature in this conditioning 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 conditioning time, temperature and pressure that will predict the properties or the relative rankings of the properties of asphalt binders after a specific set of in-service exposure conditions.

The relative degree of hardening of different asphalt binders varies with conditioning temperatures and pressures in the PAV. Therefore, two asphalt binders may age at a similar rate at one condition of temperature and pressure, but age differently at another condition. Hence, the relative rates of aging for a set of asphalts at PAV conditions may differ significantly from the actual in-service relative rates at lower pavement temperatures and ambient pressures.

1.1 This practice covers the accelerated aging (oxidation) of asphalt binders by means of pressurized air and elevated temperature. This is intended to simulate the changes in rheology which occur in asphalt binders during in-service oxidative aging but may not accurately simulate the relative rates of aging. It is normally intended for use with residue from Test Method D 2872 (RTFOT), which is designed to simulate plant aging.

Note 1—Modified asphalt binders may phase separate or form skins during oven conditioning in Test Method D 2872 (RTFOT); the results from subsequent testing of this residue may not be representative of modified asphalts short-term aged under field conditions. Phase separation, or formation of skins, or both can also occur during PAV conditioning. Therefore, the practice may not be suitable for some modified asphalts.

Note 2—PAV conditioning has not been validated for materials containing particulate materials.

1.2 The aging of asphalt binders during service is affected by ambient temperature and by mixture-associated variables, such as the volumetric proportions of the mix, the permeability of the mix, properties of the aggregates, and possibly other factors. This conditioning process is intended to provide an evaluation of the relative resistance of different asphalt binders to oxidative aging at selected elevated aging temperatures and pressures, but cannot account for mixture variables or provide the relative resistance to aging at in-service conditions.

1.3 The values stated in SI units are to be regarded as the standard. Values in parentheses in inch-pound units are provided for informational purposes only.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.