ASPHALT BINDERS AND ASPHALT MIXTURES - Materials for Civil and Construction Engineers - page 333

rheometer and prior to conditioning with the pressure-aging vessel. Under
the penetration and viscosity grading methods, the aged binder is usually
tested for penetration or viscosity and the results are compared with those of
new asphalt.

Pressure-Aging Vessel The pressure-aging vessel (PAV) consists of a tempera-
ture-controlled chamber, and pressure- and temperature-controlling and mea-
suring devices, as illustrated in Figure 9.13 (ASTM D6521). The asphalt binder
is first aged, using the rolling thin-film oven (RTFO) (ASTM D2872). A speci-
fied thickness of residue from the RTFO is placed in the PAV pans. The asphalt
is then aged at the specified aging temperature for 20 hours in a vessel under
2.10 MPa (305 psi) of air pressure. Aging temperature, which ranges between
90°C and 110°C, is selected according to the grade of the asphalt binder. Since
the procedure forces oxygen into the sample, it is necessary to use a vacuum
oven to remove any air bubbles from the sample prior to testing.
The PAV is designed to simulate the oxidative aging that occurs in asphalt
binders during pavement service. Residue from this process may be used to
estimate the physical or chemical properties of an asphalt binder after 5 to 10
years in the field.

Flash Point At high temperatures, asphalt can flash or ignite in the presence
of open flame or spark. The flash point test is a safety test that measures the
temperature at which the asphalt flashes; asphalt cement may be heated to

FIGURE 9.13 Pressure aging vessel apparatus.