ASPHALT BINDERS AND ASPHALT MIXTURES - Materials for Civil and Construction Engineers - page 332

time. These results are corrected to the minimum temperature using the
time-temperature shift factor (McGennis 1994).

■ Performance Grade Binder Characterization

Several tests are used in the Performance Grade method to characterize the
asphalt binder. Some of these tests have been used before for asphalt testing,
while others are new. The discussion that follows summarizes the main
steps and the significance of SHRP tests. With the exception of the rotational
(Brookfield) viscometer, solubility, and flash point tests, the test temperatures
are selected based on the temperature at the design location. The binder spec-
ification indicates the specific test temperatures used for various binders for
each test (McGennis 1994). Four tests are performed on the neat or tank asphalt:
flash point, solubility, rotational viscosity, and dynamic shear rheometer. To
simulate the effect of aging on the properties of the binder, the rolling thin-
film oven and pressure-aging vessel condition the binder for short-term and
long-term effects. Samples are conditioned with both the rolling thin film
oven and pressure-aging vessel before determining their characteristics with
respect to fatigue and low-temperature cracking.

9.6.2

Rolling Thin-Film Oven The rolling thin-film oven (RTFO) procedure is used
to simulate the short-term aging that occurs in the asphalt during production
of asphalt concrete. In the RTFO method (ASTM D2872), the asphalt binder
is poured into special bottles, as shown in Figure 9.12. The bottles are placed
in a rack in a forced-draft oven at a temperature of 163°C (325°F) for 75 min.
The rack rotates vertically, continuously exposing fresh asphalt. The binder
in the rotating bottles is also subjected to an air jet to speed up the aging
process. The Performance Grade specifications limit the amount of mass loss
during RTFO conditioning. Rolling thin-film oven conditioning is used to
prepare samples for evaluation for rutting potential with the dynamic shear

FIGURE 9.12 Rolling thin
film oven test apparatus.