Fundamental Properties of Asphalts and Modified Asphalts, III

figure 2-2.2.19 to show the correlation of rheological properties to field cracking performance. It
can be seen that different asphalts oxidized to the same stiffness have different phase angles.
The higher phase angle at the same oxidation stiffness indicates the asphalt has better flow
properties. Based on figure 2-2.2.19, asphalt AZ1-1 has the lowest (smallest) phase angle at the
same oxidation stiffness, indicating this asphalt will tend to become more brittle earlier than the
other three asphalts when oxidized to the same stiffness. From this figure, one can see that the
ranking (cracking potential) from laboratory rheological data agrees well with field cracking
performance. In other words, asphalt AZ1-1 has developed the most cracking so far, followed by
asphalt AZ1-2, asphalt AZ1-4, and the least tendency to crack is asphalt AZ1-3.
Complex Modulus, G*, Pa
1e+7
8e+6
6e+6
4e+6
2e+6
0
Master Curve at 10 rad/s
4th Year
30 40 50 60 70 80
Phase Angle, degree
39
Neat
AZ1-1
AZ1-2
AZ1-3
AZ1-4
Figure 2-2.2.19. Complex modulus versus phase angle with respect to
different aging times for four asphalts.
To further elucidate how phase angle relates to the flow properties of asphalt binder, the phase
angle was plotted against with reduced frequency (master curves) (figure 2-2.2.20) and
temperature (figure 2-2.2.21) for original asphalt, asphalt extracted from 4-year pavement, and
asphalt subjected to laboratory PAV aging at different aging times. A typical phase angle master
curve plot is shown in figure 2-2.2.20. The phase angle decreases as a sigmoid shape as
frequency increases. Figure 2-2.2.21 shows a similar plot for phase angle versus temperature.
All solid symbols along with solid lines represent all laboratory aging at different aging times.
The circular solid symbol represents the control sample, neat asphalt without any aging. Square,
diamond, inverted triangle, and triangle solid symbols represent 96 hours (red), 192 hours
(green), 336 hours (orange), and 504 hours (light blue), respectively, in PAV at 60°C. The
hollow symbols along with dash lines all represent 4-year old shoulder pavement at different
slices, top half inch (dark blue), 2 nd half inch (red), 3 rd half inch (dark purple) and bottom half
inch (dark cyan). Careful examination shows that the data plotted in figure 2-2.2.21 are