Fundamental Properties of Asphalts and Modified Asphalts, III

The increase in carbonyl at the center of LTA3 compared to the center of STA suggests
significant aging occurred during the eight-day oven aging period. The apparent carbonyl
gradient from the center to the edge in LTA3 suggest the oxidation reaction is diffusion
controlled and that the core has increased anisotropy due to aging.
Since the cores were prepared using AAD-1 asphalt, the observed differences in carbonyl content
were further quantified by estimating G* as shown in figure 2-2.2.18. The asphalt at the center
of STA had a G* of 10,600 Pa (at 60˚C and 10 radians/sec). The estimated G* at the center and
edge of LTA3 was 17,000 and 27,500 Pa, respectively. The complex shear modulus of AAD-1
(at 60˚C and 10 radians/sec) after standard PAV aging (20 hours, 300 psi) was 14,700 Pa., which
is somewhat less than the G* at the center of LTA3, suggesting the eight-day oven aging effect is
more severe than the standard PAV test.
Since differences in aging in the presence of aggregate at atmospheric pressure compared to
aging without aggregate at high pressure are not well understood, these results must be
considered preliminary. Some aggregates may have a catalytic effect on oxidation that is not
currently accounted for in the standard PAV test.
Log G* , Pa, 60C, 10 rad/sec
6.00
5.50
5.00
4.50
4.00
3.50
2.75E+04 Pa
1.70E+04 Pa
1.06E+04 Pa
37
y = 6.92x + 1.74
R 2 = 0.99
Linear (PAV 60C
and 80C points)
3.00
0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6
Normalized Carbonyl (total peak ht) Absorbance
Unaged
RTFO
PAV 100C
PAV 60C
PAV 80C
STA center
LTA3 center
LTA3 edge
Figure 2-2.2.18. Estimated G* of recovered asphalt from the center of STA and the center and
edge of LTA3. Correlation plot of G* versus carbonyl peak height is based on AAD-1 60˚C and
80˚C PAV’ed asphalt. Note: the infrared spectra were normalized to the umbrella bending band
at 1376 cm -1 . Unaged, RTFO and PAV 100˚C points were not included in the linear regression.