Fundamental Properties of Asphalts and Modified Asphalts, III

All different aging times were shifted to zero aging time. The aging shift factor is the amount of
shift of the complex modulus at a given aging time to the reference aging time (zero aging time
in this case) to form a single curve. The values of these shift factors can be considered to be
modulus (stiffness) changes with respect to the modulus at the reference aging time, and give an
indication of how the properties of a material change with aging time.
Figure 2-5.1 also shows the constructed complex modulus oxidation master curve for asphalt
ABD mixed with 1.5% PPA with respect to different aging times. A well-defined curve can be
seen in the figure indicating that a similarity does exist between the effects of aging and
temperature. The logarithm of the aging shift factor is the amount of shift for the complex
modulus at a given aging time to the reference aging time to form a single curve. Figure 2-5.2
shows the shift factor as a function of PAV aging time for asphalt ABD and PPA-modified ABD
aged in the absence and presence of water.
As seen from figure 2-5.2, the curve of the aging shift factor is similar to that of viscosity-aging
kinetic curves for typical asphalts and is shear rate independent. On oxidation, asphalts show an
initial rapid rate of viscosity increase followed by a slower rate of viscosity increase. This
behavior has been attributed to the formation of sulfoxide and carbonyl products in the oxidation
process of asphalt binder when exposed to atmospheric oxygen in the pavement. As seen from
figure 2-5.2, addition of PPA to asphalts increases the amount of stiffness change with respect to
the stiffness at the reference aging time, indicating that addition of PPA has changed the aging
characteristics of asphalt binders. In addition, aging in the presence of water reduces the amount
of stiffness change with respect to the stiffness at the reference aging time for neat unmodified
asphalts. However, addition of water in the pressure aging oven increases the amount of
stiffness change for PPA modified asphalt binders.
Figures 2-5.3 and 2-5.4 show similar types of plots, aging shift factors versus PAV aging times
in the presence and absence of water, for asphalts AAD-1, AAM-1, and their PPA mixtures,
respectively. Again, it can be seen that addition of PPA to asphalts increases the amount of
stiffness change due to PAV aging. As seen from both figures 2-5.3 and 2-5.4, the aging shift
factors of PPA modified asphalts after PAV aging for 326 hours in the presence of water are
similar to those of the same PPA modified asphalts at the same aging time in the absence of
water. This suggests that PPA modified asphalts AAD-1 and AAM-1 aged at 326 hours in the
PAV in the presence of water have similar complex modulus to the same materials that were
subjected to the same aging time in the absence of water. However, it is uncertain if the reduced
complex modulus at the end of aging time of 326 hours in the presence of water is due to the
presence of moisture during PAV aging or experiment error. Nonetheless, more experiments
need to be conducted to verify this observation.
During the quarter, work also continued on the study of the behavior of phosphorous containing
additives in asphalt by using NMR techniques. In particular, NMR work continued on
characterizing the behavior of phosphate ester and amine antistrip agents in asphalt. In addition,
some exploratory measurements were made to determine the feasibility of using 31 P NMR to
determine moisture in asphalt.
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