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Modeling of Asphalt Binder Rheology and Its Application to Modified Binders 55

Summary of Findings for the Damage Resistance Parameters
Based on the results and analysis of the binder rutting and fatigue studies, the following
points provide a summary of the findings:
∗
1. There are critical questions about the validity of the binder parameter G /sind.
∗
The correlation between the mixture rutting indicators and G /sind is very
poor. The parameter is derived from testing that does not provide a good
representation of traffic loading in the field. The parameter could not be found
useful in describing the accumulation of permanent flow, which is important in
rutting evaluation.
2. Repeated creep testing of binders is introduced as a better method for estimating
binder resistance to permanent strain accumulation. The viscous component of
the creep stiffness (G ) is found to be a good indicator of the rate of permanent
v
strain accumulation for binders. It is proposed as a better specification
parameter.
3. Compared to the current binder protocol, the repeated creep test protocol for
measuring binder accumulated permanent strain represents improvements in
the theoretical and practical concepts for better rating of binder properties as
related to rutting of pavements.
4. The lack of correlation between the mixture fatigue life and current binder
∗
fatigue resistance indicator, G sind, at the intermediate temperatures, indicates
that a new test for the binder fatigue resistance is needed to determine the
relation between mixture fatigue life and binder rheological properties.
5. Time sweep test is introduced as a promising binder-only fatigue test to evaluate
the fatigue resistance of the binder. The test can be conducted using the current
DSR within a relatively short testing time.
6. The dissipated energy ratio approach is employed as the method to determine
the fatigue life of binders, because of the independent nature of this approach
to the loading modes. Although the geometry has certain effects on the results,
by selecting the proper test conditions, this approach can give reliable results
that are found to correlate well with mixture performance.

Acknowledgments
A major part of the work reported in this chapter in regard to modified asphalts is based
on the SHRP and the NCHRP 9-10 project, which is sponsored by the American
Association of State Highway and Transportation officials, in cooperation with the
Federal Highway Administration. It was conducted as part of the National Cooperative
Highway Research Program, which is administrated by the Transportation Research
Board of the National Research Council. The author gratefully acknowledges this support
and also acknowledges the support of the NCHRP Project Officer Dr. E. Harrigan, and
the members of the project panel for their continuous encouragement and feedback.
Also the author gratefully acknowledges the technical support of the engineers and
scientist that contributed directly and indirectly to the results presented.