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Abstract
The Wisconsin Department of Transportation (WisDOT) has been using the tensile strength ratio (TSR) test (ASTM D-4867) to predict the potential susceptibility of asphalt mixture to moisture damage and other associated pavement deterioration. The objectives of this paper are to evaluate the relationship between the performance of asphalt pavements in the field and the TSR values measured in laboratory on the original asphalt mixtures used in constructing pavements, and to evaluate the effect of anti-stripping additives on field performance. To assess the moisture damage problem in the field, 21 existing WisDOT pavement sections that were built prior to the adoption of the TSR parameter as a requirement, were selected to cover a wide range of locations and aggregate sources. The TSR and the pavement performance data (pavement distress index or PDI) for these projects were collected from the WisDOT pavement management database. The results indicated no relationship between TSR and field pavement performance as measured by the PDI, and no relationship between TSR and specific pavement distresses that are related to moisture damage (surface raveling and rutting). To evaluate the effect of using anti-stripping additive, a database study and a laboratory study were conducted. The database showed an effect of using anti-stripping additives on the pavement performance and also on the specific pavement distresses that are related to moisture damage. In laboratory testing, anti-stripping additive was not found to change the rheological properties of asphalt binders, nor to improve the rutting and fatigue related properties of asphalt binder as measured by the dynamic shear rheometer (DSR). However, they were found to increase the adhesion of asphalt binder to selected mineral aggregate surfaces, especially when the binder bond is exposed to water. These findings lead to believe that better field performance is achieved by better adhesion between binders and aggregates. The findings also point out that although the TSR testing is sensitive to the use of anti-stripping additives, it does not provide a good simulation of factors playing roles in critical distresses such as rutting and raveling. What could be more effective is a simpler test allowing direct measure of adhesive bond between aggregates and asphalts. Such a test could replace the TSR in making a decision to require or not require the use of anti-stripping additive. The pull-off tensile strength test by the Pneumatic Adhesion Tensile Testing Instrument (PATTI) is also shown to give promising results.
Acknowledgements
This work was part of the WHRP project, which is sponsored by the Wisconsin Department of Transportation. The authors gratefully acknowledge the support of Ms Judie Ryan and Mr Tom Brokaw for their guidance and useful information regarding the project.