Test method to determine aggregate/asphalt adhesion properties and potential moisture damage
Wisconsin Highway Research Program
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The aim of this research project was to improve current practice by investigating different test methods to quantify moisture damage in an effort to serve the short and long term needs of the agency and industry. In the short term, more efficient test methods were investigated for use as a screening test to supplement current testing procedures. The Stripping Test was chosen as a candidate to serve this need. This test measures the mass loss due to moisture conditioning of a HMA loose mix. The test was evaluated in terms of serving as a screening test to waive mechanical testing requirements for mixes that display resistance to moisture damage. To serve the long term needs of the agency the use of fracture energy, a fundamental property of the asphalt mixture, was investigated as a first step in identifying a parameter that relates to pavement performance. The research involved selection and testing of common hot mix asphalt (HMA) mixes used in Wisconsin using the stripping test to measure percent mass loss and the indirect tension test to measure tensile strength and fracture energy. Test results were evaluated on an individual basis in their ability to reliably identify moisture damage due to sample conditioning and the effects of the addition of an anti-stripping agent or change in aggregate type or gradation. The results of the mechanical testing were compared to the non-mechanical test results to evaluate the possibility of incorporating a non mechanical screening test into current Wisconsin Department of Transportation (WisDOT) asphalt mixture testing specifications. Furthermore, the statistical method of analysis of variance was performed on the mechanical testing results to identify significant effects. The quality of the mechanical tests was then determined by evaluating if the significant effects were consistent between the mechanical testing parameters and with common engineering knowledge. The results of this research concluded that the Stripping Test is not adequate for use by WisDOT due to high variability within testing results for a certain mix. The fracture energy test gave promising results however, the high variability and complex test protocol prevent recommendation for the test to be implemented at this time. Recommendations from this research include improvement of the fracture energy test procedure to reduce variability, and further investigation into the physical causes of moisture damage. Specifically asphalt/aggregate adhesion, the effect of the mastic (fine aggregate and binder), and physiochemical interaction between the asphalt binder and aggregate must be understood.
Hot mix paving mixtures