United States Department of Transportation
i
Investigation of Tack Coat Materials Tracking Performance
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2019-07-01
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[PDF-1.99 MB]
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Edition:Final Report; June 2017- July 2019
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Abstract:This research evaluated the performance of asphalt emulsion tack coat used in Wisconsin to provide recommendations that make tack coat usage more efficient and effective. The study focused on measuring curing as measured by moisture loss, tracking as measured by a bond strength test and a wheel tracking device in the lab, and Interlayer Shear Strength using aa AASHTO provisional standard. The study also included a Field sampling task in which several projects in Wisconsin were included to take cores before and after application of tack coats and construction of overlays. For materials currently in use in Wisconsin, the results indicate that there is no practically significant difference between material types in terms of curing rate, however dilution is shown to significantly increase curing time for all materials. Tracking of emulsion residue is found to be primarily a function of the residual asphalt properties, and stiffness of the residual asphalt can be used to predict tracking behavior. There is no clear relationship between the shear strength of laboratory and field specimens, and shear strength of laboratory prepared specimens is primarily a function of surface texture. Considering only tack coat materials currently specified by WisDOT, no significant effect of emulsion type on shear strength is found. However, if highly stiff base asphalts are used, the base binder could influence the interlayer shear strength. Findings from the study are used to provide recommendations to modify the exiting tack coat specification in Wisconsin.
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