United States Department of Transportation
i
HMAC layer adhesion through tack coat.
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2017-02-01
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[PDF-7.49 MB]
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Abstract:Tack coats are the asphaltic emulsions applied between pavement lifts to provide adequate bond between the two surfaces. The adhesive bond between the two layers helps the pavement system to behave as a monolithic structure and improves the structural integrity. The absence, inadequacy or failure of this bond result in a significant reduction in the shear strength resistance of the pavement structure and make the system more vulnerable to many distress types, such as cracking, rutting, and potholes. In general, decisions on tack coat types and application rates are based on experience, judgment, and convenience. For this reason, unacceptable bond performance and tack coat related premature failures are inevitable due to the lack of quality-control and quality-assurance (QC/QA) procedures.
This research study presents a comprehensive field investigation consisting of field and laboratory testing, 3D finite element modeling, field coring, and construction sampling of tack coats used in Oregon. Within the study, two new tack coat materials from two companies were, for the first time, evaluated for their performance. Recommendations for the most efficient application rates along with interlayer shear strength (ISS) prediction equations based on rheological properties were developed. In this study, tools and methods (a wheel tracking device and a smart phone app) to reduce tracking were also developed. Results of the evaluation will provide valuable information about correlations between rheological tests and interlayer shear strength, as well as the effects of texture, traffic loads, and application rate on interlayer shear strength.
In this study, the Oregon Field Torque Tester (OFTT) and the wireless Oregon Field Tack Coat Tester (OFTCT) were also developed to evaluate the long-term post-construction tack coat performance of pavement sections. It was determined that OFTT and OFTCT can be successfully utilized in the field to improve tack coat bond strengths.
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