Laboratory Methods and Specifications to Test Tack Coat Materials
Loading...
Authors
Nasr, Rita
Issue Date
2024
Type
Dissertation
Language
en_US
Keywords
Alternative Title
Abstract
Tack coat, widely used as a bonding agent, is essential for reducing pavement distresses such as slippage and fatigue cracking. The impact of tack coat application on pavement interlayer shear strength (ISS) is a critical focus in asphalt and composite paving. Its effectiveness in enhancing shear strength can be influenced by various factors. While many state departments of transportation (DOTs) report successful use of tack coats to achieve adequate bonding between asphalt layers, some have not experienced such success. Selecting an appropriate tack coat is crucial for overcoming poor bonding and ensuring optimal field performance. This study aimed to evaluate the impact of different factors, such as application rate, mixture type (fine vs. coarse graded Asphalt Concrete (AC) mixture), existing pavement conditions (new, milled, aged AC, or Portland Cement Concrete (PCC) surfaces), moisture, and low-temperature conditions. The Interlayer Shear Strength (ISS) test, following AASHTO TP 114 (Standard Method for Determining ISS of Asphalt Pavement Layers), was employed to assess ISS under these varying conditions. It was found that the application rate was generally insignificant between 0.018 gsy and 0.080 gsy; however, for soft tack coat materials, a slippage plane developed at medium and high application rates. Results indicated that fine-graded mixtures exhibited higher ISS than coarse-graded mixtures. Polishing the surface of underlying HMA improved adhesion between the hot asphalt binder in the top layer and the underlying surface. Moisture conditioning negatively affected fine-graded mixtures ISS. Additionally, lower testing temperatures resulted in increased ISS, attributed to the increased stiffness of the asphalt material. Moreover, a strong correlation between tack coat rheological properties and ISS test results was observed, highlighting the importance of selecting the right tack coat material to ensure optimal pavement performance.