Evaluation of Tack Coat Bonding Performance in Flexible Pavements

Although many states report successful use of tack coats to achieve adequate bonding between asphalt layers, not all states have experienced such success. Selecting an appropriate tack coat is crucial for overcoming poor bonding and ensuring optimal performance in the field. This study aimed to provide comprehensive guidance on selecting the right tack coat material, considering various construction methods and environmental conditions, to ensure effective bonding. Two asphalt mixture types (fine and coarse) and surface conditions (new asphalt concrete [AC], milled AC, and aged AC) were adopted in this study to determine the impact of existing pavement conditions on bonding performance. The effectiveness of various tack coat materials and their rheological properties was also assessed. The American Association of State Highway and Transportation Officials (AASHTO) TP114 (“Standard method for determining interlayer shear strength [ISS] of asphalt pavement layers”) was employed to evaluate the bonding performance of different tack coat materials, mixture types, and surface conditions. It was evident that using an improper tack coat could create a slip plane and reduce the interface shear strength, a problem not observed in samples without a tack coat. Additionally, a good correlation between tack coat rheological properties and ISS test results were observed.