Recent evidence in Washington State indicates that de-bonding of HMA (Hot Mix Asphalt) surface layers may become a significant problem. “De-bonding” describes a condition where adjacent layers of HMA lose adhesion to one another and can become separated. Typically, design and construction practice is to build in a certain amount of bonding. However, the appropriate amount, testing and techniques are still under debate. For WSDOT pavements, which are generally thick and long-lasting, this de-bonding is thought to be more prevalent between the surface layer (usually applied as a preservation overlay) and underlying layers. This de-bonding may contribute to early failure of the HMA pavement surface layer, which can increase pavement preservation costs. This study gathers initial evidence on de-bonding in Washington State and attempts to define the problem scope and potential performance impacts. Specifically, it attempts to (1) determine if de-bonding occurs, (2) identify possible de-bonding mechanisms, (3) define the scope of de-bonding in WSDOT pavements, (4) determine de-bonding impacts on pavement performance, and (5) identify the role of tack coats in de-bonding.
A summary of this study with additional pictures is available on Pavement Interactive at: http://pavementinteractive.org/index.php?title=De-Bonding_of_HMA_Pavements