Investigation of the Need for an HMA Layer Bond Strength Test

Poor bonding with underlying hot mix asphalt (HMA) layers can greatly influence HMA's long-term performance in the form of premature cracking and fatigue. The primary method to achieve bonding between layers is through the use of an emulsified tack coat. The Colorado Department of Transportation (CDOT) is prescriptive in its tack coat specifications; the investigators assure responsibility for any pavement failures related to poor bonding. CDOT should consider adopting a bond strength test method and associated specification limits based on performance data. The investigators could then transfer responsibility to the contractor for determining appropriate cleaning and tack coat application rates and practices. This research will first determine if bond failure is a significant problem here. If it is, the research will develop a bond strength test and test it on several overlay projects with varying tack coats, to determine an acceptable range for the specification.