Tack coats are a vital component of an asphalt pavement’s structural system as they bond the multiple asphalt lifts into one monolithic layer. Poor tack coat application results in poor bonding of the asphalt layers. The usual pavement distresses associated with poor or no tack coat is slippage cracks (typically at locations where traffic is braking or accelerating) along with delamination of the surface lift. But quite often poor tack coat can lead to more classic structural pavement distresses, namely fatigue cracking and potholes, commonly without the poor tack being recognized as the source of these early failures.
In fact, researchers have indicated that even with a small loss in bond strength (10-30%), fatigue life can be reduced significantly (50-70%). Moreover, the cost to an agency in the event of a bonding failure can be quite large, potentially even exceeding the original costs of a maintenance overlay. Despite these facts, little attention is often paid to tack coat operations by both contractors and the agencies, and pavement performance suffers.
A significant amount of information has been compiled here on tack coats including the newest publication: NCHRP Synthesis 516.
Links to some of the more heavily relied upon documents are found below, including Asphalt Institute publications germane to tack coats.
Asphalt Institute Resources
- MS-4 The Asphalt Handbook (7th Edition)
- MS-19 Basic Asphalt Emulsion Manual
- MS-22 Construction of HMA Pavements
- Webinar – Tack Coats Part I: Purposes, Research, Materials, and Specifications
- Webinar – Tack Coats Part II: Best Practices for Preparation and Application, Bond Strength Testing, and Quality Control & Assurance
FHWA Tech Brief - Tack Coat Best Practices (2016)
Internet Resources
- NAPA’s Best Practices for Emulsion Tack Coats, 2013
- National Cooperative Highway Project Report 712 – Optimization of Tack Coat for HMA Placement, 2012
- North Carolina Tack Coat Best Practices Field Guide, 2012
- Caltrans Tack Coat Guidelines, 2009
