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.
Trying to aid state Departments of Transportation in the construction of better built and longer lasting pavements, the Federal Highway Administration (FHWA) and the Asphalt Institute produced a four-hour workshop on this topic. The workshop provides the most current information on tack coats and emphasizes the importance of providing a long lasting bond between asphalt layers.
- The Importance of Tack Coats
- Tack Coat Materials, Selection and Handling
- Tack Coat Specifications
- Topical Research
- Manuals of Practice
- Quality and Inspection
- Bond Strength Testing
- Best Practices
As seen on the following map, interest from the states was very high. 46 of the 50 states, plus Puerto Rico and the District of Columbia hosted a workshop.
Last updated July 2016
A significant amount of information has been compiled into the work-shop. Links to some of the more heavily relied upon documents are found below. Additionally, a recording of the entire workshop and other Asphalt Institute publications germane to tack coats are also below.
Asphalt Institute Resources:
- MS-4 The Asphalt Handbook (7th Edition)
- MS-19 Basic Asphalt Emulsion Manual
- MS-22 Construction of HMA Pavements
Tack Coat Workshop Resources:
- Recording of Ohio Tack Coat Workshop – 04/30/2015 (3:28 duration)
- FREE AI Webinar Recording – Tack Coat Best Practices
- Handout for Tack Coat Workshop
- Presentation Handout for Tack Coat Workshop
- Tack Coat Workshop Flyer
- NCHRP Synthesis 516 – Tack Coat Specifications, Materials and Construction Practices, 2018
- FHWA Tech Brief - Tack Coat Best Practices, 2016
- 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