ICT project R27-100: Best Practices for Implementation of Tack Coat was recognized as a 2013 AASHTO Sweet Sixteen High Value Research Project and was named the top project for AASHTO’s Region III. Investigators were Imad Al-Qadi, Alejandro Salinas, Khaled Hasiba, Hasan Ozer, and Zhen Leng of the University of Illinois at Urbana-Champaign and Enad Mahmoud of Bradley University. The Technical Review Panel chair for this project was Derek Parish, Illinois Department of Transportation (IDOT) District 4 Acting Local Roads Engineer.
Tack coat is a light layer of diluted asphalt that is applied to hot-mix asphalt (HMA) or Portland cement concrete pavement surfaces to ensure good interface bonding between layers. Too much tack coat can cause slipping between pavement layers, and too little tack coat can cause distresses in the upper pavement layer. This project sought to quantify the effects of tack coat type, application rate, cleaning techniques, and surface texture on interface bonding and overlay performance through laboratory and full-scale accelerated pavement testing, as well as extensive field testing and evaluation.
The findings from this project have enabled IDOT to revise tack coat specifications to more efficiently and effectively apply tack coat at an optimized application rate to enhance pavement performance. The new specifications will result in pavements that are more cost effective and will allow IDOT and the industry to better optimize resources and improve pavement performance.