Evaluation of the Bond Strength of Tack Coat

• Semon Rezkalla, Civil Engineering, University of Delaware

• Haritha Malladi, Civil and Environmental Engineering, University of Delaware

Evaluation of the Bond Strength of Tack Coat

Tack coat is a thin layer of asphalt emulsion that is sprayed on an existing concrete pavement surface between layers of new asphalt concrete to help them bond. Once the tack is applied to a surface, it “breaks” by evaporating its water component, leaving behind the sticky asphalt component on the applied surface. Tack coat is designed to create a strong adhesive bond without slippage onto a non-absorptive pavement surface.​ This research study was motivated by Delaware Department of Transportation (DelDOT) need to establish a performance-based standard for tack coats​. Peel test is a standard test method that is regularly used to test the strength of adhesives; our study involved using this test method to evaluate the performance of tack coats with varying application rates. We used a SS-1 grade tack coat, which is an anionic emulsion that is slow-setting, applied at Emulsion Application Rates (EAR) of 0.5, 0.7, 0.9, and 0.11 gal/yd2. Through test trials with different fabric materials, we first determined that strips of nylon power mesh were appropriate for performing the peel tests on tack coats. These fabric strips were then placed on plated with different tack coat EARs. Results indicate a variation in the peak loads with the emulsion application rates. Through these results, we can quantify the amount of strength needed to remove the tack coat in the lab, which then can be used to predict how the tack coats would behave in the field. While we have piloted this using the peel test with tack coats in this study, the test method needs further refinement to standard the fabric material and dimensions. We conclude that the peel test is promising as a test methodology that can help create performance based standards for tack coats.