Development of Guidelines for Selection and Evaluation of Tack Coats in Oklahoma

2018Final Report Oct 2015-Dec 2017PDFTech ReportFHWA-OK-18-02ODOT SPR Item Number 2273Tack coatsAsphalt pavementsAsphalt concrete pavementsComposite pavementsOptimum application rate of tack coatInterlayer shear strengthSurface conditionTracking testTrackless tack coatAnionic and cationic tack coatsUnited StatesOklahomaOklahoma. Department of TransportationGhabchi, RouzbehZaman, Musharraf M.Rani, ShivaniSouth Dakota State University. Department of Civil and Environmental EngineeringUniversity of Oklahoma. School of Civil Engineering and Environmental ScienceOklahoma. Department of Transportation. Office of Research and ImplementationUS Transportation CollectionAsphalt pavements are generally constructed by compacting asphalt mixes in multiple lifts to achieve the required density across the layers. Also, depending on pavement preservation and maintenance plan, from time to time, a thin overlay may be constructed over an existing asphalt pavement or a Portland Cement Concrete (PCC) pavement. The quality and integrity of the bond between asphalt layers, especially the bond between the existing surface and an overlay, is crucial to pavement\u2019s durability and serviceability. Inadequate interlayer bond may lead to distresses such as half-moon-shaped cracks, delamination, longitudinal wheel path cracking, potholes,fatigue cracks, slippage, and rutting. In order to improve the interlayer bonding of asphalt pavements, and create a moisture barrier at layers\u2019 interfaces, tack coats are used. Tack coats improve the interlayer bond strength and help pavement layers behave as a single cohesive system. This improves pavement\u2019s resistance to traffic and environmental stresses. The interlayer bond strength is mainly governed by the selection of tack coat product and applying it at an optimum residual application rate (referred to as application rate in this report). The optimum application rate of a tack coat, to a great extent, depends on the existing pavement surface conditions such as new, old, or milled surface, tack coat type, moisture, and temperature. This study evaluated the effectiveness of tack coats used by the Oklahoma Department of Transportation, namely SS-1, CRS-1, CBC-1H, CRS-1S, NTHAP, and NTQS-1HH with respect to their type and application rate, pavement surface conditions, moisture-induced damage, and temperature. Two test methods were used for testing the tack coats: (i) Interlayer Shear Strength (ISS) of tack coat using the Louisiana Interlayer Shear Strength Tester (LISST); and (ii)Room-Temperature Tracking (RTT) test. Also, laboratory-compacted samples and a number of field cores from selected projects were collected and tested selectively to evaluate the tack coat performance. Based on the test results, a database that can be implemented for the selection of tack coat type and application rates was developed. Also, the optimum tack coat application rates, based on their ISS values was developed and presented that can be used for selection of the tack coats depending on pavement surface types. Also, as the removal of the tack coat through tracking by the construction equipment is a concern, setting times of the tack coats were presented that can be immediately implemented. Finally, a draft special provision was developed and included for improving the current practice in using tack coats in construction of the asphalt pavements in Oklahoma.92