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Title:Best Practices for Implementation of Tack Coat: PART I - Laboratory Study
Author(s):Al-Qadi, Imad L.; Hasiba, Khaled I.; Salinas Cortina, Alejandro; Ozer, Hasan; Leng, Zhen; Parish, Derek C.; Worsfold, Stephen J.
Subject(s):Tack coat
Abstract:Tack coat is a light layer of diluted asphalt that is applied to hot mix asphalt concrete (HMA) or Portland cement concrete (PCC) pavement surfaces to ensure good interface bonding between layers. Interface bonding is affected by several factors; including tack coat (type, application rate, curing time, application temperature, and asphalt residue content), pavement surface characteristics (asphalt content, aggregate type and gradation, and surface texture), and environmental conditions. This study evaluated interface bonding between two HMA layers by conducting a laboratory shear performance test. The main objective of this study was to evaluate the performance of various tack coats and determine the optimum residual application rates for three pavement surfaces: unmilled aged nontrafficked, milled aged, and unmilled aged trafficked HMA. The study also examined the influences of tack coat curing time, temperature, HMA type, and surface texture on the performance of tack coats. The study considered four tack coat materials: SS-1hp, high float emulsion (HFE), SS-1vh (very hard, no-track emulsion), and straight asphalt (PG 64-22). The tack coat was optimized at residual rates of 0.00, 0.02, 0.04, 0.06, and 0.08 gal/yd2 (0.00, 0.09, 0.18, 0.26, and 0.36 L/m2). Three curing times were considered: 0.25, 2, and 24 hr. Two overlay mixes (9.5-mm surface mix and 4.75-mm surface mix) were used. Prior to testing, the specimens were conditioned at four temperatures: 5°F, 41°F, 77°F, and 113°F (–15°C, 5°C, 25°C, and 45°C). The study found that the optimum tack coat residual rate was 0.04 gal/yd2 (0.18 L/m2) for trafficked and nontrafficked unmilled aged HMA surfaces, while the optimum residual rate for milled HMA was 0.06 gal/yd2 (0.26 L/m2). SS-1vh tack coat showed superior performance over the other tested tack coats. The optimum curing time was determined to be 2 hr. Milling the surface improved interface shear strength. The interface shear resistance was greater when the surface nominal maximum aggregate size (NMAS) increased from 4.75 mm to 9.5 mm. Increasing the temperature resulted in a reduction in shear strength.
Issue Date:2012-07
Genre:Technical Report
Publication Status:published or submitted for publication
Peer Reviewed:not peer reviewed
Sponsor:Illinois Department of Transportation ICT R27-100
Rights Information:No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161
Date Available in IDEALS:2013-09-23

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