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Title:Development of a testing approach for tack coat application rate at pavement layer interfaces
Author(s):Hasiba, Khaled
Advisor(s):Al-Qadi, Imad L.
Department / Program:Civil & Environmental Eng
Discipline:Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
shear strength
tack coat
curing time
mix type
application rate
surface texture
Hot Mix Asphalt Concrete (HMA)
Abstract:Pavement interlayer bonding is one of the critical factors that affect the pavement service life. In addition to difficulties in compaction, lack of interface bonding can lead to serious pavement deterioration including slippage cracking, de-bonding, and early fatigue cracking, all of which eventually reduce the pavement service life. Several experimental programs and numerical research have been conducted to investigate factors that affect the interface bonding. According to the existing literature, interface bonding is affected by different factors including tack coat material, application rate and temperature, as well as pavement mix type, volumetric characteristics, surface texture and cleanliness. 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. This study evaluated interface bonding between two HMA layers utilizing 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 various pavement surface conditions: unmilled aged non-trafficked, 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 non 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 hrs. Two overlay mixes (9.5-mm surface mix and 4.75-mm 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 non-trafficked unmilled aged HMA surface, while the optimum residual rate for milled HMA was 0.06 gal/yd2 (0.26 L/m2). SS-1vh tack coat showed superior performance compared to other tested tack coats. The optimum curing time was determined at 2 hrs. 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. The initial tangent stiffness for different tack coat materials was calculated and studied at various temperatures between 5°F (-15°C) and 113°F (45°C). The analysis showed that SS-1vh had the highest stiffness compared to the materials used. However, a continuous reduction in the initial tangent stiffness was observed when increasing the temperature within the temperature range used in this study.
Issue Date:2012-05-22
Rights Information:Copyright 2012 Khaled Hasiba
Date Available in IDEALS:2012-05-22
Date Deposited:2012-05

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