Interface shear strength characteristics of emulsified tack coats

Document Type

Conference Proceeding

Publication Date

12-1-2009

Abstract

The objective of this study was to evaluate interface shear strength of emulsified tack coats under a wide range of testing conditions commonly encountered in field applications. Three types of emulsified tack coats, CRS-1, SS-1h, and Trackless, were considered at three application rates, 0.14, 0.28, and 0.70 1/m2. In addition, a "no tack coat" condition was included in the analysis. The effects of construction conditions such as wet (rainfall) and dusty conditions were also evaluated. Laboratory direct shear tests were performed at 25C under two confinement pressures, 0- and 138-kPa. To simulate these test conditions, cores were extracted from a full-scale test site that was designed and constructed using conventional tack coat application and paving equipment. Results of this analysis showed that the trackless tack coat produced the highest shear strength at the three application rates, and SS-1 and CRS-1 resulted in the medium and the lowest strength, respectively. Within the considered application rate range, it was difficult to determine the optimum residual application rate. This may be attributed to the highly-oxidized and coarse HMA surface at the selected field site that required greater tack coat rates than expected. While higher application rates may increase interface shear strength, excessive tack coat may migrate into the HMA mat during compaction causing a decrease in the air void content in the mix. The majority of the cases showed statistically significant difference between clean and dusty conditions. However, no significant difference was found between dry and wet conditions. The results presented herein were part of the National Cooperative Highway Research Program (NCHRP) Project 9-40 on the "Optimization of Tack Coat for HMA Placement.".

Publication Source (Journal or Book title)

Asphalt Paving Technology: Association of Asphalt Paving Technologists-Proceedings of the Technical Sessions

First Page

249

Last Page

276

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