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Tack Coat Optimization for HMA Overlays: Laboratory Testing

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Title: Tack Coat Optimization for HMA Overlays: Laboratory Testing
Author(s): Al-Qadi, Imad L.; Carpenter, Samuel H.; Leng, Zhen; Ozer, Hasan; Trepanier, James
Subject(s): tack coat HMA overlay
Abstract: Interface bonding between hot-mix asphalt (HMA) overlays and Portland cement concrete (PCC) pavements can be one of the most significant factors affecting overlay service life. Various factors may affect the bonding condition at the interface, including HMA material,tack coat material, tack coat application rate, PCC surface texture, temperature, and moisture conditions. The objective of this study is to quantify the impact of these parameters on the permanent deformation of the HMA overlay. This study includes three major components to achieve the objective: laboratory testing, numerical modeling, and accelerated pavement testing. This report presents and analyzes the laboratory testing results. A direct shear test device was built and utilized to investigate the characteristics of the HMA-PCC interface and to determine the interface shear strength in the lab. Tests were run in monotonic mode at a constant loading rate of 0.47 in/min (12 mm/min). Test specimens were prepared using field PCC cores, laboratory prepared HMA, and tack coat materials provided by the supplier. Parameters affecting the interface performance that were evaluated include HMA material type (SM-9.5 surface mix and IM-19.5A binder mix), tack coat type (SS-1h and SS-1hP emulsions, and RC-70 cutback), tack coat application rate, PCC surface texture, temperature, and moisture conditions. Test results showed that the asphalt emulsions SS-1h and SS-1hP produced greater interface bonding strength than the cutback asphalt RC-70. The SM-9.5 surface mix was found to have better interface strength than the IM-19.0A binder mix. The HMA tested produced the same trend of interface shear strength with tack coat application rate for various tack coat types. The optimum residual tack coat application rate for the SS-1hP emulsion using IM-19.0A binder mix was 0.04 gal/yd2 (0.18 L/m2) in the lab. The direction of tining on the PCC produced no effect on interface shear strength at 20 oC. However, the milled concrete surface provided greater interface shear strength than both tined and smooth PCC surfaces for the same tack coat application rate. At the optimum tack coat application rate, the smooth PCC surface produced higher interface shear strength than the tined surface. As temperature increased, interface bonding strength decreased. Moisture conditioning significantly decreased the interface shear strength. This reduction was more pronounced when a stripping-vulnerable binder mix IM-19.0B was used.
Issue Date: 2008-09
Publisher: Illinois Center for Transportation
Series/Report: FHWA-ICT-08-023
Genre: Technical Report
Type: Text
URI: http://hdl.handle.net/2142/12117
Publication Status: published or submitted for publication
Peer Reviewed: is peer reviewed
Sponsor: ICT- R55
Date Available in IDEALS: 2009-06-09
 

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