Optimization of Tack Coat for HMA Placement
http://www.trb.org/TRBNet/ProjectDisplay.asp?ProjectID=974
Record Type: RiP
A tack coat is typically applied just before a hot mix asphalt (HMA) layer or overlay is placed. A tack coat is a simple, relatively inexpensive process included as an incidental item in many HMA construction specifications. Indeed, a tack coat is so simple in concept that its real importance is often overlooked. An inadequate tack coat product or improper application of a good product can result in costly failure. A review of the extensive body of literature on tack coat materials and their use suggests that tack coats are placed to bond pavement layers together, with the intent of providing a monolithic, impermeable structure or preventing slippage of HMA overlays. However, these views on the function of a tack coat are not universally accepted. Studies conducted on the strength of interfaces in HMA pavements have shown that a strong tack coat bond between pavement layers is critical for transfer of radial tensile and shear stresses into the entire pavement structure. On the other hand, no tack coat bond or an insufficient bond decreases pavement-bearing capacity and may cause slippage. No bond or insufficient bond may also cause tensile stresses to be concentrated at the bottom of the wearing course. Such concentrated stress may accelerate fatigue cracking and lead ultimately to pavement failure. Few guidelines are available for proper selection of tack coat material type, application rate, and placement. Optimum tack coat type and application rate will be determined by the type and condition of the existing pavement surface as well as other factors including material type and permeability of the HMA pavement overlay to be placed, the traffic loading, and the climate. Proper, uniform tack coat application requires close attention to equipment calibration and operating parameters. The objectives of this study are to determine optimum application methods, equipment type and calibration procedures, application rates, and asphalt binder materials for the various uses of tack coats and to recommend revisions to relevant AASHTO methods and practices related to tack coats. In accomplishing these objectives, both present and emerging technology in the United States and worldwide will be evaluated.
Start date: 2005/7/1
End date: 2010/3/31
Status: Active
Contract/Grant Number: Project 9-40
Total Dollars: 350000
Source Organization: National Cooperative Highway Research Program
Date Added: 02/25/2005
Index Terms: Tack coats, Hot mix paving mixtures, Asphalt pavements, Pavement layers, Overlays (Pavements), Permeability, Research projects, National Cooperative Highway Research Program,
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National Cooperative Highway Research Program
Transportation Research Board
500 Fifth Street, NW
Washington, DC 20001
USA
American Association of State Highway & Transp Officials
444 North Capitol Street, NW, Suite 225
Washington, DC 20001
USA
Federal Highway Administration
http://www.fhwa.dot.gov/
1200 New Jersey Avenue, SE
Washington, DC 20590
USA
Phone: (202) 366-4000
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Harrigan, Edward T.
Phone: (202) 334-3232
Email: EHARRIGA@nas.edu
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Louisiana Transportation Research Center
http://www.ltrc.lsu.edu/
4101 Gourrier Avenue
Baton Rouge, LA 70808
USA
Phone: (225) 767-9102
Fax: (225) 767-9108
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Mohammad, Louay
Phone: (225) 767-9126
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