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SPR Active Projects

SPR 782

HMAC Layer Adhesion Through Tack Coat

Project Coordinator:
 Norris Shippen
Research Agency:
 Oregon State University
Principal Investigator:
 Erdem Coleri 
Start Date for ODOT:
Completion Date for ODOT:

Tack coats are the asphaltic emulsions applied between pavement lifts to provide adequate bond between the two surfaces. The adhesive bond between the two layers helps the pavement system to behave as a monolithic structure and improves the structural integrity. The absence, inadequacy or failure of this bond result in a significant reduction in the shear strength resistance of the pavement structure and makes the system more vulnerable to many distress types, such as cracking, rutting, and potholes. 

Tracking, the pick-up of bituminous material by construction vehicle tires, reduces the amount of tack coat in certain areas and creates a non-uniform tack coat distribution between the two construction lifts. This non-uniform tack coat distribution creates localized failures around the low tack coat locations and reduces the overall structural integrity of the pavement structure. In addition, tack coat type, residual application rate, temperature, and existing surface condition (cracked, milled, new, old, or grooved) are the other factors that affect the tack coat performance. By considering all these factors, a quality-control and quality-assurance process need to be developed to maximize tack coat performance during the design life. Although Louisiana Tack Coat Quality Tester (LTCQT) (Mohammed et al. 2006) can be used to predict in-situ tack coat performance, high cost of LTCQT ($40,000) may restrict its widespread use in overlay construction projects in Oregon.

 The major objective of this study is to develop a low cost test method to predict the after-construction bond performance from the tests conducted on the tack coat. In addition, the factors that influence the bond strength, such as existing surface condition, residual application rates, tack coat type, moisture, and temperature, will also be investigated to recommend revisions to current methods and practices. Using lab measurements, regression equations will be developed for different tack coat types to predict tack coat set times that can be used during construction to minimize tracking.  
HMAC Layer Adhesion Through Tack Coat Work Plan


FY 15
FY 16


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