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A tack coat is a light application of asphalt cement or asphalt emulsion used to ensure a good bond between a) an existing pavement surface and a new hot mix asphalt (HMA) overlay or b) between the layers of each lift of HMA in multi-lift overlays or full-depth asphalt pavements. Adequate bonding between construction lifts, and especially between the existing roadway surface (bare or milled) and an overlay, is critical so that the completed pavement structure behaves as a single unit and provides adequate strength. Inadequate bonding between layers can result in delamination (debonding), followed by premature failures and a reduction in pavement life.
Various factors may affect the bonding condition at the interface. These include HMA material, tack coat material, tack coat application rate, pavement surface texture and cleanliness, temperature, and moisture conditions. Several agencies have conducted research in this area to improve construction practices and ensure good performance of their HMA pavements. Trackless tack coat materials and spray pavers (where available) are now being used more frequently.
The purpose of this tech transfer project is to compile a synthesis of best practices being used by NRRA members in the area of tack coats and to identify any gaps in the research that can be filled during the next round of construction activities at MnROAD.
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Summarize each state’s current activities with regard to tack coats and develop a list of potential research ideas that can be investigated at MnROAD during future test section construction.
Note any other supporting contracts
Principal Investigator: Eddie Johnson, MnDOT
Project Technical Advisory Committee (TAP) – Email the TAP
Randy West (NCAT)
Eshan Dave (UNH)
Zhanping You (MTU)
Ed Johnson (MN)
Brandon Bever (MAPA)
Jim Trepanier (IL)
State of Practice "Tack Coats" - draft January 2017 (PDF)