The application of a tack coat is an integral part of any Hot Mix Asphalt (HMA) operation, whether the HMA is placed over compacted gravel bases, existing HMA surfaces, or over Portland Cement Concrete (PCC).

A tack coat is a very light spray application of an asphalt emulsion to create a bond between asphalt overlay and the existing surface.  Tack coat applications ensure a proper bond and enhance the shear strength between asphalt layers, as well as aiding in overall HMA compaction. Adjacent vertical surfaces, such as HMA cold joints and where HMA meets PCC, should also be tacked to help mitigate cracking and de-bonding.

Conventional Tack

The most common tack coats used are asphalt emulsions, such as: SS-1, SS-1H, CSS-1, CSS-1H and RS-1.  Certain emulsions are capable of being diluted to suit specific field applications and equipment requirements.  Application rates depend on several factors, including existing pavement conditions, surface type, temperature, and dilution rates.

Trackless Tack

Trackless tack coats serve the same functions as regular tack coat application, only it has an added benefit of a non-tacky residual binder being left on the surface.  This added benefit prevents tracking by construction vehicles and the general public, keeping a sufficient amount of tack on the base and allowing for proper bonding and shear strength to be achieved with an overlay.  This is an excellent choice for busy urban areas to eliminate unsightly tracking of tack coat.

Features and Benefits

• Prevents de-bonding of the HMA layers.

• Prevents mat-slippage and reduces top-down cracking.

• Enables super-imposed lifts to act as a monolithic layer, thus, increasing the overall
  structural capacity of the roadway.

  1. Aids in increasing mat-density during rolling operations, due to decreased slippage/forward  

   movement of the HMA being rolled.

• Increased pavement life and decreased life cycle costing.

• Small cost versus benefits.

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Tack Coat


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