Tack Coat

Definition - What does Tack Coat mean?

Tack coat is a thin layer of asphalt that ensures the bonding between old and new asphalt layers. It is also used in construction or for renovation of roads to achieve better strength.

Tack coat is sticky, which is very important for forming a secure bond between the two layers of asphalt. The lack of tack coat may result in slippage and can cause concentrated stresses leading to total pavement failure.

Tack coat is also known as bitumen.

Corrosionpedia explains Tack Coat

The best materials for tack coat are emulsions because they can be diluted. Emulsions are applied using a spray coater system tack. Before the emulsion is applied, it must be diluted with water and it must pass a compatibility test. The following steps must be followed:

  • A small quantity of emulsion is prepared.
  • The necessary quantity of water is added.
  • The emulsion must be mixed with a spatula.
  • The emulsion must be poured through a sieve pre-wetted 150µm.

If more than 1% remains in the sieve, it means that there is a compatibility problem.

Other important things to keep in mind when preparing the emulsion are:

  • Water must be added to the emulsion, and not vice versa.
  • The emulsion must be used on the same day on which it is prepared.
  • The water temperature must be 25-50°C for the viscosity to be reduced.

The surface on which the tack coat emulsion must be applied should be clean and free of all dirt and dust in order to achieve the best results. The proper amount of tack coat emulsion must be applied, because if too little is used, the bonding between the two layers of asphalt will be too weak, and if too much emulsion is used it will affect the quality of the hot mix asphalt. The application rate is very important. Thus, if the surface is absorbent, then more tack coat is needed. For stiffer materials, the tack coat layer should be thicker.

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