What Is Tack Coat In Road Construction?
What Is Tack Coat In Road Construction?
A tack coat is an adhesive material applied between layers of asphalt concrete during road construction.
It helps to prevent the degradation of the road by keeping the asphalt concrete layers together. Tack coats are typically made from cutback asphalt or emulsified asphalt (diluted).
They should be applied when the pavement surface is dry and clean, and traffic should not be allowed on tack coats until they have dried and become “tacky”.
The purpose of a tack coat is to form a bond between the asphalt base course (ABC) and the asphalt wearing course (AWC), or between a concrete deck slab of bridges and AWC laid over it.
How Is Tack Coat Applied?
Applying tack coat (road construction) correctly is essential for ensuring a longer-lasting roadway.
The tack coat material should be applied at the correct temperature and rate for the type of asphalt binder used.
Generally, the application rate should be 0.04 gallons per square yard. The amount of overlap from the spray bar to the road surface should also be considered, with double or triple laps recommended.
The tack coat material should be applied uniformly and without dilution, using nozzles of an appropriate size on the distributor spray bar.
If the existing pavement surface is dusty, additional measures may need to be taken to ensure adequate bonding between pavement layers and prevent sliding of new asphalt.
It is important to conduct a trial tack coat before starting application in order to check that the asphalt material is at the correct spraying temperature and that it meets other requirements such as residual amount and volume (gallons/square yard).
Following these steps will help ensure that a high quality tack coat is applied for optimal performance.
What Is Difference Between Prime Coat And Tack Coat?
The difference between a prime coat and a tack coat is that a prime coat is applied to a prepared base before additional layers of support or coating, while a tack coat is applied after the prime coat to form an adhesive bond between the tack coat and the next layer of coating.
A prime coat protects the integrity of the granular base during construction and helps reduce dust, while a tack coat prevents slippage and may sometimes function as a more long-term sealer to protect the substrate from moisture and bacteria.
Prime coats are used to attach asphalt to base course, while tack coats are used when attaching asphalt to asphalt or concrete.
Both types of coating offer benefits such as asphalt cracking prevention, reduced dust during construction, and stronger material bonding.
What Is The Difference Between Seal Coat And Tack Coat?
A prime coat is a thin layer of low viscosity liquid bituminous material applied to a prepared base before additional layers of support or coating.
It serves the purpose of coating and bonding loose material on the surface of the base course, blocking capillary action in the base course, and making the base course behave like an asphalt base course.
A tack coat is an application of bituminous materials over an existing impervious pavement surface.
It is applied by a mechanical sprayer and serves as a bonding coat between W.M.M or Asphalt layers.
The purpose of a tack coat is to prevent slippage and create an adhesive bond between the tack coat and the next layer of coating.
A seal coat is a thin surface treatment usually applied over an existing/worn out blacktopped surface.
Its main functions are to give a new life by patching the existing dry and weathered bituminous surface, provide waterproofing layers, and increase the lifespan of pavement.
When Should Tack Coat Be Applied?
Tack coat should be applied to a clean and dry pavement surface. It is important to select an appropriate tack coat material and calculate the correct application rate for optimal bonding.
Generally, a tack coat should be allowed enough time to break and set (emulsion) or cure (cutback) before applying the next layer of HMA. The temperature of the asphalt material should also be checked before application.
Tack coat should not be applied to a bleeding surface or an area that cannot be covered in the same day’s paving.
Additionally, it should not be applied to dusty surfaces as this may prevent adequate bonding between pavement layers or cause sliding of the new layer.
The Asphalt Institute offers general recommendations for tack coat application rates on different surfaces, however, it is important to follow any specifications outlined in Section 39 -1.09C, “Tack Coat” of the Standard Specifications when estimating tack coat quantity.
