Tack coat is a light application of asphaltic emulsion or asphalt binder applied to existing pavement surfaces, as well as in between the layers of hot mix asphalt. There are certain equations used to determine exact tack coat quantity necessary for a project.
Why Do You Need Tack Coat?
Tack coat is responsible for providing a solid bond between the existing pavement surface and any additional asphalt overlay. It also bonds the layers between each hot mix asphalt, and vertical surfaces that new hot mix asphalt is placed beside, such as curbs and construction joints.
Roadways covered in spalled pavement, where older layers of asphalt concrete show through newer layers, make for a bumpy road. As a result, drivers experience a jarring experience that can also increase vehicle-operating expenses.
Both weather and traffic play a role in the wear and tear roadways receive, but a lack of tack coat can as well. This is because tack coat plays an important role in regards to holding together the overlay with the underlying, worn pavement.
That doesn’t mean tack coat is always necessary. Consulting with an experienced contractor will help you to determine if asphalt requires tack coat or not.
Tack coat may be necessary before applying a slurry seal or micro-surfacing application if pavement is dry and raveled, or if you are dealing with concrete pavement.
Factors That Determine How Much Tack Coat Is Needed
There are different grades of tack coat, and depending on the surface area you are treating the right type will vary. Once the type tack coat is identified you’ll need to know how much tack coat is necessary in order to get the job done right.
The engineer’s estimate will include the precise tack coat quantity after the designer identifies 3 key things. First, the number of layers between planned thickness of hot mix asphalt. Secondly, the tack coat application rate. And thirdly, the area that will be paved indicated on final plans.
When working on brand new construction, tack coat is not necessary if placing hot mix asphalt over an aggregate base. In which case, reduce layers by one in order to determine exact tack coat requirements.
The total width represented on plans determines the number of tack coat layers.
0.25 foot or less = 1 layer of tack coat
0.26-0.50 foot = 2 layers of tack coat
0.51-0.75 foot = 3 layers of tack coat
0.76-1.00 foot = 4 layers of tack coat
The surface you apply tack coat to also plays a role in the number of necessary layers. If you are dealing with a dense surface, less tack coat is required. On the other hand, open textured, raveled or milled surfaces tend to require more layers of tack coat. A flushed surface will need less tack coat than a dry or older surface.
Other factors to consider include the type of tack coat material and the hot mix asphalt placed as an overlay. Emulsions include water, which influences the need for more tack coat applications in order to reduce residual rates. Emulsion application rate plays an important role in determining the necessary quantity of tack coat.
A conservative estimate will take the highest minimum application for asphaltic emulsions into consideration.
In regards to tack coat for estimating HMA Type A, Type B and RHMA-G:
New HMA placed between layers: a minimum application rate of 0.05 gallons per square yard.
Pre-existing HMA and PCC pavement: a minimum application rate of 0.07 gallons per square yard.
Planed pavement: a minimum of 0.11 gallons per square yard.
In regards to tack coat for estimating OGFC:
New HMA: a minimum application rate of 0.07 gallons per square yard.
Existing HMA and PCC pavement: a minimum application rate of 0.11 gallons per square yard.
Planned pavement: a minimum application rate of 0.12 gallons per square yard.
Designer Process For Calculating Tack Coat Quantity
1. Determine total thickness of hot mix asphalt with the comparable layers of tack coat needed for that density.
2. Identify the tack coat minimum necessary based upon hot mix asphalt or OGFC and any underlying materials.
3. Emulsion quantity can then be calculated by multiplying the number of layers needed per thickness by the application rate defined by step 2, multiply this by the estimated square yards of the area that will be paved.
4. The engineer can then estimate the amount of tack coat in tons using a special conversion process.
5. The engineer will estimate asphalt binders used as tack coat by calculating 0.25 gallons of asphalt binder per square yard of interlayer when regarding geosynthetic pavement interlayer.
It’s not an easy process, and it includes a number of skilled professionals to find the exact tack coat quantity necessary to complete the job just right. Leave it to Kleenco Construction to deal with the logistics, all while providing the highest quality commercial concrete and asphalt repairs and installations.