There are many guidelines regarding proper tack coat placement and overall usage, such as where and when should tack coat be applied, and does your project require tack coat in the first place?
Tack Coat Guidelines & Considerations
What Is Tack Coat?
Tack coat is applied to an existing surface just before a layer of asphalt or concrete pavement is placed as an overlay. The tack coat operates as a binder, securing layers together into one solid, uniform road.
Where Should Tack Coat Be Applied?
Tack coat is applied to planed surfaces, between the layers of hot mix asphalt, and to vertical surfaces that meet up with gutters, construction joints, dig-outs, milled pavements, and curbs.
Where NOT To Apply Tack Coat
Tack coat should not be used if it will not be covered in the same day. Also, it should not be applied to a bleeding surface.
If dealing with bituminous seals, you do not need tack coat prior to applying a chip seal.
Unless working with a badly aged, raveled or dry pavement surface, tack coat is generally not necessary prior to applying a slurry seal or micro-surfacing application.
Tack Coat Placement
Tack coat must be properly placed in order to do its job right. The cleanliness of the surface is of utmost important. If the surface is dirty or dusty it will prohibit the tack coat from properly bonding, and could cause a slippage plane.
Even if roads are cleaned the night before, a layer of dirt and debris can build up overnight. It’s important to bring a road sweeper in immediately before applying tack coat.
Depending on the type of traffic roadways receive there are other things besides dust and debris that may need to be cleaned off using a power washer. If water is necessary to clean roadways, we are prepared to adhere water pollution control best management practices.
Before ever applying any tack coat, the required test report and certificate of compliance for every truckload of emulsion or asphalt binder must be checked. Test results should be compared with project specifications to ensure everything is on track. If everything complies, work may begin right away before sampling and testing.
Initial load slips should be checked regarding every last load of emulsion or asphalt binder. When dealing with diluted emulsions, the weight or meter readings must be noted in order to check emulsion dilution ratio and pay quantity. When relying on partial loads, weigh-back slips are collected.
Uniform application is fundamental to a job well done. Application rates vary based upon the speed of the truck and pump rates.
Spray Bar Placement
An incorrect spray bar height will impact the quality of work. The spray bar must be placed high enough over the roadway to provide surfaces with double coverage or triple coverage if necessary. The proper spray bar nozzle placement rests at an angle between 15° and 30°.
You can identify an improperly placed spray bar if you notice streaking or puddling. This may also indicate incorrect spread rates. Coverage should appear solid and uniform, as opposed to streaky, clumpy and noticeably messy.
Speaking of spread rates, the actual spread rate should be identified with the truck driver by testing it out first. The truck should apply a layer of tack coat to a small area, which can then be measured to identify how much tack coat was distributed. This can then be multiplied out to determine if you are on track to cover the surface area with the amount of tack coat specified in plans.
Additional Tack Coat Considerations
-When applying tack coat to vertical surfaces ensure that the rate of application sufficiently covers the vertical face without producing run off.
-Apply additional tack coat to damaged areas or where any loose material has been removed right before applying hot mix asphalt.
-No traffic should drive over tack coat. For one, you don’t want tack coat to spread to pavement surfaces located beyond project lines. Make sure roads are completely closed down prior to starting construction. If cars do accidently drive over tack coat, reapply tack coat to the impacted areas before moving forward with paving. If tack coat is spread outside of the project lines, contractors should clean it up immediately.
-Asphalt binder tack coat must be between 285° F and 350° in order for proper application.
-The engineer should authorize any changes to specified tack coat residual rates before moving forward.
Our award-winning experience helps us to complete perfect projects every single time. From applying tack coat to pouring asphalt and fixing cracks in concrete, we do it right the first time around, saving your business time, money and stress.