Asphalt For Tack Coat

James Lee
• Tuesday, 11 May, 2021
• 7 min read

The usual pavement distresses associated with poor or no tack coat is slippage cracks (typically at locations where traffic is braking or accelerating) along with deamination of the surface lift. In fact, researchers have indicated that even with a small loss in bond strength (10-30%), fatigue life can be reduced significantly (50-70%).

tack asphalt coater sre spraying emulsion equipment wand system bar fixed
(Source: www.srequip.co.nz)


A significant amount of information has been compiled here on tack coats including the newest publication: CHIP Synthesis 516. Was disappointed all buckets (20) were shy approximately five inches from the top from being full, that's a lot of product you're missing out on.

Just clean the rubble of the old asphalt, then paint this on the surface. It both binds the surface of the old asphalt and creates a sticky layer for adding new asphalt.

We even poured it in the cracks in areas were the old asphalt was mapping. We then let it fully dry, and It adhered the small mapped pieces of the old asphalt together, before we added filler to the cracks.

I really love this stuff, and we could not find it anywhere but the Home Depot. Works better if you will heat it after application in pothole and then add your filler material.

This is good for putting asphalt patch in a depression... This tack coat applies well and goes far with a rubber squeegee, assuming that the blacktop is overall relatively smooth.

construction pavement flexible highway coat tack prime course binder base wearing surface seal layer protection recommended frost subbase subgrade
(Source: www.slideshare.net)

It dries shiny and tacky and fills the alligator cracks so that the sand mix repair will adhere well. I pretreated all cracked areas with this before applying sealer.

Centerlines: We have all seen areas of spelled pavement, with older layers of asphalt concrete showing through. They may not all be as bad as the example below, but they certainly make it rough going for drivers, driving up vehicle operating expenses.

Weather and traffic play a role, but the root cause is the lack of a tack coat prior to construction of the overlay. A tack coat is used to help the overlay adhere to the underlying, weathered pavement surface.

Over time, sunlight hardens the surface films and makes the asphalt less sticky. In one or two years the asphalt film is worn off the surface, leaving the aggregate exposed.

A tack coat is sprayed on the surface of an existing asphalt or concrete pavement by a distributor truck immediately prior to placing an overlay. Until a few years ago the most commonly used material for tack coats was MS-30 or MS-70 cutback asphalt.

tack coat prime gemseal asphalt gal primer pallet coats
(Source: nacsupply.com)

Today, in many areas the environmental agencies no longer allow cutbacks to be used due to a concern about the hydrocarbons they contain, such as kerosene, which evaporate into the atmosphere. Some companies have developed proprietary compounds, based on resins or less volatile hydrocarbons.

Today most state DOT Standard Specifications have requirements for tack coat materials, their method of application, and payment. In Section 702 of the 2008 NOT Standard Specifications, subsection 6, Table 702-9 lists the approved grades of anionic and cationic asphalt emulsions for use in tack coats.

The anionic grades are slightly preferred where limestone and dolomite aggregates are exposed on the old road surface. Recommended application rates and construction details are described in Section 407 of the 2008 NOT Standard Specifications.

This photo shows a four-inch diameter core hole in an older asphalt concrete surface. However, as the layer thickness goes up, the percentage of the job cost that goes into the tack coat becomes inconsequential, so I tend to agree with the “all circumstances” point of view.

The photo above shows a state highway where two one-inch MAC overlays were placed about 10 years apart. A few months after the more recent construction, surface raveling began to appear in the outer wheel path.

coat emulsion bitumen bond road construction tack asphalt anionic coats application emulsified steps paving laying drives practice research base pavement
(Source: www.forconstructionpros.com)

Wetness during late spring accelerated the stripping, and both overlays were completely removed in a matter of days. An isolated problem, as in the last picture, is easy to repair using proper techniques for a permanent pothole patch.

A cursory repair may solve the problem for a short period of time, but it will eventually come right back and continue to spread. Careful examination of the photo shows that perhaps as many as three skin patches have been applied, and all of them are raveling.

A permanent repair will require a structural overlay or removal and replacement of all the asphalt below the depth of the raveling. Had it been used during the original overlay construction, the raveling could have been prevented, and the cost of the more extensive repair might have been avoided entirely.

Generally speaking, you don’t save money in the long run when you skip that step. A tack coat is a thin bituminous liquid asphalt, emulsion or cutback layer applied between MA pavement lifts to promote bonding.

Adequate bonding between construction lifts and especially between the existing road surface and an overlay is critical in order for the completed pavement structure to behave as a single unit and provide adequate strength. Inadequate bonding between layers can result in deamination (deboning) followed by longitudinal wheel path cracking, fatigue cracking, potholes, and other distresses such as rutting that greatly reduce pavement life (Dot, 2001 ).

tack coat
(Source: www.youtube.com)

In order for this uniformity to be consistently achieved, all aspects of the application must be considered and carefully controlled. The pavement surface receiving the tack coat should be clean and dry to promote maximum bonding.

Emulsified tack coat materials may be applied to cool and/or damp pavement, however, the length of time needed for the set to occur may increase (Flexible Pavements of Ohio, 2001 ). Since existing and milled pavements can be quite dirty and dusty, their surfaces should be cleaned off by sweeping or washing before any tack coat is placed, otherwise the tack coat material may bond to the dirt and dust rather than the adjacent pavement layers.

Construction vehicles and equipment pick up the tack -dirt mixture on their tires and leave the existing roadway with little or not tack coat in the wheel paths (Figure 4). Slippage cracking and deamination are distresses typically seen when cleanliness is lacking (Flexible Pavements of Ohio, 2001 ).

Tack coat application should result in a thin, uniform coating of tack coat material covering approximately 90 percent of the pavement surface (Flexible Pavements of Ohio, 2001 ). To achieve this result, application rate will vary based on the condition of the pavement receiving the tack coat.

Too much tack coat can create a lubricated slippage plane between layers, or can cause the tack coat material to be drawn into an overlay, negatively affecting mix properties and even creating a potential for bleeding in thin overlays (Flexible Pavements of Ohio, 2001 ). Table 1 shows recommended application rates from Flexible Pavements of Ohio (2001 ).

tack coat asphalt perekat
(Source: www.youtube.com)

The surface area increase is dependent on the type, number, condition and spacing of cutting drum teeth but is typically in the range of 20 to 30 percent, which requires a corresponding increase in tack coat (20 to 30 percent more) when compared to an unfilled surface (TRY, 2000 ). Several vehicle-related adjustments and settings are critical to achieving uniform tack coat placement.

Essentially the nozzle patterns, spray bar height and distribution pressure must work together to produce uniform tack coat application. Differing coverages will result in streaks and gaps in the tack coat.

As tack coat is applied, the vehicle will become lighter causing the spray bar to rise. Pressure within the distributor must be capable of forcing the tack coat material out the spray nozzles at a constant rate.

Sometimes emulsified asphalt tack coats are diluted with water to increase the total volume of liquid while maintaining the same volume of asphalt binder within the emulsion. This can help achieve a more uniform application without applying excessive amounts of asphalt binder.

Other methods such as adjusting nozzle opening size or tack coat application pressure should be investigated before attempting dilution. Dilute only by adding water to the emulsion and not vice versa, which could cause the tack to break.

tack coat hicks ergon tom presentation asphalt
(Source: www.slideshare.net)

Although not critical for to the uniform application of tack coat or its subsequent bonding ability, there are several other noteworthy aspects to tack coats. Generally, a tack coat should be allowed enough time to break and set (emulsion) or cure (cutback) before applying the next layer of MA.

Tracking deposits tack coat material on adjacent pavement surfaces. In extreme cases, tracking may deposit enough tack coat material to distort pavement surfaces or hinder a driver’s ability to navigate (Flexible Pavements of Ohio, 2001 ).

Rubberized tack coats have an especially high propensity to stick to vehicle tires. Allowing tack coats to set (emulsions) or cure (cutbacks) before driving on them can substantially reduce tracking.

When a tacked road surface is exposed to traffic, the potential exists for reduced skid resistance, especially during wet weather (Flexible Pavements of Ohio, 2001 ). When tack coat surfaces must be opened to traffic, they should be covered with sand to provide friction and prevent pick-up.

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