Optimization of Tack Coat for HMA Placement (2012) / Chapter Skim
Currently Skimming:
Appendix F - Tack Coat Training Manual
Appendix F - Tack Coat Training Manual
Pages 106-134
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 106... ...
F-1 A p p e n d i x F Tack Coat Training Manual
|
From page 107... ...
F-3 F-5 The Purpose of a Tack Coat F-5 Types of Tack Coat Materials Performance Graded Asphalt Tack Coat Materials, F-5 Asphalt Emulsion Tack Coat Materials, F-5 Cutback Asphalt Tack Coat Materials, F-7 F-7 Conditions of the Existing Pavement Surface Dust and Dirt, F-7 New Pavement Surface, F-8 Old, Aged Asphalt Concrete Pavement Surface, F-8 Texture of the Pavement Surface, F-8 Milled Asphalt Concrete Surface, F-9 Bleeding Surface, F-9 Portland Cement Concrete Surface, F-10 F-10 Pavement Conditions and Residual Tack Coat Rate Dusty or Dirty Pavement Surface, F-10 New Asphalt Pavement Surface, F-10 Old, Aged Pavement Surface, F-10 Surface Texture, F-10 Open-Graded Asphalt Pavement Surfaces, F-11 Milled Asphalt Pavement Surface, F-11 Bleeding Surface, F-11 Portland Cement Concrete Pavement Surface, F-11 F-11 Application Rate Versus Residual Asphalt Binder F-13 Asphalt Distributors Parts of an Asphalt Distributor, F-13 Asphalt Tank, F-13 Tack Coat Material Temperatures, F-13 Cleaning the Distributor Tank, F-13 Distributor Pump, F-13 Spray Bar Nozzle Angle, F-14 Spray Bar Height, F-16 Spray Bar Nozzle Size, F-16 Distributor Truck Inspection, Calibration, and Certification, F-18 Blocked Nozzles, F-18 Hand Wand Application, F-18 Summary, F-19 F-20 Tack Coat Break Time and Set Time Type of Tack Coat Material, F-20 Factors Affecting the Break and Set Times, F-21 C o n t e n t s
|
From page 108... ...
F-4 F-22 Construction Problems Uniformity of Tack Coat Application, F-22 Pick Up of Tack Coat Material on Truck Tires, F-24 Paving Over an Unbroken Emulsion, F-26 Spray Pavers, F-26 F-26 Types of Tack Coat Failures Inadequate Bond, F-27 Delamination of the Pavement Layers, F-27 Sliding Failures, F-28 F-28 Measuring Tack Coat Material F-28 Characterization of the Interface Shear Strength F-29 Summary F-30 Closure F-30 References
|
From page 109... ...
Thus, if a PG asphalt is employed as the tack coat material, all of the material that is applied to the existing pavement surface is useful in achieving the bond between the old and new layers. For PG type asphalt, therefore, the residual asphalt binder rate and the application rate are the same.
|
From page 110... ...
Thus, if the residual amount of asphalt binder on a particular pavement surface is required to be 0.06 gallons per square yard, the application rate of the diluted asphalt emulsion would need to be 0.18 g/sy. For a 1:1 diluted emulsion, the application rate is 3.0 times greater than the residual rate of the emulsion, or 0.06 g/sy times 3.0 = 0.18 g/sy.
|
From page 111... ...
Calculation of the Application Rate for Cutback Asphalt Similar to the calculations for asphalt emulsion, to determine the application rate for cutback asphalt, the starting point is the required residual tack coat amount. Calculations must work backward from the residual amount of tack coat to arrive at the application rate for the same tack coat material.
|
From page 112... ...
In most cases, the residual rate should be approximately one-half the amount applied to an old, oxidized pavement surface. Old, Aged Asphalt Concrete Pavement Surface If the asphalt concrete pavement surface contains an extensive number of cracks, a portion of the tack coat material may flow into the cracks and not be available to create the bond between the pavement layers.
|
From page 113... ...
Bleeding Surface Care must be taken when a tack coat is applied to an existing pavement surface that is flushed or bleeding. In this situation, the tack coat application rate must be reduced in order to take into account the amount of asphalt material already Figure 2.
|
From page 114... ...
For a new, clean asphalt concrete pavement layer placed one day, and a second layer to be placed within a day or two, the residual tack coat rate on the pavement surface should be in the range of 0.03 to 0.04 g/sy. Old, Aged Pavement Surface An old, aged, oxidized asphalt pavement surface will normally absorb a significant amount of the applied tack coat material.
|
From page 115... ...
In most cases, the amount of bleeding is much greater in the wheel paths of the roadway as compared to the pavement areas between the wheel paths or outside the wheel paths. This significant difference in the condition of the pavement surface at different locations makes it extremely difficult to determine the amount of residual tack coat material that is needed to provide the proper bond between the new overlay and the existing bleeding pavement surface across the width and down the length of the roadway.
|
From page 116... ...
Condition of the Existing Pavement Surface Applied PG Asphalt Binder Rates New Asphalt 0.03 to 0.04 g/sy Old, Aged Asphalt 0.04 to 0.06 g/sy Milled Asphalt Mixture 0.03 to 0.05 g/sy Portland Cement Concrete 0.04 to 0.06 g/sy APPLICATION RATES USING UNDILUTED ASPHALT EMULSIONS Condition of the Existing Pavement Surface Applied Undiluted Asphalt Emulsion Rates New Asphalt 0.04 to 0.06 g/sy Old, Aged Asphalt 0.06 to 0.09 g/sy Milled Asphalt 0.04 to 0.07 g/sy Portland Cement Concrete 0.06 to 0.09 g/sy APPLICATION RATES USING 1:1 DILUTED ASPHALT EMULSIONS Condition of the Existing Pavement Surface Applied Diluted Asphalt Emulsion Rates New Asphalt 0.09 to 0.12 g/sy Old, Aged Asphalt 0.12 to 0.18 g/sy Milled Asphalt 0.09 to 0.50 g/sy Portland Cement Concrete 0.12 to 0.18 g/sy APPLICATION RATES USING RC-70 CUTBACK ASPHALT Condition of the Existing Pavement Surface Applied Cutback Asphalt Rates New Asphalt 0.05 to 0.07 g/sy Old, Aged Asphalt 0.07 to 0.10 g/sy Milled Asphalt 0.05 to 0.09 g/sy Portland Cement Concrete 0.07 to 0.10 g/sy Table 2. Typical application rates using PG asphalt.
|
From page 117... ...
If the tack coat material is too cold when it is sprayed onto the existing pavement surface, the material will come out in strings instead of a uniform spray. The distributor is equipped with a thermometer that displays the temperature of the tack coat materials in the tank.
|
From page 118... ...
When the speed of the distributor changes, a consistent application rate is maintained by the computer, which automatically changes the pump pressure to compensate for the change in travel speed. Tack coat material is circulated from the tank on the distributor to the spray bar.
|
From page 119... ...
This will result in a very non-uniform application of the tack coat material onto the pavement surface. Interference of the spray pattern from nozzle to nozzle will mean that some portions of the existing pavement surface will receive excessive tack coat material while adjacent portions will receive insufficient material.
|
From page 120... ...
In this case, less than 15 percent of the existing pavement surface will be covered with the tack coat material. Obviously, sufficient and uniform bond with the new overlay will not be achieved.
|
From page 121... ...
If a 1 to 1 diluted emulsion tack coat material is used, however, for the same residual rate, either the V slot tack nozzle or the S36-4 V slot nozzle could be used for the resulting application rate of 0.12 gallons per square yard. If PG asphalt were to be used as tack coat material, for a residual tack coat rate of 0.04 gallons per square yard, the application rate would be exactly the same as the residual rate (0.04 gallons per square yard)
|
From page 122... ...
Regardless of the manufacturer of the distributor, a different nozzle size would be required for the two different application rates used in this example. This same comment is applicable if the asphalt distributor was previously used to apply a prime coat material, either cutback asphalt or asphalt emulsion.
|
From page 123... ...
Summary In order for a tack coat to provide the necessary bond between the existing pavement surface and the new asphalt concrete overlay, it is extremely important that the following factors be considered: 1. Tack coat material must be maintained at the proper temperature in the distributor tank for the type of material being applied.
|
From page 124... ...
15. Tack coat material should uniformly cover 100 percent of the existing pavement surface.
|
From page 125... ...
Among the factors are: • ambient air temperature, • relative humidity, • wind speed, • temperature of the pavement surface on which the tack coat material is placed, • temperature of the tack coat material when sprayed, • application rate of the tack coat material, • dilution rate of an asphalt emulsion, and • type of emulsifying agent used in an emulsion. Asphalt Emulsion Tack Coat Material One primary factor that affects the break and set times of emulsions is the application rate.
|
From page 126... ...
the need to pave over an emulsion tack coat before it is broken and/or set. Uniformity of Tack Coat Application It is extremely important that the tack coat material be uniformly applied to the pavement surface, both in a longitudinal direction and in a transverse direction.
|
From page 127... ...
No tack coat is being applied to the pavement surface at those locations. In this case, the distributor needs to be stopped, the blocked nozzles removed and cleaned, the nozzles replaced onto the spray bar, and, only then, the application of the tack coat continued.
|
From page 128... ...
Figure 20 shows a spray pattern where some of the nozzles are not functioning, some are set at improper angles, and/or some are just dribbling tack coat material onto the pavement surface. The correct solution is to remove the distributor from the project until the spray bar nozzle problems are corrected.
|
From page 129... ...
If trafficked before it is set, pick up of the cutback asphalt tack coat by the haul truck tires will occur. Thus, to avoid pick up of the tack coat material, it is necessary for a tack coat to completely set so that it is not sticky and will not adhere to the tires of the construction vehicles.
|
From page 130... ...
Asphalt emulsion tack coat is applied to the existing pavement surface typically less than two feet in front of the placement of the mix (Figure 24)
|
From page 131... ...
With time and traffic, this deflection results in fatigue cracking of the pavement layers, from the bottom to the top. In most cases, the cracking appears on the asphalt concrete pavement surface in the form of fatigue or "alligator" cracking.
|
From page 132... ...
This temperature will be used in temperature-volume corrections for spray application and payment. The linear distance of pavement that can be covered by a tack coat material in a distributor truck can be determined as followed: L T WR = 9 Where: L = Linear distance of spray, feet T = Quantity of tack coat in distributor, gallons W = Sprayed width of pavement, feet R = Application rate, gallons per square yard L T WR = Where: L = Linear distance of spray, meters T = Quantity of tack coat in distributor, liters W = Sprayed width of pavement, meters R = Application rate, liters per square meter Characterization of the Interface Shear Strength Tack coat materials are applied onto a pavement surface before overlay construction to ensure adequate interface bond strength between the two layers.
|
From page 133... ...
It is very important to realize that there can be a significant difference in the amount of tack coat applied to a pavement surface and the residual amount of asphalt binder that remains after the tack coat material has set. For asphalt emulsion tack coats, in particular, whether the emulsion is diluted with additional water or not makes a major difference in the quantity of residual binder remaining on the existing pavement surface after the water has evaporated.
|
From page 134... ...
Closure It basically costs nothing extra to properly apply a tack coat to a pavement surface in a uniform manner. Attention by the contractor to a few basic issues, such as cleanliness of the existing pavement surface, proper temperature of the tack coat material before application, condition and position of the nozzles on the spray bar, correct application rate related to the specified residual rate for the tack coat, and pick up of the tack coat by the construction vehicles, will result in an asphalt concrete pavement structure that performs as expected under traffic.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.