Optimization of Tack Coat for HMA Placement (2012) / Chapter Skim
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Pages 7-18
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From page 7... ...
. Generally, hot paving asphalt cement, cutback asphalt, and emulsified asphalt have all been used as tack coat materials, but cutback asphalts (asphalts dissolved in solvents such as kerosene or diesel)
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From page 8... ...
Excessive tack coats may promote shear slippage at the interface. Most importantly, it is the residual amount of asphalt cement, not the application rate of diluted asphalt emulsion, that should be specified.
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From page 9... ...
Generally, the best tack coat application results from a "double lap" or "triple lap" coverage. As shown in Figure 2, good "double/triple lap" means that the nozzle spray patterns overlap one another such that every portion of the pavement surface receives spray from two or three nozzles.
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From page 10... ...
• Pressure within the distributor must be capable of forcing the tack coat material out of the spray nozzles at a constant rate. Inconsistent pressure will result in non-uniform application rates.
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From page 11... ...
One method is to apply the tack coat to the pavement surface underneath the paver just ahead of the screed. This can be done by using a special paver fitted with a tack coat spray bar, as shown in Figure 1(b)
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From page 12... ...
(23) evaluated the effect of tack coat material types and application rates on bond strength using a direct shear device on the Superpave Shear Tester (SST)
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From page 13... ...
Tack coat was sprayed on milled or unmilled pavement surface before the HMA over lay was placed and compacted; three to five cores were obtained from each field section, and then bond strength was measured using NCAT Bond Strength Test. For projects using an emulsified asphalt tack coat material, the residual application rates were 0.03, 0.045, and 0.06 gal/yd2.
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From page 14... ...
2.6 Worldwide Survey A worldwide survey on tack coat practices was conducted to better understand the current state of tack coat practices and to design a corresponding research experiment. The primary objective of the survey was to investigate the current tack coat state of practice related to types of materials used for tack coats, dilution rates of tack coat materials, residual application rates, determination of rate for different types of surfaces, methods used for tack coat distribution, and pavement failures related to tack coat application.
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From page 15... ...
Corresponding maximum displacement Lab No normal load is applied 2. LTRC Direct Shear Test Shear strength of the tack coat interlayer is measured to evaluate the bonding property of tack coat.
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From page 16... ...
Nominal average shear stress and maximum shear stiffness are measured to determine the in-layer and interlayer shear properties of asphalt concrete layers. The inlayer shear properties are used to evaluate the quality of the mixture and the interlayer shear properties are used to evaluate the tack coat properties.
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From page 17... ...
2.95 - in x 2.95 - in - square composite speci men Bond shear strength Lab or in situ Marketed by R/H Specia lty and Machine, Terre Haute, Indiana 14. Traction Test Tensile strength of the tack coat interlayer is measured to evaluate the bonding property of tack coat.
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From page 18... ...
Core sample of 3.94-in or 5.9-in diameter Bond strength In situ Developed by Highway Agency, United Kingdom 20. In situ Shear Stiffness Test The shear strength is measured to evaluate the shear properties of asphalt concrete pavements in the field.
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