Optimization of Tack Coat for HMA Placement (2012) / Chapter Skim
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From page 35... ...
. 4.1.2 Types of Tack Coat Applied to Different Pavement Surfaces Most of the respondents indicated that their agencies monitor the application of tack coats and specify ranges for dilution rates as well as application rates.
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From page 36... ...
0 20 40 60 80 100 Asphalt Cement Cutback Asphalt Emulsion Tack Coat Material Type R es po nd en ts, % Figure 26. Asphalt cements and cutbacks used as tack coats.
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From page 37... ...
The range of residual rates for cutback asphalts was 0.03 to 0.05 gal/yd2. Only 27% of the respondents gave feedback for tack coat materials used on top of surface treatments or seal coats, as well as asphalt-treated base courses (see Figures 33 and 34, respectively)
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From page 38... ...
0 5 10 15 20 25 30 35 R S1 R S1h R S2 H FM S1 H FM S2h M S1 SS -1 SS -1 h CR S1 CR S2 CM S2 CS S1 CS S1h ST -1 P TS T1P ST E1 H FE -9 0 EA P PG 7 010 PG 6 416 PG 6 422 PG 5 822 PG 5 816 A C5 R C 30 R C 70 R C 25 0 M C70 M C25 0 M C80 0 R es po nd en ts, % Figure 32. Tack coat materials placed on milled HMA surfaces.
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From page 39... ...
0 5 10 15 20 25 30 R S1 R S2 M S1 SS -1 SS -1 h CR S1 CR S2 CM S2 CS S1 CS S1h TS T1P ST E1 H FE -9 0 EA P PG 7 010 PG 6 416 PG 6 422 PG 5 822 PG 5 816 R C 70 R C 25 0 M C70 M C25 0 % o f R es po nd en ts Figure 35. Tack coat materials used on PCC surfaces.
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From page 40... ...
Only 10% verify the dilution rate daily. Traffic on Tacked Surfaces The majority of respondents -- 78% -- stated that highway traffic is not allowed on tack coat materials prior to HMA placement.
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From page 41... ...
0 5 10 15 20 25 30 35 40 45 50 0 4 12 24 120 Hours R es po n de nt s, % Figure 41. Method for applying tack coat materials.
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From page 42... ...
Pickup of Tack Material by Truck Tires Of the respondents, 67% indicated that pickup of tack coat material is a continuing problem; 38% indicated that the tack material is required to be completely set before haul trucks are allowed on it. Few respondents, 13%, allow haul trucks to drive on the tack coat material before breaking (see Figure 42)
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From page 43... ...
Cannot apply tack coat materials in foggy conditions Application Rates and Residual Tack Coat Rate Verification Of the responses, 51% indicated that measuring the change in the amount of material in the distributor tank after applying a given section was the best way to check the application rates (see Figure 45)
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From page 44... ...
The results are illustrated in Figure 48. 4.1.4 Findings Related to Tack Coat Application Pavement Failures Related to Improper Tack Rate/Material The respondents reported slippage and delamination of the pavement surface layer as approximately equal to results from poor tack coat type or application, 89% and 87%, respectively.
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From page 45... ...
Quality of Tack Coat Materials Only 18% of the responses indicated they use a field or laboratory test to evaluate tack coat material quality. Some of the procedures listed for testing the quality of tack coat materials are residual percentage test; traction test; penetration test on the residual asphalt; AASHTO M 208, Cationic Emulsified Asphalt (39)
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From page 46... ...
Improved Sensitivity/Reliability of the Actuator Rate of Loading Loading rate of the actuator was examined. Several experiments were conducted to verify the rate of loading using two tack coat materials with contrasting bond strengths: CRS-1 and PG 64-22.
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From page 47... ...
Improved Adhesion of Test Plate to Tacked Surface Most of the laboratory research that was performed to evaluate tack coat quality using the ATacker test device was performed with the tack coat applied between two metal plates. During the LTCQT tack coat field evaluation tests, poor adhesion (i.e., not measurable)
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From page 48... ...
Based on the results of this evaluation, a test procedure was written in AASHTO format. Loading Rate Since the loading rate significantly affects the test results, it is essential to select an appropriate rate that can distinguish between the tensile strength of different tack coat materials.
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From page 49... ...
. The tack coat material was then applied with a paint brush at the prescribed residual application rate and application temperature (see Figure 53c)
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From page 50... ...
PG 64-22 Trackless SS-1h CRS-1 approximately 10°C ranging from 30° to 90°C on the aforementioned four tack coat materials at a residual application rate of 0.05 gal/yd2. Three replicates were tested for each tack coat material.
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From page 51... ...
Table 15 summarizes the measured TOPT and SMAX for the four tack coat materials evaluated. 4.3 Experiment II: Rheological Properties of Tack Coat Materials and Its Relationship to Bond Strength Four consistency tests were conducted on PG 64-22 binder and the residuals of SS-1h, CRS-1, and trackless emulsions (see Figure 55)
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From page 52... ...
4.3.2 Relationship Between LTCQT Test Results and Tack Coat Rheological Properties The LTCQT test was performed on four tack coat materials: trackless, CRS-1, SS-1h, and PG 64-22. Based on these Table 16.
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From page 53... ...
Figure 58 presents the ultimate tensile loads for the four tack coat materials. The ranking of tensile strength is in good agreement with those presented in Table 17; therefore, it may be concluded that conducting the tack coat pull-off test at the softening point can successfully and consistently evaluate the quality of tack coat application in the field.
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From page 54... ...
Tensile strength at softening point for four tack coat materials. Material Type Softening Point (°C)
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From page 55... ...
Effect of Emulsified Tack Coat Types and Residual Application Rates Tables 20 and 21 present the statistical analyses of the effects of application rates and tack coat types on ISS based on a two-tailed t-test at a 95% confidence level. As shown in these Figure 59.
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From page 56... ...
Confinement Pressure (psi) Tack Coat CRS-1 Trackless Residual Appl.
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From page 57... ...
As shown in this figure, the increase in residual tack coat application rate was associated with a decrease in air Tack Coat Statistical Test Condition Confinement P-value Results SS-1h Application Rates Clean-Dry Unconfined < 0.0001 Significant Application Rates Clean-Dry Confined < 0.0001 Significant Application Rates Dusty-Dry Unconfined < 0.0001 Significant Application Rates Dusty-Dry Confined < 0.0001 Significant Application Rates Clean-Wet Unconfined < 0.0001 Significant Application Rates Clean-Wet Confined < 0.0001 Significant Application Rates Dusty-Wet Unconfined < 0.0001 Significant Application Rates Dusty-Wet Confined < 0.0001 Significant CRS-1 Application Rates Clean-Dry Unconfined 0.0010 Significant Application Rates Clean-Dry Confined 0.0893 Not Significant Application Rates Dusty-Dry Unconfined < 0.0001 Significant Application Rates Dusty-Dry Confined < 0.0001 Significant Trackless Application Rates Clean-Dry Unconfined < 0.0001 Significant Application Rates Clean-Dry Confined < 0.0001 Significant Application Rates Dusty-Dry Unconfined < 0.0001 Significant Application Rates Dusty-Dry Confined < 0.0001 Significant Table 20. Statistical analysis of the effects of application rates on ISS.
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From page 58... ...
mixture shear strength at 25°C, which was estimated at 105 psi. The worst tack coat performer -- CRS-1 -- provided only 15% of the mixture shear strength at the highest residual application rate.
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From page 59... ...
5 3. 0 0 100 200 300 400 500 Interface Shear St reng th at 25 °C (kP a)
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From page 60... ...
One possible explanation for these results is that a high-viscosity, gritty mastic was formed when tack coat combined with dust and, thus, provided a greater resistance to shear movement.
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From page 61... ...
4.4.5 Effects of Tack Coat Coverage As previously discussed, 50% tack coat coverage was only investigated for SS1-h. For the application of SS-1h, the residual application rate of 0.031 gal/yd2 was achieved with a high level of error (see Table 5)
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From page 62... ...
Dry/Clean Wet/Clean No-confinement Confinement 0 10 20 30 40 50 60 0.031 0.062 0.155 0.031 0.062 0.155 In te rfa ce S he ar S tre ng th (p si) Residual Application Rate (gal/yd2)
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From page 63... ...
Tack Coat Material 1 Residual Application Rate Tes t Temperature (°C) Maximum Tensile Load (lb)
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From page 64... ...
For both tack coat materials, as the residual application rate increased, the ISS increased at all temperatures, and the highest ISS values were measured at the rate of 0.155 gal/yd2; therefore, for the range of residual application rates from 0.031 to 0.155 gal/yd2, there was no optimum tack coat residual application rate as might have been expected. This may be attributed to the highly oxidized and coarse HMA surface at the selected site, which required greater tack coat rates than expected.
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From page 65... ...
/sin d increased, the ISS for both tack coat materials at each residual application rate also increased. On the other hand, interface stiffness did not vary noticeably with the residual application 0.0 0.5 1.0 1.5 2.0 -10 0 10 20 30 km od ul us T ra ck le ss /k -m od ul us C R S1 Temperature (ºC)
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From page 66... ...
. For old HMA and PCC surface types, the trackless tack coat exhibited the highest shear strength at the residual application rates of 0.031 and 0.062 gal/yd2 for both old HMA and PCC surfaces, and CRS-1 and SS-1 exhibited the lowest.
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From page 67... ...
Effects of residual application rates and tack coat types on ISS for (a) old HMA surface, (b)
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From page 68... ...
It is noted that differences are more pronounced at low and intermediate residual application rates and less pronounced at high residual application rates. It is likely that the effects of microstructure features that contribute to the surface roughness or texture are less pronounced when they are filled with tack coat materials.
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From page 69... ...
The most probable factor appears to be the greater asphalt film thickness at the interface of the new HMA and the smoother/flatter surface of the freshly made specimens. 4.7 Experimental VI: Effects of Texture and Permeability on Tack Coat Bond Strength The objective of this laboratory experiment was to evaluate the effects of surface texture and permeability of the existing pavement on tack coat ISS.
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From page 70... ...
Wet and Clean Dry and Clean 0 10 20 30 40 50 60 70 80 90 100 0.031 0.062 0.155 0.031 0.062 0.155 0.031 0.062 0.155 0.031 0.062 0.155 In te rf ac e Sh ea r B on d St re ng th (p si) Residual Application Rate (gsy)
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From page 71... ...
0 20 40 60 80 100 120 140 0 0.05 0.1 0.15 0.2 In te rf ac e Sh ea r S tr en gt h (p si ) Residual Application Rate (gal/yd2)
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From page 72... ...
As previously noted, all tack coat materials showed the highest strength at a residual application rate of 0.155 gsy. Within the residual application rate range considered, no optimum residual application rate was determined.
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From page 73... ...
Based on the results presented in Figures 78 and 79, Figure 80 presents the variation of the predicted shear stress ratio with the ISS for the different tack coat materials and residual application rates. As shown in this figure, a power law model is adequate in describing the relationship between the shear stress ratio and the ISS.
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From page 74... ...
06 2 0 .1 55 Sh ea r S tr es s (p si) Application Rate (gsy)
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From page 75... ...
Application Rate (gsy) ISS Shear Stress CRS- 1 SS-1h Trackless PG 64-22 Figure 78.
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From page 76... ...
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.031 0.062 0.155 0.031 0.062 0.155 0.031 0.062 0.155 0.031 0.062 0.155 Sh ea r St re ss R at io CRS-1 SS-1h Trackless PG 64-22 Limiting Ratio (c) Structure C Application Rate (gsy)
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From page 77... ...
CRS-1 SS-1h Trackless PG 64-22 (d) Structure D 0 0.1 0.2 0.3 0.4 0.5 0.6 0.031 0.062 0.155 0.031 0.062 0.155 0.031 0.062 0.155 0.031 0.062 0.155 Sh ea r St re ss R at io Application Rate (gsy)
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From page 78... ...
Design D Design E Design F Figure 80. Relationship between shear stress ratio and laboratory-measured ISS.
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From page 79... ...
Recommended tack coat residual application rates. cussions with state dots and industry personnel, Table 30 lists the recommended tack coat residual application rates for the various pavement surfaces.
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