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OCR for page 58
58
70
SS-1h
Interface Shear Strength (psi)
60
CRS-1
50
Trackless
40
30
20
10
0
0 0.05 0.1 0.15 0.2
Residual Application Rate (gal/yd2)
(a)
10
SS-1h
9
CRS-1
8 Trackless
7
6
Air Voids
5
4
3
2
1
0
0.031 0.062 0.155
Residual Application Rate (gal/yd2)
(b)
Figure 61. Variation of ISS with residual application rates
(a) and variation of air voids with residual application rates:
clean and dry condition, no confinement, 25°C (b).
voids. This may result in negative effects on the overlay perfor- and its resistance to deformation at high temperatures (G*/
mance, such as the appearance of "fat spots" on the pavement sin d) increased. Similar trends were observed at the low and
surface, which may affect the friction properties of the mat. intermediate residual application rates.
Several attempts were made to core the no-tack coat test
area; however, these specimens failed at the interface during the
4.4.2 Effect of Confining Pressure
coring process. It is noted that the best tack coat performer--
trackless at the highest residual application rate--provided Table 22 presents the statistical analysis of the effects of con-
60% of the monolithic (no interface) mixture shear strength finement on ISS based on t-tests. As shown in this table, the
at 25°C, which was estimated at 105 psi. The worst tack coat majority of the cases (17 out of the 24 cases) indicated that
performer--CRS-1--provided only 15% of the mixture confinement has a significant effect on the measured ISS. Fig-
shear strength at the highest residual application rate. This ure 63 shows the ratio of ISS between the 0 and 20 psi confine-
suggests that the construction of flexible pavements in mul- ment test conditions. The ratio of ISS between these two test
tiple layers introduces weak zones at these interfaces. conditions increased as the residual application rate decreased.
Figure 62 presents the relationships between rotational As the residual application rate decreased, increasing the con-
viscosity, G*/sin d, and the softening point of the tack base fining pressure resulted in a more pronounced contribution
asphalt with ISS at a residual application rate of 0.155 gal/ of the effect of roughness and aggregate resistance to sliding
yd2. In general, good correlations were observed between at the interface; however, at higher residual application rates
these rheological properties and the ISS values. The mea- (i.e., greater lubrication), the effect of aggregate roughness and
sured interface strength increased as the tack coat viscosity resistance to sliding was less crucial since most of the ISS was
OCR for page 59
59
3. 0 25
Dynamic Shear (G*/sin ) at 64°C
Rotational Viscosity at 135°C A
2. 5 20
2. 0 2
R = 0. 95 15
(Pa-s) a
(kPa) a
2
1. 5 R = 0. 96
10
1. 0
0. 5 5
0. 0 0
0 100 200 300 400 500 0 100 200 300 400 500
Interface Shear Strength at 25 °C (kP a) Interface Shear Strength at 25 °C (kPa)
(a) Rotational Viscosity (b) Dynamic Shear Rheometer
100
80
Softening Point (°C)
60
40
2
R = 0.96
20
0
0 100 200 300 400 500
Interface Shear Strength at 25 °C (kPa)
(c) Softening Point
Figure 62. Relationship between ISS with 0.155 gal/yd 2 and rheology test results.
Table 22. Statistical analysis of the effects of confinement on ISS.
Tack Rate Statistical Test Condition P-value Results
0.031 Unconfined vs. Confined Clean-Dry 0.0110 Significant
Unconfined vs. Confined Dusty-Dry 0.0440 Significant
Unconfined vs. Confined Clean-Wet 0.3330 Not Significant
Unconfined vs. Confined Dusty-Wet 0.0150 Significant
0.062 Unconfined vs. Confined Clean-Dry 0.0480 Significant
Unconfined vs. Confined Dusty-Dry 0.0344 Significant
SS-1h
Unconfined vs. Confined Clean-Wet 0.8279 Not Significant
Unconfined vs. Confined Dusty-Wet 0.0123 Significant
0.155 Unconfined vs. Confined Clean-Dry 0.3309 Not Significant
Unconfined vs. Confined Dusty-Dry 0.0356 Significant
Unconfined vs. Confined Clean-Wet 0.8608 Not Significant
Unconfined vs. Confined Dusty-Wet 0.0128 Significant
0.031 Unconfined vs. Confined Clean-Dry 0.0323 Significant
Unconfined vs. Confined Dusty-Dry 0.0087 Significant
0.062 Unconfined vs. Confined Clean-Dry 0.9486 Not Significant
CRS-1
Unconfined vs. Confined Dusty-Dry 0.0037 Significant
0.155 Unconfined vs. Confined Clean-Dry 0.5532 Not Significant
Unconfined vs. Confined Dusty-Dry < 0.0001 Significant
0.031 Unconfined vs. Confined Clean-Dry 0.0303 Significant
Unconfined vs. Confined Dusty-Dry 0.0407 Significant
0.062 Unconfined vs. Confined Clean-Dry 0.0087 Significant
Trackless
Unconfined vs. Confined Dusty-Dry 0.0179 Significant
0.155 Unconfined vs. Confined Clean-Dry 0.8048 Not Significant
Unconfined vs. Confined Dusty-Dry 0.0026 Significant
