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65 2.0 4.0 2 2 2 2 0.015 gal/yd 0.031 gal/yd 0.062 gal/yd k-modulus Trackless /k-modulus CRS-1 3.5 0.015 gal/yd 2 0.031 gal/yd 1.5 3.0 2 ISS Trackless / ISSCRS-1 0.062 gal/yd 2.5 1.0 2.0 1.5 0.5 1.0 0.5 0.0 0.0 -10 0 10 20 30 -10 0 10 20 30 Temperature (C) Temperature (C) (a) (b) Figure 69. Ratio of trackless to CRS-1 in terms of (a) k-modulus and (b) ISS. 4.5.2Interface Stiffness Characteristics can reach 40C or higher during the summer months, the use at Various Temperatures of a trackless-type of emulsion would provide greater shear resistance than that of the CRS-1 emulsion. Variation of the k-modulus ratio and the ISS ratio between trackless and CRS-1 are shown in Figure 69 (a and b). In Figure 69a, it is observed that the k-modulus of the trackless material 4.5.3Relationship Between Interface Shear was greater or equal to that for the CRS-1 tack coat, except for Strength and Tack Coat Rheology the residual application rate of 0.062 gal/yd2 at 30C. In addi- Interface Shear Strength versus G*/sin d tion, the difference between the two tack coats was marginal at a residual application rate of 0.031 gal/yd2, except at a test tem- The parameter G*/sin d is used as an indicator of the binder perature of 30C (see Figure 69b); however, at an application susceptibility to permanent deformation in the Superpave rate of 0.062 and 0.155 gal/yd2, the bonding performance of binder specification system. It was, however, adopted in this the trackless was superior to that of the CRS-1 as the tempera- study because it simulates oscillation in a shear mode, which ture increased. The ratio of the k-modulus and ISS was not closely resembles the interface shear mode between two layers. plotted at a temperature greater than 40C since the bonding The relationships between ISS and G*/sin d and k-modulus resistance of CRS-1 was significantly lower than the trackless and G*/sin d are presented in Figures 70 and 71, respec- material. It is worth noting that the ISS values for the trackless tively. Results presented in Figure 70 indicate that as G*/sin d emulsion tested at temperatures greater than 40C were much increased, the ISS for both tack coat materials at each residual higher than those of similar specimens with CRS-1 emulsion application rate also increased. On the other hand, interface (see Table 26). Since the temperature at a pavement interface stiffness did not vary noticeably with the residual application 3000 3000 0.07 l/m 0.07 l/m Interface Shear Strength Interface Shear Strength 2500 2500 0.14 l/m 0.14 l/m 2000 2000 0.28 l/m 0.28 l/m (kPa) (kPa) 1500 1500 1000 1000 500 500 0 0 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 G*/sin (kPa ) G*/sin (kPa) (a) Trackless (b) CRS-1 Figure 70. Relationship between ISS and G*/sin d.