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30 conditioned for at least 4 hours at the test temperature. Sam- four residual application rates--0 (No Tack), 0.031, 0.062, ples were then placed in the testing chamber while attempt- 0.155 gal/yd2. Field-cored specimens for tack coat applied ing to minimize temperature loss (Figure 22b) and were then between new and new HMA surfaces were available for conditioned for 30 minutes at the target temperature to com- SS-1h tack coat. Sample sizes and other test conditions were pensate for temperature loss during specimen placement in the the same as field-cored sample testing. Laboratory-fabricated LISST device (Figure 22c). Finally, shear load was applied by specimens consisted of two layers, with a tack coat at the the shear loading frame at a loading rate of 2.54 mm/sec until interface of these layers. The diameter of each specimen was failure, as shown in Figure 22d. 4.0 in. The bottom half of each specimen was prepared by compacting the mixture to a height of 2.0 in at 150C using the Superpave Gyratory Compactor (SGC). The compacted 3.7Experiment Plan V: Effects of specimen was then allowed to cool to room temperature, and Pavement Surface Type and its air void content was measured. Compacted bottom halves Sample Preparation Method having an air voids content of 6 1 percent were prepared. Experiment V was designed to measure and compare the The asphalt materials used as tack coat were then heated to interface shear strength for different surface types and sample the specified application temperature. The calculated amount preparation methods. For this purpose, samples were pre- of the preheated tack coat was then uniformly applied on the pared to simulate different field conditions and were tested bottom half of the specimen using a brush. Once application using the LISST device. Table 8 presents the field test matrix. of the tack coat was complete, it was allowed to cool to room Four types of field pavement surfaces and five tack coat temperature and the top half of the sample was compacted materials were evaluated. However, only one emulsion (SS-1h) by placing the bottom half in the SGC mold and compacting was used on the new HMA surface and two emulsion grades loose mix on top of the tack-coated bottom half. (SS-1h and SS-1) were used on the milled surface. Four resid- ual application rates were selected including, zero (no tack) 3.8Experiment Plan VI: Effects application rate. The effects of rainy and dusty conditions of Surface Texture and during construction operations were simulated for the differ- Permeability on Interface ent surface types as part of this experiment. Test temperature Shear Strength and the tack coat coverage rate were kept constant at 25C and 100% coverage, respectively. To assess variation in the The objective of this experiment was to evaluate the effects results, triplicate samples were tested for each condition; of surface texture and permeability on tack coat interface 375 samples were tested as part of the test matrix. shear strength using laboratory-prepared specimens. Three To assess the influence of sample preparation methods, mixture types with different texture and permeability com- laboratory-fabricated specimens were prepared using five positions (see Table 9) were considered to use as the layer on tack coat materials--SS-1h, trackless, locally-used trackless which the tack coat was applied. Table 10 presents the mix (AUT), PG 64-22, and CRS-1--as tack coat was applied at designs adopted in the preparation of the three mix types. Table 8. Test factorial for field-prepared samples. Variables* Content Levels Old HMA, new HMA, grooved PCC, Pavement surface type 4 milled HMA Tack coat material SS-1h, SS-1, CRS-1, Trackless, PG 64-22 5 2 Residual application rate 0- (No-Tack), 0.031-, 0.062-, 0.155-gal/yd 4 Wetness (Rain) condition Wet, Dry 2 Cleanliness condition Dusty, Clean 2 Test temperature 25C 1 Confinement pressure (psi) 0, 20 2 Tack coat coverage 50%, 100% 2 Number of replicates 3 3 Total Number of Samples 474 * Some variables were partially evaluated according to the test factorial.

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31 Table 9. Test matrix to evaluate effects of texture and permeability on SS-1 tack coat. Residual No. of Mixture Texture Permeability Tack Coat Application Rate Tested Type Roughness (gsy) Specimens 0.000 3 0.031 3 Sand Low Low SS-1 0.062 3 0.155 3 0.000 3 High 0.031 3 SMA Low SS-1 0.062 3 0.155 3 0.000 3 Open-graded friction 0.031 3 High High SS-1 course 0.062 3 (OGFC) 0.155 3 Table 10. Job mix formula. Mixture Type Sand SMA OGFC Binder Type PG 70-22 PG 76-22 PG 76-22 Binder Content (%) 6.0 6.2 6.5 Air Voids (%) 13.2 3.5 21.2 Aggregate Gradation Sieve Size % Passing 37.5 mm (1 in) 100 100 100 25 mm (1 in) 100 100 100 19 mm ( in) 100 100 100 12.5 mm ( in) 100 93 95 9.5 mm ( in) 100 66 67 4.75 mm (No.4) 97 29 17 2.36 mm (No.8) 90 23 8 1.18 mm (No.16) 81 19 6 0.6 mm (No.30) 66 18 5 0.3 mm (No.50) 25 15 5 0.15 mm (No.100) 8 12 4 0.075 mm (No.200) 4 8.8 3