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28 3.4Experiment Plan II: Rheological Horizontal Sensor Vertical Sensors Properties and Superpave PG of Tack Coat Materials Normal Load Actuator Shearing Frame Performance-graded and softening point tests were per- formed on the asphalt binder residues according to ASTM D 6373, Standard Specification for Performance Graded Asphalt Binder, and ASTM D 36, Standard Test Method for Soften- ing Point of Bitumen (Ring-and-Ball Apparatus) respectively Reaction Frame (38). All asphalt binder residues were obtained according to AASHTO D 244, Residue by Evaporation. While this study Figure 21. General description of the LISST device. assumed the applicability of the binder-aging protocol for tack coat emulsions, validation of this assumption was neces- sary in order to understand the aging mechanism for emulsi- the variation in the results, triplicate samples were tested. A fied tack coats. number of experiments were conducted in order to evaluate To establish sound correlations between the rheological the ruggedness and reliability of the LISST. Experiments were properties of emulsified tack coat materials and the shear also conducted comparing the results from this device with strength at the interface, two tack coat materials (trackless those of the Superpave Shear Tester. and CRS-1) were tested using the dynamic shear rheometer at temperatures ranging from -10 to 60C with a 10C inter- val. This was the same temperature range used in interface 3.6Experiment Plan IV: Effects shear testing. Testing was conducted using an AR2000 rheo of Test Temperature and meter that was set up to work in the dynamic shear mode. Its Relationship with Tack Two sample sizes were used, depending on the testing tem- Coat Rheology perature: a sample with a 25-mm diameter and a thickness Experiment IV was designed to test the effects of tempera- of 1 mm was used at high temperatures (from 40 to 60C) ture, emulsified tack coat type, and residual application rate and a sample with an 8-mm diameter and a thickness of on interface shear bond strength (see Table 7). The factorial 2 mm was used at low and intermediate temperatures (from matrix consisted of 8 temperatures, 2 emulsified tack coats, -0 to 30C). and 3 residual application rates resulting in a total of 48 test conditions. Each test condition had two replicates to mini- mize variation due to experimental errors, resulting in a total 3.5Experiment Plan III: Development of 96 interface shear tests. Test temperatures ranged from of a Laboratory Test Procedure -10 to 60C with a 10C interval. Three residual application to Measure the Interface rates were considered: 0.031, 0.062, and 0.155 gal/yd2. The Bond Strength experimental program was designed to evaluate performance A direct shear device was developed in Experiment III for of tack coats between two HMA layers, a new overlay on an the characterization of interface shear strength of cylindrical existing pavement. Tack coat was uniformly distributed with specimens in the laboratory. The device is referred to as the 100% coverage. The old HMA surface condition was dry and Louisiana Interlayer Shear Strength Tester (LISST). Details of clean before distributing tack coat in the field. Two emulsi- the development and evaluation of this device are presented fied tack coats were tested in this part of the study, a cat- in Section 5. The LISST device consists of two main parts: a ionic rapid setting (CRS-1) and a trackless tack coat, which shearing frame and a reaction frame (see Figure 21). Only the consists of a polymer-modified emulsion with a hard base shearing frame is allowed to move while the reaction frame is asphalt cement. stationary. A cylindrical specimen is placed inside the shearing The test procedure was as follows. The LISST was used to and reaction frames and is locked in place with collars. The measure ISS at different temperatures. The loading system was shearing frame is then loaded. As the vertical load is gradually a universal testing machine (manufactured by Cox & Sons increased, shear failure occurs at the interface. Company). This machine had a temperature chamber that can The LISST device was evaluated in a wide range of test control the test temperature from -20C to 80C. The maxi- conditions (see Table 4). Test specimens were obtained from mum load capacity of the actuator was 25,000 lb. Temperature pavement test sections described in the previous section. As conditioning and interface shear testing were conducted inside shown in Table 4, direct shear tests were performed at 25C the test chamber. Figure 22 illustrates the followed test pro- under two confinement conditions, 0- and 20-psi. To assess cedure. As shown in Figure 22a, two replicate samples were

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29 Table 7. Test factorial to evaluate effects of test temperatures. Variables Contents Levels Emulsified Tack Coat Trackless, CRS-1 2 2 Residual Application Rate 0.031, 0.062, and 0.155 gal/yd 3 Temperature 10, 0, 10, 20, 30, 40, 50, 60C 8 Replicates Two replicates at each temperature 2 Total Number of Tested Specimens 96 (a) Sample conditioning (4 hours) (b) Assemblage of sample and LISST device (c) Stabilization of test temperature (30 min.) (d) Application of shear loading Figure 22. Illustrations of the test procedure for interface shear testing.