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19 19 Section 3 Experimental Program 3.1Introduction test lanes, a description of the construction process and the test variables in the field experiment is presented in the fol- Based on the results of Task 1, a comprehensive experi- lowing section. mental plan was designed to identify consistent, reliable, and practical methods for (1) evalutracating the bonding charac- teristics of tack coats; (2) selecting the tack coat material type 3.2Tack Coat and Overlay and residual asphalt binder application rate required for opti- Construction at the Test Site mum performance in new HMA pavement and HMA overlay Table 4 presents the test matrix simulated in the LTRC PRF construction, rehabilitation, and reconstruction; (3) calibrat- field experiment, which used conventional paving equipment ing application equipment; and (4) maintaining field quality and a computerized tack coat distributor truck. Four types of control and quality assurance. Findings reported in Chapter 2 pavement surfaces and five tack coat materials were evaluated, also identified a number of factors that were reported to influ- but only one emulsion (SS-1h) was used on the new HMA ence interface bond strength including tack coat type, tack surface, and two emulsion grades (SS-1h and SS-1) were used coat application rate, tack coat curing time, surface condi- on the milled surface. Four residual application rates were tion, and pavement temperature. Responses from the world- selected including zero (no-tack). Effects of wet and dusty wide survey indicated that the residual application rates of conditions during construction operations were simulated emulsions typically vary from 0.02 to 0.08 gal/yd2, depending for the different surface types as part of the experimental pro- on the type of pavement surface. As pavement temperature gram. To evaluate variation in the results, triplicate samples increases, laboratory bond strength significantly decreases for were tested for each condition; 375 samples were tested as all tack coat types and application rates. The most common part of the test matrix. Laboratory specimens (cores) were types of emulsions used for tack coats include slow-setting obtained from the pavement test sections. and rapid-setting grades of emulsions. In the United States, most states use slow-setting grades of emulsions. To this end, the experimental plan investigated the influence of a number 3.2.1 HMA Pavement Surface Preparation of factors on the interface shear strength: HMA and PCC sur- Figure 11 presents a plan view of the five test lanes con- face type and properties (e.g., texture, air voids content, and structed at the LTRC PRF. Each lane was a total of 215 ft in permeability), surface cleanliness, tack coat material type, and length and 12 ft in width. It is noted that each lane contained application rate and method. test and distributor truck access areas. Each test section had The majority of the research activities conducted in this a length of 15 ft and a width of 6.5 ft. The lengths of the adja- project were based on tack coat experiments conducted in cent (access) areas were selected to ensure that the distributor a field environment. Field experiments were complemented truck could attain the required speed in order to achieve the with a number of laboratory experiments to assess the influ- correct tack coat application rate. All test lanes selected for ence of variables such as laboratory compaction, rheological this experiment contained a similar old HMA surface type. properties of tack coat materials, and test temperature. The Surface texture values for each lane were measured using a experimental program was divided into experimental test laser type device (DYNATEST 5051 Mark III road surface matrices, which answered specific objectives of the experi- profiler), according to ASTM E 1845, Standard Practice for mental program. Since all experiments made use of full-scale Calculating Pavement Macrotexture Mean Profile Depth. The