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OCR for page 20
20 Table 4. Test factorial for field-prepared samples. Variables* Content Levels Pavement surface type Old HMA, New HMA, PCC, 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 Wet (rain) condition Wet, Dry 2 Dusty 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; ~ test temperature was varied in the sub-matrix that evaluated the effect of temperature on ISS. roughness value for Lane 1, Lane 2, and Lane 3 were 0.042, the sources of the problems and correct them. Several repair 0.043, and 0.043 in, respectively. Lane 4 was not utilized for and maintenance actions were completed on the distributor the experiment because the surface texture was different truck prior to tack coat application. from that of Lanes 1, 2, 3, and 5. Figure 12 presents the mea- Application of tack coat materials was performed directly surements and markings of the grid on the actual test lanes, after testing and preparation of the existing surface was com- which correspond to the layout presented in Figure 11. The pleted. Tack materials were SS-1, SS-1h, CRS-1, PG 64-22, markings were used to assist the tack coat distributor truck and trackless (NTSS-1HM). The truck speed and spray tip in determining the correct location for each type of material used for each tack coat material along with the correspond- and the corresponding application rate. ing application rate are provided in Figure 14. As indicated in this figure, 10 passes by the distributor truck were made. A pass is completed when the distributor truck has traversed 3.2.2 Dusty and Wet Conditions Simulation a given lane. An Etnyre computerized tack coat distributor The effects of dusty or wet (rainfall) conditions of the exist- truck Model 2000 was used to apply the tack coat materials. ing pavement surface were investigated. In order to simulate The truck had a heated tank for holding tack coat materi- dusty conditions, a silty-clay-type soil, classified as A4 based als at the desired application temperature. While the track- on the AASHTO soil classification, was reasonably uniformly less tack coat was applied at 82C, the SS-1h and CRS-1 tack applied at a rate of 0.070 lb/ft2 onto the old HMA surface coat materials were applied at 68C. Tack coats were applied prior to tack coat application (see Figure 13a and b). Wet in the undiluted state. Mounted on the back of the truck, a condition was simulated by uniformly spraying water at a spray bar fitted with nozzles distributed tack coat material rate of 0.06 gal/yd2 on tacked surfaces and prior to placement at the specified application rate. The total width of the spray of the HMA mixture (see Figure 13c and d). Wet condition bar was extended to 13 ft in order to provide full coverage of was considered only for the SS-1h tack coat due to the limited a single lane. Application rate was adjusted by altering the number of test lanes that could be constructed at the PRF. truck speed and nozzle type and size. Distribution of tack coat materials was coordinated so that the wheels of the distributor truck never came in contact with 3.2.3 Tack Coat Application the tack coat material (see Figure 15). The application of SS-1h Prior to the day of tack coat application, several calibration for 100% and 50% coverage were conducted in the same man- trials were performed over a 3-month period for the comput- ner. For application of the residual rate of 0.031 gal/yd2, the erized distributor truck to ensure that the selected applica- distributor truck drove the entire span of Lanes 1 and 2 at the tion rates might be installed successfully given the restrictions specified speed to deposit the tack coat at the end of each lane. at the site. During these trials, the application rate was found The residual application rate of 0.062 gal/yd2 was applied at to be in error as much as 40%. Both the owner of the truck the specified speed in the same manner as the previous appli- and the manufacturer of the equipment worked to identify cation rate. The residual application rate of 0.155 gal/yd2 was

OCR for page 20
215 ft 4.5 ft 4.5 ft 50 ft 4.6 ft 35 ft 4.6 ft 24.9 ft 4.6 ft 4.6 ft 4.6 ft Dry Dry Adjacent Area Dry Adjacent Area Dry Adjacent Dry Wet Adjacent No Tack 0.031 gsy 0.062 gsy 0.155 gsy 0.155 gsy 0.155 gsy Area Dirt Lane 5 Area Dry Dry Adjacent Area Dry Adjacent Area Dry Adjacent Dry Wet Adjacent No Tack 0.031 gsy 0.062 gsy 0.155 gsy Area 0.155 gsy 0.155 gsy Area Clean Lane 4 Dry Dry Adjacent Area Dry Adjacent Area Dry Adjacent Area Dry Wet Adjacent Area Dirt No Tack 0.031 gsy 0.062 gsy 0.155 gsy 0.155 gsy 0.155 gsy Lane 3 Dry Dry Adjacent Area Dry Adjacent Area Dry Adjacent Area Dry Wet Adjacent Area Clean No Tack 0.031 gsy 0.062 gsy 0.155 gsy 0.155 gsy 0.155 gsy Dry Dry Wet Adjacent Area Dry Wet Adjacent Area Wet Adjacent Area Dirt No Tack 0.031 gsy 0.031 gsy 0.062 gsy 0.062 gsy No Tack Lane 2 Dry Dry Wet Adjacent Area Dry Wet Adjacent Area Wet Adjacent Area Clean No Tack 0.031 gsy 0.031 gsy 0.062 gsy 0.062 gsy No Tack 2 Dry Dry Wet Adjacent Area Dry Wet Adjacent Area Wet Adjacent Area Dirt No Tack 0.031 gsy 0.031 gsy 0.062 gsy 0.062 gsy No Tack Lane 1 Dry Dry Wet Adjacent Area Dry Wet Adjacent Area Wet Adjacent Area Clean No Tack 0.031 gsy 0.031 gsy 0.062 gsy 0.062 gsy No Tack 4.6 ft 4.6 ft 4.6 ft 50 ft 4.6 ft 4.6 ft 35.1 ft 4.6 ft 40 ft Figure 11. Layout of test lanes in the field experiment.