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OCR for page 49
49 Table 14. Test parameters in the test method. Category Level Loading Rate 0.5 in/min Contact Time 3 minutes Contact Pressure 1.5 psi Tack Coat Evaporation Time 1 hour Tack Coat Evaporation Device Infrared reflected heating (IRH) source Summary of Test Parameters on the surface (see Figure 53g). A compressive preload of 1.57 psi was applied to the surface via the LTCQT foot, load- A summary of the test parameters is shown in Table 14. ing plate, which has the polyethylene foam for 3 minutes. Field test results presented in the following sections were Then, a tensile force was applied at a displacement rate of evaluated based on these test parameters. 0.008 in/sec until failure. The tensile force was continuously recorded. The ultimate load (PULT) was measured, and the 4.2.4 LTCQT Test Procedure tensile strength (SULT) was computed and used in the analysis. Four tack coat materials--trackless, CRS-1, SS-1h, and PG The existing pavement surface at the LTRC PRF facility was 64-22--were tested in the field. A minimum of three replicate thoroughly cleaned (see Figure 53a). An area of 6 in 6 in was tests were performed for each condition. A test procedure for used for each test (see Figure 53b). The tack coat material assessing tack coat installation quality in the field using the was then applied with a paint brush at the prescribed residual LTCQT device is presented in Appendix C. application rate and application temperature (see Figure 53c). Subsequent to the application of the tack coat material, the IRH 4.2.5Effect of Tack Coat Temperature device was positioned above the test area (for emulsion only) on the Ultimate Tensile Strength for one hour to accelerate the curing time (see Figure 53d). Surface temperature was allowed to cool to the testing tem- Testing temperature plays a vital role in the response of perature, and then the cured surface was ready to test for tack the tack coat material as measured by the LTCQT. A series coat quality using the LTCQT. The LTCQT was positioned of LTCQT tests were conducted in the field at intervals of (a) Surface cleaning (b) Drawing test area (c) Tack coat application (d) Water evaporation (curing) for 1 hour Figure 53. Main steps in the LTCQT test procedure.

OCR for page 49
50 (e) Foam material attachment on loading plate (f) Foam material attachment on loading plate II (g) Placement of LTCQT (h) Pull-off testing and data recording Figure 53. (Continued). approximately 10C ranging from 30 to 90C on the afore- the closest ones at the point where the tensile strengths were mentioned four tack coat materials at a residual application measured. In general, the variation in temperature between rate of 0.05 gal/yd2. Three replicates were tested for each the start and end of each test was controlled to within 5C. tack coat material. Figure 54 presents the variation of the Tensile strength of each tack coat material increased, reached ultimate mean tensile strength (i.e., SULT, average of three a peak, and then decreased as the temperature increased (see replicates) of the tack coat materials considered in this Figure 54); however, the tensile behavior of each tack coat experiment along with the test temperatures. The tempera- material was different between the asphalt cement and emul- tures presented in these graphs are the ones measured at sions in the post-peak region. PG 64-22 exhibited a rapid soft- the end of the test. It is believed that these temperatures are ening with increasing temperature, whereas the emulsions had 5 4.5 PG 64-22 Mean Tensile Strength (psi) 4 Trackless 3.5 SS-1h 3 CRS-1 2.5 2 1.5 1 0.5 0 30 to 40 C 40 to 50 C 50 to 60 C 60 to 70 C 70 to 80 C Temperature (C) Figure 54. Variation of the mean tensile strength with temperature.