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OCR for page 55
55 Figure 59. General description of the Louisiana Interlayer Shear Strength Tester. = k (2) for SS-1h, CRS-1, and trackless tack coats, respectively. Triplicate specimens were tested for each test condition where, defined by tack coat type, residual application rate, confin- t =interlayer shear stress (ksi); ing pressure, and dusty and wet conditions. All tests were x=interlayer displacement within the interface (in); and performed at a temperature of 25C. In general, the COVs k =interlayer tangential modulus (lb/ft3). in the test results were less than 10%. As shown in the following sections, results were analyzed to investigate The k-modulus is computed by dividing the peak stress by the effects of variables considered in the test factorial on the displacement at failure from the stress versus displacement the ISS. curve (see Figure 60). Effect of Emulsified Tack Coat Types 4.4.1Effects of Tack Coat Characteristics and Residual Application Rates on Interface Shear Strength Tables 20 and 21 present the statistical analyses of the Tables 18 and 19 present the mean ISS test results along effects of application rates and tack coat types on ISS based on with their standard deviations and coefficient of variations a two-tailed t-test at a 95% confidence level. As shown in these 60 Peak stress 50 Interface Shear Stress (psi) 40 k-modulus (lb/ft3) 30 20 10 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Displacement (in) Figure 60. Typical interface shear stress versus displacement for trackless at 0.06 gal/yd 2.

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56 Table 18. ISS of SS-1h emulsified tack coat. Tack Coat SS-1h Confinement Pressure Residual (psi) Appl. Rate 0.031 0.062 0.155 (gal/yd2) Surface D1 D W2 W D D W W D D W W Condition H3 L4 H L H L H L H L H L 11.1 13.5 13.6 12.7 14.6 7.5 16.3 12.7 36.8 32.9 44.0 34.0 ISS (psi) 9.7 12.9 13.1 13.2 12.0 8.0 18.1 11.7 41.7 40.1 37.7 34.5 0 12.9 14.5 15.5 15.0 13.2 7.8 16.8 13.6 40.3 34.9 37.8 34.8 Mean 11.2 13.6 14.0 13.6 13.3 7.8 17.1 12.7 39.6 36.0 39.8 34.4 S.D. 1.6 0.8 1.3 1.2 1.3 0.3 0.9 0.9 2.5 3.7 3.7 0.4 COV 14.2 5.9 9.0 8.8 9.8 3.7 5.4 7.3 6.4 10.3 9.2 1.2 16.5 20.9 13.7 24.5 18.6 10.4 15.2 15.5 40.4 51.9 38.5 47.7 ISS (psi) 15.7 20.2 16.1 22.4 14.9 11.6 17.8 16.6 43.6 44.0 38.5 45.4 18.8 26.1 15.9 19.3 17.6 12.9 19.1 16.3 40.7 43.9 41.2 43.4 20 Mean 17.0 22.4 15.2 22.1 17.0 11.6 17.4 16.2 41.6 46.6 39.4 45.5 S.D. 1.6 3.2 1.4 2.6 1.9 1.2 1.9 0.6 1.8 4.6 1.6 2.1 COV 9.5 14.3 9.0 11.7 11.3 10.6 11.2 3.4 4.2 9.8 4.0 4.7 1 Dry Condition, 2 Wet Condition, 3Clean Condition, 4 Dusty Condition. Table 19. ISS of CRS-1 and trackless emulsified tack coat. Tack Coat CRS-1 Trackless Confinement Pressure Residual (psi) Appl. 0.031 0.062 0.155 0.031 0.062 0.155 Rate (gal/yd2) Surface D1 D D D D D D D D D D D Condition H 2 L 3 H L H L H L H L H L 6.9 10.3 12.3 10.3 12.6 24.6 13.3 20.1 28.4 51.3 58.0 60.2 ISS (psi) 6.6 10.0 11.4 13.1 15.6 23.9 16.0 22.4 24.6 49.7 61.0 60.5 0 8.5 7.8 13.3 12.2 14.3 24.1 13.9 23.6 22.2 61.2 68.1 65.1 Mean 7.3 9.4 12.4 11.8 14.2 24.2 14.4 22.0 25.1 54.1 62.4 62.0 S.D. 1.0 1.3 0.9 1.4 1.5 0.4 1.5 1.8 3.1 6.3 5.2 2.7 COV 14.1 14.2 7.6 11.9 10.9 1.5 10.2 8.1 12.3 11.6 8.3 4.4 10.2 16.9 14.0 18.8 12.9 34.2 18.0 34.3 35.2 75.2 65.2 79.6 ISS (psi) 13.3 13.6 11.5 20.3 15.6 33.4 22.6 26.4 34.0 76.9 55.8 74.9 11.0 15.4 11.7 17.5 16.8 34.2 22.2 31.9 38.6 69.7 70.2 75.3 20 Mean 11.5 15.3 12.4 18.9 15.1 33.9 20.9 30.8 35.9 73.9 63.7 76.6 S.D. 1.6 1.6 1.4 1.4 2.0 0.5 2.5 4.0 2.4 3.8 7.3 2.6 COV 14.3 10.5 11.2 7.3 13.1 1.4 12.0 13.1 6.7 5.1 11.5 3.4 1 Dry Condition, 2 Clean Condition, 3 Dusty Condition.

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57 Table 20. Statistical analysis of the effects of application rates on ISS. Tack Coat Statistical Test Condition Confinement P-value Results Application Rates Clean-Dry Unconfined < 0.0001 Significant Application Rates Clean-Dry Confined < 0.0001 Significant Application Rates Dusty-Dry Unconfined < 0.0001 Significant Application Rates Dusty-Dry Confined < 0.0001 Significant SS-1h Application Rates Clean-Wet Unconfined < 0.0001 Significant Application Rates Clean-Wet Confined < 0.0001 Significant Application Rates Dusty-Wet Unconfined < 0.0001 Significant Application Rates Dusty-Wet Confined < 0.0001 Significant Application Rates Clean-Dry Unconfined 0.0010 Significant Application Rates Clean-Dry Confined 0.0893 Not Significant CRS-1 Application Rates Dusty-Dry Unconfined < 0.0001 Significant Application Rates Dusty-Dry Confined < 0.0001 Significant Application Rates Clean-Dry Unconfined < 0.0001 Significant Application Rates Clean-Dry Confined < 0.0001 Significant Trackless Application Rates Dusty-Dry Unconfined < 0.0001 Significant Application Rates Dusty-Dry Confined < 0.0001 Significant tables, all cases except one indicated that tack coat types and around 0.062 gal/yd2. Similar trends were noted at a confine- application rates had significant effects on the measured ISS. ment pressure of 20 psi. For the residual application rates Figure 61a presents the variation of ISS with emulsified tested, it was not possible to determine the optimum residual tack coat types and residual application rates. The results were application rate. This may be attributed to the highly oxidized obtained from clean and dry specimens with no confinement HMA surface at the PRF site, which required greater tack coat at 25C. For each residual application rate, the trackless tack rates than expected. It may also indicate that, under actual coat exhibited the highest shear strength and CRS-1 exhibited field conditions, optimum residual application rates may be the lowest. Trackless and SS-1h yielded similar and higher greater than that commonly predicted from laboratory-based ISSs than CRS-1 at the low residual application rate--that is, experiments. While higher residual application rates may 0.031 gal/yd2. increase ISS, excessive tack coat may migrate into the HMA All tack coat materials showed the highest strength at a mat during compaction, causing a decrease in the air void residual application rate of 0.155 gal/yd2. Shear strength of content of the mix. Figure 61b presents the variation of the SS-1h and trackless consistently increased as residual appli- measured air voids of the overlaid mixture for each residual cation rate increased. In contrast, measured shear strength application rate. As shown in this figure, the increase in residual for CRS-1 appeared to stabilize at a residual application rate tack coat application rate was associated with a decrease in air Table 21. Statistical analysis of the effects of tack coat types on ISS. Rate Statistical Test Condition Confinement P-value Results Tack Coat Type Clean-Dry Unconfined 0.0022 Significant Tack Coat Type Clean-Dry Confined 0.0032 Significant 0.031 Tack Coat Type Dusty-Dry Unconfined < 0.0001 Significant Tack Coat Type Dusty-Dry Confined 0.0027 Significant Tack Coat Type Clean-Dry Unconfined 0.0004 Significant Tack Coat Type Clean-Dry Confined < 0.0001 Significant 0.062 Tack Coat Type Dusty-Dry Unconfined < 0.0001 Significant Tack Coat Type Dusty-Dry Confined < 0.0001 Significant Tack Coat Type Clean-Dry Unconfined < 0.0001 Significant Tack Coat Type Clean-Dry Confined < 0.0001 Significant 0.155 Tack Coat Type Dusty-Dry Unconfined < 0.0001 Significant Tack Coat Type Dusty-Dry Confined < 0.0001 Significant