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45 80 % of Yes Respondents 60 40 20 0 Time of Roadway Roadway Ambient Day vs. Traffic Use Subsequent Year Type Condition Temp. Night Overlay Thickness Responses Figure 47. Reason for tack coat rate change. 100 80 % of Respondents 60 40 20 0 Remove Reapply Price Ask Require Nothing Deduction Contractor Improved not to Repeat Next Pass Responses Figure 48. Steps to correct poor application of tack coat. test, Texas pull-off test, and Florida shear test are some of of the procedures listed for testing the quality of tack coat the laboratory and field test methods being used to quantify materials are residual percentage test; traction test; penetra- interface bond strength between pavement layers. tion test on the residual asphalt; AASHTO M 208, Cationic Emulsified Asphalt (39); and oil distillate test. Quality of Tack Coat Materials Current Research Related to Performance Only 18% of the responses indicated they use a field or of Tack Materials laboratory test to evaluate tack coat material quality. Some Of the respondents, 37% reported that their state or coun- 100 try is conducting or has recently conducted research on tack coat performance. % of Respondents 80 60 4.2Experiment I: Development of 40 a Test Device to Evaluate the Quality of the Bond Strength of 20 Tack Coat Spray Application in 0 the Field Slippage Delamination Fatigue Top-down Rutting Other Cracking Cracking The Louisiana Transportation Research Center (LTRC) Responses and InstroTek, Inc., manufacturer of the ATackerTM, part- Figure 49. Failures attributed to improper tack nered to develop the Louisiana Tack Coat Quality Tester application or type. (LTCQT), which was developed in this project to evaluate the