Development of Test Procedures to Measure Tracking Resistance of Non-Tracking Tack Coat

Non-tracking tacks, recently introduced to the paving industry, bond pavement layers while avoiding the tracking problems associated with traditional tacks. Initially, there was only one supplier of non-tracking tack in Texas, but now multiple producers are bringing products to the market. Performance to date has been good, but there are no established methods to test tackiness/tracking resistance of current and new products. The objective of this research, therefore, was to develop and assess three tests for measuring tracking resistance: the modified no-pick-up time test, the TTI sand adhesion test, and the modified DSR tackiness test. These methods were evaluated on four tack materials, three curing temperatures, and at 10-minute curing time intervals. The results from the modified no-pick-up time test were clearly influenced by curing time and curing temperature. The TTI sand adhesion test could discern among different tack materials. Track free time may be defined as less than 2 g of sand adhesion. The modified DSR tackiness test showed measurable differences among the tack types and different temperatures and times. Of these test methods, the researchers recommend adoption of the modified no-pick-up time test for routine tracking resistance testing. “Track-free time” should be defined as less than 10% tracking in 40°C curing. Testing of this and other tests should continue, especially with other conventional and non-tracking tacks.