Effects of Trackless Tack Interface on Pavement Top-down Cracking Performance

Tracking, the pick-up of bituminous materials by paving equipment tires, can occur when tack coat emulsion was not appropriately applied. This tracking can result in the existing pavement with little or no tack coat left in the wheel paths, leading to slippage and delamination. A special tack coat material, trackless tack, which does not track or pick up on paving equipment, has been developed. While researches have been conducted on the trackless tack shear strength evaluation, little work has been done on its cracking performance. Interface cracking performance of one type trackless tack at two application rates was evaluated using the composite specimen interface cracking (CSIC) test. The testing system involves repeated tensile loading and monitoring of the rate of damage development (reduction in stiffness) on composite specimens. Results indicated that trackless tack interface reduced the pavement top-down cracking performance as compared with conventional tack coat. However, it was reported in literature that trackless tack had superior shear strength than conventional tack. Therefore, it can be concluded that both shear strength along the interface and cracking resistance across the interface should be evaluated for any interface bond agents.