Quantitative Measurement of Tackiness and Bonding Potential of Trackless Tack Coat

Abstract

Application of tack coats prior to placement of a thin overlay is a prerequisite to bond between the existing and the overlaid layers. Although a conventional tack is appropriately applied to the surface, this material is likely to be picked up and contaminated by construction traffic. Trackless tacks, recently introduced to paving industries in Texas, have overcome such issue by minimizing tackiness. However, there is no specification and documentation for tackiness and bonding potential of various trackless tacks in the Texas Department of Transportation. Also, a damage model for tackiness is needed to characterize the fracture properties of the tacks. The main objectives of this study were to 1) investigate the material characterization of trackless tacks, 2) evaluate the bonding potential of trackless tacks, and 3) develop a predictive model for the tracking behavior based on a fundamental fracture theory. Six different products were used in this study. The rheological and viscoelastic properties of trackless tacks were identified using the frequency sweep test and the multiple shear creep recovery test. The contact angle was measured to determine the surface energy characteristics. Also, the tackiness was measured at different temperatures and debonding rates using the Dynamic Shear Rheometer tackiness test and quantified in terms of tack energy. Also, the bond strength and bond energy of trackless tack coats were measured in bonded pavement layers through laboratory and field testing for evaluation of their bonding potential. The results were used to classify the trackless tack coats based on their stiffness in terms of complex shear modulus. The stiff binder group showed to have lower sensitivity of non-recoverable creep compliance and percent recovery to stress level and better tracking resistance than the soft binder group. The curve of the tack energy varying bonding/debonding rates and temperatures could be fitted with a power law. Through a shear test, the surface type, tack type, and reactivation temperature were identified to be the dominant parameters that influence on bonding potential. Using the modified Paris’s law, the fracture properties of tack residue could be obtained from the tackiness test of tack materials.