Application of time-temperature superposition principle to pull-off tensile strength of asphalt tack coats

Abstract

Flexible pavements are multilayered structures that are designed to withstand vehicular traffic and thermal loading. Tack coat provides the bonding between these multilayers, which is a critical mechanism to provide a pavement with the monolithic action of asphalt layers to resist traffic and thermal loading, thereby dictating the pavement’s service life. Asphalt binder bond strength (BBS) is an indicator that can be used to evaluate the interlayer bonding ability of tack coat and changes as a function of temperature and loading rate. The focus of this paper is to prove that the time-temperature superposition principle is applicable to the BBS of various tack coat materials. In order to achieve this goal, BBS and dynamic shear rheometer (DSR) tests were conducted on four different tack coats, CRS-2, CRS-1h, NTCRS-1hM, and Ultrafuse. The Pneumatic Adhesion Tensile Testing Instrument (PATTI) was used to determine the BBS at 13 different temperatures ranging from 5 °C to 53 °C. The BBS data showed that adhesive failures between the binder and pull stub of PATTI caused the drop of BBS below 5 °C to 15 °C for hard (CRS-1h) and Non-tracking (NTCRS-1hM, Ultrafuse) tack coat. In addition to the BBS test, DSR tests were performed on the emulsion residue to measure the time-temperature shift factors at the reference temperature of 20 °C. It was found that the time-temperature shift factors determined from the DSR tests could be successfully used to shift the BBS vs. stress rate curves to construct the mastercurve for all four tack coat materials at a residual application rate of 0.14 L/m2 (0.03 Gal/yd2) as long as the BBS test exhibited cohesive failure between the binder and pull-off stubs. A simple method based on the BBS values at two temperatures is proposed to predict the mastercurve for routine characterization of the BBS mastercurve. No definite trend in the BBS mastercurve emerged among the different tack coat application rates for the different tack coats.