Effects of Temperature on Interface Shear Strength of Emulsified Tack Coats and Its Relationship to Rheological Properties

The objective of this study was to investigate tack coat interface shear bond characteristics at various temperatures and to relate tack coat characteristics in the field to the rheological test results in the laboratory. Interface shear strength (ISS) of two emulsified asphalt tack coats (CRS-1 and trackless) was evaluated at temperatures ranging from −10°C to 60°C. Two emulsified tack coats were applied on full-scale pavement test sections at application rates of 0.14, 0.28, and 0.70 L/m². Cores were then extracted from the full-scale test sites to be tested in the laboratory while simulating different field conditions. Tests were conducted with a newly developed direct shear device. The binder grade for the residue of CRS-1 emulsion was PG 58-28. The high temperature grade for the residue of the trackless emulsion was PG 82. Trackless material was brittle at a low temperature, and its low temperature PG grade could not be determined. Within the evaluated temperature range, the ISS of the tacked interface increased with the decrease in temperature. Generally, bonding performance, as measured by the ISS, of the trackless emulsion was superior to CRS-1 emulsion, specifically at temperatures greater than 40°C. In addition, results show that interface shear strength for both tack coat materials at each application rate increased with an increase of the binder rheology parameter G^*/sin δ. This relationship can be used to establish a laboratory design threshold for this parameter, to ensure that the selected application rate and tack coat material will perform adequately in the field.