Effects of Pavement Surface Type and Sample Preparation Method on Tack Coat Interface Shear Strength

The objective of this study was to quantify the effects of tack coat type, tack coat application rate, and surface type (i.e., hot-mix asphalt versus portland cement concrete) including milled versus unmilled surfaces on the interface shear strength based on full-scale test application. The variation of interface shear strength between field- and laboratory-prepared samples was also investigated. To achieve this objective, five types of tack coat materials were applied at three application rates on four types of surfaces at the Pavement Research Facility site of the Louisiana Transportation Research Center. Samples were cored from the constructed test lanes, and the interface shear strength was measured using the Louisiana Interface Shear Strength Tester. Results of this study showed that a direct relationship was observed between the roughness of the existing surface and the developed shear strength at the interface. A small amount of water seemed to negatively affect interface shear strength with PG 64-22 used as a tack coat material. However, the effect of surface wetness on interface shear strength was less evident for emulsion-based tack coat materials. Laboratory-prepared samples grossly overestimated the interface shear strength when compared with field-extracted cores. While a decreasing trend was observed in the laboratory, an increasing trend in the measured interface shear strength was observed in the field.