Impact of Emulsion Type, Application Rate, and Adverse Construction Conditions on Tack Coat Performance

The tack coat is a bonding agent applied between new and existing asphalt pavement layers. Roadway construction operations inherently introduce adverse conditions, such as dust on the pavement surface and nonuniform coverage (streaking), which can compromise tack coat bond quality. Climatic conditions such as heavy rainfall also create issues late in the construction season. Newly developed engineered tack coat emulsions, which utilize stiff asphalt binders and polymer modifiers, are purported to improve interlayer bonding characteristics and reduce the propensity of early fatigue cracking and pavement failure. This study evaluates engineered tack coats against conventionally used tack coats in a laboratory setting to identify their benefits when subjected to different pavement surface types, application rates, and commonly experienced adverse roadway construction conditions. Monotonic direct shear testing was employed to characterize interlayer bonding using two response parameters, interlayer shear strength and interlayer bond energy. This study advances the knowledge of engineered tack coat performance under real-world conditions and also employs a laboratory sample preparation methodology that is representative of pavement construction in the field.