Fatigue Performance and Prediction Model of Multilayer Deck Pavement with Different Tack Coat Materials

Concrete bridge decks overlaid with asphalt wearing courses often witness early distresses, such as shoving, potholes, raveling, and slippage cracking resulting from poor bonds between the two layers with different modulus. Frequently used laboratory tests, including direct shear test, pull-off test, and torsional shear test, can not fully represent the critical conditions happening in the fields. In this study, a shear fatigue test under repetitive loads at an angle of 45° was developed instead. Three tack coat materials, including styrene–butadiene–styrene-modified asphalt, emulsified asphalt, and epoxy resin, were chosen as binding materials to form multilayer deck pavement specimens. Their performances were evaluated through shear fatigue test on a universal test machine. The shear stress and shear displacement of each specimen at failure were first identified, and then four levels of stress were selected to perform the shear fatigue test, based on which a fatigue prediction model was developed. To approximate the laboratory results to field load scenarios, an adjustment factor, representing the impacts of different load combinations on fatigue life, was introduced. The study showed that epoxy resin material has a remarkably superior shear fatigue performance compared with the other two, and the adjustment factor is heavily affected by the load combinations.