An asphalt overlay is one of the primary options for rehabilitating existing asphalt and concrete pavements. Reflection cracking, however, has been a serious concern associated with asphalt overlays for a long time. Currently, reflection cracking is not considered in most existing asphalt overlay thickness design programs including the Mechanistic-Empirical PavementDesign Guide (MEPDG) developed under the NCHRP Project 1-37A. Therefore, there is an urgent need to develop a reflection cracking-based asphalt overlay thickness design and analysis tool for routine use. This paper firstdiscusses three reflection cracking mechanisms (bending, shearing, and thermal stress) and mechanistic modeling using fracture mechanics concepts.In this study, an M-E reflection cracking model was first proposed and developed into an asphalt overlay thickness design and analysis framework. This framework was further implemented into a Windows-based design program, making it more convenient for pavement engineers to optimize asphalt overlay thickness design based on a) traffic, b) climate conditions, c) existing pavement structure and conditions (e.g. load transfer efficiency [LTE]at joints), and d) asphalt overlay alternatives (such as single or multi-layer overlays, binder type and mix type selection). Furthermore, a sensitivity analysis was performed, and five key performance factors identifiedare 1) traffic loading level, 2) climate, 3) asphalt overlay thickness, 4) overlay mix type, and 5) LTE at joints/cracks. These five factors must be considered when designing an asphalt overlay.
Abstract