Reflection Cracking–Based Asphalt Overlay Thickness Design and Analysis Tool

Abstract

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 Pavement Design Guide 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. Three reflection cracking mechanisms (bending, shearing, and thermal stress) and mechanistic modeling are discussed according to fracture mechanics concepts. A mechanistic–empirical reflection cracking model is first proposed and then developed into an asphalt overlay thickness design and analysis framework. This framework is further implemented into a Windows-based design program, making it more convenient for pavement engineers to optimize asphalt overlay thickness design on the basis of (a) traffic, (b) climate conditions, (c) existing pavement structure and conditions (e.g., load transfer efficiency at joints), and (d) asphalt overlay alternatives (e.g., single or multilayer overlays, binder type, and mix type selection). A sensitivity analysis is also performed, and five key performance factors are identified: (a) traffic loading level, (b) climate, (c) asphalt overlay thickness, (d) overlay mix type, and (e) load transfer efficiency at joints or cracks. These five factors must be considered when designing an asphalt overlay.