OTHER INPUT VARIABLES: TRAFFIC AND ENVIRONMENTAL

This paper reviews the state of knowledge resulting from laboratory research into the phenomenological characterization of fatigue behavior. In particular, it considers the influence of various factors that affect the fatigue performance of asphalt mixes. The definition of laboratory service life and the values obtained depend on the method of testing; controlled stress loading appears to be applicable for materials used in thick asphalt construction, and controlled strain loading is more appropriate for thin layers. An equation characterizing fatigue performance is presented. Under controlled stress conditions, mixes having maximum stiffness will give longer lives; and, therefore, the choice of mix composition should be such that under compaction maximum tensile stiffness associated with minimum voids is obtained. Under controlled strain condition, longer lives are likely to be obtained from more flexible, less stiff materials. Ideally, general strain-life relations can be established for various mixes by laboratory testing and used for design purposes. Alternatively, use may be made of empirical relations relating fatigue performance to mix properties. /Author/