Review of fatigue models for concrete airfield pavement design

Most concrete airfield pavement design procedures are based on developing sufficient slab thicknesses to resist fatigue cracking, that is, structural cracking caused by repeated load applications at stress levels less than the ultimate static strength of the concrete. At the heart of these design procedures is a concrete fatigue model, which relates slab stress conditions (expressed in terms of a stress-to-strength ratio) to the allowable number of load repetitions to a pre-defined "failure" level. Although a variety of fatigue models are available for use in concrete airfield pavement design, each provides different results, largely because of the differences in the way that they were developed. As a result, one fatigue model can not be simply substituted for another in a given design procedure. This paper presents a summary of the characteristics of some of the common fatigue models used in concrete airfield pavement design. The background and basis for the development of each model are described, highlighting some of the assumptions and limitations inherent in their development. The focus of the discussion is on the development and basis of the fatigue models themselves, and not on the development and basis of the design procedure in which they may be a part. Such information is of value to pavement design practitioners in both developing effective new concrete airfield pavement designs and in conducting meaningful mechanistic "checks" of pavement designs.