A Recursive Pseudo Fatigue Cracking Damage Model for Asphalt Pavements

Abstract

Bottom-up fatigue cracking in asphalt pavements is a complex distress mechanism influenced by traffic, structural and environmental conditions. Fatigue damage itself changes the properties of the asphalt concrete (AC), which affects a pavement’s structural capacity. Most fatigue cracking damage models neglect damage induced-changes in the AC. Also, the complexity of the distress mechanism has culminated in intricate models unsuitable for routine application. This study developed a simple recursive model that simulates fatigue cracking damage more realistically by accounting for damage-induced changes in AC. The proposed pseudo fatigue cracking damage model, premised on layered elastic theory, is a strain-based phenomenological model that implements incremental-recursive damage accumulation without the need for transfer functions, a key limitation of conventional mechanistic-empirical fatigue models. The model has two key assumptions: fatigue damage causes deterioration of AC modulus, and critical tensile strain at the bottom of the AC layer is a fatigue damage determinant. Bending beam fatigue testing, an established laboratory method for simulating bottom-up fatigue cracking, was the foundation for the pseudo fatigue damage model’s development. The data comprised of 151 beam fatigue test results from 20 different AC mixtures constructed at the National Center for Asphalt Technology Pavement Test Track. A functional form was identified for the pseudo fatigue cracking damage model which, after calibration and validation, demonstrated good predictive capability for measured beam fatigue curves. The model inputs are the initial AC modulus, fatigue endurance limit, initial critical strain at the AC layer bottom and a failure criterion (reduction in initial AC modulus). The model simulates a pavement system in WESLEA, a multilayered analysis program, to generate a fatigue damage curve. Upon field validation, the pseudo fatigue damage model can be incorporated in mechanistic pavement design procedures. The pseudo fatigue damage model, by eliminating transfer functions and considering damage-induced changes in AC, represents considerable progress toward full-mechanistic fatigue analysis, a major goal of asphalt pavement research.