Influence of Asphalt Mixture Stiffness on Fatigue Failure

This paper examines the question of an appropriate failure criterion for asphalt fatigue characterization. The results presented are based on cyclic fatigue tests and obtained from three mixtures containing different penetration grade bitumens from one and the same source. The mixtures are tested at 0, 10, and $20°C$ using uniaxial testing (tension/compression) on cylindrical samples. It is found that failure can be demonstrated by studying the evolution of the strain field using three parallel extensometers (separated by $120°$ around the specimen). The failure arises from coalescence of microcracks (damage 1ocalization). The decrease in stiffness at failure is related to mixture stiffness, where stiff materials (low temperature and/or mixtures containing low pen grade binder) show comparatively small decrease. A statistical approach based on fatigue tests carried out at different temperatures is suggested, an approach which uses stiffness degradation as a measure of critical fatigue stiffness. The advantage of such a failure criterion compared to the classical failure criterion (decrease in stiffness by 50%) for different temperatures is discussed. Using the proposed criterion, higher consistency in results is achieved compared to results obtained using the classical failure criterion.