Prediction of fatigue life of asphalt concrete beams

Fatigue cracking due to repeated loading has been recognized as an important distress problem in asphalt concrete (AC) pavements. The development of fatigue laws to describe the AC beams has been carried out through two main approaches: a phenomenological approach and a fracture mechanics based approach. However, both approaches, at the present time, employ regression constants that cannot truly reflect basic material properties. The primary purpose of this paper is to develop a fracture-mechanics-based fatigue law which utilizes fundamental material parameters including fracture toughness, flexure tensile strength, as well as two other physically quantifiable model parameters: damage parameter, alpha, and critical plastic zone length, delta(c). The development of a two-stage plastic zone model is presented, followed by the derivation of a fatigue crack growth law. The significance of the damage parameter, alpha, and critical plastic zone length, delta(c), is emphasized, with a detailed discussion of the method to determine these parameters. The developed fatigue model is used to predict fatigue life of AC beams fabricated from a wide spectrum of mixture designs. The developed fatigue model predicts a much faster crack growth rate compared to the Paris law, and appears to be more sensitive to the ratio of the initial stress intensity factor over its critical value (K-0/K-c). Copyright (C) 1997 Elsevier Science Limited.