The Absolute Rate Theory (ART) allows a fundamental approach to fatigue characterisation of asphaltic mixes. In ART, material is considered on the molecular level: bond forming and bond breaking processes are described in which fatigue and crack growth properties depend on microscopic interactions between mix components. The rate is the change in time of the potential number of bonds participating in process. It is a statistical theory of rate processes, designed to deal with structural changes at molecular level during permanent deformation and/or fracture. The results from the first use of ART in which account was taken of temperature in describing deformation of bitumen under shear stress, showed that ART can potentially describe the behaviour of bitumen accurately. This paper describes ART and the determination of ART parameters for AC mixes regarding fatigue and crack growth. Main conclusions are: (1) A large advantage of ART is that it involves thermodynamic material properties; (2) The crack initiation phase can be described by one bond forming and one bond breaking process, while the crack propagation phase involves three parallel processes, cohesive crack growth, adhesive crack growth and a crack retardant process; (3) Differences in crack growth properties are explained by free activation energy; and (4) Free activation energy determined by ART is close to energy which bonds bitumen to aggregate.
Abstract