ABSTRACT
Abstract From the universal principles of the Thermodynamics of dissipative continuous media, a general formalism embodying various kinds of dissipative mechanisms of various origins that may be involved in the failure of micro-cracked granular composites like cement or bituminous concretes without prejudicial assumptions about the crack tip behaviour is presented. The emphasis is given to the determination of the structural factors and materials parameters that can be responsible for fast and far running crack propagation. It is shown that the latter obeys scaling laws that are, in many cases, antagonist of the ones governing the peak-load. Keywords: Concrete, Fracture, Continuum Thermodynamics, Crack Propagation, Unstability, Size-Effects, Scaling laws.
1 Introduction Application of Fracture Mechanics to concrete has developed on a wide scale only in the recent past. It has been observed rather soon that the most elementary tools of Fracture Mechanics, as first elaborated for glass by Griffith [1] and then - in the forties - for ceramics and metals by Orowan and Irwin, were not directly applicable to a strongly heterogeneous material like concrete. This - together with the fact that structural engineers were generally more acquainted with the theory of Plasticity than with Fracture Mechanics - has resulted in the proliferation of a large number of approaches, concepts and models, like the effective - or cohesive - crack model, the blunt crack model, the Fracture Process Zone model, the smeared crack model, the bridging crack model, etc. - extensively described in the literature, see for instance [2 -7] for some of the recent accounts, but among which it may be difficult to make a choice for a given practical case. In some instances, it has even been stated that classical Fracture Mechanics cannot at all be applied to concrete materials and structures. One main purpose of this paper is to show that - when applied at their
