Size independent fracture energy of concrete

It has been confirmed by many authors that the specific fracture energy of concrete determined by laboratory experiments depends on the shape and size of the specimen because the local energy in the fracture process zone is influenced by the free surface of the specimen. As the crack propagates towards the back face of the specimen the shape of the fracture process zone changes having a direct impact on the local fracture energy. In this paper, the authors present an original local fracture energy concept within a framework of effective crack model. Within this model the crack is modeled as an “elastically equivalent notch” with a depth equal to the effective crack length ae. The local fracture energy can be – within this model – determined using three-point-bend tests as a derivative of energy release rate with respect to the effective crack length ae. As long as the local fracture energy exhibits a plateau, size-independent fracture energy can be determined. The main advantage of suggested method is that it does not require (contrary to other methods) testing of many samples of different shapes, sizes or notch to depth ratios, thus greatly simplifying the determination of the size independent fracture energy.