Determination of specimen-size independent fracture toughness of plain concrete

Synopsis Simple analytical expressions are proposed for determining the critical stress intensity factor K c , and the critical energy release rate G c , of plain concretes in three-point bending. These expressions take into account the slow crack growth preceding fracture and the complex state of stress existing at a propagating crack front. The fracture toughness so determined is shown to be essentially independent of the test specimen dimensions and to depend only on the mix variables. It is also argued that unlike K c , or G c , the fracture energy G F of plain concretes is strongly dependent on the test specimen dimensions. It is therefore advisable to express the fracture toughness of plain concretes through the specimen-size independent parameters K c , or G c .