FRACTURE ENERGY AND FRACTURE-TOUGHNESS OF CONCRETE

The stress intensity factor for a specimen used for fracture toughness testing of cementitious materials was obtained by the finite element method using isoparametric representations and two energy approaches. A range of specimen geometries were considered and the critical strain energy release rate G(c) and critical value of an energy integral J(c) were evaluated using the failure loads obtained from laboratory tests. For linear elastic conditions G(c) is equivalent to J(c), and both quantities are regarded as the energy required to produce unit extension of the pre-existing crack. It is found that the fracture energy and the fracture toughness are independent of the specimen geometry. The fracture energy G(c) of the concrete employed in the tests is approximately 16 N m/m(2). This corresponds to a fracture toughness K-c of 0.7 MN/m(3/2), which is 40% greater than that reported in an earlier paper.