Scanning electron microscopy in conjunction with the replica technique gives a new insight of the fracture process zone in mode I crack propagation for mortar and concrete. Results lead to presume that during the crack opening, the across the crack…
Scanning electron microscopy in conjunction with the replica technique gives a new insight of the fracture process zone in mode I crack propagation for mortar and concrete. Results lead to presume that during the crack opening, the across the crack surfaces is an important source of energy dissipation which can explain the size dependence which affects the experimental specific fracture energy. We propose a simple model which describes the experimental specific fracture energy as the sum of the energy necessary for the crack propagation in Griffith's sense and the one due to the friction effect which induces a restrained widening of the crack. The validation of the model has been carried out by means of three point bending tests on notched beams. We varied the length of the specimen ligament and the roughness of the crack path which governs the friction effect. The RILEM TC-50 procedure gives experimental results which are in good agreement with the ones predicted by the proposed model.