Restrained crack widening in mode I crack propagation for mortar and concrete

Microscopical observations and macroscopical investigations of the crack propagation process have been carried out. They give a new insight into the fracture process zone, leading one to presume that during the crack propagation the crack opening is restrained. So, the crack opening cannot increase without an energy dissipation that has to be added to the one from the crack propagation. Generally, measurements of fracture energy per unit of crack surface give rise to size dependent values for mortar and concrete. We propose a simple model that takes into account the energy dissipated by restrained crack widening (RCW), with the aim to verify if it can explain the size dependence on the energy dissipated per unit of crack surface. The theoretical predictions from the proposed model and the experimental dissipated energy per unit of crack surface obtained by means of RILEM TC-50 procedure are in good agreement. So, size dependence could be mainly explained through the concept of RCW.