An explanation for rate effect of concrete strength based on fracture toughness including free water viscosity

This paper deals with the dynamic fracture initiation toughness of concrete with consideration of free water viscosity and inertia effect. In this paper, a crack in an infinite solid subjected to linear loading normal to the crack surface is considered accounting for these two effects. Results are obtained for the relationships between the dynamic fracture initiation toughness and the fracture initiation time, and between the dynamic strength enhancement and the strain rate, both with and without considering free water. A comparison between the theoretical result and the experimental data in the literature indicates that a good agreement is achieved, which implies that the model can be used to explain the rate-dependent properties of concrete.