An investigation of fracture properties and size effects of concrete using the EPSI technique

In order to study the size effect in concrete fracture, three-point bending tests are performed on five groups of geometrically similar concrete beams. The electronic speckle pattern interferometry (ESPI) technique is used to measure the full-field deformation of concrete beams. Crack opening displacement data, which is crucial for understanding crack initiation and the evolution mechanism, but which is not readily available through conventional measurement techniques, is obtained. Fracture parameters of five groups of concrete beams, including the critical crack opening displacements (i.e. CMODc and CTODc) and crack growth lengths (i.e. a(c) and a(e)) at the peak, fracture toughness (K-Ic), fracture energy (G(F)) and nominal strength (sigma(N)), are determined. The influences of beam depth on the fracture parameters of concrete are evaluated and discussed. The results show that the CMODc, CTODc, a(c), a(e), K-Ic and G(F) increase with the increase in beam depth, while sigma(N) has a decreasing trend that follows the size effect law. Size-independent fracture toughness and fracture energy are estimated and proposed.