Determination of the back boundary effect on self-compacting concrete beams: bilinear and trilinear approaches

In order to understand the fracture processes in concrete, size-dependant (\(G_f\)) and size-independant (\(G_F\)) fracture energies both need more focus. In the literature, bilinear and trilinear models based on both fracture energies are proposed to separate the unnotched ligament length into inner and outer regions. The applicability of linear elastic fracture mechanics depends on the extent of these inner and outer regions. This study explores the suitability of applying bilinear and trilinear models in the separation of the inner and outer regions by using the experimental results from self-compacting concrete beams. The size-independent fracture energies obtained from bilinear and trilinear models are found to be comparable across the mixes for the two sizes considered. For a large sized beam, the inner region obtained by both the models shows huge variation, whereas the values are comparable for a small sized beam. Acoustic emission results are also presented in support of the boundary effect.