Structural and material properties of Mini notched Round Determinate Panels

Large use of shotcrete, especially in mining and underground operations, pushed the introduction of the Round Determines Panels (RDP) test as an effective design tool for the required toughness of the concrete mix. Nevertheless, structural more than material properties can be obtained from it and there are serious concerns related to safety of experimental operations and to their costs. In order to overcome these flaws, a recent study introduced the mini notched RDP test and showed that it is possible to correlate the energy absorbed by RDP samples with equal thicknesses but different diameters. Along this line, the present study focuses on the influence of the thickness of RDP samples on their toughness; an experimental campaign has been carried out, showing that the absorbed energy is thickness-dependent; in order to validate the results, a simple analytical model has been developed, able to provide for a direct relation between the absorbed energy and the material fracture energy. As a consequence, a new design procedure based on these findings has been proposed, allowing for the use of conventional designing tools together with the mini notched RDP test. Finally, hypothesis introduced in the analytical model have been verified both experimentally and by means of a non-linear numerical model.