Direct validation of 3D meso-scale fracture modelling of UHPFRC by in-situ micro X-ray CT wedge-split tests and parametric studies

3D meso-scale finite element models of ultra high performance fibre reinforced concrete (UHPFRC) based on in-situ micro X-ray Computed Tomography (CT) images are developed and validated in this study. The CT images at 16.9 mu m voxel resolution from a progressive wedge-split test were converted into meso-scale 3D tetrahedron meshes. The short fibres, embedded in the mortar matrix, were modelled by truss elements with equivalent elastoplastic constitutive laws transformed from single fibre pullout load-displacement curves, so as to indirectly model the fibre-matrix interfaces. A concrete damage plasticity model was used to simulate damage and fracture in the mortar. The simulated load-displacement curves, final crack patterns, and loadcrack opening curves were found in good agreement with the in-situ CT test results, and the non-vertical crack path was significantly affected by the overall orientation of fibres bridging the crack. Further simulations with all the fibres perpendicular to the tensile splitting direction showed that the peak load and fracture energy increased by 42 % and 45 % respectively from 1 % to 3 % fibre volume fraction. This indicates the need to optimize the fibre orientation for best mechanical performance according to the loading conditions.