Triaxial failure criterion and multi-scale failure mechanism of hybrid steel fiber reinforced self-compacting concrete

The application of hybrid steel fiber reinforced self-compacting concrete (HSFRSCC) contributes to promoting the pouring quality and ductility of tunnel precast segments. During the stage of assembly and service, precast segments are inevitably in the complex stress state of compression, bending and shear. However, there were very limited studies on the multi-axial failure performance and mechanism of HSFRSCC. In the present research, three types of cylindrical specimens with different skeleton volume fraction (SVF) of 58 %, 60 % and 62 % were prepared to perform triaxial compression test, all of which were loaded under the confining pressures of 0, 2, ..., 14 MPa respectively. The triaxial failure criterion for HSFRSCC was established, including the formulas of triaxial compression strength, compression meridian and deviatoric plane trace. Based on the above quantitative evaluation, 62 % was proved as the optimal SVF and 19.5 % was determined as the best lateral-axial stress ratio. Through the mechanical analysis, X-ray computed tomography (CT) test and scanning electron microscope (SEM) test, the influence of confining pressure, aggregate and steel fiber on triaxial failure mechanism was elucidated from the multiscale aspects. The triaxial failure patterns of HSFRSCC were divided as five types and mainly governed by the confining pressure. The strengthening effect of steel fiber and the synergistic effect between aggregate and steel fiber were exposed and validated by the CT and SEM images. This work can comprehensively evaluate the failure behavior of HSFRSCC under complex stress, and provide a basis for the precise design of precast segments.