3D Printing Ultra-High-Performance Fiber-Reinforced Concrete under Triaxial Confining Loads (2021-12)¶

3D-printing concrete structural members may experience complex stress states, while external reinforcement (wrapping steel tube or fiber-reinforced polymer) may be one of the effective ways to improve performance. Therefore, triaxial mechanical properties of 3D-printing concrete should be explored. This study presents an experimental investigation of the triaxial behavior of 3D-printing ultra-high performance fiber-reinforced concrete (3DP-UHPFRC) loaded in the Z-direction. Mold-casting ultra-high performance fiber reinforced concrete (MC-UHPFRC) was used as the reference specimen. Based on the test data, the failure mode and mechanical properties of the 3D-printing specimens were analyzed, and the failure criteria were explored. The experimental results showed that 3DP-UHPFRC possessed triaxial failure modes, mechanical properties, and failure criteria as MC-UHPFRC. All 3DP-UHPFRC specimens exhibited oblique shear cracks under triaxial compression. The fitting effect of Mohr-Coulomb failure criterion on 3D-printing specimens without steel fiber is poor (R2 is less than 0.9), which is due to the linear relationship of Mohr-Coulomb failure criterion and the obvious nonlinear increase in strength of 3D-printing specimens without steel fiber with the confining pressure, whereas the Power-law and Willam-Warnke failure criteria were good for all 3D-printing specimens. A modified model was established for predicting the stress-strain curves of 3DP-UHPFRC under triaxial confining pressure.