Mechanical anisotropy of ultra-high performance fibre-reinforced concrete for 3D printing

In this study, a novel 3D-printing ultra-high performance fibre-reinforced concrete (3DP-UHPFRC) was developed. The effect of fibre content, fibre type and printing direction on the mechanical properties of 3DP-UHPFRC was evaluated through compressive, flexural, splitting tensile and uniaxial tensile tests, and the anisotropic properties of 3DP-UHPFRC were investigated. The experiment results indicated that 3DP-UHPFRC prepared with 1 vol% 6 mm steel fibre was more suitable for construction than 3DP-UHPFRC prepared with 1 vol% 10 mm steel fibre under the printing conditions in this test. The maximum flexural strength of 3DP-UHPFRC with 1 vol% 6 mm steel fibre reached 45.21 MPa in the Z-direction (printing direction), which was substantially higher than those obtained in previous studies. The flexural and splitting tensile failures of 3DP-UHPFRC could be either ductile or brittle in different directions; thus, the printing mode could be flexibly adjusted according to different engineering requirements. The latest test results indicated that the compressive elastic modulus was anisotropic, but there was little difference in the tensile elastic modulus in each direction.