Investigation of the Printability and Mechanical Properties of 3D Printing UHPC

The preparation and performance optimization of concrete materials is the key of 3D printing (3DP) construction technology. The research of 3D printing ultra-high performance concrete (3DP-UHPC) can promote the popularization and application of this technology. Ultra-high performance concrete (UHPC) belongs to the pseudo-plastic fluid, and shear thickening occurs under the compression, which is not conducive to 3D printing. In this paper, a modified method of cement-based composite material, which is controlled by chemical acceleration and physical flocculation, was proposed to optimize the mix proportion of sulphoaluminate cement, cellulose and clay, and to promote the gradual change of UHPC flow pseudo-plastic fluid to bingham fluid, so as to prepare 3DP-UHPC material. The basic mechanical properties of the printing material, such as compression, tensile and bending, were tested and the micro morphology was analyzed. The results show that, adjusting the acceleration/flocculation (A/F) radio is helpful to optimize the 3D printability of UHPC and enhance the mechanical properties of UHPC. When the mass fraction of sulphoaluminate cement instead of Portland cement is 10%, the fluidity is controlled in the range of 180-200 mm, and the A/F ratio meets the corresponding 3D printable performance requirements. 3DP-UHPC has compressive strength of 129.6 MPa, bending strength of 16.3 MPa, tensile strength of 4.6 MPa and ultimate tensile rate of 1.2%. The printing process is beneficial to the formation of directional distribution of steel fiber and the improvement of toughness of UHPC. © 2021, Materials Review Magazine. All right reserved.