Introducing Cement Composite Agents During Printing Process to Enhance the 3D-Printed Concrete Interfaces Between Layers and Filaments (2025-12)¶

Interface deficiencies between layers and filaments remain a significant challenge for 3D-printed concrete (3DPC). In this study, three methods with expansion agent (EA) modified cement composite agents were proposed: (1) brushing the interlayer interface slurry, (2) pre-filling inter-filament channel voids during printing process, and (3) combining the use of these two methods. 0 %, 3 %, 6 %, and 9 % were selected as the EA dosage of the agents. Four kinds of tests were conducted: compressive tests, direct tensile tests, computed tomography (CT) scanning, and scanning electron microscopy (SEM). In compressive tests, compared with the control group, the highest compressive strength occurred with the third method, increasing by 96.2 %, 136.1 %, and 77.4 % in three directions, respectively, while anisotropic parameters decreased to 0.03 from 0.22. In tensile tests, the optimal inter-filament interface bonding strengths were achieved at 9 % EA dosage with the third method, increasing by 180 %. The increase in mechanical strength resulted from the filling of channel voids and the improvement of interface microstructure. The AFt, produced from the hydration of EA, filled pores and acted as an interfacial connection bond, enhancing structural connectivity at the microscale and changing the orientation angles of micro pores. These reduce the anisotropy of 3DPC in the compressive and tensile tests. In combination with tensile test results, the inter-filament load-transfer mechanism was established. The findings reveal that the newly developed methods have the potential to address interface deficiency problems in 3DPC.