Strength and Proportioning Design of 3D Printed Concrete (3DPC) Based on Aggregate-Gradation-Optimization (2024-03)¶

The inadequate bonding between the layers in 3D printing generally leads to lower resulting concrete strength. In this study, the optimal match between aggregates was theoretically determined using the experimental method of minimum voids based on the surplus coefficient of paste and experimentally validated. The effect of the slurry ratio on the characterization was also analyzed. The concrete strength after printing was tested by cutting different segments of the printed component. The results show that the gradation optimization of 3D-printed concrete aggregate can be realized according to the minimum porosity method. The minimum porosity is 40.7%. The optimal proportion of 1.18:2.36 mm:0.6–1.18 mm:0.3–0.6 mm is 055:0.248:0.202 for quartz sand, and the optimal sand cement ratio is 1.7. The resulting concrete ratio meets the characterization requirements of 3D-printed concrete. The 28d strength is 81.9 MPa before printing and 60.4 MPa after printing; the strength loss is 26.3%. The hydration, hardening mechanism and microstructure were studied through XRD and SEM. The composition features of hydration products and microstructure characteristic were discovered. The fundamental reason why the concrete has higher mechanical properties under the 3D printing process is explored from the static dense packing filling effect of the compound system.