Shotcrete 3D Printing ‐ Effect of material‐process interaction on the global and local material density

Shotcrete 3D Printing is a 3D printing process in which the concrete is applied layer by layer using a wet mix process. In the print process, a large number of different process as well as material parameters can be varied, which also influence the hardened concrete properties. A systematic understanding of the interaction between material and process is required to define limits for material and process control variables with respect to the resulting component quality. Therefore, in this paper we present results on the effect of concrete volume flow (0.4; 0.8 m³/h), air volume flow (30; 40; 50 m³/h) and accelerator dosage (0; 3; 6 % by weight of cement) on global density, local density distribution as well as flexural strength. The results show that the combination of an increasing concrete volume flow, a decreasing air volume flow and an increasing accelerator dosage lead to a decrease in global density and flexural strength. A high correlation between the global density and flexural strength can be demonstrated despite the layer‐by‐layer fabrication. In addition, an inhomogeneous density distribution over the cross section is shown. Finally, the underlying mechanisms are discussed regarding the influence of the material and process parameters.