Instrumentation of the Extruder Nozzle Using Load Cells: Towards an In-Line Quality Control Device for 3D Printed Cement-Based Materials

3D concrete printing technology is gaining attention in smart construction due to its automation and digitization advantages. However, issues in the material supply chain during the extrusion 3D printing process can cause defects or halt printing. To address this, recording and analyzing the stresses exerted by the material on the printhead is proposed to monitor and correct its behavior in the fresh state. Implementing a system to measure the force on the die during material extrusion offers precise quantification of pressure variations from process and materials parameters. This device, comprising a die mounted freely on an extruder and connected by three load cells, can serve as a rheological and/or quality control tool. Two parametric studies are conducted. The first evaluates pressure variations induced by viscosity at the extruder die via viscosity-modifying admixture dosage variations. The second focuses on printing process parameters to characterize time-dependent material properties like cement hydration or thixotropic properties. This instrumentation allows precise assessment of the stress on concrete by the printhead during extrusion. The study's results will provide valuable insights for optimizing printing parameters, ensuring the quality of 3D printed concrete structures and their durability.