Introduction of a monitoring system for Bingham fluids in additive manufacturing with concrete

Additive manufacturing of concrete structures is a novel and emerging technology. Without a doubt, a great advantage is the free contouring which enables completely new designs in civil engineering. In future, lower construction costs are expected due to an increased construction speed and a reduction of required material and workers. Nevertheless, architects and civil engineers rely on a certain quality of execution to fulfil construction standards and codes. Although several techniques and approaches demonstrate the advantages, quality control during the printing process is considered extremely rarely. At the Bundesanstalt für Materialforschung und -prüfung (BAM), a new test rig for additive manufacturing using concrete extrusion is established. This test rig allows to manufacture structures with a maximum dimension of 1 m x 1 m x 2 m. The main purpose is the design of new cement and mortar mixtures and the measurement of their properties during the printing process. Although mortar properties vary only locally, the entire integrity of the structure may be compromised. Therefore, a real-time process monitoring is required which records and documents the entire printing process. At the end, additional destructive tests are possible to determine the mechanical properties of the printed elements. In a first approach, the water-cement ratio, the viscosity, the density, the temperature, and the volume flow are monitored. The test rig and the used measurement techniques will be described in detail. Measurement data will be shown and parameters to control the printing process are discussed. This novel process monitoring is a unique approach for a holistic quality control of additive manufactured concrete structures.