3D-Concrete Printing – Graded Concrete Extrusion

Nowadays, additive manufacturing is one of the leading research focuses in the construction sector. Among many established processes such as shotcrete, selective paste intrusion, and selective cement activation, extrusion processes represent the vast majority of methods used for large-scale printed building elements. Current extrusion processes use premixed concrete pumped through a hose, optionally accelerated at the nozzle, and then deposited. A new system approach, named Gradation-Ready Extrusion System (GRES), has been developed to exploit the benefits of additive manufacturing even better. It improves conventional extrusion by technically enabling the production of graded, multi-material building components, i.e., material properties can be varied within a single component. Thus, GRES enables sections to be made with different load-bearing capabilities or thermal conductivities. This in-situ gradation possibility significantly increases the potential use cases in concrete extrusion. GRES enables the continuous production of fresh concrete by metering and mixing raw materials directly before deposition (near-nozzle). Hence, avoiding long hose distances and the associated conflicting demands on material design; workability vs. buildability. The system design is based on material research, discrete element method simulations, and experimental prototype optimization. It comprises three sections – mixing, conveying, and compressing – each independently controllable by a programmable logic controller. Input values, for example, mix design and process parameters, are entered at the developed graphical user interface. Unlike existing extruding systems, with GRES, the concrete base mixture and its properties can be adjusted during the printing of complex geometries, resulting in multi-material graded concrete components optimized for load-bearing and insulation.