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Researchers from TU Braunschweig have presented a novel type of 3D printing process that could potentially push the limits of additive manufacturing in the construction sector, called Injection 3D Concrete Printing (I3DCP) in suspension.
Within concrete construction, current additive manufacturing techniques tend to focus on layer-by-layer printing via material extrusion, jetting, or binding. While these technologies have their merits, they can be offset by drawbacks in geometric resolution and complexity, surface quality, and low building rates.
The basic idea of I3DCP in suspension is to overcome the limitations of layered 3D printing by robotically injecting one fluid material into another. This creates a stable structure due to each material’s specific rheological properties, or how they flow in response to forces or stresses.
According to the researchers, this method offers higher building rates and the ability to print freeform trajectories that are not constrained by gravitational forces. As such, I3DCP could establish entirely new structural features and efficiencies for 3D printed concrete structures.
I3DCP in suspension applications
The first large-scale application of I3DCP was presented by French start-up Soliquid, which extruded concrete into a reusable gel matrix using a 6-axis robot to create a large-scale 2.5-ton artificial coral reef. No support structures were needed as the gel kept the component in position throughout the printing process until it had hardened and could be removed.
In the same year, an experimental design studio was set up at TU Braunschweig to design and produce small-scale spatial structures with I3DCP technology. Instead of using a gel, however, the researchers began experimenting with the use of a ground limestone suspension as the carrier liquid.
While the first applications of the technique have shown promise, more knowledge of the rheological requirements of injected concrete and the carrier liquids are required to move the technology forwards into industrial-scale applications. The researchers are also looking at the recyclability of the carrier liquid and its economic and ecological impacts.
Overcoming challenges of the I3DCP process
The success of the I3DCP process relies on the delicate balance of forces between the weight of the injected concrete material (A), the buoyancy force of the carrier liquid into which it is injected (B), the force from the printing nozzle, and the rheological properties of both materials. If the right balance between these forces is not struck, then it will lead to an undesirably shaped object.
Meanwhile, the shape of the 3D printed structure is determined by the extrusion flow rate, the velocity of the robot-guided nozzle, and the cross-sectional area of the nozzle.
Ground limestone is considered an inert filler material that is both reusable and inexpensive. According to the TU Braunschweig team, ground limestone suspensions offer advantages over gels in terms of cost, reusability, and control of the rheological properties.
To overcome the challenges of I3DCP in suspension and to test the effectiveness of their technique, the researchers conducted multiple experiments using a lightweight UR 16 robot. Three formworks were placed on two adjacent sides of the robot table and six molds were filled with the ground limestone suspension. The robot then extruded the concrete into the molds at a rate of 0.000025 m³/s.
The resulting reinforced I3DCP printed elements formed a scaled version of an arch-shaped truss bridge, which the researchers claim shows great potential for novel lightweight concrete structures. Unlike the layer-by-layer deposition of horizontal strands inherent in most 3D concrete printing technologies, the team was able to produce intricate concrete structures by printing spatially free trajectories that are not restricted by gravitational forces during printing.
Going forwards, the Braunschweig team will seek to advance their I3DCP technique by adjusting the strand diameter of the injected concrete via controlling its variable force flow. This, they believe, could see the establishment of an “entirely new, previously unseen tectonic language” and improved structural efficiency for building concrete structures.
Further information in the study can be found in the paper titled: “Injection 3D concrete printing in a carrier liquid – Underlying physics and applications to lightweight space frame structures,” published in the Cement and Composites journal. The study was co-authored by D. Lowe, A. Vandenberg, A. Pierre, A. Thoman, H. Kloft, and N. Hack.
Recent advances in concrete 3D printing
Concrete 3D printing technologies can deliver substantial cost and lead time benefits compared to conventional construction techniques. The technology can also yield sustainability benefits, with construction firms potentially able to cut their related waste by up to 60 percent by recycling additive manufactured formwork, such as that developed by BigRep and BASF subsidiary Forward AM.
Recent research into 3D printable construction materials has enabled scientists from the Swinburne University of Technology and Hebei University of Technology to turn recycled concrete aggregate, ceramsite particles, and desert sand into a low-cost extrudable building material. The new 3D printing material could potentially be used within heavy-duty construction applications.
Elsewhere, researchers from RMIT University in Australia have sought to make 3D printed concrete structures stronger by drawing inspiration from lobster shell patterns, while UC Berkeley scientists have explored incorporating 3D printed polymer octet lattices into concrete structures to reinforce them.
Most recently, architects and engineers from ETH Zurich’s Block Research Group created what is supposedly the first 3D printed concrete bridge built without reinforcement. Stable thanks only to its geometry, the bridge is formed from a newly developed concrete that is printed at specific angles in blocks that are self-supporting.
Nominations for the 2021 3D Printing Industry Awards are now open, have your say who is leading the industry now.
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Featured image shows printing around pre-installed steel reinforcement bars using the I3DCP process. Photo via TU Braunchsweig.
