How does 3D concrete printing work?

Just a few years ago, 3D printing seemed like a rather adventurous blend of science fiction and niche technology for a few selected companies worldwide. But that has changed dramatically. New applications are constantly being brought into play. One area is particularly exciting: 3D concrete printing, which can be used to create highly individual components as well as entire buildings.

The printed house

Houses from the printer? What may sound rather strange at first is one of the major technology topics of tomorrow in the construction industry. Experts, planners and companies around the world are looking for new concepts that will allow them to build quickly, in an environmentally friendly way and as cost-effectively as possible. This applies to the sprawling metropolises of industrialised nations as well as to the exploding megacities of developing and emerging countries. In the USA, the UK, China and not least in Germany, projects have been advanced to research and develop a 3D concrete printing process that is suitable for mass production.

Three different approaches currently dominate the discussion on the production of structures and parts using 3D concrete printing: powder bed technology, the currently more widespread extrusion technology and the wet spraying process.

The powder bed technique

The powder bed technique can be applied in two different ways: Either an aggregate mixture is bonded to form a composite by applying cement paste locally or consolidation is achieved by applying water to a mixture of aggregate and cement at specific points. With both techniques, even filigree structures can be produced without any problems - but numerous working passes are necessary, especially for larger components, so that the process speed is relatively low.

Extrusion technology

In extrusion technology, a die head deposits strands of material of different shapes, heights and widths on top of each other in layers. It is therefore also referred to as an additive process. The process is most comparable to established conventional 3D printing with plastic materials. Although the process is faster, it also has a weak point - in the truest sense of the word. As the strands of material are “deposited” one on top of the other, the adhesive bond is only created by pressing each new strand onto the one below it. This can therefore lead to problems under mechanical load with regard to bending tensile strength and shear strength.

The wet spraying process

The wet spraying process is also an additive process and is similar to extrusion technology. The pre-mixed wet spray material is pumped to a spray nozzle, where it is accelerated using compressed air and applied to the substrate layer by layer. Due to the high application rate and high process speed, the process is very well suited to the production of large-format, spatial components. In contrast to the extrusion process, the use of the concrete spraying process makes it possible to vary the application angle of the spray nozzle vertically and horizontally. This opens new possibilities in terms of the geometric shapes that can be produced. However, more filigree structures can hardly be achieved. In addition, the greatest advantage of the process also brings with it a challenge: on the one hand, the high pressure during application ensures an extraordinarily high compaction of the material - but this also releases more residue, which has to be dealt with in the form of dust and aerosols.

All three techniques mentioned therefore have their strengths and weaknesses. Reason enough for two German research projects to take a closer look at process optimization in 3D concrete printing.

Future technology with prospects

Although this technology is still in its infancy, it has already proven its practicality internationally on several occasions. In May 2016, the world's first fully printed office building was opened in Dubai. The United Arab Emirates is even pursuing a state-sponsored “3D printing strategy” - with the aim of producing a quarter of all new buildings in the Gulf state using 3D printing by 2030. The Chinese company “Win Sun” is also already using industrially applicable concrete 3D printing, in which the individual parts of standardized residential buildings are printed in a factory and only need to be assembled later on the construction site.

A very recent project from Milan: a single-storey demonstration building measuring around 100 square meters was constructed from 35 modular elements produced by a robot. The flexible printer needed 60 to 90 minutes to 3D print each individual element. The effective construction time for the entire building was therefore just 48 hours. 3D concrete printing is therefore well on the way to becoming an important building block in the construction world.