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Realtor Shelie Group

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Kai Martinez
Kai Martinez

Printing Liquid Concrete ((EXCLUSIVE))

We present our first experiment in rapid liquid printing of concrete (RLPC). This method makes possible 1) any shape from concrete to be printed 2) rapidly and 3) lets it reach maximum strength not being negativelly affected by too fast dehydration. In essence, the method is very similar to the rapid liquid 3d printing of polyurethanes, made at MIT in 2017 ( -liquid-printing).

Printing Liquid Concrete

RLPC appears to be ideal for concrete, because it does not require toxic, or specially designed proprietary components (gels or suspensions). The object upon printing is immersed in humid media, that is more optimal for hardening of concrete, than the air in a "standard" process of liquid deposition (LDM). One uses affordable and easily available materials: usual clay or retarded mortar as the matrix, and normal mortar paste (that turns into concrete upon hardening).

In the metal casting industry, 3D printing of molds and cores has become almost commonplace. It is a little different in the concrete casting, but that will change. Because the 3D printing of formwork elements has considerable potential, especially for the production of complex, structured and detailed elements. The voxeljet company stone shows what is possible when you combine 3D printing, concrete casting and architectural creativity.

Instead of removing material from a solid body, complex shapes are printed and later filled with liquid concrete. The work of art thus combines the latest design techniques with state-of-the-art high-tech concrete and is the basis for unprecedented applications in architecture and construction. In addition to complex curvatures that are difficult to form conventionally, 3D printing is particularly suitable for entire concrete facades or individual facade elements.

3D printing as an additive manufacturing process is conquering new fields of application in a wide variety of industries almost every day. Right at the forefront: voxeljet as a leading manufacturer of industrial 3D printers. Metal foundries have so far been the main users of the processes offered by voxeljet. With the help of 3D printing, highly complex shapes and cores can be produced from sand in the shortest possible time and with a high degree of precision. Users can save entire work steps, such as the construction of expensive molding tools, since only a CAD file is required for the production of 3D-printed sand molds and cores. The voxeljet service center then produces these forms on demand.

With the company stone made of concrete, voxeljet is showing new application possibilities for 3D printing in the architecture and construction industry. Just like metal, concrete can also be poured into the sand-printed molds. With the printing of sand molds, both reusable and lost formwork are created, depending on the application and complexity. The advantage of 3D printing lies in the tool-free, cost-optimized manufacturing process. The voxeljet 3D printing systems allow the production of molds with highly complex geometries in the shortest possible time and with impressive precision. With conventional manufacturing methods, such complex shapes would be difficult to manufacture or even completely impossible.

At the beginning there is CAD design. In order to fully utilize the advantages of 3D printing, voxeljet opted for a hybrid formwork, a combination of printed and conventional mold elements. The 3D-printed elements were limited to the complex part, the front of the company stone. Simple geometries, such as straight surfaces, are modelled with conventional wooden formwork.

The complex part of the voxeljet company stone consists mainly of the stone structure with the integrated logo, which emerges from the background structure. The design freedom of 3D printing means, that even highly complex geometries with undercuts and intentional unevenness can be realized without any problems.

In order to start the printing process, the finished CAD file was loaded onto a 3D printing system from voxeljet. The 3D printing system then produced the formwork in one go. voxeljet printed the formwork for the company stone on a VX4000, the largest industrial 3D printing system with a continuous building platform of 4x2x1m (LxWxH), in only one night.

The VX4000 applies sand in an extremely thin layer of only 300 micrometers to the building surface. The print head then bonds the layers selectively with a binding agent. Once the mold is fully printed, voxeljet specialists remove the unprinted sand and clean the mold with compressed air. In order to prepare the mold for concrete casting, the 3D printing specialists infiltrated the mold with a PU dispersion to close pores and simultaneously seal the surface.

voxeljet then sent the post-treated form to Dade-Design in Switzerland, so that the concrete casting professionals cast it there. To make it easier to remove the sand mold from the concrete after casting, Dade-Design applies a release agent to the mold.

After the printed logo had hardened, Dade Design poured the rest of the company stone in the second step. For this, the concrete foundry used a self-compacting concrete, UHPC (Ultra-High Performance Concrete). The concrete was completely cured after around 20 hours and the formwork could be carefully removed. After removing the formwork, the voxeljet company stone was as good as finished. For the final touch, employees from Dade-Design gave the stone a so-called concrete cosmetic, in which they polished the concrete in order to obtain an even and smooth surface.

A new bridge that was completely 3D printed has just opened in the Netherlands. Designed and built by engineers from the Technical University of Eindhoven and construction company BAM Infra, the cyclist bridge was printed in pieces from a concrete mixture, reinforced with steel cable, before being assembled and erected on-site.

There are a few advantages to 3D printing structures like this. Cement can be deposited only where it's needed, reducing the amount of cement required and in turn lowering CO2 emissions during production. Since no formwork structures need to be built to support the wet cement, waste materials are also reduced, as well as the time and cost involved. The researchers estimate that their process should be three times faster than conventional construction with concrete, and more unusual shapes can be built.

The bridge was built as part of the Noord-Om project, which is aiming to use innovative techniques like 3D printing to construct a new section of road near the village of Gemert. The Eindhoven researchers are also currently working on printing five houses, which will eventually be lived in.

Particle bed printing is a process where fine particles are selectively bound through the localized application of binder. For this, a thin layer of particles is evenly distributed inside a given building envelope. In a subsequent step a binder is deposited onto the particle layer, which selectively bonds the particles. Next, the particle bed is lowered, a new layer of particles is applied, and the binding process is repeated. In a layered manner, complex geometries can be fabricated, resting loosely inside the bed of unbound particles. This technology is used, for example, for the production of complex molds in metal foundry [5], but also in architecture as formwork for casting high resolution concrete parts [6]. Instead of using the printed element merely as formwork, there are also attempts to entirely print structural elements using large, room-sized particle bed printers [7].

In the extrusion-based approach to additive manufacturing, strands of fine concrete are printed layer-wise on top of each other, progressively creating a three-dimensional object. Here, predominantly two different concepts are pursued, firstly the contour crafting approach [8], and secondly the technique of 3D concrete printing [9]. Contour crafting is based on a lost formwork method where only the perimeter is printed, to create a hollow core element that is later filled with conventional concrete. Several research groups and industry professionals [10,11,12,13] have today adopted this method, also for the reason that it can be combined with the manual integration of reinforcement [14]. In the 3D concrete printing process, the entire concrete component is printed; however, channels for the placement of post-tensioning cables can be integrated in order to reinforce the component [15].

The third approach, Shotcrete 3D Printing, differs from extrusion-based concrete printing in the respect that the concrete is not deposited in strands, but is sprayed by means of compressed air [16]. This results in good layer adhesion, and the capability to spray around and hence embed structural reinforcement [17].

Material extrusion, for example, offers high building rates. Depending on the printing system, state-of the-art concrete printers reach building speeds of up to 16 cm/s [18], corresponding to an extrusion volume flow of approximately 0.6 m3/h. Even higher volume flows of currently up to 1 m3/h can be achieved with the Shotcrete 3D Printing method. However, printing speed is inversely related to geometric resolution and surface quality. Accordingly, particle bed printing is, for example, the most geometrically versatile, but also the slowest additive manufacturing process.

With the first process version, CiS, a fine grain concrete is printed into a non-hardening suspension. As such, intricate truss structures and filigree concrete space frames can be fabricated, which are otherwise difficult or impossible to manufacture. Figure 1 shows the schematic fabrication method, as well as a possibly printed object.

The second process version SiC (suspension in concrete) is the reversal of the CiS principle: in the SiC process, a non-hardening suspension is printed into a vessel filled with fresh concrete. Subsequently, the suspension is removed, leaving cavities or channels. This can be used to functionally grade concrete components through differentiated density or to utilize them for physical element activation. Figure 2 shows schematically the SiC-fabrication process as well as a printed element.


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