Do 3D Printed Houses Use Rebar?

3D printed houses are surrounded with skepticism about durability and concerns among homeowners are well-founded. With the whole concept being new and relatively untested, there are a lot of unknowns involved in determining the safety of these houses.

Rebar (short for reinforcement bars) plays a fundamental role in strengthening any construction work and is widely used in conventionally constructed homes.

It ensures strength and this method of construction has been around for a long time (which implies that it works).

So, what about 3D-printed homes? Do they use rebar? Reinforcement rebars are commonly used in 3d printed homes. 3D printed houses that use concrete usually incorporate some form of rebar in their construction such as rebar, Post-tensioned bars, Fiber, and mesh reinforcement, as it is imperative to the strength of the resultant structure.

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The use varies a lot when other materials are used. Clay, wood, and brick usually do not require steel reinforcement and this stays true for when these materials are used in 3D construction.

You can also read about the structural safety of 3D Printed Houses in Is a 3D Printed Home Structurally Safe? and Are 3D Printed Houses Hurricane Proof? and on height limits in How Tall Can You Build a 3 D Printed House?

How Is Rebar Used in 3D Printed Houses?

There are many known ways in which rebar is used in 3D printed houses. It can be as simple as inserting the steel rods after the layering process is complete or it can be as intricate as incorporating meshes and fiberglass into the concrete to give it strength.

These do deviate a bit from conventional rebar, but as long as additional strength is being achieved, any material can be classified as reinforcement.

The primary problem with using rebar in 3D printing is incorporating it in the layering process. Additive manufacturing requires there to be no disruptions in the work surface for the layering to be done.

Conventional reinforcements cannot work in this method, as steel rods sticking out would interfere with the print head.

A 3D printhead. Credits:

The current norm is to add reinforcement to the 3D printed structure after the 3D printing is finished. It is manually added to the external print surface and bonded with the structural components to give strength.

It is a labor-intensive process and hinders the efficiency of 3D construction (which is known for its speed). So, engineers are coming up with innovative ways to mitigate this problem.

Since reinforcement is fundamental to strength, there have been efforts to incorporate it into 3D printing. In the next few paragraphs, we will take a look into some of these pioneering technologies.

Smart Dynamic Casting, what is it and how does it work?

Smart Dynamic Casting (SDC) is one of the ways which allows reinforcement to be incorporated into 3D printing.

This technique was developed by researchers at ETH, Zurich, and has been successfully demonstrated in the DFAB HOUSE (a 3D printed, digitally fabricated building in Switzerland).

DFAB HOUSE. Credits:

SDC combines moving printheads and slip forming to precast structural components of various shapes, forms, and sizes. The concrete is more workable and is cast around the reinforcement.

As the printhead moves up, the concrete down below is already set enough to hold its own weight and the weight of the material being poured above it (It is activated so that it sets very quickly).

The printhead is dynamic (hence the name, Smart Dynamic Casting), which means that it can change its shape and manipulate the dimensions of the structural component it produces. This offers great versatility and since it is all pre-programmed, efficiency is achieved through repeatability. (source)

This technology has been successfully used to create structural joists and beams for houses and once it is further developed, it has great potential in the future of 3D printed construction.

Here is a video (made by NCCR Digital Fabrication, the organization responsible for the DFAB HOUSE) I found that greatly portrays SDC and hopefully the concept will make a lot more sense once you watch it too.

SDC is also a great example of hybrid construction. It combines the efficiency of 3D printing with conventional construction to produce houses that require fewer resources and are less impactful on the environment (both of which boost sustainability).

To learn more about the environmental impact of 3D printing, you may read Is 3D Printing Environmentally Friendly? what you need to know!.

Let’s look at a few other kinds of reinforcements being used in 3D-printed houses.

How do post-tensioned cables add strength to a 3D printed house?

Post-tensioned cables. Credits:

Post-tensioned cables have been used in conventional construction for quite a long time. The concept is actually pretty simple.

You put pipes in the formwork in the shape that opposes the load-bearing side of the structural member and once the concrete is poured and hardened, cables are run through those pipes and tensioned using hydraulic jacks.

This creates tension in the concrete member and increases its load-bearing capacity significantly since a lot of the weight is now being carried by the cables.

This also allows for thinner slabs of concrete and hence is more environmentally friendly. So post-tensioning is great, but how is it applicable in 3D printing?

Well, if you have noticed the pattern, 3D printing works best if there is no active disruption in the structure that is being constructed. Since the cables in tensioned concrete are put in afterward, it makes for an excellent choice in 3D construction applications.

The concrete can be layered over the pipes, cables can be run through it, and then they can be tensioned. All of this is done without any disruptions to the printing process, and that ensures that efficiency is maintained.

Fiber and Mesh reinforcement in 3D printed houses

This is one of the more innovative approaches towards reinforcement in 3D printed houses. Instead of relying on rigid, continuous steel bars running the length of concrete members, smaller reinforcement elements are utilized.

These can be either in the form of fiberglass being incorporated into the concrete mix to give it more uniform strength, or it can be meshing that is laid in front of the printhead. Both of these act like micro reinforcements that strengthen the concrete locally. (source)

The structure is as strong as its conventionally reinforced counterparts, but it inherits the advantages of 3D printing (efficiency, cost-effectiveness, repeatability, etc.).

There are also some lesser-known ways that 3D-printed houses have been reinforced. These include the use of staples, ties, ladder wire, and basalt reinforcement.

The effectiveness of their use is still relatively unknown since their applicability has not been widely tested.

Does 3D construction really need reinforcement?

Up to this point, we have been mainly focused on concrete as a raw material (as it is widely used in 3D printing construction). Concrete inherently requires reinforcement because of its weak tensile strength.

However, there are other materials used in 3D construction, that may not require reinforcement at all. There are even some techniques that can be employed in concrete construction that eliminate the need for rebar.

Wood and clay are examples of materials that do not necessarily require reinforcement. There have been examples of houses that were 3D printed using both of these materials and they did not make use of steel reinforcements. (Take a look at them here and here!).

As for techniques that eliminate the need for rebar, we can take a look at historical structures predating the concept of rebars. There are structures that can be self-supporting and free-standing, just on the basis of their geometry.

Domes are a great example of that. They have been part of architectural designs that predate modern civilization, and they are entirely independent of reinforcements.

Hagia Sophia and The Dome of the Rock are two great examples of that (the former was built in 537 A.D. and the latter was completed in 1023 A.D.)

Domes of Hagia Sophia
Dome of the Rock

These shapes have also been successfully incorporated into the 3D construction process. Tecla, the 3D printed clay house uses a dome shape to eliminate any use of rebar. This same philosophy could be applied to 3D printed concrete structures as well.

If you are still concerned about the safety of 3D printed houses, do check out our detailed article Is a 3D Printed House Safe? The Good, The Bad & What One Must Know.

Is hybrid construction the future of 3D printed houses?

The answer to that is yes, for the time being at least. It is a pipe dream of every engineer to someday have a machine that shows up on-site and after a few hours, leaves with a fully built house.

3D construction brought us really close to achieving that dream, but I think given the complexity of the variables involved, we will have to rely on a few conventional techniques for the foreseeable future.  

Don’t get me wrong, there might very well be a machine in the future that can bring that dream to fruition. However, given the current technologies that we have at our disposal, we will have to compensate by mixing 3D printing with conventional construction techniques.

After going through all this, it is also worth reading about the prices and affordability of 3D printed houses in Are 3D Printed Houses Affordable? and the use of 3D printing for MEP provisions such as mechanical and plumbing 3D Print components in Could A House Be 3D Print To Include Plumbing and Electrical Components?

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