3D Printing in Construction – What Are 3D Printed Houses Made Of?

The construction industry has traditionally been conservative when it comes to adopting advanced technologies. Innovation may come from the architect, but the builders tend to keep more or less the same process, adapting only to the project at hand.

However, by adopting additive manufacturing, the construction industry can have advantages like better creativity, design flexibility, less material waste, lower carbon footprint, and more robust structures. It’s a fast-growing industry with experts estimating the value of 3D printing construction to reach $56.4 million by 2021. This is a huge market!

3D printing construction has seen some fascinating projects and some massive 3D printers. More and more firms are joining the market, 3D printing more and more homes. This is all quite impressive, but at the end of the day, you might be asking yourself, but how can they 3D print concrete? What material are they using?

A Special Recipe

Materials play a key role in 3D printing construction. The material used must blend design with adequate consistency and workability. For structural applications, this predominantly means a concrete base, consisting of cement, sand, and other additives. However, there are a few variants that stray off this path.

The exact mix varies from purpose to purpose and even 3D printer to 3D printer. To properly understand the materials used, let’s have a look at some different examples 3D printing construction has yielded.

Apis Cor is a San-Francisco-based start-up developing unique mobile construction 3D printers that print structural components (self-supporting walls and partitions). Like most, their concrete 3D printer uses material extrusion technology.

They have developed their own material mix, which is an extrudable concrete consisting of cement, sand, geopolymers, and fibers. They prepare the final material mix by mixing the raw materials in a large hopper. This mix is then fed by a pump system to the extruder, which deposits the material.

Their 3D printer has an independent robotic arm which prints the structural components on-site. They intentionally left a small gap between the interior and exterior of walls, where they placed fiberglass reinforcements and sprayed a polyurethane-based mixture for insulation. Once the walls were printed, they removed the printer with the help of a crane to install windows, appliances, and the roof. The entire structure took just 24 hours to complete.

Material Mix: Concrete mix made out of cement, sand and other additives

COBOD is a European start-up striving towards full automation in the construction industry using 3D printing construction. In 2017, this company 3D printed the first building in Europe: The Building On Demand (BOD).

The only straight elements in the BOD structure were the windows and doors, everything else was curved. The most interesting thing about this building is that even the foundations were 3D printed. Their construction 3D printer works in three dimensions, allowing the printer to access any position within the envelope.

COBOD collaborated with FORCE Technology to develop a strong and sustainable concrete mix using recycled materials. The material delivery system consists of a mixing pump which automatically fills dry material mix from the mixer. Water is then added to the mix to keep the pump filled. In addition to 3D printing, they also use the printer as an on-site “crane” to place certain elements into the building.

Material Mix: Concrete mix made out of cement, sand and other additives

WASP is an Italian start-up with aims to provide 3D printed sustainable shelters at minimum costs using naturally available local materials. This led them to 3D print a new eco-sustainable house, the Gaia.

This was the first step towards 3D printing load-bearing earthen structures. The specially designed 3D printable material mix consisted of soil, rice fibers provided by RiceHouse, and lime. They mixed this material thoroughly in a wet pan mill to make it homogeneous and workable. The mix was then extruded with the Crane WASP 3D printer.

To get the final structure, they printed a monolithic wall and finished with a shaving clay lamina and smoothed and oiled with linseed oils. The machine is a frame based gantry setup that prints the structural components in shorter lead times.

Material Mix: Earth-based material mix consisting of 25% soil (30% clay/40% silt/30% sand), 40% straw chopped rice, 25% rice husk and 10% hydraulic lime

Winsun is a Chinese based company which developed its own construction 3D printer to print large scale building components at high speeds. They started out as a building materials supplier and later aimed to revolutionize the construction space using 3D printing technology.

They announced their arrival into the 3D printing construction market by 3D printing ten houses within 24 hours. They build the structural components using a 120 x 40 x 20 feet frame based 3D printer. Their mode of printing is off-site, where the components are generally printed in a factory. These components are then transported and assembled on-site.

Their special material mix consists of cement, sand, and fiber, along with a few additives to improve the buildability. They designed their mix in such a way that it produces zero waste and is also environment-friendly.

Material Mix: Concrete mix made out of cement, sand, fiber and additives

Tvasta is an Indian start-up striving to meet India’s affordable housing and sanitation shortfalls by providing quality construction in the remote places of the country. Tvasta recently unveiled India’s first concrete 3D printed structure and received widespread coverage from leading media houses and research groups.

Tvasta, along with IIT Madras, has developed a specialty concrete for 3D printing large scale structures. The main goals are to make it affordable and more sustainable. The mix is based on ordinary portland cement, but with a lower water–cement ratio. They reinforce it with either amorphous metal fibers or plastic fibers, depending on the application. Their 3D printers are capable of printing with aggregates up to 8 mm, which only a few research groups across the world have achieved. The resulting material provided strength equal to that of an M-35 concrete.

The structure consists of 12-mm rebar on all four corners for anchoring and in hollow sections of the wall for tensile strength. Textile reinforcements were placed at the vertical joints. While 3D printing it, the structure was specifically designed hollow to allow provisions for wiring and plumbing without damaging the wall.

Material Mix: Concrete mix based on ordinary Portland cement, but with a lower water–cement ratio and made out of cement, sand, and other additives

If you build it they will come. And if you 3D print it, they will come faster, cheaper and more sustainably.

– Ava Reichental, founder & CEO of XponentialWorks

With significant material research by top research institutions and start-ups across the world, houses can now be 3D printed without the use of formworks. For now, mostly the start-ups have been working with a concrete mix consisting of sand, cement, fly ash, and silica fume. However, there are a few others focusing on 3D printing construction with earth-based materials.

Though mix design plays a crucial role in determining the structure’s quality, it also depends on the robustness of the design and machines and the ability of architects and engineers. Researchers are working towards designing a mix with repeatable fresh properties using different aggregate sizes. Furthermore, efforts are being put on optimizing structure weight and finishing operations.

Fascinated by 3D printing construction? Check out these related articles:

• Concrete 3D Printing – How it Works & The Applications
• 3D Printed Homes – Most Fascinating Projects
• An Entire Community of 3D Printed Homes is Coming to Eindhoven Next Year

Feature image source: ETH Zurich