3D concrete printing

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TU/e Built Environment's Rohaco 3D Concrete Printer being extensively used for Concrete Printing Research. 3D Concrete Printer.jpg
TU/e Built Environment's Rohaco 3D Concrete Printer being extensively used for Concrete Printing Research.

3D concrete printing, or simply concrete printing, refers to digital fabrication processes for cementitious materials based on one of several different 3D printing technologies. 3D-printed concrete eliminates the need for formwork, reducing material waste and allowing for greater geometric freedom in complex structures. With recent developments in mix design and 3D printing technology over the last decade, 3D concrete printing has grown exponentially since its emergence in the 1990s. Architectural and structural applications of 3D-printed concrete include the production of building blocks, building modules, street furniture, pedestrian bridges, and low-rise residential structures.

Contents

History

Automating building processes has been an area of research in architecture and civil engineering since the 20th century. The earliest approaches focused on automating masonry. In 1904, a patent for a brick-laying machine was granted to John Thomas in the US. [1] By the 1960s, the technology developed significantly and functional equipment, such as the Motor-Mason, were in use on building sites. [2] [3]

At the same time, automating concrete construction processes was also being developed. Slip forming, a widely used technique today for building vertical concrete cores for high-rise buildings, was developed in the early 20th century for building silos and grain elevators. The concept was pioneered by James MacDonald, of MacDonald Engineering Chicago, and published by Milko S. Ketchum in an illustrated book: The Design of Walls, Bins, and Grain Elevators in 1907. [4] Later, MacDonald published a scientific paper: Moving Forms for Reinforced Concrete Storage Bins in 1911. [5] Finally, on 24 May 1917, MacDonald was granted a US patent for a device to move and elevate a concrete form in a vertical plane. [6]

Innovations in the automation of concreting processes continued throughout the 20th century. 3D printing processes were first developed in the 1980s for photopolymers and thermoplastics. For some time, 3D printing technology was limited to high-value-adding sectors such as aerospace and biomedical industries due to the high cost of materials. However, as the knowledge base for 3D printing grew, new additive manufacturing processes were developed for other materials, including for concrete. 3D printed concrete technology originated from Rensselaer Polytechnic Institute (RPI) in New York when Joseph Pegna first applied additive manufacturing to concrete in 1997. This experiment was just a proof of concept, but Pegna recognized the developing robotics industry and saw it as an opportunity to automate the construction process, while also decreasing costs and waste production. [7] Pegna's research would later become the basis for binder jetting, or powder based 3D concrete printing.

In 1998, Behrokh Khoshnevis at the University of Southern California developed Contour Crafting, which was the first layered extrusion device for concrete. The system used a computer-controlled crane to automate the pouring process and was capable of creating smooth contour surfaces. [8] Khoshnevis initially designed this system to serve as rapid home construction for natural disaster recovery, and he claimed that the system could complete a home in a single day. [9] With innovations in materials, mix design, and printing technology, researchers and engineers have since expanded on these two printing techniques, which will be discussed further in the following section.

Construction methods

A number of different approaches have been demonstrated to date, which include on-site and off-site fabrication of building elements or entire buildings, using industrial robots, gantry systems, and tethered autonomous vehicles (see section on 3D Printers). Demonstrations of construction 3D printing technologies have included fabrication of housing, building elements (cladding, structural panels, and columns), bridges, civil infrastructure, artificial reefs, follies, and sculptures. Three different construction methods are currently used in 3D concrete printing: binder jetting, robotic shotcrete, [10] and layered material extrusion.

Binder jetting

Binder jet 3D printing, also known as powder bed and binder 3D printing, was originally developed at the Massachusetts Institute of Technology for activating starch or gypsum powder with water as a binder, before Joseph Pegna applied the system to concrete. [11] In binder jetting, a print head selectively deposits a liquid binder on a powdered substrate, layer by layer. The layer height typically varies between 0.2 and 2 mm and determines both the speed and the level of detail in the finished part. Post-processing steps are necessary in binder-jetting once the layered fabrication is complete. First, the unconsolidated powder needs to be removed mechanically, using brushes and vacuum tubes. Additional curing steps may also be necessary in ovens with controlled humidity and temperature or microwaves. Finally, coatings may also be applied on the surface to consolidate small surface features or to improve the surface quality of the part. Typical materials used for coatings are polyester or epoxy resin. [12]

3D concrete printing with binder jetting technologies has been demonstrated at large scale by Enrico Dini with D-Shape. [13] D-Shape relies on a non-hydraulic Sorel cement that is based on sand activated with magnesium oxide in the powder bed and a liquid magnesium chloride solution as binder. The technology has mainly been used to create furniture, such as a coffee table and the Root Chair designed by KOL/MAC LLC Architecture + Design in 2009. Furthermore, D-Shape produced large architectural parts, such as the 3 × 3 × 3 m Radiolaria pavilion designed by Shiro Studio in 2008, the Ferreri House for the Triennale di Milano in 2010, and a twelve-metre-long footbridge designed by Acciona in Madrid, in 2017.

Another exponent of binder-jet 3D concrete printing is California-based firm Emerging Objects. For their Bloom pavilion built in 2015, the company used an iron oxide-free cement and organic binder. While it is unclear if there is any cement hydration involved in the process, the project is often cited among other binder-jet 3D concrete printing projects due to the use of cement in the powder bed. Unlike the structures of D-Shape, which were fabricated in one piece, Emerging Objects fabricated 840 small building blocks that were stacked to create the 3.6 × 3.6 × 2.7 m structure.[ citation needed ]

Advantages and limitations

Compared to other 3D printing methods for architectural applications, binder jetting allows for a higher degree of geometric freedom, including the possibility of creating unsupported cantilevers or overhangs and hollow parts. Unlike other 3D printing processes that require auxiliary support structures, binder jetting relies on the bed of unbonded powder to ensure continuous support for consecutive layers during fabrication.

Typically, in binder jet 3D printing, the leftover powder can be reused for future parts. However, the recyclability of the cement and aggregate powder is problematic due to the exposure to ambient humidity, which can trigger the hydration process. Therefore, binder jet 3D printing is not suitable for on-site construction. [12]

Layered extrusion 3D printing

Concrete layered extrusion 3D printing involves a numerically controlled nozzle that precisely extrudes a cementitious paste layer by layer. Layers are generally between 5 mm and a few centimeters in thickness. The extrusion nozzle may be accompanied by an automatic troweling tool that flattens the 3D-printed layers and covers the grooves at the interlayer interfaces, resulting in a smooth concrete surface. Additional automation steps have been proposed for the integration in one fabrication step of modular steel reinforcement bars or integrated building services, such as plumbing or electrical conduits. For this process, process planning and deposition speed are critical parameters that influence the material's stiffening and hardening rate. [12]

Layered extrusion 3D concrete printing is most commonly used in on-site construction and is accompanied by large-scale 3D printers (see section on 3D Printers). The technology has seen a growing interest recently, with numerous universities, start-ups, and prominent established construction companies developing dedicated hardware, concrete mixes, and automation setups for concrete extrusion 3D printing. Applications include bridges, columns, walls, floor slabs, street furniture, water tanks, and entire buildings, both in prefabrication or on-site setups.

Advantages and limitations

Unlike conventional concrete casting and spraying, layered extrusion 3D printing needs no formworks. This is a significant advantage considering the fact that formworks in concrete construction can account for 50-80% of the resources, more than raw materials, reinforcement, and labour combined. [14] The main challenges of layered concrete extrusion are the set on demand rheology of concrete, the integration of reinforcement, and the formation of cold joints at the interface between consecutive layers. [15]

Slip forming

Robotic slip-forming, a process developed at ETH Zürich under the name Smart Dynamic Casting, [16] is sometimes included in the family of concrete 3D printing processes, together with layered extrusion and binder-jetting. The process loosely fits the definition of 3D printing, due to its additive nature, with material being slowly extruded through an actuated mould that can vary its section. However, unlike the other 3D printing processes, slip forming is a continuous process, and not discrete or layer-based, and therefore it is more closely related to formative processes such as casting and extrusion.

Technology

3D printers for concrete

ICON's gantry system, known as the Vulcan, can print structures up to 3,000 square feet ICON Next-Gen Construction System.jpg
ICON's gantry system, known as the Vulcan, can print structures up to 3,000 square feet

There are a few main categories of robots that are used for 3D concrete printing, which depend on the application, scale of the project, and printing technique. All construction 3D printers generally consist of a support structure and a printer head with a nozzle that extrudes the concrete. Printers are usually used in tandem with modelling software that uploads the building plans directly to the printer.

Printer parameters

In addition to printer type, specific printer parameters significantly impact the final performance of 3D printed concrete and must be carefully selected when planning for 3D printing construction. These parameters can simply be broken down into print head design and print speed.

The print head must be selected so that the concrete mix can smoothly pass through the nozzle and create the bonding effect between each layer, while also initiating the solidification process. [8] Similar to printer selection, nozzle shapes and sizes vary depending on the application. 3D printed concrete samples from nozzles with rectangular holes typically have higher strength than those printed with circular nozzles, because there are fewer gaps between each printed layer. [8] However, circular nozzles are more adept for printing complex geometries. For samples printed from the same nozzle type, mechanical properties are improved when a larger nozzle is used. [8]

The height of the print head is the height of the nozzle relative to the printing platform. This parameter affects the surface quality between layers including bond strength, and must be precisely adjusted. A print head that is set too high will reduce the bond strength between layers, causing an unstable shape. [8] A nozzle too close to the printing surface may interfere with the printing process and place additional loads on the concrete. Research proposes a print height equal to the width of the nozzle. [8]

The speed at which the print head is set also influences the bonding strength. Increasing the nozzle speed generally decreases the adhesive strength, as the concrete has little time to set into place. However, taking too long to print successive layers reduces interlayer bonding, so a balance must be established that accounts for strength without premature collapse. [8] Other factors that influence the quality of 3D printed concrete include the pumps and controls used to monitor the printer, as well as the concrete mix design (See section on Mix Design).

3D printer suppliers

3D concrete printing technology has grown exponentially over the last decade and is expected to continue to grow as researchers learn more about the software, hardware, and construction capabilities of these printers. Below are some notable companies and 3D printers that are used globally:

Notable Suppliers of 3D Printers for Concrete
CompanyHeadquartersPrinter name (type)Notes
COBODDenmarkBOD2 (Gantry)The fastest and most widely used construction 3D printer on the market, with print speeds up to 1000 mm/s. Can achieve layer widths up to 100mm and heights up to 40 mm [18]
WASPItalyCrane Wasp (Crane/Gantry)Can reconfigure its steel supports to accommodate site constraints and project applications, printing areas up to 100 square meters [19]
VerticoNetherlandsEVA (Robotic Arm)Available as a fixed setup or on a track. Has a build volume of 2.7m x 10m x 3.0m. Also offers robotic arms for labs and smaller scaled projects [20]
CyBeNetherlandsCyBe G (Gantry)Best suited for printing modules as opposed to entire structures. CyBe also offers two robotic printers: a fixed robot arm and a portable robot arm attached to a crawler system [21]
ICONTexas, USAVulcan (Gantry)Prints areas up to 3,000 square feet (about 280 square meters) at a speed of about 5 to 7 inches per minute. Certified to perform under all weather conditions [22]
Constructions-3DFranceMaxiPrinter (Crane/Robotic Arm)Features a crane arm attached to a crawler system. Extremely portable and easy to transport due to its unique, flexible design [23]
ROSOTaiwanLiquidStoneConcreteThe 3D printing method for hollow concrete structures strategically utilizes the material only where necessary, thereby achieving a more sustainable approach to concrete architecture.
Luyten 3D Melbourne, AustraliaPlatypus X12First multi-storey 3D construction printer in the Southern Hemisphere, featuring a telescoping crane system, AI-driven precision, and a contour-compliant nozzle. [24] [25]

Mix design

Shrinkage cracking in 3D printed concrete due to insufficient mix design and curing Shrinkage Cracking in 3D printed Concrete.jpg
Shrinkage cracking in 3D printed concrete due to insufficient mix design and curing

Critical mix properties

For 3D printed concrete, buildability and extrudability are two of the most critical design properties for a mix. [26] Extrudability is the mixture's ability to pass through nozzles in the printing head, while buildability is the capacity to support additional layers. [27] These properties are governed by the consistency, cohesiveness, and stability of the mixture, which stem from the mix design and selected materials. For both properties, a balance must be met between stiffness and workability. A stiff mix will increase strength, but decrease flow rate and print speed, potentially clogging the printer head. [27] Conversely, decreasing the stiffness too much may increase workability and extrudability at the expense of strength and buildability. [27]

Since concrete is printed in layers, layers must sufficiently bond to each other to allow for proper curing and full-strength capacity. Significant research has been conducted to create an optimal mix for 3D printing, [27] although there are no current industry standards. However, the use of supplementary cementitious materials (SCMs) such as metakaolin, fly ash, silica fume, and superplasticizers are common in all 3D printed concrete mixtures (See section on Admixtures). [26]

Cementitious materials

Cementitious materials are integral to any concrete mix design. These materials serve as the binder that holds the mix together, as they chemically react with water to undergo the curing process. Portland cement is the most common material in construction for both 3D printed and traditional concrete applications due to its low cost and widespread availability. However, it's high setting time and low bonding ability are disadvantageous for 3D printed applications. [8] Therefore, polymers and other admixtures are often added to reduce shrinkage and improve adhesion. [8] Some of these polymers include rubber, mixed sand aggregates, carbon-sulfur polymers, and geopolymers, which also have added benefits of crack repair and resistance. [8]

One alternative is sulfoaluminate cement which can be mixed with Portland Cement to quicken the hydration process and help develop early concrete strength after placement. While the setting time of Portland Cement is about half an hour, the setting time for sulfoaluminate cement is just six minutes. [8] Therefore, higher strength can be achieved in a much shorter time period, increasing buildability.

Aggregates

Aggregate content and selection are just as important as the selected cementitious materials when it comes to concrete mix design. In particular, particle size has a significant effect on 3D-printed concrete mixes. Particle sizes that are too large may block the nozzle of the 3D printer, while aggregates that are too small decrease the strength of the mix and can cause cracking. [8] A rule of thumb for mix design is that the maximum aggregate particle size should be less than 1/10 of the nozzle diameter to ensure smooth extrusion. [8]

Several studies have been conducted to examine the influence of aggregate size on mechanical properties for 3D printed concrete. It was found that increasing coarse aggregate improves the volumetric stability of concrete and decreases hydration heat and shrinkage, which were common problems in early 3D-printed concrete mixes. [26] The use of coarse aggregate also increases the concrete deposition rate and printhead speed, which can increase printing efficiency and productivity. Therefore, the printed structure achieves greater stability and strength, as observed by Ivanova and Mechtcherine. [26] There is a limit to coarse aggregate content and size, as the challenge of controlling rheology becomes apparent. Natural aggregates such as sand and gravel are preferred as they require less energy to produce compared to artificial aggregates, but aggregate selection can be limited by regional deposits.

Admixtures

Admixtures include any materials outside of water, aggregates, and cementitious materials, that affect the concrete mix properties. Especially in 3D printed concrete, these admixtures are critical to balancing buildability, workability, and extrudability. Fly ash is the main admixture for high-performance 3D printed concrete, as it improves working performance and durability. [26] However, large amounts of fly ash can lead to slower development of strength and buildability, which is why it is often mixed with other admixtures like clay, to retain shape stability. [26]

Silica fume is another common admixture for 3D printed concrete mixes, as it increases the initial strength of printed concrete as well as flexural strength once the concrete cures. The main advantage of silica fume is that its small particles fill in the void spaces around the larger aggregates, which improves bonding performance with the cement binder. This also helps optimize the particle size distribution of the mix, which increases yield stress and buildability. [26]

Mechanical properties

As with standard concrete mixes, mixes for 3D printed concrete are typically tested for their compressive and flexural strength. These mechanical properties are highly dependent on the mix design and can be improved by adding admixtures such as the ones described in the above section. For a mix containing ordinary Portland Cement, fly ash, silica fume, and fine glass aggregates, the compressive strength is around 36 to 57 MPa, which is comparable to the compressive strength of normal-weight concrete. High-performance concrete strengths of over 100 MPa have also been achieved by using superplasticizers and additional chemicals, but these mixes are more energy-intensive to produce. [26]

For 3D printed concrete, the structural properties are largely influenced by the interlayer bonding performance. Increasing the print speed and printhead height can reduce the interlayer bond strength while adding a mortar between the layers can improve this strength. In particular, a resin mortar composed of black charcoal, sulfur, and sand has been found to be effective. [26]

Concrete suppliers for 3D printing

Since there are no standards set for 3D printing concrete mix design, companies often pursue their own research and development if they decide to offer 3D printing as a construction service. Below are some notable companies that have successfully implemented 3D concrete printing into their scope of services.

Notable Suppliers of 3D Printed Concrete
CompanyHeadquartersMixNotes
Sika USA New Jersey, USASikacrete 7100 3DReady-to-use mix that consists of cementitious powder with fibers and liquid polymers [28]
CyBeNetherlandsCyBe MortarSets in three minutes and achieves full strength in one hour with low concentrations of chloride and sulphates [29]
HeidelbergCement Germanyi.tech 3DUsed to construct the first 3D printed house in Germany [30]
ICONTexas, USALavacreteMix unique to ICON that is integrated with their Magma feeding system and Vulcan printers [22]
LafargeHolcim SwitzerlandTector 3D BuildThe first dry mortar product for 3D printing with strengths up to 90 MPa [31]
CEMEX MexicoD.fabHas a CO2 footprint 1.5 times lower than mortars typically used in 3D printed concrete available on the market [32]
Luyten 3D Melbourne, AustraliaUltimatecreteIndependently tested and certified by the National Association of Testing Authorities, Australia (NATA), Ultimatecrete reportedly achieves a compressive strength of 82.5MPa after 28 days. The extended product, UltraEco reduces CO2 emissions by 20% compared to the original Ultimatecrete mixture. [33] [34]

Notable projects and applications

Due to challenges of reinforcement and limitations in printing technology, applications of 3D printed concrete have been mostly limited to small-scale projects, including models and residential homes, as opposed to large commercial buildings. There are, however, some notable projects around the world that demonstrate the potential of 3D-printed concrete.

Constructions-3D: La Citadelle des savoir-faire

La Citadelle Des Savoir-Faire is a project that employs 3D concrete printing to construct complex architectural structures. Located in France, this initiative aims to demonstrate the capabilities of 3D printing technology in sustainable construction. The Citadelle serves as an educational center where professionals and students can learn about and experiment with this technology. The project focuses on using eco-friendly materials and advanced design techniques, contributing to the reduction of the construction sector's carbon footprint. Once completed, this complex will have a total internal floor space of about 2565 square meters (27 600 sq ft).

A notable achievement of La Citadelle Des Savoir-Faire is the construction of the world's tallest 3D-printed building, La Tour. Built in 2023, this three-story building has set a new world record for its height at 14.14m (46.4 ft), illustrating the potential of 3D printing technology in creating large-scale structures

ICON: 3D-printed homes

ICON is creating a community of 100 3D-printed homes in Georgetown, Texas. Reservations will begin in 2023 with starting prices in the mid $400,000. The fleet of Vulcan printers can produce eight different floor plans of 3 to 4 bedrooms and 2 to 3 baths. [22] A concrete feeding system known as Magma supplies the Vulcan printer with Icon's developed concrete mix known as Lavacrete, which can adjust for site weather conditions and supply read-to-print concrete automatically. [22] The 90 to 200m2 3D printed homes take around five to seven days to print, compared to a timber frame which would take up to 16 weeks in the same area. [22]

ICON also completed a project in March 2020 for seven 3D-printed homes in Austin, Texas. Each 400 ft2 home was printed in just 27 hours using ICON's Vulcan printer. The first residents moved into the homes in 2020 and are estimated to house 480 of the city's homeless, about 40% of the city's homeless population. [35]

The world's longest 3D printed concrete bridge in Nijmegen, Netherlands The World's Longest 3D Printed Concrete Bridge.jpg
The world's longest 3D printed concrete bridge in Nijmegen, Netherlands

Habitat for Humanity: Affordable Homes Fast

In 2021, Habitat for Humanity, the world's largest non-profit home builder organization, built two 3D-printed homes in Williamsburg, Virginia, and Tempe, Arizona. The Virginia home was 1,200 ft2 and printed in just 28 hours with a COBOD 3D printer, which was about four weeks faster than standard construction. [36] The organization estimated that the 3D-printed concrete walls saved about 15% per square foot in building costs. The 1,738 ft2 home in Arizona was constructed in the summer: a time when construction typically halts due to the extreme heat. 80% of the home was constructed using 3D printing including the interior and exterior walls, while the remainder, such as the roof, was constructed using traditional methods. [36] Habitat for Humanity hopes that 3D printed homes can be a solution for affordable housing as well as labor shortages in extreme climates and environments.

PERI: Project Milestone

The first 3D-printed residential building in Germany was constructed in September 2020 by PERI, using COBOD's BOD2 printer and Heidelberg Cement's concrete mixture. [35] 24 concrete elements were printed at a facility and then transported to the site for assembly. The printer created 1 m2 of wall every 5 minutes, completing the 160m2 home by November 2020. Only two operators were required to print the walls, which included water placement, electricity, and pipe connections. [35]

Nijmegen, Netherlands: pedestrian bridge

In 2021, the Dutch city of Nijmegen revealed the world's longest 3D-printed concrete pedestrian bridge, spanning 29 meters. [37] It was estimated that 3D printed saved about 50% in materials because concrete was only placed where structural strength was required. 3D-printed bridge components were manufactured by BAM and Weber Beamix offsite, where it was then transported and assembled on-site. The previous record holder for the longest 3D-printed concrete bridge was 26 meters, constructed by Tsinghua University in Shanghai. [37]

Economic impacts

3D printed concrete walls for wind turbine bases use less material by implementing a lattice structure 3D printed wall.jpg
3D printed concrete walls for wind turbine bases use less material by implementing a lattice structure

In terms of cost and economics, one advantage of 3D printed concrete is that it does not require formwork, which is used to form the mold for conventional concrete pouring. Formwork can account for up to 50% of total concrete construction due to material and labor costs. [38] However, there are costs associated with machinery including the print head nozzles and supplemental monitoring devices. In addition, 3D printed concrete mixtures often differ from conventional concrete with additions of nano-clay, nano-silica, and other chemical admixtures that aid the extrusion process. [38]

There are indirect economic benefits from 3D-printed concrete in terms of productivity. The construction sector is often highly traditional and for the most part, processes have remained similar over the past decades. This is in large part because current processes are still effective in many construction applications. For example, a study by Garcia de Soto compared a robotically fabricated and conventionally constructed wall assembly with different degrees of complexity and found that conventional construction outperformed robotic fabrication for simpler walls, while the robot was more productive as geometric complexity increased. [38] There was no additional cost due to robotic fabrication and for both cases, material production was the driving factor for cost, as opposed to construction procedures. [38]

Environmental impact

The environmental impact of 3D-printed concrete is heavily dependent on the processes and materials used for a given project. 3D printed concrete has the potential to reduce material in the production of concrete due to the elimination of formwork, but the specialized admixtures and required technology may have just as much of an impact on the environment as conventional concrete construction. A cradle-to-grave life-cycle assessment (LCA) comparing the environmental impact of a conventionally constructed concrete wall with a 3D-printed concrete wall revealed that the 3D-printed alternative only reduced environmental effects when no reinforcement was used. [39] The LCA impacts of global warming potential, acidification potential, eutrophication potential, and smog formation potential were used to measure environmental impacts. Once reinforcement was introduced to the 3D-printed concrete structure, these impacts were greater than conventional construction methods, specifically for global warming and smog formation potential. [39]

Another LCA conducted a similar study comparing conventional and 3D-printed concrete walls but varied the complexity of the structure. It was found that as the complexity of the structure increased, the 3D printed method how a lower environmental impact. [38] This was mostly due to the ability of 3D-printed concrete to achieve complex forms while saving building materials in terms of formwork and concrete volume. [38] Overall, the environmental impact of 3D-printed concrete is influenced by the structure's design and how well the engineer can optimize material usage. On a material basis, the environmental impacts are similar to that of conventional concrete, as a cement binder is still required. However, the streamlined construction process that comes with 3D printing decreases material waste and onsite emissions. [40]

Based on four examples, it has been estimated that the contribution of greenhouse gas emissions per square meter associated with the construction of 3D-printed houses is lower than that of conventionally built ones. [41]

Challenges and limitations

Several limitations prevent 3D concrete printing from being widely adopted throughout the construction industry. First, the material palette that can be used for 3D printed concrete is limited, particularly due to nozzle extrusion and the deposition process of concrete layers, which introduces the challenge of premature collapsing. [38] Therefore, research on material properties and developing high-quality cementitious materials that comply with both structural concrete codes and 3D printing applications is a current area of focus. Due to the sensitivity of a concrete mix, a change in cement type, aggregate, or admixture will impact concrete properties and behavior.

Current building codes consider concrete as a homogenous material when in reality, concrete is anisotropic. This anisotropy is further exposed with printed layers, so new methods for estimating deformations and cracking must be developed. In addition, current material testing for concrete consists of cylindrical specimens in accordance with ASTM C39. [42] There is currently no systematic or theoretical basis for 3D printed concrete, especially when it comes to standard testing.

Current 3D printed projects have been limited to model prototyping and low-rise, large-area buildings as opposed to high-rise commercial buildings because of restrictions in 3D printer technology. [8] Printers need to be compatible with the height of the building, so additional research in 3D printer stability and design is required. There are also challenges with reinforcement in 3D concrete printing, which is required for taller structures. See reinforcement for 3D concrete printing for more details.

Research and development

Pioneering research on the topic of 3D concrete printing is conducted at the ETH Zurich, Loughborough University, Swinburne University of Technology, Eindhoven University of Technology, and the Institute for Advanced Architecture of Catalonia, among many other institutions.

Conferences

Due to the increased interest in 3D concrete printing both from industry and academia, a number of conferences have started internationally. Two industry-focused international conferences were organized in February and November 2017 by 3DPrinthused in Copenhagen. Subsequently, the biannual Digital Concrete academic conference was organized at the ETH Zürich in 2018, the Eindhoven Institute of Technology in 2020, and at the University of Loughborough in 2022. A parallel series of recurring conferences, focusing on the Asia-Pacific region, was organized at the Swinburne University of Technology in 2018, Tianjin University in 2019, and Shanghai Tongji and Hebei Universities in 2020.

Concrete printing can be used directly to produce the final part, or indirectly, to produce formwork in which concrete is cast or sprayed. [43]

3D-printed formworks address some of the major challenges of 3D concrete printing. Reinforcement bars can be integrated conventionally, and the conventionally cast or sprayed concrete complies with building codes. Additionally, the surface quality of concrete is significantly better than in 3D concrete printing. To achieve a smooth surface, the 3D-printed formworks can be coated or polished.

3D-printed concrete as formwork

3D concrete printing with layered extrusion has been used to produce stay-in-place formworks for casting concrete. In this approach, a thin shell, consisting of one or two 3D-printed contours is produced in a first step, either in a prefabrication plant or directly in situ. Subsequently, reinforcement cages are installed and secured in position. Finally, concrete is cast inside the shell, either in one go or in several steps to prevent the build-up of hydrostatic pressure in the lower sections of the formwork. [43]

For structural calculations, the 3D-printed shell is usually ignored, and only the cast concrete is considered load-bearing. However, the 3D-printed shell may be considered for the necessary concrete reinforcement cover that protects the steel from corrosion.

3D-printed formworks for concrete

Alternatively, 3D printing with non-cementitious materials can be employed for the production of formworks for concrete. Extrusion printing with clay, foam, wax, and polymers, as well as binder jetting with sand and stereolithography, have been used for the fabrication of formworks for architectural concrete components.

See also

Related Research Articles

<span class="mw-page-title-main">Concrete</span> Composite construction material

Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures to a solid over time. Concrete is the second-most-used substance in the world after water, and is the most widely used building material. Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined.

<span class="mw-page-title-main">Reinforced concrete</span> Concrete with rebar

Reinforced concrete, also called ferroconcrete, is a composite material in which concrete's relatively low tensile strength and ductility are compensated for by the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement is usually, though not necessarily, steel reinforcing bars and is usually embedded passively in the concrete before the concrete sets. However, post-tensioning is also employed as a technique to reinforce the concrete. In terms of volume used annually, it is one of the most common engineering materials. In corrosion engineering terms, when designed correctly, the alkalinity of the concrete protects the steel rebar from corrosion.

<span class="mw-page-title-main">3D printing</span> Additive process used to make a three-dimensional object

3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer control, with the material being added together, typically layer by layer.

<span class="mw-page-title-main">Ferrocement</span> System of reinforced mortar or plaster

Ferrocement or ferro-cement is a system of construction using reinforced mortar or plaster applied over an "armature" of metal mesh, woven, expanded metal, or metal-fibers, and closely spaced thin steel rods such as rebar. The metal commonly used is iron or some type of steel, and the mesh is made with wire with a diameter between 0.5 mm and 1 mm. The cement is typically a very rich mix of sand and cement in a 3:1 ratio; when used for making boards, no gravel is used, so that the material is not concrete.

<span class="mw-page-title-main">Ready-mix concrete</span> Concrete that is manufactured in a batch plant, according to a set engineered mix design

Ready-mix concrete (RMC) is concrete that is manufactured in a batch plant, according to each specific job requirement, then delivered to the job site "ready to use".

Engineered Cementitious Composite (ECC), also called Strain Hardening Cement-based Composites (SHCC) or more popularly as bendable concrete, is an easily molded mortar-based composite reinforced with specially selected short random fibers, usually polymer fibers. Unlike regular concrete, ECC has a tensile strain capacity in the range of 3–7%, compared to 0.01% for ordinary portland cement (OPC) paste, mortar or concrete. ECC therefore acts more like a ductile metal material rather than a brittle glass material, leading to a wide variety of applications.

Self-consolidating concrete or self-compacting concrete (SCC) is a concrete mix which has a low yield stress, high deformability, good segregation resistance, and moderate viscosity.

Lunarcrete, also known as "mooncrete", an idea first proposed by Larry A. Beyer of the University of Pittsburgh in 1985, is a hypothetical construction aggregate, similar to concrete, formed from lunar regolith, that would reduce the construction costs of building on the Moon. AstroCrete is a more general concept also applicable for Mars.

<span class="mw-page-title-main">Types of concrete</span> Building material consisting of aggregates cemented by a binder

Concrete is produced in a variety of compositions, finishes and performance characteristics to meet a wide range of needs.

D-Shape is a large 3-dimensional printer that uses binder-jetting, a layer by layer printing process, to bind sand with an inorganic seawater and magnesium-based binder in order to create stone-like objects. Invented by Enrico Dini, founder of Monolite UK Ltd, the first model of the D-Shape printer used epoxy resin, commonly used as an adhesive in the construction of skis, cars, and airplanes, as a binder. Dini patented this model in 2006. After experiencing problems with the epoxy, Dini changed the binder to the current magnesium-based one and patented the printer again in September 2008. In the future, Dini aims to use the printer to create full-scale buildings.

<span class="mw-page-title-main">3D bioprinting</span> Use of 3D printing to fabricate biomedical parts

Three dimensional (3D) bioprinting is the use of 3D printing–like techniques to combine cells, growth factors, bio-inks, and biomaterials to fabricate functional structures that were traditionally used for tissue engineering applications but in recent times have seen increased interest in other applications such as biosensing, and environmental remediation. Generally, 3D bioprinting uses a layer-by-layer method to deposit materials known as bio-inks to create tissue-like structures that are later used in various medical and tissue engineering fields. 3D bioprinting covers a broad range of bioprinting techniques and biomaterials. Currently, bioprinting can be used to print tissue and organ models to help research drugs and potential treatments. Nonetheless, translation of bioprinted living cellular constructs into clinical application is met with several issues due to the complexity and cell number necessary to create functional organs. However, innovations span from bioprinting of extracellular matrix to mixing cells with hydrogels deposited layer by layer to produce the desired tissue. In addition, 3D bioprinting has begun to incorporate the printing of scaffolds which can be used to regenerate joints and ligaments. Apart from these, 3D bioprinting has recently been used in environmental remediation applications, including the fabrication of functional biofilms that host functional microorganisms that can facilitate pollutant removal.

Construction 3D Printing (c3Dp) or 3D construction Printing (3DCP) refers to various technologies that use 3D printing as a core method to fabricate buildings or construction components. Alternative terms for this process include "additive construction." "3D Concrete" refers to concrete extrusion technologies whereas Autonomous Robotic Construction System (ARCS), large-scale additive manufacturing (LSAM), and freeform construction (FC) refer to other sub-groups.

<span class="mw-page-title-main">Fused filament fabrication</span> 3D printing process

Fused filament fabrication (FFF), also known as fused deposition modeling, or filament freeform fabrication, is a 3D printing process that uses a continuous filament of a thermoplastic material. Filament is fed from a large spool through a moving, heated printer extruder head, and is deposited on the growing work. The print head is moved under computer control to define the printed shape. Usually the head moves in two dimensions to deposit one horizontal plane, or layer, at a time; the work or the print head is then moved vertically by a small amount to begin a new layer. The speed of the extruder head may also be controlled to stop and start deposition and form an interrupted plane without stringing or dribbling between sections. "Fused filament fabrication" was coined by the members of the RepRap project to give an acronym (FFF) that would be legally unconstrained in its use.

<span class="mw-page-title-main">3D printing processes</span> List of 3D printing processes

A variety of processes, equipment, and materials are used in the production of a three-dimensional object via additive manufacturing. 3D printing is also known as additive manufacturing, because the numerous available 3D printing process tend to be additive in nature, with a few key differences in the technologies and the materials used in this process.

Material extrusion-based additive manufacturing (EAM) represents one of the seven categories of 3d printing processes, defined by the ISO international standard 17296-2. While it is mostly used for plastics, under the name of FDM or FFF, it can also be used for metals and ceramics. In this AM process category, the feedstock materials are mixtures of a polymeric binder and a fine grain solid powder of metal or ceramic materials. Similar type of feedstock is also used in the Metal Injection Molding (MIM) and in the Ceramic Injection Molding (CIM) processes. The extruder pushes the material towards a heated nozzle thanks to

Multi-material 3D printing is the additive manufacturing procedure of using multiple materials at the same time to fabricate an object. Similar to single material additive manufacturing it can be realised through methods such as FFF, SLA and Inkjet 3D printing. By expanding the design space to different materials, it establishes the possibilities of creating 3D printed objects of different color or with different material properties like elasticity or solubility. The first multi-material 3D printer Fab@Home became publicly available in 2006. The concept was quickly adopted by the industry followed by many consumer ready multi-material 3D printers.

<span class="mw-page-title-main">3D food printing</span> 3D printing techniques to make food

3D food printing is the process of manufacturing food products using a variety of additive manufacturing techniques. Most commonly, food grade syringes hold the printing material, which is then deposited through a food grade nozzle layer by layer. The most advanced 3D food printers have pre-loaded recipes on board and also allow the user to remotely design their food on their computers, phones or some IoT device. The food can be customized in shape, color, texture, flavor or nutrition, which makes it very useful in various fields such as space exploration and healthcare.

The reinforcement of 3D printed concrete is a mechanism where the ductility and tensile strength of printed concrete are improved using various reinforcing techniques, including reinforcing bars, meshes, fibers, or cables. The reinforcement of 3D printed concrete is important for the large-scale use of the new technology, like in the case of ordinary concrete. With a multitude of additive manufacturing application in the concrete construction industry—specifically the use of additively constructed concrete in the manufacture of structural concrete elements—the reinforcement and anchorage technologies vary significantly. Even for non-structural elements, the use of non-structural reinforcement such as fiber reinforcement is not uncommon. The lack of formwork in most 3D printed concrete makes the installation of reinforcement complicated. Early phases of research in concrete 3D printing primarily focused on developing the material technologies of the cementitious/concrete mixes. These causes combined with the non-existence of codal provisions on reinforcement and anchorage for printed elements speak for the limited awareness and the usage of the various reinforcement techniques in additive manufacturing. The material extrusion-based printing of concrete is currently favorable both in terms of availability of technology and of the cost-effectiveness. Therefore, most of the reinforcement techniques developed or currently under development are suitable to the extrusion-based 3D printing technology.

<span class="mw-page-title-main">Self-healing concrete</span> Materials science concept

Self-healing concrete is characterized as the capability of concrete to fix its cracks on its own autogenously or autonomously. It not only seals the cracks but also partially or entirely recovers the mechanical properties of the structural elements. This kind of concrete is also known as self-repairing concrete. Because concrete has a poor tensile strength compared to other building materials, it often develops cracks in the surface. These cracks reduce the durability of the concrete because they facilitate the flow of liquids and gases that may contain harmful compounds. If microcracks expand and reach the reinforcement, not only will the concrete itself be susceptible to attack, but so will the reinforcement steel bars. Therefore, it is essential to limit the crack's width and repair it as quickly as feasible. Self-healing concrete would not only make the material more sustainable, but it would also contribute to an increase in the service life of concrete structures and make the material more durable and environmentally friendly.

Luyten 3d is an Australian, Melbourne based, robotics and 3D printers manufacturing company, that designs and manufactures AI mobile 3D printers and 3D printing mix for the building and construction industry.

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