Automation in Construction 89 (2018) 110–119

Contents lists available at ScienceDirect

Automation in Construction
journal homepage: www.elsevier.com/locate/autcon

Applications of additive manufacturing in the construction industry – A T

forward-looking review
⁎ ⁎
Daniel Delgado Camachoa, , Patricia Claytona, William J. O'Brien ,a, Carolyn Seepersadb,
Maria Juengera, Raissa Ferrona, Salvatore Salamonea
a
Department of Civil, Architectural and Environmental Engineering, The University of Texas at Austin, USA
b
Department of Mechanical Engineering, The University of Texas at Austin, USA

A R T I C L E I N F O A B S T R A C T

Keywords: Additive manufacturing (AM), also known as 3D printing, fabricates components in a layerwise fashion directly
Additive manufacturing from a digital file. Many of the early applications of AM technologies have been in the aerospace, automotive,
Construction industry and healthcare industries. Building on the advances in AM in these industries, there are several experimental
3D printing applications of AM in the construction sector. Early investigations suggest that use of AM technologies for
Productivity
construction have the potential to decrease labor costs, reduce material waste, and create customized complex
Safety
geometries that are difficult to achieve using conventional construction techniques. However, these initial in-
vestigations do not cover the full range of potential applications for construction or exploit the rapidly maturing
AM technologies for a variety of material types. This paper provides an up-to-date review of AM as it relates to
the construction industry, identifies the trend of AM processes and materials being used, and discusses related
methods of implementing AM and potential advancements in applications of AM. Examples of potential ad-
vancements include use of multi-materials (e.g., use of high-performance materials only in areas where they are
needed), in-situ repair in locations that are difficult or dangerous for humans to access, disaster relief con-
struction in areas with limited construction workforce and material resources, structural and non-structural
elements with optimized topologies, and customized parts of high value. AM's future in the construction industry
is promising, but interdisciplinary research is still needed to provide new materials, new processes, faster
printing, quality assurance, and data on mechanical properties before AM can realize its full potential in in-
frastructure construction.

1. Introduction with complex geometries [1]. Since then, AM has evolved to include
many types of functional end-use parts. Other industries, such as con-
Additive Manufacturing (AM), commonly known as 3D printing, struction, are starting to follow the early adopters of these new AM
fabricates components in a layerwise fashion directly from a digital file. technologies. Experimental applications of AM in the construction in-
AM is a rapidly growing field that is having an impact on multiple in- dustry started appearing in the late 1990's [2]. These initial proof-of-
dustries by simplifying the process to go from a 3D model to a finished concept applications helped identify potential benefits and challenges
product. AM is unlike traditional manufacturing processes, such as for AM technologies in construction.
formative processes that require the production of a mold to manu- This paper provides an up-to-date review of experimental AM
facture a product in mass quantities or subtractive processes that pro- technologies in construction, identifies the trends in AM processes and
duce significant amounts of waste material as a solid piece of material is materials used in construction, discusses related methods of im-
cut into the desired shape. AM can advantageously fabricate complex plementing AM and potential applications, and identifies research
geometries with no part-specific tooling and much less waste material, needs to foster more widespread use of AM in construction. It serves as
filling a gap left by the other manufacturing processes. a guiding point for researchers interested in the area, to understand
Aerospace, automotive, and healthcare industries have explored the what has been done so far and what needs to be done in the future.
benefits of using AM in their businesses. Initial applications focused on
rapid prototyping to reduce the time required to produce prototypes

⁎
Corresponding authors.
E-mail addresses: dec.daniel@utexas.edu (D. Delgado Camacho), clayton@utexas.edu (P. Clayton), wjob@mail.utexas.edu (W.J. O'Brien),
ccseepersad@mail.utexas.edu (C. Seepersad), mjuenger@mail.utexas.edu (M. Juenger), rferron@mail.utexas.edu (R. Ferron), salamone@utexas.edu (S. Salamone).

https://doi.org/10.1016/j.autcon.2017.12.031
Received 25 August 2017; Received in revised form 25 October 2017; Accepted 19 December 2017
Available online 03 February 2018
0926-5805/ © 2018 Elsevier B.V. All rights reserved.
D. Delgado Camacho et al. Automation in Construction 89 (2018) 110–119

2. Current construction industry and potential for AM Whether through design of complex forms or by direct deposition of
technologies final materials, AM techniques also allow architects and designers to
produce complex interior and exterior geometries that would be diffi-
To transform the current state of construction industry practice, cult (or impossible) and costly to produce using subtractive and for-
innovations are needed in the way construction is performed. mative processes. This potential benefit offers opportunities for new
Challenges to construction include: work in harsh environments, de- designs and forms, giving more freedom to architects, without affecting
crease of a skilled workforce, safety during construction, production of the complexity and productivity during construction [6,19].
large amounts of waste material, and transportation of materials to the Safety, reducing needs for skilled workers, replacing traditional
site, among others [3,4,5,6]. The construction industry tends to be very supply chains, waste reduction, and new geometries are but a few of the
fragmented. With a large number of specialized small and medium- potential applications for AM in construction, motivating further re-
sized construction firms, many are cautious to share advantageous view of AM technologies and their possibilities.
knowledge or technologies with others, further stifling potential in-
novations in the industry [7]. These challenges and limitations to in- 3. Additive manufacturing processes
novation are seen as opportunities for AM.
One prominent motivation for AM construction technologies is To understand the advantages that AM could bring to construction,
worker safety, particularly in extreme environments [8]. When con- it is important to understand the different AM processes. The American
struction in harsh environments is unavoidable, the difficulty and risks Society for Testing and Materials (ASTM) International published a
increase, adversely affecting construction quality and human safety. For document in collaboration with the International Organization for
example, working in freezing temperatures may present challenges in Standardization (ISO) to define standard terminology for AM [1]. In
excavation or concrete pouring, environments with very high tem- this document, ISO/ASTM divided AM into seven different processes:
peratures could cause dehydration to construction workers, and sites
with exposure to chemical or nuclear contamination may pose serious • Vat Photopolymerization – A process of selectively curing a liquid
human health risks [9]. A solution used to address such issues has been light-activated polymer with a laser. An example of this process is
off-site fabrication, where parts and assemblies are delivered to and stereolithography apparatus (SLA), a technique developed by Hull in
assembled on-site, reducing the amount of on-site labor and often in- the 1980's and commercialized first by 3D Systems [4,20,21].
creasing construction quality and consistency. AM could provide ser- • Material Jetting – A process of selectively depositing drops of ma-
vices to the construction industry by reducing exposure of on-site terial in a layerwise fashion. An example of this process is PolyJet
workers to harsh environments and by automating some of the con- technology from Stratasys [21].
struction tasks. • Binder Jetting – A process of depositing a powdered material layer
Another opportunity for AM involves shrinking the supply chain, upon layer and selectively dropping a liquid binding agent onto each
particularly for parts that need expedited delivery. AM allows custo- layer to bind the powders together. Binder jetting was primarily
mized parts to be printed on-demand from a 3D model without sig- developed at MIT in a process called 3D printing (3DP) [21].
nificant lead time. Using AM in construction could reduce the number • Material Extrusion – A process of extruding material through a
of steps involved in the supply chain, bringing the supplier closer to the nozzle and depositing it layer-by-layer onto a substrate. The process
customer [10,11]. Instead of having multiple companies or trades was invented by Crump and commercialized by Stratasys as Fused
producing different structural or non-structural components, each Deposition Modelling (FDM) [21], but it now forms the basis for a
component can be produced directly using AM after it is designed. This very wide variety of inexpensive personal 3D printers.
alleviates productivity problems caused by late deliverables to the job • Powder Bed Fusion – A process of selectively fusing a powder bed
site, which are known to have several deleterious effects to productivity using thermal energy, typically in the form of a laser or electron
and safety, such as working out of sequence [12]. beam. Selective Laser Sintering (SLS) was developed at the
Another motivation for AM is decreased availability of a skilled University of Texas at Austin for polymer materials and commer-
workforce. Contractors are finding it challenging to recruit a workforce cialized by DTM and 3D Systems [21]. Direct Metal Laser Sintering
with the necessary skills (e.g., experienced carpenters, heavy equip- (DMLS) [21,22] and Selective Laser Melting (SLM) are common
ment operators, welders, and fabricators) [13]. The use of AM in con- versions of powder bed fusion for fabricating metal parts.
struction should lower the demand for skilled craft while at the same • Sheet Lamination – A process of successively shaping and bonding
time opening new opportunities for jobs with different skill sets than sheets of material to form an object. An example of sheet lamination
are in current practice. process is laminated object manufacturing (LOM) developed by
Another potential benefit from AM is the reduction of formwork Helisys Inc., in which paper sheets were trimmed to size and glued
(and related temporary structures) used during construction. Concrete together [21]. Ultrasonic Additive Manufacturing (UAM), commer-
structures are commonly built using temporary formwork to maintain cialized by Solidica Inc. fabricates metal objects using ultrasonic
the desired shape of fresh concrete as it hardens, and formwork labor welding [21].
and material costs range from 35 to 60% of the overall cost of concrete • Direct Energy Deposition – A process of fusing materials with fo-
structures [14,15,16]. The most common formwork is made from wood, cused thermal energy that melts the material as it is being deposited.
using subtractive processes to cut it to the desired shape, producing An example of this process is laser engineered net shaping (LENS),
waste material before it is even used. In the 19th and 20th centuries, developed at Sandia National Laboratories [11,21], which is parti-
formwork was produced for a single use only [14]. Currently, to de- cularly useful for repair of damaged metal parts [23].
crease the cost of formwork and reduce material waste, formwork is
being reused. Reducing formwork use not only reduces waste material Although all of these processes have been explored in many dif-
produced during construction, which is considered to be about 23% of ferent industries, AM technologies in the construction sector are in the
the total material wasted in construction [2,17], but it also reduces the earlier stages of development and innovation diffusion, with initial
cost and time associated with placing and disassembling the formwork, applications primarily focused on material extrusion processes for
largely by removing the need for formwork for direct placement of the large-scale components.
construction materials. An alternate approach is to use AM techniques
to fabricate the formwork – a recent practical example is using AM 4. AM in construction
deposition of wax to create molds for precast concrete components that
can be melted and reused [18]. Table 1 presents examples of AM technologies used for construction

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Table 1
Example of AM technologies in the construction industry.

AM process Cementitious Polymer Metallic

Gantry Robotic Other Gantry Robotic Other Gantry Robotic

Binder Jetting Pegna [2]

D-Shape [24]
Material extrusion Contour Crafting XtreeE WASP [38] BAAM [39] C-Fab [41] Mini-Builders
[6,25,26,27] [35] Qingdao Unique Digital Construction [44]
Concrete Printing CyBe Products Develop [31] Platform (DCP) [42]
[28,29,30] [36] KamerMaker [40] FreeFAB™ Wax [43]
WinSun [31] Apis Cor
TotalKustom [32] [37]
BetAbram [33]
3D Concrete Printing
(3DCP) [34]
Powder bed fusion Skanskaa [45] Arupa [46,47]
Permasteelisaa [48]
Direct energy MX3D [49]
deposition

a
Company using a technology.

and the companies using these technologies, categorized by materials knowledge. For large-scale applications, vat photopolymerization
and AM processes. ISO/ASTM 52900 [1] categorizes materials for AM would require large quantities of liquid light-activated polymer and a
as metallic, polymer, ceramic, and composite, where composite mate- larger system, making this process complex and expensive to reproduce
rials are defined as any combination of the other material categories. at larger scales. Small-scale applications using vat photopolymerization
Because many of the technologies use composites (e.g., fiber reinforced and material jetting processes for construction could be explored, since
concrete or fiber reinforced polymer), this paper divides the materials the precision and quality of the finished products are very good for non-
into categories by their binder material in the composites (cementi- structural components, but degradation of the polymer's properties over
tious, polymer, and metallic), to be consistent with commonly used time often push this technology towards molding rather than final part
terms for materials in the construction industry. Table 1 also separates production. For the sheet lamination process, Fabrisonic has developed
AM technologies by the spatial delivery system for the materials used in a 1.8 m × 1.8 m × 0.9 m (6 ft. × 6 ft. × 3 ft.) ultrasonic additive
the process, such as a gantry system, robotic arm, or other (to be dis- manufacturing system, showing that a sheet lamination process is fea-
cussed in more detail later). sible for construction-scale metallic components. It has not been ex-
It can be determined from Table 1 that most of the work being done plored for construction applications thus far due to the high cost of
so far has been in cementitious material extrusion. As mentioned ear- fabrication [52].
lier, the material extrusion process is the most commonly recognized Most of the technologies deliver material using a gantry system.
AM process with many affordable and often open-source, extrusion- Gantry systems are based on a Cartesian coordinate system, where the
based printers accessible in the mainstream. Many researchers and nozzle or building platform moves in three axes (X, Y, Z) [53]. Since it is
companies are leveraging the advances and ubiquity of these open- commonly used for small-scale AM applications, this delivery method is
source platforms to start exploring the use of the extrusion process in relatively simple to mimic and enlarge for construction applications.
construction at small scales at first and then applying the same concepts Although gantry systems have been most commonly used, they do have
at larger scales. Most of the cementitious materials use portland ce- limitations as discussed by others [8,19,35,54], such as transportation,
ment, which is well known in the construction industry to provide re- installation, orthogonal deposition, and size of the system. When pro-
liable and suitable mechanical properties at a low cost. The lower price ducing a large-scale component, a gantry system must be larger than
point makes cementitous materials more affordable to explore initially the component being built, complicating not only the design of the
for AM applications than metallic materials and more functional than gantry system, based on the maximum build dimensions, but also the
polymers for structural applications. There are some AM technologies transportation and labor-intensive installation of such a system. Or-
that do not use portland cement such as D-Shape that uses sand with thogonal deposition is another limitation, since a gantry system only
magnesium oxide and magnesium chloride as the binder [50], and allows extrusion of material perpendicular to the build surface, limiting
World's Advanced Saving Project (WASP) that can use cement, but the curvature to the horizontal plane [8]. Some AM technologies have ex-
main focus is on natural mixtures that contain soil and straw [38]. plored the use of a robotic arm (e.g., C-Fab) or other systems such as
These specific technologies are worth mentioning, since they were small robots that have specific tasks (e.g., MiniBuilders) [44] and delta
considered to be in the cementitious group. Another advantage to in- systems that are similar to gantry systems without a fixed frame (e.g.,
itially exploring AM technologies using cementitious materials and WASP) [38]. Robotic arms increase freedom due to a six-axis motion
extrusion processes is that these materials can already be extruded in and flexibility to program multiple tasks. Also, a robotic arm requires
conventional construction using concrete pumps. The difference is that less space than a gantry system and can even be mounted to a trans-
AM technologies automate the process to extrude material in exact lo- portable platform to provide on-site mobility, as is the case for MIT's
cations and with desired properties. Still, there are challenges asso- Digital Construction Platform (DCP) and CyBe.
ciated with making concrete pumpable and extrudable while at the No matter the method of material delivery or AM process being
same time maintaining its shape and providing sufficient strength to used, printing rate is an important drawback of AM, making scaling AM
support its self-weight post-extrusion. Lim et al. [51] called these main technologies to large-scale applications more challenging. Printing
characteristics as “pumpability, printability, buildability, and open small-scale components already takes a significant amount of time, and
time”. printing larger volumes such as the ones in construction will require
As evidenced by their absence in Table 1, work in the area of vat much greater deposition volumes. Layer thickness also plays an im-
photopolymerization, material jetting, and sheet lamination has yet to portant role in printing time, with higher resolution requiring thinner
be explored in the construction industry to the extent of the authors' layers and more printing time [51]. This challenge may limit AM's

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competitiveness with conventional techniques. Researchers at the Oak rapidly growing. Although the use of polymers in construction is not as
Ridge National Laboratory (ORNL) identified this challenge and have common as cementitious materials or metals, polymers could be used in
been able to increase polymer deposition rates for their Big Area Ad- construction for aesthetic purposes or structural applications when
ditive Manufacturing (BAAM) system to compete with conventional combined with other strength-enhancing materials.
techniques. Now ORNL is looking to increase the deposition rate for Researchers at ORNL and Cincinnati Incorporated (CI) developed
metallic materials [52]. the BAAM system, which can print carbon reinforced (Acrylonitrile-
Additional information on key AM technologies and applications are Butadiene-Styrene) ABS polymer components with a deposition rate of
provided in the following sections as categorized by the material. 45 kg/h (100 lb/h) [60]. Qingdao Unique Products Develop and Ka-
merMaker are other AM technologies that like the BAAM system uses a
4.1. Cementitious materials gantry system to extrude polymer based materials. In collaboration
with Skidmore, Owings, & Merrill LLP (SOM) and the University of
Initial concepts for producing elements for construction using AM Tennessee, the BAAM system was used to build the Additive Manu-
were proposed in the late 1990's by Pegna [2]. One of the first to re- facturing Integrated Energy (AMIE) demonstration project [61]. AMIE
cognize its potential was the University of Southern California (USC), was built to serve as an example of the capabilities of AM in the con-
where Contour Crafting (CC) was developed [27]. BetAbram, Concrete struction industry, producing an energy efficient building with less
Printing, and 3D Concrete Printing (3DCP) are other AM technology material waste. At the same time, this project shows the need and
similar to CC. CC utilizes a gantry system to extrude thick layers of benefits of interdisciplinary research and collaboration with industry
cementitious material to increase deposition rate for large-scale struc- [61].
tures. The technology has trowels attached on the side of the nozzle to Skanska is another construction company that has utilized ad-
smooth the horizontal and vertical surfaces of the material being ex- vancements in the area of AM by printing unique cladding for the Bevis
truded [26]. CC technology was developed with the intent to print Marks Building in London. Complex connections between structural
houses faster in a single manufacturing process [6]. NASA granted CC a elements using cast steel nodes were deemed to be too costly to con-
research award to further develop the technology for space construction struct and exposed welded steel connections between structural ele-
with the intent of using in-situ materials such as regolith rock found on ments did not provide the desired aesthetic [45]. To address these
the moon [55]. NASA's interest in research using AM for construction in concerns, designers decided to use conventional welded and spliced
space directly addresses the previously mentioned construction chal- steel plate structural connections with some architectural covering to
lenges of working in harsh environments and transportation of mate- produce the desired appearance. The complex geometry of these con-
rial, where stringent weight limitations are imposed for space ex- nection regions made AM an attractive option for the architectural
ploration. cladding, which had decorative purposes only (shown in Fig. 2). Using
WinSun is a Chinese company that worked jointly with architectural polymer materials, which are already commonly used in small-scale AM
and structural design companies such as Gensler, Thornton Tomasetti, applications in other industries, for aesthetic purposes may provide a
and others to build an office building for the Dubai Future Foundation low-risk approach to introducing AM into the construction industry
(Fig. 1), which was printed in Shanghai, shipped to Dubai, and then while ongoing work is being done to address the safety and reliability of
assembled on site. The office building was printed in segments in AM technologies used in large-scale structural applications. This ap-
17 days and required only two days to assemble on-site [56]. The cost plication by Skanska proves that AM can be used to provide unique
of printing and assembling was around $140,000 USD for the 242 m2 architectural designs without requiring complex and costly production
(2600 ft2) single-story building, and compared to conventional con- processes.
struction techniques the labor was reduced by 50 to 80% and con-
struction waste was reduced by 30 to 60% [56,57]. Apis Cor is another 4.3. Metallic materials
AM technology that has successfully printed a house on-site, claiming to
reduce the costs compared to conventional construction [58]. While AM has been used to construct small-scale metallic parts in many
detailed information on the mechanical properties of their printed industries, including antenna brackets for the aerospace industry [63],
buildings is not publicly provided by WinSun, this innovation is a complex sand molds to cast a turbine wheel in a single piece for the
promising indication that industry partners are interested in the area of energy industry [64], and gas turbine burner tip repair and modifica-
AM in construction. The city of Dubai expects to have 30% of their tion for the energy industry [65]. However, when moving to larger
buildings printed by 2030 [56]. scales, factors such as printing time and cost may limit the advantages
of large-scale AM applications of metals. Table 1 shows that metallic
4.2. Polymer materials material is the group that is least explored, with two of the examples
(those using Powder Bed Fusion) being small-scale applications funded
Material extrusion using polymers is one of the most pervasive ap- by construction companies. The small-scale components built using
plications of AM at the small-scale, an area where commercialization is powder bed fusion can exhibit comparable mechanical properties to

Fig. 1. Dubai Future Foundation printed office building

[59].

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important to advance research in the area and to identify and improve

potential applications of AM using metallic materials.

5. Potential advancements in construction applications of AM

AM is starting to gain attention in the construction industry based

on the attention it is receiving in other industries such as aerospace,
automotive, and healthcare. Several proof-of-concept experimental
applications have already been implemented in construction, but fur-
ther research is needed to develop and improve the technology fully.
Some potential applications for AM technologies have been identified
and are explained in more detail next. The challenges and gaps that
must be filled to develop and implement the technology in the con-
struction sector fully are also discussed. Table 2 summarizes these po-
tential applications, relates them to some of the existing experimental
Fig. 2. Bevis marks roof (Cladding) [62]. technologies, and comments on development needs.

conventionally manufactured components in some cases, but they are 5.1. Novel forms
expensive with current AM technologies [46,47]. The advantages of AM
become more evident when building up structures or components with Architects started using AM for small-scale building models as a way
complex geometries designed to optimize weight and material use that to present a concept of their design to a customer. Large-scale AM of
would be difficult, if not infeasible, to manufacture using conventional end-use buildings and building materials is allowing architects to pro-
techniques. duce more complex interior and exterior geometries that would be
The Joris Laarman Lab and Arup are using MX3D technology, which difficult and costly to produce using conventional construction pro-
uses gas metal arc welding (GMAW) attached to a robotic arm to weld cesses. AM allows architects to rethink their design and their forms,
small stainless steel segments [49]. As a proof-of-concept of the tech- giving them more freedom without affecting complexity and pro-
nology, MX3D is currently being used to print an 8 m footbridge in ductivity during construction [6,19]. With AM, architects can design
Amsterdam with complex 3D geometries, which was planned to be based on functionality with less worry about constructability of each
finished by summer 2017 [66]. Another example of using AM for op- part. As an example of conventional construction techniques, most of
timized structural topologies was developed by Arup. The company the designs made out of concrete are done based on constructability
investigated various geometries and manufacturing processes for a (e.g., ease of casting concrete using standard formwork). As mentioned
structural node element in a project in The Hague, the Netherlands that previously, formwork in construction accounts for 35–60% of the cost
was used to connect struts and cables of a tensegrity structure used for of a concrete structure. This large cost is due to factors such as labor and
street lightning [46]. In this project, Arup designed several variations of construction time required to assemble and disassembled the formwork.
the node using conventional and AM techniques (Fig. 3) to demonstrate Using formwork with complex geometries increases the difficulty of
the potential savings that can be attained through topology optimiza- construction, increases the time required to design and produce the
tion and AM. Although the structure was already built at the time of the formwork, and increases labor and construction time overall. Since the
investigation, Arup estimated that topology optimization and AM could complex formwork is case specific, the formwork could potentially be
reduce the weight of each node by 75% compared to the original de- used only once, increasing waste during construction.
sign, resulting in an estimated reduction of more than 40% of the While it is sometimes difficult to make an economic case for AM
weight of the entire structure [47]. versus conventional fabrication techniques in other industry sectors
While the use of metallic AM applications in construction is one of [5,9,11,20,46,48,67], AM could start adding value to construction im-
the least explored areas (see Table 1) due to its high initial costs, this mediately, by using it to fabricate formwork with complex geometries,
investigative project from Arup demonstrates the potential for small- or end-use building materials with enhanced functionality, customized
scale metal components to have significant impacts on structural de- geometries, biodegradable materials, or reusability [42,43]. A rela-
signs. Developing more robust industry and academic partnerships are tively easy approach to incorporate AM in construction is the produc-
tion of complex molds, which is already done in other sectors like the
automotive industry. Voxeljet produces sand-based molds for many
industry applications; this type of manufacturing can be extended to the
construction industry immediately to produce complex formwork for
customized parts [64]. MIT suggested using DCP, which is intended to
be used in designing, sensing, and fabricating a component on site for
construction [42], to rapidly extrude foam as formwork. This leave-in-
place foam formwork would provide additional functionality such as
serving as insulation in the finished structure, or providing a desired
finish using subtractive methods. FreeFAB™ Wax, developed by Laing
O'Rourke Engineering Excellence Group, proposed printing molds for
reinforced concrete using wax material that can be created rapidly with
low precision and can later be cut to the precise shape using milling
techniques [43]. Wax would act as the mold during construction, and
then it could be heated to recover and reuse the material for other
molds.
So far, conventional construction techniques have promoted simple
and rectilinear designs to facilitate construction. As AM allows for more
unique designs and curved shapes, new structural forms need to be
Fig. 3. Arup's optimized node [47].
investigated that leverage the benefits of AM and maximize its potential

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Table 2
Potential applications of AM in the construction industry.

Potential applications Examples of current AM technologies Future development needs

Novel forms D-Shape [24], Contour Crafting [6,25,26,27], Concrete Printing [28,29,30], 3DCPa [34], XtreeE [35], Large-scale additive manufacturing
CyBea [36], Apis-cor [37], BAAM [39], KamerMaker [40], C-Fab [41], Skanska [45], Arup [46,47], Structural applications
MX3D [49], DCPa [42], FreeFAB™ Wax [43] Faster printing
On-site printing
Topology optimization D-Shape, Contour Crafting, Concrete Printing, 3DCPa, XtreeE, BAAM, KamerMaker, Skanska, Arup, Standards and testing/Quality
Permasteelisa [48], MX3D control
Precision
Large-scale testing
Structural applications
Bonding
New design approach
Customized parts Skanska Large-scale additive manufacturing
Structural applications
Faster printing
On-site printing
In situ repair Identify areas that need repair
Automation
On-site printing
Bonding
Tolerance matching/correcting Identify areas that need tolerance
matching
Automation

a
Currently under development.

in construction [19,35,42]. However, with these new geometries and construction largely consists of proof-of-concept studies, and detailed
materials, research is necessary to ensure materials and structures information about the performance of materials or finished structures is
achieve levels of reliability and safety expected by current building not always available [50]. To provide the levels of safety expected by
codes. modern engineering standards, more detailed information on material
properties, uncertainty, and quality assurance protocols are needed.
5.2. Topology optimization To begin, standardized material and structural assembly testing
methods should be established, and a database of mechanical properties
In conventional construction, designs that optimize the use of ma- of recent and new AM materials and assemblies should be compiled
terial and geometries for structural performance often result in complex [11]. To assure quality and reliability of printed materials, real-time
or inefficient structures for construction (e.g., making each beam a monitoring of environmental, material, and geometrical properties such
different size based on its load demands). The designs are often opti- as temperature, cooling rate, viscosity, defects, and dimensions of the
mized for construction simplicity, as it results in reduced construction material should be made. Further work is needed to correlate these
time and costs and limits the opportunity for construction error. When factors, as measured during printing, to expected mechanical properties
using AM to automate the process of construction based on 3D model and performance of the finished product. Without sufficient data, it is
data, construction methods are less of a concern in the design phase, unclear how imperfections or variations due to lack of precision during
allowing optimization for reduced material/weight, and potentially a construction would affect performance of structures produced using AM
more cost-effective solution. [11,34].
Topology optimization has shown benefits in other industries such Another challenge is potential scaling effects when methods devel-
as aerospace and automotive. For example, GE manufactured fuel oped and tested at small-scales are applied to large-scale applications.
nozzles as single components with AM, resulting in a 25% reduction in AM has been shown to produce reliable products in the small-scale;
weight, five times increase in strength, and improved combustion effi- however, when producing large-scale components, the structure may
ciency for their new engines compared to nozzles produced using behave differently from a small-scale component either while it is under
conventional methods [68]. As previously discussed, Arup explored use construction or in its final state. Thus, testing at the large scale is re-
of topology optimization and AM for a structural node for their ten- quired. Production of large-scale specimens requires special facilities
segrity structure project, resulting in significantly reduced weight and that may not be available to every company. Currently, testing of small
size. XtreeE has investigated optimizing an element by inserting voids specimens is done to estimate material and element behavior, but
where material is not needed for structural purposes and using those scaling effects could result in very different behaviors for materials and
voids to provide additional functionality, such as thermal insulation elements produced at larger scales. The anisotropic behavior of as-
and soundproofing [9,28,35]. Other work has explored the use of such semblies produced using extrusion-based processes, due to the layered
voids for utility access and pass-through in new construction [6,51]. deposition pattern, makes the final element vulnerable to failures along
AM and topology optimization allow architects and engineers to rethink the layer bonding interfaces [4,16,19]. For structural applications,
their design based on added functionality. work is needed to improve layer bonding performance or provide cross-
Several challenges arise when reducing the amount of material re- layer reinforcement to increase resistance to forces acting across layers.
quired for an assumed loading scenario, such as producing structures For example, AMIE's solution requires steel rods post-tensioned
and components with reliable material properties and sufficient levels throughout the building to increase layer-to-layer frictional resistance
of safety. Significant work has been done to quantify the expected va- and improve strength of the printed polymer layers [61].
lues and variation in material properties currently in use in the con-
struction industry, and testing standards have been developed to verify 5.3. Customized parts
performance. Building codes and engineering practices are based on the
experience and data available from decades of testing and research on Although construction cost can be minimized by reducing labor,
material and structural behaviors. Current research in the use of AM in material, transportation, and time required for a project, past studies

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have indicated use of AM in construction may increase costs [5,46,48]. dangerous for workers to enter these buildings to evaluate the level of
Mrazovic stated in a study done for Permasteelisa [48], that 3D printing damage and repair it. AM could be used to construct a temporary
using powder bed fusion of metallic materials is possible but will likely support structure inside the damaged building to allow for inspection
be cost prohibitive, mainly due to the processing speed (30% of the cost and even restoration, decreasing the risk to humans. AM could also be
of a steel component being the material and 70% being the processing used for the repair and maintenance of structures located in hazardous
time). Conversely, WinSun claimed that labor costs for the Dubai Future environments, such as chemical and nuclear facilities. AM with robotic
Foundation building, which is constructed from extrusion of concrete arms could operate in limited access areas as well as in harsh en-
material, were reduced by 50 to 80% using AM [57]. Once the materials vironments, adding repair material where required with precise di-
and machines become more common in the market, the cost associated mensions and avoiding worker exposure.
with using AM may also be reduced through economies of scale [10]. Future work is still needed to improve the automation process of
Until now AM appears to be most economical for producing unique placing material on an existing structure before moving to more com-
parts rather than parts that can be mass manufactured. plicated and multi-step tasks of detecting current conditions of a
The benefits of being able to manufacture unique parts on demand structure, using subtractive processes to remove damaged areas, and
without relying on an inventory of standardized parts can be leveraged then repairing what is needed. Research that focuses on the bonding
to print customized parts for each project. Architects and engineers between new layers of material to the existing structure also needs to be
have limited their designs to standardized shapes and parts to smooth investigated to assure good performance of the repaired structure.
or reduce the construction time. When a unique part is required for a Referencing Table 2, it can be seen that no research has been done that
project, it takes more than just the design to make it a finished product. includes both the use of AM and automation of tasks for repairs in
Extensive planning is required for manufacturing the part and testing it construction. Most of the existing AM technologies for large-scale ap-
to meet current standards. Although using AM would still require plications are not suitable for changing working area conditions that
testing to meet standards, it could reduce the manufacturing costs and may be encountered during repair situations. Further work is needed to
time associated with converting the design into the finished product, develop AM technologies suitable for repair applications in a range of
making it beneficial for customized part production. work conditions.
Every company and construction trade has different needs, some of
them being very specialized. AM is ideal for specialized parts with 5.5. Tolerance matching/correcting
uncommon dimensions or geometries that may not be cost effective to
produce using other conventional manufacturing processes. The con- Another potential application is the use of AM for tolerance
cept has already been demonstrated for non-structural applications, like matching. The construction industry is often faced with the challenge of
the work done by Skanska to print unique claddings. Customized parts having elements or modules on the construction site that do not have
have been produced in small-scale in other industries and have shown a precise dimensions or sufficient tolerance for assembling them, re-
great reduction in cost and time; examples include customized tools for quiring on-site modifications, complicating the assembly process, and
aircraft maintenance in the aerospace industry [69], customized dental delaying construction. Matching issues with prefabricated components
prosthetic devices in the healthcare industry [70], and custom archi- are due to the inability to maintain tight tolerances, introducing errors
tectural models to present a design or an idea to a client [20,21]. The that propagate during construction that could risk the integrity of the
construction industry should start exploring the use of AM for custo- structure [71,72]. Tolerance issues can happen in many parts of the
mized parts, beginning with small-scale parts that can be reliably fab- process starting from design all the way to assembly. Factors that create
ricated using current AM technologies. Using AM, customized parts can tolerance issues are human errors in the design, fabrication, or con-
also be built specifically for as-built dimensions, thereby enabling the struction phase, changes in dimensions of the elements due to changes
delay of part design and production. Similarly, there may be cases in in temperature during fabrication or construction, or when the ele-
which components are lost or damaged and waiting on their replace- ments are damaged during transportation or installation to mention
ments may cause construction delays. These examples are situations in some [72]. As an example, Kalasapudi et al. [71] describe a bridge
which “last minute” production of components on-site using AM can project in Iowa where misalignment issues caused rework for a pre-
add value in construction. fabricated concrete girder; bending of steel bars at the ends was re-
quired to make the component fit within the space available.
5.4. In situ repair AM brings the benefit of producing components with precise di-
mensions based on design drawings, which is important for modular
Much of the initial work investigating the use of AM in the con- construction, and at the same time the ability to match tolerances in
struction industry has been on methods of constructing new elements; real time by printing customized connectors or infill as needed on-site.
however, the potential benefits of using AM for in situ repairs of ex- AM opens the opportunity to accommodate wide tolerances for pre-
isting structures are significant. In the small-scale, other industries, fabrication and assembly, by then using AM to adjust to the required
such as the Siemens gas turbine burner tip repair [65], are already tolerances, possibly reducing the time spent during fabrication, con-
investigating the potential of repairing components using AM. Damaged struction, and on-site modifications.
areas are removed using milling techniques and then new layers of Architectural detailing requires rigorous work on-site; the use of AM
materials are added using AM to restore it to its original condition or to could ease the production of such details. AM can also be used to print
modify the component to meet current design needs. As they age, customized sleeves, sleeve connectors, and piping hangers based on the
buildings often require maintenance, rehabilitation, and replacement. space available on-site; these components are sometimes problematic
Maintenance or in-situ repairs could be done using machines that could because standard parts do not fit properly.
scan the structure, detect the areas needing a repair, and do the repairs
using AM techniques or even using hybrid systems. AM is already 6. Potential advancements in methods of implementing AM
capable of using reverse engineering to scan an object and record its
geometric data to produce a 3D model [21]. There is an opportunity to Advances in AM processes themselves may also facilitate the reali-
use the same or similar technology to measure other information such zation of potential applications in the construction industry. These
as material deformations or defects that could detect areas that need methods, including fabrication using multiple materials, using in situ
further maintenance. resources, utilizing hybrid techniques that combine AM processes with
Another potential application is repair of infrastructure that is da- subtractive and formative processes, and expanding opportunities for
maged by a natural or human-made disaster. Often, it becomes both off-site and on-site fabrication, are discussed below.

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D. Delgado Camacho et al. Automation in Construction 89 (2018) 110–119

6.1. Off-site/on-site fabrication surrounding areas. Further research is needed to decrease printing time,
provide the desired structural properties, develop customizable designs,
AM is most commonly implemented in a controlled environment for and ensure repeatability.
high quality parts in both small and large-scale applications. The con-
trolled environment is desirable as materials can react differently and 6.4. Multiple materials
provide different mechanical properties if the environment is suddenly
disturbed. For example, in a common small-scale FDM system, en- Formative processes (e.g., casting of concrete in formwork) typically
closures are used for an ABS polymer like the one used in the BAAM utilize a single type of concrete for a large portion of a structure. AM
system because the extrusion and material fusion processes are sensitive could allow multiple materials to be deposited during the construction
to temperature changes. The same problem occurs when printing with process using extrusion based processes with multiple nozzles for dif-
metallic and cementitious materials, which are also sensitive to tem- ferent materials. Bos et al. [34] proposed a concept of material custo-
perature, humidity, and other environmental factors. The current on- mization by location, for example, depositing ultra-high performance
site fabrication AM systems still require that certain environmental concrete where structural demands are largest, and low-strength con-
conditions be met for best results or that a type of enclosure is provided cretes for finishes and areas where structural demands are lower.
to keep desirable temperatures. For example, Rudenko [32] mentions Using multiple materials is not something new in construction.
that TotalKustom technology is likely to be ideal for warm regions. Concrete and steel are commonly used together due to their com-
Research is needed to develop more robust technologies and ma- plementary mechanical properties and their similar thermal expansion
terials for AM that can facilitate on-site construction. Sensitivity of part behavior. Concrete exhibits high compressive strength at a relatively
properties to environmental factors during fabrication is an important low cost, but it exhibits brittle failure and negligible tensile strength. It
topic of concern, as well as the finishing of printed components. requires the integration of steel reinforcement to resist tensile stresses
Another issue is the transportation and setup of AM equipment at the and to exhibit more ductile behavior. A combination of AM processes
building site and its ability to adapt to different applications with dif- could allow simultaneous material extrusion and direct energy de-
ferent geometries, access levels, and underlying materials. position processes to simultaneously deposit material for concrete and
steel reinforcement, respectively, resulting in reinforced concrete
6.2. Hybrid techniques structures similar to those used in practice today; however, using AM
processes allows the concrete and steel reinforcement to take on geo-
Hybrid systems that combine subtractive, formative, and additive metries that are optimized for the structural demands and that may be
processes could be implemented to facilitate the incorporation of AM in challenging to produce using conventional techniques. In this approach,
construction. Hybrid techniques can improve part resolution and sur- two nozzles could be used to fuse metals and extrude concrete sepa-
face finish without increasing printing time by, for example, utilizing rately. New cementitious and metallic materials developed for AM ap-
AM for a low resolution base part that is then finished with a sub- plication may exploit the benefits of these common construction ma-
tractive technology such as sanding, milling, or machining. Taking terials or may be completely new to the construction industry. Details
advantage of the benefits of each technique, while still exploring new on how this multi-material deposition process would be executed are
materials, processes, and technologies provided by AM, will foster an definitely worthy of future research to address challenges such as
environment for innovation in construction. An example previously temperature difference between concrete extrusion and metal fusion.
mentioned is MIT's DCP which tries to incorporate additive, subtractive, The potential of printing multiple materials, is something that could
and assembling techniques in one all-purpose construction system [42]. bring advantages in the construction industry, but research is needed to
In construction, it could be advantageous, for example, to combine AM develop new construction materials that are optimized for use in AM
of a basic construction component, with finishing processes that pro- while still providing desirable structural performance. These new ma-
vide the external appearance desired by the end customer. terials can be developed for improved fresh-state and final-state prop-
erties depending on the desired AM process and application, such as
6.3. In situ resources viscosity (for extrusion processes), early strength gain after deposition,
thermal expansion and resistivity, layer-to-layer mechanical bonding,
Using locally available resources can reduce material transportation ductility, reduced embodied energy, and more. At the same time, these
costs and provide more sustainable design solutions in locations that new materials must be economical for AM to become a feasible alter-
are difficult to access. CC and D-Shape are investigating the possibility native in construction [11].
of building structures using in situ resources such as regolith rock on
the Moon, since sending raw construction material to the Moon is very 7. Conclusion
difficult and expensive [55,73]. Another technology known as WASP
has focused on using AM technologies to build “zero-mile homes” that AM is having an impact on many industries and growing as an al-
utilize on-site materials to create housing in places where it is hard to ternative or complimentary approach relative to other manufacturing
find access to construction materials [38]. methods such as formative and subtractive processes. Aerospace, au-
Additionally, automation of construction using AM processes and tomotive, and other industries have explored the benefits of using AM
local materials would allow for disaster relief construction in disaster- in their day-to-day activities, finding new applications for different AM
affected regions that may have limited workforce and construction processes. The construction industry has become interested and has
material resources. By dropping a 3D printer and bulk supply of raw started exploring proof-of-concept AM applications that could be ap-
materials into the affected area or by using the in situ materials on site, plied in the sector, looking to mitigate current challenges such as
a minimum number of workers would be needed to construct custo- worker safety in harsh environments, decreases in skilled workforce
mized houses to satisfy personal living needs for those displaced by the availability, and waste of materials. More broadly, AM is seen as a way
disaster. Labonnote et al. [19] suggest the use of AM in construction of of addressing construction productivity challenges.
first response shelters that can be quickly deployable. The benefits of While there are a range of AM technologies, most recent work in the
AM would provide unique and customizable 3D designs that could construction industry has been focused on material extrusion process
produce printed homes to meet the long-term needs of community using cementitious materials for large-scale applications. Work with
members well after the disaster. cementitious material extrusion is perhaps due to the experience of the
Research using in situ resources is still in its early stages, only sector with the material and the availability of material extrusion sys-
proving the concept of building up layers of materials collected from tems to experiment with. Other experiments with polymers have been

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D. Delgado Camacho et al. Automation in Construction 89 (2018) 110–119

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