CHAPTER 1

INTRODUCTION

1.1 GENERAL

After more than 25 years of research, development and use, three-dimensional (3D)
printing in various industrial domains, such as aerospace, automobile and medical,
continues to grow with the addition of new technologies, methods and applications.
One of such methods being explored currently, both in academia and in construction
practice, is the 3D printing of concrete.

Conventional construction process appears to be relatively simple and

systematic,requiring two-dimensional (2D) drawings and scale models (for evaluation
of the building designs), cumbersome formwork and much skilled labour to build any
kind of free-form structures. Work-related injuries and illnesses pose a continuing
threat to the health and well-being of construction worker . Construction industry
continues to have a higher rate of fatality, injury and illness than any other industries .
This compels the introduction of 3D printing to be coupled with building information
modelling (BIM) for tracking and monitoring new variables introduces in a dynamic
working environment such as a construction site to increase workplace safety.

Combining BIM and 3D printing would also make it easier to create highly
customised building components and facilitating complex and sophisticated design;
however, there are still numerous challenges related to scale, materials, delivery
system and suitability to adverse environments. Although work by researchers in the
field of aerospace and manufacturing have shown that 3D printing could be the
solution to reduce cost, there is no investigation to support that the same savings will
apply to building and construction (B&C) industry. However, it is still appropriate to
assume that utilising 3D printing could minimise cost for the construction of B&C
applications with aesthetic design based on cost analysis investigation done by
researchers in other fields. Considering global demand to reduce CO2 emission, there
is a need for innovative construction technologies to not only pave the way towards a
future of sustainable construction, but also to reduce construction and facilities

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management costs while providing a competitive edge. Construction formwork which
typically accounts for 40% of the total budget for concrete work can be avoided
during the building process, ultimately reducing the project timeline without incurring
additional cost. With 3D printing technology, design of structures will not be limited
to a collection of monotonous prefabricated elements.

This paper introduces the variants of concrete printing process under development
around the globe and provides the latest research trend by analysing publications over
last 20 years. Subsequently, the paper will highlight the ongoing research at Singapore
Centre for 3D Printing (SC3DP) with possible topology optimisations and the
significance of incorporating BIM. Finally, by analysing the trend, some future works
are proposed that can eliminate or reduce the challenges and limitations for 3D
printing in B&C industry.

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CHAPTER 2

LITERATURE REVIEW

2.1 GENERAL

The present chapter includes the review of all possible research works regarding the
3D printing in civil engineering.

Arabella Akman et.al.,(2023) The current construction industry for civil and
structural engineering is considered to be one of the growing industries in the world.
With the push toward a more digitized industry, emerging trends such as additive
manufacturing and the use of three-dimensional (3D) printing technology, along with
consumer demand, are resulting in automated development with multiple benefits.
Successful applications for small-scale construction projects that have implemented
3D printing have shown improvements in cost, production time, and design freedom
and complexity. However, for large-scale applications, there are various limitations
and factors hindering the adoption of additive manufacturing technologies. In this
paper, a systematic literature survey of recent 3D printing technologies was conducted
specific to the area of construction engineering, and the various techniques, materials,
software, and technical and nontechnical aspects were analyzed. The key applications
and their benefits are outlined, and their potential for large-scale applications is
articulated. Future research areas for these components are suggested to strengthen the
technical readiness and feasibility of adopting 3D printing technology in construction
engineering and industries.

Xin Ning et.al.,(2021) This research investigates the use of 3D printing (3DP) in
construction, emphasizing the need for a balanced approach that considers both
technical and non-technical aspects. While past research has focused heavily on the
technical side of 3DP (materials and processes), this study argues that non-technical
challenges can hinder its real-world implementation. To address this gap, the
researchers conducted a systematic review that combined quantitative and qualitative
methods. The quantitative analysis explored the current state of 3DP research through
scientometric methods, while the qualitative analysis examined technical aspects (like

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materials and processes) alongside non-technical challenges and trends. These non-
technical considerations include economic factors (cost), environmental impact, social
acceptance, and legislative hurdles. This comprehensive approach aims to provide a
roadmap for advancing 3DP in construction. The paper offers valuable insights for
construction professionals, helping them understand existing 3DP technologies, assess
their applicability for specific projects, and identify areas where further research is
needed.

L. Romdhane et.al.,(2020) This research paper examines 3D printing in construction,

evaluating its pros and cons. 3D printing offers benefits like improved construction
methods and reduced environmental impact. However, challenges exist, mainly
related to materials. Printing materials need to be printable, structurally sound, and
have sufficient working time before hardening. Other hurdles include large-scale
printing, building code compliance, and potential risks in areas like material safety
and cyber security. This paper addresses the under explored area of risks in 3D
printing construction and proposes areas for future research.

Nithesh Nadarajah.,(2018) In the 21st century, the construction industry has

witnessed the emergence of novel methods and materials. Among these innovations,
3D printing with concrete-like material stands out. This technique offers the potential
for personalized large-scale residential housing, particularly benefiting the lower and
middle classes in Finland. By leveraging 3D printing, we can overcome traditional
shape restrictions and create customized structures. However, despite its promise, the
building industry lags behind other sectors in adopting 3D printing technology. Key
areas of exploration include optimizing the printing process, investigating new
printable materials, and understanding the unique properties of 3D-printed concrete.
The future of 3D concrete printing holds immense potential, spanning applications
from medical devices to household items. As we delve deeper into this technique, we
unlock opportunities for sustainable, cost-effective, and customizable construction.

İbrahim Engin et.al.,(2018) Technological changes have remarkable effect on

today’s business world that triggers industries to reestablish the production systems.
3D printing has evolved with the new technological developments in additive
manufacturing over the last three decades. 3D printing technologies enable design

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optimization and have advantages over conventional production methods. All
industries should adopt the new era in order to survive in a rapidly changing
competitive environment. The construction industry is also under technological
developments’ pressure to change. Therefore, 3D printing technology is under a great
attention in construction industry as a new strategic challenge. The construction
industry takes 3D printing as an idea of a new building technology. The main aim of
this paper is to review the 3D printing technology applications of other industries, to
review 3D printing attempts in construction industry and to comment on possible
application areas for 3D printing intentions in construction industry. This paper
summarizes the literature on 3D-printing applications used in other industries, with a
focus on adaption strategies in construction industry. Major literature databases are
reviewed about 3D printing researches and the trials of implementations in
construction industry. Collected data is interpreted in the construction research jargon.
The possible implementation areas in construction are suggested for future
developments. The paper results in identifying and classifying the new developments
in 3D printing technology in various industries and making projections on the possible
adaptation areas in construction industry.

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CHAPTER 3
3.1 CURRENT 3D CONCRETE PRINTING SYSTEM
3D concrete printing technology is based on modeling, using a special printer to spray
material, and then continuously increase the material layer by layer printing. 3D
printing technology is mainly divided into three categories: contour technology, D-
shape and concrete printing. 3D printing technology mainly includes modeling,
segmentation, printing, spraying and post-processing
From the point of view of the situation, there are three main types of 3D concrete
printers available. As shown in Figure 1, they are gantry system, robot system and
crane system, and there have been excellent cases of using these printers. Gantry is a
typical crane, as shown in Figure 1(a). the gantry is a very common crane, and its
height is generally fixed. However, the crane system shown in Figure 1(c), which is
adjustable in the vertical direction, offers some flexibility. Gantry printers and crane
printers are usually used because they are easily scalable in size. In contrast to these
two printers, robot printers usually have a fixed size, which makes it difficult to go to
scale. Therefore, the relative advantage of a 6-axis robot allows it to do tasks that a 4-
axis gantry printer cannot do. In addition, gantry printers are superior to robotic
printers if the design of the print target is not complex. This is because the robot costs
more and the load on the robot arm is usually lower than that of a gantry printer.

Figure :1 (a) 4 axis gantry printer (b) 6 axis robot (c) crane printer

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Figure 1(a) shows a four-axis gantry system with adjustable printing envelope, it is
reported that Wen Sun has built many houses by using this technology (gantry printer).
The printing method is similar to that of inner and outer beads in a layered manner,
and honeycomb-like internal structures (Fig1(c)).

In some cases, during printing, steel bars are manually placed between layers. The
mixture of concrete materials used by Wensun contains fiberglass, steel, cement,
hardener and recycled construction waste. However, Wen Sun built many houses are
not completely 3D printed. The structural elements are segmented in the factory and
then shipped to the site for assembly.

In the current research, 3D printed concrete technology is mainly applied to build

low-rise buildings. For high-rise buildings with complex structures, currently only
prefabricated parts can be printed one after another and then finally encapsulated
according to the assembly principle, thus losing the advantage of 3D printing itself for
rapid prototyping. Another company that uses inner and outer beads to print in a
layered way is the Sebby Additives Industry Company, founded in the Netherlands.
They printed a mortar to reach an acceptable strength in 5 minutes.

Some researchers have experimented by attaching the print head to an imprecise 6-

axis manipulator (Fig 1(b)), which takes into account the diversity of printer speeds
and heights. The additional rotational axis of the robot on the gantry printer gives the
designer more freedom to design complex shapes. With a diameter of up to 6 meters,
this robotic printer is capable of printing larger components in a short period of time.
A Russian company has developed a crane-type printer (Figure 1(c)) capable of
printing large areas of up to 58 m^2, which has almost no height limitation

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CHAPTER 4
3D CONCRETE PRINTING CONSTRUCTION
TECHNOLOGY AND MATERIALS
Dry mortar is commonly used as printer "ink" in 3D printed buildings. The material
requirements of 3D printing construction dry-mix mortar are similar to those of
printing concrete, both of which require it to have good plasticity and other properties.
Its performance requirements are very strict. Dry mixing mortar is cement, sand,
mineral admixture and functional additives according to the relevant proportion, by
professional manufacturers in the dry state of well-proportioned mixing, mixing into a
granular or powdery mixture. The next is to dry mixed mortar with dry powder
packaging or bulk transported to the site, according to the provisions of the ratio of
water mixing can be directly used. Dry-mixed mortar is favored by engineering
circles because of its convenience, flexibility and other excellent properties, and has
been more and more widely used in recent years.

4.1 Pumping and control system

The pumping of concrete material is important in 3D concrete printing system
because of its need for fast delivery and the inability to separate particles. The pump
must be able to convey the concrete material with the specified requirements, which is
a challenge. This is because of the large size of the aggregate particles and the wide
range of w/c. Freshly mixed concrete needs to retain its shape even after printing to
ensure its high viscosity, which requires relatively high pumping pressures in the
range of 1 to 4 MPa.

The mixing of concrete materials needs to be adjusted to avoid segregation under

these pumping pressures and to form a thin coating layer for good pumpability. The
separation during high pressure pumping may lead to the loss of the smear layer and
lead to material blockage in the pipeline. For better printing, a balance is needed
between the feed system, nozzle and material characteristics. The pump speed needs
to be adjusted according to the size and shape of the print object. When the angle of
the printing path changes, the deposition of materials should be controlled to avoid
higher material deposition. Print heads (nozzles) can usually change direction fairly

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quickly. However, the perfection of geometry requires a reduction in pump speed at
particularly sharp curves or discontinuities. Therefore, it requires a proper control
system to adjust the speed of the printer to accomplish the job of nozzle rotation and
pumping the material.

4.2 Building Materials

Building 3D printing technology for concrete materials can be divided into: working
performance, mechanical performance and durability. Among them, the working
performance can be divided into extrudability, bonding ability, molding ability,
setting time and printing strength control. The first step in preparing materials that can
be 3D-printed is to select constituent materials, namely raw materials. The raw
materials of 3D printed concrete studied by scholars at home and abroad mainly
include cement, fly ash, silica fume, limestone powder, meta kaolin, fine sand, nano
silicon, superplasticizer, retarder, early strength agent, viscosity modifier, water and
different kinds of fibers. Among them, cement in addition to the most widely used
ordinary Portland cement, there are sulfur aluminate cement and so on.

3D printing is very demanding and requires concrete with excellent durability. In

order to ensure durability, the material's resistance to seepage and frost must be taken
into account. In general, the use of admixture-doped concrete or high-quality cement
as the base layer of 3D printed products ensures a certain degree of insulation and
impermeability, but the actual printed concrete products are brittle and prone to
fracture. Therefore, for 3D concrete printing technology to make a breakthrough, this
requires concrete materials with excellent printing performance, structural
performance and hardening performance.Since no support formwork was used in the
printing of 3D concrete, so ordinary concrete could not be used. To ensure little or
essentially no deformation of the mat, concrete with up to zero slump needs to be used.
To facilitate pumping, low-viscosity concrete can be used, which requires intervention
by adding a chemical accelerator at the nozzle for fast setting after printing. The
production of low-slump concrete requires special attention to the granularity
characteristics of fine particles. In this respect, the particle shape has great influence
on the compacting performance and the strength of the green.

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Thixotropic properties are ideal, so materials with high static viscosity can undergo
microstructural changes and become less viscous by removing flocculation during
agitation or stress. But once squeezed out and stopped, it reforms or re-flocculates and
becomes highly viscous. Thixotropic materials subjected to rheological testing require
a higher torque (static torque) to flow when they are at rest. Over time, the torque
required for a specific angular velocity in rheological testing decreases, which is
referred to as dynamic torque. We can learn from the experience of previous concrete
applications where water/binder ratios (w/b) and chemical additives were successfully
used to adjust flocculation processes or microstructure thinning (anti-flocculation) and
reconstruction (re-flocculation) depending on the aggregate gradation

4.3 Support Materials

Many people think that 3D printing should be automatic. As soon as you press a
button, the building is automatically printed. But the reality is not so, from the printer
out of the print often have to go through a variety of surface treatment before it can be
used. The most important step in these steps is the treatment of the supporting
material, which is the post-processing we mentioned earlier. 3D printing works by
adding layers of cross sections together to form a three-dimensional object. This
forming method has certain limitations on the shape of the object. If a top level
outstanding structure object, up from one layer at the bottom of the printing, print to
objects above a sudden need to print the cross section of a large, more than all the
bottom of the print head at this time or in accordance with the need to print the
trajectory of motion, but not after extrusion due to below materials can support its
structure, material will fall under the influence of gravity. The minor consequence is
the accuracy of the print, the serious consequence is to become a messy ball, which is
a complete failure of the print. A similar problem occurs when printing objects with
hollow structures inside them.
The use of supporting materials is a solution to this situation. Support materials come
in many forms. The most common is the use of the printing material itself, by creating
a fine lattice or columnar structure under the overhanging form, so that the
overhanging part of sufficient support, at the end of the printing with a file and
sandpaper to remove the support structure.

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4.4 3D Concrete Printing Construction Process
The construction process of 3D concrete printing is mainly divided into 5 steps. It is
concrete mix proportion design, concrete preparation, concrete transportation, cloth
printing molding and finished product maintenance these steps. Flow chart shows the
steps of 3D concrete printing

Flow chart: Steps of 3D concrete printing

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4.5 Reinforcement in 3D Concrete Printing
To ensure better structural performance of the building, it is often necessary to add
suitable reinforcement to the concrete structure. Figure 4 illustrates the previous study
of SH inner and outer beads extruded by steel bars in a layered manner.

Figure 2. SH Extrusion of steel bars printed in layers with inner and outer beads

In fact, installing rebar in the 3D concrete printing process is a challenging task.

Using current printing technology. The placement of vertical steel bars and the
connection between steel bars are not simple. In order to strengthen the structural
strength of 3D concrete printing, we can try to introduce some alternative
reinforcement methods. Examples include composite fibers in mixed concrete, carbon
fibers, or fiber-reinforced polymers, but this requires thorough research and
innovative adaptation of 3D concrete printing technology. Preliminary studies have
shown that 3D prestressed concrete can significantly increase the load-bearing
capacity of structures.

We can try to develop a hybrid printing system that can respond to different needs
and thus greatly enhance the structural strength. According to experiments, it is
possible to manually place reinforcement bars, as shown in Figure 3, in the
intermediate layers (Figure 3a), or between the fiber layers (Figure 3b and Figure 3c),
or by directly extruding the concrete through the sides of the manually pre-tied

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reinforcement cage (Figure 3d). The elimination of this intervention allows for a basic
automation of the printing process, with the advantages of geometric accuracy,
reduced manufacturing time, and reduced labor costs.

Figure 3. Steel Reinforcement used in 3d printing

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4.6 Table 1. Advantages of 3D printing technology in
construction
3D printed buildings can be formed in
one time without supporting and
removing molds, which reduces the
Materials
waste of concrete materials and improve
the utilization rate of materials.

Compared with the traditional

construction technology, 3D printing
technology greatly improves the
Construction period production efficiency, which can reduce
the construction period by 50% and
shorten the payback period of
investment.

Green environmental protection The printing process produces little

n o i s e , d u s t an d st r o n g v i b r a t i o n s .

Ac c o r d i n g to th e p r e s e t co m p u t e r
program, layer by layer construction, to
Accuracy a large extent to avoid human error, to
en s u r e t h e q u a l i t y o f t h e fi n i s h e d
product.

3D printing can be done according to

different requirements, thus reducing
Immediacy inventory, and can also be formed once,
without assembly, realizing immediacy
from printing to delivery.

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 Extreme conditions refer to the
environment in which traditional
manufacturing techniques are no longer
Applicable to extreme conditions applicable and external conditions make
people's activities difficult, such as
weightlessness or extreme cold. In some
special cases, 3D printing technology
c a n re p l a c e m a n u a l c o n s t r u c t i o n .

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CHAPTER 5
5.1 Durability of 3D Printed Concrete Buildings
1 Material Composition: The choice of concrete mix and additives affects the
strength, durability, and resistance of the printed structure to environmental factors
such as moisture, chemical exposure, and temperature variations.

2 Structural Integrity: Proper design and engineering ensure that the 3D printed
structure meets required safety standards and can withstand loads and stresses over
time without deformation or failure.

3 Layer Bonding: Effective bonding between successive layers of printed material is

crucial for the structural integrity of the building. Techniques such as optimized
printing parameters, layer interlocking designs, and post-printing treatments enhance
bonding strength.

4 Quality Control: Rigorous quality control measures during the printing process,
including monitoring of material consistency, layer adhesion, and dimensional
accuracy, are essential for ensuring durability and long-term performance.

5 Testing and Certification: Structural testing and certification procedures validate

the durability and safety of 3D printed concrete buildings, providing assurance of
compliance with building codes and standards.

6 Maintenance and Repair: Regular maintenance and timely repair of any damages
or deterioration can prolong the lifespan of 3D printed concrete buildings and ensure
continued durability.

Overall, when designed, constructed, and maintained properly, 3D printed concrete

buildings have the potential to exhibit excellent durability, comparable to or even
surpassing traditional construction methods, while offering additional benefits such as
reduced material wastage and construction time. Ongoing research and development
efforts continue to enhance the durability and resilience of 3D printed concrete
structures, paving the way for their widespread adoption in the construction industry.

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5.2 Cost Implications of 3D Printing Concrete Buildings
1 Cost Efficiency:
Traditional construction methods often involve significant material wastage and high
labor costs.
In contrast, 3D printing minimizes waste by utilizing only the necessary materials,
making it an economically efficient choice.

2 Comparison with Brick Masonry:

Even though the rate per unit quantity of material for 3D printed concrete is more than
twice the rate of brick masonry, the cost of constructing a 3D printed wall for a
building can be 40% less than that required for a brick masonry wall.
This cost reduction is due to the unique structure followed for 3D printed concrete
construction and reduced labor consumption.

3 Speed of Construction:
The increased speed of 3D printing allows for early project completion, helping
consumers overcome unnecessary expenses associated with delays in construction.

4 Complex-Shaped Buildings:
These benefits are even more pronounced in complex-shaped buildings, where 3D
printing offers virtually unlimited possibilities for implementing structures with
geometric complexity.

In summary, while 3D printing technology is celebrated for its potential cost savings,
it is essential to consider the initial investment required for 3D printing technology
itself.

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CHAPTER 6
6.1 CASE STUDY
India’s first 3D printed post office in Bengaluru
Bengaluru witnessed the inauguration of India’s first 3D printed public building – the
Cambridge Layout post office. The single-story building, now operational, covers an
area of 1021 sq. ft. Construction by 3D printing was done on-site in only 43 days,
instead of the 6-8 months it would’ve taken otherwise. Likewise, at INR 2,300,000,
the construction cost was also 30-40% lower than it would be with standard
techniques.
The project was executed by Indian construction giant Larsen & Toubro (L&T) with
technical guidance from the Indian Institute of Technology (IIT) Madras. The process
utilized a BOD2, the fastest and most widely used construction 3D printer on the
market with a print speed of up to 1 meter/3 feet per second. It consists of a modular
frame (aka gantry) which was setup on site and configured specifically to the project's
area. Uniquely, the BOD2 is capable of using real (quick-drying) concrete, instead of
only ready-mix mortars, which are not only weaker but 5-10 times more expensive. In
this case, locally sourced concrete was poured layer by layer (much like in a desktop
3D printer) to create jointless curved walls consisting of three vertical layers.

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CHAPTER 7
CONCLUSION
This presentation highlights the current development of 3D printing technology in the
construction industry. With gantry, robot and crane systems, 3D printing technology
has been successfully applied in a number of exemplary construction projects that
have received extremely high ratings. Options for improving shape retention and
constructability of sublayers include developing thixotropic concrete materials or
using low-viscosity concrete that can be easily pumped and then chemically treated at
the nozzle to speed up its setting rate. However, limited data on the structural
properties, safety and economics of the materials do not allow for an in-depth
presentation. However, through the comprehensive analysis, we believe that the future
direction of 3D printing technology in the construction industry are as follows:

(1) In order to achieve proper engineering design and construction, the mechanical
properties of 3D of concrete printed elements must be characterized by standardized
material testing.

(2) In order to overcome the quasi-brittle damage of concrete materials,

reinforcement is needed. As described in this paper, manual placement of steel bars
or reinforcement assemblies provides a solution as inter layer or interline
reinforcement. Re bar placement can be carried out automatically as part of the 3D
concrete printing process or through other automatic equipment. A reasonable ratio
of steel to concrete is important in building automation in order to provide sound
design guidance for proper anchoring and reduction of reinforcement in 3D printed
concrete structures and structural members.

(3) The construction industry and government departments should accept 3D

prestressed concrete as a construction technology and there needs to be strict
standards in terms of materials, specifications, manufacturing, testing and structural
design.

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 REFERENCES
1. Arabella Akman’s Recent Development of 3D-Printing Technology in Construction
Engineering (2023).
2. Xin Ning’s 3D Printing in Construction: Current Status, Implementation
Hindrances, and Development Agenda (2021).
3. L. Romdhane’s A critical review of 3D printing in construction: benefits,
challenges, and risks (2020).
4. Nithesh Nadarajah’s Development of concrete 3D printing (2018).
5. İbrahim Engin’s The Future of 3D Printing Technology in the Construction
Industry (2018).

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