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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Serie: ISTE Consignment
- Sprache: Englisch
This book presents a comprehensive overview of the state of the art in additive manufacturing in the world of concrete construction.
3D Concrete Printing tackles its subject from several angles, including issues relating to concrete materials (such as their formulation or fresh-state behavior), the various printing processes that have been developed, and how to describe the mechanical behavior and architectural and structural designs of printed structures. This book also considers the transition to application and industrialization, and the relevance of these new technologies in reducing the environmental impact of the construction sector.
Finally, material characterization methodologies are presented with a view to describing the behavior of materials both before and after printing, and the modeling tools used to simulate the process are listed.
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Seitenzahl: 397
Veröffentlichungsjahr: 2025
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Table of Contents
Cover
Table of Contents
Title Page
Copyright Page
Preface
Chapter 1. 3D Concrete Printing: Technologies, Applications and Classifications
1.1. Introduction: the different facets of printing
1.2. 3D printing: from digital model to physical object
1.3. 3D concrete printing – application examples
1.4. Classification of concrete printing processes
1.5. Printing concrete with alternative binders or without cement?
1.6. Conclusion
1.7. References
Chapter 2. 3D Concrete Printing by Extrusion and Filament Deposition
2.1. Introduction
2.2. Major printing families
2.3. Printable materials
2.4. The main stages in 3D extrusion printing
2.5. Conclusion
2.6. References
Chapter 3. From Laboratory to Practice: Characterizing Fresh and Cured Printed Materials
3.1. Introduction
3.2. Characterization of fresh materials
3.3. Characterization of hardened materials
3.4. Durability
3.5. Conclusion
3.6. References
Chapter 4. Alternative Printing Methods for Cementitious Materials
4.1. Introduction
4.2. Methods with supports
4.3. Particle bed methods
4.4. Support-free methods
4.5. Choice of process
4.6. Prospects and opportunities
4.7. Conclusion
4.8. References
Chapter 5. Structural Applications of 3D Printing
5.1. Introduction
5.2. Assessment of hardened material properties
5.3. Masonry
5.4. 3D printing and reinforced concrete
5.5. Prestressing
5.6. Conclusion
5.7. References
Chapter 6. Reinforcement of Printed Structures
6.1. Introduction, a few reminders about the reinforcement of cementitious materials
6.2. Reinforcement methods for additively manufactured cementitious materials and structures
6.3. Details of a special in-line reinforcement, the flow-based-pultrusion concept
6.4. Conclusion and outlook
6.5. References
Chapter 7. Numerical Simulation Tools for 3D Printing
7.1. Introduction
7.2. Designing the geometric model of a virtual object
7.3. Digital modeling of the 3D printing process
7.4. Discussions on recent advances, limitations and future research directions
7.5. Conclusion
7.6. References
Chapter 8. Environmental Impact of 3D Concrete Printing
8.1. Introduction
8.2. 3D printing technology and case studies
8.3. Methodology and case studies
8.4. Results
8.5. Discussions and prospects
8.6. Conclusion
8.7. Acknowledgments
8.8. References
List of Authors
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1. Classification of printing processes according to....
Chapter 3
Table 3.1. Ability to perform active quality control dep...
Table 3.2. Raw material whose variability can be controlled
Chapter 4
Table 4.1. Advantages and limitations of alternative tech...
Chapter 5
Table 5.1. Summary of material properties to be evaluated
Table 5.2. Comparison of the performance of different...
Chapter 7
Table 7.1. Digital models of the 3D printing process at structural scale
Chapter 8
Table 8.1. Inventory for the LCA study of the masonry lattice wall
Table 8.2. Inventory for the LCA study of the reinforced concrete lattice wall
List of Illustrations
Chapter 1
Figure 1.1. Parametric design – programming and printed parts....
Figure 1.2. Example of the installation of a 3D printing system consisting...
Figure 1.3. Type of structures printed according to the type of robot used...
Figure 1.4. Elementary process classification system proposed by the RILEM...
Figure 1.5. Example of sequencing for a complete description of an automat...
Figure 1.6. Example of 3D soil printing of structures.
Chapter 2
Figure 2.1. 3D printing of mortar by extrusion and filament deposition...
Figure 2.2. Shear stress–shear rate relationship for a Bingham f...
Figure 2.3. Evolution of the microstructure of a cement suspension at...
Figure 2.4. Example of applications of models describing the evolution of...
Figure 2.5. Decomposition of extrusion flow–axisymmetric case. D is...
Figure 2.6. Cementitious material filament deposition strategies and situ...
Figure 2.7. Structure undergoing buckling during printing
Chapter 3
Figure 3.1. Types of test geometry used to study the flow of cementitious...
Figure 3.2. Shear yield stress measurements using Vane geometry: (a) con...
Figure 3.3. Test geometries for studying the elongation behavior of mat...
Figure 3.4. Example of three different loading directions for prismatic...
Figure 3.5. Example of specimen preparation in the Navier laboratory...
Figure 3.6. Example of cubic specimens from a printed object (Navier l...
Figure 3.7. Compression test completed on cubic specimen for mortar scale
Figure 3.8. Cutting prismatic specimens from a printed piece. Here,...
Figure 3.9. Three-point bending tests at the Navier laboratory
Figure 3.10. Completed four-point bending tests at the Navier laboratory
Chapter 4
Figure 4.1. Left: interior and exterior architecture of the Taichung Me...
Figure 4.2. Top left: model of robot trajectory; bottom left: textile st...
Figure 4.3. Self-supporting mineral foam formwork system. a) 3D printing...
Figure 4.4. Examples of the SDC technique. From left to right: slipformi...
Figure 4.5. Robotic concrete casting in PE film under tension (photograp...
Figure 4.6. Illustration of projects using the polymer printing techniqu...
Figure 4.7. Manufacturing a canoe by injecting cementitious material int...
Figure 4.8. Left: 3D printed mold; spraying concrete onto the mold. Righ...
Figure 4.9. Illustrations of the 3D injection printing process. From lef...
Figure 4.10. Illustration of powder bed 3D printing process (© FM1...
Figure 4.11. Examples of 3D-printed projects using shotcrete. Left: spr...
Figure 4.12. Choice of process: (a) freedom of form according to substr...
Figure 4.13. (a) Dissolvable formwork and final column developed at ETH...
Chapter 5
Figure 5.1. Evolution of the structural morphology of steel bridges
Figure 5.2. Two materials with the same average strength, but di...
Figure 5.3. Principle of Eurocode ultimate limit state design: a...
Figure 5.4. Principal stress distributions in a printed cord und...
Figure 5.5. Visualization of the deformation of an inclined cyli...
Figure 5.6. Protocol for a printed material characterization test,...
Figure 5.7. Metal spacers on an on-site printed wall (image: Peri SE)
Figure 5.8. South facade of a house in the Villiaprint project, 2022 (XtreeE)
Figure 5.9. Analogy between masonry and 3D concrete printing, according to...
Figure 5.10. Cord placement strategies according to Carneau et al. (2020)
Figure 5.11. Examples of structure types according to printing mode (Carn...
Figure 5.12. Nubian vault. Left: inclination of bead plane (orange) and s...
Figure 5.13. Viollet-le-Duc’s hypothesis on the structure of...
Figure 5.14. A tree of possibilities for printed formwork
Figure 5.15. Example of non-collaborative formwork
Figure 5.16. Fiber post in Aix-en-Provence (printing: XTreeE). Photo by...
Figure 5.17. 3D printing reinforcement methods (adapted from Kloft...
Figure 5.18. Printed and reinforced beam (SDU.Create, 3D printing:...
Figure 5.19. Post-tensioned bridge with 3D printed voussoirs, adap...
Figure 5.20. Eladio Dieste’s slim hulls: prestressing system...
Chapter 6
Figure 6.1. Palazzetto dello Sport, Rome, 1957 (GiulioCesare,...
Figure 6.2. Effect of fibers according to diameter and size (adapted...
Figure 6.3. Diagram and characteristic behavior curve (adapted from...
Figure 6.4. A posteriori reinforcement: (a) column with printed for...
Figure 6.5. Prototype of an optimized reinforced concrete beam with...
Figure 6.6. 3D printing process (AMoRC) for reinforced concrete, con...
Figure 6.7. Reinforcement with nails between layers and bending curv...
Figure 6.8. Co-extrusion of reinforced strand, reinforced by continu...
Figure 6.9. ProfiCarb process and view of the six yarns nozzle (Ivan...
Figure 6.10. Fiberized printing device: (1) coils, (2) pulleys, (3)...
Figure 6.11. Prototype 1, Navier laboratory, with fiberglass printing.
Figure 6.12. Prototype 2, XtreeE: printing with carbon fibers, evenly...
Figure 6.13. Tensile test of a 3% glass fiber-reinforced specimen and...
Figure 6.14. Curved concrete truss presented at the “FORM and...
Chapter 7
Figure 7.1. Quantifying uncertainty in the elasto-plastic properties...
Figure 7.2. Result of deterministic and reliability analyses of two...
Figure 7.3. AK-MCS reliability analyses of two failure modes (plast...
Figure 7.4. AK-MCS reliability analysis of a chair made by 3D print...
Figure 7.5. Sobol index of input parameters provided by global sens...
Chapter 8
Figure 8.1. The extrusion–deposition 3D printing cell. Image:...
Figure 8.2. Concrete 3D printing construction systems: (a, left) pr...
Figure 8.3. (a, top) Prototype of the space lattice wall (Kuzmenko...
Figure 8.4. Impact model and functional unit diagram (Kuzmenko 2021)
Figure 8.5. Variation in environmental impact of 1 m3 printed as a...
Figure 8.6. The relative contribution to the carbon footprint stud...
Figure 8.7. Comparison of the environmental impact of space lattic...
Figure 8.8. Comparison between space lattice and reinforced concre...
Guide
Cover Page
Table of Contents
Title Page
Copyright Page
Preface
Begin Reading
List of Authors
Index
WILEY END USER LICENSE AGREEMENT
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SCIENCES
Mechanics, Field Director – Gilles Pijaudier-Cabot
Civil Engineering and Construction, Subject Head – Fabrice Gatuingt
3D Concrete Printing
State of the Art and Applications
Coordinated by
Arnaud Perrot
Yohan Jacquet
First published 2025 in Great Britain and the United States by ISTE Ltd and John Wiley & Sons, Inc.
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:
ISTE Ltd27-37 St George’s RoadLondon SW19 4EUUKwww.iste.co.uk
John Wiley & Sons, Inc.111 River StreetHoboken, NJ 07030USAwww.wiley.com
© ISTE Ltd 2025The rights of Arnaud Perrot and Yohan Jacquet to be identified as the authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988.
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s), contributor(s) or editor(s) and do not necessarily reflect the views of ISTE Group.
Library of Congress Control Number: 2024946962
British Library Cataloguing-in-Publication DataA CIP record for this book is available from the British LibraryISBN 978-1-78945-200-6
ERC code:PE8 Products and Processes EngineeringPE8_3 Civil engineering, architecture, offshore construction, lightweight construction, geotechnics
Preface
Arnaud PERROT
IRDL, Université de Bretagne Sud, Lorient, France
P.1. Purpose of the book
The rapid emergence of 3D concrete printing technology has opened up exciting new perspectives in construction and engineering. Because of this rapid dynamic, we must now understand this craze and explore the limits and potential of this innovation in the field of construction. This can be done by taking stock of developments in printing technologies and applications.
Additive manufacturing of concrete structures offers significant advantages such as cost reduction, customization of architectural designs, speed of execution, improved safety and working conditions, and minimization of the volume of material used (structural efficiency, multi-functionality) and waste.
Since the early 2000s, developments and projects relating to 3D printing have been multiplying at a steady pace, resulting in an exponential increase in the number of scientific studies on the subject. The subject, which initially focused almost exclusively on the formulation of materials and robotics, now encompasses many other aspects, such as quality control, applications, the regulations that are beginning to emerge (ISO 2023), mechanical operation and characterization, durability and environmental impact, etc.
In 2019, I edited a first book on the subject of concrete 3D printing (Perrot 2019), which is now becoming almost obsolete due to recent advances in this field. Thus, writing a new, updated book dedicated to 3D concrete printing has become essential in order to document, analyze and propagate current knowledge related to this revolution in the field of construction. This book could serve as a comprehensive guide, covering the technical aspects, current challenges, potential applications, as well as the difficulties and limitations of printing methods. It would thus provide an indispensable resource for researchers, students of civil engineering, materials engineering and robotics, and construction professionals looking to stay at the forefront of this major development in the industry.
To write this book, a multidisciplinary team of academics and industrialists was brought together to deal with the various aspects of 3D printing of cementitious materials such as concrete.
P.2. Structure of the book
This book is structured into eight chapters, each dealing with a specific aspect of 3D concrete printing. In the first part, an overall presentation of concrete printing processes (which is ultimately a family of very multifaceted digital processes) is given, with a summary of the existing classifications proposed by working groups or research teams.
The next two chapters focus on the extrusion deposition printing technique. Chapter 2 depicts this process, and Chapter 3 describes the characterization techniques developed to mix-design printable materials on a laboratory scale, characterize their mechanical behavior once hardened and organize quality control during production in an industrial context.
Chapter 4 explains other families of printing and digital manufacturing techniques that have been developed for cementitious materials.
Chapter 5 defines the mechanical behavior of printed materials and structures, as well as the structural design of printed concrete. To take the structural use of printed concrete a step further, Chapter 6 presents the reinforcement techniques that have been and are currently being developed in order to guarantee the necessary mechanical performance.
Chapter 7 outlines the numerical simulation tools used to simulate the 3D concrete printing process, showing the specific characteristics of the material and its behavior that need to be taken into account in the additive manufacturing of cementitious materials.
Finally, Chapter 8 focuses on the environmental analysis of printed structures. It highlights the potential benefits of 3D printing as part of an eco-construction approach and identifies the areas with the greatest impact in terms of carbon emissions.
November 2024
P.3. References
ISO (2023). Additive manufacturing for construction: Qualification principles – Structural and infrastructure elements. Standard, ISO/ASTM 52939.
Perrot, A. (ed.) (2019).
3D Printing of Concrete: State of the Art and Challenges of the Digital Construction Revolution
. ISTE Ltd, London, and John Wiley & Sons, New York.
Note
3D Concrete Printing
, coordinated by Arnaud PERROT and Yohan JACQUET. © ISTE Ltd 2025.
13D Concrete Printing: Technologies, Applications and Classifications
Arnaud PERROT1, Yohan JACQUET2 and Sofiane AMZIANE3
1 IRDL, Université de Bretagne Sud, Lorient, France
2 Technische Universität Berlin, Germany
3 Institut Pascal, Université Clermont-Auvergne, Clermont-Ferrand, France
1.1. Introduction: the different facets of printing
Since its initial development in the early 2000s, 3D printing has always been a polymorphic process, depending on the type of material used and the robotic system employed. Initial developments such as Prof. Koshnevis’ Contour Crafting concept (Khoshnevis 2004; Khoshnevis et al. 2006; Buswell et al. 2018), based on an extrusion system, or Enrico Dini’s D-Shape process, based on a selective particle bonding printing system (Colla et al. 2013), illustrate this diversity, which has continued to increase ever since. 3D concrete printing has almost as many variations as there are printers and companies working on the subject.
The multifaceted nature of printing is reflected in ASTM F2792-12A (ASTM International 2012), which defines seven categories of additive manufacturing processes that can be used for any type of material. These categories can also be related to the different processes used today for concrete and cementitious materials.
Although there is a wide range of possible processes, 3D concrete printing techniques (which often involve mortar more frequently than concrete, as the presence of gravel requires large pumps, print heads and robots) share many points in common, particularly in the use of digital technology and robotics (Perrot and Amziane 2019).
The integration of robotics and digital technology means that the starting point is the design of a 3D model of the object to be printed, the drafting of instructions that the robot can understand and finally the production of the object by the robot.
In this chapter, we will start by presenting these stages, which are common to the printing process in general. We will then present the current applications of the 3D concrete and mortar printing, focusing on the materials used and alternatives to conventional cementitious materials.
Finally, we will present several classifications that help position a given printing process in the world of digital concrete manufacturing.
1.2. 3D printing: from digital model to physical object
1.2.1. From digital model to print
The first step in 3D printing is to design the part to be printed. This design stage always begins with creating a 3D model in CAD (computer-aided design) software.
Many 3D design solutions exist, but they differ according to the philosophy of the tool used and the complexity of the object to be modeled.
For modeling simple, perfectly vertical shapes, we may draw the deposition contours of a layer to be printed on the deposition plane and then extrude this surface in the direction perpendicular to the deposition plane (generally the vertical axis). This design and subsequent printing strategy is often referred to as 2.5D printing.
For more complex shapes with overhangs, it is necessary to work in three dimensions and use modeling solutions to represent lines and surfaces in a 3D reference frame.
Finally, in order to design architectural shapes with patterns, parametric 3D design is an extremely useful tool for obtaining shapes with repetitive patterns that provide added aesthetic value or additional functions (noise absorption, sun shading, etc.). The use of tools, such as Rhino/Grasshoppers, is among the most popular parametric design solution (Figure 1.1). This solution uses a graphical programming system to manipulate shapes and objects and repeat actions to create 3D patterns.
As part of a BIM project, geometric design in software compatible with the IFC format, the BIM exchange format may be of interest. The 3D model then needs to be exported in a format compatible with the software used to generate the robot trajectory. The goal is to export the file in a format that can generate a G-Code (Geometric Code), which is a file containing a sequence of instructions that drives a 3D printer. The .STL, .obj and .amf formats can be used for this purpose.
These export files are then imported into a “slicer”, which is used to program the trajectory of the print head and set several parameters, such as the start of extrusion, the position of the print head during deposition, the infill of a volume (pattern and density) or the start position of the print. The defined robot trajectory must then be optimized to ensure no collisions during printing and good contact between adjacent or superimposed deposits.
It is also important to note that it may be necessary to convert the G-Code to a language compatible with the printing system (such as six-axis robots).
Figure 1.1.Parametric design – programming and printed parts.
1.2.2. Printing processes
ASTM F2792-12A (ASTM International 2012) defines seven different categories of additive manufacturing methods. This standard has become the benchmark for defining 3D printing terminology.
Among these categories, the material extrusion method is certainly the most widely used, particularly in polymer 3D printing by melt extrusion/deposition. Plastic 3D printing that involves fusing filaments of different types of plastic through a thermo-regulated extrusion system has significatively contributed to the democratization of the printing process.
Jetting, either of binders or materials such as polymers or molten metals, is also listed as one of the techniques in the ASTM standard.
The lamination of sheets consists of gluing numerous sheets of material together to form a larger object. The layers can be pre-cut before bonding, or a cutting step can be carried out after bonding the sheets to create a complex shape.
Finally, the last three methods are specific techniques requiring the application of an additional energy source to ensure the fusion or hardening of the material. For example, fusion on a powder bed or the deposition of material under a directed energy flow, widely used for metals, requires the application of a significant amount of energy to melt the material, ensuring the bonding of the material once it has returned to ambient temperature. Finally, photopolymerization uses light to locally solidify a photosensitive resin to bind particles together and form a resistant matrix. This method is often called stereolithography.
1.2.3. Printing processes for cementitious materials
Not all the methods listed in ASTM F2792-12A have been adapted to concretes or other cementitious materials, especially given their non-dependence on temperature and light. However, numerous developments have been made (Buswell et al. 2020) using different techniques for different applications and at different scales.
Concrete printing by extrusion deposition was the first technique to be used. The “contour crafting” developed by Khoshnevis et al. (2006) or the “concrete printing” method from Loughborough University (Le et al. 2012; Lim et al. 2012; Perrot 2022) used the extrusion/deposition method before 2010. Since then, the 3D concrete extrusion printing method, often referred to as 3D concrete printing, has undergone many further developments with numerous variations in the printhead, notably with the advent of two-component formulations, the scale of realization, the robotic system used and finally the intended application (Wangler et al. 2016, 2022; Buswell et al. 2018). The deposition extrusion process can also be coupled with other sub-processes to perform other tasks, such as positioning reinforcement, applying a curing agent or improving surface finish (Buswell et al. 2020).
The technique of printing by injection into particle beds has also been adapted to cementitious materials (Lowke et al. 2018, 2020, 2022). In this category, two processes can be distinguished; the first concerns the technique of selective binding of aggregates by localized injection of a cementitious grout (Pierre et al. 2018; Weger et al. 2021) and the second concerns the injection of water to locally activate a powder bed containing a hydraulic binder such as cement (Mai et al. 2022; Zuo et al. 2022). Interestingly, this method was used very early on in Enrico Dini’s early work in the first half of the 2000s (Lowke et al. 2018).
The Shotcrete method, on the other hand, is similar to the “Material Jetting” method, in which a cementitious material is projected onto an object (Lindemann et al. 2019; Hack and Kloft 2020).
Finally, other so-called “digital concrete” methods appeared in the scientific literature in 2010, such as smart dynamic casting, which involves automating and robotizing the slipforming process (Lloret-Fritschi et al. 2020; Szabo et al. 2020), and the Mesh Mould technique (Hack and Lauer 2014), in which robots create a permeable formwork that can then be used to pour or apply concrete. Finally, we should also mention optimized formwork printing methods that minimize the amount of material needed to produce complex shapes which can withstand the pressure exerted by freshly poured-in-place concrete (Burger et al. 2020; Lloret-Fritschi et al. 2022).
1.3. 3D concrete printing – application examples
1.3.1. Prefabrication
1.3.1.1. Support-free printing
The use of 3D concrete printing in the prefabrication of concrete parts, which are then assembled on-site to increase precision and/or production rates (Volpe et al. 2021), or to create specific functions with unique or complex geometries (such as artificial reefs, stormwater basins, voussoirs for a bicycle bridge, prefabricated staircases, etc.; Salet et al. (2018); Ly et al. (2021)) is now commonplace. Among the additive manufacturing methods used for concrete, some do not require supports, such as extrusion-deposition methods, which are particularly developed today.
Numerous companies have developed their own printing solutions and related businesses. Examples include XtreeE in France, Hyperion Robotics in Finland, Weber, TAM and Vertico in the Netherlands, and Sika in Switzerland.
All these companies use six-axis robots to print precast-printed concrete elements. Some of these companies also use a rail on which the robot is placed to increase the available printing volume (Figure 1.2). A system for preparing and transporting the material by pumping is also a standard feature of printing plants.
Figure 1.2.Example of the installation of a 3D printing system consisting of a six-axis robot and a complementary linear conveyor (Lowke et al. 2024).
Prefabrication is often used to manufacture small parts or parts with a small cross-section. As a result, the length of the printing contour (the length of the filament of a single printed layer) imposes very short deposition times, requiring a rapid rate of elevation of the structure being printed. This fast printing rate induces rapid loading of the structure, which is not compatible with the structuring kinetics of traditional cements (Reiter et al. 2018).
There are two solutions to this problem. The first is to develop single-component formulations, which have a period of rheological stability to enable mixing and transport to the print head, followed by a period of rapid structuring of the material to enable fast printing. The other solution uses two-component materials and consists of injecting a texturizing agent or a setting accelerator at the print head to enable rapid setting kinetic growth as soon as the material is deposited.
Each method has its advantages and disadvantages: the single-component solution does not tolerate interruptions to the printing process, as otherwise, there is a risk of curing in the pump lines and consequent blockage. The two-component solution, on the other hand, adds an in-line mixing stage just before deposition, which requires a careful choice of product to accelerate curing and the design of a more complex print head with an in-line injection and mixing system (active or passive) (Tao et al. 2021; Boscaro et al. 2022; Wangler et al. 2022).
A specific two-component process called dual pumping has been developed by Ghent University (Tao et al. 2022) and enables two fluid materials with equivalent volumes to be pumped, which, once mixed just prior to extrusion, undergo rapid mechanical structuring, enabling high printing speeds.
Robotic complexity also plays an important role in 3D printing (Figure 1.3). A three-axis robot (Cartesian, delta or a six-axis robot using only three-axis) will enable a structure to be printed with a cylindrical filament cross-section, a print head that is always vertical, and limited freedom of form. Switching to four-axis adds rotation around the vertical direction and enables the use of perfectly cylindrical layer cross-sections, which is of interest for obtaining smooth vertical surfaces. Finally, using the robot’s six-axis allows printing with changing printhead orientations, providing greater freedom of form and enabling more efficient construction of arches or domes (Carneau et al. 2020).
Figure 1.3.Type of structures printed according to the type of robot used. (Top right photo: Lowke et al. 2024; Bottom right photo: XtreeE).
Printed shotcrete also makes it possible to achieve high printing speeds for precast elements, as shown by studies carried out at the Technical University of Braunschweig (Hack and Kloft 2020). 3D printing of shotcrete allows greater freedom of form.
The smart dynamic casting technique also requires no support to produce prefabricated parts such as columns or slender and slender walls (Lloret-Fritschi et al. 2017; Szabo et al. 2020). The use of a six-axis robot fitted with variable-section formwork enables these elements to be produced by adjusting the speed at which the formwork rises to match the speed at which the cementitious material is structured. If the material leaving the sliding formwork is too fluid, the structure collapses, whereas if it is too rigid, the friction at the formwork wall becomes greater than the tensile strength of the printed material section, which becomes brittle and breaks into two parts (Craipeau et al. 2021).
1.3.1.2. Printing with support
It is also possible to produce prefabricated parts using 3D printing techniques that use supports. These methods allow greater freedom of form, enabling the creation of parts with cantilevers that transition from a vertical to a horizontal structure.
The particle-bed printing technique can therefore be used to produce parts with complex shapes whose surface roughness depends on the size of the particles used. For example, the selective bonding 3D printing technique will produce parts with a rougher surface than the activation bonding technique.
Similarly, 3D printing by depositing material in a threshold fluid, such as carbopol or limestone suspensions, enables lattice structures to be produced, making it possible to use topological optimization methods for structural dimensioning (De Schutter et al. 2018; Vantyghem et al. 2020) and thus save material for the same mechanical function. It is also possible to print ultra-high-performance concrete in ordinary concrete for the same reasons of mechanical efficiency (Lowke et al. 2021).
Finally, methods for pouring concrete into printed formwork fall into this category. Since the Yhnova house printed in 2017 in Nantes with polyurethane formwork (Furet et al. 2019), numerous advances have been to reduce the weight and thickness of formwork while guaranteeing faster filling speeds, as in the In-crease (Lloret-Fritschi et al. 2022) or Eggschell (Burger et al. 2020) projects at ETH Zurich.
1.3.2. On-site printing
Current advances and technologies show that on-site 3D printing is reserved for two types of application: shotcrete and extrusion-deposition techniques. In general, these methods do not use supports except on a case-by-case basis (such as crossing openings with prefabricated lintels) (Tay et al. 2019). They must also be able to perform a structural function in their own right, and therefore incorporate reinforcements (Kloft et al. 2020; Menna et al. 2020).
Shotcrete technology can be seen as an evolution of automated shotcrete wall construction techniques for tunneling and retaining structures (Heidarnezhad and Zhang 2022). These techniques can also be used on-site to build structures independently, without relying on supports such as the soil in tunneling or geotechnical work (Girmscheid and Moser 2001).
When printing on-site, regardless of the method, it is important to bear in mind that the printed material is directly exposed to an uncontrolled environment (wind, rain and sun), unlike the conventional casting process. This direct and prolonged exposure can lead to unexpected changes in the material composition which are potentially deleterious to the material’s properties once hardened (Keita et al. 2019) such as lack of water for cement hydration due to excessive drying, or leaching of the structure by heavy rain, etc. This constraint must therefore be considered in the material specifications or by implementing additional precautions such as tenting, covering or applying a curing product.
Extrusion deposition printing is probably the most developed technique for on-site 3D concrete printing. Several robotic systems have been developed to print various sizes (Xiao et al. 2021).
For small constructions, such as single-family homes or small buildings, fixed robots such as the delta robots developed by WASP (Gomaa et al. 2022; Moretti 2023) or the transportable robotic arm developed by Construction 3D (https://www.constructions-3d.com/n.d.) are ideal.
For larger projects, the use of a large-scale Cartesian printer is a solution that has been developed for printing structures such as collective housing or wind turbine mast elements (Savić et al. 2020). This involves setting up a gantry crane equipped with a print head as an end effector (Ahmed 2023). This solution appears to be the most common on the market today, as demonstrated by the success of printers developed by Cobod.
For even larger scale impressions, it is possible to rely on cable robot technology (Barnett and Gosselin 2015; Izard et al. 2017) or on the adaptation of current construction machinery such as cranes and crane trucks (Gaël et al. 2023). However, there are still technological hurdles to overcome regarding positioning the end effector under the effect of wind, rain and external stresses. It should be noted that the idea of using cable robots as 3D printers dates back some 15 years (Pott et al. 2010), with conclusive trials that have been carried out with raw earth. The structure needed to set up a cable robot seems relatively light and can cover large surfaces. The conversion of construction site equipment into 3D printers remains at the concept stage for now, as seen in the ConPrin3D project developed by the Technical University of Dresden (Schack et al. 2017; Nerella and Mechtcherine 2019) or other initiatives (Gaël et al. 2023). Interestingly, stabilization or compensation techniques to ensure printhead trajectory are currently under development, notably by implementing gyroscopes acting to maintain printhead position.
Finally, recent work is looking at the use of multiple mobile robots for 3D printing structures or structural elements on-site (Zhang et al. 2018; Dörfler et al. 2022). This solution eliminates the need to install a structure such as an overhead crane before printing and opens the way to collaborative work by robots. This collaboration can also be used to share optimal tasks, such as placing reinforcement or lintels simultaneously with printing, either by extrusion or concrete spraying.
More recently, the use of an army of collaborative drones to carry out construction work has been imagined and validated on a small element (Zhang et al. 2022).
However, several challenges remain, such as properly managing robot tracking to prevent robot collisions without hampering production and adapting the locomotion of mobile robots to the topography of the worksite and the load to be carried.
1.3.3. Toward the democratization of 3D concrete printing?
Today, 3D concrete printing is experiencing a significant diversification in its applications and scales of realization. This diversity implies a very strong link between the properties of the material in its fresh state (and changes over time, notably the speed of mechanical structuring) (Perrot et al. 2016; Roussel 2018) and the printing process used.
These properties need to be controlled and monitored to guarantee the success of the printing process and ensure a robust production process. This is why quality control methods are currently being developed (Nicolas et al. 2022) to provide a means of controlling printability, similar to the workability tests for ordinary concrete poured into formwork using Abrams cone slump tests (Roussel and Coussot 2005). The RILEM PFC (performance requirements and testing of fresh printable cement-based materials) technical committee is working on the development of these tests.
It is also important to note that concrete printing processes mainly use mortar. However, the on-site printing of larger structures opens up the possibility of printing concrete (Ji et al. 2022), thereby reducing the cost and environmental impact of the printed material.
The printing process itself results in the creation of a structure whose constituent material may exhibit anisotropic behavior as a result of layering. This particularity must be taken into account in the design codes currently being developed by international working groups led by RILEM (TC ADC – Assessment of Additively Manufactured Concrete Materials and Structures), fiB (Fédération Internationale du Béton) and ASTM.
An initial ISO/ASTM standard describing concrete 3D printing was published at the end of 2023 (ISO/ASTM 52939 2023).
The design of the structure must also consider the reinforcement techniques used to give the structure the ability to resist tensile or shear stresses (Kloft et al. 2020; Menna et al. 2020).
These points will be developed in the following chapter of this book.
1.4. Classification of concrete printing processes
3D concrete printing is a polymorphous process that needs to be well described in order to be able to properly design the robotic complexity and the specifications of the printable cementitious material. Similarly, for a given concrete printer, we need to know what type of parts can be printed, on what scale and in what environment. A number of projects have focused on printing process classification systems that can be used to describe the specifications of a process and the possibilities available.
1.4.1. Classification proposed by Duballet and co-authors
An initial ranking of concrete printing processes has been proposed by Duballet and co-authors (Duballet et al. 2017). Based on the characteristics of the process and the printed part, the team of authors developed a classification taking into account the complexity of the robotic system, the environment and the geometry of the part to be manufactured. This classification provides an objective description of the resources required to print a given type of object.
For the moment, however, the classification is limited to the extrusion/deposition technique, although it can be transposed or adapted for other methods of printing cementitious materials. To enable the types of printing to be classified, the authors have defined a nomenclature by defining the characteristics of the process.
1.4.1.1. Scale of the printed object
The first classification parameter is the scale of the printed object. As we saw earlier, the size of the object to be printed will necessarily have an impact on the type of robot and its workspace. The scale of the object to be printed will also influence the deposition time (length of the contour to be printed) and impact the properties of the material in its fresh state (speed of structuring). The authors of the classification list four typical sizes of objects to be printed:
x
0
0
: object less than 1 m in size;
x
0
1
: object whose size is that of a standard building element: 1–4 m, for example, a beam or a column;
x
0
2
: object the size of a small single-family home: 5–10 m;
x
0
3
: object the size of an entire building.
1.4.1.2. Scaling the cross-section of printed material
The second grading parameter is that of the printed material filament. This scale depends on the rheology of the material and the cross-section of the print head, and impacts the surface roughness of the printed structure. The cross-sectional scale of a deposited layer also influences the maximum aggregate size of the cementitious mix and the printing speed. The authors define four different scales:
x
e
0
: layer thickness less than 8 mm;
x
e
1
: layer thickness between 8 mm and 5 cm;
x
e
2
: layer thickness between 5 cm and 30 cm;
x
e
3
: layer thickness greater than 30 cm.
Note that printing time is directly related to the ratio between the size of the object to be printed and the size (height) of the filaments deposited. Print time will therefore be the product of the time required to deposit a layer multiplied by the ratio between the height of the part to be printed and the height of a layer.
1.4.1.3. Printing environment
The authors of the ranking highlighted three possibilities for a direct printing environment:
e
0
: direct on-site printing;
e
1
: printing in a small mobile unit on site, allowing hygrometry and temperature control and shelter from the wind;
e
2
: printing in the prefabrication plant.
The environment will have a direct impact on the robustness of the process to be implemented. In a protected atmosphere (second or third solution), the process may be easier to implement than on site, where climatic variations and actions will have to be taken into account (protection of printed material, precision of robot positioning).
1.4.1.4. Component assembly conditions
For the printing of prefabricated parts assembled on site, the authors defined four assembly conditions that can occur during the partial (or total) printing of a building:
a
0
: no assembly;
a
1
: assembling several elements to form a larger one;
a
2
: handling elements to place them in their final position;
a
3
: assembling unprinted external elements after printing.
It is important to note that during the construction of a building, several stages require the assembly of elements. For example, printed and unprinted elements (conditions a2 and a4) can be assembled on the same construction project.
1.4.1.5. Use of supports
3D concrete printing by extrusion/deposition has its limitations in terms of freedom of form, since the stability of the structure must be ensured during printing. It is therefore possible to use temporary or permanent supports, as proposed by the authors of the classification. Four categories of support have thus been listed:
s
0
: no support;
s
1
: printed support left in place;
s
2
: printed support removed at end of printing;
s
3
: external support left in place;
s
4
: external support removed at end of printing.
As with assembly, several solutions can be used simultaneously when printing an object.
1.4.1.6. Robot complexity
Several robot configurations are possible for printing 3D structures. Collaboration between several robots to print complex structures or make assemblies can be an effective solution:
r
0
: use of a three-axis robot;
r
1
: use of a six-axis robot;
r
2
: use of a rail-mounted (or mobile) six-axis robot;
r
3
: use of two six-axis collaborative robots;
r
4
: use of two rail-mounted (or mobile) six-axis collaborative robots;
r
5
: use of a six-axis robot mounted on a rail (fixed or mobile);
r
6
: use of a six-axis robot mounted on a three-axis robot;
r
7
: use of two six-axis robots mounted on three-axis robots.
The first five parameters in the ranking will influence the specifications of the right robot for a given print job. Experience and difficulties encountered will determine the minimum robotic complexity.
1.4.1.7. Example of classification and summary of parameters
In their article, the authors of the classification classify printing processes according to the proposed classification parameters summarized in Table 1.1 (Duballet et al. 2017).
An example of classification is the contour crafting process (Khoshnevis et al. 2006): x00-1-2; xe1-2; e0; a1–a4; s3; r0.
Working scale: the process is designed for printing small buildings. It is also quite precise and can be used to produce small elements. It is therefore x
0
0
, x
0
1
or x
0
2
, depending on the size of the object to be printed.
Elemental layer thickness: printed layers are between 1 and 10 cm thick. Depending on the size chosen, the classification is x
e
1
, x
e
2
.
Environment: contour crafting is designed for on-site printing. It is therefore e
0
.
Assembly: when building a single-family home, printed elements are used to form larger structures, as well as incorporating lintels and horizontal load-bearing elements (beams) prefabricated elsewhere. Assembly steps a1 and a4 are therefore used in this case.
Use of supports: for single-family home construction, the printer uses prefabricated horizontal supports as supports. These supports play a structural role and are therefore fully integrated into the construction. The support condition is therefore s
3
. Some parts of the print do not require support. In this case, condition s
0
is met.
Robotic complexity: contour crafting uses a crane system that can be likened to a three-axis robot. In this case, robotic complexity is denoted as r
0
.
Table 1.1.Classification of printing processes according to (Duballet et al. 2017). Parameters to be taken into account
Scale of printed object
x
0
0
: <1 m
x
0
1
: 1–4 m
x
0
2
: 5–10 m
x
0
3
: building
Printed material cross-section scale
x
e
0
< 8 mm
x
e
1
: 8 mm–5 cm
x
e
2
: 5–30cm
x
e
3
: >30 cm
Printing environment
e
0
: direct on site
e
1
: T° and HR control and 0 wind
e
2
: prefabrication plant
Component assembly conditions
a
0
: 0 assembly
a
1
: Assembling several elements
a
2
: Handling elements to place them in their final position
a
3
: Assembly of unprinted exterior elements
Use of supports
s
0
: No support
s
1
: Printed support left in place
s
2
: Printed support removed at end of printing
s
3
: External support left in place
s
4
: External support removed at end
Robot complexity
r
0
: Three-axis
r
1
: Six-axis
r
2
: Six-axis rail-mounted
r
3
: Six-axis collaborative
r
4
: Six-axis collaborative rail-mounted
r
5
: Six-axis rail-mounted
r
6
: Six-axis mounted on a three-axis robot
r
7
: Six-axis mounted on three-axis robots
1.4.2. Classification proposed by RILEM
The work of RILEM’s Technical Committee No. 276 has led to the creation of a classification process (Buswell et al. 2020) that encompasses all types of manufacturing processes associated with “digital concrete”. This process takes into account a number of principles that allow all automated concrete construction processes to be encompassed.
One of the first principles is considering the printing environment: whether in the prefabrication plant or on-site. Also, the authors drew on pre-existing definitions of material shaping and assembly (Groover 2011) and incorporated standards relating to additive manufacturing (ISO 17296-3 2014; ISO/ASTM 52900 2021). Thus, the classification must account for variations in the size of printed parts and types of cementitious materials used. This classification also describes sub-processes corresponding to the manufacturing technology used (for example, particle beds, extrusion deposition for additive manufacturing). Complementary processes can also be described in the classification (surface treatment, reinforcements, etc.) that may occur sequentially, simultaneously or contiguously.
The proposed classification takes into account:
the type of material and its service life properties once cured;
the printing environment (in-plant, on-site, mixed site-plant, on-site but under a protected and regulated area);
the printed element (size, element to be assembled, resolution and geometric tolerance, etc.);
process limitations, installation and printing phasing.
The description of a printing process can thus be gathered under the acronym MAPP for Materials, Application, Product, Process, which describes the context and technical details of the printing process.
The processes are classified according to Figure 1.4 reproduced from Buswell et al. (2020). This classification is based on a core group of processes related to automated concrete placement. These include assembly and surface treatment. Sub-processes must be distinct and identified from the main concrete forming and assembly process.
It is noteworthy that a construction process using 3D printing often involves a series of manufacturing and assembly sequences representing the sequencing of each stage, along with elementary processes and sub-processes over time, which enables a clear representation of the studied process and facilitates comparisons with others. Examples of manufacturing processes are shown in Figure 1.5 for a 3D printing process using two-component extrusion/deposition reinforced with continuous glass fibers, known as anisotropic concrete (Bos et al. 2017; Ducoulombier et al. 2020), and another for 3D printing using selective particle bonding (Pierre et al. 2018; Lowke et al. 2018), in line with the classification of processes proposed by RILEM (Buswell et al. 2022).
Figure 1.4.Elementary process classification system proposed by the RILEM DFC technical committee (Buswell et al. 2020, 2022).
