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Large Scale Testing of Digitally Fabricated Concrete (DFC) Elements

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Abstract

Case study projects based on Digitally Fabricated Concrete (DFC) are presented in an increasing pace around the globe. Generally, though, it is not reported what structural requirements (if any) these structures meet and how compliance to these requirements was established. Published material research is often not connected to the presented case studies, and even when it is, it is not necessarily obvious their small scale results can be applied to full scale structures as some scale effects should be anticipated. Caution is required as DFC related material tests are still under development and scale effects in DFC have hardly been studied. Therefore, it is recommendable to perform large scale testing, in the range of 1:5 to 1:1, if DFC is applied to actual use structures. This paper presents such testing for two projects, a pavilion in Denmark (not realized) and a bridge in the Netherlands (realized). In both cases, elements printed with the 3D Concrete Printing facility of the Eindhoven University of Technology were intended for actual load bearing performance. The conservative designs past the test requirements, but nevertheless some important findings with regard to element manufacturing and structural behaviour were experienced. It is concluded that large scale testing remains advisable for DFC structures as long as not all relevant aspects of the technology are quantitatively understood, at least when new concepts are being applied.

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... Several bridge designs also broaden the range of prefabricated 3DCP applications. The bicycle bridge developed at TU Eindhoven is a demonstrator of structural elements, which are directly 3DCP [22]. The porous segments of the bridge are printed with steel wire reinforced filament and subsequently reinforced and assembled using posttensioning. ...
... In the absence of a universal reinforcement system, compatible with the 3DCP process, reinforcement integration has to be project-specific. Structural 3DCP columns can be achieved by adding a minimum shear reinforcement in between layers or directly in the extruded filament and add the main reinforcement inside cavities that follow the column height [14,22,40,41]. The main reinforcement can be external posttension or post-tension inside grouted cavities. ...
... For this research, no structural tests were performed for 1:1 scale columns; nevertheless, some proposals were reported inside the research community, and are based on the Eurocode 0, Design by testing [22]. These tests consist of destructive load tests for one prototypical specimen in combination with nondestructive tests for all the other specimens, by loading the components only with the designed load. ...
Article
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Recent developments in computational design and digital fabrication with concrete enable the realization of freeform geometries that optimize material use. 3D Concrete extrusion Printing (3DCP) is presently one of the most utilized digital fabrication methods with concrete. The expected advantages of 3DCP result from shaping concrete without formwork and from placing material only where functionally required. Although these advantages were pointed out more than 20 years ago, it is difficult to find competitive examples and their usage in real buildings. Consequently, the nonspecific character of the process acts as a shortcoming by opening up extensive possibilities without a clear direction. This paper proposes an automated 3DCP prefabrication platform for customized columns. The process-specific parameters are, therefore, fine-tuned for high-quality products with diverse forms and textures. Additionally, this paper proposes an evaluation method for geometric complexity and identifies the types of column typologies that may benefit from a 3DCP prefabrication platform.
... 1c, 6b and c). The current design of digitally fabricated concrete structures highly relies on compression-only solutions and extensive experimental testing (as carried out e.g. by Bos et al. [94]) to cover all criteria to be met for construction works (Section 1). However, this limits the possible geometries and hinders mass-market application. ...
... Materials with high paste contents commonly undergo high creep strains [94], generally leading to increased long-term deflections, which may imply the need for deeper cross-sections or load-balancing prestressing to compensate. ...
Article
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The construction industry produces buildings and infrastructure. These construction works are typically immobile and customised, and must meet many criteria to provide value to modern society: structural safety, durability, serviceability, aesthetics and integration, environmental sustainability and construction efficiency. Accordingly, traditional construction methods, along with the resulting construction works, have been adapted to comply with these multifaceted requirements for more than a century. However, the construction industry has a considerable environmental impact, with reinforced concrete as its primary driver due to its extensive use, and will be facing an ever-increasing responsibility to tackle climate neutrality in the upcoming years. Digital fabrication with concrete is a young yet already broad discipline that brings about the potential for the necessary reduction of the environmental impact and further industrialisation of the construction industry while being compatible with the multifaceted requirements for construction works. Still, it has not penetrated the construction mass market, which is paramount for making a significant difference towards improving the environmental impact of the construction industry. The present study tackles this issue by (i) assessing traditional construction and digital fabrication on a value-driven basis, identifying and summarising their inherent strengths and challenges, and (ii) proposing a value-driven ideation process to identify relevant mass-market levers of digital fabrication in the construction industry. The presented methodology indicates two exemplary applications of how traditional construction and digital fabrication processes can be combined to tackle the persistent environmental sustainability challenges.
... This is essential to establish quality control methods that are needed for an industrial scale application. As suggested by Bos et al. [151], projects applying printed concrete in practice (particularly in a structural capacity), should be subject to intense scrutiny and largescale testing (Fig. 8) as long as quality control methods have not been fully established. ...
... Large scale testing of a 1:2 scale prototype of a bridge from printed concrete. Reproduced from[151], with permission. ...
Article
Digital fabrication techniques with concrete and cementitious materials have seen a large amount of research and industrial activity recently, with industrialization of techniques such as 3D printing becoming more of a reality. The potential to revolutionize construction is real, not only through reducing costs, but also bringing more sustainability and increased functionality. Material challenges are significant, chief among them understanding and controlling early age hydration and the link to rheology, incorporation of reinforcement, and overall, the link between processing, material, and performance, both from a structural and durability point of view. Interdisciplinarity is crucial, as the field brings together many disparate fields and has been driven by fields such as architecture so far. This article is a review of the state of the art in the newly forming field of digital fabrication with concrete, and aims to provide some direction in terms of the research challenges encountered thus far.
... Although the results from printability and mechanical testing provide a basis to estimate the manufacturability of the full-scale objects, this can only definitely be established in the production phase itself. As the design is developed based on data from generic tests, projectspecific and scaling issues [15] might arise (e.g. material quality deviations due to prolonged printing, plastic deformations in large elements, compatibility with other construction materials). ...
... In projects, such as this, where 3DCP elements are applied as part of the main load-bearing structure, data on structural material properties are limited, particularly concerning the interaction with process parameters, which is significant [17]. Scale effects may also occur [15] and suitable reinforcement technologies are still under development [18]. The print mortars themselves generally contain a high amount of cement and only small aggregates, resulting in a high shrinkage and low friction resistance in cracks. ...
Article
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In this work, a framework for large-scale structural applications of 3D printed concrete is presented. The steps in this framework, consisting of a design phase, testing phase and manufactur-ing phase, towards a final output were presented and discussed theoretically. The framework was then applied to the case of a 29 m 3D printed bridge, constructed in the Netherlands. The full application of the framework illustrates that despite the absence of standards, it is possible to safely apply 3D printed structures in practice. With the gradual increase of testing data expected to become available over the coming years, the extent of the application of the framework can be reduced step-by-step.
... However, a certain lack of knowledge on the structural performance of these structures remains, since just a few tests were performed. In the last years some research groups worked on this topic: an example is a bicycle bridge printed in Gemert, the Netherlands [12]. The bridge is 6,5 m long and 3,5 m wide, it is made of segments printed vertically, placed horizontally and assembled with post-tensioning cables. ...
... The bridge is 6,5 m long and 3,5 m wide, it is made of segments printed vertically, placed horizontally and assembled with post-tensioning cables. A flexural test in the laboratory of TU Eindhoven and a non-destructive in-situ test of the completed bridge were performed [12]. Some flexural tests were also performed on lintels above window openings [13]. ...
Conference Paper
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The recent development of 3D Concrete Printing (3DPC) has introduced new possibilities for the construction of more efficient and sustainable buildings. However, despite the fact that some building prototypes have been already realized in recent years, only few specific studies have been directed to the study of structural behaviour of such elements. Accordingly, this paper deals with the experimental investigation of the role of hardened state properties of concrete on the structural response of 3DPC walls. Two full-scale walls, one without reinforcement and the other with vertical steel bars, have been printed and are going to be tested at the University of Brescia. This report focuses on the design of these walls with the identification of the main geometrical, mechanical and thermal parameters to optimize their structural and thermal behaviour.
... -To penetrate the construction mass market, it is essential for digitally fabricated ribbed concrete floor systems to comply and be designed with existing building requirements, as design by testing -as currently used for many demonstrators of digital fabrication technologies (e.g. see [53]) -is not affordable for standard cases. -The slab systems presented in Section 4 show that transporting, handling and installing digitally fabricated elements might be cumbersome and require excessive scaffolding and human labour. ...
Article
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The concrete used in floor slabs accounts for large greenhouse gas emissions in building construction. Solid slabs, often used today, consume much more concrete than ribbed slabs built by pioneer structural engineers like Hennebique, Arcangeli and Nervi. The first part of this paper analyses the evolution of slab systems over the last century and their carbon footprint, highlighting that ribbed slabs have been abandoned mainly for the sake of construction time and cost efficiency. However, highly material-efficient two-way ribbed slabs are essential to reduce the environmental impact of construction. Hence, the second part of this paper discusses how digital fabrication can help to tackle this challenge and presents four concrete floor systems built with digitally fabricated formwork. The digital fabrication technologies employed to produce these slab systems are digital cutting, binder-jetting, polymer extrusion and 3D concrete printing. The presented applications showcase a reduction in concrete use of approximately 50% compared to solid slabs. However, the digitally fabricated complex formworks produced were wasteful and/or labour-intensive. Further developments are required to make the digital processes sustainable and competitive by streamlining the production, using low carbon concrete mixes as well as reusing and recycling the formwork or structurally activating stay-in-place formwork.
... In the first place, the determination of the precise region of influence of external solicitation is mandatory, since such influence could compromise the stability of the already printed layers. Furthermore, the design of the die is crucial because it governs the orientation and shape of the layer of material being deposited [6,48]. Likewise, the velocity profile is important to control within the crosssection of the extruder in order to ensure proper placement of the layers and good adherence between layers [6]. ...
... 4. adding the reinforcement after the production (e.g. post-tensioning [81]). ...
Article
Over the past decade innovative techniques for shaping concrete have emerged, all aiming to use less material and reduce the need for traditional formwork. One very promising method is to shape concrete dynamically: referred to as Smart Dynamic Casting (SDC), this process was pioneered in 2012 as the first robotically-driven system for slipforming bespoke concrete structures. The process has successfully been adapted to produce structures using ultra-thin formworks that are cast using our digital set-on-demand procedure. More generally we frame this approach as Digital Casting Systems (DCS), which allows the user precisely to determine the hydration rate of the material, thus eliminating formwork pressure. This paper highlights the major findings from SDC that led us to continue developing DCS. It lays out the material concepts fundamental the family of DCS, which, by eliminating the need for bulky formworks, has a large potential impact on future construction methods.
... (b) Special case of (1), where in addition to the contour of the member, the interior part of the member is also printed with unreinforced concrete. Here, channels are left out in the plain concrete for post-installation of reinforcement bars, external reinforcement installation or prestressing with tendons [18,19]. ...
Article
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Reinforced concrete (RC) is by far the most widely used composite material in the world. Despite the enormous economic importance of RC construction, there is a lack of viable concepts for its digital fabrication. While 3D printing of plain concrete has been pushed forward by a growing research community in recent years, methods for integration of steel reinforcement have only scarcely been researched and little attention has been payed to meet the practical requirements of construction sites and prefabrication plants. Therefore, full-scale implementations of current approaches are hardly available. Based on both, a sound review of R&D for digital fabrication of RC structures and an analysis of practical requirements, the present paper proposes a novel 3D printing process for RC structures, called Additive Manufacturing of Reinforced Concrete (AMoRC), viable for real-world application. In this hybrid process, consisting of an intermittent stud welding process and a continuous concrete extrusion process, segmented steel reinforcing bars are joined to form a three-dimensional reinforcement mesh and simultaneously encased with extruded concrete. The paper describes the conceptual design and development of the process and demonstrates the results of preliminary investigations on its feasibility. As AMoRC enables the operation of rebar welding and concrete extrusion process with synchronized feed rates, combination of both processes in one hybrid print head for digital fabrication of RC is a key-advantage of the proposed method.
... For these approaches, however, the geometric freedom is compromised. Other approaches try to keep the concrete predominantly in a state of pure compression either by designing anti-funicular or arch geometries [13,14], which is only possible in specific cases or by post-tensioning concrete elements together [15]. Even if the concrete is kept in a state of pure compression, the printed concrete itself still needs to be reinforced with at least the minimum reinforcement to be code-compliant. ...
Chapter
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Digital Fabrication with Concrete (DFC) brings many new possibilities for the design and production of concrete structures, promising to revolutionise the concrete construction industry. While technological and material challenges have already been overcome to a large extent, there is still a lack of sufficiently mature reinforcement solutions. Therefore, most digital technologies encounter difficulties in producing load-bearing concrete members. Fibre reinforced concrete (FRC) is one of the most promising reinforcing strategies for DFC due to its capability for producing complex geometries. In conventional FRC, the fibres are dispersed randomly in the concrete matrix; for DFC applications this (i) forces to re-engineer the concrete processing (pumpability and rheology), and (ii) requires using very short and expensive fibres due to pumpability constraints. This paper presents a new reinforcement strategy for using FRC in layered DFC technologies that overcomes the stated limitations of conventional FRC. It consists in adding fibres right after the deposition of each layer of concrete in a controlled amount and orientation and providing a post-tensioning reinforcement in the perpendicular direction. The mechanical behaviour, as well as the potential and first implementation steps in the Concrete Extrusion 3D Printing and Eggshell technologies under development at ETH Zurich, are discussed. The mechanical results show a significant increase in tensile resistance of the aligned interlayer fibre reinforcement compared to conventional FRC. However, for large-scale applications, the main loads still need to be carried by post-tensioning reinforcement.
... The bicycle bridge produced by TU Eindhoven uses a concrete filament reinforced with a continuous steel cable [8]. The modules, assembled in a line, are held in compression by the main reinforcement system of post-tensioning cables. ...
Conference Paper
Although slabs are major concrete consumers, they are mostly flat, oversized, monolithic boxes with significant embodied energy. The state of the art shows how computational design can lead to structurally efficient, lightweight, functionally integrated, and aesthetically accomplished slabs. However, these non-planar geometries are fabricated using complex formwork solutions involving multiple digital fabrication processes and manual concreting.
... It is also important to keep in mind that the extrusion-based 3D printing process presents a variety of technological possibilities that ranges between two extreme cases [7]: the use of a fluid cementitious material that is easy to pump with the addition of hydration accelerator at the 75 nozzle [18 20] in order to guaranty the global stability of the in-print structure on one side and the extrusion of a firm plastic cementitious materials that presents a yield stress higher than 1 kPa that can be considered as buildable without the addition of accelerator [21,22]. ...
Article
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Among the multiplicity of construction methods based on digital concrete technologies, the most common one remains the extrusion-based process. Two opposed strategies have been developed in order to print a concrete structure using extrusion: the first one emphasizes the ease-of-pumping of material which is massively accelerated to ensure the stability of the structure, when leaving the extruder; the second one uses a firm mortar able to sustain the own weight of the structure during the printing, without requiring any accelerator. Both methods have their pros and cons and don't imply the same rheological requirements. Most of the recent literature assumes that both types of material (fluid and firm) follow the same trend of behavior and obey to the Von Mises plasticity criterion, while it has been demonstrated that firm cement-based materials can exhibit a pressure dependent behavior. Moreover, rheological study is mainly based on shear rheometry, while the extrusion-based printing process requires a description of the rheological behavior in compression to predict the global stability of the structure, and in tension to prevent cracks formation. This paper investigates the fresh behavior of cement paste and mortar under different solicitations (shear, compression, tension) for different water to cement ratios. The analysis of these results allows to describe the transition between a ductile fluid material (symmetrical in tension and compression) that obeys to a Von Mises plasticity criterion, and a brittle and firm material (asymmetrical in tension and compression) that requires a pressure dependent plasticity criterion in order to predict its strength under a given solicitation.
... The applications of AM in the construction industry has gained significant attention [8,9] because of the considerable benefits over conventional construction methods. Such benefits include improved geometrical freedom [10], greater safety in construction, formwork and mould free manufacturing, and reduction in construction time, labour, cost and waste [2][3][4]8,[11][12][13][14][15][16][17][18]. These advantages are parallel to that enabled by prefabricated modular and panelised systems and this construction system becoming popular in Sweden, Japan, UK and Australia etc. [19,20]. ...
Article
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50 days free access: https://authors.elsevier.com/a/1cMa18MoIGqTj- The application of additively manufactured, 3D printed concrete in the construction industry has been gaining attention in recent years. 3D concrete printing (3DCP) has potentials for mass customisation and off-site and rapid manufacturing of complex structural and architectural components. However, 3DCP has many challenges such as competing rheological requirements, weak interlayer bonding, difficulty in integrating reinforcement, and anisotropic material behaviour. Therefore, material properties of printed concrete are often inferior to traditional mould cast and leading to poor structural performance. Thus, satisfying performance criteria for structural applications is the key challenge of 3DCP, methods for enhancing the material properties of 3DCP are required. This article reviewed the main parameters affecting the performance of 3D printed concrete and discussed potential methods to enhance these properties. Methods investigated in this article include novel reinforcement, material modification, rheology control, nozzle design, process improvements, and interlayer bonding. Lastly, this article discussed the performance of structural elements produced by 3DCP and proposed future research areas to advance this technology in the building industry.
... cycles until well beyond the crack moment [31]. Nevertheless, this should remain a point of attention when designing a structural element that relies on unbonded tendons for its structural integrity. ...
Article
This article offers a comprehensive, systematic overview of the existing solutions for integrating reinforcement in digital concrete technologies with particular emphasis on Additive Manufacturing (AM) with concrete, also called 3D concrete printing (3DCP). While the functionalities of various types of reinforcement are briefly addressed, the major focus is on the integration process as such, i.e., on its technological aspects. On this basis a generic classification and process description outline has been developed for reinforcement integration, which is regarded as an extension of the RILEM process classification framework for Digital Fabrication with Concrete (DFC). In many instances, the integration occurs in a separate process step prior to or after concrete shaping. This holds true for all formative digital concrete shaping processes and for many 3DCP solutions. 3DCP approaches enable, however, integration of the reinforcement during concrete shaping as part of a single-step AM process in a simultaneous or contiguous manner, while placement of reinforcement is considered to be a sub-process.
... This was shown in the Office of the Future in Dubai (Dubai Future Foundation, n.d.) and the structural wall of the multi-storey house at Kamp C in Westerlo (Van Der Putten et al., 2020). The filling of cavities in the 3DCP structural system with insulation is a second approach, which has been applied to the case study of the Nyborg Studio (Bos, Wolfs, Ahmed, & Salet, 2019), and the insulated wall of the multi-storey house at Kamp C in Westerlo (Van Der Putten et al., 2020). A reverse approach using additively manufactured geometries of insulating material as lost formwork for the casting of concrete has been researched with the Digital Construction Platform by the Mediated Matter Group at MIT (Keating, Leland, Cai, & Oxman, 2017). ...
Conference Paper
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Building envelopes incorporate a multitude of functions, such as structure, room enclosure, insulation, and aesthetic appeal, typically resulting in multi-material layered constructions. With the technology of additive manufacturing, geometrical freedom can instead be utilised to integrate functional requirements into mono-material building components. In this research, the additive manufacturing method of lightweight concrete extrusion and its potential for thermal performance via geometric customisation is explored. It investigates whether the insulating performance of wall components can be increased through the creation of closed cellular structures, and further, whether these performance features can be functionally graded by locally adapting the geometric properties. A design tool for closedcell wall geometries is created, which integrates lightweight concrete extrusion related fabrication constraints and takes into account thermal and structural performance considerations. Through the simulation of heat transfer, generated wall geometries are analysed for their thermal performance. By calculating the layer cycle times and determining the overhang during extrusion, the structural capacity during printing is validated. Finally, experimental manufacturing of 1:1 scale architectural prototypes is executed to test the feasibility of the concept.
... While many of these reinforcement strategies have shown promising mechanical performance on a material scale, only a few have been studied on a structurally relevant scale [18,23,37,38]. It should be noted that all these structural tests were performed on complex geometries using only a single structure. ...
Article
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3D concrete printing (3DCP) offers many new possibilities. This technology could increase the productivity of the construction industry and reduce its environmental impact by producing optimised structures more efficiently. Despite significant developments in materials science, little effort has been put in developing reinforcement strategies compatible with 3DCP and on the characterisation of their structural behaviour. Consequently, 3DCD still lacks compliance with structural integrity requirements. This study presents an experimental investigation consisting of nine four-point bending tests on extrusion 3DCP beams reinforced with various types of reinforcement. As interlayer shear reinforcement, aligned end-hook fibres (0.3 and 0.6%) or steel cables (0.1%) placed between the layers of printed concrete were used. As longitudinal reinforcement, unbonded post-tensioning and conventional bonded passive reinforcement were explored. The crack patterns and their associated kinematics were tracked using digital image correlation. The results show that the post-tensioned beams failed in a brittle manner due to the crushing of concrete in bending, with deformations localised in a few bending cracks. In the beams with conventional bonded longitudinal reinforcement, both bending as well as shear cracks were generated, and the brittle failure of the interlayer shear reinforcement limited the ultimate load. Estimations based on the measured crack kinematics show that the interlayer shear reinforcement carried most of the applied shear force. Based on these results, a simple mechanical model is developed to understand the mechanical behaviour and to pre-design the required amount of interlayer shear reinforcement.
... The compressive strengths of 3D-printed fiber-reinforced concrete can be up to 107 MPa [23]. Long reinforcements, such as st chains [24], steel cables [13], fish lines [25], and wires [25][26][27][28], can be embedded into truded filaments during the printing process. The reinforcements can also be placed acr the interfaces to lock the adjacent layers by inserting steel rebar [29,30], nails [31], me printed rebar [16], or plastic-printed rebar [16]. ...
Article
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Lack of reinforcements is an existing drawback of 3D printed cementitious components, which is an urgent concern. A staple-inserting apparatus was developed and installed on a 3D printer and automatically fabricated 3D printed and staple-reinforced components with 98% successful insertion to achieve inner- and inter-reinforcement of the printed strips. The inserted staples inside the printed strips improved the compressive strength by 25% maximum owing to the inner locking effect by the staple pins, while the flexural strength did not increase because the scattered staples functioned separately. The staples over the strip interfaces remarkably increased the flexural stress by 46–120%. The inserted staples demonstrated a significant strip locking effect, but the unavoidable voids decreased the bonding between staples and the composite. The mechanical analysis concluded that the printing parameters considerably affected the reinforcing rate. The staple inserting technique proved the feasibility of automatic fabrication of fiber-reinforced and printed concrete structures.
... Therefore, manual rebar reinforcement and a few alternative techniques have been used in conjunction with C3DP (Classen et al., 2020). The alternative reinforcement techniques include inline reinforcement integration through the placement of steel wires or cables within concrete layers (Bos et al., 2018a) and pre-or post-tensioned tendons to realize pre-stressed 3D printed concrete behavior (Bos et al., 2018b;Asprone et al., 2018). All these reinforcement techniques are either manual or have not been evaluated thoroughly yet, to be considered as an acceptable reinforcement method to replace steel rebars. ...
... The sandwich wall elements of the Milestone house are filled with sprayed insulation. As it was known [22] the expansion and consecutive contraction of the material may cause the concrete to fracture, extensive trials were performed to find an insulation material that least posed this issue. Nevertheless, it could not be entirely avoided, and had to be remedied post factum. ...
Article
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Extrusion-based 3D Concrete Printing (3DCP) is rapidly gaining popularity in the construction industry. Trial projects are now being realized at an increasing rate around the world to test the viability of the technology against real-world requirements. This step, from the ‘simple’ deposition of filaments of self-stable concrete to its application in buildings and structures, with all associated requirements and interfaces, comes with challenges. These range from matching the design intent to the manufacturing capabilities (through structural analysis and approval, and reinforcement) to quality consistency (robustness) on large scale, and compatibility with other materials. In many of these areas, much simply remains unknown due to a lack of experimental data or information from projects where 3DCP has been applied. This paper aims at reducing this knowledge gap by presenting a systematic discussion, based on the analyses of eight realized 3DCP projects from around the world. It was found that the structural application of printed concrete is limited, due to a lack of regulatory framework for expedient approval, as well as limited reinforcement options which require to resort to unreinforced masonry analogies. The application of the technology features a host of practical issues that relate to the print process, material, site conditions, building integration and design – or to the 3DCP technology in general. Although some potential risks, such as shrinkage cracking and quality consistency are generally recognized, the measures taken to mitigate them vary considerably, and are largely based on individual expertise. The actual effectiveness is generally unknown. Finally, it was observed that, while the printing itself is fast, the preparation time is generally considerable. This is partially due to a lack of knowledge amongst professionals. In the practical production of a 3DCP project, three expertise areas are crucial: one for the digital part, one for the machine side, and one for the material side. Thus there is a strong need for educational institutions to develop dedicated training courses and incorporate relevant topics into their curricula.
... steel cable [16], steel wire [99,[132][133][134] fish cable [99], chain [122] These reinforcements were placed in the 3D-printed mortar by operations of inserting, placing, or embedding. A note of caution is that there is no compaction or vibration to the extruded mortar and the reinforcements. ...
Article
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The three-dimensional (3D) printing technique for cement-based materials has been actively investigated and utilized in civil engineering. However, there is no systematic review of the fabricating devices. This paper reviews the software and hardware for extrusion-based 3D concrete printing. Firstly, a dedicated tool path generating software is urgently needed to meet the cementitious printing applications and to improve printing quality with toolpath optimizations. Secondly, the existing printing equipment was summarized and discussed, concluding the pros and cons of various 3D motion systems, material systems, and nozzle units. Suitable choices for scientific research and engineering applications were recommended. The reinforcing techniques were categorized and concluded with the existing drawbacks and the research trend. A hybrid manufacturing system of 3D printing and the reinforcing technique was then proposed with a system diagram and flowchart.
Article
de Mit extrusionsbasierten 3D‐Druckmethoden herstellbare unbewehrte Betonbauteile sind nur in seltenen Fällen für den Einsatz in realen Bauwerken geeignet, da sie spröde versagen und unzureichende Tragfähigkeiten aufweisen. Daher werden neue Verfahren benötigt, die die Integration von Stahlbewehrung in den Betondruckprozess und damit die additive Fertigung des Verbundwerkstoffs Stahlbeton ermöglichen. Die Konzeptionierung eines praxisorientierten 3D‐Druckverfahrens für Stahlbeton, das sog. „Additive Manufacturing of Reinforced Concrete“ (AMoRC), ist daher Gegenstand des vorliegenden Beitrags. Im AMoRC‐Verfahren werden konfektionierte Stahlbewehrungsstäbe abschnittweise mit einem Lichtbogenbolzenschweißverfahren zu einer dreidimensionalen Bewehrungsstruktur gefügt und simultan mit einem Beton‐Extrusionsprozess umdruckt. Der vorliegende Beitrag beschreibt die Entwicklung des Verfahrens und erste Voruntersuchungen zur Umsetzbarkeit. Abstract en Conception of a real world 3D printing method for reinforced concrete (AMoRC) 3D printed plain concrete components (without reinforcement) produced through extrusion‐based 3D printing methods are rarely suitable for use in real structures because they fail brittle and have insufficient structural resistance. Therefore, new methods are needed that allow the integration of steel reinforcement into the concrete printing process and thus the additive production of the composite material reinforced concrete. The conceptual design of a practice‐oriented 3D printing process for reinforced concrete, the so‐called Additive Manufacturing of Reinforced Concrete (AMoRC), is therefore the subject of the present paper. In the AMoRC process, segmented steel reinforcing bars are joined to form a three‐dimensional reinforcement mesh using an arc stud welding process and simultaneously overprinted with a concrete extrusion process. This article describes the development of the process and preliminary investigations on its feasibility.
Chapter
The form freedom enabled by digital fabrication with concrete technologies provides advantages for a wide range of concrete based objects, from architectural to structural elements. The current chapter focuses on the specifics of structural design and engineering of DFC with emphasis on those technologies based on Additive Manufacturing with extrusion. Since it is a new and innovative way to build, a clear common approach to structural engineering has not yet been developed. As a result, this chapter aims to introduce the specific challenges of structural design and engineering with the additive manufacturing technology, providing an overview of structural typologies that have been developed (especially concerning the reinforcement strategies, including fibre reinforcement). Furthermore, the structural principles adopted in DFC and the codified approaches used in conventional reinforced concrete is compared, and putative structural testing procedures and validation methods for DFC are reported.
Chapter
3D printing technologies with cementitious materials have advanced dramatically in recent years. Likewise, we have also developed suitable materials with high thixotropy for layered extrusion and the gantry 3D-printing system, dealing with discontinuous geometry and multi-productions simultaneously. In this way, there have been a lot of studies particularly on material properties and printing processes so far. However, few studies have conducted structural performance testing on a large scale in a systematic manner. Hence, this structural concern is focused on and tackled in this study. The developed materials and printing system are used for the following experiments. As a preliminary test, specific characteristics such as anisotropy and creep of a layer-by-layer component are investigated for a structural design in addition to basic fresh and hardened properties. After the rational geometry is determined by topology optimization analysis, in which a practical scale pedestrian bridge under sidewalk loading is designed, its structural performance is evaluated for safety based on FEM (Finite Element Method) analysis, while considering the preliminary tests. The designed bridge structure consists of 44 segments with different complex shapes, which are printed separately, and all the segments are unified as a compression loaded structure through prestressed external reinforcement. Finally, it is confirmed whether the inherent behavior due to the laminar structure is observable in the full-scale bending test.
Article
While interest in 3D printing of concrete (3DCP) and structures has been growing, a major obstacle for implementation of 3DP construction method is the need for steel reinforcement and the challenges this presents to the 3DP process. Engineered Cementitious Composites (ECC), also known as Strain-hardening Cement-based Composites (SHCC), hold promise to attain structural integrity, durability, reliability and robustness without steel reinforcement. This article surveys the state of the art on 3DP research with ECC and suggests needed research to direct future development. Research in Asia, Europe and the United States has demonstrated printability and buildability of 3DP-ECC that exhibits characteristic tensile ductility of cast ECC. Nonetheless, a number of outstanding research areas are identified, including those associated with more sustainable mix-design, rheology control, microstructure, filament/filament interface weakness, and long-term durability. Resolution of these challenges will better position the research community to addressing full scale construction, print speed, and print quality.
Article
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3D concrete printing (3DCP) is the additive manufacturing (AM) with the use of cementitious materials. It is a layer-by-layer new construction method which can provide design flexibility, minimize material waste, improve sustainability, decrease construction period, reduce labor requirements, increase site safety and significantly reduce the overall costs. In past 10 years, significant improvements have been made in developing concrete printers to transfer 3DCP from lab-scale to the real construction-scale. In this paper, the existing techniques that have been applied in construction of largescale 3DCP are presented. The recent literature is explored for new mix characteristics, printing process parameters, insight relations of flowability-extrudability-buildability, the hardened and mechanical properties of extrusion-based 3DPC. In addition, this paper investigated the different applied techniques for reinforcing of 3DPC structures in details, because to date, the largest challenge that faced 3DPC structures is the lack of appropriate methods of reinforcement. Overall, this work presents a comprehensive systematic review of 330 most recent publications in this field, with the focus on the last 3 years.
Chapter
This chapter provides an overview of the consequences and impacts of 3D printing on architecture, structural design, society, the economy and the environment. The 3D printing of cement‐based materials provides unprecedented freedom of form for architects and designers of concrete parts. The design of building and construction structures can be done using the concept of topological optimization. The new‐found freedom of forms allows the design of structures to follow the intrinsic qualities of concrete (reduction of zones subjected to tension) and the reduction of the amounts of materials used. In addition, innovative reinforcement techniques will be tested and developed to work together with the printing process. Currently, research is carried out on the simultaneous printing of concrete and steel reinforcements. In order to provide the minimum tensile properties for cement‐based materials, many studies have proposed the addition of fibers to the mixture for printing.
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The current state of research and development into the additive manufacturing of concrete is poised to become a disruptive technology in the construction industry. Although many academic and industrial institutions have successfully realised full-scale structures, the limitations in the current codes of practice to evaluate their structural integrity have resulted in most of these structures still not being certified as safe for public utilisation and thus deemed as test prototypes for display purpose only. To realise a 3D concrete printed (3DCP) structure which could be certified safe for public use, a bridge was realised using the print facility of the Eindhoven University of Technology (TU/e) based on the concept of ‘Design by Testing’. This paper holistically discusses the complications encountered while realising a reinforced 3DCP bridge in a public traffic network and decisions taken to find solutions for overcoming them.
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The Material Deposition Method (MDM) is enjoying increasing attention as an additive method to create concrete mortar structures characterised by a high degree of form-freedom, a lack of geometrical repetition, and automated construction. Several small-scale structures have been realised around the world, or are under preparation. However, the nature of this construction method is unsuitable for conventional reinforcement methods to achieve ductile failure behaviour. Sometimes, this is solved by combining printing with conventional casting and reinforcing techniques. This study, however, explores an alternative strategy, namely to directly entrain a metal cable in the concrete filament during printing to serve as reinforcement. A device is introduced to apply the reinforcement. Several options for online reinforcement media are compared for printability. Considerations specific to the manufacturing process are discussed. Subsequently, pull-out tests on cast and printed specimens provide an initial characterisation of bond behaviour. Bending tests furthermore show the potential of this reinforcement method. The bond stress of cables in printed concrete was comparable to values reported for smooth rebar but lower than that of the same cables in cast concrete. The scatter in experimental results was high. When sufficient bond length is available, ductile failure behaviour for tension parallel to the filament direction can be achieved, even though cable slip occurs. Further improvements to the process should pave the way to achieve better post-crack resistance, as the concept in itself is feasible.
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This paper presents the hardened properties of a high-performance fibre-reinforced fine-aggregate concrete extruded through a 9 mm diameter nozzle to build layer-by-layer structural components in a printing process. The printing process is a digitally controlled additive method capable of manufacturing architectural and structural components without formwork, unlike conventional concrete construction methods. The effects of the layering process on density, compressive strength, flexural strength, tensile bond strength and drying shrinkage are presented together with the implication for mix proportions. A control concrete (mould-cast specimens) had a density of approximately 2250 kg/m3, high strength (107 MPa in compression, 11 MPa in flexure) and 3 MPa in direct tension, together with a relatively low drying shrinkage of 175 μm (cured in water) and 855 μm (cured in a chamber at 20 °C and 60% relative humidity) at 184 days. In contrast well printed concrete had a density of 2350 kg/m3, compressive strength of 75–102 MPa, flexural strength of 6–17 MPa depending on testing direction, and tensile bond strength between layers varying from 2.3 to 0.7 MPa, reducing as the printing time gap between layers increased. The well printed concrete had significantly fewer voids greater than 0.2 mm diameter (1.0%) when compared with the mould-cast control (3.8%), whilst samples of poorly printed material had more voids (4.8%) mainly formed in the interstices between filaments. The additive extrusion process was thus shown to retain the intrinsic high performance of the material.
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Additive manufacturing in construction is beginning to move from an architect's modelling tool to delivering full-scale architectural components and elements of buildings such as walls and facades. This paper discusses large-scale additive manufacturing processes that have been applied in the construction and architecture arena and focuses on ‘Concrete Printing’, an automated extrusion based process. The wet properties of the material are critical to the success of manufacture and a number of new criteria have been developed to classify these process specific parameters. These criteria are introduced and key challenges that face construction scale additive manufacturing are presented.
Conference Paper
The effect of scale on different parameters of the 3D printing of concrete is explored through the design and fabrication of a 3D concrete printed pavilion. This study shows a significant gap exists between what can be generated through computer aided design (CAD) and subsequent computer aided manufacturing (generally based on CNC technology). In reality, the 3D concrete printing on the one hand poses manufacturing constraints (e.g. minimum curvature radii) due to material behaviour that is not included in current CAD/CAM software. On the other hand, the process also takes advantage of material behaviour and thus allows the creation of shapes and geometries that, too, can't be modelled and predicted by CAD/CAM software. Particularly in the 3D printing of concrete, there is not a 1:1 relation between toolpath and printed product, as is the case with CNC milling. Material deposition is dependent on system pressure, robot speed, nozzle section, layer stacking, curvature and more-all of which are scale dependent. The paper will discuss the design and manufacturing decisions based on the effects of scale on the structural design, printed and layered geometry, robot kinematics, material behaviour, assembly joints and logistical problems. Finally, by analysing a case study pavilion, it will be explored how 3D concrete printing structures can be extended and multiplied across scales and functional domains ranging from structural to architectural elements, so that we can understand how to address questions of scale in their design.
Chapter
Recent years have seen a rapid growth of additive manufacturing methods for concrete construction. A recurring issue associated with these methods, however, is the lack of ductility in the resulting product. In cases this is solved by combining printing with conventional casting and reinforcing techniques. Alternatively, this paper presents first findings on the development of a system to directly entrain a suitable form of reinforcement during printing. A device is introduced to apply the reinforcement. Several options for online reinforcement medium are compared for printability and structural performance, based printing test runs and 4-point bending tests respectively. It is shown that high-performance steel cables can provide suitable reinforcement characteristics, although improved bond would allow better use of the cable capabilities. Significant post-cracking deformations and post-cracking strength can be achieved. Further research into optimal reinforcement placement and configuration is recommended.
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Around the globe, ground breaking projects and case studies are being presented to showcase the potential of digital fabrication with concrete, better known as 3D printing of concrete. With these explorations, underway, the key quest in 3D concrete printing is for structural stability by means of high strength and ductility. This need could be avoided by designing printable fiber reinforcement concrete or concrete with in-process ‘printed’ reinforcement. Therefore, in this paper, an experimental investigation was carried out by reinforcing short glass fiber (GF) of different lengths (3mm, 6mm and 8 mm) and percentages (0.25%-1%) in a custom-made sustainable construction material developed for 3D printing application. Thixotropic GF/geopolymer mortar was made using class F grade fly ash and loaded in different directions for measuring it’s mechanical properties. Our experimental testing results revealed, improved properties of the printed specimens with increase in fiber percentage up to 1% and an obvious directional dependency behaviour, caused by the layer wise deposition.
Article
Additive manufacturing is gaining ground in the construction industry. The potential to improve on current construction methods is significant. One of such methods being explored currently, both in academia and in construction practice, is the additive manufacturing of concrete (AMoC). Albeit a steadily growing number of researchers and private enterprises active in this field, AMoC is still in its infancy. Different variants in this family of manufacturing methods are being developed and improved continuously. Fundamental scientific understanding of the relations between design, material, process, and product is being explored. The collective body of work in that area is still very limited. After sketching the potential of AMoC for construction, this paper introduces the variants of AMoC under development around the globe and goes on to describe one of these in detail, the 3D Concrete Printing (3DCP) facility of the Eindhoven University of Technology. It is compared to other AMoC methods as well as to 3D printing in general. Subsequently, the paper will address the characteristics of 3DCP product geometry and structure, and discuss issues on parameter relations and experimental research. Finally, it will present the primary obstacles that stand between the potential of 3DCP and large-scale application in practice, and discuss the expected evolution of AMoC in general.
Influence of the interface between layers on the tensile properties of 3D-printed concrete
  • G J Slager
The effect of layered manufacturing on the strength properties of printable concrete. MSc graduation thesis
  • C C M Doomen
Numerical and experimental assesment of 3D Concrete Printed Sandwich Panels with different insulating core materials. MSc graduation thesis
  • F Vermue