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Concrete 3D Printing and Digitally-Aided Fabrication

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Construction and Building Materials".

Deadline for manuscript submissions: closed (31 December 2020) | Viewed by 99058

Special Issue Editor

Dr. Arnaud Perrot

E-Mail Website
Guest Editor
IRDL, Université Bretagne Sud, Lorient, France
Interests: 3D printing; additive manufacturing; extrusion; mix design; cement-based materials; earth-based materials; rheology; porous medium
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The concrete construction industry has improved its productivity for last 50 years. Nowadays, the development of computer-aided design tools along with the introduction of additive manufacturing in the construction industry have the ability to revolutionize the way we build construction. Those disruptive building methods require joint and multidisciplinary research development in terms of mix-design of printable materials, the definition of fresh state properties and rheological behaviour requirements, the structural and architectural designs of printed structures using topology optimization, and robotics innovation.

This Special Issue focuses on new additive manufacturing methods used for concrete: the extrusion-based method, particles-based methods, and others new techniques using shotcrete or digitally fabricated permeable formworks or fabrics. Paper topics can deal with many aspects related to the digital fabrication of concrete and cement-based materials: processing, case study, fresh state properties and rheological requirements, the mechanical behaviour of printed cement-based material, the structural design of printed parts and structures, and environmental and economic impacts.

This Special Issue is expected to provide a collection of articles showing an overview of recent advances in the field of concrete 3D printing and drawing future perspectives for these new revolutionizing methods.

Prof. Dr. Arnaud Perrot
Guest Editor

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • 3D printing
  • additive manufacturing
  • cement-based materials
  • concrete
  • rheology
  • processing
  • computer-aided methods
  • extrusion
  • particle-bed injetcion
  • structural design
  • topology optimization

Published Papers (19 papers)

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Research

23 pages, 5366 KiB  
Article
Mechanical Properties of Hardened 3D Printed Concretes and Mortars—Development of a Consistent Experimental Characterization Strategy
by Maximilian Meurer and Martin Classen
Materials 2021, 14(4), 752; https://doi.org/10.3390/ma14040752 - 05 Feb 2021
Cited by 36 | Viewed by 4251
Abstract
Today, it is already foreseeable that additive manufacturing of mortar and concrete has groundbreaking potential and will revolutionize or at least fundamentally change the way we build. In recent years, 3D concrete printing (3DCP) with extrusion-based deposition methods has been pushed forward by [...] Read more.
Today, it is already foreseeable that additive manufacturing of mortar and concrete has groundbreaking potential and will revolutionize or at least fundamentally change the way we build. In recent years, 3D concrete printing (3DCP) with extrusion-based deposition methods has been pushed forward by a growing research community. Albeit being regarded one of the most promising innovations in construction industry, a consistent characterization methodology for assessing the constitutive behavior of 3D printed, hardened cementitious materials is missing, so far, which hinders its widespread use in engineering practice. The major objective of this paper is to fill this gap by developing a new experimental framework that can thoroughly describe the mechanical properties of 3D printed cementitious materials. Based on both a review of state-of-the-art test setups and a comprehensive experimental campaign, the present paper proposes a set of easy-to-use experimental methods that allow us to assess flexural, tensile, shear and compressive strength as well as fracture energy of 3D printed concretes and mortars in a reliable and reproducible manner. The experimental results revealed anisotropic material behavior for flexural, tensile, shear and compressive loading. Furthermore, they confirm that interval time (time gap between deposition of subsequent layers) has a crucial effect on investigated material properties leading to a severe reduction in strength and fracture energy for longer interval times. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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18 pages, 3458 KiB  
Article
Particle-Bed Binding by Selective Paste Intrusion—Strength and Durability of Printed Fine-Grain Concrete Members
by Daniel Weger and Christoph Gehlen
Materials 2021, 14(3), 586; https://doi.org/10.3390/ma14030586 - 27 Jan 2021
Cited by 14 | Viewed by 2714
Abstract
The selective paste intrusion (SPI) describes a selective binding, additive manufacturing method. SPI bonds thin layers of aggregate by cement paste locally. Currently, SPI can achieve higher compressive strength, durability, and easier unpacking behavior compared to other selective binding methods suitable for the [...] Read more.
The selective paste intrusion (SPI) describes a selective binding, additive manufacturing method. SPI bonds thin layers of aggregate by cement paste locally. Currently, SPI can achieve higher compressive strength, durability, and easier unpacking behavior compared to other selective binding methods suitable for the production of concrete structures. Particle-bed based methods not only achieve much higher surface resolutions than depositing (extrusion)-based additive manufacturing methods but also have no restrictions in freedom of form. However, the mechanical performance of SPI components strongly depends on the void content between the individual layers and thus the penetration behavior of the cement paste. This paper presents direction-dependent measurements of the strength and durability of SPI-printed components compared to casted specimens with the same mixing composition. The results show compressive strength values between 70 and 78 MPa after 7 d, flexural strength of 1/10 without reinforcement, a high freeze–thaw resistance, no detectable carbonation after 182 days of exposure under ambient CO2–conditions, and after 28 days under increased CO2 content of 2 vol % as well as low chloride penetration resistances. All tests showed in almost all cases no dependency on the layer orientation. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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24 pages, 7734 KiB  
Article
Penetration of Cement Pastes into Particle-Beds: A Comparison of Penetration Models
by Daniel Weger, Alexandre Pierre, Arnaud Perrot, Thomas Kränkel, Dirk Lowke and Christoph Gehlen
Materials 2021, 14(2), 389; https://doi.org/10.3390/ma14020389 - 14 Jan 2021
Cited by 12 | Viewed by 2205
Abstract
For the selective paste intrusion (SPI) method, thin layers of aggregate are locally bound by cement paste where the structure shall arise. After completion of the printing process, the structure is excavated from the particle-bed and the unbound particles are removed. However, for [...] Read more.
For the selective paste intrusion (SPI) method, thin layers of aggregate are locally bound by cement paste where the structure shall arise. After completion of the printing process, the structure is excavated from the particle-bed and the unbound particles are removed. However, for a sufficient layer bonding and shape accuracy, the rheology of the cement paste must be adapted to the flow resistance of the particle-bed. For practical application, that means mostly time and material consuming “trial and error” tests. To prevent that, analytical models can help to predict the penetration of the cement paste. This paper presents four analytical models to calculate the penetration depth of a cement paste into a particle packing. Based on Darcy’s law, an already existing model is slightly modified (model A+) and a generalized (model C), an advanced generalized (model D) as well as a simplified model (model B/B+) are developed. Compared to conducted tests on the penetration depth, model B showed good accuracy (deviation <1.5 mm) for pastes with a yield stress ≥8.2 Pa, model A+/B+/C for ≥ 5.4 Pa and model D even for <5.4 Pa. Finally, an application guide for each model for practical use will be given. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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19 pages, 6850 KiB  
Article
Interface Behavior and Interface Tensile Strength of a Hardened Concrete Mixture with a Coarse Aggregate for Additive Manufacturing
by Arnošt Vespalec, Josef Novák, Alena Kohoutková, Petr Vosynek, Jan Podroužek, David Škaroupka, Tomáš Zikmund, Josef Kaiser and David Paloušek
Materials 2020, 13(22), 5147; https://doi.org/10.3390/ma13225147 - 15 Nov 2020
Cited by 14 | Viewed by 3280
Abstract
3D concrete printing technology (3DCP) is a relatively new technology that was first established in the 1990s. The main weakness of the technology is the interface strength between the extruded layers, which are deposited at different time intervals. Consequently, the interface strength is [...] Read more.
3D concrete printing technology (3DCP) is a relatively new technology that was first established in the 1990s. The main weakness of the technology is the interface strength between the extruded layers, which are deposited at different time intervals. Consequently, the interface strength is assumed to vary in relation to the time of concrete casting. The proposed experimental study investigated the behavior of a hardened concrete mixture containing coarse aggregates that were up to 8 mm in size, which is rather unusual for 3DCP technology. The resulting direct tensile strength at the layer interface was investigated for various time intervals of deposition from the initial mixing of concrete components. To better understand the material behavior at the layer interface area, computed tomography (CT) scanning was conducted, where the volumetric and area analysis enabled validation of the pore size and count distribution in accordance with the layer deposition process. The analyzed CT data related the macroscopic anisotropy and the resulting crack pattern to the temporal and spatial variability that is inherent to the additive manufacturing process at construction scales while providing additional insights into the porosity formation during the extrusion of the cementitious composite. The observed results contribute to previous investigations in this field by demonstrating the causal relationships, namely, how the interface strength development is determined by time, deposition process, and pore size distribution. Moreover, in regard to the printability of the proposed coarse aggregate mixture, the specific time interval is presented and its interplay with interface roughness and porosity is discussed. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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15 pages, 7672 KiB  
Article
Additive Manufacturing of Cementitious Materials by Selective Paste Intrusion: Numerical Modeling of the Flow Using a 2D Axisymmetric Phase Field Method
by Alexandre Pierre, Daniel Weger, Arnaud Perrot and Dirk Lowke
Materials 2020, 13(21), 5024; https://doi.org/10.3390/ma13215024 - 07 Nov 2020
Cited by 13 | Viewed by 2249
Abstract
The 3D printing of concrete has now entered a new era and a transformation of the construction sector is expected to reshape fabrication with concrete. This work focuses on the selective paste intrusion method, which consists of bonding dry particles of aggregate with [...] Read more.
The 3D printing of concrete has now entered a new era and a transformation of the construction sector is expected to reshape fabrication with concrete. This work focuses on the selective paste intrusion method, which consists of bonding dry particles of aggregate with a cement paste. This innovative technique could lead to the production of very precise component for specific applications. The main obstacle to tackle in order to reach a high shape accuracy of high mechanical performances of 3D printing elements by selectively activating the material is the control of the distribution of the cement paste through the particle bed. With the aim to better understand the path followed by the solution as it penetrates a cut-section of the granular packing, two-dimensional numerical modeling is carried out using Comsol software. A phase-field method combined with a continuous visco-plastic model has been used to study the influence of the average grain diameter, the contact angle, and the rheological properties of cement pastes on the penetration depth. We compare the numerical modeling results to existing experimental results from 3D experiments and a one-dimensional analytical model. We then highlight that the proposed numerical approach is reliable to predict the final penetration of the cement pastes. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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24 pages, 9290 KiB  
Article
Buildability and Mechanical Properties of 3D Printed Concrete
by Changbin Joh, Jungwoo Lee, The Quang Bui, Jihun Park and In-Hwan Yang
Materials 2020, 13(21), 4919; https://doi.org/10.3390/ma13214919 - 02 Nov 2020
Cited by 43 | Viewed by 6201
Abstract
Recently, 3D concrete printing has progressed rapidly in the construction industry. However, this technique still contains several factors that influence the buildability and mechanical properties of the printed concrete. Therefore, this study investigated the effects of the nozzle speed, the interlayer interval time, [...] Read more.
Recently, 3D concrete printing has progressed rapidly in the construction industry. However, this technique still contains several factors that influence the buildability and mechanical properties of the printed concrete. Therefore, this study investigated the effects of the nozzle speed, the interlayer interval time, the rotations per minute (RPMs) of the screw in the 3D printing device, and the presence of lateral supports on the buildability of 3D concrete printing. In addition, this paper presents the results of the mechanical properties, including the compressive, splitting tensile, and flexural tensile strengths of 3D printed concrete. The buildability of 3D printed structures was improved with an extended interlayer interval time of up to 300 s. The printing processes were interrupted because of tearing of concrete filaments, which was related to excessive RPMs of the mixing screw. The test results also showed that a lateral support with a wide contact surface could improve the resistance to buckling failure for 3D printed structures. The test results of the mechanical properties of the 3D printed concrete specimens indicated that the compressive, splitting tensile, and flexural tensile strengths significantly depended on the bonding behavior at the interlayers of the printed specimens. In addition, although metal laths were expected to improve the tensile strength of the printed specimens, they adversely affected the tensile performance due to weak bonding between the reinforcements and concrete filaments. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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17 pages, 11386 KiB  
Article
Interlayer Reinforcement Combined with Fiber Reinforcement for Extruded Lightweight Mortar Elements
by Carla Matthäus, Nadine Kofler, Thomas Kränkel, Daniel Weger and Christoph Gehlen
Materials 2020, 13(21), 4778; https://doi.org/10.3390/ma13214778 - 26 Oct 2020
Cited by 20 | Viewed by 2164
Abstract
Lightweight mortar extrusion enables the production of monolithic exterior wall components with improved thermal insulation by installing air chambers and reduced material demand compared to conventional construction techniques. However, without reinforcement, the systems are not capable of bearing high flexural forces and, thus, [...] Read more.
Lightweight mortar extrusion enables the production of monolithic exterior wall components with improved thermal insulation by installing air chambers and reduced material demand compared to conventional construction techniques. However, without reinforcement, the systems are not capable of bearing high flexural forces and, thus, the application possibilities are limited. Furthermore, the layer bonding is a weak spot in the system. We investigate a reinforcement strategy combining fibers in the mortar matrix with vertically inserted elements to compensate the layer bonding. By implementing fibers in the extruded matrix, the flexural strength can be increased almost threefold parallel to the layers. However, there is still an anisotropy between the layers as fibers are oriented during deposition and the layer bond is still mainly depending on hydration processes. This can be compensated by the vertical insertion of reinforcement elements in the freshly deposited layers. Corrugated wire fibers as well as short steel reinforcement elements were suitable to increase the flexural strength between the layers. As shown, the potential increase in flexural strength could be of a factor six compared to the reference (12 N/mm2 instead of 1.9 N/mm2). Thus, the presented methods reduce anisotropy in flexural strength due to layered production. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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23 pages, 6120 KiB  
Article
Mechanical Behavior of Printed Strain Hardening Cementitious Composites
by Stefan Chaves Figueiredo, Claudia Romero Rodríguez, Zeeshan Y. Ahmed, Derk H. Bos, Yading Xu, Theo M. Salet, Oğuzhan Çopuroğlu, Erik Schlangen and Freek P. Bos
Materials 2020, 13(10), 2253; https://doi.org/10.3390/ma13102253 - 14 May 2020
Cited by 39 | Viewed by 4230
Abstract
Extrusion based additive manufacturing of cementitious materials has demonstrated strong potential to become widely used in the construction industry. However, the use of this technique in practice is conditioned by a feasible solution to implement reinforcement in such automated process. One of the [...] Read more.
Extrusion based additive manufacturing of cementitious materials has demonstrated strong potential to become widely used in the construction industry. However, the use of this technique in practice is conditioned by a feasible solution to implement reinforcement in such automated process. One of the most successful ductile materials in civil engineering, strain hardening cementitious composites (SHCC) have a high potential to be employed for three-dimensional printing. The match between the tailored brittle matrix and ductility of the fibres enables these composites to develop multiple cracks when loaded under tension. Using previously developed mixtures, this study investigates the physical and mechanical performance of printed SHCC. The anisotropic behavior of the materials is explored by means of mechanical tests in several directions and micro computed tomography tests. The results demonstrated a composite showing strain hardening behavior in two directions explained by the fibre orientation found in the printed elements. Moreover, the printing technique used also has guaranteed an enhanced bond in between the printed layers. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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24 pages, 10174 KiB  
Article
Mastering Yield Stress Evolution and Formwork Friction for Smart Dynamic Casting
by Anna Szabo, Lex Reiter, Ena Lloret-Fritschi, Fabio Gramazio, Matthias Kohler and Robert J. Flatt
Materials 2020, 13(9), 2084; https://doi.org/10.3390/ma13092084 - 01 May 2020
Cited by 11 | Viewed by 2510
Abstract
The construction industry is a slow adopter of new technologies and materials. However, interdisciplinary research efforts in digital fabrication methods with concrete aim to make a real impact on the way we build by showing faster production, higher quality and enlarged freedom of [...] Read more.
The construction industry is a slow adopter of new technologies and materials. However, interdisciplinary research efforts in digital fabrication methods with concrete aim to make a real impact on the way we build by showing faster production, higher quality and enlarged freedom of design. In this paper, the potential and constraints of a specific digital slip-forming process, smart dynamic casting (SDC), are investigated with a material-focused approach in the complex task of producing thin folded structures. Firstly, the workability and the strength evolution of different material compositions are studied to achieve the constant processing rate for SDC. Secondly, friction between the formwork walls and the concrete, a key aspect in slip-casting, is studied with a simplified experimental setup to identify if any of these mixes would provide an advantage for processing. Finally, a theoretical framework is constructed to link the material properties, the process conditions and the designed geometry. This framework introduces the ‘SDC number’ as a simplified approach to formulate the process window, the suitable conditions for slip-forming. The experimental results prove the assumption of the model that friction is proportional to yield stress for all base compositions and acceleration methods regardless of the filling history. The results are evaluated in the context of the narrow process window of thin folded structures as well as the wider process window of columns. The necessity of consistent strength evolution is underlined for narrow windows. Further, friction is shown to be the highest initially, thus with both narrow and wide process windows, after a successful start-up the continuation of slipping is less prone to failure. The proposed theoretical model could provide material and geometry-specific slipping strategy for start time and slipping rate during production. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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13 pages, 4768 KiB  
Article
Nailing of Layers: A Promising Way to Reinforce Concrete 3D Printing Structures
by A. Perrot, Y. Jacquet, D. Rangeard, E. Courteille and M. Sonebi
Materials 2020, 13(7), 1518; https://doi.org/10.3390/ma13071518 - 26 Mar 2020
Cited by 60 | Viewed by 5816
Abstract
Today, the extrusion-based 3D printing of concrete is a potential breakthrough technology for the construction industry. It is expected that 3D printing will reduce the cost of construction of civil engineering structures (removal of formwork) and lead to a significant reduction in time [...] Read more.
Today, the extrusion-based 3D printing of concrete is a potential breakthrough technology for the construction industry. It is expected that 3D printing will reduce the cost of construction of civil engineering structures (removal of formwork) and lead to a significant reduction in time and improve working environment conditions. Following the use of this additive manufacturing layer-wise process, it is required to change the way concrete structures are designed and reinforced, especially for the parts of the structure under tension loads. Indeed, the extrusion-based concrete 3D printing process does not allow for the production of conventional reinforced concrete, and there is a need to develop other ways of compensating for the low mechanical performances of concrete, particularly in tension. In this study, the reinforcement of printed structures by using steel nails through the deposited layers of fresh concrete was investigated. Additionally, three-layer and 10-layer samples were reinforced with nails with varying inclination and spacing. The results show that inclined nails can be used to provide a flexural strengthening of the printing material in different directions. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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17 pages, 7132 KiB  
Article
Injection 3D Concrete Printing (I3DCP): Basic Principles and Case Studies
by Norman Hack, Inka Dressler, Leon Brohmann, Stefan Gantner, Dirk Lowke and Harald Kloft
Materials 2020, 13(5), 1093; https://doi.org/10.3390/ma13051093 - 01 Mar 2020
Cited by 17 | Viewed by 6386
Abstract
Today, the majority of research in 3D concrete printing focuses on one of the three methods: firstly, material extrusion; secondly, particle-bed binding; and thirdly, material jetting. Common to all these technologies is that the material is applied in horizontal layers. In this paper, [...] Read more.
Today, the majority of research in 3D concrete printing focuses on one of the three methods: firstly, material extrusion; secondly, particle-bed binding; and thirdly, material jetting. Common to all these technologies is that the material is applied in horizontal layers. In this paper, a novel 3D concrete printing technology is presented which challenges this principle: the so-called Injection 3D Concrete Printing (I3DCP) technology is based on the concept that a fluid material (M1) is robotically injected into a material (M2) with specific rheological properties, causing material M1 to maintain a stable position within material M2. Different to the layered deposition of horizontal strands, intricate concrete structures can be created through printing spatially free trajectories, that are unconstrained by gravitational forces during printing. In this paper, three versions of this method were investigated, described, and evaluated for their potential in construction: A) injecting a fine grain concrete into a non-hardening suspension; B) injecting a non-hardening suspension into a fine grain concrete; and C) injecting a fine grain concrete with specific properties into a fine grain concrete with different properties. In an interdisciplinary research approach, various material combinations were developed and validated through physical experiments. For each of the three versions, first architectural applications were developed and functional prototypes were fabricated. These initial results confirmed both the technological and economic feasibility of the I3DCP process, and demonstrate the potential to further expand the scope of this novel technology. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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19 pages, 4270 KiB  
Article
The Effect of Accelerator Dosage on Fresh Concrete Properties and on Interlayer Strength in Shotcrete 3D Printing
by Inka Dressler, Niklas Freund and Dirk Lowke
Materials 2020, 13(2), 374; https://doi.org/10.3390/ma13020374 - 14 Jan 2020
Cited by 91 | Viewed by 7602
Abstract
Recently, the progress in 3D concrete printing has developed enormously. However, for the techniques available, there is still a severe lack of knowledge of the functional interaction of processing technology, concrete rheology and admixture usage. For shotcrete 3D printing technology, we present the [...] Read more.
Recently, the progress in 3D concrete printing has developed enormously. However, for the techniques available, there is still a severe lack of knowledge of the functional interaction of processing technology, concrete rheology and admixture usage. For shotcrete 3D printing technology, we present the effect of accelerator dosages (0%, 2%, 4% and 6%) on fresh concrete properties and on interlayer strength. Therefore, early yield stress development up to 90 min is measured with penetration resistance measurements. Deformation of layers under loading is investigated with digital image correlation and a mechanical testing machine. One point in time (10 min after deposition) is examined to quantify vertical buildability of elements depending on the accelerator dosage. Four different interlayer times (0, 2, 5 and 30 min), which occur for the production of small and large elements as well as due to delay during production, are investigated mechanically as well as quantitatively with computed tomography regarding the formation of cold joints. With increased accelerator dosage, an instantaneous increase in early age yield stress and yield stress evolution was observed. An increase in interlayer time leads to a reduced strength. This is mainly attributed to the observed reduced mechanical interlocking effect of the strands. Finally, a model to describe interlayer quality is presented. In the end, advantages as well as limitations of the findings are discussed. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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13 pages, 4238 KiB  
Article
Evaluation of the Mechanical Properties of a 3D-Printed Mortar
by Hojae Lee, Jang-Ho Jay Kim, Jae-Heum Moon, Won-Woo Kim and Eun-A Seo
Materials 2019, 12(24), 4104; https://doi.org/10.3390/ma12244104 - 08 Dec 2019
Cited by 29 | Viewed by 4380
Abstract
The mechanical properties of 3D-printed mortars are determined in terms of their compressive and direct tensile bond strengths. To determine such properties using existing methods, a preliminary experiment was conducted. The compressive strength of the printed mortar was compared to mold-casted specimens and [...] Read more.
The mechanical properties of 3D-printed mortars are determined in terms of their compressive and direct tensile bond strengths. To determine such properties using existing methods, a preliminary experiment was conducted. The compressive strength of the printed mortar was compared to mold-casted specimens and it was found that the compressive strength decreased by ~30%. Among the fabrication variables, an increase in nozzle height negatively influenced the direct tensile bond strength. For the same conditions and age, the direct tensile strength decreased by as much as 16–29% when the number of layers increased from 2 to 6. When the specimens were fabricated using a specially designed stainless steel frame and core drill, followed by extraction and the application of physical impact, the 28 days compressive strength of the specimen decreased by ~50%. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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22 pages, 5159 KiB  
Article
Microstructural Characterization of 3D Printed Cementitious Materials
by Jolien Van Der Putten, Maxim Deprez, Veerle Cnudde, Geert De Schutter and Kim Van Tittelboom
Materials 2019, 12(18), 2993; https://doi.org/10.3390/ma12182993 - 16 Sep 2019
Cited by 105 | Viewed by 5548
Abstract
Three-dimensional concrete printing (3DCP) has progressed rapidly in recent years. With the aim to realize both buildings and civil works without using any molding, not only has the need for reliable mechanical properties of printed concrete grown, but also the need for more [...] Read more.
Three-dimensional concrete printing (3DCP) has progressed rapidly in recent years. With the aim to realize both buildings and civil works without using any molding, not only has the need for reliable mechanical properties of printed concrete grown, but also the need for more durable and environmentally friendly materials. As a consequence of super positioning cementitious layers, voids are created which can negatively affect durability. This paper presents the results of an experimental study on the relationship between 3DCP process parameters and the formed microstructure. The effect of two different process parameters (printing speed and inter-layer time) on the microstructure was established for fresh and hardened states, and the results were correlated with mechanical performance. In the case of a higher printing speed, a lower surface roughness was created due to the higher kinetic energy of the sand particles and the higher force applied. Microstructural investigations revealed that the amount of unhydrated cement particles was higher in the case of a lower inter-layer interval (i.e., 10 min). This phenomenon could be related to the higher water demand of the printed layer in order to rebuild the early Calcium-Silicate-Hydrate (CSH) bridges and the lower amount of water available for further hydration. The number of pores and the pore distribution were also more pronounced in the case of lower time intervals. Increasing the inter-layer time interval or the printing speed both lowered the mechanical performance of the printed specimens. This study emphasizes that individual process parameters will affect not only the structural behavior of the material, but they will also affect the durability and consequently the resistance against aggressive chemical substances. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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12 pages, 5444 KiB  
Article
The Effect of Material Fresh Properties and Process Parameters on Buildability and Interlayer Adhesion of 3D Printed Concrete
by Biranchi Panda, Nisar Ahamed Noor Mohamed, Suvash Chandra Paul, GVP Bhagath Singh, Ming Jen Tan and Branko Šavija
Materials 2019, 12(13), 2149; https://doi.org/10.3390/ma12132149 - 04 Jul 2019
Cited by 153 | Viewed by 9002
Abstract
The advent of digital concrete fabrication calls for advancing our understanding of the interaction of 3D printing with material rheology and print parameters, in addition to developing new measurement and control techniques. Thixotropy is the main challenge associated with printable material, which offers [...] Read more.
The advent of digital concrete fabrication calls for advancing our understanding of the interaction of 3D printing with material rheology and print parameters, in addition to developing new measurement and control techniques. Thixotropy is the main challenge associated with printable material, which offers high yield strength and low viscosity. The higher the thixotropy, the better the shape stability and the higher buildability. However, exceeding a minimum value of thixotropy can cause high extrusion pressure and poor interface bond strength if the printing parameters are not optimized to the part design. This paper aims to investigate the effects of both material and process parameters on the buildability and inter-layer adhesion properties of 3D printed cementitious materials, produced with different thixotropy and print head standoff distances. Nano particles are used to increase the thixotropy and, in this context, a lower standoff distance is found to be useful for improving the bond strength. The low viscosity “control” sample is unaffected by the variation in standoff distances, which is attributed to its flowability and low yield stress characteristics that lead to strong interfacial bonding. This is supported by our microscopic observations. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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23 pages, 9881 KiB  
Article
A Study into the Effect of Different Nozzles Shapes and Fibre-Reinforcement in 3D Printed Mortar
by Pshtiwan Shakor, Shami Nejadi and Gavin Paul
Materials 2019, 12(10), 1708; https://doi.org/10.3390/ma12101708 - 26 May 2019
Cited by 70 | Viewed by 8722
Abstract
Recently, 3D printing has become one of the most popular additive manufacturing technologies. This technology has been utilised to prototype trial and produced components for various applications, such as fashion, food, automotive, medical, and construction. In recent years, automation also has become increasingly [...] Read more.
Recently, 3D printing has become one of the most popular additive manufacturing technologies. This technology has been utilised to prototype trial and produced components for various applications, such as fashion, food, automotive, medical, and construction. In recent years, automation also has become increasingly prevalent in the construction field. Extrusion printing is the most successful method to print cementitious materials, but it still faces significant challenges, such as pumpability of materials, buildability, consistency in the materials, flowability, and workability. This paper investigates the properties of 3D printed fibre-reinforced cementitious mortar prisms and members in conjunction with automation to achieve the optimum mechanical strength of printed mortar and to obtain suitable flowability and consistent workability for the mixed cementitious mortar during the printing process. This study also considered the necessary trial tests, which are required to check the mechanical properties and behaviour of the proportions of the cementitious mix. Mechanical strength was measured and shown to increase when the samples were printed using fibre-reinforced mortar by means of a caulking gun, compared with the samples that were printed using the same mix delivered by a progressive cavity pump to a 6 degree-of-freedom robot. The flexural strength of the four-printed layer fibre-reinforced mortar was found to be 3.44 ± 0.11 MPa and 5.78 ± 0.02 MPa for the one-layer. Moreover, the mortar with different types of nozzles by means of caulking is printed and compared. Several experimental tests for the fresh state of the mortar were conducted and are discussed. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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16 pages, 4174 KiB  
Article
The Effect of Viscosity-Modifying Admixture on the Extrudability of Limestone and Calcined Clay-Based Cementitious Material for Extrusion-Based 3D Concrete Printing
by Yu Chen, Stefan Chaves Figueiredo, Çağlar Yalçinkaya, Oğuzhan Çopuroğlu, Fred Veer and Erik Schlangen
Materials 2019, 12(9), 1374; https://doi.org/10.3390/ma12091374 - 28 Apr 2019
Cited by 103 | Viewed by 6476
Abstract
To investigate the effects of viscosity-modifying admixture (VMA) on the extrudability of limestone and calcined clay-based cementitious materials, three mix designs with different dosages of VMA were proposed in this study. The ram extrusion was utilized as an extrusion model for exploring the [...] Read more.
To investigate the effects of viscosity-modifying admixture (VMA) on the extrudability of limestone and calcined clay-based cementitious materials, three mix designs with different dosages of VMA were proposed in this study. The ram extrusion was utilized as an extrusion model for exploring the fresh properties of printable materials. Two methods were used, based on the ram extruder setup—(a) extruding materials with the same extrusion speed at different rest times to determine how the pressure changes with time; (b) extruding materials with different extrusion speeds at the same rest time to investigate the material flow parameters using the Basterfield et al. model. The main findings of this study could be summarized as—(1) the extrusion pressure of all mix designs exhibited an increasing trend with time. At the same tested age, the extrusion pressure under 0.25 mm/s of piston speed was increased and the shape retention of the extruded filaments was enhanced by increasing the dosage of VMA; (2) the correlation between the experimental results and the Basterfield et al. model was excellent (R-squared value: 0.99). The mixture with a higher content of VMA showed an increased elongational yield stress, flow consistency, and shear yield stress. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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18 pages, 4899 KiB  
Article
Method of Optimisation for Ambient Temperature Cured Sustainable Geopolymers for 3D Printing Construction Applications
by Shin Hau Bong, Behzad Nematollahi, Ali Nazari, Ming Xia and Jay Sanjayan
Materials 2019, 12(6), 902; https://doi.org/10.3390/ma12060902 - 18 Mar 2019
Cited by 88 | Viewed by 5691
Abstract
Since the initial introduction of geopolymers, these materials have been characterised as environmentally-friendly sustainable substitutes for ordinary Portland cement (OPC). There is a routine increase in the application of geopolymers, especially in advanced technologies. Because of its better rheological characteristics compared to OPC, [...] Read more.
Since the initial introduction of geopolymers, these materials have been characterised as environmentally-friendly sustainable substitutes for ordinary Portland cement (OPC). There is a routine increase in the application of geopolymers, especially in advanced technologies. Because of its better rheological characteristics compared to OPC, geopolymers are appropriate materials for extrusion-based 3D printing technologies. This paper focuses on the optimisation of an ambient temperature cured geopolymer for 3D printing construction applications. The effects of mixture parameters, including the type of hydroxide solution (HS), the type of silicate solution (SS) and the mass ratio of SS to HS on the workability, extrudability, shape retention ability and mechanical performance of different geopolymer mixtures were investigated. Accordingly, an optimum mixture was identified for geopolymers cured at ambient temperatures. Mechanical properties of the optimised mixture, including flexural and compressive strengths, were measured in different directions with respect to the printed layers. Further, uniaxial tension tests were also conducted on the optimised mixture to measure its interlayer bond strength. The results showed that among the activators investigated, the sodium-based activator composed of sodium hydroxide and sodium silicate solutions, with a SiO2/Na2O ratio of 3.22, was the most effective activator, providing appropriate workability and extrudability, along with reasonable strength and a high shape retention ability. The acquired mechanical properties exhibited anisotropic behaviour in different testing direction. The strength of the interlayer bond was found to be adequate to avoid interfacial shear failure. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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21 pages, 10344 KiB  
Article
Rheological Property Criteria for Buildable 3D Printing Concrete
by Hoseong Jeong, Sun-Jin Han, Seung-Ho Choi, Yoon Jung Lee, Seong Tae Yi and Kang Su Kim
Materials 2019, 12(4), 657; https://doi.org/10.3390/ma12040657 - 21 Feb 2019
Cited by 72 | Viewed by 7002
Abstract
Fresh concrete used in 3D printing should ensure adequate yield stress, otherwise the printed concrete layer may suffer intolerable deformation or collapse during the printing process. In response to this issue, an analytical study was carried out to derive the initial yield stress [...] Read more.
Fresh concrete used in 3D printing should ensure adequate yield stress, otherwise the printed concrete layer may suffer intolerable deformation or collapse during the printing process. In response to this issue, an analytical study was carried out to derive the initial yield stress and hardening coefficient of fresh concrete suitable for 3D printing. The maximum shear stress distribution of fresh concrete was calculated using a stress transformation equation derived from the equilibrium condition of forces. In addition, the elapsed time experienced by fresh concrete during the printing processes was estimated and was then substituted into the elapsed time-yield stress function to calculate the yield stress distribution. Based on these results, an algorithm capable of deriving both the initial yield stress and the hardening coefficient required for printing fresh concrete up to the target height was proposed and computational fluid dynamics (CFD) analyses were performed to verify the accuracy of the proposed model. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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