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2020 | Book

Second RILEM International Conference on Concrete and Digital Fabrication

Digital Concrete 2020

Editors: Dr. Freek P. Bos, Dr. Sandra S. Lucas, Dr. Rob J.M. Wolfs, Prof. Theo A.M. Salet

Publisher: Springer International Publishing

Book Series : RILEM Bookseries

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About this book

This book gathers peer-reviewed contributions presented at the 2nd RILEM International Conference on Concrete and Digital Fabrication (Digital Concrete), held online and hosted by the Eindhoven University of Technology, the Netherlands from 6-9 July 2020. Focusing on additive and automated manufacturing technologies for the fabrication of cementitious construction materials, such as 3D concrete printing, powder bed printing, and shotcrete 3D printing, the papers highlight the latest findings in this fast-growing field, addressing topics like mixture design, admixtures, rheology and fresh-state behavior, alternative materials, microstructure, cold joints & interfaces, mechanical performance, reinforcement, structural engineering, durability and sustainability, automation and industrialization.

Table of Contents

Frontmatter

Mixture Design, Admixtures and Alternative Binder

Frontmatter
An Fe-Rich Slag-Based Mortar for 3D Printing

3D printing can lead to a technological breakthrough in the construction sector. However, the sustainability aspect of 3D printing mortar can be disputable, as 3D printable mortar contains a high amount of ordinary Portland cement (OPC). The sustainability can be increased by replacing OPC with an Fe-rich slag, which originates from the metallurgical industry and is nowadays used for low-value applications. A mortar composition consisting mainly of slag and a small amount of OPC is called a hybrid mortar and is alkali-activated to ensure that the slag is participating in the binder formation. In this study, the amount of OPC is decreased significantly, down to 6 wt% and the slag content is increased up to 28 wt% over total solid content. This work investigated the effect of several components in the hybrid mixture on the early-age stiffness development, late-age shrinkage, creep and mechanical strength and is compared to a commercial OPC-based 3D printable mortar. The components, which are important to obtain a 3D printable mixture, comprise OPC, Si fume, fine limestone, superplasticizer and carbon fibres. This study shows that the additions significantly influence the stiffness and mechanical strength development of the hybrid. The shrinkage and creep behaviour of the hybrid was considerably lower compared to the benchmark material.

Glenn Beersaerts, Sandra S. Lucas, Yiannis Pontikes
Enhancing Buildability of 3D Printable Concrete by Spraying of Accelerating Admixture on Surface

The buildability of printable concrete signifies the ability of the printed structure to retain the extruded shape and to sustain the dead load of subsequent layers on first extruded layer without collapse. Higher buildability can help in construction of tall sections in minimum possible time. The buildability depends on structural build-up rate which is controlled by cement hydration (chemical) and interaction between particles developed by flocculation (physical). In several ongoing research studies related to 3D printing, a common method for dispensing the accelerator in concrete is by adding it at the nozzle. This study aims at developing a method to increase the buildability by spraying the accelerator at higher dosages (>8% by weight of cementitious material) post printing. In the print of a full-scale specimen, an empirical method of first printing up to n layers, followed by spraying the accelerator up to n-2 layers (where n > 2) from base was done. Based on the success of this empirical study, a controlled laboratory assessment was performed. The study is divided into three parts - a) the enhancement in buildability is assessed by printing a structure of 200 mm height with spraying of accelerator, b) the depth of penetration is determined by microstructure study using XRD, c) the build-up and flow value is determined for different dosages of accelerators. The study provides a way of application of accelerating admixture in digital printing to attain higher buildability in lesser time.

Shantanu Bhattacherjee, Manu Santhanam
Effect of Wollastonite Micro-Fiber Addition on Properties of 3D-Printable ‘Just-Add-Water’ Geopolymers

This paper reports the effects of addition of wollastonite micro-fiber on the properties of a 3D-printable geopolymer for digital construction applications. Having a ‘one-part’ (just-add-water) mixture formulation, the developed 3D-printable geopolymer uses a small amount of activator powder, instead of using a large amount of the commonly used activator solution. A small portion of fine sand (10% by weight) was substituted by wollastonite powder. The fresh properties (including shape-retention-ability and yield stress evolution), as well as the hardened properties (including compressive strength and flexural strength) of the mixtures were measured. The results showed that the addition of wollastonite significantly increased the shape-retention-ability and static yield stress of the fresh mixture, which is beneficial in terms of buildability of the material. Furthermore, the results showed that addition of the wollastonite considerably enhanced the flexural strength, while the compressive strength of the hardened specimens remained unchanged.

Shin Hau Bong, Behzad Nematollahi, Arun R. Arunothayan, Ming Xia, Jay Sanjayan
Synthesis of Hybridized Rheological Modifiers for 3D Concrete Printing

Viscosity and static yield stress are key rheological properties for 3D concrete printing (3DCP), where high static yield stress is associated with high buildability and shape stability and low viscosity is associated with extrudability and pumping. The challenge in concrete rheology lies in decoupling the effect of admixtures on these two properties, i.e. achieving high static yield stresses while still maintaining moderately low viscosities. In this paper, we present a hybridized additive system of nanoclays and viscosity modifying admixtures that can tailor the rheological properties of cement composites to meet 3DCP performance requirements. Further, because 3DCP is a technology of scales, any additive must meet scalability and stability requirements for construction, i.e. ease of processing in abundance and relatively low cost, and exhibit an extended shelf life. We examine different methods of synthesizing the hybrid systems and examine their stability through measuring their effect on cement rheology at different component ratios and at different time stamps from the time of hybridization. We then demonstrate their impact on printing performance by producing complex 3D prints utilizing cement pastes modified with the hybridized additive system.

AlaEddin Douba, Clare Chan, Stephanie Berrios, Shiho Kawashima
Control of Strand Properties Produced with Shotcrete 3D Printing by Accelerator Dosage and Process Parameters

Shotcrete 3D Printing (SC3DP) has recently evolved as a large-scale additive manufacturing technique. The major advantage of this technique is the high manufacturing speed for creating large-sized monolithic structures. However, to control this technique properly, the combined effects of process parameters and rheological properties of the concrete need to be fully understood. Therefore, the effect of accelerator dosage (0%, 2%, 4%, 6%) on the material’s yield stress is quantified with a penetrometer up to 90 min after deposition. The vertical deformation of strands is also found to correlate with yield stress. Moreover, the resulting geometry of the strands is analyzed. Here, an increase in strand height and a decrease in strand width is determined with increasing accelerator dosage. Among other factors, this is deduced to the opening angle when material leaves the nozzle. To compensate unwanted changes in geometry due to accelerator, process parameters to modify the geometry are studied as well. Therefore, the effect of traverse speed, nozzle-to-strand-distance and volume air flow on the geometry is quantified.Finally, the possibilities to use the findings of the effect of accelerator dosage and process parameters during printing process purposefully are discussed.

Inka Dressler, Niklas Freund, Dirk Lowke
Comparison of Printable Inorganic Binders - Key Properties for 3D Printable Materials

Four 3D printable Portland cement-based mix designs were developed. A method for determination of compressive and flexural strength of 3D printed prisms (taking into account the effects of 3D printing on the surface of the object) and a comparison to molded samples are presented. Prisms prepared by 3D printing show interfilament voids but have nevertheless mean values of compressive strength which are comparable to molded prisms. Flexural strength was strongly affected by surface irregularities introduced by manufacturing by 3D printing and is in every case lower as for molded specimens. In most cases, the variation of strength values of 3D printed test specimens was considerably higher than for molded equivalents. The presented Portland cement-based mix designs include a mix with the use of an ordinary Portland cement (OPC) clinker mixed with a calcium sulfate addition which is lower than in standard OPC which was also successfully utilized for 3D printing. This mix performed best in compressive and flexural strength. The developed materials were further examined by slump test and ultrasonic wave velocity.

Tamino Hirsch, Tobias Dorn, Clemens Ehm, Dietmar Stephan
Design of Energy-Efficient White Portland Cement Mortars for Digital Fabrication

Additive manufacturing, i.e. three-dimensional (3D) printing technology has many advantages over traditional processes and the related technology is continuously improving. This study aims to develop an energy- efficient White Portland cement (WPC) mortar mix suitable for 3D printing applications. The mortar mix contained a blended binder content using Çimsa Recipro50 calcium aluminate cement (CAC) along with Çimsa Super WPC (sWPC). Microencapsulated Phase Change Materials (mPCMs) added to the mix enhance thermal performance through latent heat storage capability. The CAC used in the study has an alumina content of at least 50% Mineralogical analysis of the CAC and sWPC binder were characterized by the XRD-Rietveld method. In terms of material design for 3D printing, printable mortars must be workable enough to be extruded (extrudability) and retain its shape with little or no deformation after extrusion (buildability). In this study, the printability of mortar was evaluated through workability loss, open time, green strength, and early-age compressive strength. Results showed that use of sWCP and CAC composite enables a thixotropic behavior, which is required for 3D printing. The designed mortar mixes can enable high flowability necessary for successful extrusion and have high green strength at fresh state to maintain stable printing. The results also showed that the use of mPCMs can influence printability while improving buildability.

Sibel Kurt, Yiğit A. Atalay, Ozan E. Aydın, Berrak Avcıoğlu, Tayfun Yıldırım, Gizem B. Göktepe, Sedat Emir, Zeynep B. Bundur, Halime Ö. Paksoy
Use of the Chemical and Mineral Admixtures to Tailor the Rheology and the Green Strength of 3D Printing Cementitious Mixtures

Concrete 3D printing is an innovative manufacturing technic grasping a great interest in the construction industry. However, the materials engineering is still a challenge for an accurate large-scale 3D printing process. One promising solution is to tailor the rheological properties of the printing materials. Cementitious materials used for extrusion-based 3D printing should exhibit high static yield stress and well-adapted structuration (i.e. build-up) kinetics. These properties are mainly influenced by the mixture composition, including the use of the chemical and mineral admixtures. An experimental investigation was conducted to study the structuration kinetics of various mixtures by means of flowability and static yield stress evolution. Four mortar mixtures were developed using compatible chemical and mineral admixtures promoting the thixotropic behavior of printing materials. In addition, the green strength of mixtures was monitored up to 40 min after mixing. An empirical test setup and a novel sampling method were proposed to evaluate the behavior of the fresh 3D printed layers during the printing process.

Mohammad Amin Moeini, Masoud Hosseinpoor, Ammar Yahia
Characterising Concrete Mixes for 3D Printing

The construction industry is currently experiencing significant change as building information modeling (BIM), digital design and construction automation are exerting intense pressure on traditional technologies. As an advanced manufacturing technology, three-dimensional (3D) printing has significant potential applications in the construction sector, by utilizing a programmable robotic arm with a nozzle jet, 3D printing can enable us to construct complex concrete structures layer by layer. This new construction technique offers an advanced approach that can potentially accelerate the construction time and improve efficiency. They can work 24/7, even in a hazardous environment while minimising human errors. However, as an advanced cutting-edge technology, there are several remaining challenges to be overcome in comparison to traditional concrete casting, and these include appropriate pumpability, extrudability, buildability, compressive strength and open time for printing concrete. To overcome these challenges this project will investigate the effect of nanoclay to improve the fresh properties of printing concrete. It is considered that by utilizing different amounts of nanoclay and superplasticiser in the mix it will be possible to significantly affect the fresh properties of 3D printed concrete.Printable materials, like any other cementitious materials, flow only when submitted to stresses higher than a critical yield stress. In this project, a shear vane test was used to measure the yield stress of cement-based materials in the lab.

Atteyeh S. Natanzi, Ciaran McNally
Digital Fabrication of ‘Just-Add-Water’ Geopolymers: Effects of Curing Condition and Print-Time Interval

A 3D-printable one-part geopolymer concrete has recently been developed by the authors of this study for construction automation applications. Instead of large amounts of alkaline solutions, a small amount of sodium metasilicate powder as the solid activator was used to formulate the ‘just-add-water’ geopolymer binder. Development of such 3D-printable concrete tackles the challenges associated with handling of hazardous activator solutions and enhances the commercial viability of using geopolymer as a sustainable binder for 3D-printable concretes. This paper presents the effects of curing conditions (i.e. curing temperature and curing time) and the print-time interval on the properties of the developed printable concrete. Workability, setting time, static yield stress evolution of the mixture were measured. In addition, compressive strength and flexural strength in different loading directions, as well as the inter-layer strength of the printed specimens were measured. According to the results, the compressive and flexural strengths of the specimens printed with different delay times were comparable in all loading directions. In addition, the compressive and flexural strengths of the printed specimens subjected to 28 days of ambient temperature curing were higher than those of the counterpart heat cured specimens. Furthermore, the static yield stress of the fresh mixture increased linearly for up to 60 min of rest time.

Behzad Nematollahi, Shin Hau Bong, Ming Xia, Jay Sanjayan
Advances in Binder-Jet 3D Printing of Non-cementitious Materials

Additive Manufacturing techniques enable an unprecedentedly fine-grained control over the material they process, both in terms of its geometric distribution and its very composition. With the rapid development of printing methods suitable for the production of large-scale objects together with their respective material systems, applications in the construction industries showcase an expanding portfolio of practical examples. However, considering the more and more critical demand for minimizing the environmental impact due to construction activities, the aim for mechanical stability of a material system is no longer sufficient and needs to be flanked by attentive considerations over the sustainability of its components.The presented research investigates to which extent cement can be either accompanied or replaced by more sustainable material sources, with specific focus on geopolymer and its application in the production of stay-in-place, self-supporting and waste-free formwork systems for modular building components. The manufacturing technique considered for such investigation is binder jet 3d printing, on the basis of the remarkable flexibility it offers in terms of material processing workflow. Three selected material systems, each one introducing recycled and/or repurposed byproducts of different industrial processes (such as stone cutting and demolition activities), will be evaluated and benchmarked against the output of commercially available organic-based BJ systems.Finally, a brief overview of the prototypical binder jet printing setup specifically developed for material testing at construction-scale will be presented, mainly focusing on the control parameters that have a larger impact on the overall properties of printed output.

Pietro Odaglia, Vera Voney, Benjamin Dillenburger, Guillaume Habert
Rubber-Cement Composites for Additive Manufacturing: Physical, Mechanical and Thermo-Acoustic Characterization

The purpose of this work is to study the possibility of modifying a 3D printable cement-based mix by adding recycled tire rubber (TR) particles to replace the mineral aggregates. This strategy aims to evaluate the variation of some physical-mechanical properties of the material (lightness, durability, vibration absorption, acoustic and thermal insulation), promoting the disposal of the waste tires and the reduction in the consumption of natural resources. The rubberized mixture, in addition to offering interesting properties in terms of engineering performances (fundamentally important in the construction sector), can be used in additive manufacturing in the production of “bi-functional” applications. “Bi-functionality” refers to the possibility of giving a component, specific properties dependent on both the material properties and morphological-structural features.Several printing mixtures, obtained for partial or total replacement of mineral aggregates with two types of rubber fillers (rubber powder and rubber granules), have been developed. After proper printability tests, an extensive experimental campaign was performed on printable rubber-cement composites: physical characterization, morphological analysis, mechanical characterization and evaluation of acoustic and thermal insulation properties. The rubber aggregates preserve optimal rheological properties related to the printability of the mixture. Besides, the synergy between the two types of polymer fillers in the cement matrix results in some interesting physical and mechanical effects: ductility, plastic energy absorption, durability, acoustic damping, and thermal inertia.

Matteo Sambucci, Marco Valente, Abbas Sibai, Danilo Marini, Alessia Quitadamo, Ettore Musacchi
Properties of Composite Modified with Limestone Powder for 3D Concrete Printing

The design of proper mixes for 3D concrete printing has been already a subject of many studies. Modification to mixes aim to obtain certain properties (extrudability, workability, flowability, open time or buildability) which allow for proper printing of the material. There are different types of reactive or non-reactive mineral additives that were already used to modify the mixes for 3D concrete printing. Studies have already shown the usefulness of fly ash, silica fume, metakaolin, limestone powder or quartz powder. The properties of the mix can also be changed with different chemical admixtures such as plasticizer, accelerators or retarders and viscosity modifying agents. Use of different admixtures can however significantly increase the cost of designed mixes. The study determined the influence of non-reactive limestone powder on the properties of the mix. The mixes were modified with 10% to 50% of additive, that replaced the fine aggregate. Rheological properties of the mixes were studied in this research. The stiffness and load-bearing capacity of mixes (t ≤ 45 min) were tested. Chosen mixes were printed out to experimentally verify the results. The study has shown that the limestone powder can successfully be used to improve the properties of printing mixes with simultaneous reduction of cement content. The results are promising regarding the sustainable development attitude in modern constructions.

Szymon Skibicki, Maria Kaszyńska, Nawid Wahib, Mateusz Techman, Karol Federowicz, Adam Zieliński, Tomasz Wróblewski, Norbert Olczyk, Marcin Hoffmann
Effect of Limestone Powder Substitution on Fresh and Hardened Properties of 3D Printable Mortar

Great progress has been made in 3D concrete printing (3DCP) in the past few years. The unique advantages of 3DCP over conventional concrete construction may include saving costs and labor, eliminating formwork, reducing the construction time, as well as increasing flexibility in architectural design. To satisfy the printing requirements, a high amount of binders is used for 3DCP. Among all the binders, ordinary Portland cement (OPC) is the most commonly used binder for 3DCP. However, producing OPC consumes high amounts of energy and exhausts high amounts of greenhouse gases. Therefore, with a high amount of OPC, 3DCP cannot be treated as a sustainable and environmental friendly construction method. Partially replacing OPC by supplementary cementitious materials (SCMs) might be a proper solution to make the 3D printable concrete sustainable. Limestone powder (LP) is one of the SCMs with the advantage of wide availability and low cost. This study analyzed the impact of substituting OPC by LP on the fresh and hardened properties of 3D printable mortar. Six mixtures with three LP substitution rates (0%, 25%, and 50% by volume of OPC) were designed. In the fresh stage, a squeeze flow test was used for evaluating the shape stability. In the hardened stage, drying shrinkage and mechanical properties were investigated. The results showed that a high amount of LP substitution had negative effects on both fresh properties and hardened properties. However, for a lower replacement percentage (i.e. a 25% replacement rate), the strength loss is still within reasonable limits.

Yaxin Tao, Karel Lesage, Kim Van Tittelboom, Yong Yuan, Geert De Schutter
Rheology Evaluation of Cement Paste with Nanoclays, Nanosilica and Polymeric Admixtures for Digital Fabrication

Additive and digital manufacturing have opened wide new opportunities in architectonic design with cement based materials. However, there are still some issues to be addressed regarding rheological properties’ control. Among rheology modifiers, nanoclays, nanosilica and polymeric admixtures can be used to adjust rheological properties of cement paste, as yield stress, viscosity and thixotropy. These rheological properties are a key factor to control technological requirements as pumpability, extrudability and buildability. An experimental study was carried out to evaluate the combined effects of nanoclays, nanosilica and polymeric admixtures on cement paste rheology for digital fabrication, considering their interactions and synergies. A reference paste with ordinary Portland cement blended with limestone filler, 2:1 by cement weight, and a low water to binder ratio was designed. Then, four different nanoclays - attapulgite, bentonite and two types of sepiolite-, a commercial nanosilica, two types of viscosity modifying admixtures (VMA) and a high range water reducing admixture (HRWRA) were added. Flowability of cement pastes was assessed with the minicone slump test and the synergetic effect and interactions between nanoclays, nanosilica and polymeric admixtures were evaluated.

Hugo Varela, Gonzalo Barluenga, Irene Palomar
Geopolymer Formulation for Binder Jet 3D Printing

The construction industry is a significant emitter of CO2 and it uses more than 40% of the resources consumed worldwide, which are becoming scarce. 3D printing can help to reduce the material consumption by enabling the manufacturing of structurally optimized building parts and formworks since material is only placed where needed. To combine the reduction of material consumption with less CO2 emissions, the raw materials that are currently used in 3D printing in construction need to be replaced by materials with lower carbon footprint. Among the materials with high potential for this application, geopolymer is a good candidate to fulfill the required criteria in terms of performances and embodied energy as they can be built from waste materials such as slag, fly ash or glass waste as aluminosilicate source.The objective of this research is thus to define a mix design strategy to allow the implementation of geopolymers in powder bed 3D printing with various waste materials. In this technique, an aluminosilicate powder bed is activated through the deposit of an alkaline silicate solution. This selective binder activation approach requires to master the spreading of the liquid into the powder bed and to ensure that the reaction takes place where it is needed. A series of experiments at the droplet level were performed to estimate the relationship between the initial liquid to solid ratio and the packing of the powder bed. Based on this a mix design strategy for the printing solution was developed and proofed by SEM/EDX analysis.

Vera Voney, Pietro Odaglia, Coralie Brumaud, Benjamin Dillenburger, Guillaume Habert
Lightweight Concrete 3D Printing by Selective Cement Activation – Investigation of Thermal Conductivity, Strength and Water Distribution

The 3D printing technology Selective Cement Activation (SCA) is a particle-bed-based additive manufacturing method in which a dry mixture of sand and cement is spread in thin layers and solidified with water. SCA allows the production of complex and high-resolution components without the necessity for additional support structures. One drawback of concrete 3D-printing for free formed facade elements has been the need for additional thermal insulation to fulfil relevant building requirements. This causes an additional economic and ecological effort to create custom-built insulation to fit the 3D facade. Therefore, this paper discusses the fabrication of lightweight concrete through SCA by replacing the sand (S) with lightweight aggregates (LA, expanded glass beads) in order to decrease the thermal conductivity. However, the open pore structure of the lightweight aggregate could also change the water distribution behavior between the layers which would positively affect the hydration process.Test series with different w/c-ratios (0.3, 0.4 and 0.5) and type of aggregate (S and LA) were produced. Additionally, the test series with LA were fabricated without and with methylcellulose to further increase water absorption. The strength (compressive and flexural) and thermal conductivity were measured direction dependent to take anisotropic effects into account. Additionally, the water distribution perpendicular to the layers was determined using 1H-NMR.Specimens produced with LA showed a 3.5 to 4.4 times lower thermal conductivity compared to the specimens produced with S. However, using LA affected the density and thus the strength values of the material. Additionally, the open pore structure of the LA affected the water distribution between the layers which lead to an increase in strength with decreasing w/c-ratio. This is contrary to previous experiments using SCA and sand where strength has improved with increasing w/c-ratio [1–3].

Daniel Weger, Heejeong Kim, Daniel Talke, Klaudius Henke, Thomas Kränkel, Christoph Gehlen

Rheology and Fresh State Behaviour

Frontmatter
Numerical Model Describing the Early Age Behavior of 3D Printed Concrete – Work in Progress

A numerical model used to predict the behavior of 3D printed concrete in the early age phase up until the point of collapse is presented. An incremental creep model for the material including aging and temperature effects is suggested. Furthermore, kinematic nonlinear effects are included in order to predict instability. The input parameters to the numerical model are determined through an optimization process where the displacement error between a finite element method (FEM) model and digital image correlation (DIC) measurements from an actual 3D print are minimized. A simplified (current state) version of the suggested numerical model was used to predict at how many layers a specific 3D print collapsed, with an error of 58%. This was concluded to be expected, since the numerical model is not fully implemented yet.

Sebastian Andersen, Wilson Ricardo Leal da Silva, Ieva Paegle, Jens Henrik Nielsen
Characterisation of the Layer Pressing Strategy for Concrete 3D Printing

3d printing of cementitious material by pressing layers during the extrusion is a strategy that requires a rather low initial yield stress so the material can deform without cracking. It allows to perfectly control the height of the layer and gives freedom in the orientation of the printing head and of the layer allowing for a wider range of printable geometry than the classic so-called “infinite brick” extrusion. This strategy has however some drawbacks as pressing the material on the previous layers may lead to a deformation of the sub-layers and even failure of the structure. In this work; we make a first step into understanding forces involved in such a process and measure their dependency on material fresh properties and printing parameters.

Paul Carneau, Romain Mesnil, Nicolas Ducoulombier, Nicolas Roussel, Olivier Baverel
A Compendious Rheo-Mechanical Test for Printability Assessment of 3D Printable Concrete

A successful 3D concrete print (3DCP) is controlled by a sound buildability and good pumpability. Since both factors rely on the behavior of concrete in the fresh state, rheological assessment is crucial prior to 3DCP. In a previous study done by Roussel [1], a correlation of numerical simulation of ASTM mini-slump cone flow and rheometer results was successfully addressed. As the model solely considers material flow under gravitational loading, this model can be adjusted with an external source of energy in the form of impact loading by vertical drop from a certain height to emulate the agitation and deposition process of 3DCP. A flow table and rheometer tests were executed with 5 samples of different consistency. Consecutively, 3DCP validation was performed except for the sample with no superplasticizer content. The study shows the relative deformation (%) varied in a range of 34% - 89% after the drops according to the consistency of the sample. The initial static and dynamic yield stresses are also presented in a range of 0.94–6.82 kPa and 0.54–4.73 kPa respectively. Based on the results, flow table reading ranges are suggested for suitable 3D printability.

Seung Cho, Jacques Kruger, Frederick Bester, Marchant van den Heever, Algurnon van Rooyen, Gideon van Zijl
Effect of Metakaolin, Fly Ash and Polypropylene Fibres on Fresh and Rheological Properties of 3D Printing Based Cement Materials

The aim of this paper is to investigate the effect of mix composition such as the percentages of metakaolin (MTK) and fly ash (FA) on the fresh and rheological properties and also the percentage of polypropylene fibres. Several tests were used to determine the rheological properties such as the flow table test, the cylindrical slump test and penetrometer test. The estimated yield stress values were then calculated from the results of cylindrical slump test and the fresh density of mortar.The extrusion of layers for 3D printing was carried out using a controlled air pressure gun. This tool made it possible to test the extrusion of each mortar mix directly after mixing by producing several layers on top of each other. The use of MTK had a significant effect on the fresh and rheological proprieties. It was observed that replacing cement with MTK led more cohesive and dry mixes and therefore difficult to extrude. Using a combination of FA and MTK has increased the yield stress, cohesion, reduced the penetration and improved the shape stability and printability. It also reduced bleeding and segregation. Finally, adding more polypropylene fibres reduced the workability by improving the cohesion with a denser fibre network and reduced the penetration. Thus led to an increase in the yield stress and a reduction of the fresh properties. Good relations were observed between the fresh and rheological properties.

M. Dedenis, M. Sonebi, S. Amziane, A. Perrot, G. Amato
“The Slug Test”: Inline Assessment of Yield Stress for Extrusion-Based Additive Manufacturing

Successful and efficient fabrication using robotic extrusion of cementitious materials mainly relies on the mastering of the printable material fresh state behavior. This paper tackles this aspect by introducing a novel rheological apparatus dedicated to the yield stress measurement at nozzle exit in extrusion-based manufacturing. It is based on the analysis of the specific gravity-induced flow that takes place at nozzle exit, which is at the origin of the formation of material drops or so-called “slugs”. Using a simple connected balance with a high measurement frequency gives access to these slugs average mass and, in turn, to the yield stress. Due to its convenience, the protocol is appropriate for setting the printing parameters according to the yield stress measurement at the nozzle exit in order to ensure successful fabrication.

Nicolas Ducoulombier, Paul Carneau, Romain Mesnil, Léo Demont, Jean-François Caron, Nicolas Roussel
Fresh and Hardened Properties of 3D-Printed Concrete Made with Dune Sand

This paper examines the performance of 3D-printed concrete made with locally abundant desert dune sand. Cement was replaced by up to 10% silica fume and 30% fly ash to reduce its detrimental environmental footprint. The water-to-binder ratio used in the mix ranged between 0.35 and 0.40. Also, a superplasticizer was added in the range of 1 to 3%, by binder mass. Concrete mixes were proportioned to attain optimum fresh and hardened properties. A control mix with crushed dolomitic limestone aggregates served as a reference. The performance of 3D-printed concrete mixes was assessed based on slump flow, pumpability, and compressive strength. Experimental results showed a reduction in slump flow and pumpability with an increase in dune sand content. In turn, the compressive strength increased by 3% when 20% dune sand was utilized, but decreased by an average of 3% for every additional 10% subsequently. Concrete mixes incorporating a superplasticizer and higher water-to-binder ratio exhibited improved workability. While the former caused limited change to compressive strength, the latter resulted in a notable decrease. Upon replacing cement with silica fume and fly ash, the slump flow and pumpability increased. In fact, 3D-printed concrete made with 3% superplasticizer, 20% fly ash, and 10% silica fume experienced a 230 and 79% increase in slump flow and pumpability, respectively. Compressive strength increased by an average of 4% for every 10% fly ash replacement. The incorporation of 10% silica fume improved the strength by an additional 14%. Analytical models were developed to correlate slump flow to pumpability and 3D-printed concrete compressive strength to that of typical concrete cubes, serving as guidelines to produce optimal concrete mixes for large-scale concrete 3D printers.

Hilal El-Hassan, Fady Alnajjar, Hamad Al Jassmi, Waleed Ahmed
An Experimental Testing Procedure to Assess the Buildability Performance of 3D Printed Concrete Elements

Digital fabrication of concrete products represents a breakthrough in the field of civil engineering, revolutionizing the way of conceiving and create architectural/structural elements. Being a new technology, the designers have very few tools to predict and control the time dependent structural response of printed concrete elements, either during and after the production process; furthermore, no testing guidelines exist yet in this specific field. An experimental testing procedure is herein presented to establish the buildability performances of 3D printed concrete elements as a function of the printing layout (e.g. single layer width or thickness). Based on experimental outcomes of uniaxial compression tests performed on cylindrical sample of fresh printable mortar, an analytical model is adopted to estimate the maximum number of concrete layers which can be stacked during a generic printing process before the failure; plastic yielding in compression and self-buckling failure modes are considered to this aim.

Laura Esposito, Costantino Menna, Domenico Asprone, Chiara Rossino, Maurizio Marchi
Investigation on the Rheological Behavior of Lightweight Foamed Concrete for 3D Printing Applications

Unlike ordinary concrete, lightweight foamed concrete (LWFC) has the benefit of decreasing the self-weight of constructive elements while ensuring an efficient thermal insulation and acoustic absorption as well as high fire resistance. A novel version of LWFC has been recently developed by the authors, with the unique property of “extrudability” in a wide density range, meaning that its production process can be carried out without formworks and exploiting innovative 3D printing technologies. The present contribution is focused on the rheological behaviour of this innovative extrudable LWFC (ELWFC). The rheological behaviour in terms of yield stress of the ELWFC is studied via a rotational rheometer in two different modalities, namely constant shear rate and increasing shear rate. Comparison of the rheological behaviour between ELWFC and classical LWFC is also presented. Additionally, the dimensional stability of the cementitious paste at the fresh state having a given yield stress is assessed through an extrusion test. In particular, the experimental investigation is focused on a target dry density of 800 kg/m3, which is identified as a good compromise between insulating features and mechanical strengths. The experimental results show that the considered ELWFC, characterized by a zero slump in the extrusion test, has a yield stress of around 150 Pa (constant shear rate) and 130 Pa (increasing shear rate).

Devid Falliano, Giuseppe Crupi, Dario De Domenico, Giuseppe Ricciardi, Luciana Restuccia, Giuseppe Ferro, Ernesto Gugliandolo
Experimental Investigation on the Early Age Tensile Strength of Fiber Reinforced Mortar Used in 3D Concrete Printing

Digital fabrication with cement-based materials requires specific attention to be paid to the rheological and mechanical material properties both in the fresh and hardened state. For the layered extrusion process, the cement-based material needs to satisfy the “printability” requirement. Generally, printable mortars exhibit brittle mechanical behaviour due to the absence of reinforcement. In order to overcome this issue, many different strategies can be implemented. Among them, the addition of short fibers in the mortar represents a first step towards the development of robust materials for 3D printing in construction. In this context, the paper focuses on the early stage tensile properties of fiber-reinforced cement-based material to be used in the layered extrusion process. The embedment of discrete fibers in a printable mix is expected to improve the mechanical behaviour but, at the same time, it implicates a loss of workability in the mix, which could lead to problems during the printing process (in terms of extrudability and pumpability of the mix). In this paper, the mechanical response under direct tensile is investigated as a function of the type/concentration of fibers as well as the mortar resting time. Furthermore, the effect of varying the amount of the superplasticizer to guarantee the printability requirement of the printable mortar is also investigated. In a quality control framework, the development of tensile fracture properties, in the considered production time frame, is fundamental to determine the printability of the mix, with reference not only to the quality of the finishing but also to the speed of the printing process.

Marta Fioretti, K. Sriram Kompella, Francesco Lo Monte, Laura Esposito, Costantino Menna, Sandro Moro, Domenico Asprone, Liberato Ferrara
Transition from Fluid to Solid Concrete in the Flexible Mould Process

The transition period between the mixing of concrete and the begin of setting increasingly receives attention, as special production processes can be developed with tailor-made fresh state characteristics. In this publication the two processes of 3D Concrete Printing (3DCP) and the production with the Flexible Mould Process (FMP) are discussed and compared.The FMP is a relatively new manufacturing method that was developed to allow the efficient production of curved thin concrete panels for cladding or structural use. The term ‘flexible’ refers to the deformation into the required curved shape of both the compliant mould surface and the fresh concrete contained by the mould shortly after casting. After that deformation, both the mould and the concrete are left for further hardening until demoulding is possible. The development of the 3DCP technique progresses fast, hereby new perspectives are gained with regard to mix design, production and structural performance. Sideway, test methods need to be developed or re-evaluated. The early age strength and strain capacity are important parameters for both processes, although they are not the same with regard to magnitude, period or time after mixing. Both processes can be executed within an open window and with specific boundary conditions only. This publication discusses and compares both processes. The implications of these recent findings are translated to practical aspects with regard to the production with the FMP.

Steffen Grünewald, Roel Schipper
Physico-Chemical Characterization at Early-Age of 3D Printed Mortar

The rheology is the key factor that controls the 3D printability of cement-based materials. Indeed, the printed material should satisfy both good workability retention to ensure successful extrusion and a well-adapted green strength to support subsequent layers without collapsing. This requires a tricky control of the physico-chemical structuration kinetics. In the present study, in addition to dynamic rheology, ultrasonic wave propagation test was used to monitor the evolution of the elastic and shear moduli with time. Furthermore, isothermal calorimetry measurements were carried out to quantify the chemical evolutions underlying the early-age behavior of 3D printable cement-based material. A comparative analysis was conducted to correlate rheological measurements with those obtained using non-destructive and calorimetry test methods. Based on the obtained results, a new testing methodology combining the rheological and mechanical properties, as well as isothermal calorimetry measurements is proposed. The proposed method allows a better understanding of the physico-chemical structuration kinetics during the setting process, hence allowing proper optimization of the mixture design from rheological and mechanical points of view.

Ilhame Harbouz, Emmanuel Roziere, Ammar Yahia, Ahmed Loukili
Gravity Driven Tests to Assess Mechanical Properties of Printable Cement-Based Materials at Fresh State

The prediction of the stability of fresh cementitious materials during 3D printing is required in order to find adequate process parameters such as building rate or time gap between layers. Schematically, the process efficiency depends on a balance between the rate of strengthening of the material and the building rate that increases the self-weight that the freshly printed structure must withstand. The first deposited layer of fresh cementitious material must be stiff enough to avoid squeezing effect, and the material has to be rigid enough for the in-print structure not to buckle. This is even more crucial for slender cantilevered structures. Also, cracks may appear in sharp angles of the printed shapes. To predict and avoid those printing defects, the determination of various rheological (shear, compression and tensile yield stresses) and fresh-state parameters of the material (elastic modulus) are required. As rheometer and ultrasonic measurement devices are not usually available on the production site, there is need to develop simple and accurate tests that can provide mechanical parameters for the prediction/verification of the stability of the structure during printing. For instance, instantaneous and continuous penetration tests can be used to evaluate the material yield stress and its evolution over time.In this work, a special attention will be paid to simple tests such as the bending of a circular cross-section beam of fresh cementitious materials and/or the self-tension tests of cylindrical cross-section laces. The first one can be used to compute the apparent elastic modulus, while the second provides the tensile yield stress. Measured parameters are then compared with the ones computed from dimensional compression test and shear vane tests in order to validate the obtained results.

Yohan Jacquet, Vincent Picandet, Damien Rangeard, Arnaud Perrot
Characterizing Extrudability for 3D Concrete Printing Using Discrete Element Simulations

3D Concrete Printing (3DCP) is a novel automation construction technique, which interested many researchers extensively in the past few years. Among the major research interests in the specific area, the rheology of 3DCP material attracted more researchers recently. Due to the significantly different rheological requirements in extrusion and layer-wise construction stages, proper understanding and characterization of the rheology of 3D printable concrete are required. Extrudability criteria of the material highly depend on the extrusion geometry, extrusion parameters, and the flow type occurring while extruding (i.e. plug flow or highly sheared flow). Hence, numerical simulation tools may be important to understand the flow behavior and extrudability criteria of 3DCP. Therefore, in the current study, the Discrete Element Method (DEM) was used to model the flow behaviour of 3D printing concrete and to characterize the extrudability. A user-defined two-phase hardcore-softshell contact model was developed for particle interactions and the model was calibrated using the experimental orifice extrusion test results. The developed model was then used to simulate the flow inside a hopper with rotating augur. The extrusion pressure in the simulation was compared with the experimental relative power consumption to discharge ratio (pressure) for different rotational speeds. The results for the simulation show good agreements with the experimental pressure values. Based on the results, suggestions were provided to improve the numerical model predictions and the developed numerical model can be used to quantify the extrudability of 3DCP material using either ram-type or rotating screw-type extruders.

Roshan Jayathilakage, Jay Sanjayan, Pathmanathan Rajeev
Investigation on Structural Build-Up of 3D Printable Foam Concrete

Over the last decade the use of foam concrete in the construction industry has become popular due to its high thermal and acoustic insulation capacity in combination with sufficient strength characteristics. The use of foam concrete in 3D printing (3D Foam Concrete Printing) is a perspective approach which should enable automated freeform construction without formwork and at the same time would contribute to sustainability and energy efficiency of the structures. Since 3D-printing requires very specific rheological properties of foam concrete in its fresh state, a systematic research on this subject is needed. For this purpose, foam concrete mixtures containing more than 35 vol% protein-based foam and fresh density of approx. 1200 kg/m3 were developed and investigated with respect to their suitability for 3D printing by extrusion-based selective material deposition. Constant shear rate rheometer tests were performed to determine static yield stress and critical strain at flow onset at concrete ages of 30 min to 150 min, the time interval specifically relevant for the 3D printing process. Finally, the estimation of structural build-up was verified by manufacturing 800 mm long foam concrete walls until their collapse.

Viacheslav Markin, Irina Ivanova, Shirin Fataei, Silvia Reißig, Viktor Mechtcherine
Effect of Cement Type and Limestone Powder Content on Extrudability of Lightweight Concrete

Extruded lightweight aggregate concrete (LAC) enables to unite static and building physics properties within monolithic structures. Besides, material demand can be reduced according to necessity. However, the contradicting requirements in extrusion for pumpability and buildability are intensified compared to normal concrete due to the change of LAC fresh properties during pumping. This paper focusses on the effect of cement type and amount of limestone powder on the pumpability of LAC at comparable buildability. We show that the pumping performance enhances with increasing limestone powder content. Furthermore, we find that the increase in density during the pumping process is affected by the water retention of the material, which in turn correlates with the limestone powder content. The resulting strength can thus be consciously improved. The amount of limestone powder has only a minor effect on structural build-up and static yield stress and thus, on buildability. However, we find a general strong increase in static yield stress during pumping of LAC, which further facilitates the buildability in addition to the positive effect of the low density of LAC resulting in reduced weight loads to bear during extrusion. Another advantage is that reasonable replacement of cement by limestone powder leads to less drying shrinkage without significantly reducing the strength. Concluding, the requirements for extrusion of LAC – for both pumpability as well as buildability – can be fulfilled and adjusted to necessity by partly substitution of the cement with limestone powder.

Carla Matthäus, Daniel Back, Daniel Weger, Thomas Kränkel, Jennifer Scheydt, Christoph Gehlen
Numerical Modeling of an Extrusion-Based 3D Concrete Printing Process Considering a Spatially Varying Pseudo-Density Approach

During the past few years, additive manufacturing techniques for concrete have gained extensive attention. In particular, the extrusion-based 3D concrete printing exhibited a rapid development. However, further progress is hampered by a time-consuming trial-and-error exploration, i.e., mainly experimental studies have been performed so far. A more fundamental understanding of the relations between the printing process, the process parameters and the properties of the printed product could be achieved by means of numerical simulations. They enable to study a wide range of parameters such that dependencies of properties of the printed product on different influencing factors can be identified. Taking into account the uncertain nature of the process and material parameters of the extrusion-based 3D concrete printing, the process can be reliably controlled and finally optimized.The present study introduces a novel modeling approach, applying the Finite Element (FE) method while considering a pseudo-density approach. This density is used to define the material properties of each FE, similarly to the soft-killing approaches in topology optimization. Along with the progressing printing process, a previously generated FE mesh is activated layer by layer. Additionally, all material parameters vary temporarily due to the time dependency of the curing process. The numerical simulation allows to investigate the deformation behavior of the printed wall for different printing velocities.

Meron Mengesha, Albrecht Schmidt, Luise Göbel, Tom Lahmer
Evaluating the Influence of Aggregate Content on Pumpability of 3D Printable Concrete

3D concrete printing technology has gained huge momentum in the past two decades. The enhanced geometric freedom associated with 3D concrete printing could be beneficial for a variety of applications. However, the relatively high binder content in 3D printable concrete makes them less sustainable compared to mould-cast concrete. Therefore, developing printable mixtures with the required rheological behaviour combined with enhanced sustainability is very important. In this study, different concrete mixtures were prepared by replacing ordinary portland cement with ground granulated blast furnace slag. A polycarboxylate-ether-based superplasticizer and a cellulose-based viscosity modifying agent were used as chemical admixtures. A maximum aggregate size of 2 mm was used, and the aggregate-to-binder ratio (a/b) was varied from 1.0 to 1.8 to reduce the binder amount. The designed mixtures were tested for their pumpability with a screw-based pump system allowing to measure the discharge rate and pumping pressure. The pumping pressure increases as the aggregate content increases. Rheological properties of these mixtures were determined by fitting to the Bingham model. The yield stress and viscosity were found to increase with an increase in the aggregate content of the mixtures.

Manu K. Mohan, A. V. Rahul, Kim Van Tittelboom, Geert De Schutter
2D Numerical Modelling of Particle-Bed 3D Printing by Selective Paste Intrusion

Additive manufacturing of concrete and cement based materials is expected to revolutionize how structures are built. 3D printing processes by means of extrusion-deposition have recently been developed at the scale of few meters for houses or structural elements but not yet for several floors. Among the 3D printing processes which have also gained attention, particle-bed methods could be designated as an innovative one. In the case of the selective paste intrusion technique, the nozzle of the 3D printer applies the binder composed of water, mineral material and admixtures to a particle bed of sand particles. To reach a homogeneous material using the selective paste intrusion method, the aggregate layer made of sand must be completely penetrated by the cement paste to bond with the other layers. Such an issue is challenging regarding the rheological requirements of the binder to ensure the complete penetration of the aggregates layer. Therefore, this paper aims to provide and validate the penetration of yield stress fluids through sand particle layers using numerical simulation. A 2D numerical analysis is carried out to study the preferential flow path comparing to previous unidirectional modeling. A level-set method and a continuous viscoplastic model have been used to simulate the penetration and to compare the numerical results with experimental and analytical models from the literature. We describe the penetration as a function of the yield stress, the contact angle at the interface, the medium diameter of the sand particles, the void fraction of the sand packing and the dimension of the sand layer. We show that the numerical modelling is able to predict the evaluation of penetration depth as a function of the yield stress of the fluid measured from rheological measurements and the sand particles bed properties.

Alexandre Pierre, Daniel Weger, Arnaud Perrot, Dirk Lowke
Effect of Vibration on the Rheology of Concrete for 3D Printing

A primary challenge in concrete 3D printing is the need for low yield stress for good flow through the printer and high yield stress for sustaining the self-weight and the weight of subsequent layers. The current 3D printable concrete mixture designs make limited use of aggregates. Aggregates could significantly increase the yield stress of concrete mixtures but are not used since they impede the flow of concrete through a nozzle. A novel idea is presented in this work where vibration is used to control the rheology of concrete. By including coarse aggregate, a high yield stress concrete mixture can be obtained which when vibrated loses its yield stress instantly. Granular suspensions like concrete recover their yield stress immediately after the vibration ceases. The effect of vibration on the yield stress of concrete with varying aggregate content and packing fraction is also described. It is shown that the yield stress of concrete is significantly greater than that of cement mortar and paste and this high yield stress is lost when the concrete is vibrated.

K. Pattaje Sooryanarayana, P. Stynoski, D. Lange
Prediction of the Yield Stress of Printing Mortar Ink

The development of printable cement-based materials is a high priority in the field of 3D printing for construction. There are many admixtures available for the design of the printing mortar ink which can influence the wet and final properties of the mortar. In this work, artificial intelligence has been utilized to predict those properties and guide the dosage of each admixture. The algorithms were developed from a factorial experimental plan. The mortar investigated consists of cement blended with silica fume to reduce the embodied carbon of the mixture. The selected admixtures were a superplasticizer, a viscosity modifying agent, nano-clay, C-S-H seeds and an accelerator with a water-reducing effect. A rotary rheometer was used to measure the viscosity and the dynamic yield stress of both mortar and cement-paste mixtures. Additional tests were conducted such as the small Abrams cone and the ASTM C1437 flow test. Several predictive algorithms were developed and compared, in which artificial neural networks were used. Furthermore, to enhance the performance of the neural network, a genetic algorithm was used to optimize the network parameters. To evaluate the performance of the models, the normalized root mean square error (NRMSE), and coefficient of determination (R2) were calculated. This approach is a single-objective prediction which yields promising capability to predict the wet properties of both mortar and cement pastes, which can be later expanded into a multi-objective approach.

Sergis Vasileios, Malo Charrier, Claudiane M. Ouellet-Plamondon
Dynamic and Static Yield Stress Determination of Cementitious Paste with Admixtures

The 3D printing of cementitious material requires an understanding of the printing material’s rheological properties, especially yield stress and viscosity. The ability to adjust and control these properties in the 3-D printing process represents a breakthrough for the construction sector. The aim of this paper is to experimentally determine the dynamic yield stress and static yield stress of cementitious materials with admixtures. Unlike conventional rheometer geometries, the National Institute of Standard and Technology (NIST) spindle geometry is used in this work for the measurement of both yield stresses. While dynamic yield stress was measured by increasing and decreasing the rotational velocity, the static yield stress was characterized by two methods: the torque increase method and the constant rotational speed method. For both yield stresses, a total of 16 mixtures were studied in a factorial experimental design of the chemical admixtures. The impact of each admixture has been highlighted. The structural build up was assessed through the structuration rates. The temperature effect on the early age properties was studied for the most promising formulations.

Karim Zongo, Malo Charrier, Corentin Duval, Claudiane M. Ouellet-Plamondon
Penetration Study of Liquid in Powder Bed for 3D Powder-Bed Printing

Powder-bed 3D printing technology is attractive as it allows to build complex structures and optimize cost and time. The liquid is sprayed to bond the powder bed at pre-determined positions layer by layer. After print, the non-bonded particles are removed during post-processing. From a material point of view, it is crucial to understand the interactions between liquid and powder bed. Indeed, the spreading of water in the powder bed impacts the hardened performances of the printed elements. In the current work, we first measure the one-dimension water penetration over time for pure cement powder, pure plaster powder and a modified plaster powder suitable for 3D printing. We then show the hardened morphology of water penetrated and bonded area. Our results and analysis suggest that for common inorganic reactive powder, the penetration depth is higher than the one required to control the shape. Thus, it is necessary to modify transfer properties in order to control the liquid penetration depth. We furthermore identify key parameters to design applicable dry powder mixtures for 3D powder-bed printing technology.

Wenqiang Zuo, Chenghao Dong, Emmanuel Keita, Nicolas Roussel

Mechanical Performance

Frontmatter
Quantitative Evaluation of Orientation of Steel Fibers in 3D-Printed Ultra-High Performance Concrete

Despite the growing interest in 3D concrete printing, the inset of tensile reinforcement poses severe limitation to the advancement of the technology. Inclusion of short steel fibers is a potential alternative to improve the tensile properties of 3D-printed concrete. In the extrusion-based printing process, steel fibers tend to align predominantly in the printing direction. However, currently there is no quantitative evaluation of the orientation of fibers in 3D-printed fiber-reinforced concrete. An experimental program was designed in this study to quantitatively investigate the fiber alignment in a non-proprietary 3D-printable ultra-high performance fiber-reinforced concrete (UHPFRC). Digital image analysis was performed on thin UHPFRC specimens to quantify the fiber orientation distribution. In addition, the effect of the fiber orientation on the mechanical response of the 3D-printed UHPFRC with 2% by volume of micro steel fibers was determined by means of three-point bending tests. Conventionally mold-cast UHPFRC specimens were also prepared and tested for comparison purposes. The results of the digital image analysis revealed an enhanced fiber alignment parallel to the printing direction in the 3D-printed specimens, which in turn significantly enhanced the flexural performance of the printed UHPFRC as compared to the mold-cast counterpart.

Arun R. Arunothayan, Behzad Nematollahi, Jay Sanjayan, Ravi Ranade, Shin Hau Bong, Kamal Khayat
Steel Fiber Links in 3D Printed Concrete

3D concrete printing exhibits the potential to proliferate the industrialization of the concrete construction sector, which is notoriously conservative and indolent towards change. This emerging technology is propitious given its advancements in geometric design freedom, reductions in construction time, waste and material usage through formwork-free construction. However, when 3D concrete printing is fastidiously compared to current methods of concrete construction, a detrimental disadvantage, the absence of effective steel reinforcement is evident. Therefore, the amelioration of the brittle interlayer interface is the focus of several 3DCP research and industry endeavors. Steel reinforcement is favored as most modern concrete structures rely on the compressive and tensile strength of concrete and steel, respectively. However, a significant technical challenge is posed by the addition of reinforcement during the automated 3DCP process. Thus, the post-crack behavior of specimens reinforced during the printing process with straight steel fibers orthogonal to the interlayer interface is experimentally evaluated through four-point flexural tests in this research. The brittle interfacial failure is ameliorated through the addition of steel fibers that link consecutively deposited layers.

Frederick Bester, Marchant van den Heever, Jacques Kruger, Seung Cho, Gideon van Zijl
Mechanical Characterization of Cement-Based Mortar Used in 3DCP Including Early-Age Creep Effects

Digital fabrication techniques combined with suitable cementitious materials have successfully led to the implementation of innovative manufacturing processes for concrete-like products. However, although significant advantages are expected in layered extrusion (LE) concrete technology, manifold engineering challenges arise from the process itself, such as the full control of the mechanical properties evolution during printing. Primarily, printed materials should satisfy specific early-age mechanical and rheological requirements, whose definition remains unstandardized. Additionally, scarce literature on testing procedures for early-age printable mortars is currently available. In this paper, uniaxial compressive tests are performed on cylindrical samples to determine the time-dependent compressive behavior and the early-age creep effects on fresh concrete. The load application conditions are varied in the experimental campaign in order to propose a proper mechanical characterization procedure for 3D printable cementitious mortars. Finally, results are implemented in an analytical model to predict the accumulated creep strain during the printing process. The outcomes highlight the role of the early-age creep in the development of global deformations.

Lorenzo Casagrande, Laura Esposito, Costantino Menna, Domenico Asprone, Ferdinando Auricchio
Influence of Pumping/Extrusion on the Air-Void System of 3D Printed Concrete

3D printing with concrete offers many advantages over conventional construction methods and interest in this field of research has seen a rapid rise in recent years. While there have been large number of cases of successful fabrication of 3D printed structures, ensuring the long-term durability performance of the fabricated structures is equally important. Freeze-thaw damage is one such deterioration issue, especially in cold places like Switzerland. This study investigated the effect of the different processing conditions encountered in 3D printing, namely pumping, acceleration/mixing and extrusion on the air void system of a standard 3D printable mortar mix. The 3D void size distribution of the air voids obtained using a recently developed stereological model, along with the ASTM C457 results showed that pumping had the major impact on the void structure as both air content and spacing factor decreased significantly. The effect of acceleration/change in rheology and extrusion on the void structure was also prominent from the obtained results. The 3D protected paste volume (PPV) curves showed that pumping and acceleration processes could enhance the freeze-thaw performance.

Arnesh Das, Yu Song, Sara Mantellato, Timothy Wangler, Robert J. Flatt, David A. Lange
Fire Behavior of a Printed Sample for Building

Two tests have been performed at CSTB on test specimens printed in the Civil and Environmental engineering department of IMT Lille Douai. First, Compression and bending tests have been carried out at several temperatures (20 °C, 120 °C, 250 °C, 400 °C, 600 °C) on printed elements, both perpendicularly and alongside the direction of the printed layers. Temperature measurements using a thermal camera, and Digital Image Correlation analysis have been carried out.The test results highlight that the printed material resists to an unloaded fire test without displaying any significant damage during the fire duration. The material exhibited a structural integrity as well as no leakage of the hot gas after 120 min of heating and after cooling. A comparative study of the mechanical strengths and of the thermal curvatures of the printed material according to the orientation of the layers allowed the assessment of the isotropic characteristic of the printed material and the characterization of the behavior of the joints between layers under thermal stress.

Melody D’Hondt, Sébastien Rémond, Philippe Leblond, Bunthan Iea, Estelle Hynek, Nicolas Pinoteau
Effect of Metallic Fibers on the Print Quality and Strength of 3D Printed Concrete

3D concrete printing is a promising technology in the construction field. Un-availability of standards/specifications related to certification of 3D printed structures and lack of reinforcement in printed concrete are the major factors behind the under-utilization of such innovative technology. Addition of fibers as reinforcement in the printable mix could be considered as viable solution to improve mechanical properties of printable mix particularly tensile strength. In this regard, recently carried out studies have used mostly non-metallic fibers with low modulus of elasticity and tensile strength. In this study, effect of adding flexible amorphous metallic fibers on the print quality and mechanical properties (flexural and direct tensile strengths) of resulting mixes has been investigated. Fibrous and non-fibrous mixes were designed. To prepare fibrous mixes, metallic fibers were used at dosage of 20 kg/m3, 30 kg/m3 and 40 kg/m3. Further, to study the influence of fiber length on the print quality and strength, fibers of length 5 mm, 10 mm and 15 mm were used. Reference specimens for tensile and flexural strength tests were also cast in molds using all mixes used for printing. Results showed that addition of metallic fibers of length 10 mm and 15 mm exhibited detrimental effects on the print quality, however, strength values, particularly tensile strength of printed concrete were observed to be enhanced by the addition of these fibers. Although print quality of mix containing fibers of 5 mm length was least affected, no positive impact of these fibers on the mechanical strength of printed concrete was noticed.

Rashid Hameed, Aurélie Papon, Arnaud Perrot, Damien Rangeard
Facilitating Ductile Failure of 3D Printed Concrete Elements in Fire

This research investigates 3D printed concrete behaviour at elevated temperatures. Preliminary studies indicate that delamination of filament layers occurs at elevated temperatures, as opposed to thermo-hygral spalling, which typically occurs in conventionally cast high-performance concrete samples. Brittle structural failure may therefore occur during a fire scenario since little to no reinforcement is currently included in the 3DCP process. This research proposes the incorporation of steel fibres into the additive manufacturing process to facilitate ductile failure and increase interlayer mechanical properties. The fibres are vertically aligned, orthogonal to the printing plane, and strategically positioned to bridge multiple filament layers. 3D printed rectangular samples are heated via radiant gas panels and thereafter tested in four-point bending once they have cooled down to ambient temperature to determine post-fire flexural capacity and ductility properties. This study shows that steel fibre inclusion improves the structural fire performance of 3D printed elements by 33% and provides post-peak mechanical ductility to yield deflection softening. More research is required to ultimately develop a standardized economical structural fire design process for 3DCP.

Jacques Kruger, Antonio Cicione, Frederick Bester, Marchant van den Heever, Seung Cho, Richard Walls, Gideon van Zijl
High-Performance Light-Weight Concrete for 3D Printing

The aim of this experimental study is to develop high strength, lightweight concrete mixture suitable for 3D printing in construction. This work investigates the effect of replacing normal aggregate either partially or totally with expanded perlite aggregate. This material allows for better thermal insulation properties, thus decreasing the energy usage within the life cycle of the concrete structure. Expanded perlite aggregate was used in concrete by 20 vol.-%, 40 vol.%, 60 vol.%, 80 vol.-% and 100 vol.-% in replacement of the natural aggregate. Material characterization tests of compressive strength, flexural strength, and thermal conductivity were carried out for six concrete mixtures. The proposed concrete mixture, which has 100% of expanded perlite aggregate achieved reduction percentage of thermal conductivity around 62% (0.69 W/mK) relative to normal weight concrete the mixture has a compressive strength of 42 MPa at 28 days. This mixture is appealing for 3D printing in 3D concrete printing as it reduces the environmental impact of the built environment by improving the thermal insulation and decreasing the energy consumption during building operation phase.

Malek Mohammad, Eyad Masad, Thomas Seers, Sami G. Al-Ghamdi
Mechanical Characterization of Layer-by-Layer Interface in Concrete Elements Obtained by Additive Manufacturing

The anisotropic behavior of the 3D concrete printing elements represents a crucial key feature to be closely investigated. It is mainly due to the layered extrusion process, the most widespread digital concrete technology, which creates weak planes at the interface, known as “Cold Joints”, by placing material layer upon layer. To investigate the interface bond failure mechanism, the bond strength at the interface between layers was measured in this study, especially with respect to printing time gap between layers. In particular, this work provides a characterization of the mechanical properties of 3D printed concrete elements’ interfaces through the design and the implementation of an experimental setup supported by DIC technique, in order to study the shear behavior of layer interfaces. The study investigates different 3d concrete elements produced with 100 s, 200 s, 1800 s as time gap between layer deposition, showing a significant decrease in terms of maximum load up to about 50% for the elements realized with the higher value of resting time compared to bulk elements.

Rosanna Napolitano, Costantino Menna, Domenico Asprone, Lorenzo Del Giudice
Dynamic Behaviour of Layered 3D Printed Concrete Elements

Recently, the interest in digital fabrication techniques, such as 3D concrete printing, has grown at a dizzying speed, but at the same time many critical issues are still wide-open. Weak strength at the bond interface of two concrete layers, also referred as cold joint, is one such critical task to be scientifically investigated, especially in dependence on waiting time parameter between layers. It is a topic very structural engineering sensitive, because of the loss of instability and durability due to the occurrence of interface failure.The aim of this work is the study of the effect of interfaces on mechanical performance of 3D printed cementitious elements under dynamic loading conditions. In order to achieve this, an experimental campaign was performed on 3d printed concrete elements varying the time intervals between placements of subsequent layers, through high and medium strain rate tensile tests, using a Hydro-pneumatic machine and a Modified Hopkinson bar apparatus, respectively. The results exhibited a decrease in the dynamic interface tensile strength with the waiting time up to over 90% for a medium strain-rate of about 10 s−1 and over 20% for a high strain-rate.

Rosanna Napolitano, Costantino Menna, Daniele Forni, Domenico Asprone, Ezio Cadoni
Characterizing the Fissility of 3D Concrete Printed Elements via the Cohesive Zone Method

This research examines the differential interlayer capacity of 3D concrete printed (3DCP) specimens via mechanical characterization procedures, comprising of direct tension test (DTT), Iosipescu shear test (IST), and orthogonal compression tests. The experimental findings are subsequently correlated to cohesive parameters that represent the adhesive capacity of the interfacial transition zone (ITZ). Furthermore, the cohesive parameters are validated via supplementary mesoscale analytical calibration and finite element (FE) analysis procedures. The experimental works conducted are envisioned to take an incremental step towards detailed design specifications that allow for the rational design of load-bearing 3DCP components and structures at a macroscale.

Marchant van den Heever, Frederick Bester, Mohammad Pourbehi, Jacques Kruger, Seung Cho, Gideon van Zijl
3D Printing of Concrete: The Influence on Chloride Penetration

3D concrete printing is one type of additive manufacturing (AM) which comprises all modern techniques of fabricating building elements layer by layer. It shows great perspectives with respect to freedom of form, time management and eco-friendly use of the material as the material is only applied where it is necessary. However, due to the lack of formwork and the layered end result, this construction technique induces more shrinkage, internal voids and crack formation, increasing the amount of preferential ingress paths for chemical substances. The additional amount of voids caused by this layered fabrication technique will not only induce anisotropic properties on a structural level, but will also affect the microstructure and durability of the printed specimens. For the aim of this research, 3 different time gaps are selected to investigate the influence of the layered construction process on chloride penetration and a comparison with traditional cast concrete was made. First results showed that the print process affects the chloride penetration in a significant way. Although the ingress front is uniform in both cases, the chloride ingress is approximately three times higher in case of specimens fabricated with a zero minute time gap compared with traditional cast elements and this only after one week of chloride exposure. An increased time gap increases the porosity at the interface and consequently also the chloride ingress rate of the printed elements.

Jolien Van Der Putten, Melissa De Volder, Philip Van den Heede, Geert De Schutter, Kim Van Tittelboom
Effect of Heat Curing and E6-Glass Fibre Reinforcement Addition on Powder-Based 3DP Cement Mortar

Powder-based 3D printing is one of the most promising techniques in additive manufacturing. The speed, resolution of the printed part and complicated geometries are important features in this technique and these features are usually not experienced in traditional construction techniques. This study aims to discuss the concept of using a custom-made powder (cement mortar) instead of a commercial (gypsum) powder in 3DP. Therefore, broad investigations are required to study and understand the details of the cement mortar 3D printed scaffold. This paper discovers the effect of heat-curing and addition of E6-glass fibres as reinforcement for the printed specimens. The results show that the mechanical properties of the cement mortar are improved through a heat-curing procedure. Addition of fibre reinforcement enhances powder flowability consistency and surface roughness throughout. Experiments are conducted on printed 50 mm cubic specimens, cured in an oven at different temperatures. The optimum heat-curing temperature is found to be 80 °C to achieve the highest compressive strength in cement mortar specimens. Detailed 3D laser scanning of the printed cement mortar specimens is conducted. The 3D laser scanning results found rougher surface in cement mortar when it is not reinforced with glass fibre.

Pshtiwan Shakor, Shami Nejadi, Nadarajah Gowripalan
Effect of Polypropylene Fibres on the Mechanical Properties of Extrudable Cementitious Material

3D Concrete Printing (3DCP) has aa potentiality to produce complex, geometries and can modify the details rapidly using a printer integrated with a pump and nozzle. From the earlier studies on 3DCP, it is distinguished that the rheological behaviour of the material, printing direction, and printing time may have significant effects on the overall structural behaviour of the printed structure. The layered concrete may create weak joints in the specimens and reduce the load bearing capacity in terms of compressive, tensile and flexural strength that requires stress transfer across or along these joints The present study focuses on the examination of the effect of adding polypropylene (PP) fibres on the failure behaviour of print mortar on printed concrete, on different print directions. The Silica Fume (SF) based control mix was used in the analysis with fibre addition in different mass fraction of binder ranging from 0.5% to 3.0%. Those mixes were designated after the detailed fresh property analysis and control cementitious specimens without fibre inclusion were also printed for comparison. The specimens were collected in different orientations from manual extruded concrete blocks and tested for mechanical properties. For the materials tested, it is found that the mechanical properties such as compressive and flexural strength of extruded samples are governed by its printing directions. The mixes with 1.0% and 0.5% PP fibre addition exhibit the better performance in terms of flexural strength and 0.5% PP mix can be considered as the optimum fibre content with respect to the compressive strength.

Thadshajini Suntharalingam, Brabha Nagaratnam, Keerthan Poologanathan, Phil Hackney, Jeffri Ramli
Improving the Bonding Adhesion of the Cold Joints of Normal and Lightweight 3D Printing Mortars

Two types of mortars were developed for 3D Construction Printing (3DCP), which are normal and lightweight 3D mortars (termed as LATICRETE ® 3D Printing Mortar NW and LATICRETE ® 3D Printing Mortar LW, respectively). This paper presents the properties of the aforementioned mortars in fresh and hardened states, as well as states of curing for cold joint testing. The fresh properties assessed consist of the determination of flow, viscosity, initial set time, and unit weight. In its hardened state, each type of mortar was tested for its mechanical (i.e., compressive and tensile strengths) and freeze-thaw (i.e., ASTM C666) properties. The printability of the mortars was demonstrated by printing small (20-layer; 12 cm high with 6 mm layer thickness; within 5 min) and large-scale structures (a full-scale villa – normal 3D mortar only). Furthermore, a lab-scale test was developed to assess the bonding strength between layers (both cold and fresh joints). The results of the test indicate that the interlayer adhesion at the cold joint can be improved by applying a bonding agent (i.e., LATICRETE® 254 Platinum) on its surface prior to the print.

Kho P. Verian, Jarron Ashcroft, Matthew D. Carli, Randall P. Bright, Eerik Maandi, Avak Avakian, Edouard Baaklini
Interlayer Effect on Fracture Behavior of 3D Printing Concrete

Concrete additive manufacturing, also known as concrete 3D printing, opens new opportunities in the construction industry and architectural design. The layer-by-layer additive manufacture process introduces printing filaments and interlayers into the concrete components. How this new manufacturing process affects the fracture behavior of 3D printed concrete components has not been well understood. In this study, we characterized the fracture behavior of 3D printing concrete at printing interlayers in comparison with printing filaments. 3D printing concrete specimens containing notches at interlayer or filament locations were loaded in a servo-controlled testing system with closed-loop control through a high-resolution digital image correlation system that measures crack opening displacement and crack extension during loading. The plane-strain fracture toughness and critical effective crack length at the interlayer and the filament were experimentally determined. The results revealed that fracture toughness at the interlayer was 20–26% lower than at the filament. This indicates that compared with filaments, the interlayers under stress are more sensitive to defects and imperfections that can cause crack propagation and fracture failure. The results are important for understanding the effect of the 3D printing manufacturing process on the mechanical behavior of concrete components, paving the way for more rational analysis and design of highly loaded structures made of 3D printed concrete.

Yun-Chen Wu, Jason Cotrell, Mo Li
Auxetic Behavior of Cementitious Cellular Composites Under Uniaxial Compression and Cyclic Loading

Mechanical behavior of cementitious cellular composites (CCC) with auxetic behavior was investigated under uniaxial compression and cyclic loading. Three cellular structures with different geometrical parameters are designed and prepared by 3D printing technique. Meanwhile, plain mortar and fiber reinforced mortar are used as constituent material, respectively. Ductility of the constituent materials is evaluated by four-point bending tests. Uniaxial compression and cyclic loading tests are performed on the CCCs. Experiments show that with proper structure and constituent material, CCCs can exhibit auxetic behavior. For the tested CCCs (P25 and P50), negative Poisson’s ratio is obtained: as a result, strain hardening behavior can be identified in the stress-strain curve under uniaxial compression. In addition, large reversible deformation under cyclic loading is obtained on P25 under cyclic loading. Hysteretic behavior in the stress-strain curve can be identified in a single cycle, which means that CCCs dissipates energy in each cycle. After 3000 cycles, the maximum load and energy dissipation of each cycle increased owing to the slip hardening behavior of the PVA fibers in the constituent material. Owing to the excellent energy dissipation property, these auxetic CCCs may be used for vibration resistance structures in the engineering practice in the future.

Yading Xu, Erik Schlangen, Branko Šavija
Impact of Particle Size and Grading on Aggregate-Bed 3D Concrete Printing

This research aims to investigate the effects of different parameters involved in particle-bed concrete printing on the quality of aggregate-bed concrete printing products. In particular, particle size and grading of aggregates were investigated by adopting two groups of single-size aggregates and a group of mix-size aggregates. The printed products were characterized by mechanical performance, CT scanning and visual appearance. The result reveals that the 3D printed products have layered structures, which is different from conventional casting concrete. The mechanical properties and macrostructure of printed specimens were significantly influenced by the adopted aggregate size and grading.

Shiwei Yu, Jay Sanjayan, Hongjian Du
Drying of 3D Printed Mortar Filaments at Early Age Assessed by X-Ray Computed Tomography

3D extrusion-based additive manufacturing is known as the most widely applied printing strategy for digital fabrication of civil engineering materials. This construction method does not only require specific rheological properties and structural build-ups rates, but also mechanical properties comparable to conventional materials. In the current work, manually cast mortar filaments consisting of cement paste and glass beads are used to mimic the 3D printed cement-based materials. We first compare the 3D tomography of mortar between sealed and dried conditions with or without mold constraint at early age. We then carry out the 3-point-bending tests for sealed and dried mortar. Our results suggest that at very early age before setting, drying phenomena induce irreversible microcracks which lead to a deterioration of mechanical strength of the filaments.

Wenqiang Zuo, Emmanuel Keita, Michel Bornert, Nicolas Roussel

Structural Engineering and Reinforcement

Frontmatter
Printed Concrete as Formwork Material: A Preliminary Study

Production of complex formwork with conventional materials can be expensive due to the intensive labor during the manufacturing process. The introduction of printed concrete as formwork material could resolve this problem. The combination of the automated robotic manufacturing and the high degree of freedom could benefit the production process. However, the material characteristics of printed concrete are less suitable then for conventional materials. The low tensile strength of printed concrete formwork could endanger the stability of the formwork during casting of the concrete. This experimental study identifies the most important stresses and parameters to be studied while casting concrete in a printed concrete formwork. The investigation was performed on a printed concrete cylindrical formwork filled with self-compacting concrete. During casting, the strain on the outside of the formwork was measured in time as well as in function of the changing pressure head. Results showed that the strain on the outside of the formwork increased in time, with increasing pressure head.

Michiel Bekaert, Kim Van Tittelboom, Geert De Schutter
Bond of Reinforcement Cable in 3D Printed Concrete

The use of high strength steel cables directly entrained into printed concrete during the printing process, has previously been introduced as a method to provide reinforcement to objects being manufactured through a layer-extrusion based 3D concrete printing process. The bond between the cable and the cementitious mortar is a crucial parameter for the structural performance of such reinforcement, and was hence subject of a detailed study presented in this paper. The bond performance was studied in direct and flexural pull-out tests on cast and printed specimens and further analyzed by microscopic analysis of the bond surface. Two effects were identified that significantly decrease the bond strength. Firstly, chemical reactions create a spongy interface of poor strength. Secondly, the flow of mortar around the cable tends to create a cavity underneath the cable which reduces the effective bond surface. Mortar viscosity, nozzle design and filament pressure, were thus identified as important parameters for the bond quality. The average bond quality seems to reduce with embedment length. As a consequence, cable breakage was not achieved, in spite of considerable embedment lengths that were tested. Likely, this was caused by the cumulative probability of critical defects along the increasing embedment length, in combination with a non-constant shear distribution. All test series showed significant scatter. It was concluded that, although this reinforcement method is promising as it can potentially provide sufficient post-cracking strength, the bond quality must be improved considerably both in terms of average strength and reduction of scatter.

Freek Bos, Steven Dezaire, Zeeshan Ahmed, Anne Hoekstra, Theo Salet
Experimental Investigation of Topology-Optimized Deep Reinforced Concrete Beams with Reduced Concrete Volume

This paper presents an experimental investigation of digitally manufactured, reinforced concrete beams designed with topology optimization. The backbone of the current work is a hybrid mesh topology optimization algorithm that automatically generates strut-and-tie layouts. The resulting designs have tensile truss elements describing the reinforcing phase and compressive continuum force flow elements that illustrates how the concrete is carrying load. The aim of this work is to investigate the effect of removing a percentage of the non-load carrying concrete phase. A beam is designed with a standard, by-hand approach and the same steel amount is used in to generate a topology-optimized design. This work considers three beam designs; (i) the standard, (ii) a topology-optimized beam with a prismatic section (i.e. 100% concrete), and (iii) the topology-optimized steel layout in a beam with a reduced concrete volume (herein 75%). An alternative reinforcement method is used in which steel plates are cut by waterjet. To improve the bond quality between concrete and reinforcement, corrugations and anchors are added to the steel layouts. However, as opposed to previous experimental tests conducted by the authors, a poor bond quality is achieved, leading to premature failures of all test specimens. Due to the lack of proper bonding, comparison can only be made in the early elastic range. Here, a significant trend is that the by-hand and the topology-optimized specimens with 75% concrete exhibit near identical behaviors.

Yan Liu, Jackson L. Jewett, Josephine V. Carstensen
Studying the Bond Properties of Vertical Integrated Short Reinforcement in the Shotcrete 3D Printing Process

Additive manufacturing techniques in construction open up new possibilities with regard to geometric complexity as well as structural and material efficiency. However, at this point in time the integration of reinforcement is still subject of research. In the presented experiments, an integration of short reinforcement bars perpendicular to Shotcrete 3D printed layers is investigated. The focus of this study is on the bond quality and the mechanical characterization of the bond behavior between reinforcement and surrounding material for different vertical integration techniques. In this context, three methods are investigated: (1) direct insertion into the printed concrete, (2) insertion into a grouting mortar and (3) screwing the bar into the printed concrete. Steel and carbon reinforcement bars with a diameter of 12 mm are surveyed. The bond of the inserted reinforcement bars is analyzed mechanically by using standardized pull-out tests. Additional micro level analysis of the bond is performed by evaluation of computer tomography images. Directly inserted reinforcement bars show a reduced bonding compared to the other techniques due to a process-related cavity between the reinforcement and the surrounding material. By using the grouting mortar as well as by screwing the reinforcement, a significant increase of bond is achievable.

Niklas Freund, Inka Dressler, Dirk Lowke
Aligned Interlayer Fibre Reinforcement and Post-tensioning as a Reinforcement Strategy for Digital Fabrication

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.

Lukas Gebhard, Jaime Mata-Falcón, Ana Anton, Joris Burger, Ena Lloret-Fritschi, Lex Reiter, Benjamin Dillenburger, Fabio Gramazio, Matthias Kohler, Robert Flatt, Walter Kaufmann
Bending and Pull-Out Tests on a Novel Screw Type Reinforcement for Extrusion-Based 3D Printed Concrete

The lack of available reinforcement methods suitable for extrusion-based 3D concrete printing is well known. Because conventional methods using pre-placed steel bars are incompatible with this manufacturing method, several alternatives are under development. This paper introduces a novel reinforcement application method, based on screwing. Contrary to placement methods based on pushing, i.e. only a translational movement, the combination of translation and rotation inherent in the screwing motion, allows a practically void-free mechanical interlock with which a high level of bond can be attained. The concept makes use of the fact that the print mortar is still highly pliant for some time after deposition, allowing screws to be inserted without fracturing the concrete. The translational-rotational movement needs to be externally controlled, as the material at the early age does not provide sufficient resistance to pull in the screw on application of the rotation. Pull-out tests from printed and cast samples and 3-point bending tests on printed specimens showed a high bond strength and thus underline the feasibility of this concept.

Lauri Hass, Freek Bos
Load Carrying Capacity and Failure Mode of 3D Printing Mortar Wall Panel Under Axial Compression Loading

A major portion of today’s construction cost is attributed from a labor cost, and this labor cost tends to increase every year. Therefore, construction industries worldwide propose several modern solutions to cut back the labor cost, which consequently lead to lower overall construction cost. A 3D printing (3DP) technology using cement mortar can be one of such solutions proposed to lower the labor cost. Many research programs determining the 3DP concrete panel are being carried out. This study presents results from a scaled test of a complex shaped 3D printed wall panel with the dimension of 1.3 m height by 0.9 m width by 0.125 m thickness. The experiment aims to investigate its load carrying capacity behavior and failure mode under an axial compression loading. Test results indicate that the axial load capacity of the tested 3DP panel is significantly lower than that calculated from the material compressive strength. It is found that the geometry of the scaled panel plays an important role in the hardened performance characteristics. The 3DP wall panel was failed by the panel geometry, not by the maximum material performance due to the delaminating behavior between the layers during loading. The results from this study offers technical information used for a future optimized design of 3D printed structures in terms of shape, amount of material used, load carrying capacity, and possible failure modes.

Patiphat Jiramarootapong, Lapyote Prasittisopin, Chalermwut Snguanyat, Ganchai Tanapornraweekit, Somnuk Tangtermsirikul
Application of 3D Printed Segments Designed by Topology Optimization Analysis to a Practical Scale Prestressed Pedestrian Bridge

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.

Koji Kinomura, Satoshi Murata, Yujin Yamamoto, Hirotoshi Obi, Akihito Hata
Potential Approaches for Reinforcing Complex Concrete Structures with Integrated Flexible Formwork

Conventional construction of doubly-curved concrete structures is a time-, labour- and cost-intensive process. Flexible formworks have already been identified as a possible solution to produce such structures more efficiently. The KnitCrete technology developed at ETH Zurich uses 3D weft-knitted fabrics as stay-in-place formwork, which deliver multiple advantages over woven textiles due to their wider range of feasible geometries and possibility to include features and local material properties. The textile is initially coated with a fast-setting high-strength cement paste. The stiffened membrane is stable enough to serve as formwork for the final concrete layer. This paper discusses potential reinforcing strategies to guarantee structural safety and serviceability in KnitCrete structures. Possible approaches range from the use of the textile as a stay-in-place formwork as well as final reinforcement (by utilising high-strength fibrous materials such as aramid, glass or carbon fibre) to the implementation of geometric features, such as channels within the textile to guide conventional reinforcement or post-tensioning tendons. The feasibility and efficiency of the proposed reinforcement strategies have to be experimentally verified, for which a systematic methodology is proposed. Preliminary analyses of the experimental campaign show the beneficial effect of the knitted reinforcement on the cracking behaviour of the textile-concrete composite material. Additional research is needed to exploit the potential of possible hybrid solutions using short steel fibres, post-tensioning or linear steel or glass fibre reinforcement.

Minu Lee, Jaime Mata-Falcón, Mariana Popescu, Philippe Block, Walter Kaufmann
Penetration Reinforcing Method for 3D Concrete Printing

Large scale construction 3D Concrete Printing (3DcP) has gained much attention worldwide with the recent developments of many new technologies and proof of concept structures. One inherent limitation in 3DcP is the automatic laying of reinforcement. So far, the methods proposed for integrating vertical reinforcement are rudimentary and involve manual post processes. Majority of 3DcP wall structures overcome this issue by using the printed section as a shell and after hardening involve manual post processes to reinforce the structure. In this paper a new method of reinforcing is introduced termed the Layer Penetration Reinforcing Method (LPRM). This process involves the printing of a predetermined number of layers, then the subsequent penetration of pre-cut reinforcement through the fresh layers. To prove the concept a lab scale wall (300 mm tall) is printed and reinforced with 7 mm deformed steel bar and ×9 mm stainless steel helical bar. The wall is cut into 100 mm × 60 mm × 300 mm beam sections and tested in 3-point bending with the bar sitting a depth of approximately 70 mm to measure the flexural strength. The samples are compared to conventionally reinforced concrete. Results have shown that the printed beams with deformed bar and helical bar increase the flexural strength of the wall by 184% and 142% respectively. Deformed bar proved superior over helical bar in reinforcing a 3DcP section by obtaining a flexural strength 83% that of a conventional reinforced section, compared to 47% for helical bar.

Taylor Marchment, Jay Sanjayan
Combining Multiple Loads in a Topology Optimization Framework for Digitally Fabricated Concrete Structures

In recent literature, topology optimization gathered growing interests given its interplays with digital fabrication and additive manufacturing technologies. Notably, the topological optimization of concrete-like elements requires the study of stress-constrained optimization problems due to strength anisotropy, whose solution presents more challenges with respect to classical stiffness-to-weight maximization. For the purpose of fostering the use of topology optimization techniques in real-application scenarios, in this work we present an iterative algorithm to design lightweight structural concrete elements in presence of multiple load actions, and under the restriction of anisotropic stress-constraints. More specifically, our framework is based on the combined use of a proportional material distribution scheme and a Risk-Factor paradigm, to design performative solutions while limiting the failure probability of the structural element. To validate our approach, we define a parametric set of actions which combine bending and axial load, as commonly utilized in a structural engineering framework. In our computational experiments, we assess the robustness of our method and study the relationships connecting load parameters with the resulting solution properties.

Tommaso Pastore, Costantino Menna, Domenico Asprone
Potential for the Integration of Continuous Fiber-Based Reinforcements in Digital Concrete Production

While digital concrete production is a highly promising and vibrant research topic regarding an increase of the degree of automation in the construction industry, some critical questions remain unanswered. One of these challenging questions concerns the integration of reinforcement into the production process. In this paper, the authors present continuous fiber-based materials as a viable and promising alternative reinforcing material for the integration in digital concrete production. To this end, current approaches for the integration of reinforcement into digital concrete production are summarized. The production process of different continuous fiber-based materials is described and their application in textile reinforced concrete is explained. The authors also evaluate the feasibility of one specific approach to the integration of textiles into the digital concrete production process.

Martin Scheurer, Gözdem Dittel, Thomas Gries
3D Concrete Printing on Site: A Novel Way of Building Houses?

As a result of the constantly increasing world population and its purchasing power, it becomes more and more clear that raw materials are finite and the capacity of the earth to renew the stock of raw materials is almost exceeded. This is also important for construction industry as half of the extracted materials and about one third of the water consumption is absorbed by this sector. During the last years, a lot of progress has been made in creating more energy efficient buildings, but unfortunately, construction represents at this moment still 40% of the energy demand in Europe and 36% of the total CO2 emission [1]. However, the construction sector offers significant potential to handle these struggles and a possible solution to improve the sustainability is through automated construction by for example 3D printing the structural components. This new way of manufacturing has the advantage that there is no need for energy demanding and expensive molding, there is a larger freedom of form and there is the opportunity to use the material in a more eco-friendly way since it is only used where necessary. However, before acceptation of this technique on the construction site, it is necessary to compare the structural behavior of printed and cast specimens. For that reason, two wall types were tested on their compressive strength and also two types of reinforcement above a window opening were investigated through 3-point bending tests. These results showed that, in general, the mechanical performance of the suggested wall types is greater than that of traditional walls consisting of brickwork. This, in combination with the lack of molding and the higher construction speed, can accelerate the application of 3D printing on site.

Jolien Van Der Putten, Alex Van Olmen, Marijke Aerts, Emiel Ascione, Joeri Beneens, Jan Blaakmeer, Geert De Schutter, Kim Van Tittelboom
Design Optimization for 3D Concrete Printing: Improving Structural and Thermal Performances

This paper focuses on optimizing the shape of prefabricated building components that are produced using 3D concrete printing (3DCP) techniques. The proposed method is to improve the structural and thermal properties using heuristic optimization algorithms, as such that they meet the minimum standards determined by building design codes. First, a case study is constructed that is based upon an existing module design found in literature, and a single segment from this design is isolated. The influence of the overall shape and the curvature of the infill line is investigated, and the structural performance is optimized for the hardened material state. In a second attempt, the heat transfer through the segment is also minimized. In parallel to the design’s optimization process, of course, the manufacturing challenges and process limitation need to be considered as well. Therefore, the influence of the infill line on the buildability of a 3DCP element is also demonstrated in a fresh material state (i.e. during printing). For this, the complete printing process of a wall segment is simulated and allows for the prediction of printing failure, elastic buckling and plastic collapse. Based on the outcome of the FEM-based calculations, a design could then be marked fit for printing or allow for further optimization.

Gieljan Vantyghem, Marijke Steeman, Wouter De Corte, Veerle Boel
Flexural Behaviour of AR-Glass Textile Reinforced 3D Printed Concrete Beams

3D concrete printing (3DCP) enables automation of construction manufacturing through digital design and workflow, adding value through high degrees of form freedom. The process constraints during the printing, however, hamper the application of reinforcement and hence limit the ductile behaviour that is achievable in 3D printed concrete structures. Although a number of reinforcement strategies have been developed and these strategies can to some extent address these limitations, the reinforcement challenges of 3D printed concrete structures are not satisfactorily addressed yet. This paper proposes another reinforcement strategy of incorporating alkali-resistant (AR)-glass textile between the printed concrete layers. To validate the strategy, small-scale printed concrete beam specimens reinforced with one to three layers of textiles were tested under three-point bending. The results were compared to those obtained from equivalent ‘cast’ specimens. Comparable flexural behaviours were observed between the cast and printed textile reinforced concrete (TRC) specimens. Moreover, the flexural behaviours of printed specimens exhibited lower scatter than the flexural behaviours of cast specimens, which was probably due to the precise digitally controlled printing process. Future research should focus on the application of textile reinforcement in more complex 3D printed concrete structures.

Weiqiang Wang, Nikolaos Konstantinidis, Simon A. Austin, Richard A. Buswell, Sergio Cavalaro, Domenico Cecinia

Digital design, Technologies and Industrialization

Frontmatter
3D Concrete Printing - Free Form Geometries with Improved Ductility and Strength

Additive manufacturing (AM) or 3D printing is a rapid prototyping process that has captured the attention of architects and designers worldwide in the last few years. Multiple research groups and commercial entities are exploring different areas of 3D concrete printing (3DCP) with one of the main topics being the potential to improve the design freedom, while simultaneously achieving sufficient structural ductility. Based on the target design impression of a free form 3DCP structure, this study presents a number of 3DCP strategies to print arbitrary double-curved geometries with improved concrete ductility. A digital design-to-fabrication workflow was applied, consisting of defining parameters at various stages of the process. Two case study objects have been printed, both featuring double-curved surfaces achieved through cantilevered printing with support material, and by printing on a curved support surface, respectively. The former object acted as support for the latter. Entrained cables and secondarily added glass fibres were used to obtain ductility. The result is a double-curved 1 $$\times $$ 1 m panel with fibre-reinforced printed concrete, as well as a double curved print bed, reinforced with high strength steel cables.

Zeeshan Ahmed, Alessia Biffi, Lauri Hass, Freek Bos, Theo Salet
Print-Cast Concrete: Additive Manufacturing for 3D Printing Mortar in Robotically Fabricated Green Sand Molds

The research investigates architectural-scale concrete 3D printing in robotically fabricated recyclable molds for the fabrication of rapidly constructed, structurally optimized, architectural-scale concrete structures. The research of Print-Cast Concrete utilizes a three-dimensional extrusion path for deposition of material over a subtractive shaped sub-structure of CNC tooled compacted green sand. This process expedites the production of doubly curved concrete geometries by replacing traditional formwork casting or horizontal corbeling with spatial concrete arching deposited in relation to optimized structural loads. Creating robust non-zero Gaussian curvature in concrete, this method increases speed over typical pre-cast concrete fabrication practices, especially when producing mass customized unique elements. Through the casting component of this method, concrete 3D prints have greater resolution along the edge condition resulting in tighter assembly tolerances between multiple aggregated components. Addressing digital form finding and optimization, material behaviors, and novel utilization of robotic fabrication, this research work displays a series of key concepts within Print-Cast Concrete, advancing edge condition precision of extrusion-based 3DCP.

Christopher A. Battaglia, Martin F. Miller, Kho P. Verian
3D Printing of a Cement-Based Mortar in a Complex Fluid Suspension: Analytical Modeling and Experimental Tests

New techniques of 3D printing bring innovations to the construction industry. However, printing cantilevered elements or complex geometries which initially need some temporary support or lost formwork to ensure their mechanical stability is still challenging with 3D extrusion printing. A possible way is to print them directly in a yield stress fluid which could ensure their stability. In this study, a cantilevered cementitious material was printed in a Carbopol gel where the stability of the element and its geometry were thoroughly investigated. The rheological properties of the Carbopol gel and mortar were tailored to sustain the gravity effect of the cantilevered structure and an analytical model has been developed to propose an optimization method of the rheological properties of both the yield stress fluid and the mortar. In order to validate the model, experimental investigations have been carried out by images tracking. The developed model is reliable with the experimental data considered of the densities, the yield stress of both materials and the geometry of the printed shape. The prediction of failure by bending is possible, implying that the model could help making better designs of complex cement-based elements and optimizing their temporary support with elasto-plastic fluids.

Abdeslam Benamara, Alexandre Pierre, Abdelhak Kaci, Yannick Melinge
Experimental Study on 3D Printing of Concrete with Overhangs

The construction industry has been receiving in the recent past years the 3D printing technology as an emerging technology. Several researchers and companies have been reporting a number of case studies that show the possibilities of this technology regarding the dimensions, shape, building time, finishing and the material characteristics. It is commonly accepted that one of the big advantages of 3D printing is its possibility regarding the shape of the printed object since it can be easily changed each time a new piece is printed. This possibility raises some challenges regarding the printing limits, that are needed to the project design, such as to create overhangs. In this sense, a work was carried out to evaluate and optimize concrete printing mixtures and assess the 3D concrete printing of elements with overhangs. This paper presents the work carried out, showing the optimization of mixture composition for the binder/aggregate ratio, cement/fly ash ratio, and amount of superplasticizer and hardening accelerator, and evaluating their printing performance and mechanical properties. Printing of overhangs was possible for angles with the vertical direction till 17.5º.

Francis Brun, Florindo Gaspar, Artur Mateus, João Vitorino, Francisco Diz
Inspection Methods for 3D Concrete Printing

3D Concrete Printing (3DCP) is being used for off-site manufacture of many elements found in the built environment, ranging from furniture to bridges. The advantage of these methods is the value added through greater geometrical freedom because a mould is not needed to create the form. In recent years, research has focused on material properties both in the wet and hardened state, while less attention has been paid to verifying printed forms through geometry measurement. Checking conformity is a critical aspect of manufacturing quality control, particularly when assembling many components, or when integrating/interfacing parts into/with existing construction. This paper takes a case study approach to explore applications of digital measurement systems prior to, during, after manufacture using 3DCP and after the assembly of a set of 3DCP parts and discusses the future prospects for such technology as part of geometry quality control for the procurement of 3DCP elements for the built environment.

Richard Buswell, Peter Kinnell, Jie Xu, Norman Hack, Harald Kloft, Mehdi Maboudi, Markus Gerke, Peter Massin, Georg Grasser, Rob Wolfs, Freek Bos
DIGITAL CONSTRUCTION: 3D Printing for Performative Houses

The climatic change that is affecting widely our everyday life needs an adequate cultural and technological response in order to develop performative dwellings for sustainable living. The aim of this paper is to summarize the DIGITAL CONSTRUCTION [DC] applied research that we have developed for the Ance, the Italian National Association of Construction Companies. The research agenda is based on a multi-parametric approach to architectural design, integrating digital manufacturing technologies into the fabrication and construction process. Such approach investigates on the relation between industry 4.0 opportunities and the constraints of the world of building construction with the aim to bridge different knowledge through a series of concrete case studies. Therefore, the paper talks about the first [DC] design protocol for a modular house anti-seismic, robotically 3D printed and assembled on site using a mix of recycled materials.With this premise, we have developed a design to manufacturing methodology able to control many aspects at the same time: environmental performances, structural efficiency and end ergonomic comfort.

Paolo Cascone, Maddalena Laddaga, Federico Forestiero
Extended Lattice Model to Simulate the Printing Process of 3D Printed Cementitious Materials

This paper reports an extended lattice model for printing process simulation of 3D printed cementitious materials. In this model, several influencing factors such as material and geometric nonlinearity are considered. Using this model, green strength of cementitious material is investigated, deformation and crack pattern can be derived, which is close to the experimental result. Subsequently, numerical analysis of 3D printing is conducted for the simulation about printing process. Imperfections arising in the printing process can be incorporated and two failure modes including the elastic buckling and plastic collapse can be simulated through this model.

Ze Chang, Erik Schlangen, Branko Šavija
Quality Assessment of Printable Strain Hardening Cementitious Composites Manufactured in Two Different Printing Facilities

Over the past few years, several studies have shown the potential of three-dimensional concrete printing (3DCP) for applications in building and civil engineering. However, only a few studies have compared the properties of the fresh printing material and the quality of the printed elements from different printing facilities. Variations in the manufacturing conditions caused by the mixing procedures, the pumping device and the nozzle shape and/or dimensions may influence the quality of the printed elements. This study investigates the differences in the fresh and hardened properties of a printing material tested in two different printing facilities. The pump pressure and temperature experienced by the printing material during the printing session are monitored real-time. Hardened properties are measured for the printed elements, such as the bending capacity, the apparent density, and the air void content. The research shows that two different printing facilities may result in printed elements with relative differences in flexural strength and volumetric density of 49% and 7%, respectively.

Stefan C. Figueiredo, Anne L. van Overmeir, Karsten Nefs, Erik Schlangen, Theo A. M. Salet, Branko Šavija, Akke S. J. Suiker, Freek P. Bos
More Than Meets the Eye? Robotisation and Normativity in the Dutch Construction Industry

Construction robots are becoming more common in the Netherlands, but remain rarities in contexts aside from state-of-the-art factories owned by wealthy or technologically-orientated companies. In its current state, the construction industry would have to change significantly to make room for robots. To understand whether these changes are welcome or not, this paper presents qualitative, exploratory research concerning 10 stakeholders’ perspectives of robotisation and construction robots in the Dutch construction industry.

Chantal E. Muishout, Tom N. Coggins, H. Roel Schipper
Influence of Processing Parameters on the Layer Geometry in 3D Concrete Printing: Experiments and Modelling

This paper presents the numerical simulation results of a computational fluid dynamics (CFD) model that describes the layer shape in extrusion-based 3D Concrete Printing (3DCP). The simulation outcome is validated through an experimental program in which we investigated the influence of 3DCP processing parameters on the geometry of a single layer. Specifically, a set of single layers were printed using a Ø25 mm nozzle mounted on an 6-axis industrial robotic arm travelling at different speeds and with different layer heights. A fresh concrete – comprising CEM I 52,5 R - SR 5 (EA), limestone filler, fine sand, water, and admixtures (i.e. viscosity modifying agent, high-range water-reducing admixtures and a hydration retarder) – was pumped and extruded at a fixed volumetric rate. Once hardened, the extruded layers were sliced to examine the resulting cross-sections. Specifically, the cross-sections’ geometry were obtained by a custom image processing algorithm. Next, the extrusion flow was modelled with a CFD simulation using the software FLOW-3D®. The constitutive behavior of fresh concrete was modelled as a Bingham fluid, while the volume-of-fluid method was used to predict the free surface of the concrete and, thus, the layer geometry. The numerical results agree qualitatively with the experimental observations, enabling us to identify two non-dimensional 3DCP processing parameters that influence the overall cross-sectional shapes: 1) the geometric ratio between layer height and nozzle diameter, and 2) the ratio between the nozzle velocity and the extrusion volumetric flux. These findings – when complemented with a model describing the overall deformation of stacked layers – serve as the basis for correlating material rheological properties to 3DCP process parameters, promoting a better link between design and fabrication in a 3DCP context.

Raphael Comminal, Wilson Ricardo Leal da Silva, Thomas Juul Andersen, Henrik Stang, Jon Spangenberg
Automating Concrete Construction: Digital Design of Non-prismatic Reinforced Concrete Beams

The construction industry is responsible for nearly half of the UK’s carbon emissions, mainly due to the large amount of concrete used. Traditional formwork methods for concrete result in prismatic building elements with a constant cross-section, but the shear forces and bending moments that beams have to withstand are far from constant along their length. Up to 40% of the concrete in a typical beam could be removed. An iterative optimisation process has been implemented in a parametric modelling framework to generate and analyse optimal forms for non-prismatic beams that take into account the constraints imposed by the fabrication process, namely the use of fabric formwork. The aim of the resulting design tool is to facilitate the adoption of non-prismatic elements by the construction industry.

Eduardo Costa, Paul Shepherd, John Orr, Tim Ibell, Robin Oval
Free Deposition Printing for Space Truss Structures

This paper proposes a specific extrusion method for 3D printing of mortar called free deposition by the authors. It consists in letting a fine mortar flow through a moving nozzle above a support, here EPS foam. The aim is to obtain a regular lace, thus to avoid instability phenomena like coiling, and ensure a regular diameter, without stretching the lace. A rheological characterisation is proposed and is experimentally tested. This work takes place in the context of the building of space trusses in 3D printed concrete thanks to progressively assembled EPS foam blocks acting as support.

Romain Duballet, Romain Mesnil, Nicolas Ducoulombier, Paul Carneau, Leo Demont, Mahan Motamedi, Olivier Baverel, Jean-François Caron, Justin Dirrenberger
Rapid Composite Formwork: An Automated and Customizable Process for Freeform Concrete Through Computational Design and Robotic Fabrication

This paper presents a series of case studies that incorporate industrial robotics and rapid prototyping tools in the fabrication of custom molds for pre-cast concrete construction. The research documents the fabrication of molds for customizable pre-cast concrete panels in non-standard shapes with unique surface textures. Materials including sand, expanded polystyrene (EPS) and polylactic acid (PLA) are employed to produce robust, reusable, and multiple component molds and inscribe custom surface textures through concrete casting. The fabrication workflows incorporate the limits and constraints of digital processes such as fused deposition modeling (FDM) and robotic hot wire cutting (RHWC). The application of FDM and RHWC to concrete formwork fabrication presents unparalleled opportunities to produce performance embedded prefabricated concrete. In the production of jointing conditions, reinforcing and support structures, and the embedding of conduits and insulating cavities, FDM of concrete formwork in PLA offers an integrated process for an interdisciplinary design and production of smart concrete forms. By combining the flexibility, precision, and speed of RHWC and FDM, this research demonstrates the capacity of this process to efficiently produce high-fidelity, intricate, complex and performance embedded geometries in concrete.

Guy E. Gardner, Kristen Forward, Kim Tse, Karan Sharma
Simultaneous Reinforcement of Concrete While 3D Printing

In order to fully realize the disruptive nature proposed by concrete printing for the construction industry, key challenges need to be overcome to enable the scaling up of this technology. Chief amongst them is the incorporation of reinforcement to absorb tensile stresses and support the structure not only during the printing and curing but also during its service life. Numerous strategies have been tested that allow for embedding reinforcement in the form of filaments, cables, rods or mesh during and/or post printing. This paper explores a strategy for in-situ printing that attempts to embed discrete U-shaped reinforcement elements “staples” vertically interlocking layers simultaneously while printing. A tool, developed for this purpose, trails the extruder and discharges a reinforcement staple that embeds itself into the printed layers. The staples not only penetrate multiple layers, but also interlock to form a reinforcement matrix in the concrete along the vertical axis capable of absorbing limited amounts of tensile stresses. When subject to a 3-point bending test, the reinforced printed elements exhibited an increase in tensile properties. Nevertheless, further research into shape and size of the reinforcement staple is needed to achieve optimum results. Furthermore, with the assistance of robotic fabrication strategies, every position within the print geometry can be identified accurately and reinforcement can be positioned precisely. These positions and their properties/states can be informed by simulating the performance of the geometry under load conditions. The ability to place reinforcement discreetly and accurately can help localize the reinforcement to key stress areas within the geometry thereby optimizing its performance and the use of material.

Omar Geneidy, Sujay Kumarji, Alexandre Dubor, Aldo Sollazzo
Additive Manufacturing by Extrusion of Lightweight Concrete - Strand Geometry, Nozzle Design and Layer Layout

In additive manufacturing by concrete extrusion, objects are built up by depositing strands of fresh concrete. The form and size of the strands as well as the order in which they are arranged are decisive parameters for the properties of the resulting construction element. Extrusion of lightweight concrete can be used as a method to construct monolithic structural building elements with an optimized thermal insulation. They may have zones of different functionality and can be augmented by voids to house building technology. This paper discusses the possibilities and limitations in the design of appropriate strand structures and gives recommendations on how strand geometry, nozzle design and layer layout have to be chosen to obtain the desired results.

Klaudius Henke, Daniel Talke, Carla Matthäus
Extrusion Nozzle Shaping for Improved 3DP of Engineered Cementitious Composites (ECC/SHCC)

This paper focuses on the development of a nozzle steering and shaping system for concrete 3D printing (3DCP) of Engineered/Strain Hardening Cementitious Composites (ECC/SHCC). The investigation highlights the development of an integrated system that includes robotic end-effector tooling, automated control associated with the delivery and deposition processes, as well as multi-axis nozzle steering for enhanced surface quality of the printed components. The results are discussed along with demonstrated prototypes. While significant improvements to the speed and efficiency of 3DP cementitious materials have been developed in recent years, only a few precedents, discussed in the paper, have aimed to improve geometric surface quality of the final printed components. In addition to improving the surface quality, the designed extrusion shaping process has the potential to improve mechanical performance of ECC by maximizing interfacial surface area and improving fiber alignment. Material effects will also be discussed in relation to the development of the overall system. An overview of the geometric capabilities and limitations of the proposed system will be presented in comparison with existing 3DP techniques.

Wes McGee, Tsz Yan Ng, Kequan Yu, Victor C. Li
Buildability of Geopolymer Concrete for 3D Printing with Microwave Heating

A novel application of microwave heating was investigated to attain on-demand setting of concrete for the improvement in buildability of 3D printable geopolymer concrete. An integrated microwave heating facility at the nozzle head was replicated using laboratory experiments to understand its effect on the structural build-up of printed filaments. Different microwave heating durations of 5, 10 and 20 s were studied, and the fresh and hardened properties were compared with control specimen (without microwaving). At optimised heating, the interlayer bond strength was found to be increased by 127% and 122% at 7 and 28 days respectively. Furthermore, structural recovery of material after extrusion that governs its buildability, showed a tremendous improvement at optimum heating period. Control specimens could only recover up to 32% of the initial viscosity, whereas addition of microwave heating for 10 s enhanced the viscosity recovery to more than 70%. Effect of microwave heating on cement based concrete 3D printing was also studied to assess the robustness of this technique. Outcomes from this study proposes a novel approach of applying microwave heating to construction 3D printing to achieve “set-on-demand” printable concrete. This study provides a starting point to develop new generation of print head to combat issues faced by current 3D printing practices.

Shravan Muthukrishnan, Sayanthan Ramakrishnan, Jay Sanjayan
High-Resolution Additive Formwork for Building-Scale Concrete Panels

The paper discusses the technical developments in using 3D printed reusable formworks for the production of high-resolution building-scale concrete panels. The research looks at innovation in the production of concrete elements and extends current design possibilities with economically viable moulds. The relation occurring between the presented manufacturing technique, namely Fused Deposition Modelling 3D printing, and diverse designed morphologies is studied, assessing limits and opportunities of the application through an experimental setup. The first experiment analyzes a set of thermoplastics to identify suitable materials for the specific application in concrete formworks. The second experiment tests a consistent workflow for the digital modelling and optimization, 3D printing and concrete casting of a series of unique panels that challenge the formal possibilities of concrete manufacturing. The outcomes are analyzed quantitatively and qualitatively, in terms of formal possibilities offered by the approach, material behaviour, ease of manufacturing, and achievable precision, discussed for relevant applications in architectural envelopes.

Roberto Naboni, Luca Breseghello
Architectural Applications and Workflows for Additive Fabrication with Concrete

Although the fundamental scientific understanding of the relations between design, material, process, and product in additive manufacturing with concrete is already being explored, the relevance of this construction method for architecture and building is still limited. Additive manufacturing holds the promise that any computer-generated geometry can be produced. However, especially FDM-based processes are currently limited by geometrical and material-related restrictions. This study reflects on the digital workflow between architectural design, the geometry, and numeric data produced, construction processes and the material parameters in the research project “BauProAddi” on additive manufacturing with concrete. The purpose of the research is to integrate the knowledge of material and process specialists and requirements of the building industry at an early stage of the design process in a workflow for on-site additive manufacturing.

Pfeiffer Sven, Tobias Dorn, Tamino Hirsch, Clemens Ehm, Dietmar Stephan, Dimitrios Vassiliadis
ACDC: The Admixture Controlled Digital Casting and Its Application to Thin Folded Concrete Structures

Digital concrete technologies aim to minimize or eliminate the need for formwork, produce less waste, and build material efficient designs at increased productivity. This paper discusses how Admixture Controlled Digital Casting (ACDC) could address these aims by producing thin folded structures. For the process, a set on demand concrete composition was used to achieve minimal deformations when robotically filling weakly supported formworks. The formworks were constructed from bendable materials such as foil, geotextile or paper tensed between a frame on top and bottom and could be reconfigured for different geometries. The prototypes were assembled and post-tensioned to achieve a one-to-one scale fully functional architectural roof element. With the demonstrator presented, ACDC challenges the way we think about casting and formworks in the construction industry at the age of the 4th industrial revolution.

Anna Szabo, Lex Reiter, Ena Lloret-Fritschi, Timothy Wangler, Fabio Gramazio, Matthias Kohler, Robert J. Flatt
Robot-Controlled Fabrication of Sprayed Concrete Elements as a Cyber-Physical-System

In order to make the mass production of free-formed concrete elements for architectural and engineering projects possible and financially achievable new ways of production has to be developed. This paper presents a robot-controlled fabrication of sprayed concrete elements as a cyber-physical-system. It utilizes the concept of Industry 4.0 and IoT-technology together with automatized fabrication methods and developed sophisticated software solutions for communication, planning, modeling and analyzing. This concept bases on a decentralized system of fabrication, analytic and path-planning services connected with a mqtt-communication protocol. Next to the system- and software development a special material based on concrete is developed, shotcrete, which is adapted to needs for the application of spraying.

Ilija Vukorep, Gregor Zimmermann, Tino Sablotny
Reinforced Particle-Bed Printing by Combination of the Selective Paste Intrusion Method with Wire and Arc Additive Manufacturing – A First Feasibility Study

The selective paste intrusion (SPI) is a particle-bed based Additive Manufacturing technology, which spreads particles in small layers and bonds them locally with cement paste. One advantage of this technology compared to other AM processes is that no support structures for cantilevers are required. Furthermore, SPI-made components achieve almost isotropic compressive strength (>70 MPa), high durability, and shape accuracy. However, to qualify the SPI process for the production of structural concrete elements, the inclusion of reinforcement is necessary.This paper presents an approach to print the reinforcement during SPI simultaneously by using Wire and Arc Additive Manufacturing (WAAM). WAAM enables the fabrication of geometrically complex steel reinforcement structures with high build-up rates, whereby properties similar to those of construction steel can be achieved. This allows producing reinforced concrete structures according to the principle “form follows force”, which leads to ecological and economical components.The major challenge that arises from the combination of WAAM and SPI is the occurrence of high temperatures (approx. 1600 °C) during WAAM. Thus, a detrimental effect on the penetration behaviour and loss of strength of the concrete matrix is expected. This paper focusses on the heat propagation during WAAM and its potential effect on the paste rheology.The results of the rheological measurements show that an application of both tested cement paste mixtures is possible for welding distances of approx. 62–68 mm and 82–84 mm to the particle-bed which reduce the temperature to 70 °C and 50 °C without additional cooling.

Daniel Weger, Daniel Baier, Alexander Straßer, Sophia Prottung, Thomas Kränkel, Andreas Bachmann, Christoph Gehlen, Michael Zäh
Knitting Concrete

Due to concrete’s traditional role as a casting material its appearance as a uniform solid mass is one of the material’s most distinct traits. When poured in a mould fresh concrete adheres to the shape of the formwork and material distribution is not adaptable at a more detailed level. This paper explores how deposition-based additive manufacturing opens up new opportunities for controlling the distribution of concrete at a previously neglected intermediate scale - the meso-scale. By adopting principles of knitting to toolpath planning, the paper presents a computational method for varying the density, porosity, and surface articulation of the material, previously inconceivable due to the limitations of formwork.

Helena Westerlind, José Hernández
Concrete 3D Printing: System Development, Process Planning and Experimental Results

Concrete 3D printing is a new construction technology that deposits the concrete from the bottom up layer by layer. The printer and process used in this technology are different from traditional extrusion-based printing technology. This work developed a concrete 3D printing system and its process planning from the point of considering the “large-scale” of the printer and the thixotropy of the concrete. Firstly, the components of the printer were introduced, and the screw as the key part of the extruder subsystem was optimized based on ANSYS Fluent. Secondly, the key technical problems in the process of tool path generation and parameter design were discussed. Lastly, the feasibility of the concrete 3D printing system and process planning were verified by a pavilion printing experiment.

Yu Wang, Shuaishuai Li, Tian Qin, Ying Yu, Jianzhuang Xiao
Shape Accuracy Evaluation of Geopolymer Specimens Made Using Particle-Bed 3D Printing

The primary benefit offered by the particle-bed 3D concrete printing process (3DCP) is the high flexibility in design for manufacture of concrete components with complex geometrical features. Accuracy evaluation has become a critical issue need to be overcome before a more widespread application of the particle-bed 3DCP technique in construction. This study reports an inexpensive image acquisition and processing technique using a flatbed scanner for shape accuracy evaluation of geopolymer specimens made using the particle-bed 3DCP process. A set of image processing algorithms is developed to extract useful shape information from the scanned images without any human intervention. Centroid distance function is used as the shape error representation under the Polar coordinate system for the shape error measurement. A color-labeled map in conjunction with the root mean square error are used for assessment of the shape accuracy. The results show that the developed method can satisfactorily be used for shape accuracy measurement of the particle-bed 3D printed specimen.

Ming Xia, Behzad Nematollahi, Jay Sanjayan

Sustainability, LCA and Economical Analyses

Frontmatter
Environmental Impacts of 6-Axes Robotic Arm for 3D Concrete Printing

This paper presents an environmental assessment of a 6-Axis robotic Arm for extrusion-based 3D Concrete Printing technology using Life Cycle Assessment method. In addition, the other components of a printing cell are assembled within a life cycle model and the relative contribution of the cell to the printing process is evaluated. The results show that, per one hour of printing, an environmental impact coming from the production phase of robotic printing cell would represent 2,2 kg CO2 Eq for the category of Climate Change. Hourly contributions are also calculated for the rest of environmental indicators.

Kateryna Kuzmenko, Adélaïde Feraille, Olivier Baverel, Nicolas Roussel
Preliminary Productivity Analysis of Conventional, Precast and 3D Printing Production Techniques for Concrete Columns with Simple Geometry

Significant advancement has been made in the field of additive manufacturing as applied to the construction industry. However, little attention has been paid to the implications of additive manufacturing, in particular 3D concrete printing (3Dcp), on the productivity of construction projects. The purpose of this study is to conduct a preliminary analysis of the productivity, measured in terms of cost and time per amount of material, for the construction of simple geometry concrete columns using conventional, precast, and 3Dcp techniques. The complexity of the geometry that can be achieved using 3Dcp was not factored in the comparison. Discrete-event simulations with data from the Concrete Choreography project were run. These results were compared with the productivity level achieved in the construction of a reinforced concrete column using conventional and precast construction methods. As expected, it was found that for the construction of simple geometry columns, 3Dcp is still not as productive as the other methods. These results should not be misunderstood as a lack of competitiveness of 3Dcp versus traditional methods. On the contrary, these results highlight the many benefits and capabilities of 3Dcp, which surpass the cost and time components. Some of them include topological optimization, geometric freedom, as well as increased transparency during the planning, design, and construction processes, which bring tremendous value to the 3Dcp elements. Quantifying these benefits is not trivial and is beyond the scope of this study; however, ongoing research is being conducted to address that.

Raitis Pekuss, Borja García de Soto
Preliminary Study of the Implications of 3D Printing on the Construction Supply Chain

Construction projects face several challenges, such as budget overruns, project delays, rework, and waste of materials. Most of them are caused by lengthy and complex supply chains involving multiple entities, processes, and interactions. Studies suggest that technologies like robotics, 3D printing, and artificial intelligence have the potential to reduce the complexity of traditional supply chains. In the context of 3D concrete printing, researchers have focused on the robotic systems and suitable construction materials. However, limited attention was focused on the impact on the construction supply chain (CSC). Although studies in healthcare and aviation investigated the implications of new technologies in their supply chains, the outcome cannot be directly applied to the CSC. In addition, studies that assessed the impact of new technologies on the CSC are limited and mostly qualitative. This study addresses this gap by developing a methodology to simulate the implications of 3D printing on the CSC. The methodology adopted contains four elements: 1) Develop supply chain networks, b) Identify input parameters c) Simulate the supply chain networks, and d) Analyze and discuss results. Results from this preliminary study indicate 15.8% and 52.6% lesser entities in CSC-2 and CSC-3, respectively, when compared to CSC-1; a 0.2% and 28.2% decrease in overall effort in CSC-2 and CSC-3. respectively, when compared to CSC-1; and an overall cumulative performance increase of 18.5% and 51.6% in CSC-2 and CSC-3, respectively, when compared to CSC-1. Findings from this study can help construction professionals to understand the implications of 3D printing in the CSC and to assist in easier adoption into the industry. However, caution should be exercised when generalizing to other CSC scenarios or the entire construction industry.

Ayyagari Ramani, Borja Garcia de Soto

Applications and Case Studies

Frontmatter
Fast Complexity: Additive Manufacturing for Prefabricated Concrete Slabs

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.This paper puts forward a novel fabrication method for the construction of materially lean concrete slab systems using two different Additive Manufacturing (AM) processes: Binder Jetted (BJ) formwork and 3D Concrete extrusion Printing (3DCP). A reusable formwork is fabricated first, using the BJ, and the loadbearing part of the slab element is then directly 3D-printed on top. This method combines the essential advantages of the two fabrication techniques: the high precision of BJ and the higher fabrication speed characteristic to 3DCP.The described 3DCP process uses a set on demand concrete that is activated inline, immediately before leaving the extruder-tool. A technical innovation is identified in dynamically varying the amount of activator for changing contour length.

Ana Anton, Andrei Jipa, Lex Reiter, Benjamin Dillenburger
Architectonic Explorations of the Possibilities of 3D Concrete Printing: The Historic Building Fragment as Inspiration for New Applications with 3D Concrete Printing in Architecture

The scope of this one-year research, carried out within a graduation studio consisting of 16 students, was to explore how this novel technique can lead to the development of new architectural forms. The graduation-studio called ‘De Centrale Gent, with 3D Concrete Printing’ explored the technique of 3DCP within the historical city of Ghent and through researching, designing and testing by printing.Fase 1: We investigated what the application of this technique could mean for architecture itself, taking the historical facades of the city of Ghent as an inspiration for the development of new printing techniques in 3DCP. We focused on developing a design-‘instrumentarium’ that is specific for the concrete printing technique, as well as on techniques that could push the boundaries of the so far known possibilities in shape, materiality’s, and ornamentation with Concrete Printing in relation to architecture. The research aimed to discover new aesthetic and sustainable qualities in 3D-printed manufacturing, through 5 main topics: light, joints, and patterns, supporting material, and assembling. The research was developed at the Eindhoven University of Technology and the prints were made with the 3DCP in the laboratory of the faculty of the Built Environment.Fase 2: Printing prototypes: A selection of results and findings of the one-year research in the graduation studio have been elaborated and collated into a new final product and summary design for three columns, featuring new aesthetic possibilities in 3DCP. The three columns were printed and exhibited at the DDW 2019

Juliette Bekkering, Barbara Kuit, Alessia Biffi, Zeeshan Yunus Ahmed
A Robust Mortar and Printing System

In this paper the motivation and the choices for a mortar that is being used in the print factory jointly owned by Weber Beamix and BAM is discussed in general. Attention will be given to the choice of binder for the mortar. The results obtained during quality control from a large project will clearly show that with this mortar concept monolithic objects can be obtained with no influence of the printing direction on the parameters measured (compressive strength and flexural strength). Also some results from interfacial fracture toughness measurements will be presented. These results also indicate the formation of monolithic material. Results of durability tests (frost/thaw de-icing salt resistance) will be presented showing that this material is safe to use in outdoor applications. The printing system with an in-line quality monitoring system of the fresh mortar will be presented. The modifications of the mixing unit have led to a finely controlled water dosage during the mixing step of the mortar. With the in-line sensor, measuring the yield of the pump, the viscosity and the density of the pumped mortar, it has been possible to implement a feedback loop to the water dosage and to the yield of the pump. The yield of the pump is very important especially when layers adjacent to each other are required to form a monolithic structure. With the feedback loop of the viscosity measurements to the water dosage it has been possible to print with this mortar with a very low water dosage over long periods of time (6–8 h.) and still not having issues with blockage of hoses etc.

J. Blaakmeer, B. Lobo
Design and Fabrication of a Non-standard, Structural Concrete Column Using Eggshell: Ultra-Thin, 3D Printed Formwork

This paper describes the design and fabrication process of a concrete column cast in ultra-thin, 3D printed formwork, using a process known as Eggshell. The column was prefabricated as part of a real-world construction project, serving as the main load-bearing element for a reciprocal timber frame structure. The fabrication of the column required upscaling of the Eggshell process, to allow for the fabrication of elements of an architectural scale. Furthermore, several challenges had to be addressed such as: integration of reinforcement, establishing the formwork design space, and scaling up the 3D printing process. For the production of the final column a 1.5 mm thin formwork was 3D printed, after which it was combined with a prefabricated reinforcement cage and filled with concrete in a set-on-demand casting process. The successful realization of the project provides a first example of a full-scale building element produced with the Eggshell fabrication process. By 3D printing the formwork, geometrical freedom in concrete construction is greatly expanded, as well as formwork waste reduced.

Joris Burger, Ena Lloret-Fritschi, Nizar Taha, Fabio Scotto, Thibault Demoulin, Jaime Mata-Falcón, Fabio Gramazio, Matthias Kohler, Robert J. Flatt
Complex Architecture in Printed Concrete: The Case of the Innsbruck University 350th Anniversary Pavilion COHESION

During the summer semester 2018–2019, a 3D concrete printed (3DCP) pavilion consisting of 47 unique free form parts was realized in the central square of the engineering campus of the University of Innsbruck. In a period of just 11 weeks, it was designed, engineered, manufactured, and assembled on-site to provide an attractive meeting space for students and staff alike. The parts were printed off-site in an extrusion layering process, using variable print speeds and filament heights to obtain radially fitting segments that were transported to the building site. A selection of parts was reinforced with innovative woven carbon fiber reinforced polymer (CFRP) strands, while the others were reinforced with in-laid conventional reinforcement bars. The parts were bolted to an on-site cast fibre-reinforced concrete floor and the seams were sealed with a silicone adhesive. This paper presents the entire project, including architectural considerations, geometrical parametric modelling, structural (safety) principles and design, manufacturing, and construction, including connections.

G. Grasser, L. Pammer, H. Köll, E. Werner, F. P. Bos
Shotcrete 3D Printing Technology for the Fabrication of Slender Fully Reinforced Freeform Concrete Elements with High Surface Quality: A Real-Scale Demonstrator

This paper presents the recent advances in the development of a novel 3D concrete printing technology called Shotcrete 3D Printing (SC3DP). In order to demonstrate the unique assets of this technique a design and fabrication strategy for fully reinforced, double curved concrete demonstrator featuring high surface quality was developed, and is described in detail in this paper. In particular, two topics were highlighted in this demonstrator, firstly the integration of structural reinforcement in both principal directions and secondly an automated surface finishing process for a high-quality concrete surface. This combination of additive fabrication and formative and subtractive postprocessing was demonstrated at the unique large-scale Digital Building Fabrication Laboratory (DBFL) of Technische Universität Braunschweig. The result of this fabrication experiment, a 2.5 * 2.3 * 0.18 m concrete wall element, is finally discussed in relation to the state of the art in 3D concrete printing.

Norman Hack, Harald Kloft
UHPFRC Pavilion of 3-Dimentional Pentagon Tiling

The pavilion of ultra-high performance fiber reinforced concrete (UHPFRC) was fabricated in the form of 3-dimensional pentagonal tiling by wood formwork. Mann/McLoud/Von Derau discovered a 15th monohedral tiling convex pentagon in 2015 using a computer algorithm. Each unit of UHPFRC pentagon in 2-dimensional plane is the same but they are changed into different shapes in 3-dimensional vault type for the pavilion. To generate the 3-D shape two attractor points were located on the ground level. The transformation from 2-dimensional pentagonal tiling into 3-D vault was generated by Reino® and Grass hoper®. The data of formwork for units of UHPFRC was generated and then fabricated by wood. The fabrication of wood formwork relies on 6-axis robot cutting. To give structural stability of the vault the thickness of lower units was increased. The advantage of flow of UHPFRC enabled us to place UHPFRC into each of wood formworks. The lateral pressure of young UHPFRC was controlled by external screw jacks to avoid the deformation of wood formworks during curing. The connections between units relied on bolts and elastic pads. The connection behavior of bolts to transfer shear was guaranteed by the experimental program for strength.

Sung-Gul Hong, John Juhyung Chun, Sung-Hoon Kang, Minsoo Kim
Field Considerations for Deploying Additive Construction

While the additive construction printing systems and applications have grown in size, number and types, they represent and benefit specific needs of individual programs or business interests. Work of start-up companies, construction firms, and research institutions has focused on applications for the commercial construction industry. The development of printing systems are directly connected to the application. Each application requires a different range of mobility, from stationary machines to machines capable of being setup in minutes instead of hours. These printers are based on pre-existing equipment types including gantry, robotic arm, cable bot, and jib crane. Alternatively, this technology has clear applications for Humanitarian Assistance and Disaster Response (HADR) and military deployed operations. Unique requirements of these operations include the necessity for using highly deployable mobile printers with local or indigenous materials. The US Army Construction Engineering Research Laboratory (CERL) has developed collapsible deployable printing systems, trained military personnel to independently operate these systems, and performed demonstrations using locally available materials with applicable reinforcing methods. The results of this work not only applies to military construction, but to the construction industry. Through larger demonstrations, CERL has started to confront the struggles that the industry faces. These challenges include continuous equipment operation and maintenance cycles, the development of printable mixes with variable local materials, the development of printing systems that can accommodate variations in materials, and applicable construction methods.

Eric Kreiger, Brandy Diggs-McGee, Tanner Wood, Bruce MacAllister, Megan Kreiger
Sustainable Reinforced Concrete Beams: Mechanical Optimisation and 3D-Printed Formwork

The embodied energy of a building is not only but essentially determined by the quantity of material in its structure. Current fabrication techniques of optimised reinforced concrete (RC) structural elements have not proved sufficient economic competitiveness to be broadly accepted by the construction industry. This partly explains why the construction industry has not yet been able to reduce the embodied energy of newly-constructed buildings or civil works. However, most of the researches driven in the academic world on digital fabrication with concrete are focused on the construction of non-standard structures. The application of digital fabrication to standard structures could help bridge the gap between the need for lower-carbon structures and the economic interest of players in the construction industry.This paper questions the compatibility of existing building codes with digital manufacturing techniques and presents a novel method for the fabrication of sustainable optimised reinforced concrete beams, compliant with EN 1992-1-1 design requirements.

Sébastien Maitenaz, Romain Mesnil, Paul Onfroy, Nicolas Metge, Jean-François Caron
Thermal and Sound Insulation of Large-Scale 3D Extrusion Printing Wall Panel

A 3D printing technology for construction has been developed for some decades. This technology presents a great potential applying into existing construction and is believe to encourage a sustainable construction. This is because of its perceptible benefits of free-form fabrication without formwork, enhanced product quality, minimized waste produced, and reduced labor workforce. The technology also presents consequential automated advancements and is poised to be a disruptive force in the evolving global construction industry. Presently, it is found that many cementitious materials have been developed to have the fresh characteristics suitably for a large-scale extrusion 3D printer. Previous research reported that a large-scale 3D-printed wall panel with the size larger than 1-m by 1-m exhibited better thermal and sound insulating performance characteristics, when compared to a traditional concrete wall panel. These better performance characteristics were indicated when using a high-strength 3D extrusion printing wall panels with the 28-day compressive strength value greater than 50 MPa. The large-scale 3D extrusion printing wall panels having normal 28-day compressive strengths of 25 MPa and 35 MPa should be assessed. This work aims to present results on investigating its thermal and sound insulating performance of the 3D extrusion printing wall panels with mortar having different compressive strengths. Three mortar types having various 28-day compressive strengths are developed and printed into the wall panel with different surface textures using the large-scale 3D extrusion printer. The printed wall panels are investigated on their benefits for thermal and sound insulating performance. In additional, other hardened performance characteristics of mortars developed herein such as density, porosity, flexural strength, drying shrinkage, and thermal conductivity of the mortar materials are evaluated.

Lapyote Prasittisopin, Kittisak Pongpaisanseree, Patiphat Jiramarootapong, Chalermwut Snguanyat
Backmatter
Metadata
Title
Second RILEM International Conference on Concrete and Digital Fabrication
Editors
Dr. Freek P. Bos
Dr. Sandra S. Lucas
Dr. Rob J.M. Wolfs
Prof. Theo A.M. Salet
Copyright Year
2020
Electronic ISBN
978-3-030-49916-7
Print ISBN
978-3-030-49915-0
DOI
https://doi.org/10.1007/978-3-030-49916-7

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