CPTworldwide CONSTRUCTION PRINTING TECHNOLOGY - Digital Concrete 2020

 
CPTworldwide CONSTRUCTION PRINTING TECHNOLOGY - Digital Concrete 2020
CPT
worldwide
                                 CONSTRUCTION
                                 PRINTING
                                 TECHNOLOGY
                                                        2.2020

                                                www.cpt-worldwide.com

                                                 MEDIA PARTNER

GREEN WAY TO 3D PRINT

3D PRINTED CUSTOM BLOCK PAVEMENT AND OBJECTS

INDUSTRIAL CONCRETE PRINTING SOFTWARE

3D PRINTED STAIR MOLDS
CPTworldwide CONSTRUCTION PRINTING TECHNOLOGY - Digital Concrete 2020
3D printed homes
         for homeless in Austin
                                  page
        Bedroom, bath, kitchen,
    living room and large porch   60

 © www.iconbuild.com

2002_cpt_c1-4.indd 2                     06.05.20 21:05
CPTworldwide CONSTRUCTION PRINTING TECHNOLOGY - Digital Concrete 2020
EDITORIAL

                          GLOBAL TRENDS
                          AND CREATIVE SOLUTIONS
                                                                    The whole world is holding its breath while the Corona
                                                                    pandemic is affecting our private lives and professional work
                                                                    in a completely unprecedented manner. However, we have
                                                                    no choice but to move on and plan for the future. We need to
                                                                    develop creative solutions in order to avoid further standstill as
                                                                    much as possible. During the past weeks and months, countless
                                                                    trade fairs and technical conferences in the construction sector
                                                                    had to be cancelled, and organizers are all facing the same ques-
                                                                    tion: should the events be postponed to a later date, or cancelled
                                                                    altogether?

                          In some instances, both of these choices may be unsuitable, and a more innovative approach has to
                          be considered. The organizers of Digital Concrete 2020, which under normal circumstances would
                          have taken place at the beginning of July at Eindhoven University of Technology in the Netherlands,
                          are setting a good example in this regard. This unique event is an absolute highlight for the global
                          construction printing industry and a cancellation is certainly not an option. However, postponing the
                          event to a later date is also close to impossible, considering that the participants would have to travel
                          from all over the world, which at the moment is very difficult to plan and organize. Consequently, an
                          alternative solution will be implemented, which probably is the only sensible response to the situation:
                          Digital Concrete 2020 will take place as a full online conference.

                          The organizers simply reverted to modern technology to provide maximum value for their clients and
                          partners. This creative approach is fitting for this cutting-edge technical event, as it perfectly well reflects
                          the developments in 3D construction printing technology. Construction printing is at the forefront of tech-
                          nical innovation, attracts an increasing international attention, and paves the path into the future of con-
                          struction and manufacturing methods. On all continents, experts are dedicating their professional efforts
                          to this technology and contribute to the translation of an idea into a global trend. In the current edition of
                          CPT Construction Printing Technology, we report on social housing projects in the USA and the construc-
                          tion of medical facilities in China. We hope that you, dear readers, find inspiration in these projects, which
                          were successfully completed with 3D printing technology.

                          Without doubt, Contour Crafting belongs to the pioneers of concrete printing and we are pleased to pres-
                          ent you with a comprehensive account of the company. Also discussed in this edition – a Russian company
                          that is investigating the application of geopolymer concrete in 3D printing. With respect to research and
                          development, we have included interesting technical papers by the Technical University of Dresden and
                          the Danish Technological Institute.

                          Despite the difficult circumstances faced by us all, we are pleased to have delivered another edition of
                          CPT Construction Printing Technology that is true to its aim of being at the forefront of the industry.
                          Enjoy reading through the journal and stay healthy!

                          Any further suggestions? Would you possibly like to publish in CPT? Please feel free to contact me
                          anytime at editor@cpt-worldwide.com
                                                                                       Dipl.-Ing. Mark Küppers, editor in chief

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CPTworldwide CONSTRUCTION PRINTING TECHNOLOGY - Digital Concrete 2020
CONTENT

                                   6

                              66

                                   32

                              44

                                   54

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CPTworldwide CONSTRUCTION PRINTING TECHNOLOGY - Digital Concrete 2020
CONTENT

                  NEWS
             6   Contour Crafting Corporation will print                  10 3D Concrete printing and other digital
                 four low-income housing units in Los Angeles                concrete construction technologies
                 Los Angeles County Development Authority (LACDA) Award      2nd German Industry Seminar, October 28th, 2020, Dresden
             8   Additive Manufacturing in Construction (AMC) –           11 Acciona launches global 3D printing center in Dubai
                 The challenge of large scale                                Culmination of an internal development process
                 DFG funds new CRC/Transregio at TU Braunschweig          11 Unlocking new potential
                 in collaboration with Technical University of Munich        New partnership
             9   Digital Concrete 2020                                    12 Exclusively designed furniture
                 Full online conference                                      More than just an eye catcher

                                                                              RESEARCH & DEVELOPMENT
                                                                          14 CONPrint3D
                                                                             On-site, large-scale, monolithic 3D concrete printing
                                                                          23 Towards sustainable 3D Concrete Printing
                                                                             Next Generation 3D-printed Concrete Structures (N3XTCON)

                                                                              MATERIALS
                                                                          32 Green Way to 3D Print
                                                                             Geopolymer concrete
                                                                          37 Partnership to develop printable concrete
                                                                             Specially formulated concrete

                                                                              DIGITAL PLANNING
                                                                          38 Industrial concrete printing software
                                                                             Specifically designed to assist research and industry

                  PRODUCTION & APPLICATION                                    PROJECTS
             42 3D concrete printing with an industrial robotic arm       60 3D printed homes for homeless in Austin
                Next step towards digital project implementation             Bedroom, bath, kitchen, living room and large porch
             44 3D printed stair molds                                    64 3D printed isolation houses
                Reach new design heights                                     Case studies
             48 Contour Crafting: A revolutionary platform technology     66 Live 3D construction printing of a small house
                Pioneer of construction 3D printing                          In front of thousands of visitors
             54 3D printed custom block pavement and objects
                New approach
             58 Robots bring the idea from birth to realization
                3D printing of buildings and production
                of non-standard concrete moulds

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NEWS

              CONTOUR CRAFTING CORPORATION
              WILL PRINT FOUR LOW-INCOME
              HOUSING UNITS IN LOS ANGELES
              Los Angeles County Development Authority (LACDA) Award

              In an open competition, proposal solicitation (RFP NO.           novative project will showcase the potential of the Contour
              LACDA19-125) and selection process, the Los Angeles              Crafting technology in addressing the homelessness problem
              County Development Authority (LACDA) has awarded                 in Los Angeles and worldwide. The freedom in the architectur-
              Contour Crafting Corporation (CC Corp) a project on using        al design and high degree of customization which is possible
              construction 3D printing for affordable housing.                 using CC Corp technologies will be utilized to create a livable,
                                                                               sustainable and vibrant community.
              CC Corp, in collaboration with the design firm HDR and the
              supportive services provider Volunteers of America Los Ange-     In this project, CC Corp’s engineered printing mixture will be
              les (VOALA) is tasked with building four low-income housing      used to print safe and durable houses. Various fresh and hard-
              units at a designated site in the Los Angeles County. This in-   ened properties of the CC Corp’s printing mixtures have been

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CPTworldwide CONSTRUCTION PRINTING TECHNOLOGY - Digital Concrete 2020
NEWS

            tested in order to provide conclusive data and assure the sat-      content, and the result is a more sustainable and eco-friendly
            isfactory performance of the material. This mixture includes        construction material. CC Corp is currently investigating the
            gravel, and therefore it is classified as concrete as opposed to    use of supplementary cementitious materials to further re-
            mortar which is commonly used by many other construction            duce the Portland cement content in its engineered printing
            3D printing systems.                                                mixture in order to further improve the sustainability of future
                                                                                printed buildings.
            Use of concrete for building these units is advantageous due
            to numerous technical, economical, and environmental con-           Finally, during this project CC Corp and VOALA will organize
            siderations. From a technical standpoint, using gravel can im-      a job training program. Multiple workshops and hands-on
            prove the dimensional stability of the hardened material, can       training sessions will be held to educate local workers and
            reduce the risk of cracking in the structure, and can improve       vulnerable population on practical aspects of the CC tech-
            the long-term durability of the printed structure.                  nology and to engage local workers in different stages of this
                                                                                innovative construction project.
            From an economical viewpoint, inclusion of large aggregate
            in CC Corp’s printing mixture has made it possible to reduce
            the Portland cement content, which is the most expensive in-
            gredient of cementitious mixtures. Consequently, the cost of
            CC Corp’s printing material is very similar to the cost of tradi-
            tional concrete which has been used for decades.

            The third advantage of inclusion of large aggregates in                                Contour Crafting Corporation
            CC Corp’s printing mixture is reduction in the carbon footprint                        215 South Douglas Street, El Segundo
            of the printed units. Production of Portland cement produc-                            Los Angeles, CA 90245, USA
            es significant amount of CO2. Inclusion of gravel in the print-                        www.contourcrafting.com
            ing mixture makes it possible to reduce the Portland cement

                                                                                                                           CC Corp, in collaboration
                                                                                                                     with the design firm HDR and the
                                                                                                                  supportive services provider Volunteers
                                                                                                                 of America Los Angeles (VOALA) is tasked
                                                                                                                  with building four low-income housing
                                                                                                                     units at a designated site in the
                                                                                                                            Los Angeles County.

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CPTworldwide CONSTRUCTION PRINTING TECHNOLOGY - Digital Concrete 2020
NEWS

              ADDITIVE MANUFACTURING
              IN CONSTRUCTION (AMC) –
              THE CHALLENGE OF LARGE SCALE
              DFG funds new CRC/Transregio at Technische Universität Braunschweig
              in collaboration with Technical University of Munich

              Additive Manufacturing (3D printing) is a new manufactur-         The basic principles of Additive Manufacturing are based on
              ing technology that is now introduced in many industrial          digitally controlled layer-by-layer component design, without
              sectors. If the potential of this technology is transferred       any mould making or forming processes. “This represents a
              to the large scale of construction, new design possibilities      paradigm shift to the predominantly manual construction
              and more efficient, resource-saving construction meth-            techniques, which promote simple element forms and ineffi-
              ods can be created. The aim of the TRR 277, funded by the         cient material utilization,” says the designated spokesperson
              German Research Foundation (DFG), is to fundamentally             Professor Harald Kloft of the Institute of Structural Design at
              investigate Additive Manufacturing in interdisciplinary re-       the TU Braunschweig. Against the background of the enor-
              search for the implementation into construction industry.         mous demand for resources in the construction industry with
              The DFG is establishing a total of ten new Collaborative          its significant contribution to global CO2 emissions, this novel
              Research Centres to strengthen cutting-edge research at           technology will provide an efficient use of material.
              universities. Starting on 1 January 2020, they will initially
              receive a total of around 101 million euros in funding for        “Great news – for a project in which scientifically outstanding
              four years.                                                       colleagues are working in an exciting field for research,” says

                    Example of Additive Manufacturing in Construction (AMC)
                at the Institute of Structural Design (ITE), TU Braunschweig.

              Credit: ITE

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NEWS
            Professor Anke Kaysser-Pyzalla, President of the TU Braun-
            schweig. “I am proud of the team effort across the borders of
            TUM and TU Braunschweig and look forward to further coop-
            eration on an issue that is highly relevant to society and the
            economy”.

            “I am particularly pleased with the positive assessment of
            the transregional project,” said Professor Peter Hecker, Vice
            President for Research and Young Scientists at the TU Braun-
            schweig. “The SFB/TRR is an award for our research focus
            ‘City of the Future’ and contributes to raising the profile of
            civil engineering at the TU Braunschweig”.

            The two universities, TU Braunschweig and TUM, have been
            working together for many years in various fields of engineer-
            ing disciplines and in particular in the field of Additive Man-
            ufacturing. Due to the excellent equipment with large-scale
            research facilities at both locations, a wide variety of mate-
                                                                                    Visualization
            rial-process combinations can be investigated right from the        of TRR277.
                                                                                                                                  Credit: ITE

            beginning.

            The TRR 277 promotes the future strategic orientation of both       Transregional projects (TRR) are a variant of the classical Col-
            universities. Thus, the CRC/Transregio is integrated into the       laborative Research Centres. This enables universities in Ger-
            research focus City of the Future/Future City at TU Braun-          many to closely network and apply for and carry out research
            schweig and strengthens the action agenda TUM.additives of          projects on fundamental issues across all locations.
            the TUM as part of the “Bavarian Additive Manufacturing Clus-
            ter”. The TRR 277 aims to contribute to the development of
            Additive Manufacturing as a key technology for the digitaliza-
            tion of the construction industry, with increased productivity
            and an efficient use of resources.
                                                                                Technische Universität Braunschweig
            Collaborative Research Centres and Transregional Projects           Institute of Structural Design (ITE)
                                                                                Prof. Dr.-Ing. Harald Kloft
            Collaborative Research Centres enable innovative, challeng-         Pockelsstraße 4, 38106 Braunschweig, Germany
            ing and long-term research projects to be carried out in a col-     T +49 531 391 3571
            laborative effort and are thus intended to serve as focal points    h.kloft@tu-braunschweig.de
            and structures for the applicant universities.                      ite.tu-braunschweig.de

            DIGITAL CONCRETE 2020
            Full online conference

            Due to the Corona virus outbreak, the Digital Concrete             multi-day workshop in Eindhoven will be organized
            2020 Organizing Committee, in close coordination with              in 2021, focusing particularly on interaction within the
            RILEM, has decided to reshape the conference in a differ-          Digital Concrete-community. This event will include a PhD
            ent format.                                                        course, an excursion and site-visits, too.

            Digital Concrete 2020 will take place as a full online confer-
            ence, in the same week as originally planned, starting on
            July 6. Over the course of 4 days, there will be online ses-
            sions of approximately 4 hours, including keynote lectures,
            parallel sessions, Q&A options, and meet & greet facilities.
            In addition to the online conference, a shorter on-location        www.digitalconcrete2020.com

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CPTworldwide CONSTRUCTION PRINTING TECHNOLOGY - Digital Concrete 2020
NEWS

              3D CONCRETE PRINTING
              AND OTHER DIGITAL CONCRETE
              CONSTRUCTION TECHNOLOGIES
              2nd German Industry Seminar, October 28th, 2020, Dresden, Germany

              3D concrete printing is particularly suitable both for dig-      The seminar offers an exhibition options for national and
              ital construction on-site and manufacturing of concrete          international companies active in the field of construction
              elements in prefabrication. In combination with digital          printing which should contribute to intensive exchange be-
              planning, such new technologies can open up the way              tween participants.
              to Construction Industry 4.0. The digitisation and auto-
              mation of relevant production processes constitute the           The event venue is the Alte Mensa Event Hall (“Dülfersaal“,
              most promising approach to introducing urgently needed           1st floor) at the Technische Universität Dresden, Mommsen-
              changes into the practice of construction.                       strasse 13/15, D-01069 Dresden. The seminar language will be
                                                                               German.
              After the successful start last year, the 2nd German Industry
              Seminar on 3D Concrete Printing and Other Digital Concrete       Further information: http://tu-dresden.de/bau/3ds2020
              Construction Technologies aims to present once again a com-
              prehensive overview of the most important developments,
              which will be scrutinized critically and impartially. The sem-
              inar will take place on October 28th, 2020 at the TU Dresden,
              Germany. The organizers are the Institute of Construction
              Materials, the Endowed Chair of Construction Machinery, and      Technische Universität Dresden
              the Institute of Construction Management.                        Institut für Baustoffe
              Presentations from industry and science will provide an up-      Martina Awassi
              to-date overview of the state of the art, relevant development   01062 Dresden, Germany
              trends, but also the challenges in dealing with the new pro-     T +49 351 46336311
              duction processes.                                               i.baustoffe@tu-dresden.de

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NEWS

            ACCIONA LAUNCHES GLOBAL
            3D PRINTING CENTER IN DUBAI
            Culmination of an internal development process

            Acciona, a leading company in sustainable infrastructure           of cultural heritage made on a real scale using 3D printing on
            solutions, inaugurated in Dubai a new global 3D printing           concrete, the Romanesque arch of San Pedro de las Dueñas,
            center to meet the growing demand for 3D printed infra-            in collaboration with the National Archaeological Museum of
            structure.                                                         Spain (MAN).
                                                                               Acciona has chosen Dubai to install its 3D printing center in
            The new facilities feature one of the world’s largest operation-   order to support the emirate’s commitment to deploying this
            al 3D printers using powder bed technology. This technology        technology in all economic fields and, specifically, in the con-
            is particularly suitable for generating highly resistant struc-    struction sector.
            tural parts. In addition, the technique uses concrete as base      The “Dubai 3D Printing Strategy” is integrated into the
            material, which renders it an ideal solution for architectural,    Emirate’s strategic development plan for cost reduction, pro-
            urban and building applications.                                   ductivity and performance improvement of products and
            The printer, with 6x3x2 meters in size, allows greater efficien-   environmental impact mitigation. The Strategy aims to make
            cy and automation of the construction processes. The 3D            Dubai a world-class 3D printing hub.
            technology offers a freedom of architectural and urban de-         Among the concrete initiatives included in the Strategy is the
            sign that had previously been unthinkable. It also opens the       introduction of a new law under which 25% of new build-
            way to scientifically documenting heritage items and making        ings’ components must be manufactured with 3D technology
            replicas from their digital copies, which enables the public to    by 2025.
            contemplate identical reproductions.
            Acciona’s new production facility is the culmination of an in-
            ternal development process in the Innovation area starting in
            2016, which has enabled the technology to be fine-tuned for
            commercial use.
            During this process, Acciona achieved milestones such as
            one of the first walkways in the world made using 3D print-
            ing, in Alcobendas (Madrid, Spain), or the architectural piece     www.acciona.com

                 UNLOCKING NEW POTENTIAL
                 New partnership

                 IRS Robotics and Vertico are partnering to provide world
                 class 3D concrete printing technology solutions to the             Vertico XL 3D Printing
                 market.
                                                                                    www.vertico.xyz
                 As an experienced player in the concrete printing market, Ver-
                 tico has the know-how to provide turn-key, full service con-
                 crete printing solutions. IRS Robotics installed a refurbished
                 ABB IRB6640 IRC5 for them on a 6 meter ABB track. Unlocking
                 new potential for the 3D concrete printing market.                 www.irsrobotics.com

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NEWS

         EXCLUSIVELY
           DESIGNED
          FURNITURE
                     More than just an eye catcher

              3D concrete provides creative oppor-
              tunities for architects and planning
              agencies. The Austrian enterprise 3D
              Betondruck Solutions has been a pio-
              neer in this innovative technology.

              Based on intense development efforts
              unique solutions for indoor and outdoor
              use, such as exclusively designed furni-
              ture can be realized. Possible re-use as
              recycled granulate guarantees sustain-
              ability. Different surfaces and colouring
              of the concrete set individual accents.

              www.3dbetondrucksolutions.at

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NEWS

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RESEARCH & DEVELOPMENT

                                  CONPRINT3D
                  On-site, large-scale, monolithic 3D concrete printing

              The construction industry faces severe problems resulting
              from low productivity and increasing shortages of skilled
              labor. The purposeful digitalization and automation of all
              relevant stages, from design and planning to the actual
              construction process appears to be the only feasible solu-
              tion to master these urgent challenges. Additive concrete
              construction has a high potential to be a key part of the
              solution. In the first place, technologies are of interest
              which would enable large-scale, on-site manufacturing
              of concrete structures in accordance with the demands
              of contemporary architectural and structural design. The
              article at hand presents the CONPrint3D concept for on-
              site, large-scale, monolithic 3D printing as developed at
              the TU Dresden. This concept is driven by the demands
              and boundary conditions of construction practice. It com-
              plies with common architectural standards, valid design
              codes, existing concrete classes and typical economic
              constraints. Furthermore, it targets the use of existing
              construction machinery to the highest possible extent.

                            Viktor Mechtcherine, Venkatesh Naidu Nerella,          however, making compromises in the geometrical precision
                         Frank Will, Mathias Näther, Jens Otto, Martin Krause,     of structural elements to be built. A comprehensive state of
                                        TU Dresden, Germany                        the art can be found in [1], which also provide more details on
                                                                                   the technology presented in this article.

                                                                                   The authors started work on the concept of a formwork-free,
              CONPrint3D concept                                                   monolithic construction process using 3D-printing in the
              Most of the known 3D concrete printing approaches are based          framework of the research initiative ZukunftBau of the
              on layered extrusion and most of them do not comply with             German Federal Institute for Research on Building, Urban
              the requirement of large-scale, on-site mass construction.           Affairs and Spatial Development (BBSR). They named it
              The main reason is their focus on high spatial resolution, the       CONPrint3D®, which stands for large-scale, on-site 3D-print-
              use of fine filaments, and the concentration on in-plant- rath-      ing. The concept was first presented at bauma 2016 (Munich),
              er than on on-site-fabrication. Apart from high resolution,          which is the world’s leading trade fair for construction ma-
              the use of fine filaments offers additional advantages such          chinery, and it was granted the ‘Innovation Award’ in the cat-
              as lightweight printheads, which can be of very simple de-           egory ‘research’. The corresponding video and description to
              sign as well; often a circular, vertically oriented nozzle is suf-   the concept were published in [2-4], respectively. Since then
              ficient to provide the necessary control of material flow and        the researchers continued to develop this approach further
              the precision of material placement. However, fine filaments         toward its deployment in the practice of construction by
              also mean both low production rates and the need for very            working closely with various industrial stakeholders.
              fine-grained mortars, which do not comply with existing con-
              crete codes. In contrast, the use of large-size filaments would      The CONPrint3D concept should make a time-, labor-, and re-
              enable high productivity and use of concrete with coarse ag-         source-efficient, advanced construction process possible, but
              gregates in accordance with valid national and international         make the new process economically viable while achieving
              norms. Since large-scale, on-site mass construction requires         broader acceptance from industry practitioners as well. The
              rather massive cross-sections of simple geometrical shape,           main features of the new concept which distinguish it from
              high spatial resolution is not needed. This does not mean,           other approaches are:

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Figure 1: Fragment of a wall
                         structure 3D-printed using CONPrint3D
                                                                                                    RESEARCH & DEVELOPMENT
                         technology; two options for application
                             of reinforcement are indicated
                                         as well.

                                                                                                    Viktor Mechtcherine is Director of
            Adaptation of concrete-3D-printing to today’s architecture and structural design      the Institute for Construction Mate-
            Other extrusion-based methods are more suitable for producing filigreed elements       rials and Professor at the Technis-
            with more complex geometries, which currently, however, are used relatively rarely.   che Universität Dresden, Germany.
                                                                                                    He is Coordinator of the German
            CONPrint3D is developed for monolithic construction with sharp corners and pre-
                                                                                                  Research Foundation (DFG) Priority
            dominantly straight walls (see Figure 1).                                              Program SPP 2005 „Opus Fluidum
                                                                                                    Futurum – Rheology of reactive,
            Maximum use of common construction machinery                                           multiscale, multi-phase construc-
                                                                                                  tion materials“ and Speaker of the
            At present, concrete printers are expensive special machines. For reasons of econ-
                                                                                                   DFG Research Training Group GRK
            omy and early deployment into the practice of construction, the maximum use of        2250 „Mineral-bonded composites
            existing construction machinery, with some necessary upgrading, would be of great        for enhanced structural impact
            advantage. CONPrint3D implies upgrading such machines as a mobile concrete            safety“. Prof. Mechtcherine is Editor
                                                                                                   of the Journals “Cement and Con-
            pump for use as a 3D printer, see Figure 2.
                                                                                                   crete Composites” and “Materials
                                                                                                     and Structures”, Member of the
            Concrete composition and properties of hardened concrete                                Science Academy of Saxony and
            within existing concrete standards                                                    the Russian Engineering Academy,
                                                                                                    Chair of RILEM TC RSC-260 „Rec-
            The development of new standards and their eventual implementation are tedious
                                                                                                   ommendations for Application of
            and expensive. Therefore, in the near and medium terms, one should work as far as      Super Absorbent Polymers in Con-
            possible with printable concrete within the existing concrete standards. For CON-     crete Construction“ and Member of
            Print3D, concrete compositions with maximum aggregate size of 8 mm have been          the Research Advisory Board of the
                                                                                                  German Committee for Reinforced
            developed. In addition to ordinary and high-performance concrete, foam concrete
                                                                                                      Concrete (DAfStb). He is RILEM
            [13] and fiber reinforced concrete [8] can be printed.                                    Fellow and awardee of Wason
                                                                                                      Medal for Materials Research
            Printheads which enables surface quality and precision /                                 by American Concrete Institute
                                                                                                   (ACI) and Innovation Award of the
            tolerances according to existing standards
                                                                                                           bauma 2016 Munich.
            At present, printheads are in the main merely simple nozzles. Due to the lack of         mechtcherine@tu-dresden.de
            smoothing post-processing, on the one hand a “sausage look” is created which is

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RESEARCH & DEVELOPMENT

                             Venkatesh Naidu Nerella is a
                          postdoctoral fellow at Institute of     Figure 2: Illustration of CONPrint3D approach depicting a truck-mounted concrete pump as
                           Construction Materials, TU Dres-     manipulator for on-site concrete printing.
                           den, where he has been working
                           as research assistant since 2012.
                           He has completed his PhD titled
                          “Development and characterisa-
                         tion of cement-based materials for
                                                                not always acceptable. On the other hand, total control of the material flow as well
                           extrusion-based 3D-printing” in      as the precision of the material placement and its final shape are often insufficient
                          2019. His main research interests     if simple printheads are utilized. Furthermore, the forming of sharp corners and pre-
                             include digital construction,      cise openings is problematic. CONPrint3D printheads are designed to deposit large-
                         rheology and numerical modeling.
                         He is a member of RILEM technical
                                                                scale filaments of defined geometrical shape and surface quality, while enabling
                          committee on “Digital fabrication     manufacturing sharp corners as well as accurate endings and openings.
                            with cement-based materials”.
                            nerella@msx.tu-dresden.de           At the present stage the CONPrint3D concept focuses on replacing masonry walls as
                                                                a first step. For such applications steel reinforcement is not needed. While the au-
                                                                thors have been working on various approaches of introducing reinforcement into
                                                                the concept (see, e. g., [19-21] and Figure 1), comprehensively presenting this work
                                                                here would overload this article. Thus, the following deliberations are limited to
                                                                non-reinforced concrete.

                                                                Printer – Manipulator system
                                                                Most of the known concrete printing projects rely on the use of proven robotics con-
                                                                cepts from other industrial applications for moving the printhead. These concepts
                                                                seem less suitable if they are to be used for large-scale printing of buildings directly
                                                                on the construction site because there are, in part, completely different conditions:

                                                                •   rough environment, dirt, weather;
                         Frank Will is holder of the Endowed    •   frequent assembly and disassembly;
                         Chair of Construction Machinery at     •   necessity of easy handling for cleaning and maintenance;
                          Dresden Technical University since    •   required machine mobility for quick changeover between construction sites;
                          2017. The three major focal topics
                          of the chair are machine automa-      •   frequently untrained personnel and resulting lack of care in the handling of
                          tion, construction techniques and         sensitive technology;
                           drive systems & components. His      •   conservative attitude of the construction industry to modern technology.
                          professional background is based
                          on a PhD in Mechanical Engineer-
                         ing and 20 years of industrial expe-   From the authors’ point of view, it is advisable therefore to search for the concrete
                         rience from different management       printing manipulator in the field of existing construction machinery, which have
                            positions in machine and plant      been specially developed for this harsh working environment and have proven
                                engineering companies.          themselves over many years. The truck-mounted concrete pump is particularly in-
                              frank.will@tu-dresden.de
                                                                teresting for concrete printing. On the one hand, it has the needed concrete convey-
                                                                or technique on board and, on the other hand, it has a long, foldable boom whose
                                                                range (total lengths of up to 70 m) is large enough to print multi-story buildings.
                                                                The CONPrint3D process therefore aims to use a truck-mounted concrete pump as
                                                                a large-scale manipulator for the printhead; see Figure 2.

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RESEARCH & DEVELOPMENT

                1

                2

                3

                                                                                                   Mathias Näther has been working
                Figure 3: Precision measurements on truck-mounted concrete pump M38-5:
                                                                                                      as a research assistant at the
            1 – target reflector, 2 – printhead dummy, 3 – target-tracking tachymeter.
                                                                                                     endowed chair of construction
                                                                                                    machinery at Dresden University
                                                                                                    of Technology since 2012, where
                                                                                                   he works on the simulation of com-
            Several years of research work at the TU Dresden have been concerned with the in-       plex technical systems in the field
                                                                                                   of construction machinery and the
            vestigation and modification of the boom drive in order to optimize the positioning    development of concrete-3D-print-
            accuracy of these machines. For example, measurements were carried out to deter-        ing technology. His work focuses
            mine the position deviations and mast oscillations of conventional truck-mounted        mainly on the development of the
            concrete pumps; see Figure 4. With the help of this data, optimized drive compo-        printhead and handling systems
                                                                                                      suitable for construction sites.
            nents, control algorithms, and control systems can now be developed to reduce          mathias.naether@tu-dresden.de
            the oscillation amplitudes by up to 95 % and positioning accuracy can be increased
            [4,5,6].

            Printhead for concrete printing
            Contrary to the described concrete printing approaches that mostly print thin lay-
            ers of fine-grained concrete, the goal of the CONPrint3D technology from TU Dres-
            den is to print massive, monolithic wall structures with concrete containing coarse
            aggregates. This results in more ambitious requirements for the concrete conveyor
            and the shaping tools of the printhead with regard to delivery rates, robustness and
            wear resistance. In addition to the requirement of processing concrete with coarse
            aggregates, the printhead was designed with respect to the following specifica-
            tions:

            •       high output of concrete for economical print speeds;
            •       high level of automation;
            •       high level of modularity;                                                       Jens Otto is professor of construc-
            •       variable wall cross-sections and smooth wall surfaces;                             tion management at Dresden
            •       minimal weight;                                                                   Technical University and heads
                                                                                                        the institute of construction
            •       easy cleaning and handling.                                                      management since 2017. Before
                                                                                                    returning to the university he was
            The CONPrint3D method includes the conveying and dosing technology directly                working in leading positions in
            at the printhead; see Figure 4a. This allows better control of the concrete flow. In   large construction companies. Due
                                                                                                     to his experience in construction
            addition, the fresh concrete properties can be determined and adjusted according         process management, Prof. Otto
            to the requirements directly before printing. After further development steps, the       has an extensive expertise in the
            forming system at the concrete outlet will be able to automatically adapt the noz-      fields of project management and
            zle cross-section to the desired layer geometry. Several automatically controlled       digital processes for planning and
                                                                                                       execution. He works in various
            shaping elements ensure precise shaping of the building-specific wall geometry;             committees and is author of
            see Figure 5.                                                                             several books and publications.
                                                                                                         jens.otto@tu-dresden.de

                                                                                                                                          2.20 | 17

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RESEARCH & DEVELOPMENT

                                                       a)        b)
              Figure 4: Current printhead for CONPrint3D:
          a) general view including printhead and laboratory manipulator, and
          b) detailed view of the base nozzle with a nozzle closure.

                                                                 The currently most frequently used CONPrint3D printhead is designed to print
                                                                 monolithic wall profiles using concrete with an aggregate size of up to 10 mm.
                                                                 It is capable of printing concrete layers with a cross-section of (width x height =)
                                                                 150 mm x 50 mm at speeds of up to 10 m/min. During the development of the print-
                                                                 head, special attention was given to a modular design. This allows, for example,
                                                                 the use of different conveying mechanisms or the exchange and optimization of
                                                                 particular components. As indicated above, the printhead can also be equipped
                                                                 with different forming systems adjusted to the respective printing principle:

                                                                 •    Simple outlet nozzles with a fixed cross-section for production of test speci-
                                                                      mens and wall with unvaried thickness; see Figure 4b;
                                                                 •    Complex forming systems with several actuators for printing complex filament
                                                                      shapes and various filament cross-section / wall thicknesses; see e. g. Figure 5;
                                                                 •    Alternative forming systems for printing finer, curved structures.
                         Martin Krause has been working as
                         a research assistant at the Institute
                                                                 Through various measurement points, the printhead provides important data
                            for Construction Management
                         since 2014. His research focuses on     for understanding and controlling the printing process, especially during the test
                           the economical and managerial         phase in the laboratory.
                           aspects of 3D concrete printing.
                          This includes both the analysis of
                                                                 Properties of printable concrete in fresh and hardened states
                          economy and the process-specific
                            boundary conditions as well as       Extrudability, buildability, workability and open-time are the key requirements for
                         the optimization of the 3D printing     3D-printable concretes. Printability can be defined as the property of a material
                            strategy. His doctoral thesis on     to satisfy these requirements without formation of weak layer-to-layer interface
                          the topic of „Construction process
                                                                 bonds [7]. There are no established process-specific material design approaches
                          optimization of massive concrete
                          wall production by 3D printing“ is     and test methods for 3D-printable concrete. Thus, various test methods have been
                            due to be completed this year.       developed as part of CONPrint3D research framework, see e. g. [8,9,10] and used for
                          martin.krause3@tu-dresden.de           designing 3D-printable concretes in a performance-based approach. A comprehen-
                                                                 sive overview of these methods is provided in [11]. Note that due to the presence
                                                                 of coarse aggregates in concrete, testing of its rheological properties relevant for

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RESEARCH & DEVELOPMENT

                                                                                          www.tu-dresden.de

                                                                                          28th October 2020
                                                                                 1        Dresden, Germany

                                                                                 2
                           4
                                                                                 3

                                                                                                           2        nd          German
                Figure 5: Printhead under development: (1) extruder and the complex
            forming system with (2) nozzle, (3) shaping plates, (4) shutter and several
                                                                                                                                Industry
            actuators for printing filaments with varied cross-section / walls with
            varied thickness.
                                                                                                                                Seminar

                                                                                                 3D Concrete Printing
            3D-printing becomes even more challenging when compared                           and other Digital
            to mortar.
                                                                                            Concrete Construction
            Within the scope and length of the paper at hand, it is not pos-
            sible to present results for all process-relevant properties for              Technologies
            the newly developed 3D-printable concretes containing coarse
            aggregates. Thus, only some material parameters will be pre-                  - STATE OF THE ART
            sented, and this exemplarily for one printable concrete with
            maximum aggregate size of 8 mm; see Table 1.
                                                                                          - CHALLENGES
                Table 1. Composition of printable concrete with maximum aggregate
            size of 8 mm.                                                                 - PERSPECTIVES
             Con-        CEM    FA     MSS      Aggregates [mm]            Water SP
             stituent
                                                0.06-   0-1   0-2   2-8
                                                0.2

             Dosage      350    140    105      427     427   325   310    179       5
             [kg/m3]

                                                                                                                  Further information
            A combination of CEM I 52.5 R Portland cement, micro-
                                                                                                                 can be obtained under
            silica (MSS) and fly ash (FA) was used as binder. The 3PC had
            43.4 % binder paste by volume. The equivalent water-to-cement
                                                                                                             http://tu-dresden.de/bau/3ds2020
            ratio (w/c)eq was 0.51, calculated in accordance with EN 206-1.
            Very fine quartz sand (0.06-0.2 mm), two natural river sands
                                                                                                           Technische Universität Dresden
            (0-1 mm and 0-2 mm) and gravel (2-8 mm), all complying with
                                                                                                         Institut für Bausto e
            EN 12620/13139, were used as aggregates. The polycarbox-
                                                                                                        Martina Awassi
            ylate-based, high-range water reducing agent was added as
                                                                                                      01062 Dresden, Germany
            superplasticizer (SP).
                                                                                                    T +49 351 46336311
                                                                                                 i.bausto e@tu-dresden.de
                                                                                                                                  2.20 | 19
                                                                                              The seminar language will be German.

3_cpt_2002_14-31_Research_Development.indd 19                                                                                         07.05.20 14:48
RESEARCH & DEVELOPMENT

                a)                                                        b)

                 Figure 6: Specimens’ extraction and test setup: a) compression tests and b) bending tests.

              The workability of fresh PC was estimated by means of flow                   Table 2 shows the results of mechanical tests performed on
              table tests according to EN 12350-5. In view of a spread value               the hardened concrete. The compressive strengths of the cast
              of 36 cm at an age of 20 min, the 3PC at hand can be classified              and printed specimens (both for cubes and prisms’ halves)
              into consistency class F3 (plastic) according to the EN 206-1.               are nearly the same, when printed specimens are tested in
              The extrudability of the composition was proven by printing                  the parallel case. In contrast, the printed specimens exhibit
              concrete at various concrete ages up to 90 minutes from wa-                  about 20 % lower strength values than the cast specimens
              ter addition using equipment as presented in Figure 4.                       when tested in the perpendicular case; see Table 2. An expla-
                                                                                           nation can be found in [12]. The flexural strengths of printed
              Extruded layers had right-angled edges with high surface                     specimens in all cases except Par3, are not significantly differ-
              quality; see Figure 4b. Specimens for mechanical tests were                  ent from cast specimens (below 10 %). The critical case Par3,
              extracted from several printed little walls. The time interval               however, showed the least flexural strength: 66 % lower than
              between depositions of subsequent layers was 3 minutes.                      that of the cast prisms. The large size of layers, horizontal lay-
              The compressive and flexural strengths were measured ac-                     ing (required for such large filaments) instead of vertical pres-
              cording to EN 1015-11 on cubical specimens (100 mm x 100                     sure-deposition, stiff composition, absence of curing meas-
              mm) and prismatic specimens (160 mm x 40 mm x 40 mm),                        ures and smooth nozzle inner surfaces are the suggested
              respectively, cut out of printed wall elements. In addition,                 causes for such relatively weak bond. The bond could be sig-
              compressive strength was measured on prism halves after                      nificantly enhanced and the anisotropy reduced by adequate
              the flexural tests. To assess possible anisotropy, the speci-                preventive measures. This is the subject of ongoing research.
              mens were tested in various directions with respect to the
              layer-to-layer interface; see Figure 6. In addition, reference               For widespread use of the new technology, a range of printa-
              specimens were cast and tested to assess the influence of the                ble compositions is needed which are suitable for various ap-
              printing process on the hardened-state properties. All speci-                plication scenarios and machine setups. To meet particular
              mens were tested at an age of 10 days, under consideration of                requirements with respect to structural design, construction
              the anticipated high speed of digital construction.                          physics and durability, compositions and properties of 3PCs

                  Table 2. Average strength values of the 3D-printable coarse aggregate concrete at an age of 10 days
              (in MPa; standard deviations are given in parenthesis).

                                                  Cast                  Printed cubes                            Printed prisms

              Test                      C-Cubes      C-Prisms       PerpC         ParC     Perp1         Par1           Perp2      Par2      Par3

                                    57.7            57.3        46.9           58.2      46.8         57.5         48.6         54.7      53.3
              Compression
                                    (1.2)           (2.9)       (1.0)          (1.8)     (3.3)        (2.9)        (4.4)        (2.5)     (2.6)
                                                    7.41                       6.70      6.72         6.75         7.45         2.52
              Flexure               X                           X
                                                    (0.25)                     (0.29)    (0.37)       (0.37)       (0.45)       (0.93)

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RESEARCH & DEVELOPMENT

            should be versatile. Currently this translates into 3PCs with       1,9 m3/h taking into account some delays for wall connec-
            aggregate sizes ranging from 2 mm to 16 mm and compres-             tions [16]. Two workers are scheduled for the printing pro-
            sive strengths from 1 MPa (foam concrete) to 80 MPa. For ex-        cess: A specially trained machine operator and a professional
            ample, in the project CONPrint3D Ultralight, the authors de-        skilled worker. Further information to economic prospects of
            veloped a series of load-bearing, lightweight printable foam        3D concrete printing can be found in [16].
            concrete with densities ranging from 600 kg/m3 to 1500 kg/m3
            and compressive strengths from 1 to 10 MPa [13]. Reduction          Compared to conventional construction methods, the num-
            of carbon footprint and sustainable construction are a cru-         ber of qualified skilled workers is significantly reduced. On
            cial requirement for the seminal construction materials and         the one hand, this has a positive effect on the construction
            processes. While the concretes developed for CONPrint3D             costs. On the other hand, in Central Europe the trend is be-
            applications have lower cement content in comparison to the         ing recognized that fewer and fewer workers are available
            most known examples of printable concrete, see Table 1, fur-        for skilled manual labor. In less developed countries, there
            ther reduction of clinker content in 3PCs is targeted in ongo-      is usually enough affordable labor. But often the workers are
            ing research using limestone calcined clay cements and novel        not sufficiently qualified to build high-quality concrete struc-
            binder systems.                                                     tures.

            Economic feasibility, market potential and data management          To be able to produce building structures autonomously with
            Concrete work is still considered to be labor-intensive and         concrete 3D-printing, the demanding boundary conditions
            time-consuming. In particular, the formwork significant-            of the construction processes must be mastered by the ma-
            ly determines the execution time and take at about 25 % to          chine. For this purpose, the construction machine must be
            35 % a high proportion of the total cost of the structural work,    controlled by means of specially prepared data structures
            even for relatively simple geometrical configurations. There is     and sophisticated data management. The basis is a Build-
            consensus in science that the introduction of additive manu-        ing Information Model (BIM) containing geometric and ma-
            facturing in construction has significant economic potential        terial-specific information. The digital structure required for
            [3,14,15].                                                          the concrete 3D printing process has to be extracted from
                                                                                the BIM model, then sliced, and after that converted into a
            An essential criterion for a successful market launch of CON-       machine-readable G-Code. Therefore, an integrated digital
            Print3D® is the economic competitiveness with convention-           process chain must be developed. This topic is addressed in
            al construction methods. The aim of the first development           detail in [17,18].
            step is the automated production of unreinforced concrete
            walls, continuously and reliably, in order to replace manual        Summary and outlook
            masonry construction. With 75 % of the total construction           The article at hand elaborated the necessity of developing
            volume, traditional masonry construction is still the most          digitized, fully automatic technology for large-scale concrete
            commonly used method in residential constructions in Ger-           construction. Against this background the authors presented
            many. The building materials bricks (about 32 %), sand-lime         their concept CONPrint3D for on-site, monolithic 3D-printing.
            bricks (about 17 %), cellular concrete (22 %) and lightweight       The concept is based on layered extrusion as the most exist-
            concrete (4 %) are used in residential construction [15]. This      ent approaches. The main features of the new concept which
            already illustrates the high market potential in Germany only.      distinguish it from other approaches are:
            In addition, the process can be certified as highly competitive
            worldwide for buildings up to five stories. In particular, poten-   •   adaptation of concrete-3D-printing to today’s architecture
            tials are seen also in the emerging economies, where there              and structural design (sharp corners, straight-line geome-
            is a high demand for simple, solid constructions. In a second           tries, wide monolithic cross-sections);
            development step, reinforced concrete components are to be          •   maximum use of the common construction machinery,
            produced in order to expand the application scenarios suc-              such as truck-mounted concrete pumps;
            cessively. In a third development step finally installations of     •   concrete composition and properties of hardened
            thermal insulation and technical building equipment, such as            concrete within the existing concrete standards;
            electricity, water and sewage are to be integrated.                 •   printhead which enables surface quality and precision
                                                                                    according to existing standards.
            In economic feasibility studies, the execution time and con-
            struction costs of CONPrint3D were investigated. Using the          While introducing CONPrint3D, various perspectives were
            example of one floor of a detached house, a comparison              presented, namely those of mechanical engineering, con-
            was made between CONPrint3D and conventional masonry                crete technology, and construction management. At the
            construction. As a result, cost savings potential of 25 % and       present stage the main challenge in applying truck-mounted
            four to six times shorter execution times were estimated.           concrete pumps as on-site 3D-printer is the insufficient posi-
            The wall-printing of a floor with a space of approximately          tioning accuracy of the printhead. Currently optimized drive
            130 m2 can be realized in about one day [15]. The currently         components as well as measurement and control systems are
            conceivable printing speed is 150 mm/s with layer heights of        being implemented to considerably improve the movement
            50 mm. This enables a printing performance of approximately         precision of the pump mast.

                                                                                                                                            2.20 | 21

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RESEARCH & DEVELOPMENT

              Concrete compositions for large-size filament printing were                        Acknowledgements
              developed. While the mechanical performance of the print-                          Authors express their sincere gratitude to the German Federal
              ed specimens was nearly identical to that of the cast speci-                       Ministry for the Environment, Nature Conservation, Building
              mens made of the same concrete mixture, testing of the print-                      and Nuclear Safety (BMUB) for funding the preceding re-
              ed concrete in various directions yielded a certain extent of                      search projects through the research initiative Zukunft Bau of
              anisotropy resulting primarily from the quality of the interlay-                   the Federal Institute for Research on Building, Urban Affairs
              er bond. Another challenge the authors deal with is enhanc-                        and Spatial Development (BBSR). Furthermore, the financial
              ing robustness of the mixtures specifically with respect to                        support of the German-Czech project digiCON2 - Digital Con-
              on-site applications.                                                              crete Construction by the Federal Ministry of Education and
                                                                                                 Research (BMBF) is highly acknowledged. We also thank our
              In its present form, CONPrint3D technology is designed as an                       industrial partners: OPTERRA Zement GmbH (Werk Karsdorf),
              alternative to manual erection of masonry walls. The market                        MC-Bauchemie Müller GmbH & Co. KG, BAM Deutschland AG
              shares and economic viability of this alternative have been                        (Dresden branch), KNIELE GmbH, Cervenka Consulting and
              explained. The use of large-size filaments for printing massive                    CERION GmbH.
              walls requires particular printing strategies and purposeful
              adaptation of the data from digital planning.

                     References                                                                  [11] V. Mechtcherine, V. Nerella: Fresh state requirements to 3D-printable
                 [1] V. Mechtcherine, V.N. Nerella, F. Will, M. Näther, J. Otto, M. Krause:           cement-based materials. Construction Printing Technology 1 (2020)
                      Large-scale digital concrete construction – CONPrint3D concept for              10–17.
                      on-site, monolithic 3D-printing. Automation in Construction 107 (2019)     [12] V.N. Nerella, S. Hempel, V. Mechtcherine: Effects of layer-interface
                      102933.                                                                         properties on mechanical performance of concrete elements produced
                 [2] CONPrint3D: 3D-Druck mit Beton - YouTube, Technische Universität                 by extrusion-based 3D-printing. Construction and Building Materials
                      Dresden (2016). https://www.youtube.com/watch?v=EhNGgY42e-                      205 (2019) 586–601.
                      qY&t=16s (accessed April 26, 2019).                                        [13] V. Mechtcherine, V. Markin, F. Will, M. Näther, J. Otto, M. Krause, V.N.
                 [3] V.N. Nerella, M. Krause, M. Näther, V. Mechtcherine: 3D-Druck-Techno-            Nerella, C. Schröfl: CONPrint3D Ultralight - Herstellung monolithischer,
                      logie für die Baustelle - Interdisziplinäres Forschungsprojekt der TU           tragender, wärmedämmender Wandkonstruktionen durch additive
                      Dresden. Concrete Plant International / BetonWerk International 4               Fertigung mit Schaumbeton. Bauingenieur 94(11) (2019) 405–415.
                      (2016) 36–41.                                                              [14] G. De Schutter, K. Lesage, V. Mechtcherine, V.N. Nerella, G. Habert,
                 [4] M. Näther, V.N. Nerella, M. Krause, G. Kunze, V. Mechtcherine,                   I. Agusti-Juan, Vision of 3D printing with concrete — Technical,
                      R. Schach: Beton-3D-Druck Machbarkeitsuntersuchungen zu kontinu-                economic and environmental potentials. Cement and Concrete
                      ierlichen und schalungsfreien Bauverfahren durch 3D-Formung von                 Research 112 (2018) 25–36.
                      Frischbeton. Projektbericht (AZ: SWD-10.08.18.7-14.07) Dresden, 2016.      [15] R. Schach, M. Krause, M. Näther, V.N. Nerella, CONPrint3D: 3D-Concre-
                      ISBN 978-3-7388-0028-9.                                                         te-Printing as an Alternative for Masonry. Bauingenieur 92 (5) (2017)
                 [5] S. Zorn: Regelungstechnische Stabilisierung mehrgliedriger Ausleger              355–363.
                      am Beispiel der Autobetonpumpe. ATZ Offhighway 03 (2018) 46–51.            [16] J. Otto, J. Kortmann, M. Krause: Wirtschaftliche Perspektiven von Be-
                 [6] S. Zorn, F. Will, P. Mögle: Control stabilization of multilink manipula-         ton-3D-Druckverfahren. Beton- und Stahlbetonbau 115 (2020) Heft 5.
                      tors in a truck-mounted concrete boom pump. ATZheavy duty world-                doi:10.1002/best.201900087.
                      wide 3 (2018) 44–49.                                                       [17] M. Krause, J. Otto, 3D-Concrete-Printing: Digital data flow with BIM.
                 [7] V. Mechtcherine, F. P. Bos, A. Perrot, W. R. Leal da Silva, V.N. Nerella,        Bauingenieur 94 (5) (2019) 171–178.
                      S. Fataei, R. J. M. Wolfs, M. Sonebi, N. Roussel: Extrusion-based          [18] M. Krause, J. Otto, A. Bulgakov, D. Sayfeddine: Strategic optimization
                      additive manufacturing with cement-based materials –                            of 3D concrete printing using the method of CONPrint3D.
                      Production steps, processes, and their underlying physics:                      In: Proceedings of the 35th ISARC, IAARC, Berlin, 2018 1-7.
                      A review. Cement and Concrete Research 132 (2020) 106037.                       DOI: 10.22260/ISARC2018/0002.
                 [8] V.N. Nerella, M. Näther, A. Iqbal, M. Butler, V. Mechtcherine: Inline       [19] H. Ogura, V.N. Nerella, V. Mechtcherine: Developing and testing of
                      quantification of extrudability of cementitious materials for digital           strain-hardening cement-based composites (SHCC) in the context
                      construction. Cement and Concrete Composites 95 (2019) 260–270.                 of 3D-printing. Materials 11 (2018) 1375.
                 [9] V. Mechtcherine, V.N. Nerella, K. Kasten: Testing pumpability of concre-    [20] V. Mechtcherine, J. Grafe, V.N. Nerella, E. Spaniol, M. Hertel, U. Füssel:
                      te using Sliding Pipe Rheometer. Construction and Building Materials            3D-printed steel reinforcement for digital concrete construction –
                      53 (2014) 312–323.                                                              Manufacture, mechanical properties and bond behavior.
                 [10] V.N. Nerella, M.A.B. Beigh, S. Fataei, V. Mechtcherine: Strain-based            Construction and Building Materials 179 (2018) 125–137
                      approach for measuring structural build-up of cement pastes in the         [21] V. Mechtcherine, V.N. Nerella: Integration der Bewehrung beim
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                      (2019) 530–544.

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                                                                   TOWARDS SUSTAINABLE
                                                                   3D CONCRETE PRINTING
                                                                                        Next Generation 3D-printed Concrete Structures (N3XTCON)

            The number of extrusion-based 3D Concrete Printing                             The N3XTCON project aims at developing technologies that
            (3DCP) applications has increased rapidly over the past                        bring 3D Concrete Printing (3DCP) to an industrial scale – with
            few years. This indicates an industrial strive to explore                      a clear focus on sustainability and new architectural designs.
            new construction methods, aiming at boosting productiv-                        Its scope includes both on-site and prefabrication applica-
            ity and obtaining new architectural designs; thus, shifting                    tions based on extrusion-based 3DCP, including the produc-
            building methods into a manufacturing process. To ena-                         tion of large-scale reinforced concrete structures as well as
            ble that, it is necessary to create a seamless link between                    residential buildings. The project is funded by the Innovation
            design, materials, and processes in construction. This                         Fund Denmark and runs until 2022.
            calls for research on material development, process mon-
            itoring, and material characterisation methods [1]. To ad-                     The developments covered in the project range from material
            dress such need, while generating new knowledge to the                         characterisation to numerical modelling and process control
            construction industry, the Danish Technological Institute                      as illustrated in the diagram shown in Figure 1. Whereas Fig-
            – in collaboration with key players from the Danish con-                       ure 2 depicts some of the initial project results; specifically:
            struction industry – started the project “Next Generation                      a Finite Element Model describing the failure of printed ele-
            3D-printed Concrete Structures” (N3XTCON).                                     ments, a Computational Fluid Dynamics model describing
                                                                                           the shape of extruded layers depending on 3DCP process
                                                                                           parameters, and a Digital Image Correlation (DIC) character-
                                                                                           isation method used to monitor layer deformation on printed
                Wilson Ricardo Leal da Silva, Danish Technological Institute, Denmark      elements.
                         Sergio Ferreiro Garzón, Cementir Holding N.V., Italy
                  Thomas Juul Andersen, Danish Technological Institute, Denmark            In this publication, we present the results of a N3XTCON case
                            Ingrid Ahrenkilde, Cementir Holding N.V., Italy                study related to the fabrication of a concrete column using a
                                                                                           novel cement type developed by Cementir Holding N.V. and

                 Figure 1: Development steps covered in the N3XTCON project.

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