The potential of digitally fabricated concrete (DFC) to produce terrain responsive designs has not been thoroughly investigated. Existing research indicates diverse benefits of DFC, such as the rapid fabrication of customized geometries. This research clarifies the advantages and design processes involved in creating site-specific DFC structures. Existing literature is analyzed to provide an overview of fabrication methods and their impacts and constraints on design. Parametric scripting is used to develop an interactive toolkit that integrates aesthetic, structural, and fabrication considerations into the design process. This toolkit specifically focuses on unreinforced retaining walls with interchangeable modules for terrain analysis, wall form generation, structural analysis, and fabrication analysis. The toolkit provides valuable feedback, such as identifying optimum wall proportions, and enables rapid design explorations. The findings affirm the value of exploratory design tools in managing fabrication complexities. Additionally, by recreating an existing amphitheater, the research indicates that DFC can create site-specific geometries that draw from the surrounding terrain.

Additive manufacturing is becoming more popular as a construction technique for various design fields. 3D Concrete Printing is one type of additive manufacturing in which layers of concrete are stacked on top of each other by pushing concrete through a nozzle onto a printing bed. These layers create three-dimensional solid objects from a digital file. 3D Concrete Printing promises to be extremely beneficial for design flexibility, cost, time, safety, environmental impact, and error reduction. This study explores the potential of 3D Concrete Printing technology in landscape architecture by exploring current research, case studies, expert interviews, and design prototype documentation. The study results indicate that 3D Concrete Printing technology has great potential for future use; however, there are also some challenges. Analysis of the responses aims to provide a basis for understanding the technology's performance, design process, and the potential of the 3DCP in landscape architecture design.

Der 3D-Druck mit Beton zählt zu den vielversprechendsten Methoden der automatisierten Bauweise. Er bietet zahlreiche Vorteile gegenüber konventionellen Bauverfahren, wie beispielsweise Kostenersparnis, erhöhte Produktivität und architektonische Gestaltungsfreiheit. In den letzten Jahren hat sich der 3D-Druck mit Beton von einer gewagten Vision zu einer zukunftsweisenden Baumethode entwickelt. In mehreren Ländern konnte die praktische Anwendbarkeit der neuen Technologie durch zahlreiche Demonstratorobjekte bewiesen werden. Um eine breite Anwendung in der Baupraxis zu ermöglichen, müssen jedoch noch einige material- und technologiespezifische Fragestellungen gelöst werden. Eine davon ist die Rissbildung der gedruckten Betonelemente aufgrund von Schwindverformungen. Das Ausmaß der Schwindverformungen ist vor der Verfestigung der gedruckten Schichten am größten. Diese Verformungen werden als plastisches Schwinden bezeichnet. Das plastische Schwinden wird maßgeblich durch die hohe Wasserverdunstung im jungen Alter des Betons und dem dadurch folgenden inneren Spannungsaufbau in den Kapillaren hervorgerufen. Im Fall, dass die Verformungen eines Elements z. B. durch Schichtverbund oder Bewehrungselemente gehindert werden und daraus resultierende Spannungen höher als die Zugfestigkeit des Betons sind, kann es zur Rissbildung kommen. 3D-gedruckte Betonelemente sind stärker als konventionell gefertigte vom plastischen Schwinden bedroht. Dies hängt vor allem mit der schalungsfreien Bauweise und den spezifischen Zusammensetzungen der druckbaren Betonrezepturen zusammen. Risse, die durch das plastische Schwinden entstehen, können sich über den gesamten Querschnitt eines gedruckten Elements ausbreiten. Die dadurch verursachten Schäden gefährden die Dauerhaftigkeit, die Gebrauchstauglichkeit, beeinträchtigen die Ästhetik und können sogar zum Stabilitätsverlust führen. Trotz der Signifikanz dieser Problematik und der möglichen Schäden durch später auftretende Schwindarten wie z.B. Trocknungsschwinden und autogenes Schwinden, wurden bis jetzt nur wenige Studien diesem Thema gewidmet. Auch wurden die Quantifizierungs- und Vorbeugungsmethoden bisher ungenügend erforscht. Die vorliegende Dissertation befasst sich eingehend mit den Mechanismen des plastischen Schwindens und der damit verbundenen Rissbildung bei 3D-gedruckten Betonelementen. Da es keine standardisierte oder allgemein anerkannte Methode zur Quantifizierung des plastischen Schwindens und der damit verbundenen Rissbildung von 3D-druckbaren Betonen gibt, wurde in dieser Arbeit eine zuverlässige und einfach anwendbare Messmethode entwickelt. Diese Methode ermöglicht gleichzeitig die Quantifizierung des ungehinderten und gehinderten plastischen Schwindens sowie die Ermittlung relevanter Materialeigenschaften. Die durchgeführten statistischen Analysen bestätigten die Reproduzierbarkeit der erzielten Ergebnisse. Die Ergebnisse dieser Arbeit tragen zur Etablierung einer einheitlichen Methodologie für die Untersuchung des plastischen Schwindens und der damit verbundenen Rissbildung bei 3D-gedruckten Betonen bei. Auf Grundlage der entwickelten Versuchsaufbauten wurden spezifische Mechanismen des plastischen Schwindens und der damit verbundenen Rissbildung von 3D-gedruckten Elementen erforscht. Die experimentellen Untersuchungen wurden durch eine numerische Simulation von der Entwicklung des Kapillarporendrucks in gedruckten Elementen ergänzt. Ein besonderes Augenmerk lag auf dem Einfluss der Schichtdicke und dem Ausmaß der der Austrocknung ausgesetzten Fläche. Es wurde ein spezifisches Verformungsverhalten bei 3D-gedruckten Betonelementen festgestellt. Der Zeitpunkt, die Richtungen und das Ausmaß der schwindbedingten Verformungen wurden umfassend analysiert. Überdies wurde an einem analytischen und numerischen Modell zur Vorhersage der Schwindverformungen in 3D-gedruckten Betonelementen gearbeitet. Praktische Empfehlungen auf Grundlage der Analyse verschiedener Maßnahmen zur Vorbeugung und Reduzierung des plastischen Schwindens und der damit verbundenen Rissbildung bilden den Abschluss dieser Arbeit.:Abstract I Kurzfassung II Vorwort des Herausgebers IV Acknowledgement V Contents VI Notations and abbreviations XI 1 Introduction 1 1.1 Motivation 1 1.2 Relevance of the research 2 1.3 Objectives and research questions 2 1.4 Dissertation structure 3 2 Theoretical background 5 2.1 Plastic shrinkage of cementitious materials 5 2.1.1 Mechanisms of plastic shrinkage 5 2.1.2 Mechanisms of plastic shrinkage cracking 6 2.1.3 Experimental methods 7 2.1.4 Numerical methods 8 2.1.5 Mitigation techniques 9 2.1.5.1 Active mitigation approaches 9 2.1.5.2 Passive mitigation approaches 9 2.2 3D concrete printing 11 2.2.1 Flashback to history 11 2.2.2 Current state 14 2.2.3 Significance of the PS and PSC for 3D-printed concrete elements 14 2.2.3.1 Specifics of material compositions 14 2.2.3.2 Production related issues 14 2.2.3.3 Case studies 15 2.2.4 Previous studies on PS and PSC of 3D-printed concrete elements 19 2.3 Chapter summary 19 3 Materials and methods 21 3.1 Reference composition 21 3.2 Experimental methods 22 3.2.1 3D concrete printing test device 22 3.2.2 Wind tunnel and climate control chamber 23 3.2.3 Determination of the specific material properties 23 3.2.3.1 Air content and spread flow 23 3.2.3.2 Capillary pressure 24 3.2.3.3 Ultrasonic pulse velocity 24 3.2.3.4 Tempe cell and self-desiccation tests 24 3.2.3.5 Falling-head method 25 3.2.3.6 Tea bag test 25 3.2.3.7 Confined uniaxial compression test 26 3.2.3.8 Penetration test 26 3.2.3.9 Microscopy 27 3.2.4 Digital image correlation 27 3.3 Numerical method 28 3.4 Chapter summary 28 4 Quantification of plastic shrinkage and plastic shrinkage cracking of the 3D-printable concretes using 2D digital image correlation 29 4.1 Novel setups for quantification of the PS and PSC 29 4.2 Materials and methods of investigation 30 4.2.1 3D printing and preparation of samples 30 4.2.2 Evaluation of the deformations 32 4.2.3 Experimental setup and procedure 33 4.3 Experimental results 33 4.3.1 Penetration force 33 4.3.2 Free shrinkage behaviour 34 4.3.2.1 Vertical settlement 34 4.3.2.2 Horizontal shrinkage 35 4.3.3 Shrinkage behaviour in partially and fully restrained tests 35 4.3.3.1 Vertical shrinkage 35 4.3.3.2 Horizontal shrinkage 36 4.3.3.3 Shrinkage-induced cracking 38 4.3.4 Influence of the paint on the surface 41 4.4 Discussion of the test setups and measuring techniques 42 4.5 Chapter summary 43 5 Repeatability of the experimental results 45 5.1 Followed statistical approach for assessment of the repeatability 45 5.2 Experimental program 46 5.3 Preparation of the samples and the experimental procedure 46 5.4 Results and discussion 48 5.4.1 Repeatability of the experimental results in previous studies 48 5.4.2 Free shrinkage 49 5.4.2.1 Spread flow, density and air content 49 5.4.2.2 Ambient conditions 49 5.4.2.3 Water loss 50 5.4.2.4 Evolution of the capillary pressure 50 5.4.2.5 Temperature 51 5.4.2.6 Shrinkage 52 5.4.2.7 Evaluation of the repeatability 55 5.4.3 Restrained shrinkage 56 5.4.3.1 Basic fresh-state properties 56 5.4.3.2 Ambient conditions 56 5.4.3.3 Water loss 57 5.4.3.4 Evolution of the capillary pressure 58 5.4.3.5 Temperature 58 5.4.3.6 Shrinkage 59 5.4.3.7 Cracking 60 5.4.3.8 Evaluation of repeatability 62 5.5 Chapter summary 63 6 Specifics of plastic shrinkage and related cracking in 3D-printed concrete elements 65 6.1 Materials and methods 65 6.1.1 Impact of layer width 66 6.1.2 Reduction of the area exposed to desiccation 67 6.2 Results and discussion 68 6.2.1 The influence of the width of the layer 68 6.2.1.1 Evolution of the capillary pressure 68 6.2.1.2 Waterloss and temperature 69 6.2.1.3 Plastic shrinkage 71 6.2.1.4 Plastic shrinkage cracking 72 6.2.1.5 Discussion 74 6.2.2 The impact of formwork-free production technique 75 6.2.2.1 Plastic shrinkage 75 6.2.2.2 Evaporative behaviour 77 6.2.2.3 Evolution of the capillary pressure 78 6.2.2.4 Discussion 80 6.3 Chapter summary 83 7 Deformation behaviour of the 3D-printed concrete elements due to plastic shrinkage 85 7.1 Materials and methods 85 7.2 Experimental results 86 7.2.1 Shrinkage-induced deformations 86 7.2.2 Allocation of the deformations to the reference coordinate system 88 7.2.3 Deformations dependent on the considered surface plane and position 88 7.2.3.1 Surface A 88 7.2.3.2 Surface B 90 7.2.3.3 Surface C 93 7.3 Proposed deformation model of the 3D-printed concrete elements due to PS 94 7.4 Formulation of the deformation functions 95 7.5 Verification of the proposed model 97 7.5.1 Experimentally obtained deformations 97 7.5.2 Modelled deformations 99 7.6 Discussion 99 7.6.1 Differences between cast and formwork-free produced elements 99 7.6.2 Applicability and limitations of proposed deformation models 102 7.7 Chapter summary 102 8 Evolution of capillary pressure in 3D-printed concrete elements: numerical modelling and experimental validation 105 8.1 Introduction to the modelling approach 105 8.1.1 Flow in the saturated medium 106 8.1.2 Flow in the unsaturated medium 107 8.1.3 Shrinkage 108 8.2 Boundary conditions and mesh 109 8.3 Experimental investigations 110 8.3.1 Preparation of the specimens 110 8.3.2 Experimental setup and procedure of the experiment 111 8.3.3 Determination of the input parameters for numerical simulation 112 8.4 Results and discussion 112 8.4.1 Model input parameters 112 8.4.1.1 Temperature and evaporation of the water 112 8.4.1.2 Bulk modulus 114 8.4.1.3 Water retantion curve 117 8.4.1.4 Air entry curve 117 8.4.1.5 Summary of the input parameters 118 8.4.2 Experimental results 118 8.4.2.1 Capillary pressure 118 8.4.2.2 Shrinkage test 119 8.4.3 Verification of the model output 121 8.4.3.1 Effect of the bulk modulus 121 8.4.3.2 Effect of the Poisson's ratio 122 8.4.3.3 Influence of the defined boundary conditions 122 8.4.4 The final model output result 124 8.4.4.1 Capillary pressure 124 8.4.4.2 Plastic shrinkage 125 8.5 Chapter summary 126 9 Advancement of the experimental technique for quantification of the plastic shrinkage cracking 127 9.1 Experimental program 127 9.2 Preparation of the samples and the experimental procedure 129 9.3 Results and discussion 130 9.4 Chapter summary 131 10 Mitigation of plastic shrinkage and plastic shrinkage cracking 133 10.1 Experimental program 133 10.2 Methods of investigation and materials 134 10.2.1 Passive mitigation approaches 134 10.2.1.1 Reduction of the paste content 134 10.2.1.2 Substitution of the cement content 134 10.2.1.3 Addition of the SAP 134 10.2.1.4 Addition of the SRA 138 10.2.1.5 Addition of fibres 138 10.2.2 Active mitigation approaches 138 10.2.3 Production of the specimens 138 10.2.3.1 General investigations 138 10.2.3.2 3D-printing of the demonstrator structure 140 10.3 Results and discussion 141 10.3.1 Modification of the reference composition 141 10.3.1.1 Reduction of the paste content 141 10.3.1.2 Substitution of the cement content 142 10.3.1.3 Addition of the SAP 142 10.3.1.4 Addition of the SRA 144 10.3.1.5 Addition of the fibres 144 10.3.2 Efficacy of mitigation strategies 145 10.3.2.1 Evolution of the capillary pressure 145 10.3.2.2 Plastic shrinkage 146 10.3.2.3 Cracking 148 10.3.3 Demonstrator structures 149 10.3.3.1 Evolution of the temperature and capillary pressure 149 10.3.3.2 Horizontal shrinkage 150 10.3.3.3 The effect of thermal expansion 151 10.3.3.4 Alteration of the surface qualities 152 10.3.4 Discussion 153 10.4 Chapter summary 154 11 Final conclusions and outlook 155 11.1 Summary and conclusions 155 11.2 Application of the findings 158 11.3 Future research topics 158 References 160 Appendices 170 A.1 Mixture compositions 170 A.2 Implementation of the deformation model 172 A.3 Implementation of the numerical model 173 A.4 Complementary results 175 A.4.1 Repeatability of the experimental results 175 A.4.2 Specifics of plastic shrinkage 180 A.4.3 Deformation behaviour 181 A.4.4 Numerical modelling and experimental validation 183 A.4.5 Mitigation methods 186 Curriculum vitae 190 List of publications 191 / Among various techniques for automated construction, 3D concrete printing (3DCP) counts as the most promising. 3D printing with concrete offers multiple advantages in cost savings, increased productivity and design freedom. 3DCP has rapidly transformed from a bold vision to a promising construction method in recent years. Manufacturing numerous demonstrators in several countries has proven the applicability of the new technology in various construction fields. Despite this, some issues still need to be resolved before 3DCP can be widely applied in construction practice. One among them is the early-age cracking of printed concrete elements due to shrinkage-induced deformations. Volumetric contractions related to shrinkage are at their highest before the solidification of 3D-printed layers. This type of shrinkage is attributed to the plastic shrinkage. Plastic shrinkage occurs due to the extensive water loss followed by the rise of the negative capillary pressure in the system. The negative pressure in the capillaries of concrete forces the system to contract. If the volumetric contractions are hindered by, e.g., layer bonding or rebar, and the occurred stresses are higher than the tensile strength of concrete, cracks begin to form. 3D-printed concrete elements are suspended to a much higher propensity to plastic shrinkage and related cracking than conventionally cast concrete. Cracks initiated due to plastic shrinkage can propagate through the entire cross-section of the printed wall. The damages caused by plastic shrinkage can severely affect durability, serviceability, and aesthetics and even jeopardise structural stability. Despite the importance of controlling and mitigating plastic shrinkage and later appearing shrinkage types, such as drying and autogenous shrinkage, until now, only a few studies have been dedicated to these topics. This dissertation focuses on the mechanisms of plastic shrinkage and related cracking of 3D-printed concrete elements. Since there is no standardized or commonly recognized method for quantification of the plastic shrinkage and related cracking of the printable concretes, in this study, affordable and easy-to-apply experimental setups for measuring unrestrained and restrained shrinkage-induced deformations along with relevant material properties of 3D-printed concretes were developed. The statistical analysis verifies the reliability of the experimental results obtained with developed setups. The findings of this study contribute to establishing a unified testing framework for studying the shrinkage and related cracking of 3D-printable concretes. On the basis of the developed experimental methodology, specifics of the mechanisms involved in the plastic shrinkage and related cracking of the 3D-printed elements were studied. The numerical simulation of the evolution of capillary pressure in 3D-printed elements supplemented experimental investigations. Special attention was paid to the analysis of the effect of the layer width and the influence of the surface area exposed to desiccation on the extent of the plastic shrinkage and cracking in 3D-printed concrete elements. It was found that the deformative behaviour due to shrinkage-induced stresses greatly differs from those of the cast concrete elements. The onset, directions and extent of the shrinkage-induced deformations in 3D-printed elements were thoroughly analysed, and as a result, analytical and numerical models for the prediction of shrinkage-induced deformations in the 3D-printed concrete elements were developed. Finally, various approaches for mitigating plastic shrinkage and cracking are analysed, and practical solutions for reducing the damages caused by shrinkage-induced deformations are suggested.:Abstract I Kurzfassung II Vorwort des Herausgebers IV Acknowledgement V Contents VI Notations and abbreviations XI 1 Introduction 1 1.1 Motivation 1 1.2 Relevance of the research 2 1.3 Objectives and research questions 2 1.4 Dissertation structure 3 2 Theoretical background 5 2.1 Plastic shrinkage of cementitious materials 5 2.1.1 Mechanisms of plastic shrinkage 5 2.1.2 Mechanisms of plastic shrinkage cracking 6 2.1.3 Experimental methods 7 2.1.4 Numerical methods 8 2.1.5 Mitigation techniques 9 2.1.5.1 Active mitigation approaches 9 2.1.5.2 Passive mitigation approaches 9 2.2 3D concrete printing 11 2.2.1 Flashback to history 11 2.2.2 Current state 14 2.2.3 Significance of the PS and PSC for 3D-printed concrete elements 14 2.2.3.1 Specifics of material compositions 14 2.2.3.2 Production related issues 14 2.2.3.3 Case studies 15 2.2.4 Previous studies on PS and PSC of 3D-printed concrete elements 19 2.3 Chapter summary 19 3 Materials and methods 21 3.1 Reference composition 21 3.2 Experimental methods 22 3.2.1 3D concrete printing test device 22 3.2.2 Wind tunnel and climate control chamber 23 3.2.3 Determination of the specific material properties 23 3.2.3.1 Air content and spread flow 23 3.2.3.2 Capillary pressure 24 3.2.3.3 Ultrasonic pulse velocity 24 3.2.3.4 Tempe cell and self-desiccation tests 24 3.2.3.5 Falling-head method 25 3.2.3.6 Tea bag test 25 3.2.3.7 Confined uniaxial compression test 26 3.2.3.8 Penetration test 26 3.2.3.9 Microscopy 27 3.2.4 Digital image correlation 27 3.3 Numerical method 28 3.4 Chapter summary 28 4 Quantification of plastic shrinkage and plastic shrinkage cracking of the 3D-printable concretes using 2D digital image correlation 29 4.1 Novel setups for quantification of the PS and PSC 29 4.2 Materials and methods of investigation 30 4.2.1 3D printing and preparation of samples 30 4.2.2 Evaluation of the deformations 32 4.2.3 Experimental setup and procedure 33 4.3 Experimental results 33 4.3.1 Penetration force 33 4.3.2 Free shrinkage behaviour 34 4.3.2.1 Vertical settlement 34 4.3.2.2 Horizontal shrinkage 35 4.3.3 Shrinkage behaviour in partially and fully restrained tests 35 4.3.3.1 Vertical shrinkage 35 4.3.3.2 Horizontal shrinkage 36 4.3.3.3 Shrinkage-induced cracking 38 4.3.4 Influence of the paint on the surface 41 4.4 Discussion of the test setups and measuring techniques 42 4.5 Chapter summary 43 5 Repeatability of the experimental results 45 5.1 Followed statistical approach for assessment of the repeatability 45 5.2 Experimental program 46 5.3 Preparation of the samples and the experimental procedure 46 5.4 Results and discussion 48 5.4.1 Repeatability of the experimental results in previous studies 48 5.4.2 Free shrinkage 49 5.4.2.1 Spread flow, density and air content 49 5.4.2.2 Ambient conditions 49 5.4.2.3 Water loss 50 5.4.2.4 Evolution of the capillary pressure 50 5.4.2.5 Temperature 51 5.4.2.6 Shrinkage 52 5.4.2.7 Evaluation of the repeatability 55 5.4.3 Restrained shrinkage 56 5.4.3.1 Basic fresh-state properties 56 5.4.3.2 Ambient conditions 56 5.4.3.3 Water loss 57 5.4.3.4 Evolution of the capillary pressure 58 5.4.3.5 Temperature 58 5.4.3.6 Shrinkage 59 5.4.3.7 Cracking 60 5.4.3.8 Evaluation of repeatability 62 5.5 Chapter summary 63 6 Specifics of plastic shrinkage and related cracking in 3D-printed concrete elements 65 6.1 Materials and methods 65 6.1.1 Impact of layer width 66 6.1.2 Reduction of the area exposed to desiccation 67 6.2 Results and discussion 68 6.2.1 The influence of the width of the layer 68 6.2.1.1 Evolution of the capillary pressure 68 6.2.1.2 Waterloss and temperature 69 6.2.1.3 Plastic shrinkage 71 6.2.1.4 Plastic shrinkage cracking 72 6.2.1.5 Discussion 74 6.2.2 The impact of formwork-free production technique 75 6.2.2.1 Plastic shrinkage 75 6.2.2.2 Evaporative behaviour 77 6.2.2.3 Evolution of the capillary pressure 78 6.2.2.4 Discussion 80 6.3 Chapter summary 83 7 Deformation behaviour of the 3D-printed concrete elements due to plastic shrinkage 85 7.1 Materials and methods 85 7.2 Experimental results 86 7.2.1 Shrinkage-induced deformations 86 7.2.2 Allocation of the deformations to the reference coordinate system 88 7.2.3 Deformations dependent on the considered surface plane and position 88 7.2.3.1 Surface A 88 7.2.3.2 Surface B 90 7.2.3.3 Surface C 93 7.3 Proposed deformation model of the 3D-printed concrete elements due to PS 94 7.4 Formulation of the deformation functions 95 7.5 Verification of the proposed model 97 7.5.1 Experimentally obtained deformations 97 7.5.2 Modelled deformations 99 7.6 Discussion 99 7.6.1 Differences between cast and formwork-free produced elements 99 7.6.2 Applicability and limitations of proposed deformation models 102 7.7 Chapter summary 102 8 Evolution of capillary pressure in 3D-printed concrete elements: numerical modelling and experimental validation 105 8.1 Introduction to the modelling approach 105 8.1.1 Flow in the saturated medium 106 8.1.2 Flow in the unsaturated medium 107 8.1.3 Shrinkage 108 8.2 Boundary conditions and mesh 109 8.3 Experimental investigations 110 8.3.1 Preparation of the specimens 110 8.3.2 Experimental setup and procedure of the experiment 111 8.3.3 Determination of the input parameters for numerical simulation 112 8.4 Results and discussion 112 8.4.1 Model input parameters 112 8.4.1.1 Temperature and evaporation of the water 112 8.4.1.2 Bulk modulus 114 8.4.1.3 Water retantion curve 117 8.4.1.4 Air entry curve 117 8.4.1.5 Summary of the input parameters 118 8.4.2 Experimental results 118 8.4.2.1 Capillary pressure 118 8.4.2.2 Shrinkage test 119 8.4.3 Verification of the model output 121 8.4.3.1 Effect of the bulk modulus 121 8.4.3.2 Effect of the Poisson's ratio 122 8.4.3.3 Influence of the defined boundary conditions 122 8.4.4 The final model output result 124 8.4.4.1 Capillary pressure 124 8.4.4.2 Plastic shrinkage 125 8.5 Chapter summary 126 9 Advancement of the experimental technique for quantification of the plastic shrinkage cracking 127 9.1 Experimental program 127 9.2 Preparation of the samples and the experimental procedure 129 9.3 Results and discussion 130 9.4 Chapter summary 131 10 Mitigation of plastic shrinkage and plastic shrinkage cracking 133 10.1 Experimental program 133 10.2 Methods of investigation and materials 134 10.2.1 Passive mitigation approaches 134 10.2.1.1 Reduction of the paste content 134 10.2.1.2 Substitution of the cement content 134 10.2.1.3 Addition of the SAP 134 10.2.1.4 Addition of the SRA 138 10.2.1.5 Addition of fibres 138 10.2.2 Active mitigation approaches 138 10.2.3 Production of the specimens 138 10.2.3.1 General investigations 138 10.2.3.2 3D-printing of the demonstrator structure 140 10.3 Results and discussion 141 10.3.1 Modification of the reference composition 141 10.3.1.1 Reduction of the paste content 141 10.3.1.2 Substitution of the cement content 142 10.3.1.3 Addition of the SAP 142 10.3.1.4 Addition of the SRA 144 10.3.1.5 Addition of the fibres 144 10.3.2 Efficacy of mitigation strategies 145 10.3.2.1 Evolution of the capillary pressure 145 10.3.2.2 Plastic shrinkage 146 10.3.2.3 Cracking 148 10.3.3 Demonstrator structures 149 10.3.3.1 Evolution of the temperature and capillary pressure 149 10.3.3.2 Horizontal shrinkage 150 10.3.3.3 The effect of thermal expansion 151 10.3.3.4 Alteration of the surface qualities 152 10.3.4 Discussion 153 10.4 Chapter summary 154 11 Final conclusions and outlook 155 11.1 Summary and conclusions 155 11.2 Application of the findings 158 11.3 Future research topics 158 References 160 Appendices 170 A.1 Mixture compositions 170 A.2 Implementation of the deformation model 172 A.3 Implementation of the numerical model 173 A.4 Complementary results 175 A.4.1 Repeatability of the experimental results 175 A.4.2 Specifics of plastic shrinkage 180 A.4.3 Deformation behaviour 181 A.4.4 Numerical modelling and experimental validation 183 A.4.5 Mitigation methods 186 Curriculum vitae 190 List of publications 191

This diploma thesis deals with a design and manufacture of an active print head used for 3D printing of concrete mixtures. The aim is to ensure functional parameters of the print head at a minimal mass. Extrusion of the material from the print head is ensured by a screw conveyor, shaping of the material is carry out by a rotatably mounted nozzle provided with trowels. The dimensioning of the main elements of the print head is based on the parameters measured during tests with the older version of the print head and on the FEM analysis. The print head was manufactured and is able to extrude concrete mixture with an admixture of aggregate (fraction 4–8 mm) at a rate of 0,5–2 m3•h-1. The weight of the print head is 16.4 kg, which is 30 percent less than an older print head weighed. The manufactured print head was tested during the printing of a real object and met all the required parameters. The print head is ready for implementation in a machine providing large-scale printing of parts in the construction industry.

Die selektive Zementaktivierung (SCA) ist ein additives Fertigungsverfahren zur Herstellung von Bauteilen aus Beton. Die SCA gehört zu den Verfahren des selektiven Bindens, bei denen schüttfähiges Material (hier eine Trockenmischung aus Zement und Gesteinskörnung) in dünnen Schichten ausgebracht und durch Einbringen einer flüssigen Komponente (hier Wasser) selektiv gebunden wird. Verglichen mit anderen Verfahren der additiven Fertigung mit Beton sind bei der SCA sowohl die Auflösung als auch die geometrische Freiheit besonders hoch. ... / Selective cement activation (SCA) is an additive manufacturing process for the fabrication of concrete elements. SCA belongs to the group of the selective binding processes in which bulk material (here a dry mixture of cement and aggregate) is spread in thin layers and selectively bound by applying a liquid component (here water). Compared to other additive manufacturing processes using concrete, both resolution and geometric freedom are particularly high with SCA. ...

Incorporating reinforcement into the practice of digital concrete construction, often called 3D-concrete-printing, is a prerequisite for wide-ranging, structural applications of this new technology. Strain-Hardening Cement-based Composites (SHCC) offer one possible solution to this challenge. In this work, printable SHCC were developed and tested. The composites could be extruded through a nozzle of a 3D-printer so that continuous filaments could be deposited, one upon the other, to build lab-scaled wall specimens without noticeable deformation of the bottom layers. The specimens extracted from the printed walls exhibited multiple fine cracks and pronounced strain-hardening characteristics under uniaxial tensile loading, even for fiber volume fractions as low as 1.0%. In fact, the strain-hardening characteristics of printed specimens were superior to those of mold-cast SHCC specimens.

Dieser Beitrag bietet einen Überblick über den aktuellen Sachstand auf dem Gebiet der additiven Fertigungsverfahren mit Beton, auch 3D-Betondruck genannt. Im Einzelnen wird auf die zugehörige Materialprüfung von druckbarem bzw. gedrucktem frischem, erhärtendem und erhärtetem Beton eingegangen. Außerdem werden mögliche Varianten zur Integration der Bewehrung in die additive Fertigung mit Beton dargelegt.

Conventional construction of concrete shells involves a costly and time-consuming erection of custom formwork. An alternative approach that avoids this is an on-site assembly of shells from prefabricated modules. This article presents a new, highly automated method for the production of such modules. The proposed method combines the technology of full-width 3D concrete printing using strain-hardening cement-based composite and the technology of robotic textile mesh production from mineral-impregnated carbon yarns.