Corrosion of reinforcing steel in concrete is a significant problem around the world. In the United States, there are approximately 600,000 bridges. From those bridges 24% are considered structurally deficient or functionally obsolete based on the latest, December 2010, statistic from the Federal Highway Administration (FHWA). Mainly, this is due to chloride attack present in deicing salts which causes the reinforcing steel to corrode. Different solutions have been developed and used in practice to delay and prevent corrosion initiation. The purpose of this research is to investigate the influence of corrosion on the failure mechanism that occurred on an Interstate 81 bridge deck. After 17 years in service, a 3ft x3ft closure pour section punched through. It was part of the left wheel path of the south bound right lane of the bridge deck. The bridge deck was replaced in 1992 as part of a bridge rehabilitation project, epoxy coated reinforcement were used as the reinforcing steel. Four slabs from the bridge deck, containing the closure, were removed and transported to the Virginia Tech Structures and Materials Research Laboratory for further evaluation. Also, three lab cast slabs were fabricated as part of the assessment program. Corrosion evaluation and concrete shrinkage characterization were conducted in this research. The corrosion evaluation study included visual observation, clear concrete cover depth, concrete resistivity using single point resistivity, half-cell potential, and linear polarization using the 3LP device. Shrinkage characteristics were conducted on the lab cast slabs only, which consisted of monitoring shrinkage behavior of the specimens for 180 days and comparison of the data with five different shrinkage models. Based on the research results, guidance for assessment of other bridge decks with similar conditions will be constructed to avoid similar types of failures in the future. / Master of Science

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

The influence of several hardwoods and softwoods pulp fibre on the free shrinkage of isotropic paper sheets was investigated. The effect of properties such as density, grammage, Fractional Contact Area (FCA), Water Retention Value (WRV), fines content and fibre morphology were also investigated on the free shrinkage of isotropic paper sheets. Further, the influence of Lyocell fibre and glycerol on the free shrinkage of isotropic paper sheets is reported. Experimental results showed that in general the free shrinkage of hardwood pulps is a few percent higher than that of softwood pulps at the same density. It was found that although free shrinkage increases with fines content, a high fines content does not imply high shrinkage, and some pulp samples with higher amount of fines, exhibited lower free shrinkage. For all pulps at low densities there is little influence of grammage on free shrinkage, though as density increases a significant dependence is observed. The results showed that the free shrinkage of isotropic paper sheets formed from hardwood pulps is more sensitive to grammage compared to that of softwood pulps. Interestingly, it was shown that some pulp samples with the same intrinsic density, WRV and FCA exhibited different free shrinkage over the range of grammages. In addition, some pulp samples with stiffer fibres but higher amount of fines exhibited higher free shrinkage. Experimental results showed that longitudinal shrinkage of a fibre is an important parameter and pulp samples with higher microfibril angle (MFA) exhibited higher longitudinal shrinkage. Finally, the free shrinkage of isotropic paper sheets was reduced by applying Lyocell fibre and glycerol. Interestingly, by adding a small amount of Lyocell fibre, 2%, an increase in tensile index, tensile energy absorption (TEA) and modulus is observed, while the free shrinkage reduced up to 2%. In addition, adding glycerol to the pulp samples not only reduced the free shrinkage of isotropic paper sheets up to 1.5%, but also mechanical properties, such as tensile index and stretch slightly improved.

This thesis investigates improved estimators of the parameters of the linear regression models with normal errors, under sample and non-sample prior information about the value of the parameters. The estimators considered are the unrestricted estimator (UE), restricted estimator (RE), shrinkage restricted estimator (SRE), preliminary test estimator (PTE), shrinkage preliminary test estimator (SPTE), and shrinkage estimator (SE). The performances of the estimators are investigated with respect to bias, squared error and linex loss. For the analyses of the risk functions of the estimators, analytical, graphical and numerical procedures are adopted. In Part I the SRE, SPTE and SE of the slope and intercept parameters of the simple linear regression model are considered. The performances of the estimators are investigated with respect to their biases and mean square errors. The efficiencies of the SRE, SPTE and SE relative to the UE are obtained. It is revealed that under certain conditions, SE outperforms the other estimators considered in this thesis. In Part II in addition to the likelihood ratio (LR) test, the Wald (W) and Lagrange multiplier (LM) tests are used to define the SPTE and SE of the parameter vector of the multiple linear regression model with normal errors. Moreover, the modified and size-corrected W, LR and LM tests are used in the definition of SPTE. It is revealed that a great deal of conflict exists among the quadratic biases (QB) and quadratic risks (QR) of the SPTEs under the three original tests. The use of the modified tests reduces the conflict among the QRs, but not among the QBs. However, the use of the size-corrected tests in the definition of the SPTE almost eliminates the conflict among both QBs and QRs. It is also revealed that there is a great deal of conflict among the performances of the SEs when the three original tests are used as the preliminary test statistics. With respect to quadratic bias, the W test statistic based SE outperforms that based on the LR and LM test statistics. However, with respect to the QR criterion, the LM test statistic based SE outperforms the W and LM test statistics based SEs, under certain conditions. In Part III the performance of the PTE of the slope parameter of the simple linear regression model is investigated under the linex loss function. This is motivated by increasing criticism of the squared error loss function for its inappropriateness in many real life situations where underestimation of a parameter is more serious than its overestimation or vice-versa. It is revealed that under the linex loss function the PTE outperforms the UE if the nonsample prior information about the value of the parameter is not too far from its true value. Like the linex loss function, the risk function of the PTE is also asymmetric. However, if the magnitude of the scale parameter of the linex loss is very small, the risk of the PTE is nearly symmetric.

Published Article / Metal injection moulding (MIM) offers advantages for mass production of components over conventional production methods for parts with complex shapes and large production runs. The MIM process includes mixing a fine metallic powder with a polymeric binder to produce a homogeneous feedstock. This enables the production of metallic components in a similar manner to plastic injection moulding. After undergoing a process of binder removal the components undergo a conventional sintering cycle. As significant shrinkage occurs (as much as 30%) this must be considered when designing the die cavity. This paper describes the design and manufacture of a die to produce tensile specimens. Extensive injection moulding trials to produce acceptable tensile components were undertaken. The complexities and possible implications of the design of a mould on the process are discussed. The outcomes of this research will be used by the CSIR for further development and application of the MIM technology for manufacture of high value components, such as dental implants.

The focus for this research is to develop and apply statistical methods to analyze and interpret high-throughput biological data. We developed a novel correlation coefficient, shrinkage correlation coefficient (SCC), that fully exploits the similarity between the replicated microarray experimental samples. The methodology considers both the number of replicates and the variance within each experimental group in clustering expression data, and provides a robust statistical estimation of the error of replicated microarray data. Applying SCC-based hierarchical clustering to the replicated microarray data obtained from germinating spores of the fern Ceratopteris richardii, we discovered two clusters of genes with shared expression patterns during spore germination. This computational approach is not only applicable to DNA microarray analysis but is also applicable to proteomics data or any other high-throughput analysis methodology. The suppression of APY1 and APY2 in mutants expressing an inducible RNAi system resulted in plants with a dwarf phenotype and disrupted auxin distribution, and we used these mutants to discover what genes changed expression during growth suppression. We evaluated the gene expression changes of apyrase-suppressed RNAi mutants that had been grown in the light and in the darkness, using the NimbleGen Arabidopsis thaliana 4-Plex microarray, respectively. We compared the two sets of large-scale expression data and identified genes whose expression significantly changed after apyrase suppression in light and darkness, respectively. Our results allowed us to highlight some of the genes likely to play major roles in mediating the growth changes that happen when plants drastically reduce their production of APY1 and APY2, some more associated with growth promotion and others, such as stress-induced genes, more associated with growth inhibition. There is a strong rationale for ranking all these genes as prime candidates for mediating the inhibitory growth effects of suppressing apyrase expression, thus the NimbleGen data will serve as a catalyst and valuable guide to the subsequent physiological and molecular experiments that will be needed to clarify the network of gene expression changes that accompany growth inhibition. / text

<div>Process induced dimensional changes in composite parts has been the topic of interest for many researchers. The residual stresses that are induced in composite laminates during curing process while the laminate is in contact with the process tool often lead to dimensional variations such as spring-in of angles and warpage of flat panels. The traditional trial-and-error approach can work for simple geometries, but composite parts with complex shapes require more sophisticated models. When composite laminates are subjected to thermal stresses, such as the heating and cooling processes during curing, they can become distorted as the in-plane and the throughthickness</div><div>coffcients of thermal expansion are different, as well as chemical shrinkage of the resin, usually cause spring-in. Deformed components can cause problems during</div><div>assembly, which significantly increases production costs and affects performance. This thesis focuses on predicting these shape deformations using software simulation of composite manufacturing and curing. Various factors such as resin shrinkage, degrees of cure, difference between through thickness coefficient of thermal expansion of the composite laminate are taken into the consideration. A cure kinetic model is presented which illustrates the matrix behavior during cure. The results obtained using the software then were compared with the experimental values of spring-in from the available literature. The accuracy of ACCS package was validated in this study. Analyzing the effects of various parameters of it was estimated that 3D part simulation is an effective and cost and time saving method to predict final shape of the composite part.</div>

RESUMO Dada sua versatilidade e excelência estética, a resina composta é o material restaurador direto mais utilizado nas intervenções da clínica odontológica. Uso tão intenso levou pesquisadores e fabricantes a trabalharem na evolução deste material, conferindo-lhe aumento em sua resistência à compressão e abrasão, bem como melhora em seu comportamento estético. Infelizmente, um problema intrínseco da resina, a contração de polimerização é sua principal desvantagem, e caracteriza-se pela alteração volumétrica que sofre quando as moléculas de seus monômeros se unem para a formação das cadeias poliméricas. Uma das principais técnicas para combater os efeitos nocivos desta alteração volumétrica é a inserção incremental do material na cavidade a ser restaurada. Nesta pesquisa, a contração de polimerização de uma resina composta de uso universal (Charisma Heraeus Kullser) será avaliada variando-se a técnica de inserção do material na cavidade em incremento único ou três incrementos oblíquos, através do método da picnometria a gás. O picnômetro Accupyc 1330 (Micromeritics) permite medições rápidas e fiéis do volume da resina composta antes e após a fotoativação. Os resultados mostram que ocorreram diferenças estatísticas entre as duas técnicas, sendo a técnica de único incremento a que apresentou menor contração de polimerização. / Because of its versatility and aestetic excellency, composite resin is one of the most utilized direct restorative materials. Because of the resin intense use, the number of researches to improve its performance are numerous, and can be verified by the resin aestethetic behavior and its compressive and abrasion strenght increase. In spite of the mentioned developments, the polymerization shrinkage inherent of the material had been a major deficiency, and can be understood by the alteration in volume of the material after the polymerization process. In the present study, the polymerization shrinkage of the restorative material Charisma (Heraes Kulzer), was evaluated using bulk and incremental placement techniques and measured by gas pycnometer. Accupyc 1330 (Micromeritics, USA) pycnometer measures the helium displacement with great precision, allowing fast and accurate measurements of the volume of the composite resin before and after polymerization, without interference of the moisture or temperature. The results showed statistically significant diferences between the two placement techniques, with the bulk technique showing lower polymerization shrinkage than the incremental technique.

Submitted by Eunice Novais (enovais@uepg.br) on 2018-05-21T18:29:42Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Manoella Maria Machado Costa.pdf: 2056005 bytes, checksum: cea06c624bdf599dba9ef2d9e2c099ab (MD5) / Made available in DSpace on 2018-05-21T18:29:42Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Manoella Maria Machado Costa.pdf: 2056005 bytes, checksum: cea06c624bdf599dba9ef2d9e2c099ab (MD5) Previous issue date: 2018-02-16 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O objetivo do estudo foi avaliar a influência dos modos de fotoativação Contínua e Ramp nas propriedades de contração de polimerização e alteração térmica de uma resina composta Filtek™Bulk Fill Flow. Foram selecionados 30 dentes terceiros molares hígidos nos quais foi preparada uma cavidade de Classe I oclusal (4 mm de comprimento x 4 mm de largura x 4 mm de profundidade). Para o posicionamento dos sensores de Bragg, um sensor foi posicionado no sentido mésio-distal diretamente em contato com a resina que mediu a deformação de contração, e outro no interior de uma agulha hipodérmica no sentido vestíbulo-lingual que mediu somente a temperatura. Os dentes foram restaurados com a resina Filtek ™ Bulk Fill Flow de acordo com as recomendações do fabricante. Posteriormente, utilizou-se uma fórmula para obter o valor de deformação pura do material em μstrain. A análise estatística foi obtida por meio de análise de variância e teste t de Student. Os resultados revelaram não haver diferenças estatísticas significativas para os valores de contração entre os dois protocolos de fotoativação (Contínuo e Ramp) e entre os tempos de 500s, 1500s, 2500s e 3500s. Ao final de 3500s observou-se uma tendência à estabilização das curvas para ambos os modos de fotoativação. A fotoativação Ramp revelou maior valor de variação de temperatura (16,32°C) quando comparada à fotoativação Contínua (7,8°C). Os sensores de Bragg foram capazes de medir a alteração de contração e a variação térmica. A fotoativação contínua demorou mais para retornar ao valor inicial de temperatura (2,85 min) que a Ramp (1,65 min). Futuros estudos devem monitorar a contração de polimerização por um intervalo de tempo maior necessário para a estabilização total da curva. / The objective of this study was to evaluate the influence of Continuous and Ramp photoactivation modes on the shrinkage polymerization, and thermal change properties of a Filtek™ Bulk Fill Flow composite. 30 third molar teeth were selected. An occlusal Class I cavity (4 mm length x 4 mm wide x 4 mm depth) was prepared.For the positioning of the Bragg sensors, a sensor was positioned in the mesio-distal direction directly in contact with the composite that measured the shrinkage deformation, and another sensor inside a hypodermic needle in the lingual-lingual direction that measured only the temperature. The teeth were restored with Filtek™Bulk Fill Flow resin according to the manufacturer's recommendations. Subsequently, was used a formula to obtain the pure deformation value of the material in μstrain. Statistical analysis was obtained through analysis of variance and Student's t-test. The results showed no significant statistical differences for the shrinkage values between the two photoactivation protocols (Continuous and Ramp) and among 500s, 1500s, 2500s and 3500s times. At the end of 3500s a tendency to stabilize the curves for both modes of photoactivation was observed. The Ramp photoactivation revealed a higher value of temperature variation (16.32°C) when compared to Continuous photoactivation (7.8 °C). The Bragg sensors were able to measure the shrinkage, and the thermal variation. Continuous photoactivation took longer to return to the initial temperature value (2.85 min) than ramp (1.65 min). Future studies should monitor the shrinkage of polymerization for a longer period of time necessary for the total stabilization of the curve.

This study investigated the effectiveness of various analytical methods used for estimating R2 shrinkage in multiple regression analysis. Two categories of analytical formulae were identified: estimators of the population squared multiple correlation coefficient (ρ2), and estimators of the population cross-validity coefficient (ρc2). To avoid possible confounding factors that might be associated with a real data set such as data nonnormality, lack of precise population parameters, different degrees of multicollinearity among the predictor variables, and so forth, the Monte Carlo method was used to simulate multivariate normal sample data, with prespecified population parameters such as the squared multiple correlation coefficient (ρ2), number of predictors, different sample sizes, known degree of multicollinearity, and controlled data normality conditions. Five hundred replicates were simulated within each cell of the sampling conditions. Various analytical formulae were applied to the simulated data in each sampling condition, and the "adjusted" coefficients were obtained and then compared to their corresponding population parameters (ρ2 and ρc2). Analysis of the results indicates that the currently most widely used (in both SAS and SPSS) "Wherry" formula is probably not the most effective analytical formula in estimating ρ2. Instead, the Pratt formula appeared to outperform other analytical formulae across most of these sampling conditions. Among the analytical formulae designed to estimate ρc2, the Browne formula appeared to be the most effective and stable in minimizing statistical bias across different sampling conditions. The study also concludes that it is the n/p (sample size/number of predictor variables) ratio that affects the performances of these analytical formulae the most; different degrees of multicollinearity among predictor variables do not have dramatic influence on the performances of these analytical formulae. Further replicants on both real and simulated data re still needed to investigate the effectiveness of these analytical formulae.