The objective of this study is to evaluate the bond durability of an epoxy-based polymer concrete wearing surface bonded to aluminum bridge decks. In the bridge design, an aluminum alloy bridge deck is used with a polymer concrete wearing surface. A modified mixed mode flexure fracture test was developed to assess the bond durability of specimens aged in the following environmental conditionings: 30°C [86°F], 98% RH; 45°C [113°F], 98% RH; 60°C [140°F], 98% RH; freezing and thawing; salt (NaCl) water soak; and 60°C [140°F], dry. The exposure times varied from none to twelve months. The critical strain energy release rate (Gc) of the bond was determined using a compliance technique. In spite of considerable scatter in the data, the results suggested that the interfacial bond toughness had been degraded by exposure conditions. The aging appeared to affect the polymer concrete overlay (silica aggregates/epoxy bond) as well. Fracture analysis and finite element modeling were completed for linear elastic behavior. Analytical and numerical solutions were in reasonably good agreement. Characterization of the bridge components and failure specimens were accomplished using analytical measurements including thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Techniques employed in the surface analysis included x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). / Master of Science

Proton exchange membrane fuel cells typically consist of stacks of membrane electrode assemblies sandwiched between bipolar plates, effectively combining the individual cells in series to achieve the desired voltage levels. Elastomeric gaskets are commonly used between each cell to insure that the reactant gases are isolated; any failure of a fuel cell gasket can cause the reactants to mix, which may lead to failure of the fuel cell. An investigation of the durability of these fuel cell seals was performed by using accelerated characterization methods. A hydrocarbon sealant was tested in five different environments to simulate fuel cell conditions. Viscoelastic properties of these seals were analyzed using momentary and relaxation compressive stress tests. Material properties such as secant modulus at 100% strain, tensile strength, and strain at failure were determined using dog-bone samples aged at several different imposed strains and aging times in environments of interest. Tearing energy was evaluated using trouser test samples tested under different rates and temperatures after various environmental aging conditions. Additionally, tearing tests were conducted on samples tested in liquid environment. A viscoelastic and mechanical property characterization of these elastomeric seals under accelerated aging conditions could help understand the behavior and predict durability in the presence of mechanical and environmental loading. Additionally, the effects of confinement have been evaluated for a bonded joint with varying thickness along the bonded direction. The Dreaming project is a glass art project in Fredrick, MD which incorporates such a varying thickness joint where thermal expansion of the adhesive has caused the glass adherend to break and debonding of the sealant. To examine this joint design, finite element analysis has been used to determine the effects of thermal expansion on such a complex geometry. Nine different test geometries have been evaluated to determine the effect of confinement coupled with thermal expansion on joint design with an elastomeric adhesive. Once evaluated, design changes were performed to try to reduce the loading while maintaining the general joint design. Results of this analysis can be used to determine the effects of confinement on a complex elastomeric joint. / Master of Science

A group of researchers, engineers, and government transportation officials have teamed up to design two bridges with simply-supported FRP composite structural beams. The Toms Creek Bridge, located in Blacksburg, Virginia, has been in service for six years. Meanwhile, the Route 601 Bridge, located in Sugar Grove, Virginia, has been in service for two years. Researchers have conducted load tests at both bridges to determine if their performance has changed during their respective service lives. The key design parameters under consideration are: deflection, wheel load distribution, and dynamic load allowance. The results from the latest tests in 2003 yield little, yet statistically significant, changes in these key factors for both bridges. Most differences appear to be largely temperature related, although the reason behind this effect is unclear. For the Toms Creek Bridge, the largest average values from the 2003 tests are 440 me for service strain, 0.43 in. (L/484) for service deflection, 0.08 (S/11.1) for wheel load distribution, and 0.64 for dynamic load allowance. The values for the Route 601 Bridge are 220 me, 0.38 in. (L/1230), 0.34 (S/10.2), and 0.14 for the same corresponding paramters. The recommended design values for the dynamic load allowance in both bridges have been revised upwards to 1.35 and 0.50 for the Toms Creek Bridge and Route 601 Bridge, respectively, to account for variability in the data. With these increased factors, the largest strain in the toms Creek Bridge and Route 601 Bridge would be less than 13% and 12%, respectively, of ultimate strain. Therefore, the two bridges continue to provide a large factor of safety against failure. / Master of Science

[ES] La corrosión de las armaduras es una de las principales causas de deterioro y fallo prematuro de las estructuras de hormigón armado. La preocupación en torno a este fenómeno ha propiciado el desarrollo de numerosos sistemas de monitorización embebidos. Esta metodología de control permite detectar procesos de corrosión antes de que comprometan la seguridad estructural y, de esta forma, evitar costosas reparaciones. Sin embargo, los sistemas de monitorización existentes están basados normalmente en la inserción de un elemento sensor que permanece aislado eléctricamente del resto del armado de la estructura y sobre el que se aplica una técnica electroquímica de medida. Esta aproximación ignora los procesos de macrocelda que se generan, por lo que los resultados obtenidos no son representativos del estado real de las armaduras, pudiendo conducir a errores en la estimación del daño por corrosión. El presente trabajo recoge un análisis de los procesos de macrocelda que se producen internamente en las estructuras de hormigón armado y los factores que más influyen en la intensidad a la que se desarrollan. Además, y mediante un caso práctico de seguimiento de la corrosión en diferentes armaduras, este trabajo demuestra que las corrientes de macrocelda pueden incrementar de manera significativa la velocidad de corrosión y reducir el periodo de iniciación, por lo que no pueden ser ignoradas por los sistemas de monitorización. Como respuesta a las limitaciones de los sistemas embebidos empleados actualmente, en este trabajo se presenta un sistema de monitorización en continuo que incluye como sensor de corrosión un segmento de armadura conectado eléctricamente al armado de la estructura para hacerle partícipe de los procesos de macrocelda. De esta forma, el método de monitorización propuesto es capaz de ofrecer un resultado representativo del armado donde el sensor está embebido, ya que se tienen en cuenta tanto los fenómenos de macrocelda como de corrosión local. Para la determinación de la velocidad de corrosión local se propone asimismo una nueva técnica de medida basada en la voltametría mediante escalones de potencial y el estudio de la carga eléctrica acumulada y que, además, prácticamente no polariza la armadura. Asimismo, este procedimiento de medida incluye una secuencia de pulsos inicial para el cálculo de la resistencia óhmica, evitando la necesidad de calcular todos los componentes del circuito equivalente. El sistema de monitorización propuesto ha sido implementado y validado en diferentes probetas y elementos estructurales fabricados a escala reducida. Los resultados obtenidos han demostrado una gran precisión y una mejora en la fiabilidad respecto a los sistemas tradicionales, habiendo contrastado los resultados con métodos gravimétricos y técnicas electroquímicas de referencia. / [CA] La corrosió de les armadures és una de les principals causes de deteriorament i fallada prematura de les estructures de formigó armat. La preocupació al voltant d'aquest fenomen ha propiciat el desenvolupament de nombrosos sistemes de monitoratge embeguts. Aquesta metodologia de control permet detectar processos de corrosió abans que comprometen la seguretat estructural i, d'aquest mode, evitar costoses reparacions. No obstant això, els sistemes de monitoratge existents estan basats normalment en la inserció d'un element sensor que roman aïllat de la resta de l'armat de l'estructura. Sobre aquest element s'aplica una tècnica electroquímica de mesura de la corrosió. Aquesta aproximació ignora els processos de macrocelda que es generen i, per tant, els resultats obtinguts no són representatius de l'estat real de les armadures, el que pot conduir a errors en l'estimació del dany per corrosió. El present treball recull una anàlisi dels processos de macrocelda que es produeixen internament en les estructures de formigó armat i els factors que més influeixen en la intensitat a la qual es desenvolupen. A més a més, i mitjançant un cas pràctic de seguiment de la corrosió en diferents armadures, aquest treball demostra que els corrents de macrocelda poden incrementar de manera significativa la velocitat de corrosió i reduir el període d'iniciació, per la qual cosa no poden ser ignorats pels sistemes de monitoratge. Com una resposta a les limitacions dels sistemes utilitzats normalment, en aquest treball es presenta un sistema de monitoratge en continu que inclou com sensor de corrosió un segment d'armadura connectat elèctricament a l'armat de l'estructura per poder participar en els processos de macrocelda. D'aquesta manera, el mètode proposat és capaç d'oferir un resultat representatiu de l'armat on es troba el sensor, ja que es tenen en compte tant els fenòmens de macrocelda com de corrosió local. Així mateix, per a determinar la velocitat de corrosió local es proposa una nova tècnica de mesura basada en la voltametria mitjançant escalons de potencial i estudi de la càrrega elèctrica transferida, el qual pràcticament no polaritza l'armadura. A més a més, aquest procediment d'anàlisi inclou una seqüència de polsos inicial per al càlcul de la resistència òhmica, la qual cosa permet evitar la necessitat de calcular tots els components del circuit equivalent. El sistema de monitoratge proposat ha sigut implementat i validat en diferents provetes i elements estructurals fabricats a escala reduïda. Els resultats obtinguts han demostrat una gran precisió i una millora en la fiabilitat respecte als sistemes tradicionals. Aquestes dades han sigut validades mitjançant mètodes gravimètrics i tècniques electroquímiques de referència. / [EN] Rebar corrosion is one of the main causes of deterioration and early failure of reinforced concrete structures. Concerns voiced about this phenomenon have favoured many embedded monitoring systems being developed. This control methodology allows corrosion processes to be detected before structural security is compromised and, thus, avoids costly repair works. However, today's monitoring systems are normally based on inserting a sensor element, which is electrically isolated from the remaining structure's reinforcement, and on applying an electrochemical measuring technique. As this approach ignores macrocell processes, the obtained results are not representative of the real rebar state and may lead to mistakes being made when estimating the corrosion damage. This work analyses internally produced macrocell processes in reinforced concrete structures and the factors that most influence the intensity that these processes develop. With a practical corrosion follow-up case in different rebars, it also demonstrates that macrocell currents can significantly increase the corrosion rate and shorten the initiation period. Therefore, monitoring systems should not ignore these currents. To overcome the limitations of currently used embedded systems, an innovative alternative is presented. The system presented includes a rebar segment that is electrically connected to the structure's reinforcements to act as a corrosion sensor, so that it can participate in macrocell processes. Hence, the proposed monitoring method can provide representative outcomes for the rebars where the sensor is embedded by contemplating both macrocell and local corrosion processes. A new measuring technique is also proposed to determine the local corrosion rate. It is based on Potential Step Voltammetry (PSV) and on studying accumulated electric charge. The new technique does not practically polarize the rebar. This measurement procedure also includes an initial sequence to calculate the ohmic resistance in order to do away with having to determine all the equivalent circuit components. The proposed monitoring system has been implemented and validated in different test specimens and structural elements manufactured on a small scale. The obtained results demonstrated high precision and improved reliability compared to traditional systems. The results were compared to gravimetric methods and reference electrochemical techniques. / Agradezco a la Universitat Politècnica de Valencia su apoyo económico con la concesión de la Beca de Formación de Personal de Investigación [FPI-2018] / Lliso Ferrando, JR. (2022). Monitorización de la durabilidad de estructuras existentes de hormigón armado mediante la inserción de una red de sensores [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/184378

No / Incorporating nanomaterials brings great changes in tailoring the nano-/micro-/macroscale structures of bulk cement paste phase and interfacial transition zone in the cementitious composites through the nano-core effect, thus achieving stronger, more durable, and smart/multi-functional cementitious composites. Owing to the nano-modification of cement paste in combination with the supplement of nanoscale continuity for multiscale raw materials of cementitious composites, nanomaterials gradually show the potential to become the indispensable seventh component of cementitious composites besides cement, water, fine aggregates, coarse aggregates, chemical additives, and mineral additives. Therefore tailoring cementitious composites with nanomaterials provides a promising approach to develop the new generation of cementitious composites (e.g., ultra-high performance, smart/multi-functional, and resilient) and sustainable infrastructures. This chapter aims to provide a systematic overview of tailoring cementitious composites with various types of nanomaterials. It initially covers the principle of tailoring cementitious composites with nanomaterials and dispersion of nanomaterials in cementitious composites. It then presents the properties of cementitious composites with 0D, 1D, and 2D nanomaterials, namely, hydration, rheology, workability, durability, functional, and mechanical properties. It also highlights various applications of cementitious composites with nanomaterials, including structural health monitoring, traffic detection, and pollutant purification. This chapter concludes by presenting the future prospects of cementitious composites with nanomaterials.

Yes / Considering the continuous development of sustainable development, energy saving, and emission reduction concepts, it is very important to reduce concrete's cement content in order to improve its environmental impact. Using a reactive admixture to replace part of the cement in ultra-high-performance concrete (UHPC) can effectively improve the overall performance of the concrete and reduce carbon dioxide emissions, which is an important aspect of environmental protection. Here, industrial waste residue (fly ash and slag), sea sand (SS), and manufactured sand (MS) were used to produce UHPC under standard curing conditions to reduce the material cost and make it more environmentally friendly and sustainable. The effects of water-binder ratio, contents of cementitious materials, types of sands, and content of steel fibers on the mechanical performance of UHPC under standard curing were investigated experimentally. In addition, evaluations of the impermeability, chloride, and freeze-thaw resistance of various UHPCs produced were conducted by investigating the effects of various factors on the depth under hydraulic pressure and electric flux of UHPC, as well as the mass loss, relative dynamic modulus of elasticity, flexural strength, and compressive strength of UHPC specimens after freeze-thaw cycles. The obtained experimental results show that the SS-UHPC and MS-UHPC prepared by standard curing exhibit high strength, excellent impermeability, and chloride resistance. The frost-resistant grade of all groups of UHPCs prepared by standard curing was greater than F500 and had excellent freeze-thaw resistance, including those produced with local tap water or artificial seawater. The investigation presented in this paper could contribute to the production of new low-cost and environmentally friendly UHPCs and accelerate the application of UHPC in engineering structures.

It is widely known that the textile industry is a large polluter and that fast fashion in particular has sustainability issues. Meanwhile, second-hand stores struggle to sell their products in Europe, leading to most clothes either being exported and/or landfilled. This issue is partially driven by costumers not knowing what performance they can expect from second-hand products. In this study, the water repellency of used hardshell jackets will be evaluated with the goal of proving that second-hand products still have enough performance for reuse. This implies that prolonging the lifetime of waterproof jackets is possible, which will reduce CO2 emissions. Various standards are evaluated and a new method, dubbed the stream impact test is defined, trialed and compared to results from the ISO 4920 spray test. In order to estimate the full potential of reusing jackets, the effects of rejuvenating used jackets, by washing the mand using water repellent spray, are also tested. The current standards for aging fabric used by the industry to prove the durability of water repellency will be evaluated using both the ISO 4920 spray test and the new stream impact test. The testing concludes that while the new method has certain issues, it does achieve it’s core objectives and provides a new perspective on the water repellency of new, used and rejuvenated fabrics. It also shows that, on average, rejuvenating jackets has a good effect on the water repellency of jackets and that. During the testing of used jackets with the stream impact method, jackets are found with water repellent properties between those of new fabric and very old fabric. This suggests that there are jackets with a lot of technical performance left that are discarded, which would be ideal for reuse and allowing the clothing industry to become more sustainable.

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 construction and property sector account for a significant portion of Sweden's greenhouse gas emissions, with 21.7% of the total emissions in 2021. The sector's high construction rate poses a challenge to achieving Sweden's climate goal of net zero emissions by 2045. According to a report from the Swedish Environmental Protection Agency, it is unlikely that the goal will be achieved. The Norrbotnia railway is a planned 270-kilometer railway between Umeå and Luleå, considered to be an important part of the future Northern European railway system. It is expected to bring significant benefits to both the population and businesses in northern Sweden and neighboring regions by improving connections to the existing railway network. The construction of the railway is complex and requires both technical expertise and careful consideration of environmental and sustainability aspects. The Norrbotnia Railway project faces geotechnical challenges, particularly in handling extensive loose soil areas. This requires specific reinforcement measures to ensure the stability of the railway and meet settlement requirements. In large projects like this, it is crucial to carefully plan and implement ground reinforcement measures with regard to ecological, economic, and social sustainability. To enable an assessment of suitable reinforcement methods for a selected stretch along the railway, interviews have been conducted with clients, authorities, consultants, and university lecturers. Additionally, various foundation reinforcement methods have been compared in a climate calculation to evaluate their environmental impact and efficiency. The results of this study provide valuable insights into how to combine technical feasibility with sustainable solutions. / Bygg- och fastighetssektorn står för en betydande del av Sveriges växthusgasutsläpp, med 21,7% av de totala utsläppen år 2021. Sektorns höga byggtakt utgör en utmaning för att nå Sveriges klimatmål om nettonollutsläpp till 2045. Enligt en rapport från Naturvårdsverket är det osannolikt att målet kommer att uppnås. Norrbotniabanan är en planerad 27 mil lång järnväg mellan Umeå och Luleå, och anses vara en viktig del av det framtida nordeuropeiska järnvägssystemet. Den förväntas medföra stora fördelar för både befolkningen och näringslivet i norra Sverige och angränsande regioner genom att förbättra kopplingarna till det befintliga järnvägsnätet. Byggandet av järnvägen är komplext och kräver både teknisk expertis och noggrann hänsyn till miljö- och hållbarhetsaspekter. Projektet Norrbotniabanan står inför geotekniska utmaningar, särskilt när det gäller hanteringen av omfattande lösmarksområden. Detta kräver specifika förstärkningsåtgärder för att säkerställa järnvägens stabilitet och uppfylla sättningskraven. Vid stora projekt som detta är det avgörande att noggrant planera, genomföra grundförstärkningsåtgärder med hänsyn till ekologisk, ekonomisk och social hållbarhet. För att möjliggöra en bedömning av lämpliga förstärkningsmetoder för en utvald sträcka längs järnvägen, har intervjuer utförts med beställare, myndigheter, konsulter och universitetslektorer. Dessutom har olika grundförstärkningsmetoder ställts mot varandra i en klimatkalkyl för att utvärdera deras miljöpåverkan och effektivitet. Resultaten från denna studie ger värdefulla insikter i hur man kan kombinera teknisk genomförbarhet med hållbara lösningar.

Master of Science / Department of Civil Engineering / Kyle Riding / Corrosion of reinforcing steel is one of the most common and serious causes of reinforced concrete deterioration. While corrosion is normally inhibited by a passive layer that develops around the reinforcing steel due to the high pH environment of the surrounding concrete, chlorides will break down this protective layer, leading to reinforcement corrosion. Decreasing the diffusivity of the concrete would slow the ingress of chlorides into concrete, and is one of the most economical ways to increase the concrete service life. Optimized concrete mixtures blending portland cement and supplementary cementing materials (SCMs) have become popular throughout the construction industry as a method of improving both fresh and long-term concrete properties such as workability, strength and porosity. It has been shown that use of Class F fly ash, silica fume and ground granulated blast furnace slag (GGBFS) in binary concrete mixture blends can result in a significant reduction in concrete diffusivity. This study investigates the ability of Class C fly ash and ternary concrete mixture blends to also aid in diffusivity reduction. In order to study the effect of incorporation of SCMs into concrete, mixtures containing Class C and Class F fly ash, silica fume and GGBFS were tested following the ASTM C 1556 procedures to measure the concrete’s apparent chloride diffusivity. Structure life cycles were modeled using the measured apparent chloride diffusivities with two finite-difference based life-cycle analysis software packages. To determine whether a correlation between diffusivity and deterioration due to freezing and thawing exists, samples were also tested for their ability to resist deterioration from freezing and thawing cycles using a modified ASTM C 666 Procedure B test. Results show that the use of Class C fly ash yields some service life improvements as compared to the portland cement control mixtures, while ternary mixture blends performed significantly better than the control mixture and equal to or better than the binary SCM mixtures tested. Freeze-thaw tests showed all mixtures to be equally resistant to deterioration due to freezing and thawing.