Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A evolução dos concretos utilizados nas últimas décadas deu origem ao Concreto de Alto Desempenho (CAD), que tem, entre suas características, alta resistência à compressão e baixa permeabilidade. Com o desenvolvimento dos produtos químicos utilizados na construção civil, em especial os superplastificantes e superfluidificantes, a utilização desse tipo de concreto tornou-se cada vez mais freqüente pela possibilidade de se obter uma mistura suficientemente trabalhável utilizando-se fatores água/cimento menores do que 0,35. Devido à sua microestrutura mais homogênea, esse tipo de concreto apresenta um comportamento mais frágil do que os concretos convencionais, exigindo uma melhor caracterização do material. A partir do final da década de 70 começou-se a aplicar os conceitos da Mecânica da Fratura para análise do comportamento de estruturas construídas com esse tipo de concreto. Como em algumas situações a resistência nominal de peças de concreto diminui com o aumento de suas dimensões, houve a necessidade de se considerar o efeito de escala das estruturas a fim de se obter níveis de segurança mais adequados no seu dimensionamento, o que justificou a utilização da Mecânica da Fratura. Neste trabalho a energia de fraturamento foi obtida experimentalmente pelo método do trabalho de fraturamento e pelo método do efeito de escala, por meio de ensaios estáveis de flexão de três pontos em amostras de concreto de alto desempenho com entalhe. Foi também desenvolvida a simulação numérica de uma viga com entalhe, analisada pelo método dos elementos finitos e empregando-se na modelagem constitutiva os conceitos da Mecânica da Fratura aplicada ao concreto. As vigas foram moldadas e ensaiadas no Instituto Politécnico do Rio de Janeiro (IPRJ) da Universidade do Estado do Rio de Janeiro (UERJ) na cidade de Nova Friburgo. Os ensaios foram realizados com controle de deslocamento da célula de carga. Foram ensaiadas três séries de 12 vigas, com quatro dimensões diferentes, geometricamente proporcionais, e três amostras para cada dimensão, totalizando 36 vigas. As alturas utilizadas para as vigas foram 38, 76, 152 e 304 mm, e sua espessura foi mantida constante igual a 38 mm. Os corpos de prova cilíndricos, para caracterização da resistência à compressão do concreto, foram moldados no IPRJ e rompidos no laboratório de engenharia civil da UERJ, na cidade do Rio de Janeiro. Os concretos utilizados apresentaram resistência à compressão média de 70 MPa. / The evolution of the concrete mixes used during the last decades gave birth to the High Performance Concrete (HPC), which, among its main characteristics, presents high strength and low permeability. With the development of chemical products used in civil engineering constructions, mainly the superplasticizers, the use of this kind of concrete has become more and more frequent due to the possibility of obtaining a workable mixture with a water/cement ratio lower than 0.35. Due to its more homogeneous microstructure, the HPC presents a more fragile behavior than the conventional concrete, demanding a better characterization of the material. At the end of the 1970s, concepts of the Fracture Mechanics started to be used for the analysis of the structural behavior of concrete structures. As the nominal stress of the material decreases as the size of the structure increases, it became necessary to consider this size effect in the analysis in order to obtain more suitable levels of security. This fact justifies the use of the Fracture Mechanics in the structural analysis of concrete structures. In this work, the fracture energy was experimentally obtained using the work-offracture method and the size effect method by performing three-point bend tests in HPC notched beams. It was also developed a numerical simulation of the tests, performing the analysis through the Finite Element Method and applying the concepts of the Fracture Mechanics of Concrete into the constitutive model. The notched beams were molded and tested at the Polytechnic Institute of the State University of Rio de Janeiro (IPRJ/UERJ), located in the city of Nova Friburgo. The tests were controlled by the vertical displacement of the load cell. Three series of twelve beams with four geometrically similar sizes were tested. Three samples for each size were cast, making an amount of 36 beams. The beams were 38, 76, 152 and 304 millimeters high and the width was kept constant equal to 38 millimeters. To characterize the concrete compression strength, 100x200 millimeters cylinders were molded at the IPRJ and tested at the UERJ civil engineering laboratory in the city of Rio de Janeiro. The tested concretes presented a medium compressive strength of 70 MPa.

This work is devoted to study the influence of the composition on mechanical properties of high performance concret based on portland cement. 29 samples of high performance concrete (HPC) warying in composition were prepared. The constituents used for HPC preparation were: cement Aalborg White, silica fume, finelly ground blast furnace slag, finelly ground silica, calcinated bauxite and polycarboxylate based superplasticizer. The mechanical parameters (flexural and compressive strength) of the samples were observed after 7 and 28 days of moist curing. Compressive strength values after 28 days were in the range of 92 to 194 MPa and the flexural strength values were in the range of 7 to 23 MPa (without using of fiber reinforcement). The graphs showing mechanical parameters depending on the mixture composition were constructed and consequently evaluated.

The aim of this thesis is to assess the time-dependent behavior of a new kind of composite railway bridge deck composed by two precambered and prestressed beams. The method used until now to design these bridge decks is a simple classical computation method with a variable modular ratio. They have been placed only with simply supported spans up to 26 m.<p>It is now considered to apply this construction method for the building of continuous bridges (with larger spans) by connecting simply supported decks on their supports. It is known that this kind of construction will induce an additional and strong time-dependent redistribution of internal forces within the structure. It was felt that an in-depth understanding of the influence of the concrete time-dependent effects in this kind of composite structures is needed before proceeding with the design of statically indeterminate bridges. Two cross-section analysis programs applying the principle of superposition were developed: the first used the age adjusted effective modulus method and the second the step-by-step method. However, it is known that the delayed behavior of concrete does not fully comply with the principle of superposition. It appears that after a period of compression creep, creep recovery is significantly less than predicted by the superposition principle. In the construction phases of this bridge deck, the concrete fibers belonging to the bottom side of prestressed beams undergo a stress/strain history of significant unloading when the permanent loads are applied step-by-step. Moreover, these methods assume that the relative humidity remains constant. Finally, a lot of bridge decks are heated in order to transfer the prestressing as soon as possible. To evaluate more finely the time-dependent effects of concrete in such composite (and rather complex) structures with variable loading history, several steps have been carried out: <p>-Analysis of the influence of the heat treatment applied in the workshop and the level of applied stress on the creep and the shrinkage of the concrete.<p>-Analysis of the recovery phenomenon of the concrete resulting in the selection of the two-function method with the recovery function proposed by Yue and Taerwe.<p>-Development of a cross-section analysis program applying the two-function method to take into account more finely the recovery phenomenon, what resulted in a optimization of the phases of construction of the bridge decks by decreasing the minimum age of concrete before prestressing from 40 hours to 20 hours. <p>-Development of a structural analysis program with beam finite elements and applying the two-function method,what has resulted in an optimization of the phases of construction of continuous bridges composed by the junction of two bridge decks. <p>-Proposition of a modelling based on the understanding of the physico-chemical phenomenona which are at the origin of the delayed effects and coupled to a local analysis of the evolution of the degree of hydration and the internal relative humidity in order to take into account the changes of the boundaries conditions in terms of heat and moisture exchanges occurring along the construction history of the bridge decks in the evaluation of their long-term behavior. For each component of the delayed strains (the thermal strain, the autogenous shrinkage, the desiccation shrinkage, the desiccation creep, the basic creep), a modelling has been proposed.<p>-Development of a cross-section analysis program based on the numerically stable algorithm with increasing time steps for integral-type aging creep proposed by Bažant and including the different components of the delayed effects according to the proposed modelling.<p>The results seem to be very promising since it was possible to reproduce in a more realistic way the evolutions of the measured strains of the composite railway bridge deck instrumented in June 2000 and situated near Brussels South Station. <p><p><p>L’objectif de cette thèse est de prédire le comportement à long terme de structure mixte type pont-bac composée de poutres préfléchies, précontraintes et construites par phases. A l’heure actuelle, ils sont dimensionnés à l’état limite de service par une méthode traditionnelle pseudo-élastique avec un coefficient d’équivalence acier-béton variable. Il est envisagé d’étendre ce type de construction à la réalisation de viaducs hyperstatiques permettant de franchir de plus grandes portées en établissant une continuité entre deux travées au droit de leur support commun. Il est connu que ce type de construction induit une importante redistribution des efforts internes dans la structure. Il est donc indispensable d’évaluer très finement l’influence des effets différés du béton sur ce type de construction. Deux programmes généraux d’analyse de section basés sur la méthode du module effectif ajusté et la méthode pas-à-pas ont tout d’abord été développés. Ces méthodes appliquent le principe de superposition. Des limitations propres à ces méthodes ont été relevées pour des historiques où le béton subit plusieurs déchargements significatifs par rapport à son état de contrainte initial juste après le transfert de la précontrainte. Ces méthodes ont aussi l’inconvénient de supposer une humidité relative constante. Enfin,pour pouvoir être mis en précontrainte le plus tôt possible, les ponts-bacs sont chauffés. Les caractéristiques de retrait et de fluage s’écartent de celles déterminées en laboratoire sur des éprouvettes conservées à 20°C. Pour lever les limitations des méthodes classiques et évaluer plus finement l’état de contrainte et de déformation à long terme dans ce type de structure, plusieurs étapes ont été effectuées :<p>-Analyse de l’influence d’un traitement thermique appliqué dans les mêmes conditions que celles effectuées chez le préfabricant ainsi que du niveau de contrainte appliqué sur les déformations différées du béton. <p>-Analyse de l’influence de l’application de déchargements à des âges divers sur les éprouvettes de béton permettant de mettre en évidence le fait que la méthode dite aux deux fonctions avec la fonction de recouvrance proposée par Yue et Taerwe reproduit la plupart des résultats expérimentaux de manière très satisfaisante.<p>-Développement d’un programme d’analyse en section suivant la méthode pas-à-pas étendu à la méthode aux deux fonctions afin de mieux tenir compte de la recouvrance, ce qui a permis d’optimiser les phases de préfabrication des ponts-bacs en changeant l’instant de mise en précontrainte. Les simulations ont montré que si le béton du pont-bac est chauffé, la mise en précontrainte peut s’effectuer à 20 heures d’âge du béton. <p>-Développement d’un programme d’analyse de structure au moyen d’éléments finis de type poutre et dont l’algorithme de résolution applique la méthode aux deux fonctions, ce qui a permis d’optimiser les phases de construction de viaducs hyperstatiques constitués par la jonction de deux ponts-bacs. <p>-Proposition d’une modélisation fondée sur la compréhension des phénomènes physico-chimiques à l’origine des effets différés et couplée à une étude locale de l’évolution du degré d’hydratation et de la teneur en eau permettant de tenir compte des changements de conditions aux limites en terme d’échange de chaleur et d’humidité qui ont lieu au cours de l’histoire des ponts-bacs dans l’évaluation de leur comportement à long terme. Pour chaque composante des déformations différées (le retrait thermique, le retrait endogène, le retrait et le fluage de dessiccation, le fluage fondamental), une modélisation a été proposée.<p>-Développement d’un programme d’analyse de section basé sur une approche incrémentale avec l’algorithme récursif et exponentiel proposé par Bažant et dans lequel les composantes des effets différés ont été intégrées suivant la modélisation proposée. <p>Les résultats sont encourageants car ils ont permis de reproduire de manière beaucoup plus réaliste les évolutions des déformations mesurées dans le pont-bac instrumenté à Bruxelles. <p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished

Die vorliegende Arbeit befaßt sich mit der experimentellen Analyse des Tragverhaltens von Hochleistungsbeton unter mehraxialer Beanspruchung. Dabei wurden sowohl die zwei und die dreiaxiale Drucktragfähigkeit als auch das Verhalten unter zweiaxialer kombinierter Druck Zug Beanspruchung untersucht. Für die Analyse kamen jeweils drei Betonfestigkeitsklassen zum Einsatz, C 55/67, C 70/85 und C 90/105. Innerhalb der durchgeführten Versuchsreihen wurden sowohl die jeweiligen Bruchlasten als auch die Spannungs Dehnungs Beziehungen ermittelt. Die Ergebnisse dieser Untersuchungen wurden mit denen verglichen, die an Normalbeton gewonnen wurden. Aus diesem Vergleich wurden Schlußfolgerungen für den Einsatz von Hochleistungsbetonen abgeleitet. Zur mathematischen Beschreibung des Tragverhaltens von Hochleistungsbeton wurden für die untersuchten Beanspruchungsregime Näherungsfunktionen angegeben. / The subject of this paper is the experimental analysis of the behavior of High Performance Concrete under multiaxial loading. Thereby the behavior under bi- and triaxial compression as well as the behavior under combined compression-tension stresses were examined. Three concrete grades were examined, C 55/67, C 70/85 and C 90/105. Within the test series, the ultimate loads and the stress-strain-relationships were determined. The results of the examinations were compared to the results which are already known for normal strength concrete. From these comparisons conclusions for the usage of high performance concrete were made. For the examined states of stress mathematical approximations are specified.

Die Vision bei diesem Projekt bestand darin, zukünftig anstelle massiver Betontragsysteme mit meist ungleichmäßiger Materialausnutzung am Kraftfluss orientierte, filigrane, stabartige Tragwerke zu entwerfen, die sich neben der Gewichtsreduktion und einer höheren Transparenz auch durch eine bessere Ressourcennutzung auszeichnen. Dabei wurde eine modulare Bauweise angestrebt, bei der die Einzelkomponenten Druckstab und vorgespannter Zugstab sowie Teile des Verbindungsknotenelements vorgefertigt und am Einsatzort zusammengefügt werden. Sowohl im Hinblick auf die Tragfähigkeits- und Verbundeigenschaften als auch auf die Dauerhaftigkeit sollten die Stäbe aus faserverstärktem Ultrahochleistungsbeton (UHPFRC) hergestellt sowie ausschließlich mit nichtmetallischen Elementen aus faserverstärkten Kunststoffen (FVK) bewehrt bzw. vorgespannt werden. Im geförderten Zeitraum lag das Hauptaugenmerk auf der Entwicklung filigraner, formoptimierter Druck- und vorgespannter Zugstäbe. Zum Knotenelement wurden theoretische Überlegungen sowie erste Tastversuche angestellt. [Aus: Projektidee und Zielsetzung] / The vision of this project was to replace massive concrete structures with mostly inhomogeneous material utilization in the future by designing filigree concrete truss supporting structures in accordance with the principle form follows force instead. Thus, besides weight reduction and a higher transparency also a higher resource efficiency can be achieved. A modular construction method, in which the components compression strut, prestressed tie and connection joint elements are prefabricated and joined together at the construction site, was aspired. With regard to load-bearing capacity and bonding behaviour as well as durability, the struts and ties are made of Ultra-High Performance Fibre-Reinforced Concrete (UHPFRC) and are reinforced or prestressed exclusively with non-metallic elements made of f bre-reinforced polymers (FRP). Within the funding period, the focus was on the development of f ligree, shape-optimized struts and prestressed ties. Regarding the connection joint element, theoretical considerations were made and first basic tests were carried out. [Off: Vision and objective]

Byggindustrin har i dagsläget en negativ klimatpåverkan och infrastrukturen likaså. Många länder har därför försökt undersöka möjligheten att hitta ett långsiktigt och hållbart alternativ till det konventionella reparationsmaterialet. Olika material undersöks, olika optimerade betongrecept testas för att förstå hur miljöpåverkan har minimeras för att förlänga livslängden hos betongkonstruktioner. Vid reparation av en bro är det viktigt att ta hänsyn till både kostnader och miljöpåverkan under hela dess livscykel. Kostnader som uppstår är investeringskostnader samt drift- och underhållskostnader. Miljöpåverkan från betongkonstruktioner i produkt skedet består av materialframställning, byggtransporter och produktion på byggarbetsplatserna. totala växthusgasutsläppet summeras och beräknas i kg CO2-ekv. Syftet med detta examensarbete är att studera den långsiktiga hållbarheten hos UHPC med hjälp av beräkningsmodeller såsom livscykelanalys och livscykelkostnadsanalys med avsikt att applicera reparationstekniken. Flera UHPC recept ställs mot det konventionella reparationsmaterialet detta för att kunna bedöma miljöpåverkan och kostnadseffektiviteten hos materialen. Dvs om det går det att minska klimatutsläppet och kostnaderna. De jämförda recepten är olika UHPC-recept samt traditionell betong. Recepten appliceras slutligen på en befintlig bropelare för att undersöka de olika receptens tillämpbarhet som reparationsmaterial ur ett hållbarhetsperspektiv. Det saknas tillräckligt med kunskap om UHPC:s långtidseffekter, speciellt om reparationsintervall. Med åtanke på materialets höga draghållfasthet och beständighet tillsammans med UHPC:s strukturella egenskaper har antaganden gjorts att materialet är reparationsfri under konstruktionens livslängd. Det vill säga att bropelaren som undersökts med UHPC i studien inte behövt repareras under sin livslängd. Resultatet från livscykelkostnadsanalysen visar att UHPC är dyrare i både kubikmeter (m3) och kvadratmeter (m2) med tanke på täckskiktets tjocklek än traditionell betong i materialpriset. Men med tanke på att UHPC är underhållsfritt har den en mindre livscykelkostnad. Resultatet från livscykelanalysen visar att UHPC blandningarna har större miljöpåverkan per kubikmeter. Då de olika täckskiktetstjocklek relateras till pelarens längd erhålls resultat där UHPC medför slankare konstruktioner och besparingar upp emot 50% mindre betongvolym (för den 6 m långa pelaren i fallstudien). Med UHPC som reparationsmaterial medför det till att bron inte behöver repareras under dess livslängd. Bropelaren som repareras med UHPC kommer därför ha en mindre miljöpåverkan än den traditionella betongen. Långsiktig hållbarhet och mindre totala växthusgasutsläpp (som är i riktlinje med EU:s och regeringens klimatkrav) erhålls för anläggningskonstruktioner med UHPC. / The construction industry has a negative climate impact and so does the infrastructure. Which is due to frequent repairs that are not sustainable. Many countries have therefore tried to explore the possibility of finding a long-term and sustainable alternative to conventional repair materials. Different materials are examined, different optimized concrete recipes are tested to understand how the environmental impact can be minimized and the service life of concrete structures extended. When repairing a bridge, it is important to take into account both costs and environmental impact throughout its life cycle. Costs that arise are investment costs as well as operating and maintenance costs. The environmental impact from concrete structures in the product phase consists of material production, construction transports and production at construction sites. The total greenhouse gas emissions are summed up and calculated in kg CO2 eq. The purpose of this thesis is to study the long-term sustainability of UHPC using calculation models such as life cycle analysis and life cycle cost analysis with the intention of applying the repair technique. Several UHPC prescriptions are set against the conventional repair material in order to be able to assess the environmental impact and cost-effectiveness of the materials. That is, if it is possible to reduce climate emissions and costs. The compared recipes are different UHPC recipes and traditional concrete. The recipes are finally applied to an existing bridge pillar to investigate the applicability of the various recipes as repair materials from a sustainability perspective. There is a lack of knowledge about the long-term effects of UHPC, especially about repair intervals. Given the high tensile strength and durability of the material together with the structural properties of the UHPC, it has been assumed that the material is repair-free for the life of the structure. That is, the bridge pillar examined with UHPC in the study did not need to be repaired during its lifetime. The results from the life cycle cost analysis show that UHPC is more expensive in both cubicmeters (m3) and square meters (m2) given the thickness of the cover layer than traditional concrete in the material price. However, given that UHPC is maintenance free, it has a lower lifecycle cost. The results from the life cycle analysis show that the UHPC mixtures have a greater environmental impact per cubic meter when the cover layer varies. As the thickness of the different cover layers is related to the length of the pillar, results are obtained where UHPC leads to slimmer constructions and savings of up to 50% less concrete volume (for the 6 m long pillar in the case study). With UHPC as repair material, this means that the bridge does not need to be repaired during its service life. The bridge pillar that is repaired with UHPC will therefore have a smaller environmental impact than the traditional concrete. Long-term sustainability and smaller total greenhouse gas emissions (which are in line with EU and government climate requirements) are obtained for plant constructions with UHPC.