O concreto de elevado desempenho (CED) é aquele que atende aos requisitos de durabilidade e de resistência mecânica da construção, produzido a partir de materiais selecionados, com equipamentos eficientes e procedimentos controlados. Desenvolveu-se, assim, um estudo experimental, tendo como objetivo principal analisar e estabelecer correlações a partir de propriedades mecânicas e de durabilidade com a microestrutura da matriz. Para tanto, considera-se: a) emprego de agregados da região de São Carlos SP, analisando as suas características fundamentais; b) o emprego de cimentos Portland CP II E 32, CP V ARI Plus e CP V ARI RS em conformidade com ABNT, estabelecendo uma sinergia com os outros materiais envolvidos; c) o estabelecimento de dosagens buscando uma maior compacidade; d) a relação entre os constituintes, correlacionando-os com as formas produtivas e características de aplicações; e) o acompanhamento do desenvolvimento da hidratação e da microestrutura das composições estabelecidas e da influência adição da sílica ativa na matriz como um todo. A análise da microestrutura fundamentou-se em ensaios de poro simetria por intrusão de mercúrio, poro simetria por adsorção de gás nitrogênio, microscopia eletrônica de varredura, termogravimetria e difração de raio-X. Os resultados indicam que a sílica ativa tem forte influência na qualidade dos concretos de alto desempenho, principalmente quando em associação com escória de alto fomo, indicando a possibilidade de se produzir concretos duráveis. Da mesma forma, os resultados mecânicos sugerem excelentes perspectivas na produção do CED, com altas resistências à compressão, na faixa de até 110MPa, à tração na flexão da ordem de 10MPa e resistência à abrasão cerca de 40% superior a dos concretos convencionais. / High performance concrete (HPC) is concrete that meets the requisites of hardness and mechanical strength of construction applications, and is produced with selected materiaIs, efficient equipment and controlled procedures. An experimental study was carried out with the main purpose of analyzing and establishing correlations based on mechanical properties and durability of the matrix\'s microstructure. To this end, the following factors were taken into consideration: a) the use of aggregates available in the region of São Carlos, SP, analyzing their fundamental characteristics; b) the use of Portland CP II E 32, CP V AR! Plus and CP V AR! RS cements according to the ABNT code, establishing a synergy with the other materiais involved; c) the establishment of dosages in the search for greater compactness; d) the relation among the constituents, correlating them with the forms of production and characteristics of application; e) follow-up of the development of hydration and of the microstructures of the compositions established, and the influence of the addition of active silica in the matrix as a whole. The microstructural analysis was based on tests of porosity by mercury intrusion, porosity by adsorption of nitrogen gas, scanning electron microscopy, thermogravimetry and X-ray diffraction. The results indicate that active silica exerts a strong influence on the quality of high performance concretes, particularly when associated with slag, indicating the possibility of producing durable concretes. Similarly, the mechanical findings suggest excellent prospects for HPC production, with high compressive strength in the range of up to 110MPa, flexural strength in the order of 10MPa, and abrasive strength approximately 40% superior to that of conventional concretes.

A incorporação de resíduos industriais ao concreto, tais como as pozolanas, é uma das soluções para o aproveitamento de subprodutos poluentes estando em acordo com os princípios da sustentabilidade. É objetivo do trabalho discutir e analisar a viabilidade da aplicação de um resíduo das termoelétricas da indústria de beneficiamento do arroz, a cinza da casca de arroz (CCA), como adição mineral em concretos duráveis. Com 88% de sílica em sua composição, a CCA tem grande potencial de utilização em concretos porque possibilita o aumento da resistência à compressão pelas suas características de alta pozolanicidade e grande finura. Misturas de argamassas padrão contendo 0, 5, 10 e 15% de CCA moídas apenas industrialmente e com moagem adicional de 1 hora, foram confeccionadas a fim de se avaliar o comportamento do aglomerante (CPV - ARI PLUS + CCA) em relação à resistência mecânica. Concretos com traços 1:3,5, 1:5 e 1:6,5, relação água-aglomerante igual a 0,45 e 15% de CCA foram ensaiados à compressão. Os ensaios mostraram que a CCA é predominantemente cristalina e tem alta pozolanicidade. Quanto às argamassas padrão e aos concretos, os resultados mostraram que a utilização da CCA em compósitos à base de cimento é viável, além de ser ecologicamente correta. / Industrial residues, such as pozzolan, can be incorporated in concretes as a solution for polluter refuses, according to sustainable principles. The objective of this work it is to discuss and analyze the use of rice thermoeletrical industry residue, the rice rusk ash (RHA), as mineral addition in durable concretes. The RHA can be used to increase the compression strength of concretes once it has high pozzolanicity and thinness, composed by 88% of silica. It was created mixtures of standard mortars containing 0, 5 10 and 15% of industrial grounded RHA and also with one hour of additional grind. The idea of those mixtures was to evaluate the mechanical strength of the agglomerate (pure Portland cement + RHA). Compression tests in poor, normal and rich concretes with water/agglomerate ratio of 0,45 and 15% of RHA were set too. The tests indicated that the RHA is predominant crystalline and it is a high pozzolanicity material. All the analyses showed that the material has suitable and competitive characteristics for application as agglomerate component.

Os investimentos iniciais em moldes na indústria de pré-moldados de concreto de cimento Portland, em geral, são altos, havendo a necessidade de utilizá-los o mais intensivamente possível entre uma e outra moldagem. A conseqüência é que a desforma pode ocorrer em instantes inadequados, comprometendo a durabilidade do produto. Isto contraria o conceito fundamental da pré-moldagem que está relacionado ao rigoroso controle de qualidade do produto. A cura térmica é uma alternativa, pois é utilizada para acelerar a resistência mecânica inicial do concreto. Esse beneficio imediato é acompanhado por uma redução na resistência final comparativamente à cura normal em câmara úmida. Esta redução é atribuída ao desenvolvimento de uma microestrutura modificada. Para investigar esse fenômeno, com base nos conhecimentos em ciência e engenharia dos materiais, desenvolve-se um estudo experimental, aplicado a pré-moldados com pequena espessura. O objetivo principal é analisar tais modificações e os compostos hidratados, formados ao longo do tempo após a cura térmica, considerando os materiais empregados e estabelecendo relações com a perda de resistência final. Leva-se em conta a influência das adições e da duração dos ciclos térmicos. A análise da microestrutura está baseada nos seguintes ensaios: porosimetria por intrusão de mercúrio, microscopia eletrônica de varredura, termogravimetria e difração de raio-X. Confirma-se com base nos resultados que a cura térmica favorece a maior formação de portlandita e também acelera a reação pozolânica. Para a composição entre cimento Portland, a escória de alto forno (30%) e a sílica ativa (10%), submetidas a ciclos térmicos longos (12 horas Tmax=61°C), observa-se a maior perda na resistência mecânica a longo prazo. Neste caso, há fortes indícios de que há formação de fases com menor desempenho mecânico. Através de micrografias, para essa amostra, sugere-se a formação da etringita secundária com maior prejuízo na interface pasta-agregado. As conclusões sugerem que para minimizar as interferências no processo de cura e garantir resistências mínimas nas desmoldagens rápidas, com poucas perdas a longo prazo, é interessante associar ciclos térmicos curtos, cimento de alta resistência inicial, sílica ativa e superplastificante. / The initial investments of molds in the industry which makes pre-cast of Portland cement concrete is usually very high, thus creating a necessity to maximize the utilization of each moldings. The consequence is that the forms can be removed at inadequate time, which compromise the durability of the product. This contradicts the fundamental concepts of the pre-castings, which is related to a severe quality control. Steam curing is an alternative treatment and is used to accelerate the initial mechanical resistance of the concrete. This immediate benefit is accompanied by the decrease on final resistance compared to normal curing in humid chamber. This reduction is attributed to the development of a modified microstructure. To investigate this phenomenon, based on knowleledge of materials science and engineering, an experimental study is developed which is applied in pre-cast wich small thichness. The main objective of this work is to analyze the microstructure modifications and the hydrated compounds formed, after a period of steam curing, taking in account the used materiaIs, also to establish a relations with the loss of final strength. The influence of additions and duration of steam cycles are considered. The analyses of microstructures are based on the following tests: mercury intrusion porosimetry, scanning electron microscope, thermogravimetry and X-ray diffraction. Based on the results it can be confirmed that steam curing favors a large formation of ponlandite and also accelerates pozzolanic reaction. For the composition of Portland cement, slag fumace blast (30%) and active silica (10%), submitted for long period of thermal cycles (12 hours, Tmax=61°C), a great loss strength was observed. In this case it is possible the formation of phases with poor mechanical performance. Through micrographs, for this sample, it is observed the formation of secondary ettringite with a large damage in the interface aggregate-paste. The conclusions suggest that to minimize the interference in the process of curing and to guarantee a minimum strength during the rapid separation of the concrete from the molds, with a minor loss in a long term, it is interesting to associate short steam cycles, high initial resistance cement, adive silica and superplasticizer.

Submitted by Vanessa Nunes (vnunes) on 2015-03-31T13:19:31Z No. of bitstreams: 1 RobertoChrist.pdf: 9317574 bytes, checksum: 23b19b5dd98381b184ffb8f3c20b2951 (MD5) / Made available in DSpace on 2015-03-31T13:19:31Z (GMT). No. of bitstreams: 1 RobertoChrist.pdf: 9317574 bytes, checksum: 23b19b5dd98381b184ffb8f3c20b2951 (MD5) Previous issue date: 2014-02-20 / itt Performance - Instituto Tecnológico em Desempenho da Construção Civil / O desenvolvimento de novos concretos vem sendo ampliado ao longo dos anos, o que ocorre paralelamente ao aprimoramento dos cálculos estruturais e ao maior conhecimento sobre as propriedades dos materiais, o que conduz os projetistas ao desenvolvimento de estruturas que necessitam ter características específicas. Com isso surge a necessidade de se desenvolver concretos especiais, que apresentam elevada resistência mecânica e durabilidade. O concreto de pós reativos, também chamado de CPR, é um exemplo destes materiais. Trata-se de um concreto de ultra alto desempenho, com elevada resistência mecânica, extremamente dúctil e de baixa porosidade. Este tipo de concreto apresenta propriedades mecânicas superiores em comparação aos concretos de alta resistência, chegando a resistências à compressão de 200 MPa, à tração de 45MPa e módulo de elasticidade superior a 50 GPa. O consumo de cimento neste tipo de concreto pode atingir 800 kg/m3, além de incorporar elevado volume de sílica ativa. A otimização granular dos constituintes, realizada através de métodos de empacotamento de partículas, faz com que seja possível obter um material com o mínimo de vazios e elevada densidade. As fibras introduzidas no composto proporcionam elevada ductilidade. Neste trabalho, parte do cimento Portland foi substituído por cinza volante, para desenvolver um CPR com baixo consumo de aglomerantes. Também foi estudada a incorporação de dois tipos de fibras, ou hibridização, para uma matriz de CPR com menor consumo de cimento. A introdução de dois tipos distintos de fibras proporciona ao material maior sinergia, diminuindo a formação e a propagação de fissuras durante o carregamento. Os resultados obtidos nesta pesquisa mostram que a substituição parcial do cimento por cinza volante apresentou melhor desempenho mecânico, atingindo resistência à compressão de aproximadamente 190 MPa com 30% de adição. A incorporação de dois tipos distintos de fibras, aço e polipropileno em teores de 80% e 20% respectivamente, proporcionou ao material elevada resistência à tração na flexão e tenacidade. Portanto, é possível dosar CPR com menores consumos de cimento e uso de dois tipos de fibras, melhorando as propriedades da mistura e obtendo um compósito com reduzido impacto ambiental. / The development of new concretes is being expanded over the years, withal the improvements in structural design, along the increased knowledge of materials properties, which leads the designers to develop structures with specific requirements. It arises the need of the development of special concretes, with have enhanced mechanical strength and durability. Reactive powder concrete, also called RPC, is an example of these materials. This is an ultra-high-performance concrete with high mechanical strength, extremely ductile and low porosity. This type of concrete has superior mechanical properties compared to high strength concrete, reaching compressive strengths of 200 MPa, tensile strengths of 45 MPa and modulus higher than 50 GPa. The cement consumption in this type of concrete may reach 800 kg/m3, while incorporating high volumes of silica fume. The optimization of granular constituents accomplished by particle packing methods provides a material with a minimum of voids and also high density. The fiber introduced into the material compound provides high ductility. On this report, fly ash was used to replace some part of the cement, aiming the development of a RPC with low agglomerate consumption. It was also studied the use of two types of fiber, or hybridization, to a RPC matrix array of CPR with less consumption of cement. The introduction of two distinct types of fibers gives the material improved synergy, decreasing the formation and propagation of cracks during the charging. The results obtained in this study show that the partial replacement of cement by fly ash gives better mechanical performance, reaching the compressive strength of approximately 190 MPa with 30% addition. The incorporation of two different types of fibers, steel and polypropylene at levels of 80% and 20% respectively, provided the materials high tensile strength and toughness. Therefore, it is possible to compose an RPC with lower cement consumption and use of two types of fibers, improving the properties of the mixture and obtaining a composite with reduced environmental impact.

Cette thèse étudie la rétention d’eau à haute HR et le retrait sous température modérée des bétons CEMI et CEMV de l’Andra, en lien avec leur microstructure.Pour étudier l’origine des variations de Sw à haute HR, du béton est séché à HR= 92-100%. Pour les deux bétons, l’échantillonnage influe significativement sur Sw. Pour le CEMI, à HR=100%, la taille joue aussi, en lien avec un mécanisme de séchage par désorption de surface ; à HR=92&98%, ce béton n’est plus sensible aux effets de surface ; il est sensible aux conditions expérimentales. Pour le CEMV, l’effet de la taille existe quelle que soit l’HR, mais il est peu sensible aux conditions expérimentales.A partir de 60°C, le retrait de dessiccation présente quatre phases en fonction de la perte de masse relative. Pour le béton CEMI séché jusqu’en phase 3 ou 4, la possible rigidification de la matrice solide est investiguée par un essai couplé de poro-élasticité et transport de gaz. Pour un même échantillon en phase 3 puis en phase 4, on mesure une légère augmentation du Ks ; la perméabilité au gaz est significativement plus sensible au confinement. Par contre, la rigidification du matériau est limitée en comparaison de l’effet d’échantillonnage.Au MEB, les phases et la morphologie des bétons sont quantifiées. Le CEM I et le CEM V ont des phases solides identiques, mais le CEM V comprend des phases spécifiques (ajout de laitiers et cendres volantes). Les C-S-H du CEM V ont un rapport C/S globalement plus bas que le CEM I. Ce rapport reste similaire pour trois gâchées différentes. Par contre, l’occurrence de pores millimétriques varie significativement, du fait de modes de mise en oeuvre sensiblement différents / This thesis focuses on water retention at high relative humidity (RH) (92-100%) and dessiccation shrinkage under moderate temperature (60-80°C) for two high performance concretes CEMI and CEMV (from Andra), in relation with their microstructure.To investigate the origins of the variations in water saturation degree Sw at high RH, both concretes are dried at RH=92, 98 and 100%, from the fully saturated state. For both concretes, sampling affects significantly Sw. For CEMI at 100%RH, sample size also affects Sw, due to surface drying (desorption); at 92 and 98%RH, CEMI is no longer sensitive to surface drying effects; it is sensitive to experimental conditions (RH, T). CEMV is affected by sample size whatever the RH, but not by experimental conditions.From 60°C drying temperature, the relationship between shrinkage and relative mass loss presents four distinct phases. CEMI concrete is dried at 65°C until phase 3 or 4, and then submitted to a coupled poro-mechanical and gas permeability test. For the same sample tested in phase 3 and then 4, a difference in solid skeleton incompressibility modulus Ks is measured, which is significantly lower than the differences in Ks due to sampling.With the Scanning Electron Microscope, the solid phases and morphology of both concretes are quantified. CEM I and CEM V comprise identical phases, even portlandite, yet CEM V concrete has some specific phases, owing to the addition of slag and fly ash. The C-S-H in CEM V have a lower C/S ratio than in CEM I. The (C/S) ratio remains similar when comparing between three different batches. Besides, millimetric pores vary significantly, owing to differences in manufacturing

Os investimentos iniciais em moldes na indústria de pré-moldados de concreto de cimento Portland, em geral, são altos, havendo a necessidade de utilizá-los o mais intensivamente possível entre uma e outra moldagem. A conseqüência é que a desforma pode ocorrer em instantes inadequados, comprometendo a durabilidade do produto. Isto contraria o conceito fundamental da pré-moldagem que está relacionado ao rigoroso controle de qualidade do produto. A cura térmica é uma alternativa, pois é utilizada para acelerar a resistência mecânica inicial do concreto. Esse beneficio imediato é acompanhado por uma redução na resistência final comparativamente à cura normal em câmara úmida. Esta redução é atribuída ao desenvolvimento de uma microestrutura modificada. Para investigar esse fenômeno, com base nos conhecimentos em ciência e engenharia dos materiais, desenvolve-se um estudo experimental, aplicado a pré-moldados com pequena espessura. O objetivo principal é analisar tais modificações e os compostos hidratados, formados ao longo do tempo após a cura térmica, considerando os materiais empregados e estabelecendo relações com a perda de resistência final. Leva-se em conta a influência das adições e da duração dos ciclos térmicos. A análise da microestrutura está baseada nos seguintes ensaios: porosimetria por intrusão de mercúrio, microscopia eletrônica de varredura, termogravimetria e difração de raio-X. Confirma-se com base nos resultados que a cura térmica favorece a maior formação de portlandita e também acelera a reação pozolânica. Para a composição entre cimento Portland, a escória de alto forno (30%) e a sílica ativa (10%), submetidas a ciclos térmicos longos (12 horas Tmax=61°C), observa-se a maior perda na resistência mecânica a longo prazo. Neste caso, há fortes indícios de que há formação de fases com menor desempenho mecânico. Através de micrografias, para essa amostra, sugere-se a formação da etringita secundária com maior prejuízo na interface pasta-agregado. As conclusões sugerem que para minimizar as interferências no processo de cura e garantir resistências mínimas nas desmoldagens rápidas, com poucas perdas a longo prazo, é interessante associar ciclos térmicos curtos, cimento de alta resistência inicial, sílica ativa e superplastificante. / The initial investments of molds in the industry which makes pre-cast of Portland cement concrete is usually very high, thus creating a necessity to maximize the utilization of each moldings. The consequence is that the forms can be removed at inadequate time, which compromise the durability of the product. This contradicts the fundamental concepts of the pre-castings, which is related to a severe quality control. Steam curing is an alternative treatment and is used to accelerate the initial mechanical resistance of the concrete. This immediate benefit is accompanied by the decrease on final resistance compared to normal curing in humid chamber. This reduction is attributed to the development of a modified microstructure. To investigate this phenomenon, based on knowleledge of materials science and engineering, an experimental study is developed which is applied in pre-cast wich small thichness. The main objective of this work is to analyze the microstructure modifications and the hydrated compounds formed, after a period of steam curing, taking in account the used materiaIs, also to establish a relations with the loss of final strength. The influence of additions and duration of steam cycles are considered. The analyses of microstructures are based on the following tests: mercury intrusion porosimetry, scanning electron microscope, thermogravimetry and X-ray diffraction. Based on the results it can be confirmed that steam curing favors a large formation of ponlandite and also accelerates pozzolanic reaction. For the composition of Portland cement, slag fumace blast (30%) and active silica (10%), submitted for long period of thermal cycles (12 hours, Tmax=61°C), a great loss strength was observed. In this case it is possible the formation of phases with poor mechanical performance. Through micrographs, for this sample, it is observed the formation of secondary ettringite with a large damage in the interface aggregate-paste. The conclusions suggest that to minimize the interference in the process of curing and to guarantee a minimum strength during the rapid separation of the concrete from the molds, with a minor loss in a long term, it is interesting to associate short steam cycles, high initial resistance cement, adive silica and superplasticizer.

abstract: Being a remarkably versatile and inexpensive building material, concrete has found tremendous use in development of modern infrastructure and is the most widely used material in the world. Extensive research in the field of concrete has led to the development of a wide array of concretes with applications ranging from building of skyscrapers to paving of highways. These varied applications require special cementitious composites which can satisfy the demand for enhanced functionalities such as high strength, high durability and improved thermal characteristics among others. The current study focuses on the fundamental understanding of such functional composites, from their microstructural design to macro-scale application. More specifically, this study investigates three different categories of functional cementitious composites. First, it discusses the differences between cementitious systems containing interground and blended limestone with and without alumina. The interground systems are found to outperform the blended systems due to differential grinding of limestone. A novel approach to deduce the particle size distribution of limestone and cement in the interground systems is proposed. Secondly, the study delves into the realm of ultra-high performance concrete, a novel material which possesses extremely high compressive-, tensile- and flexural-strength and service life as compared to regular concrete. The study presents a novel first principles-based paradigm to design economical ultra-high performance concretes using locally available materials. In the final part, the study addresses the thermal benefits of a novel type of concrete containing phase change materials. A software package was designed to perform numerical simulations to analyze temperature profiles and thermal stresses in concrete structures containing PCMs. The design of these materials is accompanied by material characterization of cementitious binders. This has been accomplished using techniques that involve measurement of heat evolution (isothermal calorimetry), determination and quantification of reaction products (thermo-gravimetric analysis, x-ray diffraction, micro-indentation, scanning electron microscopy, energy-dispersive x-ray spectroscopy) and evaluation of pore-size distribution (mercury intrusion porosimetry). In addition, macro-scale testing has been carried out to determine compression, flexure and durability response. Numerical simulations have been carried out to understand hydration of cementitious composites, determine optimum particle packing and determine the thermal performance of these composites. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2018

It is important to ensure that vulnerable structures (federal and provincial offices, military structures, embassies, etc) are blast resistant to safeguard life and critical infrastructure. In the wake of recent malicious attacks and accidental explosions, it is becoming increasingly important to ensure that columns in structures are properly detailed to provide the ductility and continuity necessary to prevent progressive collapse. Research has shown that steel fibre reinforced concrete (SFRC) can enhance many of the properties of concrete, including improved post-cracking tensile capacity, enhanced shear resistance, and increased ductility. The enhanced properties of SFRC make it an ideal candidate for use in the blast resistant design of structures. There is limited research on the behaviour of SFRC under high strain rates, including impact and blast loading, and some of this data is conflicting, with some researchers showing that the additional ductility normally evident in SFRC is absent or reduced at high strain loading. On the other hand, other data indicates that SFRC can improve toughness and energy-absorption capacity under extreme loading conditions. This thesis presents the results of experimental research involving tests of scaled reinforced concrete columns exposed to shock wave induced impulsive loads using the University of Ottawa Shock Tube. A total of 13 half-scale steel fibre reinforced concrete columns, 8 with normal strength steel fibre reinforced concrete (SFRC) and 5 with an ultra high performance fibre reinforced concrete (UHPFRC), were constructed and tested under simulated blast pressures. The columns were designed according to CSA A23.3 standards for both seismic and non-seismic regions, using various fibre amounts and types. Each column was exposed to similar shock wave loads in order to provide direct comparisons between seismic and non-seismically detailed columns, amount of steel fibres, type of steel fibres, and type of concrete. The dynamic response of the columns tested in the experimental program is predicted by generating dynamic load-deformation resistance functions for SFRC and UHPFRC columns and using single degree of freedom dynamic analysis software, RCBlast. The analytical results are compared to experimental data, and shown to accurately predict the maximum mid-span displacements of the fibre reinforced concrete columns under shock wave loading.

The load-carrying and energy-dissipation capacities of ultra-high-performance concrete (UHPC) under dynamic loading are evaluated in relation to microstructure composition at strain rates on the order of 10⁵ s⁻¹ and pressures of up to 10 GPa. Analysis focuses on deformation and failure mechanisms at the mesostructural level. A cohesive finite element framework that allows explicit account of constituent phases, interfaces, and fracture is used. The model resolves essential deformation and failure mechanisms in addition to providing a phenomenological account of the effects of the phase transformation. Four modes of energy dissipation are tracked, including pressure-sensitive inelastic deformation, damage through the development of distributed cracks, interfacial friction, and energy released through phase transformation of the quartz silica constituent. Simulations are carried out over a range of volume fractions of constituent phases to quantify trends that can be used to design materials for more damage-resistant structures. Calculations show that the volume fractions of the constituents have more influence on the energy-dissipation capacity than on the load-carrying capacity, that inelastic deformation is the source of over 70% of the energy dissipation, and that the presence of porosity changes the role of fibers in the dissipation process. The results also show that the phase transformation has a significant effect on the load-carrying and energy-dissipation capacities of UHPC for the conditions studied. Although transformation accounts for less than 2% of the total energy dissipation, the phase transformation leads to a twofold increase in the crack density and yields nearly an 18% increase to the overall energy dissipation. Microstructure-behavior relations are established to facilitate materials design and tailoring for target-specific applications.

Der vorliegende Bericht beschreibt das Verhalten von ultrahochfestem Beton unter zweiaxialer Druckbeanspruchung. Bisher wurden ein Feinkornbeton und zwei Grobkornbetone mit unterschiedlichen Faserzusätzen untersucht. Die Zylinderdruckfestigkeiten nach 28 Tagen betragen rund 150, 160 und 170 N/mm². Besonders bei dem Feinkornbeton wurde eine überwiegend horizontale Ausrichtung der Stahlfasern festgestellt, die zu einer Anisotropie im Materialverhalten führte. Zusammenfassend muss festgestellt werden, dass die zweiaxiale Druckfestigkeit von UHPC nur geringfügig größer ist als die einaxiale. Für die Mischungen mit 2,5 Vol.-% Fasergehalt übersteigt die Festigkeit bei einem Spannungsverhältnis von Spannung 1 zu Spannung 2 gleich Eins die einaxiale Festigkeit um 7 bzw. 10 %. Bei dem Beton mit 0,9 Vol.-% Fasergehalt lag diese zweiaxiale Festigkeit sogar geringfügig unter der einaxialen. Bei der Bemessung von UHPC dürfen somit die vom Normalbeton bekannten Festigkeitssteigerungen unter mehraxialer Druckbelastung, wie sie z.B. bei reinen Druckknoten von Stabwerkmodellen angesetzt werden, nicht verwendet werden! Für die Beschreibung der Bruchkurve kann nach jetzigem Erkenntnisstand das Bruchkriterium nach OTTOSEN als eine gute Näherung empfohlen werden. Die Versuche haben gezeigt, dass sich UHPC in vielen, zum Teil sicherheitsrelevanten Bereichen anders verhält als Normalbeton. Für eine umfassende Beschreibung des Tragverhaltens sind weitere Versuche unter dreiaxiale Druckbelastung und kombinierter Druck-Zug-Belastung notwendig.