No description available.

Shotcrete or sprayed concrete has become an inevitable material for stabilising and supporting hard rock tunnels. To prevent rock block fallouts in the excavated tunnel, shotcrete is pneumatically projected under high pressure on the rock surface. This method has proven to reduce the construction time drastically, and the addition of fibres in the shotcrete material results in Fibre Reinforced Shotcrete (FRS). The fibres increased the strength of the parent matrix and made the reinforcement bar (mesh) placing procedure with its heavy labour work unnecessary. Even though FRS have been in use for many years, to design FRS lining there are currently no complete, widely used guidelines. Traditionally, the most frequently used testing was a traditional beam testing method which helps to determine the FRS mechanical properties. Previous studies prove that the result from beams often show a high scatter in the results. Another proposed standard testing method is the Round Determinate Panel method to determine the energy absorption capacity. This method has the potential to be a reliable test procedure with a repeatable and predictable crack pattern.In this project, an experimental investigation was carried out to understand the behaviour of macro fibres of steel, basalt and synthetic materials in FRS. The specimens were sprayed in situ and cast in laboratory, of which the in situ samples were assigned to different curing conditions. The test standard ASTM C-1550 was used to design the round panels and SS-EN 14488-3 for the beams. Each type of FRS specimen’s compressive strength was tested, evaluated and compared. The single fibre pullout strength was tested to determine the bond strength between shotcrete and fibres.The calculated results showed the coefficient of variation (COV) of energy absorption capacity from panels varied within 3 % – 13 % and the residual strength of beams within 12 % – 35 %. Irrespective of testing method, the Dramix 3D steel fibre and Minibars basalt fibre for the tested cases showed the lowest dispersion of result. Minibars showed a significant increase in compressive strength compared to the other fibres. Single fibre pullout testing concluded that the steel fibre had superior load capacity at the first crack. Minibars showed a strength close to that of steel fibres and a failure mode similar to that with synthetic fibres.

Aluminum alloys have increasing applications in construction and transportation industries. Both 5xxx-series (Al-Mg) and 6xxx-series (Al-Mg) alloys are frequently used in marine construction because of their light weight, high strength, and corrosion resistance. One of the major concerns regarding the marine application of aluminum alloys is their mechanical performance in fire scenarios. The material strength may be degraded due to both thermal and mechanical damage during fire exposure. This work emphasizes the stress-induced mechanical (physical) damage and its impact on the residual (post-fire) performance of 5083-H116 and 6061-T651 aluminum alloy. Thermo-mechanical tests were performed at various temperatures and stresses to study the stress-induced damage at induced plastic creep strain levels. Unstressed thermally exposed and thermo-mechanically damaged samples were examined to separate the stress-induced microstructural damage. The stress-induced microstructural damage primarily manifests itself as dynamic recovery at low creep temperatures, while cavitation, dynamic recrystallization and dynamic precipitation (in Al6061) are the types of damage developed in the high creep strains at high exposure temperatures. Different creep mechanisms are also studied for both Al5083 and Al6061. The post-fire mechanical response at room temperature after thermo-mechanical damage was investigated with reference to the damaged microstructure present in the material. Residual material strengths based on deformed cross sectional area after the creep test were calculated to provide insight into how microstructural damage affects the post-fire material performance. The competing effects of strength degradation caused by cavitation and strengthening due to grain elongation and subgrain refinement were investigated. Engineering residual material strengths calculated based on the original cross sectional area prior to creep tests were also studied to provide guidance for structural design. / Ph. D.

[pt] O concreto é conhecido por ter um bom desempenho quando exposto a altas temperaturas pelo fato de apresentar baixa condutividade térmica, ser incombustível e não exalar gases tóxicos. Entretanto, devido à sua composição heterogênea, o concreto sofre alterações físicas, químicas e mecânicas que podem comprometer sua integridade estrutural. Em estruturas de concreto armado, deve-se ter atenção especial aos pilares, cuja capacidade portante é reduzida significativamente em altas temperaturas e seu colapso, de natureza brusca, pode resultar na instabilidade global da estrutura. As reduções nas propriedades mecânicas dos materiais aliadas a lascamentos, fissuras e deformações excessivas podem comprometer seu desempenho, tornando-se necessária a verificação da segurança em situações de incêndio. Com o objetivo de analisar a resistência residual de colunas de concreto armado submetidas a altas temperaturas, foram realizados ensaios de compressão em corpos-de-prova cilíndricos de concreto simples de 5x10 cm submetidos a diferentes temperaturas (200, 400, 600, 800 e 1000 graus Celsius) e de concreto armado de 15x30 cm com diferentes configurações de estribos e submetidos a distintos tempos de exposição (30, 60, 90 e 120 minutos). Em ambos os ensaios, os corpos-de-prova foram resfriados em temperatura ambiente. Os resultados do programa experimental comprovam a perda de resistência à compressão e seus valores foram comparados a modelos numéricos e ao Método da Isoterma de 500 graus Celsius constante na ABNT NBR 15200 de 2004 e no EUROCODE 2. / [en] Concrete is well-known for exhibiting good performance when exposed to elevated temperatures because its low thermal conductivity coefficient, noncombustible properties and reduced emission of toxic gases. However, due to its heterogeneous composition, concrete undergoes physical, chemical and mechanical alterations that can compromise its structural integrity. In reinforced concrete structures, special attention should be paid to the columns, in bearing capacity is reduced significantly at elevated temperatures and their collapse, naturally brittle, may result in overall instability of structure. Reductions in the mechanical properties of the steel and concrete combined with spalling, cracking and excessive deformation compromise its performance, making it necessary to verify the safety in fire situations. In order to analyze the residual strength of reinforced concrete columns submitted to elevated temperatures, compression tests were carried out on plain concrete cylindrical specimens of 5x10 cm exposed to different temperatures (200, 400, 600, 800 and 1000 degrees Celsius) and on reinforced concrete of 15x30 cm considering different stirrups configuration and exposure times (30, 60, 90 and 120 minutes). In both tests, the specimens were cooled to room temperature. The results of the experimental program demonstrate the loss of compression strength and their values were compared to those obtained numerical models and to the Isotherm Method of 500 degrees Celsius, recommended in ABNT NBR 15200 of 2004 and in EUROCODE 2.

Die Arbeit beschäftigt sich mit der Weiterentwicklung des verdämmten Druckversuches zur Bestimmung experimenteller Daten an verschiedenen Keramik- und Glassorten. Die untersuchten Materialien (Al2O3, TiB2, B4C, Floatglas, schweres Flintglas) lagen in Form von Fragmenten (Bruchstücken) vor und wurden aus realen Impaktexperimenten wiedergewonnen. Zusätzlich wurden thermisch vorgeschädigte Aluminiumoxidzylinder in die Betrachtungen einbezogen. Daten granulierter bzw. vorgeschädigter spröder Materialien sind von besonderem Interesse für Finite Element Rechnungen, um beispielsweise experimentell sehr aufwendige Beschußversuche rechnerisch zu simulieren.Als Untersuchungsmethode wurde der verdämmte Druckversuch verwendet und sowohl an quasistatische als auch an schlagdynamische Belastungsbedingungen angepaßt. Außerdem wurden die entwickelten Testaufbauten für sehr hohe hydrostatische Drücke optimiert. In den quasistatischen Experimenten konnten damit Drücke von 380 MPa bis 1960 MPa und in den dynamischen Versuchen von 495 MPa bis 2060 MPa erreicht werden. Im Ergebnis wurden mechanische Kennwerte der granulierten bzw. vorgeschädigten Materialien ermittelt (Restfestigkeit, Verdichtungsverhalten) und deren Schädigungsgrad vor und nach den Versuchen bestimmt (Rasterelektronenmikroskopie und Messung der spezifischen Oberfläche). Die vielversprechenden Resultate der verschiedenen Keramiken und Gläser wurden verglichen und die Materialien im Hinblick auf ihr Energieaufnahmevermögen unter schlagartiger Belastung bewertet.

The objective of this study is to develop test protocols for comparing the effectiveness of fiber-reinforced concrete (FRC) mixtures with high-performance steel fibers. Steel fibers can be added to fresh concrete to increase the tensile strength, ductility, and durability of concrete structures. In order to quantify steel fiber-reinforced concrete (SFRC) mixtures for field applications, a material test capable of predicting the performance of SFRC for field loading conditions is required. However, current test methods used to evaluate the structural properties of FRC (such as residual strength and toughness) are widely regarded as inadequate; a simple, accurate, and consistent test method is needed. It was determined that the Double-Punch Test (DPT), originally introduced by Chen in 1970 for plain concrete, could be extended to fiber-reinforced concrete to satisfy this industry need. In the DPT, a concrete cylinder is placed vertically between the loading platens of the test machine and compressed by two steel punches located concentrically on the top and bottom surfaces of the cylinder. It is hypothesized that the Double-Punch Test is capable of comparing future fiber-reinforcement design options for use in structural applications, and is suitable for evaluating FRC in general. The DPT Research and Testing Program was administered to produce sufficient within-laboratory data to make conclusions and recommendations regarding the simplicity, reliability, and reproducibility of the DPT for evaluating the performance of SFRC. Several variables (including fiber manufacturer, fiber content, and testing equipment) were evaluated to verify the relevance of the DPT for FRC. In this thesis, the results of 120 Double-Punch Tests are summarized and protocols for its effective application to fiber-reinforced concrete are recommended. Also, fundamental data is provided that indicates the DPT could be standardized by national and international agencies, such as the American Society of Testing and Materials (ASTM), as a method to evaluate the mechanical behavior of FRC. This project is sponsored by the Texas Department of Transportation (TxDOT) through TxDOT Project 6348, "Controlling Cracking in Prestressed Concrete Panels and Optimizing Bridge Deck Reinforcing Steel," which is aimed at improving bridge deck construction through developments in design details, durability, and quality control procedures. / text

Alvenaria estrutural é um sistema construtivo em que paredes exercem tanto função estrutural como de vedação. Apesar de ser largamente utilizada no Brasil atualmente, não há uma norma nacional com procedimentos para o dimensionamento deste sistema em situação de incêndio. Muito se deve pelo fato de as pesquisas nesta área serem substancialmente escassas se comparadas com os sistemas construtivos em concreto armado ou aço. Neste contexto, este trabalho tem por objetivo realizar ensaios experimentais para avaliar a resistência residual de compressão da alvenaria estrutural com blocos de concreto. Foram avaliadas duas variações de blocos de concreto, com resistências características de 4,0 e de 10,0 MPa, ambos com espessura nominal de 140 mm e os corpos de prova estudados foram os prismas e as pequenas paredes. Realizou-se a caracterização física, geométrica e mecânica da alvenaria em temperatura ambiente e na sequência os corpos de prova foram submetidos a uma simulação de incêndio-padrão normalizado pela ISO 834-1:1999, durante 120 minutos que é o TRRF máximo recomendado pela ABNT NBR 14432:2001. Na primeira fornada foram avaliados os elementos de 140 mm sem revestimento e segunda fornada todos os elementos revestidos com uma camada de 5 mm de gesso. Após o resfriamento lento até a temperatura ambiente, os corpos de prova foram submetidos ao ensaio de compressão simples para avaliar a resistência residual de compressão dos blocos, prismas e pequenas paredes. Em todos os casos as resistências encontradas ficaram abaixo do suficiente para garantir a segurança durante a ação de um incêndio, uma vez que o máximo de resistência residual encontrado foi de 22%. A influência da compartimentação na resistência residual das pequenas paredes, foi brevemente avaliada, para isso três pequenas paredes de 4,0 MPa e 140 mm com o interior isolado dos gases externos foram submetidas ao incêndio-padrão e compressão pós resfriamento, verificou-se que a perda de resistência neste caso foi de 54% enquanto nas pequenas paredes com fogo em todas as faces e expostas ao fogo pelo mesmo período a perda foi de 86%. Estas pequenas paredes compartimentadas foram instrumentadas com a finalidade de avaliar a transferência de calor ao longo da sessão transversal e verificar o tempo de atendimento do critério de isolamento, que neste caso foi de 62 minutos, abaixo do TRRF máximo de 120 minutos. / Structural masonry is a building system that walls work as structure and has sealing function too. Even though it is widely used in Brazil nowadays, there is no national standardization for the masonry design in fire situation. One of the reasons is that researches in this area are substantially sparse if compared with other building systems like reinforced concrete and steel. In this context, the purpose of this work is to evaluate the residual compressive strength of concrete structural masonry by experimentally tests. Two concrete block variations were evaluated, with strengths of 4,0 and 10,0 MPa, both with 140 mm nominal thickness, the elements studied were prisms and walls, beyond blocks. In the first stage, the masonry was characterized in ambient temperature and in the second stage, the elements were submitted to fire simulation standardized by ISO 834-1: 1999 for 120 minutes, which is the maximum TRRF recommended by ABNT NBR 14432: 2001. In the first fire simulation the 140 mm elements were evaluated without covering and in the second one, all the elements were covered with 5 mm layer of plaster. Then, after slow cooling until ambient temperature, the residual compressive strength of the blocks, prisms and walls was evaluated by compression test. In all cases the resistances were not enough to ensure safety during the fire, since the maximum residual resistance found was 22%. Still in this stage, the influence of the compartmentation on the residual resistance of the walls was briefly evaluated. Three walls of 4.0 MPa and 140 mm were placed in a triangle that was thermally insulated inside, and after the fire simulation were subjected in a post-cooling compression test. The loss of resistance found in this case was 54% while in the walls with fire on all faces and exposed to fire for the same period the loss was 86%. These compartmentalized walls were instrumented with the purpose of evaluating the heat transfer along the cross section and to check the time of the isolation criterion attendance, which in this case was 62 minutes, below the 120-minute established as maximum TRRF.

O refinamento dos poros, associado à reação pozolânica e ao efeito filer, reduz a permeabilidade do concreto com cinza de casca de arroz (CCA), o que pode antecipar a sua degradação em altas temperaturas. A literatura mostra que o concreto reidratado em água pode recuperar substancialmente a sua resistência inicial, porém, os estudos sobre a reidratação ao ar e sobre a influência do modo de resfriamento na reidratação são escassos. A pesquisa desenvolvida teve como principal objetivo avançar na análise experimental de concretos convencional e com CCA em altas temperaturas e na reidratação. Na etapa exploratória se avaliou a influência da temperatura de exposição, da adição mineral, do ambiente de acondicionamento, da taxa de aquecimento e do tempo de exposição na resistência à compressão e módulo de elasticidade. Na etapa principal se avaliou a influência do modo de resfriamento, da adição e da idade de reidratação na resistência residual. Complementarmente se utilizou o ensaio de velocidade de pulso ultrassônico (VPU) para avaliar o grau de microfissuração e correlacionar a VPU com as propriedades mecânicas residuais. Na etapa exploratória concluiu-se que a adição, a temperatura, a taxa de aquecimento e o tempo de exposição influenciaram significativamente os resultados. O concreto com CCA cristalina apresentou pior desempenho em altas temperaturas. O concreto com CCA amorfa apresentou desempenho ligeiramente inferior ao concreto convencional em 200°C, devido ao efeito da poro-pressão. No entanto, ambas as CCA podem ser alternativas viáveis considerando sustentabilidade. Na etapa principal, o resfriamento brusco com água provocou maior redução na resistência devido aos gradientes térmicos, porém, permitiu maior recuperação logo nos primeiros sete dias de reidratação. Apesar da recuperação parcial, a resistência ao fim de 154 dias foi inferior a 40% do valor inicial. Nas análises térmicas e de DRX foi possível observar nos concretos resfriados com água a recristalização dos aluminatos de cálcio, do C-S-H e da portlandita, em maior grau no concreto convencional. Foi possível observar correlações fortes entre as variáveis de resposta na etapa exploratória, porém, o mesmo não ocorreu na etapa principal, devido à fissuração e presença de água nos poros. / The pore refinement, associated with the pozzolanic reaction and the filler effect, reduces the permeability of blended concrete with rice husk ash (RHA), which can anticipate its degradation at high temperatures. The literature shows that concrete rehydrated with water can recover substantially its initial strength, but studies on rehydration in air and on the influence of the cooling method on rehydration are scarce. The main objective of this research was to evaluate the performance at high temperatures and in rehydration of conventional and blended concretes with RHA. In the exploratory stage, the influence of exposure temperature, mineral admixture, conditioning environment, heating rate and exposure time on residual strength and modulus of elasticity of heated concrete was evaluated. In the main stage, the influence of cooling method, mineral admixture and time of rehydration in an unsaturated environment on residual strength of concrete was evaluated. The ultrasonic pulse velocity test (UPV) was used to evaluate the degree of micro cracking of concrete and to correlate the UPV with residual strength and modulus. In the exploratory stage it was concluded that mineral admixture, temperature, heating rate and time of exposure significantly influenced the results. In general, concrete with partially crystalline RHA presented the worst performance at high temperatures. Concrete with amorphous RHA presented worse performance than conventional concrete only at 200°C, due to the pore-pressure effect. Despite these results, RHA can be a viable option considering sustainability and high temperatures performance. In the main stage, the rapid cooling with water caused a greater reduction in strength, due to thermal gradients, however, caused a greater strength recovery in the first seven days of rehydration. Despite this partial recovery, the final strength of both concretes after 154 days of rehydration was less than 40% of the initial value. In water-cooled concretes thermal and XRD analyzes show recrystallization of the calcium aluminates, C-S-H and portlandite, to a greater degree in conventional concrete. In the exploratory stage it was possible to observe strong correlations between the independent variables; however, the same did not occur in the main stage, due to cracking and to the presence of water in the pores.

No description available.

Cette thèse s’intéresse à l’étude l’effet de la corrosion sur les propriétés mécaniques des armatures corrodées et les performances mécaniques résiduelles des poutres corrodées. L’étude est basée sur deux poutres corrodées notées B2CL2 et B2CL3, conservées respectivement 26 ans et 28 ans en ambiance saline. Deux poutres non corrodées B2T2 et B2T3 conservées en conditions ambiantes ont également été testés afin d’identifier l'effet de la corrosion indépendamment du vieillissement.Les propriétés mécaniques des armatures corrodées ont été étudiées par des essais de traction.La limite d'élasticité et résistance à la rupture ont été étudiées sur la base de la section transversale résiduelle évaluée par perte de masse. Les résultats ont montré que les effets de la corrosion sur la diminution ductilité étaient très importants. La forme de la section transversale résiduelle apparait comme étant un paramètre essentiel affectant la ductilité de l'armature.Les performances résiduelles en flexion des poutres corrodées ont été étudiées. Les résultats montrent que la corrosion réduit la capacité portante et de façon plus significative, la flèche maximale à rupture en raison d’un changement de mode de rupture. La diminution de la charge de plasticité apparait en relation avec la perte de section d’acier tendu due à la corrosion Des poutres de portées courtes ont été réalisées à partir des poutres corrodées après les essais de flexion. Les tests mécaniques ont été effectués en flexion pour vérifier la réponse des poutres courtes corrodées. Les poutres courtes corrodées ont péri en flexion avec une bonne ductilité tandis que les poutres courtes non corrodées ont péri comme prévu en cisaillement suivant un mode de rupture fragile, qui a montré que la corrosion de l'armature pouvait modifier les modes de défaillance.Les produits de corrosion ont été recueillis à partir de l'armature corrodée de B2Cl3. Des expériences XRD et TG ont été menées afin d'identifier la composition des produits de corrosion. Le coefficient d'expansion des produits de corrosion a été déduit, ce qui pourrait être utile pour les recherches futures concernant le mécanisme de fissuration du béton d'enrobage. / The thesis aims to study the influence of chloride corrosion on the mechanical properties ofthe reinforcement and RC beams. The experiments were based on two corroded beams named B2Cl2 and B2Cl3, with a corroded age of 26 years and 28 years respectively. Two noncorroded beams B2T2 and B2T3 which were cast in the same condition and same time were also tested in order to make clear the corrosion effect.The mechanical properties of the corroded reinforcement were investigated by the tensiontests. The yield strength and ultimate strength were studied based on the residual gravimetrical cross-section. The results found that the impact of corrosion on the ductility was more significant than that of the strength. The shape of residual cross-section was considered to be in deep relationships with the ductility of the reinforcement.The flexural performances of the beams were studied. The results showed that the corrosion deteriorated the capacity and the ductility of the corroded beams. The corrosion degree of reinforcement was found in linear with the residual yield capacity of the corroded beams.The short-span beams were formed from the corroded beams after bending tests. Mechanical tests were carried out directly to check the response of the corroded beams. The corroded short-span beams failed in bending mode with good ductility while the non-corroded beams performed a brittle shear failure mode, which showed that the corrosion of reinforcement could change the failure modes.The corrosion products were collected from the corroded reinforcement of B2Cl3. XRD andTG experiments were conducted so as to identify the composition of the corrosion products.The expansive coefficient of the corrosion products was deduced, which could be helpful forthe further research on the cracking mechanism of the concrete cover