Dissertations / Theses on the topic 'Cementitious matrix'

The objective of this thesis was to investigate whether the addition of carbon nanofibers had an effect on the splitting tensile strength of Hydro-Stone gypsum concrete. The carbon nanofibers used were single-walled carbon nanotubes (SWNT), buckminsterfullerene (C60), and graphene oxide (GO). Evidence of the nanofibers interacting with gypsum crystals in a connective manner was identified in both 1 mm thick concrete discs and concrete columns possessing a height of 2 in and a diameter of 1 in. Before imaging, the columns were subjected to a splitting tensile strength test. The results illustrate that while there is a general decrease in strength with an increase in nanofibers for the nanotubes and graphene oxide, the addition of C60 did not noticeably effect the strength. This trend is consistent with trends determined by previous studies.

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
O uso de todos os tipos de amianto na construção civil tem diminuído drasticamente devido a problemas sérios de saúde associados a sua manipulação. De fato é previsto banir totalmente o seu uso, dentro de um curto espaço de tempo, nos países desenvolvidos bem como nos em desenvolvimento. Na necessidade de se encontrar um substituto adequado para o amianto, tem-se pesquisado compósitos de argamassa reforçada com fibras vegetais e polpas celulósicas. Devido ao processo de polpação, que remove as impurezas não celulósicas, como a lignina e a hemicelulose, diminuindo o ataque às fibras, sem a necessidade de recorrer a modificações na matriz cimentícia, as polpas celulósicas podem ser o substituto ideal para o amianto. Assim sendo, o principal objetivo desta dissertação é determinar experimentalmente as características mecânicas e os parâmetros de fratura de compósitos de matriz cimentícia reforçada por polpa de bambu refinada e sem refino. As polpas celulósicas foram utilizadas nas porcentagens de 8 e 14 por cento em relação à massa do cimento, porcentagens estas que, conforme a literatura, são associadas à otimização da energia absorvida no ensaio de flexão. A avaliação do comportamento mecânico dos compósitos considerados neste trabalho foi realizada através de ensaios de compressão e impacto, bem como de flexão em três pontos em espécimes não entalhados e em outros contendo entalhes de raios de curvatura diferentes. Propriedades mecânicas, tais como módulo de elasticidade, resistência à compressão, ao impacto e à flexão, bem como integral J na carga máxima, são apresentadas e discutidas em termos de aspectos microestruturais e fractográficos dos corpos de prova ensaiados.
As handling and manipulation of asbestos pose grave health hazards, its use in civil construction has been drastically dwindling and will in fact be completely prohibited, in a few years, in developed countries. With the need arising to find an adequate substitute, vegetable fibers and cellulosic pulps have been considered to be viable alternatives. Taking into account the fact that the process for pulp production entails the removal of impurities, such as lignin and hemicellulose, cellulosic pulps seem to be the ideal substitute to asbestos, as their use does not necessitate modifications in the cementitious matrix. Accordingly, the purpose of this work is to experimentally determine basic mechanical characteristics and pertinent fracture parameters of bamboo pulp reinforced cement. Refined and non-refined pulps were used in the proportions of 8 and 14 percent of the weight of dry cement. These percentages were adopted as they imply, according to literature, in optimizing the energy absorbed by the composite in bend loading. Evaluation of the mechanical behavior of the composites considered in this work was realized by means of compression and impact testing. Three point bend tests were also carried out using unnotched as well as notched specimens of different notch root radii. Mechanical properties such as modulus of elasticity, compressive, impact and bend strengths, and J integral at maximum load are presented and discussed in terms of pertinent microstructural and fractographic aspects of test specimens.

The increasing use of Fiber Reinforced methods for strengthening existing brick masonry walls and columns, especially for the rehabilitation of historical buildings, has generated considerable research interest in understanding the failure mechanism in such systems. This dissertation is aimed to provide a basic understanding of the behavior of solid brick masonry walls unwrapped and wrapped with Fiber Reinforced Cementitious Matrix Composites. This is a new type of composite material, commonly known as FRCM, featuring a cementitious inorganic matrix (binder) instead of the more common epoxy one. The influence of the FRCM-reinforcement on the load-carrying capacity and strain distribution during compression test will be investigated using a full-field optical technique known as Digital Image Correlation. Compression test were carried on 6 clay bricks columns and on 7 clay brick walls in three different configuration, casted using bricks scaled respect the first one with a ratio 1:2, in order to determinate the effects of FRCM reinforcement. The goal of the experimental program is to understand how the behavior of brick masonry will be improved by the FRCM-wrapping. The results indicate that there is an arching action zone represented in the form of a parabola with a varying shape according to the used configuration. The area under the parabolas is considered as ineffectively confined. The effectively confined area is assumed to occur within the region where the arching action had been fully developed.

The rehabilitation of existing masonry elements through jacketing of columns using composite materials is becoming a remarkable technique in several applications that aim to increase the strength of existing masonry building. An experimental campaign was conducted with Steel- and -Basalt Fiber Reinforced Cementitious Matrix (FRCM) systems, in order to test new products that might increase the advantages in terms of good adhesion to masonry substrate, breathability of the system, efficiency in aggressive environments, ease of installation and reversibility, which are essential for the preservation of historical buildings. The mean objective of this experimental study was to investigate the state of the improvement of square masonry columns, built in alternate stretcher and header bond configuration using as material confinement Steel- and-Basalt FRCM system, subjected to axial compression. Moreover, the effectiveness and influence of the confinement in terms of load-bearing capacity and strain distribution with respect to unconfined prisms was carried out. An optical technique, known as Digital Image Correlation (DIC), was employed to understand the interaction between the unit masonry components.

Unreinforced masonry (URM) walls are commonly found in existing and heritage buildings in Canada, either as infill or load-bearing walls. Such walls are vulnerable to sudden and brittle failure under blast loads due to their insufficient out-of-plane strength. The failure of such walls under blast pressures can also result in fragmentation and wall debris which can injure building occupants. Over the years, researchers have conducted experimental tests to evaluate the structural behaviour of unreinforced masonry walls under out-of-plane loading. Various strengthening methods have been proposed, including the use of concrete overlays, polyurea coatings and advanced fiber-reinforced polymer (FRP) composites. Fabric-reinforced cementitious matrix (FRCM) is an emerging material which can also be used to strengthen and remove the deficiencies in unreinforced masonry walls. This composite material consists of a sequence of one or multiple layers of cement-based mortar reinforced with an open mesh of dry fibers (fabric). This thesis presents an experimental and analytical study which investigates the effectiveness of using FRCM composites to improve the out-of-plane resistance of URM walls when subjected to blast loading. As part of the experimental program, two large-scale URM masonry walls were constructed and strengthened with the 3-plies of unidirectional carbon FRCM retrofit. The specimens included one infill concrete masonry (CMU) wall, and one load-bearing stone wall. The University of Ottawa Shock Tube was used to test the walls under gradually increasing blast pressures until failure, and the results were compared to those of control (un-retrofitted) walls tested in previous research. Overall, the FRCM strengthening method was found to be a promising retrofit technique to increase the blast resistance of unreinforced masonry walls. In particular, the retrofit was effective in increasing the out-of-plane strength, stiffness and ultimate blast capacity of the walls, while delaying brittle failure and reducing fragmentation. As part of the analytical research, Single Degree of Freedom (SDOF) analysis was performed to predict the blast behaviour of the stone load-bearing retrofit wall. This was done by computing wall flexural strength using Plane Section Analysis, and developing an idealized resistance curve for use in the SDOF analysis. Overall, the dynamic analysis results were found to be in reasonable agreement with the experimental maximum displacements.

This paper focuses on two experimental methods that give indicators linked to the impregnation level of the yarn / matrix interface, in the case of Textile Reinforced Concrete (TRC). These methods have been tested on three different glass yarns laid in a cementitious matrix, with three different impregnation levels resulting from the manufacturing process. The first method (comparative mercury intrusion porosity test) is based on the evaluation by mercury intrusion porosity of the pores volume associated to the porosity inside and near the yarn. The second method (flow test) consists in measuring the flow rate of water along the yarn, with imposed flow conditions. The physical parameters measured by these two methods are both related to the pore size and to the porosity of the yarn / matrix interface. The results of the two methods are discussed and drawn in parallel to a qualitative characterization of the yarn matrix interface made by scanning electron microscopy. As a result, the connection between the results of the two methods and the SEM characterization is studied. It is shown how these methods can participate to characterize the yarn impregnation. Limitations of the methods are also discussed.

Ordinary Portland cement (OPC) is the main constituent of concrete works as a principal binder for aggregates and intrinsically transmits the brittleness into concrete through the formation of hydration crystals in the cement microstructure. A number of nano cementitious composites were developed in recent years to offset the brittleness with newly discovered nanomaterials and the most prevalent among those is the graphene oxide (GO). The main objective of this PhD research work is to develop nano graphene cementitious composites (NGCC) using low cost, two dimensional (2D) graphene nanoplatelets (GNPs) and one dimensional (1D) graphited carbon nanofibres (GCNFs) with unique conical surface morphology. The GNPs were sourced synthesised in an environmental friendly way via plasma exfoliation whereas, GCNFs were manufactured through catalytic vapour grown method. The project further investigated the effect of these nanomaterials in regulating the distinctive microstructure of cement matrix leading to enhance its mechanical properties. Three different types of high-performance NGCC namely NGCC-Dot, NGCC-Fnt and NGCC-CNF, are developed by activating pristine GNPs (G-Dot), functionalised GNPs (G-Fnt) and graphited nanofibers (G-CNFs) into the cement matrix respectively. It is found through various characterization and experimental techniques that both GNPs and GCNFs regulated the cement microstructure and influenced the mechanical properties of NGCC uniquely. A remarkable increase in the flexural and the tensile strength of newly developed NGCC has been achieved and that could be attributed to the formation of distinctive microstructure regulated by catalytic activation of these nanomaterials. The shape (1D, 2D) and unique morphology of these nanomaterials played a vital role in the mechanism of crystal formation to regulate the cement microstructure. Based on the observations of test results and comprehensive characterization, the possible mechanisms of crystal formation and development of distinctive microstructure of NGCC has been established which has then proceeded to the development of a physical model for NGCC development.

Unreinforced masonry (URM) walls are often used as load-bearing or infill walls in buildings in many countries. Such walls are also commonly found in existing and heritage buildings in Canada. URM walls are strong structural elements when subjected to axial loading, but are very vulnerable under out-of-plane loads. This type of loading may come from different sources , including seismic or blast events. When subjected to blast, wall elements experience large pressures on one of their faces due to the high pressure produced in the air when an explosion takes place. This wave of compressed air travels in a very short time and hits the wall causing immense stresses, which result in large shear and bending demands that may lead to wall failure, and the projection of debris at high velocities that can injure building occupants. This failure process is highly brittle due to the very low out-of-plane strength that characterize such walls. In the past years, many investigations have been carried out to enhance the structural behaviour of unreinforced masonry walls under out-of-plane loading. Different strengthening methods have been studied, which include the use of polyurea coatings, the application of advanced fiber-reinforced polymer (FRP) composites or the use of concrete overlays in combination with high performance reinforcement. Fabric-reinforced cementitious matrix (FRCM) is a new composite material that overcomes some of the drawbacks of FRP. This composite material consists of applying coatings which consist of one or more layers of cement-based mortar reinforced with a corresponding open mesh of dry fibers (fabric). This material has been studied as a strengthening technique to improve in-plane and out-of-plane capacity of existing URM walls as well as other structural elements, mostly under seismic actions. This thesis presents an experimental and analytical study which investigates the effectiveness of using FRCM composites to improve the out-of-plane resistance of URM walls when subjected to blast loading. As part of the experimental program, three large-scale URM masonry walls were constructed and strengthened with 1,2 and 3 layers of FRCM using unidirectional carbon fabrics. In all cases the specimens were built as load-bearing concrete masonry (CMU) walls. To increase shear resistance, two of the walls were also grouted with a flowable self-compacting concrete (SCC) mortar. Blast tests were conducted using the University of Ottawa Shock Tube and the results are compared with control walls tested in previous research at the University of Ottawa. The experimental results show that the FRCM retrofit significantly improved the blast performance of the URM load-bearing walls, allowing for increased blast capacity and improved control of displacements. The performance of the retrofit was found to be dependent on the number of retrofit layers. As part of the analytical research, Single Degree of Freedom (SDOF) analysis was carried out to predict the blast behaviour of the strengthened walls. This was done by computing wall flexural strength using plane sectional analysis and developing idealized resistance curves for use in the SDOF analysis. In general, the analysis procedure is found to produce reasonably accurate results for both the resistance functions and wall mid-height displacements under blast loading.

This thesis investigates the repair of impact-damaged prestressed concrete bridge girders with strand splices and fabric-reinforced cementitious matrix systems, specifically for repair of structural damage to the underside of an overpass bridge girder due to an overheight vehicle collision. Collision damage to bridges can range from minor to catastrophic, potentially requiring repair or replacement of a bridge girder. This thesis investigates the performance of two different types of repair methods for flexural applications: strand splice repair, which is a traditional repair method that is often utilized, and fabric-reinforced cementitious matrix repair, which is a relatively new repair method. The overarching goal of this project was to provide guidance for assessment and potential repair of impact-damaged girders. Prestressed concrete girders were tested to failure in flexure in this research. After a control test to establish a baseline for comparison, five tests were performed involving damaging a girder, repairing it using one of the repair methods, and testing it to failure. These tests showed that both strand splice repairs and fabric-reinforced cementitious matrix repairs can adequately restore the strength of an impact-damaged girder when up to 10% of the prestressing strands are severed. Combined repairs can also be a viable option if more than 10% of the prestressing strands are severed, though as the damage gets more severe, girder replacement becomes a more attractive option.
Master of Science

La capacité de déformation améliorée et la résistance à la fissuration par retrait rendent les composites cimentaire caoutchoutés adaptés aux applications de grande surface telles que les chaussées et les rechargements minces adhérents à base cimentaire. Cependant, le défaut d'adhérence entre les agrégats de caoutchouc et la matrice cimentaire, bien connu, demeure nuisible aux propriétés mécaniques et de transferts de ces matériaux. De plus, en raison de la faible rigidité des granulats caoutchouc, il est universellement accepté une réduction de certaines propriétés mécaniques des composites caoutchoutés à base de ciment. Néanmoins, leurs propriétés de transfert pourraient être compétitives avec le mortier à base de granulats naturels si la liaison à l'interface caoutchouc-ciment est améliorée. Afin d'améliorer l'interface, les granulats caoutchouc ont d'abord été revêtus d'un copolymère styrène-butadiène et après densification complète de ce copolymère à la surface des agrégats caoutchouc, ils ont été incorporés au mélange cimentaire. Dans un premier temps, une analyse microstructurale utilisant la microscopie électronique à balayage (MEB), la spectrométrie de rayons X à dispersion d'énergie (EDS) et la diffraction des rayons X (DRX) a permis de préciser que la pâte de ciment adhérait fermement aux granulats caoutchouc revêtus de copolymère. Dans un second temps, les propriétés mécaniques et de transfert de ce mortier ont ensuite été comparées à celles du mortier témoin (granulats naturels) et de deux autres mortiers caoutchoutés dans lesquels l'un d'entre eux a été ajouté un désentraineur d'air pour produire un mélange caoutchouté ayant la même teneur en air que le mortier témoin. Les résultats ont démontré une interface améliorée du caoutchouc-ciment fournissant une amélioration significative des propriétés de transfert telles que la perméabilité à l'air et l'absorption capillaire d'eau. Cependant, la diminution des propriétés mécaniques (résistance à la compression et module d'élasticité) demeure en raison de la faible rigidité des granulats caoutchouc. Quant à la résistance à la traction et la résistance résiduelle post-pic témoignent d'une énergie de rupture plus élevées dans le cas de granulats revêtus du copolymère, démontrant un effet de pontage amélioré rendu possible par la liaison entre les granulats caoutchouc et la matrice de ciment. Cet effet de pontage a également contribué à améliorer la résistance des composites caoutchoutés à la fissuration par retrait empêché Afin d'étayer les effets d'une interface caoutchouc-ciment améliorée, la durabilité des mortiers caoutchoutés dans des environnements agressifs a été étudiée. En ce qui concerne l'attaque à l'acide acétique, une faible profondeur dégradée et une réduction de la perte de masse et de résistance à la compression des mortiers caoutchoutés revêtus de copolymère ont été observés par rapport au mortier témoin. Le mortier caoutchouté enduit de copolymère se comporte également mieux en empêchant la diffusion du sulfate de sodium dans le composite. La dégradation des mortiers dans des environnements agressifs a également été évaluée sur la base d'une variable d'endommagement. Il en ressort que les matériaux caoutchoutés revêtus de copolymère étaient plus durables que les matériaux non traités exposés à des environnements agressifs
Properties of improved strain capacity and high shrinkage cracking resistance make rubberized cement-based composites suitable for large surface applications such as cement-based pavements and thin bonded overlays. However, bond defect between rubber aggregates (RA) and cement matrix is well-known and detrimental to properties of rubberized cement-based materials. It is universally accepted a reduction in some mechanical properties of rubberized cement-based composites mainly due to low stiffness of RA. Nevertheless, their transfer properties could indeed be competitive with control mortar (without RA) if bond at rubber-cement matrix interface is improved. In order to enhance the interface, RA were firstly coated with styrene-butadiene copolymer and after complete densification of this copolymer on surface of RA, they were mixed with the pre-mixed cementitious mixture. Microstructural analysis using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectrometry (EDS), and X-Ray Diffraction (XRD) clarified that cement paste bonded firmly on copolymer-coated RA. Mechanical and transfer properties of this mortar were then compared to that of control mortar and two rubberized mortars in which one of them air-detraining admixture was added to produce rubberized mixture with the similar air content as the control mortar. Findings have demonstrated an enhanced rubber-cement matrix interface provided a significant improvement on transfer properties such as air permeability and water capillary absorption. However, a reduction in mechanical properties (compressive strength and modulus of elasticity) was still observed due to low stiffness of RA. Rubber coating appeared to limit the reduction in tensile strength and to result in a higher residual post-peak strength and fracture energy, demonstrating an improved material bridging effect made possible by the bond between RA and cement matrix. The bridging effect also contributed to improve resistance of rubberized composites to shrinkage cracking even under high restrained conditions. Based on above-mentioned characteristics, the study further investigated the durability of rubberized mortars under aggressive environments to observe the effects of RA incorporation and of an enhanced rubber-cement matrix interface. Regarding acetic acid attack, a low degraded depth and a reduction in loss of both mass and compressive strength of rubberized mortars, especially the one incorporating copolymer-coated RA, were observed compared to the ones of the control mortar. The coated rubberized mortar also behaves better in preventing sodium sulfate diffusion into the composite. The degradation of mortars under aggressive environments was also evaluated based on a damage variable, which was defined as a relative change in equivalent load-resisting area of mortar specimens between their original condition and at a given time when they were exposed to acid or sulfate solutions. From damage variable values, it can be concluded that coated rubberized mortar was more durable than the untreated one against aggressive environments. The durability of untreated and coated rubberized mortars under freeze-thaw cycles was also carried out and compared to that of control mortar. The rubberized cement- based composites were more resistant to freezing and thawing than the control one, especially in terms of dimensional expansion. The better performance can be attributed to high energy absorption of RA and to higher porosity, lower water capillary absorption and high strain capacity of rubberized mortars. Rubber coating, even reducing the permeability of rubberized cement-based composites, still remained high durability of their applications under frost environment

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2005.
192 leaves on CD format, preliminary i-xii pages and numbered pages 1-135. Includes bibliography, list of figures and tables.
ENGLISH ABSTRACT: As a fibre reinforced material, engineered cementitious composite (ECC) has tough, strain-hardening behaviour in tension despite containing low volumes of fibres. This property can be brought about by developments in fibre, matrix and interfacial properties. Poly Vinyl Alcohol (PVA) fibre has been developed in recent years for ECC, due to its high tensile strength and elasticity modulus. However, the strong interfacial bond between fibre surface and matrix is a challenge for its application. This study focuses on the tailoring of matrix and fibre/matrix interfacial properties by cement replacement with fly ash (FA) and Ground Granulated Corex Slagment (GGCS). In this study the direct tensile test, three point bending test, micro-scale analysis, such as X-Ray Fluorescence Spectrometry analysis (XRF), Scanning Electron Microscope (SEM), are employed to investigate the influence of cement replacement, aging, Water/Binder (W/B) ratio, workability on ECC behaviour. This study has successfully achieved the aim that cement replacement by FA and GGCS helps to improve the fibre/matrix interfacial properties and therefore enhances the ECC tensile behaviour. Specifically, a high volume FA-ECC has stable high tensile strain capacity at the age of 21 days. This enables a constant matrix design for the investigation of other matrix influences. The Slag-ECC has a higher tensile strength but lower tensile strain capacity. The combination of FA and GGCS, moderate tensile strength and strain capacity is achieved Both tensile tests and Micro-scale analyses infer that the high volume FA-ECC has an adhesive type fibre/matrix interfacial interaction, as opposed to the cohesive type of normal PVA fibre-ECC. The different tensile behaviour trend of steel fibre-ECC and PVA fibre-ECC with the FA content is presented and discussed in this research. The investigations of aging influence indicate that the high volume FA-ECC has a beneficial effect on the properties of the composite at an early stage. However, at a high age, it has some difficulty to undergo multiple cracking and then leads to the reduction of tensile strain capacity. The modified mix design is made with the combination of FA and GGCS, which successfully increases the interfacial bond and, thereby, improves the shear transfer to reach the matrix crack strength. Therefore, an improved high age tensile behaviour is achieved. The W/B and fresh state workability influence investigations show that the W/B can hardly affect the tensile strain at early age. However, the workability influences on composite tensile strain significantly, because of the influence on fibre dispersion. Other investigations with regard to the hybrid fibre influences, the comparison of bending behaviours between extruded plate and cast plate, the relation between bending MOR and tensile stress, and the relation between compression strength and tensile strength contribute to understand ECC behaviour.
AFRIKAANSE OPSOMMING: As ‘n veselversterkte materiaal, het ontwerpte sementbasis saamgestelde materiale, taai vervormingsverhardingseienskappe in trek, ten spyte van lae veselinhoud. Hierdie eienskap word bewerkstellig, deur ontwikkelings in vesel, matriks en tussenveselbindingseienskappe. Poli-Viniel Alkohol (PVA) vesels is ontwikkel vir ECC, as gevolg van die hoë trekkrag en hoë modulus van hierdie veseltipe. Die sterk binding tussen die PVA-veseloppervlak en die matriks is egter ‘n uitdaging vir sy toepassing. Hierdie studie fokus op die skep van gunstige matriks en vesel/matriks tussenvesel-bindingseienskappe deur sement te vervang met vlieg-as (FA) en slagment (GGCS).In hierdie navorsing is direkte trek-toetse, drie-punt-buigtoetse, mikro-skaal analise (soos die X-straal ‘Fluorescence Spectrometry’ analise (XRF) en Skanderende Elektron Mikroskoop (SEM))toegepas. Hierdie metodes is gebruik om die invloed van sementvervanging,veroudering, water/binder (W/B)-verhouding en werkbaarheid op die meganiese gedrag van ECC te ondersoek.Die resultate van hierdie navorsing toon dat sementvervanging deur FA en GGCS help om die vesel/matriks tussenveselbindingseienskappe te verbeter. Dus is die ECC-trekgedrag ook verbeter. Veral ‘n hoë volume FA-ECC het stabiele hoë trekvervormingskapasiteit op ‘n ouderdom van 21 dae. Dit bewerkstellig ‘n konstante matriksontwerp vir die navorsing van ander matriks invloede. Die Slag-ECC het ‘n hoër treksterkte, maar laer trekvervormingskapasiteit. Deur die kombinasie van FA en GGCS word hoë treksterkte, sowel as gematigde vervormbaarheid in trek verkry. Beide trektoetse en mikro-skaal analise dui aan dat die hoë volume FA-ECC ‘n adhesie-tipe vesel/matriks tussenvesel-bindingsinteraksie het, teenoor die ‘kohesie-tipe van normale PVA vesel-ECC. Die verskille in trekgedrag van staalvesel-ECC en PVA vesel-ECC ten opsigte van die FA-inhoud is ondersoek en word bespreek in die navorsing. Die navorsing toon verder dat die hoë volume FA-ECC goeie meganiese eienskappe het op ‘n vroeë ouderdom. Op hoër ouderdom word minder krake gevorm, wat ‘n verlaging in die trekvervormingskapasiteit tot gevolg het. Met die kombinasie van FA en GGCS, word die vesel-matriksverband verhoog, waardeur ‘n verbetering in die skuifoordrag tussen vesel en matriks plaasvind. Verbeterde hoë omeganiese gedrag word daardeur tot stand gebring. Navorsing ten opsigte van die invoed van die W/B en werkbaarheid dui daarop dat die W/B slegs geringe invloed het op die trekvormbaarheid, terwyl die werkbaarheid ‘n dominerende rol speel in hierdie verband.Verdere studies sluit in die invloed van verskillende vesels, die vergelyking van die buigingsgedrag van geëkstueerde plate en gegote plate, die verhouding tussen buigsterkte en treksterkte, en die verhouding tussen druksterkte en treksterkte dra by tot beter begrip van die gedrag van ECC.

Ingeniera Civil, Mención Estructuras
Las tecnologías para la rehabilitación de estructuras dañadas resultan de especial relevancia en países sísmicos. En el caso de estructuras frágiles de hormigón armado y de albañilería se han estudiado diferentes sistemas de reparación estructural, en busca de un refuerzo cuyas propiedades sean compatibles con las del sustrato y que restituyan la integridad y recuperen o aumenten de buena manera la capacidad portante de los elementos. El objetivo principal del presente trabajo de título consiste en el estudio de la metodología de diseño de uno de estos sistemas de refuerzo, sistema conocido como FRCM*. Este tipo de refuerzo es un material compuesto, constituido por aglomerante cementíceo como matriz y malla de fibras minerales como refuerzo, el cual se adhiere externamente a los elementos de hormigón armado, con mínima alteración arquitectónica. Este sistema de refuerzo es considerado como una solución prometedora para la recuperación de estructuras dañadas. En este trabajo se realiza primeramente una revisión bibliográfica de manera de contextualizar los avances y las principales características del refuerzo y comparar con el método actualmente en uso, refuerzo conocido como FRP**, variante del cual surge el desarrollo del FRCM. Uno de los objetivos de esta memoria es el estudio la precisión del método de diseño, que se realiza a partir de las disposiciones que establece el manual de diseño ACI 549, para elementos representativos de vigas y columnas a partir de resultados experimentales obtenidos de estudios de laboratorios de otros autores. De estos análisis comparativos se concluye que la norma de diseño cuantifica de manera conservadora los aumentos de capacidad de los elementos. Como aplicación de la metodología a un caso práctico, se estudia el diseño del refuerzo FRCM para una estructura real, que ha sufrido deterioro en su manto, con agrietamiento y deslaminación. Se trata de una chimenea de hormigón armado perteneciente a una termoeléctrica de carbón, ubicada en Ventanas, V región. Se propone realizar la consolidación del manto exterior, lo que permite llevar la estructura a su estado original, recuperando la capacidad estructural y prolongando su período de servicio. *FRCM: Fabric Reinforced Cementitious Matrix **FRP: Fiber Reinforced Polymer

A lower-alkalinity cement based on MgO and SiO2 blends is analysed to develop clinker-free Fibre Reinforced Cementitious Composites (FRCC) with cellulosic fibres in order to solve the durability problems of this type of fibres when used in FRCC with Portland cement. Hydration evolution from 7 to 28 days of different MgO-SiO2 formulations is assessed. The main hydration products are Mg(OH)2 and M-S-H gels for all the formulations studied regardless of age. Hardened pastes are obtained with pH values < 11 and good mechanical properties compared to conventional Portland cement. 60% MgO-40% SiO2 system is chosen as optimal for the development FRCC since is the most mechanical resistant and is less alkaline compared with 70% MgO-30% SiO2. FRCC based on magnesium oxide and silica (MgO-SiO2) cement with cellulose fibres are produced to study the durability of lignocellulosic fibres in a lower pH environment than the ordinary Portland cement (PC). Flexural performance and physical tests (apparent porosity, bulk density and water absorption) of samples at 28 days and after 200 accelerated ageing cycles (aac) are compared. Two types of vegetable fibres are utilised: eucalyptus and pine pulps. MgO-SiO2 cement preserves cellulosic fibres integrity after ageing, so composites made out of MgO-SiO2 exhibit significant higher performance after 200 cycles of accelerated ageing than Portland cement composites. High CO2 concentration environment is evaluated as a curing treatment in order to optimise MgO- SiO2 matrices in FRCC. Samples are cured under two different conditions: 1) steam water curing at 55°C and 2) a complementary high CO2 concentration (20% by volume). In carbonated samples, Mg(OH)2 content is clearly lowered while new crystals of hydromagnesite [Mg5 (CO3)4⋅(OH) 2⋅4H2O] are produced. After carbonation, M-S-H gel content is also reduced, suggesting that this phase is also carbonated. Carbonation affects positively to the composite mechanical strength and physical properties with no deleterious effects after ageing since it increases matrix rigidity. The addition of sepiolite in FRCC is studied as a possible additive constituent of the binding matrix. Small cement replacement (1 and 2% wt.) by sepiolite is introduced and studied in hardened cement pastes and, later, in FRCC systems. When used only in cement pastes, it improves Dynamic Modulus of Elasticity over time. Bending tests prove the outcome of this additive on the mechanical performance of the composite: it improves composite homogeneity. Ageing effects are reported after embedding sisal fibres in MgO-SiO2 and PC systems and submitting them to different ageing conditions. This comparative study of fibre degradation applied in different cementitious matrices reveals the real compatibility of lignocellulosic fibres and Mg-based cements. Sisal fibres, even after accelerated ageing, do neither suffer a significant reduction in cellulose content nor in cellulose crystallinity and crystallite size, when exposed to MgO-SiO2 cement. Fibre integrity is preserved and no deposition of cement phases is produced in MgO-SiO2 environment.
Um cimento de baixa alcalinidade à base de blendas de MgO e SiO2 é analisado para o desenvolvimento de Compósitos Cimentícios Reforçados com Fibras (CCRF) celulósicas sem clínquer para resolver os problemas de durabilidade de este tipo de fibras quando são usadas em CCRF com cimento Portland. A evolução da hidratação, desde 7 aos 28 dias, das diferentes formulações é avaliada. Os principais produtos hidratados são o Mg(OH)2 e o gel M-S-H para todas as formulações independentemente da idade estudada. As pastas endurecidas apresentam valores de pH < 11 e bom desempenho mecânico comparado com o cimento Portland convencional. O sistema 60% MgO-40% SiO2 é escolhido como a formulação ótima para o desenvolvimento de CCRF já que é a mais resistente e menos alcalina comparada com 70% MgO-30% SiO2. CCRF com cimento à base de óxido de magnésio e sílica (MgO-SiO2) e fibras celulósicas são produzidos para a análise da durabilidade das fibras lignocelulósicas em ambientes com valores de pH mais baixos comparados com o cimento Portland (PC). O desempenho mecânico a flexão e os ensaios físicos (porosidade aparente, densidade aparente e absorção de água) são comparados aos 28 dias e após de 200 ciclos de envelhecimento acelerado. O cimento à base de MgO-SiO2 preserva a integridade das fibras após o envelhecimento. Os compósitos produzidos com este cimento exibem melhores propriedades após 200 ciclos de envelhecimento acelerado que os compósitos produzidos com cimento Portland. Ambientes com alta concentração de CO2 são avaliados como tratamento de cura para otimizar as matrizes MgO- SiO2 nos CCRF. As amostras são curadas sob 2 condições diferençadas: 1) cura com vapor de água a 55oC e 2) cura com alta concentração de CO2 (20% do volume). As amostras carbonatadas apresentam teores reduzidos de Mg(OH)2 enquanto é produzida uma nova fase cristalina: hidromagnesita [Mg5 (CO3)4⋅(OH) 2⋅4H2O]. Após a carbonatação, o conteúdo de gel M-S-H é reduzido também, indicando uma carbonatação desta fase. A carbonatação aumenta a rigidez da matriz o que influi positivamente no desempenho mecânico e as propriedades físicas dos compósitos sem efeitos prejudiciais ao longo prazo. A adição de sepiolita em CCRF é estudada como possível adição na composição da matriz aglomerante. Baixos teores (1 e 2% em massa) de cimento são substituídos por sepiolita para o estudo das pastas de cimento hidratado e, posteriormente, dos compósitos. O Módulo Elástico Dinâmico das pastas é incrementado com o tempo pela adição de sepiolita. Os ensaios a flexão demostram que a adição de sepiolita melhora a homogeneidade dos compósitos. Reportam-se os efeitos das fibras de sisal após da exposição a sistemas MgO-SiO2 e PC e submetidas a diferentes condições de envelhecimento. Este estudo comparativo da degradação das fibras expostas a diferentes matrizes cimentícias mostra a compatibilidade das fibras lignocelulósicas com os cimentos à base de Mg. As fibras de sisal, inclusive após o envelhecimento acelerado, não apresentam nem redução significativa no conteúdo de celulose nem na cristalinidade da celulose assim como do tamanho de cristalito, quando expostas a cimentos MgO-SiO2.

Materiais aplicados na construção civil são importantes para fornecer segurança e conforto às pessoas. Quanto mais adequadas as propriedades térmicas, menos energia é necessária para aquecer ou resfriar uma área construída. A NBR 15575:2013 - Desempenho de Edificações Habitacionais, padronizou desempenhos térmicos para construções. Os blocos estruturais cerâmicos atendem o padrão mínimo, porém acredita-se que seu desempenho possa ser melhorado utilizando materiais de características isolantes dentro de seus furos verticais. Assim, o objetivo deste trabalho é investigar compósitos de matriz cimentícia com agregados leves para o aprimoramento térmico de blocos estruturais cerâmicos. Para o estudo, quatro corpos de prova foram produzidos preenchendo o vazado dos blocos com compósitos de matriz cimentícia utilizando 80% agregados leves (argila expandida, vermiculita, poliestireno expandido (EPS) e perlita expandida), 20% de cimento, além de uma amostra preenchida com graute estrutural que é comumente utilizado em edificações de alvenaria estrutural. Também foram produzidos corpos de prova com os compósitos, para a análise de massa específica, microscopia, resistência à compressão, absorção de água e desempenho térmico medido por termografia. Nos blocos, analisou-se massa final preenchido, absorção de água e desempenho térmico. No estudo termográfico, os blocos preenchidos foram comparados ao bloco cerâmico vazado padrão. Concluiu-se que o preenchimento dos vazados dos blocos com todos os compósitos leves e com o graute estrutural proporcionou um desempenho térmico melhor que o do bloco padrão, se destacando o EPS como melhor desempenho. O desempenho térmico dos prismas de compósitos confirmou o que foi observado nos corpos de prova de blocos. Assim foram feitos novos corpos de prova maximizando o teor de EPS para 85% e 90%. A análise térmica destas amostras apresentou melhor resultado para EPS 90%. O aumento do teor de EPS diminuiu a resistência à compressão e aumentou a absorção de água, porém, como o foco é o desempenho térmico e o bloco preenchido com o compósito EPS (90%) atende as características normativas, esta pode ser uma solução interessante.
Materials applied in civil construction are important to provide security and comfort to people. The more appropriate the thermal properties are, the less energy it is necessary to provide heat or cold to a constructed area. The NBR 15575:2013 standard, which deals with the Performance of Residential Constructions, has standardized thermal performances for buildings. Structural ceramic blocks meet the minimum standard, but it is believed that their performance can be improved by means of materials with isolating characteristics within their vertical holes. Thus, the aim of this paper is to investigate cementitious matrix composites with lightweight aggregates for thermal improvement of ceramic structural blocks. For the study, four specimens were produced by filling the hollow spaces of the blocks with cementitious matrix composites using 80% of lightweight aggregates (expanded clay, vermiculite, expanded polystyrene – EPS –, and expanded perlite), and 20% of cement. These were compared to a sample filled with structural grout, which is commonly used in structural masonry buildings. Specimens were also produced with the composites for specific mass analysis, microscopy, compression resistance, water absorption and thermal performance measured by thermography. In the blocks, the final, filled weight was analyzed, as well as water absorption and thermal performance. In the thermographic study, the filled blocks were compared to standard ceramic hollow blocks. It was concluded that filling the hollow spaces of the blocks with all the lightweight composites and structural grout provided a better thermal performance than that of standard blocks, highlighting EPS as having the best performance. Thermal performance of the composite prisms confirms what was observed in the block specimens. Thus, new specimens were made maximizing the EPS content to 85% and 90%. Thermal analysis of these samples presented better results for EPS 90%. The increase in the EPS content decreased compression resistance and increased water absorption. However, as the focus is thermal performance and as the block filled with EPS composite (90%) meets the requirements of the standard, this may be an interesting solution.

Strain-hardening cement-based composites (SHCC) are a special class of fiber-reinforced concrete which develop multiple, fine cracks when subjected to increasing tensile loading, reaching strain capacities of up to several percent. The tensile behavior of SHCC is a result of a purposeful material design accounting for the mechanical and physical properties of the cementitious matrix, of the reinforcing fibers and of their interaction. The exceptionally high energy dissipation through inelastic deformations before reaching tensile strength makes SHCC suitable for manufacturing or strengthening of structural elements which may be subjected to impact loading. However, the tensile behavior of SHCC is highly strain rate dependent, both in terms of tensile strength and strain capacity. The different strain rate sensitivities of the constitutive phases of SHCC (matrix, fiber and interfacial bond) lead to disproportionate dynamic alteration of their mechanical properties under increasing strain rates and, consequently, to an impairment of the micromechanical balance necessary for strain-hardening and multiple cracking. Thus, high energy dissipation under impact loading can only be ensured through a targeted material design. This work presents a series of mechanical experiments at different strain rates and different scales of investigation with the goal of developing a qualitative and quantitative basis for formulating material design recommendations for impact resistant SHCC. Three different types of SHCC were investigated, consisting of two types of polymer fibers (polyvinyl-alcohol and high-density polyethylene) and cementitious matrices (normal-strength and high-strength). Uniaxial tension experiments were performed on SHCC specimens and on non-reinforced matrix specimens with different testing setups at strain rates ranging from 10-4 to 150 s-1. Besides the measured mechanical properties, special attention was paid to the crack patterns and the condition of fracture surfaces. Additionally, micro-scale investigations were performed to quantify the strain rate dependent changes in the mechanical behavior of individual component phases, i.e., matrix, fibers and fiber-matrix bond. The results obtained from the micromechanical investigations were used in an analytical model for crack bridging. The model links the micromechanical parameters and their strain rate sensitivities to the single-crack opening behavior under increasing displacement rates, making it useful for material design purposes. If given an extensive experimental basis for the fracture mechanical properties of the non-reinforced cementitious matrices, the model can be extended for predicting the strain capacity (multiple cracking) of SHCC under different strain rates
Die hochduktilen Betone (Engl.: Strain-Hardening Cement-based Composites – SHCC) bilden eine besondere Klasse von Faserbetonen, die eine multiple Rissbildung unter zunehmenden Zugspannungen aufweisen, was zu einer sehr hohen Bruchdehnung führt. Das dehnungsverfestigende, hochduktile Zugverhalten der SHCC wird durch eine gezielte Materialentwicklung erreicht, die die mechanischen und physikalischen Eigenschaften der zementgebundenen Matrizen, der Kurzfasern und deren Zusammenwirkung berücksichtigt. Das außergewöhnliche Energieabsorptionsvermögen der SHCC durch plastische Verformungen vor dem Erreichen der Zugfestigkeit qualifiziert diese Verbundwerkstoffe für die Herstellung oder Verstärkung von Bauteilen, die Impaktbeanspruchungen ausgesetzt sein könnten. Jedoch weisen SHCC sowohl bezüglich deren Zugfestigkeit als auch deren Dehnungskapazität ein ausgeprägtes dehnratenabhängiges Verhalten auf. Unter zunehmenden Dehnraten führen die unterschiedlichen Dehnratensensitivitäten der gestaltenden Phasen von SHCC (Matrix, Faser und deren Verbund) zur Beeinträchtigung des mikromechanischen Gleichgewichts, welches für die Dehnungsverfestigung und multiple Rissbildung erforderlich ist. Eine hohe Energiedissipation unter Impaktbeanspruchungen kann deshalb nur durch eine gezielte Materialentwicklung der SHCC hinsichtlich deren Verhaltens unter hohen Dehnraten gewährleistet werden. Die vorliegende Arbeit umfasst eine Reihe von experimentellen Untersuchungen mit verschiedenen Dehnraten und an unterschiedlichen Betrachtungsebenen, mit dem Ziel eine qualitative und quantitative Basis für Empfehlungen zur Materialentwicklung von Impakt-resistenten SHCC zu schaffen. Drei verschiedene SHCC-Zusammensetzungen wurden untersucht. Die Referenz-Zusammensetzung aus einer normalfesten zementgebundenen Matrix und Polyvinyl-Alkohol-Kurzfasern wurde mit zwei unterschiedlichen SHCC verglichen (hochfest und normalfest), die mit Kurzfasern aus hochdichtem Polyethylen bewehrt wurden. Einaxiale Zugversuche wurden an SHCC-Proben und unbewehrten Matrix-Proben mit verschiedenen Prüfvorrichtungen bei Dehnraten von 10-4 bis 150 s-1 durchgeführt. Zusätzlich zu den gemessenen mechanischen Eigenschaften wurden die Rissbildung und die Bruchflächen detailliert untersucht. Darüber hinaus wurden mikromechanische Untersuchungen durchgeführt, um die Dehnratensensitivität der einzelnen Phasen, d.h. Matrix, Faser und deren Verbund zu beschreiben. Die aus den mikromechanischen Untersuchungen erzielten Ergebnisse wurden als Eingangswerte in einem analytischen Einzelriss-Modell verwendet. Das entwickelte Modell verbindet die mikromechanischen Parameter und deren Dehnratenabhängigkeit mit dem Rissöffnungsverhalten von SHCC bei zunehmenden Verschiebungsraten. Das macht es vorteilhaft für Materialentwicklungszwecke. Das Modell kann für die Vorhersage der Dehnungskapazität von SHCC bei diversen Dehnraten weiterentwickelt werden, wenn eine umfassende experimentelle Basis für die bruchmechanischen Eigenschaften der Matrizen vorliegt

Nella tesi viene trattato il recupero delle strutture murarie tramite l’utilizzo di materiali compositi, in particolare si trattano i Fyber Reinforced Polymers (FRP) e i Fybers Reinforced Cementitious Matrix (FRCM). Ad oggi le principali tecniche di consolidamento si basano sull’utilizzo di materiali “classici”, come acciaio o cemento armato, dei quali esistono dettagliate indicazioni progettuali, ma che presentano la controindicazione di essere invasive e, quindi, di modificare il comportamento statico del sistema a cui vengono applicate. Utilizzando materiali compositi, invece, si possono ottenere importanti miglioramenti senza apportare cambiamenti statici, con l’ulteriore vantaggio di poter essere nascosti da intonaci. Prendendo come riferimento le normative in via di costituzione per la progettazione di interventi con FRCM, si sottolineano le principali differenze in termini di metodologie di verifica e di risultati tra i due materiali di interesse. L'obiettivo è quello suggerire delle indicazioni di riferimento utili al momento della selezione di un composito anziché l’altro. Si dimostra che è possibile realizzare interventi migliorativi sulla muratura con entrambi i materiali citati: a seconda della situazione risulteranno differenti le formule di verifica e gli ambiti in cui un composito è più indicato. Grazie alle caratteristiche di traspirabilità e permeabilità al vapore, oltre alla flessibilità che permette modeste deformazioni del supporto, i compositi FRCM sono particolarmente indicati all’applicazione su apparati murari. Tuttavia, non tutti i meccanismi di collasso possono essere recuperati equivalentemente con ambo i materiali, principalmente perché gli interventi con FRCM richiedono una maggiore superficie di applicazione.

O presente trabalho tem como objetivo identificar e analisar parâmetros que influenciam a aderência de matrizes cimentícias a substratos apontando soluções técnicas para a melhoria de tal propriedade. Para tanto, foram desenvolvidos três estudos independentes: primeiro, a elaboração e validação de um modelo matemático com base na restrição geométrica para verificar a contribuição da penetração de partículas em meios porosos. O modelo considera que, após serem lançadas sobre a superfície, as partículas com área de projeção no plano menor ou igual à área do poro podem penetrá-la; segundo, um estudo experimental comparando substratos cimentícios com mesmas características topográficas (rugosidade/porosidade) e diferentes níveis de absorção obtidos mediante tratamentos superficiais: aplicação de silano e lixamento para verificar o efeito da absorção do substrato. O controle da absorção foi realizado por medições do ângulo de contato aparente e ensaios de absortividade; e por último, a influência do teor de ligante da matriz foi avaliada pela substituição de 30% e 60% do cimento por finos calcários, com duas distribuições granulométricas, em argamassas aplicadas sobre blocos cerâmicos. O efeito da aglomeração de partículas foi estudado pela adição de dispersante a base de policarboxilato num teor de 0,02% em relação ao volume total de sólidos. As características reológicas das argamassas foram medidas por reometria rotacional. O desempenho mecânico da interface matriz-substrato foi avaliado pela resistência de aderência ä tração. Os resultados mostraram que a aderência depende de parâmetros mais complexos que a simples absorção do substrato e, consequente ancoragem mecânica pela penetração de partículas nos poros. O uso de partículas finas associadas a dispersantes e tratamentos superficiais do substrato aumentaram aderência pelo acréscimo de contato matriz-substrato.
This study aims to identify and analyse parameters that influence the adhesion among cementitious matrices and substrates pointing out technical solutions to improve this property. The research has been developed by means of three independent studies. The first one concerns the development and validation of a mathematical model, based on geometric constraints, for the estimation of the particles potential penetration in porous media. The model considers particles with projected area less than or equal to the pore area can penetrate the pore. The second study is an experimental comparison among cementitious substrates with same porosity and roughness and different levels of absorption achieved by surface treatment. The application of abrasive methods and a water repellent have been used to manage the effect of the absorption of substrates. The control of wettability and absorption has been carried out by measuring the apparent contact angle and sorptivity. The third one regards the evaluation of binders content in cementitious matrices. Mortars, with two different limestone fines, have been made and applied on red ceramic substrates (clay bricks). The limestone fines, with two different particle size distributions, have been added at rates of 30% and 60% as replacement of binders volume. The agglomeration of particles has been assessed adding a polycarboxylate type admixture (0.02% of total solids volume), whereas the rheological behavior have been determined using a rotational rheometer. The performance of interface between matrix and substrate has been determined measuring the tensile adhesive strength. Results showed that the adhesion depends on parameters more complex than the simple absorption of substrate and the consequent mechanical interlocking of particles into pores. The use of fine particles, combined with the dispersant and with the silane surface treatment increased the adhesion through the increase of the contact area.

La prédiction du comportement à long terme des matériaux cimentaires est un enjeu majeur pour contribuer à l'étude de la durabilité des structures précontraintes. Le présent travail porte sur l'utilisation de la méthode de l'inclusion équivalente, approche d'homogénéisation multi-échelle simplifiée, pour la prédiction du fluage dans ces matériaux. Le fluage est modélisé par la viscoélasticité linéaire sans vieillissement. La méthode de l'inclusion équivalente permet de contourner certaines difficultés et limitations que présentent les approches classiques. Pour les matériaux cimentaires, fortement hétérogènes, les approches multiéchelles classiques sont ou bien numériquement lourdes et très complexes à mettre en œuvre, ou bien pas suffisamment détaillées pour prendre en compte les spécificités d'une microstructure. La méthode de l'inclusion équivalente présente un juste-milieu et permet de calculer des microstructures simplifiées de type matrice-inclusions et de fournir des estimations ou des bornes sur le comportement homogénéisé. Sous sa forme variationnelle, la méthode de l'inclusion équivalente n'a jusqu'alors été mise en œuvre que pour des inclusions de forme sphérique. Le présent travail propose d'étendre cette méthode à des inclusions de forme ellipsoïdale dont la variation de l'élancement permet de modéliser de nouveaux éléments asphériques tels que les fissures, les fibres et les cristaux de portlandite. Cette complexification de la géométrie a un impact sur le temps de calcul, qui est amplifié dans le cadre du fluage. Le second volet du travail porte alors sur l'extension de la méthode de l'inclusion équivalente à la viscoélasticité linéaire sans vieillissement par l'intermédiaire de la transformée de Laplace-Carson. Une méthodologie efficace (tant du point de vue de la précision que de celui du temps de calcul) est finalement proposée pour effectuer l'inversion numérique de cette transformée
The prediction of long-term behaviour of cementitious materials is a major concern which contributs to the study of the durability of prestressed structures. This work focuses on the use of the equivalent inclusion method, simplified multi-scale homogenization approach, for the prediction of creep in these materials. Creep is modelled by the non-ageing linear viscoelasticity. The equivalent inclusion method overcomes certain difficulties and limitations posed by conventional approaches. For cementitious materials (highly heterogeneous), conventional multi-scale approaches are, either digitally heavy and complex to implement, or not sufficiently detailed to take into account the specificities of a microstructure. The equivalent inclusion method presents a middle way and allows the calculation of simplified matrix-inclusion type microstructures and to provide estimates or bounds on the homogenized behaviour.Under its variational form, the equivalent inclusion method has, up to now, been implemented only for spherical inclusions. This work proposes to extend this method to ellipsoidal inclusions whose variation of slenderness allows the modelling of new aspheric elements such as cracks, fibers and portlandite crystals. Such enrichment of the geometry has an impact on the computation time, that is amplified in the context of creep. The second aspect of the work then applies to the extension of the equivalent inclusion method to the non-ageing linear viscoelasticity by means of the Laplace-Carson transform. An effective methodology (both from the viewpoint of precision and calculation time) is finally proposed to perform the numerical inversion of this transform

Fiber reinforced cementitious matrix (FRCM) composites represent a newly-developed promising alternative to traditional materials for strengthening and retrofitting reinforced concrete and masonry structures. FRCM composites present several advantages with respect to fiber reinforced polymers (FRP) composites. However, while FRP composites have been extensively studied in the last decades and several design guidelines and analytical formulations are available, FRCM composites are still in their infancy and very few data are present in the literature. Thus, another issue that should be solved regards the stated need for the anchorage systems to improve FRP and FRCM strength in situations where debonding or lack of development length is a problem. In this study, the effectiveness of the anchorage system and the interaction with an externally bonded FRCM were studied on both concrete beams and masonry columns. The columns and beams were tested until failure condition in the Laboratory of Structural and Geotechnical Engineering (DICAM – LISG) of the University of Bologna, via del Lazzaretto 15/5, Bologna. Test parameters considered for this study are: density of steel fibers, type of anchorages and bending inclination of the fiber exerted as anchorage, respectively 45° for concrete beam and 90° for masonry column. Test results demonstrate that the introduction of additional anchorages improves the effectiveness of the FRCM composites in terms of resistance and loading capacity.

Negli ultimi decenni sono state sviluppati nuovi materiali e tecnologie per il rinforzo e la riabilitazione delle strutture esistenti. I sistemi più recenti per il rinforzo esterno ed il recupero strutturale sono materiali compositi costituiti da fibre raggruppate in forma di tessuto ed impregnate ed immerse in una matrice inorganica. Quando il tessuto è composto da fibre di aramide, vetro, basalto, PBO o carbonio, questi compositi sono comunemente definiti Fabric Reinforced Cementitious Matrix (FRCM), mentre, quando il tessuto è fatto da micro-trefoli di acciaio, sono definiti Steel Reinforced Grout (SRG). In accordo con le rispettive normative, negli Stati Uniti le proprietà meccaniche dei compositi FRCM/SRG si misurano tramite una prova di tensione diretta su provini caricati utilizzando ancoraggi a forcella (clevis grip). In Europa, invece, si ricorre ad una prova di aderenza o single-lap shear su compositi applicati su un substrato cementizio o in muratura. L’obiettivo di questa tesi è confrontare i risultati ottenuti mediante i due metodi di caratterizzazione sviluppando una campagna sperimentale su due diversi tipi di compositi: un FRCM con fibra di carbonio (CFRCM) e un composito SRG. L’effetto di tre diverse lunghezze di ancoraggio è stato studiato per il sistema CFRCM. L’influenza del numero di strati di tessuto è stata analizzata sia per il sistema CFRCM che SRG considerando uno o due strati. I risultati mostrano che le differenti condizioni al contorno influenzano in modo significativo la caratterizzazione dei compositi. Per ottenere una misura rappresentativa delle proprietà meccaniche dei compositi FRCM/SRG, è richiesta una lunghezza di ancoraggio sufficiente. Questo studio contribuisce a sviluppare un database sperimentale che consenta la definizione di affidabili protocolli di caratterizzazione. Inoltre, fornisce informazioni rilevanti ai fini progettuali riguardo la lunghezza di ancoraggio adeguate e all’efficacia di applicazioni multistrato.

Le bâtiment est un secteur particulièrement émissif en gaz à effet de serre. Pour tenter de réduire l’impact des matériaux sur l’environnement, de nombreuses recherches visent à étudier différentes alternatives pour limiter l’épuisement des ressources, la consommation d’énergie et le rejet de composés polluants. Dans ce contexte, les bétons biosourcés se positionnent comme une alternative sérieuse au béton traditionnel, avec une empreinte carbone plus faible.Cette thèse industrielle, portée par l’entreprise ALKERN, leader en France et en Belgique de produits préfabriqués en béton, a pour objectif de contribuer à la formulation d’un béton végétal incorporant des co-produits / déchets de bois structurel à impact environnemental plus faible que le Naturbloc®, un bloc actuellement sur le marché. Ce dernier produit est constitué de granulats de bois minéralisé puis introduit dans une matrice cimentaire.Ce travail s’articule en trois volets. Les bois témoin (non traité) et de référence (minéralisé) ont d’abord été caractérisés. Dans un second temps, des traitements alternatifs à la minéralisation du bois ont été testés et caractérisés, notamment au regard de leur reprise en eau et leur aptitude à relarguer ou contenir les extractibles présents dans les végétaux. Leur compatibilité avec une matrice cimentaire a également été évaluée. Il a ainsi pu être mis en évidence que la nature du substrat influence les résultats et l’interaction des granulats avec la pâte cimentaire.Enfin, le bois traité a été introduit dans la matrice cimentaire témoin et dans une matrice alternative à plus faible impact environnemental. Cette dernière a été obtenue soit par un changement de liant, soit par une adjuvantation spécifique du béton. L’ensemble des résultats montrent qu’il existe un lien direct entre les propriétés physico-chimiques des granulats et les performances mécaniques obtenues pour le béton
The construction industry produces a high amount of greenhouse gases. In order to reduce the impact of materials on the environment, a lot of researches are focused on the study of different alternatives to limit the exhaustion of resources, the energy consumption and the rejection of polluting compounds. In this context, bio-based concrete seem to be a serious alternative to traditional concrete, with a lower carbon footprint.The aim of this industrial thesis, supported by the company ALKERN, leader in France and in Belgium for precast concrete products, is to contribute to the formulation of structural green concrete incorporating co-products / wood waste with an environmental impact lower than the Naturbloc®, a block already available on the market. This last product is made of wood aggregates mineralized and then introduced in a cementitious matrix.This work is divided into three parts. Firstly, the control wood (untreated) and reference wood (mineralized) were characterized. Then, alternative treatments to replace cement coating of wood were tested and characterized, especially in terms of water uptake and ability to leach or hold the extractives present in vegetables back. Their compatibility with a cementitious matrix was also evaluated. The study highlights the fact that the nature of the substrate has an influence on the results and on the interaction between aggregates and cementitious paste.Finally, treated wood was introduced into a cementitious matrix and in an alternative matrix with a lower environmental impact. The latter was obtained either by change of the binder or by use of additives in bio-based concrete. All the results show the existence of a direct link between physico-chemical properties of aggregates and mechanical performances of concrete

The use of FRCM composites (Fiber Reinforced Cementitious Matrix) is becoming more and more widespread. The inorganic matrix guarantees many advantages, especially when dealing with masonry substrates, including a good compatibility from both a physical and a chemical point of view and the lower sensitivity to debonding phenomena at the interface. Compared to FRP composites, which presents many data in the literature, FRCM composites must be studied in detail and research in this field has only begun in recent years. This work deals with an important problem: the realization of an anchorage system to improve the strength of composites and allow their use even in the absence of adequate development length. In this study, the effectiveness of the anchorage system and the interaction with an externally bonded FRCM were studied on masonry columns. The columns were tested until failure condition in the Laboratory of Structural and Geotechnical Engineering (DICAM – LISG) of the University of Bologna, via del Lazzaretto 15/5, Bologna. Test results demonstrate that the introduction of additional anchorages improves the effectiveness of the FRCM composites in terms of resistance and loading capacity.

Master of Science
Department of Civil Engineering
Hayder A. Rasheed
Throughout history natural fiber was used as one of the main building materials all over the world. Because the use of such materials has decreased in the last century, not much research has been conducted to investigate their performance as a reinforcing material in cement and concrete. In order to investigate one of the most common natural fibers, wheat fibers, as a reinforcing material, 156 mortar specimens and 99 concrete specimens were tested. The specimens were tested in either uniaxial compression or flexure. The uniaxial compression test included 2 in (50.8 mm) mortar cubes and 4x8 in (101.6 x 203.2 mm) concrete cylinders. As for the flexure test, they were either 40x40x160 mm cementitious matrix prisms or 6x6x21 in (152.4x152.4x533.4 mm) concrete prisms. Several wheat fibers percentages were studied and compared with polypropylene fiber as a benchmarking alternative. The average increase in the uniaxial compression strength for cementitious matrix cubes reinforced with 0.5% long wheat fiber exceeded that of their counterparts reinforced with polypropylene fiber by 15%. Whereas for concrete cylinders reinforced with 0.75% long wheat fiber, their strength exceeded that of their counterparts reinforced with polypropylene fiber by 5% and that of the control by 7%. The flexural strength of cementitious matrix prisms reinforced with 0.75% long wheat fiber exceeded that of their counterparts reinforced with polypropylene fiber by 27%. Meanwhile, concrete prisms reinforced with both long wheat fiber and polypropylene fiber showed deterioration in strength of up to 17%. Finally, ABAQUS models were developed for concrete cylinders and prisms to simulate the effect of inclusion of the wheat fibers.

Les composites à matrice cimentaire et renforts textiles, du fait de leur compatibilité mécanique, environnementale et esthétique, sont utilisés sur une large échelle pour la réhabilitation et le renforcement du patrimoine bâti et des ouvrages du génie civil. Sous l'effet de sollicitations mécaniques ou environnementales, les phénomènes d'interaction et d'endommagement entre le renfort textile et la matrice cimentaire s'avèrent plus complexes que dans le cas des composites à matrice polymères. Celles-ci sont liées principalement au comportement fissurant du composite, à la nature fragile de la matrice et à l'adhérence renfort/matrice à prépondérance mécanique. Plus particulièrement, la connaissance et la compréhension des mécanismes de transfert de charge à l'interface renfort/matrice et l'initiation des fissures restent des verrous scientifiques majeurs.Les techniques de mesure classiques utilisées pour la caractérisation du comportement mécanique des composites à matrice cimentaire (extensomètres mécaniques, corrélation d'image digitale, etc.) sont en mesure de donner des informations sur l'état de déformation et de contrainte de la surface du corps d'épreuve. Les différents mécanismes de sollicitation et de dégradation des composants (renfort, matrice, interface) sont déduits en utilisant les approches de la mécanique des milieux continus et de la rupture.Dans ce contexte, ce travail a pour finalité la mise en place et l'adaptation d'un système de mesure intégrable à l'intérieur des composites : capteurs à base de fibres optiques distribuées. Cette technique de mesure est couplée à la corrélation d'image digitale et des jauges en surface des composites. L'objectif principal est d'analyser plus finement les paramètres mécaniques à l'échelle micro et les mécanismes de transfert de charge, d'initiation et de propagation de fissures, ainsi que les mécanismes d'endommagement. Sur la base d'essai de traction uni-axiale couplé à l'instrumentation choisie, une méthodologie d'identification de lois locales d'interaction renfort/matrice est mise en œuvre. La finalité du travail de thèse sera, grâce à ces lois locales, de déterminer les paramètres matériels du composite (longueur de transfert de charge, contrainte de cisaillement à l'interface renfort/matrice, etc.), et l'établissement des paramètres mécaniques caractéristiques du comportement local (fissuration, endommagement, comportement des interfaces, etc.) et global (lois de comportement, ouverture des fissures). Neuf configurations sont testées et analysées dans ce travail : deux types de matrice, deux types de renfort textile et trois taux de renfort. L'adaptation du protocole expérimental et la fiabilité des résultats obtenus sont validées. Le comportement global et local du composite, de la matrice, du textile et de l'interface sont mesurés et analysés. La longueur de transfert de charge, la contrainte de cisaillement à l'interface textile/matrice, l'endommagement de l'interface et l'ouverture des fissures sont quantifiés et discutés. Les effets du taux de renfort, du type de la matrice et du textile, des paramètres mécaniques et géométriques du composite sur sa réponse mécanique en traction sont identifiés et évalués. Ces résultats sont utilisés pour le perfectionnement et/ou le développement des modèles mécaniques du comportement en rigidité et à la rupture des composites à renfort textile et matrice cimentaire
Due to their mechanical, environmental and aesthetic compatibility, textile reinforced cementitious matrix composites are used on a large scale for rehabilitation and reinforcement of the built heritage and civil engineering structures. Under the effect of mechanical or environmental loads, the phenomena of interaction and damage between the textile reinforcement and the cementitious matrix are more complex than in the case of polymer matrix composites. These are mainly related to the cracking behaviour of the composite, the fragile nature of the matrix and the behaviour of the reinforcement/matrix bond. In particular, knowledge and understanding of the load transfer mechanisms at the reinforcement/matrix interface and crack initiation remain a major scientific challenge.Conventional measurement techniques used to characterise the mechanical behaviour of cementitious matrix composites (mechanical extensometers, digital image correlation, etc.) are able to provide information on the strain and stress state at the surface of a tested specimen. The different mechanisms of internal forces and degradation of the components (reinforcement, matrix, interface) are deduced using approaches of continuum and fracture mechanics.In this context, this work aims at implementing and adapting a measurement system that can be integrated into the core of composites: distributed optical fibre sensors. In order to check its reliability, this measurement technique is coupled with classical extensometer technics such as strain gauges implemented on the surface of the composites and digital image correlation. The main objective is to analyse more precisely the mechanical parameters at the micro scale and the load transfer mechanisms, crack initiation and propagation as well as damage mechanisms. On the basis of uni-axial tensile tests, coupled with the chosen instrumentation, a methodology for identifying local laws of reinforcement/matrix interaction is implemented. The aim of the thesis work is, using these local laws, to determine the micro-mechanical parameters of the composite (load transfer length, shear stress at the reinforcement/matrix interface, etc.) and to establish parameters characteristic of the local and global behaviour (cracking pattern and crack opening, damage indicators, constitutive equations, etc.). Nine configurations are tested and analysed in this work: two types of matrix, two types of textile reinforcement and three reinforcement ratios. The adaptation of the experimental protocol and the reliability of the results obtained are validated. The global and local behaviour of the composite, matrix, textile and their interface are measured and analysed. Load transfer length, shear stress at the textile/matrix interface, interface damage and crack opening are quantified and discussed. The effects of reinforcement ratio, matrix and textile type, mechanical and geometrical parameters of the composite on its mechanical tensile response are identified and evaluated. These results are used for the refinement and/or development of mechanical models of the stiffness and fracture behaviour of textile and cement-matrix reinforced composites

Ce travail s’intéresse au renforcement des matériaux cimentaire mis en œuvre par fabrication additive à grande échelle. Ce nouveau procédé permet une complexité géométrique importante, généralement fortement consommatrice de moyens matériels et humains. De plus, il rend théoriquement possible l’industrialisation de la fabrication d’éléments constructifs singuliers, par exemple optimisés par répondre à un chargement mécanique donné. Cependant, il n’existe à l’heure actuelle aucune méthode de renforcement standardisée permettant d’obtenir la résistance en traction et la ductilité nécessaire pour leur utilisation dans les structures des bâtiments. Ce qui limite fortement leur utilisation dans la pratique.Si de nombreuses méthodes sont envisagées dans la littérature pour le renforcement des matériaux cimentaires mis en œuvre par impression 3D, celles-ci sont généralement calquées sur les méthodes traditionnelles du renforcement : bétons fibrés, armatures passives et câble de précontraintes. Ce travail de thèse propose un procédé de renforcement alternatif, breveté au cours de ce travail de thèse, qui tire parti de la spécificité du procédé d’extrusion. De nombreux renforts continus sont en effet insérés dans la filière d’extrusion, appelé ici tête d’impression et entrainé par le débit du matériau cimentaire, ce dernier fournissant la force nécessaire aux déroulements des renforts continus. Le matériau extrudé est alors un composite unidirectionnel à matrice cimentaire renforcé par de nombreuses fibres continues alignées selon la direction du parcours d’impression.Ce travail définit alors le cahier des charges du procédé en termes de propriétés rhéologiques de la matrice cimentaire au moment du dépôt et le type de renfort à privilégier permettant l’obtention d’une bonne adhérence des renforts à la matrice cimentaire, nécessaire au développement d’un renforcement significatif en traction. Le comportement mécanique de l’interface est par ailleurs étudié précisément grâce aux développements d’essais micromécaniques dédiées et l'observation de l’endommagement par microtomographie aux rayons X. Les perspective de ce travail sont la caractérisation et la modélisation multi-échelles du comportement du composite à matrice cimentaire et la proposition de systèmes constructifs innovants
This work focuses on the reinforcement strategies for large scale additive manufacturing of cementitious materials. This new process allows an important geometrical complexity for constructive elements, generally consuming a lot of material and human resources. In addition, it makes it theoretically possible to industrialize the manufacture of singular constructive elements, for example optimized to meet a given mechanical load. However, there is currently no standardized reinforcement method for obtaining the tensile strength and ductility required for their use in building structures. This severely limits their use in practice.While many reinforcement methods are considered in the literature for the 3D-printed cementitious materials, they are a direct transcription of the traditional reinforcement methods such as fibre-reinforced concrete, passive reinforcement and post-tension method. This thesis work proposes an alternative reinforcement process, patented during this thesis work, which takes advantage of the specificity of the extrusion process. Many continuous reinforcements can be inserted before the extrusion die and driven by the flow of the cementitious material, the latter providing the force necessary for the unwinding of each individual continuous reinforcements. The extruded material is then a unidirectional cementitious matrix composite reinforced by many continuous fibers aligned in the direction of the printing path.This work then defines the specifications of the process in terms of rheological properties of the cementitious matrix at the time of deposition and the type of reinforcement to be preferred, allowing good cohesion between the reinforcements and the cementitious matrix necessary for the development of a significant tensile reinforcement. The mechanical behaviour of the interface is also precisely studied thanks to the development of dedicated micromechanical tests and the observation of the damage by X-ray microtomography. The perspectives of this work are the characterization and multi-scale modeling of the behavior of the cementitious matrix composite and the proposal of innovative constructive systems

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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
This research was motivated by the requirement of asbestos s replacement in building systems and the need to generate jobs and income in the country side of the state of Bahia, Brazil. The project aimed at using fibers from licuri leaves (syagrus coronata), an abundant palm in the region, to produce composites appropriate for the sustainable production of cement fibre reinforced products in small plants. The composites were produced in laboratory using Portland cement CP-II-F32, sand, water, licuri palm fiber contents of 1.0, 1.5 and 2.0% by weight of binder (two different fiber length) and metakaolin. The latter was chosen as an additional binder for its efficiency to reduce the alkalinity of cementitious matrixes therefore preventing the degradation of vegetable fibers. The characterization of the composite components was carried out by sieving and laser particle size analyses, thermal analysis, fluorescence and X-ray diffraction. The composites performance was evaluated by 3- point-bending tests, compressive strength, ultrasound module of elasticity, free and restrained shrinkage, water capillarity absorption and apparent specific gravity. It has been found that the addition of fibers increased the time to onset of cracking over 200.00% and a 25% reduction in cracks opening in the restrained shrinkage test. The capillary absorption reduced about 25% when compared to fiber-free composites. It was also observed with regard to flexural strength, compressive strength and specific gravity, that the addiction of fibers did not affect the composite performance presenting similar results for compounds with and without fibers. In general it can be stated that the reinforced composite fibers of palm licuri presents physical and mechanical characteristics which enable them to be used in the intended proposals of this research
A exig?ncia da substitui??o do amianto em sistemas construtivos em conjunto com a necessidade de gera??o de renda no sert?o da Bahia fez nascer o projeto do aproveitamento da fibra da palma do licuri (syagrus coronata), palmeira abundante na regi?o, na produ??o de comp?sitos para a fabrica??o artefatos de cimento refor?ados com fibras para a constru??o civil de maneira sustent?vel, em pequenas unidades fabris. Os comp?sitos foram produzidos em laborat?rio utilizando cimento Portland CP II-F32, areia, ?gua, metacaulinita e fibra da palma do licuri. As fibras foram adicionadas em teores de 1,0, 1,5 e 2,0% da massa do aglomerante e com dois comprimentos de fibra diferentes. A metacaulinita foi selecionada como aglomerante suplementar de forma a agir na redu??o da alcalinidade da matriz ciment?cia na perspectiva de diminuir ou at? mesmo eliminar a degrada??o das fibras vegetais em meio alcalino. Foram realizados ensaios de caracteriza??o dos componentes do comp?sito, incluindo granulometria, an?lise t?rmica, fluoresc?ncia e difratometria de Raios-X. A verifica??o do desempenho dos comp?sitos foi feita com ensaios de flex?o em tr?s pontos, resist?ncia ? compress?o axial, m?dulo de elasticidade por ultrassom, retra??o livre e restringida, absor??o de ?gua por capilaridade e massa espec?fica aparente. Verificou-se que a presen?a das fibras de licuri aumentou o tempo para o surgimento da fissura??o acima de 200,00% e redu??o de 25% na abertura das fissuras no ensaio de retra??o restringida. Com rela??o ? absor??o capilar ocorreu uma redu??o de 25%, quando comparados com os materiais sem fibras. Observou-se que, com rela??o ? resist?ncia a flex?o, compress?o axial e massa espec?fica aparente, a adi??o de fibras n?o afeta o desempenho dos materiais, apresentando resultados similares para materiais com e sem fibras. De uma maneira geral pode-se afirmar que os comp?sitos refor?ados com fibras da palma do licuri apresentam caracter?sticas f?sicas e mec?nicas que viabilizam sua aplica??o dentro das condi??es estabelecidas neste trabalho

The interface between aggregate grains and matrix in cementitious composites is their weakest element. The topic is particularly significant in the case of high performance and high strength concrete technology for which the eliminination or reduction of these weak links are necessary. The aim of this thesis is to determine the influence of the interface on the fracture behaviour of the cementitious composites. The fracture experiments were performed for this purpose and were complemented by the nanoindentation’s results and scanning electron microscopy results. Numerical model was created in ANSYS software on the basis of these data and the fracture toughness values of the interface were evaluated by means of the generalized fracture mechanics principles. Conclusion of the thesis is proof that the interface properties have a significant influence on the fracture behaviour of cementitious composites.

An experimental investigation into the direct shear behaviour of steel fibre reinforced composites utilising discrete fibres at pre-defined angles and fibres randomly distributed is described. The direct shear tests encompassed the complete range of loading from its initial application to failure of the double L-shaped push-off specimens. Hooked-ended and straight steel fibres were used in the tests with the fibres oriented at angles of ??75??, ??60??, ??45??, ??30??, ??15?? and 0?? with respect to a plane normal to the loading direction. The embedment lengths of the fibres, related to the total fibre length lf , each side of the shear plane were 0.5lf :0.5lf and 0.25lf :0.75lf . In addition to the single fibre tests, tests were conducted on randomly oriented steel fibre reinforced composites with fibre volumes of 0.005, 0.010, 0.015, and 0.020 with hooked-ended and straight steel fibres. In addition to the tests outlined above, a series of non-destructive tests employing radiographic techniques was carried out to produce photographic images of events taking place of fibres pulling out from a cementitious element. The tests consisted of hooked-ended steel fibres oriented at angles of -60??, -30??, 0??, +30?? and +60?? to the cracking plane and straight fibres oriented at angles of -60??, 0?? and +60??. The non destructive technique allowed the internal behaviour occurring within the specimen along the shear plane to be investigated without impacting on the direct shear tests. The angle of the fibre to the interface plane is an important parameter in determining the behaviour of the fibres under load and for the mode of failure; viz fibre pullout or fibre fracture. The effect of the end hook on behavioural aspects becomes increasingly less significant for more acute fibre angles where bending and snubbing effects become increasingly influential on the load versus displacement behaviour and mode of failure. Contrary to expectations, the fibre embedment length had little influence over the peak loads attained for the discrete fibre tests and, in a number of specimens, fibres pulled out from the longer embedded side. This observation is contrary to the generally accepted assumption that a fibre remains rigidly embedded on the long side and pulls out from short side. The traditional role that uniform bond stresses along a fibre length and friction have played in the description of fibre behaviour is not as significant as previously reported, other effects such as snubbing are more important in anchoring a fibre. Various models need to be revised with this observation in mind. The experimental results and observations from the discrete hooked-ended and straight steel fibres investigation are incorporated in the development of a behavioural model, the Variable Engagement Model II (VEMII). The VEMII describes the behaviour of randomly oriented discontinuous steel fibre reinforced composites loaded in shear. The model is verified against a series of randomly distributed fibre reinforced mortar specimens carried out in this study. Two forms of models are analysed: 1) a model based on the observation of lumped shear stresses at the fibre hook and in the snubbing zone; and 2) a uniform fibre bond stress applied along the embedded part of the fibre. The lumped bond stress approach and the uniform approach were found to give reasonable comparisons with the test data for the hooked-ended fibres but were conservative for the straight fibres. The VEMII confirms the applicability of the uniform bond approach adopted by previous researchers even though it does not correspond to the observations of fibre pullout behaviour of single fibres. The VEMII model provides a versatile approach that can also be applied to hybrid fibre combinations.

Strain-hardening cement-based composites (SHCC) are a special class of fiber-reinforced concrete which develop multiple, fine cracks when subjected to increasing tensile loading, reaching strain capacities of up to several percent. The tensile behavior of SHCC is a result of a purposeful material design accounting for the mechanical and physical properties of the cementitious matrix, of the reinforcing fibers and of their interaction. The exceptionally high energy dissipation through inelastic deformations before reaching tensile strength makes SHCC suitable for manufacturing or strengthening of structural elements which may be subjected to impact loading. However, the tensile behavior of SHCC is highly strain rate dependent, both in terms of tensile strength and strain capacity. The different strain rate sensitivities of the constitutive phases of SHCC (matrix, fiber and interfacial bond) lead to disproportionate dynamic alteration of their mechanical properties under increasing strain rates and, consequently, to an impairment of the micromechanical balance necessary for strain-hardening and multiple cracking. Thus, high energy dissipation under impact loading can only be ensured through a targeted material design. This work presents a series of mechanical experiments at different strain rates and different scales of investigation with the goal of developing a qualitative and quantitative basis for formulating material design recommendations for impact resistant SHCC. Three different types of SHCC were investigated, consisting of two types of polymer fibers (polyvinyl-alcohol and high-density polyethylene) and cementitious matrices (normal-strength and high-strength). Uniaxial tension experiments were performed on SHCC specimens and on non-reinforced matrix specimens with different testing setups at strain rates ranging from 10-4 to 150 s-1. Besides the measured mechanical properties, special attention was paid to the crack patterns and the condition of fracture surfaces. Additionally, micro-scale investigations were performed to quantify the strain rate dependent changes in the mechanical behavior of individual component phases, i.e., matrix, fibers and fiber-matrix bond. The results obtained from the micromechanical investigations were used in an analytical model for crack bridging. The model links the micromechanical parameters and their strain rate sensitivities to the single-crack opening behavior under increasing displacement rates, making it useful for material design purposes. If given an extensive experimental basis for the fracture mechanical properties of the non-reinforced cementitious matrices, the model can be extended for predicting the strain capacity (multiple cracking) of SHCC under different strain rates.
Die hochduktilen Betone (Engl.: Strain-Hardening Cement-based Composites – SHCC) bilden eine besondere Klasse von Faserbetonen, die eine multiple Rissbildung unter zunehmenden Zugspannungen aufweisen, was zu einer sehr hohen Bruchdehnung führt. Das dehnungsverfestigende, hochduktile Zugverhalten der SHCC wird durch eine gezielte Materialentwicklung erreicht, die die mechanischen und physikalischen Eigenschaften der zementgebundenen Matrizen, der Kurzfasern und deren Zusammenwirkung berücksichtigt. Das außergewöhnliche Energieabsorptionsvermögen der SHCC durch plastische Verformungen vor dem Erreichen der Zugfestigkeit qualifiziert diese Verbundwerkstoffe für die Herstellung oder Verstärkung von Bauteilen, die Impaktbeanspruchungen ausgesetzt sein könnten. Jedoch weisen SHCC sowohl bezüglich deren Zugfestigkeit als auch deren Dehnungskapazität ein ausgeprägtes dehnratenabhängiges Verhalten auf. Unter zunehmenden Dehnraten führen die unterschiedlichen Dehnratensensitivitäten der gestaltenden Phasen von SHCC (Matrix, Faser und deren Verbund) zur Beeinträchtigung des mikromechanischen Gleichgewichts, welches für die Dehnungsverfestigung und multiple Rissbildung erforderlich ist. Eine hohe Energiedissipation unter Impaktbeanspruchungen kann deshalb nur durch eine gezielte Materialentwicklung der SHCC hinsichtlich deren Verhaltens unter hohen Dehnraten gewährleistet werden. Die vorliegende Arbeit umfasst eine Reihe von experimentellen Untersuchungen mit verschiedenen Dehnraten und an unterschiedlichen Betrachtungsebenen, mit dem Ziel eine qualitative und quantitative Basis für Empfehlungen zur Materialentwicklung von Impakt-resistenten SHCC zu schaffen. Drei verschiedene SHCC-Zusammensetzungen wurden untersucht. Die Referenz-Zusammensetzung aus einer normalfesten zementgebundenen Matrix und Polyvinyl-Alkohol-Kurzfasern wurde mit zwei unterschiedlichen SHCC verglichen (hochfest und normalfest), die mit Kurzfasern aus hochdichtem Polyethylen bewehrt wurden. Einaxiale Zugversuche wurden an SHCC-Proben und unbewehrten Matrix-Proben mit verschiedenen Prüfvorrichtungen bei Dehnraten von 10-4 bis 150 s-1 durchgeführt. Zusätzlich zu den gemessenen mechanischen Eigenschaften wurden die Rissbildung und die Bruchflächen detailliert untersucht. Darüber hinaus wurden mikromechanische Untersuchungen durchgeführt, um die Dehnratensensitivität der einzelnen Phasen, d.h. Matrix, Faser und deren Verbund zu beschreiben. Die aus den mikromechanischen Untersuchungen erzielten Ergebnisse wurden als Eingangswerte in einem analytischen Einzelriss-Modell verwendet. Das entwickelte Modell verbindet die mikromechanischen Parameter und deren Dehnratenabhängigkeit mit dem Rissöffnungsverhalten von SHCC bei zunehmenden Verschiebungsraten. Das macht es vorteilhaft für Materialentwicklungszwecke. Das Modell kann für die Vorhersage der Dehnungskapazität von SHCC bei diversen Dehnraten weiterentwickelt werden, wenn eine umfassende experimentelle Basis für die bruchmechanischen Eigenschaften der Matrizen vorliegt.

Dissertação de mestrado integrado em Engenharia Civil
O desenvolvimento de materiais compósitos com fibras e nanomateriais tem sido cada vez mais investigado pelas comunidades académica e industrial. Este tipo de materiais apresenta propriedades mecânicas e elétricas que fazem deles, materiais bastante apetecíveis no reforço de matrizes cimentícias. Atualmente, a monitorização de estruturas de betão pode ser realizada em tempo real através de materiais condutores, como as fibras e os nanomateriais. Desta forma, o objetivo principal da dissertação foi o desenvolvimento de compósitos cimentícios condutores e a análise do seu comportamento elétrico quando sujeitos a uma carga de tração uniaxial. Assim, foram preparados dois tipos de compósitos de matriz cimentícia, um reforçado com fibras curtas de carbono e um outro compósito híbrido reforçado simultaneamente com nanotubos e fibras curtas de carbono. A correta dispersão da fibra de carbono e dos nanotubos na matriz cimentícia é chave para a melhorias das propriedades mecânicas e elétricas. Os resultados obtidos demostraram que efetivamente os nanotubos e as fibras curtas de carbono dispersos nas matrizes cimentícias originam compósitos capazes de apresentar uma variação da resistência elétrica sob carga de tração uniaxial, demonstrado o seu potencial para uso como sensores de deformação. Dos ensaios realizados, os melhores resultados obtidos do compósito cimentício enquanto sensor elétrico foram verificados na percentagem de 0.5% de fibras curtas de carbono, para o ensaio de tração cíclico, e com 0.75% de fibras curtas de carbono e 0.1% de nanotubos de carbono, para o ensaio monotónico. De um modo geral, os nanotubos e as fibras curtas de carbono num compósito de matriz cimentícia tem a capacidade de ser utilizado enquanto sensor elétrico de cargas e deformações.
The use of fibers and nanomaterials for composite material reinforcements has been increasingly investigated by the academic and industrial communit ies. This type of material present mechanical and electrical properties that make them very desirable as reinforcing materials in cementitious matrices. Currently, monitoring of concrete structures can be performed in real time through conductive materials such as fibers and nanomaterials. The main goal of this dissertation was to analyze the electrical resistance of cimenticious based composite materials when subjected once uniaxial tensile load. Thus, there were prepared two kinds of cementicious composites: one reinforced with short carbon fibers and other reinforced simultaneously with nanotubes and short carbon fibers. The correct dispersion of carbon nanotubes and fibers in the cementitious matrix is the key to the improvement on mechanical and electrical properties. The results showed that effectively carbon nanotubes and carbon short fibers reinforcing cementitious matrices lead to a variation of the electrical resistance under uniaxial tensile load. Among the various tests performed, the best results were observed in the percentage of 0.5% short carbon fibers, for cyclic tensile testing, and 0.75% of short carbon fibers and 0.1% of carbon nanotubes, for monotonic tensile test. In general, nanotubes and short carbon fibers in a cementitious matrices composite presente the capability to sense loads and deformations.

Dissertação de mestrado integrado em Engenharia Civil
Marine environment is one of the most challenging environments for concrete structures. Structural concrete exposed to marine environment deserves special attention as the sea salts chemically react with the cement matrix which results in loss of strength, cracking, spalling etc. In the present work, the behaviour of two different composites were study: Engineered Cementitious Composites (ECC) and another one based on an Alternative Binder System. A series of experiments, including compressive testing and uniaxial tension were carried out to characterize the mechanical properties of both types of materials. The single crack tension test was performed in the ECC compositions to assess the influence of the type of water used in the composition, at the micromechanical level. The most important characteristic of ECC, multicracking behaviour at increasing tensile strains when subject to direct tension, was confirmed in all mixtures and in all types of cures. Self-healing ability was studyed in ECC mixtures and the results showed that is possible verify that the specimens subjected to lower preloading levels and cured in the same water used to prepare the mixtures have almost fully recovered their initial mechanical characteristics. In the metakaolin based geopolymer, as an alternative binder system, the strain hardening behaviour was reached with one mixture. The geopolymer material is a more sustainable option due to the utilization of by-products and / or wastes materials when compared to the cementitious matrix composite.
O ambiente marítimo é um dos mais desafiadores para as estruturas de betão. Betão armado exposto, ao ambiente marítimo, merece especial atenção devido á presença de sais do mar que reagem com matriz de cimento o que resulta em perda de resistência, fendas, fragmentação, entre outros problemas. Este trabalho consiste no estudo do comportamento mecânico de dois compósitos diferentes: um compósito de matriz cimentícia com endurecimento em tração e um material alternativo de matriz não cimentícia. Os testes de compressão e tensão uniaxial foram realizados de modo a avaliar as propriedades mecânicas dos dois compósitos. Os resultados demonstraram que é possível o aparecimento de múltiplas fendas com o aumento da carga de tração em todas as misturas e em todos os tipos de curas. A capacidade de self-healing de materiais compósitos com endurecimento em tração foi estudado nos compósitos de matriz comentícia e os resultados mostraram que é possível concluir que as amostras submetidas a baixos níveis de pré-carga, curadas na mesma água utilizada para preparar as misturas, tenham recuperado quase totalmente as suas características mecânicas iniciais. O endurecimento à tração também foi obtido por uma mistura de geopolímero que é um material alternativo ao cimento Portland. O geopolímero é uma opção mais sustentável devido à utilização de sub-produtos e/ou resíduos quando comparado com o compósito de matriz cimentícia.