No / An extensive study of the fibre orientation structures developed in a transverse ribbed plate during injection moulding, and the use of these structures to investigate the effect of local fibre orientation state on crack initiation resistance, is reported. The fibre orientation results for the ribbed plate, measured using large area image analysis system developed at Leeds University, showed that after an initial settling down period, the central core region, where the fibres are aligned perpendicular to the flow direction, decreased in size monotonically, with an associated monotonic increase in the outer shell regions, where the fibres are aligned preferentially along the injection direction. Interestingly, the level of orientation in the two regions remained almost constant: only the proportions of the two regions were found to change with flow length. Across the plate, close to the gate, the central core region was found to have a lens-like shape, while at the other end of the plate the core was thinner and also consistent in thickness across the sample width. The transverse rib was found to cause little disturbance to the fibre orientation of the base plate. The different proportions of the shell and core regions at different locations over the ribbed plate provided an ideal case to test the proposition of Friedrich that the crack resistance of a short fibre reinforced material depends on the number of fibres that are perpendicular to the crack tip. The impact test results gathered in this way confirmed this hypothesis of Friedrich.

The shear capacity of headed studs in precast concrete hollow-core slab construction has been determined experimentally in 12 full-scale push-off tests. The tests were used to study the effects of the size of the gap between the ends of the precast slabs, and the amount of tie steel placed transversely across the joint, and the strength of concrete infill. Under certain situations the capacity of the stud is reduced compared with that in a solid reinforced concrete slab. Maximum resistances are compared with the predictions of BS 5950 and EC4, and a reduction formula for the precast effect is derived.

<p dir="ltr">Brute force guessing attacks continue to pose a significant threat to user passwords. To protect user passwords against brute force attacks, many organizations impose restrictions aimed at forcing users to select stronger passwords. Organizations may also adopt stronger hashing functions in an effort to deter offline brute force guessing attacks. However, these defenses induce trade-offs between security, usability, and the resources an organization is willing to investigate to protect passwords. In order to make informed password policy decisions, it is crucial to understand the distribution over user passwords and how policy updates will impact this password distribution and/or the strategy of a brute force attacker.</p><p dir="ltr">This first part of this thesis focuses on developing rigorous statistical tools to analyze user password distributions and the behavior of brute force password attackers. In particular, we first develop several rigorous statistical techniques to upper and lower bound the guessing curve of an optimal attacker who knows the user password distribution and can order guesses accordingly. We apply these techniques to analyze eight password datasets and two PIN datasets. Our empirical analysis demonstrates that our statistical techniques can be used to evaluate password composition policies, compare the strength of different password distributions, quantify the impact of applying PIN blocklists, and help tune hash cost parameters. A real world attacker may not have perfect knowledge of the password distribution. Prior work introduced an efficient Monte Carlo technique to estimate the guessing number of a password under a particular password cracking model, i.e., the number of guesses an attacker would check before this particular password. This tool can also be used to generate password guessing curves, but there is no absolute guarantee that the guessing number and the resulting guessing curves are accurate. Thus, we propose a tool called Confident Monte Carlo that uses rigorous statistical techniques to upper and lower bound the guessing number of a particular password as well as the attacker's entire guessing curve. Our empirical analysis also demonstrate that this tool can be used to help inform password policy decisions, e.g., identifying and warning users with weaker passwords, or tuning hash cost parameters.</p><p dir="ltr">The second part of this thesis focuses on developing stronger password hashing algorithms to protect user passwords against offline brute force attacks. In particular, we establish that the memory hard function Scrypt, which has been widely deployed as password hash function, is maximally bandwidth hard. We also present new techniques to construct and analyze depth robust graph with improved concrete parameters. Depth robust graph play an essential rule in the design and analysis of memory hard functions.</p>

[pt] A susceptibilidade à corrosão sob tensão em aços para dutos é dependente de uma série de eventos que vão desde a manufatura do aço, fabricação do tubo, montagem dos dutos e tipo de substância transportada pelo duto. O procedimento de soldagem envolvido na montagem dos dutos pode modificar as propriedades mecânicas do metal de base na região da zona termicamente afetada (ZTA), assim como as propriedades metalúrgicas e de resistência à corrosão, tornando potencialmente a região da junta soldada com maior probabilidade de incidência de corrosão sob tensão.Este trabalho tem como objetivo estudar a resistência à corrosão sob tensão em presença de sulfeto e fragilização pelo hidrogênio, em soldas circunferenciais de tubo API 5L X80. Foram realizados: -Ensaios de acordo com norma NACE TM0177/96, Método A -Ensaios de Baixa Taxa de Deformação (BTD) de acordo com a norma ASTM G129-00/2006, em solução contendo Tiossulfato de Sódio. Os resultados mostraram que o metal base foi considerado aprovado segundo os requisitos dos testes NACE TM0177/96. Porém as juntas soldadas originadas nos diferentes processos de soldagem estudados apresentaram susceptibilidade à corrosão sob tensão em presença de sulfeto e fragilização pelo hidrogênio, segundo o mesmo critério, fraturando em um período inferior a 720h. Esta susceptibilidade foi comprovada com os resultados dos ensaios de tração BTD, tendo sido constatada uma queda significativa no limite de resistência, alongamento e tempo de ruptura, em comparação aos ensaios realizados ao ar na mesma taxa de deformação. O mecanismo de fratura predominante nos ensaios foi fratura transgranular. / [en] The susceptibility of pipeline steels to stress corrosion cracking (SCC) depends on a series of factors ranging from the manufacture of the steel, the pipe fabrication, the assembly of the pipeline and the type of substances to be transported. Additionally, the welding procedures adopted during the production of the tubes and for construction of the pipelines (field welding), can modify the properties of the base metal in the heat affected zone (HAZ), potentially rendering this region susceptible to sulphide stress corrosion cracking and hydrogen embrittlement.This study evaluates the resistance of girth welds in API 5LX80 pipes to hydrogen embrittlement and also to stress corrosion cracking in the presence of sulphides. The evaluation was performed according to NACE TM0177/96, Method A, applying the criterion of fracture/no fracture, and slow strain rate tensile tests (SSRT) were undertaken using a sodium thiosulphate solution according to the ASTM G29 standard. According to the requirements of the NACE TM0177/96 test, the base metal was considered approved. The weld metal exhibited susceptibility to SCC in the presence of sulphides, failling in a period of less than 720h. The susceptibility of the welded joint to SCC in the presence of sulphides was confirmed by the results obtained with SSRT tensile tests, where a significant decrease in the ultimate tensile strength, elongation and time to fracture were observed. The mechanism of fracture for the tests was predominantly transgranular.

Due to the increasing use of cyclically loaded cast aluminum components in automotive and aerospace applications, fatigue and fatigue crack growth characteristics of aluminum castings are of great interest. Despite the extensive research efforts dedicated to this topic, a fundamental, mechanistic understanding of these alloys' behavior when subjected to dynamic loading is still lacking. This fundamental research investigated the mechanisms active at the microstructure level during dynamic loading and failure of conventionally cast and SSM Al-Si-Mg alloys. Five model alloys were cast to isolate the individual contribution of constituent phases on fatigue resistance. The major constituent phases, alpha-Al dendrites, Al/Si eutectic phase, and Mg-Si strengthening precipitates were mechanistically investigated to relate microstructure to near-threshold crack growth (Delta Kth) and crack propagation regimes (Regions II and III) for alloys of different Si composition/morphology, grain size, secondary dendrite arm spacing, heat treatment. A procedure to evaluate the actual fracture toughness from fatigue crack growth data was successfully developed based on a complex Elastic-Plastic-Fracture-Mechanics (EPFM/J-integral) approach. Residual stress-microstructure interactions, commonly overlooked by researches in the field, were also comprehensively defined and accounted for both experimentally and mathematically, and future revisions of ASTM E647 are expected.

Il est prévu d’augmenter la durée de vie des centrales nucléaires actuellement opérationnelles. Le vieillissement des structures en béton armé telles que les tours aéroréfrigérantes doit être évalué, son incidence sur la capacité portante calculée. Dans le cas de fortes dégradations, le renforcement doit être envisagé, afin d’assurer la pérennité de ces tours face aux sollicitations extrêmes telles que les tempêtes de vent et les séismes. Ce travail vise à quantifier les effets néfastes que peut générer la réduction de section des aciers induite par la corrosion, en particulier sur la capacité portante des tours dans des conditions de sollicitations extrêmes monotones ou cycliques de types vent et séisme. Ces sollicitations sont certainement les plus sévères, entrainant la structure dans le domaine non linéaire, elles sont susceptibles d’induire des endommagements de type fissuration qui dans le cas de sollicitation cycliques peuvent s’avérer néfastes. Des modélisations numériques sont proposées pour déterminer la réponse quasi-statique ou dynamique de la structure, en tenant compte des apparitions de fissures dans le béton et de leur évolution via des lois de comportement appropriées du matériau béton, ainsi que la plastification des aciers. Dans le cas d’une sollicitation sismique, dans le but de comparer les approches de modélisation du séisme et d’évaluer la robustesse des résultats, les réponses dynamiques sont évaluées par trois méthodes différentes de calcul : l’approche dynamique temporelle non linéaire, la méthode spectrale et la méthode modale temporelle. Des études paramétriques portant sur l’amortissement, les combinaisons de charges et les configurations structurales, sont aussi menées. Dans le cas d’une sollicitation de type vent, la technique de renforcement à l’aide de matériaux composite, tel que le tissu de fibres de carbone (TFC) est modélisée. Le comportement de la structure endommagée présentant un taux de corrosion avancée, est évalué dans le régime pré- et post-fissuration, comparativement à la structure intègre. La perte de capacité portante est quantifiée, un renforcement permettant de restaurer l'intégrité et donc d’augmenter la durée de vie de la structure est proposé. / The authorities have planned to increase the lifetime of currently operating nuclear power plants. The ageing of reinforced concrete structures such as cooling towers should be evaluated and its impact on the bearing capacity calculated. In the case of significant damage, the strengthening must be considered to ensure the sustainability of these towers facing the risk of storms and earthquakes becoming more and more frequent. This work aims to quantify the adverse effects that can generate concrete cracks and rebar section loss induced by corrosion, especially on the bearing capacity of nuclear power plant cooling towers under monotonic or cyclic extreme load conditions (wind and earthquake). These loads are certainly the most severe, since they take the structure into the nonlinear domain and can induce or amplify cracking damage. Numerical simulations are proposed to determine the quasi-static or dynamic response of the structure, taking into account appearance of concrete cracks and their evolution via an appropriate material concrete law and rebar's yielding. In the case of a seismic load, the responses are evaluated by three different methods; the nonlinear response history analysis (NLRHA), the response spectrum analysis and the modal response history analysis (MRHA) in order to compare the earthquake modeling approaches and to evaluate the robustness of the results. Parametric studies on damping, load combinations and structural configurations, are also performed. In the case of a wind load, the strengthening technique using composite materials, such as carbon fiber reinforced plastic (CFRP) is modeled. The behavior of the damaged structure with an advanced corrosion rate is estimated in the pre- and post-cracking regime, compared to the undamaged structure. The drop of bearing capacity is quantified, a reinforcement designed is proposed to restore the integrity and thus increase the lifetime of the structure.

A l’heure actuelle où la préservation de notre environnement est primordiale, les constructions en béton font intervenir de plus en plus des ciments comprenant des ajouts minéraux, tels que le laitier, les cendres volantes… En effet, la production des ciments composés permet de réduire le dégagement des gaz à effets de serre et de réutiliser des déchets industriels. Les bétons formulés à base de ciment au laitier de haut-fourneau (CEM III) sont également largement utilisés suite à leur bonne résistance aux réactions alcali-silices, à la diffusion des chlorures et aux attaques sulfatiques… Cependant, certains ouvrages construits avec ce type matériau ont présenté au jeune âge des problèmes de fissuration liés à la restriction de leurs déformations différées, telles que le retrait endogène, thermique et de dessiccation. Suite à cette observation, des essais préliminaires ont été réalisés au laboratoire du service BATir de l’Université Libre de Bruxelles. Ils ont mis en avant plusieurs caractéristiques du comportement de ces matériaux :<p><p>1. Lors du suivi du retrait restreint à l’aide de l’essai à l’anneau en condition de dessiccation, le béton formulé à base de ciment au laitier de haut-fourneau a fissuré bien avant le béton formulé à base de ciment Portland.<p>2. Le retrait total en condition libre du béton formulé à base de ciment au laitier de haut-fourneau est nettement supérieur à celui du béton formulé à base de ciment Portland. Cette différence de comportement est principalement due à l’accroissement rapide et plus élevé du retrait endogène des bétons formulés à base de ciment au laitier de haut-fourneau.<p><p>Au vu de ces résultats expérimentaux, il a semblé intéressant de déterminer quel était l’impact de la déformation endogène des bétons formulés à base de ciments au laitier de haut-fourneau (CEM III) sur leur sensibilité à la fissuration. Afin de répondre à cette question, les déformations différées (retrait endogène, fluage propre en compression et en traction) au jeune âge de trois compositions de béton avec différentes teneurs en laitier (0, 42 et 71%) ont été étudiées expérimentalement en conditions libre et restreinte. Cependant, le suivi du retrait endogène libre et restreint a nécessité le développement de plusieurs dispositifs expérimentaux limitant au maximum les artefacts de mesure, tels que la TSTM (Temperature Stress Testing Machine). De plus, l’interprétation de ces résultats expérimentaux a également nécessité une caractérisation du comportement de ces matériaux à l’échelle macro- et microscopique. <p><p>Finalement, cette étude a montré que malgré une déformation endogène plus élevée, les bétons formulés à base de ciment au laitier de haut-fourneau fissurent après le béton formulé à base de ciment Portland. Ce comportement est dû à :<p>-l’impact du laitier sur la réaction d’hydratation du matériau cimentaire ;<p>-la présence d’une expansion de la matrice cimentaire des bétons formulés à base de ciment au laitier de haut-fourneau au jeune âge qui retarde l’apparition des contraintes de traction au sein du matériau ;<p>-la plus grande capacité de ces matériaux cimentaires à relaxer les contraintes de traction/<p>Today, the use of concretes with mineral additions (fly ash, slag) for civil engineering structures is spreading worldwide. Indeed, the production of blended cements is more respectful of the environment than the production of Portland cement, because it allows reducing greenhouse gas emissions and using industrial wastes. Slag cement concretes are also largely used for their good resistance to alkali-silica reactions, sulphate attacks and chloride diffusion. However, some of constructions built with slag cement concretes have exhibited cracking at early age due to their restrained deformations, such as thermal, autogenous and drying shrinkage. Following these observations, a preliminary experimental study was realized in the laboratory of BATir Department at ULB. It revealed several characteristics of the behaviour of slag cement concretes:<p>1. The study of restrained deformations under drying conditions by means of ring tests showed that the slag cement concretes seem more prone to crack than the Portland cement concretes;<p>2. The total free shrinkage for slag cement concrete is clearly larger than for Portland cement concrete. This difference of behaviour is mainly due to the fast and large increase in the autogenous deformation of the slag cement concrete.<p><p>Following these experimental results, the effect of the autogenous deformation on the cracking sensibility of slag cement concretes seemed interesting to investigate. Their deformations (autogenous deformation, compressive and tensile basic creep) have been studied at early age for three concretes characterized by different slag contents (0, 42 and 71%) under free and restrained conditions. For monitoring free and restrained autogenous deformations, several test rigs aimed at limiting artefacts were designed, like the TSTM (Temperature Stress Testing Machine). Moreover, the behaviour of these concretes was also characterized by a study at a macro- and microstructure scale.<p><p>Finally, this study shows that the slag cement concretes under sealed and fully restrained conditions crack later than the Portland cement concrete, despite the fact that they are characterized by the largest autogenous deformation. This behaviour is due to:<p>- the slag effect on the hydration reaction of cementitious material;<p>- the cement matrix expansion of the slag cement concretes at early age which delays the occurrence of tensile stresses inside the material;<p>- the largest capacity of this concrete to relax tensile stresses.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Tesis por compendio / [ES] Todas estructuras, especialmente las conformadas con hormigón armado, no solo deben cumplir con la seguridad necesaria bajo los Estados Límites Últimos (ULS), además es imprescindible que garanticen un comportamiento adecuado frente a condiciones de servicio. En general, los requisitos fundamentales de servicio que debe cumplir este tipo de estructuras son: la funcionalidad, comodidad para el usuario y la apariencia. Sin embargo, estos no se pueden verificar de forma directa; por lo tanto, ha sido necesario definir criterios de desempeño tales como control de deflexión, control de vibración y control de agrietamiento para dar cumplimiento a lo indicado anteriormente. Además, se dificulta el cálculo de la capacidad de servicio debido al fenómeno de agrietamiento, el efecto de rigidez por tensión, la contracción y los efectos de fluencia. Por lo tanto, el control de la fisuración en estructuras de hormigón armado generalmente se logra limitando la tensión en el refuerzo de acero y la matriz de hormigón. Siendo así que, en los diseños incluidos en códigos relevantes a hormigón, especifican la tensión máxima del refuerzo de acero después de la fisuración y el ancho máximo de fisura para los miembros estructurales de CR o FRC, no obstante los aspectos de capacidad de servicio del diseño para el hormigón reforzado con fibras de ultra alto rendimiento reforzado (R-UHPFRC), no han sido incluidos en los códigos o recomendaciones de UHPFRC. A pesar de que se han realizado muchos esfuerzos en la investigación tanto experimental como teórica sobre el comportamiento de servicio de los elementos estructurales de CR o FRC durante las últimas décadas, para el R-UHPFRC se debe desarrollar aún más su conocimiento relacionado con los requisitos para el diseño de capacidad de servicio, incluyendo su comportamiento de tensión y agrietamiento. En este marco, el objetivo principal de la presente tesis doctoral es evaluar el comportamiento de servicio de R-UHPFRC. Por tal razón, es fundamental realizar la evaluación del comportamiento de deformación y fisuración de los elementos de tracción R-UHPFRC. Para ello, se abordaron y cumplieron adecuadamente dos puntos principales. El primero, diseñar una metodología de prueba innovadora y adecuada para ejecutar los experimentos requeridos para este proyecto de doctorado. En segundo lugar, se llevó a cabo la evaluación de la respuesta de rigidez a la tensión y el comportamiento de agrietamiento del R-UHPFCR, que son parámetros primordiales para el diseño de capacidad de servicio. Para estudiar estos dos parámetros, se consideraron algunos parámetros importantes tales como: el efecto del volumen del contenido de fibra, el tipo de fibra, el efecto del tamaño, el efecto de la relación de refuerzo y el efecto de la contracción. Finalmente, para evaluar los parámetros mencionados, se presentan cuatro campañas experimentales. Cada una de ellas, representa un nivel diferente de estudio. El primero corresponde a la validación de la metodología de ensayo de tracción propuesta y examinar los datos experimentales obtenidos, para emplearlos en futuros estudios de este proyecto. El segundo nivel consistió en establecer y realizar experimentos completos con dos tipos de fibra de acero, modificando además su cantidad, es así como se utilizaron diferentes proporciones de refuerzo y sección transversal para evaluar el efecto tanto del tamaño como del contenido de fibra, respectivamente. También, en un estudio experimental específico se indagó sobre el efecto de la combinación de micro y microfibras de acero en la deformación y el comportamiento de agrietamiento de los elementos R-UHPFRC de tracción. El tercer nivel corresponde a una prueba de contracción intensiva, necesaria para obtener el valor de contracción del UHPFRC utilizado en esta investigación. El último nivel comprende la modificación de la geometría de la probeta y el uso de probetas en forma de hueso de perro para evaluar el ancho medio y máximo de fisura (valor / [CA] Totes les estructures, especialment les conformades amb formigó armat, no només han de complir amb la seguretat necessària sota els Estats Límits Últims (ULS), a més és imprescindible que garanteixin un comportament adequat davant de condicions de servei. En general, els requisits fonamentals de servei que ha de complir aquest tipus d'estructures són: la funcionalitat, la comoditat per a l'usuari i l'aparença. Això no obstant, aquests no es poden verificar de forma directa; per tant, ha calgut definir criteris d'acompliment com ara control de deflexió, control de vibració i control d'esquerdament per a donar compliment al que s'ha indicat anteriorment. A més, es dificulta el càlcul de la capacitat de servei a causa del fenomen d'esquerdament, l'efecte de rigidesa per tensió, la contracció i els efectes de fluència. Per tant, el control de la fissuració en estructures de formigó armat generalment s'aconsegueix limitant la tensió al reforç d'acer i la matriu de formigó. És així que en els dissenys inclosos en codis rellevants a formigó, especifiquen la tensió màxima del reforç d'acer després de la fissuració i l'amplada màxima de fissura per als membres estructurals de CR o FRC, no obstant els aspectes de capacitat de servei del disseny per al formigó reforçat amb fibres d'ultra alt rendiment reforçat (R-UHPFRC), no han estat inclosos als codis o recomanacions d'UHPFRC. Tot i que s'han realitzat molts esforços en la investigació tant experimental com teòrica sobre el comportament de servei dels elements estructurals de CR o FRC durant les últimes dècades, per al R-UHPFRC s'ha de desenvolupar encara més el seu coneixement relacionat amb els requisits per al disseny de capacitat de servei, incloent el comportament de tensió i esquerdament. En aquest marc, l'bjectiu principal de la present tesi doctoral és avaluar el comportament de servei de R-UHPFRC. Per aquesta raó, és fonamental fer l'avaluació del comportament de deformació i fissuració dels elements de tracció R-UHPFRC. Per això, es van abordar i van complir adequadament dos punts principals. El primer, dissenyar una metodologia de prova innovadora i adequada per executar els experiments requerits per a aquest projecte de doctorat. En segon lloc, es va fer l'avaluació de la resposta de rigidesa a la tensió i el comportament d'esquerdament del R-UHPFCR, que són paràmetres primordials per al disseny de capacitat de servei. Per estudiar aquests dos paràmetres, es van considerar alguns paràmetres importants com ara l'efecte del volum del contingut de fibra, el tipus de fibra, l'efecte de la mida, l'efecte de la relació de reforç i l'efecte de la contracció. Finalment, per avaluar els paràmetres mencionats, es presenten quatre campanyes experimentals. Cadascuna representa un nivell diferent d'estudi. El primer correspon a la validació de la metodologia dassaig de tracció proposada i examinar les dades experimentals obtingudes, per a emprar-les en futurs estudis daquest projecte. El segon nivell va consistir a establir i realitzar experiments complets amb dos tipus de fibra d'acer, modificant-ne a més la quantitat, és així com es van utilitzar diferents proporcions de reforç i secció transversal per avaluar l'efecte tant de la mesura com del contingut de fibra, respectivament. També, en un estudi experimental específic, es va indagar sobre l'efecte de la combinació de micro i macrofibres d'acer en la deformació i el comportament d'esquerdament dels elements R-UHPFRC de tracció. El tercer nivell correspon a una prova de contracció intensiva, necessària per obtenir el valor de contracció de l'UHPFRC utilitzat en aquesta investigació. L'últim nivell comprèn la modificació de la geometria de la proveta i l'ús de provetes en forma d'os de gos per avaluar l'amplada mitjana i màxima de fissura (valor real detectat) provocat per esforços de tracció en els elements de tracció R-UHPFRC . És important esmentar que es van fer diferents anàlisis per a cada investigació experimental i es van ac / [EN] All structures, particularly reinforcement concrete structures, apart from meeting necessary security against Ultimate Limit States (ULS), must exhibit appropriate behaviour under service conditions. Generally, the fundamental serviceability requirements that concrete structures should meet are functionality, user comfort and appearance. These requirements cannot, however, be directly checked. Therefore, performance criteria, such as deflection control, vibration control and cracking control, are defined to meet these requirements. Serviceability calculation is complicated because of the cracking phenomenon, the tension stiffening effect, shrinkage, and creep effects. Cracking control in reinforced concrete (RC) structures is generally achieved by limiting stress in steel reinforcement and the concrete matrix. Many concrete code designs specify a maximum steel reinforcement stress after cracking and a maximum crack width for RC or fibre-RC (FRC) structural members, while the design serviceability aspects for Reinforced Ultra-High Performance Fibre-Reinforced Concrete (R-UHPFRC) are poorly considered in UHPFRC codes or recommendations. Many efforts have been made in experimental and theoretical research into the serviceability behaviour of RC or FRC structural elements in the last few decades. However, for R-UHPFRC, knowledge about tension and cracking behaviour must improve and serviceability design requirements have to be further studied. Within this framework, the main purpose of the present PhD thesis is to evaluate the serviceability behaviour of R-UHPFRC. For this purpose, the evaluation of the deformation and cracking behaviour of R-UHPFRC tensile elements is essential. To that end, two main items were addressed and adequately met. The first one was to design an innovative and adequate test methodology to carry out the experiments required for this PhD project. The second involved evaluating the tension stiffening response and cracking behaviour of R-UHPFRC, which are fundamental parameters for R-UHPFRC structures' serviceability design. To study these two parameters, important parameters were considered, such as fibre content, fibre type, size effect, reinforcement ratio and shrinkage effect. In order to evaluate the aforementioned parameters, four experimental campaigns are presented. Each campaign represents a different study level. The first corresponds to the validation of the proposed tensile test methodology and to the examination of the obtained experimental data for future studies required for this PhD project. The second experimental study level corresponds to establishing and undertaking comprehensive experimental programmes with two different steel fibre types and fibre contents. Different cross-section and reinforcement ratios were used to evaluate the size effect and fibre content effect, respectively. The effect of the micro- and macro-steel fibres combination on the deformation and cracking behaviour of tensile R-UHPFRC elements was investigated in a specific experimental study. The third level corresponds to an intensive shrinkage test, which was conducted to obtain the shrinkage value of the UHPFRC used in this PhD study. The final level corresponds to a specific experimental study, done by modifying the specimen's geometry and using the dog bone-shaped specimens to evaluate the average and maximum crack width (real detected value) caused by tensile stresses in R-UHPFRC tensile elements. It is worth mentioning that different analyses were performed for each experimental research and appropriate results were achieved to fulfil the thesis aims. Keywords: cracking behaviour, design criteria, durability, fragility curve, post-cracking tensile stiffness, serviceability behaviour, shrinkage, SLS requirements, structural design, tensile elements, tension stiffening, test method, tie, UHPFRC. / This work is part of Project “BIA2016-78460-C3-1-R” supported by the State Research Agency of Spain / Khorami, M. (2023). Serviceability Behaviour of Reinforced UHPFRC Tensile Elements [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/192683 / Compendio

Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Strain Hardening Cement-based Composite (SHCC) is part of the High Performance Fibre Reinforced Cement-based Composite (HPFRCC) family and is a relative new concrete composite. This Fibre Reinforced Cement-based Composite (FRCC) contains randomly distributed short fibres and when subjected to a uni-axial tensile load multiple cracking occurs. The multiple cracking generates fine cracks which are normally smaller than 100 μm and achieve a strain capacity of more than 5 %. There are limited publications regarding the research of sustained tensile tests on SHCC and especially the cracking behaviour of SHCC under quasi-static uni-axial as well as sustained tensile loads. The cracking behaviour is described as the average crack width, number of cracks and descriptive statistical properties which could be used to represent the distribution of the multiple fine cracks under uni-axial tension. There are two types of tests that were under consideration to determine the cracking behaviour of SHCC. The first is quasi-static uniaxial tensile tests and the second is sustained tensile tests. The latter was dependant on the uni-axial tensile tests in terms of the sustained load applied. The sustained loads ranged from 40 % to 80 % of the ultimate tensile resistance recorded from the uni-axial tensile tests that correspond with a strain rate of 0.001 /s. Different strain rates were used for the uni-axial tensile tests to determine the effect on the cracking behaviour. The cracking behaviour was determined with the aid of a non-contact optical 3D digital deformation measuring device called ARAMIS. The content of this thesis gives a background study of the cracking behaviour and relevant research performed on SHCC under certain loads as well as some literature about the timedependant effects of a cement-based composite. The functioning of the device called ARAMIS is explained as well as the resulting effects of this device on the preparation of the test specimens. The experimental framework for the uni-axial and sustained tensile tests is discussed. Thereafter, the experimental results of the tests are depicted and discussed. The results shed some light on the basic material properties such as the average ultimate stress and average ultimate strain, Young’s modulus, etc. for the quasi-static tensile tests as well as shrinkage and creep of SHCC. The cracking behaviour such as the average crack width, number of cracks, the variance and skewness of the distribution of the crack widths in the test specimens for the quasi-static uni-axial and sustained tensile tests are depicted and discussed. The cracking behaviour when subjected to uni-axial tensile tests with different strain rates is significantly governed by the formation of new cracks and the average crack width remains small with increase in strain. There is no significant difference for the cracking behaviour found when subjected to different strain rates. However, when SHCC is subjected to a sustained load then the average crack width is dependant on the number of cracks that form over time as well as the load level. The formation of fewer and wider cracks was observed for specimens loaded at average 40 % of the ultimate tensile resistance stress, however at loading percentages of higher than 65 % more cracks developed which resulted in a smaller average crack width. / AFRIKAANSE OPSOMMING: Vervorming Verharding Sement gebaseerde samestelling “Strain Hardening Cement-based Composite” (SHCC) is deel van die familie van “High Performance Fibre Reinforced Cement-based Composite” (HPFRCC) en is ʼn relatiewe nuwe beton samestelling. Hierdie vesel versterkte sement gebaseerde beton bevat willekeurig verspreide kort vesels en veelvoudige klein krake vorm onder monotoniese trekkragte. Hierdie veelvoudige klein krake is minder as 100 μm wyd en lei tot ʼn vervorming van meer as 5 %. Daar is ʼn tekort aan navorsing oor die kruip van SHCC sowel as die kraak gedrag van hierdie sement gebaseerde samestelling onderhewig aan trek. Die kraak gedrag word beskryf as die gemiddelde kraakwydte, aantal krake en ʼn paar beskrywende statistiese parameters. Hierdie kraak gedrag parameters kan gebruik word om ʼn verdeling te kan weergee van die veelvoudige klein krake onder ʼn trek belasting. Twee tipes toetse was uitgevoer om die kraak gedrag te beskryf. Die eerste tipe toets was monotoniese trek toetse en die tweede tipe was kruip toetse. Die tweede toets was afhanklik van die monotoniese trek toetse in terme van die belasting wat gebruik was vir die kruip toetse. Die belasting was gevarieer vanaf 40 % tot 80 % van die breekbelasting wat bepaal is met die monotoniese trektoetse wat ooreenstem met ʼn vervorming tempo van 0.001 /s. Verskillende vervorming tempo’s vir die monotoniese trektoetse was uitgevoer om te bepaal wat die effek is op die kraak gedrag. Die kraak gedrag was bepaal met behulp van ʼn geen-kontak optiese 3D digitale deformasie meet instrument genoem ARAMIS. Die inhoud van die tesis bevat ʼn kort opsoming oor ʼn agtergrond studie van die kraak gedrag en relevante navorsing oor vesel versterkte sement gebaseerde beton, sowel as literatuur oor die tydafhanklike effekte van ʼn sement gebaseerde samestelling. Die beheer en gebruik van die meet instrument ARAMIS word verduidelik, sowel as die effek van hierdie masjien op die voorbereiding vir die eksperimente. Die eksperimentele uiteensetting vir die monotoniese en kruip toetse word beskryf. Daarvolgens is die resultate van die eksperimentele toetse getoon en verduidelik. Die resultate verduidelik die basiese materiaal eienskappe, byvoorbeeld die gemiddelde breekspanning met die ooreenkomstige breekvervorming, Young’s modulus en so voorts vir die monotoniese trektoetse, sowel as eienskappe met betrekking tot krimp en kruip van SHCC. Die kraak gedrag naamlik die gemiddelde kraakwydte, aantal krake per meter, variansie en die skuinsheid van die ontwikkelde krake met die toets proefstukke vir die monotoniese en kruip trek toetse word weergegee en verduidelik. Die kraak gedrag van SHCC wanneer getoets word met verskillende monotoniese trektoets tempo’s word beheer deur die ontwikkeling van nuwe krake en die gemiddelde kraakwydte is beduidend laag met toenemende vervorming. Daar is geen beduidende verskil in die kraak gedrag ten opsigte van die verskillende monotoniese trek tempo’s nie. In teendeel, wanneer SHCC belas word met ʼn konstante las oor tyd word die gemiddelde kraakwydte beheer deur die ontwikkeling van nuwe krake sowel as die belasting wat aangewend is. Onder ʼn belasting van so laag as 40 % van die breekbelasting vorm daar minder krake, maar met ʼn groter gemiddelde kraakwydte. Wanneer belas word met meer as 65 % van die breekbelasting vorm meer krake wat lei tot ʼn kleiner gemiddelde kraakwydte.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Flexible pavement designers have a choice of two wearing course: either asphalt concrete or surfacing seals. The latter have been widely used by several countries as their preferred wearing course over other methods, especially countries with a limited number of average inhabitants per square kilometre. Moreover, the surfacing seals were identified as an efficient cost effective road preventive maintenance technique. Surfacing seals in New Zealand, South Africa and Australia cover about 65%, 80% and 90% of their surfaced road networks respectively. The preference of surfacing seals is due to their competitive initial cost and ease of construction. In South Africa, the life expectancy of surfacing seals varies between 8 and 12 years with an average of 10 years. This has not been the case in a number of surfacing seals constructed in winter, especially when the night recorded temperature is below 10oC. The dominant failure mechanism is ravelling (chip loss) soon after construction due to traffic loading. This chip loss is linked to the poor adhesion bond development rate in the bitumen-aggregate system during winter adverse conditions. In order to address the issue of premature chip loss the need for the development of a robust adhesion test method was identified. For that purpose, recently, researchers in the bitumen industry developed the Bitumen Bond Strength test method. This method was used in this study. This study intends to contribute to the understanding of binder-aggregate adhesion bond development for winter surfacing seals using the BBS test. Binder type, precoat type and conditioning, aggregate type and curing time are amongst the factors influencing winter seals adhesion bond performance. An experimental matrix involving three types of binder, two types of aggregate, four different precoating fluids, two precoat conditionings and two binder-curing times were then developed and investigated. Winter weather parameters affecting adhesion properties were also taken into consideration during the course of the investigation. Throughout the test, the procedure described in AASHTO TP 91-11 was followed. However, in order to enhance the control of the binder application temperature, a new method for hot applied binder sample preparation was developed as part of this study. The findings show that there is a significant difference between adhesion properties of the hot applied binders (70/100 and S-E1) and the emulsion (SC-E1). In most of the cases, the hot applied binders performed better than the emulsion. The failure mode observed was found to be linked to the condition of the precoating. The influence of the precoat type and conditioning, and effect of binder curing time were significantly highlighted. The use of a dry precoat benefited the adhesion bond strength up to around 50% relatively to the corresponding non-precoated combination. However, a decrement in the bond strength due to precoating of up to 28.7% was also observed. A statistical analysis using ANOVA did not illustrate any statistical significant effect of the aggregate type. The interaction effects analysis using ANOVA revealed the aggregate type interacting with precoat type to be the most influential interaction at level two. The precoat conditioning implication to the adhesion development rate, which influences the time for opening to traffic after construction, was illustrated. Insightful aspects on the compatibility between the binder type and precoat type and conditioning during the aggregate precoating practices and on the time for opening to traffic are highlighted. Finally, the repeatability analysis proved the BBS test to be a repeatable testing method with caution. Recommendations for further studies that could support the conclusions drawn in this study were provided. / AFRIKAANSE OPSOMMING: Buigbare plaveiselontwerpers het 'n keuse van twee deklae: óf Asfalt of oppervlak seëls. Laasgenoemde word algemeen gebruik deur verskeie lande as hul voorkeur deklaag, veral die lande met beperkte aantal gemiddelde inwoners per vierkante kilometer. Verder, is die seëls geïdentifiseer as 'n doeltreffende koste-effektiewe deklaag tegniek. Oppervlakseëls in Nieu-Seeland, Suid-Afrika en Australië dek ongeveer 65%, 80% en 90% van hul padnetwerke onderskeidelik. Die seëls se voorkeur is te danke aan hul mededingende aanvanklike koste en eenvoudige vorm van die konstruksie. In Suid-Afrika wissel die seël se lewensverwagting tussen 8 en 12 jaar met 'n gemiddeld van 10 jaar. Dit is egter nie die geval van 'n aantal seëls wat in die winter gebou word nie, veral wanneer die aangetekende nagtemperatuur onder 10o C daal nie. Die dominante swigtingsmeganisme is stroping (klipverlies) kort na konstruksie. Hierdie klipverlies is gekoppel aan die power kleef-ontwikkeling van bitumen gedurende die winter. Ten einde die probleem van voortydige klipverlies aan te spreek het die behoefte vir die ontwikkeling van 'n robuuste toetsmetode ontstaan. Om hierdie rede het navorsers onlangs in die bitumenbedryf die “BBS toetsmetode” ontwikkel en is dié toetsmetode in hierdie studie gebruik. Hierdie studie beoog om by te dra tot die begrip van bindmiddel-klip kleefontwikkeling vir die winter seëls dmv die BBS toets. Die faktore, insluitend maar nie beperk tot bindmiddeltipe, voorafdekking (“PRECOAT”) -tipe en kondisionering, aggregaattipe en kuurtyd beïnvloed winter seëls se kleefeienskappe. 'n Eksperimentele matriks met drie tipes bindmiddels, twee tipes aggregate, vier verskillende voorafdekking-vloeistowwe, twee voorafdekking kondisionering en twee bindmiddel kuurtye is toe ontwikkel en ondersoek. Winter weer parameters wat kleefeienskappe beïnvloed is ook in ag geneem tydens die verloop van die ondersoek. Regdeur die studie is die prosedure AASHTO TP 91-11 gevolg, maar ten einde die beheer van die bindmiddel spuittemperatuur te verbeter, is ‘n nuwe metode vir warmspuit-bindmonsters voorbereiding ontwikkel as deel van hierdie studie. Die bevindinge toon dat daar 'n beduidende verskil tussen die kleefeienskappe van die warm aangewende bindmiddels (70/100 en S-E1) en die emulsie (SC-E1) is. In die meeste van die gevalle het die warmspuit-bindmiddels beter as emulsie gevaar. Daar is gevind dat die swigtingsmeganisme verbind word met die toestand van die voorafdekking. Die invloed van voorafdekkingtipe, kondisionering, en die effek van bindmiddelkuurtyd is duidelik uitgelig. Die gebruik van droë voorafdekking het die kleefkrag tot sowat 50% verhoog relatief tot die ooreenstemmende onbedekte klipkombinasie. Daar is egter ook ‘n verlaging van die kleefkrag weens voorafdekking gevind van tot so hoog soos 28,7 persent. Die statistiese ontleding met behulp van ANOVA het geen statisties beduidende effek van die verksillende aggregaattipe te vore gebring nie. Die interaksie-effek analise, met behulp van ANOVA, het wel die interaksie met voorafdekkingtipe met aggregaat die mees invloedryke bevestig. Die voorafdekking kondisioneering het ver rykende kleefkrag implikasies bloot gelê, wat die tyd vir die opening van die verkeer na konstruksie beïnvloed. Insigwekkende aspekte oor die versoenbaarheid tussen die bindmiddeltipe, voorafdekkingtipe, kondisionering, voorafdekkingpraktyk en tyd tot opening vir verkeer word uitgelig. Ten slotte, die herhaalbaarheidsanalise het die BBS toets as 'n herhaalbare toetsmetode met omsigtigheid bewys. Daar is aanbevelings tot verdere studies, wat uit die gevolgtrekking gekom het, gemaak.