Mechanical behaviour of laminated functionally graded fibre-reinforced self-compacting cementitious composites

El hormigón autocompactante (HAC) es una nueva tipología de hormigón o material compuesto base cemento que se caracteriza por ser capaz de fluir en el interior del encofrado o molde, llenándolo de forma natural, pasando entre las barras de armadura y consolidándose únicamente bajo la acción de su peso propio, sin ayuda de medios de compactación externos, y sin que se produzca segregación de sus componentes. Debido a sus propiedades frescas (capacidad de relleno, capacidad de paso, y resistencia a la segregación), el HAC contribuye de forma significativa a mejorar la calidad de las estructuras así como a abrir nuevos campos de aplicación del hormigón. Por otra parte, la utilidad del hormigón reforzado con fibras de acero (HRFA) es hoy en día incuestionable debido a la mejora significativa de sus propiedades mecánicas tales como resistencia a tracción, tenacidad, resistencia al impacto o su capacidad para absorber energía. Comparado con el HRFA, el hormigón autocompactante reforzado con fibras de acero (HACRFA) presenta como ventaja una mayor fluidez y cohesión ofreciendo, además de unas buenas propiedades mecánicas, importantes ventajas en relación con su puesta en obra. El objetivo global de esta tesis doctoral es el desarrollo de nuevas soluciones estructurales utilizando materiales compuestos base cemento autocompactantes reforzados con fibras de acero. La tesis presenta una nueva forma de resolver el problema basándose en el concepto de los materiales gradiente funcionales (MGF) o materiales con función gradiente (MFG) con el fin de distribuir de forma eficiente las fibras en la sección estructural. Para ello, parte del HAC se sustituye por HACRFA formando capas que presentan una transición gradual entre las mismas con el fin de obtener secciones robustas y exentas de tensiones entre capas con el fin de aplicar el concepto “MGF-laminados” a elementos estructurales tales como vigas, columnas, losas, etc. El proceso incluye asimismo el propio método de fabricación que, basado en la tecnología HAC, permite el desarrollo de interfases delgadas y robustas entre capas (1-3 mm) gracias a las propiedades reológicas del material. Para alcanzar dichos objetivos se ha llevado a cabo un amplio programa experimental cuyas etapas principales son las siguientes: • Definir y desarrollar un método de diseño que permita caracterizar de forma adecuada las propiedades mecánicas de la “interfase”. Esta primera fase experimental incluye: o las consideraciones generales del propio método de fabricación basado en el concepto de fabricación de materiales gradiente funcionales denominado “reología y gravedad”, o las consideraciones específicas del método de caracterización, o la caracterización de la “interfase”. • Estudiar el comportamiento mecánico sobre elementos estructurales, utilizando distintas configuraciones de MGF-laminado frente a acciones tanto estáticas como dinámicas con el fin de comprobar la viabilidad del material para ser usado en elementos estructurales tales como vigas, placas, pilares, etc. Los resultados indican la viabilidad de la metodología de fabricación adoptada, así como, las ventajas tanto estructurales como en reducción de costes de las soluciones laminadas propuestas. Es importante destacar la mejora en términos de resistencia a flexión, compresión o impacto del hormigón autocompactante gradiente funcional en comparación con soluciones de HACRFA monolíticos inclusos con un volumen neto de fibras (Vf) doble o superior. Self-compacting concrete (SCC) is an important advance in the concrete technology in the last decades. It is a new type of high performance concrete with the ability of flowing under its own weight and without the need of vibrations. Due to its specific fresh or rheological properties, such as filling ability, passing ability and segregation resistance, SCC may contribute to a significant improvement of the quality of concrete structures and open up new field for the application of concrete. On the other hand, the usefulness of steel fibre-reinforced concrete (SFRC) in civil engineering applications is unquestionable. SFRC can improve significantly the hardened mechanical properties such as tensile strength, impact resistance, toughness and energy absorption capacity. Compared to SFRC, self-compacting steel fibre-reinforced concrete (SCSFRC) is a relatively new type of concrete with high flowability and good cohesiveness. SCSFRC offers very attractive economical and technical benefits thanks to SCC rheological properties, which can be further extended, when combined with SFRC for improving their mechanical characteristics. However, for the different concrete structural elements, a single concrete mix is selected without an attempt to adapt the diverse fibre-reinforced concretes to the stress-strain sectional properly. This thesis focused on the development of high performance cement-based structural composites made of SCC with and without steel fibres, and their applications for enhanced mechanical properties in front of different types of load and pattern configurations. It presents a new direction for tackling the mechanical problem. The approach adopted is based on the concept of functionally graded cementitious composite (FGCC) where part of the plain SCC is strategically replaced by SCSFRC in order to obtain laminated functionally graded self-compacting cementitious composites, laminated-FGSCC, in single structural elements as beams, columns, slabs, etc. The approach also involves a most suitable casting method, which uses SCC technology to eliminate the potential sharp interlayer while easily forming a robust and regular reproducible graded interlayer of 1-3 mm by controlling the rheology of the mixes and using gravity at the same time to encourage the use of the powerful concept for designing more performance suitable and cost-efficient structural systems. To reach the challenging aim, a wide experimental programme has been carried out involving two main steps: • The definition and development of a novel methodology designed for the characterization of the main parameter associated to the interface- or laminated-FGSCC solutions: the graded interlayer. Work of this first part includes: o the design considerations of the innovative (in the field of concrete) production method based on “rheology and gravity” for producing FG-SCSFRC or as named in the thesis FGSCC, casting process and elements, o the design of a specific testing methodology, o the characterization of the interface-FGSCC by using the so designed testing methodology. • The characterization of the different medium size FGSCC samples under different static and dynamic loads patterns for exploring their possibilities to be used for structural elements as beams, columns, slabs, etc. The results revealed the efficiency of the manufacturing methodology, which allow creating robust structural sections, as well as the feasibility and cost effectiveness of the proposed FGSCC solutions for different structural uses. It is noticeable to say the improvement in terms of flexural, compressive or impact loads’ responses of the different FGSCC in front of equal strength class SCSFRC bulk elements with at least the double of overall net fibre volume fraction (Vf)

Muong Livelihoods and the Role of Education in Their Development: A case study of a Muong community in Cam Thuy District, Thanh Hoa Province, Vietnam

This dissertation is an attempt to clarify the role played by education in the livelihoods of the Muong minority people who live in remote mountainous areas of Vietnam. The argument focuses on critical factors that impact on livelihood performance such as livelihood assets, government policies and non-government programs. Indigenous mountain people, including the Muong, throughout their history have relied on natural resources to secure their livelihood. In the past it was thought that they lived sustainably in harmony with their environment but the impact of globalisation and the growth of the monetary economy has changed all this. Formerly isolated communities have been increasingly drawn into the modern state’s system of governance and this has resulted in reforms that, while considered good for the nation, have disadvantaged highland peoples. The views of policy makers and program designers are too often quite at odds with the needs of local indigenous people. This study was conducted in Muot village in the Thanh Hoa Province of Vietnam. In the village 98% of the villagers are of Muong descent. The research used a mixed method approach which included the use of questionnaires to collect quantitative survey data from 154 of the total of 198 households (population 678) and 75 school aged children. I was also permitted to access data from a household poverty survey initiated and authorized by the provincial committee in which I participated as an enumerator. All of this data was supplemented by qualitative engagements with both the students and householders who had participated in the personal surveys. I used a handful of participant observation techniques including informal interviews, observations made in the course of household visits, village walks, and otherwise engaging with villagers as they went about their daily activities, and focus group discussions. The mixed method approach enabled me to answer my principal questions: what are the current challenges faced by Muong in securing a livelihood? How effective are government policies in promoting economic development? How do they respond to government policies? What role does education play in Muong socioeconomic development? The content of both the quantitative and qualitative data collected was summarized in a format acceptable to SPSS, analyzed and subjected to critical analysis. Understanding what indigenous Muong need is truly important for both scholars and policy makers in Thanh Hoa province as well as Vietnam as a whole. This study found that human capital is the most significant factor in improving sustainable livelihoods. It concluded that the case for improving human resources in remote mountainous areas is paramount and that the government and local people should do more to make the best of education. Integration into the national economy and mainstream life of the nation is inevitable and education has the capacity to make a major contribution to easing this process

Die Verschwörungserzählung als profanisierte Hinterwelt

Geht es um die Frage, welche Faktoren zur Akzeptanz und Verbreitung von Verschwörungserzählungen beitragen, so verweist die Forschungsliteratur zur Erklärung oft auf sehr allgemeine Bedürfnisse, die in der Regel als anthropologische Gegebenheiten aufgefasst werden, wie etwa das Bedürfnis nach Sinngebung und Orientierung. Der vorliegende Artikel weist auf die möglichen Probleme einer anthropologischen Verkürzung der Sachlage bei solchen Erklärungsansätzen hin und formuliert einen genealogischen Ansatz, der es erlaubt, jene Bedürfnisse, die den Verschwörungsglauben begünstigen, als Resultat eines historisch voraussetzungsreichen Subjektivierungsprozesses zu begreifen. Zur Beschreibung jenes Prozesses werden in Auseinandersetzung mit Nietzsches Genealogie der Moral insbesondere die Motive des Ressentiments und der Schuld als Triebkräfte herangezogen, die insbesondere unter säkularen Bedingungen Projektionsweisen befördern, auf denen Verschwörungserzählungen beruhen

High performance concrete mixture proportioning: multi-objective optimization approach

This paper presents the application of multi-objective optimization approach to high performance concrete mixture proportioning. An integrated mathematical model was developed in order to optimize six criteria, which are the chlorine ion diffusion coefficient, per cubic meter cost, the amount of cement, fly ash, slag, chemical admixture. This model needs to satisfy with ten functional constraints and seven design variables. The Visual Interactive Analysis Method (VIAM) was used to solve the multicriteria task. Eventually, twelve solutions have been found for the different cases in terms of criteria during the process of proportioning high performance concrete mixture. They are all Pareto solutions, which allow experts to choose in the proposed cases

Research on dynamic interactions between the pipe and coral foundation of the Spratlys islands

This paper presents some results of geological construction characteristics by depth of the Southwest Cay Island’s coral foundation, the Spratlys Islands, and the interaction between pipe and coral foundation under the effect of load of shockwave bombs. The problem of interaction between the pipes and coral foundation is resolved on the basis of finite element method and Matlab programming. The results could contribute to research on calculating, designing and constructing projects on the island to serve for defense of the country and livelihoods on the island