Influencia de las condiciones de ejecución en la resistencia de anclajes en convencional y autocompactante

A través de los años las estructuras de hormigón armado han ido aumentando su cuota de mercado, sustituyendo a las estructuras de fábrica de piedra o ladrillo y restándole participación a las estructuras metálicas. Uno de los primeros problemas que surgieron al ejecutar las estructuras de hormigón armado, era cómo conectar una fase de una estructura de este tipo a una fase posterior o a una modificación posterior. Hasta los años 80-90 las conexiones de una fase de una estructura de hormigón armado, con otra posterior se hacían dejando en la primera fase placas de acero con garrotas embebidas en el hormigón fresco o barras grifadas recubiertas de poliestireno expandido. Una vez endurecido el hormigón se podían conectar nuevas barras, para la siguiente fase mediante soldadura a la placa de la superficie o enderezando las barras grifadas, para embeberlas en el hormigón fresco de la fase siguiente. Estos sistemas requerían conocer la existencia y alcance de la fase posterior antes de hormigonar la fase previa. Además requerían un replanteo muy exacto y complejo de los elementos de conexión. Otro problema existente en las estructuras de hormigón era la adherencia de un hormigón fresco a un hormigón endurecido previamente, ya que la superficie de contacto de ambos hormigones suponía un punto débil, con una adherencia baja. A partir de los años 80, la industria química de la construcción experimentó un gran avance en el desarrollo de productos capaces de generar una buena adherencia sobre el hormigón endurecido. Este avance tecnológico tenía aplicación tanto en la adherencia del hormigón fresco sobre el hormigón endurecido, como en la adherencia de barras post-instaladas en agujeros de hormigón endurecido. Este sistema se denominó “anclajes adherentes de barras de acero en hormigón endurecido”. La forma genérica de ejecutarlos es hacer una perforación cilíndrica en el soporte de hormigón, con una herramienta especifica como un taladro, limpiar la perforación, llenarla del material adherente y finalmente introducir la barra de acero. Los anclajes adherentes se dividen en anclajes cementosos y anclajes químicos, siendo estos últimos los más habituales, fiables, resistentes y fáciles de ejecutar. El uso del anclaje adherente de barras de acero en hormigón endurecido se ha extendido por todo el espectro productivo, siendo muy habitual tanto en construcción de obras de hormigón armado de obra civil y edificación, como en obras industriales, instalaciones o fijación de elementos. La ejecución de un anclaje de una barra de acero en hormigón endurecido depende de numerosas variables, que en su conjunto, o de forma aislada pueden afectar de forma notable a la resistencia del anclaje. Nos referimos a variables de los anclajes, que a menudo no se consideran tales como la dirección de la perforación, la máquina de perforación y el útil de perforación utilizado, la diferencia de diámetros entre el diámetro del taladro y la barra, el tipo de material de anclaje, la limpieza del taladro, la humedad del soporte, la altura del taladro, etc. La utilización en los últimos años de los hormigones Autocompactables, añade una variable adicional, que hasta ahora apenas ha sido estudiada. En línea con lo apuntado, la presente tesis doctoral tiene como objetivo principal el estudio de las condiciones de ejecución en la resistencia de los anclajes en hormigón convencional y autocompactable. Esta investigación se centra principalmente en la evaluación de la influencia de una serie de variables sobre la resistencia de los anclajes, tanto en hormigón convencional como en un hormigón autocompactable. Para este estudio ha sido necesaria la fabricación de dos soportes de hormigón sobre los cuales desarrollar los ensayos. Uno de los bloques se ha fabricado con hormigón convencional y el otro con hormigón autocompactable. En cada pieza de hormigón se han realizado 174 anclajes con barras de acero, variando los parámetros a estudiar, para obtener resultados de todas las variables consideradas. Los ensayos a realizar en ambos bloques son exactamente iguales, para poder comparar la diferencia entre un anclaje en un soporte de hormigón con vibrado convencional (HVC) y un hormigón autocompactante (HAC). De cada tipo de ensayo deseado se harán dos repeticiones en la misma pieza. El ensayo de arrancamiento de las barras se realizara con un gato hidráulico hueco, con un sistema de instrumentación de lectura y registro de datos en tiempo real. El análisis de los resultados, realizado con una potente herramienta estadística, ha permitido determinar y evaluar numéricamente la influencia de los variables consideradas en la resistencia de los anclajes realizados. Así mismo ha permitido diferenciar los resultados obtenidos en los hormigones convencionales y autocompactantes, tanto desde el punto de vista de la resistencia mecánica, como de las deformaciones sufridas en el arrancamiento. Se define la resistencia mecánica de un anclaje, como la fuerza desarrollada en la dirección de la barra, para hacer su arrancamiento del soporte. De la misma forma se considera desplazamiento, a la separación entre un punto fijo de la barra y otro del soporte, en la dirección de la barra. Dichos puntos se determinan cuando se ha terminado el anclaje, en la intersección de la superficie plana del soporte, con la barra. Las conclusiones obtenidas han permitido establecer qué variables afectan a la ejecución de los anclajes y en qué cuantía lo hacen, así como determinar la diferencia entre los anclajes en hormigón vibrado convencional y hormigón autocompactante, con resultados muy interesantes, que permiten valorar la influencia de dichas variables. Dentro de las conclusiones podemos destacar tres grupos, que denominaremos como de alta influencia, baja influencia y sin influencia. En todos los casos hay que hacer el estudio en términos de carga y de desplazamiento. Podemos considerar como de alta influencia, en términos de carga las variables de máquina de perforación y el material de anclaje. En términos de desplazamiento podemos considerar de alta influencia además de la máquina de perforación y el material de anclaje, el diámetro del taladro, así como la limpieza y humedad del soporte. Podemos considerar de baja influencia, en términos de carga las variables de tipo de hormigón, dirección de perforación, limpieza y humedad del soporte. En términos de desplazamiento podemos considerar de baja influencia el tipo de hormigón y la dirección de perforación. Podemos considerar en el apartado de “sin influencia”, en términos de carga las variables de diámetro de perforación y altura del taladro. En términos de desplazamiento podemos considerar como “sin influencia” la variable de altura del taladro. Podemos afirmar que las diferencias entre los valores de carga aumentan de forma muy importante en términos de desplazamiento. ABSTRACT Over the years the concrete structures have been increasing their market share, replacing the masonry structures of stone or brick and subtracting as well the participation of the metallic structures. One of the first problems encountered in the implementing of the reinforced concrete structures was connecting a phase structure of this type at a later stage or a subsequent amendment. Until the 80s and 90s the connections of one phase of a reinforced concrete structure with a subsequent first phase were done by leaving the steel plates embedded in the fresh concrete using hooks or bent bars coated with expanded polystyrene. Once the concrete had hardened new bars could be connected to the next stage by welding them to the surface plate or by straightening the bent bars to embed them in the fresh concrete of the next phase. These systems required a previous knowledge of the existence and scope of the subsequent phase before concreting the previous one. They also required a very precise and complex rethinking of the connecting elements. Another existing problem in the concrete structures was the adhesion of a fresh concrete to a previously hardened concrete, since the contact surface of both concretes leaded to a weak point with low adherence. Since the 80s, the chemicals construction industry experienced a breakthrough in the development of products that generate a good grip on the concrete. This technological advance had its application both in the grip on one hardened fresh concrete and in the adhesion of bar post-installed in holes of hardened concrete. This system was termed as adherent anchors of steel bars in hardened concrete. The generic way of executing this system is by firstly drilling a cylindrical hole in the concrete support using a specific tool such as a drill. Then, cleaning the bore and filling it with bonding material to lastly, introduce the steel bar. These adherent anchors are divided into cement and chemical anchors, the latter being the most common, reliable, durable and easy to run. The use of adhesive anchor of steel bars in hardened concrete has spread across the production spectrum turning itself into a very common solution in both construction of reinforced concrete civil engineering and construction, and industrial works, installations and fixing elements as well. The execution of an anchor of a steel bar in hardened concrete depends on numerous variables which together or as a single solution may significantly affect the strength of the anchor. We are referring to variables of anchors which are often not considered, such as the diameter difference between the rod and the bore, the drilling system, cleansing of the drill, type of anchor material, the moisture of the substrate, the direction of the drill, the drill’s height, etc. During recent years, the emergence of self-compacting concrete adds an additional variable which has hardly been studied so far. According to mentioned this thesis aims to study the main performance conditions in the resistance of conventional and self-compacting concrete anchors. This research is primarily focused on the evaluation of the influence of several variables on the strength of the anchoring, both in conventional concrete and self-compacting concrete. In order to complete this study it has been required the manufacture of two concrete supports on which to develop the tests. One of the blocks has been manufactured with conventional concrete and the other with self-compacting concrete. A total of 174 steel bar anchors have been made in each one of the concrete pieces varying the studied parameters in order to obtain results for all variables considered. The tests to be performed on both blocks are exactly the same in order to compare the difference between an anchor on a stand with vibrated concrete (HVC) and a self-compacting concrete (SCC). Each type of test required two repetitions in the same piece. The pulling test of the bars was made with a hollow jack and with an instrumentation system for reading and recording data in real time. The use of a powerful statistical tool in the analysis of the results allowed to numerically determine and evaluate the influence of the variables considered in the resistance of the anchors made. It has likewise enabled to differentiate the results obtained in the self-compacting and conventional concretes, from both the outlook of the mechanical strength and the deformations undergone by uprooting. The mechanical strength of an anchor is defined as the strength undergone in a direction of the bar to uproot it from the support. Likewise, the movement is defined as the separation between a fixed point of the bar and a fixed point from the support considering the direction of the bar. These points are only determined once the anchor is finished, with the bar, at the intersection in the flat surface of the support. The conclusions obtained have established which variables affect the execution of the anchors and in what quantity. They have also permitted to determine the difference between the anchors in vibrated concrete and selfcompacting concrete with very interesting results that also allow to assess the influence of these mentioned variables. Three groups are highlighted among the conclusions called high influence, low influence and no influence. In every case is necessary to perform the study in terms of loading and movement. In terms of loading, there are considered as high influence two variables: drilling machinery and anchorage material. In terms of movement, there are considered as high influence the drilling diameter and the cleaning and moisture of the support, besides the drilling machinery and the anchorage material. Variables such as type of concrete, drilling direction and cleaning and moisture of the support are considered of low influence in terms of load. In terms of movement, the type of concrete and the direction of the drilling are considered variables of low influence. Within the no influence section in terms of loading, there are included the diameter of the drilling and the height of the drill. In terms of loading, the height of the drill is considered as a no influence variable. We can affirm that the differences among the loading values increase significantly in terms of movement.

Comportamiento frente a la durabilidad de morteros de reparación de cemento modificados con polímeros

El auge que ha surgido en los últimos años por la reparación de edificios y estructuras construidas con hormigón ha llevado al desarrollo de morteros de reparación cada vez más tecnológicos. En el desarrollo de estos morteros por parte de los fabricantes, surge la disyuntiva en el uso de los polímeros en sus formulaciones, por no encontrarse justificado en ocasiones el trinomio prestaciones/precio/aplicación. En esta tesis se ha realizado un estudio exhaustivo para la justificación de la utilización de estos morteros como morteros de reparación estructural como respuesta a la demanda actual disponiéndolo en tres partes: En la primera parte se realizó un estudio del arte de los morteros y sus constituyentes. El uso de los morteros se remonta a la antigüedad, utilizándose como componentes yeso y cal fundamentalmente. Los griegos y romanos desarrollaron el concepto de morteros de cal, introduciendo componentes como las puzolanas, cales hidraúlicas y áridos de polvo de mármol dando origen a morteros muy parecidos a los hormigones actuales. En la edad media y renacimiento se perdió la tecnología desarrollada por los romanos debido al extenso uso de la piedra en las construcciones civiles, defensivas y religiosas. Hubo que esperar hasta el siglo XIX para que J. Aspdin descubriese el actual cemento como el principal compuesto hidraúlico. Por último y ya en el siglo XX con la aparición de moléculas tales como estireno, melanina, cloruro de vinilo y poliésteres se comenzó a desarrollar la industria de los polímeros que se añadieron a los morteros dando lugar a los “composites”. El uso de polímeros en matrices cementantes dotan al mortero de propiedades tales como: adherencia, flexibilidad y trabajabilidad, como ya se tiene constancia desde los años 30 con el uso de caucho naturales. En la actualidad el uso de polímeros de síntesis (polivinialacetato, estireno-butadieno, viniacrílico y resinas epoxi) hacen que principalmente el mortero tenga mayor resistencia al ataque del agua y por lo tanto aumente su durabilidad ya que se minimizan todas las reacciones de deterioro (hielo, humedad, ataque biológico,…). En el presente estudio el polímero que se utilizó fue en estado polvo: polímero redispersable. Estos polímeros están encapsulados y cuando se ponen en contacto con el agua se liberan de la cápsula formando de nuevo el gel. En los morteros de reparación el único compuesto hidraúlico que hay es el cemento y es el principal constituyente hoy en día de los materiales de construcción. El cemento se obtiene por molienda conjunta de Clínker y yeso. El Clínker se obtiene por cocción de una mezcla de arcillas y calizas hasta una temperatura de 1450-1500º C por reacción en estado fundente. Para esta reacción se deben premachacar y homogeneizar las materias primas extraídas de la cantera. Son dosificadas en el horno con unas proporciones tales que cumplan con unas relación de óxidos tales que permitan formar las fases anhidras del Clínker C3S, C2S, C3A y C4AF. De la hidratación de las fases se obtiene el gel CSH que es el que proporciona al cemento de sus propiedades. Existe una norma (UNE-EN 197-1) que establece la composición, especificaciones y tipos de cementos que se fabrican en España. La tendencia actual en la fabricación del cemento pasa por el uso de cementos con mayores contenidos de adiciones (cal, puzolana, cenizas volantes, humo de sílice,…) con el objeto de obtener cementos más sostenibles. Otros componentes que influyen en las características de los morteros son: - Áridos. En el desarrollo de los morteros se suelen usar naturales, bien calizos o silícicos. Hacen la función de relleno y de cohesionantes de la matriz cementante. Deben ser inertes - Aditivos. Son aquellos componentes del mortero que son dosificados en una proporción menor al 5%. Los más usados son los superplastificantes por su acción de reductores de agua que revierte en una mayor durabilidad del mortero. Una vez analizada la composición de los morteros, la mejora tecnológica de los mismos está orientada al aumento de la durabilidad de su vida en obra. La durabilidad se define como la capacidad que éste tiene de resistir a la acción del ambiente, ataques químicos, físicos, biológicos o cualquier proceso que tienda a su destrucción. Estos procesos dependen de factores tales como la porosidad del hormigón y de la exposición al ambiente. En cuanto a la porosidad hay que tener en cuenta la distribución de macroporos, mesoporos y microporos de la estructura del hormigón, ya que no todos son susceptibles de que se produzca el transporte de agentes deteriorantes, provocando tensiones internas en las paredes de los mismos y destruyendo la matriz cementante Por otro lado los procesos de deterioro están relacionados con la acción del agua bien como agente directo o como vehículo de transporte del agente deteriorante. Un ambiente que resulta muy agresivo para los hormigones es el marino. En este caso los procesos de deterioro están relacionados con la presencia de cloruros y de sulfatos tanto en el agua de mar como en la atmosfera que en combinación con el CO2 y O2 forman la sal de Friedel. El deterioro de las estructuras en ambientes marinos se produce por la debilitación de la matriz cementante y posterior corrosión de las armaduras que provocan un aumento de volumen en el interior y rotura de la matriz cementante por tensiones capilares. Otras reacciones que pueden producir estos efectos son árido-álcali y difusión de iones cloruro. La durabilidad de un hormigón también depende del tipo de cemento y su composición química (cementos con altos contenidos de adición son más resistentes), relación agua/cemento y contenido de cemento. La Norma UNE-EN 1504 que consta de 10 partes, define los productos para la protección y reparación de estructuras de hormigón, el control de calidad de los productos, propiedades físico-químicas y durables que deben cumplir. En esta Norma se referencian otras 65 normas que ofrecen los métodos de ensayo para la evaluación de los sistemas de reparación. En la segunda parte de esta Tesis se hizo un diseño de experimentos con diferentes morteros poliméricos (con concentraciones de polímero entre 0 y 25%), tomando como referencia un mortero control sin polímero, y se estudiaron sus propiedades físico-químicas, mecánicas y durables. Para mortero con baja proporción de polímero se recurre a sistemas monocomponentes y para concentraciones altas bicomponentes en la que el polímero está en dispersión acuosa. Las propiedades mecánicas medidas fueron: resistencia a compresión, resistencia a flexión, módulo de elasticidad, adherencia por tracción directa y expansión-retracción, todas ellas bajo normas UNE. Como ensayos de caracterización de la durabilidad: absorción capilar, resistencia a carbonatación y adherencia a tracción después de ciclos hielo-deshielo. El objeto de este estudio es seleccionar el mortero con mejor resultado general para posteriormente hacer una comparativa entre un mortero con polímero (cantidad optimizada) y un mortero sin polímero. Para seleccionar esa cantidad óptima de polímero a usar se han tenido en cuenta los siguientes criterios: el mortero debe tener una clasificación R4 en cuanto a prestaciones mecánicas al igual que para evaluar sus propiedades durables frente a los ciclos realizados, siempre teniendo en cuenta que la adición de polímero no puede ser elevada para hacer el mortero competitivo. De este estudio se obtuvieron las siguientes conclusiones generales: - Un mortero normalizado no cumple con propiedades para ser clasificado como R3 o R4. - Sin necesidad de polímero se puede obtener un mortero que cumpliría con R4 para gran parte de las características medidas - Es necesario usar relaciones a:c< 0.5 para conseguir morteros R4, - La adición de polímero mejora siempre la adherencia, abrasión, absorción capilar y resistencia a carbonatación - Las diferentes proporciones de polímero usadas siempre suponen una mejora tecnológica en propiedades mecánicas y de durabilidad. - El polímero no influye sobre la expansión y retracción del mortero. - La adherencia se mejora notablemente con el uso del polímero. - La presencia de polímero en los morteros mejoran las propiedades relacionadas con la acción del agua, por aumento del poder cementante y por lo tanto de la cohesión. El poder cementante disminuye la porosidad. Como consecuencia final de este estudio se determinó que la cantidad óptima de polímero para la segunda parte del estudio es 2.0-3.5%. La tercera parte consistió en el estudio comparativo de dos morteros: uno sin polímero (mortero A) y otro con la cantidad optimizada de polímero, concluida en la parte anterior (mortero B). Una vez definido el porcentaje de polímeros que mejor se adapta a los resultados, se plantea un nuevo esqueleto granular mejorado, tomando una nueva dosificación de tamaños de áridos, tanto para el mortero de referencia, como para el mortero con polímeros, y se procede a realizar los ensayos para su caracterización física, microestructural y de durabilidad, realizándose, además de los ensayos de la parte 1, mediciones de las propiedades microestructurales que se estudiaron a través de las técnicas de porosimetría de mercurio y microscopia electrónica de barrido (SEM); así como propiedades del mortero en estado fresco (consistencia, contenido de aire ocluido y tiempo final de fraguado). El uso del polímero frente a la no incorporación en la formulación del mortero, proporcionó al mismo de las siguientes ventajas: - Respecto a sus propiedades en estado fresco: El mortero B presentó mayor consistencia y menor cantidad de aire ocluido lo cual hace un mortero más trabajable y más dúctil al igual que más resistente porque al endurecer dejará menos huecos en su estructura interna y aumentará su durabilidad. Al tener también mayor tiempo de fraguado, pero no excesivo permite que la manejabilidad para puesta en obra sea mayor, - Respecto a sus propiedades mecánicas: Destacar la mejora en la adherencia. Es una de las principales propiedades que confiere el polímero a los morteros. Esta mayor adherencia revierte en una mejora de la adherencia al soporte, minimización de las posibles reacciones en la interfase hormigón-mortero y por lo tanto un aumento en la durabilidad de la reparación ejecutada con el mortero y por consecuencia del hormigón. - Respecto a propiedades microestructurales: la porosidad del mortero con polímero es menor y menor tamaño de poro critico susceptible de ser atacado por agentes externos causantes de deterioro. De los datos obtenidos por SEM no se observaron grandes diferencias - En cuanto a abrasión y absorción capilar el mortero B presentó mejor comportamiento como consecuencia de su menor porosidad y su estructura microscópica. - Por último el comportamiento frente al ataque de sulfatos y agua de mar, así como al frente de carbonatación, fue más resistente en el mortero con polímero por su menor permeabilidad y su menor porosidad. Para completar el estudio de esta tesis, y debido a la gran importancia que están tomando en la actualidad factores como la sostenibilidad se ha realizado un análisis de ciclo de vida de los dos morteros objeto de estudio de la segunda parte experimental.In recent years, the extended use of repair materials for buildings and structures made the development of repair mortars more and more technical. In the development of these mortars by producers, the use of polymers in the formulations is a key point, because sometimes this use is not justified when looking to the performance/price/application as a whole. This thesis is an exhaustive study to justify the use of these mortars as a response to the current growing demand for structural repair. The thesis is classified in three parts:The first part is the study of the state of the art of mortars and their constituents.In ancient times, widely used mortars were based on lime and gypsum. The Greeks and Romans developed the concept of lime mortars, introducing components such as pozzolans, hydraulic limes and marble dust as aggregates, giving very similar concrete mortars to the ones used currently. In the middle Age and Renaissance, the technology developed by the Romans was lost, due to the extensive use of stone in the civil, religious and defensive constructions. It was not until the 19th century, when J. Aspdin discovered the current cement as the main hydraulic compound. Finally in the 20th century, with the appearance of molecules such as styrene, melanin, vinyl chloride and polyester, the industry began to develop polymers which were added to the binder to form special "composites".The use of polymers in cementitious matrixes give properties to the mortar such as adhesion, Currently, the result of the polymer synthesis (polivynilacetate, styrene-butadiene, vynilacrylic and epoxy resins) is that mortars have increased resistance to water attack and therefore, they increase their durability since all reactions of deterioration are minimised (ice, humidity, biological attack,...). In the present study the polymer used was redispersible polymer powder. These polymers are encapsulated and when in contact with water, they are released from the capsule forming a gel.In the repair mortars, the only hydraulic compound is the cement and nowadays, this is the main constituent of building materials. The current trend is centered in the use of higher contents of additions (lime, pozzolana, fly ash, silica, silica fume...) in order to obtain more sustainable cements. Once the composition of mortars is analyzed, the technological improvement is centred in increasing the durability of the working life. Durability is defined as the ability to resist the action of the environment, chemical, physical, and biological attacks or any process that tends to its destruction. These processes depend on factors such as the concrete porosity and the environmental exposure. In terms of porosity, it be considered, the distribution of Macropores and mesopores and pores of the concrete structure, since not all of them are capable of causing the transportation of damaging agents, causing internal stresses on the same walls and destroying the cementing matrix.In general, deterioration processes are related to the action of water, either as direct agent or as a transport vehicle. Concrete durability also depends on the type of cement and its chemical composition (cement with high addition amounts are more resistant), water/cement ratio and cement content. The standard UNE-EN 1504 consists of 10 parts and defines the products for the protection and repair of concrete, the quality control of products, physical-chemical properties and durability. Other 65 standards that provide the test methods for the evaluation of repair systems are referenced in this standard. In the second part of this thesis there is a design of experiments with different polymer mortars (with concentrations of polymer between 0 and 25%), taking a control mortar without polymer as a reference and its physico-chemical, mechanical and durable properties were studied. For mortars with low proportion of polymer, 1 component systems are used (powder polymer) and for high polymer concentrations, water dispersion polymers are used. The mechanical properties measured were: compressive strength, flexural strength, modulus of elasticity, adhesion by direct traction and expansion-shrinkage, all of them under standards UNE. As a characterization of the durability, following tests are carried out: capillary absorption, resistance to carbonation and pull out adhesion after freeze-thaw cycles. The target of this study is to select the best mortar to make a comparison between mortars with polymer (optimized amount) and mortars without polymer. To select the optimum amount of polymer the following criteria have been considered: the mortar must have a classification R4 in terms of mechanical performance as well as in durability properties against the performed cycles, always bearing in mind that the addition of polymer cannot be too high to make the mortar competitive in price. The following general conclusions were obtained from this study: - A standard mortar does not fulfill the properties to be classified as R3 or R4 - Without polymer, a mortar may fulfill R4 for most of the measured characteristics. - It is necessary to use relations w/c ratio < 0.5 to get R4 mortars - The addition of polymer always improves adhesion, abrasion, capillary absorption and carbonation resistance - The different proportions of polymer used always improve the mechanical properties and durability. - The polymer has no influence on the expansion and shrinkage of the mortar - Adhesion is improved significantly with the use of polymer. - The presence of polymer in mortars improves the properties related to the action of the water, by the increase of the cement power and therefore the cohesion. The cementitious properties decrease the porosity. As final result of this study, it was determined that the optimum amount of polymer for the second part of the study is 2.0 - 3.5%. The third part is the comparative study between two mortars: one without polymer (A mortar) and another with the optimized amount of polymer, completed in the previous part (mortar B). Once the percentage of polymer is defined, a new granular skeleton is defined, with a new dosing of aggregate sizes, for both the reference mortar, the mortar with polymers, and the tests for physical, microstructural characterization and durability, are performed, as well as trials of part 1, measurements of the microstructural properties that were studied by scanning electron microscopy (SEM) and mercury porosimetry techniques; as well as properties of the mortar in fresh State (consistency, content of entrained air and final setting time). The use of polymer versus non polymer mortar, provided the following advantages: - In fresh state: mortar with polymer presented higher consistency and least amount of entrained air, which makes a mortar more workable and more ductile as well as more resistant because hardening will leave fewer gaps in its internal structure and increase its durability. Also allow it allows a better workability because of the longer (not excessive) setting time. - Regarding the mechanical properties: improvement in adhesion. It is one of the main properties which give the polymer to mortars. This higher adhesion results in an improvement of adhesion to the substrate, minimization of possible reactions at the concrete-mortar interface and therefore an increase in the durability of the repair carried out with mortar and concrete. - Respect to microstructural properties: the porosity of mortar with polymer is less and with smaller pore size, critical to be attacked by external agents causing deterioration. No major differences were observed from the data obtained by SEM - In terms of abrasion and capillary absorption, polymer mortar presented better performance as a result of its lower porosity and its microscopic structure. - Finally behavior against attack by sulfates and seawater, as well as to carbonation, was better in the mortar with polymer because of its lower permeability and its lower porosity. To complete the study, due to the great importance of sustainability for future market facts, the life cycle of the two mortars studied was analysed.

La introducción del hormigón armado en España: razón constructiva de su evolución

España se incorporó a la técnica del hormigón armado con más de dos décadas de retraso respecto a Francia o Alemania. En 1890, en Europa se construían ya estructuras de hormigón armado de cierta envergadura y complejidad. En España hubo que esperar hasta 1893 para la primera obra en hormigón armado, que fue un sencillo depósito descubierto en Puigverd (Lérida), ejecutado por el ingeniero militar Francesc Macià con patente Monier. En 1898, de la mano de Hennebique, se empezó la construcción de los dos primeros edificios con estructura de hormigón armado en España. Fueron dos obras puntuales, con proyectos importados de Francia, pero necesarias para introducir de manera definitiva el material. En paralelo, en París, se estaban edificando en hormigón armado la mayoría de los pabellones de la Exposición Universal de 1900. En el cambio de siglo, las construcciones de hormigón armado habían alcanzado ya la madurez proyectual y técnica en Europa. A pesar de la incorporación tardía, se puede constatar por las obras ejecutadas que en un periodo corto de tiempo, entre 1901 y 1906, se alcanzó en España prácticamente el mismo nivel técnico y constructivo que tenían el resto de los países que fueron pioneros en el empleo del hormigón armado. El desarrollo e implantación de una técnica constructiva no es un proceso lineal, y son muchos los factores que intervienen. Las patentes tuvieron una gran importancia en el desarrollo inicial del hormigón armado. Estas ofrecían un producto que funcionaba. Las primeras estructuras de hormigón armado no se calculaban y se construían siguiendo una reglamentación, se compraban. Y el resultado de esa “compra” solía ser, en la mayoría de los casos, satisfactorio. Las patentes vendían sistemas estructurales cuyo funcionamiento estaba corroborado por la experiencia y la pericia de su inventor. Esta investigación parte de la hipótesis de que las patentes sobre cemento y hormigón armado depositadas en España entre 1884 y 1906 fueron uno de los factores que proporcionaron a los técnicos y a las empresas españolas una pericia constructiva sólida en el empleo del hormigón armado. En este trabajo se aborda el estudio del proceso de introducción del hormigón armado en España desde una perspectiva fundamentalmente técnica, incorporando las patentes como una de las razones constructivas que explican su rápida evolución y generalización en un periodo de tiempo breve: 1901-1906. En este proceso se contextualiza y analiza una de las figuras que se considera fundamental en los primeros años del hormigón armado en España, la del ingeniero Juan Manuel de Zafra y Estevan. Esta tesis analiza las patentes de hormigón armado desde el punto de vista estadístico y constructivo. Desde ambas perspectivas se verifica la hipótesis de partida de esta investigación, concluyendo que las patentes fueron una de las razones constructivas de la evolución del hormigón armado en España y de su rápida implantación. ABSTRACT Spain incorporated the reinforced concrete technique more than two decades after France and Germany. In central Europe reinforced concrete structures of considerable size and complexity were being built in 1890, while in Spain it was not until 1893 that the first work, a simple open air water tank, was implemented in Puigverd (Lleida) by the military engineer Francesc Macià with a Monier patent. In 1898 the construction of the first two buildings with reinforced concrete structure in Spain started, with the guidance by Hennebique. They were two isolated cases with projects imported from France, but playing a key role to definitively introduce the material in Spain. In parallel, in Paris, most of the pavilions of the 1900 World Expo were being built in reinforced concrete. At the turn of the century reinforced concrete buildings had reached maturity both as a technology and as a design practice. Despite the late assumption of the material, the works carried out in the very short period between 1901 and 1906 clearly show that Spain reached practically the same technical and constructive level as the other pioneering countries in the use of reinforced concrete. The development and implementation of a constructive technique is never a linear process, there are many factors involved. The patents offered a successful product. Initial reinforced concrete structures were not calculated and built according to regulations, they were bought. And this purchase in most cases was satisfactory for the required use. Patents sold structural systems whose performance was supported by the experience and expertise of its inventor. The hypothesis of this research is based upon the assumption that the cement and concrete patents registered in Spain between 1884 and 1906 were one of the factors that provided Spanish technicians and companies with a solid constructive expertise in the use of reinforced concrete. This investigation studies the introduction of reinforced concrete to Spain from a predominantly technical perspective, incorporating patents as the constructive reason for the rapid evolution and spread in such a short period of time: 1901-1906. Along the way, the role of engineer J. M. de Zafra, generally considered a key agent in the initial years of reinforced concrete in Spain, is contextualized and analyzed. This dissertation analyzes the patents of reinforced concrete from a statistical and constructive point of view. From both perspectives the hypothesis of this research is verified, concluding that patents were one of the constructive reasons for the development of reinforced concrete in Spain.

Experience and lessons learnt from the SMART 2013 Benchmark

The French CEA, together with EDF and the IAEA, recently organised an international benchmark to evaluate the ability to model the mechanical behaviour of a typical nuclear reinforced concrete structure subjected to seismic demands. The participants were provided with descriptions of the structure and the testing campaign; they had to propose the numerical model and the material laws for the concrete (stage #1). A mesh of beam and shell elements was generated; for modelling the concrete a damaged plasticity model was used, but a smeared crack model was also investigated. Some of the initial experimental results, with the mock-up remaining in the elastic range, were provided to the participants for calibrating their models (stage #2). Predictions had to be produced in terms of eigen-frequencies and motion time histories. The calculated frequencies reproduced reasonably the experimental ones; the time histories, calculated by modal response analysis, also reproduced adequately the observed amplifications. The participants were then expected to predict the structural response under strong ground motions (stage #3), which increased progressively up to a history recorded during the 1994 Northridge earthquake, followed by an aftershock. These results were produced using an explicit solver and a damaged plasticity model for the concrete, although an implicit solver with a smeared crack model was also investigated. The paper presents the conclusions of the pre-test exercise, as well as some observations from additional simulations conducted after the experimental results were made available.

A first approach to earthquake damage estimation in Haiti: advices to minimize the seismic risk

This study is in the frame of the cooperative line that several Spanish Universities and other foreign partners started with the Haitian government in 2010. According to our studies (Benito et al. in An evaluation of seismic hazard in La Hispaniola, after the 2010 Haiti earthquake, 33rd General Assembly of the European Seismological Commission, Moscow, Russia, 2012) and recent scientific literature, the earthquake hazard in Haiti remains high (Calais et al. in Nat Geosci 3:794–799, 2010). In view of this, we wonder whether the country is currently ready to face another earthquake. In this sense, we estimated several damage scenarios in Port-au-Prince and Cap-Haitien associated to realistic possible major earthquakes. Our findings show that almost 50 % of the building stock of both cities would result uninhabitable due to structural damage. Around 80 % of the buildings in both cities have reinforced concrete structure with concrete block infill; however, the presence of masonry buildings becomes significant (between 25 and 45 % of the reinforced concrete buildings) in rural areas and informal settlements on the outskirts, where the estimated damage is higher. The influence of the soil effect on the damage spatial distribution is evident in both cities. We have found that the percentage of uninhabitable buildings in soft soil areas may be double the percentage obtained in nearby districts located in hard soil. These results reveal that a new seismic catastrophe of similar or even greater consequences than the 2010 Haiti earthquake might happen if the earthquake resilience is not improved in the country. Nowadays, the design of prevention actions and mitigation policies is the best instrument the society has to face seismic risk. In this sense, the results of this research might contribute to define measures oriented to earthquake risk reduction in Haiti, which should be a real priority for national and international institutions.

Optimization of wireless power transfer via magnetic resonance in different media

A wide range of non-destructive testing (NDT) methods for the monitoring the health of concrete structure has been studied for several years. The recent rapid evolution of wireless sensor network (WSN) technologies has resulted in the development of sensing elements that can be embedded in concrete, to monitor the health of infrastructure, collect and report valuable related data. The monitoring system can potentially decrease the high installation time and reduce maintenance cost associated with wired monitoring systems. The monitoring sensors need to operate for a long period of time, but sensors batteries have a finite life span. Hence, novel wireless powering methods must be devised. The optimization of wireless power transfer via Strongly Coupled Magnetic Resonance (SCMR) to sensors embedded in concrete is studied here. First, we analytically derive the optimal geometric parameters for transmission of power in the air. This specifically leads to the identification of the local and global optimization parameters and conditions, it was validated through electromagnetic simulations. Second, the optimum conditions were employed in the model for propagation of energy through plain and reinforced concrete at different humidity conditions, and frequencies with extended Debye's model. This analysis leads to the conclusion that SCMR can be used to efficiently power sensors in plain and reinforced concrete at different humidity levels and depth, also validated through electromagnetic simulations. The optimization of wireless power transmission via SMCR to Wearable and Implantable Medical Device (WIMD) are also explored. The optimum conditions from the analytics were used in the model for propagation of energy through different human tissues. This analysis shows that SCMR can be used to efficiently transfer power to sensors in human tissue without overheating through electromagnetic simulations, as excessive power might result in overheating of the tissue. Standard SCMR is sensitive to misalignment; both 2-loops and 3-loops SCMR with misalignment-insensitive performances are presented. The power transfer efficiencies above 50% was achieved over the complete misalignment range of 0°-90° and dramatically better than typical SCMR with efficiencies less than 10% in extreme misalignment topologies.

Optimization of Wireless Power Transfer via Magnetic Resonance in Different Media

A wide range of non-destructive testing (NDT) methods for the monitoring the health of concrete structure has been studied for several years. The recent rapid evolution of wireless sensor network (WSN) technologies has resulted in the development of sensing elements that can be embedded in concrete, to monitor the health of infrastructure, collect and report valuable related data. The monitoring system can potentially decrease the high installation time and reduce maintenance cost associated with wired monitoring systems. The monitoring sensors need to operate for a long period of time, but sensors batteries have a finite life span. Hence, novel wireless powering methods must be devised. The optimization of wireless power transfer via Strongly Coupled Magnetic Resonance (SCMR) to sensors embedded in concrete is studied here. First, we analytically derive the optimal geometric parameters for transmission of power in the air. This specifically leads to the identification of the local and global optimization parameters and conditions, it was validated through electromagnetic simulations. Second, the optimum conditions were employed in the model for propagation of energy through plain and reinforced concrete at different humidity conditions, and frequencies with extended Debye's model. This analysis leads to the conclusion that SCMR can be used to efficiently power sensors in plain and reinforced concrete at different humidity levels and depth, also validated through electromagnetic simulations. The optimization of wireless power transmission via SMCR to Wearable and Implantable Medical Device (WIMD) are also explored. The optimum conditions from the analytics were used in the model for propagation of energy through different human tissues. This analysis shows that SCMR can be used to efficiently transfer power to sensors in human tissue without overheating through electromagnetic simulations, as excessive power might result in overheating of the tissue. Standard SCMR is sensitive to misalignment; both 2-loops and 3-loops SCMR with misalignment-insensitive performances are presented. The power transfer efficiencies above 50% was achieved over the complete misalignment range of 0°-90° and dramatically better than typical SCMR with efficiencies less than 10% in extreme misalignment topologies.

Evaluation of the performance of steel fibre reinforced self-compacting concrete in elevated slab systems; from the material to the structure

Degree of Doctor of Philosophy of Structural/Civil Engineering

Towards a professional army. Changes to the structure of the officer cadre and the manning system of the Russian armed forces. OSW Commentary No. 73, 2012-03-28

The structure of the Russian army’s personnel has undergone a major transformation in recent years. The Armed Forces are no longer a downsized continuation of the Soviet-era mass army, but are gradually becoming a de facto professional army in which conscription, now employed on a diminishing scale, will primarily constitute a first step towards a continued professional military career. The cornerstone for the process of professionalisation has been laid by a personnel reform which cut the number of officer posts by nearly half and considerably restricted the recruitment of new officers, thus restoring traditional proportions to the structure of the officer corps. The plans to ultimately implement a manning system based predominantly on contract service are a natural consequence of these changes. The ongoing professionalisation of the Russian Armed Forces should be treated as a conscious effort which is mainly necessitated by global trends: despite the demographic changes taking place, Russia could still maintain an army with a declared strength of one million soldiers, most of them conscripts.

Safety analysis of nuclear concrete containment structure /

"NRC FIN no. B5688."

Parametric model for the analysis of concrete expansion due to alkali-aggregate reaction

The alkali-aggregate reaction (AAR) is a chemical reaction that provokes a heterogeneous expansion of concrete and reduces important properties such as Young's modulus, leading to a reduction in the structure's useful life. In this study, a parametric model is employed to determine the spatial distribution of the concrete expansion, combining normalized factors that influence the reaction through an AAR expansion law. Optimization techniques were employed to adjust the numerical results and observations in a real structure. A three-dimensional version of the model has been implemented in a finite element commercial package (ANSYS(C)) and verified in the analysis of an accelerated mortar test. Comparisons were made between two AAR mathematical descriptions for the mechanical phenomenon, using the same methodology, and an expansion curve obtained from experiment. Some parametric studies are also presented. The numerical results compared very well with the experimental data validating the proposed method.

A NEW DIAGNOSTIC OF THE RADIAL DENSITY STRUCTURE OF Be DISKS

We analyze the intrinsic polarization of two classical Be stars in the process of losing their circumstellar disks via a Be to normal B star transition originally reported by Wisniewski et al. During each of five polarimetric outbursts which interrupt these disk-loss events, we find that the ratio of the polarization across the Balmer jump (BJ+/BJ-) versus the V-band polarization traces a distinct loop structure as a function of time. Since the polarization change across the Balmer jump is a tracer of the innermost disk density whereas the V-band polarization is a tracer of the total scattering mass of the disk, we suggest that such correlated loop structures in Balmer jump-V-band polarization diagrams (BJV diagrams) provide a unique diagnostic of the radial distribution of mass within Be disks. We use the three-dimensional Monte Carlo radiation transfer code HDUST to reproduce the observed clockwise loops simply by turning ""on/off"" the mass decretion from the disk. We speculate that counterclockwise loop structures we observe in BJV diagrams might be caused by the mass decretion rate changing between subsequent ""on/off"" sequences. Applying this new diagnostic to a larger sample of Be disk systems will provide insight into the time-dependent nature of each system's stellar decretion rate.

Analysis of a semi-rigid connection for precast concrete

This paper presents a study of a specific type of beam-to-column connection for precast concrete structures. Furthermore, an analytical model to determine the strength and the stiffness of the connection, based on test results of two prototypes, is proposed. To evaluate the influence of the strength and stiffness of the connection on the behaviour of the structure, the results of numerical simulations of a typical multi-storey building with semi-rigid connections are also presented and compared with the results using pinned and rigid connections. The main conclusions are: (a) the proposed design model can reasonably evaluate the studied connection strength; (b) the evaluation of strength is more accurate than that of stiffness; (c) for a typical structure, it is possible to increase the number of storeys of the structure from two to four with lower horizontal displacement at the top, and only a small increase of the column base bending moment by replacing the pinned connections with semi-rigid ones; and (d) although there is significant uncertainty in the connection stiffness, the results show that the displacements at the top of the structure, and the column base moments present low susceptibility deviations to this parameter.

Model to predict the chloride penetration in concrete with profile forming peak: verification of its precision

Chloride attack in marine environments or in structures where deicing salts are used will not always show profiles with concentrations that decrease from the external surface to the interior of the concrete. Some profiles show an increase in chloride concentrations from when a peak is formed. This type of profile must be analyzed in a different way from the traditional model of Fick`s second law to generate more precise service life models. A model for forecasting the penetration of chloride ions as a function of time for profiles having formed a peak. To confirm the efficiency of this model, it is necessary to observe the behavior of a chloride profile with peak in a specific structure over a period of time. To achieve this, two chloride profiles with different ages (22 and 27 years) were extracted from the same structure. The profile obtained from the 22-year sample was used to estimate the chloride profile at 27 years using three models: a) the traditional model using Fick`s second law and extrapolating the value of C(S)-external surface chloride concentration; b) the traditional model using Fick`s second law and shifting the x-axis to the peak depth; c) the previously proposed model. The results from these models were compared with the actual profile measured in the 27-year sample and the results were analyzed. The model was presented with good precision for this study of case, requiring to be tested with other structures in use.

Finite element analysis of concrete cracking at early age

The study of the early age concrete properties is becoming more important, as the thermal effects and the shrinkage, even in the first hours, could generate cracks, increasing the permeability of the structure and being able to induce problems of durability and functionality in the same ones. The detailed study of the stresses development during the construction process can be decisive to keep low the cracking levels. In this work a computational model, based on the finite element method, was implemented to simulate the early age concrete behavior and, specially, the evaluation of the cracking risk. The finite element analysis encloses the computational modeling of the following phenomena: chemical, thermal, moisture diffusion and mechanical which occur at the first days after the concrete cast. The developed software results were compared with experimental values found in the literature, demonstrating an excellent approach for all the implemented analysis.