Estudio, fabricación y aplicación de redes de período largo en fibras ópticas para el desarrollo de sensores de humedad embebibles en materiales cementíceos
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2023-12-14
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La necesidad de contar con estructuras civiles confiables es un fuerte desafío de la Ingeniería Civil. La falta de mantenimiento trae como consecuencia un alto costo económico en reparación de estructuras que presentan evidencias de deterioro avanzado. Por este motivo, la implementación de sistemas de alarma temprana que detecten la aparición de procesos agresivos para la salud de las estructuras, es susceptible de ser tenida en cuenta en cualquier proyecto asociado a una estructura de gran porte. Las técnicas de monitoreo de salud de estructuras demostraron ser mecanismos beneficiosos para alcanzar metas de mantenimiento, en particular aquellas vinculadas a estructuras de hormigón armado. En este escenario y considerando la permanente superación tecnológica que se verifica en el ámbito de las fibras ópticas, los sensores implementados con éstas se presentan en la actualidad como elementos de sensado altamente atractivos para asistir a la Ingeniería Civil en el objetivo de lograr sistemas de monitoreo de salud confiables, robustos y durables. Una estructura de hormigón interactúa con su entorno de diferentes maneras durante su ciclo de vida. Más allá de las interacciones para las que se diseñó, existen otras que pueden generar cambios en su desempeño funcional, de seguridad o estético. Algunos agentes ambientales son considerados nocivos para el hormigón porque representan posibles causas de daño estructural (por ejemplo, pueden aparecer diferentes patologías debido a procesos de carbonatación, ingreso de cloruros y/o sulfatos, entre otros). La presencia de agua (en fase líquida o gaseosa) dentro del material juega un rol preponderante en todos los fenómenos de transporte y de degradación. Por ello, el conocimiento del nivel de humedad interna en diferentes ubicaciones estratégicas de una estructura de hormigón es un elemento de juicio de gran importancia para los ingenieros civiles durante la instancia de tomar decisiones relacionadas con el mantenimiento. Desde el punto de vista físico, el vapor de agua se difunde dentro de la matriz de hormigón debido a un gradiente de concentración del contenido de moléculas de agua que existe entre el entorno que rodea la estructura y el interior del material en sí mismo. Por ello, contar con sensores embebidos en la estructura de hormigón para monitorear la humedad relativa interna representa un recurso tecnológico de gran valor.
En este trabajo de Tesis Doctoral se presentan los resultados obtenidos en el estudio y fabricación local de un tipo de dispositivo grabado dentro de una fibra óptica llamado red de período largo, con el objetivo de ser aplicado como elemento sensor en la determinación del nivel de humedad en un dado punto interno de una estructura de material cementíceo. Las acciones asociadas al plan de actividades de esta Tesis Doctoral fueron ejecutadas empleando métodos y técnicas esencialmente experimentales. Entre los emergentes del trabajo se observa la adaptación, depuración e implementación práctica de una técnica de generación de redes de período largo en fibras ópticas que potencialmente puede proveer de este tipo de elementos tanto al Sistema Científico y Tecnológico Nacional como al campo industrial privado, considerando que no existen antecedentes publicados al respecto en el ámbito nacional. Los resultados de los estudios realizados acreditan el esfuerzo de evaluar el uso de los materiales y dispositivos ópticos ensayados para un potencial desarrollo de un sensor de HR basado en los emergentes de la misma. Se concluyó que tanto la simpleza de implementación de las técnicas empleadas como las bondades observadas en los resultados de desempeño general del sensor de HR, son elementos de juicio que merecen ser evaluados en caso de efectivizarse un desarrollo tecnológico orientado al diseño de un sensor basado en redes de período largo en fibra óptica.
The need for reliable civil structures is a really tough challenge for Civil Engineering. The lack of maintenance generates a high economic cost in repairing structures which have evidence of advanced deterioration. For this reason, the implementation of early warning systems that detect the appearance of aggressive processes for the health of structures is likely to be taken into account in any project associated with a large structure. Structure health monitoring techniques have proven to be beneficial mechanisms to achieve maintenance goals related to reinforced concrete structures. In this scenario and considering the continuous technological improvement in the field of optical fibers, the sensors implemented with them are nowadays presented as highly attractive sensing elements to assist Civil Engineering in order to achieve reliable, robust and durable monitoring systems. A concrete structure interacts with its environment in different ways during its life cycle. Beyond the interactions for which the structure was designed, there are other interactions that can generate changes in its functional, safety or aesthetic performance. Some environmental agents are considered harmful to concrete because they represent possible causes of structural damage (for example, different pathologies may appear due to carbonation processes, entry of chlorides and/or sulfates, among others). The presence of water (liquid or vapor) within the material plays an essential role in all transport and degradation phenomena. For this reason, knowledge related to the internal humidity level in different strategic places of a concrete structure is a highly important element of judgment for civil engineers when making maintenance decisions. From a physical point of view, water vapor diffuses within the concrete matrix due to a concentration gradient of water molecule that exists between the structure surrounding environment and the interior of the material itself. Therefore, having sensors embedded in the concrete structure to monitor internal relative humidity represents a technological resource of great value. This Doctoral Thesis presents the results obtained in the study and local manufacture of a type of device engraved inside an optical fiber called long period grating, with the aim of being applied as a sensor element in the determination of a civil structure internal humidity level. All the actions related with the activity plan were executed using essentially experimental methods and techniques. One of the main goals of this Doctoral Thesis is the adaptation, improvement and practical implementation of a technique to generate long period grating in optical fibers that can potentially provide this type of elements to both, the National Scientific and Technological System as well as the private industrial field. The results presented here justify evaluating the use of the materials and optical devices studied and tested in this Thesis for a potential development of a humidity sensor based on long period gratings in optical fiber. It is concluded that both the simplicity of implementation of the techniques used and the acceptable results of the general performance of the humidity sensor are elements of judgment that deserve to be evaluated in a potential technological development oriented towards the design of a sensor like the one implemented in this Thesis.
The need for reliable civil structures is a really tough challenge for Civil Engineering. The lack of maintenance generates a high economic cost in repairing structures which have evidence of advanced deterioration. For this reason, the implementation of early warning systems that detect the appearance of aggressive processes for the health of structures is likely to be taken into account in any project associated with a large structure. Structure health monitoring techniques have proven to be beneficial mechanisms to achieve maintenance goals related to reinforced concrete structures. In this scenario and considering the continuous technological improvement in the field of optical fibers, the sensors implemented with them are nowadays presented as highly attractive sensing elements to assist Civil Engineering in order to achieve reliable, robust and durable monitoring systems. A concrete structure interacts with its environment in different ways during its life cycle. Beyond the interactions for which the structure was designed, there are other interactions that can generate changes in its functional, safety or aesthetic performance. Some environmental agents are considered harmful to concrete because they represent possible causes of structural damage (for example, different pathologies may appear due to carbonation processes, entry of chlorides and/or sulfates, among others). The presence of water (liquid or vapor) within the material plays an essential role in all transport and degradation phenomena. For this reason, knowledge related to the internal humidity level in different strategic places of a concrete structure is a highly important element of judgment for civil engineers when making maintenance decisions. From a physical point of view, water vapor diffuses within the concrete matrix due to a concentration gradient of water molecule that exists between the structure surrounding environment and the interior of the material itself. Therefore, having sensors embedded in the concrete structure to monitor internal relative humidity represents a technological resource of great value. This Doctoral Thesis presents the results obtained in the study and local manufacture of a type of device engraved inside an optical fiber called long period grating, with the aim of being applied as a sensor element in the determination of a civil structure internal humidity level. All the actions related with the activity plan were executed using essentially experimental methods and techniques. One of the main goals of this Doctoral Thesis is the adaptation, improvement and practical implementation of a technique to generate long period grating in optical fibers that can potentially provide this type of elements to both, the National Scientific and Technological System as well as the private industrial field. The results presented here justify evaluating the use of the materials and optical devices studied and tested in this Thesis for a potential development of a humidity sensor based on long period gratings in optical fiber. It is concluded that both the simplicity of implementation of the techniques used and the acceptable results of the general performance of the humidity sensor are elements of judgment that deserve to be evaluated in a potential technological development oriented towards the design of a sensor like the one implemented in this Thesis.
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Fibras ópticas, Redes de período largo, Sensor de humedad
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