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Abstract(s)
As construções de betão armado, apesar de todos os desenvolvimentos tecnológicos entretanto alcançados, apresentam uma durabilidade limitada no tempo devido à sua interação com o meio envolvente. Em geral, os projetos de estruturas tendem a definir o horizonte de 50 anos para a sua vida útil e, em casos excecionais pelo custo ou relevância da obra, 100 anos de vida útil. Embora exista um enquadramento legal que define os critérios a adotar para atingir esses objetivos de durabilidade, são muitos os exemplos de envelhecimento precoce de edifícios e infraestruturas, o que se traduz em elevados custos económicos e sociais, resultantes da necessidade de efetuar obras de reparação não previstas ou pela redução dos níveis de serviço disponibilizados. Uma forma de mitigar os efeitos do envelhecimento das estruturas pode ser a implementação de sistemas de gestão da manutenção que permitam detetar problemas e efetuar reparações através da sua deteção precoce, visando incrementar a sua vida útil. A digitalização do setor da construção, designadamente pela introdução da metodologia BIM para gerir todo o processo construtivo, pode ser a chave para ancorar novos modelos e sistemas de gestão da manutenção. Neste cenário, a monitorização da degradação das estruturas com sensores permitirá recolher informação integrável em ferramentas de manutenção interligadas a modelos 3D e à base de dados dos edifícios.
O foco desta tese é a analise e tratamento de informação sobre o estado de degradação de estruturas de betão armado, obtidos com o auxílio de sistemas de monitorização eletroquímica que recorrem a sondas embebidas no betão, para posterior integração em ferramentas de gestão da manutenção, com o objetivo de identificar processos que indiquem a possibilidade do desenvolvimento de fenómenos de degradação do betão ou de corrosão das armaduras nele inseridas. Os sistemas utilizados, de natureza eletroquímica, permitem avaliar alterações ao nível da condutividade iónica do betão, resultantes da sua contaminação química, e fenómenos de corrosão das armaduras, que ocorrem em fases avançadas do processo de degradação.
A metodologia adotada envolveu a realização de ensaios em laboratório e a monitorização de um equipamento em operação numa ETAR. Em laboratório foram efetuadas duas séries de ensaios com provetes de betão armado. O primeiro grupo de provetes foi sujeito à ação de cloretos e o segundo grupo exposto ao ataque por sulfatos de sódio e magnésio. Na ETAR testou-se o funcionamento do sistema de monitorização da resistividade iónica do betão sujeito à ação de águas residuais urbanas em três zonas com diferentes exposições. Nos provetes ensaiados em laboratório adotaram-se quatro soluções diferentes para o reforço do betão, armaduras correntes sem proteção e pintadas com tinta acrílica e armaduras protegidas catodicamente por galvanização e por corrente imposta. Todos os provetes foram monitorizados com dois sistemas de monitorização eletroquímica. O primeiro sistema recorre a sondas que medem a resistividade iónica do betão e é constituído por um par de elétrodos iguais, com 30 mm de diâmetro e 50 mm de altura, colocados de forma a ficarem afastados entre si de 50 mm. O outro sistema é composto por um único bloco que integra a ligação à armadura do provete, dois elétrodos de referência (grafite), dois elétrodos de aço inox e dois elétrodos de aço macio, que permite a medição do potencial de corrosão e da resistência de polarização das armaduras.
Os resultados obtidos ao longo deste trabalho mostram que a monitorização de estruturas é uma ferramenta válida para integrar os sistemas de gestão da manutenção, permitindo identificar processos de degradação do betão armado e detetar o inicio da corrosão das armaduras. Com a utilização de dois sistemas de monitorização foi possível observar o processo de degradação do betão armado que, numa primeira fase, envolve alterações ao nível da resistividade iónica do betão e, numa segunda fase, conduz à queda do potencial de corrosão e da resistência de polarização linear das armaduras sinalizando o inicio do processo de corrosão destas.
Ao longo dos ensaios foi possível detetar diferenças de comportamento entre os vários tipos de armaduras utilizados, tendo-se verificado que as armaduras galvanizadas apresentaram um melhor comportamento face à ação dos cloretos que as armaduras correntes ou as revestidas.
The reinforced concrete constructions, regardless of all the technological developments reached, have a limited durability in time due to their interaction with the surrounding environment. Structural projects tend to define the horizon of 50 years for their service life and, in exceptional cases due to the cost or relevance of the work, 100 years of service life. Although there is a legal framework that defines the criteria to be adopted to achieve these levels of durability, there are many examples of early aging of buildings and infrastructures, which translates into high economic and social costs resulting from the need to carry out repair work not forseen or by reducing the levels of service available. One way to mitigate the effects of aging structures can be to implement maintenance management systems that allow problems to be detected and repaired through early detection to extend their life. The digitization of the construction sector, namely by introducing the BIM methodology to manage the entire construction process, can be the key to anchoring new models and maintenance management systems. In this scenario the monitoring of the degradation of the structures with sensors will allow to collect information integrable in maintenance tools interconnected to 3D models and the database of the buildings. The focus of this thesis is the analysis and treatment of information on the degradation state of reinforced concrete structures, obtained with the aid of electrochemical monitoring systems that use probes embedded in the concrete, for later integration in tools of maintenance management, with the objective of identifying processes that indicate the possibility of the development of phenomena of degradation of the concrete or of corrosion of the reinforcement inserted therein. The electrochemical systems allow to evaluate changes in the ionic conductivity of the concrete resulting from its chemical contamination and the corrosion phenomena of the reinforcement, occurring in the advanced stages of the degradation process. The methodology adopted involved laboratory tests and the monitoring of an equipment in operation in a WWTP. In the laboratory, two sets of tests were carried out with reinforced concrete test pieces. The first group of specimens was subjected to the action of chlorides and the second group were exposed to attack by sodium and magnesium sulfates. At the WWTP the performance of the ionic resistivity monitoring system of the concrete subjected to urban waste water was tested in three zones with different exposures. In the laboratory specimens, four different concrete reinforcement solutions were used, unprotected reinforcement and painted with acrylic paint and protected reinforcement by galvanization and through impressed current. All probes were monitored with two electrochemical monitoring systems. The first system uses probes that measure the ionic resistivity of the concrete and consists of a pair of equal electrodes, 30 mm in diameter and 50 mm high. These electrodes were placed with a 50 mm spacing. The other system consists of a single block that integrates the connection to the specimen armature, two reference electrodes (graphite), two stainless steel electrodes and two mild steel electrodes, which allows the measurement of the corrosion potential and the resistance of polarization of the reinforcement. The results obtained during this work show that the structure monitoring is a valid tool to integrate the maintenance management systems, allowing to identify concrete degradation processes and to detect the beginning of the corrosion of the reinforcement. With the use of two monitoring systems, it was possible to observe the degradation process of the reinforced concrete, which in the first phase involves changes in the ionic resistivity of the concrete and, in a second phase, leads to a fall in corrosion potential and linear polarization of the armatures signaling the beginning of the process of corrosion of these. Throughout the tests it was possible to detect differences in behavior between the various types of reinforcement used, and it was verified that the galvanized reinforcements showed a better behavior against the action of the chlorides than the current or coated reinforcements.
The reinforced concrete constructions, regardless of all the technological developments reached, have a limited durability in time due to their interaction with the surrounding environment. Structural projects tend to define the horizon of 50 years for their service life and, in exceptional cases due to the cost or relevance of the work, 100 years of service life. Although there is a legal framework that defines the criteria to be adopted to achieve these levels of durability, there are many examples of early aging of buildings and infrastructures, which translates into high economic and social costs resulting from the need to carry out repair work not forseen or by reducing the levels of service available. One way to mitigate the effects of aging structures can be to implement maintenance management systems that allow problems to be detected and repaired through early detection to extend their life. The digitization of the construction sector, namely by introducing the BIM methodology to manage the entire construction process, can be the key to anchoring new models and maintenance management systems. In this scenario the monitoring of the degradation of the structures with sensors will allow to collect information integrable in maintenance tools interconnected to 3D models and the database of the buildings. The focus of this thesis is the analysis and treatment of information on the degradation state of reinforced concrete structures, obtained with the aid of electrochemical monitoring systems that use probes embedded in the concrete, for later integration in tools of maintenance management, with the objective of identifying processes that indicate the possibility of the development of phenomena of degradation of the concrete or of corrosion of the reinforcement inserted therein. The electrochemical systems allow to evaluate changes in the ionic conductivity of the concrete resulting from its chemical contamination and the corrosion phenomena of the reinforcement, occurring in the advanced stages of the degradation process. The methodology adopted involved laboratory tests and the monitoring of an equipment in operation in a WWTP. In the laboratory, two sets of tests were carried out with reinforced concrete test pieces. The first group of specimens was subjected to the action of chlorides and the second group were exposed to attack by sodium and magnesium sulfates. At the WWTP the performance of the ionic resistivity monitoring system of the concrete subjected to urban waste water was tested in three zones with different exposures. In the laboratory specimens, four different concrete reinforcement solutions were used, unprotected reinforcement and painted with acrylic paint and protected reinforcement by galvanization and through impressed current. All probes were monitored with two electrochemical monitoring systems. The first system uses probes that measure the ionic resistivity of the concrete and consists of a pair of equal electrodes, 30 mm in diameter and 50 mm high. These electrodes were placed with a 50 mm spacing. The other system consists of a single block that integrates the connection to the specimen armature, two reference electrodes (graphite), two stainless steel electrodes and two mild steel electrodes, which allows the measurement of the corrosion potential and the resistance of polarization of the reinforcement. The results obtained during this work show that the structure monitoring is a valid tool to integrate the maintenance management systems, allowing to identify concrete degradation processes and to detect the beginning of the corrosion of the reinforcement. With the use of two monitoring systems, it was possible to observe the degradation process of the reinforced concrete, which in the first phase involves changes in the ionic resistivity of the concrete and, in a second phase, leads to a fall in corrosion potential and linear polarization of the armatures signaling the beginning of the process of corrosion of these. Throughout the tests it was possible to detect differences in behavior between the various types of reinforcement used, and it was verified that the galvanized reinforcements showed a better behavior against the action of the chlorides than the current or coated reinforcements.
Description
Keywords
Estruturas de betão armado - Durabilidade Estruturas de betão armado - Tipologias de degradação Estruturas de betão armado - Monitorização e manutenção