Dosagem de concreto autoadensável para produção de postes de concreto armado expostos à ambiente litorâneo
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Data
2018-10-10
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Mascolo, Rafael
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No Brasil, até a segunda metade do século passado, as redes de energia elétrica existentes eram compostas principalmente por postes de madeira. No entanto, com o aumento da demanda, foi necessária a construção de redes com maior capacidade, implicando em um significativo crescimento da procura por postes de
concreto armado, visto que estes apresentam maior resistência e durabilidade que os de madeira, aumentando a vida útil das estruturas. Dessa maneira, se mostra importante a realização de estudos que busquem adequar a vida útil dessas estruturas em relação ao desempenho requerido. Um dos parâmetros determinantes na durabilidade de postes de concreto armado é a qualidade do concreto, que além das propriedades mecânicas é o responsável pela proteção das armaduras em relação ao ingresso de agentes agressivos no meio em que está exposto. Considerando zonas naturais não poluídas, o ambiente marinho é o que apresenta maior índice de agressividade, pois os íons de cloreto, presentes em ambientes próximos ao mar, são extremamente agressivos às armaduras e consequentemente causam a degradação das estruturas de concreto armado. Assim, a partir de um traço de concreto autoadensável empregado por uma empresa fabricante de postes de concreto armado da cidade de Teutônia/RS, foi proposta uma adequação a mistura utilizada para que atenda as exigências de desempenho estabelecidas pela NBR 8451-1 (ABNT, 2011) para a classe de agressividade ambiental III, procurando adequar as características relacionadas à durabilidade e ao custo-benefício do traço utilizado, substituindo parte do cimento por adições minerais. Assim sendo, foram
desenvolvidos 5 traços, um referência, similar ao utilizado na fábrica, e outros quatro traços com teores de 10% e 20% de cinza de casca de arroz e sílica ativa em substituição ao cimento. Para avaliar as propriedades de durabilidade das misturas, foram realizados ensaios de trabalhabilidade, resistência à compressão, absorção de água por imersão, penetração de cloretos, e por fim, uma análise de custos para determinar qual o traço com maior viabilidade financeira de aplicação. Conclui-se que os traços com utilização de 10% e 20% de sílica ativa atenderam o desempenho mínimo requerido pela empresa e pelas normas vigentes, sendo que o traço com 10% de sílica ativa destacou-se como sendo o mais barato a ser empregado.
In Brazil, until the second half of the last century, the existing electric power network were composed mainly of wooden poles. However, with the increase in demand, it was necessary to build networks with higher capacity, implying a significant increase in the demand for reinforced concrete poles, since these have greater strength and durability than the ones of wood, increasing the useful life of the structures. Thus, it is important to carry out studies that seek to adapt the useful life of these structures regarding the required performance. One of the determining parameters in the durability of reinforced concrete poles is the concrete quality, which besides the mechanical properties is responsible for the protection of the reinforcement considering the entrance of aggressive agents in the environment where it is exposed. Considering non-polluted natural areas, the marine environment is the one with the highest aggressiveness, because the chloride ions, present in environments near the sea, are extremely aggressive to the reinforcement and consequently cause the degradation of the structures of reinforced concrete. Therefore, from a self- compacting concrete trait used by a manufacturer of reinforced concrete poles in the Vale do Taquari region, a suitability was proposed for the mixture used to meet the performance requirements established by NBR 8451-1 (ABNT, 2011) for the environmental aggression class III, seeking to adapt the characteristics related to the durability and cost-benefit of the traces used, replacing part of the cement with mineral additions. So 5 traces were developed, a reference, similar to the one used in the factory, and other four traces with contents of 10% and 20% of rice husk ash and active silica replacing the cement. In order to evaluate the durability properties of the mixtures, tests of workability, compressive strength, water absorption by immersion and chloride penetration were performed, and finally, a cost analysis was carried out to determine which trait had the highest financial feasibility of application. The conclusion was that the traces using 10% and 20% of active silica met the minimum performance required by the company and the current standards, and the trace with 10% active silica stood out as being the cheapest to be used.
In Brazil, until the second half of the last century, the existing electric power network were composed mainly of wooden poles. However, with the increase in demand, it was necessary to build networks with higher capacity, implying a significant increase in the demand for reinforced concrete poles, since these have greater strength and durability than the ones of wood, increasing the useful life of the structures. Thus, it is important to carry out studies that seek to adapt the useful life of these structures regarding the required performance. One of the determining parameters in the durability of reinforced concrete poles is the concrete quality, which besides the mechanical properties is responsible for the protection of the reinforcement considering the entrance of aggressive agents in the environment where it is exposed. Considering non-polluted natural areas, the marine environment is the one with the highest aggressiveness, because the chloride ions, present in environments near the sea, are extremely aggressive to the reinforcement and consequently cause the degradation of the structures of reinforced concrete. Therefore, from a self- compacting concrete trait used by a manufacturer of reinforced concrete poles in the Vale do Taquari region, a suitability was proposed for the mixture used to meet the performance requirements established by NBR 8451-1 (ABNT, 2011) for the environmental aggression class III, seeking to adapt the characteristics related to the durability and cost-benefit of the traces used, replacing part of the cement with mineral additions. So 5 traces were developed, a reference, similar to the one used in the factory, and other four traces with contents of 10% and 20% of rice husk ash and active silica replacing the cement. In order to evaluate the durability properties of the mixtures, tests of workability, compressive strength, water absorption by immersion and chloride penetration were performed, and finally, a cost analysis was carried out to determine which trait had the highest financial feasibility of application. The conclusion was that the traces using 10% and 20% of active silica met the minimum performance required by the company and the current standards, and the trace with 10% active silica stood out as being the cheapest to be used.
Descrição
Palavras-chave
Poste de concreto; Concreto autoadensável; Durabilidade; Adições minerais
Citação
BRENTANO, Luis Carlos. Dosagem de concreto autoadensável para produção de postes de concreto armado expostos à ambiente litorâneo. 2018. Monografia (Graduação em Engenharia Civil) – Universidade do Vale do Taquari - Univates, Lajeado, 04 jul. 2018. Disponível em: http://hdl.handle.net/10737/2251.