Degradação do concreto de uma Estação de Tratamento de Esgoto (ETE) por ácido sulfúrico biogênico
Abstract
RESUMO
Em ETEs, o ataque ácido (associado ao ataque por sulfatos como consequência secundária) afeta a pasta de cimento formando etringita e/ou gipsita, provocando expansão, fissuração e friabilidade do material. Este mecanismo de degradação do concreto atinge, também, o C-S-H, reduzindo a capacidade portante e a vida útil da estrutura. O objetivo deste trabalho é apresentar resultados de uma inspeção de uma ETE em funcionamento há aproximadamente 15 anos, onde há visÃvel degradação do concreto por ataque combinado de ácido e sulfato. A análise contempla resultados de amostra coletada em região imediatamente acima do nÃvel do efluente, onde há maior concentração de bactérias, e de testemunho extraÃdo da laje de cobertura do tanque de tratamento. A resistência à compressão do testemunho atende o valor especificado no projeto, apesar de ensaios de microscopia eletronica de varredura e difração de raios-X identificarem a formação de gipsita e etringita no interior do concreto.
Palavras chaves: ataque ácido; ataque por sulfatos; durabilidade; concreto armado.
ABSTRACT
At sewage treatment plants, acid attack (and sulfate attack as a secondary consequence) degrades the cement paste, forming ettringite and/or gypsum, causing expansion, cracking and brittleness. The degradation mechanism of concrete in sewage treatment plants also affects the calcium silicate hydrate (C-S-H), reducing the mechanical capacity and service life. The aim of this paper is to present results of the inspection of a sewage treatment plant, which has been operating for about 15 years, where there is noticeable degradation of concrete by a combined acid and sulfate attack. The analysis includes results of a sample collected in the region immediately above the effluent, which had the highest concentration of bacteria and a specimen extracted from the treatment tank slab. Compressive strength of the specimen is consistent with the project, although scanning electron microscopy images and X-ray diffraction identified the formation of gypsum and ettringite within the concrete.
Keywords: acid attack; sulphate attack; durability; reinforced concrete.
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References
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