Study on the incorporation of sewage sludge ash in alkali-activated materials
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Data
2021-07-21
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Universidade Estadual Paulista (Unesp)
Resumo
O manejo sustentável e inteligente de resíduos urbanos é uma questão primordial para garantir que futuras gerações tenham as condições de viver em equilíbrio com a natureza e o meio urbano. Da mesma maneira, garantir que no futuro existam materiais alternativos e sustentáveis para a construção civil também é necessário para tal equilíbrio. Neste sentido, os materiais ativados alcalinamente são interessantes por abranger sistemas que incorporam resíduos de origem urbana, industrial e agro-industrial como matéria-prima. Por definição, os materiais ativados alcalinamente são produtos resultantes de reações químicas que se iniciam em decorrência de um ataque alcalino à precursores ricos em cálcio e/ou silica e alumina. Com base em estudos recentes que apontam estes sistemas como uma alternativa para a imobilização de cinza de lodo de esgoto (SSA), este trabalho avaliou os efeitos da incorporação de SSA como precursor em substituição ao metacaulim (MK) e à escória de alto-forno (BFS) para a produção de argamassas ativadas alcalinamente, assim como a otimização desses sistemas em termos de resistência à compressão. Inicialmente, a SSA, obtida por meio de uma auto-combustão do lodo de esgoto, foi caracterizada físico-químicamente, assim como sua reatividade química foi avaliada. O desempenho mecânico de argamassas à base de MK e SSA foi avaliado por meio de ensaios de resistência à compressão, e pastas foram quimicamente avaliadas através de análises de difração de raio-X (XRD), espectroscopia de infra-vermelho por transformada de Fourier (FTIR), termogravimetria (TG/DTG) e microscopía eletrônica de varredura (SEM). Por fim, uma otimização do ativador alcalino foi realizada por meio da pré-ativação de cinza de casca de arroz (RHA) para produção de sistemas binários de SSA e BFS, sendo estes sistemas mecanicamente avaliados por resistência à compressão. Para a caracterização destes sistemas binários (pastas), análises de XRD, TG/DTG, SEM, e porosimetria por intrusão de mercúrio foram realizadas. De acordo com os resultados, apesar de apresentar um moderado comportamento pozolânico em misturas com cimento Portland, a SSA desmonstrou um baixa reatividade em materiais ativados alcalinamente. Em geral, a substituição de MK ou BFS por SSA diminui a resistência à compressão das argamassas. Porém, em determinadas condições, como para argamassas à base de MK e SSA em cura térmica (banho térmico, 65°C), a SSA ofereceu um retardo da perda de resistência à compressão, que ocorre devido a cristalização da matriz geopolimérica. A performance mecânica dos sistemas binários compostos por BFS e SSA foi melhorada em função da pré-ativação da RHA, empregada na forma de ativador alcalino, o que permitiu produzir argamassas com até 40% de SSA em sua constituição, alcançando uma resistência à compressão de até 30 MPa.
The sustainable and smart management of urban wastes is a key issue to ensure that future generations can live in balance with nature and the urban environment. Similarly, sustainable materials for building construction are also necessary to guarantee such a balance. Therefore, alkali-activated materials are an interesting option by incorporate by-products and urban wastes from the agro-industry as raw material. The alkali-activated materials (AAMs) result from chemical reactions that start due to an alkaline attack on precursor materials that contain calcium and/or silica and alumina in their composition. Recently, these systems have been recognized as an alternative for the immobilization of sewage sludge ash (SSA). Accordingly, in this work, the effect of SSA incorporation in AAMs by means of replacing metakaolin (MK) and blast furnace slag (BFS) was evaluated, as well as the optimization of these systems in function of the compressive strength performance. Firstly, SSA, generated by means of uncontrolled combustion of sewage sludge, was physiochemically characterised and its chemical reactivity was evaluated. The mechanical performance of mortars based on MK and SSA were evaluated by means of compressive strength tests, as well as pastes were chemically evaluated by means of X-ray diffraction (XRD), Fourier transform infra-red fluorescence (FTIR), thermogravimetry (TG/DTG), and scanning electron microscopy (SEM). The optimization of the alkaline activator, by the pre-activation of rice husk ash (RHA), to produce binary alkali-activated mortars composed of SSA and BFS as the binder, was also carried out. These binary mortars were mechanically evaluated by compressive strength tests, as well as pastes were characterised by means of XRD, TG/DTG, SEM, and mercury intrusion porosimetry (MIP) analyses. According to the results, despite the SSA presenting a moderate reactive behaviour, characterised as pozzolanic, in AAMs showed a low reactivity. Generally, as the replacement of MK or BFS with SSA increases, the compression strength of mortars decreases. However, in geopolymeric mortars based on MK and SSA thermally cured (thermal bath, 65 ° C), SSA offers a delay in the compressive strength loss, which commonly occurs due to crystallization of the geopolymeric matrix. The mechanical performance of the binary systems composed of BFS and SSA was improved using RHA in the activator, which guarantees to produce mortars with up to 40 wt.% SSA in their composition, reaching a compressive strength of up to 30 MPa.
The sustainable and smart management of urban wastes is a key issue to ensure that future generations can live in balance with nature and the urban environment. Similarly, sustainable materials for building construction are also necessary to guarantee such a balance. Therefore, alkali-activated materials are an interesting option by incorporate by-products and urban wastes from the agro-industry as raw material. The alkali-activated materials (AAMs) result from chemical reactions that start due to an alkaline attack on precursor materials that contain calcium and/or silica and alumina in their composition. Recently, these systems have been recognized as an alternative for the immobilization of sewage sludge ash (SSA). Accordingly, in this work, the effect of SSA incorporation in AAMs by means of replacing metakaolin (MK) and blast furnace slag (BFS) was evaluated, as well as the optimization of these systems in function of the compressive strength performance. Firstly, SSA, generated by means of uncontrolled combustion of sewage sludge, was physiochemically characterised and its chemical reactivity was evaluated. The mechanical performance of mortars based on MK and SSA were evaluated by means of compressive strength tests, as well as pastes were chemically evaluated by means of X-ray diffraction (XRD), Fourier transform infra-red fluorescence (FTIR), thermogravimetry (TG/DTG), and scanning electron microscopy (SEM). The optimization of the alkaline activator, by the pre-activation of rice husk ash (RHA), to produce binary alkali-activated mortars composed of SSA and BFS as the binder, was also carried out. These binary mortars were mechanically evaluated by compressive strength tests, as well as pastes were characterised by means of XRD, TG/DTG, SEM, and mercury intrusion porosimetry (MIP) analyses. According to the results, despite the SSA presenting a moderate reactive behaviour, characterised as pozzolanic, in AAMs showed a low reactivity. Generally, as the replacement of MK or BFS with SSA increases, the compression strength of mortars decreases. However, in geopolymeric mortars based on MK and SSA thermally cured (thermal bath, 65 ° C), SSA offers a delay in the compressive strength loss, which commonly occurs due to crystallization of the geopolymeric matrix. The mechanical performance of the binary systems composed of BFS and SSA was improved using RHA in the activator, which guarantees to produce mortars with up to 40 wt.% SSA in their composition, reaching a compressive strength of up to 30 MPa.
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Palavras-chave
Cinza de lodo de esgoto, Ativação alcalina, Geopolímero, Metacaulim, Escória de alto-forno