Desenvolvimento de nanopartículas de hidróxidos duplos lamelares (HDL) de Mg e Al intercalados com ânions carbonato para aplicação em materiais cimentícios
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Data
2019-09-13
Autores
Almeida, Adriana de Araújo
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Universidade Estadual Paulista (Unesp)
Resumo
Os hidróxidos duplos lamelares (HDL) são argilas aniônicas também conhecidas como compostos do tipo hidrotalcita, esses materiais são amplamente estudados devido a uma importante propriedade denominada de efeito memória. O efeito memória consiste na regeneração da estrutura lamelar a partir dos precursores óxidos mistos dos metais componentes (CHDL) em contato com água ou soluções aniônicas. Os óxidos mistos obtidos pela decomposição térmica do HDL, podem ser incorporados ao cimento hidratado, de modo a auxiliar no preenchimento de poros durante a regeneração da estrutura lamelar e na imobilização de ânions indesejados. Logo, contribuindo para aprimorar as propriedades de materiais cimentícios a partir da redução da porosidade, ganho de resistência mecânica, alterando o processo de hidratação e melhorando o comportamento reológico do cimento. No presente trabalho, investigou-se a viabilidade da aplicação dos CHDL, derivados da calcinação à 500 °C de nanopartículas de HDL (Mg-Al) intercaladas com ânions carbonato, como aditivos no cimento Portland CPV. A cinética de regeneração dos óxidos mistos em contato com água deionizada e água de cimento foi acompanhado pela técnica de espalhamento de raios X a alto ângulo (WAXS), o que possibilitou verificar que a restruturação do HDL ocorre nos primeiros 10 min do contato com as soluções aquosas analisadas. Ademais, a análise de WAXS permitiu constatar que as partículas das amostras calcinadas foram capazes de regenerar a estrutura lamelar tanto nas soluções quanto na pasta do cimento. Os espaçamentos basais foram calculados por meio dos dados de difração de raios X (DRX) para as amostras de HDL antes e após a regeneração em água de cimento, água deionizada e soluções simuladas de poros de cimento (SCPS1 e SCPS2). Esses resultados mostraram a elevada capacidade do HDL em intercalar ânion carbonato, um dos principais íons responsáveis pela corrosão de estrutura metálica no concreto armado pelo processo de carbonatação. Quando adicionadas ao cimento, as nanopartículas de óxido misto alteraram o comportamento reológico da pasta, contribuindo para a rápida consolidação da mesma. Ademais, o aditivo influenciou significativamente no fluxo de calor liberado durante as reações de hidratação, na estrutura porosa e com a redução expressiva da área específica do cimento hidratado.
Layered double hydroxides (LDH) are anionic clays also known as hydrotalcite-like compounds, these materials are widely studied because of an important property called memory effect. The memory effect consists of the regeneration of the lamellar structure from the mixed metal oxide precursors of the component metals in contact with water or anionic solutions. The mixed metal oxides obtained by the thermal decomposition of LDH can be incorporated into the cement, in order to assist in the filling of faults during the regeneration of the lamellar structure and in the immobilization of undesired anions. Thus, contributing to improve the properties of cementitious materials by reducing porosity, increasing mechanical resistance, altering the hydration process and improving the rheological behavior of cement. In the present work, the feasibility of the application of the mixed oxides as additives in the cement Portland CPV using LDH (Mg-Al) nanoparticles intercalated with carbonate anions calcined at 500 ° C. The regeneration kinetics of the lamellar structure induced by the addition of deionized water and cement water were studied in situ by time-resolved wide-angle X-ray scattering (WAXS), suggesting that recovery of the LDH structure occurs in the first 10 min of the contact of the mixed oxide with the analyzed solutions. In addition, the WAXS results allowed verifying that the calcined LDH particles were able to regenerate the lamellar structure also when incorporated in the paste of the cement. The basal spacing were calculated by X-ray diffraction (XRD) data for HDL samples before and after regeneration in cement water, deionized water and simulated cement pore solutions (SCPS1 and SCPS2). These results showed the high capacity of HDL in the intercalation of carbonate anion, one of the main ions responsible for the corrosion of metallic structure in the reinforced concrete by the carbonation process. When added to the cement, the mixed oxide nanoparticles changed the rheological behavior of the paste, contributing to the rapid consolidation of the same. In addition, the additive significantly influenced the flow of heat released during the hydration reactions, as well as the porous structure and reducing specific surface area of the cement.
Layered double hydroxides (LDH) are anionic clays also known as hydrotalcite-like compounds, these materials are widely studied because of an important property called memory effect. The memory effect consists of the regeneration of the lamellar structure from the mixed metal oxide precursors of the component metals in contact with water or anionic solutions. The mixed metal oxides obtained by the thermal decomposition of LDH can be incorporated into the cement, in order to assist in the filling of faults during the regeneration of the lamellar structure and in the immobilization of undesired anions. Thus, contributing to improve the properties of cementitious materials by reducing porosity, increasing mechanical resistance, altering the hydration process and improving the rheological behavior of cement. In the present work, the feasibility of the application of the mixed oxides as additives in the cement Portland CPV using LDH (Mg-Al) nanoparticles intercalated with carbonate anions calcined at 500 ° C. The regeneration kinetics of the lamellar structure induced by the addition of deionized water and cement water were studied in situ by time-resolved wide-angle X-ray scattering (WAXS), suggesting that recovery of the LDH structure occurs in the first 10 min of the contact of the mixed oxide with the analyzed solutions. In addition, the WAXS results allowed verifying that the calcined LDH particles were able to regenerate the lamellar structure also when incorporated in the paste of the cement. The basal spacing were calculated by X-ray diffraction (XRD) data for HDL samples before and after regeneration in cement water, deionized water and simulated cement pore solutions (SCPS1 and SCPS2). These results showed the high capacity of HDL in the intercalation of carbonate anion, one of the main ions responsible for the corrosion of metallic structure in the reinforced concrete by the carbonation process. When added to the cement, the mixed oxide nanoparticles changed the rheological behavior of the paste, contributing to the rapid consolidation of the same. In addition, the additive significantly influenced the flow of heat released during the hydration reactions, as well as the porous structure and reducing specific surface area of the cement.
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Palavras-chave
Hidróxidos duplos lamelares, Cimento Portland, Óxidos metálicos, Nanopartículas, Layered double hydroxides, Metal oxides, Portland cement, Nanoparticles