Estudo da aderência de concretos ativados alcalinamente à base de cinza da casca de arroz e metacaulim
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Data
2019-05-21
Autores
Guimarães, Paulo Victor Campos
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Universidade Estadual Paulista (Unesp)
Resumo
A indústria do cimento Portland é responsável direta por uma carga de poluentes de significativo dano ambiental. Os Concretos Ativados Alcalinamente (CAA) são matrizes compostas por um ativador alcalino e um aglomerante alternativo. O material comumente utilizado para a ativação alcalina é o silicato de sódio, cuja fabricação também se mostra como ambientalmente nociva. O silicato de sódio, junto ao cimento Portland, podem ser dispensados, uma vez que a produção do ativador pode se dar através de um composto rico em silício (materiais pozolânicos no geral), sendo a cinza da casca de arroz (CCA) o instrumento de estudo do trabalho apresentado, e a soda cáustica como fornecedora de sódio (meio alcalino). Os concretos CAA foram definidos conforme o parâmetro ξ (CAA-ξ), que representa a relação molar entre SiO2 e Na2O, com as variações ξ = 1,2, ξ = 1,6 e ξ = 2,0, esta última representando o concreto ativado alcalinamente com maior taxa de CCA. Este trabalho tem como intuito a avaliação das propriedades mecânicas dos concretos CAA, comparando-as, em seguida, com duas tipologias de concreto com cimento Portland CPV-ARI, com distintos fatores água cimento (0,45 e 0,55). A variação na relação a/c teve como intuito a análise de duas referências com valores diferentes de fck. Os resultados demonstram que a resistência à compressão axial e diametral (sete dias de cura) para os concretos CAA se encontraram na faixa de 25 a 30 MPa, e de 1,5 a 3,5 MPA, respectivamente. Não foram observados ganhos expressivos na transição entre as idades de 7 e 28 dias, e 28 e 90 dias. Os concretos convencionais utilizados como referência atingiram resistência à compressão axial na faixa de 30 a 40 MPa, e diametral de cerca de 5 MPa, aos sete dias, apresentando um ganho significativo aos 28 e 90 dias idade. Os módulos de elasticidade dos concretos CAA resultaram valores entre 10 e 20 GPa. Já os concretos convencionais evidenciaram valores do módulo de elasticidade superiores a 25 GPa, já em idades mais curtas. Com relação à aderência, existe um distanciamento do concreto com fator água/cimento 0,45 em relação aos ativados alcalinamente, resultado este também evidenciado nas demais propriedades estudadas. Entretanto, a descrição da curva de arrancamento é similar para os dois grandes grupos trabalhados, em especial no pareamento entre as amostras CAA-2,0 e CPV-ARI 0,55, aquela sendo a de maior eficiência dentre as tipologias alternativas. Os concretos alternativos evidenciaram ganhos baixos para a tensão de aderência média nas transições entre as idades de 7, 28 e 90 dias, de modo que houve o alcance de 12,61 MPa (5mm) e 17,29 MPa (8mm) aos 90 dias para a amostra CAA-2,0. Observaram-se ganhos mais expressivos na transição das idades para as amostras de cimento Portland, de maneira que aos 90 dias as tensões de aderência médias observadas para o CPV-ARI 0,55 foram de 10,18 MPa (5mm) e 18,16 MPa (8mm). Contudo, uma clara proximidade para com a amostra CAA-2,0 foi evidenciada. Considerando a característica de sustentabilidade inerente aos concretos CAA, tais alternativas se mostram promissoras, uma vez que dadas todas as propriedades mecânicas levantadas, os concretos ativados alcalinamente trazem um comportamento mecânico eficiente, com possível aplicação em múltiplas atividades na construção civil.
The Portland cement industry is directly responsible for a load of pollutants of significant environmental damage. Alkali-Activated Concrete (AAC) is a matrix with prior activation and alternative binder. The catalyst material commonly used for prior activation is the sodium silicate, the manufacture of which is also environmentally harmful. Sodium silicate, together with Portland cement, can also be dispensed with, since the activator can be produced through a silicon-rich compound (pozzolanic materials in general), with the rice husk ash (RHA) being the instrument of study of the work presented, and caustic soda as a supplier of sodium. The AAC concretes were defined according to the parameter ξ (AAC- ξ), which represents the molar ratio of SiO2 and Na2O, with the variations ξ = 1.2, ξ = 1.6 and ξ = 2.0, the latter representing the AAC with higher RHA rate. This work intends to evaluate the mechanical properties of AAC, comparing them to two types of concrete with ordinary Portland cement with high early resistance, with different water cement factors (0.44 and 0.55). The variation in the water/binder mass ratio was intended to analyze two references with different values of compressive strength class. The results demonstrate that the axial and diametric compression strength (seven days cure) for the AAC concretes were in the range of 25 to 30 MPa, and of 1.5 to 3.5 MPA, respectively. There were no significant gains in the transition between the ages of 7 and 28 days, and 28 and 90 days. The conventional concretes used as reference reached resistance to axial compression in the range of 30 to 40 MPa, and diametric of about 5 MPa at seven days, presenting a significant gain at 28 and 90 days old. The modulus of elasticity of AAC resulted in values between 10 and 20 GPa, while the conventional concretes showed modulus of elasticity values higher than 25 GPa, at shorter ages. Regarding the adhesion, there is a distancing between the OPC concrete with a water/cement ratio of 0.45 and the alkali-activated ones. This result is also evident in the other properties studied. However, the description of the pullout curve is similar for the two main groups (alternative and reference), especially in the matching between the AAC-2.0 and OPC 0.55 samples, the first being the one with the highest efficiency among the alternative samples. The alternative concretes highlighted low gains for medium bond strength at the transitions between the ages of 7, 28 and 90 days. Hence, it was verified a range of 12.61 MPa (5mm) and 17.29 MPa (8mm) at 90 days for the AAC-2.0 type. More significant gains were observed amongst age transition for Portland cement samples, as of 90 days of test the medium bond strength observed for OPC 0.55 were 10.18 MPa (5mm) and 18.16 MPa (8mm). Yet, a clear proximity to the AAC-2.0 sample was evident. Considering the sustainability display inherent to AAC concretes, such alternatives are promising, given all the mechanical properties raised. The alkali-activated concretes bring a mechanical display of high behavior and can be applied to many construction purposes.
The Portland cement industry is directly responsible for a load of pollutants of significant environmental damage. Alkali-Activated Concrete (AAC) is a matrix with prior activation and alternative binder. The catalyst material commonly used for prior activation is the sodium silicate, the manufacture of which is also environmentally harmful. Sodium silicate, together with Portland cement, can also be dispensed with, since the activator can be produced through a silicon-rich compound (pozzolanic materials in general), with the rice husk ash (RHA) being the instrument of study of the work presented, and caustic soda as a supplier of sodium. The AAC concretes were defined according to the parameter ξ (AAC- ξ), which represents the molar ratio of SiO2 and Na2O, with the variations ξ = 1.2, ξ = 1.6 and ξ = 2.0, the latter representing the AAC with higher RHA rate. This work intends to evaluate the mechanical properties of AAC, comparing them to two types of concrete with ordinary Portland cement with high early resistance, with different water cement factors (0.44 and 0.55). The variation in the water/binder mass ratio was intended to analyze two references with different values of compressive strength class. The results demonstrate that the axial and diametric compression strength (seven days cure) for the AAC concretes were in the range of 25 to 30 MPa, and of 1.5 to 3.5 MPA, respectively. There were no significant gains in the transition between the ages of 7 and 28 days, and 28 and 90 days. The conventional concretes used as reference reached resistance to axial compression in the range of 30 to 40 MPa, and diametric of about 5 MPa at seven days, presenting a significant gain at 28 and 90 days old. The modulus of elasticity of AAC resulted in values between 10 and 20 GPa, while the conventional concretes showed modulus of elasticity values higher than 25 GPa, at shorter ages. Regarding the adhesion, there is a distancing between the OPC concrete with a water/cement ratio of 0.45 and the alkali-activated ones. This result is also evident in the other properties studied. However, the description of the pullout curve is similar for the two main groups (alternative and reference), especially in the matching between the AAC-2.0 and OPC 0.55 samples, the first being the one with the highest efficiency among the alternative samples. The alternative concretes highlighted low gains for medium bond strength at the transitions between the ages of 7, 28 and 90 days. Hence, it was verified a range of 12.61 MPa (5mm) and 17.29 MPa (8mm) at 90 days for the AAC-2.0 type. More significant gains were observed amongst age transition for Portland cement samples, as of 90 days of test the medium bond strength observed for OPC 0.55 were 10.18 MPa (5mm) and 18.16 MPa (8mm). Yet, a clear proximity to the AAC-2.0 sample was evident. Considering the sustainability display inherent to AAC concretes, such alternatives are promising, given all the mechanical properties raised. The alkali-activated concretes bring a mechanical display of high behavior and can be applied to many construction purposes.
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Palavras-chave
Geopolímeros, Materiais alternativos, Pull-out test, Geopolymers, Alternative materials