Evaluation of the effect of varying the workability in concrete pore structure by using X-ray microtomography

Bernardes, E. E.; Magalhães, Aldo Giuntini de; Vasconcelos, Wander L.; Nunes, Eduardo H.M.

doi:10.1590/s1983-41952013000400005

Cited by 2 publications

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References 11 publications

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“…When the binarized images are compared to the grayscale images, it is concluded that the material present in the outer region (green) of the specimen has a lower density, since in the gray scale, this region has become darkest. Similar results have been found in other studies [15]. Specifically in this analysis, it was not possible to detect the densification of the outer layer of the specimen, due to formation of CaCO 3 .…”

Section: Figuresupporting

confidence: 90%

“…Specimens with reduced sizes were used in order to make the sample compatible with the reading capacity of the X-ray microtomography equipment used in this research [15]. The molding of the test specimens was done according to the procedures established by standard NBR 7215 [16] and was carried out in an environment with relative humidity of (65 ± 2) %, and temperature of (26 ± 1.0) ºC.…”

Section: Dosage Molding and Curing Of Specimensmentioning

confidence: 99%

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Monitoring the carbonation front progress in a cementitious composite having its pore structure analyzed through μ-CT imaging

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Magalhães

Bernardes

et al. 2017

Rev. IBRACON Estrut. Mater.

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Monitoring the carbonation front progress in a cementitious composite having its pore structure analyzed through µ-CT imaging Acompanhamento do avanço da frente de carbonatação em compósito cimentício com sua estrutura de poros analisada por microtomografia computadorizada de raios X (µ-CT) Abstract ResumoThe carbonation process is one among the primary factors that cause a reduction in the hydrogen ionic potential (pH) of cementitious composites that may lead to a depassivation of the reinforcement structures, thus furnishing conditions for corrosion processes to begin. In this paper, the research sought to monitor the advancement of the carbonation front in compliance with the European standard, EN 14630, whilst concurrently measuring the pH variation on the surface of the cementitious composite. Cylindrical mortar specimens of (2x4) cm were placed in a carbonation chamber, keeping up the humidity 65%, temperature 28° C and a CO 2 concentration of 5%. The structure of voids in the matrix was assessed with the µ-CT imaging technique. The pH reading enabled the monitoring of the carbonation front progress as a function of the loss of alkalinity, before the process established by standard EN 14630. The images obtained by µ-CT did not enable the visualization of the densification of the material found in the outer layer of the specimen.Keywords: mortar, carbonation, pH, Xray microtomography.O processo de carbonatação é um dos causadores da redução do potencial hidrogeniônico (pH) em compósitos cimentícios, o qual pode levar a despassivação das armaduras, dando condições ao início de um processo de corrosão. Neste trabalho, buscou-se acompanhar o avanço da frente de carbonatação conforme a norma europeia EN 14630 paralelamente à medição da variação do pH na superfície do compósito cimentício. Foram utilizados corpos de prova cilíndricos (CP) de argamassa, com dimensão de (2x4) cm, acondicionados em câmara de carbonatação com condições controladas, mantendo-se a umidade em 65 %, a temperatura em 28º C e a concentração de CO 2 em 5 %. A estrutura de vazios da matriz foi avaliada por meio da técnica de microtomografia computadorizada de raios X (µ-CT). A leitura de pH permitiu um monitoramento do avanço da frente de carbonatação, em função da perda de alcalinidade, antes do processo estabelecido na norma EN 14630. As imagens obtidas por meio da µ-CT não permitiram visualizar a densificação do material presente na camada mais externa do CP.Palavras-chave: argamassa, carbonatação, pH, microtomografia de raios X.

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Section: Figuresupporting

confidence: 90%

Section: Dosage Molding and Curing Of Specimensmentioning

confidence: 99%

Monitoring the carbonation front progress in a cementitious composite having its pore structure analyzed through μ-CT imaging

Lacerda

Magalhães

Bernardes

et al. 2017

Rev. IBRACON Estrut. Mater.

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“…The study showed that the comparison of porosity results obtained from the techniques of picnometry and microtomography may be feasible [2,23], however, the sample preparation process should be reevaluated, especially with regard to the use of temperature for drying the material at earlier ages, since the procedure was feasible for the age of 28 days, but influenced the results at 7 days. The large number of studies addressing the pore microstructure of cementitious materials, and especially the use of μ-CT, emphasizes the need to elaborate a procedure for the preparation of specimens with reduced dimensions.…”

Section: Discussionmentioning

confidence: 99%

“…In general, the methodologies adopted in these studies involve the molding of test specimens from which the samples are extracted. To perform this extraction, the processes of fragmentation or extraction of testimony are mainly used [2][3][4]. However, these processes may lead to micro-fissures, thus causing alterations in the microstructure of the materials.…”

Section: Introductionmentioning

confidence: 99%

Characterization of test specimens produced in reduced size for X-ray microtomography (µ-CT) tests

Bernardes

Magalhães

Vasconcelos

et al. 2017

Rev. IBRACON Estrut. Mater.

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ResumoThe need to use reduced sample sizes, in order to attain improved spatial resolution in (µ-CT) tests applied in Portland cement composites, makes researchers perform the fractionation of materials to obtain samples with dimensions compatible with the capacity of the scanning equipment, which might cause alterations in the microstructure under analysis. Therefore, a test specimen (TS) with dimensions compatible with the scanning capacity of a microtomography system that operates with an X-ray tube and voltage ranging from 20 to 100 kV was proposed. Axial compression strength tests were made and their total porosity was assessed by an apparent density and solid fraction density ratio, which were obtained by means of mercury and helium pycnometry and µ-CT technique, respectively. The adoption of that TS has shown to be viable for providing a sample with a higher level of representation.Keywords: X-ray microtomography, fractionation of samples, test specimen, pycnometry, pore structure.A necessidade de se utilizar amostras de tamanho reduzido, para a obtenção de uma melhor resolução espacial nos ensaios de µ-CT em compósitos de cimento Portland, leva os pesquisadores a realizar o fracionamento do material para a obtenção de amostras com dimensões compatíveis com a capacidade de leitura do equipamento, o que pode ocasionar alterações da microestrutura em análise. Assim, foi proposto um corpo de prova (CP) com dimensões compatíveis com a capacidade de leitura de um microtomógrafo com tubo de raios X que opera dentro de um intervalo de tensão de 20 a 100 kV.Foram realizados testes de resistência à compressão axial e avaliação da sua porosidade total por meio da relação entre a densidade aparente e a densidade da fração sólida, obtidas respectivamente pelas técnicas de picnometria (de mercúrio e hélio) e pela técnica de µ-CT. A adoção deste CP se mostrou viável por proprocionar uma amostragem com maior nível de representatividade.Palavras-chave: microtomografia de raios X; fracionamento de amostras, corpo de prova, picnometria, estrutura de poros.

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Evaluation of the effect of varying the workability in concrete pore structure by using X-ray microtomography

Cited by 2 publications

References 11 publications

Monitoring the carbonation front progress in a cementitious composite having its pore structure analyzed through μ-CT imaging

Monitoring the carbonation front progress in a cementitious composite having its pore structure analyzed through μ-CT imaging

Characterization of test specimens produced in reduced size for X-ray microtomography (µ-CT) tests

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