• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.766-769
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• 2010

본 논문은 콘크리트 구조물 중 원전구조물에서 열화요인에 따른 미세구조적 변화에 대해서 평가하였다. 이는 원전구조물의 경우 열화현상이 발생하게 되면 일반 구조물에 비해 심각한 영향을 초래하기 때문에 기존의 열화 평가 방법에 의존하기 보다는 미세구조적 관점에서 콘크리트의 열화를 재평가해야 한다. 그에 일환으로 열화 요인 중 동결 융해와 황산염에 대한 미세구조 평가를 실시하였다. 동결융해의 경우, 미세구조적 관점에서의 미세공극의 양이 증가하는 것을 확인하였으나 그 증가 폭이 크지 않음을 알 수 있었으며, 물리적 실험에서도 그 변화가 매우 작음을 확인할 수 있다. 그리고 황산염에서는 초지 침지 구간에서는 플라이 애쉬를 사용한 원전 콘크리트 배합이 콘크리트에 더 유리하게 작용함을 알 수 있다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.1
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• pp.1-7
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• 2023

A set of foamed concrete specimens with different densities were prepared, and several microscopic techniques, such as scanning electron microscope (SEM) and X-ray micro-computed tomography (micro-CT) were used to characterize the foamed specimens. The pore and solid characteristics of the specimens at different ages were examined to investigate the effect of aging on the materials. The compressive strength and the thermal conductivity of the foamed specimens were also evaluated, and the relationship between the material characteristics and properties was integrated to identify the effect of density and aging on the material properties.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.3
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• pp.90-96
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• 2018

In this study, the mechanical and micro-structural change of cement pastes incorporating Stainless-Steel Slag Argon Oxygen Decarburization Slag (STS-A) containing ${\gamma}-C_2S$ as a carbon capture materials were investigated with carbonation curing condition. ${\gamma}-C_2S$ is non-hydraulic, therefore does not react with water. But ${\gamma}-C_2S$ has a reactivity under carbonation curing condition with water. The reaction products fill up the pore in pastes. The microstructure of STS-A blended cement pastes could be densified by this reaction. The pore structure of cement pastes incorporating STS-A was measured using mercury intrusion porosimetry (MIP) after carbonation curing ($CO_2$ concentration is about 5%). Also the fractal characteristics were investigated for the effect of carbonation curing on the micro-structural change of paste specimens. From the results, the compressive strength of carbonated specimens incorporating STS-A increased and pore-structure of carbonated paste is more complicated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.2
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• pp.207-217
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• 2016

Permeability can not be expressed as a function of porosity alone, it depends on the porosity, pore size and distribution, and tortuosity of pore channels in concrete. There has been considerable interest in the relationship between microstructure and transport in cementitious materials, however, it is very rare to deal with the theoretical study on gas permeability coefficient in connection with carbonation of concrete and the effect of volumetric fraction of cement paste or aggregate on the permeability coefficient. The majority of these researches have not dealt with this issue combined with carbonation of concrete, although carbonation can significantly impact on the permeability coefficient of concrete. In this study, fundamental approach to compute gas permeability of (non)carbonated concrete is suggested. For several compositions of cement pastes, the gas permeability coefficient was calculated with the analytical formulation, followed by a microstructure-based model. For carbonated concrete, reduced porosity was calculated and this was used for calculating the gas permeability coefficeint. As the result of calculation of gas permeability for carbonated concrete, carbonation leaded to the significant reduction of gas permeability coefficient and this was obvious for concrete with high w/c ratio. Meanwhile, the relationship between gas permeability and water permeability has a linear function for cement paste based on Klinkenberg effect, however, which is not effective for concrete. For the evidence of the modeling, YOON's test was accomplished and these results were compared to each other.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.36 no.5
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• pp.339-346
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• 2023

The uncertainties of microstructural features affect the properties of materials. Numerous pores that are randomly distributed in materials make it difficult to predict the properties of the materials. The distribution of pores in cementitious materials has a great influence on their mechanical properties. Existing studies focus on analyzing the statistical relationship between pore distribution and material responses, and the correlation between them is not yet fully determined. In this study, the mechanical response of cementitious materials is predicted through an image-based data approach using a convolutional neural network (CNN), and the correlation between pore distribution and material response is analyzed. The dataset for machine learning consists of high-resolution micro-CT images and the properties (tensile strength) of cementitious materials. The microstructures are characterized, and the mechanical properties are evaluated through 2D direct tension simulations using the phase-field fracture model. The attributes of input images are analyzed to identify the spot with the greatest influence on the prediction of material response through CNN. The correlation between pore distribution characteristics and material response is analyzed by comparing the active regions during the CNN process and the pore distribution.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.1038-1041
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• 2004

In this study, developed a micro-level experimental setup to measure pore pressure and poroelastic modulus in various strain and strain rate about a stress in micro-structure of bone tissue. It is essential device in the development of the model to analysis the interstitial bone fluid flow of the lacuno-canalicular system to be known that would effect on the bone remodeling. The constitution of the experimental setup is as follows, microscopic image processing system; actuator control unit; load measurement system. A pilot study was used an artificial chemical wood to have similar poroelastic property of bone matrix and conducted to validate the suitability of the measurement system.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.647-656
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• 2011

In radioactive waste repositories constructed in underground, concrete member could be in contact with groundwater for a long time. However, this pure water creates concentration gradients which lead to the diffusion of Ca ions from the pore water and the degradation of underground concrete. Therefore, this study is aimed at investigating the alteration of pore structure and loss of compressive strength associated with dissolution. The results showed that as the leaching period became longer, the pore volume within 50 nm to 500 nm in diameter is greatly increased. Also, the volume of pores larger than 200 nm rapidly increased during initial leaching time and those below 200 nm gradually increased. Furthermore, the compressive strength gradually decreased with increase of degraded thickness. The residual strength of the degraded concrete with OPC was in the range of 33% to 58%.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.639-647
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• 2009

In order to evaluate the durability of reinforced concrete structures under chloride attack from sea water and frost damage, it is important to analyze both the microstructural characteristics of concrete and its diffusion resistance of concrete against chloride ingress. In this study, a relation between micro-pore structures of concrete obtained by the Mercury Intrusion Porosimetry and accelerated chloride diffusivity as well as long term chloride diffusivity were studied for ground granulated blast furnace slag(GGBS) concrete. Different water-cement ratio of 40, 45, 50% and different unit cement concrete of 300, 350, 400 or 450 kg/$m^3$ of the GGBS concrete along with OPC concrete were used and freeze and thawing, and the change in diffusivity and microstructure were observed for both GGBS concrete and damaged GGBS concrete due to rapid freezing and thawing.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.2
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• pp.127-134
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• 2021

A hydrophobic emulsion consisting of PMHS and PVA was mixed into a cement mortar to observe changes in cement hydrate and microstructure, and to experimentally evaluate compressive strength and flexural strength. The hydrophobic emulsion was added with metakaolin and PVA fibers, and the stirring speed and sequence were adjusted to prepare a shell-concept hydrophobic emulsion. It was then mixed when mixing mortar to enhance filling of the internal pores and change of the hydrates. It was observed that the mortar mixed with a hydrophobic emulsion was filled with micropores and a coating film was formed on the surface of the hydrates by the emulsion. It was analyzed that the total pore area and porosity of the mortar mixed with the emulsion decreased from 30% to 60% compared to OPC, excluding the 50MK variable, which was extremely reduced and the median pore diameter decreased in some variables. It was also found that the compressive strength of the mortar mixed with emulsion 1% was increased up to 20%, but the strength of the mortar specimen mixed with 2% decreased to 50%.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.4
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• pp.419-426
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• 2020

Understanding the pore structure including pore shape and connectivity in unconventional reservoirs is essential to increase the recovery rate of unconventional energy resources such as shale gas and oil. In this study, we found analysis condition to probe the nanoscale pore structure in shale reservoirs using Focused Ion Beam (FIB) and Ion Milling System (IMS). A-068 core samples from Liard Basin are used to probe the pore structure in shale reservoirs. The pore structure is analyzed with different pretreatment methods and analysis condition because each sample has different characteristics. The results show that surface milling by FIB is effective to obtain pore images of several micrometers local area while milling a large-area by IMS is efficient to observe various pore structure in a short time. Especially, it was confirmed that the pore structure of rocks with high content of carbonate minerals and high strength can be observed with milling by IMS. In this study, the analysis condition and process for observing the pore structure in the shale reservoirs is established. Further studies are needed to perform for probing the effect of pore size and shape on the enhancement of shale gas recovery.