• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.4
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• pp.637-645
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• 2017

Jeju Island is composed of irregular volcanic rock layers formed by several volcanic activities. Since structure such as the offshore wind turbine has to support considerably large over turning moment due to long distance from foundation to load point and relatively large horizontal load. Pile foundations are needed to economically support such structure even in the case of rock layer. Therefore, in this study, mechanical performances are estimated by mixing ratio of water, cement, and sand to figure out optimal mixing ration of filling material for pile penetrated to rocky layers, and outcomes of this study are compared and analyzed with results of other researches. In the same conditions, mechanical performances of the mortar (S/(S+C)=20~40%) are better than those of cement paste and soil cement. On the basis of major outcome of this study, appropriate range of mixing and a strengthening model are suggested.

• Journal of the Korea Concrete Institute
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• v.20 no.1
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• pp.67-75
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• 2008

An engineered cementitious composite produced with slag particles (Slag-ECC) had been developed based on micromechanical principle. Base grain ingredients were properly selected, and then the mixture proportion was optimized to be capable of achieving robust tensile ductility in the hardened state. The rheological design is performed in the present study by optimizing the amount of admixtures suitable for self-consolidating casting and shotcreting process in the fresh state. A special focus is placed on the rheological control which is directly applicable to the construction in field, using prepackaged product with all pulverized ingredients. To control the rheological properties of the composite, which possesses different fluid properties to facilitate two types of processing (i.e., self-consolidating and shotcreting processing), the viscosity change of the cement paste suspensions over time was initially investigated, and then the proper dosage of the admixtures in the cement paste was selected. The two types of mixture proportion were then optimized by self-consolidating & shotcreting tests. A series of self-consolidating and shotcreting tests demonstrated excellent self-consolidation property and sprayability of the Slag-ECC. The rheological properties altered through this approach were revealed to be effective in obtaining Slag-ECC hardened properties, represented by pseudo strain-hardening behavior in uniaxial tension, allowing the readily achievement of the desired function of the fresh Slag-ECC. These ductile composites with self-consolidating and shotcreting processing can be broadly utilized for a variety of applications, e.g., in strengthening seismic resistant structures with congested reinforcements, or in repairing deteriorated infrastructures by shotcreting process.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.1
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• pp.51-61
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• 2018

Foundation of tower structures such as wind turbine, pylon, and chimney have to resist considerably large overturning moment due to long distance from foundations to load point and large horizontal load. Pile foundations subjected to uplift force are needed to economically support such structure even in the case of rock layer. Therefore, this research performed the laboratory model tests with the variables, W/C ratio and sand proportion, to evaluate the effect of the mix proportion of grouting material on shaft resistance. In the case of cement paste, maximum and residual shaft resistance were distributed in uniform range irrespective of the changes of W/C ratio. However in the case of mortar, they were decreased with increasing W/C ratio, while they were increased and then decreased with increasing sand proportion. In the case of no sand, the maximum shaft resistance was about 540~560kPa regardless of the W/C ratio. When the sand proportion was 40%, it was about 770~870kPa depending on W/C ratio, which was about 40~50% higher than that without sand. The optimum proportion found in this research was around 40% of sand proportion and 80~100% of W/C ratio.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.2
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• pp.143-149
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• 2024

Segmentation of material phases through image analysis is essential for analyzing the microstructure of materials. Micro-CT images exhibit variations in grayscale values depending on the phases constituting the material. Phase segmentation is generally achieved by comparing the grayscale values in the images. In the case of waste concrete used as a recycled aggregate, it is challenging to distinguish between hydrated cement paste and natural aggregates, as these components exhibit similar grayscale values in micro-CT images. In this study, we propose a method for automatically separating the aggregates in concrete, in micro-CT images. Utilizing the Unet-VGG16 deep-learning network, we introduce a technique for segmenting the 2D aggregate images and stacking them to obtain 3D aggregate images. Image filtering is employed to separate aggregate particles from the selected 3D aggregate images. The performance of aggregate segmentation is validated through accuracy, precision, recall, and F1-score assessments.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.3
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• pp.81-90
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• 1992

This study gives results of 1aboratory investigations to minimize the slump loss of concrete using high range water reducing admixture (HRWR). Various factors influencing on the slump loss such as cement type, HRWR type and dosage time are investigated. The acquired results indicated that 30 minutes delayed dosage of HRWR is very effective on reducing the slump loss though this tendency makes a difference to some extent according to cement and HRWR type. For the most part, the more usage of HRWR increases, the higher the slump loss occurs and concrete using ordinary portland cement has the highest slump loss and concrete using fly ash 20% replacement cement with HRWR of naphthalene type has the good effect on reducing the slump loss.

• Journal of the Mineralogical Society of Korea
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• v.27 no.1
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• pp.17-30
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• 2014

Waste cement generated from recycling processes of waste concrete is a potential raw material for mineral carbonation. For the $CO_2$ sequestration utilizing waste cement, this study was conducted to obtain basic information on the aqueous carbonation methods and the characteristics of carbonate mineral formation. Cement paste was made with W:C= 6:4 and stored for 28 days in water bath. Leaching tests using two additives (NaCl and $MgCl_2$) and two aqueous carbonation experiments (direct and indirect aqueous carbonation) were conducted. The maximum leaching of $Ca^{2+}$ ion was occurred at 1.0 M NaCl and 0.5 M $MgCl_2$ solution rather than higher tested concentration. The concentration of extracted $Ca^{2+}$ ion in $MgCl_2$ solution was more than 10 times greater than in NaCl solution. Portlandite ($Ca(OH)_2$) was completely changed to carbonate minerals in the fine cement paste (< 0.15 mm) within one hour and the carbonation of CSH (calcium silicate hydrate) was also progressed by direct aqueous carbonation method. The both additives, however, were not highly effective in direct aqueous carbonation method. 100% pure calcite minerals were formed by indirect carbonation method with NaCl and $MgCl_2$ additives. pH control using alkaline solution was important for the carbonation in the leaching solution produced from $MgCl_2$ additive and carbonation rate was slow due to the effect of $Mg^{2+}$ ions in solution. The type and crystallinity of calcium carbonate mineral were affected by aqueous carbonation method and additive type.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.3
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• pp.213-221
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• 1987

To use fly ash as an additive for concrete, authors collected 15 kinds of domestic fly ashes and tested the chemical compositions and physical properties of the fly ashes. Fluidity of the fly ash paste was also investigated. The result shows that the chemical compositions of the fly ashes were in the range of regulation of Korean Industrial Standards except ignition loss and the following relationships in fly ash were studied; specific surface and residue in standard sieve, specific surface and unit weight, residue in standard sieve and ignition loss. For the given flow properties, fly ash paste required higher water-binder ratio than cement paste.

• Magazine of the Korea Concrete Institute
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• v.9 no.4
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• pp.125-135
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• 1997

경량기포콘크리트란 시멘트슬러리 속에 미리 생성된 기포를 혼합시켜 양생시킴으써 동일한 체적의 보통콘크리트보다 가볍게 만든 콘크리트를 의미한다. 따라서 경량기포콘크리트는시멘트풀 결합재내에 기포가 무작위로 분포된 복합재료이다. 본 연구의 목적은 이러한경량기포콘크리트의 탄성계수 추정식을 미시역학적 이론을 바탕으로 추정하는데 있다. 이르 위해 본 논문에서는 미시역학적인 미분법에 Hansen의 수정기법을 적용한 수정미분법을 사용하여 경량기포콘크리트의 탄성계수 추정식을 제안하였다. 제안된 추정식을 사용하여 얻어진 결과는 실험결과와 잘 일치하였고 기존의 어떤 추정식보다도 우수한 결과를 보였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.2
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• pp.55-66
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• 1992

The cement pastes, mortar and concrete specimens were immersed in artificial seawater and five kinds of chemical solution and tested the change of compressive strength and weight. The reaction products and microstructure were looked over by using X-ray, SEM and EDS. The results show that the formation of ettingite and gypsum because of penetration of ${SO_4}^{2-}$ ion are the reason for deterioration in sulfuric acid and sulphate solution. In the chlorid solution, it is found that the attack of $Cl^-$ ion on the concrete plays an important role of the deterioration of concrete.

• 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.