• Advances in concrete construction
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• 제4권2호
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• pp.71-88
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• 2016

Metakaolin, a dehydroxylated product of the mineral kaolinite, is one of the most valuable admixtures for high-performance concrete applications, including constructing reinforced concrete bridges and impact- and fire-resistant structures. Concretes produced using metakaolin become more homogeneous and denser compared to normal-strength concrete. Yet, these changes cause a change of volume throughout hardening, and increase the brittleness of hardened concrete significantly. In order to examine how the use of metakaolin affects the fracture and mechanical behavior of high-performance concrete we produced concretes using a range of water to binder ratio (0.42, 0.35 and 0.28) at three different weight fractions of metakaolin replacement (8%, 16% and 24%). The results showed that the rigidity of concretes increased with using 8% and 16% metakaolin, while it decreased in all series with 24% of metakaolin replacement. Similar effect has also been observed for other mechanical properties. While the peak loads in load-displacement curves of concretes decreased significantly with increasing water to binder ratio, this effect have been found to be diminished by using metakaolin. Pore structure analysis through mercury intrusion porosimetry test showed that the addition of metakaolin decreased the critical pore size of paste phases of concrete, and increasing the amount of metakaolin reduced the total porosity for the specimens with low water to binder ratios in particular. To determine the optimal values of water to binder ratio and metakaolin content in producing high-strength and high-performance concrete we applied a multi-objective optimization, where several responses were simultaneously assessed to find the best solution for each parameter.

• 한국토양비료학회지
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• 제46권3호
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• pp.187-192
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• 2013

This study was carried out to investigate the incorporation effect of green manure crops (GMC) such as the hairy vetch on improvement of soil environment in reclaimed land during silage corn cultivation over the past two years. Plots consisted of conventional fertilization (CF) and incorporation of GMC were divided by addition rate of nitrogen fertilizer (100 kg $ha^{-1}$) with 30 - 100% of non nitrogen fertilization (NNF). Soil physico-chemical properties and growth and yield potential of silage corn were examined. The tested soils showed strong alkali and saline properties with low contents of organic matter and available phosphate while contents of exchangeable sodium and magnesium were high. Soil salinity increased during cultivation of summer crop. However, corn was not affected by salt content. The fresh weight of GMC at incorporation time was 18,345 kg $ha^{-1}$. Content of total nitrogen was 3.09% and the C/N ratio was 12.8 at incorporation time. Fresh and dry matter yield of silage corn were higher in the order of N30% reduction, CF, N50% reduction, N70% reduction, N100% reduction and NNF. Fresh and dry matter yield potential of silage corn for N30% reduction were comparable to those of CF. Bulk density of the soil decreased with incorporation of GMC, while porosity was increased. The soil pH decreased while content of exchangeable calcium, available phosphate, and organic matter increased. Also contents of exchangeable sodium and potassium decreased with incorporation of GMC. The data indicate that incorporation of hairy vetch can improve soil physical and chemical properties and reduce nitrogen fertilizer application especially for alkali saline reclaimed soil such as Saemangeum reclaimed land.

• 한국건설순환자원학회논문집
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• 제7권4호
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• pp.413-422
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• 2019

콘크리트 혼화재인 보통 포틀랜드 시멘트를 대체하기 위하여 페로실리콘 산업부산물을 적용하였다. 페로실리콘의 원재료 비표면적, 비중과 같은 기초물성은 실리카퓸과 매우 유사하다. 따라서 전체 혼화재 중량의 10%를 페로실리콘 또는 실리카퓸으로 치환한 콘크리트와 모르타르를 제작하여 페로실리콘의 혼화재로써의 사용 타당성을 평가하였고, 보통 포틀랜드 시멘트, 페로실리콘, 실리카퓸 콘크리트에 대한 비교 분석 결과를 나타냈다. 페로실리콘 콘크리트의 수화특성은 X선 회절 분석을 통하여 수행하였다. 페로실리콘 콘크리트는 압축강도, 염분침투 저항성, 공극 저감의 측면에서 보통 포틀랜드 시멘트 콘크리트 보다 장점을 보였으나 그 정도는 실리카퓸 보다 낮았다. 페로실리콘 콘크리트에 대하여 알칼리-실리카 반응에 의한 팽창 가능성이 확인되었는데 이는 실리카 입자의 뭉쳐진 덩어리 크기 때문인 것으로 판단된다.

• Journal of Microbiology and Biotechnology
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• 제30권9호
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• pp.1310-1320
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• 2020

Low-quality soil for land reuse is a crucial problem in vegetation quality and especially to waste disposal sites in mining areas. It is necessary to find suitable materials to improve the soil quality and especially to increase soil microbial diversity and activity. In this study, pot experiments were conducted to investigate the effect of a mixed material of humic acid, super absorbent polymer and biochar on low-quality soil indexes and the microbial community response. The indexes included soil physicochemical properties and the corresponding plant growth. The results showed that the mixed material could improve chemical properties and physical structure of soil by increasing the bulk density, porosity, macro aggregate, and promote the mineralization of nutrient elements in soil. The best performance was achieved by adding 3 g·kg^-1 super absorbent polymer, 3 g·kg^-1 humic acid, and 10 g·kg^-1 biochar to soil with plant total nitrogen, dry weight and height increased by 85.18%, 266.41% and 74.06%, respectively. Physicochemical properties caused changes in soil microbial diversity. Acidobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Firmicutes, Nitrospirae, Planctomycetes, and Proteobacteria were significantly positively correlated with most of the physical, chemical and plant indicators. Actinobacteria and Armatimonadetes were significantly negatively correlated with most measurement factors. Therefore, this study can contribute to improving the understanding of low-quality soil and how it affects soil microbial functions and sustainability.

• 폴리머
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• 제32권6호
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• pp.603-609
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• 2008

본 연구에서는 MMA(methyl methacrylate)와 BA(buthyl acrylate)를 단량체로 이용한 폴리머 시멘트 모르타르의 단량체 비에 따른 성질을 파악하고 시멘트 혼화용 폴리머로 활용하기 위한 기초적 자료를 얻고자 하였다. 본 연구결과 MMA/BA를 이용한 폴리머 시멘트 모르타르의 전 세공용적은 MMA/BA의 단량체 비가 증가할수록 감소하는 것으로 나타났다. 강도특성에서는 전체적으로 MMA/BA의 단량체 비가 70 : 30, 그리고 80 : 20일 때, 폴리머 시멘트 비가 15%일 때 가장 우수한 증진효과를 나타냈다. 폴리머 시멘트 모르타르의 내구성을 측정하는 흡수율, 염화물 이온 침투 저항성, 중성화 저항성에서는 단량체 비에 따른 개선보다는 폴리머 시멘트 비에 따른 개선효과가 더 큰 것으로 나타났다.

• Membrane and Water Treatment
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• 제8권2호
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• pp.113-123
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• 2017

This study investigated effects of physical and chemical cleaning methods on the initial flux recovery of fouled membrane in membrane distillation process. A laboratory scale direct contact membrane distillation (DCMD) experiment was performed to treat digested livestock wastewater with 3.89 mg/L suspended solids, 874.7 mg/L COD, 543.7 mg/L nitrogen, 15.6 mg/L total phosphorus, and pH of 8.6. A hydrophobic PVDF membrane with an average pore size of $0.22{\mu}m$ and a porosity of 75 % was installed inside a direct contact type membrane distillation module. The temperature difference between feed and permeate side was maintained at $40^{\circ}C$ with the feed and permeate stream velocity of 0.18 m/s. The results showed that the permeate flux decreased from $22.1L{\cdot}m^{-2}{\cdot}hr^{-1}$ to $19.0L{\cdot}m^{-2}{\cdot}hr^{-1}$ after 75 hours of distillation. The fouled membrane was cleaned first by physical flushing and consecutively by chemicals with NaOCl and citric acid. After the physical cleaning the flux was recovered to 92 % as compared with the initial clean water flux of the virgin membrane. Then 94 % of the flux was recovered after cleaning by 2,000 ppm NaOCl for 90 minutes and finally 97 % of flux recovered after 3 % citric acid for 90 minutes. SEM-EDS and FT-IR analysis results presented that the foulants on the membrane surface were removed effectively after each cleaning step. The contact angle measurement showed that the hydrophobicity of the membrane surface was also restored gradually after each cleaning step to reach nearly the same hydrophobicity level as the virgin membrane.

• 한국건설순환자원학회논문집
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• 제9권2호
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• pp.127-134
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• 2021

PMHS와 PVA를 혼합한 소수성 유액을 시멘트 모르타르에 혼입하여 수화생성물과 미세구조의 변화를 관찰하고, 압축강도와 휨강도를 실험적으로 평가하고자 하였다. 소수성 유액은 메타카올린과 PVA 섬유를 추가하고 교반속도와 순서를 조정하여 쉘형태의 유액을 제조하였으며, 모르타르배합시 혼입하여 내부 공극의 충진과 수화생성물의 변화를 도모하고자 하였다. 소수성 유액이 혼입된 모르타르는 미세공극이 충진되고 수화생성물표면이 유액에 의해 도막이 생성되는 것이 관찰되었다. OPC와 비교하여 유액이 혼입된 모르타르의 전체 기공면적과 기공률이 감소하는 것으로 분석되었으며, 일부 변수에서 기공지름의 중간값의 감소가 나타났다. 유액을 1% 혼입한 경우에 압축강도의 증가가 나타났으며, 2% 혼입시에는 강도의 감소가 발생하였다.

• Advances in concrete construction
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• 제7권2호
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• pp.87-96
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• 2019

Self-compacting concretes (SCC) are highly fluid concrete which can flow without any vibration. Their composition requires a large quantity of fines to limit the risk of bleeding and segregation. The use of crushed sand rich in limestone fines could be an adequate solution for both economic and environmental reasons. This paper investigates the influence of quarry limestone fines from manufactured crushed sand on rheological, mechanical and durability properties of SCC. For this purpose, five mixtures of SCC with different limestone fines content as substitution of crushed sand (0, 5, 10, 15 and 20%) were prepared at constant water-to-cement ratio of 0.40 and $490kg/m^3$ of cement content. Fresh SCC mixtures were tested by slump flow test, V-funnel flow time test, L-box height ratio, segregation resistance and rheological test using a rheometer. Compressive and flexural strengths of SCC mixtures were evaluated at 28 days. Regarding durability properties, total porosity, capillary water absorption and chloride-ion migration were studied at 180 days. For the two test modes in fresh state, the results indicated compatibility between slump flow/yield stress (${\tau}_0$) and V-funnel flow time/plastic viscosity (${\mu}$). Increasing the substitution level of limestone fines in SCC mixtures, contributes to the decrease of the slump flow and the yield stress. All SCC mixtures investigated achieved adequate filling, adequate passing ability and exhibit no segregation. Moreover, the inclusion of limestone fines as crushed sand substitution reduces the capillary water absorption, chloride-ion migration and consequently enhances the durability performance.

• 한국환경과학회지
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• 제33권1호
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• pp.17-25
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• 2024

This study aimed to determine the most suitable coir substrate mixing ratio for optimizing the growth and yield of the "lpduelkkae 1" cultivar. We comprehensively analyzed the physicochemical properties, growth, and yields of four different substrate combinations: perlite (coir with mixing ratios of 70:30 (PC30), 50:50 (PC50), and 30:70 (PC70)) and 100% coir (C100). The results revealed substantial differences in substrate properties. C100 exhibited the highest total porosity and the lowest solid phase, indicating excellent air permeability. The pH levels and electrical conductivity (EC) values ranged from 5.4-6.8 and 1.2-3.1 dS·m^-1, respectively. Leaf growth parameters, including length, width, and dry weight, showed positive correlations with high coir ratios, except for PC30. PC70 and C100 outperformed other substrates in stem growth, exhibiting superior stem diameter and fresh and dry weights. The quantity of marketable leaves was the highest in the C100 substrate. Furthermore, C100 comprised integrated levels of essential nutrients, such as Ca and Mg, owing to its high coir content. In conclusion, a coir ratio of approximately 70% (v/v) should be maintained in the substrate for creating an optimal cultivation environment. Furthermore, the selection of humidity-resistant varieties as well as precise nutrient and moisture management for different seasons and growth stages are crucial for a successful perilla leaf hydroponic cultivation.

• Geomechanics and Engineering
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• 제36권5호
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• pp.465-474
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• 2024

Uniaxial compressive strength (UCS) is a critical geomechanical parameter that plays a significant role in the evaluation of rocks. The practice of indirectly estimating said characteristics is widespread due to the challenges associated with obtaining high-quality core samples. The primary aim of this study is to investigate the feasibility of utilizing the gene expression programming (GEP) technique for the purpose of forecasting the UCS for various rock categories, including Schist, Granite, Claystone, Travertine, Sandstone, Slate, Limestone, Marl, and Dolomite, which were sourced from a wide range of quarry sites. The present study utilized a total of 170 datasets, comprising Schmidt hammer (SH), porosity (n), point load index (Is(50)), and P-wave velocity (Vp), as the effective parameters in the model to determine their impact on the UCS. The UCS parameter was computed through the utilization of the GEP model, resulting in the generation of an equation. Subsequently, the efficacy of the GEP model and the resultant equation were assessed using various statistical evaluation metrics to determine their predictive capabilities. The outcomes indicate the prospective capacity of the GEP model and the resultant equation in forecasting the unconfined compressive strength (UCS). The significance of this study lies in its ability to enable geotechnical engineers to make estimations of the UCS of rocks, without the requirement of conducting expensive and time-consuming experimental tests. In particular, a user-friendly program was developed based on the GEP model to enable rapid and very accurate calculation of rock's UCS, doing away with the necessity for costly and time-consuming laboratory experiments.