• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.789-792
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• 2008

최근 건설폐기물 중 가장 높은 비율을 차지하는 폐콘크리트는 과거 단순매립 처리의 한계를 넘어 무 단폐기로 인한 환경오염 증대의 결과를 초래하고 있다. 이와 더불어 천연 골재의 부족 및 국가 자원의 절약, 환경보전적 측면에 대한 관심이 증대되면서 이런 시대적 흐름을 배경으로 폐콘크리트의 재처리 과 정에서 파생되는 재생골재가 환경적 경제적 측면에서 그 사용의 필요성이 대두되고 있다. 그러나 재생골재의 사용이 제한적인 이유는 콘크리트의 강도, 내구성 저하와 재생골재에 존재하는 시멘트 페이스트에 의한 알칼리 골재반응의 발생 우려 때문이다. 또한, 건설수요의 증대로 천연골재가 고갈되어 제염사의 이용이 증대되고 있으며, 산업폐기물의 재이용 등의 이유로 플라이애시, 고로슬래그 미분말 등의 이용이 확대되고 있다. 한편 고로슬래그 미분말은 자체의 잠재수경성에 의하여 수밀성, 장기강도의 향상 및 화학저항성의 증대를 도모 할 수 있으나, 사용시 점성의 저하 및 초기강도 저하, 중성화저항성 저하 등의 문제점이 보고되고 있다. 현재 국내에서 생산되고 있는 고로슬래그 미분말은 보통 포틀랜드 시멘트에 비해 수화발열속도가 작고, 알칼리 골재 반응 억제 효과 및 수밀성, 염분차단성, 내해수성, 내약품성 등이 향상되는 장점이 있다는 특징을 가지고 있다. 그러나 고로슬래그 미분말의 경우 자경성을 가지고 있지 않아 수화하기 위해서는 알칼리등의 자극제를 필요로 하는 혼화재료이다. 따라서, 수산화칼슘이 용출되는 재생골재와 알칼리 자극을 필요로 하는 고로슬래그를 동시에 사용하면 상호보완적인 역할이 가능한 자원 순환형 건설재료로써 사용이 가능할 것으로 예상된다.

• 콘크리트학회논문집
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• 제23권1호
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• pp.99-107
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• 2011

이 연구는 대용량 지상식 LNG 저장탱크에 사용할 고강도 자기충전 콘크리트의 최적배합 조건을 도출하고, 현장적용을 위한 기본 자료를 제안하기 위한 것이다. 60~80 MPa 고강도 자기충전 콘크리트를 적용하면, 벽체두께의 감소와 자기충전성에 따른 인력절감 및 품질확보 등을 통하여 경제성을 확보할 것으로 예상된다. 시멘트 및 분체는 점성 증대 및 수화열 저감에 우수한 플라이애쉬와 저열 시멘트(벨라이트)를 사용하였다. 플라이애쉬의 치환율은 구속수비 및 배합변수 실험을 통해 정하였으며, 배합변수는 단위수량(W), 플라이애쉬 치환율(FA), 물-결합재비(W/B) 및 잔골재율(S/a)로 하여, 최적배합비 및 경제성 평가를 실시하였다. 실험 결과, 설계기준강도 60 MPa의 경우에는 단위수량 165 $kg/m^3$, 플라이애쉬 치환율 20% 및 물-결합재비 27~30%로 나타났으며, 설계기준강도 80 MPa의 경우에는 단위수량 165 $kg/m^3$, 플라이애쉬 치환율 10% 및 물-결합재비 25%로 나타났다. 또한, 기존의 설계기준강도 40 MPa과 비교해 볼 때, 압축강도 증가에 따른 재료비 상승은 60 MPa의 경우 14~22% 및 80 MPa의 경우 33%로 나타나, 현장관리 및 인력절감 등과 함께 매우 경제적인 것으로 나타났다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.369-372
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• 2000

This investigation aims at the optimum mixing of flexible flowable-fill made of Bottom-ash as an industrial waste. Flowable-fill refer to self-compacted, cementitious material used primarily as a backfill in lieu of compacted fill. The two primary advantages of flowable fill over traditional methods are its ease of placement and the elimination of settlement. Therefore, in difficult compaction areas or areas where settlement is a concern, flowable fill should be considered. This study compares Bottom-ash with fine aggregate in physical character. The mixing design indicates a various mixing-rate.

• 수산경영론집
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• 제41권2호
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• pp.1-23
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• 2010

This study is to evaluate member fisheries cooperatives' self-effort for managerial improvement qualitatively and quantitatively. The impaired member cooperatives' got grant from National Federations of Fisheries Cooperatives for managerial improvement for 2003~2004 with establishment of MOU. This MOU describes a self-effort of memebr cooperatives' required fulfillment items for managerial improvement. From the various level of analyses, we conclude that per capita total return or ROA has direct and positive effect on the improvement of net capital ratio or profit ratio. However, other MOU items like human resource management or an investment increment did not have a correlation with it. In addition, an aggregate financial indicator, such as ROA, seems to have a positive effect on the improvement of net capital ratio or profit ratio for the group of well restructured member cooperatives, but does not for the bad performance group. This is because the good performance has leads to the improvement of net capital ratio for the well-restructured member cooperatives since there is little chance to have additional weakness. From this study we can check the proper selection of MOU items should be based on the analysis of its effect on the managerial improvement.

• Structural Engineering and Mechanics
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• 제51권1호
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• pp.1-13
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• 2014

This paper reports an experimental study into the rheological behaviour of self consolidating concrete (SCC). The investigation aimed at quantifying the impact of the varying amounts of mineral admixtures on the rheology of SCC containing natural sand. Apart from the ordinary Portland cement (OPC), the cementitious materials such as fly ash (FA), ground granulated blast furnace slag (GGBS) and micro-silica (MS) in conjunction with the mineral admixtures were used in different percentages keeping the mix paste volume and flow of concrete constant at higher atmospheric tempterature ($30^{\circ}$ to $40^{\circ}C$). The rheological properties of SCC were investigated using an ICAR rheometer with a four-blade vane. The rheological properties of self-consolidating concrete (SCC) containing different mineral admixtures (MA) were investigated using an ICAR rheometer. The mineral admixtures were fly ash (FA), ground granulated blast furnace slag (GGBS), and micro silica (MS). The results obtained using traditional workability results are compared with those obtained using ICAR rheometer. The instrument ICAR (International Center for Aggregate Research) rheometer employed in the present study for evaluating the rhelogical behaviour of the SCC is found to detect systematic changes in workability, cementitious materials, successfully. It can be concluded that the rheology and the slump flow tests can be concurrently used for predicting the flow behaviours of SCC made with different cementitious materials.

• Computers and Concrete
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• 제19권5호
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• pp.555-566
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• 2017

Recently some efforts have been performed to combine the advantages of light-weight and self-compacting concrete in one package called Light-Weight Self-Compacting Concrete (LWSCC). Accurate prediction of hardened properties from fresh state characteristics is vital in design of concrete structures. Considering the lack of references in mixture design of LWSCC, investigating the proper mixture components and their effects on mechanical properties of LWSCC can lead to a reliable basis for its application in construction industry. This study utilizes wide range of existing data of LWSCC mixtures to study the individual and combined effects of the components on the compressive strength. From sensitivity of compressive strength to the proportions and interaction of the components, two equations are proposed to estimate the LWSCC compressive strength. Predicted values of the equations are in good agreement with the experimental data. Application of lightweight aggregate to reduce the density of LWSCC may bring some mixing problems like segregation. Reaching a higher strength by lowered density is a challenging problem that is investigated as well. The results show that, the compressive strength can be improved by increasing the of mixture density of LWSCC, especially in the range of density under $2000Kg/m^3$.

• Computers and Concrete
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• 제5권1호
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• pp.61-74
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• 2008

Digital image processing algorithms for the analysis and characterization of grains and voids in cemented materials were developed using toolbox functions of a mathematical software package. Utilization of grayscale, color and watershed segmentation algorithms and their performances were demonstrated on artificially prepared self-compacting concrete (SCC) samples. It has been found that color segmentation was more advantageous over the gray scale segmentation for the detection of voids whereas the latter method provided satisfying results for the aggregate grains due to the sharp contrast between their colors and the cohesive matrix. The watershed segmentation method, on the other hand, appeared to be very efficient while separating touching objects in digital images.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2019년도 춘계 학술논문 발표대회
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• pp.203-204
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• 2019

Recently, exposed concrete designs have been placed everywhere due to increased interest in indoor residential environments. In addition, in order to overcome the disadvantages of litracon, which was developed by mixing optical fiber, LEFC(Light Emotion Friendly Concrete) was developed in Korea, which improved unit price and constructivity by inserting hard acrylic rods. LEFC, using foaming agent and lightweight aggregate for light weighting, has disadvantages that decrease mechanical properties, and thus improved mechanical properties by using ultra-high performance concrete. Also, due to the characteristics of UHPC materials, it showed excellent self-consolidating performance. Considering these characteristics, a LEFC mold with pattern design was developed. The LEFC blocks were built so that pattern shapes could be seen and these were applied on-site to Sewoon plaza, located in Seoul.

• Computers and Concrete
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• 제29권1호
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• pp.47-57
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• 2022

The increase in waste tires has brought serious environmental problems. Using waste tires rubber particles as aggregate in concrete can reduce pollution and decrease the usage of natural aggregate. The paper describes an investigation on flexural bearing capacity of self-compacting concrete (SCC) pavement slabs containing crumb rubber. Cyclic loading tests with different stress ratios and loading frequencies are carried out on SCC pavement slabs containing crumb rubber. Based on Paris Law and test data, the fatigue life of SCC pavement slab containing crumb rubber is discussed, and a revised mathematical model is established to predict the fatigue life of SCC pavement slab containing crumb rubber. The model applies to different stress ratios and loading frequencies. The fatigue life of SCC pavement slab containing crumb rubber is affected by the stress ratio and loading frequency. The fatigue life increases with the increase of stress ratio and loading frequency. Real-time acoustic emission (AE) signals in the SCC pavement slab containing crumb rubber under cyclic loading are measured, and the characteristics of crack propagation in the SCC pavement slab containing crumb rubber under different stress ratios and loading frequencies are compared. The AE signals provide abundant information of fracture process zone and crack propagation. The variation of AE ringing count, energy and b-value show that the fracture process of SCC pavement slab containing crumb rubber is divided into three stages.

• 대한전자공학회논문지TC
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• 제47권5호
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• pp.9-17
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• 2010

본 논문에서는 이동 Ad-hoc 네트워크를 지원하여 확장성과 광대역의 무선 환경을 제공하는 무선 메쉬 네트워크인 무선 하이브리드 메쉬 구조를 고려하여, 이에 효율적으로 적용될 수 있는 무선 하이브리드 메쉬 네트워크를 위한 계층구조의 라우팅 기법을 제안하였다. 무선 하이브리드 메쉬 네트워크상에서 효율적인 토폴로지 관리와 소스노드에서 목적노드로 라우팅 패스를 설정할 시에 발생하는 트래픽을 감소시키고 노드간 링크 안정성을 고려하고, 노드의 문제 또는 링크간 장애로 인한 잦은 라우팅 재설정 문제를 해결하는 계층구조의 라우팅 기법을 제안하였다. 또한 case study를 통하여 본 논문에서 제안된 계층구조의 라우팅 기법을 이용하여 네트워크 클러스터링 및 토폴로지 관리의 효율성을 인지할 수 있었으며, 성능분석 결과에서는 제안된 방법을 적용하였을 때, 링크의 상태가 좋지 않을 경우 기존 HOLSR (hierarchical optimized link state routing) 방법보다 데이터 전송에 따른 종단간 지연시간이 감소되고 aggregate goodput과 packet delivery ratio가 향상됨을 알 수 있었다.