• Corrosion Science and Technology
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• 제8권5호
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• pp.171-176
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• 2009

The chloride threshold level (CTL) in mixed concrete containing, ordinary Portland cement (OPC), pulverized fuel ash (PFA) ground granulated blast furnace slag (GGBS), and silica fume (SF) is important for study on corrosion of reinforced concrete structures. The CTL is defined as a critical content of chloride at the steel depth of the steel which causes the breakdown of the passive film. The criterion of the CTL represented by total chloride content has been used due to convenience and practicality. In order to demonstrate a relationship between the CTL by total chloride content and the CTL by free chloride content, corrosion test and chloride binding capacity test were carried out. In corrosion test, Mortar specimens were cast using OPC, PFA, GGBS and SF, chlorides were admixed ranging 0.0, 0.2, 0.4, 0.8, 1.0, 1.5, 2.0, 2.5 and 3.0% by weight of binder. All specimens were cured 28 days, and then the corrosion rate was measured by the Tafel's extrapolation method. In chloride binding capacity, paste specimens were casting using OPC, PFA, GGBS and SF, chlorides were admixed ranging 0.1, 0.2, 0.3, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0% by weight of binders. At 28days, solution mixed with the powder of ground specimens was used to measure binding capacity. All specimens of both experiments were wrapped in polythene film to avoid leaching out of chloride and hydroxyl ions. As a result, the CTL by total chloride content ranged from 0.36-1.44% by weight of binders and the CTL by free chloride content ranged from 0.14-0.96%. Accordingly, the difference was ranging, from 0.22 to 0.48% by weight of binder. The order of difference for binder is OPC > 10% SF > 30% PFA > 60% GGBS.

• Corrosion Science and Technology
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• 제8권2호
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• pp.74-80
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• 2009

The high alkaline property in the concrete pore solution protects the embedded steel in concrete from corrosion due to aggressive ions attack. However, a continuous supply of those ions, in particular, chlorides altogether with a pH fall in electrochemical reaction on the steel surface eventually depassivate the steel to corrode. To mitigate chloride-induced corrosion in concrete structures, finely grained mineral admixtures, for example, pulverized fuel ash (PFA), ground granulated blast furnace slag (GGBS) and silica fume (SF) have been often advised to replace ordinary Portland cement (OPC) partially as binder. A consistent assessment of those partial replacements has been rarely performed with respect to the resistance of each binder to corrosion, although the studies for each binder were extensively looked into in a way of measuring the corrosion rate, influence of microstructure or chemistry of chlorides ions with cement hydrations. The paper studies the behavior of steel corrosion, chloride transport, pore structure and buffering capacity of those cementitious binders. The corrosion rate of steel in mortars of OPC, 30% PFA, 60% GGBS and 10% SF respectively, with chloride in cast ranging from 0.0 to 3.0% by weight of binder was measured at 7, 28 and 150 days to determine the chloride threshold level and the rate of corrosion propagation, using the anodic polarization technique. Mercury intrusion porosimetry was also applied to cement pastes of each binder at 7 and 28 days to ensure the development of pore structure. Finally, the release rate of bound chlorides (i.e. buffering capacity) was measured at 150 days. The chloride threshold level was determined assuming that the corrosion rate is beyond 1-2 mA/$m^3$ at corrosion and the order of the level was OPC > 10% SF > 60% GGBS > 30% PFA. Mercury intrusion porosimetry showed that 10% SF paste produced the most dense pore structure, followed by 60% GGBS, 30% PFA and OPC pastes, respectively. It was found that OPC itself is beneficial in resisting to corrosion initiation, but use of pozzolanic materials as binders shows more resistance to chloride transport into concrete, thus delay the onset of corrosion.

• 한국건축시공학회지
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• 제6권3호
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• pp.75-82
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• 2006

This study investigates the influence of various blending factors on cement paste fluidity and find out the most effective evaluation method of cement paste flow, comparing flow test apparatuses such as ring flow(R-F), flow cone(F-C) and mini slump(M-S). A viscometer also measures the rheology coefficients to secure faithful numerical data. Firstly, series I examines cement paste, affected by several cement products and mineral admixture types in the range of W/B 40%, ordinary fluidity, and W/B 30%, high fluidity. In this series, the three types of cement product depended on companies, are randomly used and the mineral admixture, such as fly ash, blast furnace slag and silica fume, are incorporated in the cement paste, in response to the ratio of 10, 20, to 30%, respectively. In addition, series II studies various chemical admixture types, affecting the cement paste. This series is carried out with manufacturing companies and component types in the range of W/C 30%, high fluidity. For the manufacturing companies, randomly four products are used and for the component types, polycaboxylate, melamine, naphthalene and lignosulfonate type are chosen. Test results showed that in the fluidity test of cement paste considering various types of blending factors, R-F exhibited similar tendency with F-C and M-S. In the analysis of consistency curves measured by viscometer, the fluidity evaluation method using flow test apparatuses was significantly effective, except for the some of the low fluidity specimens. In conclusion of this study, R-F was the most convenient, faithful and effective fluidity evaluation method of cement paste.

• 대한토목학회논문집
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• 제14권4호
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• pp.783-794
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• 1994

근래에 들어 대형 구조물의 시공실패사례가 보고되고 있어 이에 대한 개선이 시급하게 요청되고 있다. 이러한 실패사례의 주요원인은 콘크리트의 품질문제이며 따라서 고품질 콘크리트의 개발과 사용이 절실히 필요하다. 콘크리트의 품질향상을 위한 방안으로 현재 주목받고 있는 것은 유동성의 확보와 함께 각기 다른 독특한 특성을 보이는, 플라이 애쉬, 고로 슬래그, 실리카 흄 등 혼화재의 혼입이다. 따라서, 본 연구에서는 슬럼프를 $17{\pm}1cm$로 제어하여 기본적인 유동성을 확보한 콘크리트 배합에 대하여, 위의 혼화재들의 혼입률에 따른 역학적 특성과 내구적 특성을 고찰하여 보았다. 본 연구에서 고려한 주요 실험변수들로는 혼화재의 종류와 혼입률, 두 종류의 단위시멘트량과 물/시멘트비의 조합 등이다. 이들 실험변수들을 고려하여 14개 시리즈에 대한 포괄적인 실험을 수행하였으며, 각 혼화재 혼입량에 따른 재령별 압축강도 증진양상과 콘크리트내에 매립된 철근씩 부삭특성을 분석, 고찰하였다. 본 실험연구로부터 각 경우별 최적의 혼화재 혼입량과 성능을 도출하였으며 이것은 앞으로 고성능 콘크리트의 활용에 토대가 될 것으로 사료된다.

• Advances in concrete construction
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• 제9권1호
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• pp.55-70
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• 2020

In this research article, acid resistance, sulphate resistance and sorptivity of self compacted concrete (SCC) prepared from C&D waste have been discussed. To improve the above properties of self compacted recycled aggregate concrete (SCRAC) along with mechanical and durability properties, different two stage mixing approaches (TSMA and TSMAsfc) were followed. In the proposed two stage mixing approach (TSMAsfc), silica fume, a proportional amount of cement and a proportional amount of water were mixed in premix stage which fills the pores and cracks of recycled aggregate concrete (RAC). The concrete specimen prepared using above mixing approaches were immersed in 1% concentration of sulphuric acid (H2SO4) and magnesium sulphate (MgSO4) solution for 28, 90 and 180 days for evaluating the acid resistance of SCRAC. Experimental results concluded that the proposed two stage mixing approach (TSMAsfc) is most suitable for acid resistance and sulphate resistance in terms of weight loss and strength loss due to the elimination of pores and cracks in the interfacial transition zone (ITZ). In modified two stage mixing approach, the pores and cracks of recycled concrete aggregate (RCA) were filled up and make ITZs of SCRAC stronger. Microstructure analysis was carried out to justify the reason of improvement of ITZs by electron probe micro analyser (EPMA) analysis. X-ray mapping was also done to know the presence of strength contributing elements presents in the concrete sample. It was established that SCRAC with modified mixing approach have shown improved results in terms of acid resistance, sulphate resistance, sorptivity and mechanical properties.

• 콘크리트학회논문집
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• 제22권3호
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• pp.305-311
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• 2010

최근 국제적으로 급속한 경제성장으로 인한 산업부산물이 기하급수적으로 늘어가고 있다. 현재 국내 산업부산물은 매립, 소각, 저장과 같은 1차원적인 처리에도 그 한계를 드러내고 있는 실정이다. 따라서 이 연구에서는 자원재활용을 목적으로 산업부산물을 이용한 고성능 숏크리트용 최적 배합비를 도출하고자 한다. 이 연구에서는 경제적 재활용, 장기강도 및 내구성 향상을 위해 콘크리트에 다양하게 적용되고 있는 혼화재인 산업부산물(플라이애쉬, 실리카퓸)를 적용하여 숏크리트 현장에 적용할 수 있는 적정 배합비에 대한 변수를 설정하여 압축강도 실험을 수행하였고, 외부 환경 변화에 따른 내구성능을 평가하기 위하여 촉진염소이온침투시험 및 염화물확산계수측정시험을 실시하여 외부환경에 대한 내구특성을 평가하였다. 실험 결과 모든 실험에서 국내외 기준을 만족하였고, 내구성에서는 기존 숏크리트 보다 뛰어난 것으로 나타났다.

• 콘크리트학회논문집
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• 제23권4호
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• pp.441-448
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• 2011

이 연구에서는 실리카퓸 및 수축 저감제, 팽창재, 고성능 감수제의 혼입을 변수로 한 초고성능 시멘트 복합체(UHPCC)의 초기 수축 거동을 평가하기 위하여 화학수축 및 자기수축 실험을 수행하고, 응결 측정 결과와 비교하여 UHPCC의 자기건조 시작 시점에 대하여 분석하였다. 실험 결과, 실리카퓸 및 수축 저감제는 초기 화학수축을 증가시키는 경향을 보였으며, 고성능 감수제는 시멘트와 배합수의 수화 반응을 지연시키고 화학수축을 저감시키는 것으로 나타났다. 수축 저감제와 팽창재를 조합하여 적용한 경우 약 49%의 자기수축 저감 효과를 보였으며, 팽창재는 경화를 촉진 시키는 것으로 나타났다. 또한 UHPCC는 다수의 섬유 혼입과 낮은 물-결합재비에 의해 초결 이전부터 자기건조 현상이 발생하는 것으로 나타났다.

• 콘크리트학회지
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• 제10권6호
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• pp.169-178
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• 1998

고성능 belite 시멘트 콘크리트에 대한 부착특성에 대하여 코\ulcorner리트의 강도, 슬럼프, 배근위치, 피복두께 등의영향요인을 보단부시험체와 이음길이 보시험체를 통해 연구하였다. 동일한 압축강도의 1종 보통 포틀랜드 시멘트 콘크리트에 비해 부착강도는 약 10%증가하였고 압축강도 600kg/$\textrm{cm}^2$의고강도 belite 콘크리트에서 부착강도가 대체로 {{{{ SQRT { f'c} }} }}에 비례하였다. 유동성에 있어서 높은 슬럼프에 비해 ACI 318-95 규준에서 제시하는 상부근 계수 1.3이하의범위에 있었으며 이것은 고유동 belite 콘크리트가 블리이딩이나 골재분리가 적은 것으로 보여졌다. 또한 고강도 belite시멘트 콘크리트를 사용한 이음길이 보시험체에서 부착강도는 기존 예측식의 값보다다소 높게 나타났으며, 실리커흄, 플라이애쉬를 사용한 고강도 콘크리트 부착강도의 기존연구결과인 낮은 값과 차이를 보였다. 이상의 결과로 고유동, 고강도 belite 시멘트 콘크리트는 철근과의 부착성능이 다른 재료에 비해 양호한 것으로 나타났다.

• 한국산학기술학회논문지
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• 제20권11호
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• pp.416-424
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• 2019

우리나라에서 지하층 누름콘크리트는 주로 무근 콘크리트를 사용하고 있다. 이러한 시스템에서는 건조수축이나 불규칙한 온도 분포로 인하여 바닥콘크리트의 균열이 빈번히 발생되고 있다. 이러한 문제점을 해결하고자 과거에는 메탈라스, 섬유 등을 사용하였지만 균열을 제어하기에는 효과가 미비한 점이 있었다. 이에, 본 연구에서는 여러 가지 혼화 재료를 혼입한 지하층 누름콘크리트의 균열 저감 효과에 관하여 분석하였다. 혼화재료의 종류에 따른 균열저감 효과를 알아보기 위해 공기량 실험, 슬럼프 실험, 압축강도 실험, 소성수축 실험을 실시하였다. 공기량 실험결과, 혼화재료들을 혼입한 시편들은 Plain과 유사한 공기량(4.5±1.5%)을 나타내었으며, 슬럼프 실험에서는 고성능 감수제를 혼입한 시편들이 Plain에 비하여 가장 높게 나타내었지만, 폴리머를 혼입한 경우 Plain과 유사하게 나타났다. 압축강도 실험에서는 실리카 흄, 고성능 감수제 및 SBR을 혼입한 시편들이 Plain에 비하여 10-15% 높게 나타났다. 소성수축 실험결과 MC, 고성능 감수제, SBR를 혼입한 시편들이 Plain에 비하여 균열발생이 적었으며, 특히 MC섬유를 혼입한 시편은 균열이 발생하지 않았다.

• 한국산업융합학회 논문집
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• 제16권1호
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• pp.1-8
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• 2013

In case that W/B is 20%, 30%, 40% respectively, the effects of additive and shrinkage reducing agent on the autogenous shrinkage for high strengthen concrete through the substitution of FA and SF analysis were obtained as following conclusions. When the ratio of FA increased, the compressive strength of high strengthen concrete is decreased in the early times. As the ratio of SF increase, the compressive strength also increased. Comparing with PC(Portland Cement) for 7 days curing, the strength is 13.8% of FA10 + SR0.5 and 19.2% of FA15 + SR0.5 decreased when W/B is 20%, and 6.1% of SF7.5 + SR0.5, 4.8% of SF15 + SR0.5, the strength are increased. In case that W/B is 30%, 13.1% of FA10 + SR0.5 19.1% of FA15 + SR0.5 the strength is decreased and 4.1% of SF 7.5 + SR0.5, 7.2% of SF15 + SR0.5 the strength are increased. In case of W/B 40%, 4.3% of FA10 + SR0.5, and 8.7% of FA15 + SR0.5, the strength is decreased and 3.3% of SF7.5 + SR0.5, 6.3% SF15 + SR0.5 the strength is increased. When the ratio of SR is 0.5%, autogenous shrinkage strain of OPC concrete appeared $-417{\times}10-6$ in 56days curing, the shrinkage strain is decreased 23.7%. The reducing effects of autogenous shrinkage when the mineral and shrinkage agent are used are the same as ones when only shrinkage agent used.