• 한국건설순환자원학회논문집
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• 제8권1호
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• pp.8-16
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• 2020

환경오염 저감을 위해 순환유동층 보일러를 활용한 발전이 증가함에 따라 CFBC 플라이애시가 많이 생산되고 있다. CFBC 플라이애시내는 수화반응 중 시멘트의 팽창과 급격한 초기응결을 발생시킬 수 있는 free CaO를 포함하고 있기 때문에 콘크리트에서의 사용이 제한적이다. 본 연구에서는 고로슬래그시멘트의 초기강도 증진을 위해 CFBC 플라이애시와 인산석고와 같이 혼합함으로서 천연석고를 대체하는 자극제로 활용하고자 하기 위하여 미세구조와 초기강도 특성을 실험적으로 분석하였다. 인산석고는 배면탈황석고와 인산중화석고를 사용하였으며, 이수상태와 무수상태로 각각 혼합하여 실험하였다. 실험결과 CFFA와 dihydrate 형태의 이수석고를 혼합하는 경우에는 상대적으로 초기강도 발현이 낮아지나, CFFA와 anhydriteII 결정형태인 무수인산석고를 혼합한 배합의 강도 증진효과가 천연석고를 사용한 경우와 유사하여 혼합시멘트로 활용 가능성이 높은 것으로 분석되었다.

• 상하수도학회지
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• 제19권1호
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• pp.53-60
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• 2005

Ferrous cement hydrates made from hydrating Portland cement doped with Fe (II) were reported to reductively dechlorinate chlorinated organics and to reduce Cr (VI) to Cr (III). In this study, kinetics of nitrate removal by ferrous cement hydrates were investigated. Nitrate removal kinetics were characterized by experimental variables such as cement hydration, amount of cement addition, Fe (II) dose, pH, and byproducts. As a result, hydrated cement showed better performances than non-hydrated cement due to the formation of LDH (layered double hydroxide). Doping of Fe (II) into the cement was found to improve removal efficiency at high pHs by association with Fe (II) sorbed on cement hydrates as a reactive reductant. Reduction of nitrate produced ammonium as a major product, which accounted for 63.5% of the final products, and nitrite (0.15%) as a minor product. These results indicate that the developed media are effective as sorbent/reducing agents in the nitrate removal and the reaction mechanisms of nitrate removal are sorption and reduction.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.556-559
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• 2004

In this Paper, concrete durability, coefficient variation of compressive strength, and hydration heat development characteristics of concrete using different types binder for 2nd Phase Construction in IIA were investigated. The experimental results show that the coefficient variation of compressive strength decreased with the slag cement when compared with the replacement of granulated blast furnace slag powder. And the diffusion coefficient of chloride ion decreased with use of a blended cement when compared with using a only portland cement. Also the type of low heat cement is very suitable to reduce the thermal crack caused by hydration heat development.

• Structural Engineering and Mechanics
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• 제31권1호
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• pp.1-10
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• 2009

An experimental investigation was conducted to evaluate the performance of mortars with and without Metakaolin (MK) exposed to elevated temperatures $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$ and $800^{\circ}C$ for two hours. The binder to sand ratio was kept constant (1:5.23). The ordinary Portland cement (OPC) was replaced with MK at 0%, 5%, 10% 20% and 30%. All mixtures were designed to have a flow of $94{\pm}5%$. The compressive strength of mortars before and after exposure to elevated temperature was determined. The formation of various decomposition phases were identified using X-ray diffractometry (XRD) and differential thermal analysis (DTA). The microstructure of the mortars was examined using scanning electron microscope (SEM). Test results indicated that MK improves the compressive strength before and after exposure to elevated temperature and that the 20% cement replacement of MK is the optimum percentage.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 가을 학술발표회 논문집
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• pp.408-415
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• 1997

Bond strength of reinforcing bar to high-performance concrete using Belite cement is explored using beam end test specimen. The key parameters for the bond test are slump of concrete, top bar effect, and strength of concrete in addition to concrete covers. Specimen failed in the typical brittle bond failure splitting the concrete cover as the wedging action. The test results show that for the group with portland cement I using superplasticizer additional slump does not decrease the bond strength of the top bar is less than bond strength of bottom bar, but the top bar factor satisfy the modification factor for top reinforcement. The result also show that bond strength is function of square root of concrete compressive strength and cover thickness. More detailed evaluation will be conducted from the test specimen with high strength concrete using the belite cement.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 가을 학술발표회 논문집
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• pp.203-206
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• 1997

In this paper, the properties of Interlocking block contained blast furnace slag cement are compared with that with O.P.C.(ordinary portland cement) and are analyzed under various mix proportions and the dosage of AE agent. According to the experimental results, compressive strength and flexural strength of interlocking block with blast furnace slag cement are lower than that with OPC. Also the strength and the ratio of absorption decrease with higher dosage of AE agent. although interlocking block with OPC has better performance than that of blast furnace slag in the side of quality, it is worth while to use the blast furnace slag as materials of interlocking block considered the side of recycling of resources and economy.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.1175-1180
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• 2000

Recently, the crack of concrete induced by the heat of hydration of cement is a serious problem for more greater, special and higher strength of concrete structures. The increasing concrete's temperature is mainly caused by the heat of hydration of cement and so, to control the thermal stress of concrete structure is desirable to use low heater material of hydration. There are many methods to diminish the increasing of concrete temperature such as using of low heat cement, addition of fly-ash, application of pre-cooling, etc., and in this study, we evaluate the heating and mechanical properties of ultra low heat mass concrete using Low Heat Portland(KS Type IV) cement with 30% of limestone powder. The results of this study will be applied to side wall and bottom of No. 15 and 16 of underground LNG tank in Inchon.

• Computers and Concrete
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• 제21권6호
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• pp.649-659
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• 2018

Adaptive neuro-fuzzy inference systems (ANFIS) can be efficient in modelling non-linear, complex and ambiguous behavior of cement-based materials undergoing combined damage factors of different forms (physical and chemical). The current work investigates the use of ANFIS to model the behavior (time of failure (TF)) of a wide range of concrete mixtures made with different types of cement (ordinary and portland limestone cement (PLC)) without or with supplementary cementitious materials (SCMs: fly ash and nanosilica) under various exposure regimes with the most widely used chloride-based de-icing salts (individual and combined). The results show that predictions of the ANFIS model were rational and accurate, with marginal errors not exceeding 3%. In addition, sensitivity analyses of physical penetrability (magnitude of intruding chloride) of concrete, amount of aluminate and interground limestone in cement and content of portlandite in the binder showed that the predictive trends of the model had good agreement with experimental results. Thus, this model may be reliably used to project the deterioration of customized concrete mixtures exposed to such aggressive conditions.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2005년도 춘계 학술기술논문발표대회 논문집
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• pp.61-64
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• 2005

Recently, there have been many studies about recycling cementitious powder from concrete waste(hereinafter referred to as waste powder), generated after recycle aggregate production. Previous studies showed that when the heating process of waste powder at $700^{\circ}C,\;Ca(OH)_2$ in paste is dehydrated making possible the restoration of hydraulic properties. Recycled cement with hydraulic properties restored is thought to be re-hydrated through the mechanism of hydration, which is almost similar in Portland cement. This clearly suggests that the hydrate of recycled cement is alkali in type. Like in general concrete, if recycled cement is used as a structural material, resistance performance against carbonation or neutralization by $CaCO_3$ in air probably would be most influential to the life of steel-reinforced concrete structure. Thus the purpose of this study is to make an experimental review on chemical properties of recycled cement, manufactured with concrete waste as base material, and investigate the durability of concrete using recycled cement through evaluating the cement s performance of resistance to carbonation in accordance with its accelerating age. Based on its results, further, the study seeks to provide basic information about ways of utilizing recycled cement.

• 한국건축시공학회지
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• 제6권4호
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• pp.61-68
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• 2006

Recently, there have been many studies about recycling cementitious powder from concrete waste(hereinafter referred to as waste powder), generated after recycle aggregate production. Previous studies showed that when the heating process of waste powder at $700^{\circ}C,\;Ca(OH)_2$ in paste is dehydrated making possible the restoration of hydraulic properties. Recycled cement with hydraulic properties restored is thought to be re-hydrated through the mechanism of hydration, which is almost similar in Portland cement. This clearly suggests that the hydrate of recycled cement is alkali in type. Like in general concrete, if recycled cement is used as a structural material, resistance performance against carbonation or neutralization by $CaCO_3$ in air probably would be most influential to the life of steel-reinforced concrete structure. Thus the purpose of this study is to make an experimental review on chemical properties of recycled cement, manufactured with concrete waste as base material, and investigate the durability of concrete using recycled cement through evaluating the cement's performance of resistance to carbonation in accordance with its accelerating age. Based on its results, further, the study seeks to provide basic information about ways of utilizing recycled cement.