• 콘크리트학회지
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• 제7권1호
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• pp.126-135
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• 1995

콘크리트의 압축강도는 구조물 설계의 기본요소이며, 압축강도의 증진전개 과정을 통하여 전반적인 시멘트와 콘크리트의 특성을 알 수 있다. 실험결과에 의하면 애쉬(OPC/PFA) 콘크리트는 일반적으로 보통 (OPC)콘크리트보다는 낮은 조기강도를 보여 주었으며 (콘크리트 타설 후 28일 전까지), 그리고 압축강도의 차이점은 콘크리트에 섞은 PFA의 양이 증가할수록 커졌다(애쉬에 의한 시멘트 대체량은 15%, 30% 그리고 45%). 그러나 비록 높은 비율의 애쉬량을 콘크리트에 사용했어도 (대체량 45%) 조기강도 시멘트를 사용한 애쉬( RHPC/PFA 45) 콘크리트의 조기강도는 보통 콘크리트와 비슷한 강도를 보여 주었다. 28일에서 3년까지의 강도실험에서는 애쉬 콘크리트가 포졸라닉(pozzolanic)영향에 의햐여 보통 콘크리트 보다 항상 높은 강도를 보여 주었다. 보통 양생온도 조건보다 높거나 낮은 온도에서는 (5$^{\circ}C$ 그리고 5$0^{\circ}C$) 애쉬 콘크리트가 항상 높은 압축강도를 나타내었다. 그러나 건조 양생시 낮은 양생온도 조건에서는 보통 콘크리트가 더 높은 압축 강도를 나타내었다.

• 한국건축시공학회지
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• 제19권2호
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• pp.131-138
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• 2019

최근에는 열악한 환경에 노출되는 콘크리트 구조물의 품질 확보에 대하여 관심이 증대되고 있다. 그 중에서 낮은 외 기온 조건에서의 초기양생 불량은 콘크리트 구조물의 초기 동해 피해를 일으킬 수 있는 것으로 알려지고 있다. 그러므로 본 연구에서는 겨울철 외기온 조건에서 결합재 종류 및 콘크리트 부재 두께 변화가 콘크리트의 초기동해 깊이에 미치는 영향 분석 및 초기동해 피해를 입은 구조체에 대하여 그 깊이를 명확히 판정하고자 하였다. 실험결과 초기동해피해의 경우 3성분계 혼합시멘트를 사용하고, 부재 두께가 얇을수록 초기동해 깊이가 깊고 코어 공시체의 명도 증가가 지연되었는데, 이는 초기발열량 저하로 콘크리트의 조직 이완이 용이하게 발생하여 흡수율이 증가하기 때문인 것으로 분석된다. 초기동해 깊이 판정은 24시간 침수 후 온도 $20^{\circ}C$, 상대습도 60 %전후인 실내에서 30분 전후로 건조를 시킬 경우 명도값(L) 45 이하의 짙은색과 밝은색으로 구별되는데, 짙은 색부분을 버니어캘리퍼스 등으로 측정하면 손쉽게 판단할 수 있다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.583-586
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• 2005

Strength of concrete is very important factor in design and quality management and may represent overall quality of concrete. Such strength of concrete may differ depending on amount of cement mixed, water and fine aggregate ratio. Classic concrete products have been produced mainly with ordinary portland cement(hereinafter 'cement'), water and fine aggregate as shown above, but various additives and mixture materials have been used for concrete manufacturing, along with development of high functional concrete and diversification of structures. Various kinds of chemical mixtures agents and mixture materials have been used as it requires concretes with other features which cannot be solved with existing materials only, such as high strength, high flexibility and no-separation in the water. Such addition of various mixture agents may cause change in cement hydrate, affecting strength. Hydration of cement is the process of producing potassium hydroxide, C-S-H, C-A-H and Ettringite, while causing heat generation reaction after it is mixed with water, and generation amounts of such hydrates play lots of roles in condensation and hardening. This study aims to analyze its strength and features with hydrates by making specimen according to curing temperature, types of mixture agent, mixing ratio and ages and by analyzing such hydrates in order to analyze role of cement hydrate on early strength of concrete.

• 미생물학회지
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• 제24권2호
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• pp.184-193
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• 1986

Interrelation between environmental influences on soil microorganisms and it's effect on disease development in ginseng (Panax ginseng C.A. Meyer) field were studied to obtain a preventive measures against the root rot of ginseng caused by soil-borne pathogens in soil in three major Korean ginseng producing areas such as Kumsan, Goesan and Poonggi. Populations of actinomycetes were relatively high in fall season from September to November. Their numbers were highly populated in healthy plot in field than replanted disease field of ginseng, whereas ratio of Trichoderma spp to actinomycetes increased in healthy plot of field indicating the higher numbers of Trichoderma spp pressented in healthy plot field. The numbers of propagules of Trichoderma spp generally increased in early summer through early fall season. Their numbers were also highly populated in the healthy plot of fields. The contents of organic matter and phosphate in healthy plot of field were somewhat high, and phophate/organic matter ratio and Mg content were high in diseased replanted field. All of the soil samples showed a weak acidic pH from 4.5 to 4.7. Soilmoisture content was increased during winter season and it did not show any significant changes curing the growing period, showing 24.6% in healthy plot in field and 19.5% in deseased plot in field respectively. Soil temperature was highest in July and August and lowest in January and February.

• Advances in concrete construction
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• 제11권4호
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• pp.307-314
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• 2021

Activated hwangtoh (ACT) is a natural resource abundant in South Korea, approximately 15.0% of soil. It is an efficient mineral admixture that has activated pozzolanic properties through high-temperature heating and rapid cooling. The purpose of this study is to improve a curb mixture that can reduce NOx outside and investigate durability performance. To this end, mortar curb specimens were manufactured by replacing OPC with ACT. The ACT substitution ratios of 0.0, 10.0, and 25.0% were considered, and mechanical and durability tests on the curb specimens were conducted at 28 and 91 days of age. Steam curing was carried out for three days for the production of curbs, which was very effective to strength development at early ages. The reduction in strength at early ages could be compensated through this process, and no significant performance degradation was evaluated in the tests on chloride attack, carbonation, and freezing and thawing. The mortar curb with an ACT of 10.0~25.0% replacement ratio exhibited clear NOx reduction through photocatalytic (TiO2) treatment. This is due to the increase in physical absorption through surface absorption and the photocatalyst-containing TiO2 coating. In this study, the reasonable range of the ACT replacement ratio for NOx reduction was quantitatively evaluated through a comprehensive analysis of each test.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.490-493
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• 2004

In the analysis of early-age concrete behavior, the fresh concrete is considered as a structural element immediately after mixing. But for the activation of real structural behavior in the fresh concrete, the so-called setting time is necessary a few hours after the beginning of hydration reaction. In this paper, analysis on the setting behavior is carried out by proposing an analytical model based on the percolation theory as well as the expanding cluster model by defining the setting as a microstructure formation in fresh concrete. An experimental investigation is also carried out to show the influences of curing temperature, mineral admixtures and chemical admixture on setting behavior of fresh concrete. Finally, the analytical results using proposed model are compared with the experimental results for the sake of verification.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2001년도 학술발표회 발표논문집
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• pp.119-122
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• 2001

Annual demand of a precast concrete bench flume used in the irrigation canal of arable land readjustment has continuously increased units recently. The average life time of the precast concrete bench flume was estimated $8{\sim}10$ years, which is too shorter than the life time of in-site placed concrete structures. In order to increase the compressive strength of the precast concrete bench flumes, the highest temperature of being lower than $95^{\circ}C$ was suggested in this study, Through analyzing the relation between the compressive strength and the amount of chloride penetration into concrete specimens, a new formula early estimating durability of the concrete structure was suggested.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.287-292
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• 1999

Mass concreting in cold weather environment should be focused on the control of thermal crack caused by high hydration heat rather than curing method for protecting from frost damage at early age because the thermal stress have much influence on the quality of structure placed in cold weather. Therefore, in this paper, the control of thermal crack of mass concrete in cold weather environment are dealt with preparing the practice plan for mass concrete and placing the concrete according to the plactice plan. According to the results, we can obtain good quality mass concrete without thermal crack caused by the difference of temperature between inner part and outer part.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2012년도 춘계 학술논문 발표대회
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• pp.251-252
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• 2012

The exiting studies on the strength prediction by maturity method is mainly focused on concrete using OPC, meanwhile the study on the concrete mixing blast furnace slag powder (BFSP) is insufficient. The purpose of this study is to investigate the relationships between compressive strength and equivalent age by existing Maturity functions, i.e., Nurse-saul function Arrhenius function. This study also compared and examined the strength prediction of concrete mixing BGSP using ACI model and Logistic Curve prediction equation. Therefore, it is intended that fundamental data are presented for quality management and process management of concrete mixing BFSP.

• 한국건축시공학회지
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• 제12권5호
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• pp.503-509
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• 2012

In this study, the potential use of indigenous natural loess(Hwangtoh) as a new construction material, via alkali activation in conjunction with microwave heating, was investigated. Hwangtoh pastes with three different mix proportions of varying alkali liquid concentrations at a constant liquid-to-Hwangtoh ratio of 0.55 were prepared. Through the investigation it was found that it is possible to prepare Hwangtoh paste with $19.02N/mm^2$ at the age of 4 hours with the alkali solution of 8M NaOH and 1:4.5 mass ratio of liquefied $Na_2SiO_3$ at the curing temperature of $60^{\circ}C$ by microwave heating. The strength development at early age of the alkali activated Hwangtoh paste specimens may be attributed to both a higher rate of reaction and moisture evaporation due to microwave heating.