• 콘크리트학회지
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• 제7권3호
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• pp.137-148
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• 1995

본 연구에서는 매스콘크리트의 온도응력을 해석적으로 검토하기 위하여 수화열 및 온도등력 해석용 프로그램을 개발하여 실구조물에 설치한 게이지에 의해 측정한 실측치와 비교검토를 하였다. 또한, 개발한 프로그램의 해석결과와 범용프로그램인 ADINA-T 및ADINA와 해석결과를 비교하였다. 그 결과, 본 연구에서 개발한 해석시스템의 해석결과는 범용프로그램의 해석결과와도 좋은 일치를 보였고, 내부구속이 강한구조물이나 외부구속이 강한 구조물 모두 내부의 온도 및 온도응력분포를 잘 평가하고 있음을 알았다. 따라서 본 연구에서 개발한 수화열 및 온도응력해석 프로그램은 매스콘크리트의 온도응력을 평가하는 데에 충분히 사용할 수 있음이 입증되었다.

• Computers and Concrete
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• 제17권2호
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• pp.173-188
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• 2016

Generally, thermal stress induced by hydration heat causes cracking in mass concrete structures, requiring a thorough control during the construction. The prediction of the thermal stress is currently undertaken by means of numerical analysis despite its lack of reliability due to the properties of concrete varying over time. In this paper, a method for the prediction of thermal stress in concrete structures by adjusting thermal stress measured by a thermal stress device according to the degree of restraint is proposed to improve the prediction accuracy. The ratio of stress in concrete structures to stress under complete restraint is used as the degree of restraint. To consider the history of the degree of restraint, incremental stress is predicted by comparing the degree of restraint and the incremental stress obtained by the thermal stress device. Furthermore, the thermal stresses of wall and foundation predicted by the proposed method are compared to those obtained by numerical analysis. The thermal stresses obtained by the proposed method are similar to those obtained by the analysis for structures with internally as well as externally strong restraint. It is therefore concluded that the prediction of thermal stress for concrete structures with various boundary conditions using the proposed method is suggested to be accurate.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.267-270
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• 2003

This study is intended to investigate the engineering properties of concrete, in which cement and fine aggregate are replaced with cement kiln dust(CKD), such as the properties of fresh concrete and hardened concrete and hydration heat history, for effective using method of CKD, a by-product produced in the process of making cement. According to the results, as the replacing ratio of CKD increases, slump and air content of concrete decreases remarkably due to an increase of viscosity and filling of the pores. As the properties of setting, initial and final setting time are shortened with an increase of the replacing ratio of CKD, and as the replacement of CKD for fine aggregate increases, setting time is shortened more greatly. Compressive strength increases due to filling of the pores and reduction of air content in comparison with plain concrete. When the replacement ratio of CKD for cement is 10% and 15%, peak temperature of hydration heat lowers slightly, but it goes up in the case of replacement of CKD for fine aggregate. Also, when cement and fine aggregate is replaced with CKD by 2.5% and 7.5% respectively(1C3S) in the case of replacement of CKD for cement and fine aggregate, it is highest.

• 한국안전학회지
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• 제31권5호
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• pp.74-81
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• 2016

This paper presents an experimental study to ivestigate mechanical property of concretes according to addition of urea and urea-water soluble sulfur contents. Urea was added at 5~20% replacement by weight of water, and water soluble sulfur was used at 2%, 4% replacement by weight of cement. The setting times, the hydration heat, the compressive strength, and the drying shrinkage, were measured on concretes with single and binary admixtures. From the test result, it was confirmed that the hydration heat of urea-water soluble sulfur was lower than that of normal concrete by $10.1^{\circ}C$, and the drying shrinkage of urea-water soluble sulfur concrete was more excellent than normal concrete. In the case of urea of 5%, Compressive strength were improved with an increase of water soluble sulfur contents. The urea-water soluble sulfur used in this research can be used as improvement materials for drying shrinkage and compressive strength.

• 한국철도학회논문집
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• 제9권6호
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• pp.657-663
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• 2006

By measuring concrete temperature and strains of concrete and reinforcing bars throughout gages embedded and also by observing the crack occurrence, this study aims at the characteristics of structural behavior of subway wall structure in associate with concrete ages. The length of 23.5m, thickness of 2.0m of real subway custody line was selected as a representative structure and 7 thermocouples and 6 strain gages were installed to measure the behavior of wall structure. The results were compared and verified with analytical results using MIDAS in order to show their usefulness. It was found that only attachment of strain gages on the surface of reinforcing bars can figure out the timing of crack occurrence and hydration heat program is useful to estimate comparatively exact magnitudes of temperature. Since estimated time of crack occurrence throughout thermal stress analysis depends on the period of transferred thermal stress from concrete to reinforcing bars, however, cracks from naked eyes were identified later than analytical results. Cracks were observed first at the center of wall line and then to the end of line symmetrically.

• 한국세라믹학회지
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• 제43권7호
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• pp.408-414
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• 2006

Properties of slag cement that contained 50 wt% of blast furnace slag were studied when replaced blast furnace slag powder with electric arc furnace slag powder. Electric arc furnace slag was aged for about 2 months in the air by being crushed to be 1-3 mm in size. As a result of the experiment, it was proven that the water content for obtaining the same consistency became decreased as slag is replaced with electric arc furnace slag instead of blast furnace slag. Also, the workability of mortar increased about 30% at the same ratio of water to binder when blast furnace slag was completely replaced with electric arc furnace slag. The compressive strength of mortar on the 28 days increased when a slag replacement rate became 10 wt%, however, it rather decreased when the slag replacement rate exceeded 10 wt%. The heat of hydration became higher for the first 14 h in case of the replacement of slag cement by electric arc furnace slag. Yet, it decreased when 14 h had passed. Therefore, when all blast furnace slag was replaced with electric arc furnace slag, about 15 cal/g heat of hydration decreased when it passed about 72 h.

• The Korean Journal of Ceramics
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• 제6권3호
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• pp.318-321
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• 2000

Most compressive strengths commonly used in the construction field are in a range of 240 to 300 kgf/$\textrm{cm}^2$ at 28 days. To get this rage of strengths, however, high-flowing concrete requires cementitious binders more than 400 to 450 kg/$\textrm{cm}^2$ for preventing segregation and sedimentation of aggregates. This amount of cementitious binder generates a large emission of excessive hydration heat, which may consequently induce harmful cracks in concrete structure. In order to reduce excessive hydration heat, thus, this paper aims at fabricating a high-flowing concrete under the condition that cement content is kept as low as 350kg/$\textrm{cm}^3$ by using viscose agents. In a parametric study, effects of cement types such as a ternary blended cement and Type V on he physical characteristics of high-flowing concrete were evaluated. In addition, the influence of viscosity was also investigated by applying two different viscose agents, one in a range of 6,000 to 10,000 cps and the others of 10,000 to 14,000 cps. In terms of chemical admixtures used in concrete mixture, the superplasticizer was Sulfonated Melamine-Formaldehyde Condensate with about 30,000 of molecular weight, and main component of viscose agent was HPMC (Hydroxy Propyl Methyl Cellulose). Slump flow was fixed at 50cm with different dosages of superplasticizer in weight.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1992년도 가을 학술발표회 논문집
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• pp.67-72
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• 1992

The heat of hydration of cement causes the internal temperature rise at early age, particulary in massive concrete structures such as a footing of nuclear reactor building or a dam. As the result of the temperature rise and restraint of foundation, the thermal stress may induce cracks in concrete. Therefore, the prediction of the thermal stress is very important in the design and construction stages in order to control the cracks developed in massive concrete structures. And, in case of young concrete, creep effect by the temperature load is larger than That of old concrete. Thus the effect of creep must be considered for checking the cracks, serviceability, durability and leakage. This study is composed of two items. The first, it is to develop a finite element program which is capable of simulating the temperature history in mass concrete. The second, when the thermal stress of mass concrete structures considering creep is calculated by using the modified elastic modulus due to the inner temperature change. It is shown that the analytical results of this study is in comparably good agreement with JCI's analytical results.

• 한국구조물진단유지관리공학회 논문집
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• 제5권4호
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• pp.121-129
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• 2001

The semi-adiabatic temperature rise and the losses of temperature of cement paste, mortar and concrete were measured by an apparatus of semi-adiabatic temperature. Heat of hydration was measured by a conduction calorimeter and adiabatic temperature rise of concrete was measured by an adiabatic calorimeter. The derived equation which can assume the adiabatic temperature was proposed by measuring the semi-adiabatic temperature of concrete. The maximum adiabatic temperature rise of concrete obtained by the derived equation of adiabatic temperature, $T_{ad}(t)=T_{sad}(t)+T_{dis}(t)$, showed $55^{\circ}C$ approximately and it had good relation with the other one obtained by the heat of hydration of cement paste and with maximum value which was measured by the adiabatic calorimeter. The adiabatic temperature rise obtained by derived equation was a different information in comparison with the value obtained by adiabatic temperature rise equations by Hell and et. al. in early age, but it showed similar tendencies with the other one according to elapsed time. Adiabatic temperature rise of lich mix concrete with highly cement content was predicted. The adiabatic temperature rise of cement paste and mortar obtained by derived equation from us showed comparatively matching results to compared with that of obtained by adiabatic temperature equation from concrete standard specification.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2004년도 학술대회지
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• pp.33-38
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• 2004

This study was performed to know watertightness and reduction effect and crack occurred by hydration heat, restraint of multiplication of hydration heat, through mechanical test, strength test and crack control test using fluosilicate salt based inorganic compound made from by-product during phosphoric acid manufacturing process. Mix proportions for experiment were modulated at 0.45 of water to cement ratio and $0.5-2.0\%$ of adding ratio of fluosilicate salt based inorganic compound. Evaluation for watertightness of concrete was carried out permeability, absorption test and porosity analysis. Effect of crack reduction was evaluated by length, drying shrinkage as well as stress change of hardened concrete at unrestraint/restraint state and also elucidated crack pattern on the concrete surface. It is ascertained that characteristics of crack resistance and watertightness for concrete was improved by an adequate addition of fluosilicate salt based inorganic compound.