• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.745-750
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• 2001

This study is about application to real construction site of estimating a early strength with use of microwave. Based on the exist studies, it is tried to confirm the correlation between curing temperature and estimating early strength method with microwave. The result of this study are as follows. 1) Coefficient figure of common use concrete's accelerating strength and 28 days strength after curing at $10^{\cire}C$, $20^{\cire}C$, $30^{\cire}C$ is 0.84, 0.80, 0.80 2) Coefficient figure of concrete's-has a low fine aggregate ratio- accelerating strength and 28 days strength after curing at $10^{\cire}C$, $20^{\cire}C$, $30^{\cire}C$ is 0.86, 0.82, 0.81

• 한국구조물진단유지관리공학회 논문집
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• 제8권2호
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• pp.177-183
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• 2004

적산온도은 시멘트 수화의 결과로서 시간이 경과함에 따라 콘크리트 강도가 얻어진다는 것으로 콘크리트의 강도는 시멘트의 수화반응과 관계가 있다. 시멘트의 수화반응은 온도와 경과시간에 큰 영향을 받는다. 따라서 본 연구에서는 콘크리트 강도예측에 있어서 양생시간과 온도의 함수인 적산온도와 고강도콘크리트 강도의 상관성을 검토하고자 하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.237-242
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• 2003

The object of this study is to investigate the strength development properties and the strength prediction of three-component concrete using the fly ash and the blast-furnace slag by a maturity method. The results were as follows. The values of the activation energy on this experiment are calculated as 38.69, 36.47, 32.46, 30.99 KJ/mol in the W/B 60, 55, 50, 45%. And it is considered that the equivalent age can be used to predict strength of the three-component concrete in the optional age. Also the strength of the three-component concrete can be predicted from the result of high correlation between predicted strength and measured strength.

• 콘크리트학회논문집
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• 제12권6호
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• pp.67-74
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• 2000

The usage of nondestructive testing on early-aged concrete leads to enhacned safty and allows effective scheduling of construction, thus making it possible to maximize the time and cost efficiencies. In this study, a reliable nondestructive strength evaluation method for early-aged concrete using the longitudinal wave velocity is proposed. Compression tests were performed to examine factors influencing the velocity-strength relationship of concrete, such as water-cement (w/c) ratio, fine aggregate ratio, curing temperature, and curing condition. The test results show that a change in the w/c ratio and curing temperature has minor effect on the velocity-strength relationship/ However, curing condition significantly influences the velocity-strength relationship of early-aged concrete. Moreover, the longitudinal wave velocity increases with decreasing fine aggregate ratio. It is concluded from this study that the strength evaluation of early-age concrete can be achieved by a nonlinear equation which considers the effects of curing condition and fine aggregate ratio.

• 한국재료학회지
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• 제23권12호
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• pp.687-694
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• 2013

This study was performed with an aim to improve the early-age strength of concrete containing fly ash, which is known to increase the long-age strength of concrete, reduce drying shrinkage, and enhance water tightness. The composition was partially substituted with calcium sulfoaluminate (CSA), from which ettringite is actively produced, in the early stages of hydration to verify its effect on improving the early-age strength and to determine the optimal mixing ratio. For this purpose, up to 30 % of the cement weight was substituted with fly ash, and the amount of CSA substitution was 8% of the fly ash weight. The mixtures were then fabricated into concrete specimens for compressive strength measurement and analysis of the correlation between the hydration products and the compressive strength.

• 한국구조물진단유지관리공학회 논문집
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• 제5권3호
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• pp.123-130
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• 2001

The purpose of this study is to suggest the non-destructive equation for the estimation of concrete strength by ultrasonic pulse velocity at the Age of 28day compressive strength of $600{\sim}1000kg/cm^2$. For this purpose, selected test variables were water-hinder ratio, replacement ratio of silica fume, binder content, maximum size of coarse aggregate and sand-aggregate ratio. From the results, the average increase or decrease of ultrasonic pulse velocity is 61m/sec for each 1% of moisture content. And the correlation equation between the ultrasonic pulse velocity and the compressive strength of concrete is as follows. $F_c=896.3V_p-3514$ ($R^2$ = 0.81) where, $F_c$ : compressive strength($kgf/cm^2$), $V_p$ : ultrasonic velocity(km/sec).

• 한국운동역학회지
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• 제24권1호
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• pp.85-93
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• 2014

The purpose of this study was to investigate a relationship among Taekwondo, soccer and gymnastic athletes their balance ability and lower extremity muscle strength, muscle endurance and also whether these variables show differences by sports type. For this purpose, 10 Taekwondo athletes, 10 soccer athletes and 10 gymnastic athletes that is a high school in I area were selected and their balance ability, isokinetic muscle strength and muscle endurance were measured by using force platform (AMTI) and isokinetic measurement (HUMAC NORM). Then the following results were obtained by conducting pearson product-moment correlation analysis and one-way ANOVA. In case of both right and left foot one-leg standing with open-eyes, there was a relation between both knee extension maximal muscle strength of Taekwondo, soccer, gymnastic athletes and balance ability, and in case of right foot one-leg standing with open-eyes, there was a relation between that is right plantar flexion and dorsi flexion maximum muscle strength and muscle endurance of Taekwondo, soccer, gymnastic athletes and their balance ability. Furthermore, in case of left dorsi flexion maximum muscle strength, there were significant differences in order of Taekwondo, gymnastics and soccer, and for isokinetic plantar flexion maximum muscle endurance, both right and left showed significant differences in order of Taekwondo, gymnastic and soccer.

• Geomechanics and Engineering
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• 제23권3호
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• pp.227-244
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• 2020

Earthen structures have an excellent bioclimatic performance, but they are vulnerable against earthquakes. In order to investigate the edification process and costs, a full-scale rammed soil house was constructed in 2004. In 2016-2019, it was studied its seismic damage, durability and degradation process. During 2004-2016, the house presented a relatively good seismic performance (M_w=5.6-6.4). The damaged cover contributed in the fast deterioration of walls. In 2018 it was observed a partial collapse of one wall due to recent seismicity (M_w=5.6-6.1). The 15-year-old samples presented a reduced compressive strength (0.040 MPa) and a minimum moisture (1.38%). It is estimated that the existing house has approximately a remaining 20% of compressive strength with a degradation of about 5.4% (0.0109 MPa) per year (considering a time frame of 15 years) if compared to the new soil samples (0.2028 MPa, 3.52% of moisture). This correlation between moisture and compressive strength degradation was compared with the study of new soil samples at the same construction site and compared against the extracted samples from the 15-year-old house. At 7-14-days, the specimens presented a similar compressive strength as the degraded ones, but different moisture. Conversely, the 60-days specimens shown almost five times more strength as the existing samples for a similar moisture. It was observed in new rammed soil that the lower the water content, the higher the compressive/shear strength.

• 한국콘텐츠학회논문지
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• 제17권8호
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• pp.90-97
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• 2017

본 연구는 초등학생의 가족건강성과 문제해결능력이 학교생활적응에 미치는 영향을 확인하는데 목적이 있다. 이를 위해 S시 학교사회복지사업 운영 초등학교의 학생들을 대상으로 조사한 자료를 사용하였고, 연구대상은 2,422명이다. 본 연구의 자료는 SPSS 20을 사용하여 빈도분석, 상관관계분석, 회귀분석을 하였다. 연구결과는 다음과 같다. 첫째, 가족건강성과 문제해결능력, 그리고 학교생활적응은 서로 유의미한 상관관계를 보였다. 둘째, 가족건강성은 학교생활적응에 매개변인 없이도 직접적인 영향을 주고 있었다. 셋째, 가족건강성은 문제해결능력을 매개로 학교생활적응에 유의미한 영향을 미치는 것으로 나타났다. 이 연구결과를 바탕으로 학교생활적응을 높이기 위해서는 이에 영향을 미치는 가족의 건강성을 높이고, 문제해결능력을 키우는 제반 환경적 자극을 통해 아동들의 적절한 발달적 과업을 이루도록 돕는 전략이 필요하다고 할 수 있다.

• 한국콘텐츠학회논문지
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• 제16권3호
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• pp.638-648
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• 2016

본 연구는 영유아교사의 자아강도, 자기효능감이 문제해결력에 미치는 영향을 알아보고자 실시하였다. 연구대상은 K시와 J지역에 재직하고 있는 영유아교사 293명이다. 연구도구는 자아강도 척도와 자기효능감 척도, 문제해결력 척도를 사용하였다. 자료는 t검증, 일원변량분석, 상관관계, 회귀분석으로 처리하였다. 연구결과, 영유아교사의 자아강도와 자기효능감, 그리고 문제해결력은 상관관계가 있었으며 문제해결력에 자아강도와 자기효능감이 영향을 주는 변인임이 밝혀졌다. 영유아교사는 자신에게 일어난 문제를 얼마나 효율적으로 해결하고 있는가에 따라 문제해결과 대처능력의 차이를 보이며 자아를 통합하는 자아강도에 중요한 요소로 자기효능감과도 연관이 있다. 자신의 심리적인 갈등과 불안을 해결하지 못한 교사는 영유아를 따뜻하고 편안하게 돌보고 지도하기에 미흡하므로 긍정적인 자기상(self-image)을 형성하여 문제해결을 증진시킬 수 있는 자아성장 프로그램 개발의 필요성을 시사하고 있다.