• The Korean Journal of Rheology
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• v.3 no.1
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• pp.47-55
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• 1991

본 연구에서는 구형기포가 미분형의 upper convected Maxwell 모델을 따르는 유체 내에서 수축할 때의 현상을 이론적으로 해석하였다. 수치해법으로는 Lagrangian 좌표계에서 지배방정식을 유도 사용함으로써 자연스럽게 자유표면을 추적하는 동시에 압력변수도 반복 에 의하지 않고 직접적인 방법으로 계산할 수 있는 Galerkin-유한요소법을 개발사용하였다. 본연구의 결과 유체의 탄성은 변형초기에 충분히 발달치 못하기 때문에 수축을 가속화시키 지만 수축 후기에는 지연시킴을 알 수 있었다. 수축의 속도는 적분형 Maxwell 유체에서 보 다 빠른 것을 알수 있었는데 이는 유체의 정지이력에 의한 것으로 판단되었다, 또한 Maxwell 유체내에서 기포가 수축할 경우 탄성에 의한 반동현상이 나타나며 반동이 점성에 의하여 감쇄될 때의 진폭과 주기는 비례함을 보였다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.5
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• pp.3535-3541
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• 2015

In this study, series of tests were performed for drying shrinkage characteristics of concrete with power type shrinkage reducing agent (SRA) and fly ash as a part of research to reduce drying shrinkage of concrete. Firstly, for the mechanical properties, a target strength was acquired securely. In the unrestraint shrinkage tests, the SRA decreased the drying shrinkage about $200{\mu}{\varepsilon}$. Lastly, in the ring tests, due to the tensile creep effect, the concrete with SRA showed the cracking times as much again as the concrete with ordinary Portland cement only did.

• 전기의세계
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• v.14 no.1
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• pp.1-4
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• 1965

한국전력주식회사의 초청으로 1962년 5월 26일-27일 화천발전소를 시찰할 수 있는 기회를 얻어 현장에서 기술차에 의해 제시된 발전기 축진동에 관한 문제를 1963년 5월 연구의뢰를 받는 이래 3회에 걸쳐 현장에서 실험측정을 행하였고 수축형 수차발전기의 축진동의 제원인과 그 원인들에 의해서 발생하는 축진동을 해석하여 측정된 진동곡선에서 주원인이 무엇인가를 찾아낼 수 있는 일반 판별법을 만들고 이 방법에 의하여 화천발전소에서 측정 실측자료로서 진동의 주요 원인을 판별하기로 하였다.

• Journal of the Korea Concrete Institute
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• v.28 no.1
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• pp.41-48
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• 2016

This research investigates the effects of shrinkage reducing agent (SRA) on the mechanical behavior of strain-hardening cement composite (SHCC). SHCC material with specified compressive strength of 50 MPa was mixed and tested in this study. All SHCC mixes reinforced with volume fraction of 2.2% polyvinyl alcohol (PVA) fiber and test variables are type and dosage of shrinkage reducing agents. The shrinkage reducing materials used in this study are phase change material as the thermal stress reducing materials that have the ability to absorb or release the heat. The effect of SRA was examined based on the change in length caused by shrinkage and hardened mechanical properties, specially compressive, tensile and flexural behaviors, of SHCC material. It was noted that SRA reduces change in length caused by shrinkage at early age. SRA can also improve the tensile and flexural strengths and toughness of SHCC material used in this study.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.6
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• pp.693-699
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• 2016

In this study, the replacement effects of cementitious materials (fly ash, blast furnace slag, and blended mixtures) were assessed for normal strength concrete with very low shrinkage properties under $350{\mu}{\varepsilon}$ strain using a powder type shrinkage reducing agent. In addition, through mock-up tests of actual size walls restrained with four sides, the shrinkage characteristics using the power type shrinkage reducing agent were measured and the crack reducing ability was assessed. The slump and air contents were measured as the properties of fresh concrete, and the length changes of the prismatic specimens, $100{\times}100{\times}400mm$ in size, were measured for the shrinkage characteristics. To reduce the shrinkage of concrete, the maximum replacing ratio of the fly ash is effective to 20 percent; however, the use of blast furnace slag and ternary mixtures did not reduce the shrinkage.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.102-108
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• 2016

The purpose of this study is to examine the reduction effect of shrinkage reducing agent for drying shrinkage induced cracking and suggest the method of controlling the cracking in concrete box culvert for power transmission. Based on drying shrinkage cracking mechanism, it is necessary to perform the numerical analysis, which involves shrinkage reducing effect of shrinkage reducing agent. From the numerical results, it is found that cracking behavior for longitudinal direction and transverse direction due to differential drying shrinkage of box culvert can occur and the experimental observation of concrete cracks support the numerical predictions. The shrinkage reducing agent reduced the concrete cracking by 40~50%, which shows the methodology of controlling of drying shrinkage cracks in box culverts in real construction site.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.117-124
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• 2017

In this study, to evaluate the setting time, compressive strength and drying shrinkage of ordinary Portland cement and Portland blast-furnace slag cement mortar with 0, 10, 20, 30 wt.% alpha-calcium sulfate hemihydrate. As a results, as the replacement ratio of alpha-calcium sulfate hemihydrate increased, the initial setting time of ordinary Portland cement and Portland blast-furnace slag cement mortar was faster. In addition, the compressive strength decreased with increasing replacement ratio of alpha-calcium sulfate hemihydrate in both ordinary Portland cement mortar and Portland blast-furnace slag cement mortar. The strength development of Portland blast-furnace slag cement mortar with alpha-calcium sulfate hemihydrate was effective than that of ordinary Portland cement mortar. On the other hand, in the case of the mortar with alpha-calcium sulfate hemihydrate, it was confirmed that shrinkage deformation was reduced at the early age by growth pressure of needle-shaped ettringite crystals produced by incorporation of alpha-calcium sulfate hemihydrate. However, the effect of inhibiting shrinkage deformation of mortar with alpha-calcium sulfate hemihydrate was not significant as the age passed. Therefore, it is considered that the alpha-calcium sulfate hemihydrate is useful as a construction material.

• Journal of Energy Engineering
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• v.28 no.1
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• pp.17-21
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• 2019

Calcium sulfaluminate (CSA) was synthesized to improve the shrinkage of OPC. In this study, the setting time, the compressive strength and the length change ratio were confirmed by replacing the synthesized CSA with OPC by 10% and 13% by 16%. In the case of shrinkage-reducing type cement, formation of Ca-Al-$H_2$-based hydrate was activated. Therefore, the setting time was shortened. The compressive strength of the shrinkage - reducing type cement is comparable to that of OPC after 7 days' strength. However, shrinkage reducing type cement showed improved initial strength compared to OPC. The length change ratio was found to be improved by drying shrinkage from -0.075% to -0.047% on the 28th day.

• Journal of the Korea Concrete Institute
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• v.25 no.4
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• pp.371-379
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• 2013

This paper investigates the cracking and tension-stiffening behavior of 100 MPa shrinkage-compensated strain-hardening cement composite (SHCC) and conventional concrete tie elements in monotonic and cyclic tension. Strain and surface crack formation of tension ties were monitored with two strain displacement transducers and a photo microscope with a lens of magnification 50 times. Three different cement composites such as conventional concrete, shrinkage-compensated SHCC, and normal SHCC were used in the tie specimens to investigate the influence of the cement composite type on the tension stiffening and cracking behavior. Test results indicated that initial shrinkage of the ultra high-strength cement composites is greatly reduced as the 10% replacement of cement by the shrinkage-compensating admixture based on calcium sulfo-aluminate (CSA). The test results on the SHCC tension ties showed that the first cracking load decreases proportionally to the initial shrinkage strain. Reinforced ultra high-strength SHCC ties with the initial shrinkage compensation exhibited improved tension stiffening and smaller crack spacings, i.e. the reduction in crack width. Cyclic loading did not have a significant effect on tension stiffening and cracking behavior of tension ties with normal concrete and SHCC materials.

• The Journal of Korean Academy of Prosthodontics
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• v.48 no.1
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• pp.55-60
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• 2010

Purpose: The shrinkage of dental resin cement may cause several clinical problems such as distortion that may jeopardize the accurate fit to the prepared tooth and internal stress within the restorations. It is important to know the polymerization shrinkage-strain of dental resin cement to reduce clinical complications. The purpose of this study was to investigate the polymerization shrinkage-strain kinetics of six commercially available dental resin cements. Material and methods: Three self-cure resin cements (Fujicem, Superbond, M-bond) and three dual-cure resin cements (Maxcem, Panavia-F, Variolink II) were investigated. Time dependent polymerization shrinkage-strain kinetics of the materials were measured by the Bonded-disk method as a function of time at $23^{\circ}C$, with values particularly noted at 1, 5, 10, 30, 60, 120 min after mixing. Five recordings were taken for each materials. The data were analyzed with one-way ANOVA and Scheffe post hoc test at the significance level of 0.05. Results: Polymerization shrinkage-strain values were 3.72%, 4.19%, 4.13%, 2.44%, 7.57%, 2.90% for Fujicem, Maxcem, M bond, Panavia F, Superbond, Variolink II, respectively at 120 minutes after the start of mixing. Panavia F exhibited maximum polymerization shrinkage-strain values, but Superbond showed minimum polymerization shrinkage-strain values among the investigated materials (P < .05). There was no significant differences of shrinkage-strain value between Maxcem and M bond at 120 minutes after the start of mixing (P > .05). Most shrinkage of the resin cement materials investigated occurred in the first 30 minutes after the start of mixing. Conclusion: The onset of polymerization shrinkage of self-cure resin cements was slower than that of dual-cure resin cements after mixing, but the net shrinkage strain values of self-cure resin cements was higher than that of dual-cure resin cements at 120 minutes after mixing. Most shrinkage of the dental resin cements occurred in the first 30 minutes after mixing.