• Title, Summary, Keyword: Shrinkage

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A Study on Modelling for Prediction of Concrete Drying Shrinkage according to Properties of Aggregate (잔골재 특성에 따른 콘크리트 건조수축 모델링에 관한 연구)

  • Park Do-Kyong;Yang Keek-Young
    • Journal of the Korea Institute of Building Construction
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    • v.6 no.1
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    • pp.73-77
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    • 2006
  • Drying Shrinkage has much complexity as it has relations with both internal elements of concrete and external factors. Therefore, experiments on Concrete Drying Shrinkage are carried out in this study under simplified circumstances applying temperature & Humidity test chamber which enables constant temperature and humidify. Comparative analyses have been made respectively according to the consequences aiming at modelling for prediction of Concrete Drying Shrinkage and making out measures to reduce it. As a result Strain Rate of Drying Shrinkage of concrete was measured to increase by average $10{\times}10^{-5}$ in proportion to additional 4% increase in fine aggregate ratio, when water/cement ratio constant. Strain Rate of Drying Shrinkage in pit sand concrete increased 20% higher than measured when in river sand under the condition of 90-day material age. 6. Strain Rate of Drying Shrinkage in sea sand concrete increased $10%{\sim}15%$ higher than measured when in river sand. The results of prediction of Rate of Drying Shrinkage by Response Surface Analysis are as fellows. The coefficient of correlation of Drying Shrinkage in concrete was over 90%.

A Basic Study on Autogenous Shrinkage and physical property of the Ultra-High-Strength Concrete (초고강도 콘크리트의 자기수축 및 물리적 특성에 관한 기초적 연구)

  • Park, Hyun;Yoon, Ki-Hyun;Cho, Seung-Ho;Kim, Kwang-Ki;Kim, Woo-Jae;Jung, Sang-Jin
    • Proceedings of the Korean Institute of Building Construction Conference
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    • pp.57-60
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    • 2009
  • In ultra-high-strength concrete, autogenous shrinkage is larger than dry shrinkage due to the consume of a large amount of cement and cementitous material, and this is a factor deteriorating the quality of structures. Thus, we need a new technology for minimizing the shrinkage strain for ultra-high-strength concrete. So, this paper have prepared super-high-strength concrete with specified mixing design strength of over 150MPa and have evaluated a method of reducing autogenous shrinkage by utilizing expander and shrinkage-reducing agent. According to the results of this study, with regard to the change in length by autogenous shrinkage, an expansion effect was observed until the age of seven days. The expansion effect was higher when the contents of the expander material were higher. In addition, ultra-high-strength concrete showed a shrinkage rate that slowed down with time, and the effect of the addition of expander material on compressive strength was insignificant. That is shown that required more database to be accumulated through experimental research for the shrinkage strain of members.

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The Behavior of Shrinkage on PMMA in Injection Compression Molding (사출압축성형시 PMMA 재료의 성형수축거동)

  • Choi Y.S.;Kang C.M.;Jeong Y.D.
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • pp.589-592
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    • 2005
  • Molding shrinkage s variation is one of the problems to be solved in conventional injection molding. Despite many trying-out has been to solve these, intrinsic causes of shrinkage such as orientation and thermal exchange between melt and mold has yet not solved. For reducing shrinkage and residual stress on molding, injection compression molding process was invented. In this study, experiments about effect of injection compression molding's parameters on shrinkage of molding were conducted with PMMA and compared with conventional injection molding's shrinkage. Before the injection compression molding experiment, molding shrinkage rate was predicted by analyzing pvT graph and was compared with the results of experiment. The shrinkage rate of injection compression molding was lower than convention injection molding' one but was different from the predicted shrinkage. The reason was observed that experiment mold as not positive type, flowing backward of melt into nozzle and unreasonable mechanism of injection molding machine.

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A Study on Modelling for Prediction of Concrete Drying Shrinkage according to Aggregate Ratio of Concrete (잔골재율 변화에 따른 콘크리트 건조수축 모델링에 관한 연구)

  • Park, Do-kyong;Yoon, Yer-Wan;Kim, Kwang-Seo
    • Journal of the Korea Institute of Building Construction
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    • v.4 no.4
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    • pp.71-77
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    • 2004
  • Drying Shrinkage has much complexity as it has relations with both internal elements of concrete and external factors. Therefore, experiments on Concrete Drying Shrinkage are carried out in this study under simplified circumstances applying temperature & Humidity test chamber which enables constant temperature and humidity. Comparative analyses have been made respectively according to the consequences aiming at modelling for prediction of Concrete Drying Shrinkage and making out measures to reduce it. Strain Rate of Drying Shrinkage of concrete under the condition of dry air appears to rise by about 20%-30% in proportion as the temperature rises $5^{\circ}C$ when the humidity was held below 10% compared under the condition of dry temperature & Humidity test chamber. Strain Rate of Drying Shrinkage in pit sand concrete increased 20% higher than measured when in river sand under the condition of 90-day material age. A general formula with two variables is derived as follow ${\varepsilon}={\alpha}_1+{\beta}_1x_1+{\beta}_2x_2+{\beta}_3x_1^2+{\beta}_5x_2^2$. and also graphed in 3 dimensions, enabling to apply to actual design and predict Strain Rate of Drying Shrinkage in concrete. The results of prediction of Rate of Drying Shrinkage by Response Surface Analysis are as follows. The coefficient of correlation of Drying Shrinkage in Concrete was over 90%.

Shrinkage of Knitted Fabric Depending on the Condition of Air Drying (자연 건조 조건에 따른 니트 소재 수축)

  • Ju, Jeongah;Kyung, Moonsoo;Kim, Jeehoon;Park, Yongwan;Kim, Sangyoung;Oh, Youngkee
    • Journal of the Korean Society of Clothing and Textiles
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    • v.41 no.6
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    • pp.1050-1059
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    • 2017
  • Drying processes often cause knitted fabrics to shrink. This study obtains proper drying conditions for in the dryer use that can minimize knitted fabric shrinkage by investigating changes in shrinkage according to drying conditions. The experiment samples were all machine washable plain, mesh, and lacoste knitted fabrics made of 100% cotton. Samples were first washed in a washing machine on a normal cycle. They were then layered on a flat surface in an artificial climate chamber and dried for 24 hours at $20^{\circ}C$ and $40^{\circ}C$, respectively. Shrinkage was measured for 180 minutes at 30 minute intervals after washing. The comparison results of the shrinkage in the washing and drying process indicate that 80.0% and 23.0% shrinkage of plain knitted and lacoste knitted fabrics occurred during the washing process. As the samples dried, the shrinkage of the plain and lacoste knitted fabrics then rapidly increased after approximately 30.0% moisture content. The highest air drying shrinkage occurred over one cycle with insignificant changes in shrinkage after repeated treatments.

Physical Properties and Drying Shrinkage of Concrete Using Shrinkage Reducing Admixtures (수축저감제를 사용한 콘크리트의 물성변화 및 건조수축 저감 특성)

  • Han, Cheon-Goo;Song, Seung-Heon
    • Journal of the Korea Institute of Building Construction
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    • v.5 no.3
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    • pp.101-107
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    • 2005
  • This paper reports the contribution of Shrinkage reducing admixture(SRA) to the physical properties and drying shrinkage of concrete. Dosage of SRA is varied with. For the properties of fresh concrete, an increase in SRA dosage results in a decrease in fluidity and air content, while setting time is accelerated. For the properties of hardened concrete, the incorporation of mineral admixture leads to a decrease in compressive strength at early age, whereas after 28 days, the incorporation of fly ash(FA) and blast furnace slag(BS) has greater compressive strength than conventional concrete without admixture. The use of SRA results in a decrease in compressive strength. The incorporation of SRA with every $1\%$ increase causes the decrease of compressive strength by as much as $3\~6\%$. For drying shrinkage properties, the incorporation of FA and BS reduces drying shrinkage slightly. The use of SRA also decreases drying shrinkage. Every $1\%$ of increase in SRA dosage can reduce drying shrinkage by as much as $10\~15\%$

The Behavior of Shrinkage on PMMA in Injection Molding Compression Molding (사출압축성형시 PMMA 재료의 성형수축거동)

  • Choi, Y.S.;Han, S.R.;Jeong, Y.D.
    • Journal of the Korea Society For Power System Engineering
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    • v.9 no.4
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    • pp.83-89
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    • 2005
  • Molding shrinkage is one of the problems to be solved in conventional injection molding. Despite many trying-out has been to solve it, intrinsic cause of shrinkage such as orientation and thermal exchange between melt and mold has not been solved yet. For reducing shrinkage and residual stress on molding, injection compression molding process was invented. In this study, experiments about effects of injection compression molding's parameters on shrinkage of PMMA molding were conducted and compared with conventional injection molding's shrinkage. Before the injection compression molding experiment, molding shrinkage rate was predicted by analyzing pvT diagram and was compared with the results of experiment. The shrinkage rate of injection compression molding was lower than convention injection molding's one which was different from the predicted shrinkage. The reason was observed that the experimental mold was not a proper type for injection compression, flowing backward of melt into nozzle and unreasonable mechanism of injection molding machine.

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Experimental and Computational Study on the Mold Shrinkage of PPS Resin in Injection Molded Specimen

  • Pak, Hyosang;Sim, Hyojin;Oh, Hyeon-Kyung;Lee, Guen-Ho;Kang, Min-A;Lyu, Min-Young
    • Elastomers and Composites
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    • v.55 no.2
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    • pp.120-127
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    • 2020
  • In this study, molding shrinkage of PPS resin was investigated. Two types of PPS resins with differing glass fiber and calcium carbonate content were used for this purpose. To observe mold shrinkage, molding conditions based on injection temperature, injection speed, and the position of the cushion were selected. Circular and rectangular specimens were used for the study model. Injection molding simulation was performed to predict the filling pattern and mold shrinkage, and the simulation results were compared with the experimental conclusions. It was observed that the mold shrinkage showed the highest shrinkage (distributed from 0.05% to 0.32%) dependence on the injection temperature, and the lowest shrinkage (distributed from 0.05% to 0.31%) dependence on the injection speed. The role of the position of the cushion in mold shrinkage was difficult to observe. The results of the simulation mostly agreed with the experimental results; however, for some molding conditions, the mold shrinkage in the simulation was overestimated as compared to that in the experiment.

Shrinkage Properties of High Early Strength Fiber Reinforced Concrete (초기강도 섬유보강 콘크리트의 수축특성)

  • 원종필;김현호
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.43 no.5
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    • pp.124-131
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    • 2001
  • The shrinkage properties of high early strength concrete were investigated. One of the method to control microcrack and crack development due to restrained shrinkage is to reinforce concrete with randomly distributed fibers. Regulated-set cement and two different types of fiber were adopted. The experiments for heat of hydration, drying and autogenous shrinkage were conducted. The desirable resistance of high early strength fiber reinforced concrete to restrained shrinkage microcracking was achieved. These results indicate that use of fiber in high early strength concrete plays an important role in control of crack development due to restrained shrinkage.

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Effects of Binder Burnout Temperatures on Sintering Shrinkage of Multilayer Ceramics (다층 세라믹스의 소결 수축율에 대한 Binder Burnout 온도의 영향)

  • 성재석;구기덕;윤종광
    • Journal of the Korean Ceramic Society
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    • v.33 no.12
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    • pp.1373-1379
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    • 1996
  • Change of sintering shrinkage in alumina-based multilayer ceramics was observed in various lamination condi-tions and binder burnout (BBO) temperatures. It was found that the linear shrinkages in X and Y directions were nearly the same with the BBO temperatures but a large shrinkage difference in Z direction was observed. However this phenomenon was diminished when BBO temperature was increased. A linear relationship between the laminated density and the sintering shrinkage was found and the slope was independant on the BBO temperature but dependant on the shrinkage direction.

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