• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.2
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• pp.1-9
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• 2009

Water binder ratio combine high-performance concrete shrinkage of less than 0.4 to determine the transformation to a total shrinkage of water to move outside and internal consumption of moisture due to drying shrinkage and autogenous shrinkage, and then, the relative humidity changes and strain to be approached by surface physics describe the relationship between self-desiccation and autogenous shrinkage was set. To verify the self-desiccation in the humidity shrinkage and humidity measurements performed, and the research model, Tazawa, CEB-FIP model than to let the measure and the most similar results in this study based on self-desiccation model, autogenous shrinkage didn't represent the linear shrinkage by the drying shrinkage of the external moving but exponential relationships, unlike with the nature and rapid in the early age properly describes the attributes in shrinkage could see. After this research to move moisture and to reflect the shrinkage model, temperature, moisture transfer, strain analysis by multi-physics model is very similar to the results of mock-up specimen measurements performed for this research, the value measured by the internal consumption of moisture, therefore self-desiccation and a multi-physics model considering autogenous shrinkage might be relevant.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.937-940
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• 2008

Recently, the recycling and reusing of construction and demolition waste concrete is urgently required because generation quantity of construction and demolition waste concrete is greatly increased according to the rapid increasing of urban redevelopment project. On the other hand, the problem solution for demand and supply unbalance of fine aggregate is urgently required because of the restriction of collecting sea fine aggregate by intensification of environment influence evaluation and the shortage of river fine aggregate. but a quality of aggregate as building structure is not demonstrated. Therefore it is the objective of this study to estimate plastic and early dry shrink crack of fiber reinforced concrete using a recycled aggregate by plat-ring test and mock-up test of exposure to the air. as a result, in case of plat- ring test, developing crack is wider using recycled aggregate concrete than natural aggregate concrete, is wider using fiber reinforced concrete than non fiber. in case of mock-up test of exposure to the air, it is similar to plat-ring test.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.821-824
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• 2008

In this study, it is willing to present that fundamental data for proposing quantitatively shrinkage cracking evaluation method such as plat-ring type restrained test method. It is possible to decide that specimen diameter is s 150mm with evaluating restrained shrinkage crack properties of concrete according to change of ring diameter in specimen. Also, effectiveness of test method according to mixing of PVA fiber is evaluated as part of a repeatability verification experiment of plat-ring type restrained test method using ring which diameter is 150mm. As a result, it is possible to measure the crack due to the plastic shrinkage which was occurred within 48hours at early age with plat-ring type restrained test method. Hereafter, it is considered that the study concerning environmental condition and mixing factor in plat-ring type restrained test method is need.

• Journal of the Korea Institute of Building Construction
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• v.19 no.1
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• pp.59-66
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• 2019

In this study, the effects of blast furnance slag cement and frost-resistant accelerator on shrinkage properties and shrinkage properties of mortar were examined. As a result, the addition of the frost-resistant accelerator to both OPC and BB has a small effect on the flash properties of mortar and the compressive strength increases from the early ages. In addition, when a frost-resistant accelerator is used in excess of the standard usage amount, it is necessary to examine the relationship of the expansion behavior at the early age, especially, between the compressive strength development and the expansion property. And it was confirmed that the addition of the frost-resistant accelerator tended to increase the shrinkage of mortar using the OPC and BB. With the addition of the frost-resistant accelerator, the amount of pores with a diameter of under the 30nm, especially, the amount of pores with a diameter of 20 to 30nm and the amount of pores with an ink-bottle decrease, and the shrinkage increases. And it is considered that a change in the amount this range of pores has a large effect on the shrinkage property.

• Magazine of the Korea Concrete Institute
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• v.5 no.3
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• pp.152-160
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• 1993

양생 초기에 있어서 콘크리트의 투수계수는 콘크리트의 건조수축에 영향을 미치는 요인으로서 콘크리트내의 물의 이동과 관련된 중요한 변수이다. 콘크리트의 특수성에 관한 연구는 주로 콘크리트의 건조수축이나, 동결융해에 대한 내구성 등과 연관되어 있다. 이들 대부분의 측정결과는 염소 이온등을 이용한 간접 측정방법이거나 충분히 양생된 안정한 콘크리트를 대상으로 하는 것이 대부분이므로 양생초기의 콘크리트의 투수계수에 관한 연구는 거의 없다고 할 수 있다. 본 연구에서는 싸이크로미터라는 수리에너지를 측정하는 쎈서를 이용하여 콘크리트의 투수계수의 측정을 시도하였다. 콘크리트의 투수계수와 확산계수를 측정하기 위한 세가지의 방법을 제시하였으며, 이를 적용하는 실험도 실시하였다. 또한 투수계수와 확산계수간의 변환을 위한 등온 흡수선을 개발, 적용하였다.

• Journal of Oral Medicine and Pain
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• v.23 no.4
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• pp.433-445
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• 1998

본 연구는 정상인의 저작근에서 지속적인 등척성 수축후 근전도 power spectrum과 압력통각 역치의 회복 특성을 구명하기위해 시행되었다. 악안면 영역의 동통과 긴으장애의 벙력 및 현증이 ㅇ벗고 정상적인 교합관계를 가진 26명의 정상인(남자 14명, 여자 12명) 을 대상으로 최대근활성도의 70% 수준에서 인내가능 할 때까지의 등척성 수축과 수축후 회복기 동안의 근전도 power spectrum과 압력통각 역치를 컴퓨터를 이용한 근전도 시스텀과 전자식 압력통각계를 사용하여 분석한 결과 다음과 같은 결론을 얻었다. 1. 지속적인 등척성 수축 시작 시점의 중간주파수에서 남녀간에는 통계적으로 유의한 차이가 관철되지 않았지만, 근육간 비교에서는 전측두근에서 교근보다 유의하게 높게 나타났다(p<0.05). 2. 지속적인 등척성 수축전 암력통각 역치는 전축두근에서 교근보다 유의하게 높았고(p<0.001), 남성에서 여성보다 유의하게 높게 나타났다(p<0.05). 3. 지속적인 등척성 수축시 중간주파수와 압력통각 역치의 변화량은 성별간, 근육간에 우의한 차이가 관찰되지 않았다. 4. 지속적인 등척성 수축말기 중간주파수는 수축초기에 비하여 유의하게 감소하였으며(p<0.001), 이의 회복은 모든 근육에서 60초와 120초 사이에서 이루어 졌다. 5. 지속적인 등척성 수축후 압력통각역치는 수축전에 비해 유의하게 감소하였으며(p<0.001), 수축전 수준으로의 회복은 여자군의 전측두근과 교근에서는 30분후에 남자구느이 전측두근과 교근에서는 50분 후에 이루어졌다. 6. 지속적인 등척성 수축후 주관적인 동통이 소실된 시각은 여자군의 전축두근에서는 28분, 교근에서는 42분으로 남자군의 전측두근에서는 30분, 교근에서는 40분으로 나타났다.

• Magazine of the Korea Concrete Institute
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• v.7 no.5
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• pp.164-171
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• 1995

Drying shrinkage and hydration heat are important factors on the initiation of the crack in con crete at early age. Therefore, the stress caused by hydration heat and drying shrinkage should be .analyzed to predict whether the crack occurrs or not. And, mechanical properties of early age concrete is also required for the predicting crack formation In this study, non-destructive test method of resonance frequency was used to find the relation between dynamic modulus and mechanical properties of concrete in early age. Test results were compared with existing equations, and a new equation based on test. results in this study and other data was also proposed

• Korean Journal of Fisheries and Aquatic Sciences
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• v.21 no.1
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• pp.11-15
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• 1988

Square slices of sea tangle was dried in constant condition of thickness (1.54mm), air temperature $(50^{\circ}C)$, relative humidity $(30\%)$ and air velocity (0.4m/s). The shrunk surface area and the shrinking rate were investigated. The results obtained are summarized as follows : 1) Comparing the shrinking of transverse section with that of vertical section, the transverse section was proceeded more double shrinkage than vertical section. 2) The shrunk surface area curve showed nearly a linear shrinkage up to 90min of drying time. 3) The shrinking rate was rapidly increased in first falling rate period, and was largest in the early period of second falling rate period.

• Journal of the Korea Concrete Institute
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• v.14 no.1
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• pp.76-82
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• 2002

The rapid-set cement concrete causes high hydration temperature and nay result in a high drying shrinkage and shrinkage-induced cracking. This problem may be fixed by incorporating polypropylene fibers in rapid-set cement concrete, because of increased toughness, resistance to impact, corrosion, fatigue, and durability. A series of concrete drving shrinkage tests was peformed in order to investigate the shrinkage properties of polypropylene fiber reinforced concrete with experimental variables such as concrete types, fiber reinforcement, W/C ratio, with and without restraint. Uni-axially restrained bar specimens were used for the restrained shrinkage tests. The results were as follows; The dry shrinkage of rapid-set cement concrete was much lessor than that oi OPC, probably because of smaller weight reduction rate by early hydration and strength development. The constraint and bridging effects caused by polypropylene fibers were great for the rapid-setting cement concrete when compared with that of plain concrete, and this resulted In increased resistance against tensile stress and cracking.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.1
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• pp.97-102
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• 2010

The objective of this paper is to explore the possibility of reuse of waste vegetable oil (WO) as an autogenous shrinkage reducer for high strength concrete and to compare the amount of autogenous shrinkage of the mortar using existing shrinkage reducing agent(SR) and expansive additives(EA). According to test results, as the dosages of WO increased, flow value exhibited to decrease, while the use of SR increased flow value. For the effect of WO on strength, although the use of SR and WO resulted in a slight decrease in compressive strength at early age, at 91 days they had similar strength level of the plain mixture. For autogenous shrinkage, as expected, the addition of WO, SR and EA resulted in a decrease of autogeneous shrinkage considerably especially, WO had superiority in autogenous shrinkage reducing effect compared with the case of SR and EA.