• Title/Summary/Keyword: Self shrinkage

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Differential Drying Shrinkage and Autogenous Shrinkage of Concrete at Early Ages (초기재령 콘크리트의 부등건조수축과 자기수축에 관한 연구)

  • 김진근;이칠성
    • Proceedings of the Korea Concrete Institute Conference
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    • 1998.04a
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    • pp.309-314
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    • 1998
  • The moisture diffusion and self-desiccation cause the differential drying shrinkage and autogenous shrinkage at early ages, respecitvely. Thus total shrinkage strain includes the differential drying shrinkage and self-desiccation shrinkage. Thus in this study the shrinkage strain was measured at various positions in the exposed concrete and in the sealed concrete the self-desiccation shrinkage was measured. In low-strength concrete, the differential drying shrinkage increases very rapidly, but self-desiccation shrinkage is very small. But high-strength concrete shows the reverse result. And the analytical results for differential drying shrinkage were in good agreement with the test results.

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Multi-physics Modelling of Moisture Related Shrinkage in Concrete (콘크리트 수분관련 수축에 관한 다중물리모델)

  • Lee, Chang-Soo;Park, Jong-Hyok
    • 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.

Life Experiences of Middle School Students from Broken Homes (결손가정 중학생의 생활경험)

  • Choe, Gee-Hyun;Chung, Yeon-Kang;Yeoum, Soon-Gyo
    • Journal of the Korean Society of School Health
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    • v.10 no.2
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    • pp.271-283
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    • 1997
  • This study is designed for the school health education, contributing experience of life from middle school students from broken homes by describing specifically what they go through. And on this basis this study works out a grounded theory on the experience of life for middle school students from broken homes. The data was collected through a series of interviews with nine subjects singled out at each stage of research. With the permission of the subjects, the interviews were recorded and transcribed. The interviews lasted from 30 minutes up to one hour and 20 minutes. The in-depth interviewing methods and observations was used for data collection. The data was analyzed in the framework of grounded theory as mapped out by Strauss & Corbin (1990). By analyzing the materials eighty-three concepts were extracted, and they were united into 21 subordinate categories through the course of analysis. These were classified into nine precedence categories. The core category was found to be the adaptation of 'Wichookdem" or "Shrinkage". "Shrinkage" widows experienced was showed as the results "Self-reliance" and "Overcoming" through the course of generation and reaction, confrontation, and adaptation. According to the analysis findings of materials, the central phenomenon was showed as "shrinkage", the causal condition as "surprise", "Darkness", "Grudge", "Desolate", "Empty". The veins as presence of those around people and existence of support, and the meditate situation as self-support. For the strategy in solving "shrinkage", preparations of countermeasure and self-reinforcement were showed. And self-reliance and overcoming were the results. Through the contrast to the cases of ground materials, relation statements as follows were induced; (1) The weaker the suffering is, the weaker the "shrinkage" tends to be. (2) The stronger the suffering is, the stronger the "shrinkage" tends to be. (3) The more frequent and serious the suffering, the stronger the "shrinkage" tend to be. (4) The more infrequent and not serious the suffering is, the weaker the "shrinkage" tends to be. (5) The weaker the "shrinkage" is, the more self-control1ed the responses tends to be. (6) The stronger the "shrinkage" is, the more impulsive the responses tends to be. (7) The more satisfying the support is, the more self-controlled the responses to the "shrinkage" tends to be. (8) The more dissatisfying the support is, the more impulsive the responses to the "shrinkage" tends to be. (9) The more concrete the type of support is, the more self-controlled the responses to the "shrinkage" tends to be. (10) The more superficial the type of support is, the more impulsive the responses to the "shrinkage" tends to be. (11) The more self-controlled the responses are, the more self-reliant the subjects tends to be. (12) The more impulsive the responses are, the more conflict and wandering the subjects tends to be. (13) Whether the responses to the "shrinkage" express themselves in self-control or an impulse, it will be resulted in the form of either tension or pain. The following two were confirmed on the basis of repetitive relations; (1) If a subject's suffering is weak, infrequent and not serious, the "shrinkage" is weak. Also the subject's support is highly satisfying, and the support type is concrete. The responses to the "shrinkage" result in self-control which consequence is self-reliance with part. of it resulting in tension and pain. (2) If a subject's suffering is strong, frequent and serious, the "shrinkage" is strong. Also the subject's support is dissatisfying, and the support type is superficial. The responses to the "shrinkage" result in an impulsion whose consequence is wandering with part of it resulting in tension and pain. Through the results in this study, the following is to be suggested; O This research is basically aimed at analyzing the experience of the middle school students living in broken homes, for the more inclusive approach, the study for them is made systematically according to the type of their problems.

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Cracking of Fiber-Reinforced Self-Compacting Concrete due to Restrained Shrinkage

  • Kwon, Seung-Hee;Ferron, Raissa P.;Akkaya, Yilmaz;Shah, Surendra P.
    • International Journal of Concrete Structures and Materials
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    • v.1 no.1
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    • pp.3-9
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    • 2007
  • Fiber-reinforced self-compacting concrete (FRSCC) is a new type of concrete mix that can mitigate two opposing weaknesses: poor workability in fiber-reinforced concrete and cracking resistance in plain SCC concrete. This study focused on early-age cracking of FRSCC due to restrained drying shrinkage, one of the most common causes of cracking. In order to investigate the effect of fiber on shrinkage cracking of FRSCC, ring shrinkage tests were performed for polypropylene and steel fiber-reinforced SCC. In addition, finite element analyses for those specimens were carried out considering drying shrinkage based on moisture diffusion, creep, cracking resistance of concrete, and the effect of fiber. The analysis results were verified via a comparison between the measured and calculated crack width. From the test and analysis results, the effectiveness of fiber with respect to reducing cracking was confirmed and some salient features on the shrinkage cracking of FRSCC were obtained.

Numerical modeling of drying shrinkage behavior of self-compacting concrete

  • Chen, How-Ji;Liu, Te-Hung;Tang, Chao-Wei
    • Computers and Concrete
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    • v.5 no.5
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    • pp.435-448
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    • 2008
  • Self-compacting concrete (SCC), characterized by the high flowability and resistance to segregation, is due to the high amount of paste (including cement and mineral admixtures) in contrast with normal concrete (NC). However, the high amount of paste will limit the volume fractions of coarse aggregate,and reduce the tendency of coarse aggregate to suppress drying shrinkage deformations. For this reason, SCC tends to produce higher values of drying shrinkage than NC for the most part. In order to assess the drying shrinkage of SCC quantitatively for application to offshore caisson foundations, the formulas presented in the literatures (ACI 209 and CEB-FIP) are used to predict the values of drying shrinkage in SCC according to the corresponding mix proportions. Additionally, a finite element (FE) model, which assumes concrete to be a homogeneous and isotropic material and follows the actual size and environmental conditions of the caisson, is utilized to simulate stress distribution situations and deformations in the SCC caisson resulting from the drying shrinkage. The probability of cracking and the behavior of drying shrinkage of the SCC caisson are drawn from the analytic results calculated by the FE model proposed in this paper.

Evaluation on the shrinkage crack of concrete with crack self-healing agent (균열 자기치유형 혼화재 적용 콘크리트의 수축균열 평가)

  • Hong, Seok-Beom;Yoo, Jo-Hyeong;Kim, Woo-Jae
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2014.05a
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    • pp.82-83
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    • 2014
  • Concrete with self-healing admixture can reduce the crack width by using a compound for chemical reaction with incoming water and carbon dioxide through the crack. Also, concrete with self-healing admixtures can reduce early-age shrinkage crack by using a inorganic expansive agent. In this research, we perform the basic workability test and compressive test. Also, We measure the drying shrinkage of concrete specimen. Finally, we make mock-up (3m X 3m X 0.23m) and monitor the crack width and length for 3 months.

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Evaluating Early Age Shrinkage Behavior of Ultra High Performance Cementitious Composites (UHPCC) with CSA Expansive Admixture and Shrinkage Reducing Agent (CSA계 팽창재 및 수축 저감제의 혼입에 따른 UHPCC의 초기 수축 거동 평가)

  • Yoo, Doo-Yeol;Park, Jung-Jun;Kim, Sung-Wook;Yoon, Young-Soo
    • Journal of the Korea Concrete Institute
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    • v.23 no.4
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    • pp.441-448
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    • 2011
  • In this study, experimental tests of chemical and autogenous shrinkage were performed to evaluate the early age shrinkage behaviors of ultra high performance cementitious composites (UHPCC) with various replacement ratios of silica fume (SF), shrinkage reducing agent (SRA), expansive admixture (EA), and superplasticizer (SP). Starting time of self-desiccation, was analyzed by comparing the setting times and the deviated point of chemical and autogenous shrinkage strains. The test results indicated that both SF and SRA augment the early age chemical shrinkage, whereas SP delays the hydration reaction between cement particles and water, and reduces chemical shrinkage. About 49% of autogenous shrinkage was depleted by synergetic effect of SRA and EA. The hardening of UHPCC was catalyzed by containing EA. Self-desiccation of UHPCC occurred prior to the initial setting due to the high volume fraction of fibers and low water-binder ratio (W/B).

Drying Shrinkage and Pore Structure of Self-Healing Epoxy-Modified Mortars Using Expansive Admixtures (팽창성 혼화재를 병용한 에폭시수지 혼입 자기치유 모르타르의 건조수축 및 세공구조)

  • Ham, Seong-Min;Kim, Wan-Ki
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2015.05a
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    • pp.166-167
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    • 2015
  • The purpose of this study is to examine the effect on drying shrinkage of self-healing epoxy-modified mortars(EPMMs) using expansive admixtures. The EPMMs are prepared with polymer-binder ratios of 0 and 10%, and tested for drying shrinkage and pore structure analysis. As a result, regardless of the expansion and swelling agent content, the drying shrinkage of the EPMMs is remarkably decreased than that of unmodified mortars. Also, the pore size distribution of the EPMMs is moved to smaller size in comparison with unmodified mortars. In this study, the EPMM with expansive agent 7.5% and swelling agent 2.5% is recommended as a optimal mix proportion for reduction of drying shrinkage.

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Behaviour of Consolidation in Dredged and Reclaimed Soil Considering the Effect of the Desiccation (건조효과를 고려한 준설매립토의 압밀거동)

  • Yoo, Nam-Jae;Park, Byung-Soo;Lee, Myung-woog;Lee, Joo-Won
    • Journal of Industrial Technology
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    • v.20 no.A
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    • pp.93-100
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    • 2000
  • This research is to investigate the self-weight consolidation settlement and desiccation shrinkage settlement of soft marine dredging clay by performing numerical and experimental works. Large column test were carried out investigate the consolidation settlement considering effect of the self-weight and desiccation shrinkage, and centrifuge model test was also carried out investigate self-weight consolidation settlement. Results of centrifuge model and large column experiments about changes of settlement with time were analyzed by using the numerical technique of explicit finite difference method considering effect of the self-weight and desiccation based on the finite strain consolidation theory. Centrifuge model test results were in relatively good agreements with analyzed results in terms of self-weight consolidation settlement with time. Large column test results showed quite different values from the numerically estimated one, carried by experimental conditions.

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Reduction of Autogenous Shrinkage of HPFRCC Depending on Changes of ERCO Replacement Ratio and Fiber Replacement Ratio (ERCO 혼입율과 섬유혼입비 변화에 따른 HPFRCC의 자기수축저감)

  • Lee, Jea-Hyeon;Baek, Cheol;Jo, Man-Ki;Jo, Sung-Jun;Lee, Jong-Tea;Han, Cheon-Goo
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2016.05a
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    • pp.30-31
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    • 2016
  • As the treatments of many kinds of explosive objects increase recently, it is in the trend that explosion accidents increase. Thus, many studies on HPFRCC (High-performance Fiber-reinforced Cement Composites) whose ductility is enhanced are being conducted actively in order to minimize the damages from explosion accidents. However, HPFRCC, the self-shrinkage of HPFRCC is on the rise as a problem since it becomes ultra-high strengthened by using low W/B. Thus, in this study, it is intended to evaluate the capacity for reducing the self-shrinkage of HPFRCC depending on some changes of ERCO(Emulsified Refined Cooking Oil) replacement ratio and the fiber replacement ratio between some short steel fibers (SS) and some long organic fibers (OL). As a result, it was found that some excellent effects are exerted since the self-shrinkage was reduced a lot as the ERCO replacement ratio increases and the fiber replacement ratio of SS rather than OL increases.

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