• Title/Summary/Keyword: Thermal cracks

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Humidity Absorbing Deterioration Characteristics of Modified Epoxy Resin System with SN (SN으로 개질된 에폭시 수지 계의 흡습열화 특성)

  • 조영신;심미자;박수길;김상욱
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 1996.11a
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    • pp.421-424
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    • 1996
  • Effects of humidity absorbing deterioration on AC dielectric breakdown characteristics of modified epoxy resin system with SN(succinonitrile) were investigated. As the forced humidity absorbing deterioration proceeded under high temperature and humidify, glass transition temperature increased. The dielectric breakdown strength increased and then decreased at deterioration cycles higher than 2. Not only, the increment of thermal stability but also, the physical detects such as Internal cracks and voids occurred during the humidity absorbing deterioration cycle were the main causes of the change in dielectric properties.

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A Study on Shrinkage Crack of Steel Composite Concrete Box Structure (Transfer Girder) (강합성 콘크리트 박스구조물(트랜스퍼 거더)의 건조수축 균열에 대한 연구)

  • Choi, Jung-Youl;Kim, Dae-Ill
    • The Journal of the Convergence on Culture Technology
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    • v.8 no.6
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    • pp.685-691
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    • 2022
  • This study was based on the steel composite concrete box structure (Transfer girder) which was installed to support the skyscrapers directly above the subway line. In this study, it was analytically proved that the cause of cracks on the steel composite concrete box structure were the shrinkage cracks by comparing the results of crack investigation and numerical analysis. As the results, it was found that the internal temperature difference between concrete and steel members occurred according to the shape of the steel frame embedded in concrete, the location of vertical stiffener, and the closed section area. The narrower spacing of vertical stiffener was occurred the internal temperature concentration of the structure and the temperature difference increased. And the location of higher thermal strain and temperature were similar to the location of actual cracks by the visual inspection. Therefore, the internal temperature concentration parts were formed according to the presence and spacing of the vertical stiffeners and the inspection passage in the central part of the structure. The shrinkage cracks were occurred by the restrained of temperature expansion and contraction of the concrete. As the results of this study, it was important to separate and manage the non-structural cracks caused by shrinkage and the structural cracks in the maintenance of serviced steel-composite concrete structures.

Evaluation of Thermal Characteristics in Association with Cement Types in Massive Concrete Structure (매스콘크리트 구조물에서의 시멘트 종류별 수화발열 특성 평가)

  • 김상철;강석화;김진근
    • Journal of the Korea Concrete Institute
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    • v.11 no.6
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    • pp.3-12
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    • 1999
  • The larger, loftier and more highly strengthened the recent structures become, the greater attention is paid to the problem of thermal crack occurrence associate with hydration heat. As one of methods to solve the problem, a care has been taken to the improvement of construction such as the application of pre-cooling or pipe-cooling, adjustment of concrete block size, concrete placement timing, joint arrangement and so on. But it is expected that a proper selection of cement shall additionally contribute to the control of thermal cracks. In this study, thus, we selected 4 types of cements such as Type V for anti-sulphate, blast furnace cements (slag content of 45% and 65% respectively)and ternary blended low heat cement, and carried out mock-up tests. In every assigned time, temperatures and thermal stresses were measured and calculated from raw data. As a result of measurement, it was found that the magnitude of hydration heat is in order of blast furnace slag cement. Type V and ternary blended low heat cement. Results of thermal stresses were same as the order of temperature. In addition, thermal stresses calculated from the data of strain gauges showed almost similar to those measured from effective stress gauges only when strain values were adjusted properly in accordance with initial time of stress appearance. Theoretical results agreed well with the measured values comparatively, but showed slight differences. It is inferred that these differences shall be reduced if more tests capable of evaluating thermal characteristics of concrete are carried out.

A Study on the Evaluation of Thermal Stress of Massive Concrete Structure (매스콘크리트구조물의 온도응력평가에 관한 연구)

  • 강석화;정철헌;정한중;이용호;박칠림
    • Magazine of the Korea Concrete Institute
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    • v.7 no.2
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    • pp.126-135
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    • 1995
  • Thermal cracks are occured when thermal stress due to the hydration of cement exceeds the tens~le strength of concrete. Since crackmg causes poor durability of concrete, the effect of ther ma1 cracking should be includod for the design and construction of massive concrete structures. In this study, an experiment is performed for the investigation of time dependent thermal stress history. In order to evaluate thermal stress. two methods are employed. One 1s the evaluation method of thermal stress based on the measurement from embedment stram gauge with non-stress strain gauge and the other 1s based on the measurement from concrete stress gauge. As a result of this study, the value corrected by the former shows good agreement with the latter. The validity of the proposed method for the evaluation of thermal stress 1s explored.

Microstructure and Thermal Shock Properties of SiC Materials (SiC 재료의 미세조직 및 열충격 특성)

  • Lee, Sang-Pill;Cho, Kyung-Seo;Lee, Hyun-Uk;Son, In-Soo;Lee, Jin-Kyung
    • Journal of Ocean Engineering and Technology
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    • v.25 no.3
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    • pp.28-33
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    • 2011
  • The thermal shock properties of SiC materials were investigated for high temperature applications. In particular, the effect of thermal shock temperature on the flexural strength of SiC materials was evaluated, in conjunction with a detailed analysis of their microstructures. The efficiency of a nondestructive technique using ultrasonic waves was also examined for the characterization of SiC materials suffering from a cyclic thermal shock history. SiC materials were fabricated by a liquid phase sintering process (LPS) associated with hot pressing, using a commercial submicron SiC powder. In the materials, a complex mixture of $Al_2O_3$ and $Y_2O_3$ powders was used as a sintering additive for the densification of the microstructure. Both the microstructure and mechanical properties of the sintered SiC materials were investigated using SEM, XRD, and a three point bending test. The SiC materials had a high density of about 3.12 Mg/m3 and an excellent flexural strength of about 700 MPa, accompanying the creation of a secondary phase in the microstructure. The SiC materials exhibited a rapid propagation of cracks with an increase in the thermal shock temperature. The flexural strength of the SiC materials was greatly decreased at thermal shock temperatures higher than $700^{\circ}C$, due to the creation of microcracks and their propagation. In addition, the SiC materials had a clear tendency for a variation in the attenuation coefficient in ultrasonic waves with an increase in thermal shock cycles.

Root Cause Analysis of Axial ODSCC of Steam Generators Tubes of OPR1000 (한국표준형 원전 증기발생기 전열관 축방향 ODSCC 발생원인 분석)

  • Kim, Hong-deok;Park, Su-ki;Yim, Chang Jae;Chung, Han Sub
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.6 no.1
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    • pp.83-88
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    • 2010
  • Domestic nuclear steam generators with Alloy 600 HTMA tubes have experienced axial cracking at eggcrate tube support plates(TSPs). The axial stress corrosion cracks were observed at the crevice between outside of tubes and eggcrate TSPs. The root cause of axial cracking was investigated by thermal hydraulic analysis and sludge distribution diagnosis. It is suggested that deposition of sludge at eggcrate TSPs could increase the outside surface temperature of tube and promote the enrichment of impurities at crevice, and thus accelerate cracking. Additionally strategy for reducing the sludge ingress to steam generators is discussed.

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A Study on the Control of Hydration Heat of Mass Control Using Super Retarding Agent (초지연제를 이용한 매스콘크리트의 수화열 조정에 관한 연구)

  • 유동수;심보길;윤치환;한민철;한천구
    • Proceedings of the Korea Concrete Institute Conference
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    • 2001.05a
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    • pp.469-474
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    • 2001
  • Mass concrete is placed considering placing lifts in order to reduce thermal cracks by hydration heat. But they results in cold joint between placing lifts, which bring about the loss of strength, water tightness and undesirable appearance. Therefore, in this paper, mechanical and hydration heat of mass concrete using super retarding agent developed through previous study are investigated in order to reduce the hydration heat and place it without place lift. According to test results, placing lifts combined with normal concrete and concrete containing super retarding agent have positive effects on reducing hydration heat. Especially, the crack index by thermal stress of the concrete containing super retarding agent less than a quarter, compared to that of plain concrete without placing lifts, and less than a half, compared to that of plain concrete with placing lifts.

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A Study on the Control of Hydration Heat of Mass Concrete Using Super Retarding Agent (초지연제를 이용한 매스콘크리트의 수화열 조정에 관한 연구)

  • 유동수;심보길;윤치환;한민철;한천구
    • Proceedings of the Korea Concrete Institute Conference
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    • 2001.05a
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    • pp.515-520
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    • 2001
  • Mass concrete is placed considering placing lifts in order to reduce thermal cracks by hydration heat. But they results in cold joint between placing lifts, which bring about the loss of strength, water tightness and undesirable appearance. Therefore, in this paper, mechanical and hydration heat of mass concrete using super retarding agent developed through previous study are investigated in order to reduce the hydration heat and place it without place lift. According to test results, placing lifts combined with normal concrete and concrete containing super retarding agent have positive effects on reducing hydration heat. Especially, the crack index by thermal stress of the concrete containing super retarding agent less than a quarter, compared to that of plain concrete without placing lifts, and less than a half, compared to that of plain concrete with placing lifts.

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A Fundamental Study on the Control of Hydration Heat of Mass Concrete Using Setting Time Difference (응결시간차를 활용한 매스콘크리트의 수화열 조정에 관한 기초적 연구)

  • 배정렬;윤치환;김기철;한민철;오선교;한천구
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2002.05a
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    • pp.41-45
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    • 2002
  • Placing lift is applied to place mass concrete in order to reduce thermal cracks by hydration heat. But they results in cold joint between placing lifts, which bring about the loss of strength, water tightness and undesirable appearance. Therefore, in this paper, mechanical and hydration heat of mass concrete using super retarding agent developed through previous study are investigated in order to reduce the hydration heat and place it without place lift. According to test results, placing lifts combined with normal concrete and concrete containing super retarding agent have positive effects on reducing hydration heat. Especially, the crack index by thermal stress of the concrete containing super retarding agent less than a quarter, compared to that of plain concrete without placing lifts, and less than a half, compared to that of plain concrete with placing lifts.

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Flow properties of Ultra Fine Cement with Superplasticizer (유동화재 변화에 따른 초미립자 시멘트의 유동특성)

  • 채재홍;이종열;이웅종;박경상;김진춘;이세웅
    • Proceedings of the Korea Concrete Institute Conference
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    • 1999.04a
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    • pp.58-63
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    • 1999
  • Almost all concrete structures have many inevitable cracks for various reasons such as drying shrinkage, heat liberation of cement, fatigues or repeating loads and movements. Conventionally, they are repaired with epoxy materials. The Epoxy resins used by repair materials are different from properties of the base concrete materials such as thermal and mechanical properties - thermal expansion coefficients, bending strength. And the epoxy resin cannot release the water inside the concrete structure and cause corrosion of the steel bars. In this study, before the experiment got launched, we had analyzed cement and slag. Then We blended the two grades of ultra fine cement using high blaine cement and slag. And the cement slurry was produced by water and suprplasticizer to each blended ultra fine cement in various conditions. The slurry produced by each conditions was evaluated with flow properties such as viscosity, dropping time, segregation and observation of dry surface after injection.

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