• Title/Summary/Keyword: 수화열 균열

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A Study of the Thermal Analysis for the Crack Control of Underground Pier Footing (지하 교각 기초의 온도균열 제어를 위한 수화열 해석 연구)

  • Park, Weon-Tae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.10 no.2
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    • pp.91-101
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    • 2006
  • Lately, massive concrete structures are increasingly built. In such massive structures, the heat of hydration of mass concrete causes thermal cracks. To avoid thermal crack, methods widely acceptable for practical use are pre-cooling, pipe cooling and control of placing height. Thermal stress analysis is performed to find the way of controlling the thermal crack of pier footing mat in this paper. The footing mat model for the analysis is $12m{\times}14m$area and 3m height. The analysis results are compared with method of control of lift height and method of pipe cooling. The analysis results show that thermal crack can be removed by method of placing control and pipe cooling at footing mat placed on the ground.

A Parametric Study on the Reason and Control of Crack during the Construction of Pier in Urban Transit (도시철도 교각의 시공중 균열발생 원인과 제어방안을 위한 매개변수 연구)

  • Park, Seong-Kyu
    • Journal of the Korean Society for Railway
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    • v.14 no.6
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    • pp.555-561
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    • 2011
  • This paper is designed to propose methods to both analyze and control the reasons for cracks appearing during the construction of piers. For this aim, a numerical analysis was performed to identify the properties of crack which resulted from heat of hydration and differential drying shrinkage with the key influence factors considered. The results show that the thermal cracks occurred within a few days, and the drying shrinkage cracks within a few weeks. Meanwhile, settlement shrinkage cracks occurred within a few hours. Discussing the control methods based on the time of the cracks appearing, quality control, reduction of the unit quantity of cement, and the preservation of moisture on the surface are proposed as the realistic and effective methods for preventing settlement cracks, thermal cracks, and drying shrinkage cracks respectively.

An Experimental Study on Properties of Concrete Using Latent Heat Binder (잠열성 결합재를 활용한 콘크리트의 특성에 관한 실험적 연구)

  • Kim, Yong-Ro;Kim, Do-Su;Khil, Bae-Su;Kim, Ook-Jong;Lee, Do-Bum
    • Journal of the Korea Concrete Institute
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    • v.20 no.5
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    • pp.661-668
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    • 2008
  • It is necessary to develop a new technology for effectively reducing hydration heat and controlling thermal cracking caused increasing construction of large size massive concrete structures such as mat foundation of high-rise building, grandiose bridge, and LNG tank. Therefor, to develop a new technology for reducing hydration heat of large size massive concrete in this study, after developing the latent heat binder for controling hydration heat of concrete by application of latent heat material, it was investigated basic properties and durability such as slump, air content and compressive strength, shrinkage properties, permeability, freezing and thawing resistance, corrosion, and hydration heat generation properties of concrete using latent heat binder. As a test result, it was confirmed that latent heat binder was not affected adversely the basic property and durability of concrete, and was advanced on the reduction of hydration heat and control of thermal crack. It is expected to be applied as the excellent technology on the management of hydration heat and thermal crack in large size mass concrete structures.

Innovative Transient Thermal Gradient Control to Prevent Early Aged Cracking of Massive Concrete (매스콘크리트의 열경사 조절에 의한 수화열과 온도균열의 방지)

  • Kim, Seong-Soo;Cho, Tae-Jun;Lee, Jeong-Bae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.12 no.6
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    • pp.164-172
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    • 2008
  • The heat of hydration for early aged mass concrete induces high temperature with the hydration. Control of the temperature difference across a section is an effective strategy to minimize the hydration heat induced cracks for the structures where internal restraint is dominant. The current prevention methods for hydration cracking show some limitations for the control of thermal gradients, and these limitations could make micro and macro cracks in surface and core of concrete. Especially cooling methods can decrease the increasing hydration temperature, but it can not prevent the problem while decreasing temperature. Consequently heating pipes are added simultaneously with the cooling pipes in order to control the temperature gradients between core and surface of the concrete, followed by the finite element analysis (FEA). Based on the FEA, the proposed method using cooling pipe and heating pipes together has been found to be an effective alternative in thermal gradient control, in terms of controlling temperature induced cracks significantly.

A Study on Crack Control of Early-aged Reinforced Concrete Rahmen Bridge (초기재령 철근큰크리트 라멘교의 균열제어에 관한 연구)

  • Jung Hee-Hyo;Lee Sung-Yeol;Kim Woo-Jung
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.19 no.1 s.71
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    • pp.15-25
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    • 2006
  • The researches on the early-aged concrete hydration process and the techniques for the early-aged concrete crack control mainly have been focused and developed on the massive concretes in both experimental and numerical studies. However, those researches for relatively thin members such as the upper slab of the reinforced concrete rahmen bridge have nearly been attempted. In this study, a designing technique for crack controlling in the thin members of the early-aged reinforced concrete rahmen bridges based on measured temperature history, strength revelation model and sinkage model is proposed. A method of calculating the reinforcing bar area for crack controlling is also proposed and it is found that the distributing bars under the design loads become the main reinforcing bars in the temperature stress analysis of the early-aged reinforced concrete rahmen bridges. It is shown that the proposed analysis technique is able to use the design of crack control for the early-aged reinforced concrete rahmen bridge.

A Study on the Crack Control of Retaining Wall of Mass Concrete Structure (지하옹벽 매스콘크리트 구조물의 균열제어에 관한 연구)

  • 장동일;채원규;조광현;김광일;손영현
    • Proceedings of the Korean Institute of Industrial Safety Conference
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    • 1997.11a
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    • pp.289-294
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    • 1997
  • 매스콘크리트 구조물에서는 이미 경화된 콘크리트가 새로이 타설된 콘크리트의 변형을 제한하여 시공직후에 부재의 길이방향에 수직한 균열이 발생하는 경우가 자주 보고 되고 있다. 이 균열은 먼저 타설된 바닥에 대하여 벽체의 변위가 제한될 때 구속인장응력에 의해 발생된다. 이러한 균열의 발생원인은 몇 가지로 살펴볼 수 있는데, 그 하나는 먼저 타설한 바닥 콘크리트와 새로 타설한 벽체 콘크리트와의 수화열 발생의 차이에 의한 것이며, 두번째 이유로 바닥과 벽체사이의 건조수축의 차이를 들 수 있다. (중략)

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Determination of Thermal Cracking Index of Internal Restricted Mass Concrete Using a Numerical Analysis (수치분석을 통한 내부구속 매스콘크리트의 온도균열지수 결정)

  • Seo, Ki-Young;Kim, Hee-Sung;Jin, Chi-Sub
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.11 no.1
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    • pp.57-67
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    • 2007
  • The service life of concrete structure is to a great extent influenced by crack developed at early ages of concrete material. Especially, hydration heat is a main cause of thermal cracking at mass concrete structures. The thermal cracking of massive structure is analyzed of the thermal cracking index which was presented Concrete Standard Specifications. The thesis analyzed the thermal cracking index which considered various variable (cement type, height of casting, curing condition, concrete mixing temperature, the unit cement content) at internal restricted mass concrete. The analysis result is denoted increase and decrease rate of thermal cracking index whenever the variables change. The results is helped to understand thermal cracking every time structures is designed and constructed. And I think that it is useful economic and stable design of mass concrete structures.