• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.249-252
• /
• 2008

In recent large-scale structures, as mass concrete type structure is frequently applied to the building, temperature crack due to hydration heat needs to be considered. Since a volume change is internally or externally restricted in a mold after placing concrete, temperature crack of mass concrete takes place. By this reason, the reduction method to control this crack is required. In this study, low heat mixture and hydration heat difference is used to execute the analysis of hydration heat, considering the changes of heat transfer coefficient according to curing conditions and block placement of mass concrete. For the analytical modelling, original portland cement and concrete of low heat mixture are placed in the upper and lower payer, respectively. A convection boundary condition is fixed because mass concrete of block placement is characterized by the difference of mold form and curing condition. Through the analysis results considering the changes of low heat mixture, block placement, and heat transfer coefficient, we check out the temperature and stress distribution and analyze the temperature crack reduction effect.

• Magazine of the Korea Concrete Institute
• /
• v.14 no.6
• /
• pp.82-87
• /
• 2002

매스 콘크리트 구조물에서는 콘크리트의 타설후 시멘트의 수화반응에 의해 발생하는 수화열로 인하여 적지 않은 크기의 인장응력이 유발되어 균열이 발생할 가능성이 크다. 토목분야에서 통용되고 있는 많은 범용구조해석 프로그램들은 유한요소법을 이용하여 수화열에 의한 온도분포해석 및 열응력해석을 수행할 수 있는 기능을 내장하고 있다. 그러나, 다른 모든 구조해석들이 그러하듯이 수화열 해석 역시 해석자가 적절한 입력자료를 프로그램에 제공하지 않았을 경우 예상과는 다른 결과를 산출할 수 있다.(중략)

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.493-496
• /
• 2008

The risk of transverse cracking in concrete decks of composite bridges is affected by many factors related to the bridge design, materials, and construction. Among others, the thermal and shrinkage stresses are the most important factors that affect the transverse cracking in early-age concrete decks. The thermal stress at the concrete deck is mainly affected by both ambient temperature and solar radiation. The shrinkage stress at the general strength concrete deck is mainly affected by drying shrinkage and the high strength concrete deck is mainly affected by autogeneous shrinkage. Three-dimensional finite element models of composite bridges were made to investigate the stress due to thermal and shrinkage stress.

• Journal of the Korea Concrete Institute
• /
• v.26 no.3
• /
• pp.287-297
• /
• 2014

Heat of hydration of mass concrete is one of the most important factors that significantly affect structural quality and construction period. Therefore, appropriate methods to control heat of hydration are essential technologies for mass concrete construction. In this study, probability of thermal cracking was checked by thermal analysis prior to the construction of a turbine foundation in a domestic power plant. Subsequently, changes of concrete mix proportion and an effective curing method were proposed to control heat of hydration of mass concrete structures. Concrete manufactured by slag cement was proposed instead of concrete produced by ordinary Portland cement, and an automated curing method was proposed to improve the curing method using typical moist curing with blanket. The automated curing method maintains the temperature difference between center and surface of concrete below a setting value by temperature monitoring. Concrete with slag cement was used for actual construction. One of two identical turbine foundations was cured by an insulated curing method, and the other was cured by the automated curing method to compare the curing methods. And then, the effects of control of heat of hydration were evaluated based on temperature/strain monitoring and crack investigations.

• 레미콘
• /
• no.10 s.73
• /
• pp.2-12
• /
• 2002

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.4 no.3
• /
• pp.292-298
• /
• 2016

In this research, considering the practical situation of separated placing method for mass concrete structure, an efficient method of controlling the heat of hydration is suggested by comparing between the simulated values and actual measurements conducted with the optimum mix design obtained from the various mix conditions with different types and amount of supplementary cementitious materials(SCMs). As the result of the research, firstly, the optimum mix designs for top and bottom layers were determined by Midas gen as OPC to FA of 85 to 15, and OPC to FA to BS of 50 to 20 to 30, respectively. The concrete mixtures prepared with the mix designs determined from the simulation satisfied the target performance range in slump, air content and compressive strength. Additionally, from temperature measurement for the actual mass concrete placed during spring, the maximum temperature difference between surface and core was about $10^{\circ}C$ with 59 and $49^{\circ}C$ for top and bottom layers, respectively, and 1.4 of cracking index was obtained. Therefore, considering the practical conditions of mass concrete construction, it is considered that the different heat of hydration method using different mix designs with SCMs can be an efficient method for controlling thermal cracking and settling cracking of mass concrete.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.38 no.1
• /
• pp.1-10
• /
• 2018

It is difficult to predict the early-age cracks of strain restrained concrete members due to environmentally sensitive parameters. A new method is proposed to predict the cracks by test of autogenous deformation and self-induced restrained stress of specimens which simulates early-age crack state by hydration heat of the'Wall-On-Foundation'members. For this purpose, thermal analysis of entire structure considering the environmental condition is performed at first, and the specimens are set up where hydration heat was electronically controlled according to the analysis results. By measuring free deformation and force to compensate the autogenous strain including relaxation, feasibility of cracks can be estimated. The proposed method can predict the occurrence of cracks better than the material test of the early age concrete which has large variance. The method of this study is particularly useful when it is used as a preliminary experiments to predict the crack more precisely before full-scale concrete placement in construction of large structures.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.3
• /
• pp.126-135
• /
• 2013

Recently, mass concrete with high flowability are widely used to improve the quality and constructability in the longer span construction of prestressed concrete bridges, but it may induce nonstructural cracks due to the hydration heat and autogenous shrinkage etc. The stresses in concrete were evaluated by various experiments and numerical analysis. The tensile stress in mass concrete was increased in connection with the accumulation of hydration heat. Moreover, large amount of autogenous shrinkage from powder type admixture could add the tensile stress to mass concrete near anchorage zone. The tensile stresses in anchorage zone by heat and autogenous shrinkage exceeded the tensile strength of early stage of concrete, and small amounts of stress increasement were shown in other parts of PSC girder.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.9 no.6
• /
• pp.1705-1710
• /
• 2008

In this paper, a program for simulating hydration heat and stresses was developed. And an effective methods were proposed for reduction of hydration heat stresses using flyash and steel fiber. It was shown that flyash replacement made reduction of peak temperature due to hydration heat. However, the effectiveness of reduction of tensile stress was not as good as it of peak temperature. Not only peak temperature but also tensile stress were reduced by the addition of steel fiber.

• 레미콘
• /
• no.2 s.91
• /
• pp.31-50
• /
• 2007