• 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.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.403-413
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• 2017

In this paper, to increase the use of industrial byproducts for $CO_2$ reduction and to improve construction performance, it was manufactured that $CO_2$ reduction type quaternary component high fluidity concrete (QC-HFC) with Reduced cement usage by more than 80% and its quality and hydration characteristics were evaluated. QC-HFC was found to satisfy the target performance, and the flow and mechanical properties were similar to those of conventional concrete. The drying shrinkage of QC-HFC decreased about twice compared with the conventional blend, and the hydration heat decreased about 36%. As a result, it can be concluded that the amount of cracks can be reduced by reducing temperature stress due to hydration heat reduction effect and reducing deformation due to relatively small temperature difference between inside and outside. Also, As a result of the simulation of the mass structure, the temperature cracking index of QC-HFC is 1.1 or more, and the cracking probability is reduced by about 35%, so that the crack due to temperature can be reduced.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.1
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• pp.1-10
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• 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 Korean Recycled Construction Resources Institute
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• v.4 no.3
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• pp.62-68
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• 2009

This research examined engineering properties of high performance concrete, when substitution rate of BS increases. A summary of the test result is as follows. The fluidity of unset concrete increases as the substitution rate of BS increases. The amount of air is reduced more or less, but it seems that enough amount of air can be secured by using more air-entraining agent. Setting time is dramatically delayed as the substitution rate of BS increases. The compressive strength of hardening concrete was weaker than OPC before 28 days passes, due to latent hydraulic property of BS. However, after 28 days, it shows same or better property, which is exceptional for the practical uses of hyper strength concrete. Changes in drying shrinkage rate is quite much, because when hydration happens, the amount of free water in concrete increased as W/B gets larger. The amount of drying shrinkage increases as BS substitution rate increases, but every composition shows less than $-500{\times}10^{-6}$, which is relatively fine.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.74-82
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• 2017

This research presents the results of the strength and drying shrinkage properties to study the effect of ground granulated blast furnace slag(GGBFS), fly ash(FA) and calcium sulfoaluminate(CSA) for activated ternary blended slag cement. The activated ternary blended cement(ATBC) mortar were prepared having a constant water-cementitious materials ratios of 0.4. The GGBFS contents ratios of 100%, 80%, 70% and 60%, FA replacement ratios of 10%, 20%, 30% and 40%, CSA ratios of 0%, 10%, 20% and 30% were designed. The superplasticizer of polycarboxylate type were used. The activator was used of 10% sodium hydroxide(NaOH) + 10% sodium silicate($Na_2SiO_3$) by weight of binder. Test were conducted for mini slump, setting time, V-funnel, water absorption, compressive strength and drying shrinkage. According to the experimental results, the contents of superplasticizer, V-funnel and compressive strength increases with an increase in CSA contents for all mixtures. Moreover, the setting time, water absorption ratios and drying shrinkage ratio decrease with and increase in CSA. One of the major reason for the increase of strength and decrease of drying shrinkage is the accelerated reactivity of GGBFS with alkali activator and CSA. The CSA contents is the main parameter to explain the strength development and decreased drying shrinkage in the ATBC.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.3
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• pp.30-37
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• 2023

The PSCB girder bridge is a closed cross-section in which the top and bottom flanges and the web are integrated, and the structural characteristics are generally different from the bridges in which the girder and the floor plate are separated, so a maintenance plan that reflects the characteristics of the PSCB girder bridge is required. As a result of analyzing damage types by collecting detailed safety diagnosis reports of highway PSCB girder bridges, most of the deterioration and damage occurring during use is concentrated on the top flange. In particular, cracks in the bridge direction on the underside of the top flange occurred in about 70 % of the PSCB girder bridges to be analyzed, and these cracks were judged to be caused by indirect loads such as heat of hydration and drying shrinkage rather than structural cracks caused by external loads. In order to improve durability and reduce maintenance costs of PSCB girder bridges in use, it is necessary to control restraint drying shrinkage cracks from the design stage. Therefore, in this paper, the cracks caused by drying shrinkage under restraint, which is the main cause of cracks under the flanges of the top part of the PSCB girder bridge, were directly calculated using the Gilbert Model, and the influencing factors such as the amount of reinforcing bars, diameter and spacing of reinforcing bars were analyzed. As a result of the analysis, it was found that the crack width caused by restraint drying shrinkage exceeded the allowable crack width of 0.2 mm for reinforcing bars with a reinforcing bar ratio of 0.01 or less based on the H16 reinforcing bar and a reinforcing bar with a diameter greater than H19 based on the reinforcing bar ratio of 0.01. Finally, based on the results of the crack width review, a method for controlling the crack width of the top flange of the PSCB girder bridge was proposed.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.10a
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• pp.11-18
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• 1992

프리텐션방식 원심력 고강도콘크리트 말뚝(KS F4306) 콘크리트의 압축강도가 800kg/$\textrm{cm}^2$이상인 고강도콘크리트를 요구하고 있으나 국내에서는 500kg/$\textrm{cm}^2$ 이상의 콘크리트 말뚝제조가 불가한 실정이므로 본 연구에서는 고황산염시멘트를 이용한 고강도콘크리트 말뚝제조에 관한 공학적 특성 연구의 일환으로써 고황산염시멘트의 수화특성 및 고강도 발현기구 구명과 공학적 특성중에서 압축.휨강도의 내동해성, 건조수축 특성 및 화학저항성등을 비교 고찰하여 보통 시멘트보다 품질 특성이 우수함을 확인하였다. 또한 고강도 콘크리트 말뚝의 시제품 제조를 위하여 2개 공장에서 현장 실험한 결과 94.7kg/$\textrm{cm}^2$의 양호한고강도콘크리트를 얻었다. 향후 고강도콘크리트 말뚝 제조의 공업화 및 양산회가 기대된다.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.725-728
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• 1999

The bridge slab of express railway was designed for high strength concrete (design strength 400kgf/$\textrm{cm}^2$). In case the slab is made with the concrete using type I cement, used much amount of cement can cause cracks through concrete by hydration heat or dry shrinkage. In this study we targeted to solve above problems using type III cement. We could decrease the cement ratio in concrete using type III cement than type I cement. The concrete using type III cement showed good workability and compressive strength, and showed better properties in hydration heat and dry shrinkage than that using type I cement

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.291-292
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• 2010

In this study, high-strength concrete mixtures were made with blast-furnace slag of 50% and 70% replacement level to evaluate material properties including compressive strength development, adiabatic temperature rise, autogenous shrinkage and chloride-ion migration coefficient. Test results showed that the use of high percentage blast-furnace slag in high-strength concrete can reduce heat of hydration and chloride-ion migration coefficient, result in control thermal cracking and improve durability performance especially under high corrosive environment.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.457-462
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• 2003

It studies the non-structural crack factors that are produced in Steel Box Girder Bridge concrete floor plate using analytical method. It mainly studies humidity and design standard of concrete strength. It used MIDAS CIVIL Ver 5.4.0, a general structure analysis program that applies drying shrinkage rate of domestic road bridge design standard and standard value of creep coefficient, CEF-FIP standard equation and ACI standard equation from the aspect of creep, drying shrinkage and hydration heat to see the effect of the two factors on concrete crack and found the following result. The analytical results of this study showed that the initial stress, which was obtained by ACI standard, exceeds the allowable tensile stress between 5 to 18 days. This result means that even if a bridge is designed and constructed according to design standard, the bridge can have cracks due to various variables such as drying shrinkage, hydration heat and creep that produce stress in slab.