• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.413-416
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• 2008

Reinforcement corrosion is generally prohibited under normal condition by the alkalinity of the pore water in the concrete. However, concrete structures in marine environment are subjected to chloride attack due to the high salinity of the sea water. Thus the probability of steel corrosion becomes higher when the chloride ions are introduced into the concrete. Steel corrosion is a decisive factor for the determination of service life of the marine concrete structure because chloride ions are abundant in the sea, and piers are the typical construction elements in concrete structures in marine environment. Hence, it is of great importance to evaluate the service life of the piers. In this paper, chloride penetration analysis for the rectangular pier in the marine environment is performed considering the diffusion and convection movement of chlorides. Result reveals that the service life of the reinforcement with drying-wetting cycles is much shorter than that of the reinforcement with saturated condition. This may be due to the fact that moisture movement is much faster that chloride diffusion.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.973-976
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• 2008

Recently, it is increasingly reported that the deterioration of concrete structure under marine environments is due to diffusion and penetration of chloride ions. It is very important to estimate the diffusion coefficient of chloride ion in concrete. Estimation methods of chloride diffusivity by concentration difference is time-consuming. Therefore, chloride diffusivity of concrete is mainly conducted by electrically accelerated method, which is accelerating the movement of chloride ion by potential difference. However, there has not been any proper method for field quality control to closely determine the diffusion coefficient of chloride ion through accelerated tests using potential difference. In this paper, the various test methods for determination of chloride diffusion coefficient in concrete were investigated through comparison accelerated tests. From the results of estimated diffusion coefficient of chloride ion, relationship between the ponding test and acceleration test was examined.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.1A
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• pp.61-69
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• 2010

Unbonded precast concrete piers have better seismic performances than conventional reinforced concrete piers. In this research, seismic performances of unbonded precast prestressed concrete piers are analyzed using OpenSEES. Main parameters of analysis are concrete strength, jacking force ratio, ratio of tendon, and size of precast segment. In results, as the ratio of tendon and jacking force ratio increase, the flexural strength increases at softening state and ultimate state. Concrete strength and size of precast segment are negligible. But initial jacking force ratio leads to early yielding of prestressing tendon. Since compressive strain in core concrete is much less than ultimate strain, it can be expected that the amount of transverse steel reinforcement is to be reduced in comparison with conventional reinforced concrete column.

• Journal of the Korea Concrete Institute
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• v.28 no.6
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• pp.703-711
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• 2016

The present study is mainly aimed at securing adequate pores which are applicable to the aquatic environment and satisfying the required strength of porous concrete as a structure by substituting pumice for crushed stone which is usually used for the fabrication of porous concrete. Accordingly, in order to deduce the optimum mixing conditions applicable to the aquatic environment, we sought to evaluate the porosity, coefficient of permeability and compressive strength of porous concrete based on the target porosity and the mixing factors for pumice. By examining the porosity and coefficient of permeability of porous concrete and the physical properties of its compressive strength based on the target porosity and the mixing factors for pumice, it is judged that the optimum mixtures for porous concrete applicable to the aquatic environment which satisfy both the necessity of securing adequate pores and the required strength for porous concrete as a structure are PC I I-10-0, PC I I-10-5 and PC I I-10-10.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• autumn
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• pp.379-382
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• 2003

Construction concrete needs to maintain suitable environment which contains temperature and humidity etc. Then concrete shows own strength. The environment is not regular and contains many variables. Especially the climate element occupies many parts of variables. We have the climate environment which goes down to $-4^{\circ}C$. The factor that obstruct to construction is the failure at a construction progress. But it must be processed to be scheduled. Therefore we have to do the special care for factor of climate that obstruct to construction. We must make assurance doubly sure at the quality of concrete. We need maintenance of temperature and humidity for the hardening until the requirement period after a concrete pured in. We must do the care of curing sufficiently not to take the influence of injurious activity. This causes strength of concrete. Specific method of curing is according to each situation which is environment element. We wish to analyze curing course in construction of concrete at the paper. Also we wish to predict the problem as to consider curing and suggest the improvement plan through the paper.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.467-468
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• 2010

Over the past few decades, considerable numbers of studies on the durability of concrete have been carried out extensively. The majority of these researches have been performed on sound uncracked concrete, although most of in-situ concrete structures have more or less micro-cracks. It is only recent approach that the attention has shifted towards the influence of cracks and crack width on the penetration of chloride into concrete. The penetration of chlorides into concrete through the cracks can make a significant harmful effect on reinforcement corrosion. Author of this study examined the effect of cracks on chloride penetration by short term experiment. However, it is necessary to accomplish the effect by long term experiment to get reliable goal. In this study, the long term and short term experiments were carried out. This can be useful for establishing new species model of chloride penetration through cracks in concrete.

• Magazine of the Korea Concrete Institute
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• v.9 no.6
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• pp.175-183
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• 1997

경제성장에 따른 항만구조물의 건설 및 유지관리에 관한 관심이 급격히 고조되고 있다. 이러한 항만구조물은 해양환경에 노출되어 콘크리트에 매입된 철근의 부식을 야기시키는 요인에 접해있다. 한편, 콘크리트 내부의 염분침투는 매입철근의 부식을 가속화시켜 콘크리트 구조물의 내구성에 상당히 큰 피해를 입힐 수 있다. 본 연구의 목적은 여러 가지 방식제를 사용함과 동시에 물/시멘트을 달리한 실험변수를 이용한 시험체에 대한 부식평가 및 매입철근의 적절한 부식방지 기법의 개발에 있다. 해양환경 조건을 simulation한 해수 및 담수 순환장치를 이용한 실내 시험체의 철근 부시도 평가 및 항만현장에 직접 거치된 시험체 등 다양한 조건하의 2년간의 실험이 현재 진행 중에 있다. 40주에 걸쳐 간헐 침투되는 해수조건에서 60개의 콘크리트 시험체의 철근 부시도 평가결과를 기초하여 180여개의 콘크리트 시험체를 새로이 제작하여 Half-Cell Test를 통한 Instant-Off Potential, Current Method를 통한 Corrosion current, Chloride Content 및 시험 종료후 시험체를 파쇄하여 부식된 철근의 무게측정등을 통하여 거동 및 부식을 예측.평가하고 이를 통한 부식방지기법을 개발하고자 한다.

• Proceedings of the Korea Water Resources Association Conference
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• 2017.05a
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• pp.259-259
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• 2017

국내 하천에는 하천을 가로지르는 보나 낙차공과 같은 횡단구조물이 약 5만여개에 달하고 있다. 이러한 횡단구조물은 작업의 용이성 및 높은 강도로 인해 오랜 시간 콘크리트 소재로 사용되어 왔다. 기존 콘크리트 소재의 공법은 설치되어 있는 한 세굴 방지에 좋은 효과를 발휘한다는 장점이 있지만 포설된 공법은 시간이 지남에 따라 마모되거나 소실되는 문제가 발생되며, 최종적으로 하천횡단구조물의 안전성 및 심미성에도 영향을 미치게 된다. 이와 더불어 최근 기후변화로 인해 강우량의 증대 및 집중호우 등의 돌변하는 하천환경변화에 대한 적용 가능한 기술이 미비한 실정이다. 이러한 문제와 더불어 환경에 대한 관심이 높아짐에 따라 자연친화적 하천 및 생태복원 하천에 대한 하천 수질 및 생태학적 건강성에 대한 연구의 관심이 높아지고 있다. 최근 연구결과에 따르면 콘크리트 소재를 활용하여 횡단구조물을 설치할 경우, 콘크리트 소재의 문제점으로 제기되는 납, 크롬 등과 같은 중금속 용출과 석회석으로부터 유출되는 강염기성 물질로 인한 하천의 수질악화와 수생 생물이 독성환경에 노출되어 다양한 환경 생태학적 문제를 발생시킬 수 있다고 보고되어 있다. 본 연구에서는 콘크리트 소재의 대안으로 무 저독성 소재인 식물성 폴리우레탄을 이용하여 연구를 수행하였다. 기초 조사를 통해 콘크리트 소재의 대안으로 사용가능성을 확인하기 위하여 식물성 폴리우레탄의 물리적 강도를 확인하였으며, 환경에 미치는 영향을 파악하기 위하여 대한 생태학적 건강성을 확인하였다. 품질 특성은 바인딩강도, 내구성, 압축강도, 휨강도, 투수계수 등을 확인하였으며, 생태학적 건강성을 확인하기 위하여 양서 파충류의 독성 실험, 어류 독성평가, 부착조류에 대한 실험을 수행하였다. 이러한 결과를 바탕으로 시범지역인 대청천 일부 구간에 대하여 계절별 물리/화학/생물(식생, 어류, 저서동물)에 대한 모니터링을 수행하였다. 또한 홍수 전 후의 하상변동을 통해 개발기술의 안전성을 확인하였다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.1
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• pp.39-55
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• 2022

This study carried out the laboratory tests for AE signal attenuation to determine the attenuation coefficient (α) of silo concrete in Gyeongju low and intermediate-level disposal environments. The concrete samples were prepared by satisfying the concrete mixing ratio used in the Gyeongju disposal silo, and these samples were additionally exposed depending on the temperature conditions and saturation and, dry condition. As a result of attenuation tests according to the transmission distance on three concrete specimens for each disposal condition, the AE amplitude and absolute energy measured on the saturated concrete were higher than that of the dry concrete in the initial range of the signal transmission distance, but the α of the saturated concrete was higher than that of the dry concrete. Regardless of the saturation and dry conditions, the α tended to decrease as the temperature increases. The α had a more major influence on the saturation and dry condition than the temperature condition, which means that the saturation and dry condition is the main consideration in measuring the signal attenuation of a concrete disposal structure. The α of concrete in the disposal environment expect to be used to predict the integrity of silos concrete in Gyeongju low and intermediate-level disposal environments by estimating the actual AE parameter values at the location of cracks and to determine the optimum location of sensors.

• Journal of the Korea Concrete Institute
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• v.18 no.3 s.93
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• pp.425-429
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• 2006

Horizontal cracks at the mid-depth of concrete slabs were observed at a section of the continuously reinforced concrete pavement(CRCP) structures on the Korea Highway Corporation's Test Road. To investigate the existence and the extent of horizontal cracks in the concrete slab, a number of cores were taken from the section of CRCP. To identify the causes of horizontal cracks, numerical analyses were conducted. Several variables relative to design, material, and environment were considered in the studies to evaluate possible causes of horizontal cracking. A numerical model of CRCP was developed using the finite element discretization, and the shear and normal tensile stress distributions in CRCP were investigated with the model. Numerical analysis results show that the maximum shear and normal tensile stresses develop near the depth of steel bars at transverse cracks. If those maximum stresses reach the strength of concrete, horizontal cracks occur. The maximum stresses become higher as the environmental loads, coefficient of thermal expansion of concrete, and elastic modulus of concrete increase.