• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
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• pp.245-248
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• 2005

It should be noted that the critical chloride threshold level is not considered to be a unique value for all conditions. This value is dependent on concrete mixture proportions, cement type and constituents, presence of admixtures, environmental factors, steel reinforcement surface. conditions, and other factors. In this study, the accelerated corrosion test for reinforcing steel was conducted by electrochemical and cyclic wet and dry seawater method, respectively and during the test, corrosion monitoring by half cell potential method was carried out to estimate the chloride corrosion threshold value when corrosion for reinforcing steel in concrete was perceived. For this purpose, lollypop and right hexahedron test specimens were made for 31.4$\%$, 41.5$\%$ and 49.7$\%$ of w/c, respectively and then the accelerated corrosion test for reinforcing steel was executed. It was observed from the test that the time to initiation of corrosion was found to be different with water-cement ratio and accelerated corrosion test method, respectively and the chloride corrosion threshold value was found to range from 0.91 to 1.43 kg/$m^{3}$.

• Corrosion Science and Technology
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• 제19권6호
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• pp.326-336
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• 2020

Galvalume steel (GL) is widely used in marine and industrial environments. It is characterized by better corrosion resistance than carbon steel. However, corrosion and economic losses may occur as the usage time is increased. Therefore, in this study, an outdoor exposure test of GL for 36 months was conducted across six regions of Korea. Parameters such as corrosion rate, chrominance (color, chroma, and brightness), glossiness, and surface appearance were analyzed. The results showed no significant change in appearance, and the initial corrosion rate was large, but a tendency to decrease with time was observed. Increased outdoor exposure time led to increase in the level of corrosion products. In the case of coastal areas where S, Cl, and other elements were detected, a relatively high decrease in Zn content was observed. Al forms a protective oxide film and exists in the coating layer, but Zn dissolves due to its chemical activity and low potential.

• Corrosion Science and Technology
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• 제22권5호
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• pp.377-386
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• 2023

Aircraft washing is performed periodically for corrosion control. Currently, the aircraft washing interval is qualitatively set according to the geographical conditions of each base. We developed a washing interval determination algorithm based on atmospheric corrosion environment monitoring data at the Republic of Korea Air Force (ROKAF) bases and United States Air Force (USAF) bases to determine the optimal interval. The main factors of the washing interval decision algorithm were identified through hierarchical clustering, sensitivity analysis, and analysis of variance, and criteria were derived. To improve the classification accuracy, we developed a washing interval decision model based on an artificial neural network (ANN). The ANN model was calibrated and validated using the atmospheric corrosion environment monitoring data and washing intervals of the USAF bases. The new algorithm returned a three-level washing interval, depending on the corrosion rate of steel and the results of the ANN model. A new base-specific aircraft washing interval was proposed by inputting the atmospheric corrosion environment monitoring results of the ROKAF bases into the algorithm.

• Structural Engineering and Mechanics
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• 제30권6호
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• pp.713-732
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• 2008

Serviceability and durability of the concrete members can be seriously affected by the corrosion of steel rebar. Carbonation front and or chloride ingress can destroy the passive film on rebar and may set the corrosion (oxidation process). Depending on the level of oxidation (expansive corrosion products/rust) damage to the cover concrete takes place in the form of expansion, cracking and spalling or delamination. This makes the concrete unable to develop forces through bond and also become unprotected against further degradation from corrosion; and thus marks the end of service life for corrosion-affected structures. This paper presents an analytical model that predicts the weight loss of steel rebar and the corresponding time from onset of corrosion for the known corrosion rate and thus can be used for the determination of time to cover cracking in corrosion affected RC member. This model uses fully the thick-walled cylinder approach. The gradual crack propagation in radial directions (from inside) is considered when the circumferential tensile stresses at the inner surface of intact concrete have reached the tensile strength of concrete. The analysis is done separately with and without considering the stiffness of reinforcing steel and rust combine along with the assumption of zero residual strength of cracked concrete. The model accounts for the time required for corrosion products to fill a porous zone before they start inducing expansive pressure on the concrete surrounding the steel rebar. The capability of the model to produce the experimental trends is demonstrated by comparing the model's predictions with the results of experimental data published in the literature. The effect of considering the corroded reinforcing steel bar stiffness is demonstrated. A sensitivity analysis has also been carried out to show the influence of the various parameters. It has been found that material properties and their inter-relations significantly influence weight loss of rebar. Time to cover cracking from onset of corrosion for the same weight loss is influenced by corrosion rate and state of oxidation of corrosion product formed. Time to cover cracking from onset of corrosion is useful in making certain decisions pertaining to inspection, repair, rehabilitation, replacement and demolition of RC member/structure in corrosive environment.

• Steel and Composite Structures
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• 제33권4호
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• pp.615-627
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• 2019

This paper aims to study the compressive behavior of circular hollow and concrete-filled steel tubular stub columns under simulated marine atmospheric corrosion. The specimens after salt spray corrosion were tested under axial compressive load. Steel grade and corrosion level were mainly considered in the study. The mechanical behavior of circular CFST specimens is compared with that of the corresponding hollow ones. Design methods for circular hollow and concrete-filled steel tubular stub columns are modified to consider the effect of marine atmospheric corrosion. The results show that linear fitting curves could be used to present the relationship between corrosion rate and the mechanical properties of steel after simulated marine atmospheric corrosion. The ultimate strength of hollow steel tubular and CFST columns decrease with the increase of corrosion rate while the ultimate displacement of those are hardly affected by corrosion rate. Increasing corrosion rate would change the failure of CFST stub column from ductile failure to brittle failure. Corrosion rate would decrease the ductility indexes of CFST columns, rather than those of hollow steel tubular columns. The confinement factor ${\xi}$ of CFST columns decreases with the increase of corrosion rate while the ratio between test value and nominal value shows an opposite trend. With considering marine atmospheric corrosion, the predicted axial strength of hollow steel tubular and CFST columns by Chinese standard agree well with the tested values while the predictions by Japanese standard seem conservative.

• Journal of Advanced Marine Engineering and Technology
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• 제27권3호
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• pp.447-452
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• 2003

Crevice corrosion is localized form of corrosion usually associated with a stagnant solution on the micro-environmental level. Such stagnant micro environments tend to occur in crevices (shielded areas) such as those formed under gaskets washers insulation material. fastener heads. surface deposits. disbonded coatings. threads. lap joints and clamps. Crevice corrosion is initiated by changes in located electrochemical reaction within the crevice such as a) depletion of inhibitor in the crevice b) depletion of oxygen in the crevice c) a shift to acid conditions in the crevice and d) build-up of aggressive ion species (e.g chloride) in the crevice. In this study. the mechanism of crevice corrosion for Type 430 stainless steel is investigated undercondition that the size of specimen is $15{\times}20\{times}3mm$, in 1N $H_2SO_4$ + 0.05N NaCl solution. and the artificial crevice gap size of 3 x 0.2 x 15 mm. Crevice corrosion is measured under applied potential -300mV(SCE) to the external surface. The obtained result of this study showed that 1) the induced time for initiation of crevice is 750 seconds. 2) potential of the crevice was about from -320mV to -399mV. which is lower than that of external surface potential of -300mV It is considered that potential drop in the crevice is one of mechanisms for the crevice corrosion

• Corrosion Science and Technology
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• 제7권1호
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• pp.27-34
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• 2008

In industrial and fluid handling systems, frequently the protective film forming materials suffer from severe corrosion due to microbial effects. As an example, various micro-organisms, including bacteria, exist in seawater normally fed to power and desalination plants. Unless seawater intakes are properly disinfected to control these microbial organisms, biological fouling and microbial induced corrosion (MIC) will be developed. This problem could destroy metallic alloys used for plant construction. Seawater intakes of cogeneration plants are usually disinfected by chlorine gas or sodium hypochlorite solution. The dose of disinfectant is designed according to the level of contamination of the open seawater in the vicinity of the plant intake. Higher temperature levels, lower pH, reduced flow velocity and oxidation potential play an important role in the enhancement of microbial induced corrosion and bio-fouling. This paper describes, in brief, the different types of bacteria, mechanisms of microbiological induced corrosion, susceptibility of different metal alloys to MIC and possible solutions for mitigating this problem in industry. A case study is presented for the power plant steam condenser at Al-Taweelah B-station in Abu Dhabi. The study demonstrates resistance of Titanium tubes to MIC.

• Corrosion Science and Technology
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• 제16권6호
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• pp.273-277
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• 2017

Atmospheric corrosion is clearly the most noticeable of all corrosion processes. A tremendous amount of economic losses are caused by atmospheric corrosion. Thus, it is imperative to know the level of atmosphere's aggressiveness or in other words "corrosivity", before designing or planning any corrosion prevention strategy. In Singapore, corrosivity values were not recorded earlier though the process of measurement and recording was prevalent in other countries. With an aim of filling this gap, three test sites were setup at three locations in Singapore to represent marine, industrial and urban atmospheres or their mixtures. Subsequently, corrosivity readings were measured and recorded according to ISO 9223:2012 for the first time in Singapore. Salient atmospheric constituents or parameters like time of wetness (TOW), $Cl^-$, $SO_2$, $NO_2$, $O_3$, and $HNO_3$ were measured at all sites over a period of time to categorize corrosivity of particular atmosphere. The effect of the atmosphere on corrosion of steel, Cu, Al, and Zn has also been investigated and quantified. "Estimated" and "determined" corrosivities were quantified and compared according to ISO 9223 standard. The study data along with final corrosivity measurements will be presented and discussed in the present work.

• Earthquakes and Structures
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• 제16권2호
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• pp.235-251
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• 2019

Corrosion of reinforcement is the greatest threat to the safety of existing reinforced concrete (RC) structures. Most of the olden structures are gravity load designed (GLD) and are seismically deficient. In present study, investigations are carried out on corrosion damaged GLD beam-column sub-assemblages under reverse cyclic loading, in order to evaluate their seismic performance. Five GLD beam-column sub-assemblage specimens comprising of i) One uncorroded ii) Two corroded iii) One uncorroded strengthened with steel bracket and haunch iv) One corroded strengthened with steel bracket and haunch, are tested under reverse cyclic loading. The performances of these specimens are assessed in terms of hysteretic behaviour, energy dissipation and strength degradation. It is noted that the nature of corrosion i.e. uniform or pitting corrosion and its location have significant influence on the behaviour of corrosion damaged GLD beam-column sub-assemblages. The corroded specimens with localised corrosion pits showed in-cyclic strength degradation. The study also reveals that external strengthening which provides an alternate force path but depends on the strength of the existing reinforcement bars, is able to mitigate the seismic risk of corroded GLD beam-column sub-assemblages to the level of control uncorroded GLD specimen.

• 한국지반공학회논문집
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• 제20권2호
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• pp.27-36
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• 2004

극성저항 계측법과 전기화학 임피던스 분광학을 이용하여 영구적 지반 앵커의 부식율을 계측하는 절차를 제시하였다. 극성저항 계측법을 이용하여 대표지반의 종류와 철의 부식률에 관한 특성관계를 도출하였고, 전기화학 임피던스 분광학을 이용하여 시간의존 부식 반응과 다양한 종류의 코우팅 시스템의 평가, 그리고 시멘트 그라우팅이 부식에 미치는 영향에 대하여 각각 평가하였다. 실험 결과 점성토와 사질토의 pH 지수가 5이하인 경우 부식발생이 용이한 지반으로서 영구적 지반 앵커의 부식반응에 심각한 영향을 미치리라 판단된다. 또한 중성 또는 알카리성의 지반은 부식진행이 관찰되지 않았으며 부식률은 pH지수에 관계없이 일정한 결과를 보였다. 포설린 점성토의 경우 pH지수의 변화가 철의 부식에 매우 낮은 영향을 미쳤다. 한편 시멘트 그라우팅의 사용은 철의 부식율을 약 0.003-0.0lmm/y 정도로 낮출 수 있었으며 에폭시 혼합 코우팅의 경우도 부식의 영향을 받지않고 원 상태를 유지할 수 있어 매우 효과적으로 부식효과를 감소시킬 수 있었다.