• Corrosion Science and Technology
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• 제12권5호
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• pp.209-214
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• 2013

In the industry, accelerated corrosion test is used for the life time prediction. When anti-corrosion test proceeds in real environments, it is difficult that we predict and evaluate the corrosion life time because of the long test time such as 10 years or more time. Accelerated corrosion test and Salt spray test are able to test corrosion life time of products in the laboratory instead of outdoor corrosion test. Experimental procedure is selected for the corrosion standard specimen, exposure of the specimens, measurements of the mass loss and evaluating the mass loss data. As a result, the acceleration factor of the accelerated corrosion test to the outdoor corrosion test is 414.8. Therefore we can predict the corrosion life time of carbon steel during a short time period.

• Corrosion Science and Technology
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• 제3권6호
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• pp.245-250
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• 2004

A series of classical G109 type concrete specimens was exposed to cyclic wet and dry ponding with 15 w/o NaCl solution for approximately five years. Mix design variables included 1) three cement alkalinities (EqA of 0.97, 0.52, and 0.36) and 2) three water-cement ratios (0.50, 0.41, and 0.37). To determine the corrosion initiation time, corrosion potential and macro-cell current between top and bottom bars were monitored. Subsequent to corrosion initiation, specimens were autopsied and visually inspected. Concrete powder samples were collected from top rebar trace and chloride concentration was measured. Also, time-to-corrosion, $T_i$, for specimens of the individual mix designs was represented using Weibull analysis. Time-to-corrosion was a distributed parameter; and because of this, corrosion initiation of four identical specimens for each mix varied, often over a relatively wide range. Specimens fabricated using the lowest water cement ratio and the highest alkalinity cement exhibited the longest time-to-corrosion initiation and the highest chloride threshold levels. Time-to-corrosion did not increase monotonically with cement alkalinity, however, presumably as a consequence of relatively high $Cl^-$ binding in the lower pore water pH range. The chloride threshold level, $Cl_{th}$, increased with increasing $T_i$ and, consequently, was greatest for the highest cement alkalinity specimens.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.657-666
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• 2020

A reliable and cost-effective technique for the development of corrosion damage model is introduced to predict nonlinear time-dependent corrosion wastage of steel structures. A detailed explanation on how to propose a generalised mathematical formulation of the corrosion model is investigated in this paper (Part I), and verification and application of the developed method are covered in the following paper (Part II) by adopting corrosion data of a ship's ballast tank structure. In this study, probabilistic approaches including statistical analysis were applied to select the best fit probability density function (PDF) for the measured corrosion data. The sub-parameters of selected PDF, e.g., the largest extreme value distribution consisting of scale, and shape parameters, can be formulated as a function of time using curve fitting method. The proposed technique to formulate the refined time-dependent corrosion wastage model (TDCWM) will be useful for engineers as it provides an easy and accurate prediction of the 1) starting time of corrosion, 2) remaining life of the structure, and 3) nonlinear corrosion damage amount over time. In addition, the obtained outcome can be utilised for the development of simplified engineering software shown in Appendix B.

• 한국표면공학회지
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• 제49권5호
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• pp.431-438
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• 2016

This research investigated the relationship between the corrosion damage characteristics of offshore wind steel substructure and the time of current density application by electrochemical accelerated short-term corrosion test. The galvanostatic corrosion was conducted on the steel specimens in natural seawater with a constant current density ranging from $1mA/cm^2$ to $200mA/cm^2$ for 1 ~ 180 min. Macro and micro observation was carried out on the surface of the corrosion damaged area using SEM and 3-dimensional analysis microscope. The weight loss of the specimens before and after was calculated as the difference between the initial weight prior to corrosion and weight after removal of the corrosion product. It was shown that during galvanostaic corrosion process, the corrosion behavior could be characterized by the onset of pitting corrosion in the early stage and the uniform corrosion in the late stage, showing damage development in the depth direction with the time of current application. The result of the 3D analysis revealed that both damage depth and surface roughness increased with increasing time of current application. The weight loss curves with time showed that a coefficient of determination ($R^2$) was relatively high for the relationship between the time of current application and weight loss. As a result, the degree of corrosion can be controlled by simply varying the time of current application.

• Structural Engineering and Mechanics
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• 제65권2호
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• pp.191-201
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• 2018

The corrosion environments in a steel structure are significantly different depending on the individual parts of the members. To ensure the safety of weathering steel structures, it is important to evaluate the time-dependent corrosion behavior. Thus, the progress and effect of corrosion damage on weathering steel members should be evaluated; however, the predicted corrosion depth, which is affected by the corrosion environment, has not been sufficiently considered until now. In this study, the time-dependent thicknesses of the corrosion product layer were examined to quantifiably investigate and determine the corrosion depth of the corroded surface according to the exposure periods and corrosion environments. Thus, their atmospheric exposure tests were carried out for 4 years under different corrosion environments. The relationship between the thickness of the corrosion product layers and mean corrosion depth was examined based on the corrosion environment. Thus, the micro corrosion environments on the skyward and groundward surfaces of the specimens were monitored using atmospheric corrosion monitor sensors. In addition, the evaluated mean corrosion depth was calculated based on the thickness of the corrosion product layer in an atmospheric corrosion environment, and was verified through a comparison with the measured mean corrosion depth.

• Structural Engineering and Mechanics
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• 제56권2호
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• pp.257-273
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• 2015

Numerical value of correlation between effective parameters in the strength of a structure is as important as its stochastic properties in determining the safety of the structure. In this article investigation is made about the variation of coefficient of correlation between effective parameters in corrosion initiation time of reinforcement and the time of concrete cover cracking in reinforced concrete (RC) structures. Presence of many parameters and also error in measurement of these parameters results in uncertainty in determination of corrosion initiation and the time to crack initiation. In this paper, assuming diffusion process as chloride ingress mechanism in RC structures and considering random properties of effective parameters in this model, correlation between input parameters and predicted time to corrosion is calculated using the Monte Carlo (MC) random sampling. Results show the linear correlation between corrosion initiation time and effective input parameters increases with increasing uncertainty in the input parameters. Diffusion coefficient, concrete cover, surface chloride concentration and threshold chloride concentration have the highest correlation coefficient respectively. Also the uncertainty in the concrete cover has the greatest impact on the coefficient of correlation of corrosion initiation time and the time of crack initiation due to the corrosion phenomenon.

• 지질공학
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• 제26권1호
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• pp.79-85
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• 2016

방사성폐기물 처분시설 공학적방벽을 구성하는 콘크리트는 주변 환경의 영향으로 내구 수명에 영향을 받게 된다. 현재까지 개발된 수치해석 모델 및 실험을 통하여 방사성폐기물 처분시설 공학적방벽 소재로 가장 널리 사용되는 콘크리트에 대해 주변환경을 고려하여 그 영향을 살펴보았다. 본 연구에 해당하는 철근 콘크리트 구조물은 지리적으로 해안과 인접한 지하수 포화대에 위치하고 있다. 일반적인 철근콘크리트 구조물의 가장 민감한 열화인자인 염해에 의한 철근부식에 대한 영향을 염화물 확산모델을 이용하여 평가한 결과 철근 부식 개시기간이 1,284년이며, 최종적으로 구조물이 내구수명을 상실하는데 도달하는 시간은 1,924년인 것으로 예측되었다. 또한, Mock-up 실험을 통해 공극분포, 공극률, 부식정도 등 물리화학적 특성을 평가한 결과 콘크리트 내 철근 부식정도는 미비한 것으로 나타나 500년 이상의 상당히 오랜 기간 건전성을 유지할 수 있는 것으로 판단된다.

• 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.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.771-774
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• 1999

This study was carried out to quantitatively investigate the amount of corrosion at the time of onset of cracks in cover concrete due to rebar corrosion. In this experiments, the accelerated galvanostatic corrosion method was carried out. FEM analyses were also conducted to investigate the expansive behaviors due to rebar corrosion and the mechanical properties of corrosion products. As a result, it was concluded that the corrosion ratio at the time of onset of cracks in cover concrete was 3% by weight. The onset of cracks in cover concrete due to rebar corrosion could be analyzed by the finite element method.

• Corrosion Science and Technology
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• 제4권3호
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• pp.75-80
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• 2005

This work dealt with the evaluation of galvanic corrosion rate in a corrosion cell having annular gap of 0.5 mm between carbon steel 1018 and alloy 600 as a function of temperature and boron concentration. Temperature and boron concentration were ranged from 110 to 300 $^{\circ}C$ and 2000~10000 ppm, respectively. After the operating temperature of the corrosion cell where the electrolyte was injected was attained at setting temperature, galvanic coupling was made and at the same time galvanic current was measured. The galvanic corrosion rate decreased with time, which was described by corrosion product such as protective film as well as boric acid deposit formed on the carbon steel with time. From the galvanic current obtained as a function of temperature and boron concentration, it was found that the galvanic corrosion rate decreased with temperaturewhilethe corrosionrate increasedwith boronconcentration. The experimental resultsobtained from galvanic corrosion measurement were explained by adhesive property of corrosion product such as protective film, boric acid deposit formed on the carbon steel wall and dehydration of boric acid to be slightlysolubleboric acid phase.Moreoverthe galvaniccorrosionrate calculatedusing initialgalvaniccoupling current instead of steady state coupling current was remarked, which could give us relatively closer galvanic corrosion rate to real pressurized water reactor.