• Journal of the Korean GEO-environmental Society
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• v.25 no.2
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• pp.5-14
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• 2024

Reinforced concrete bridge decks are the first to be damaged by vehicle loads and rain infiltration. Concrete deterioration primarily occurs owing to the corrosion of rebars and other metal components by chlorides used for snow and ice melting. The structural condition and concrete deterioration of the bridge decks within the pavement were evaluated using ground-penetrating radar (GPR) survey data. To evaluate concrete deterioration in bridges, it is necessary to develop GPR data analysis techniques to accurately identify deteriorated locations and rebar positions. GPR exploration involves the acquisition of reflection and diffraction wave signals due to differences in radar wave propagation velocity in geotechnical media. Therefore, a full-waveform inversion (FWI) method was developed to evaluate the deterioration of reinforced concrete bridge decks by estimating the radar wave propagation velocity in geotechnical media using GPR data. Numerical experiments using a GPR velocity model confirmed the deterioration phenomena of bridge decks, such as concrete delamination and rebar corrosion, verifying the applicability of the developed technology. Moreover, using the synthetic GPR data, FWI facilitates the determination of rebar positions and concrete deterioration locations using inverted velocity images.

• KEPCO Journal on Electric Power and Energy
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• v.4 no.1
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• pp.25-31
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• 2018

A boiler system transforms water to pressured supercritical steam which drives the running of the turbine to rotate in the generator to produce electricity in power plants. Materials for building the tube system face challenges from high temperature creep damage, thermal fatigue/expansion, fireside and steam corrosion, etc. A database on the creep resistance strength and steam oxidation of the materials is important to the long-term reliable operation of the boiler system. Generally, the ferritic steels, i.e., grade 1, grade 2, grade 9, and X20, are extensively used as the superheater (SH) and reheater (RH) in supercritical (SC) and ultra supercritcal (USC) power plants. Currently, advanced austenitic steel, such as TP347H (FG), Super304H and HR3C, are beginning to replace the traditional ferritic steels as they allow an increase in steam temperature to meet the demands for increased plant efficiency. The purpose of this paper is to provide the state-of-the-art knowledge on boiler tube materials, including the strengthening, metallurgy, property/microstructural degradation, oxidation, and oxidation property improvement and then describe the modern microstructural characterization methods to assess and control the properties of these alloys. The paper covers the limited experience and experiment results with the alloys and presents important information on microstructural strengthening, degradation, and oxidation mechanisms.

• Journal of the Korean Institute of Gas
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• v.22 no.3
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• pp.1-6
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• 2018

Reliability based design and assessment (RBDA) methodology is one of the newest directions of natural gas pipeline design method. Reliability targets are used to ensure that safety levels are met relevant limit states in the stage of design and maintenance. The target reliability for ultimate limit states such as large leak and rupture were developed using tolerable risk criteria for individual and societal risk. This paper shows the reliability target can be met through the implementation of periodic maintenance measures during the life cycle of the pipelines. The case study involves the calculation of the failure probability due to equipment impact, the calculation of the failure probability due to corrosion, and the estimation the re-inspection interval for domestic natural gas transmission pipelines.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.10
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• pp.1101-1109
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• 2012

Accelerometers play a key role in the structural assessment. However, the current electric type accelerometers have certain limitations to apply some structures such as heavy cabling labor, installed sea structure and sensitivity to electromagnetic fields. An optical Fiber Bragg Grating (FBG) accelerometer has many advantages over conventional electrical sensors since their immunity to electromagnetic interference and their capability to transmit signals over long distance without any additional amplifiers, and there is no corrosion from sea water. In this paper, we have developed a new FBG-based accelerometer. The accelerometer consists of two cantilevered type beams and a mass and two rollers. A bragg grating element is not directly glued to a cantilever to avoid possible non-uniform strain in the element. Instead, the bragg grating element will be attached to rotation part that rolled inducing vertical movement of the mass and support cantilever beams so that the bragg grating element is uniformly tensioned to achieve a constant strain distribution. After manufacturing, we will prove the performance and the natural frequency of the accelerometer through the experiment with a vibration shaker. The FBG-based accelerometer is developed for measuring the vibration not exceeding 50 Hz for the marine and civil structures.

• Journal of Soil and Groundwater Environment
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• v.21 no.4
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• pp.1-9
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• 2016

Rehabilitation for low-yielding wells resulting in improvement on groundwater quantity and quality is considered to be the most economic and ecofriendly method against the increasing demand to groundwater due to frequent drought and the increase in numbers of agricultural complex for growing horticultural crops. This study suggests standard, stepwise diagnostic fuctions consisting of four steps (Basic inspection, Specific inspection, Rehabilitation, and Management) for an optimal management to the wells. Basic inspection can provide information on current groundwater quantity and quality compared with those on its initial stage. Specific-inspection based on hydrogeology can scientifically demonstrate causes of deterioration on groundwater quantity and quality. Results of specific inspection can suggest an optimal rehabilitation method to solve deteriorating problems including clogging and corrosion for the wells. After rehabiliating the wells, an assessment on groundwater quantity and quality would be conducted to identify the suitability of the applied method and improvement of the wells. A short-term, periodic management to the wells is considered as the key to save a public management budget. Suggested diagnostic functions can possibly induce sustainable supply of agricultural groundwater to the farm land and finally contribute the increase on rural household income.

• Journal of the Korean Society of Safety
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• v.33 no.5
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• pp.60-69
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• 2018

This study aims to investigate in the assessment of salt damage conditions in concrete structures under marine environment conditions. It aims also to improve the durability of new concrete bridge through applying the life prediction method of salt damaged bridges. As measuring chloride contents of these bridges on the southwest coastal area, it is shown that the average amount of chloride on these surfaces close to shore is $10.5kg/m^3$. This figure is much higher than that of the Standard Specification for Concrete($1.5kg/m^3{\sim}2.5kg/m^3$). In contrast, it is shown the average amount of chloride on these surfaces in tide zone is $13.1kg/m^3$. Its figure is much lower than that of the Standard Specification for Concrete($20kg/m^3$). And the life of bridges is estimated about 17 years. To improve the durability for salt damage, these bridges are applied to surface treatment method which the replacement rate of furnace slag is 60%. Under this condition, it is expected to be 110 years. Consequently, it is clear that the use of slag replacement rate, surface treatment agent, and anti-corrosion agent to control chloride penetration effects of a submerge-based concrete bridge will be required.

• Journal of Korean Society of Environmental Engineers
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• v.36 no.9
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• pp.614-623
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• 2014

Customers water quality complaints by foreign substance in local water service can be able to call the main cause bring the distrust for tap water and inhibiting the rate of drinking water. In this study, foreign substances were collected in the target region. Foreign objects were subjected to qualitative and quantitative analysis of compounds and elements components to reveal the cause of detection. Also, resolve the complaints by foreign substance and improve the reliability for tap water providing high quality water supply scheme. Collected substances at the water quality complaint area were included in inorganic compounds due to internal corrosion and aging pipeline, as well as organic compounds containing a large amount of carbon (C) and oxygen (O) component. To decide and reduce for foreign substance, objective assessment of pipe condition in target area was required.

• Advances in concrete construction
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• v.10 no.5
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• pp.393-402
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• 2020

The given research focuses on examining the effect of relatively humidity (RH) and curing temperature on the hydrates as well as the porosity of calcium sulfoaluminate (CSA) cement pastes. Numerous tests, which consist of mercury intrusion porosimetry (MIP), thermosgravi metric (TG) and X-ray diffraction (XRD) were conducted. Various characterization techniques which include, scanning electron microscopy, Fourier transform microscopy along with X-ray diffraction evaluations were conducted on the samples to examine phase formation and crystallinity, morphology and microstructure along with bond formations and functional groups, respectively. During long-term study, the performance of concrete which consisted of limestone and flash-calcined was close to those from standard Portland cement concrete. Traditional classifications and methods of corrosion were widely used for the assessment of steel in concrete which may get employed to concrete which contains LC3 to recalibrate the range of polarization resistance for passitivity condition. For example, there is up to 79.5% and 146% respective flexural and compressive strengths. Moreover, they developed more advance electrical and thermo-mechanical performance with a substantial reduction in absorption of water of close to 400%. These advantages allow this research crucial to evaluate how these methods can be applied. Additionally, the research evaluates developed and more advanced cement preservation and repair techniques. The conclusion suggests concerted efforts by various stakeholders such as policy makers to enable low-carbon rates.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.185-188
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• 2008

Fiber reinforced polymer(FRP) bars are proving to be a valuable solution in the corrosion problem of steel reinforced concrete structures. As such, a number of guidelines for their use have been developed. These guidelines are primarily based on modifications to existing codes of practice for steel reinforced concrete structures. These guidelines are also similar in that though the design equations are presented in the partial factor formats that are often used in probability based design, they are not true probabilistic codes. Instead, they typically make use of already existing design factors for loads and resistances. Thus, when concrete structures reinforced FRP bars are designed, the structural reliability levels are not known. This paper investigates uncertainties of concrete beams reinforced with GFRP bars. Also, the structural reliability levels are evaluated for the flexural failure mode.

• Smart Structures and Systems
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• v.21 no.3
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• pp.305-320
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• 2018

The second half of the 20th century was marked with a significant raise in amount of railway bridges in Austria made of reinforced concrete. Today, many of these bridges are slowly approaching the end of their envisaged service life. Current methodology of assessment and evaluation of structural condition is based on visual inspections, which, due to its subjectivity, can lead to delayed interventions, irreparable damages and additional costs. Thus, to support engineers in the process of structural evaluation and prediction of the remaining service life, the Austrian Federal Railways (${\ddot{O}}$ BB) commissioned the formation of a concept for an anticipatory life cycle management of engineering structures. The part concerning concrete bridges consisted of forming a bridge management system (BMS) in a form of a web-based analysis tool, known as the LeCIE_tool. Contrary to most BMSs, where prediction of a condition is based on Markovian models, in the LeCIE_tool, the time-dependent deterioration mechanisms of chloride- and carbonation-induced corrosion are used as the most common deterioration processes in transportation infrastructure. Hence, the main aim of this article is to describe the background of the introduced tool, with a discussion on exposure classes and crucial parameters of chloride ingress and carbonation models. Moreover, the article presents a verification of the generated analysis tool through service life prediction on a dozen of bridges of the Austrian railway network, as well as a case study with a more detailed description and implementation of the concept applied.