• Journal of the Korea Concrete Institute
• /
• v.29 no.3
• /
• pp.307-314
• /
• 2017

Concrete is a durable and cost-benefit construction material, however performance degradation occurs due to steel corrosion exposed to chloride attack. Penetration of chloride ion usually decreases due to hydrates formation and reduction of pores, and the reduced chloride behavior is considered through decreasing diffusion coefficient with time. In the work, HPC (High Performance Concrete) samples are prepared with 3 levels of W/B (water to binder) ratios of 0.37, 0.42, and 0.27 and 3 levels of replacement ratios of 0%, 30% and 50%. Several tests containing chloride diffusion coefficient, passed charge, and compressive strength are performed considering age effect of 28 days and 180 days. Chloride diffusion is more reduced in OPC concrete with lower W/B ratio and GGBFS concrete with 50% replacement ratio shows significant reduction of chloride diffusion in higher W/B ratio. At the age of 28 days, GGBFS concrete with 50% replacement ratio shows more rapid reduction of chloride diffusion than strength development, which reveals that abundant GGBFS replacement has effective resistance to chloride penetration even in the early-aged condition.

• Journal of Sensor Science and Technology
• /
• v.9 no.6
• /
• pp.404-415
• /
• 2000

This paper describes several performances and nondestructive inspection for deterioration due to forest fires in overhead transmission lines. After discussing corrosion mechanism such as atmospheric and galvanic corrosion for aged ACSR conductors and its detection for them are presented. Through impedance analysis of a solenoid coil, it is shown that the eddy current sensor may be available to inspect severe fault or local corrosion. As the solenoid coil changes its impedance when the test conductor is inserted into the coil, it can be possible to measure deterioration degree caused by forest fires. Tensile strength, extension rate and sensor impedance are tested for some samples degraded by artificial fire. As increasing blazed period to some extent, the strength of aluminum strand begins to be reduced remarkably, while galvanized steel strand holds the similar strength to the initial value, despite of appearing a little loss of zinc layer. In general, it is shown that the sensor impedance would be increased while the tension load of conductor is reduced and the extension rate is contrarily increased. Therefore, the sensor output could exhibit the changes of mechanical performances, and would be used to detect such deterioration caused by forest fire in ACSR conductors built on the ridge of mountains. Finally, it was verified that the solenoid coil could be applicable to obtain any crucial inform for serious deterioration due to forest fires.

• Journal of the Korean Institute of Gas
• /
• v.22 no.6
• /
• pp.44-51
• /
• 2018

As the LNG storage tank is aged, if there is a crack in the outer wall concrete or corrosion of the reinforcing steel, there is a risk of a major accident such as collapse of the structure depending on the type and degree of damage. Since 2014, LNG storage tanks have undergone precise safety diagnosis and safety inspection has been carried out. The condition evaluation criteria for each component have been revised and applied in January 2016. The condition evaluation standard is to evaluate the status of storage tanks based on the appearance survey and material test results of LNG storage tanks and it is important for maintenance. In addition, the representative condition evaluation standard that shows the comprehensive state of each LNG storage tank is important in maintenance, but the related standard for LNG storage tank outer concrete is not available in Korea and abroad, and development of the condition evaluation standard is necessary. In this paper, we examined the structural characteristics of LNG storage tanks, analyzed the status of the condition evaluation criteria for each member, and developed a comprehensive status rating system by weighting the members. We used the AHP(Analytic Hierarchy Process) technique and developed a representative conditon evaluation criteria through surveys of professional organizations.

• Land and Housing Review
• /
• v.13 no.1
• /
• pp.141-150
• /
• 2022

Responding to the increasing demand for research on seismic resistance of structures triggered by a large-scale earthquake in Korea, the Ministry of the Interior and Safety revised the typical application of the existing seismic design standards with the national seismic performance target enhanced. Therefore, in this paper, the dam body of the aged Test-Bed and the penstock with fluid were modeled by the three-dimensional finite element method by introducing several variables. The current seismic design standard law confirmed the safety of the dam structure and penstock against seismic waves. As a result of the 3D finite element analysis, the stress change due to the water impact of the penstock was minimal, and it was confirmed that the effect of the hydraulic pressure was more significant than the water impact in the earthquake situation. When the hydrostatic pressure is in the form of SPH, it was analyzed that the motion of the fluid and the location of stress caused by the earthquake can be effectively represented, and it will be easier to analyze the weak part. As a result of the analysis, which considers penstock's corrosion, the degree of stress dispersion gets smaller because the penstock is embedded in the body. The stress result is minimal, less than 1% of the yield stress of the steel. In addition, although there is a possibility of micro-tensile cracks occurring in the inlet of the dam, it has not been shown to have a significant effect on the stress increa.

• Korean Journal of Environmental Agriculture
• /
• v.14 no.2
• /
• pp.186-201
• /
• 1995

In order to elucidate the fate of the residues of the pyrethroid acaricide-insecticide, acrinathrin in soil, maize plants were grown for one month on the specially-made pots filled with two different types of soils containing fresh and one-month-aged residues of [$^{14}C$]acrinathrin, respectively. The mineralization of [$^{14}C$]acrinathrin to $^{14}CO_2$ during the one-month period of aging and of maize cultivation amounted to $23{\sim}24%$ and $24{\sim}33%$, respectively, of the original $^{14}C$ activities. At harvest after one-month growing, the shoots and roots contained less than 0.1% and 1% of the originally applied $^{14}C$ activity, respectively, whereas the $^{14}C$ activity remaining in soil was $65{\sim}80%$ in both soils. Three degradation products with m/z 198(3-phenoxybenzaldehyde), m/z 214(3-phenoxybenzoic acid), and m/z 228(methyl 3-phenoxybenzoate) besides an unknown were identified from acetone extracts of both soils without and with maize plants after treatment of [$^{14}C$]acrinathrin, by autoradiography and GC-MS, and those with m/z 225(3-phenoxybenzaldehyde cyanohydrin) and m/z 198 (3-phenoxybenzaldehyde) from acetone extract of the Soil A treated with 50 ppm acrinathrin and grown with maize plants for 30 days were identified by mass spectrometry. These results suggested that the hydrolytic cleavage of the ester linkage adjacent to the $^{14}C$ with a cyano group, forming 3-phenoxybenzaldehyde cyanohydrin. The removal of hydrogen cyanide therefrom leads to the formation of 3-phenoxybenzaldehyde as one of the major products. The subsequent oxidation of the aldehyde to 3-phenoxybenzoic acid, followed by decarboxylation would evolve $^{14}CO_2$. Solvent extractability of the soils where maize plants were grown for 1 month and/or [$^{14}C$]acrinathrin was aged for 1 month was less than 31% of the original $^{14}C$ activity and over 95% of the total $^{14}C$ activity in soil extracts was distributed in the organic phase. Accordingly, acrinathrin turned out to be degraded rapidly in both soils and be bound to soil constituents as well, not being available to crops.

• The korean journal of orthodontics
• /
• v.27 no.4 s.63
• /
• pp.559-568
• /
• 1997

For orthodontic tooth movement, optimal orthodontic force should be maintained without periodontal breakdown and alveolar bone should be remodeled physiologically Therefore, To obtain proper occlusion through tooth movement within alveolar bone, we should know the biomechanics of teeth and supporting 4issues. The present study was performed to observe histologic changes of periodontal tissue immediately after application of orthodontic force and during the retention period in growing young adult dogs. In this study, experimental group contained between mandibular left canine and 1st molar and control group contained contralateral teeth of same animal. The .018'x.022' stainless steel closed coil spring(Dentaurum Co.) was ligated on the experimental teeth at initial 200gm-force from mandibular canine to 1st molar The animals(4 to 6 months aged young adult dogs) were sacrificed on 0, 14, 28 days after the finish of appliance activation, and then tissue samples were divided into hematoxylin-eosin(HE) staining section, ground section, alkaline phosphatase(ALP) staining section, and tartrate-resistant acid phosphatase(TRAP) staining section. Thereafter, the preparations were examined under light microscopy The following results were obtained: 1. Immediately after the finish of appliance activation, the periodontal space was increased in tension side, but decreased in pressure side compared to that of control. The hyalinized zone was also observed in the periodontium. 2. After the 14-day retention, peridontal space was decreased in tension side and slightly increased in pressure side compared to that of immediately after the finish of appliance activation. The hyalinized zone was repaired and a few osteoblasts showing slightly new bone formation were seen. Osteoblasts were scarcely observed along the alveolar bone. 3. Aftter the 28-day retention, the periodontal fibers are normally repaired. A lot of TRAP(+) osteoclasts md increased alveolar bone resorption were observed in pressure side, and AP(+) osteoblast and increased new bone formation were observed in tension side.