• Journal of the Korea Concrete Institute
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• v.29 no.3
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• pp.299-306
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• 2017

In this research, it was examined chloride ion penetration resistance of slag-replaced concrete and cementless slag concrete considering marine environmental exposure conditions of splash zone, tidal zone and immersion zone. In the design strength of grade 24 MPa, the specimens were tested to determine their compressive strength, scanning electron microscopy images and chloride migration coefficient. Further, chloride ion penetration depth and carbonation depth of specimens exposed to marine environment were measured. Experimental results confirm that chloride migration coefficient of specimens tended to decrease with increasing the replacement ratio of ground granulated blast-furnace slag in accelerated laboratory test. In addition, the specimens exposed to the tidal zone were found to be the greatest chloride ion penetration depth compared to splash zone and immersion zone. On the other hand, the chloride ion penetration depth of the specimens exposed to splash zone tended to increase with increasing the replacement ratio of ground granulated blast-furnace slag in contrast with the results for the tidal zone and immersion zone.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.3
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• pp.533-544
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• 2015

Unlike the concrete structure built on land, that exposed to the marine environment is greatly degraded in durability due to the exposure to not only the physical action caused by sea wind, tide, and wave, but also the harsh conditions, including the chemical erosion and freeze-thaw which result from $SO_4{^{2-}}$, $Cl^-$ and $Mg^{2+}$ ions in seawater. In the process of the large scaled construction of submerged concrete structures, of course environmental hazardous substance, such as alkaline (pH) and heavy metals, may be leached. Thus, this issue needs to be adequately reviewed and studied. Therefore, this study attempted to develop a CSA (Calcium Sulfo Aluminate) activator using electric arc furnace reducing slags, as well as the eco-friendly concrete for artificial reefs using electric arc furnace oxidizing slag as aggregate for concrete. The strength properties of the eco-friendly concrete exposed to the marine environment were lower than those of the normal concrete by curing 28 days. This suggest that additional studies are needed to improve the early strength of the eco-friendly concrete. With respect to seawater resistance of the eco-friendly concrete, the average strength loss against 1 year of curing days reached 8-9%. the eco-friendly concrete using high volume of ground granulated blast furnace slags and high specific gravity of electronic arc furnace oxidizing slag demonstrated the sufficient usability as a freeze-thaw resistant material. With respect to heavy metal leaching properties of the eco-friendly concrete, heavy metal substances were immobilized by chemical bonding in the curing process through the hydration of concrete. Thus, heavy metal substances were neither identified at or below environmental hazard criteria nor detected, suggesting that the eco-friendly concrete is safe in terms of leaching of hazardous substances.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.681-686
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• 2003

One of the major degradation processes of reinforced concrete (RC) structure is corrosion of reinforced steel due to chloride attack. Severe environments, such as marine environment and exposure to de-icing salts, could accelerate the steel corrosion of RC structures through the chloride ion intrusion into concrete. In order to delay this degradation process, several kinds of admixtures have been used in concrete mix. In this study, effective diffusion coefficient of chloride ion ($D_{eff}$) and total passed charge of concrete with and without fly ash were measured using electrical method. It is found that fly ash concrete has much less chloride ion coefficient than ordinary concrete at later age. By analyzing the test results, $D_{eff}$ at 28 and 90 days was obtained as a function of water-binder ratio (W/B) and an equation for predicting $D_{eff}$ with age was proposed considering the decreasing rate of $D_{eff}$.

• International Journal of Naval Architecture and Ocean Engineering
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• v.11 no.2
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• pp.851-857
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• 2019

A new robust sliding mode control with disturbance and state observers has been proposed to control the nozzle angle of a water-jet system for a Unmanned Surface Vehicle (USV). As the water-jet system of a ship is subjected to direct disturbances owing to the exposure to the marine environment in water, it requires a robust control. A state observer and a disturbance observer are added to the water jet nozzle control system to achieve a robust control against disturbances. To verify the performance of the proposed algorithm, a test bed is constructed by a propulsion system used in the popular USV. This proposed algorithm has been evaluated by comparing to the existing algorithm through experiments. The results show that the performance of the proposed algorithm is better than that of the conventional PID or sliding mode controller when controlling the steering of the USV with disturbances.

• Journal of Life Science
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• v.15 no.6 s.73
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• pp.979-986
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• 2005

Lead (Pb) exposure during development can produce neurological deficits. In this study, the effect of Pb exposure during neonatal development via lactation on anxiety of brain function was investigated. Long-Evans strain rats were raised through two generations. At the birth of the second generation, the dams were subdivided into two groups and supplied drinking water containing either $0.2\%$ Pb (Pb-treated group) or sodium (Na, Control group) acetate until weaning. Rats were sacrificed at 3 (weaning) and 11 weeks (maturity) for brain Pb and fatty acid analysis. Motor activity and elevated plus maze tests were initiated at 9 weeks. The brains in the Pb-treated group at weaning and maturity contained 1486$\pm$98 and $270{\pm}46$ ng Pb/g, respectively The control group showed the background level of Pb ($3.7{\pm}1.0_{ng}$ Pb/g) in both ages. The alterations in brain fatty acid composition induced by Pb exposure were more evident in 3 wks old than 11 wks old. For example, in 3 wks old, the percentages of $18:2_{n-6}$, $20:2_{n-6}$ and $18:2_{n-6}$ were decreased in the Pb-treated group with an increase in $20:4_{n-6}$ In motor activity test, there was a tendency of hyperactivity in the Pb-treated group compared with the control group but the difference was not significant. In elevated plus maze test, the Pb-treated group showed fewer numbers of visits to the open arms (P < 0.05), indicating that Pb exposure may lead to anxiogenic effect.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.6
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• pp.672-678
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• 2015

The types of hazardous and noxious substances (HNS) being transported by sea in Korea are at about 6,000, HNS transport volume accounts for 19% of total tonnage shipped in Korea, and the increase rate of seaborne HNS trade in Korea is 2.5 times higher than the average increase rate of the world seaborne HNS trade. Reflecting this trend, HNS spill incidents have been frequently reported in Korean waters, and there are increasing social demands to develop HNS management technology for the preparedness, response, post-treatment and restoration in relation to HNS spill incidents at sea. In this study, a risk-based HNS prioritization system was developed and an HNS risk database was built with evaluation indices such as sea transport volume, physicochemical properties, toxicities, persistency, and bioaccumulation. Risk scores for human health and marine environments were calculated by multiplying scores for toxicity and exposure. The top-20 substances in the list of HNS were tabulated, and Aniline was ranked first place, but it needs to be managed not by individuals but by HNS groups with similar score levels. Limitations were identified in obtaining data of chronic toxicity and marine ecotoxicity due to lack of testing data. It is necessary to study on marine ecotoxicological test in the near future. Moreover, the priority list of HNS is expected to be utilized in the development of HNS management technology and the relevant technologies, after the expert's review process and making up for the lack of test data in the current research results.

• Journal of the Korean Society for Marine Environment & Energy
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• v.10 no.3
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• pp.127-137
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• 2007

To confirm whether or not the Electrochemical Disinfection System (EDS) meet with the D-2 regulation established by IMO (International Maritime Organization), the biological treatment efficacy of the EDS was assessed using three groups of natural marine plankton (bacteria, $10-50\;{\mu}m$ and $>50\;{\mu}m$ sized organisms). Influent water was passed through the EDS under the flow velocity ($23.8\;m^3/hr$) and test design was consisted of control (no treatment) and experimental (10 ppm and 30 ppm) condition for total residual chlorine (TRC). And the biological condition of the influent water followed the standards established by the guidelines for the approval of ballast water management systems. The disinfection efficacy of the $10-50\;{\mu}m$ sized organisms (phytoplankton) was assessed by three kinds of measurements using photomicroscope, epifluorescence microscope and fluorometer (fumer Designs 10-AU). After being passed through the EDS, all motile phytoplankton lost their motility under photomicroscope, the colour of chlorophyll fluorescence fumed from red into green under epifluorescence, and the high chlorophyll fluorescence (Expt. 1: 6.95, Expt. 2: 7.11) detected by fluorometer decreased into value not detected. These results indicated phytoplankton community was totally killed after electrochemical disinfection treatment. Survivorship of the larger organisms than $50\;{\mu}m$ was determined based on the appendage's movement under a stereomicroscope. Natural assemblage collected from ambient seawater was killed shortly after being passed through the EDS, whereas some Artemia remained alive. However, no live Artemia was found after 24 hour further exposure to each TRC concentration (10 and 30 ppm) under darkness. After electrochemical treatment, the target bacteria such as aerobes, coliform and Escherichia coli were completely killed on the basis of CFU (colony forming unit) on Petrifilm plate ($3\;M^{TM}$) after 48 hr incubation. Moreover, no regrowth was found in the three groups of plankton during five days under additional exposure to the treated water. These results indicated that the disinfection efficiency of the EDS on the three groups of plankton satisfy D-2 regulation.

• Corrosion Science and Technology
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• v.7 no.2
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• pp.119-124
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• 2008

Steel is generally not corrosion resistant to water with formation of non protective rusts on its surface. Rusts are composed of iron oxides such as $Fe_3O_4$, $\alpha-$, $\beta-$, $\gamma-$and ${\delta}-FeOOH$. However, steel, particularly weathering steel containing small amounts of Cu, Ni and Cr etc., shows good corrosion resistance against rural, industrial or marine environment. Its corrosion rate is exceedingly small as compared with that of carbon steel. According to the exposure test results undertaken in outdoor environments, the atmospheric corrosion rate for weathering steel is only 1 mm for a century. Atmospheric corrosion for steels proceeds under alternate dry and wet conditions. Dry condition is encountered on steel surface on fine or cloudy days, and wet condition is on rainy or snowy days. The reason why weathering steel shows superior atmospheric corrosion resistance is due to formation of corrosion protective rusts on its surface under very thin water layer. The protective rusts are usually composed of two layer rusts; the upper layer is ${\gamma}-FeOOH$ termed as lepidocrocite, and inner layer is nano-particle ${\alpha}-FeOOH$ termed as goethite. This paper is aimed at elucidating the atmospheric corrosion mechanism for steel in comparison with corrosion in bulky water environment by use of empirical data.The summary is as follows: 1. No corrosion protective rusts are formed on steel in bulky water. 2. Atmospheric corrosion for steel is the corrosion under wetting and drying conditions. Corrosion and passivation occur alternately on steel surface. Steel, particularly weathering steel with small amounts of alloying elements such as Cu, Ni and Cr etc. enhances forming corrosion protective rusts by passivation.

• Journal of Conservation Science
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• v.29 no.2
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• pp.187-196
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• 2013

This study is on the corrosion of iron objects caused by sulfides in undersea environment. The corrosion state of objects in seawater and their damage state after underwater and left in highly humid air were studied. The samples of this study were four iron objects which had been taken out from undersea mud layer located in Taean Mado, Chungcheongnamdo. SEM-EDS and XRD analyse on the objects to check whether they have sulfides or not. The result of analysis suggested that the major component of corrosion product generated in undersea deposit soil is sulfur(S) and iron sulfide(FeS) is formed as sulfide. However, there was no clear corrosion on the surface of objects which was exposed to sea water because of the impact of concretion which covered the surface. In order to check the damage status of iron objects after they had been taken out of sea water, exposure tests in high humidity environment and dehumidified environment were done on the corrosion products. The result of the test suggested that the oxidization of iron sulfide corrosion product makes iron sulfate ($FeSO_4$) and sulfuric acid ($H_2SO_4$) and they can cause secondary corrosion of iron objects. Therefore, it is believed that the iron sulfide corrosion product of iron objects taken out from underwater environment should be removed by all means and the keeping environment of the iron objects should also maintain dehumidified state.

• Journal of the Korean Society for Marine Environment & Energy
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• v.9 no.1
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• pp.21-28
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• 2006

Since the usage of tributyltin(TBT) has been banned, many chemicals including Sea-Nine 211, Cu-pyrithione, and Zn-pyrithione were developed to use as antifouling agents for ships and coastal structures. However, the toxicity of these antifouling chemicals have not been systematically evaluated in ecotoxicological and biological studies. In this study, we investigated the effect of four antifouling substances on survival of estuarine rockfish, Sebastes schlegeli and amphipod, Monocorophium acherusicum. Survival of S. schlegeli and M. acherusicum during the 96-h exposure period were used to estimate the median lethal concentrations(LC50s) of test chemicals for each test species. Among antifouling agents, Cu-pyrithione($56{\mu}g{\cdot}1^{-1}$;96-h LC50) was most toxic to S. schlegeli, followed by $TBT(73{\mu}g{\cdot}1^{-1}),\;Sea-Nine(184{\mu}g{\cdot}1^{-1})\;and\;Zn-pyrithione(l707{\mu}g{\cdot}1^{-1})$, while TBT($26{\mu}g{\cdot}1^{-1}$) was most toxic to M. acherusicum followed by Sea-Nine($49{\mu}g{\cdot}1^{-1}$), Cu-pyrithione($119{\mu}g{\cdot}1^{-1}$) and Zn-pyrithione($334{\mu}g{\cdot}1^{-1}$). Effect concentrations of the antifouling chemicals estimated in this study can be used when assessing the potential risks of these substances, of which usage is increasing in the coastal environment.