• Journal of the Korean Chemical Society
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• v.29 no.1
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• pp.15-22
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• 1985

Kinetic studies of nucleophilic substitution reaction of substituted benzoyl cyanides and benzoyl chlorides with pyridines were conducted at 25$^{\circ}C$ in pure acetone solvent. Results showed that (ⅰ) magnitudes of $_{\rho}_S$, $_{\rho}_N$ and ${\beta}$ associated with a change of substituent in the nucleophile indicate relatively advanced bond-formation in the transition state, (ⅱ) the potential energy surface model is able to predict the reaction mechanism, but it is unable to predict the transition state variation to a more product-like transition state, where bond-formation is much more progressed than bond breaking, upon changing the leaving group to that with better leaving ability (ⅲ) the quantum mechanical model predicted the product-like transition state and slightly better leaving ability of CN- as compared with Cl-.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.529-532
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• 2008

Domestic area of most be happened chloride deicer damage. Because daily mean temperature is below 0$^{\circ}C$ from the area of domestic most. Use of deicing chemicals has been and will continue to be a major part of highway snow and ice control methods. Chloride-containing chemicals such as calcium chloride or rock salt are main deicers for the road. Extensive use of chloride deicers is, however, not only the source of substantial cost penalties due to their corrosive action and ability to deterioration roadway surface materials but also the source of environmental damages. Particularly, it has been recognized that chlorides present in deicing agents can significantly increase concrete surface scaling. In severe cases, scaling can result in dislodgement of coarse aggregate. This research estimates that pH and test of specific pollutants, dynamic modulus of elasticity for freeze-thaw test of concrete were higher than those NaCl, $CaCl_2$, and NaCl+$CaCl_2$(7:3, w/w), also weight losses for scaling test of concrete were much lower than those of NaCl, $CaCl_2$, and NaCl+$CaCl_2$(7:3, w/w).

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.3
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• pp.23-30
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• 2012

For cracked concrete, it is obvious that cracks should be preferential channel for the penetration of aggressive substances such as chloride ions according to the previous researches. In order to extend the lifetime of cracked concrete, critical issues in the performance of the concrete is the risk of chloride-induced corrosion. Even though crack width can be reduced due to the high reinforcement ratio, the question is to which extend these cracks may jeopardize the durability of cracked concrete. If the size of crack is small, surface treatment system can be considered as one of the best options to extend the service life of concrete structures exposed to marine environment simply in terms of cost effectiveness versus durability performance. Thus, it should be decided to undertake an experimental study on the effect of surface coating system, which can be able to seal the concrete and the cracks to aggressive substances-induced corrosion in particular. In this study, it is excuted to examine the effect of surfaced treated systems on chloride penetration and carbonation through compressive stress induced cracks. Experimental results have showed conclusively that critical stress linked with deterioration, should be existed in compressive stress ratio 50 ~ 70% for chloride penetration and 70 ~ 80% for carbonation, respectively. When the critical stress is exceeded in concrete, a comparatively large deterioration was measured where the critical stress in concrete, the increase in the mass transportation is marginal in spite of the large increase in micro-cracks. As for the effect of surface coating system on crack-sealing, it can be seen conclusively that cracks can be healed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5A
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• pp.729-735
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• 2008

For well-constructed concrete, its service life is a long period and it has an enough durability performance. For cracked concrete, however, it is clear that cracks should be a preferential channel for the penetration of aggressive substance such as chloride ions accoding to author's previous researches. Even though crack width can be reduced due to the high reinforcement ratio, the question is to which extend these cracks may jeopardize the durability of cracked concrete. If the size of crack is small, surface treatment system can be considered as one of the best options to extend the service life of concrete structures exposed to marine environment simply in terms of cost effectiveness versus durability performance. Thus, it should be decided to undertake an experimental study to deal with the effect of different types of surface treatment system, which are expected to seal the concrete and the cracks to chloride-induced corrosion in particular. In this study, it is examined the effect of surfaced treated systems such as penetrant, coating, and their combination on chloride penetration through microcracks. Experimental results showed that penetrant can't cure cracks. However, coating and combined treatment can prohibit chloride penetration through cracks upto 0.06 mm, 0.08 mm, respectively.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.1
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• pp.36-42
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• 2018

GGBFS(Ground Granulated Blast Furnace Slag)-replacement is very effective for improving resistance to chloride attack and this can induce a long service life for RC(Reinforced Concrete) structures exposed to chlorides. In the work, the design parameters such as cover depth, surface chloride content, critical chloride content, and replacement ratio of GGBFS are considered, and optimum replacement ratio of GGBFS are derived with intended service life. The changes of surface chloride content and cover depth show 3.16~3.38 and 3.02~3.34 times of service life variation, which are most influencing parameters. Critical chloride content shows 1.53~1.57 times of service life variation regardless of w/b(Water to Binder) ratios. In the case of surface chloride content $18.0kg/m^3$, the most severe condition, cover depth over 70 mm and GGBFS replacement ratio over 42% are required with concrete containing w/b ratio under 0.42 for 100 years of intended service life. The condition of $13.0kg/m^3$, GGBFS replacement over 35% is required. For reasonable durability design, quantitative exterior condition and critical chloride content should be determined, and the criteria in Domestic Specification is evaluated to be conservative.

• Korean Journal of Materials Research
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• v.14 no.9
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• pp.634-641
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• 2004

The photocatalytic performance of $TiO_2$ thin films coated on porous alumina balls using various aqueous $TiOCl_2$ solutions as starting precursors, to which 1.0 $mol\%$ transition metal ($Ni^{2+},\;Cr^{3+},\;Fe^{3+},\;Nb^{3+},\;and\;V^{5+}$) chlorides had been already added, has been investigated, together with characterizations for $TiO_2$ sols synthesized simultaneously in the same autoclave through hydrothermal method. The synthesized $TiO_2$ sols were all formed with an anatase phase, and their particle size was between several nm and 30 nm showing ${\zeta}-potential$ of $-25{\sim}-35$ mV, being maintained stable for over 6 months. However, the $TiO_2$ sol added with Cr had a much lower value of -potential and larger particle sizes. The coated $TiO_2$ thin films had almost the same shape and size as those of the sol. The pure $TiO_2$ sol showed the highest optical absorption in the ultraviolet light region, and other $TiO_2$ sols containing $Cr^{3+},\;Fe^{3+}\;and\;Ni^{2+}$ showed higher optical absorption than pure sol in the visible light region. According to the experiments for removal of a gas-phase benzene, the pure $TiO_2$ film showed the highest photo dissociation rate in the ultraviolet light region, but in artificial sunlight the photo dissociation rate of $TiO_2$ coated films containing $Cr^{3+},\;Fe^{3+}\;and\;Ni^{2+}$ was measured higher together with the increase of optical absorption by doping.

• Journal of the Korean Society of Safety
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• v.22 no.3 s.81
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• pp.57-64
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• 2007

Recently, the corrosion of concrete structures has received great attention related with the deterioration of sea-side structures, such as new airport, bridges, and nuclear power plants. In this regards, many studies have been done on the chloride attack in concrete structures. However, those studies were confined mostly to the single deterioration due to chloride only, although actual environment is rather of combined type. The purpose of the present study is, therefore, to explore the influences of carbonation and freezing-thawing action to chloride attack in concrete structures. The test results indicate that the chloride penetration is more pronounced than the case of single chloride attack when the carbonation process is combined with the chloride attack. It is supposed that the chloride ion concentration of carbonation region is higher than the sound region because of the separation of fixed salts. Though the use of fly ash pronounces the chloride ion concentration in surface, amounts of chloride ion penetration into deep region decreases with the use of fly ash. The small reduction of relative dynamic elastic modulus induced from freezing-thawing increases the chloride ion penetration depths much. The present study allows more realistic assessment of durability for such concrete structures which are subjected to combined attacks of both chlorides and carbonation or freezing-thawing but the future studies for combined environment will assure the precise assessment.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.829-839
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• 2003

Recently, the corrosion of reinforced concrete structures has received great attention related with the deterioration of sea-side structures, such as new airport, bridges, and nuclear power plants. In this regards, many studies have been done on the chloride attack in concrete structures. However, those studies were confined mostly to the single deterioration due to chloride only, although actual environment is rather of combined type. The purpose of the present study is, therefore, to explore the influences of carbonation to chloride attack in concrete structures. The test results indicate that the chloride penetration is more pronounced than the case of single chloride attack when the carbonation process is combined with the chloride attack. It is supposed that the chloride ion concentration of carbonation region is higher than the sound region because of the separation of fixed salts. Though the use of fly ash pronounces the chloride ion concentration in surface, amounts of chloride ion penetration into deep region decreases with the use of fly ash. The present study allows more realistic assessment of durability for such concrete structures which are subjected to combined attacks of both chlorides and carbonation but the future studies for combined environment will assure the precise assessment.

• The Journal of Engineering Geology
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• v.26 no.1
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• pp.79-85
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• 2016

A concrete silo plays an important role in subsurface low- and intermediate-level waste facilities (LILW) by limiting the release of radionuclides from the silo geosphere. However, due to several physical and chemical processes the performance of the concrete structure decreases over time and consequently the concrete loses its effectiveness as a barrier against groundwater inflow and the release of radionuclides. Although a number of processes are responsible for degradation of the silo concrete, it is determined that the main cause is corrosion of the reinforcing steel. Therefore, the time it takes for the silo concrete to fail is calculated based on two factors: the initiation time of corrosion, defined as the time it takes for chloride ions to penetrate through the concrete cover, and the propagation time of corrosion. This paper aims to estimate the time taken for concrete to fail in a LILW disposal facility. Based on the United States Department of Energy (DOE) approach, which indicates that concrete fails completely once 50% of the volume of the reinforcing steel corrodes, the corrosion propagation time is calculated to be 640 years, which is the time it takes for corrosion to penetrate 0.640 cm into the reinforcing steel. In addition to the corrosion propagation time, a diffusion equation is used to calculate the initiation time of corrosion, yielding a time of 1284 years, which post-dates the closure time of the LILW disposal facility if we also consider the 640 years of corrosion propagation. The electrochemical conditions of the passive rebar surface were modified using an acceleration method. This is a useful approach because it can reduce the test time significantly by accelerating the transport of chlorides. Using instrumental analysis, the physicochemical properties of corrosion products were determined, thereby confirming that corrosion occurred, although we did not observe significant cracks in, or expansion of, the concrete. These results are consistent with those of Smartet al., 2006 who reported that corrosion products are easily compressed, meaning that cracks cannot be discerned by eye. Therefore, it is worth noting that rebar corrosion does not strongly influence the hydraulic conductivity of the concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.4
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• pp.25-33
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• 2012

In electric power transmission tower structures on offshore, implementation of life management using the event data of regular safety inspections for structural and material damages is strongly recommended. In this study, six tower structures in Sihwa Lake around Yeoungheung island were target bodies for the safety inspections. safety inspections for deterioration about each of six towers were performed about three items for steel member, five items for concrete foundation, and four items for steel-pipe pile in seawater and seawater itself. Safety inspections for steel members included the visual observations of surface appearances, the measurements of member thicknesses, and the checks of painting states. Also safety inspections for concrete foundations comprised the estimation of crack features, the evaluation of non-destructive compression strengths, and the measurements of neutralization depths and chlorides contents. For steel-pipe piles in seawater the inspections comprised the surveys of corrosion states in accordance with potential levels tests and anode tests, the analyses of photos taken on surfaces of the piles as well as the evaluation of seawater quality. A set of deterioration inspections was performed at the same positions around october of each year for three consecutive years. As a result in this study, Newly developed deterioration indexes have been applied profitably to maintain structural safety for electric power transmission towers by utilizing these event data systematically.