• Corrosion Science and Technology
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• v.8 no.5
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• pp.171-176
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• 2009

The chloride threshold level (CTL) in mixed concrete containing, ordinary Portland cement (OPC), pulverized fuel ash (PFA) ground granulated blast furnace slag (GGBS), and silica fume (SF) is important for study on corrosion of reinforced concrete structures. The CTL is defined as a critical content of chloride at the steel depth of the steel which causes the breakdown of the passive film. The criterion of the CTL represented by total chloride content has been used due to convenience and practicality. In order to demonstrate a relationship between the CTL by total chloride content and the CTL by free chloride content, corrosion test and chloride binding capacity test were carried out. In corrosion test, Mortar specimens were cast using OPC, PFA, GGBS and SF, chlorides were admixed ranging 0.0, 0.2, 0.4, 0.8, 1.0, 1.5, 2.0, 2.5 and 3.0% by weight of binder. All specimens were cured 28 days, and then the corrosion rate was measured by the Tafel's extrapolation method. In chloride binding capacity, paste specimens were casting using OPC, PFA, GGBS and SF, chlorides were admixed ranging 0.1, 0.2, 0.3, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0% by weight of binders. At 28days, solution mixed with the powder of ground specimens was used to measure binding capacity. All specimens of both experiments were wrapped in polythene film to avoid leaching out of chloride and hydroxyl ions. As a result, the CTL by total chloride content ranged from 0.36-1.44% by weight of binders and the CTL by free chloride content ranged from 0.14-0.96%. Accordingly, the difference was ranging, from 0.22 to 0.48% by weight of binder. The order of difference for binder is OPC > 10% SF > 30% PFA > 60% GGBS.

• Corrosion Science and Technology
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• v.8 no.2
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• pp.74-80
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• 2009

The high alkaline property in the concrete pore solution protects the embedded steel in concrete from corrosion due to aggressive ions attack. However, a continuous supply of those ions, in particular, chlorides altogether with a pH fall in electrochemical reaction on the steel surface eventually depassivate the steel to corrode. To mitigate chloride-induced corrosion in concrete structures, finely grained mineral admixtures, for example, pulverized fuel ash (PFA), ground granulated blast furnace slag (GGBS) and silica fume (SF) have been often advised to replace ordinary Portland cement (OPC) partially as binder. A consistent assessment of those partial replacements has been rarely performed with respect to the resistance of each binder to corrosion, although the studies for each binder were extensively looked into in a way of measuring the corrosion rate, influence of microstructure or chemistry of chlorides ions with cement hydrations. The paper studies the behavior of steel corrosion, chloride transport, pore structure and buffering capacity of those cementitious binders. The corrosion rate of steel in mortars of OPC, 30% PFA, 60% GGBS and 10% SF respectively, with chloride in cast ranging from 0.0 to 3.0% by weight of binder was measured at 7, 28 and 150 days to determine the chloride threshold level and the rate of corrosion propagation, using the anodic polarization technique. Mercury intrusion porosimetry was also applied to cement pastes of each binder at 7 and 28 days to ensure the development of pore structure. Finally, the release rate of bound chlorides (i.e. buffering capacity) was measured at 150 days. The chloride threshold level was determined assuming that the corrosion rate is beyond 1-2 mA/$m^3$ at corrosion and the order of the level was OPC > 10% SF > 60% GGBS > 30% PFA. Mercury intrusion porosimetry showed that 10% SF paste produced the most dense pore structure, followed by 60% GGBS, 30% PFA and OPC pastes, respectively. It was found that OPC itself is beneficial in resisting to corrosion initiation, but use of pozzolanic materials as binders shows more resistance to chloride transport into concrete, thus delay the onset of corrosion.

• Journal of the Korea Institute of Building Construction
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• v.6 no.3 s.21
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• pp.75-82
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• 2006

This study investigates the influence of various blending factors on cement paste fluidity and find out the most effective evaluation method of cement paste flow, comparing flow test apparatuses such as ring flow(R-F), flow cone(F-C) and mini slump(M-S). A viscometer also measures the rheology coefficients to secure faithful numerical data. Firstly, series I examines cement paste, affected by several cement products and mineral admixture types in the range of W/B 40%, ordinary fluidity, and W/B 30%, high fluidity. In this series, the three types of cement product depended on companies, are randomly used and the mineral admixture, such as fly ash, blast furnace slag and silica fume, are incorporated in the cement paste, in response to the ratio of 10, 20, to 30%, respectively. In addition, series II studies various chemical admixture types, affecting the cement paste. This series is carried out with manufacturing companies and component types in the range of W/C 30%, high fluidity. For the manufacturing companies, randomly four products are used and for the component types, polycaboxylate, melamine, naphthalene and lignosulfonate type are chosen. Test results showed that in the fluidity test of cement paste considering various types of blending factors, R-F exhibited similar tendency with F-C and M-S. In the analysis of consistency curves measured by viscometer, the fluidity evaluation method using flow test apparatuses was significantly effective, except for the some of the low fluidity specimens. In conclusion of this study, R-F was the most convenient, faithful and effective fluidity evaluation method of cement paste.

• Journal of Environmental Science International
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• v.24 no.5
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• pp.699-708
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• 2015

This study was performed to identify the state of the exposure and characteristics of pollutants by each process at 4 casting sites located in Gyeongsang-do from April to November 2013. The concentrations of methanol, crystallized silica glass, formaldehyde and phenol were analyzed by different process - casting process, molding process, core process, and shakeout & finishing process. The highest concentration of methanol was found in casting and molding process, whereas the highest concentration of crystalline quartz(Silica) was observed in core process. The most oxidized steel dusts and the highest concentration of fume were found in shakeout & finishing process. As a result of this study, those labors working at the casting site were found to be constantly exposed to various forms of hazardous chemicals; therefore, it is considered that this is the time to manage and plan how to reduce them. In addition, it is required to thoroughly manage the local exhauster, and improve the process and working environment to reduce various forms of hazardous chemicals.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.783-794
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• 1994

Recently, several failure cases of concrete structures during construction have been reported. The main reason for these failures is attributed to the poor quality of concrete during construction. It is, therefore. necessary to develop and use high quality concrete. The purpose of the present study is to explore the characteristics of superplasticized concrete, especially the effects of mineral admixtures on the fluidity and strength characteristics of high performance concrete. The mineral admixtures considered in the present study are fly ash, blast furnace slag and silica fume, respectively. The major test variables include the amount of these mineral admixtures, cement contents and water-cement ratios. The compressive strengths for various cases were measured and reported. Optimum contents of mineral admixtures for strength development were derived. The corrosion phenomena of reinforcements embedded in various concrete specimens have been also studied. The present study provides useful basis to apply high-performance concrete to actual structures.

• Advances in concrete construction
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• v.9 no.1
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• pp.55-70
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• 2020

In this research article, acid resistance, sulphate resistance and sorptivity of self compacted concrete (SCC) prepared from C&D waste have been discussed. To improve the above properties of self compacted recycled aggregate concrete (SCRAC) along with mechanical and durability properties, different two stage mixing approaches (TSMA and TSMAsfc) were followed. In the proposed two stage mixing approach (TSMAsfc), silica fume, a proportional amount of cement and a proportional amount of water were mixed in premix stage which fills the pores and cracks of recycled aggregate concrete (RAC). The concrete specimen prepared using above mixing approaches were immersed in 1% concentration of sulphuric acid (H2SO4) and magnesium sulphate (MgSO4) solution for 28, 90 and 180 days for evaluating the acid resistance of SCRAC. Experimental results concluded that the proposed two stage mixing approach (TSMAsfc) is most suitable for acid resistance and sulphate resistance in terms of weight loss and strength loss due to the elimination of pores and cracks in the interfacial transition zone (ITZ). In modified two stage mixing approach, the pores and cracks of recycled concrete aggregate (RCA) were filled up and make ITZs of SCRAC stronger. Microstructure analysis was carried out to justify the reason of improvement of ITZs by electron probe micro analyser (EPMA) analysis. X-ray mapping was also done to know the presence of strength contributing elements presents in the concrete sample. It was established that SCRAC with modified mixing approach have shown improved results in terms of acid resistance, sulphate resistance, sorptivity and mechanical properties.

• Fire Science and Engineering
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• v.31 no.3
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• pp.73-78
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• 2017

In this paper, the fire risk using a bimetal type thermometer for construction installation is presented. Because construction equipment is used widely in the field and the site is exposed to explosions and fire by combustible gas or fume, strong restrictions on the structure and usage are applied. Moreover, the risk of fire increases as precise temperature measurements are poorly conducted via an inner temperature sensor inside construction furnace. Therefore, this paper presents the results of structural analysis of a bimetal temperature sensor which is used widely in construction installation and temperature measurement experiments relative to the material property of the target object. The results revealed the relatively precise temperature of the liquid object, whereas those of the gas and solid object showed a lower temperature compared to the real temperature. This shows that bimetal-type temperature sensor is more suitable for measuring a liquid state object than measuring a gas or solid state object.

• Tuberculosis and Respiratory Diseases
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• v.62 no.3
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• pp.223-226
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• 2007

Tetrafluoroethylene is a colorless gas that can be used to synthesize a variety of fluoride compounds by polymerization (e.g., Teflon). Fluoride compounds have many applications in industry. There are several reports of inhalation injury from the pyrolytic product of fluoride compounds. When the polymer is heated under the conditions of inadequate ventilation, the fumes can cause polymer fume fever or pulmonary edema which manifested as symptoms such as fever, chill, profuse sweating, cough and dyspnea. However there are no reports of a direct lung injury caused by tetrafluoroethylene. We report a case of a 27-year-old male presented with acute lung injury after inhaling concentrated tetrafluoroethylene. He complained of cough and dyspnea after the accidental inhalation of tetrfluoroethylene at his workplace. The symptoms improved without any complications after conservative treatment with oxygen and steroid.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.25 no.4
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• pp.472-481
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• 2015

Objectives: Welding is a major task in shipbuilding yards that generates welding fumes. A significant amount of welding in shipbuilding yards is done on steel. Inevitably, manganese is present in the base metals being joined and the filler wire being used and, consequently, in the fumes to which workers are exposed. The objective of this work was to characterize manganese exposure associated with work area, total and particle size-selective mass concentration, and compare the mass concentrations obtained using a three-piece cassette sampler, size-selective impactor sampler and blood manganese concentrations. Materials: All samples were collected from the main work areas at one shipbuilding yard. We used a three piece cassette sampler and the eight stage cascade impactor sampler for the airborne manganese mass concentration of total and all size fractions, respectively. In addition, we used the results of health examination of workers sampled for airborne manganese. Results: The oder of high concentration of airborne manganese in shipbuilding processes was as follows; block assembly, block erection, outfitting installation, steel cutting, and outfitting preparation. The percentages of samples that exceeded the OES of the ministry of employment and labor by the cassette sampling method was 12.5%, however 59.1% of sampled workers by the impactor sampling method exceeded the TLV of the ACGIH. Conclusions: Even though the manganese concentrations in blood of workers exposed to higher airborne manganese concentration were higher than among those exposed to lower concentrations, there was no difference in blood manganese concentrations among work duration. The data analyzed here by characterizing size-selective mass concentrations indicates that the inhaled manganese of welders in shipbuilding yards could be mostly manganese-containing respirable particle sizes.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.305-311
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• 2010

The industrial by-product market has increased at a geometric rate worldwide with the rapid economic growth. At present time, conventional disposal methods of industrial by-products in Korea including landfill, incineration and storage already have reached their limits. In this study, the industrial by-products such as fly ash and silicafume were used as mineral admixtures, which are commonly added to concrete mix to inhance the economic efficiency, long-term strength and durability of concrete, to determine the optimized mix proportion of high performance shotcrete. Through the series of tests (compressive strength test, accelerated chloride ion penetration test, measurement of chloride diffusion coefficient). The results of the study showed that the proposed mix proportions satisfied the requirements of domestic as well as international guidelines for shotcrete, with a higher durability than the existing shotcrete.