• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.505-508
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• 2003

The rheological properties of cement paste system mixed with mineral admixture for the purpose of increasing the strength and improving durability and rheology of concrete were investigated. The results were as follows: The rheological properties of one-ingredient paste system were improved with increasing the dosage of superplasticizer. For two-ingredients paste system, increasing the replacement rate of BFS(blast furnace slag) and FA(fly ash), the yield value and plastic viscosity were decreased compared with non-replacement. In the OPC(ordinary portland cement)-SF(silica fume) system, increasing the replacement rate of SF, the plastic viscosity and yield value increased linearly. In three-ingredients paste system, both OPC-BFS-SF and OPC-FA-SF system, the rheological properties were improved compared with the only replacement of SF. Both two- and three- ingredients paste system, the rheological properties using BFS were improved more than FA.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.25-29
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• 1995

To perform high-strength of concrete, fine powers of pozzolan such as fly ash, silica fume mixed with cement. But mobility of cement and concrete decreased due to using of these powers. To control decrease of this mobility, it is required that mobility is improved by using of chemical admixture such as superplasticizer. We used admixtures -NSF, NM-2, NT-2 etc- in order to improve mobility of cement paste being substituted by 10, 20% of pozzolans respectively. It proved that optimum dosage of NSF, NT-2 was 2.0% for being substituted 10%, 3.0% for 20% so as to increase mobility of cement paste mixed paste mixed with fine powers of pozzolan at W/C=0.40.

• International Journal of Concrete Structures and Materials
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• v.9 no.3
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• pp.267-281
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• 2015

Six full-scale prestressed concrete (PC) I-beams with steel fibers were tested to failure in this work. Beams were cast without any traditional transverse steel reinforcement. The main objective of the study was to determine the effects of two variables-the shear-span-to-depth ratio and steel fiber dosage, on the web-shear and flexural-shear modes of beam failure. The beams were subjected to concentrated vertical loads up to their maximum shear or moment capacity using four hydraulic actuators in load and displacement control mode. During the load tests, vertical deflections and displacements at several critical points on the web in the end zone of the beams were measured. From the load tests, it was observed that the shear capacities of the beams increased significantly due to the addition of steel fibers in concrete. Complete replacement of traditional shear reinforcement with steel fibers also increased the ductility and energy dissipation capacity of the PC I-beams.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.349-354
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• 2003

The objective of this paper is to investigate the length change of high performance concrete using expansive additives to reduce autogenous shrinkage and drying shrinkage. The kinds and the contents of expansive additives are varied. The expansive additives are used made from Japan(CSA type;JEA), China(CSA type;CEA) and Korea(gypsum type; KEA), respectively. According to results, remarkable variations of the properties at fresh concrete are not found with dosage of expansive additives. For compressive strength, it decreases about 6-10% with expansive additives of 10%. Autogenous shrinkage decreases about 32%, and drying shrinkage does about 35%, respectively, with expansive additives of 5%, and about 68% and about 55%, with expansive additives of 10%. Accordingly, expansive additives demand requires 10% by cement weight in order to reduce shrinkage of high performance concrete more effectively in the sphere of this study, and JEA shows the best shrinkage reducing performance among the tested expansive additives.

• Journal of Environmental Science International
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• v.12 no.3
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• pp.319-324
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• 2003

The characteristics of photocatalytic decomposition of dye waste water by titanium dioxide was studied in a batch reactor under constant strength of ultra-violet ray. The decomposition rate of methyl orange by TiO$_2$ was pseudo-first order, anatase type TiO$_2$ was more effective than rutile type below the dosage of 5g. The decomposition rate was increased with decreasing initial pH, increasing reaction temperature and oxidant concentration. The decomposition rate of water soluble dyes was decreased in order of rhodamine B>eosin Y>methyl orange.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2000.11a
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• pp.136-139
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• 2000

Fenton-like oxidation of para-nitrophenol(PNP) was studied using hydrogen peroxide iii combination with steeler's dust substituted for ferrous iron in Fenton's reaction. Various factors critical in the degradation of PNP were studied, including hydrogen peroxide dosage, concentration of steeler's dust. and initial pH. Experimental results showed that 1,000mg/L PNP and its oxidation intermediate could be mostly decomposed within 30m1n by 10g/L steeler's dust, 0.25% hydrogen peroxide, and initila pH of 3.0. The reaction rate constant (k) of CODcr concentration were calculated with the addition of steeler's dust(0.0059 min$^{-1}$ (g/L)$^{-1}$ ) and hydrogen peroxide(0.2965 min$^{-1}$ (%)$^{-1}$ ), respectively.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.266-270
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• 1996

The objective of this study is to develop the Non-compacting concrete with mormal strength in practice by using viscosity agent and flyash. In this paper, we present the reference data about not only the properties of Non-compacting concrete at fresh state such as flowability, segregation-resistibility, placebility and so on but, optimum mixing design using viscosity agent and flyash. The test results indicate that optimum dosage of viscosity agent in combination of flyash in 50% of W/C is about 400g/$\textrm{m}^3$ with 20% of the ratio of flyash replacement.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.501-504
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• 2005

This paper discusses the development of drying shrinkage reducing type superplasticizer(DSRS) by varying dosage of polycarboxylic based superplasticizer, liquid type expansive admixture and antifoaming agent. Adequate mixture proportion of each admixture is fixed at 0.3$\%$ of superplasticizer, 0.15$\%$ of liquidtype expansive admixture and 0.0005$\%$ of antifoaming agent to insure the improvement in drying shrinkage as well as comparable to the slump and air content of conventional concrete. With this mixture proportion, compressive strength of concrete using DSRS is comparable to that of conventional concrete. The use of DSRS studied by the authors has a favorable effect on reducing drying shrinkage due to the effect of water content and expansion by expansive admixture.

• Biotechnology and Bioprocess Engineering:BBE
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• v.6 no.2
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• pp.112-116
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• 2001

The production of extracellular polysaccharide, EPS WN9, from Paenibacillus sp. and its suitability as a viscosity modifying admixture for cement mortar mixing were investigated. After 48h culture in an optimized medium, cell growth and EPS production were 1.2g/L and 4.0g/L, respectively. By adding EPS WN9 to mortar, it was possible to prepare a homogeneous mortar without material segregation and excess air entrapment. The optimal amount of EPS addition to mortar found to be 0.02 to 0.05%(w/w) of the cement used. Increasing the dosage of EPS WN9 from 0 to 0.05%(w/w) resulted in a setting retardation of 0.14h to 0.8h and an increase in the compressive strength of mortar of 10 to 20%.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.313-323
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• 1998

Fluidity retention of concrete used high range water reducing AE agent(HWAE) is varied according to main component, dosage amount and dosing method of HWAE. The type and substitution ratio of mineral admixture also have influence on the fluidity retention of concrete used HWAE. In this study, for the purpose of improving the fluidity retention in concrete used HWAE. 3 types of HWAE and ground granulated blast furnace slag(SG) are used in cement paste, mortar and concrete varing dosage amount and dosing time of HWAE and substitution ratio of SG respectively. According to using the HWAE of naphthalene sulfonates and SG, the fluidity retention of mortar and concrete is improved remarkably. And after 30 min, dosing method of HWAE is very effective in improving the fluidity retension and strength of concrete regardless of type of HWAE.