• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.641-646
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• 2001

Generally, when Fly-Ash was used as replacement material of cement in concrete, it might occur retardation of setting and hardening. So, it is unable to use a large amount of Fly-Ash as replacement for cement. However, if it is used as replacement material of fine aggregate in concrete, we can use a large amount of Fly-Ash and settle a problem of natural-aggregate exhaustion. Furthermore, engineering properties of High Volume Fly-Ash Concrete Is better than that of plain concrete But, the larger Fly-Ash is replaced, the more fluidity of High Volume Fly-Ash Concrete decrease, because porous organization of Fly-Ash adsorb water and Superplasticizer. In this study, after appending additional water to High Volume Fly-Ash Concrete in proportion to weight of Fly-Ash, we intend to find proper ratio which doesn't affect strength and satisfy fluidity As a result of this study, it was found that fluidity of mortar with 25~28 percentage of additional water was satisfied with fluidity of plain mortar, and compressive strength of that was similar to plain mortar's

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.507-512
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• 2001

An investigation into using Oyster Shells partially or wholly as aggregate in concrete is reported. The proportion of shells was varied with ratios of 10, 30, 50 and 100% by volume of fine and coarse aggregate. Two water/cement ratios of 0.45, 0.55 were considered and air-entraining superplasticizer was used to improve concrete workability Two strength properties (compressive and flexural) were considered. Strength tests were carried out at the ages of 1, 3, 7, 14 and 28 days. The variations of workability, weight and density of the specimens with different proportions of Oyster Shells were also studied. Results showed that compressive and flexural strengths decreased with increase in proportion of Oyster Shells to aggregate in the reference mixes. The workability of concrete batches decreased with increase in the proportion of Oyster Shells in the mixes. The same trend was observed with density and weight of the specimens

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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• pp.254-259
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• 1994

Recycling of waste concrete will contribute not only to the solution of a growing waste disposal problem, also help to conserve natural resources of aggregate and to secure future supply of reasonably priced aggregates for building construction purpose within large urban areas. But there recycled aggregates are more porous and less resistant to mechanical actions. In comparison with natural aggrete concrete, recycled aggregate concrete shows reductions in strength and other engineering properties. And it may also be less durable due to increase in porosity and permeability. Economical ways of improving the quality of recycled aggregate concrete are: (1)by reducing the water-cement ratio; (2)by reducing the water content using a superplasticizer without affecting the workability; (3)addition of pozzolan, such as fly ash; and (4)blending of recycled aggregate with the natural aggretes.

• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1261-1267
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• 1997

Four kids of powder admixtures(A, B, C, D) based on anhydrite were manufactured by mixing at a fixed rate of II-anhydrite, fly ash and active silica as an industrial by-product. Fluidity properties of cement paste such as mini-slump, apparent viscosity with elapsed time, as well as setting time of cement pastes of these admixtures substituted up to 11wt% of cement were compared to those of cement paste(SS) substisuted by marketed high-strength powder admixture(S). Among these powder admixtures, the fluidity of cement pastes(PA, PC) substituted by A and C powder admixtures manufactured from II-anhydrite and fly ash had an excellent property than that of cement paste substituted by marketed powder admixture and also a good fluidity-retention effect with elapsed time by adding of superplasticizer. The setting time of cement paste substituted by powder admixtures based on anhydrite slightly retarded than that of cement paste substituted by marketed powder admixture.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2005.05a
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• pp.41-44
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• 2005

The aim of this study is to develop experimentally ultra high-strength concrete with compressive strength over 100MPa with current materials by important factors to influence the compressive strength of concrete. There are so many factors which influence the manufacturing of ultra high-strength concrete. But the experimental factors selected in this study are the sand aggregate ratio, the silica fume replacement ratio, the type of aggregate. the type of superplasticizer, the fiber mixing ratio. The results of this experimental study show that. it is possible to applicate in the field

• Journal of the Korean Society of Safety
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• v.16 no.1
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• pp.65-72
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• 2001

Portland cement concrete is made with coarse aggregate, fine aggregate, portland cement, water and, in some cases, selected chemical admixture such as air-entraining agents, water reducer, superplasticizer, and so on, and mineral admixture such as fly ash, silica fume, slags, etc. Typically, in the concrete, the coarse aggregate and fine aggregate will occupy approximately 80 percent of the total volume of the finished mixture. Therefore, the coarse and fine aggregates affect to the properties of the portland cement concrete. As the deposits of natural sands have slowly been depleted, it has become necessary and economical to produce crushed sand(manufactured fine aggregate). It is reported that crushed sand differs from natural sands in gradation, particle shape and texture, and that the content of micro fines in the crushed sand affect to the quality of the portland cement concrete. Therefore, the purpose of this paper is to investigate the characteristics of fresh and hardened concrete with higher micro fines. This study provides a firm data to apply crushed sand with higher micro fines.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10c
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• pp.191-196
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• 1998

Under concentrational paste and dilute suspension systems, we have been tested the effects in the dosage of two superplasticizers [naphtalenic(NSF) and polycarboxylic(NT-2)] which has been varied from 0 to 2.0 wt%, in both one case of cement Ⅱ-anhydrite and fly ash itself and the other case that cement has been substituted 10wt% to Ⅱ-anhydrite and fly ash. The result of tested zeta potential tells that zeta potential values increase in addition to increasing of the NSF dosage. And it's effect was high in case of fly ash. We has confirmed the 10wt% substitution of Ⅱ -anhydrite and fly ash would be more effective than the cement itself in initial fluidity and stable fluidity. And in case of NT-2 and NSF, addition of 1.0wt% NT-2 improved the fluidity of paste cement more than that for NSF.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.227-232
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• 2001

In this research we made cement particle with the average size of 4 ${\mu}{\textrm}{m}$ which can penetrate even minor cracks based on the theory of J. K. Michel who reported particles can penetrate the crack of width up to 3 times of maximum particle size. The inorganic crack injection materials were produced by adding superplasticizer. Physical properties of hardened slurry with JIS molds were also tested at 3, 7 and 28 days and the adhesion properties of the slurry in various process conditions were also tested at 3, 7 and 28 days. The cracked specimens which were repaired with slurries produced at various conditions were tested after 3, 7 and 28 days curing in the air and split tensile strength properties were characterized.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.245-250
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• 2001

Ultrasonic pulse velocity(UPV) is a useful tool for examining the property of early-age mortar or concrete. Thus, UPV has been used for a long time to characterize setting and hardening of cementitious materials. In this study, in order to investigate the characteristics of setting for mortar, UPV was measured using automatic monitoring system up to 3 days after casting. Test results show that UPV of high water to binder ratio(w/b) mortar remained constant at the beginning of hydration and then abruptly began to increase. However, UPV of low w/b mortar gradually increase due to setting retard caused by use of superplasticizer. Furthermore, the development of UPV for mortar with fly ash is slower than that of mortar without fly ash. It was concluded that the property change of mortar or concrete, such as setting and hardening can be assessed by monitoring of UPV.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.73-78
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• 2001

Portland cement concrete is made with coarse aggregate, fine aggregate, portland cement, water and, in some cases, selected chemical admixtures such as air-entraining agents, water reducer, superplasticizer, and so on, and mineral admixtures such as fly ash, silica fume, slags, etc. Typically, in the concrete, the coarse aggregate and fine aggregate will occupy approximately 80 percent of the total volume of the final mix. Therefore, the coarse and fine aggregates affect to the properties of the portland cement concrete. As the natural sands are drained, it is necessary and economical to utilize crushed sands(manufactured fine aggregate). It is reported that crushed sands differ from natural sands in gradation, particle shape and texture, and the micro fines in the crushed sands affect to the quality of the portland cement concrete. Therefore, the purpose of this paper is to investigate the characteristics of fresh and hardened concrete with high content of micro fines. This study provides firm data for the use of crushed sands with higher micro fines.