• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.207-210
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• 1999

This experimental study was carried out to estimate the effects of mixing dosage rate and blaine on the mechanical properties of concrete admixed with ground granulated blast-furnace slag (BFS) powder. According to the test results, compressive strength of concrete admixed with slag not more than 35% was at least 80% of compressive strength of OPC concrete at 3 days age, and much bigger than that of OPC concrete at 28 days age. Consequently, in order to apply the BFS to the concrete is demanded, and rigorous construction management should be followed.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.791-794
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• 1999

Exact estimation of cement content in a hardened concrete can provide useful data to evaluate the quality and strength of the concrete and might be used to inspect the quality of precast concrete secondary products. Observation obtained in this research included : (1) the volume of coarse aggregate in the hardened concrete measured by the area comparison method has a high accuracy ; (2) the cement content in the mortar and the X-ray intensity of Ca-K$\alpha$ have a correlation factor of 0.96 ; (3) the cement content in the ready mixed concrete was estimated with high accuracy such as correlation factor of 0.99 and standard deviation of 0.64.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.725-730
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• 2002

The durability of concrete involves resistance to freeze-thaw action, corrosion, permeation, carbonation, chemical attack and so on. Generally, properties of concrete have been well understood under the separate action of these deterioration mechanisms. However, in practice, the degradation of concrete usually is the result of combined action of physical and chemical attack and can be accelerated by the combined action of several deterioration mechanisms. In the present study, to evaluate the combined deterioration by freeze-thaw action and seawater attack, ground granulated blast-furnace slag or silica fume concrete with water or seawater as mixing water was exposed to 210 cycles of freeze-thaw action. Tests were conducted to determined the relative dynamic modulus of elasticity and compressive strength. Furthermore, The XRD, SEM and EDS analysis were performed on the deteriorated part of concrete due to freeze-thaw action and seawater attack.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.183-188
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• 2002

When Concrete work during winter is placed, it has anxiety that concrete freeze at low temperature. As concrete's freezing cause reduction of durability, it is necessary for mixing to pay attention to Air content and W/C ratios. Accordingly, in this study, we set up three series and evaluate a frost-resistance of concrete with admixture, like fly-ash and blast-furnace slag, for early curing method and types of chemical admixture..The study is composed as; I series : Analysis for early curing method and types of chemical admixture in laboratory II series : Analysis for early curing method and types of chemical admixture in batcher plant and measured concrete' temperature. The result of this study, it was more effective the use of super-plasticizers than air entraining agent.

• Journal of the Korea Concrete Institute
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• v.11 no.5
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• pp.99-105
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• 1999

In producing high strength concrete, the most practical method is to use high range water reducing admixture(HRWR). Workabili쇼 of concrete using HRWR varies rapidly with elapsed time after mixing. Effects of fly ash and gypsum on slump loss and compressive strength of concrete were examined by experiment in this study. The slump loss of high strength concrete was reduced with increase of substitution ratio of fly ash. When 2~4% gypsum of cement weight was applied, the reduction of slump loss was not prominent and strength increase appeared at all test ages.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.490-493
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• 2004

In the analysis of early-age concrete behavior, the fresh concrete is considered as a structural element immediately after mixing. But for the activation of real structural behavior in the fresh concrete, the so-called setting time is necessary a few hours after the beginning of hydration reaction. In this paper, analysis on the setting behavior is carried out by proposing an analytical model based on the percolation theory as well as the expanding cluster model by defining the setting as a microstructure formation in fresh concrete. An experimental investigation is also carried out to show the influences of curing temperature, mineral admixtures and chemical admixture on setting behavior of fresh concrete. Finally, the analytical results using proposed model are compared with the experimental results for the sake of verification.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.224-227
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• 2004

The cement can be influenced by the temperature. Especially, when it is cold weather, it causes some problems in such properties as mixing, placing and curing of concrete. According to the Concrete Standard Specification(2003), in case of the average daily outdoor temperature below $4^{\circ}C$, it recommends to use the cold weather concrete. In this research, the on-site quality characteristics of the cold weather concrete using high early strength portland cement(Type III cement) were studied. As a result, the cold weather concrete using high early strength portland cement can obtain its excellent properties and benefit the cost of construction.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.825-830
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• 1999

The purpose of this study is to improve overall performance of prefoamed lightweight cellular concrete for On-Dol system floor. This study includes 4 sections as follows. \circled1 Analysis of the structural characteristics of On-Dol System focusing on the lightweight cellular concrete insulation layer. \circled2 Establishment of the mixing design equations. \circled3 Development of some admixtures used with foaming agent. \circled4 Improvement of the equipment for onsite production. This study has proven that, compared with the current existing one, the newly developed lightweight cellular concrete has been reduced the usage of cement by 20% and the cracks caused by cement drying shrinkage up to 80% but has shown the increased compression strength by 20% at 7 days curing period. The volume contraction of freshly prepared cellular concrete by the loss of foam was hardly found in newly developed lightweight cellular concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.243-244
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• 2009

Fibers reinforced concrete(FRC) has abilities to make up for brittleness fracture as one of the material characteristics of concrete. However, being mixed with steed fibers in concrete mixes could set off a "Fiber Ball". The Fiber ball formation could be one of the main reasons to decrease the quality of Fibers reinforced concrete. In order to eliminate the fiber ball formation and improve the deficient flowablitiy, The necessity of research for fiber reinforced self-compacting concrete(FRC-SCC) should be raised.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.261-264
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• 2003

Cold weather can lead to many problems in mixing, placing, setting time, and curing of concrete that can have harmful effects on its properties and service life. Korean Concrete Institute (KCI) defines cold weather as a period when the average daily air temperature is less $4^{\circ}C$ and recommends to cast concrete with special care such as shielding, heating and so on. The use of high early strength cements may improve the rate of hardening characteristics of concrete in cold weather by making it possible to achieve faster setting time and evolving more hydration heat than ordinary Portland cement. Higher early strength can be achieved using Type III cement especially during the first 7 days. The strength increase property of Type III cement at low temperature was studied. As a conclusion the heat or heat insulation curing period can be reduced to 50~75%. So, it can be used for cold weather concreting to reduce construction cost and extend the construction season.