• Journal of the Korea Concrete Institute
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• v.11 no.5
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• pp.131-137
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• 1999

The use of higher strength materials with the strength methed of design has resulted in more slender member and shallower sections. For this reason, it is necessary to satisfy the requirements of serviceability even though the structural safety is the most important limit state. This paper is only concerned with the control of deflections in the serviceability. In this study, an analytical model is presented to predict the deflections of reinforced concrete beams to given loading and environmental conditions. This model is based on the finite element approach in which a finite element is generally divided into a number of stiffening effect due to cracking, creep and shrinkage. Comparisons are made with available measured deflections reported by others to assess the capability of the layered beam model. The calculated values of instantaneous and long-term deflection show good agreement with experimental results in the range of tension stiffening parameter $\beta$ between 2.5 and 3.0.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.175-180
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• 1999

The heating system of korea apartment house is called Ondol. The surface finishing mortar of this floor system typically used the cement based mortar, where the surface finishing mortar easily appears the crack. To order to crack control, the cement that added expansive additive used to reducing dry-shrinkage. For the surface finishing mortar, the types of shrinkage is known as plastic shrinkage, dry-shrinkage and autogenous This experimental study is to investigate the difference on dry-shrinkage of the cement that added expansive additives and OPC. The test method is varied the ration of water/cement (W/C) and the ratio of sand/cement(S/C). For OPC, The increase of the ratio of S/C is reduced dry-shirnkage but for the cement that added expansive additives, the increase of the ratio of S/C is augmented dry-shrinkage For OPC, The increase of the ratio of W/C is augmented dry-shrinkage but for the cement that added expensive, the increased of the ratio of W/C is reduced dry-shrinkage.

• Magazine of the Korea Concrete Institute
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• v.8 no.1
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• pp.111-120
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• 1996

Drying shrinkage is a very important properties of concrete, which is affected by environmental conditions. The environmental conditions are temperature, relative humidity, and wind speed, which is quite variable and its effct on drying shrinkage is quite complex, too. In this study, environmental effects on drying shrinkage wrer integrated into one variable-evaporation rate. In several different environmental conditions, evaporation rate was measured with Evaporometer and compared with PCA chart, and also compared with measured drying shirnkage to verify the possibility of being a single parameter. The results are summarized in a prediction chart and prediction equation for drying shrinkage.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.633-636
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• 2008

Concrete structures are occur many various deteriorations in the course of time and many efforts have progressed to improve on performance of concrete. The purpose of this study is to evaluate the durability of latex modified mortar in order to repair concrete structure which are happened deterioration. In this study, we tested plastic shrinkage, drying shirnkage, repeated freezing and thawing, permeability and resistance of chemical solution. Latex modified mortar and two kinds of sprayed polymer mortar used on durability test. As a result of test, latex modified repair mortar was exhibited durablilty improvement compared to the conventional sprayed polymer mortars. It is judged the fact that latex modified mortar have no problem in site application but additionally many research will be necessary.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.56-62
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• 1997

The PAN (Polyacrylonitrile) based carbon fiber-ceramic composites (CFCC) were prepared from mixtures of short carbon fibers, phenolic resin and ceramic binder. The effects of carbonization temperature of a pre-cursor fiber, the stabilized PAN fiber, on the specific surface area and the bending strength of the activated CFCC were studied in this work. The precursor fiber was carbonized at 80$0^{\circ}C$ and 100$0^{\circ}C$, respectively. The CFCC were activated at 85$0^{\circ}C$ in carbon dioxide for 10~90 minutes. As the burn-off of the activated CFCC made of the precursor fiber carbonized at 80$0^{\circ}C$ was increased from 37% to 76%, the specific surface area in-creased from 493m2/g to 1090m2/g, and the bending strength decreased from 4.5MPa to 1.4MPa. These values were about two times larger than those of the activated CFCC of which precursor fiber was car-bonized at 100$0^{\circ}C$. The effects of carbonization temperature of a precursor fiber on the specific surface area and bending strength of the activated CCFC were explained by bonding force between carbon fiber and car-bonized phenolic resin as well as by relative shirnkage between carbon fiber and ceramic film.