• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.147-150
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• 1999

Glossing Exposure Concrete is a high quality architectural concrete, i.e., appearance of natural stone and a marbling effect concrete to achieve high quality glassy reflective surface for outer wall of the building. In this study to obtain the conservation and durability of gloss of the "glossing exposure concrete" we developed a from practice and the best mix proportion and derived the optimistic removal time of form to bring out the durable glassy reflective surface and durable concrete. Hereby with the "glossing exposure concrete" obtained, we investigate the accelerate carbonation and accelerate durability test to evaluate the durability factor of this type of concrete.is type of concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.651-654
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• 1999

It is required that the compressive strength of concrete should be estimated accurately from the view point of efficient quality control and maintenance of buildings. In this paper, the equations to estimate the compressive strength of concrete using granite aggregates were suggested for both rebound hammer method and ultrasonic pulse velocity method. The results were compared with those for different age or curing condition. The rebound numbers for concrete cured in air were larger than for concrete cured in water. The difference between rebound numbers for concrete cured in water and in air was larger than for concrete cured in water. The difference between rebound numbers for concrete cured in water and in air was larger when water cement ratio was high. Also, with the increase of age, the velocity of ultrasonic pulse for concrete cured in air was measured larger when compared with that in water.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.285-288
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• 1999

Creep is a major parameter to represent long-term behavior of concrete structures concerning serviceability and durability. The effect of creep is recently taking account into crack resistance analysis of early-age concrete concerning durability evaluation. Since existing creep prediction models were proposed to predict creep for hardened concrete, most of them cannot consider effectively the information on microstructure formation and hydration developed in the early-age concrete. In this study, creep tests for early-age concrete made of the type I cement and the type V cement are carried out respectively and creep prediction models are evaluated for the prediction of creep behavior in early-age concrete. A creep prediction model is modified for the prediction of creep in early-age concrete and also verified by comparing prediction results with results of creep tests on early-age concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.107-110
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• 1999

The objective of this study is to obtain characteristics of early age pore-structure and carbonation of concrete using ground granulated blast furnace slag (GGBFS). The durability of GGBFS concrete should be evaluated for wide use of the GGBFS. As for that evaluation, an analysis on early age pore-structure characteristics of GGBFS concrete are very important, Carbonation depths of GGBFS concrete, which are known to be larger than that of OPC, are different according to replacement ratios and fineness of slag. Because sea sand as fine aggregate is much used recently, it is also necessary to analyze characteristics of carbonation of GGBFS concrete. In this study, The micro-pore structure formation characteristics of GGBFS concrete are obtained through the test of GGBFS mortars with different fineness and replacement ratio of GGBFS. The carbonation of GGBFS concrete is also investigated by acclerated carbonation test for early age GGBFS concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.463-468
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• 2001

A lot of considerations on the spatting by fire of high performance concrete should be taken into for fire resistance of the concrete structures. In this paper, fire resistance of high performance concrete is described using polypropylene fiber, which is known to be contributed to fire resistance. Strength level and member size are varied with. According to test results, spatting by fire takes place more easily, as W/C increases and member size decreases. It shows that concrete containing polypropylene fiber has good effects on preventing spatting by fire. In case high performance concrete does not contain polypropylene fiber, residual strength shows to be decreased remarkably compared :o that of normal concrete. Whereas, in case 0.1% of polypropylene fiber contents, high performance concrete shows higher residual strength than that of normal concrete. As member size is smaller, residual strength shows to be decreased.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.757-762
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• 2001

CFT concrete has high flowing, high strength and resistance to material separation to use skyscraper structure. It is considered that concrete could fill the lower part of Diaphragm up. This kinds of CFT concrete hardly apply to building below 20 stories. Using the common use strength concrete to building below 20 stories brings to reduce construction cost. This concrete is needed that valid fluidity and packing ability with unit cement content as common use strength concrete. Offering a fundamental data and proportioning in CFT concrete of below 20 stories, it is executed basic property test, analysis of proportioning and mock up test.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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• pp.65-70
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• 1994

Reinforced concrete and prestressed concrete structures consist of different materials, namely concrete, reinforcing steel and/or prestressing steel. Reinforcing and prestressing steels can be considered homogeneous materials, and their properties are generally well defined. Howefer, concrete is a heterogeous materials, and it is difficult to define its properties accurately. Both concrete and steel exhibit various nonlinear materials properties. The stress-strain relationship of concrete is not only nonlinear, but it differs in compression and tension. And, tensile cracking is one of the most importnat factors which contribute to the nonlinear behavior of reinforced concrete structrures. In this strudy, the various stress-strain relationships of concrete and reinforcing steel in nonlinear analysis of RC and PC structures are examined.

• International Journal of Concrete Structures and Materials
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• v.18 no.2E
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• pp.133-142
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• 2006

An experimental study was conducted to investigate the effectiveness of transverse steel in reinforced concrete tied columns subjected to monotonically increasing axial compression. Eighteen large-scale columns($260{\times}260{\times}1,200mm$) were tested. Effects of such main variables as concrete compressive strength, configurations of transverse steel, transverse reinforcement ratio, spacing of transverse steel, and spalling of concrete cover were investigated. High-strength concrete columns under concentric axial loads show extremely brittle behavior unless the columns are confined with transverse steel that can provide sufficiently high lateral confinement pressure. A consistent decrease in the deformability of the column test specimens was observed with increasing concrete strength. Test results of this study were compared with existing confinement models of modified Kent-Park, Sheikh-Uzumeri, Mander, and Saatcioglu-Razvi. The comparison indicates many existing models to predict the behavior of confined concrete overestimate or underestimate the ductility of confined concrete.

• International Journal of Concrete Structures and Materials
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• v.4 no.1
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• pp.17-23
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• 2010

The feasibility of the use of scrap tire rubber in concrete was investigated. The tests conducted in two groups: replacing of coarse aggregates with crumb rubber and cement particles with rubber powder. To distinguish the properties of new concrete, the following mechanical and durability tests were designed: compressive, tensile and flexural strength, permeability and water absorption. Rubber addition could affect the concrete properties depend on the type and percentage of the rubber added. Although the rubber addition modifies the mechanical characteristics of concrete in a way, but higher rubber content could not be useful. Concrete durability showed more dependency to the type of rubber instead of percentage of rubber. Moreover, to optimize the mechanical and durability of rubberized concrete, the useful percentage of rubber has been recommended.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.433-438
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• 2001

In recent years, the construction methods of precast prestressed concrete beam bridges by using tendon have been increasingly proposed. The properties of flexural tensile strength between precast prestressed concrete beam and cast-in-place concrete is an important factor that affects the structural performance. This paper aims at evaluating the tensile strength between old and new concrete. Tensile strength gain, with age after placing new concrete was evaluated. Test results show that the tensile strength between old and new concrete is much smaller than that of monolithic concrete. Also, it is shown that the curing condition of concrete has the tremendous effect on tensile strength.