• Journal of Industrial Technology
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• v.25 no.B
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• pp.73-80
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• 2005

Durability of concrete structures is seriously compromised by cracking at early-age concretes, particularly in high-strength or high-performance concrete structures. Since early-age cracking is influenced by various factors that affect the hydration process, early-age shrinkage and stress/strain development, the behavior at early-age is highly complex and no rational methodologies for its control have yet been established. Concrete structures often present volumetrical changes particularly due to thermal and moisture related shrinkages. Volumetric instability is detrimental to the performance and durability of concrete structures because structural elements are usually restrained. These restrained shrinkages develope tensile stresses which often results in cracking in combination with the low fracture resistance of concrete. Early-age defects in high-performance concrete due to thermal and autogenous deformation shorten the life cycle of concrete structures. Thus, it is necessary to examine the behavior of early-age concrete at the stages of design and construction. The purpose of this study was to propose a shrinkage models of VES-LMC (very-early strength latex-modified concrete) at early-age considering thermal deformation and autogenous shrinkage.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.11a
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• pp.75-79
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• 2006

Recently, more highly effective construction materials are needed for the reasonable and economical structure system is required as the construction structures become more multi storied, large-sized and diversified. That is to say, the highly qualified concrete is positively promoted as a part of plan to establish the effective space according to the dead load of structures and diminish of segment profile and to build up the economic structures. However, the high strength concrete has the problems such high brittleness and low ductility. Specially, for the high strength concrete, it has different strength from normal concrete as the internal temperature goes up steadily due to high heat of hydration by the quantities of highly level of cement, so the concrete which is mixed with various miscible materials is used. As the development and study for high strength concrete (more than $100N/mm^2$) is under way actively and the strength of high strength concrete increases, the strength different from the existing high strength concrete of ten than $100N/mm^2$, but the study for this is not adequate and indefinite. In addition, the study and report to apply the strength expression and analysis results of internal structure. Therefore, this study is an experiment about using the miscible materials affects what happens to the longitudinal physical property.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.505-508
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• 2008

In this study, temperature increase and strength development of concretes with different types of cement were investigated to construct dam drop spillway. For this purpose, boxes of 1${\times}$1${\times}$1m size with 4 different concrete mixtures were made. The types of concrete were Type I cement concrete, fly ash cement concrete and two type concrete with ternary cement, respectively. The temperature at each point were monitored in these boxes. Based on the Box test, hydration analysis of slab of 2.0m thickness was carried out. This paper presents these experimental and analytical results.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.04b
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• pp.108-113
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• 1993

The material for the machine tool structure should have high static stiffiness and damping in its property to improve both the static and dynamic performances. The static stiffness of a machine tool can be inceased by using either higher modulus material in the structure of a machine tool. However, the machine tool structrue with high stiffness but low damping is vulnerable to vibration at the resonance frequencies of the structure . For the high precision and highsped machine tool structure, therefore, the high damping capacity is most important in order to suppress vibration. The damping of a machine tool can not be increased by increasing the static stiffness. The best way to increase the damping capacity of the machine tool structure is to use a composite material which is composed of on material with high stiffness with low damping and another material with low stiffness with high damping. Therefore, in this paper, the bed of the ultra high precision grinding machine for mirror surface machining of brittle materials such as ceramics and composite materials was designed and manufactured with the epoxy concrete material. The epoxy concrete material was prepared by mixing epoxy resin with different size sands and gravels. The modulus, compressive strength, coefficient of thermal expansion, specific heat, and damping factor were measured by varying the compaction ratio, sizes and contents of the ingredients to assess the effect of the processing parameters on the mechanical properties of the material. Based of the measured properties, the prototype epoxy resin concrete bed for the mirror surface CNC grinding machine was designed and manufactured.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.433-436
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• 2006

This study is basic experiment for estimating influence of strength by curing temperature of concrete's heat of hydration and estimate relationship of compressive strength development by initial curing temperature factor, and then asume temperature factor which influence compressive strength development and for showing basic document of quality control. According to the result of managerial test pieces by the curing temperature factor high-curing temperature shows high strength on 3 day compare with low curing-temperature, shows higher strength than the piece of high curing temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.259-260
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• 2010

This study is to investigate each mix property and physical properties and reduction properties of heat of hydration as basic experiment of reviewing the applicability of low calorific concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.47-52
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• 2000

Recently, it is very necessary the development of the manufacturing techniques for high strength concrete(HSC) for the large-scale size and good quality of civil structure. But, the manufacture and quality control of HSC of which shrinkage, heat of hydration and workability at construction filed are considered, is very difficult due to its low water-cement ratio and high quantity of unit cement content. In the present study, we tried to know and assess the influences of chemical and physical properties of cement on the material properties of HSC. We analyzed basic properties of 4 kinds of cement whose chemical and physical properties are different each other through various tests such as chemical analysis and mortal test. Also, we performed the assessment of the material properties of HSC for each dement by the test for the conditions of same mix design and similar compressive strength. From the results in the study, the assessment of the important quality factors of cement influencing the properties of HSC may be utilized to quality control of applied cement to manufacture the HSC of high quality.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.637-640
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• 2008

In this study, the characteristics of strength development on high volume fly ash concrete(HVFAC)with Type 4 cement was experimentally investigated. Three levels of W/B were selected. Four levels of fly ash replacement ratios and two levels of silica fume replacement ratios were adopted. In the concrete mix, the water content of 125kg/m$^3$ was used, which is less than that of usual water content. As a result, it appeared that the compressive strength gradually decreased with increasing fly ash replacement ratio until 91days. However, regarding the compressive strength, the proper replacement ratio is about 20%, which is low compared to Type I cement case. It was observed that the tensile strength is proportional to the 0.72 power of the compressive strength. It appears that the prediction equation presented in Concrete Standard Specification overestimate the tensile strength in the low strength range, underestimate the tensile strength in the hi호 strength range.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.889-892
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• 2008

This study, having combined and displaced fly ash known as admixture material that delays hydration reaction with coarse particle cement("CC" hereinafter) collected in particle classification method during ordinary portland cement("OPC" hereinafter), reviewed the hydration heat characteristics affecting the concrete. To reduce hydration heat, the study plain-mixed which used 100% OPC for WB 50% level 1, displaced CC at level 3 of 25%, 50% and 75% for OPC, and by displacing FA with admixture material at level 5 of 0%, 10%, 20%, 30% and 40%, experimented totally 16 batches. As a result of experiment, in the case of flow, the more CC displacement rate increased, the more it tended to decrease, and the more FA displacement rate increased, the more it decreased. As for simple adiabatic temperature rise by the CC and FA displacement rates, it decreased as displacement rate increased, and particularly in the case of FA40, temperature rise amount, $5.8{\sim}7.4^{\circ}C$, was very low. Compressive strength decreased in proportion to displacement rate, however strength reduction increment was shown to decrease with age progress.

• Journal of Ocean Engineering and Technology
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• v.25 no.1
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• pp.73-79
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• 2011

The various properties of concrete have been required, as civil engineering structures are getting larger and complicated. Therefore, the high performance of concrete, such as high strength, high fluidity, and low hydration heat, has been investigated largely. In this study, the properties of lightweight concrete-reducing self-weight of structure member have been studied in order to check the applicability of lightweight aggregate concrete to structural material. The experiments on compressive strength, splitting tensile strength, unit weight, and modulus of elasticity have been conducted with varying PLC, LWCI, LWCII, LWCII-SF5, LWCII-SF15 to check the basic properties. The compressive strength of 21MPa was obtained easily by using lightweight aggregate concrete and the addition of silica fume to increase the compressive strength slightly. To use lightweight aggregate concrete for civil engineering structures, systematic and rigorous studies are necessary.