• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.159-162
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• 2004

The processing of phenolic composite reinforced with hybrid of PAN based/Rayon based carbon fabrics using FBG sensor and thermocouple was studied. Once the composite is cured, the reflection spectrum from the FBG sensor shifted the center wavelength with an increase in the temperature. Also, the change in the form of the reflection spectrum obtained during the cooling process of the cure cycle was caused by the thermal shrinkage. During the curing process, uniform distribution of the temperature profile was observed throughout the sample.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.89-94
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• 1997

As the reinforced concrete structures are aged, repair and rehabilitation materials and techniques have ben developed. However, most of the repair materials and methods are imported from abroad and theoretical study and repairing techniques are also not well established yet. A specification for quality of repair materials should be established, in order to secure the stability and to improve the serviceability of the repaired structures. In this study, long term properties of repair materials such as thermal expansion coefficient, hardening shrinkage, creep, and chemical resistance have been tested. The material properties shows to be affected many actors such as curing period, temperatures, relative humidity, and etc. The repair material should be selected by considering the cause and shape of the defects, mix properties, workability, quality control of construction, and etc.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.41-46
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• 2003

Until now, the quantity to recycle wasted concrete as the great supplementary value was very little. But considering a insufficiency of the present state of aggregates, the recycling of wasted aggregates is indispensable. This study will offer the basic application data of the recycled aggregates to make by the new attempt and offer the basic data of the great supplementary value of recycled aggregate to make good use of precast process. The result of compressive strength, tensile strength, flexural strength and drying shrinkage test of concrete by recycled aggregates were similar to the property of normal aggregate concrete, and the contrary effect of recycled aggregate by high temperature steam curing do not have been found out. Therefore the great supplementary value of recycled aggregate to make good use of precast process is possible way to be helpful to a insufficiency of the present state of aggregates.

• Transactions of Materials Processing
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• v.13 no.3
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• pp.236-241
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• 2004

UV-molded microlens arrays with high replication quality were fabricated using a parametric design method. It is important to maximize the replication quality, because one can obtain the replicated micro-optical components with desired properties by accurate control of the shape. In the present study, nickel mold inserts for microlens arrays with lenses having diameters between $3\mu\textrm{m}$ and $230\mu\textrm{m}$ were fabricated by electroforming process. An UV-molding system was designed and constructed, a simple technique to avoid micro-air bubbles was first suggested, and the effects of the compression pressure and UV-curing dose on the replication quality of UV-molded microlens arrays with a diameter of $14\mu\textrm{m}$ were examined experimentally. Finally, geometrical and optical properties of the replicated microlens arrays were measured and analyzed.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.269-272
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• 2005

Epoxy resins are gradually becoming some of the most important and versatile polymers in modem civil engineering. Because epoxy resins have some unigue properties, such as toughness, versatility of viscosity and curing conditions, good handling characteristics, high adhesive strength, inertness, low shrinkage compared to most other thermo-setting resins and concrete, and resistance to chemicals, they have found many applications in construction castings, repair materials, road or bridge deck pavements, coatings, and as structural or non structural adhesives. In this applications, epoxy resins are widely used for polymer concretes, grouting materials, injection glues, and sealants. In this paper, characteristics of deformation of repair material after repaired have been investigated by viscosity of repair material and the width of crack. It is believed that flexural strength of epoxy resin with low viscosity is high because tensile strength is high and elongation at break is low, fracture energy is low.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.9-10
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• 2014

Cracks on the surface of latex-modified concrete using ready mix concrete (R-LMC) are attributable to its sensitivity to air temperature, relative humidity and wind velocity. Insufficient curing under the windy condition causes plastic shrinkage cracks. The cracked areas should be replaced to prevent development of larger cracks. This paper investigated how the vibration resulted from crushing concrete for replacement of the partial cracked area affects bond strength of R-LMC at early age. To analyze bond strength of R-LMC, the commercial Finite Element (FE) program, ABAQUS Standard/Implicit version 6.12 was used, and bond strength was tested by ASTM C1583-04. The real vibration was applied to this FE model using an acceleration measurement equipment.

• Journal of the Korean Ceramic Society
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• v.37 no.4
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• pp.388-394
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• 2000

The C4A3S clinker was prepared by the solid-state reaction. The mixture of raw materials; calcite, kaoline and gypsum, was fired at 135$0^{\circ}C$ for 1hr and cooled rapidly in air. C4A3S type expansive was made with C4A3S clinker, CaO and CaSO4. The cement replaced by 10 wt.% C4A3S type expansive was investigated by the measurement of the strength(compressive, tensile, flexural) and length change at various curing conditions. Hydration products were mainly ettringite, monosulfate and Ca(OH)2. The densification and the expansion due to the formation of ettringite during the hydration increased strength and reduced the drying shrinkage of hardened cement.

• The Journal of the Korean dental association
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• v.12 no.1
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• pp.37-42
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• 1974

To ascertain if the ultrasonic cleaning technique caused any dimensional changes in heat and cold curing and fluid resin denture bases and in addition to evaluate the dimensional changes of the resin denture bases stored in water and air, the author measured the distance between the outsides of two pins embedded in methyl methacrylate test denture bases by mean of 12 inch vernier caliper, accurate to 0.02mm. The results were as follows; (1) Ultrasonic cleaning didn't cause any permanent dimensional changes, but only affected temporary dimensional expansion in 16 test denture bases. (2) Temporary expansion rate caused by 10 minutes' ultrasonic cleaning was 0.29% and at the maximal temperature of the cleaning solution it was 0.64%. (3) The half of the denture bases stored in water showed the dimensional expansion rate of 0.47% while the others stored in air showed the dimensional shrinkage rate of 0.15% after 4 months.

• Journal of the Korea Institute of Building Construction
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• v.18 no.1
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• pp.25-31
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• 2018

In this study, the Controlled Low Strength Material (CLSM) was investigated to utilize the bottom ash and fly ash generated in the Circulating Fluidized Bed Combustor (CFBC). It was confirmed that the CFBC fly ash (CFBC-F) and CFBC bottom ash (CFBC-B) had an irregular particle shape through SEM measurement. According to the results of the hazard analysis, it was also confirmed that they were environmentally safe. In the case of mixing with CFBC-F, the unit quantity was increased. Regarding the rate of change of length, shrinkage in the range of -0.05~0.50% occurred in the air dry curing condition and expansion in the range of 0.1~0.6% in the sealed curing condition. Compressive strength was increased in the sealed curing condition compared to the air dry curing condition because there was enough moisture for hydration reaction in the long term. Therefore, the results of this study are likely be used as basic research data of mine filler materials.

• Journal of the Korea Institute of Building Construction
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• v.15 no.3
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• pp.265-271
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• 2015

This study is intended to produce a PC (Precast Concrete) member without a steam curing process in developing the high early strength concrete satisfying the condition of 10MPa in compressive strength at the age of 6 hours, and is intended to ensure economic feasibility by increasing the turnover rate of concrete form. Hence, high early strength cement with high $C_3S$ content and the hardening accelerator of powder type accelerating the hydration of $C_3S$ was used. And the properties of concrete were evaluated according to the hardening accelerator mixing ratio (0, 1.2, 1.6, 2.0). No big difference was found from the tests of both slump and air content. When 1.6 % or higher amounts of the hardening accelerator were mixed, the compressive strength of 10MPa was achieved at the age of 6 hours. From the test results of autogenous (drying) shrinkage and plastic shrinkage, it can be seen that there was a difference according to hydration reaction rate due to the addition of the hardening accelerator. However, it was shown that no problem arose with crack and durability. And it was shown that resistance to freezing-thawing, carbonation, and penetration were excellent.