• Journal of the Korean Ceramic Society
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• v.47 no.3
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• pp.223-231
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• 2010

The serious issue of tall building is to ensure the fire-resistance of high strength concrete. The fire resistant finishing method is necessarily essential in order to satisfy the fire resistance time of 3 h required by the law. The fire resistant finishing method is installed by applying a fire resistant material as a method of shotcrete or a fire resistant board to high strength concrete surface. This method can reduce the temperature increase of the reinforcement embedded in high strength concrete at high temperature due to the installation thickness control. This study is interested in identifying the effectiveness of inorganic alumino-silicate compounds including the inorganic admixture such as fly ash and meta-kaolin as the fire resistant finishing materials through the analysis of fire resistance and components properties at high temperature. The study results show that the fire resistant finishing material composed of fly ash and meta-kaolin has the thermal stability of the slight decrease of compressive strength at high temperature. These thermal stability is caused by the ceramic binding capacity induced by alkali activation reaction by the reason of the thermal analysis result not showing the decomposition of calcium hydrate. Inorganic compounds composed of fly ash and meta-kaolin is evaluated to be very effective as the fire resistance material for finishing to protect the concrete substrate by the reason of those simplicity in both application and manufacture. The additional study about the adhesion in the interface with concrete substrate is necessary for the purpose of the practical application.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.277-280
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• 2008

Reinforced concrete structures have an excellent durability under a good construction and continuous maintenance. But reinforced concrete construction is influenced by atmospheric phenomena and it is creating a deterioration. One of the deterioration cause on concrete is a freezing and thawing action. Freezing and thawing leads to the reduction in concrete durability by the cracking or surface spalling. If we are carried out freezing and thawing, deterioration of reinforced concrete construction will be reduction. Therefore, this study was performed to investigate the flexural behavior of reinforced concrete beams exposed to freezing and thawing cycles. Thee presence of damage and cycles were considered as variablees in this study.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.405-408
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• 2008

This study, as mock-up test for applying Polylon Fiber engineering method to the field, analyzed the fundamental characteristics and the fireproof characteristics of high strength concrete mixed with Polylon Fiber 0.05% and the results are summarized as followings. From the characteristic of the fresh concrete, both slump flow and air content were appeared to satisfy target range. And from the characteristic of hardened concrete, all compressive strengths according to the curing conditions were appeared to satisfy design standard strength of 60 MPa. From the fireproof characteristic, small scaling and spalling phenomenon were partially appeared on the surface part of specimens, but generally the excellent fireproof capacities were appeared. From the characteristic of temperature hysteresis, the highest temperature and the average temperature of reinforcing part after fire-resistant test for 3 hours were $531^{\circ}C$ and $405{\circ}C$, respectively and then satisfied fireproof standard of the Ministry of Land Transportation and Maritime Affairs.

• Journal of Technologic Dentistry
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• v.23 no.2
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• pp.161-170
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• 2002

The Purpose of this study was to investigate the chemically improvement of metal-ceramics bond strength in the course of recasting Ni-Cr metal composite system with 10wt.%, 20wt.% and 30wt.% aluminum respectively. We have tested the bond strength, micro-structure, chemical composition of each metal composites and metal- ceramic bond interfaces by 3-point bending strength tester, SEM and EDS. We have made the conclusions through this study as follow: 1. The most suitable amount of aluminum to the Ni-Cr metal composite recasting is 20wt. % for improving metal-ceramics bond strength with debonding strength value of 49.54 kgf/mm2. 2. The aluminum must be changed to small spread alumina like phases and second aluminum-metal composites phases in the morphology of Ni-Cr metal composite system by adding during it's casting. These second phases have inclined functional oxide phases mixed with metal elements and they must take roll to improvement of metal-ceramics bond strength. 3. In the case of 30wt.% aluminum appended to Ni-Cr metal composite system, an excess of second inclined functional oxide phases produce cracks and spalling of them apart from it's base material. It must be a important factor of reduction of metal-ceramics bond strength.

• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.88-94
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• 1997

The oxidation behavior of the NiCrAlY bond coat and thermal fatigue failure in the plasma-sprayed thermal barrier coating system, ZrO2.8wt%Y2O3 top coat/Ni-26Cr-5Al-0.5Y bond coat/Hastelloy X superalloy substrate, in commercial use for finned segment of gas turbine burner were investigated. The main oxides formed in the bond coat were NiO, Cr2O3, and Al2O3. It divided the oxide distribution at this interface into two types whether an Al2O3 thin layer existed beneath ZrO2/bond coat interface before operation at high temperature or not. While a continuous layer of NiO was formed mainly in the region where the Al2O3 thin layer was present, the absence of it resulted in the formation of mixture of Cr2O3 and Al2O3 beneath NiO layer. Analyses on the fracture surface of specimen spalled by thermal cycling showed that spalling occurred mainly along the ceram-ic coat near ZrO2/bond coat oxide layer interface, but slightly in the oxide layer region.

• Journal of Ocean Engineering and Technology
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• v.20 no.2 s.69
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• pp.59-65
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• 2006

Steel, as a reinforcing mechanism in concrete, provides the tensile strength that is lacking in concrete, alone, and the high alkaline environment (pH 12.5) in concrete offers satisfactory protection against most corrosion of the steel. However, the corrosion of reinforcing steel in concrete can occur by chloride attack or carbonation, and it can cause a loss of integrity a section and concrete failure through cracking and spalling. In this study, a transient electro magnetic method (TEM) of a nondestructive technique is adapted to study the measuring method of steel corrosion in mortar. The sensor was made of an enameled wire, with a diameter of 0.25mm and anacril. He sensor configuration used was a coincident loop type. The secondary electro motive force (2nd EMF) was measured with SIROTEMIII, which equipped the accelerator. The accelerator allowsthe transmitter to turn off approximately $10\sim15$ times faster than normal. The high-resolution time series, used for very shallow or a high resistivity investigation was selected. After steels were corroded by the salt spray, during 4, 8, 15 and 25 days, they were embedded in mortar. The content results acquired in this study are as follows. The variation of the secondary electro motive force (2nd EMF) was shown by the change of steel surface with different corrosion time steel. It was confirmed that measurement of steel corrosion in mortar by a transient electro-magnetic method (TEM) can be possible.

• Tribology and Lubricants
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• v.31 no.2
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• pp.35-41
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• 2015

A water-pump located in the cooling area of a car circulates cooling water. A particular bearing element, known as a water-pump bearing, installed in the rotating part carries the entire load. The failure of this water-pump bearing has a direct impact on the failure of the automobile engine, and so securing its reliability is crucial. Several researchers have examined the design principles of the water-pump bearing, but there are no reports on the life characteristic of the bearing yet. Herein, we report the construction of test equipment to reproduce the spalling of the roller contact, which is the main failure mode of the chosen water-pump bearing. We chose the radial load as an accelerated stress factor and validated the failure mode by monitoring the surface defects. We conducted the accelerated life test after determining the accelerated stress level through a combination of finite element analysis and a preliminary test. In the life tests, we used an accelerometer to perform failure diagnosis. In the last stage of this study, we present a statistical reliability analysis. Thus, we fully estimated the shape parameter of the water-pump bearing, accelerating level on the load , and the lifetime (MTTF and B₁₀ life) under real use conditions, and finally proposed an interval estimation value considering the uncertainty of the estimated value.

• Structural Engineering and Mechanics
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• v.76 no.4
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• pp.465-477
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• 2020

This paper presents an investigation on the dynamic behavior of SRC columns with built-in cross-shaped steels under impact load. Seven 1/2 scaled SRC specimens were subjected to low-speed impact by a gravity drop hammer test system. Three main parameters, including the lateral impact height, the axial compression ratios and the stirrup spacing, were considered in the response analysis of the specimens. The failure mode, deformation, the absorbed energy of columns, as well as impact loads are discussed. The results are mainly characterized by bending-shear failure, meanwhile specimens can maintain an acceptable integrity. More than 33% of the input impact energy is dissipated, which demonstrates its excellent impact resistance. As the impact height increases, the flexural cracks and shear cracks observed on the surface of specimens were denser and wider. The recorded time-history of impact force and mid-span displacement confirmed the three stages of relative movement between the hammer and the column. Additionally, the displacements had a notable delay compared to the rapid changes observed in the measured impact load. The deflection of the mid-span did not exceed 5.90mm while the impact load reached peak value. The impact resistance of the specimen can be improved by proper design for stirrup ratios and increasing the axial load. However, the cracking and spalling of the concrete cover at the impact point was obvious with the increasing in stiffness.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.6 s.58
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• pp.126-134
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• 2009

Generally, reinforced concrete structures exposed to the outside temperature are affected by freezing and thawing process during winter and early spring. These freeze-thawing process can lead to the reduction in durability of concrete as cracking or surface spalling. This paper is to study the flexural behavior of RC beams exposed to freeze-thawing environments. To compare the difference in flexural behavior of RC Beams, limited tests were conducted under different types of Longitudinal steel ratio and freeze-thawing cycles. For this purpose, fourteen small-scale RC beams ($100mm{\times} 100mm {\times}600mm$) were strengthened in monotonic and cyclic loadings, subjected to up to 150, 300 cycles freeze-thawing from $-18{\sim}4^{\circ}C$. It is thought that experimental results will be used as basic data to evaluate flexural behavior of RC beams exposed to freeze-thawing.

• Journal of the Society of Disaster Information
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• v.8 no.1
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• pp.18-26
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• 2012

Accordingly architectural structure is getting high-rise and bigger, a use of high strength and high performance concrete has been increasing. High performance concrete has cons of explosion in a fire. This Explosion in the fire can cause the loss of the sheath on a concrete surface, therefore it effects that increasing a rate of heat transmission between the steel bar and inner concrete. Preventing this explosion of high performance concrete in the fire, many kinds of researches are now in progressing. Typically, researches with using Polypropylene-fiber and Steel-fiber can prove controling the explosion, but the reduction of mobility was posed as a problem of workability. Consequently, to solve the problem as mentioned above, concrete cans secure fire resisting capacity through the using of coating liquid, including Ester-lubricant and non-ionic characteristic surfactant. This research has been drawn a ideal condition in compressive strength areas of concrete by an experiment. When applying 13mm of polyamide-fiber, proper fiber mixing volume by compressive strength areas of concrete is $0.8kg/m^3$ in 60MPa, $1.0kg/m^3$ in 80MPa, $1.5kg/m^3$ in $100MPa/m^3$. These amount of a compound can control the explosion.