• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.2
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• pp.16-25
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• 2018

Concrete is a suitable construction material for long-term structure, however, it is needed to understand the calcium leaching damage caused by exposure to underground pure water for a long time. In this paper, it is experimentally investigated that the characteristics of flexural behavior in RC member damaged by calcium leaching degradation. From the test results, when calcium leaching is happened, yielding load and flexural rigidity is reduced, neutral axis depth and displacement is increased. That is, calcium leaching degradation adversely affects RC member performance. And, when the mineral admixture is used in the calcium leaching environment, it is considered that the optimal replacement ratio should be prepared according to the type of mineral admixture.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.122-129
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• 2019

Cracks in concrete structures are inevitable phenomena caused by shrinkage, hydration heat, and external loads. These cracks facilitate the penetration of external harmful ions into the concrete, which greatly reduces its durability. Recently, self-healing concrete has been actively studied. Also, self-healing fiber-reinforced concrete have been studied to control the crack in concrete and to maximize the shelf-healing capability. In this study, mortar specimens containing PVA fiber, fly ash and crystalline admixture were fabricated. The compressive and flexural strength were evaluated. Also, the self-healing performance was evaluated by the absorption test. From the results, it was confirmed that the amount of water absorbed by healing of the crack decreased as time increased. It was also found that PVA fiber is beneficial for the production of calcium carbonate, an additional healing product.

• Journal of the Korea Institute of Building Construction
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• v.21 no.4
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• pp.269-279
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• 2021

Palm Oil Fuel Ash(POFA) has been widely used to replace Portland cement to enhance the mechanical properties and durability of concrete. However, it reduces the workability of concrete due to the high content of unburnt carbon and its angular shape requiring the usage of superplasticizer to ensure a proper flowability. In this study, effects of different types and dosage of superplasticizer on the early mechanical and hydration properties of cement paste containing micro-POFA were evaluated using mini-slump test, early compressive strength, TGA, XRD, and SEM. The results indicated that the flowability of cement paste containing micro-POFA reduced as the replacement ratio of micro-POFA increased. As the dosage of superplasticizer increased, the flowability was also increased. In addition, the usage of superplasticizer reduced the early compressive strength, and the strength decreased with an increase in the dosage of superplasticizer. It was confirmed that superplasticizer hindered the formation of C-S-H leading to a relative increase in the formation of Ca(OH)₂.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.6
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• pp.47-52
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• 2008

Deicer has been generally used for prevention of a road freezing in winter, and the usage amount is increasing every year. However, deicer may induce the decrease of bond strength, surface scaling, and environmental pollution. In this study, the field test was performed to investigate the deterioration of concrete road structures used for 17 years. And, the corrosion resistance characteristics were compared for the existing deicer and eco-friendly deicer. According to the field test results, the penetration depth of limit chloride amount was about 40mm, and the average concentration of chloride was $3.45kg/m^3$ at the surface of structures. On the contrary, the carbonation depth was slight. The penetration depth of eco-friendly deicer was less than the existing deicer, and the corrosion resistance of eco-friendly deicer was higher.

• Journal of the Korea Concrete Institute
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• v.23 no.2
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• pp.225-233
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• 2011

The volume change in concrete takes place with changes in temperature and water content immediately after concrete casting. In the early age stage, the thermal and drying shrinkages can cause cracks that are very crucial to the durability of concrete. It was reported that when the cement with lightly-burnt MgO powder was used, the shrinkage of concrete can be reduced. This study investigates fundamental properties of cement composites with lightly burnt MgO powder by performing various experiments. The stability test results verified that MgO powder in cement composites does not cause any abnormal expansion. Also, the hydrate product analysis results obtained from MgO cement paste showed that MgO powder reduces the shrinkage at the longterm ages. In addition, the cement composites containing the proper amount of MgO powder could improve compressive strength. Finally, the shrinkage reduction from using MgO powder can be optimized by increasing MgO replacement level and curing temperature.

• International Journal of Highway Engineering
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• v.8 no.1 s.27
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• pp.33-43
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• 2006

Pull-out strength of tie-bin used in pavement construction is not an issue because those are embedded in newly placed concrete slabs. However, sufficient pull-out strength should be secured in widening constructions because, in case, the tie-bars are inserted into drilled holes of the existing slabs with liquid filler. Insufficient pull-out strength will result in lowered load transfer efficiency between adjacent slabs in addition to poor serviceability and durability due to joint widening. The pull-out strength of the tie-bars installed by current method is evaluated and improved methods are proposed. The field pull-out strength obtained by the current method was only 42.7% of required strength. Its first counterproposal is using to insert the liquid filler into drilled holes and stoppers to prevent it from flowing out of the holes. However, this method was not judged to secure desired level of quality control. The second counterproposal which substitutes the existing type of the tie-bars by SL anchor bolts was judged to secure sufficient pull out-strength in addition to the quality control and constructibility.

• Journal of the Korean Ceramic Society
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• v.39 no.6
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• pp.576-581
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• 2002

In order to simultaneously vitrify the ton Exchange Resin(IER) and Dry Active Waste(DAW) generated from the Nuclear Power Plants, a vitrification pilot test was conducted using an induction cold crucible melter. The PCT result evaluating the chemical durability of the vitrified from showed that the final glass was more durable than the benchmark glass. Liquidus temperature for the final vitrified form was 1048 K(775$\^{C}$) fur heat treatment experiments. The value of the compressive strength for the vitrified form was ninety times higher than the regulation limit, 34 kg/㎠. The glasses on bottom, middle and top of the CCM were homogeneous with no secondary phase. The precipitation of the magnetic metal phase was able to be avoided by simultaneously fEeding of DAW with IER containing strongly reducing organics. Volume reduction factor of 74 was achieved through the vitrification Pilot test for mixed waste.

• Journal of KIISE
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• v.42 no.11
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• pp.1314-1321
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• 2015

Mobile devices employ buffer cache mechanisms, just as in computer systems such as desktops or servers, to mitigate the performance gap between main memory and secondary storage. However, DRAM has a problem in that it accelerates battery consumption by performing refresh operations periodically to maintain the stored data. In this paper, we propose a novel buffer cache scheme to increase the battery lifecycle in mobile devices based on a hybrid main memory architecture consisting of DRAM and non-volatile PCM. We also suggest a new buffer cache policy that allocates buffers based on process states to optimize the performance and endurance of PCM. In particular, our algorithm allocates each page to the appropriate position corresponding to the state of the application that owns the page, and tries to ensure a rapid response of foreground applications even with a small amount of DRAM memory. The experimental results indicate that the proposed scheme reduces the elapsed time of foreground applications by 58% on average and power consumption by 23% on average without negatively impacting the performance of background applications.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.3
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• pp.42-48
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• 2016

Extensive research effort has been made during the last decade to utilize wireless smart sensors for evaluating and monitoring structural integrity of civil engineering structures. The wireless smart sensor commonly has sensing and embedded computation capabilities as well as wireless communication that provide strong potential to overcome shortcomings of traditional wired sensor systems such as high equipment and installation cost. However, sensor malfunctioning particularly in case of long-term monitoring and unreliable wireless communication in harsh environment are the critical issues that should be properly tackled for a wider adoption of wireless smart sensors in practice. This study presents a wireless smart sensor network(WSSN) that can estimate unmeasured responses for the purpose of data recovery at unresponsive sensor nodes. A software program that runs on WSSN is developed to estimate the unmeasured responses from the measured using the Kalman filter. The performance of the developed network software is experimentally verified by estimating unmeasured acceleration responses using a simply-supported beam.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.2
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• pp.100-106
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• 2014

High strength concrete has a structural advantage as well as superior usability and durability, so that its application in building is being steadily augmented. However, in the high temperature like in a fire, the high strength concrete has extreme danger named explosive spalling. It is known that the major cause of explosive spalling is water vapour pressure inside concrete. General solution for preventing concrete from spalling include applying fire protection coats to concrete in order to control the rising temperature of members in case of fire. The purpose of this study is to investigate the high temperature properties of fireproof mortar using organic fiber and various types of fine aggregate for fire protection covering material. The results showed that addition of perlite and polypropylene fiber to mortar modifies its pore structure and reduces its density. This causes the internal temperature to rise. As a results, it is found that a new fireproof mortar can be used in the fire protection covering material in high strength concrete.