• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.475-481
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• 2022

Recycled aggregates show high water absorption rate compared to natural aggregates due to microcrack developed during production process and adhered cement pastes at the surface of recycled aggregates. This leads to the deterioration of mechanical properties and slow work flow. Currently it is getting hard to satisfy high demand for natural aggregates. Utilizing recycled aggregate more widely may be a substitutable countermeasure for the shortage of natural resources. In this study, two-stage mixing approach(TSMA) suggested by Tam et al. is used to produce recycled aggregate concrete(RAC) with 100 % replacement of coarse natural aggregate and tests for compressive strength, elastic modulus, and chloride ion diffusion coefficient are conducted to find out the effect of TSMA compared to normal mixing method. According to experimental result compressive strength and elastic modulus of RAC with TSMA was superior to those of RAC with normal mixing irrespective of water-cement ratio, and in some cases mechanical properties of RAC with TSMA approached to those of natural aggregate concrete(NAC). However, chloride ion diffusion coefficient of RAC was higher than that of NAC. This illustrates that TSMA is not an appropriate method in reducing chloride ion diffusion coefficient, resulting in inconsequential contribution of TSMA to the durability of RAC.

• Journal of the Korea Institute of Building Construction
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• v.22 no.6
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• pp.663-672
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• 2022

The purpose of this study is to evaluate the magnesium sulfate resistance of a geopolymer mixed with rice husk powder. General concrete, silica fume mixed concrete, and binary blended geopolymer were selected as comparison targets to confirm the magnesium sulfate resistance, and sulfate deterioration was calculated using the compressive strengths with ages. In addition, the weight change rate and the relative dynamic coefficient of the geopolymer were comparatively analyzed, and the degree of etteringite formation was confirmed using X-ray diffraction analysis. the experiment, the geopolymer mixed with 10% rice husk powder showed 10.8% higher compressive strength than concrete with silica fume when submerged for 56 days. Also, the geopolymer mixed with rice husk powder showed a small weight change rate of 0.9 to 1.45%. composition after immersion in magnesium sulfate through X-ray diffraction analysis, it was observed that a small amount of ettringite was dispersed in the geopolymer containing rice husk powder. Thus, there is a high correlation with the corrosion resistance of magnesium sulfate

• Journal of Conservation Science
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• v.18 s.18
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• pp.63-74
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• 2006

All rock materials of the three storied stone pagoda in Seoakri were composed of light gray alkali granite with medium grained and developed with small mialolitic cavities. This stone pagoda is preserving almost archetype except the head part because there was repair work already. But, foundation, basement and roof rocks are serious state by microbial invasion such as lichens. Because there are tree and grass that cause direct effect to stone pagoda surrounding. Therefore, conservation treatment executed the primary dry cleaning and secondary wet cleaning treatment. Stone surface is partly not removed well such as lichens which part removed using cleansing device that use high temperature steam. Some treated part concrete and epoxy resin remove and retreatment with mixing talc and alkali granite powder to epoxy resin. Did color matching at mixing process of epoxy resin and fillers to properties with set the feel of a material. Also, drainage ditched to minimize inflow of rainwater fall from slope that is on the east of stone pagoda, tree and grass in stone pagoda surrounding wished to do remove and control occurrence of lichens hereafter minimizing moisture conteats.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.5
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• pp.30-39
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• 2023

Large dams, which are critical infrastructures for disaster prevention, are exposed to various risks such as aging, floods, and earthquakes. Better dam safety inspection and diagnosis using digital transformation technologies are needed. Traditional visual inspection methods by human inspectors have several limitations, including many inaccessible areas, danger of working at heights, and know-how based subjective inspections. In this study, drone photogrammetry was performed on two large dams to evaluate the applicability of digital data-based dam safety inspection and propose a data management methodology for continuous use. High-quality 3D digital models with GSD (ground sampling distance) within 2.5 cm/pixel were generated by flat double grid missions and manual photography methods, despite reservoir water surface and electromagnetic interferences, and severe altitude differences ranging from 42 m to 99.9 m of dam heights. Geometry profiles of the as-built conditions were easily extracted from the generated 3D mesh models, orthomosaic images, and digital surface models. The effectiveness of monitoring dam deformation by photogrammetry was confirmed. Cracks and deterioration of dam concrete structures, such as spillways and intake towers, were detected and visualized efficiently using the digital 3D models. This can be used for safe inspection of inaccessible areas and avoiding risky tasks at heights. Furthermore, a methodology for mapping the inspection result onto the 3D digital model and structuring a relational database for managing deterioration information history was proposed. As a result of measuring the labor and time required for safety inspection at the SYG Dam spillway, the drone photogrammetry method was found to have a 48% productivity improvement effect compared to the conventional manpower visual inspection method. The drone photogrammetry-based dam safety inspection is considered very effective in improving work productivity and data reliability.

• 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 institute for structural maintenance and inspection
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• v.9 no.2
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• pp.155-162
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• 2005

This paper presents an invetigation into the cause of deterioration of wet surrounding RC structures subjected to checmical attacks such as sewage. The antibacterial-reforming agent is developed after determining the permeability of the RC structure. After application of the anitbacterial-reforming agent through SEM, the permeability, compressive strength properties and the micro-structure of the concrete were evaluated for durability. In addition, the antibacterial-reforming agent was combined with a protective coating for the wet surrounding RC structure and evaluated for durability. The combined effect of the antibacterial-reforming agent and the protective coating were evaluated in field tests in both sewer system and tunnel sites.

• Fire Science and Engineering
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• v.25 no.1
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• pp.63-71
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• 2011

When it comes to slim floor using asymmetric H-beam, it was designed that the steel member is embedded in concrete with relatively low thermal conductivity so as to minimize the deterioration of rigidity of steel member in fire. But given the bottom flange of asymmetric H-beam is directly exposed to the fire, the measure of applying the fireproof coating to improve the fire rate performance of slim floor beam was sought. The test was aimed at comparing the fireproof performance by adjusting the load ratio of 0.4 and 0.3, and The test was carried out to identify the 3-hour fire performance by reinforcing the beam as well as applying the fireproof coat, In the wake of comparing the specimen depending on variation of load ratio, lowering load ratio by 0.1 resulted in difference of 12 minutes and deflection was 39 mm. It was able to improve 12 minutes by reinforcing the beam and up to 102.4 mm in deflection.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6A
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• pp.427-435
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• 2012

In order to evaluate the effects of exposure conditions on the resistance to sulfate attack of normal and blended cement mortars, several mechanical characteristics of the mortars such as expansion, strength and bulk density were regularly monitored for 52 cycles under sodium sulfate attack. The mortar specimens were exposed to 3 different types of exposure conditions; 1) continuous full immersion(Exposure A), continuous half-immersion(Exposure B) and cyclic wetting-drying(Exposure C). Experimental results indicated that the maximum deterioration was noted in OPC mortar specimens subjected to Exposure B, showing the wide cracks in the portions where attacking solution is adjacent to air. Additionally, the beneficial effect of ground granulated blast-furnace slag and silica fume was clearly observed showing a superior resistance against sodium sulfate attack, because of its lower permeability and densified structure. Thus, it is suggested that when concrete made with normal cement is exposed to sulfate environment, proper considerations on the exposure conditions should be taken.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.6
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• pp.67-80
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• 2011

This paper presents the results of shaking table tests on a 1:5 scale 10-story R.C. wall-type residential building model. The following conclusions are drawn based on the test results. (1) The model responded linear elastically under the excitations simulating an earthquake with a return period of 50 years, and showed a nonlinear response under the excitations simulating the design earthquake of Korea. (2) The model showed a significant strength drop under the maximum considered earthquake, with a return period of 2400 years. (3) The major portion of the resistance to lateral inertia forces came from the walls used for the elevator and stair case. (4) Finally, the damage and failure modes appear to be due to the flexural behavior of walls and slabs. A significant deterioration of stiffness and an elongation of the fundamental periods were observed under increased earthquake excitations.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.157-169
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• 2007

This study aimed to quantify the deterioration of tunnel structural members such as concrete lining and shotcrete lining after a tunnel fire accident by measuring their mechanical properties between $300^{\circ}C$ and $1,000^{\circ}C$. From the experiments, it was revealed that the critical temperature where mechanical properties start to decrease linearly was approximately $300^{\circ}C$. In addition, the other critical temperature where macro-cracks are induced in specimens was around $600^{\circ}C$. From a series of regression analysis, the optimum regression function with correlation coefficients over 0.99 for mechanical properties at different temperature levels was obtained as the Boltzmann function. Finally, a schematic diagram to estimate temperature distribution inside structural members as well as their mechanical properties at corresponding temperature levels quantitatively was newly proposed for RABT and RWS fire scenarios.