• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.6
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• pp.673-680
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• 2017

Research and commercialization of wood chips-urethane resin mixtures as paving materials for park trails and tourist attractions are underway. The aim of this study was to expand the use of such paving materials to the playgrounds, where vigorous physical movements occur frequently. For this purpose, the physical properties and safety of the paving material, in which some or all of the wood chips(passing through a 10mm sieve and remaining in a 3mm sieve) were replaced with sawdust, were studied experimentally. Strength, elastic modulus, slip resistance, shock absorption and heavy metal content tests were carried out by varying the mixing ratio of urethane resin, sawdust and wood chip. As a result, in the case of wood chip-resin mixtures with mass ratios of the resin to total mass of sawdust and wood chips of 1.0 and 1.2 and having a ratio of sawdust mass to total mass of sawdust and wood chips of 0-0.4, it was found that the properties satisfied KS F 3888-2. On the other hand, in case of using sawdust only as a woody material, the shock absorbability was below standard, and the mass ratio of resin to sawdust required 1.2 or more to ensure the specified tensile strength.

• Korean Journal of Construction Engineering and Management
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• v.16 no.6
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• pp.136-143
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• 2015

Snow-melting system has been applied not only to roads for car traffic but also to pavement for the pedestrians safety reason in some of the developed countries such as USA and Canada based on countermeasures against Natural Disasters Act revised in 2000. Even though this system was introduced in korea in 2006 and has been partly applied to car traffic roads, there is few places that the system has been applied. Therefore, in this research a snow-melting system with a block-type to cover a pavement that efficiently transfers heat form heat rays to the top of a pavement and protects the heat rays. A quality check showed that compression and bending strength was improved approximately 5 times stronger and 7 to 10 times more absorption rate than the KS(Korea Industrial Standard) requirement. Moreover, only 10 minute was required to increase temperature above zero with a block-type snow-melting system whereas approximately 180 minute was spent with the existing system. This research is expected to contribute to environmental issues and reduce accidents on a slippery road.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.27-33
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• 2016

Military textiles with breathable waterproof materials are expanding as form of winter clothes. Waterproof moisture-permeable clothes are very important for soldiers to survive in cold weather operations because they prevent loss of body heat from the penetration of water into the human body. Korea military uses the water resistance and moisture permeability to test the performance of waterproof moisture-permeable materials. Moisture permeability is measured according to the amount of evaporated water vapor passing through a fabric under specified temperature and humidity by using acetic acid potassium presented in KS K 0594. However, the test procedure for measuring the moisture permeability in the standard is presented only briefly and the preparation procedures for the test in accredited testing institutions are applied differently, leading to significant deviation of the results. This paper compares the procedures of testing institutions and examines the factors that affect moisture permeability. Finally, we propose a procedure to reduce the deviation of results and apply the proposed procedure in testing institutions. Our analysis results with one-way ANOVA under significant level (0.05) confirm that the deviation of results is reduced.

• Fire Science and Engineering
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• v.32 no.6
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• pp.28-33
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• 2018

To measure the full scale fire test and heat release rate of bed mattresses according to the building compartment space, a fire test was performed using the Standard test method to determine the heat release rate of mattresses and mattress sets (KS F ISO 12949: 2011). Both test locations showed similar fire growth until approximately 3 minutes after burner ignition. After 3 minutes, the heat release rate in the test room was higher than the open calorimeter. For bed mattresses (SS), the maximum heat release rate in the open calorimeter was 735 kW and the maximum heat release rate in the test room was 992 kW. For bed mattresses (Q), the heat release rate in the test room increased more rapidly than the open calorimeter. The maximum heat release rate in the open calorimeter was 1,087 kW (346 s) and the maximum heat release rate in the test room was 2,127 kW (287 s). The difference between the maximum heat release rate and the measurement time according to the test location was confirmed.

• Resources Recycling
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• v.32 no.6
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• pp.10-17
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• 2023

Calcium silicate cement (CSC) is an environmentally sustainable, low-carbon cement and has garnered significant attention in recent studies. However, the pre-curing step required to activate the carbon dioxide reaction and to handle the sample. This study aimed to examine the viability of extending the application of CSC without pre-curing by enhancing initial strength by mixing calcium sulfoaluminate (CSA) fast-hardening cement into CSC. The investigation assessed changes in compression strength and Q-XRD mineral characteristics concerning variations in the mixing ratio of CSC and CSA fast-hardening cement within a carbon dioxide atmosphere. The compressive strength results indicated that the 3-day and 7-day strengths were 14.18 MPa and 22.98 MPa, respectively, under the 50% CSC condition, meeting the type 1 cement KS standard. Mineral characteristics analysis revealed an increase in calcite mineral, a byproduct of the carbon dioxide reaction, contributing to strength enhancement. Even after seven days, substantial quantities of unreacted rankinitene and pseudowollastonite were observed, as well as dicalcium silicate and yeelimite, which are hydrated minerals. This observation was confirmed the possibility of strength improvement after 7 days.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.233-238
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• 2020

Although the interest in NBR has been increasing due to the recent developments of the aerospace sector, there are few reports on HNBR's aeronautical oil, particularly evaluations of the accelerated life of harsh factors. In this study, the tensile strength was adopted as a performance evaluation factor to evaluate the accelerated life of HNBR used in the aviation field. The accelerated stress factor affecting the performance-aging characteristics was defined as temperature. The acceleration stress factor was determined to be temperature, and the result of measuring the tensile strength change over time. The sample for the acceleration condition was taken out of the oven for a certain period and left at room temperature for 24 hours. The dumbbell type 3 specimens were manufactured according to the standard specified in KS M 6518 and were measured the tensile strength, a factor in accelerated life evaluations. The activation energy was 0.895, and the shape parameter was 1.152 using the Arrhenius model. The characteristic life obtained from the tensile strength of the HNBR specimen immersed in aviation oil at 20℃ was 272,256 hours; the average life was 258,965 hours, and the B10 life was 38,624 hours.

• The Journal of the Acoustical Society of Korea
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• v.32 no.5
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• pp.430-437
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• 2013

The present study examined whether sentence perception scores were changed under various conditions of time alteration (compression and/or expansion) and selective word stress in normal hearing listeners. Twenty young normal hearing adults (ten males) were participated. As stimuli, Korean standard-sentence list for adults (KS-SL-A) modified to semantically anomalous sentences was newly recorded by a female speaker. Seven different time-altered conditions (e.g., ${\pm}60%$, ${\pm}40%$, ${\pm}20%$, 0 %) were controlled. To see the effect of selective word stress (i.e., the emphasis of specific syllables in the sentence), all subjects were tested twice 2 weeks apart. The results showed 1) there was significantly different sentence perception scores among the different time-altered conditions, yet only in the 60 % compression condition; 2) there was no significant difference of the sentence perception scores in the effect of stress; however, there was a positive effect of the selective word stress in the sentences consisting of 6 ~ 7 syllables at the 40 % compression condition; 3) there was no significant gender difference. The pattern of results suggests that the combination of time compression and selective word stress is more effective to understand speech, instead of only using time expansion condition. However, further studies should be needed for standardization.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.973-981
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• 2002

Recently, the use of high strength concrete (HSC) has increased dramatically md however, few studies have been conducted on the early-age properties of HSC such as setting. The penetration resistance test (specified by KS F 2436) that is the standard test method for determining initial and final setting times of concrete, may not be appropriate for HSC because of the high viscosity of the mortar mixture. To address this issue, an ultrasonic pulse velocity (UPV) monitoring system was used to investigate the setting behavior of mortar and concrete. The experimental study was carried out to measure the UPV's of mortars and concretes having various water/binder ratios (W/B) and various fly ash replacement levels, during the first 24 hours of testing. Test results showed that the UPV in concrete was developed faster than that of mortar with the same W/B, and that of ordinary concrete was greater than that of fly ash concrete. Typical values of UPV were suggested that correspond to the initial and final setting times, based on following criteria: (1) the penetration resistance method; (2) the instant when the UPV begins to develop; and (3) the instant when the UPV development rate is maximum. The method and UPV monitoring device used in this study is promising for the setting assessment of concrete, particularly for HSC.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.27-35
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• 2004

Most of concrete fatigue tests currently used are flexural tension or compression methods to investigate the tensile or compressive properties, respectively. However, the concrete pavement or concrete slab is actually subjected to a combined stress condition such as biaxial or triaxial. The split tension test may result in similar stress condition to biaxial stress condition. The purposes of this study were to evaluate the split tension fatigue test method for application in concrete. These were done by a finite element analysis and experimental series. The results were as follows: The optimum configuration of split tension fatigue test was a cylinder of 15cm in diameter and 7.5cm in thickness, which had a little different thickness compared to the KS standard cylinder of ${\phi}15{\times}30cm$. The concrete stress ratio of compressive against horizontal from FEA was 3.1, while that from theory was 3.0. The stress distributions of mortar and steel were almost similar at different thicknesses. The measured static split tensile strengths of concrete and mortar were quite similar at 30cm and 7.5cm thickness cylinders. The measured stress-strain relationship showed their consistency at all specimens regardless of thickness, and confirmed the results from FEA. As a results, the concrete split tension specimen, cylinder of 15cm in diameter and 7.5cm in thickness, could be used at fatigue test because of its accuracy, simplicity and convenience.

• Journal of Food Hygiene and Safety
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• v.14 no.3
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• pp.277-281
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• 1999

Chemical composition of imported table salts from China (sun dried), Thailand (sun dried) and Australia (rock salt) were compared the mineral content and heavv metal contamination with Korean sun dried salt. Kimchies prepared by those salts were analyzed the quality by pH, acidity and sensory evaluation. Chemical compositions were as follows : moisturefrom 1.7% (Australia) to 8.7% (Korea), sodium chloride-from 86.7% (China, summer) to 97% (Australia), insoluble matter in water-from 0.02% (Australia) to 0.18 (China), and sulfate ionfrom 0.03% (Australia) to 1.65% (China, summer). Judging by Korean Standard(KS) of salt, salt from Australia and Thailand belong to 1st grade, Korean and Chinese (winter) to 2nd grade, and China (summer) were out of 3rd grade. Ca and Mg content of the salts tested were 0.022% (Australia) to 0.246 (China, winter), 0.036% (Australia) to 0.841% (China, summer) respectively and Pb was 1.23 ppm(China, summer)~0.61ppm(Korea) which is within the Korean regulation. The other heavy metals, Pb, Cd, As and Hg were not detected in all salts tested. The quality of Kimchi prepared by those salts were significantly no difference with Korean sun dried salt.