• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.781-784
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• 2006

This paper investigates the fundamental properties of light weight foamed concrete with the variances in unit weight of concrete and adding ratio of stability agent(SA). Test showed that concrete adding SA slightly decreased fluidity but secured stable flow appearances without segregation of concrete components. All specimens in a standard condition represented that a sinking depth was not observed, while, in the wet condition, a specimen adding SA decreased the sinking depth $2{\sim}4mm$ more than control concrete. Compressive strength values of control concrete showed $0.03{\sim}0.3MPa$ higher than the concrete adding SA. As for the tensile strength, the specimen adding SA also had lower value, while the ratios of comp. to tens. strength presented $0.43{\sim}0.62$, which is relatively higher than ordinary concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.401-404
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• 2006

This study is the part of the investigation of the state of the art in ultra high flowing concrete (UHFC), applied in practical field construction, in order to develop the technology for improving workability. This paper includes a brief introduction of water content variance properties in UHFC before and after the pumping operation. Test showed that water content in all parameters decreased after the pumping. This is due to the increase of an absorption ratio of coarse aggregate by the pressure of the pumping operation. thus decreasing the water content. Therefore it should be considered to find out the possibility, which can improve the workability, suffering from over viscosity by the lower water content, in field construction.

• Journal of the Korean Society of Safety
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• v.12 no.2
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• pp.133-139
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• 1997

Conventional concrete mixing method is to put all of the materials simultaneously into a mixer and mix for a required time. However, recently concrete researchers have reported that mixing sequence iufluences the properties of concrete. This study discusses the influence of mixing sequence and partitioning addition of mixing water. Concrete, by method of partitioning addition of mixing water, was found to have substantially stronger strength than conventional concrete with the same water-cement ratio. This means that a higher strength concrete could be obtained by using “Sand Enveloped with Cement”(S.E.C) mixing technique. Both a high bond strength between cement paste and aggregate, and elimination of bleeding both contribute to improving the strength of S. E. C concrete.

• 한국정보통신설비학회:학술대회논문집
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• 2008.08a
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• pp.292-295
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• 2008

We propose a PON repeater system which transports multiple PON channels at the same time over the physical limit of the standard E-PON reach. To increase the physical reach up to 60km, we used the O-E-O (optic-electric-optic) signal regeneration on an active remote terminal which is placed between a central office and passive remote nodes. Also, by incorporating the well-established WDM technology to aggregate multiple E-PON channels, we successfully increased the split ratio (the number of subscribers per fiber core) to over 256.

• Proceedings of the Korea Information Processing Society Conference
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• 2007.05a
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• pp.1310-1312
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• 2007

Throughput improvement problem in wireless mesh network can be alleviated by equipped mesh router with multiple radios tuned into orthogonal channels. However, some links on the same channel also can be activated concurrently if the Signal-to-Noise and Interference Ratio (SNIR) at their receiver endpoints is not lower than the threshold. We propose a greedy algorithm to investigate the problem of how to schedule a set of feasible transmission under physical interference model by using the spatial time-division multiple-access (STDMA) scheme. We also consider the fairness in scheduling to prevent some border nodes from starvation. We evaluate our algorithms through extensive simulation and the results show that our algorithms can achieve better aggregate throughput and fairness performance than 802.11 standard.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.8
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• pp.2137-2156
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• 2024

Customer reviews are the second-most reliable source of information, followed by family and friend referrals. However, there are many existing customer reviews. Some online shopping platforms address this issue by ranking customer reviews according to their usefulness. However, we propose an alternative method to rank customer reviews, given that this system is easily manipulable. This study aims to create a ranking model for reviews based on their usefulness by combining product and seller service aspects from customer reviews. This methodology consists of six primary steps: data collection and preprocessing, aspect extraction and sentiment analysis, followed by constructing a regression model using random forest regression, and the review ranking process. The results demonstrate that the ranking model with service considerations outperformed the model without service considerations. This demonstrates the model's superiority in the three tests, which include a comparison of the regression results, the aggregate helpfulness ratio, and the matching score.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.11
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• pp.1116-1122
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• 2008

The existing technology which is for recycling aggregate using dried swage sludge have been limited for practical application, because the properties of aggregate are not regular and don't meet the recycling aggregate standard. In this research, an innovative slag-producing technology is developed by addition of oyster shell, waste cast-sand and iron-rust as inorganic waste additives. The mixed slag with the additives was evaluated at the various ratio of CaO/SiO$_2$, SiO$_2$/Al$_2$O$_3$ and Fe$_2$O$_3$/SiO$_2$. When the waste sludge was melted at 1,400$^{\circ}C$ during 20 minutes, the optimal ratio of CaO/SiO$_2$ for the slag added the oyster shell, SiO$_2$/Al$_2$O$_3$ for added the waste cast-sand and Fe$_2$O$_3$/SiO$_2$ for added the iron-rust were 1.00, 3.00 and 0.60, respectively. At the optimal condition, the bulk density of the slag was 2.24 g/cm$^3$, 2.45 g/cm$^3$ and 2.73 g/cm$^3$, And the 24 h water adsorption was 4.72%, 1.44% and 0.37%, respectively. Therefore it is proved that adding the waste additives to the process of the slag production contributed for elevation of recycling aggregate properties. And also it is expected that production cost can be reduced by decreased melting temperature.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.75-81
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• 2012

In case of crushing rock to produce materials for lean concrete subbase layer in concrete pavement, natural sand is used for the gradation adjustment of aggregates, and the percentage of natural sand used is 30%~40% of the weight ratio of aggregate mix. The supply of natural sand that is used in lean concrete as a fine aggregate is getting harder due to the current of exhaustion of source, and the cost for the purchase of natural sand is included in the cost of roadway construction. This study, therefore, was conducted in order to resolve the exhaustion of materials and economize in construction expenditure by the application of screenings, which is by-product of crushing rock in quarry, as an alternative to natural sand. As a result of a comparative analysis on the application of screenings and natural sand with typical types of rock that is produced in domestic, which was conducted in the first year, It is found out that the use of screenings as a fine aggregate showed better unconfined compression strength. Verification of actual application of screenings was conducted in the second year, after test construction and follow-up investigation. The compressive strength, compaction density, settlement of screenings applied case was higher than that of natural sand. Thus, it is expected that application of screenings to construction in field will contribute to the cost saving, material recycling and the protection of environment.

• The Journal of Engineering Geology
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• v.21 no.3
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• pp.239-246
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• 2011

Upon encountering weathering soil at a construction site, it may be necessary to change the design and construction plans for geotechnical structures. When weathering soil is exposed to air, the weathering process proceeds rapidly, resulting in significant damage to geotechnical structures, particle defects, and an increase in moisture sensitivity. The management of weathering-soil compaction is challenging. Because the engineering properties of weathering-soils vary regionally, it is important to report the result of research into the regional characteristics of such soils. At two locations of granite gneiss in the Gansung area of Gangwon-do, geological studies were performed at 22 and 8 sites, respectively. At each site, test samples were collected for analysis by XRD and to measure particle size, consistency, and compaction. To evaluate the suitability of the material for road subgrade, we examined the interrelationship between CBR value and the uniformity coefficient, the 200 sieve passing ratio and the aggregate ${\geq}$ 2 mm) content. We found that for the weathered granite soil, aggregate sized > 2 mm has a significant effect on the CBR value. In addition, the mixing of aggregate sized > 2 mm with sub-quality soil improves the soil condition.

• Journal of Conservation Science
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• v.32 no.3
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• pp.299-312
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• 2016

The Daehan Uiwon (Historic Site No. 248) in which the predecessor of Seoul National University Hospital is a crucial medical institution that built in the Korean Empire period. One of them, East 1 Affiliated Ward that attached to Daehan Uiwon was built with concrete foundation in 1908 and extended two times in 1935 and 1954. As a result of material scientific analysis for concrete foundation, all of the foundation is composed of mortar and stone aggregates, however, the mixing proportions between the aggregate and the mortar were confirmed to be different with construction periods. To determine the mixing proportion, and physical properties by ultrasonic velocity and rebound hardness, the concrete foundations by construction period were obtained. In result, 1954's mixing proportion of concrete between mortar and stone aggregate indicated the highest ratio of aggregates with 1 : 35, mean value of ultrasonic velocity and unconfined compressive strength were calculated with 450 m/s and 18.92 MPa in 1954's constructions that is the lowest values compared with other times. As a result, the difference characteristics of physical properties by construction periods are possible interpreted with porosities and mixing ratios of stone aggregates.