• Korean Journal of Environment and Ecology
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• v.26 no.6
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• pp.911-922
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• 2012

This study aim that definite the relationship between coastal environment and different sand bar communities, as well as to analyze their spatial distribution of barrier island in the Nakdong river estuary. Survey method follow by Braun-Blanquet(1965) and there a total of 118 relev$\acute{e}$'s were undertaken. Definition of the relationships between species and environmental variables with Canonical Correlation Analysis(CCoA) and that to applied these relev$\acute{e}$'s with the RIM(Kim and Kim, 2006) program and that to classification used the SYN-TAX 2000 program(Podani 1979). On the basis of about 118 phytosociological releve's, the vegetation of xeric and hydric type was arranged in twelve plant communities: Xeric type-Pinus thunbergii community,Vitex rotundifolia community, Carex pumila community, Imperata cylindrica var. koenigii community, Miscanthus sacchariflorus community and Calystegia soldanella community, Hydric type-Salix dependens-Calamagrostis epigeios community, Calamagrostis epigeios-Phragmites communis community, Phragmites communis-Ischaemum aristatum community, Phragmites communis community, Scirpus planiculmis community and Suaeda glauca-S. japonica community.These plant communities represents sand dune vegetation and salt marsh vegetation. Widely distributing types in the actual vegetation map were sea club-rush community, reed community in salt marsh, and dry grassland. The edge in the coastal sand bars has zonation that almost distribution by the reed community in salt marsh. But outside of it were distributed sea club-rush community. Dry grassland type distributes higher zone of the center in coastal sand bars. Respectively, the coastal sand dune and salt marsh vegetation types were distributed ocean and inland on the frontier of it.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.8 no.6
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• pp.13-20
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• 2005

This study was conducted to examine the growth and physiological characteristics of Polystichum lepidocaulon native fern as affected by soil mixture as an environment modeled on habitate where was sunken-condition. 1. Polystichum lepidocaulon grew well sunken more than non-sunken condition. Under soil mixture of field soil : sand : leaf mold, Plant height, frond width, frond length, stipe length and ornamental value were increased compared with the other soil mixture. 2. Fresh and dry weight of fronds were higher with non-sunken than sunken condition. In sunken condition, fresh and dry weight were better with field soil : sand : leaf mold than the other soil mixture. 3. Number of spore fronds were increased with sunken condition. As sunken condition, sand : leaf mold was better than field soil : sand : leaf mold or leaf mold. 4. Photosynthetic rate, $CO_2$ absorption rate and water efficiency were higher with field soil : sand : leaf mold than that of sand : leaf mold or leaf mold. expect of stomatal conduction and $CO_2$ use efficiency.

• Journal of the Korean GEO-environmental Society
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• v.7 no.6
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• pp.67-73
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• 2006

In this study, basic physical tests and mechanical tests of crushed rock were performed in order to investigate the field application of crushed rock as substitute materials of sand that is commonly being used as foundation and backfill materials of sewer conduit. Particle-size distribution curve of crushed rock is similar to sand and also it is well-graded soil than common sand. Maximum dry unit weight in proctor compaction test for crushed rock is higher than the values of common sand. So we can estimate that the crushed rock has advantages in workability than sand for the backfill compaction after construction of sewer conduit. When we investigate the results of direct shear test and triaxial compression test on the crushed rock, it has a similar value of shear strength parameters to sand at the same stress state and as time goes by, it tends to increase the unconfined compression strength. But, because the strength reaches at the constant value after 6~7 days, we expect that it can absorb the lateral strain of flexible conduit well. All the above experimental results just proves that crushed rock can substitute for sand as backfill materials and foundation of sewer conduit.

• Journal of Korea Foundry Society
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• v.25 no.4
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• pp.173-178
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• 2005

The vacuum molding process is one of the clean-foundry molding-processes that can recycle molding sands repeatedly, because molding can be accomplished by introducing vacuum only among dry molding sands in flask. The effects of molding conditions such as sand grain fineness, vacuum pressure and coating thickness on the fluidity of A356 Al alloy were studied and the results was obtained that the fluidity length was decreased as the sand grain fineness number and coating thikness were decreased and the vacuum pressure was increased. A large amount of heat removal from the molten metal resulting from the vacuum suction during the vacuum molding process was the principal cause of this decrease in fluidity.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.09a
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• pp.239-242
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• 2002

Removal of phenanthrene by electrokinetic (EK) method combined with Fenton-like process was studied in a model system. Sand and phenanthrene were selected as a model soil and a representative PAH. Sand was contaminated at the concentration of 500 mg phenanthrene/kg dry sand. Bentonite and kaolinite were inserted into the space between reservoir and contaminated soil. When hydrogen peroxide supplied to a soil system from the anode reservoir was transported through the soil by EK process, the Fenton-like reaction was occurred by naturally existing iron minerals in soil. When hydrogen peroxide was supplied into the system, it showed higher removal efficiency than when just water was used. Maximum removal efficiency of phenanthrene was 81.2 % for 7 days.

• Journal of the Korean Ceramic Society
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• v.53 no.5
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• pp.541-547
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• 2016

In developing high temperature molds with advantages of the sand and precision (investment) castings, mechanical properties of the mold were improved through homogeneous coating of starting powders with an inorganic binder and improvement of fabrication process. Beads with mullite composition were employed for properties of the mold under high temperature, which was compared with artificial sands. Precursors of silica and sodium oxide were used as starting materials for an inorganic binder to achieve homogeneous coating on the starting powders. Strength was enhanced by the glass phase converted from the inorganic binder through heat treatment process. Also, two kinds of process, wet and dry processes, were incorporated to prepare mold specimens. Consequently, fabrication process of the mold with superior strength and high temperature applicability, compared with the previous molds for sand casting, could be suggested through control of the starting material and enhancement of the vitrification efficiency.

• Geomechanics and Engineering
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• v.13 no.1
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• pp.25-41
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• 2017

In recent years, the amount of sludge ash (SA) has considerably increased due to rapid urbanization and population growth. In addition, its storage in landfills induces environmental pollution and health problems. Therefore, its disposal in an environmentally friendly way has become more important. The main goal of this study is to investigate the reusability of sludge ash as an additive with polypropylene fiber (PF) to stabilize marginal sand based on the compressive strength performances from UCS tests. For this purpose, a series of UCS tests was conducted. Throughout the experimental study, the used inclusion rates were 10, 15, 20 and 30% for sludge ash and 0, 0.5 and 1% for polypropylene fiber by total dry weight of the sand+sludge ash mixture and the prepared samples were cured for 7 and 14 days prior to the testing. Freezing and thawing resistance of the mixture including 10% sludge ash and 0, 0.5 and 1% polypropylene fiber was also examined. On the basis of UCS testing results, it is said that sludge ash inclusion remarkably enhances UCS performance of sand. Moreover, the addition of polypropylene fiber to the admixtures including sand and sludge ash significantly improves their stress-strain characteristics and post-peak strength loss as well as UCS. As a result of this paper, it is suggested that sludge ash be successfully reused with polypropylene fiber for stabilizing sand in soil stabilization applications. It is also believed that the findings of this study will contribute to some environmental concerns such as the disposal problem of sludge ash, recycling, sustainability, environmental pollution, etc. as well as the cost of an engineering project.

• Advances in concrete construction
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• v.9 no.2
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• pp.207-215
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• 2020

This paper describes the experimental studies carried out to determine the properties of fresh and hardened concrete with Recycled Plastic Waste (RPW) as a partial replacement material for fine aggregates. In the experimental study, RPW was used for replacing river sand and manufactured sand (M sand) aggregates in concrete. The replacement level of fine aggregates was ranging from 5% to 20% by volume with an increment of 5%. M40 grade of concrete with water cement ratio of 0.40 was used in this study. Two different types of RPW were used, and they are (i) un-activated RPW and (ii) activated RPW. The activated RPW was obtained by alkali activation of un-activated RPW using NaOH solution. The hardened properties of the concrete determined were dry density, compressive strength, split tensile strength, flexural strength and ultrasonic pulse velocity (UPV). The properties of the concrete with river sand, M sand, activated RPW and un-activated RPW were compared and inferences were drawn. The effect of activation using NaOH solution was investigated using FT-IR study. The micro structural examination of hardened concrete was carried out using Scanning Electron Microscopy (SEM). The test results show that the strength of concrete with activated RPW was more than that of un-activated RPW. From the results, it is evident that it is feasible to use 5% un-activated RPW and 15% activated RPW as fine aggregates for making concrete without affecting the strength properties.

• Journal of the Korean Geotechnical Society
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• v.24 no.4
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• pp.67-78
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• 2008

In this study, artificial cemented sand made of a few portland cement and Nak-Dong river sand was researched closely to investigate cementing effect quantitatively through unconfined tests and triaxial tests. The peak strength and elastic modulus increased and dilation of cemented sand was restricted by the cementation, but after breakage of the cementation, dilation and negative excess pore water pressure increased. In stress-strain curve, strain-softening behavior appeared in drained condition but strain-hardening behavior was appeared in undrained condition as a result of the increase of effective stress. The test was quantitatively analyzed by multiple regression models, correlating each response variable with input variable. The equations are valid only over the range investigated. Its adjusted coefficient of determination was $0.81{\sim}0.91$, and dry density is important factor for estimating strength of cemented sand.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.8
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• pp.3719-3725
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• 2012

Due to the recent shortage of well-graded river sand resulting from a rapid growth of concrete construction, sea sand, crushed sand, and etc. are increasingly used instead. It is, however, well noted that non-washed sea sand leads to corrosion of the reinforcing steel in concrete, and thus eventually results in damage to concrete. Also, the crushed sand is not being widely used, since it is difficult to maintain the allowable amount of passing 0.08mm sieve and to adjust grading. On the other hand, because the fine sand of Nakdong-River has a poor grading but good quality as a fine aggregate for concrete, it is strongly needed to investigate the fine sand as an alternative fine aggregate. Thus, the purpose of this research is to evaluate the physical properties of the fine sand of Nakdong-River to utilize it actively as a fine aggregate. For this purpose, after the sand samples were collected according to typical location of main stream of Nakdong-River, the physical properties such as density in oven-dry condition, grading, unit volume mass, and etc. of them were estimated. It was observed from the test results that physical properties of the fine sand of Nakdong-River except grading were found to be excellent.