• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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• pp.249-255
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• 2006

Recently, interest grew on the quality of aggregates following the diminution of primary resources from river as to grow construction demand and the low grade of nature sand like sea sand. following, need is to diversify the supply sources of fine aggregates which are excessively relying on sea sand and urgency is to find as soon as possible aggregate resources that can substitute sea sand. On the other hand, various fine aggregates we utilized to produce concrete in the domestic construction fields. However, few studies have been systematically investigated on the effects of such fine aggregates on concrete properties. Therefore, this study examined the effects of comparatively widely used fine aggregates in the domestic construction fields on the shrinkage, durability and watertightness of concrete. Results revealed that drying shrinkage increases, and durability and watertightness degrades for concrete using crushed sand than natural fine aggregates like sea sand and river sand. Especially, the use of crushed sand exhibiting bad grain shape and grade was larger adverse effect on the quality of concrete. In addition, appropriate adjustment of the grain shape and grade during the blending of crushed sand exhibiting bad grain shape and grade with natural aggregates appeared to enhance the shrinkage and durability of concrete.

• ALGAE
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• v.37 no.4
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• pp.293-299
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• 2022

To examine the effects of substratum types on the growth of Caulerpa okamurae, sand surface and sand burial experiments were conducted. Five assimilators (erect fronds) per replicate were cultured for 15 d on the surface of three different treatments: fine sand (200 ㎛), coarse sand (600 ㎛), and no sand (control). Also, three stolons and three assimilators were buried by fine grain or coarse grain sands and incubated for 15 d. In both experiments, other culture conditions included 25℃, 30 μmol photons m^-2 s^-1, and 16 : 8 h L : D (light : dark). In both experiments, stolon + assimilator-, assimilator-, and stolon-weights were measured. Relative growth rates (RGRs) of stolon + assimilator weights ranged from 0.43 to 1.95% d^-1 at no sand and fine sand treatment, respectively. RGRs for the weight of stolon + assimilator and new assimilators were significantly greater on the fine- and coarse sand surface than the control. In the burial experiments, RGRs of stolons (4.28% d^-1 at coarse sand and 5.57% d^-1 at fine sand, respectively) were significantly greater than those of assimilators (1.38% d^-1 at fine sand and 1.82% d^-1 at coarse sand, respectively). When stolons were buried, RGRs for assimilators were greater at the fine sand than at the coarse sand treatment. On the other hand, RGRs of buried assimilators for total frond weights and for newly produced stolons were significantly greater at the coarse sands than at the fine sands. In conclusion, C. okamurae grew well with all substrates of sands and showed better growth on fine sands than coarse ones. This result suggests that the growth of stolons and assimilators of C. okamurae is stimulated after stable attachment to the sand substrates by rhizophores. In addition, stolons showed higher growth rates than the assimilators in the sand burial states, indicating that stolons are more tolerant to low light than assimilators of C. okamurae.

• Magazine of the Korea Concrete Institute
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• v.5 no.3
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• pp.107-115
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• 1993

최근 건설공사의 급증으로 인한 하천골재의 고갈로 콘크리트용 대체골재로서 해사\ulcorner선사 등이 대구되고 있다. 그러나 해사는 세척하지 않고 그대로 콘크리트에 사용할 경우 콘크리트중의 철근부식 촉진에 따른 콘크리트의 균열발생 등 조기 노후화현상으로 내구성에 많은 문제점을 내포하고 있고, 산사는 국내 연구실적이 전혀 없는 상태에서 지역적으로 무분별하게 사용되고 있어 이들에 관한 제반 공학적 특성 및 활영방안 연구가 시급한 실정이다. 따라서 본 연구는 산사\ulcorner해사를 사용한 콘크리트의 압축강도 특성 및 해사의 염분함량과 콘크리트의 물-시멘트비에 따른 철근부식량과의 관계를 구명하였다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.13 no.1
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• pp.1-5
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• 1977

A series of echo-sounding and current measurements as well as the drogue and the drift bottle experiments were carried out in Asan Bay since November 1974. Several sand bars or sand flats covered by silts were developed at ebb tide in the bay. Sand waves and sand ripples were seen on the surface of the sand bars, around which sea channels of 8~ 12 meters in depth are formed. The main stream axis of the flood current which is separated into east and west branch flows southward. A cyclonic and an anticyclonic eddy are developed at the early stage of flood tide. They are transformed into a clockwise eddy before the slack water. The maximum tidal current speed observed was 3.1 ~ 3.2 knots at the entrance of the bay, while it was 1.O ~ 2.8 knots in the bay. The location of the main stream axis of the tidal current coincides well with the sea channel. A salt wedge was observed at the estuary of the Sabgyo-cheon River.

• 한국해양학회지
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• v.29 no.3
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• pp.278-286
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• 1994

Tidal sand ridges, which develop in Kyeonggi Bay generally parallel to the direction of tidal current on the sea bottom are also well shown in seismic profiles, surface and core samples were obtained from sand ridge field near the Palmi Do for the study of origin and sedimentary environments of these sand ridges. Sand ridge field near Palmi Do can be divided into 3 seismic units(unit A, B, C), and each unit has one sand ridge(ridge A, B, C), Ridge A that shows clinoform prograding southeastwards is generally parallel with tidal current trending northeast to southwest(40$^{\circ}$). It means that sand ridge is migrating to southward. Unit B includes a sand ridge and a channel fill structure in seismic profiles. Compared with ridge A, ridge B has similar direction, magnitude and internal reflectors. So ridge B developed in the similar sedimentary environments to ridge A about 10 m lower than present sea level. As the rise of sea level, channel fill structure formed as the deposit of fine sediments with the shape of conformable bedding or horizontal bedding.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.12 no.3
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• pp.21-32
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• 2009

Coastal sand dune area is the important ecosystem as an ecotone which located between coastal area and terrestrial area. Moreover, it is very complicate landscape that have geomorphological interaction between erosion and accumulation of sand. Therefore, it is necessary to understand the sand dune ecosystem in view point of landscape scale including background landscape affecting origin of sand dune. Landscape ecological approach in the complicate ecosystem already started in developed countries, and it is applied to land management and biodiversity conservation strategies even in national scale. In this paper, landscape ecological analysis using landscape pattern analysis was carried out on 7 study areas (Yellow Sea : Hakampo and Doksan, South Sea : Namyeol and Balpo, East Sea : Hosan, Hupo and Goraebul) in Korean coastal sand dune ecosystem. Landscape elements were composed by 9 elements in these study areas. Major background landscape elements was the forest land and agricultural field. Namyeol (S06) has larger patch landscape compare to other areas. In patch shape indices, Hupo (E10) shows more complicate patch shapes. The high landscape heterogeneity showed in the Doksan sand dune area and that of Hosan. It shows that these areas were composed by various patch types. However, using landscape indices have to use very carefully because several variables have influence to the result such as scale and spatial pattern of study areas. Although landscape analysis through landscape indices shows sometimes difficult to explain the ecosystem, landscape scale approach on ecosystem assessment still useful to interpret in ecological process in large range of habitat.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.3 no.1
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• pp.27-32
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• 1970

A study on the purification of the surf clam Mactra Sulcataria REEVE for the remove of sand and fecal piles was conducted in the laboratory. The sand was mostly distributed around the inhalent and exhalent siphon, mantle and gill, and were also distributed in the digestive tract including the mid-gut gland. The sand particles in the digestive tract were extremely small and their sizes were about $180\times10\mu\;to\;550\times200\mu$. It could be seen that there was little, if any, difference in the rate of sand removal when either the hanging Purification method was used or the method of laying the surf clams in thick or thin layers on the bottom of the experimental vessel was used. The surf clam removed about $50\%$ of its sand during the first hour of purification. The weight of the removed sand and fecal piles on a dry basis reached a constant value after 22 to 26 hours of purification. After 42 hours of Purification, no sand could be seen in the fecal piles. The surf clam removed the sand in its body more rapidly when it was in sea water with the pH of 8.75 than when it was in natural sea water. Also high temperature had a much greater depressing effect upon the removal of sand In the surf clam than did natural sea water. Also low salinity had greater accelerating effect upon the removal of sand in the body than did natural sea water. However the surf clam died when the salinity was $8.19\%_{\circ}$.

• Journal of the Korea Concrete Institute
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• v.18 no.3 s.93
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• pp.415-423
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• 2006

As the shortage of natural & good quality aggregate for concrete, it is needed development of alternative aggregate. At the present time, the crushed sand is widely used among the alternation aggregate, and the usage of crushed sand will be increased more and more. Generally, crushed sud is produced with wet process in domestic, but some manufacturing companies which are handicapped with local restrict are produced by dry process. In this study, analyzing the facilities of dry crushed sand, the quality properties of dry crushed sand was done by Korean Industrial Standards. Based on the quality results of dry crushed sand, the experiment of concrete with the dry crushed sand which is substitute for sea sand was done. As the results of basic qualities, the amount of 0.08 mm sieve passing ratio was over KS criteria, and the fineness modulus was higher than sea sand, and the other physical properties of dry crushed sand was similar to sea sand. The results of concrete experiment, according to the substitutive ratio of dry crushed sand is increased, the slump and air content of concrete was decreased by increase of fine particles of dry crushed sand, and the unit weight content, compressive & tensile strength of concrete were increased on the contrary. The physical properties of concrete used dry crushed sand were showed same tendency without relation to W/B. Consequently, if the fine particle contents of dry crushed sand was lower, it is judged that dry crushed sand is no problem to use for concrete aggregate and the amount of usage will be increased.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.806-813
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• 2008

In this research, mainly research about the structural and functional stability of sea dyke with variation of seepage condition after final closure. The piezometric head (water head in embankment) monitoring system was installed at two representative final closure section. The dredged fine sand filling condition was evaluated by in-situ test results. Also, the numerical analysis was performed to determine the permeability of bottom protection layer filled with dredged fine sand by monitoring results. According to numerical back analysis results, the coefficient of permeability of bottom protection section of is $7.6{\times}10^{-6}$ m/sec. These results are noted that the bottom protection layer of sea dyke was strong and intensively filled with dredged sand. Also, based on the seepage analysis, the seepage flux of this sea dyke was calculated about $2.42m^3$/day/m which is 29% decreased value compare with adjacent sea dyke.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2003.10a
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• pp.175-178
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• 2003

There is a case to use dredged-sea sand as a filling material because of difficulty of obtaining required filling material for tideland reclamation project from the land. At this time, side slope erosion is occurred because the precipitation falling to the top of bank acts as infiltration water when it pass through inside of the semi-permeable filling section. This study has confirmed the declining effect of permeability by conducting permeability test to the condition of mixing of bentonite to the dredged sea-sand. And also this study has confirmed that the above processed-soil could be used as a water-proof layer to protect infiltration of water through the infiltration flow analysis.