• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.223-230
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• 2002

The main intent of this research was to determine the feasibility of utilizing recycling bottom ash as CLSM (controlled low-strength material). CLSM is a cementitious material, commonly a blend of portland cement, fly ash, sand, and water, that is usually flowable and self-leveling at the time of placement. The durability characteristics of mixtures made bottom ash we compared with those of fly ash CLSM in order to evaluate the effectiveness and suitability of bottom ash as material in CLSM. A comprehensive evaluation of the bottom ash in CLSM and mix proportions indicated that the bottom ash are capable of performing as CLSM mixtures. The durability characteristic of CLSM incorporating the bottom ash under various physical and chemical causes of deterioration were investigated. Test results indicated that CLSM using bottom ash has acceptable durability performance. CLSM incorporating with bottom ash were also found to be environmentally safe.

• Journal of Navigation and Port Research
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• v.36 no.9
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• pp.741-751
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• 2012

This article analyzes the interdependency between nonrenewable marine sand resources and renewable fishery resources by the developed dynamic bioeconomic model. The developed bioeconomic model is applied to a case study of efficient sustainable management for marine sand mining, which adversely affects a valuable blue crab fishery and its habitat in Korea. The socially-efficient extraction plan for marine sand and the time-variant environmental external costs to society in terms of diminished harvest rate of blue crab are determined. To take into account long-term effects from destroyed fishery habitat, a Beverton-Holt age structure model is integrated into the bioeconomic model. The illustrative results reveal that the efficient sand extraction plan is dynamically constrained by the stock size of the blue crab fishery over time. Thus, the dynamic environmental external cost is more realistic resource policy option than the classical fixed external cost for determining socially optimal extraction plans. Additionally, the economic value of bottom habitat, which supports the on- and off-site commercial blue crab fishery is estimated. The empirical results are interpreted with emphasis on guidelines for management policy for marine sand mining.

• Journal of environmental and Sanitary engineering
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• v.14 no.3
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• pp.71-79
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• 1999

The Hg, Cd, Cu, Mn, and Zn in bottom sediments of han river and their tributaries were analyzed to evaluate the seasonal variations of heavy metals. Leaching tests were also performed for estimation of availability of heavy metal retention in sediments. Sediments of Anyang stream showed the highest concentration of heavy metal in the sediment samples. Heavy metal concentration was heavily depended upon the heavy metal source of tributaries of han river and particle distribution. Clay and silt had higher concentration of heavy metals than very fine san and fine sand due to difference of retention capability of heavy metal. The highest concentration of heavy metal was observed in bottom sediments irrespective of sites investigated. Heavy metals and ignition loss showed positive relations, and higher relationships with p-value <0.01 were observed between copper and lead. copper and zinc, and depended on the pH condition of leaching test, and leachated fraction increased with decrease of the pH.

• Geomechanics and Engineering
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• v.37 no.5
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• pp.431-441
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• 2024

A newly developed line-style sand pluviator has been calibrated to prepare repeatable sand specimens of specific statuses of compactness and homogeneity for laboratory tests. Sand is falling via a bottom slot of a fixed hopper, and by moving the sample container under the slot, the container is evenly filled with sand. The pluviator is designed with high flexibility: The falling height of sand, the hopper's opening width and the relative moving speed between the hopper and the sample box can be easily adjusted. By changing these control factors, sand specimens of a wide range of densities can be prepared. A series of specimen preparation was performed using the coarse Merwede River sand. Performance of the pluviator was systematically evaluated by exploring the alteration of achievable density, as well as checking the homogeneity and fabric of the prepared samples by CT scanning. It was found that the density of prepared coarse sand samples has monotonic correlations with none of the three control factors. Furthermore, CT scanning results suggested that the prepared samples exhibited excellent homogeneity in the horizontal direction but periodical alteration of density in the vertical direction. Based on these calibration test results, a preliminary hypothesis is proposed to describe the general working principles of this type of pluviators a priori, illustrating the mechanisms dominating the non-monotonic correlations between control factors and the relative density as well as the vertically prevalent heterogeneity of specimens. Accordingly, practical recommendations are made in a unified framework in order to lessen the load of similar calibration work.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.294-300
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• 2001

The effectiveness of bottom ash on the mechanical and physical properties of Controlled Low-Strength Material(CLSM) is investigated in this study, CLSM is defined by the ACI Committee 229 as a cementitious material that is in a flowable state at the time of placement and having a specified compressive strength of 83 kgf/$\textrm{cm}^2$ or less at the age of 28 days. This study was undertaken on the use of bottom ash as a fine aggregate in CLSM. Four different levels of bottom ash with fly ash contents, 25%, 50 %, 75%, 100%, are investigated. Laboratory test results conclude that inclusion of bottom ash increases the demand for mixing water in obtaining the required flow. However, the sand was reduced because it was adjusted to maintain a constant total volume. Miかe proportions were developed for producing CLSM at three 28-day strength levels: removal with tools (less than 7 kgf/$\textrm{cm}^2$), mechanical means (less than 20 kgf/$\textrm{cm}^2$), and power equipment (less than 83 kgf/cm\`). The physical and mechanical properties supports the concept that by-product bottom ash can be successfully used in CLSM.

• Earthquakes and Structures
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• v.26 no.1
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• pp.77-86
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• 2024

To investigate the seismic performance of steel pipe-aeolian sand recycled concrete columns, this study designed and produced five specimens. Low-cycle repeated load tests were conducted while maintaining a constant axial compression ratio. The experiment aimed to examine the impact of different aeolian sand replacement rates on the seismic performance of these columns. The test results revealed that the mechanical failure modes of the steel pipe-recycled concrete column and the steel pipe-aeolian sand recycled concrete column were similar. Plastic hinges formed and developed at the column foot, and severe local buckling occurred at the bottom of the steel pipe. Interestingly, the bulging height of the damaged steel pipe was reduced for the specimen mixed with an appropriate amount of wind-deposited sand under the same lateral displacement. The hysteresis curves of all five specimens tested were relatively full, with no significant pinching phenomenon observed. Moreover, compared to steel tube-recycled concrete columns, the steel tube-aeolian sand recycled concrete columns exhibited improved seismic energy dissipation capacity and ductility. However, it was noted that as the aeolian sand replacement rate increased, the bearing capacity of the specimen increased first and then decreased. The seismic performance of the specimen was relatively optimal when the aeolian sand replacement rate was 30%. Upon analysis and comparison, the damage analysis model based on stiffness and energy consumption showed good agreement with the test results and proved suitable for evaluating the damage degree of steel pipe-wind-sand recycled concrete structures.

• 한국해양학회지
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• v.26 no.4
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• pp.340-349
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• 1991

From tidal current measurements on a tidal sand ridge in the Gyeonggi Bay from August 24 to September 29, 1987, tidal current velocities at 1.0 m above bottom (U/SUB 100/) and boundary shear velocities (U/SUB */) are calculated. The mean speeds of tidal current for flood and ebb over the entire period are 56.3 cm/sec and 63.7 cm/sec in mid-depth (9.0 m above bottom), and 43.9 cm/sec and 43.8 cm/sec in near-bottom (1.5 m above bottom). The exponent(P) in "power law", which is generally used for extrapolation from the mid-depth current velocity to that at the top of nationally logarithmic layer, is estimated to be 0.15 in the study area. Using logarithmic velocity profile assumption, mean values of U/SUB 100/ and U/SUB */ are calculated to be 41.4 cm/sec and 2.39 cm/sec, respectively. The mean value of U/SUB */ (2.39 cm/sec) is much higher than the critical shear velicity (U/SUB *c/) of 1.40 cm/sec reported by Choi (1990). and thus, it can be suggested that the most of sands on the tidal sand ridge in the study area are easily eroded and transported for the greater part of tidal period.

• Journal of Environmental Science International
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• v.1 no.1
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• pp.77-88
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• 1992

Distribution patterns of the chemical species, contained or dissolved in the sediments and porewater, were studied from the submarine environments around Deok-Jeok Island, Yellow Sea. The sediments in the study area are predominantly composed of medium to coarse sands, and consequently of very low organic carbon (0.003%) -0.26%o dry weight sediments). As opposed to the strong enrichment of porewater with nutrients and heavy metals in the ordinarily muddy, organic-rich sediillents, the porewater enrichment is not intense in this sandy, organic-poor sediments: porewater phosphate is enriched to the maximum of only seven (average two) times over that in the bottom water. Concentrations of the heavy metals dissolved in porewater show a bit greater enrichment than the nutrient: Zn shows the lowest enrichment (7 times that of the bottom water) and Mn the highest (450 times that of the bottom water). However, these enrichments of the chemical species in porewater are the natural consequences of decomposition of the organic matter in sediments, and still fall short in the magnitude of those in the muddy, organic-rich sediments. Mining of the sands in the study area may pose a threat to the seawater quality as it causes a large scale porewater discharge to the bottom water. The additional supply of the nutrients by this discharge may develop an eutrophic state and, in consequence, an excessive nitrification of the water column. Since the residence times of the nutrients are much longer than those of the heavy metals, a long-term monitoring of the concentration changes in the porewater nutrients is very important to assess the potential deterioration of the seawater associated with the sand mining in the study area.

• Journal of The Geomorphological Association of Korea
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• v.26 no.3
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• pp.31-42
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• 2019

The geomorphological changes of an unvegetated part of the Okjukdong coastal dune were analyzed between 2008 and 2018. Its natural landscape has been destroyed after artificial forestation, but there is no quantitative evidence on these changes. In this study, we measured the unvegetated area using a total station and a network RTK-GPS in 2008, 2014, and 2018. Using Krging method for the three point data sets, we constructed digital elevation models (DEMs) and analyzed topographic changes between the three years. The results showed that the sand of the study area decreased in volume from 2008 to 2014, because sand supply from the nearby beach was blocked by coastal forests. The sand volume temporarily increased from 2014 to 2018, because of the dune nourishment conducted in 2017. It seems that the upper part of the sand dune has shrunk, but the sand at the bottom has increased over the last decade.

• 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.