• Journal of The Geomorphological Association of Korea
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• v.27 no.4
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• pp.1-11
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• 2020

Coastal dunes play an important role in coastal defense. The Moraeul dune in Daecheongdo Island is representative in this regard. However, there is little knowledge, concerning the morphology, grain size, and formation timing of the dune. This study investigated the geomorphological characteristics of the Moraeul dune using topographic surveys, grain size analyses, and OSL dating. The dune was classified as 'single accreted foredune', which was developed under dense vegetation cover and efficient sand trapping. The dune consisted of fine to medium sand with 1.6Φ of mean grain size, and was covered with pine trees (> 100 years old). The samples from the upper part of the dune yielded quartz OSL ages ranging 0.5 ~ 0.7 ka. Therefore, it is likely that the dune developed at least before the Little Ice Age and became what it is today about one century ago.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.35 no.1
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• pp.1-7
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• 1986

The GaAs bulk single crystals are grown by the Horizontal Bridgman method. During the growth, one of the problems in Bridgman method is the boat wetting between GaAs molten and silica boat. This boat wetting may result in another nucleation to form twin crystals. In this study, We find that the optimal size for sand blasting is 320 mesh. Backfilling the ampoule with argon gas during the vaccum bake-out decreaes the boat wetting. The reaction mechanism of Ga with quartz to produce suboxide, Ga2O, and sillion is discussed.

• Economic and Environmental Geology
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• v.15 no.3
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• pp.113-122
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• 1982

The surveyed Boseong river, flows from south to north crossing Boseong gun Mirukg myon, Nodong myon, Yuleo myon, Bocgnae myon, Mundeog myon, and Seungju gun Nam myon, Jeonranam do. The geology of the surveyed area consists of age-unknown composite gneiss and schist, crystaline chlorite gneiss, porphyroblastic gneiss and granite gneiss, and metasediments of Myon Bong formation and Seologri formation. These metamorphic rocks are intruded by cretaceous biotite granite, granodiorite, and quartz diorite. The heavy sands occur in Quarternary alluvium and colluvium. The composition of the river bed is sand 60%, gravel 30%, and clay 10%. The gravel content of the river bed decreases as the increases. The average depth of auger boring is 0.87 m. The average heavy mineral composition of the heavy sand is monazite 6.83%, zircon 4.88%, ilmenite 11.36%, magnetite 8.36% and garnet 4.84%. The best heavy minerals separation procedure would be primary treatment of the sand by humphrey spiral and table, and retreatment of the table concentrate by magnetic separator. The minimum economically feasible capacity of gravity and magnetic separation plant would be 500 ton/hr when only the heavy minerals are recovered but it may be reduced to 100 ton/hr. capacity, if gravels and sands are added to the valuable products.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.16 no.4
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• pp.169-179
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• 2011

To investigate the controlling factor and accumulation of trace metal concentrations in Chun-su Bay sediments, grain-size, specific surface area, organic carbon content, calcium carbonate content, and concentration of Al, Fe, Na, K, Mg, Ca, Ti, Mn, P, S, Ba, Sr, Li, Co, Cr, Ni, Cu, Zn, As, Cd, Cs, Sc, V, Sn were analyzed. Controlling factors of metals were quartz-dilution, calcium carbonate and coarse sand or K-feldspar. Although the distribution of V, Co, Cr, Ni, Cu, Zn, Sn, and Cd concentration was explained by grain-size effiect, Mn and As showed the similar importance of grain-size effect and coarse sand or K-feldspar factors. By virtue of enrichment factor and 1 M HCl experiment, there were little enrichment in all the trace metals in bay sediments, which were explained well by geochemical properties of sediments. Since the concentration levels of As in coarse sand were high as much as those in fine-grained sediments and it was combined with Mn oxide (1 M HCl leached) and K-feldspar (residual), it was suggested that when the enrichment of As in sediments would be assessed, it is necessary to separate the coarse sand from bulk sediments or to use only sediments with higher than 10% in < $16{\mu}m$ fraction.

• Advances in concrete construction
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• v.9 no.4
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• pp.387-395
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• 2020

This study has been carried out in two-phases to develop Fiber Reinforced Self-Compacting Concrete (FRSCC) performance. In the first phase, the composition of the quaternary composite binder compromised CEM I 42.5N (58-70%), Rice Husk Ash (25-37%), quartz sand (2.5-7.5%) and limestone crushing waste (2.5-7.5%) were optimized. And in the second phase, the effect of two fiber types (steel brass-plated and basalt) was investigated on the SCC optimized with the optimum CB as disperse reinforcement at 6 different ratios of 1, 1.2, 1.4, 1.6, 1.8, and 2.0% by weight of mix for each type. In this study, the theoretical principles of the synthesis of self-compacting dispersion-reinforced concrete have been developed which consists of optimizing structure-formation processes through the use of a mineral modifier, together with ground crushed cement in a vario-planetary mill to a specific surface area of 550 m2 / kg. The amorphous silica in the modifier composition intensifies the binding of calcium hydroxide formed during the hydration of C3S, helps reduce the basicity of the cement-composite, while reducing the growth of portlandite crystals. Limestone particles contribute to the formation of calcium hydrocarbonate and, together with fine ground quartz sand; act as microfiller, clogging the pores of the cement. Furthermore, the results revealed that the effect of fiber addition improves the mechanical properties of FRSCC. It was found that the steel fiber performed better than basalt fiber on tensile strength and modulus of elasticity; however, both fibers have the same performance on the first crack strength and sample destruction of FRSCC. It also illustrates that there will be an optimum percentage of fiber addition.

• Geomechanics and Engineering
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• v.36 no.1
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• pp.51-69
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• 2024

Currently, composite lining mountain tunnels in China are generally classified based on the [BQ] method for the surrounding rock grade. Increasingly, tunnel field construction is replicated indoors for scale down model tests. However, the development of analogous materials for model tests of composite lining tunnels with different surrounding rock grades is still unclear. In this study, typical Class III and V surrounding rock analogous materials and corresponding composite lining support materials were developed. The whole processes of excavation-support dynamics of the mountain tunnels were simulated. Data on the variation of deformations, contact pressures and strains on the surrounding rock were obtained. Finally, a comparative analysis between model tests and numerical simulations was performed to verify the rationality of analogous material development. The following useful conclusions were obtained by analyzing the data from the tests. The main analogous materials of Class III surrounding rock are barite powder, high-strength gypsum and quartz sand with fly ash, quartz sand, anhydrous ethanol and rosin for Class V surrounding rock. Analogous materials for rockbolts, steel arches are replaced by aluminum bar and iron bar respectively with both shotcrete and secondary lining corresponding to gypsum and water. In addition, load release rate of Class V surrounding rock should be less than Class III surrounding rock. The fenestration level had large influence on the load sharing ratio of the secondary lining, with a difference of more than 30%, while the influence of the support time was smaller. The Sharing ratios of secondary lining in Class III surrounding rock do not exceed 12%, while those of Class V surrounding rock exceed 40%. The overall difference between the results of model tests and numerical simulations is small, which verifies the feasibility of similar material development in this study.

• Journal of Environmental Science International
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• v.23 no.6
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• pp.1165-1173
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• 2014

For the field application of dielectric barrier discharge plasma reactor in nutrient solution culture, a filtration-DBD (dielectric barrier discharge) plasma reactor was investigated for the Ralstonia solanacearum which causes bacterial wilt in aquiculture. The filtration-DBD plasma reactor system of this study was consisted of filter, plasma reactor, reservoir. The DBD plasma reactor consisted of a quartz dielectric tube, discharge electrode (inner) and ground electrode (outer). The experimental results showed that the inactivation of R. solanacearum with filter media type in filter reactor ranked in the following order: anthracite > fiber ball > sand > ceramic ball > quartz ceramic. In filtration + plasma process, disinfection effect with the voltage was found to small. In disinfection time of 120 minutes, residual R. solanacearum concentration was 1.17 log (15 CFU/mL). When the continuous disinfection time was 120 minute, disinfection effect was thought to keep the four days. In sporadic operation mode of 30 minutes disinfection - 24 hours break, residual R. solanacearum concentration after five days was 0.3 log (2 CFU/mL). It is considered that most of R. solanacearum has been inactivated substantially.

• Structural Engineering and Mechanics
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• v.77 no.1
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• pp.103-114
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• 2021

Ultra high strength concrete (UHSC) originally proposed by Richards and Cheyrezy (1995) composed of cement, silica fume, quartz sand, quartz powder, steel fibers, superplasticizer etc. Later, other ingredients such as fly ash, GGBS, metakaoline, copper slag, fine aggregate of different sizes have been added to original UHSC. In the present investigation, the combined effect of coarse aggregate (6mm - 10mm) and steel fibers (0.50%, 1.0% and 1.5%) has been studied on UHSC mixes to evaluate mechanical and fracture properties. Compressive strength, split tensile strength and modulus of elasticity were determined for the three UHSC mixes. Size dependent fracture energy was evaluated by using RILEM work of fracture and size independent fracture energy was evaluated by using (i) RILEM work of fracture with tail correction to load - deflection plot (ii) boundary effect method. The constitutive relationship between the residual stress carrying capacity (σ) and the corresponding crack opening (w) has been constructed in an inverse manner based on the concept of a non-linear hinge from the load-crack mouth opening plots of notched three-point bend beams. It was found that (i) the size independent fracture energy obtained by using above two approaches yielded similar value and (ii) tensile stress increases with the increase of % of fibers. These two fracture properties will be very much useful for the analysis of cracked concrete structural components.

• Environmental Engineering Research
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• v.15 no.3
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• pp.149-156
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• 2010

The objective of this study was to investigate microbial removal using layered double hydroxides (LDHs) and iron (hydr)oxides (IHs) immobilized onto granular media. Column experiments were performed using calcium alginate beads (CA beads), LDHs entrapped in CA beads (LDH beads), quartz sand (QS), iron hydroxide-coated sand (IHCS) and hematite-coated sand (HCS). Microbial breakthrough curves were obtained by monitoring the effluent, with the percentage of microbial removal and collector efficiency then quantified from these curves. The results showed that the LDH beads were ineffective for the removal of the negatively-charged microbes (27.7% at 1 mM solution), even though the positively-charged LDHs were contained on the beads. The above could be related to the immobilization method, where LDH powders were immobilized inside CA beads with nano-sized pores (about 10 nm); therefore, micro-sized microbes (E. coli = 1.21 ${\mu}m$) could not diffuse through the pores to come into contact with the LDHs in the beads, but adhere only to the exterior surface of the beads via polymeric interaction. IHCS was the most effective in the microbial removal (86.0% at 1 mM solution), which could be attributed to the iron hydroxide coated onto the exterior surface of QS had a positive surface charge and, therefore, effectively attracted the negatively-charged microbes via electrostatic interactions. Meanwhile, HCS was far less effective (35.6% at 1 mM solution) than IHCS because the hematite coated onto the external surface of QS is a crystallized iron oxide with a negative surface charge. This study has helped to improve our knowledge on the potential application of functional granular media for microbial removal.

• Journal of Conservation Science
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• v.32 no.1
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• pp.75-88
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• 2016

In this study, 5 mural paintings in the Buddhist temples of Joseon era were researched for component analysis on the soil contained in the walls. The results of particle size analysis showed that the ratio of particle contents were different in each layer. In the finishing layer, the distribution of the middle sand fraction is higher than that of the middle layer. The results of XRD analysis showed that quartz, feldspar, and clay mineral are the main components of sand, suggesting similar mineral composition to that of ordinary soil component. It seems weathered rocks were used for construction of the walls. The main chemical components detected from EDX analysis were Si, Al, Fe, and K. Also the SEM images showed sand or clay sized minerals. In conclusion, the walls of the buddhist mural paintings in Joseon Dynasty had been constructed by using the loess, and had been produced by using mixture of clay and sand particles of different sizes for each layer. This study identified the characteristics of the materials and the manufacturing technologies used on the walls of mural paintings of Buddhist temples in Joseon era.