• Magazine of the Korean Society of Agricultural Engineers
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• v.40 no.4
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• pp.103-108
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• 1998

This study examines the physical and mechanical properties of the concrete using rice straw ash. Materials used for this experiment are rice straw ash, normal portland cement, superplasticizer, natural sand and gravel. Test results show that the unit weights of concrete using rice straw ash were decreased 1 ∼ 3% and the highest strengths were achieved by 5% filled rice straw ash concrete, with increase of compressive strength by 19%, tensile strength by 53% and bending strength by 16%, as compared with those of the normal cement concrete. The strength ratio of rice straw ash concrete was higher than that of the normal cement concrete. Also, the durability against sulfuric acid 5% solution was increased with increase of the content of rice straw ash. It was 1.33 times of the normal cement concrete by 10% filled rice straw ash concrete and 1.47 times by 15% filled rice straw ash concrete, respectively Accordingly, rice straw ash concrete will greatly improve the properties of concrete.

• Magazine of the Korean Society of Agricultural Engineers
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• v.42 no.1
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• pp.92-98
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• 2000

This study is performed to evaluate the elastic properties of rice straw ash concrete using reices straw ash, cement, natural sand, gravel, and superplasticizer. The following conclusions are drawn ; The ultrasonic pulse velicity is in the range of 4,084 ~4,336m/s , which has showed about the same compared to that of the normla cement concrete. The highest ultrasonic pulse velocity is showed by 5 % rice straw ash filled rice straw ash concrete. The dynamic and static modulus of elasticity is in the range of 294 $\times$10$^3$ ~347 $\times$ 10$^3$ and 266 $\times$10$^3$~328 $\times$10$^3$kgf/㎤ , respectively. It is showed about the same compared to that of the normal cement concrete. The Poisson's number of rice straw ash concrete is less than that of the normal cement concrete.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.818-823
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• 2006

In this study, the suitability of CFGD(concrete faced gravefill dam) was investigated by examining the strength and deformation characteristics of a gravelfill material, a CFGD main fill material, and comparing them with those of several rockfill dam materials. The gravelfill material exhibited similar strength and deformation properties to those of the main fill materials of existing stable large rockfill dams. Since not only CFGD has environmental and economic advantages over CFRD, but its main fill material compares favorably with those of the existing stable CFRDs, CFGD may be the best choice when natural gravel materials are abundant in the vicinity of the dam construction location.

• Economic and Environmental Geology
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• v.54 no.5
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• pp.515-533
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• 2021

Based on the supply location, demand location, and transportation network, aggregate supply-demand characteristics and aggregate distribution status were analyzed from the results of the closest distance, service areas, and location-allocation scenarios using GIS network analysis. As a result, it was found that the average transport distance of aggregates from the supplier was 6 km on average, the average range of 7 km for sand, and 10 km for gravel was found to reach the destination. In particular, the simulated service area covers about 92% in Seoul-Gyeonggi Province, 85% in Busan-Ulsan-Gyeongnam Province, and more than 90% in Daejeon-Sejong-Chungnam Province. These results have a significant implication in quantitatively interpreting primary data on aggregate supply-demand. Furthermore, these results suggest the possibility of a wide-area quantitative analysis of aggregate supply regions necessary for establishing a basic aggregate plan. The results also evaluated by the site-allocation scenario show that aggregate supply may be possible through companies less than 200 with large-amounts quarries, which is the 700 companies currently supplying small amounts of aggregates on the country. Therefore, in terms of distribution of aggregates, a policy approach is needed to form an appropriate market for regions with high and low density of aggregate supply services, and the necessity of regional distribution and re-evaluation is suggested through an aggregate supply analysis demand across the country. Furthermore, in analyzing the supply-demand network for the aggregate market, additional research is needed to establish long-term policies for the aggregate industry and related industries.

• Korean Journal of Ichthyology
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• v.21 no.4
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• pp.253-261
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• 2009

Habitat environment and feeding habitat of Iksookimia koreensis and Cobitis lutheri were investigated in the Mangyeong River, Jeollabuk-do, Korea from 2005 to 2006. They together inhabit the upper and middle stream, but they showed differences in their microhabitat. I. koreensis inhabited the stony zones of relatively rapid waters with a water depth of 30~60 cm, whereas C. lutheri lived in the sandy zones of relatively slow waters with a depth of 30~100 cm. The two species were active during daylight hours from March to October but hibernated in the winter season. During hibernation I. koreensis still lived in the gravel and stone and C. lutheri burrowed in the sand. I. koreensis ingested mainly chironomid and other aquatic insects, whereas C. lutheri fed mainly on Chironomidae, Copepoda and Branchiopoda. The feeding rate of both species was highest in April and September, but they did not feed in the winter.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.10
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• pp.530-537
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• 2017

Scales generated inside pipes cause negative effects on heat transfer performance, pressure loss and flow rate due to increased thermal resistance and reduced flow cross-sectional area. If these scales are not prevented or eliminated, thermal-fluid performance of the facilities can be deteriorated, or in extreme cases, accidents such as explosion due to overheating can occur. There are two ways to remove the scales, physically and chemically. Removing the scales physically needs specific machines which are expensive, and removing them chemically may provoke corrosion or shorten the age of the facilities. In this study, an eco-friendly pipe scale cleaner using natural organic acid is developed by applying the concept of a limestone cave generation. The manufactured scale cleaner is applied to remove the scales in industrial, water heating and urinal pipes. The results show that this cleaner removes scales more effectively and safely compared to existing scale treatments. Scale removal efficiencies of this work is 1.2~10.7 times for industrial pipes and 1.8~15.5 times for boiler water heating pipes higher than those of conventional cleaners.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.613-617
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• 2006

Bed material in natural streams is affected by geological characteristics of upstream and acting focre by flow of stream. Acting force in streams are also affected by bed slope and discharge of streams. Yamamoto(1994) suggested that channel reaches with similar slope share similar characteristics values in representative bed material size, tractive force, channel width and depth. He also suggested that main factors dominating channel characteristics are mean annual discharge, epresentative bed material size and bed slope. Bed material shows physical and ecological characteristics of channels. In this research, characteristics of bed material in natural or close to natural streams were studied and compared with Janpanese stream data. In the result, characteristics of gravel and sand material can be presented in the term of non-dimensional tractive force, bed slope and bed material size.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.1661-1665
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• 2006

In a natural river, cross sections of a channel vary according to inner or outer parts of meandering. Generally, depth of outer parts is deeper than that of inner parts. This kind of cross section change by meandering can be demonstrated by Beta distribution. The objects of this research is a 3D simulation of primary and secondary flow in the meandering natural channel. FLOW-3D program, a numerical model using CFD technique, and LES method was used for this research. 3D simulations were conducted in the channels having Beta distribution cross sections which have beds of mortar, gravel and vegetation. Two types of water stages and discharge were applied to each channel. In this research, primary flows are located in the outer parts of a top of bend and secondary flows rotate in the bottom on outer parts.

• Korean Journal of Ichthyology
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• v.4 no.2
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• pp.63-71
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• 1992

The Ichthyofauna was investigated at the seven sites in Paikchon streams from August 1990 to March 1991. The collected fishes were classified to 22 species belong to 19 genera and 11 families, of which 5 species were tentatively identified as endemic species in Korea. Three species, Odontobutis obscurus interrupta, Luciogobius guttatus and Mactopodus chinensis, are collected for the first time in this area. Dominant species were Squalidus gracilis majimae(40.8%), Zacco temmincki(24.2%), Z. platypus(13.3%) and Cobitis koreensis pumilus(7.7%). Stomach contents of S. gracilis majimae were mainly taxa belong to Bacillariophyceae of micro-algee attached to sand or gravel.

• Geomechanics and Engineering
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• v.12 no.3
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• pp.399-415
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• 2017

A series of direct shear tests were conducted to investigate the frictional properties of the interface between structures and the filling soil of Chongqing airport fourth stage expansion project. Two types of structures are investigated, one is low carbon steel and the other is the bedrock sampled from the site. The influence of soil water content, surface roughness and material types of structure were analyzed. The tests show that the interface friction and shear displacement curve has no softening stage and the curve shape is close to the Clough-Duncan hyperbola, while the soil is mainly shear contraction during testing. The interface frictional resistance and normal stress curve meets the Mohr-Coulomb criterion and the derived friction angle and frictional resistance of interface increase as surface roughness increases but is always lower than the internal friction angle and shear strength of soil respectively. When surface roughness is much larger than soil grain size, soil-structure interface is nearly shear surface in soil. In addition to the geometry of structural surface, the material types of structure also affects the performance of soil-structure interface. The wet interface frictional resistance will become lower than the natural one under specific conditions.