• Journal of the Korea Concrete Institute
• /
• v.22 no.2
• /
• pp.199-208
• /
• 2010

In order to substitute FRP bar for steel bar in new structures, it is necessary to establish a reliable design code. But relatively little research has been conducted on the material in Korea. So, a total of 22 beam specimens (18 GFRP reinforced concrete and 4 conventional steel reinforced concrete) were constructed and tested. In the first phase of the experiment, it was carried out to observe flexural behavior, and collect deflection and crack data. In order to eliminate of the uncertainty by the shear reinforcements and induce flexural failure mode, any stirrup were not used and only shear span-depth ratio were adjusted. However, almost beams were broken by shear and the ACI 440.1R, CSA S806, which were used to design test beams, showed considerable deviation between prediction and test results of shear strengths. Therefore in the second phase of the study, shear failure modes and behavior were observed. A standard specimen had dimensions of 3,300 mm long ${\times}$ 800 mm wide ${\times}$ 200 mm effective depth. Clear span and shear span were 2,800 mm, 1,200 mm respectively. Control shear span-depth ratio was 6.0. Four-point bending test over simple support was conducted. Variables of the specimens were concrete compressive strength, type and elastic modulus of reinforcement, shear span-depth ratio, effective reinforcement ratio, the effect of bundle placing method and cover thickness.

• Journal of the Korea Concrete Institute
• /
• v.29 no.1
• /
• pp.3-10
• /
• 2017

In case of Korea highways, about 60% of highways are paved by concrete and more than 50% of them were repaired due to reduction in required performance such as damage in pave or joint and delamination of cover pavement. However, repairing old material in such structure generally costs a lot of money and induces difficulty in maintenance. Thus, enhanced material for ensuring economic efficiency should be developed. The present study designed concrete mixtures with 3 levels of replacement using OPC (0, 10, 20%) in calcium aluminate cement and to evaluate material performance for load pavement, experimental works for setting time, compressive strength and flexural strength were carried out on those materials. As a result, 20% replacement for OPC was determined as an optimized material in terms of required physical performance and its unit price. Moreover, to determine cost in load pavement economy analysis using a program (CA4PRS) was conducted with widely used paving materials. Result showed that application for 20% replacement for OPC was the most efficient in economical aspect, arising from 4.052 and 1.577 billion won for total construction and user cost, respectively.

• Korean Journal of Environment and Ecology
• /
• v.31 no.2
• /
• pp.188-201
• /
• 2017

Based on a total of 272 vegetation data collected by the ZM school phytosociological study method, the composition and structural characteristics of the forest vegetation in the Sogwang-ri forest genetic resource reservoir located in Uljin-gun, Gyeongsangbuk-do were compared using the table comparison method and the TWINSPAN method, And their ecological characteristics were analyzed. The types of forest vegetation were classified into 7 types, and it was divided into two major groups, 'Slope and Ridge type', which characterized by Quercus mongolica, Pinus densiflora for. erecta, Lespedeza bicolor etc. and 'valley and concave slope', which characterized by Cornus controversa, Fraxinus mandshurica, Morus bombycis, Hydrangea serrata for. acuminata etc. The hierarchy of the vegetation unit was 2 community groups, 4 communities, and 6 subcommunities. The structural characteristics such as the total percent cover, species importance value, species diversity of the constituent species per unit area($/100m^2$) of each type of forest vegetation were also identified. In order to understand the spatial distribution of forest vegetation, 1/5,000 large-scale physiognomic vegetation map was created by the uppermost dominant species. The composition and structural characteristics of Geumgang pine(P. densiflora for. erecta) forest, which is a core community of protected area by natural and anthropogenic influences, appear as a subtype of Quercus mongolica forest, which is a potential natural vegetation, Appropriate maintenance measures seemed urgently needed.

• Korean Journal of Agricultural Science
• /
• v.41 no.3
• /
• pp.163-167
• /
• 2014

The average temperatures for year and winter season have been risen by $0.7{\circ}C$ and $1.4{\circ}C$, respectively, during the last 30 years. Recently abnormal climate phenomena occurred frequently results in severe loss of vegetable crops grown in Korea. Specially, Chinese cabbages grown in the southern area of Korea are often significantly affected by sudden cold waves during winter season before harvest. This experiment was conducted to find out a potential role of covering materials on the protection of frost damage of 'Bularm' chinese cabbage in the winter season. The lowest temperature was $-15.8^{\circ}C$ in non-covering, $-8.1^{\circ}C$ in the PE film covering and $-4.6^{\circ}C$ in the non-woven fabric covering with PE film, respectively. The cumulative times below $4.0^{\circ}C$ were 145.5 hours for the non-covering treatment, 94 hours in the PE film covering and 14.5 hours in the non-woven fabric covering with PE film, respectively. The symptoms of frost damage were severe at non-covering chinese cabbages compared to polyethylene film (PE) non-woven fabric with PE covering ones. Microscopic studies showed the normal anatomical structure of palisade and spongy tissue of cabbage leaves covered with non-woven fabric with PE film. Leaf cells, however, were slightly damaged in cabbages covered with PE film alone, and both palisade and spongy cells were were completely collapsed in uncovered cabbages. The result of this study suggests that chinese cabbages is required to be covered with non-woven fabric with PE film to minimize the frost damage by sudden cold wave below $-7^{\circ}C$.

• Korean Chemical Engineering Research
• /
• v.45 no.3
• /
• pp.249-257
• /
• 2007

The periodic square wave (PSW) model was successfully applied to the optimal design of a batch-storage network. The network structure can cover any type of batch production, distribution and inventory system, including recycle streams. Here we extend the coverage of the PSW model to multitasking semi-continuous processes as well as pure continuous and batch processes. In previous solutions obtained using the PSW model, the feedstock composition and product yield were treated as known constants. This constraint is relaxed in the present work, which treats the feedstock composition and product yield as free variables to be optimized. This modification makes it possible to deal with the pooling problem commonly encountered in oil refinery processes. Despite the greater complexity that arises when the feedstock composition and product yield are free variables, the PSW model still gives analytic lot sizing equations. The ability of the proposed method to determine the optimal plant design is demonstrated through the example of a high density polyethylene (HDPE) plant. Based on the analytical optimality results, we propose a practical process optimality measure that can be used for any kind of process. This measure facilitates direct comparison of the performance of multiple processes, and hence is a useful tool for diagnosing the status of process systems. The result that the cost of a process is proportional to the square root of average flow rate is similar to the well-known six-tenths factor rule in plant design.

• Journal of Korean Society of Forest Science
• /
• v.106 no.1
• /
• pp.1-9
• /
• 2017

Forest harvest as large scale artificial disturbance makes edge environment in both clear-cutted and forested habitat. To clarify the development and recovery process of forest edge after disturbances is essential to understand vegetation responses and landscape level consequences such as edge-distance. In Korea, after clear-cutting, edge-related changes of environment and vegetation was not clarified yet. In Korean red pine (Pinus densiflora) forest, by applying space-for-time approach (sites with undisturbed and 1, 3, 10, 16 yr after cutting), the edge-related change of plant abundance and abiotic factors were determined for 20 line-transect (60 m) and 340 ($1m{\times}5m$) quadrats, and clarified depth and duration of the disturbance. Immediately after edge formation, within 15m form the edge, biotic and abiotic factors such as cover, richness, canopy openness, temperature and moisture content exhibited larger changes compared to forest interior. Plant abundance and abiotic variables were stabilized at the level of forest inside within 16 yr and 10 yr after edge creation, respectively. Woody (tree and shrub) species generally was showed larger increment with proximity to edge than did herb or graminoid species. In addition, negative interactions between woody and herbaceous species were detected during the period of forest edge closure. Our results suggested that depth of forest edge formed by clear-cutting of Korean red pine forest was at least from 15 m to 20 m and edge effect were likely sustained more than 16 years. As the first empirical study on edge-distance between two contrast habitats of clear-cutted and adjacent forest in South Korea, the analytical reality on landscape structure and habitat patches can be improved.

• Journal of the Korean Geographical Society
• /
• v.41 no.3 s.114
• /
• pp.331-345
• /
• 2006

This study deals with geomorphological process of the sand dune landform including the distribution and surface environments, characteristics of sediments, origins and moving processes in lower reach and mouth delta of Duman River, Northeast Korea and China. The methodology of the study includes image analysis of Landsat TM(1992.10) and ETM(2000.9) and Spot(2005.4) for analysis of land cover, 2 times field survey for recognition of landform and acquisition of sediments raw data materials, and grain analysis and exoscopy about raw data materials. The geomorphic elements from satellite image analysis are composed of the delta, sand spit, active and stable dune, sand bar and riparian vegetated zone. Results of the grain analysis indicate the sediments originated from marine coastal zone than riverine one. This means that present sand dune not so much reflect present climatic and geomorphic environments. Result of the exoscopy analysis show that ratio of quartz, which is comparatively resistant to environment, is highest as $65{\sim}83%$ out of sediments. But the surface of the $30{\sim}40%$ of mineral grains was coated by yellow-colored stained materials, due to chemical weathering. Some grains show rough skin, looking as acicular, network structure and etching pits, affected by physical and chemical weathering.

• Korean Journal of Materials Research
• /
• v.4 no.5
• /
• pp.600-607
• /
• 1994

Optimum exper~mental conditions were established for the growth of heteroepitaxial GaAs layers on InP using liquid phase epitaxy (LPE) technique. Results showed that the optimum growth temperature was $720^{\circ}C$ at a cooling rate of $0.5^{\circ}C$/min. Surface morphology of the grown layers significantly improved by addition of about 0.005wt% Se to the Ga growth melt, which effectively suppressed melt-back of InP substrates into the melt during the initial stage of growth. It was observed that the quality of GaAs layers also improved substantially when the substrates patterned with grating structure were used, as determined by the (400) double crystal X-ray diffraction. The transmission electron microscopy observation indicated t.hat the misfit dislocations interact with each other at the grating region, resulting in a lower dislocation density in the upper GaAs layer.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.9 no.3
• /
• pp.236-245
• /
• 2021

It is very important for structure designer to understand the service life variation since a wide range of service life is evaluated with changing exposure conditions and design parameters. Recently, for zero-carbon, waste plastic has been used for fuel for clinker production and this yields increase in chloride content in cement. This study is for evaluation of changing service life in the concrete with increasing initial chloride content due to usage of plastic-SRF(Solid Refuse Fuel) considering various exposure conditions and design parameters. For this, 4 levels of initial chloride content were assumed, and the service life was assessed using LIFE 365 program considering various environmental conditions including 3 levels of surface chloride content. As for analysis parameters, critical/initial chloride content, blast furnace slag powder replacement ratio, W/B(Water to Binder) ratio, cover depth, and unit mass for binder are adopted. Service life decreases with increasing initial chloride content and a significant reduction of service life is not evaluated permitting up to 1,000ppm of initial chloride content. With increasing slag replacement ratio, a longer service life can be secured since blast furnace slag powder has the effect of reducing the diffusion of external chloride ions and fixing the free chloride. It is thought that increasing initial chloride content up to European standard is helpful for enhancing sustainability and reducing carbon emission. Though the reduction in service life due to an increase in the initial chloride content is not significant in slag-concrete with low surface chloride content, careful consideration for mixing design should be paid for the exposure environment with high surface chloride content.

• Applied Chemistry for Engineering
• /
• v.32 no.4
• /
• pp.361-370
• /
• 2021

Carbon fiber reinforced polymer (CFRP) is one of the composite materials, which has a unique property that is lightweight but strong. The CFRPs are widely used in various industries where their unique characteristics are required. In particular, electric and unmanned aerial vehicles critically need lightweight parts and bodies with sufficient mechanical strengths. Vehicles using the battery as a power source should simultaneously meet two requirements that the battery has to be safely protected. The vehicle should be light of increasing the mileage. The CFRP has considered as the one that satisfies the requirements and is widely used as battery housing and other vehicle parts. On the other hand, in the battery area, carbon fibers are intensively tested as battery components such as electrodes and/or current collectors. Furthermore, using carbon fibers as both structure reinforcements and battery components to build a structural battery is intensively investigated in Sweden and the USA. This mini-review encompasses recent research trends that cover the classification of structural batteries in terms of functionality of carbon fibers and issues and efforts in the battery and discusses the prospect of structural batteries.