• Korean Chemical Engineering Research
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• v.54 no.4
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• pp.453-458
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• 2016

Microbial fuel cells (MFC) were operated with pig wastes and PEMFC (Proton Exchange Membrane Fuel Cells) MEA (Membrane and Electrode Assembly). Performance of hydrocarbon membrane was compared with that of perfluoro membrane at MFC condition. Sulfonated-Poly(Arylene Ether Sulfone) was used as hydrocarbon membrane and Gore membrane was used as perfluoro membrane. OCV of sPAES MEA was 50mV higher than that of Gore MEA and power density of sPAES MEA was similar that of Gore MEA. Reinforcement of sPAES membrane stabilized the performance of MEA in MFC. The highest performance was obtained at temperature of $45^{\circ}C$ and with culture solution circulation rate of 50 ml/min. The highest power density was $1,100mW/m^2$ at optimum condition in MFC using pig waste.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.4
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• pp.94-101
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• 2010

Recently, the interest of precast concrete is increased for rapid construction in construction fields. Experimental study about the shear performance of the joint between hollow core slabs which have internal core to reduce their weight was performed. Main test variables were thickness of the topping concrete and existence of the wiremesh. Total 8 specimens including 4 in-plane shear and 4 out of plane shear were tested. Test results were analyzed in terms of cracking load, failure load, failure aspect, stiffness and ductility, and compared its design load to develop optimum design details. Test results indicated that the shear performance of the non-shrinkage mortar specimen was similar to that of 30mm thickness topping concrete specimen, and the effect of wiremesh reinforcement did not affect the failure load or stiffness of the specimens but the increase of ductility. And this paper presents the comparison results of the test results and design load to provide the optimum detail of the joint design between the hollow core slabs.

• Journal of Ocean Engineering and Technology
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• v.30 no.4
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• pp.294-302
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• 2016

Because of the importance of steel material saving and rational ship structural design due to the rapid increase in steel prices, a ship structural design system was developed for plate members reinforced by doubler plates subjected to biaxial in-plane compressive loads. This paper mainly emphasizes the design system improvement and upgrade according to the change in the in-plane loading condition of the doubler plate from the single load discussed in a previous paper to the biaxial in-plane compressive load discussed in this paper. A direct design process by a structural designer was added to this developed optimized system to increase the design efficiency and provide a way of directly inserting a designer's decisions into the design system process. As the second stage of preliminary steps of doubler design system development, design formulas subjected to these biaxial loads used in the doubler plate design system were suggested. Based on the introduction of influence coefficients $K_t_c$, $K_t_d$, $K_b_d$ and $K_a_d$ based on the variations in the doubler length, breadth, doubler thickness, and average corrosion thickness of the main plate reinforced by the doubler plate, respectively, the design formulas for the equivalent plate thickness of the main plate reinforced by the doubler plate were also developed, and a hybrid design system using these formulas was suggested for the doubler plate of a ship structure subjected to a biaxial in-plane compressive load. Using this developed design system for a main plate reinforced by a doubler plate was expected to result in a more rational reinforced doubler plate design considering the efficient reinforcement of ship plate members subjected to these biaxial loads. Additionally, a more detail structural analysis through local strength evaluations will be performed to verify the efficiency of the optimum structural design for a plate member reinforced by a doubler plate.

• Advances in concrete construction
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• v.8 no.3
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• pp.207-215
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• 2019

Application of nanotechnology can be used to tailor made cementitious composites owing to small dimension and physical behaviour of resulting hydration products. Because of high aspect ratio and extremely high strength, carbon nanotubes (CNTs) are perfect reinforcing materials. Hence, there is a great prospect to use CNTs in developing new generation cementitious materials. In the present paper, a parametric study has been conducted on cementitious composites reinforced by two types of multi walled carbon nanotubes (MWCNTs) designated as Type I CNT (10-20 nm outer dia.) and Type II CNT (30-50 nm outer dia.) with various concentrations ranging from 0.1% to 0.5% by weight of cement. To evaluate important properties such as flexural strength, strain to failure, elastic modulus and modulus of toughness of the CNT admixed specimens at different curing periods, flexural bending tests were performed. Results show that composites with Type II CNTs gave more strength as compared to Type I CNTs. The highest increase in strength (flexural and compressive) is of the order of 22% and 33%, respectively, compared to control samples. Modulus of toughness at 28 days showed highest improvement of 265% for Type II 0.3% CNT composites. It is obvious that an optimum percentage of CNT could exists for composites to achieve suitable reinforcement behaviour and desired strength properties. Based on the parametric study, a tentative optimum CNT concentration (0.3% by weight of cement) has been proposed. Scanning electron microscope image shows perfect crack bridging mechanism; several of the CNTs were shown to act as crack arrestors across fine cracks along with some CNTs breakage.

• Korean Journal of Materials Research
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• v.29 no.11
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• pp.690-696
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• 2019

Geopolymer is an alumina silicate-based ceramic material that has good heat-resistance and fire-resistance; it can be cured at room temperature, and thus its manufacturing process is simple. Geopolymer can be used as a reinforcement or floor finish for high-speed curing applications. In this manuscript, we investigate a high-speed curing geopolymer achieved by adding calcium to augment the curing rate. Metakaolin is used as the main raw material, and aqueous solutions of KOH and $K_2SiO_3$ are used as the activators. As a result of optimizing the high bending strength as a target factor for geopolymers with $SiO_2/Al_2O_3$ ratio of 4.1 ~ 4.8, the optimum ranges of the active agent are found to be $0.1{\leq}K_2O/SiO_2{\leq}0.4$ and $10{\leq}H_2O/K_2O{\leq}32.5$, and the optimum range of the curing accelerator is found to be $$0.82{\leq_-}Ca(OH)_2/Al_2O_3{\leq_-}2.87$$. The maximum flexural strength is found to be 1.35 MPa at $Ca(OH)_2/Al_2O_3=2.82$, $K_2O/SiO_2=0.3$, and $H_2O/K_2O=11.3$. The physical and thermal properties are analyzed to validate the applicability of these materials as industrial insulating parts or repairing finishing materials in construction.

• Journal of the Korean Society of Industry Convergence
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• v.2 no.1
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• pp.45-52
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• 1999

It is difficult to keep the balance of supply and demand for natural aggregates in recent years, because natural resources have become to be almost exhausted. Crushed stone is already used for coarse aggregate instead of river gravel at present. Now, crushed sand or sea sand should be used for fine aggregate, because natural sand also has been exhausted with a few exceptions around Nakdong River. The sea sand has a lot of problems which are the corrosion of reinforcement bars, the investment of facility for cleansing salt and the cost increase due to the insufficiency of industrial water. Therefore, it is necessary to produce and to utilize the crushed sand very actively, but some material properties which are related to water absorption, strength and chemical durability, prevent from determining the generalized criteria because its rocks make much differences in its physical and chemical characteristics. In this paper, fundamental physical properties of crushed sand, which comes from Daegu Subway construction fields, have been investigated for the usability on basic material of concrete. The optimum replacement ratio and the strength estimation method of crushed sand replacing natural sand also have been presented here through the compressive strength test of ready-mixed concrete cylinders.

• Computers and Concrete
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• v.9 no.5
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• pp.327-340
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• 2012

The search for a design that meets both performance and safety, with minimal cost and lesser environmental impact was always the goal of structural engineers. In general, the design of conventional reinforced concrete structures is an iterative process based on rules of thumb established from the personal experience and intuition of the designer. However, such procedure makes the design process exhaustive and only occasionally leads to the best solution. In such context, this work presents the development and implementation of a mathematical formulation for obtaining optimal sections of reinforced concrete columns subjected to uniaxial flexural compression, based on the verification of strength proposed by the Brazilian standard NBR 6118 (ABNT 2007). To minimize the cost of the reinforced concrete columns, the Simulated Annealing optimization method was used, in which the amount and diameters of the reinforcement bars and the dimensions of the columns cross sections were considered as discrete variables. The results obtained were compared to those obtained from the conventional design procedure and other optimization methods, in an attempt to verify the influence of resistance class, variations in the magnitudes of bending moment and axial force, and material costs on the optimal design of reinforced concrete columns subjected to uniaxial flexural compression.

• Journal of The Korean Society of Agricultural Engineers
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• v.52 no.4
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• pp.73-81
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• 2010

The cemented sand and gravel (CSG) method is a construction technique that adds cement and water to rock-like materials, such as rivered gravel or excavation muck which can be obtained easily at areas adjacent to dam sites. This study was performed to evaluate the compaction and compressive strength properties of stress-strain, elastic modulus and fracture mode CSG materials reinforced polypropylene fiber. Polypropylene fiber widely used for concrete reinforcement is randomly distributed into cemented sand. The two types of polypropylene fiber (monofillament and fibrillated fiber) were used and fiber fraction ratio was 0, 0.2 %, 0.4 %, 0.6 % and 0.8 % by the weight of total dry soil. The effect of fiber fraction ratio and fiber shape on compaction and compressive strength were investigated. The optimum moisture contents (OMC) of CSG material increased as fiber fraction increased and the dry density of CSG material decreased as fiber fraction. Also, the maximum increase in compressive strength was obtained at 0.4 % content of monofillament and fibrillated fiber. CSG material behaviour was controlled not only by fiber fraction but also fiber distribution, fiber shape and fiber type.

• Journal of Korea Foundry Society
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• v.21 no.6
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• pp.359-365
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• 2001

The superplastic behavior of whisker reinforced aluminum alloy matrix composites fabricated by squeeze casting as one of high pressure routes was investigated. The preforms of ${\alpha}-Si_3N_4$ and ${\beta}-SiC$ whiskers without any binder as a reinforcement were used. The matrix materials were 2024 and 7075 aluminum alloys. For the purpose of optimum superplastic condition, respectively, the whiskers volume fraction, extrusion temperature, tensile test temperature and initial strain rate were changed. Fracture surface of tested specimens were observed by SEM. By the results, it became possible to produce superplastic composites by applying only a hot extrusion process to composites obtained by the squeeze casting. The superplastic composites developed are ${\alpha}-Si_3N_4w/7075$, ${\alpha}-Si_3N_4w/2024$ and ${\beta}-SiCw/2024$ systems at high strain rate.

• Proceedings of the KSR Conference
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• 2003.10b
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• pp.73-78
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• 2003

As a fundamental study to develop the retaining wall of new type, short-fibers are mixed with soils and a series of compaction tests and triaxial compression tests for short-fiber reinforced soils are performed. From the results of compaction tests, optimum moisture content is increased and maximum dry unit weight is decreased with fiber mixing ratio. When 60mm fibrillated fiber of 0.2$\%$ mixing ratio is added to SM soil, strength increment of short-fiber reinforced soil is above 1.2 times compared to soil only. Strength increment shows maximum value for composite reinforced soil, namely, soil+short-fiber+planar reinforcement. But in case of mixing with ML soil and short-fiber, the strength of short-fiber reinforced soil is nearly the same as soil only. Internal angle of short-fiber reinforced soil is increased about $2\~3$ degrees and cohesion is also increased above 10kPa compared to soil only. Therefore, it is judged that short-fiber is a good material to strengthen the soil.