• Journal of the Korean Wood Science and Technology
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• v.50 no.2
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• pp.93-103
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• 2022

Currently, biofibers are used as a reinforcement in polymer composites for structural elements and construction materials instead of the synthetic fibers which cause environmental problems and are expensive. One of the chemicals with a pH close to neutral that can be potentially used as a modified fiber material is sodium chloride (NaCl). Therefore, this study aims to investigate the characteristics of a composite board made from NaCl-treated kenaf fiber. A completely randomized design method was used with consideration of two factors: the content of NaCl in the treatment solution (1 wt%, 3 wt%, and 5 wt%) and the duration of immersion of fibers in the solution (1 h, 2 h, and 3 h). The NaCl treatment was conducted by soaking the fibers in the solution for different durations. The fibers were then rinsed with water until the pH of the water reached 7 and subsequently dried inside an oven at 80℃ for 6 h. Kenaf fiber and epoxy were mixed manually with the total loading of 20 wt% based on the dry weight of the fiber. Physical and mechanical properties of the fibers were then evaluated based on JIS A 5908 particleboard standards. The results showed that increasing NaCl content in the fiber treatment solution can increase the physical and mechanical properties of the composite board. The properties of fibers treated with 5 wt% NaCl for 3 h were superior with a modulus of elasticity of 2.085 GPa, modulus of rupture of 19.77 MPa, internal bonding of 1.8 MPa, thickness swelling of 3%, and water absorption of 10.9%. The contact angle of untreated kenaf fibers was 104°, which increased to 80° and 73° on treatment with 1 wt% and 5 wt% NaCl for 3 h, respectively.

• Steel and Composite Structures
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• v.46 no.3
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• pp.385-401
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• 2023

Steel is becoming increasingly popular due to its high strength, excellent ductility, great assembly performance, and recyclability. In reality, steel structures serving for a long time in atmospheric, industrial, and marine environments inevitably suffer from corrosion, which significantly decreases the durability and the service life with the exposure time. For the mechanical properties of corroded steel, experimental studies are mainly conducted. The existing numerical analyses only evaluate the mechanical properties based on corroded morphology at the isolated time-in-point, ignoring that this morphology varies continuously with corrosion time. To solve this problem, the relationships between pit depth expectation, standard deviation, and corrosion time are initially constructed based on a large amount of wet-dry cyclic accelerated test data. Successively, based on that, an in-situ pitting evolution method for evaluating the residual tensile strength of corroded steel is proposed. To verify the method, 20 repeated simulations of mass loss rates and mechanical properties are adopted against the test results. Then, numerical analyses are conducted on 135 models of corrosion pits with different aspect ratios and uneven corrosion degree on two corroded surfaces. Results show that the power function with exponents of 1.483 and 1.091 can well describe the increase in pit depth expectation and standard deviation with corrosion time, respectively. The effect of the commonly used pit aspect ratios of 0.10-0.25 on yield strength and ultimate strength is negligible. Besides, pit number ratio α equating to 0.6 is the critical value for the strength degradation. When α is less than 0.6, the pit number increases with α, accelerating the degradation of strength. Otherwise, the strength degradation is weakened. In addition, a power function model is adopted to characterize the degradation of yield strength and ultimate strength with corrosion time, which is revised by initial steel plate thickness.

• Geomechanics and Engineering
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• v.34 no.3
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• pp.251-265
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• 2023

In urban construction projects, it is crucial to evaluate the impacts of excavation-induced ground movements in order to protect surrounding structures. These ground movements resulting in damages to the neighboring structures and facilities (i.e., parking basement) are of main concern for the geotechnical engineers. Even more, the danger exists if the nearby structure is an ancient or masonry brick building. The formations of cracks are indicators of structural damage caused by excavation-induced ground disturbances, which pose issues for excavation-related projects. Although the effects of deep excavations on existing brick masonry walls have been thoroughly researched, the impact of twin excavations on a brick masonry wall is rarely described in the literature. This work presents a 3D parametric analysis using an advanced hypoplastic model to investigate the responses of an existing isolated brick masonry wall to twin perpendicular excavations in dry sand. One after the other, twin perpendicular excavations are simulated. This article also looks at how varying sand relative densities (D_r = 30%, 50%, 70%, and 90%) affect the masonry wall. The cracks at the top of the wall were caused by the hogging deformation profile caused by the twin excavations. By raising the relative density from 30% to 90%, excavation-induced footing settlement is greatly minimized. The crack width at the top of the wall reduces as a result of the second excavation in very loose to loose sand (D_r = 30% and 50%). While the crack width on the top of the wall increases owing to the second excavation in medium to very dense sand (D_r = 70% and 90%).

• Journal of Soil and Groundwater Environment
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• v.29 no.1
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• pp.28-38
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• 2024

Phytoremediation presents a low-carbon and eco-friendly solution for heavy metal-contaminated soils, which pose great health and environmental risks to humans and ecosystems. A hydroponic culture was used to quantitatively assess the phytoremediation potential of plant species to remediate As or Cd-contaminated soil in field application. This study examined the growth, uptake, and distribution of Cd in the roots and shoots of Phalaris arundinacea and Brassica juncea in hydroponic conditions with Cd concentrations ranging from 0 to 20 mg/L for 10 days. Additionally, Aster koraiensis and Pteris multifida were cultivated in hydroponic conditions containing As concentrations ranging from 0 to 40 mg/L for 10 days. The concentrations of Cd in the above-ground part and root tissues of P. arundinacea and B. juncea reached a maximum of 147.7 and 1926.7 mg/kg-D.W.(Dry Weight), and 351.6 and 11305.5 mg/kg-D.W., respectively. Bioconcentration factor (BCF) for P. arundinacea and B. juncea were 68.9 and 122.3, respectively. Both species exhibited a translocation factor (TF) of less than 0.1, indicating their eligibility for phytostabilization. Aster koraiensis exhibited significant As accumulation of 155.1 and 1306.7 mg/kg D.W. in the above-ground part and root, respectively. However, this accumulation resulted with substantial weight loss and the manifestation of toxic symptoms. P. multifida exhibited higher accumulation of As (345.1 mg/kg-D.W.) in the fronds than in the roots (255.4 mg/kg-D.W.), corresponding to BCF values of 18.6 and 7.6, respectively, and a TF greater than 1.2. A TF value greater than 1.0 indicates that P. multifida is a viable option for phytoextraction.

• The Journal of the Acoustical Society of Korea
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• v.36 no.5
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• pp.329-337
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• 2017

In USA and UK, the standards of both reverberation time and background noise level have been established for the appropriate aural environment in classrooms. In order to realize this, guidelines for architectural planning and interior finishing have been also suggested. However, in Korea, there has hardly been any guidelines for satisfying background noise criteria and investigation about sound insulation performance of current walls of classrooms. The present study investigates the structure of outer wall and walls between classrooms of two middle schools in order to analyze the sound insulation performance against both exterior and interior noises. Acoustic parameters including transmission loss, standardized sound level difference, and signal to noise ratio have been measured and analyzed for sound insulation performance of walls and flanking noises. As a result, concerning the walls in between classrooms, it was found that walls of dry construction have greater sound insulation performance rather than the walls of wet construction especially in mid and high frequency bands. Also, It was revealed that thermopane, insulated pair glass, of outer walls, has greater sound insulation performance than the double window consisted of two single pane glass. Regarding flanking noises, the standards were exceeded when all windows, or windows and doors front onto corridor were opened. It denotes that students could be disturbed with the sound transmission by the interior noises.

• Journal of the Korea Organic Resources Recycling Association
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• v.4 no.1
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• pp.43-51
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• 1996

Qualititative changes in water extracts during food waste composting were studied in order to identify parameters that can be used as indicaters of compost maturity. Materials used in this study were food wastes, office paper, newspaper and leaves. Three different compositions of food wastes were used : average composition food waste generated in Korea, a high cereal (carbohydrate) content food waste and a high meat (protein) content food waste. Experimental results indicated that parameters which can be used for compost maturity evaluation were water soluble TOC and water soluble $C_{org}/N_{org}$ ratio. In case of water soluble TOC, it is considered as one of the most desirable parameters, since it showed quite distinct decrease pattern than any other parameters. The $C_{org}/N_{org}$ ratio in the water extracts can also be considered as a appropriate index of the compost maturity since this ratio reached a narrow range (5~6) at the end of composting process regardless of initial raw waste compositions. Water soluble TKN was undesirable parameter as a compost maturity index. The ammonia nitrogen content in water extracts varied considerably during composting process, but finally reached a range of 0.067, 0.085% based on dry compost.

• Journal of Korean Society of Steel Construction
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• v.26 no.6
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• pp.549-558
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• 2014

Buckling restrained braces(BRBs) developed as a seismic protection element, hysteretic damper, have been investigated in America and Japan mainly. BRBs are composed of a steel core and concrete-filled steel casing. It is one of the major causes of drop in productivity to fill the steel casing with concrete. To improve this problem, the BRB is introduced in which the steel core is restrained with a pair of semicircular springs. In this paper, the numerical and analytical investigation about the desirable configuration for a semicircular spring is presented. Firstly, the stiffness and strength of semicircular spring is determined theoretically to buckle into a very high-order modes. Then, the required stiffness and strength are calculated under the practical design conditions and considered as reference values to find a proper configuration. The material strength and thickness of semicircular spring are chose from the finite element analysis for 5 semicircular springs with varying height. Finally, the nonlinear buckling analysis of BRB with proper semicircular springs shows that the bucking strength of the whole BRB is very similar to the strength of steel core with length between semicircular springs.

• The Journal of Engineering Geology
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• v.20 no.3
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• pp.297-310
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• 2010

This study represents basic research into the utilization of mixed ash (fly ash and bottom ash) from the ash pond of the Taean Thermal Power Plant as a construction material. We conducted physical and mechanical experiments on the mixed ash and examined its engineering characteristics in terms of its use as a material for road landfill and structure backfill. We evaluated the physical and chemical characteristics of the ash by performing tests to determine specific gravity, maximum and minimum density, liquid limit and plastic limit, grain size distribution, composition (by X-ray diffraction), and loss on ignition. We also evaluated the mechanical characteristics by testing for permeability, compaction, CBR, and tri-axial compression. The experiments on the mixed ash yielded a specific gravity of 2.18-2.20, dry density of $9.38-13.32\;kN/m^3$, modified CBR of 16.5%-21%, permeability coefficient of 1.32 to $1.89-10^{-4}cm/sec$, and drained friction angle of $36.43^{\circ}-41.39^{\circ}$. The physical and mechanical properties of the mixed ash do not meet the quality standards stipulated for road landfill and structure backfill materials. Mixed ash with a high content of fly ash failed to meet some of the quality standards. Therefore, in order to utilize the mixed ash as a material for road landfill and structure backfill, it is necessary to improve its properties by mixing with bottom ash.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.435-441
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• 2017

Studies on self-healing have currently been diversified and the methods to evaluate the studies have become more diversified as well. Among them, the back-scattered electron (BSE) image acquired through the scanning electron microscope (SEM) is attempted as the means to evaluate the self-healing effect on cracks. In order evaluate by the BSE image, sophisticated pre-processing of specimen is critical and this injected inside the particle, pore and artificial crack of the hardener to stabilize the structure of the newly generated self-healing product and it enables to endure the stress on polishing without deformation. The impregnated specimen smoothen the surface to obtain the BSE image of high resolution that polishing is made for diamond suspension for wet polishing after dry polishing. As a result of evaluating the self-healing product on the impregnated and polished self-healing specimen, the generated product is formed from the surface of the artificial crack and the self-healing substances are confirmed as $Ca(OH)_2$ and C-S-H.

• Journal of Korea Water Resources Association
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• v.42 no.9
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• pp.747-758
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• 2009

In this study, long-term variabilities of rainfall-occurrence characteristics are analyzed using rainfall data at Seoul, which is the longest data record existing in world. first, the accuracy of Chukwooki data set (CWK) are evaluated in view of rainfall-occurrence probability by analyzing the transition probabilities and occurrence characteristics based on Markov chain. And long-term inter-monthly variabilities of transition probabilities are analyzed using two dimensional LOWESS regression. From the results of analyzed transition probabilities and occurrence characteristics, it is different that rainfall-occurrence characteristics between CWK and modern rain gage data set (MRG) for original rainfall data sets (M00). For characteristics of rainfall series, occurrences probabilities of rainfall are increased and durations of each rainfall are shorter than past. And from the results of analyzing the long-term inter-monthly variabilities of transition probabilities, in case of M20, lengths of dry spells between CWK and MRG are not different significantly and lengths of wet spells are decreased persistently after A.D. 1830. Especially, decreasing trend for lengths of wet spells at recent september are appeared significantly. These results are considered with increasing trend of recent rainfall, it is concluded that recent frequencies and intensities of rainfall are increasing.