• International Journal of Concrete Structures and Materials
• /
• v.10 no.3
• /
• pp.383-391
• /
• 2016

This paper reports the results of an experimental program involving several small-scale columns which were constructed to simulate corrosion damage in the field using two accelerated corrosion techniques namely, constant voltage and constant current. A total of six columns were cast for this experiment. For one pair of regular RC columns, corrosion was accelerated using constant voltage and for another pair, corrosion was accelerated using constant current. The remaining pair of regular RC columns was used as control. In the experiment, all the columns were subjected to cyclic wetting and drying using sodium chloride (NaCl) solution. The currents were monitored on an hourly interval and cracks were visually checked throughout the test program. After the specimens had suffered sufficient percentage steel loss, all the columns including the control were tested to failure in compression. The test results generated show that accelerated corrosion using impressed constant current produces more corrosion damage than that using constant voltage. The results suggest that the constant current approach can be better used to simulate corrosion damage of reinforced concrete structures and to assess the effectiveness of various materials, repair strategies and admixtures to resist corrosion damage.

• Proceedings of the Korea Technical Association of the Pulp and Paper Industry Conference
• /
• 1999.04b
• /
• pp.361-365
• /
• 1999

This study examined the effects of multiple recycling on deinkability and properties of recycled paper from laser computer printout (LCPO). First, alkaline paper with a 20% printed area was disintegrated by TAPPI standard disintegrator at room temperature. After dewatering, the pulp was flotated and dried in oven at80$^{\circ}C$ for 24 hrs. A sequence of wetting, disintegrating, flotating and drying was one recycling cycle and this cyclic treatment was repeated from zero to five times. The recycled handsheet dropped to 90% of the original brightness after five cycles, and lost the most brightness after five cycles, and lost the most brightness in the first two cycles. However, it had a gain of 10% in opacity after five cycles as the same as the case of nonprinting. And, in this study, the method for determining residual ink(toner) content in recycled handsheets ere established by means of SEM-EDX and Py-GC. The change of residual ink percentage on recycled paper showed the effect of recycling numbers on deinkability of waste paper. A slight decrease in deinkability was noted for the recycled handsheets, which may be due to the change of fiber surface free energy connected with fiber swelling.

• Magazine of the Korea Concrete Institute
• /
• v.9 no.3
• /
• pp.189-197
• /
• 1997

This paper describes an experimental study on the seawater resistance of steel fiber reinforced concrete. The test methods adopted for this study are divided into long-term immersion test and acceleration test by wetting and drying. Tests were carried out to evaluate the procedures which were measured for nine months about reduction in dynamic modulus, length change and compressive strength. Resistance indicators are the water-cement ratio, the content of steel fiber, the content of fly ash, the immersion water(artificial seawater or freshwater) and the types of curing. The seawater resistance of the appropriate additions of steel fiber and fly ash have apparently increased.

• Journal of Environmental Impact Assessment
• /
• v.18 no.6
• /
• pp.331-346
• /
• 2009

The serious problem facing two-dimensional finite element hydraulic model is the treatment of wet and dry areas. This situation is encountered in most practical river and coastal engineering problems, such as flood propagation, dam break analysis and so on. Especially, dry areas result in mathematical complications and require special treatment. The objective of this study is to investigate the wet and dry parameters that have direct relevance to model performance in situations where inundation of initially dry areas occurs. Several numerical simulations were carried out, which examined the performance of the marsh porosity method of RMA-2 model to investigate for application of parameters. Experimental channel with partly dry side slopes, straight channel with irregular geometry and Han river were performed for tests. As a result of this study, effectively applied marsh porosity method provide a reliable results for flow distribution of wet and dry area, it could be further developed to basis for extending to water quality and sediment transport analysis.

• Journal of Korea Water Resources Association
• /
• v.33 no.4
• /
• pp.483-493
• /
• 2000

Two dimensional finite element model, RMA, is used to simulate flood inundation phenomena from main channel to floodplain. The marsh porosity method allows finite elements to simulate gradual transition between wet and dry states. The model is applied to prismatic trapezoidal channel to test the applicability of wetting and drying. The floodwave in a river which meanders through a floodplain is also analyzed. The short-circuiting effects, in which the flow leave the meandering main channel and takes a more direct route on the floodplain, are analyzed with various sinuosity factor and roughness coefficients. Finally, the model is applied to the midstream of the Keum River. Wet/dry calculation can simulate the various discharge condition with the same finite element networks.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.37 no.1
• /
• pp.81-89
• /
• 1995

The aim of the work described in this paper is to develope a constitutive model for the prediction of an unsaturated Soil and to confirm the application of the model, which is composed of the elastic and plastic part in consideration of the matric suction and the net mean stress. From test results, volume changes and deviator stresses are analyzed at each state and their relationships are formulated. And the application of the model to silty sands is con- firmed by the comparison between test and predicted results. During drying-wetting and loading-unloading processes for isotropic states, the agreement between predicted and test results are satisfactory. And predicted deviator stresses are well agreed with test results in shearing process. Overall acceptable predictions are reproduced in high confining pressure. Usefulness of the model is confirmed for the unsat- urated soil except volumetric strain, which is not well agreed with the test results due to deficiency of dilatancy of the model in low confining pressure. It is, therefore, recom- mended to study the behavior of dilatancy for an unsaturated soil.

• Journal of the Korean Society of Clothing and Textiles
• /
• v.28 no.1
• /
• pp.112-118
• /
• 2004

Recently, as the percentage of women employment has been growing, the demand for various facilities and services regarding household duties and infant rearing is increasing and so do the amount of the disposable diaper used. Among the components of disposable diaper, the top sheet contacting with infant skin directly is usually made with nonwoven textiles. Therefore, the mechanical and surface characteristics of the nonwovens used in disposable diaper are important for the skin health of infants. In this study, we have explored the mechanical and surface properties, such as friction coefficient, fluid permeability and strength, of the nonwovens used for disposable diaper top sheet and observed the variation of their properties with abrasion cycles. Nonwoven materials examined in this study are 100% cotton spunlace, 100% tencel spunlace, 100% polypropylene (PP) thermal bonding and 100% PP air through (Thru-air bonded carded web). From the result of KES-F analysis, we've found that 100% PP air through type nonwoven had a low friction coefficient and showed a little change in surface properties as increasing abrasion cycles. Moreover, it revealed superior fluid permeability and quick-drying character. On the other hand, though showing an excellent absorption force, the spun lace type nonwoven made of 100% cotton and 100% tencel displayed relatively low abrasion strength especially in wetting condition.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.38 no.3
• /
• pp.101-110
• /
• 1996

The aim of the work described in this paper is to develope a constitutive model for the prediction of an unsaturated clayey soil and to confirm the application of the model. To this end a series of suction controlled isotropic and triaxial compression tests are conducted on clayey soils. Matric suction is controlled by the axis translation technique using high air entry ceramic disk. Total volume change, air and water volume changes are measured by the device made for the experiment. The specimens are compacted by dynamic compaction using a half of Proctor compaction energy with the water contents of 5% drier than the optimum moisture contents. From test results, volume changes and deviator stresses are analyzed at each state and their relationships are formulated. And the application of the model to clayey soils is confirmed by the comparison between test and predicted results. During drying-wetting and loading-unloading processes for isotropic states, the agreement between predicted and test results are satisfactory. And predicted deviator stresses are well agreed with the test results in shearing process, but volumetric strain is not well agreed with the test results in high suctions.

• Journal of Environmental Science International
• /
• v.3 no.2
• /
• pp.89-100
• /
• 1994

It is very important to assess accurately the terms which are included in the heat budget equation of soil surface because they are used in the UM and miso-scale circulation modeling as well as in the micrometeorological studies. Each terms in the heat budget equation change according to the soil moisture content. So, it is necessary to specify clearly the relations between soil moisture content and these terms. Special experiment with micrometeorological measurements was executed to study these relations at Environmental Research Center of Tsukuba University, Japan. The results are as follow: 1. The soil moisture contents of 1 cm and 4 cm depth are oscillated with one day Period in drying process and the amplitude of variation of 1 cm depth is greater than that of 4 cm. 2. Increase in soil moisture contents due to precipitation result in decrease of albedo with step function. 3. Sensible heat is in reverse proportion to the soil moisture content and latent heat is in direct proportion to it. Latent heat is more sensitive than sensible heat according to the soil moisture variation. Net long wave radiation have high correlation with soil moisture. 4. Comparing with the radiative term with the flux term in wetting process due to precipitation, the energy transfer of the aero and thermodynamic flux is greater than that of the radiative heat flux.

• The Journal of Engineering Geology
• /
• v.24 no.1
• /
• pp.1-8
• /
• 2014

Numerical stability analysis of an unsaturated infinite slope under rainfall-induced infiltration conditions was performed using generalized effective stress to unify both saturated and unsaturated conditions The soil-water characteristic curve (SWCC) of sand with a relative density of 75% was initially measured for both drying and wetting processes. The hydraulic conductivity function (HCF) and suction stress characteristic curve (SSCC) were subsequently estimated. Under the rainfall-induced infiltration conditions, transient seepage analysis of an unsaturated infinite slope was performed using the finite element analysis program, SEEP/W. Based on these results, the stability of an unsaturated infinite slope under rainfall-induced infiltration conditions was examined in relation to suction stress. According to the results, the negative pore-water pressure and water content within the slope soil changed over time due to the infiltration. In addition, the variation of the negative pore-water pressure and water content led to a variation in suction stress and a subsequent change in the slope's factor of safety during the rainfall period.