• Journal of the Korean Geosynthetics Society
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• v.10 no.3
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• pp.33-41
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• 2011

In this study, it conducted a compaction quality control test in 29 domestic construction sites and investigated the relationship between classical method (Cyclic Plate bearing test) and LFWD test with subgrade materials which consist in sandy soil and gravelly soil. According to the test results, the most of soil types were mostly satisfied with specification criterion and gravelly soils were easily satisfied with values over 3 times greater than specification criterion. In term of the correlation relation of soil modulus with the two compaction quality control test methods, it is shown that the sandy soil types were a good correlation, while gravelly soil types with a high stiffness materials were indicated less correlation. After the compensation for stress condition, a linear regression for elastic modulus were higher correlation.

• Journal of the Korean Geotechnical Society
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• v.25 no.8
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• pp.95-106
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• 2009

This study was intended to identify the effect of the wetting on a long-term compression settlement of the rock/soil mixture used as fill material, depending on compaction and grading conditions. The relatively large settlement happened under the fully-submerged condition, and a repeated settlement was monitored when moisture content increased over and over again like the rainfall infiltration. In case of the materials without fine fractions or compacted in wet condition, the settlement caused by wetting was relatively low. In conclusion, the long-term compression settlement of granular (rock/soil mixture) fill material is more affected by the increase of water content and temperature change (freezing and thawing) than creep.

• Journal of Powder Materials
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• v.30 no.3
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• pp.249-254
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• 2023

The influence of MgO addition on the densification and microstructure of alumina (Al₂O₃) was studied. Compacted alumina specimens were manufactured using ball-milling and one-directional pressing followed by sintering at temperatures below 1700℃. Relative density, shrinkage, hardness, and microstructure were investigated using analytical tools such as FE-SEM, EDS, and XRD. When the MgO was added up to 5.0 wt% and sintered at 1500℃ and 1600℃, the relative density exhibited an average value of 97% or more at both temperatures. The maximum density of 99.2% was with the addition of 0.5 wt% MgO at 1500℃. Meanwhile, the specimens showed significantly lower density values when sintered at 1400℃ than at 1500℃ and 1600℃ owing to the relatively low sintering temperature. The hardness and shrinkage data also showed a similar trend in the change in density, implying that the addition of approximately 0.5 wt% MgO can promote the densification of Al₂O₃. Studying the microstructure confirmed the uniformity of the sintered alumina. These results can be used as basic compositional data for the development of MgO-containing alumina as high-dielectric insulators.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.5
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• pp.191-198
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• 2022

Zirconia and titanium alloys, which are mainly used for dental implant materials, have poor osseointegration and osteogenesis abilities due to their bioinertness with low bioactivity on surface. In order to improve their surface bioinertness, surface modification with a bioactive material is an easy and simple method. In this study, akermanite (Ca₂MgSi₂O₇), a silicate-based bioceramic material with excellent bone bonding ability, was synthesized by a solid-state reaction and investigated its bioactivity from the analysis of surface dissolution and precipitation of hydroxyapatite particles in SBF solution. Calcium carbonate (CaCO₃), magnesium carbonate (MgCO₃), and silicon dioxide (SiO₂) were used as starting materials. After homogeneous mixing of starting materials by ball milling and the drying of at oven, uniaxial pressing was performed to form a compacted disk, and then heat-treated at high temperature to induce the solid-state reaction to akermanite. Bioactivity of synthesized akermanite disk was evaluated with the reaction temperature from the immersion test in SBF solution. The higher the reaction temperature, the more pronounced the akermanite phase and the less the surface dissolution at particle surface. It resulted that synthesized akermanite particles had high bioactivity on particle surface, but it depended on reacted temperature and phase composition. Moderate dissolution occurred at particle surfaces and observed the new precipitated hydroxyapatite particles in synthetic akermanite with solid-state reaction at 1100℃.

• Journal of the Korean Geotechnical Society
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• v.16 no.1
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• pp.179-189
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• 2000

The purpose of this research is to complement the existing researches on landfill bottom liners behavior during the periods of freeze and thaw. Landfill-related researches have been typically focused on small-scale soil samples that are often compacted under conditions different from those used in the field. Although these tests have been invaluable in clarifying the problem of freeze and thaw, extending the results of such experimental studies to prototype landfills are questionable. In this investigation, the author utilized a large scale laboratory simulation allowing inclusion of the field depth of the cover systems, layered soil profiles, rainfall simulation, a cold climate and boundary conditions similar to those encountered in the landfill. The soil materials were stabilized soils (mixed clays, cements, and minerals) instead of clays. The bottom liners are made up of drainage layer (30 cm), stabilized layer (75 cm), and leach collection layer (60 cm). The stabilized layers are made up of supporting layer (45 cm) and low permeable layer (30 cm) - consisting of $P_A\; and\; P_B$ layer. As a results, depths of penetration increased by about 2~5 more centimeters at rainfall simulated designs than those at no rainfall simulated designs (that is design 3, design 5 and design 7) - it increased by about 20mm/day in the bottom liners and frost heaves also increased it by a few millimeters. Also, a few cracks appeared partly. According to these results, we can surmise that the compacted stabilized soil is more reliable than the compacted clay liners for construction of the landfill liners.

• Progress in Superconductivity
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• v.12 no.2
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• pp.88-92
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• 2011

[ $MgB_2$ ]superconducting sheets have been fabricated using powder roll compaction method. Sheet-type $MgB_2$ bulk samples were successfully fabricated using the pre-reacted $MgB_2$ powders. In this work, $MgB_2$ powders were compacted by two rotating rolls and squeezed out as a form of $MgB_2$ sheets of ~1 mm thickness. The rolling speed of 0.3-0.7 rpm and the gap distance of 0.3-0.8 mm between the two rollers were carefully controlled to get a full compaction of the powders into bulk $MgB_2$ sheets. The densities of $MgB_2$ sheets were 1.98-2.05 g/$cm^3$, which is 75.44-77.99 % of the theoretical value of 2.63 g/$cm^3$. And the density comparison was made compared to those of typical $MgB_2$ bulks from uni-axial pressing and $MgB_2$ wires from Powder-In-Tube processing.

• Korean Journal of Materials Research
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• v.3 no.2
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• pp.111-120
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• 1993

Abstract In this study, the Mo-Hf-O ingots containing 0.31-1.14at % Hf and 0.08-1.00at % 0 were prepared by plasma arc melting. The change of microstructure depending on the condition of heat treatmen~ was analysed by optical microscophy, auger electron microscophy, and transmission electron microscophy. Molybdenum powder with the oxygen content of 830ppm was compacted, and then melted. The oxygen content of molybdenum ingots was detected to be 40 -130ppm. As the contents of Hf and 0 increased, the grain size of ingots decreased. When molybdenum igot containing l.14at % Hf and 1.00at % C was heat treated, p-molybdenum carbide in grains was transformed into ${\alpha}$-molybdenum carbide at 130$0^{\circ}C$. Between 140$0^{\circ}C$ and 150$0^{\circ}C$, the precipitation of hafnium carbide was due to the reaction of solute Hf and C, and the hafnium carbide was saturated at grain boundaries at 150$0^{\circ}C$. When the sample was heat treated from 150$0^{\circ}C$ to 170$0^{\circ}C$, Hafnium oxide more stable thermodynamically precipitated both at grain boundaries and in grains after hafnium carbide had been dissolved at grain boundaries.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.1
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• pp.21-30
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• 2017

The surface temperature of disc brakes varies during braking, which can affect the friction and wear behavior of braking systems. In order to develop an efficient braking system, the friction and wear behaviors of brake materials need to be clearly understood. In this work, the friction and wear behavior of the C/C-SiC-Cu composite and the Al/SiC composite, which are used in disc braking systems, were investigated. Both the surface temperature and contact pressure were studied. A pin-on-reciprocating tribotester was used for this purpose, in order to control temperature and load. Results showed that the friction varied significantly with temperature and sliding distance. It was found that a transfer layer of compacted wear debris formed on the wear track of the two materials. These layers caused the surface roughness of the wear track to increase. The outcome of this work is expected to serve as a basis for the development of braking systems under various operating conditions.

• Journal of the Korean Geotechnical Society
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• v.38 no.7
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• pp.25-37
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• 2022

In this paper, a small-scale model testing system was developed using a series of small-scale model tests to analyze the mechanism of compaction pile formation and evaluate the quality of controlled grading aggregates proposed as an alternative material to the sand compaction pile (SCP) method and granular compaction pile (GCP). These are the most typical ground improvement methods in field practice, particularly for soft grounds. However, the SCP has faced difficulties due to the supply shortage of natural sand and the corresponding price surge of sand. The GCP is limited in marine soft grounds because of the failure occurring at the pile tip caused by excessive expansion of the deeper bulbs, leading to uneven bulb formation. The uniformity of compacted pile bulbs is critical to ensuring the bearing capacity and quality of the compaction pile. This study aims to evaluate the performance of the new material and controlled grading aggregates using small-scale model tests simulating field compaction process to investigate its potential application in comparison with SCP. The compaction piles are examined in four cases according to different materials used for compaction pile and clay strength. The compaction pile materials, which are made of sand and controlled grading aggregates, used in this study were compared to reveal the mechanism of the bulb creation. The experimental data confirm that the bulb formation quality of the traditional sand and the new material, controlled grading aggregates are comparable. The compaction pile made of controlled grading aggregates presents higher bearing capacity than that of marine sand.

• Korean Journal of Soil Science and Fertilizer
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• v.40 no.3
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• pp.189-195
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• 2007

Using fractal dimensionality theory proposed by Riew and Sposito (1991), we attempted to analyze quantitatively the characteristics of porous distribution for built-in soils in the mini-lysimeter and artificial seed-bed media. The 2" stainless core soil samples were taken from lysimeter soils. Artificial seed-bed media were compacted in the acrylic core filled with raw materials consisted of cocopeat, zeolite and perlite. N (Constant number of partitioned group size smaller media volumes) and r (Self-similarity ratio) parameters consisting of fractal dimension D=log(N)/log(1/r) were obtained by Excel Programme using the Riew and Sposito's fractal model. The pore distribution of tested media was screened in pore size and its occurring frequency. The results reveal that the distribution range of pores is wider in the lysimeter soils than in the seed-bed media, while average size of pores in the media is smaller in lysimeter core soils than in seed-bed media.