• Title/Summary/Keyword: Cementation

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Change of Geotechnical Properties of Sand due to Cementation (고결(Cementation)에 의한 모래의 지반공학적 특성 변화)

  • Lee, Moon-Joo;Kim, Seung-Han;Choi, Sung-Kun;Lee, Woo-Jin
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.153-160
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    • 2006
  • In this study, the change of getechnical properties of sand due to cementation was investigated by undrained triaxial test of isotropicallv consolidated sample. For inducing the cementation, $5\sim20%$(sand weight) gypsum were included in the sand and cured in the mold under the overburden pressure 55kPa. The yielding strength and stiffness of cemented sand were increased and also the aspects of effective pore water pressure were changed as the degree of cementation and the relative density. Generally the degree of cementation exerted more influence on the behavior of cemented sand than the relative density.

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Recovery of Copper Powder form MoO3 Leaching Solution Using Cementation Reaction System (MoO3 침출공정 폐액으로부터 치환반응 시스템을 이용한 구리 분말 회수에 대한 연구)

  • Kim, Geon-Hong;Hong, Hyun-Seon;Jung, Hang-Chul
    • Journal of Korean Powder Metallurgy Institute
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    • v.19 no.6
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    • pp.405-411
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    • 2012
  • Recovery of copper powder from copper chloride solution used in $MoO_3$ leaching process was carried out using a cementation method. Cementation is a simple and economical process, necessitating less energy compared with other recovery methods. Cementation utilizes significant difference in standard reduction potential between copper and iron under standard condition. In the present research, Cementation process variables of temperature, time, and added amount of iron scraps were optimized by using design of experiment method and individual effects on yield and efficiency of copper powder recovery were investigated using bench-scale cementation reaction system. Copper powders thus obtained from cementation process were further characterized using various analytical tools such as XRF, SEM-EDS and laser diffraction and scattering methods. Cementation process necessitated further purification of recovered copper powders and centrifugal separation method was employed, which successfully yielded copper powders of more than 99.65% purity and average $1{\mu}m$ in size.

Changes of Undrained Shear Behavior of Sand due to Cementation (고결(Cementation)에 따른 모래의 비배수 전단거동 변화)

  • Lee Woo-Jin;Lee Moon-Joo;Choi Sung-Kun;Hong Sung-Jin
    • Journal of the Korean Geotechnical Society
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    • v.22 no.4
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    • pp.85-94
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    • 2006
  • Triaxial tests at isotropic confining pressure of 200 kPa were carried out to show the undrained shear behavior of artificially cemented sands, which were cemented by gypsum, and the influences of relative density and DOC (degree of cementation) were investigated from the results. The yield strength, the elastic secant modulus at yield point and the peak frictional angle of cemented sands increased abruptly compared to uncemented sands, and it was checked that cementation exerts more influence on the behavior of sand than the relative density. But after breakage of the cementation bonds, the relative density was more important factor on the behavior of sand than the cementation. Because the compressibility md the excess pore pressure of cemented sands were reduced due to the cementation bonds, the effective stress path of cemented sands was going toward to the total stress path of uncemented sands. The cementation of sand restricted the dialtion of sand at the pre-yield condition, but induced more dilation in the post-yield condition.

Study of screw loosening in cementation type implant abutment

  • Hwang, Bo-Yeon;Kim, Yung-Soo;Kim, Chang-Whe
    • The Journal of Korean Academy of Prosthodontics
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    • v.38 no.6
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    • pp.765-781
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    • 2000
  • The purpose of this study was to compare the screw loosening characteristics of three avail-able cementation type abutments: one-piece cementation type abutment; two-piece cementation type abutment using titanium abutment screw; two-piece cementation type abutment using gold abutment screw. Two implant supported three-unit superstructures were fabricated using a pair of 3 kinds of abutments for each experimental model. Cyclic loading was applied on the specimen, and made to stop when the superstructure showed movement over threshold range. The loaded cycle was counted until the machine stopped. Frequency analysis was done to measure the change of natural frequency before and after the application of cyclic load and to find the effect of screw loosening on the change of natural frequency. The specimen assembly was modeled to perform the finite element analysis to see the distribution of the stress induced by the application of preload over the screw joint and to compare the pattern of the distribution of stress induced by the external force with the change of the preload condition. The following results were obtained: 1. The failure loading cycle of two-piece cementation type abutment using gold screw was significantly greater than those of the other groups. 2. One-piece cementation type abutment applied to multi-unit restoration case did not show greater resistance to screw loosening compared to two-piece cementation type abutments. 3. Frequency analysis showed decrease in natural frequency when screw loosening occured.

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Possibility of cementation of soft soil using Bacteria (Bacteria를 이용한 연약한 흙의 고결화 가능성)

  • Kim, Dae-Hyeon;Kim, Ho-Chul;Park, Kyoung-Ho
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.379-391
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    • 2010
  • In order to understand the mechanism of cementation of soft soils treated with bacteria, three types of specimens(untreated, normal bacteria concentration treated, and high bacteria concentration treated) were made. Scanning Electron Microscope(SEM), EDX and X-ray diffraction(XRD) analyses were performed on the soft silt and loose sand specimens. Compared with the untreated specimen, a clearer cementation between particles was observed in the high bacteria concentration treated specimen. Based on the scanning electron microscope(SEM) EDX analyses, more calcium carbonate was observed in the specimen treated with high bacteria concentration than other specimens. On the basis of the preliminary results, it appears that microbial cementation can occur in the soft soil. Further study on the cementation of soils using bacteria is necessary to validate this result.

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Undrained Shear Behavior of Cemented Sand (고결모래의 비배수 전단거동)

  • Lee, Moon Joo;Choi, Sung Kun;Hong, Sung Jin;Lee, Woo Jin
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.3C
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    • pp.181-190
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    • 2006
  • The behavior of artificially cemented sands were investigated by undrained triaxial test of isotropically consolidated sample. The cementation were induced by gypsum that is generally used for the aitificial cementation of sands. The gypsum of 5~20%(sand weight) were included in the sand and cured in the mold under the overburden pressure 55kPa. The yielding strength and stiffness of cemented sand were increased as the degree of cementation. And the dilation of sand was restricted by the cementation bonds, but after breakage of the bonds, it was increased more abrupt than the uncemented sands. The effective stress path showed that the aspects of effective pore water pressure were changed as the degree of cementation and the relative density. The effective stress ratio of cemented sand in the phase transformation line and the failure line were changed by the cementation. Generally the behavior of cemented sand more influenced by the degree of cementation than the relative density.

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Effect of Stress Level on Strength Parameters of Cemented Sand (응력조건에 따른 고결모래의 강도정수 평가)

  • Lee, Moon-Joo;Choi, Sung-Kun;Choo, Hyun-Wook;Cho, Yong-Soon;Lee, Woo-Jin
    • Journal of the Korean Geotechnical Society
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    • v.23 no.5
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    • pp.143-151
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    • 2007
  • The factors affecting the geotechnical properties of cemented sands are known to be relative density, cementation level, stress level, and particle characteristics such as particle size, shape and surface conditions. It has been widely accepted that the friction angle of cemented sands is not affected by cementation while the cohesion of cemented sands was significantly influenced by cementation. The cementation that is a critical component of the strength of cemented sands will be broken with increasing confining pressure and great caution is required in evaluating the cohesion of cemented specimens due to their fragilities. In this study, a series of drained shear tests were performed with specimens at various cementation levels and confining stresses to evaluate the strength parameters of cemented sands. From the experiments, it was concluded that the cohesion intercept of cemented sand experiences three distinctive zone(cementation control zone, transition zone, and stress control zone), as the cementation level and the confining stress varies. In addition, for accurate evaluation of the strength parameters, the level of confining stress triggering the breakage of cementation bond should be determined. In this study, the relationship between the maximum confining stresses capable of maintaining the cementation bond intact and unconfined compression strength of the cemented sand was established.

Evaluation of removal forces of implant-supported zirconia copings depending on abutment geometry, luting agent and cleaning method during re-cementation

  • Rodiger, Matthias;Rinke, Sven;Ehret-Kleinau, Fenja;Pohlmeyer, Franziska;Lange, Katharina;Burgers, Ralf;Gersdorff, Nikolaus
    • The Journal of Advanced Prosthodontics
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    • v.6 no.3
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    • pp.233-240
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    • 2014
  • PURPOSE. To evaluate the effects of different abutment geometries in combination with varying luting agents and the effectiveness of different cleaning methods (prior to re-cementation) regarding the retentiveness of zirconia copings on implants. MATERIALS AND METHODS. Implants were embedded in resin blocks. Three groups of titanium abutments (pre-fabricated, height: 7.5 mm, taper: $5.7^{\circ}$; customized-long, height: 6.79 mm, taper: $4.8^{\circ}$; customized-short, height: 4.31 mm, taper: $4.8^{\circ}$) were used for luting of CAD/CAM-fabricated zirconia copings with a semi-permanent (Telio CS) and a provisional cement (TempBond NE). Retention forces were evaluated using a universal testing machine. Furthermore, the influence of cleaning methods (manually, manually in combination with ultrasonic bath or sandblasting) prior to re-cementation with a provisional cement (TempBond NE) was investigated with the pre-fabricated titanium abutments (height: 7.5 mm, taper: $5.7^{\circ}$) and SEM-analysis of inner surfaces of the copings was performed. Significant differences were determined via two-way ANOVA. RESULTS. Significant interactions between abutment geometry and luting agent were observed. TempBond NE showed the highest level of retentiveness on customized-long abutments, but was negatively affected by other abutment geometries. In contrast, luting with Telio CS demonstrated consistent results irrespective of the varying abutment geometries. Manual cleaning in combination with an ultrasonic bath was the only cleaning method tested prior to re-cementation that revealed retentiveness levels not inferior to primary cementation. CONCLUSION. No superiority for one of the two cements could be demonstrated because their influences on retentive strength are also depending on abutment geometry. Only manual cleaning in combination with an ultrasonic bath offers retentiveness levels after re-cementation comparable to those of primary luting.

An Environmentally Friendly Soil Improvement Technology with Microorganism

  • Kim, Daehyeon;Park, Kyungho
    • International Journal of Railway
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    • v.6 no.3
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    • pp.90-94
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    • 2013
  • Cement or lime is generally used to improve the strength of soil. However, bacteria were utilized to produce cementation of loose soils in this study. The microo rganism called Bacillus, and $CaCl_2$ was introduced into loose sand and soft silt and $CaCO_3$ in the voids of soil particles were produced, leading to cementation of soil particles. In this study, loose sand and soft silt typically encountered in Korea were bio-treated with 3 types of bacteria concentration. The cementation (or calcite precipitation) in the soil particles induced by the high concentration bacteria treatment was investigated at 7 days after curing. Based on the results of Scanning Electron Microscope (SEM) tests and EDX analyses, high concentration bacteria treatment for loose sand was observed to produce noticeable amount of $CaCO_3$, implying a significant cementation of soil particles. It was observed that higher calcium carbonate depositions were observed in poorly graded distribution as compared to well graded distribution. In addition, effectiveness of biogrouting has also been found to be feasible by bio-treatment without any cementing agent.

Oxidation Resistant SiC Coating for carbon/carbon Composites

  • Joo, Hyeok-Jong;Lee, Nam-Joo;Oh, In-Seok
    • Carbon letters
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    • v.4 no.1
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    • pp.24-30
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    • 2003
  • In this study, densified 4D carbon/carbon composites were made from carbon fiber and coal tar pitch through the process of pressure impregnation and carbonization and then followed by carbonization and graphitization. To improve the oxidative resistance of the prepared carbon/carbon composites, the surface of carbon/carbon composites was coated on SiC by the pack cementation method. The SiC coated layer was created by depending on the constitution of pack powder, and reaction time of pack-cementation. The morpology of crystalline and texture of these SiC coated carbon/carbon composites were investigated by XRD, SEM/EDS observation. So the coating mechanism of pack-cementation process was proposed. The oxidative res istance were observed through the air oxidation test, and then the optimal condition of pack cementation was found by them. Besides, the oxidative mechanism of SiC formed was proposed through the observation of SiC coated surface, which was undergone by oxidation test.

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