• Journal of the Korean Society of Safety
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• v.33 no.5
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• pp.60-69
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• 2018

This study aims to investigate in the assessment of salt damage conditions in concrete structures under marine environment conditions. It aims also to improve the durability of new concrete bridge through applying the life prediction method of salt damaged bridges. As measuring chloride contents of these bridges on the southwest coastal area, it is shown that the average amount of chloride on these surfaces close to shore is $10.5kg/m^3$. This figure is much higher than that of the Standard Specification for Concrete($1.5kg/m^3{\sim}2.5kg/m^3$). In contrast, it is shown the average amount of chloride on these surfaces in tide zone is $13.1kg/m^3$. Its figure is much lower than that of the Standard Specification for Concrete($20kg/m^3$). And the life of bridges is estimated about 17 years. To improve the durability for salt damage, these bridges are applied to surface treatment method which the replacement rate of furnace slag is 60%. Under this condition, it is expected to be 110 years. Consequently, it is clear that the use of slag replacement rate, surface treatment agent, and anti-corrosion agent to control chloride penetration effects of a submerge-based concrete bridge will be required.

• The Journal of the Korean dental association
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• v.58 no.2
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• pp.83-92
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• 2020

In the anterior maxillary area, dental implants for tooth replacement are challenging due to the need to satisfy high esthetic level as well as functionality. Immediate implant placement and provisionalization can dramatically reduce the edentulous period, and then fulfill patient's demand for esthetics. The aim of present case report is to demonstrate two cases that successfully restored single tooth with immediate implant placement and provisionalization in the anterior maxillary area. A 47 years old female was scheduled to replace her maxillary right central incisor due to crown-root fracture by trauma. Another 54-year-old female was planned to place dental implant following tooth extraction of maxillary right lateral incisor owing to continuous pus discharge despite repetitive treatments including apicoectomy. In these two cases, surgical and prosthetic procedures progressed in a similar way. After minimal flap elevation, atraumatic tooth extraction was performed. Implant was placed in proper 3-dimensional position and angulation with primary stability. Bone graft or guided bone regeneration for peri-implant bone defect was conducted simultaneously. Provisionalization without occlusal loading was carried out at the same day. Each definitive crown was delivered at 7 and 5 months after the surgery. Two cases have been followed uneventfully for 2 to 5 years of loading time. In conclusion, Immediate implant placement and provisionalization could lead to esthetic outcome for single tooth replacement with dental implant under proper case selection.

• Computers and Concrete
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• v.23 no.3
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• pp.161-170
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• 2019

This paper aims at presenting a numerical method for estimating the elastic modulus of recycled concrete with crushed aggregates. In the method, polygonal aggregates following a given sieve curve are generated, and placed into a square simulation element with the aid of the periodic boundary condition and the overlap criterion of two polygonal aggregates. The mesostructure of recycled concrete is reconstructed by embedding an old interfacial transition zone (ITZ) layer inside each recycled aggregate and by coating all the aggregates with a new ITZ layer. The square simulation element is discretized into a regular grid and a representative point is selected from each sub-element. The iterative method is combined with the fast Fourier transform to evaluate the elastic modulus of recycled concrete. After the validity of the numerical method is verified with experimental results, a sensitivity analysis is conducted to evaluate the effects of key factors on the elastic modulus of recycled concrete. Numerical results show that the elastic modulus of recycled concrete increases with the increase of the total aggregate content and the elastic moduli of old and new ITZ but decreases with increasing the replacement ratio of recycled aggregate and the thicknesses of old and new ITZ. It is also shown that, for a replacement ratio of recycled aggregate smaller than 0.3, the elastic modulus of recycled concrete is reduced by no more than 10%.

• Journal of Medicine and Life Science
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• v.20 no.2
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• pp.60-66
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• 2023

Gentamicin-loaded bone cement used in total joint arthroplasty is indispensable, as it provides stability by directly binding the surfaces of implants and bones. Depending on multiple factors, including the material of the bone cement used, common complications, such as aseptic loosening, osteolysis, and infection can occur postoperatively. In clinical practice, Doujet bone cement is easy to handle (pre-packed all-in-one system), and has shown low failure rates and non-inferior results compared with similar available products. We conducted a retrospective comparative study to analyze the clinical and radiological results of each bone cement group to establish the safety and usefulness of Doujet bone cement. From July 2020 to July 2022, we enrolled 198 patients in this study after an average follow-up period of 37 months (range, 6-48 months). In 99 patents, Doujet^® bone cement (Injecta, Gunpo, Korea) was used for total knee arthroplasty (TKA), while Refobacin^® bone cement (Biomet, Warsaw, IN, USA) was used in 99 patients. The average range of motion (ROM) of the knee increased by 2.4° (from 127.0° preoperatively to 129.4° postoperatively) in the Doujet group, and by 0.1° (from 128.7° to 128.8°) in the Refobacin group (P=0.701). The Western Ontario and McMaster Universities (WOMAC) osteoarthritis index scores decreased from 44.1 to 7.8 in the Doujet group, and from 44.2 to 6.3 in the Refobacin group (P=0.162). Complications, such as osteolysis or post-operative wound infection, did not occur in more than two cases in both groups. The WOMAC and ROM of the knee in both groups had no clinical differences. Both Doujet and Refobacin similarly showed low complication rates after TKA.

• Advances in concrete construction
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• v.13 no.2
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• pp.163-181
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• 2022

To study the mechanical properties of steel reinforced recycled concrete (SRRC) filled circular steel tube columns under eccentric compression loads, this study presents a finite element model which can simulate the eccentrically compressed columns using ABAQUS software. The analytical model was established by selecting the reasonable nonlinear analysis theory and the constitutive relationship of materials in the columns. The influences of design parameters on the eccentric compressive performance of columns were also considered in detail, such as the diameter-thickness ratio of circular steel tube, replacement percentage of recycled coarse aggregate (RCA), slenderness ratio, eccentricity, recycled aggregate concrete (RAC) strength and steel strength and so on. The deformation diagram, stress nephogram and load-displacement curves of the eccentrically compressed columns were obtained and compared with the test results of specimens. The results show that although there is a certain error between the calculation results and the test results, the error is small, which shows the rationality on the numerical model of eccentrically compressed columns. The failure of the columns is mainly due to the symmetrical bending of the columns towards the middle compression zone, which is a typical compression bending failure. The eccentric bearing capacity and deformation capacity of columns increase with the increase of the strength of steel tube and profile steel respectively. Compared with profile steel, the strength of steel tube has a greater influence on the eccentric compressive performance of columns. Improving the strength of RAC is beneficial to the eccentric bearing capacity of columns. In addition, the eccentric bearing capacity and deformation capacity of columns decrease with the increase of replacement percentage of RCA. The section form of profile steel has little influence on the eccentric compression performance of columns. On this basis, the calculation formulas on the nominal eccentric bearing capacity of columns were also put forward and the results calculated by the proposed formulas are in good agreement with the test values.

• Journal of the Korea Concrete Institute
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• v.14 no.2
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• pp.216-222
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• 2002

With deterioration of the nation's infrastructure comes the growing, need for effective means of rehabilitating structures. Possibly one for the most challenging tasks is to upgrade the overall capacity of concrete structure. Therefore, considerable efforts are still being made to develop new construction materials. Rehabilitation of damaged RC structures occasionally requires the removal and replacement of concrete in the tension zone of the structural members. Typical situation where the tension zone repair is necessary is when the concrete in the tension zone in beams or slabs has spalled off as a result of corrosion in the bottom reinforcing bars or due to extensive fire. The rehabilitation of such conditions normally involves the removal of the concrete beyond the reinforcement bars, cleaning or replacing the tensile bars and reinstatement of concrete to cover the steel bars the original shape and size. This study focused on the flexural behavior of reinforced concrete beams strengthened by steel strand and carbon fiber sheet in the tension zone. The properties of beams are 15$\times$25 cm rectangular and over a 200cm span. Test parameters in this experimental study were strengthening methods, jacking volume, the number of sheet. We investigated the flexural behavior of simply supported RC beams which are strengthened with the carbon fiber sheet, monotonic loads. Attention is concentrated upon overall bending capacity, deflection, ductility index, failure mode and crack development of repaired and rehabilitated beams.

• 한국정보컨버전스학회:학술대회논문집
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• 2008.06a
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• pp.99-102
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• 2008

Mineralogical studies of ore and alteration minerals have been conducted for the Hugo Dummett porphyry copper deposit. The Hugo Dummett porphyry copper gold deposit is located in the South Gobi region, Mongolia and currently being explored. This deposit divided into the Cu-rich Hugo Dummett South and the Cu-Au-rich Hugo Dummett North deposits. The Hugo Dummett deposits contain 1.08% copper(1.16 billion tonnes in total) and 0.23 g/t gold(Oyunchimeg et al., 2006). Copper-gold mineralization at these deposit are centered on a high-grade copper(typically>2.5%) and gold(0.5-2 g/t) zone of intense quartz stockwork veining. The high grade copper and gold zone is mainly within the Late Devonian quartz monzodiorite intrusions and augite basalt, also locally occurs in dacitic rocks. Intense quartz veining forms a lens up to 100 m wide hosted by augite basalt and partly by quartz monzodiorite. Although many explorations have been carried out, only a few scientific works were done in the Oyu Tolgoi mining area. Therefore the nature of copper-gold mineralization and orgin of the deposit is not fully understood. Copper-gold mineralization in the Hugo Dummett deposits occurs in dominantly quartz monzodiorite and minor augite basalt, dacitic rocks and locally biotite granodiorite. Chalcopyrite, pyrite, bornite, molybdenite, tennantite, tetrahedrite, enargite, sphalerite, chalcocite, covellite, eugenite, galena and gold occur as main ore minerals in the Hugo Dummett North and South deposits. These sulfides occur as: (1) a vague vein-like trail 1-3cm long and 2-3 mm wide, (2) minute, discontinuous cracks within quartz(micron scales), and (3) irregular blebs/spots(micron scales)and (4) disseminated within the sericite and plagioclase, commonly concentrated in the quartz. Sulfide minerals commonly display as a replacement, intergrown and minor exsolution texture in the both of the Hugo Dummet deposits.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.09a
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• pp.83-92
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• 2005

Fluid conductivity logging has been applied in the boreholes to identify the permeable fi:actures and estimate the origin of saline groundwater in coast area. Fluid replacement technique measures the fluid electrical conductivity with depth at different times in a well after the borehole is first washed out with different water by passing a tube to the borehole bottom. Then formation water flows into the borehole through aquifer such as permeable fractures or porous formation during ambient or pumping condition. Measured conductivity profiles with times therefore indicate the locations of permeable zone or fractures within the open hole or the fully slotted casing hole. As a result of fluid conductivity logging for three boreholes in the study area, it is interpreted that saline groundwater is caused by seawater intrusion through fractured rock, although the effect by land reclamation partially remains. We are planning the quantitative analysis to estimate the hydraulic characteristics using fluid replacement technique, and this approach might be usefully utilized for assessing the characteristics of seawater intrusion, the design of optimal pumping, and estimating the hydraulic properties in coastal aquifer.

• Economic and Environmental Geology
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• v.6 no.4
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• pp.195-200
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• 1973

Temperature environments of the formation of fluorite deposits in the Wolaksan area and the Cheonil Mine, Chungcheongbuk-Do are presented and interpreted in brief. These deposits occur more or less near the contact zone between the Paleozoic limestone formations and the Cretaceous biotite granites as a number of hydrothermal veins or replacement deposits. The homogenization temperatures of fluorite crystals from the Wolaksan area fall within the narrow range of $149{\sim}167^{\circ}C$, of which lower limit is quite high, while those of the Cheonil Mine show wide range of $126{\sim}177^{\circ}C$, which indicates much lower mean temperature of formation. If the possible correction for pressure, which may not exceed $+30^{\circ}C$ as the depth of the deposits was 1.5km, were applied, the possible highest value of the true formation temperatures of fluorites in both area might be reached to around $200^{\circ}C$ that means these deposits were formed as a series of early products of the epithermal stage of hydrothermal processes.

• Earthquakes and Structures
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• v.14 no.5
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• pp.379-388
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• 2018

This study aims to identify the effect of both longitudinal reinforcement details and damage level on making a decision of repairing pre-damaged bridge columns using basalt fiber reinforced polymer (BFRP) jackets. Two RC bridge columns with improper details of the longitudinal and/or transverse reinforcement were tested under the effect of a constant axial load and increasing lateral cyclic loading. Test results showed that the lap-splice column exhibited an inferior performance where it showed rapid degradation of strength before achieving the theoretical strength and its deformation capacity was limited; however, quick restoration is possible through a suitable rehabilitation technique. On the other hand, expensive repair or even complete replacement could be the decision for the column with the confinement failure mode. After that, a rehabilitation technique using external BFRP jacket was adopted. Performance-based design details guaranteeing the enhancement in the inelastic performance of both damaged columns were addressed and defined. Test results of the repaired columns confirmed that both reparability and the required repairing time of damage structures are dependent on the reinforcement details at the plastic hinge zone. Furthermore, lap-splice of longitudinal reinforcement could be applied as a key design-tool controlling reparability and restorability of RC structures after massive actions.