• Computers and Concrete
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• v.34 no.3
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• pp.297-305
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• 2024

This study investigates the buckling behavior of CNTRC beams on a Winkler-Pasternak elastic foundation, considering their stiffness. To achieve the highest accuracy, the shear stiffness is taken into account based on the Higher-order Shear Deformation Theory (HSDT). A novel exponential power-law distribution of the CNT volume fraction across the beam thickness is employed to model CNTRC beams. Various reinforcement patterns are incorporated into the polymer matrix, featuring single-walled carbon nanotubes (SWCNT) that are both aligned and distributed. The effective mechanical properties of the CNTRC beam are predicted using the rule of mixtures. Hamilton's principle is applied to derive the differential equations of motion. This theoretical framework enables the validation of the approach by comparing numerical simulation results with previous studies. The impact of the exponent order (n), CNT volume fraction, geometrical ratio, and Winkler-Pasternak parameters on buckling analysis is thoroughly presented and discussed. The results indicate that, among the different types of analyzed CNTRC beams, the X-Beam pattern demonstrates the highest buckling load capacity.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.95-102
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• 2012

The serious issue of tall building is to ensure the fire resistance of high strength concrete. Therefore, Solving methods are required to control the explosive spalling. The fire resistant finishing method is installed by applying a fire resistant material as a light-weight material to structural steel and concrete surface. This method can reduce the temperature increase of the reinforcement embedded in structural steel and concrete at high temperature due to the installation thickness control. This study is interested in identifying the effectiveness of light-weight fire protection material compounds including the inorganic admixture such as fly ash, meta-kaolin and light-weight aggregate as the fire resistant finishing materials through the analysis of fire resistance and components properties at high temperature. Also, this paper is concerned with change in microstructure and dehydration of the light-weight fire protection materials at high temperatures. The testing methods of fire protection materials in high temperature properties are make use of SEM and XRD. The study results show that the light-weight fire resistant finishing material composed of fly ash, meta-kaolin and light-weight aggregate has the thermal stability of the slight decrease of compressive strength at high temperature. These thermal stability is caused by the ceramic binding capacity induced by alkali activation reaction by the reason of the thermal analysis result not showing the decomposition of calcium hydrate. Developed light-weight fire protection materials showed good stability in high Temperatures. Thus, the results indicate that it is possible to fireproof panels, fire protection of materials.

• Journal of the Korean GEO-environmental Society
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• v.10 no.2
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• pp.21-28
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• 2009

A grouting method has been widely used in construction of large-scale structure to reduce permeability and reinforce the ground. If cement and grout material were not mixed well in the injection tip equipment, an opposite flow and interception state of the chemical grouting can occur. McG (Multi-mixing counterflow prevented Grouting, McG) method installed a special grouting device to allow better mixing of the grouting material(above fineness $6,000cm^2/g$) and prevent backward flow. The block of nozzle also diversify powder rate of cement. YSS (Youngil Special Silicate, YSS) that lowers $Na_2O$ and thereby increases durability was developed by gel-forming reaction material. The seepage state and unconfined compressive strength of the injection material using the special injection tip equipment was tested in this study. The results of this study showed that the uniaxial compressive strength, permeability, N-value, TCR and RQD were improved by this method. Engineering characteristics obtained by the special injection tip method will be compared with those by the other method through various field tests from now on.

• Journal of Chest Surgery
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• v.42 no.3
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• pp.337-343
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• 2009

Background: Postoperative recurrence is a major problem after performing video-assisted thoracic surgery for the treatment of primary pneumothorax. This study was designed to evaluate the efficacy and safety of a bioabsorbable staple line reinforcement (GORE $SEAMGUARD^{(R)}$) for preventing recurrence after bullectomy. Material and Method: From January 2000 to December 2004, 300 patients underwent video assisted thoracoscopic surgery for the treatment of primary penumothorax. 143 patients were treated with bioabsorbable staple line reinforcement (Group A) and 142 patients were treated with stapling of the bullae (Group B). Mechanical pleural abrasion was performed in all the patients. The operating time, the duration of the indwelling chest tube, the length of the hospital stay and the number of recurrences after operation were compared between the groups. Result: No operative deaths occurred. The conversion rate to an open procedure was 5% (15/300). Comparison with these groups (Group A versus Group B) showed the following results: the operating time ($49.6{\pm}25.6$ vs $51.8{\pm}30.4$ minutes, respectively, p=0.514), the duration of an indwelling chest tube ($5.8{\pm}2.5$ vs $7.2{\pm}3.3$ days, respectively, p<0.005), the hospital stay ($10.9{\pm}4.3$ vs $12.5{\pm}4.3$ days, respectively, p<0.005) and the number of recurrences (14 (9.8%) vs 10 (7.0%), respectively, the over all rate: 8.4% p=0.523), and the mean follow up period. ($48.1{\pm}36.6$ vs $36.5{\pm}24.4$ months, respectively). Conclusion: There were advantages to use synthetic absorbable staple line reinforcement over the usual method for the treatment of primary pneumothorax in regard to the duration of an indwelling chest tube and the hospital stay, but here was no significant difference between the groups for postoperative recurrence.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.4
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• pp.279-284
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• 2012

Purpose: This study evaluated the effect of glass fiber pre-impregnated with light-curing resin on the fracture strength and fracture modes of a maxillary complete denture. Materials and methods: Maxillary acrylic resin complete dentures reinforced with glass fiber pre-impregnated with light-curing resin (SES MESH, INNO Dental Co., Yeoncheongun, Korea) and without reinforcement were tested. The reinforcing material was embedded in the denture base resin and placed different regions (Control, without reinforcement; Group A, center of anterior ridge; Group B, rugae area; Group C, center of palate; Group D, full coverage of denture base). The fracture strength and fracture modes of a maxillary complete denture were tested using Instron test machine (Instron Co., Canton, MA, USA) at a 5.0 mm/min crosshead speed. The flexure load was applied to center of denture with a 20 mm diameter ball attachment. When fracture occurred, the fracture mode was classified based on fracture lines. The data were analyzed with one-way ANOVA at the significance level of 0.05. Results: There were non-significant differences (P>.05) in the fracture strength among test groups. Group A showed anteroposterior fracture and posterior fracture mainly, group B, C and control group showed partial fracture on center area mostly. Most specimen of group D showed posterior fracture. Conclusion: The location and presence of the fiber reinforcement did not affect the fracture strength of maxillary complete denture. However, reinforcing acrylic resin denture with glass fiber has a tendency to suppress the crack.

• Composites Research
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• v.35 no.4
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• pp.248-254
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• 2022

In this study, TiB₂-steel composite with high-fractional TiB₂ reinforcement was fabricated by gas pressure infiltration process and the microstructure analysis and compressive strength and hardness were evaluated. To elucidate the correlation between microstructure and mechanical properties for fabricated composite, after the compression test of TiB₂-steel composite, the fracture surface was analyzed and the fracture behavior on compression test was predicted. As a result of the compression fracture surface analysis, interfacial failure trace between the steel matrix and the reinforcement was observed, and the interface between the steel matrix and the reinforcement was analyzed using TEM. From the result of microstructure analysis on the fabricated composite, it was confirmed that, in addition to TiB₂ reinforcement and steel matrix, TiC phase and coarse (Fe,M)₂B (M=Cr,Mn) phase were formed. Throughout the thermodynamic calculation, it was confirmed that TiC and (Fe,M)₂B can be formed as a stable phase under the process condition. The fabricated TiB₂-steel composite had a significantly increased hardness, and the compressive strength and Young's modulus were improved by 3.07 times and 1.95 times, respectively, compared to steel matrix. It seems that the coarse (Fe,M)₂B (M=Cr,Mn) phase formed throughout the composite causes the deterioration of mechanical properties, and by controlling the formation of the (Fe,M)₂B (M=Cr,Mn) phase, it is judged that the mechanical properties of the TiB₂-steel composite can be further improved.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.41 no.4
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• pp.8-20
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• 2023

Although the landscape architectural facilities need to be repaired according to historical and authentic techniques, the repair criteria of the standard specification for repairing cultural heritages still remain at a theoretical level, and there are little research analyzing detailed techniques from specific cases. This study discussed the repair techniques based on historical facts, around terraced flower beds, ponds, waterways and pavement in the government-managed spaces in the Joseon Dynasty. It analyzed the materials and finish of stone wall elements, the structural reinforcement and backfill materials, and topsoil surface protection measures, and drew out stones for foundation reinforcement, plastering material for agglutination, and stone processing techniques for the terraced flower beds. It examined the materials and structures of the rock revetment, foundation reinforcement and waterproofing techniques and drew out the outstanding characteristics of the foundation work, the recycle of used elements and the management of water quality, for the ponds. It primarily investigated the materials, foundation reinforcement and waterproofing techniques and discovered the repair techniques such as cover stone finishing methods, foundation and backfill materials, and flow reduction methods, for the waterways. Finally, it provided actual cases of the foundation composition, auxiliary materials and tools, and the use of cyperaceae and highlighted the existence of professional craftsmen called Bangjeonjang(方磚匠), for the pavement. This study is expected to be a staring point for discovering the repair techniques for landscape architectural facilities and used as basic data for revising specifications in the future.

• Journal of the korean academy of Pediatric Dentistry
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• v.48 no.2
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• pp.198-208
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• 2021

The aim of this study was to evaluate the antibacterial effect on Enterococcus Faecalis and physical properties of chitosan added calcium hydroxide canal filling material. Low, medium, high molecular weights of chitosan powder were mixed with calcium hydroxide canal filling material. Also, for each molecular weight group, 1.0, 2.0, 5.0 wt% of chitosan powder were added. An overnight culture of E. faecalis was adjusted to 1 × 10⁶ CFU/ml. For test of antibacterial effect, three different molecular weights of 2.0 wt% chitosan and three different concentrations of high molecular weight chitosan were mixed with calcium hydroxide canal filling material. The absorbance of plates was analyzed using spectrophotometer at 570 nm with a reference wavelength of 600 nm. Physical properties such as flow, film thickness and radiopacity were examined according to ISO 6876 : 2012. All molecular weight type of chitosan containing material showed inhibitory effect against E. faecalis growth compared to non-chitosan added calcium hydroxide canal filling material group (p < 0.05). High molecular weight chitosan containing material showed the most antibacterial effect. Also, the antibacterial effect decreased as the incorporated amount of chitosan decreased (p < 0.05). Every molecular weight group of material containing chitosan had a tendency for reduced flow and radiopacity, increased film thickness according to amount of chitosan. Low molecular weight of 1.0 wt% chitosan addition did not show any significant difference of physical properties compared to conventional calcium hydroxide canal filling material. In conclusion, for reinforcement of antibacterial effect against E. faecalis and for favorable physical properties, 2.0 wt% of chitosan adding is recommended. Considering its antibacterial effect of chitosan, further studies are required for clinical application of chitosan in endodontics and pediatric dentistry.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.763-771
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• 2007

Over the last few decades, many researches have been conducted in order to find solution to the problem of corrosion in steel reinforced concrete. As a result, methods such as the use of stainless steel bars, epoxy coatings, and concrete additives, etc., have been tried. While effective in some situations, such remedies may still be unable to completely eliminate the problems of steel corrosion. Fiber reinforced polymer (FRP) elements are appealing as reinforcement due to some material properties such as high tensile strength, low density, and noncorrosive. However, due to the generally lower modulus of elasticity of FRP in comparison with the steel and the linear behavior of FRP, certain aspects of the structural behavior of RC members reinforced with FRP may be substantially different from similar elements reinforced with steel reinforcement. This paper presents the flexural behavior of one-way concrete slabs reinforced with FRP bars. They were simply supported and tested in the laboratory under static loading conditions to investigate their crack pattern and width, deflections, strains and mode of failure. The experimental results shows that behavior of the FRP reinforced slabs was bilinearly elastic until failure. Also, the results show that the FRP overreinforced concrete beams in this study can be safe for design in terms of deformability.

• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.399-407
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• 2010

The flexural behaviors of two types of beam members exposed to freeze-thaw cycles were evaluated. This study aims to examine the effect of freeze-thaw cycles on the behavior characteristics of reinforced concrete (RC) beams. For the purpose, a part of the beam specimens were damaged until yielding of tension reinforcement was reached, before they were exposed to 150 and 300 cycles of freeze-thaw. Cyclic tests, as well as monotonic tests, were conducted to evaluate the stiffness degradation characteristics when same cycle is repeated. The material tests showed that relative dynamic modulus of concrete exposed to 300 cycles of freeze-thaw moderately decreased to 86.8% of normal concrete, indicating that concrete used in this study has good durability against freeze and thaw damage. The results of monotonic tests showed reduction of flexural strength, ductility and stiffness of the beam specimens exposed to freeze-thaw cycles compared with those of the control speciments. In particular, BDF13 specimens, which had been subjected to artificial cracking damage, did not showed enough flexural strength to satisfy nominal moment required by current concrete structure design code. In the monotonic tests results, BF75 specimens exposed to freeze-thaw cycles showed 10% or more cyclic stiffness degradation. Therefore, it was thought that deformation of concrete in compression have to be considered in design process of members under cyclic load, such as seismic device.