• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.2
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• pp.97-106
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• 2009

self-loading, various problems related to construction can be solved as well as the save of construction cost. Thus, this study has an aim of applying foam concrete to structural purpose by adding bottom ash as a reinforcing material like fine aggregate, in contrast to conventional non-structural usage such as soundproofing or insulating materials. In addition, it was evaluated in terms of unit volume weight, flow value, air void, water absorption and dosage of foam agent wether replacement of cement by granulated blast furnace slag or fly-ash has an effect on the material characteristics of foam concrete. As results of experiments, it can be found that the increase of fine aggregate ratio, that is to say, the increase of bottom ash results in the increase of unit volume weight, while decreasing air void and flow value. But, appropriate addition of bottom ash to foam concrete makes it easy to control a homogeneous and uniform quality in foam concrete due to less sensitive to bubbles. As the replacement ratio of mineral admixtures such as granulated blast furnace slag and fly-ash increases, as unit volume weight tends to decrease. In the meanwhile, serious effects were shown on fluidity of foam concrete when more than limit of replacement ratio was applied.

• Journal of Korean Neurosurgical Society
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• v.30 no.7
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• pp.907-915
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• 2001

Objective : Percutaneous vertebroplasty is often complicated by the presence of multiple fractures or non-localizing pain in the patients with osteoporotic vertebral fractures. The purpose of this study is to estimate the value of preoperative radiologic studies in the localization of symptomatic vertebrae and to determine the factors which can influence on the clinical results. Materials and Methods : We retrospectively reviewed the clinical and radiologic data of 57 vertebrae in 30 patients underwent percutaneous vertebroplasty for osteoporotic vertebral compression fractures. Inclusion criteria was severe pain(McGill-Melzack score 3, 4 or 5) associated with the acute vertebral fractures and absence of spinal nerve root or cord compression sign. Acute symptomatic vertebral fracture was determined by the presence of signal change on MR images or increased uptake on whole body bone scan. Results : Pain improvement was obtained immediately in all patients and favorable result was sustained in 26 patients(86.7%) during the mean follow-up duration of 4.7 months(5 complete pain relief, 21 marked pain relief). Those who underwent vertebroplasty for all acute symptomatic vertebrae had significantly better clinical result than those who did not. Further vertebral collapse and eventual bursting fracture occurred in 1 vertebra which showed intradiskal leakage of bone cement and disruption of cortical endplate on postoperative CT scan. Conclusion : Preoperative MR imaging and whole body bone scan are very useful in determining the symptomatic vertebrae, especially in the patients with multiple osteoporotic vertebral fractures. To obtain favorable clinical result, the careful radiologic evaluation as well as clinical assessment is required. Control of PMMA volume seems to be the most critical point for avoiding complications.

• Restorative Dentistry and Endodontics
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• v.25 no.2
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• pp.262-271
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• 2000

The purpose of this study was to estimate shear bond strength according to difference in Targis surface treatment and storage condition. 140 non-carious extracted human molars and Targis D210(Ivoclar, Liechtenstein) were used in the present study and were divided into 7 experimental groups respectively according to surface treatment of Targis. Group 1 ; No treatment, Group 2 ; $50{\mu}m$ aluminium oxide blasting, Group 3 ; 4% HF etching for 3 minutes, Group 4 ; 4% HF etching after blasting, Group 5 ; silane treatment after blasting, Group 6 ; silane treatment after 4% HF etching, Group 7 ; silane treatment after blasting and 4% HF etching. In Each group, one half of 20 specimens was stored in distilled water at $37^{\circ}C$ for 24 hours and the other half was stored at atmosphere for 24 hours respectively. Dentin surface was etched with 10% $H_3PO_4$ for 15 seconds and luting cement(Variolink II, Vivadent, Liechtenstein) was applied by manufacturer's recommendation. Shear bond strength for each group was then measured. To examine the failure patterns after shear bond test and to observe the change after surface treatment of Targis. Specimens were fabricated and observed under the SEM. Statistical analysis was performed by One Way ANOVA test and t-test. The results were as follows ; 1. The shear bond strength of the groups stored in water significantly lower than that of groups stored at atmosphere (P<0.05). 2. There was no significant difference in shear bond strength in groups stored in water (P>0.05). 3. The shear bond strength without surface treatment of Targis were lowest among all experimental groups in atmosphere condition(P<0.05). 4. There was no significant difference in bond strength between groups using the silane or not(P>0.05). 5. The groups treated by blasting, hydrofluoric acid and silane sequentially showed highest bond strength than that of other groups in atmosphere condition, but there was no significant difference(P>0.05). 6 The proportions of the specimens showing the mixed fracture failure were 20% in HF etching group and blasting + HF group, 40% in blasting + HF + silane group in atmosphere condition. All the specimens stored in water showed adhesive fracture failure.

• Restorative Dentistry and Endodontics
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• v.23 no.1
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• pp.443-460
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• 1998

The purpose of this study was to estimate the changes of tensile bond strength according to the difference in lining materials and lining area. Seventy non-carious extracted human molars were used in the present study, and they were randomly assigned into 2 experimental groups according to the difference in lining materials. Each experimental group was subdivided into 3 groups according to the difference in lining area. Circular cavities were prepared on the dentin surface to a diameter of 1.5mm, 2.0mm, 2.5mm and the prepared cavities were filled with Fuji II LC( Glass Ionomer Cement : GIC) or Dycal. Dentin specimens without circular cavity were used as control group. The primer and bonding agent of All-Bond 2 and composite resin (Z-100, 3M Dental Products, U. S. A.) were applied to the exposed dentin surface with or without lining. Tensile bond strengths for the experimental specimens were then measured. To examine the interface between dentin and liner & between liner and composite resin, two specimens from each group were fabricated and observed under the SEM. The results were as follows. 1. Tensile bond strength for the specimens lined with GIC was higher than that for specimens lined with Dycal. However, there was no significant difference between two groups(p>0.05). 2. Tensile bond strength for the specimens lined with GIC in a diameter of 1.5mm(GIC-1.5mm lining group) was statistically higher than that for the GIC-2.0mm lining group and GIC-2.5mm lining group(p<0.05). 3. Tensile bond strength for the specimens lined with Dycal in a diameter of 2.5mm (Dycal-2.5mm lining group)was statistically lower than that for Dycal-1.5mm lining group and Dycal-2.0mm lining group(p<0.05). 4. It was possible to observe the good adhesion of the resin composite to the GIC and the presence of a fissure between GIC and dentin all along the interface. Interfacial gaps of 7.2-$72.2{\mu}m$ between GIC and dentin were observed. The interfacial gap between GIC and dentin at the cavity base was greater. However, the gap was gradually decreased toward the occlusal portion. 5. It was possible to observe the poor adhesion of the resin composite to the Dycal. The detachment of Dycal was occurred all along the composite resin-Dycal interface, and the gaps of 2.0-$30.1{\mu}m$ were formed. In all the specimens, polymerization shrinkage of resin composite caused the detachment of Dycal from the body of Dycal. At a Dycal-dentin interface. it was possible to observe the good adhesion. but poor adhesion with interfacial gap of 2.9-$26.8{\mu}m$ was observed partially.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.4
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• pp.99-107
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• 2003

Normally coating is used a method for protecting reinforced concrete. For this purpose, organic as well as inorganic coatings are used. The advantages of inorganic coatings are lower absorption of UV, non-burning etc. On the other hand, organic coatings have the advantage of low permeability of $CO_2$, $SO_2$ and water. Organic coatings provide better protection for reinforced concrete. However, in organic coatings such as epoxy, urethane and acryl, long-term adhesive strength is reduced and the formed membrane of those is blistered by various causes. Also when organic coatings are applied to the wet surface of concrete, they have a problem with adhesion. So, we developed coating material, WGS-Eco which was hybridized with polymer and cement based material to protect concrete structures and solve problems of organic coatings. This study was conducted an comparative evaluation on physical and durable performance of developed coating material and previously used coating materials. As a result, the performance of developed coating material was not inferior to organic coating materials. So, the developed coating material was considered as a suitable coating material which had advantages of inorganic and organic coatings for protecting concrete.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.2
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• pp.87-92
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• 2011

This paper describes a study on the permeability reduction of the riverbed ground during urban railway tunnel construction. The research is mainly concentrated on the study of the grouting or injection methods among permeability reduction methods which can be adapted in the riverbed ground. The design technology of grouting methods considering the long term hydro-geological behaviour in the riverbed, was suggested. Two injection methods namely, Natural Durable Stabilizer (N.D.S) and Space-Multi Injection Grouting (S.M.I) methods, were introduced as new approach methods which could be adapted to modify the riverbed ground. In order to evaluate the performance of the improved ground by the N.D.S and S.M.I method, a series of pilot tests including the field and laboratory permeability tests, were carried out in the river crossing tunnel construction sites. The results obtained from pilot test program, were also reviewed. The results, the grouting efficiency of the S.M.I method using the non-alkalimeter silica sol is better than that of N.D.S method using cement. In addition, it is anticipated that the current research results are contributed to develop the grouting design technology.

• Journal of the Korean GEO-environmental Society
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• v.20 no.5
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• pp.31-38
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• 2019

Recently, there has been an increasing number of ground subsidence (sink-hole) in the downtown areas, and in such a case, it is important to minimize accidents and passages through prompt recovery. With respect to the present recovery method for ground subsidence, the methods of applying the back filling after excavating the ground subsidence or using the grouting injected materials to restore the ground are mostly used, but there has been few studies on materials used for recovering the ground subsidence. Therefore, in order to clarify the characteristics of back filling materials used in the ground subsidence, this study uses the environment-friendly hardening agent to improve the dredged clay, and then, the mixture ratio of hardening agent and mixture ratio of decomposed granite soil is changed to cure for 3, 7, 14 and 28 days to analyze the intensity characteristics of the unconfined compression, and it was compared with the unconfined compression intensity for the previously used cement, a hardening agent. In order to evaluate the characteristics of intensity on the back filling materials, the C.B.R test was carried out, and for the review on whether the back filling materials influence on corrosion of water and sewer pipes and others, the soil non-resistance test was carried out. As a result of the test, for the case of the recovery work of the ground subsidence that requires urgency, it is considered as prudent if the hardening agents of 12% are integrated to cure for 3 days or longer, and for not having the influence on the corrosion of the gas tube or water pipes, it is proposed to mix for 30% or more of the decomposed granite soil. Door model test were conducted To confirm the bearing capacity characteristics of the solidified layer.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.498-505
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• 2020

Aggregate occupies about 70-85% of the concrete volume and is an important factor in reducing the drying shrinkage of concrete. However, when constructing high-rise buildings, it acts as a problem due to the high load of natural aggregates. If the load becomes large during the construction of a high-rise building, creep may occur and the ground may be eroded. Material costs increase and there are financial problems. In order to reduce the load on concrete, we are working to reduce the weight of aggregates. However, artificial lightweight aggregates affect the interface between the aggregate and the paste due to its higher absorption rate and lower adhesion strength than natural aggregates, affecting the overall strength of concrete. Therefore, in this study, in order to grasp the interface between natural aggregate and lightweight aggregate by type, we adopted a method of measuring electrical resistance using an EIS measuring device, which is a non-destructive test, and lightweight bone. The change in the state of the interface was tested on the outside of the material through a blast furnace slag coating. As a result of the experiment, it was confirmed that the electric resistance was about 90% lower than that in the air-dried state through the electrolyte immersion, and the electric resistance differs depending on the type of aggregate and the presence or absence of coating. As a result of the experiment, the difference in compressive strength depending on the type of aggregate and the presence or absence of coating was shown, and the difference in impedance value and phase angle for each type of lightweight aggregate was shown.

• Journal of the Korean Geotechnical Society
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• v.25 no.6
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• pp.31-45
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• 2009

The aim of this study is to evaluate the applicability of Granulated Blast Furnace Slag to the development of the Powdered Ready-mixed Shotcrete. First of all, after accomplishing SEM analysis and Leaching Test, the laboratory and field experiments for evaluating the utility of Granulated Blast Furnace Slag were performed. As a result of SEM and Leaching test, the environmental stability was confirmed. That is, non-detection of harmful lists and dense shotcrete structure result from mixing Granulated Blast Furnace Slag. As a result of lab. and field test, Blast Furnace Slag is superior to Plain Batch in improving strength and durability. And it will be able to improve to some extent the problem caused by the delayed reaction of existing Granulated Blast Furnace Slag with alkali activated material. Also the proper amount of Granulated Blast Furnace Slag is estimated to be under 30%. Finally, it is possible that Granulated Blast Furnace Slag can apply to economical recycling and development of the Ready-mixed Shotcrete for its price is only about 5% of Silica-finne's price.

• The Journal of Korean Academy of Prosthodontics
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• v.46 no.5
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• pp.479-489
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• 2008

Statement of the problem: Under anatomical limitations on maxillary posterior region, a poor crown-to root ratio acting on dental implants can result in undesirable stress in surrounding bone, which in turn can cause bone defects and eventual failure of implants. Purpose: The purpose is to compare stress distribution due to different crown-root ratio and effect of splinting between natural teeth and implants in maxillary molar area under different loads. Material and methods: Analysis of stress arising supporting bone of the natural teeth and the implant was made with 3-dimensional finite element method. The model simulated naturel teeth was made with 2nd premolar and 1st molar in the maxillary molar region (Model T). The model simulated implants placed on same positions with two parallel implants of Straumann Dental Implant cemented abutment (Model I). Each model was designed in different crown-root ratio (0.7:1, 1:1, 1.25:1) and set cement type gold crown to make it non-splinted or splinted. After that, 300 N force was loaded to each model in five ways (Load 1: middle of occlusal table, Load 2: middle of buccal cusp, Load 3: middle of lingual cusp, Load 4: horizontal load to buccal cusp of anterior abutment only, Load 5: horizontal load to middle of buccal cusp of each abutment), and stress distribution was analyzed. Results and conclusion: On all occasions, stress was concentrated at the cervical region of the implant. Under load 1, 2 and 3, stress was not increased even when crown-root ratio increases, but under load 4 and 5, when crown-root ratio increases, stress also increased. There was difference in stress values between natural teeth and implants when crown-root ratio gradually increases; In case of natural teeth, splinting decreased stress under vertical and horizontal loads. In case of implants, splinting decreased stress under vertical loads 1,2 and 3, but increased maximal stress under loads 2 and 3. Under horizontal loads, splinting decreased stress, however the effect of splinting decreased under load 5 than load 4. Furthermore, the stress was increased, when crown-root ratio is 1.25:1. Clinical implications: This limited finite element study suggests that the stress on supporting bone may be increased under non-axial loads and poor crown-root ratio. Under poor crown-root ratio, excessive stress was generated at the cervical region of the implant, and decreased splinting effect for stress distribution, which can be related to clinical failure.