• The Journal of Korean Academy of Prosthodontics
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• v.58 no.1
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• pp.58-66
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• 2020

Implant-Assisted Removable Partial Dentures (IARPDs) treatment is being performed in a fully edentulous patient using implant surveyed prosthesis as an abutment. Implant-supported prosthesis as an abutment of IARPDs is classified into screw-retained and cement-retained type according to the retention type, and each has advantages and disadvantages. The EZ crown system (Samwon DMP, Yangsan, Korea) has a cylinder combined with abutment, and the nickel-titanium spring in this cylinder provides a constant force on the zirconia ball to obtain retention in EZ crown system. In this patient, the natural abutment teeth of the mandibular overdenture was hopeless. We planned implant assisted removable partial denture using anterior implant surveyed prosthesis considering functional and esthetical rehabilitation, cost and patient's needs. When fabricating IARPDs using implant as abutment, we could compensate for the shortcomings of existing implant-supported prosthesis retention type and made the design of removable partial denture easy due to using EZ crown system.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.157-163
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• 2018

This study is aimed at controlling the fiber orientation and improve the fiber distribution in fiber-reinforced cement composites using blades that can be placed inside the existing nozzles. To optimize the blade parameters, multi-physics finite element analysis was performed that could account for the flow of the cementitious matrix material, the movement of the entrained fibers, and the interactions with the nozzle. As a result, this study defined the blade distance, length, and position as a function of the fiber length to be used in the field. The blades with a distance from 1.2 to 2.4 times the fiber length and length from 4 to 8 times the fiber length, as well as located at below 14 times the fzfiber length from the nozzle exit maintained the fiber orientation angle less than $5^{\circ}$. In addition, the blade-type nozzle proposed in the study can be attachable and detachable to the conventional casting equipment, and thus it can provide the usability and convenience in practical applications.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.5
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• pp.148-155
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• 2017

In this study, by using the international standards ISO TS 16774, Part 2 Test method for chemical resistance as a quality control method of injection type repair material used for leakage crack of underground concrete structure, the performance requirement against of chemical environment of underground concrete structures for repair materials was tested. For this testing 3 types for each of the 2 classes of repair materials(synthetic rubber, cement), with a total of 9 types repair materials, were selected and examined. As a result, the test results showed that the smallest performance deterioration by the change in the mass was with the synthetic rubber(RG) type as opposed to the cement type system, showing that the synthetic rubber type had the strongest relative resistance to chemical exposure. Furthermore, it is necessary to investigate the material with high resistance to chemical substances and to examine the material which can increase resistance to sodium hydroxide and sodium chloride in cement system. These results can be used as a basic index for the selection of repair materials with the strongest resistance to chemical environment found in concrete structures. In addition, it is expected that the test results derived in this study can be used as reference data that can be reflected in the quality improvement of the maintenance material to be developed later.

• Journal of the Korea Concrete Institute
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• v.22 no.5
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• pp.727-736
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• 2010

This paper describes results of an preliminary study to produce strain hardening cement-based composites (SHCCs)with consideration of sustainability for infrastructure applications. The aims of this study are to evaluate the influence of recycled materials on the mechanical characteristics of SHCCs, such as compressive, four-point bending, and direct tensile behaviors, and to give basic data for constitutive model for analyzing and designing infra structures with SHCCs. In this study, silica sand, cement, and PVA fibers, were partially replaced with recycled sand, fly-ash, and FET fibers in the mixture of SHCCs, respectively. Test results indicated that fly-ash could improve both bending and direct tensile performance of SHCCs due to increasing chemical bond strength at the interface between PVA fibers and cement matrices. However, SHCCs replaced with PET fibers showed much lower performance in bending and direct tensile tests due to originally low mechanical properties of own fibers, although compressive behavior is similar to PVA2.0 specimen. Also, it was noted that the recycled sand would increase elastic modulus of SHCCs due to larger grain size compared to silica sand. Based on pre-set target value to maintain the performance of SHCCs, it was concluded that the replacement ratio below 20% of fly-ash or below 50% of recycled sands would be desirable for creating sustainable SHCCs.

• Journal of the Korea Institute of Building Construction
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• v.16 no.5
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• pp.405-412
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• 2016

In order to examine the possibility of practical use of concrete at low-temperature environment using high early strength cement with cold resistance admixture, an experimental study on workability, freezing temperature and compressive strength of the mortar with different types of anti-freezer, water reducing agent and accelerator for freeze protection at low-temperature were evaluated. Compressive strength was increased in use of anti-freezer, especially SN anti-freezer was higher than CN anti-freezer. 0min flow was increased, the 20min flow was decreased. And 20min flow was improved in use of FR, RT water reducing agent. CF, LS accelerator for freeze protection, regardless of the type of water reducing agent, compressive strength was increased.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.1
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• pp.108-115
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• 2020

In this study, the flexural performance of Highly Ductile Cement Composites(HDCC) mimicking boundary conditions of shellfish skin layer was evaluated. To improve ductility by mimicking the boundary skin layer structure of shellfish, the method of stratification by charging between precast panels using HDCC and the method of distributing PE-mesh to the interface surface were applied. Evaluation of flexural performance of layered cement composite materials mimicking boundary conditions of shellfish skin layer resulted in increased ductility of all test specimens applied with stratified cross-section compared to typical bending test specimens. The layered method by inserting PE-mesh showed excellent ductility. This is most likely because the inserted PE-mesh made an interface for separating the layers while the HDCC pillars in the PE-mesh gave adhesion between layers.

• The Journal of Korean Academy of Prosthodontics
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• v.56 no.3
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• pp.206-211
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• 2018

Purpose: Recently, a method of forming a slot in the prosthesis lingual has been introduced to solve the occlusal and aesthetic disadvantages of screw-retained prosthesis in the manufacture of implant-fixed prosthesis and to ensure retrievability in cement retained prostheses. The purpose of this study is to investigate the effect of the internal gap on the removal of the prosthesis in the preparation of cement-retained implant prostheses with lingual slots. Materials and methods: Titanium abutment and internal gap of the zirconia prosthesis to be attached to the upper part were set to 30, 35, and $50{\mu}m$, respectively. Three for each type total 15 were produced for each type. The zirconia prosthesis formed a retrievable cement-type slot with a space of 1 mm at the location where the titanium abutment meets the shelf area. Autocatalytic resin cement was used for bonding of abutment and zirconia prosthesis, and the maximum removal stress value was measured in units of Ncm by using the customized equipment of the cemented specimen. The Kruskal-Wallis test was used to compare the three groups by statistical analysis (${\alpha}=.05$), modified by post hoc test the Mann-Whitney U-test and the Bonferroni correction method were used to compare the two methods (${\alpha}=.017$). Results: There was no statistically significant difference in removal stress between the $30{\mu}m$ group and the $35{\mu}m$ group in the internal gap (P = .032), and there was a significant difference between the $30{\mu}m$ group and the $50{\mu}m$ group, between the $35{\mu}m$ group and the $50{\mu}m$ group (P < .017). Conclusion: Thus, the internal gap of computer-aided design affected the retention between the zirconia prosthesis and the titanium abutment.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.5
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• pp.94-104
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• 2013

Experiments were divided into two parts; one part is to understand the basic properties of high flowable VA/VeoVa-modified cement mortar with different polymer cement ratio (P/C) and the weight ratio of fine aggregate to cement (C:F) and the other part is to investigate the effect of surface water spread on the concrete substrate on adhesion in tension. To understand the basic performance, the specimens were prepared with proportionally mixing VA/VeoVa redispersible powder, ordinary portland cement, silica sand, superplasticizer and viscosity enhancing agent. Here, P/C were 10, 20, 30, 50 and 75% and C:F were 1:1 and 1:3. As the change of P/C and C:F unit weight, flow test, crack resistance and adhesion in tension were measured. Three specimens with good adhesion properties were selected among specimens with different P/C and C:F. The effect of surface water evenly sprayed on concrete substrate on adhesive strength is investigated. The results show that surface water on concrete substrate increases the adhesion in tension of high flowable VA/VeoVa-modified cement mortar and additionally improves the flowability compared to the non-sprayed case.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.3 s.55
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• pp.173-180
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• 2009

Very-early strength latex-modified concrete(below ; VES-LMC) was developed for possible early-opening-to-traffic after overlay of bridge deck concrete. The purpose of this study is to analyze the cause of map, transverse and longitudinal cracking in VES-LMC and to provide a control method for minimizing occurrence of cracking. The proposed prevention method against map and transverse cracking was verified by field data. VES cement was modified as the unit cement content was reduced from 390kg/$m^3$ to 360kg/$m^3$. The maximum size of coarse aggregate was increased from 13mm to 19mm. The wire mesh and steel fiber were adopted in concrete mixture. From the results, the proposed prevention method against map and transverse cracking was verified since structural cracking was not occurred until 3 years after overlay.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.5
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• pp.71-80
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• 2007

Because of the characteristics relating to high tensile ductility, High Performance Fiber Reinforced Cementitious Composites (HPFRCC) are studied to be adopted in repair and retrofit of buildings. A series of three shear wall specimens was tested under constant axial stress and reversed cyclic lateral loading in order to evaluate the seismic retrofit that had been proposed for the shear wall with the opening. The retrofit involved the use of newly developed ECC and MDF(Macro Defect Free), both of which are sprayed through the high pressure pump, over the entire face of the wall. The results indicate that two difference types of retrofitting strategy make the different effects of a rise in the strength and ductility of each specimen.