• Journal of dental hygiene science
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• v.18 no.1
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• pp.42-49
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• 2018

The computer-aided design/computer-aided manufacturing (CAD/CAM) system was introduced to shorten the production time of all-ceramic restorations and the number of patient visits. Among these types of ceramic for dental CAD/CAM, they have been processed into inlay, onlay, and crown shapes using leucite-reinforced glass-ceramics to improve strength. The purpose of this study was to observe the mechanical properties and microstructure of leucite-reinforced glass-ceramics for dental CAD/CAM. Two types of leucite-reinforced glass-ceramic blocks (IPS Empress CAD, Rosetta BM) were prepared with diameter of 13 mm and thickness of 1 mm. Biaxial flexural testing was conducted using a piston-on-three-ball method at a crosshead speed of 0.5 mm/min. Weibull statistics were used for the analysis of biaxial flexural strength. Fracture toughness was obtained using an indentation fracture method. Specimens were observed by field emission scanning electron microscopy to examine the microstructure of the leucite crystalline phase after acid etching with 0.5% hydrofluoric acid aqueous solution for 1 minute. The results of strength testing showed that IPS Empress CAD had a mean value of $158.1{\pm}8.6MPa$ and Rosetta BM of $172.3{\pm}8.3MPa$. The fracture toughness results showed that IPS Empress CAD had a mean value of $1.28{\pm}0.19MPa{\cdot}m^{1/2}$ and Rosetta BM of $1.38{\pm}0.12MPa{\cdot}m^{1/2}$. The Rosetta BM sample exhibited higher strength and fracture toughness. Moreover, the crystalline phase size and ratio were increased in the Rosetta BM sample. The above results are expected to elucidate the basic mechanical properties and crystal structure characteristics of IPS Empress CAD and Rosetta BM. Additionally, they will help develop leucite-reinforced glass-ceramic materials for CAD/CAM.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.137-140
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• 2008

If the flexural member of concrete is designed using the FRP rebar, suddenly brittleness destruction resulted from the fracture of FRP rebar is generated in the extreme situation because of brittleness characteristics of FRP rebar and concrete when designed to be less than balanced reinforcement ratio, so it is recommended to design the flexural member of concrete to be more than balanced reinforcement ratio. In ACI 440.1R-06 proposes the different bending strength decrease coefficient according to destructive form of concrete flexural member using the FRP rebar. However, ACI 440.1R-06 applies the same strength decrease coeffient to all FRP rebars made of diverse materials. If the same strength decrease coefficient is applied to all FRP rebars, effect of increasing the reinforcement ratio and selection of FRP rebar will be considerably limited. In this regard, we are to propose the formula to calculate the bending strength decrease coefficient in consideration of change in characteristics of FRP rebar and L/D through the reliability analysis in this paper.

• Journal of the Korea Institute of Building Construction
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• v.13 no.2
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• pp.131-138
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• 2013

This study was carried out to investigate the possibility of using basalt powder sludge instead of sand in a normal cement dry mortar as a way to recycle basalt powder sludge, which is a waste product from the manufacturing a process of basalt in Jeju. Basic performance evaluations of the dry mortar material included a compressive strength test, a flexural strength test, and SEM to observe the micro structure. The compressive and flexural strengths were increased to a replacement ratio of 21% of basalt powder sludge, whereby a strength enhancement of about 40% greater than that of normal dry mortar was shown. However, the creation of hydration products affected the replacement ratio of the basalt powder sludge. The possibility of using basalt powder sludge waste was identified in this study, and results showed that the basalt powder sludge waste could be used as a material for a secondary product of concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.915-920
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• 2001

This study was conducted to analysis the distribution of the rectangular stress block for high-strength polymer concrete beam. C-shaped specimens were produced and tested to compute parameters of the rectangular stress block. They were $\kappa_{1}$ = 0.73, $\kappa_{3}$ = 0.94 and $\gamma$= 0.845, respectively. Experimental value of flexural strength of beam was same to be compared with theoretical value. But there is desirable to need many experimental data in order to exact design of polymer concrete structure.

• Computers and Concrete
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• v.21 no.3
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• pp.261-267
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• 2018

This paper discusses a study of cement mortar reinforced with Graphene Oxide (GO) flakes carried out at the University of Plymouth. Over 60 specimens were prepared and tested to obtain the tensile, compressive and flexural strengths of cement mortar with/without 0.5% GO flakes by weight of cement. The dispersion of the GO flakes and the effect of the use of polycarboxylate ether superplasticizer (0.2% by weight of cement) on the material strength are discussed. Images of the particle sizes of GO are presented from the transmission electron microscopy analysis. In addition, the images from the field emission scanning electron microscope analysis are also presented to show the difference of the microscopic structure of cement mortar with/without GO. The results of the strength tests are presented. It is shown that the inclusion of the GO flakes in general led to positive results, which suggest that GO improved the tensile, compressive and flexural strengths of cement mortar.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.57-60
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• 2005

The objective of this paper is to investigate and analyze the behaviour of prestressed I section structural members constructed with ultra high perfomance steel fiber reinforced cementitious concrete (SFR-UHPC). This material is known as reactive powder concrete (RPC) mixed with domestic materials and its compressive strength is over 150MP. The parameters of test specimens were span to depth ratio, prestressing force, prestressing wire placement and web width. Most influential parameter to determine the failure mode between shear and flexural action was proved to be shear span ratio. The characteristics of ultra high-strength concrete is basically brittle, but due to the steel fiber reinforcement behaviour of this structure member became ductile after the peak load. As a result of the test, the stress block of compressive zone should be redefined. The proposed analytical calculation of internal force capacity based by plastic analysis gave a good prediction for the shear and flexural strength of specimens. The numerical verification of the finite element model which constitutive law developed for Mode I fracture of fiber reinforced concrete correctly captured the overall behaviour of the specimens tested.

• Korean Journal of Materials Research
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• v.19 no.7
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• pp.391-396
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• 2009

2-dimensional silica-silica Continuous Fiber-reinforced Ceramic.matrix Composites (CFCCs) were fabricated by a sol-gel infilitration method that has a changing processing condition, such as the repetitions of infilitration. In order to investigate the relationship between the processing condition and the mechanical properties of composites, the mechanical properties of specimens were measured by means of a 4-point flexural strength test while the evidence of strength degradation were microstructurally characterized. There seemed to be a minimum density value that existed at which the delamination between the fabrics would not occur. In the case that the density of silica CFCCs exceeded 1.55 g/$cm^3$, the flexural strength also exceeded approximately 18 MPa at least. By applying the Minimum Solid Area (MSA) analysis of the porous structure, the correlation between the relative density and the mechanical properties of composites will be discussed.

• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.171-179
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• 2014

The purpose of this study is to evaluate the structural performance of DH beams. DH beam construction method uses thin steel plates as form-works and structural elements. The prefabricated plates and rebars of DH beams were transported to a construction site and erected for casting concrete at the site. In this study, the contribution of steel plates to the flexural strength was evaluated since the plates were expected to play a role as reinforcements. Five test specimens were made for experimental and analytical studies. They consisted of two DH beams for the positive moment test and two DH beams for the negative moment test and a RC beam for the comparison purpose. Test results on DH beams were compared with design equations and the RC beam test result. It was proven that DH beams demonstrated the good flexural behavior showing sufficient strengths and deformation capacities. Flexural strengths, principal strains of concrete, and rebar stresses were evaluated through nonlinear finite element analyses for two test beams. The analyses also showed that steel plates can contribute to the enhancement of flexural strength of DH beams. Based on experimental and analytical studies, it was concluded that steel plates of DH beams can be used as good flexural reinforcements.

• Journal of Korean Society of Steel Construction
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• v.18 no.3
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• pp.339-347
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• 2006

This study proposes a double-composite section to enhance the s serviceability of twin-girder railway bridges, especially in terms of the flexural stiffness of the composite section in negative-moment regions. This paper deals with experiments on continuous twin-girder bridge models with 5m-5m span length with the proposed double-composite action. From results of static tests on the bridge models, several design considerations were investigated including effective width, shear connection and ultimate strength of the double-composite concrete slab showed full shear connection, which verified the suggested empirical equation. From the flexural behavior of the double-composite section, the effective width of the bottom concrete slab can be evaluated as that of the concrete slab under compression. The ultimate flexural strength of the bridge models verified the validity of the rigid plastic analysis of the double-composite section. Design guidelines were suggested based on the test results.

• Steel and Composite Structures
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• v.34 no.4
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• pp.525-545
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• 2020

This paper presents a new structural system to use as retaining walls. In civil works, there is a general trend to use traditional reinforced concrete (RC) retaining walls to resist soil pressure. Despite their good resistance, RC retaining walls have some disadvantages such as need for huge temporary formworks, high dense reinforcing, low construction speed, etc. In the present work, a composite wall with only one steel plate (steel-concrete) is proposed to address the disadvantages of the RC walls. In the proposed system, steel plate is utilized not only as tensile reinforcement but also as a permanent formwork for the concrete. In order to evaluate the efficiency of the proposed SC composite system, an experimental program that includes nine SC composite wall specimens is developed. In this experimental study, the effects of different parameters such as distance between shear connectors, length of shear connectors, concrete ultimate strength, use of compressive steel plate and compressive steel reinforcement are investigated. In addition, a 3D finite element (FE) model for SC composite walls is proposed using the finite element program ABAQUS and load-displacement curves from FE analyses were compared against results obtained from physical testing. In all cases, the proposed FE model is reasonably accurate to predict the behavior of SC composite walls under out-of-plane loads. Results from experimental work and numerical study show that the SC composite wall system has high strength and ductile behavior under flexural loads. Furthermore, the design equations based on ACI code for calculating out-ofplate flexural and shear strength of SC composite walls are presented and compared to experimental database.