• Proceedings of the Korean Society of Precision Engineering Conference
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• 2011.06a
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• pp.901-902
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• 2011

• The Journal of Korean Academy of Prosthodontics
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• v.43 no.3
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• pp.293-305
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• 2005

Statement of problems. Conventional feldspathic porcelain is used extensively as a restorative material and it is subjected to grinding and polishing during fabrication and delivery procedures. There is still considerable controversy concerning the best methods to achieve the strongest porcelain restorations after such adjustments. Purpose. The objective of this study was to investigate the effects of (1) overglazing, (2) selfglazing, and (3) fine polishing on the flexural strength and fracture toughness of feldspathic dental porcelain. Material and method. Ninety porcelain disks were prepared for flexural strength test and sixty porcelain disks were fabricated for fracture toughness test. Specimens were divided into three groups for each test as follows: 1) overglazed 2) self-glazed 3) polished. The flexural strength of feldspathic porcelains was determined by ring-on-ring biaxial flexural strength test. The fracture toughness values of three experimental groups were obtained by indentation fracture toughness test. Results. The flexural strength of overglazed group was significantly higher than that of selfglazed and polished group (P<0.05), while the difference between self-glazed and polished group was not significant (P>0.05). The fracture toughness values of overglazed and polished group were significantly higher than that of self-glazed group (P<0.05), while the difference between overglazed and polished group was not significant (P>0.05). Conclusions. This results supported the use of polishing as an alternative to glazing metal ceramic restorations, as it was not detrimental in flexural strength and fracture toughness. But, under the conditions of this study, overglazing was the ideal surface finishing method of feldspathic dental porcelain.

• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.523-530
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• 2009

For designing concrete structures, engineers are provided data from unidirectional flexure test in most cases. But real structural components such as pavements and deck panel are subjected to multiaxial stress throughout their body. Therefore, biaxial flexure test for concrete may be considered as a gage of the performance of concrete in service. In this paper, we propose the optimum biaixial flexture test (BFT) to measure the biaxial flexural strength of concrete. This method are an improved version of the ring-on-ring test which have been used extensively in the fields of ceramics and biomaterials. The optimum geometry of the test specimen was determined by using a three-dimensional finite element analysis. A series of test data obtained from the proposed test method is provided to show that the proposed optimum biaxial flexure test method can be used to identify the biaxial tensile strength of concrete.

• Journal of Korean Society of Steel Construction
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• v.26 no.3
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• pp.219-229
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• 2014

The experiment and FE analysis of ultimate behavior of GFRP cylindrical shell structure stiffened by steel pipe ring instead of rectangular cross-section ring was presented. Four kinds of test models were designed and flexural failure experiment was performed to investigate ultimate behavior characteristic according to the size of cross section of steel pipe ring and diameter of GFRP shell. Material properties of specimens were experimented by bending, tensile and compressive test. Displacements and strains were measured to evaluate failure behavior of steel pipe ring and GFRP shell structure. The experimental results were compared with the FEA results by commercial program ABAQUS. It is observed that GFRP shell structure stiffened by steel ring have enough ductility to bending failure, and an increase of bending rigidity of steel ring is very effective to increase of failure strength of GFRP shell structure.

• Advances in concrete construction
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• v.5 no.1
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• pp.31-48
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• 2017

Supplementary cementitious materials (SCM) have turned out to be a vital portion of extraordinary strength and performance concrete. Metakaolin (MK) is one of SCM material is acquired by calcinations of kaolinite. Universally utilised as pozzolanic material in concrete to enhance mechanical and durability properties. This study investigates the fresh and hardened properties of conventional concrete (CC) and self compacting concrete (SCC) by partially replacing cement with MK in diverse percentages. In CC and SCC, partial replacement of cement with MK varies from 5-20%. Fresh concrete properties of CC are conducted by slump test and compaction factor tests and for SCC, slump flow, T500, J-Ring, L-Box, V-Funnel and U-Box tests. Hardened concrete characteristics are investigated by compressive, split tensile and flexural strengths at age of 7, 28 and 90 days of curing under water. Carbonation depth, water absorption and density of MK based CC and SCC was also computed. Fresh concrete test results indicated that increase in MK replacement increases workability of concrete in a constant w/b ratio. Also, outcomes reveal that concrete integrating MK had greater compressive, flexural and split tensile strengths. Optimum replacement level of MK for cement was 10%, which increased mechanical properties and robustness properties of concrete.

• Advances in concrete construction
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• v.4 no.1
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• pp.49-69
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• 2016

This work investigates the mechanical properties of conventional concrete (CC) and self compacting concrete (SCC) using fine rubber and silpozz were accompanied by a comparative study between conventional rubberized concrete (CRC) and self compacting rubberized concrete (SCRC). Fine rubber (FR) from scrap tires has replaced the fine aggregate (FA) and Silpozz has been used as a replacement of cement at the proportions of 5, 10 and 15%. Silpozz as a partial replacement of cement in addition of superplasticiser (SP) increases the strength of concrete. Fresh concrete properties such as slump test, compaction factor test for CRC, whereas for SCRC slump flow, $T_{500}$, V-funnel, L-box, U-box, J-ring tests were conducted along with the hardened properties tests like compressive, split tensile and flexural strength test at 7, 28 and 90 days of curing. The durability and microstructural behavior for both CRC and SCRC were investigated. FR used in the present study is 4.75 mm passing with fineness modulus 4.74.M30 grade concrete is used with a mix proportion of 1:1.44:2.91 and w/c ratio as 0.43. The results indicate that as FR quantity increases, workability of both CRC and SCRC decreases. The results also show that the replacement of natural fine aggregate (NFA) with FR particles decreases the compressive strength with the increase of flexural strength observed upto 5% replacement of FR. Also replacement of cement with silpozz resulted enhancement of strength in SCRC.

• Journal of Powder Materials
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• v.24 no.6
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• pp.450-456
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• 2017

Reaction-bonded silicon carbide (RBSC) is a SiC-based composite ceramic fabricated by the infiltration of molten silicon into a skeleton of SiC particles and carbon, in order to manufacture a ceramic body with full density. RBSC has been widely used and studied for many years in the SiC field, because of its relatively low processing temperature for fabrication, easy use in forming components with a near-net shape, and high density, compared with other sintering methods for SiC. A radiant tube is one of the most commonly employed ceramics components when using RBSC materials in industrial fields. In this study, the mechanical strengths of commercial RBSC tubes with different sizes are evaluated using 3-point flexural and C-ring tests. The size scaling law is applied to the obtained mechanical strength values for specimens with different sizes. The discrepancy between the flexural and C-ring strengths is also discussed.

• Computers and Concrete
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• v.20 no.1
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• pp.39-47
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• 2017

In this paper, mode I fracture toughness of rock was determined by direct and indirect methods using Particle Flow Code simulation. Direct methods are compaction tension (CT) test and hollow centre cracked quadratic sample (HCCQS). Indirect methods are notched Brazilian disk (NBD) specimen, the semi-circular bend (SCB) specimen, hollow centre cracked disc (HCCD), the single edge-notched round bar in bending (SENRBB) specimen and edge notched disk (END). It was determined that which one of indirect fracture toughness values is close to direct one. For this purpose, initially calibration of PFC was undertaken with respect to data obtained from Brazilian laboratory tests to ensure the conformity of the simulated numerical models response. Furthermore, the simulated models in five introduced indirect tests were cross checked with the results from direct tests. By using numerical testing, the failure process was visually observed. Discrete element simulations demonstrated that the macro fractures in models are caused by microscopic tensile breakages on large numbers of bonded discs. Mode I fracture toughness of rock in direct test was less than other tests results. Fracture toughness resulted from semi-circular bend specimen test was close to direct test results. Therefore semi-circular bend specimen can be a proper test for determination of Mode I fracture toughness of rock in absence of direct test.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.11a
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• pp.55-59
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• 2009

The epoxy resin without hardener can harden by a ring-opening reaction in the presence of the alkalies produced by the hydration of cement in epoxy-modified mortars and concretes. This paper investigates the effect of curing conditions on the strength improvement of polymer-modified mortars using bisphenol A-type epoxy resin without hardener. The polymer-modified mortars using epoxy resin are prepared with various polymer-cement ratios, and subjected to ideal, water, dry and heat cures. In the heat cure, the epoxy-modified mortars are sealed or unsealed with a PVDC (polyvinylidene chloride) film. The epoxy-modified mortars are tested for flexural and compressive strengths at desired curing methods. The microstructures of the epoxy-modified mortars are also observed by scanning electron microscope. The effects of curing conditions on the strength development of the epoxy-modified mortars are examined. From the test results, the marked effectiveness of the heat cure under the PVDC film sealing against the development of the strength of the epoxy-modified mortar without the hardener is recognized. The flexural and compressive strengths of 7-day-90℃ heat-cured, PVDC film-sealed epoxy-modified mortars without hardener reach 7 to 17MPa and 24 to 44MPa respectively, and are two to three times of Unmodified mortar. Such high strength development of the epoxy-modified mortars may be achieved by the dense microstructure formation by cement hydrates and the hardening of the epoxy resin in the mortars.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.6
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• pp.120-131
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• 2019

Recently, the level of fine dust and ultrafine dust has reached its highest level, threatening the public's health. If the air purifier was not operated indoors, natural ventilation would not be possible. In this study, photocatalyst is applied to building materials to purify air in a passive manner. In order to use photocatalyst for LEFC(Light Emotion Friendly Concrete), it is necessary to secure self-consolidating capability. Therefore, self-consolidating performance was evaluated by slump test, J-ring test and L-box test with UHPC materials applied. Based on these results, the mixture proportion was determined, and the mechanical performance was evaluated by compressive and flexural tests. Concrete blocks were constructed with a fabrication method that improved the existing process of making LEFC. Also, the concrete block was emptied as a way to reduce the use of expensive photocatalyst. Finally, in order to identify the distribution of TiO₂, an EDS analysis was performed.