• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.4
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• pp.299-306
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• 2023

Environmental pollution problems are occurring due to the negative treatment of basalt waste in Jeju Island. This study identifies the characteristics of permeable block with basalt with physical and chemical adsorption mechanisms and examines their applicability and functionality as building materials. This experiment is basic data for evaluating the functionality of the permeable block by analyzing flexural strength, compressive strength, permeability coefficient, carbon dioxide, and fine dust adsorption rate by producing a permeable block using a basalt waste rock. As the basalt waste stone replacement rate increased, the flexural strength and compressive strength tended to decrease, and as the replacement rate increased, the water permeability coefficient, absorption rate, carbon dioxide, and fine dust adsorption rate tended to increase. Therefore, it is judged that the permeable block using the basalt waste rock is superior to the existing permeable block.

• Journal of the korean academy of Pediatric Dentistry
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• v.30 no.1
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• pp.161-170
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• 2003

The aesthetic restorative materials are widely used in recent dentistry, showed not only the different quality between each component but also showed that the environment of the material has important effect on the physical properties of the material. Especially, when the restoratives are restored in the mouth, and since saliva is existing, the restoratives are always exposed to water and affected by the saliva. The purpose of this study was to research and compare the change of the degree of water sorption after water immersion of three types of the resin-based materials and the compressive strength, and observe the relation between the change of the water absorbing degree and the compressive strength. Z-100(3M, U.S.A) as a composite resin, F-2000(3M, U.S.A) as a compomer and Vitremer Restoratives(3M, U.S.A) as a resin-modified GIC were used, and each specimen was made to measure the water sorption and to evaluate the compressive strength. The specimens for measurement of the water sorption and the compressive strength were divided into 4 groups(1 day, 2 weeks, 4 weeks, and 8weeks). Each specimen was filled in the 30cc vial with 20cc of distilled water during the fixed amount of period in $37^{\circ}C$. The water sorption is decided by dividing the difference of weight before and after the immersion by the volume, and the compressive strength was measured by using the instron after the immersion. The following results were obtained ; 1. The more the water sorption increased, the more the immersion period of three restorative materials was long. And the most of water sorption was obtained during the first 2 weeks(P<0.001). 2. The water sorption of resin-modified GIC was higher than composite resin and compomer. 3. The more the compressive strength decreased, the more the immersion period of three restorative materials increased(composite resin and compomer: P<0.001, resin-modified GIC: P<0.05). Especially, the amount of the reduction in compressive strength of the composite resin was the highest. 4. The more the water sorption of all materials increased, the more the compressive strength decreased(P<0.05).

• Composites Research
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• v.22 no.2
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• pp.24-29
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• 2009

This study aims to investigate the residual strength of sandwich composites with Al honeycomb core and carbon fiber face sheets after the quasi-static indentation damage by the experimental investigation. The 3-point bending test and the edge-wise compressive strength test were used to find the mechanical properties, and the quasi-static point load was applied to introduce the simulated damage on the specimen. The damaged specimens were finally assessed by the 3-point bending test and the compressive strength test. The investigation results revealed the residual strength of the damaged specimens due to the quasi-static indentation. The both test results showed that the residual strength of the damaged specimen was decreased according to increases of the damaged depth.

• Korean Journal of Agricultural Science
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• v.18 no.1
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• pp.33-40
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• 1991

This study was performed to obtain the basic data applied to use of synthetic lightweight aggregate concrete affected by alkali silica reaction. The results obtained were summarized as follows; 1. The compressive strength of type A concrete was increased with increase of curing age. At the curing age 28 days, the highest compressive strength was showed at type Band C concrete, respectively. But, it was gradually decreased with increase of curing age at those concrete. 2. The flexural strength of type A concrete was increased with increase of curing age. At the curing age 14 days, the highest flexural strength was showed at type Band C concrete, respectively. But, it was gradually decreased with increase of curing age at those concrete. 3. The correlation between compressive and flexural strength of the sample was shown highly significant only at type A concrete. 4. It was shown that the water absorptions of the type Band C were 7.0-7.8 times higher than the type A concrete. It was significantly higher at the early stage of immersed time at all sample. 5. The correlation between compressive strength and water absorption of the sample was significant only at the type A concrete.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.934-941
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• 2002

It is important to consider the effect of member size when estimating the ultimate strength of a concrete flexural member because the strength always decreases with an increase of member size. In this study, the size effect of a reinforced concrete (RC) beam was experimentally investigated. For this purpose, a series of beam specimens subjected to four-point loading were tested. More specifically, three different effective depth (d$\approx$15, 30, and 60 cm) reinforced concrete beams were tested to investigate the size effect. The shear-span to depth ratio (a/d=3) and thickness (20 cm) of the specimens were kept constant where the size effect in out-of-plane direction is not considered. The test results are curve fitted using least square method (LSM) to obtain parameters for the modified size effect law (MSEL). The analysis results show that the flexural compressive strength and the ultimate strain decrease as the specimen size increases. In the future study, since $\beta_1$ value suggested by design code and ultimate strain change with specimen size variation, a more detailed analysis should be performed. Finally, parameters for MSEL are also suggested.

• Journal of the Korea Concrete Institute
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• v.13 no.5
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• pp.423-429
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• 2001

In this study, strength characteristics of concrete specimens subjected to horizontal continuous vibration during initial curing were investigated. As experimental variables, vibration velocity(0.25, 0.5, 1.0, 2.0, 4.0 kine) and vibration time(3, 6, 12, 24 hrs) were used. Density and segregation of the specimens were also investigated. Vibrating was started soon after placing, and strengths investigated consist of compressive strength, splitting tensile strength, and bond strength. Strengths decrease were hardly occurred at 0.25 kine vibration velocity regardless of vibration times and all strengths were increased for 3 hrs vibration at 0.5 kine vibration velocity. Density was increased for all specimens due to the vibration and there was no serious segregation under even 4 kine vibration velocity.

• Journal of the Korea Institute of Building Construction
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• v.9 no.6
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• pp.113-119
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• 2009

This study is to investigate the fundamental and fireproof qualities of high strength concrete corresponding to changes in the curing factors and the PP fiber ratio. The results were as follows. For the fundamental characteristics of concrete, the fluidity was reduced in proportion to the increase in the PP fiber ratio. The compressive strength was somewhat reduced according to an increase in the PP fiber ratio. However, it had the high strength scope of more than 60 MPa at 7 days and of more than 90 MPa at 28 days. On the spalling mechanism followed by changes of the water content ratio, spalling was prevented in all combinations, except the specimen without PP fiber and subjected to 3.0% of moisture contents. When spalling was prevented at that time, the residual compressive strength ratio was 22%~41% and the mass reduction ratio was 5%~7%, which was relatively favorable. As the spalling mechanism corresponds to changes in the curing method, spalling was prevented in concrete with a PP fiber mixing ratio of more than 0.05% in the event of standard curing, and in concrete with a PP fiber mixing ratio of more than 0.10% in the case of steam curing and autoclave curing. In these cases, when spalling was prevented, the residual compressive strength ratio was 23~42% and the mass reduction ratio was 7~11%. In these results, the ease of spalling prevention in high strength concrete was inversely proportional to the water content ratio. Depending on the curing method, spalling was prevented in concrete with over 0.05% PP fiber with standard curing and in concrete with over 0.1% PP fiber with steam curing and autoclave curing.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1261-1266
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• 2012

In this study, salt-water immersion tests were experimentally performed for up to 12 months to investigate the hygrothermal effect of salt-water environments on the mechanical properties of carbon/epoxy composites. The composites were manufactured by laminating prepregs composed of carbon plain-woven fabric and epoxy resin. The specimens were subjected to temperatures of 35, 55, and $75^{\circ}C$ while being exposed to the salt-water environments. Mechanical test results showed that the tensile modulus and tensile strength decreased at a small rate, and the compressive modulus and compressive strength decreased at a relatively larger rate, as the exposure temperature and time increased. The rate of decrease in compressive strength became larger as the exposure temperature became higher. This is because a higher environmental temperature accelerates the salt-water uptake; this, in turn, reduces the compressive strength more rapidly.

• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.87-95
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• 2012

This study investigated the compressive strength, flexural strength, setting time, and rebound when blast furnace slag and anhydrite, which are widely used mineral admixtures for concrete, are applied to shotcrete. When Ordinary Portland Cement (OPC) was replaced at a rate of 10% with blast furnace slag and anhydrite, the initial and final setting time requirements were all satisfied. However, when OPC was replaced at a rate of 20%, final setting was delayed, revealing that this mixture was not suitable for shotcrete. Compressive strength test results showed that the mixture with 10% OPC replacement rate met the target strength at 1 day and 28 days for permanent tunnel support usage. Particularly, the mixture designed with OPC replacement by blast furnace slag and anhydrite at rates of 5% showed the highest compressive strength. Rebound measurements revealed that this mixture exhibited excellent performance with 23% reduction in the rebound compared to the shotcrete that was produced with only OPC binder.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.6
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• pp.56-62
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• 2012

The results presented in this paper form part of an investigation into the optimization of a ternary blended cementitious system based on ordinary Portland cement (OPC)/blast furnace slag(BFS)/fly ash(FA) for the development of ultra high strength concrete. Concrete covering a wide range of BFS/FA blending proportions were investigated. Compressive strength at the ages of 3, 7 and 28 days for concrete specimens containing 0%, 10%, 20% and 30%FA along with 0%, 30%, 40% and 50%BFS as partial cement replacement at a water-binder ratio of 0.18 were investigated. Tests on porosity and pore size distribution were conducted using mercury intrusion porosimetry. The results show that the combination of FA10 and BFS30 can improve both short- and long-term properties of concrete as results of reducing of pores larger than 50nm.