• Journal of the Korea Institute of Building Construction
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• v.14 no.3
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• pp.252-258
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• 2014

With the vision of 'a low carbon green develop' various industrial by-products were used as replacement of cement, in order to reduce $CO_2$ emissions from the manufacturing process of cement. Blast furnace slag is one of the industrial by-products. Due to the similar chemical compositions to ordinary Portland cement, blast furnace slag have been widely used in concrete with minimum side effects. Hence, in recent years, alkali activated slag-based composites are extensively studied by many researchers. However, the alkali activator can cause a number of problems in practice. Therefore, in this study, an alternative way of activating the slag was investigated. To activate the slag without using an alkali activator, calcium sulfate dihydrate was chosen and mixed with natural recycled fine aggregate. Fundamental properties of the slag-based mortar were tested to evaluate the effect of calcium sulfate dihydrate.

• Journal of the Korean Geosynthetics Society
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• v.13 no.4
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• pp.57-68
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• 2014

This study categorizes the distributed sand around coastal area of Jeju volcanic Island into three groups according to their components, and arranges their characteristics. In the case of basic physical properties, the silicate sand has slightly greater specific gravity than general sand, and the carbonate sand with widespread distribution has a lower specific gravity. In the gross, the carbonate sand has poor particle classifying and low uniformity coefficient because carbonate minerals of relatively large grain size are mixed. The relation between compressive strength and components shows conflicting tendency that silicate and carbonate components have positive correlation and negative correlation with compressive strength, respectively. Based on the components ratio of one to one, the sand having low carbonate component ratio is expected to be able to utilize in construction fine aggregate. To compare between square root (ACI 308) and cube root (KCI 2012) of compressive strength at computation of elastic modulus, it is considered to non-dimensional elastic modulus.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.1
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• pp.9-14
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• 2022

Most of the existing research on ferronickel slag has focused on its potential as aggregate and fine aggregate, this study was conducted focusing on the potential of ferronickel slag powder as a concrete admixture. For concrete, which fly ash, blast furnace slag, and FSP were mixed with each 10 % type the reactivity was evaluated by applying ASTM C 1260 of the United States. As a result, compared with the control group, the expansion rate of fly ash decreased by 8.43 % and that of fine blast furnace slag powder decreased by 14.46 %, while the expansion rate of ferronickel slag decreased by 49.40 %. it was confirmed that ferronickel slag can sufficiently be replaced existing supplementary cementitious admixtures such as fly ash and blast furnace slag in terms of suppressing the reactivity of aggregates. However as a result of SEM analysis, ettringites were generated, and additional research about how it affects concrete is needed.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.1
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• pp.74-79
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• 2022

In this study, the effect of a sudden decrease in internal humidity and a decrease in hydration level due to the tight internal structure of high-strength concrete and cement composites was investigated. To verify the change in the internal Si hydration, waste glass foam beads were used as a lightweight aggregate, and the internal unreacted hydrate reduction and hydrate formation tendency were identified over the mid- to long-term. Waste glass foam beads were mixed with 5, 10, and 20 %, and were used by pre-wetting. As the mixing rate of the waste glass foamed beads increased, the strength showed a tendency to decrease. In addition, when the mixing amount of pre-wetted waste glass foam beads increases inside through XRD analysis, TGA analysis, and Si NMR analysis, it is judged that the hydration degree of internal Si is different because moisture is supplied to the paste.

• Journal of Korean Dental Science
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• v.17 no.1
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• pp.36-44
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• 2024

Purpose: This study investigated the effect of dentin bonding agent acidity on surface microhardness of MTA. Materials and Methods: Forty cylindrical molds (3 mm×5 mm) were prepared, and three dentin bonding agents with different acidities: Adper Single Bond 2 (ASB), Single Bond Universal (SBU), and Clearfil SE bond 2 (CSE) were applied to the inner surface of the molds (n=10). No bonding agent was applied in the control group. MTA was mixed and inserted into the molds and sealed with a wet cotton pellet for 4 days. After setting, the Vickers microhardness (HV) test was done at 200, 400, 600 ㎛ from the inner surface of the mold. One-way ANOVA was conducted for all samples. A P-value of less than .05 was considered significant. Tukey HSD test was performed for post-hoc analysis. Results: The mean HV values and standard deviations were 67.02±11.38 (Con), 48.76±11.33 (ASB), 43.78±11.19 (CSE), 37.84±9.36 (SBU), respectively. The difference between the control group and the experimental groups was statistically significant (P<0.001). The difference between ASB and SBU was statistically significant (P<0.001), while the difference between SBU and CSE was not. There were no statistically significant differences between the various points from the inner surface of the mold within each group (P>0.05). Conclusion: Results of the current study indicate that use of dentin bonding agents with MTA can reduce the surface microhardness of MTA. Moreover, there is a direct relationship between the acidity of dentin bonding agents and the surface microhardness of MTA.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.2A
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• pp.129-136
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• 2011

Recently studies on functional concrete with a photocatalytic material such as $TiO_2$ have actively been carried out in order to remove air pollutants. The absorbtion of $TiO_2$ from those studies is applied by it being directly mixed into concrete or by suspension coated on the surface. When it comes to the effectiveness, the former process is less than that of the latter compared with the $TiO_2$ use. As a result, the direct coating of $TiO_2$ on materials' surface is more used for effectiveness. The Surface spread of it needs to have a more than $400^{\circ}C$ heat treat done to stimulate the activation and adhesion of photocatalysis. Heat treat consequently leads hydration products in concrete to be dehydrated and shrunk and is the cause of cracking. The study produces $TiO_2$ used Sol-gel method which enables it to be coated with a low temperature treat, applies it to pearlite using Lightweight Aggregate Concrete fixed with a low temperature treat and evaluates the spread performance of it. In addition to this, the size of pearlite is divided into two types: One is 2.5 mm to 5.0 mm and the other is more than 5.0 mm for the benefit of finding out the removal characteristics of $CH_3CHO$ whether they are affected by pearlite size, mixing method and ratio with $TiO_2$ and elapsed time. The result of this experiment shows that although $TiO_2$ produced by Sol-gel method is treated with 120 temperature, it maintains a high spread rate on the XRF(X ray Florescence) quantitative analysis which ranks $TiO_2$ 38 percent, $SiO_2$ 29 percent and CaO 18 percent. In the size of perlite from 2.5 mm to 5.0 mm, the removal characteristic of $CH_3CHO$ from a low temperature heated Lightweight concrete appears 20 percent higher when $TiO_2$ with Sol-gel method is spreaded on the 7 percent of surface. In other words, the removal rate is 94 percent compared with the 72 percent where $TiO_2$ is mixed in 10 percent surface. In more than 5.0 mm sized perlite, the removal rate of $CH_3CHO$, when $TiO_2$ is mixed with 10 percent, is 69 percent, which is similar with that of the previous case. It suggests that the size of pearlite has little effects on the removal rate of $CH_3CHO$. In terms of Elapsed time, the removal characteristic seems apparent at the early stage, where the average removal rate for the first 10 hours takes up 84 percent compared with that of 20 hours.

• The Journal of Engineering Geology
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• v.17 no.2 s.52
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• pp.279-287
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• 2007

An ore of stone obtained from quarry lose its about 60% such as the muck and the stone-dust during the process of making the architectural block, the crushed aggregate and so on. A part of the muck is only reutilized for the crushed aggregate as road pavement materials, while the most of the muck in the shape of powder is mixed with water and then it is deposited in a sludge tank. The muck in the shape of powder is called the stone-dust. If the stone-dust is discharged and sprayed, an ecosystem will have terrible damage because the seepage of surface water, the flow of ground water and the movement of air are not occurred smoothly by packing the void of soils. As the Waste Management Law (2003) in Korea, the stone-dust is sorted out the industrial waste and the most of that is dumped in ground. Therefore, the establishments of an efficient recycling plan are necessary through the improvement of engineering properties of the stone-dust. To investigate the possibility of recycle and improvement for the stone-dust, the stone-dust and natural soils are sampled from six quarries in Korea. The various soil tests are performed by use of the mixed soils with the stone-dust content ratio. As the result of various soil tests, the recycle possibility of the stone-dust is analyzed as subbase layer materials of the roads.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.3
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• pp.185-196
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• 2006

Fracture toughness is a material property for crack initiation and propagation in fracture mechanics. For mode I fracture toughness measurement in concrete, RILEM committees 89-FMT proposed three-point bend tests based on the two-parameter fracture model. But, there is no proposed test method as a standard for mixed mode test for now. And RILEM three-point bend test procedure is complicate. Therefore, in this study, brazilian disks of various size were designed as the concrete with a similar specified concrete strength and maximum size of coarse aggregate($G_{max}$) were respectively 20mm and 40mm. And mode I fracture toughness of brazilian disks was compared with that of RILEM three-point bend test. As a result, it was suggested appropriate size(thickness, diameter) and notch length ratio of brazilan disk on the $G_{max}$. And it was verified that stress intensity factors for mixed mode can be easily calculated with the disk specimen. Stress intensity factors of a concrete brazilian disk were evaluated with finite element analysis and five terms approximation for comparison.

• The Plant Pathology Journal
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• v.18 no.4
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• pp.192-198
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• 2002

Mixed infections of two economically important viruses, Turnip mosaic virus(TuMV) in the family Potyviridae and Ribgrass mosaic virus(RMV) in the genus Tobamo-virus, were studied ultrastructurally on oriental cabbage. TuMV-ACl8 (alpine isolate in Korea) induced chlorotic spots on inoculated leaves of both ‘SSD63’ inbred line known as susceptible to TuMV, and ‘Tambok’ commercial cultivar, known as resistant to the virus, in the early stages of infection. TuMV-C5 (Taiwan isolate) caused severe mosaic and malformation on the upper leaves of ‘SSD63’, and necrotic spots in both inoculated and upper leaves of ‘Tambok’. RMV-CA1 (oriental cabbage isolate from alpine in Korea) induced vein chlorosis, leaf malformation, and midrib necrotic streak in the upper leaves of both ‘SSD63’ and ‘Tambok’. Both oriental cabbages infected with a combination of TuMV-ACl8 and RMV-CA1 showed synergistic symptoms of severe yellowing, severe mosaic, and necrotic spot or vein necrosis on their leaves. A combination of TuMV-C5 and RMV-CA1 produced synergistic symptoms only in ‘SSD63’. In ‘Tambok’ infected with the combination of TuMV-C5 and RMV-CA1, the number of necrotic spots on the inoculated leaves was one half lesser than that on singly infected with TuMV-C5. A few necrotic spots progressed systemically. In cells infected with a combination of TuMV-ACl8 and RMV-CA1 or TuMV-C5 and RMV-CA1, the particles of the two viruses made nonagon-like rings(NLR); one TuMV particle was surrounded loosely by nine RMV particles. Two unrelated viruses of TuMV and RMV were compacted in the central part of the spiral aggregates(SA) that was induced strikingly in cells by the mixed infections. The SA showed NLR in its center of the cross-sectioned side. Many particles of RMV of Tobamovirus were closely associated with Potyvirus-characteristic cylindrical inclusions. The SAs in the mixed infections were formed easily by the Potyvirus of TuMV-ACl8 or -C5 isolates.

• Journal of the Korean GEO-environmental Society
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• v.21 no.10
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• pp.5-10
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• 2020

As the demand for the recycling of industrial by-products increases due to various environmental restrictions including the prohibition of ocean disposal, various studies regarding the recycling of industrial by-products are currently being carried out. One of the industrial by-product, coal ash is produced from thermal power generation; studies on the recycling of fly ash have been actively carried out and it is currently recycled in various fields. In the case of bottom ash, however, only a portion of the total amount generated is primarily processed into a particle size of 2~4mm or less than 2mm to be used for gardening purpose and light weight aggregate and so on. The remaining amount is buried at ash disposal sites. Therefore, various studies are needed to develop measures to use bottom ash. This study aimed at identifying the optimal particle size and mixing ratio of bottom ash to be used as CLSM aggregate. To this end, it evaluated the usability of bottom ash as CLSM aggregate, by investigating the flowability and strength change characteristics of CLSM produced with regard to the mixing ratio of weathered granite soil and bottom ash, particle size of bottom ash to be mixed and soil binder addition rate and conducting a heavy metal leaching test.