• Journal of the Korean Recycled Construction Resources Institute
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• v.12 no.2
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• pp.143-151
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• 2024

This study was analyzed the relationship between concrete slump, compressive strength and other factors such as the quantity of chloride or others using statistics method. The amount of chloride in cement was selected to range from 236 to 794 ppm, and cement that satisfied the KS L 5201 standard for other physical properties was used for this experiment. As a result, no factors had a interrelationship for initial slump and the strong-negative correlation between concrete slump elapsed time and the quantity of chloride. The proportion of chloride was shown as a strong-positive correlation for compressive strength from 1-day to 7-day curing. However, there was no correlation between chloride and compressive strength at 28-day curing.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.5 s.57
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• pp.133-141
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• 2009

50 year-old masonry buildings which had been constructed using lime mortar have caused lots of problems because of using different material, cement mortar, when they repair them. Also, there is little information on structural capacities and details of masonry buildings built using lime mortar. In addition, it is difficult to evaluate the structural capacities of the buildings which were often constructed by untrained labors. To preserve the original masonry construction, the study on their construction materials and methodologies has to be carried out. This paper provides basic information for establishing standard details of masonry works using lime mortar in order to overcome these problems when cultural properties are repaired or retrofitted. To do this, compression tests of lime mortar were preformed with the parameters of mixing ratios, mixing material, curing time and curing conditions etc. Based on the test results, the differences between lime mortar and cement mortar were specified and the structural characteristics of lime mortar were also presented in this paper.

• Journal of the Korea Convergence Society
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• v.9 no.9
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• pp.117-122
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• 2018

In this study, HU(hounsfield unit) value of CT generated by dental prosthesis was measured according to the type of metal when PET-CT was performed, and the degree of distortion and standard deviation of SUV(standard uptake value) and to propose a method to reduce errors in image reading. PET-CT was performed using actual teeth, metal crown, gold crown, titanium, and zirconia dental prosthesis. Compared with general teeth, the SUV value increased with increasing HU value. The SUV value of metal crown, titanium, and zirconia was increased by 37% and the gold crown increased by 45.4%. In addition, image distortions were small in general teeth, metal crown, titanium, and zirconia, but hard curing of the gold crown occurred and image distortion occurred. Therefore, since the metal type of the dental prosthesis affects the SUV value, the NAC(non attenuation correction) PET image of the dental prosthesis can be helpful in the diagnosis of the patient using the gold material.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.781-784
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• 2008

Recently as application of high-strength concrete on concrete structures has been on the rise, use of non-standard specimen is increasing. Therefore, this study investigated the effect of specimen's size effect, ratio of height/diameter and curing conditions on concrete compressive strength. Results of experiments showed that as size of specimen increased as much as 1 mm, standard design compressive strength of 24MPa fell as much as0.15MPa 40MPa fell as much as 0.1MPa 80MPa fell as much as 0.3MPa, and it indicates that as the level of strength is intensified, the decrement of compressive strength increases. As ratio of height/diameter increased as much as 1.0, compressive strength of 24MPa fell as much as 2.9MPa 40MPa fell as much as 3.7MPa 80MPa fell as much as 9.8MPa, and it means that as strength of concrete is higher, influence of ratio of height/diameter becomes bigger.

• Applied Chemistry for Engineering
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• v.10 no.7
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• pp.990-995
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• 1999

To determine the effect of chemical structure of linear amine curing agents on thermal and mechanical properties, standard epoxy resin DGEBA was cured with ethylene diamine(EDA) and hexamethylene diamine(HMDA) in a stoichiometrically equivalent ratio. From this work, the effect of linear amine curing agents on the thermal and mechanical properties is significantly influenced by the chemical structure or chain length of curing agents. In contrast, the results show that the DGEBA/EDA system having the two carbons had higher values in the thermal stability, maximum conversion of epoxide, density, glass transition temperature, tensile modulus, flexural strength, and flexural modulus than the DGEBA/HMDA system having the six carbons, whereas the DGEBA/EDA cure system had relatively low values in the shrinkage(%), thermal expansion coefficient, tensile strength, and had similar values in the maximum exothermic temperature, and conversion of epoxide compared to the DGEBA/HMDA cure system. This findings indicate that packing ability in the HMDA structure affects the thermal and mechanical properties.

• International Journal of Highway Engineering
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• v.20 no.1
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• pp.69-76
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• 2018

PURPOSES : This study determined the optimal usage rate of RAP (reclaimed asphalt pavement) using cold central-plant recycling (CCPR) on a road-surface layer. In addition, a mixture-aggregate gradation design and a curing method based on the proposed rate for the surface-layer mix design were proposed. METHODS : First, current research trends were investigated by analyzing the optimum moisture content, mix design, and quality standards for surface layers in Korea and abroad. To analyze the aggregate characteristics of the RAP, its aggregate-size characteristics were analyzed through the combustion asphalt content test and the aggregate sieve analysis test. Moreover, aggregate-segregation experiments were performed to examine the possibility of RAP aggregate segregation from field compaction and vehicle traffic. After confirming the RAP quality standards, coarse aggregate and fine aggregate, aggregate-gradation design and quality tests were conducted for mixtures with 40% and 50% RAP usage. The optimum moisture content of the surface-layer mixture containing RAP was tested, as was the evapotranspiration effect on the surface-layer mixture of the optimum moisture content. RESULTS : After analyzing the RAP recycled aggregate size and extraction aggregate size, 13-8mm aggregate was found to be mostly 8mm aggregate after combustion. After using surface-chipping and mixing methods to examine the possibility of RAP aggregate segregation, it was found that the mixing method contributed very little for 3.32%, and because the surface-chipping method applied compaction energy directly as the maximum assumption the separation ratio was 15.46%. However, the composite aggregate gradation did not change. Using a 40% RAP aggregate rate on the surface-layer mixture for cold central-plant recycling satisfied the Abroad quality standard. The optimum moisture content of the surface-layer mixture was found to be 7.9% using the modified Marshall compaction test. It was found that the mixture was over 90% cured after curing at $60^{\circ}C$ for two days. CONCLUSIONS : To use the cold central-plant recycling mixture on a road-surface layer, a mixture-aggregate gradation design was proposed as the RAP recycled aggregate size without considering aggregate segregation, and the RAP optimal usage rate was 40%. In addition, the modified Marshall compaction test was used to determine the optimum moisture content as a mix-design parameter, and the curing method was adapted using the method recommended by Asphalt Recycling & Reclaiming Association (ARRA).

• Restorative Dentistry and Endodontics
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• v.22 no.1
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• pp.358-373
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• 1997

Resin modified glass ionomers were introduced in 1988 to overcome the problems of moisture sensitivity and low early mechanical strength of conventional glass ionomers and to maintain their clinical advantages. The purpose of this study was to evaluate the color stability of four resin modified glass ionomers(Fuji II LC, Vitremer, Dyract and VariGlass), one resin composite material(Z-100), and one conventional glass ionomer(GC Fuji II) under several conditions. These conditions were as follows: 1) before curing, 2) after curing, 3) after polishing, 4) after 500 thermocycling, 5) after 1,000 thermocycling, 6) after 1,500 thermocycling and 7) after 2,000 thermocycling. Three specimens of each material/shade combination were made. Materials were condensed into metal mold with a diameter of 10 mm and a thickness of 2.0 mm, and were pressed between glass plates. The material was polymerized using a light polymerizing unit(Visilux II, 3M, USA). After removal of excess, the surface was polished sequentially on wet sandpapers. A reflection spectrophotometer(Model TC-6FX, Tokyo Denshoku Co., Japan) was used to determine CIELAB coordinates($L^*,a^*$ and $b^*$) of each specimen. CIE standard illumination C was used as the light source. The results were as follows : 1. In comparing different shades of same material, CIELAB color difference(${\Delta}E^*$) value was not significantly different from each other(p>0.05). 2. CIELAB color difference(${\Delta}E^*$) values between after-curing and after-polishing were ranged from 5.53 to 27.08. These values were higher than those of other condition combinations. 3. CIELAB color difference(${\Delta}E^*$) values between before-thermocycling and after-thermocycling were ranged from 1.40 to 7.81. Despite the number of thermocycling increased, CIELAB color difference(${\Delta}E^*$) value was low. 4. The color stability of resin modified glass ionomers was more stable than that of conventional glass ionomers but less stable than that of Z100.

• Journal of the korean academy of Pediatric Dentistry
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• v.42 no.2
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• pp.151-157
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• 2015

The purpose of this study was to evaluate the effects of Photochemotherapy using a combination of erythrosine and standard halogen dental curing lights on the viability of Streptococcus mutans in the biofilm phase. To investigate the optimum treatment parameters, the researchers controlled the concentration of erythrosine, light irradiation time and the treatment time of erythrosine. The higher concentration of erythrosine (0, 10, 20, 40, 80 M) in the presence of light irradiation created greater effects in reducing the viability of S. mutans. The results showed a statistically significant difference among the antimicrobial effects in 20, 40, 80 M erythrosine. The higher irradiation time of light (0, 5, 15, 30, 60, 75s) in the presence of erythrosine showed greater effects in reducing the viability of S. mutans. There was statistically significant difference in 30, 60, 75 seconds. The higher treatment time of erythrosine (0, 1, 2.5, 5min) in the presence of erythrosine created greater effects on reduction of S. mutans viability. Statistically significant differences were found between 2.5 and 5 minutes of erythrosine treatment time. The results of this study showed that the photochemotherapy on S. mutans using erythrosine and the halogen dental curing lights conventionally used in dental clinics is effective in the condition of 20-40 M erythrosine concentration, irradiation time over 30 seconds, and erythrosine treatment time over 2.5 minutes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.3
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• pp.103-110
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• 2019

Damage to the pavement system due to various causes will be required rapid repair work for reopening the vehicle traffic. The magnesium oxide phosphate composite(MPC) has a short curing time and is capable of early compressive strength development, is suitable for rapid repair materials. The aim of this study was to evaluate the hardening and compressive strength characteristics of MPC according to the water-binder (W / B) ratio and magnesium-phosphate(M / P) ratio in order to develop repair materials consisted with light burned magnesia and potassium dihydrogen phosphate. In order to ensure the workability in the field application, the difference of mechanical properties according to standard sand and ordinary sand and performance of retards were evaluated. The mix proportion with W/B ratio was about 35% and the M/P ratio was about 1.0 ~ 1.2 has a superior perfomance with strength and hardening condition. Especially, the strength of composite at only 1 day curing with W/B ratio of 0.35 and the M/P ratio of 1.2 was shown the higher than 25.0 MPa. Boric acid as a retarder was found to be suitable for ensuring the working time, and the purity of magnesium oxide was about 90 ~ 95%, which is effective for ensuring curing time and strength.

• Resources Recycling
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• v.32 no.6
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• pp.10-17
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• 2023

Calcium silicate cement (CSC) is an environmentally sustainable, low-carbon cement and has garnered significant attention in recent studies. However, the pre-curing step required to activate the carbon dioxide reaction and to handle the sample. This study aimed to examine the viability of extending the application of CSC without pre-curing by enhancing initial strength by mixing calcium sulfoaluminate (CSA) fast-hardening cement into CSC. The investigation assessed changes in compression strength and Q-XRD mineral characteristics concerning variations in the mixing ratio of CSC and CSA fast-hardening cement within a carbon dioxide atmosphere. The compressive strength results indicated that the 3-day and 7-day strengths were 14.18 MPa and 22.98 MPa, respectively, under the 50% CSC condition, meeting the type 1 cement KS standard. Mineral characteristics analysis revealed an increase in calcite mineral, a byproduct of the carbon dioxide reaction, contributing to strength enhancement. Even after seven days, substantial quantities of unreacted rankinitene and pseudowollastonite were observed, as well as dicalcium silicate and yeelimite, which are hydrated minerals. This observation was confirmed the possibility of strength improvement after 7 days.