• Journal of the Korea Institute of Building Construction
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• v.20 no.2
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• pp.123-128
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• 2020

γ-dicalcium silicate(γ-C₂S) is known as a polymorphism of belite. Due to its high CO₂ fixing capacity and the production process with low CO₂ emission, γ-C₂S has attracted more attention of researchers. For the further development of γ-C₂S applications in construction industry, this study aims to investigate the method for synthesizing high purity of γ-C₂S. The influence of raw materials and calcination temperatures on the purity of γ-C₂S was evaluated. Several Ca bearing materials were selected as the calcium source, the materials which's main component is SiO₂ were used as the silicon source. Raw materials were mixed and calcined under different temperatures. The results revealed that the highest purity could be obtained using Ca(OH)₂ and SiO₂ powder as raw materials. In addition, a relatively economic synthesis method using natural mineral materials-limestone and silica sand as raw materials were developed for the practical application. The purity of synthetic γ-C₂S was recorded up to 77.6%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.604-609
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• 2020

There are various methods of finishing concrete surfaces, and when considering workability, the spray method is effective, but rebound occurs. The allocation of rebound occurrence control should be adjusted according to the materials used. Thus, a basic study was conducted on multiple techniques for reducing the rebound incidence that are suitable for surface finishing materials containing a photocatalyst. A prior study derived the reduction effect and optimal mix ratio for photocatalytic performance. Based on that study, the rebound reduction was verified according to the specifications of the content and the mechanical durability characteristics of the mixed materials. Rebound, compressive strength, flexural rigidity, and table flow tests were done. The flow was fixed at 170±10 mm considering the workability of the mortar spray equipment. For the experimental variables, the rebound number was adjusted to the silica sand variables relative to the cement weight, and silica sands No. 5 and No. 7 were used. The results show the highest compression strength in the final S-1 variable, and the amount of rebound was minimized. These results were sufficiently filled with the bindings of the silica pores, which increased the binding force between the aggregates, resulting in a lower amount of rebound.

• Journal of Conservation Science
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• v.28 no.2
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• pp.141-151
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• 2012

It was the 1900s that the damaged materials of stone heritages began to be preserved and managed for the purpose of reuse, especially since cement, an inorganic material, began to be used during the Japanese colonial period. Epoxy resin, an organic material, was introduced to architecture around the turn of the 1990s, and has been being used across the board. In particular, filler mixtures began to be aggressively used for the structural reinforcement of severed materials. The problem was metal stiffeners used for structural reinforcement. The anchorage length varied depending in different conservation scientists, and as a result the secondary damage was apt to occur in the materials. In this study, hereat, a calculation was made of the most effective anchorage length with the minimization of material damage. The results were as in the following: the anchorage length of an 8-milimeter-across (ø8) metal stiffener was found to be most effective at 60.88mm. Those of ø12 and ø16 were 60.88mm and 91.32mm respectively. In the case of other calibers, the anchorage length was calculated by a formula ${\ell}_d=a_tf_y/u{\Sigma}_0$. In the experiment, helically-threaded round bars were used as metal stiffeners in order that they could bear surcharge loads such as bending, shear and constriction.

• Journal of the Korea Concrete Institute
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• v.21 no.5
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• pp.565-572
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• 2009

In this study, corrosion resistance of palm oil fuel ash (POFA) concrete as a blended concrete is evaluated by using electrochemical technique. The POFA is an industrial byproduct obtained from fuel ash after extracting palm oil from palm-tree. In order to obtain basic material characteristics of the POFA concrete, tests on compressive strength, slump, weight loss, bleeding and expansion ratio were carried out the early-aged POFA concrete. On the other hand, durability characteristics, both chloride penetration and carbonation depth test, were also conducted. Finally, corrosion resistance were evaluated by applying electro-chemical artificial crack healing technique, and the tests on the impressed voltage characteristic, galvanic current and linear polarization resistance. From the experimental results, it was found that long-term strength, bleeding, lower slump ratio, expansion ratio, chloride penetration, carbonation and corrosion resistance were improved by using the POFA due to activated pozzolanic reaction. It can be also mentioned that POFA concrete has a potential to be used as a cementitious binder for green-recycling resources.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2006.04a
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• pp.166-170
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• 2006

본 연구에서는 폐광산 주변에 산재되어 있는 광미/광폐석을 처리하기 위하여 고형화 실증 실험을 수행하였다. 고형화 공정에서 흔히 사용하는 포틀랜드 시멘트와 MSG-E, MSG-N을 고화제로 사용하였으며 현장 광미 및 광폐석을 대상으로 고화체를 양생하고 고화체의 압축강도 및 중금속 용출 정도를 측정하였다. 고화체의 물리/화학적 특성을 비교하기 위해 광미/고화제 비율, 배합수/고화제 비율 그리고 고화체 양생기간을 실험인자로 설정하였다. 실험 결과 광미/고화제의 비율 1:1 만을 고려하더라도 중금속 용출의 급격한 감소가 이루어지는 것을 확인할 수 있었으며 광미/고화제의 비율을 3:1 이하로 유지시키는 경우, 고화체의 압축강도가 현행 폐기물 관리법(20조 관련)에서 규정하고 있는 차단형 매립시설 내부막의 압축강도 기준인 $0.21kgf/mm^2$ 보다 높은 것으로 나타났다. 다양한 pH를 갖는 수용액에 대하여 시간에 따른 고화체의 중금속 용출률을 측정한 결과, 수용액의 pH가 1과 13인 강산/강염기 용액에서 일부 중금속의 용출 농도가 지하수 생활용수 기준치를 초과하였으나, pH와 3 - 11인 경우에는 중금속 용출률이 급격히 감소하여 모두 기준치 이하를 나타내었다. 또한, pH가 1과 13인 수용액의 경우에도 고화체와 반응하는 시간이 증가할수록 고화체의 buffering 효과에 의해 수용액의 pH가 감소하였다. 이러한 결과는 현장에서 접촉수의 pH가 강산이나 강염기라 하여도, 고화체의 buffering 효과에 의해 시간이 지남에 따라 수용액의 pH가 낮아져 고화체로부터의 중금속 용출은 매우 감소할 것임을 의미한다.ss of an active application defined using the model. The technique is developed in a platform- and language-independent way, and it is algorithmic and can be automated by computer program. We give an example dealing with network auction to illustrate the use of the model and the verification technique.품으로 내부 온도분포를 측정하였으며, 유한차분법 프로그램으로 대류열전달계수를 결정하였다. 대류열전달계수는 792에서 2,107 W/m$^2$로 분석되었다. 대류열전달 계수는 액상식품과의 상대속도가 증가함에 따라서 증가하였고, 점도가 증가함에 따라서는 감소하였다.ce of precision/recall of 90.99%/92.52%, and 93.39%/93.41% respectively. 의한 변성에 부분적으로 보호 작용을 나타 낼 것으로 추정된다.경(製麴72時間頃)의 활성(活性)은 보리쌀국(麴), 밀가루국(麴), 찹쌀국(麴), 고구마국(麴)의 순이었다.험 결과 오전용 사료는 관행적인 산란계 배합사료에서 Ca공급제를 제외한 것을 급여하고, 오후용 사료는 Ca공급제를 3배 첨가한 T2처리로 15:00~16:00시에 교체급여를 하면 사료섭취량 감소와 사료비 절감면에서 바람직할 것으로 사료되며, 고에너지-고단백질-저Ca의 분말사료와 저에너지-저단백질-고Ca의 펠렛사료를 혼합급여하면 산란계의 사료

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.117-125
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• 2017

The role of fly ash in concrete become impotent with finding the characteristics of fly ash in which it is used as cement replacement material. In this paper, corrosion test results obtained by two test methods such as the long-term exposure corrosion test and the accelerated corrosion test method, were compared to investigated the corrosion resistance between fly ash concrete and normal concrete. Corrosion initiation time was measured in two types of concrete, i.e., one mixed with fly ash(FA) and the other without admixture(OPC). The accelerated corrosion test was carried out by four case, i.e., two samples is a cyclic drying-wetting method combined without carbonation(case 1) and combined with carbonation(case 2), and the other two samples is a artificial seawater ponding test method combined without carbonation(case 3) and combined with carbonation(case 4). Whether corrosion occurs, it was measures using half-cell potential method. The ponding test combined without carbonation was most effective in accelerating corrosion time of steel bars. The results indicated that the corrosion of rebar embedded in concrete occurred according to the order of OPC, FA. The delay relative ratio of corrosion obtained by corrosion initiation time between FA and OPC is 1.04 to 1.27. Consequently, fly ash concrete as the age increases its corrosion resistance was improved compared with OPC concrete.

• Journal of dental hygiene science
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• v.8 no.4
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• pp.353-359
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• 2008

To find out the relationship between the experience of clinical practice and the performance confidence, some 2nd and 3rd grade students in D health college who completed clinical practice in 2008. Sept. were surveyed. The results are as follows. 1. During the clinical practice of the dental hygiene students, the performance experience was highest in the basic prep. part among every part. As for the dental hygiene part, the students showed more than 70%, rather higher performance experience in the following parts: arrangement before and after treatment, suction, basic instruments setup, local anesthesia setup, extraction setup, resin filling setup, temporary filling setup, cements mixing, and ligation and removal setup. 2. As for performance confidence, those with performance experience showed higher performance confidence than those with only observation experience or with no experience in every treatment field except basic prep. (p < 0.001). 3. It was proven that the hygiene students have seldom had performance experience in other treatment parts except in assisting treatment part in clinical practice. In order to improve future performance experience on dental hygiene activities, subsequent research is needed to set more specific and objective criterion about the dental hygiene students' clinical practice.

• The Journal of the Convergence on Culture Technology
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• v.6 no.2
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• pp.553-560
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• 2020

In the existing research paper, we developed Mechanical Pressurizing Equipment(MPE) that can apply a certain amount of pressure and found out about improving the bonding strength of repair materials constructed in the repair section, and if pressurized, the bonding strength could be increased. In this study, the pressure of Mechanical Pressurizing Equipment(MPE) was changed to 0, 10, 30, 50, and 80 kPa, and the test was conducted to select effective pressure by measuring the flexural, compressive, and bonding strength of the specimens and deformation of the pressure plate at the age of 3 and 28th days. As a result of the test, 30 kPa was the most efficient pressure for the MPE. After producing the specimen with three types of repair materials with different main components, the bonding strength was measured according to dry and wet conditions, construction site (ceiling, wall and floor), and whether or not pressurized, on the 3rd, 7th, 14th, and 28th, indicating that the repair materials mixed with cellulose fiber was most effective for the MPE.

• Journal of Dental Rehabilitation and Applied Science
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• v.29 no.4
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• pp.359-365
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• 2013

The aim of this study was to evaluate the effect of temporary restorative and filling material on bonding strength between lithium disilicate glass-ceramic and dentin. 60 extracted human molars were cross-sectioned at occlusal third and were embedded into self-cure acrylic resin. Then the teeth were randomly divided into four groups of 15 each. Lithium disilicate glass-ceramic is cemented to dentin as follows: after no any application of the provisional materials (Group A), after application of ALIKETM (GC America Inc.)(Group B), after application of Luxatemp$^{(R)}$ Automix plus (DMG, Germany)(Group C), after application of Fermit$^{(R)}$ (Ivoclar Vivadent, Leichtenstein)(Group D). After the specimens were stored in distilled water for 24 hours, the shear bond strength of the specimens were measured using UTM (Zwick 1456 41, Zwick, Germany) at a crosshead speed of 1mm/min. The data were analysed by one-way ANOVA and Tukey HSD tests. There were no statistically significant differences of bond strength among the groups. Fracture type was showed mixed type of adhesive and cohesive fracture in most of specimens. Within the limitation of this study, bond strength of adhesive resin cement between lithium disilicate glass-ceramic and dentin was not affected by provisional restorative and filling materials.

• Restorative Dentistry and Endodontics
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• v.32 no.3
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• pp.198-207
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• 2007

The purpose of this study was to investigate the effect of calcium hydroxide on dentin bonding strength of various dentin bonding systems as a function of time in composite resin restoration. Dentin adhesives used in this study were Scotchbond Multipurpose, Single Bond, SE Bond and Prompt L-Pop. Flat dentin surfaces adjacent to pulp chamber were created, then $Ca(OH)_2$ and saline were mixed and applied on dentin surface of experimental group, then IRM was used to cover the mixture on dentin surface and the specimens were stored at $36.5^{\circ}C$ for experiment period (7 days, 30 days). After removing IRM and $Ca(OH)_2$, each dentin adhesives were treated on dentin surfaces. Composite resin (Z-250, 3M) was placed with S mm height and was light-cured for 20 seconds. After stored in distilled water for 24 hours, each dentin-composite bonded spicemen was embedded in epoxy resin and sectioned into $1.0\times1.0mm^2$ cross section composite-dentin beams. Specimen was mounted on zig of Universal testing machine and ${\mu}TBS$ test was performed. SEM analysis was performed to examine the fractured surfaces. The results suggested that applying calcium hydroxide did not show significant difference in dentin bonding strength.