• 한국주조공학회지
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• 제26권5호
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• pp.222-226
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• 2006

Steel making slag has gained a considerable attraction as one candidate of eco-materials in research fields for recycling resources. Thus, many researches have been performed but were limited to development of substitute for cement being used in the construction field. A little research work also has been done on development of higher value-added materials, including heat resistant and sound absorbing materials. For this reason, the present study were focused on macrostructure characterization of fabricated slag fibers which are applicable to heat resistant materials. The slag fibers were fabricated through a modified melt extraction method. The processing variables employed were the wheel speed and molten slag temperature. The synthesized fibers were characterized by optical microscope and scanning electron microscopy. It was found that the wheel speed of 1400 rpm generated better quality of mineral fibers in terms of the relative amount of shot, diameter and length. This was attributed to the relative extent of contact width between the flowing melt and the rotating wheel. The thickness of the slag fibers also were decreased with increasing the slag melt temperature due mainly to significant decrease in the viscosity of the slag melt. In addition, the lower melt temperature caused an increase in number of shots plus the mineral fibers.

• 대한토목학회논문집
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• 제32권6A호
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• pp.419-426
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• 2012

굳지않은 콘크리트에는 항상 일정량의 잉여수가 발생하게 된다. 이러한 잉여수는 콘크리트 내부에서 갇힌공기로 남게 되어 내구성을 저하시키는 요인이 되므로 잉여수를 제거할 수 있다면 구조물의 내구성 향상에 큰 도움이 될 것이다. 기존에 많은 연구가 있었지만 투수시트의 특성에 대한 상세한 검토는 부족한 상태이며, 거푸집의 천공에 따른 시공성 저하는 여전히 의문이 있다. 따라서, 본 논문에서는 투수거푸집 시스템에서 직포 및 부직포 투수시트를 적용할 경우의 기초적인 특성을 실험을 통하여 검토하고 시공성 향상을 위해 거푸집에 천공을 하지 않는 투수거푸집에 대한 연구를 진행하였다. 그 결과 투수거푸집에서 직포와 부직포 투수시트를 사용한 경우 직포의 조밀성 및 부직포의 두께 등에 따라 일부 차이가 있었지만 W/C 감소, 표면 평탄성 증가, 표면부 강도 향상이 있었으며, 시멘트손실은 미미하여 적용성이 우수한 것으로 나타났다. 또한, 투수시트 내부에 탈수된 잉여수의 배수통로를 가지고 있는 배수 부직포 투수시트를 적용한 경우 거푸집에 천공을 하지 않고서도 필요한 탈수성능을 발휘할 수 있어 시공성 향상에 기여할 것으로 판단된다.

• The Journal of Advanced Prosthodontics
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• 제3권3호
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• pp.126-131
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• 2011

PURPOSE. The aim of this in vitro study was to examine the curing efficiency of various resin-based materials polymerized through ceramic restorations with 3 different thicknesses. Curing efficiency was evaluated by determining the surface microhardness (VHN) of the resin specimens. MATERIALS AND METHODS. Four kinds of resin materials were used. Z350 (3M ESPE $Filtek^{TM}$ Z350: A2 Shade), Z250 (3M ESPE $Filtek^{TM}$ Z250: A2 Shade) and $Variolink^{(R)}$ II (VL: Ivoclar vivadent, base: transparent) either with or without a self-curing catalyst (VLC: Ivoclar vivadent, catalyst: low viscosity/transparent) were filled into the silicone mold (10 mm diameter, 1 mm thick). They were cured through ceramic discs (IPS e.max Press MO-0 ingot ivoclar vivadent, 10 mm diameter, 0.5, 1 and 2 mm thicknesses) by LED light-curing units for 20 and 40 seconds. Vicker's microhardness numbers (VHNs) were measured on the bottom surfaces by a microhardness tester. Data were analyzed using a 3-way analysis of variance (ANOVA) at a significance level of 0.05. RESULTS. The thickness of ceramic disc increased, the VHNs of all four resin types were decreased (P<.05). The mean VHN values of the resins light cured for 40 seconds were significantly higher than that of LED for 20 seconds in all four resin materials (P<.05). VLC showed significantly higher VHN values than VL regardless of other conditions (P<.05). Z350 and Z250 showed higher values than VL or VLC (P<.01). CONCLUSION. Thinner ceramic disc with increased curing time resulted higher VHN values of all resin materials. The use of a catalyst produced a greater hardness with all polymerization methods. Restorative resin materials (Z350, Z250) showed higher VHN values than resin cement materials (VL, VLC).

• Structural Engineering and Mechanics
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• 제65권3호
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• pp.315-325
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• 2018

This paper predicts the flexural behaviour of reinforced concrete (RC) beams strengthened with a precast strip of ultra-high performance fiber-reinforced concrete (UHPFRC). In the first phase, ultimate load capacity of preloaded and strengthened RC beams by UHPFRC was predicted by using various analytical models available in the literature. RC beams were preloaded under static loading approximately to 70%, 80% and 90% of ultimate load of control beams. The models such as modified Kaar and sectional analysis predicted the ultimate load in close agreement to the corresponding experimental observations. In the second phase, the famous fatigue life models such as Papakonstantinou model and Ferrier model were employed to predict the number of cycles to failure and the corresponding deflection. The models were used to predict the life of the (i) strengthened RC beams after subjecting them to different pre-loadings (70%, 80% and 90% of ultimate load) under static loading and (ii) strengthened RC beams after subjecting them to different preloading cycles under fatigue loading. In both the cases precast UHPFRC strip of 10 mm thickness is attached on the tension face. It is found that both the models predicted the number of cycles to failure and the corresponding deflection very close to the experimental values. It can be concluded that the models are found to be robust and reliable for cement based strengthening systems also. Further, the Wang model which is based on Palmgren-Miner's rule is employed to predict the no. of cycles to failure and it is found that the predicted values are in very good agreement with the corresponding experimental observations.

• 품질경영학회지
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• 제45권4호
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• pp.995-1002
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• 2017

Purpose: The purpose of this study was to evaluate the color stability of composite resins used for splinting teeth by comparing a self-cure resin cement (Superbond C&B, SB), a flowable composite resin (G-aenial Universal Flo A2, GU), and a composite resin exclusively used for splinting teeth (G-Fix, GF) before and after aging in NaOCl. Methods: Resin samples were fabricated to a size of 2 mm thickness and 8.5 mm diameter and light-cured with an LED light curing unit (G-Light, n = 12). Immediately after fabrication, CIE L*a*b* values of the resin samples were measured with a spectrophotometer (CM-5) as baseline. Then, the resin samples were immersed in 5% NaOCl at $60^{\circ}C$ and the color was measured after 23 hours every day for 4 days. Data were analyzed with one-way ANOVA followed by Duncan post hoc test (p<0.05), and color differences (${\Delta}E$) of resin samples before and after NaOCl aging were also calculated. Results: For SB, there were no changes in L* and a* values but changes were observed in b* values. For GU, there were no changes in L* and b* values but in a* values. For GF, changes were observed in L*, a*, and b* values. All resin samples showed highest ${\Delta}E$ between baseline and the 1st day of NaOCl immersion. ${\Delta}E$ of SB, GU, and GF was 4.6 - 5.8, 4.9 - 7.9, and 9.9 - 16.9, respectively. GF showed highest color change during NaOCl aging. Conclusion: The results of this color quality evaluation showed that the composite resin exclusively used for splinting teeth might be more vulnerable to color change during intraoral service.

• 자원환경지질
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• 제4권3호
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• pp.113-119
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• 1971

The Daeheung Dolomite Mine, which is about 6km south of Danyang, Chungcheongbugdo, is coincided with almost central portion of the Danyang quardrangle scaled in 1 : 50,000. The purpose of this report is to prepare a information for the economic evaluation on the mine. Geology of the region is composed of worm-eaten limestone, crystalline limestone, crystalline dolomite rock, sandstone and shale from bottom, those are applicable to socalled Dumugol and Maggol formation of Ordovician, and batholithic biotite granite is intruded the west-side of the ditto sedimentary rocks. The dolomite bed, emplaced in bottom of the upper limestone formation, so-called Maggol formation, is about 270m in thickness, and dips $30^{\circ}{\sim}50^{\circ}$ northwest. The facies of the dolomite rock contained many brucite crystals is not only coarse-grained crystalline, but also micro crystalline in contact metasomatic parts. 25 samples were taken from the two series, A and B, in the nearly crossed direction to the strike of the dolomite bed as shown in the geological map. They were chemically analysed on the components of MgO, CaO, and $SiO_2$ as shown in Table 2. The estimate ore reserves total some 107,200,000 metric tons above the 320m level with the following average contents: MgO 21.80%, CaO 29.27% and $SiO_2$ 0.64%. It is caused by brucite minerals that MaO content in the dolomite rock is higher than pure dolomite (21.7%). The dolomite ore is possible in use for magnesian fertilizer, magnesian cement and refractory material, especially the microcrystalline dolomite ore is useful for a refractory material in furnaces of iron industries.

• 한국구조물진단유지관리공학회 논문집
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• 제19권3호
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• pp.30-38
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• 2015

적설한랭지의 경우, 동절기의 동해 및 적설에 의한 교통통행의 원활을 기하기 위하여 제설제를 사용한다. 이와 같은 제설염의 사용은 동결융해 및 염화물에 의해 콘크리트의 급속한 스케일링 피해를 야기시킨다. 이에 대한 피해로 인하여 콘크리트 포장은 콘크리트의 피복두께 감소에 따른 조기 열화 및 사용자의 안정성 등 여러 가지 문제를 발생시킨다. 이에 따라 국외적으로 이와 같은 현상에 대하여 평가를 하기 위해 다양한 시험 및 평가 방법이 제시되고 있다. 하지만 국내에서는 아직 평가방법에 대한 규정은 없으며, 관련 연구 또한 미미한 수준이다. 따라서 본 논문에서는 각 기관 및 나라에서 제시되고 있는 평가방법을 조사하고, 각각의 규정에 따라 실험을 수행하여 결과를 도출하여 비교 분석하였다. 나아가 이와 같은 실험방법과 실험결과의 고찰을 통하여 국내현장에 맞는 실험법을 제안하고자 한다.

• 콘크리트학회논문집
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• 제23권3호
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• pp.257-264
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• 2011

이 연구는 부착형 정착 장치를 갖는 CFRP(carbon fiber reinforced polymer) 긴장재의 정착에 관한 실험 연구이다. 적절한 채움재를 도출하기 위해 예비 실험을 수행하였고, 에폭시 또는 콘크리트 모르타르와 같은 5종의 재료가 채움재로 사용되었다. 실험 결과 무수축 모르타르를 사용한 시편에서 최대 인장강도를 보이므로 이 연구에서는 CFRP 긴장재용 강관 몰드의 채움재로써 무수축 모르타르를 결정하였다. 예비 실험으로 도출된 채움재를 이용하여 강관 몰드의 적정 제원을 도출하기 위해 외경, 두께 및 길에 대한 추가 실험을 수행하였다. 이 실험을 통해 무수축 모르타르를 사용한 강관 몰드의 적정 제원이 도출되었고, 이러한 제원의 강관 몰드로 정착된 CFRP 긴장재는 안정적인 인장 성능을 보였다.

• International Journal of Concrete Structures and Materials
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• 제11권2호
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• pp.343-363
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• 2017

The objective of this work was finding out the most advisable testing conditions for an effective and robust characterization of the tensile strength (TS) of concrete disks. The independent variables were the loading geometry, the angle subtended by the contact area, disk diameter and thickness, maximum aggregate size, and the sample compression strength (CS). The effect of the independent variables was studied in a three groups of experiments using a factorial design with two levels and four factors. The likeliest location where failure beginning was calculated using the equations that account for the stress-strain field developed within the disk. The theoretical outcome shows that for failure beginning at the geometric center of the sample, it is necessary for the contact angle in the loading setup to be larger than or equal to a threshold value. Nevertheless, the measured indirect tensile strength must be adjusted to get a close estimate of the uniaxial TS of the material. The correction depends on the loading geometry, and we got their mathematical expression and cross-validated them with the reported in the literature. The experimental results show that a loading geometry with a curved contact area, uniform load distribution over the contact area, loads projected parallel to one another within the disk, and a contact angle bigger of $12^{\circ}$ is the most advisable and robust setup for implementation of BT on concrete disks. This work provides a description of the BT carries on concrete disks and put forward a characterization technique to study costly samples of cement based material that have been enabled to display new and improved properties with nanomaterials.

• Journal of Advanced Marine Engineering and Technology
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• 제39권4호
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• pp.456-462
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• 2015

본 연구는 토네이도와 축류펌프의 원리를 적용하여 마중물 없이 슬러리를 송출할 수 있는 새로운 펌프기술 개발을 목적으로 한다. 개발한 로터형 슬러리 펌프는 전동모터, 구동축 및 커플링, 로터, 임펠러 그리고 흡입 및 송출관으로 구성된다. 청수를 이용한 성능실험에서는 로터의 설계조건에 따른 송출량, 소비 전력량 그리고 흡입관 부압특성에 대해 모터의 회전수를 변수로 검증하였으며, 시멘트를 이용하여 제조한 슬러리의 고형물 농도에 따른 송출량 특성에 대한 검증연구를 수행하였다. 로터의 직경과 높이가 커지면 송출량과 소비되는 전력량은 증가하지만 흡입관 부압은 감소하였으며, 송출량과 부압에 미치는 로터 두께의 영향은 거의 나타나지 않았다. 개발지표로 제시하였던 18 % 이상의 고형물 농도에서도 슬러리의 송출이 가능함을 확인하였다.