• KCI Concrete Journal
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• 제12권1호
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• pp.79-89
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• 2000

This research developed an accelerated curing processe for cellulose fiber reinforced cement composites using vigorous reaction between carbon dioxide and cement paste. A wet-processed cellulose fiber reinforced cement system was considered. Carbonation curing was used to complement conventional accelerated curing. The parametric study followed by optimization investigation indicated that the carbonation curing can enhance the productivity and energy efficiency of manufacturing cellulose fiber reinforced cement composites. This also adds environmental benefits to the technical and economical advantages of the technology.

• 대한치과보철학회지
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• 제42권2호
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• pp.142-153
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• 2004

Statement of problem: Increasing demand of esthetic restorations made lots of kinds of ceramic materials. Among them, zirconia has been being focused by many dentists. But, mechanical properties of zirconia were still unclear. Purpose : The purposes of this study were to analyze the flexural strength of various zirconia ceramics which had been currently used for clinic i.e., In-Ceram Zirconia(Vita Zahnfabrik, Bad $S\"{a}ckingen$, Germany), Celay Zirconia(Vita Zahnfabrik, Bad $S\"{a}ckingen$, Germany) and CAD/CAM Zirconia (Adens Zi-Ceram. Seoul , Korea). Material and methods: The four point bending test(ASTM Cl161) was used to measure the flexural strength of a specimen before and after circular heat treatment and fatigue loading. Results : 1. The average value of flexural strengths of CAD/CAM Zirconia, Celay Zirconia, In-Ceram Zirconia in dry condition were 806.5 MPa, 669.9 MPa, 605.6 MPa, respectively. There was a statistically significant difference in strength among the types (P<0.05). 2. After thermocycling, the average flexural strengths of CAD/CAM Zirconia, Celay Zirconia, In-Ceram Zirconia were 791.2 MPa, 604.2 MPa, 605.4 MPa, respectively. CAD/CAM Zirconia showed statistically significant higher strength(P<0.05). The others showed no significant difference after thermocycling(P>0.05). 3. After fatigue loading in wet condition. the average flexural strengths of CAD/CAM Zirconia, Celay Zirconia, In-Ceram Zirconia were 806.0 MPa, 674.9 MPa, 601.7 MPa, respectively. There was a significant difference in strength among the types(P<0.05). 4. There was no statistically significant difference in strength of the specimens according to experimental methods except for before and after thermocycling in Celay Zirconia(P>0.05). Conclusion: Besides high esthetic quality, zirconia had sufficiently high mechanical strength.

• Journal of the Korean Wood Science and Technology
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• 제17권2호
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• pp.20-25
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• 1989

This study was carried out in order to investigate the treatment effect of PEG soln which is a common dimensional stabilizer to green log. sawing panel etc, on bonding product including plywood widely-used in secondary processing unit. The 30% concentration of aqueous PEG soln. with molecular weight of 400, 1.000 and 4,000 were prepared respectively, and also dipping the veneer in the PEG soln. spreading the PEG soln. on veneer and mixing the PEG soln. in the adhesive were allowed. Then the ratio of PEG impregnation on veneer, the adhesive strength of plywood were epitomized as follows: The ratio of impregnation by PEG 4,000 at dipping condition was highest. while that by PEG 400 at same condition was lowest. However, the effect of PEG molecular weight on the ratio of impregnation at spreading condition did not occur. 2. The adhesive strength was great in the order of 4,000>400>1,000 in molecular weight of PEG at dipping and spreading conditions. In case of mixing the PEG soln. in the adhesive, the adhesive strength was great in the order of 400>1,000>4,000 in molecular weight of PEG. Throughout three treatment conditions, PEG 400 was relatively favourable with about 10kg/$cm^2$ dry strength. 3. The adhesive strength was great 10 the order of spreading >dipping >mixing condition. 4. Although adhesive strength with the 30% concentration of aqueous PEG soln. was decreased by 35% and over, compared to control (non-treatment) adhesive strength, all types of PEG treatment except mixing the PEG soln. in the adhesive exceeded the standard dry strength for common use panel. 7.5kg/$cm^2$. 5. In warm water-proof test, the adhesive strengths by all PEG treatment conditions were less than the standard wet strength, 7.5kg cot, and also delamination of glue line occured mostly in mixing in the PEG soln. in the adhesive condition.

• 콘크리트학회논문집
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• 제23권6호
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• pp.817-826
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• 2011

에코시멘트를 이용한 콘크리트는 장기강도 발현이 취약한 문제가 지적되고 있지만 현재까지 그 원인이 불분명하여 구조재료로써 널리 사용되지 않고 있다. 이 연구에서는 에코시멘트를 이용한 콘크리트의 장기강도 발현에 미치는 양생 습도의 영향을 검토함과 동시에 강도 특성과 세공구조의 관계에 대해 검토하였다. 그 결과, 수중양생을 실시한 높은 물-시멘트비 공시체에서 심각한 장기강도 정체가 나타났다. 이것은 재령이 경과하여도 10 nm이상의 세공량이 감소하지 않는 것에 기인하고 있다. 반면, 기중양생의 경우에는 에코시멘트에서도 안정적인 장기강도 증진이 확인되었다. 나아가, 에코시멘트를 보다 안정된 재료로 사용하고자 보통 포틀랜드 시멘트 및 미분쇄 플라이애쉬 혼입에 의한 장기강도 개선에 관한 연구를 실행하였다. 그 결과, 이 연구 범위 내에서 장기강도 개선을 기대할 수 있었고, 더불어 재령이 경과함에 따라 세공구조가 치밀해지는 효과를 얻을 수 있었다.

• Journal of the Korean Wood Science and Technology
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• 제11권1호
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• pp.12-17
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• 1983

본(本) 실험(實驗)에서는 합판(合板) 및 파티클보드 공장(工場)에서 폐기물(廢棄物)로 버려지고 있는 Douglas-fir 수피분말(樹皮粉末)과 particle-board sander dust(PSD)를 요소수지접착제(尿素樹脂接着劑)의 증량재료(增量材料)로 이용(利用)하여 제조(製造)한 합판(合板)과 밀가루를 증량재료(增量材料)로 이용(利用)하여 제조(製造)한 합판(合板)과의 상태(常態) 및 내수접착력(耐水接着力)을 비교(比較)하였다. 또한 접착제(接着劑)의 증량비율(增量比率)을 수지액(樹脂液)의 중량(重量)에 대(對)하여 5, 10, 20, 30% 순(順)으로 증가(增加)시켜서 각(各) 증량재료(增量材料)의 적정증량조건(適定增量條件)을 찾고자 하였다. 실험(實驗) 결과(結果), 실험(實驗)에 이용(利用)된 증량재료(增量材料) 모두가 증량비율(增量比率) 5 %일 때 상태접착력(常態接着力)이 가장 높았으며, 내수접착력(耐水接着力)은 무증량(無增量)과 증량비율(增量比率) 5%일 때 가장 높았다. Douglas-fir 수피분말(樹皮粉末)은 증량비율(增量比率) 10%까지, PSD는 증량비율(增量比率) 20%까지 밀가루와 비슷한 상태(常態) 및 내수접착력(耐水接着力)을 보였으나 증량비율(增量比率) 30%에서는 밀가루의 상태(常態) 및 내수접착력(耐水接着力)이 높았다. Douglas-fir 수피분말(樹皮粉末)과 PSD는 도포작업성(塗布作業性)을 개선(改善)하고 접착시(接着尸)의 두께를 가능한 얇게하여 접착력(接着力)을 높이기 위해서는 매우 고운 분말(粉末)로 만들어져야 하다고 생각된다.(325 mesh screen 통과(通過)) 그러나, 본(本) 실험(實驗)에서는 100 mesh screen을 통과(通過)하는 것을 사용(使用)하였다.

• Journal of the Korean Wood Science and Technology
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• 제31권2호
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• pp.77-83
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• 2003

본 연구에서는 대나무 Zephyr 보드에 있어서 열압조건이 보드의 성능에 미치는 영향을 조사하기 위하여 다양한 열압시간과 열압온도를 적용하여 보드(목표밀도 0.7 g/cm³, 400×400×12 mm)를 제조하고 그 기본적인 물성을 비교, 검토해 보았다. 제조된 보드는 KS F 3104와 KS F 3113에 준하여 성능평가를 하였으며 그 결과는 다음과 같다. 보드의 상태 휨강도는 열압조건에 관계없이 전반적으로 상당히 높은 값을 나타내었으며 그 중 span에 대한 평행 방향에 있어서는 열판온도 160℃에서 12분 동안 열압하여 제조한 보드가 가장 높은 강도를 보였다. 보드의 박리강도 시험에서는 모든 열압시간에서 열압온도가 높을수록 상대적으로 더 높은 값을 나타내었으며, 그 결과 200℃에서 압체된 보드가 가장 높은 강도를 보였다. 보드의 습윤 휨강도 시험에서는 총 열압시간 12분과 10분일 때 각각 160℃와 180℃의 온도에서 제조된 보드가 상대적으로 높은 강도를 나타내었다. 더욱이, 200℃에서 8분 동안 열압하여 제조한 보드의 경우 상태 휨강도에 거의 육박하는 가장 높은 습윤 휨강도를 보였다. 두께 팽창율 시험에서는 모든 보드에서 전반적으로 6% 미만의 낮은 값을 나타내어 높은 치수안정성을 가지는 것을 알 수 있었다.

• 펄프종이기술
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• 제41권1호
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• pp.17-23
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• 2009

The influence of different forming elements on the local paper structure and the related paper properties was investigated in this study. Specifically, a conventional papermaking foil system and a velocity induced drainage (VID) system were compared. The study involved the analysis of the product samples obtained from the commercial machine trials. The paper samples produced with VID forming systems showed better formation. The deterministic patter in the local structural profile map of the Foil samples indicated the structure of foil samples was more supple after forming process and then easier to be marked by various fabrics such as wet pressing fabric. The higher bulk was observed in the VID samples, which resulted in higher scattering coefficient, lower ZDT strength, and higher bending stiffness.

• 한국세라믹학회지
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• 제30권5호
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• pp.420-426
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• 1993

The machinability of ceramics has been experimentally studied. The experiments were conducted on alumina cernmics of various purity, quartz, and cordierite using the sintered diamond tools and CBN tools. Tool wasre, surface roughness, and cutting resistence were measured and analysed. It was found that the workpieces could be machined with the diamond and CBN tools, but the sintered diamond tools were more efficient for the machining of the high strength ceramics. The machining of alumina ceramics with sintered diamond tools showed that (1) wet machining prolonged tool life comparing with dry machining, (2) workpiecewith higher purity had better surface roughness, (3) severe cutting conditions led to the chipping and fracture of tool and increase of the surface roughness and cutting resistance, (4) 20~40m/min of cutting speed, 0.01~0.02mm/rev of feed, and 0.1~0.2mm of cutting depth are suggested as proper cutting conditions for the high strength ceramics.

• 펄프종이기술
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• 제38권1호통권113호
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• pp.34-44
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• 2006

A new composition of paper coating adhesives was prepared by using a nano-filler of an organically-modified montmorillonite (O-MMT). The new O-MMT coating adhesives were applied to the paper, and the properties of coated papers including surface morphology, optical and physical properties, and printing properties were investigated. The use of O-MMT improved the mechanical properties, such as folding endurance, tearing strength, and tensile strength, while the surface smoothness decreased. It decreased especially when the dosage was high enough, approximately above 6 parts. The printing properties such as wet- and dry-pick were enhanced with addition of O-MMT.

• 한국농공학회지
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• 제38권4호
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• pp.137-146
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• 1996

This paper presents the results of field experience from an experimental pavement construction on a low volume road using recycled concrete. The recycled concrete was prepared by replacing a half of coarse aggregate with recycled aggregate. Virgin natural sand was used as fine aggregate together a plasticizer and a fly ash (0.8% and 5% by wt. of cement, respectively). The load bearing capacity of the subbase made of recycled aggregate was acceptable. The length, thickness and width of the pavement were l00m, 20cm and 3m, respectively. From construction experience, it was found that workability and finishability of the recycled concrete mixture were relatively poor, but strengths were satisfactory. Flexural strength, compressive strength and elastic modulus at 28 days were 54Kg/$cm^2$, over 250Kg/$cm^2$, and 220,OOOKg/$cm^2$, respectively. The construction could be performed by hand without much difficulty. The surface was finished smoothly by wet fabric and only minor cracks were found on the surface.