• Advances in concrete construction
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• 제13권1호
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• pp.71-81
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• 2022

Aluminosilicate materials as precursors are heterogenous in nature, consisting of inert and partially reactive portion, and have varying proportions depending upon source materials. It is essential to assess the reactivity of precursor prior to synthesize geopolymers. Moreover, reactivity may act as decisive factor for setting molar concentration of NaOH, curing temperature and setting proportion of different precursors. In this experimental work, the reactivities of two precursors, low calcium (fly ash (FA)) and high calcium (ground granulated blast furnace slag (GGBS)), were assessed through the dissolution of aluminosilicate at (i) three molar concentrations (8, 12, and 16 M) of NaOH solution, (ii) 6 to 24 h dissolution time, and (iii) 20-100℃. Based on paratermeters influencing the reactivity, different proportions of ternary binders (two precursors and ordinary cement) were activated by the combined NaOH and Na2SiO3 solutions with two alkaline activators to precursor ratios, to synthesize the geopolymer. Reactivity results revealed that GGBS was 20-30% more reactive than FA at 20℃, at all three molar concentrations, but its reactivity decreased by 32-46% with increasing temperature due to the high calcium content. Setting time of geopolymer paste was reduced by adding GGBS due to its fast reactivity. Both GGBS and cement promoted the formation of all types of gels (i.e., C-S-H, C-A-S-H, and N-A-S-H). As a result, it was found that a specified mixing proportion could be used to improve the compressive strength over 30 MPa at both the ambient and hot curing conditions.

• 접착 및 계면
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• 제12권2호
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• pp.47-55
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• 2011

자외선 경화형 도료는 기계적 물성과 내화학성, 내마모성 등이 우수하고, 빠른 경화시간으로 경제성이 우수하며, 휘발성유기용제의 양을 줄일 수 있어 환경친화적이기 때문에 다양한 산업분야에서 널리 사용되고 있다. 이에 반해, 유연성이 떨어지는 도막을 형성하기 때문에 최근 활발히 연구되고 있는 선도장 후성형의 pre-coated metal용 도료로 사용하는 데 문제점을 지니고 있다. 본 연구에서는 polycarbonate diol, isophorone diisocyanate와 2-hydroxyethyl methacrylate를 이용해 polyurethane methacrylate를 합성하여 성형 시 필요한 유연성을 향상시켜 선도장 강판용 도료의 적용 가능성을 살펴보았다. 또한, 폴리올의 분자량, 광개시제의 함량, 모노머의 함량이 경화거동, 유연성, 도막물성에 미치는 영향을 평가하였다. Photo-DSC를 이용하여 광경화 거동을 살펴보았고, 진자경도, 인장강도, 점탄성을 측정하여 경화도막의 유연성 및 도막물성을 평가하였다.

• 접착 및 계면
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• 제7권4호
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• pp.28-31
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• 2006

Due to the miniaturization of MEMS and microelectronics the joining techniques also have to be adjusted. The dosing technology with viscous adhesives does not permit reproducible adhesive volumes, which are clearly under a nano-liter. A nano-liter means however a diameter of bonding area within the range of several 100 micrometers. Additional, viscous adhesives need a certain time, until they are cross linked or cured. The problem especially in the MEMS is the initial strength, since it gives the time, which is needed for joining an individual adhesive joint. The time up to the initial strength is with viscous, also with fast curing systems, within the range of seconds until minutes. Until the reach of the initial strength, the micro part must be fixed/held. Without sufficient adjustment/clamping it can come to a shift of the micro parts. Also existing micro adhesive bonding processes are not batch able, i.e. the individual adhesive joints of a micro system must be processed successively. In the context of the WCARP III 2006 now an innovative method is to be presented, how it is possible to solve the existing problems with micro bonding. i.e. a method is presented, which is batch able, possess a minimum joining geometry with some micrometers and is so fast that no problems with the initial strength arise. It is a method, which could revolutionize the sticking technology in the micro system engineering.

• 보존과학회지
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• 제28권3호
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• pp.265-276
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• 2012

석조문화재의 보존 복원 작업에 적용할 수 있는 에폭시 수지의 성능을 개선하기 위해 다양한 성분을 조합하여 경화 거동을 제어할 수 있는 접착 시스템을 연구하였다. 사용된 에폭시 수지 주제는 hydrogenated Bisphenol-A (HBA), 경화제로 속경화형 경화제 FH와 저속 경화제 SH를 구성하였으며, 반응성 희석제는 difunctional polyglycidyl epoxide (DPE), 무기 첨가물은 탈크를 사용하였다. 에폭시 수지와 경화제의 혼합 조건에 따라 경화 시 점도, 온도 및 differental scanning calorimetry(DSC)를 이용하여 경화 동력학을 측정하였고, 기계적 특성을 확인하기 위해 무기 첨가물의 함량에 따른 굴곡강도, 인장강도, 압축전단접착강도를 측정하였다. 연구 결과, 다양한 석조문화재의 보존처리 작업에 맞춰 에폭시 수지 구성물의 성분 조합을 통해 경화 특성을 제어하고, 무기 첨가물의 도입을 통해 기계적 특성을 조절하여 성능 개선 및 작업 효율성을 향상 시킨 새로운 접착 시스템을 개발하였다.

• 한국지반신소재학회논문집
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• 제20권4호
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• pp.133-140
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• 2021

기존 현장시험법을 이용한 유동성 채움재의 강도 및 강성 특성을 추정하는 연구는 미미한 실정이다. 본 연구에서는 LWD를 이용하여 CLSM에 대한 강성 특성을 평가하였으며, 일축압축강도시험에서 도출되는 일축압축강도와 할선탄성계수에 대한 상관성을 분석하였다. 5종류의 배합비로 조성된 CLSM시료의 유동성 및 경화특성을 평가하기 위해 플로우시험, 응결시간시험을 수행하였다. 조기 강도 및 강성 특성을 평가하기 위하여, 양생 1일 및 7일이 경과된 시료를 이용하여 일축압축강도시험을 수행하였다. CLSM시료의 회복탄성계수를 추정하기 위하여 LWD 시험도 수행되었다. 실험결과, 양생 1일된 시료에서는 초속경 모르타르의 비율이 증가될수록 일축압축강도와 할선탄성계수가 동시에 증가하였으며, 초속경 모르타르의 비율이 가장 큰 시료에서 양생 7일 후 급격한 일축압축강도와 할선탄성계수의 증가를 보여주었다. LWD 시험결과, 양생 1일된 시료에서는 초속경 모르타르의 비율이 증가할수록 회복탄성계수가 증가되었으나, 양생 7일이 경과되면 초속경 모르타르의 비율이 증가할수록 회복탄성계수가 감소되는 경향이 나타났다. 상관성 분석결과, 일축일축압축강도와 할선탄성계수가 증가할수록 회복탄성계수도 증가되는 선형관계를 보여주었다.

• Journal of the Korean Wood Science and Technology
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• 제51권6호
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• pp.431-446
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• 2023

Samama wood (Anthocephalus macrophyllus (Roxb) Havil) is a fast-growing and lesser-utilized wood species that has inferior properties; therefore, its quality needs to be improved. This research aimed to determine the effect of citric acid impregnation at high curing temperatures on the dimensional stability and mechanical properties of wood. Citric acid solution with 10% concentration (w/w) was impregnated into wood samples by vacuum-pressure method (-0.5 cmHg, 30 min; 0.7 MPa, 3 h), followed by curing process at 140℃, 160℃, and 180℃ of temperature for 1 h. In comparison, the other wood samples were heat treated at the same temperatures and time. The results showed that the increase in curing and heat temperatures for both treatments were directly proportional to the dimensional stability, but inversely proportional to the mechanical properties. Citric acid impregnated had higher density, dimensional stability, and mechanical properties, except for modulus of rupture, than that of heat treatment. The optimum temperature is suggested at 160℃ in both treatments.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2002년도 학술발표회 발표논문집
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• pp.157-160
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• 2002

This study was developed high-quality a large size precast channel structure using polymer concrete to improve quality of the product as well as to enhance construction quality. Practical precast channel structure design and manufacture procedure for the high polymer concrete were described in this paper. Precast PC represent the fastest growing segment of the polymer concrete industry. The fast curing, high strength, and low impermeability permit thin section and rapid reuse of moulds. Precast channel structure will carry out structural experiment and analysis.

• Journal of the Korean Wood Science and Technology
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• 제23권3호
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• pp.33-39
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• 1995

To accelerate the cure of phenolic resin adhesives for plywood, the complexation with melamine resin and the addition of cure-accelerating agents were discussed. The hot-pressing temperature and time of phenol resin could be decreased by complexation with melamine resin. but the wet glue-joints strength of phenol melamine resin was lower than that of ordinary phenol resin in case of plywood using spruce veneer at core layer. Among the tested cure-accelerating agents. the sodium carbonate showed the greatest effect on shortening gelation time of phenolic resin. In addition, in the manufacturing scale test, the hot-pressing time of phenol resin with the addition of 5 parts sodium carbonate could be shortened about 20% compared with ordinary phenol resin which had same glue-joints properties.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.169-172
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• 2000

In this paper applicabilities of coolant wastes are an admixture, which are produced from cooling line of the cars and industrial engines, to concrete under cold climate are investigated. According to the test results, as the contents f coolant wastes increase, setting time of cement mortar is shown to be delayed. However, when coolants wastes are overadded, it appears to be fast. In case of compressive strength, It tends to decline as the contents of coolant waste increase. Under low curing temperature, compressive strength of cement mortar containing coolant wasted with the increase of the contents of coolants wastes.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.1077-1080
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• 2003

High reactivity metakaolin (HRM) is a manufactured pozzolan produced by thermal processing of purified kaolinitic clay. Field performance and laboratory research of concrete containing HRM have demonstrated its value for bridge decks, bridge deck overlays, high-strength concrete and masonry products. This paper discusses laboratory evaluations to assess the physical properties of antiwashout underwater concrete (AWC) containing HRM, such as pH value, suspended solids, slump flow, and compressive strength. There were not much variations of pH value with the changing HRM contents, but suspended solid test showed that the amount of suspended solids of AWC with 10 and 20% of HRM were reduced in comparison with plain. Due to the fast hydration and reaction property of HRM, slump flow was decreased with increasing HRM contents. According to the results of compressive strength test, AWC with 10 and 20% of HRM showed higher strength characteristic than plain at all curing ages.