• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.391-396
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• 2002

The so called setting is defined as the onset of rigidity in fresh concrete. In the analysis of the early-age concrete behavior, we consider fresh concrete as a structural element immediately after mixing. But for the activation of real structural behavior of fresh concrete, it takes some time after the beginning of hydration reaction. So, the very early age deformations due to hydration heat and shrinkage which occur before the setting do not produce restraint stresses. In this paper, we propose a setting characteristic model based on the so called percolation theory. From the analysis using the model, the influence of curing temperature is investigated and analytical results are compared with experimental results. From the comparison, the validity of proposed model is verified. This model is also applied to evaluate stress development in a temperature-stress test machine (TSTM) specimen and then the effect of setting time on the stress development is discussed.

• Korea-Australia Rheology Journal
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• v.21 no.2
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• pp.91-102
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• 2009

This paper describes an extension of viscoelastic Group Interaction Modelling (GIM) to predict the relaxation response of linear, branched and cross-linked structures. This model is incorporated into a Monte Carlo percolation grid simulation used to generate the topological structure during the isothermal cure of a gel, so enabling the chemorheological response to be predicted at any point during the cure. The model results are compared to experimental data for an epoxy-amine systems and good agreement is observed. The viscoelastic model predicts the same exponent power-law behaviour of the loss and storage moduli as a function of frequency and predicts the cross-over in the loss tangent at the percolation condition for gelation. The model also predicts the peak in the loss tangent which occurs when the glass transition temperature surpasses the isothermal cure temperature and the system vitrifies.

• Computers and Concrete
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• v.18 no.5
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• pp.937-950
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• 2016

This study applied autoclave expansion and heat curing to accelerate the hydration of concrete and investigated how these methods affect the expansion rate, crack pattern, aggregate size effect, and expansion of electric arc furnace oxidizing slag (EOS)-containing concrete. An expansion prediction model was simulated to estimate the expansion behavior over a long period and to establish usage guidelines for EOS aggregates. The results showed that the EOS content in concrete should range between 20% and 30% depending on the construction conditions, and that coarse aggregates with a diameter of ${\geq}4.75-mm$ are not applicable to construction engineering. By comparison, aggregates with a size of 1.18-0.03 mm resulted in higher expansion rates; these aggregates can be used depending on the construction conditions. On Day 21, the prediction model attained a coefficient of determination ($R^2$) of at least 0.9.

• Polymer(Korea)
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• v.26 no.6
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• pp.728-736
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• 2002

The thermal and dielectric properties of unsaturated polyester resin system during cure were analyzed under Isothermal conditions. Both $varepsilon$′ and $varepsilon$" decreased and dipole relaxation was observed under isothermal conditions during cure. The ionic conductivity decreased linearly with the conversion according to the Kienle-Rate equation (ln($varepsilon$"$_{ionic}$we$_{0}$)=C$_{r}$$alpha$+C$_{0}$) up to $alpha$=0.15, after which it aparted from the relationship due to the entanglement of polymer chains. The effect of ionic conductivity was revealed to be larger than that of dipole motion during the whole cure through the electrical modulus analysis. Although dielectric motion was analyzed with Debye model, it was observed only at a narrow time region of middle stage of cure. In order to estimate the dielectric properties during the whole cure, the Havriliak-Negami model was considered and modified with the strong effect of ionic conductivity. The changes of $varepsilon$′ and $varepsilon$" were well estimated with this modified Havriliak-Negami model.

• Advances in concrete construction
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• v.7 no.3
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• pp.167-174
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• 2019

Metakaolin (MK), which is increasingly being used to produce high performance concrete, is produced by calcining purified kaolinite between 650 and $700^{\circ}C$ in a rotary kiln. The carbonation resistance of metakaolin blended concrete is lower than that of control concrete. Hence, it is critical to consider carbonation durability for rationally using metakaolin in the concrete industry. This study presents microstructure modeling during the carbonation of metakaolin blended concrete. First, based on a blended hydration mo del, the amount of carbonatable substances and porosity are determined. Second, based on the chemical reactions between carbon dioxide and carbonatable substances, the reduction of concrete porosity due to carbonation is calculated. Furthermore, $CO_2$ diffusivity is evaluated considering the concrete composition and exposed environment. The carbonation depth of concrete is analyzed using a diffusion-based model. The proposed microstructure model takes into account the influences of concrete composition, concrete curing, and exposure condition on carbonation. The proposed model is useful as a predetermination tool for the evaluation of the carbonation service life of metakaolin blended concrete.

• Polymer(Korea)
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• v.37 no.2
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• pp.240-248
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• 2013

The curing behaviors of diglycidyl ether of bisphenol A (DGEBA) with mercaptan hardener were studied by the comparison with amine-adduct type hardener. Curing behaviors were evaluated by DSC at dynamic and isothermal conditions. In the DSC, the dynamic experiments were based on the method of Kissinger's equation, and the isothermal experiments were fitted to the Kamal's kinetic model. Activation energy of epoxy/amine-adduct type hardener was ca. 40 kcal/mol. As the functional group of mercaptan hardener, -SH increased, on epoxy/mercaptan hardeners, the activation energies decreased from 28 to 19 kcal/mol. Epoxy/amine-adduct type hardener was initiated at $90^{\circ}C$ or higher. However, epoxy/mercaptan hardeners reduced the initiation temperatures below $80^{\circ}C$ and shortened the durations of curing reaction within 10 min. We found out that the reaction kinetics of epoxy with mercaptan hardener followed the autocatalytic reaction models, and the maximum reaction rates were shown at the conversions of 20~40%.

• Journal of the korean academy of Pediatric Dentistry
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• v.23 no.2
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• pp.357-364
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• 1996

The purpose of this study was to asses the shear bond strengths of 3 types of light-curing Glass Ionomer cement to dental amalgam with or without an intermediary agent. 60 amalgam adherent specimens were prepared and aged in water at $37^{\circ}C$ for 3 days. Before bonding, the amalgam surfaces were finished flat on 600-grit silicon carbide paper. 30 specimens among 60 were used for bonding in this condition, and the other 30 were covered with a thin layer of light-curing intermediary agent. Shear bond strengths were measured with universal testing machine (Instron, Model 4301) and statistically processed by ANOVA and t-test. On completion of bond test, the fracture surfaces were examined under light microscope so that the mode of bond failure could be assessed The results were as follows : 1. Bond strength of Fuji II LC group showed the hightest value and was followed by Vitremer, Vitrebond groups (p<0.05). 2. The bond strengths achieved without an intermediary agent were higher than those obtained with intermediary agent (p<0.05). 3. For the specimens bonded with intermediary agent, bond failures occured mostly at the agent-amalgam interface. So, the use of intermediary bonding agent was thought not recommendable at glass ionomer-amalgam interface.

• Journal of the Korean Society of Tobacco Science
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• v.13 no.2
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• pp.59-65
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• 1991

There was no a difference of genetic analysis among methods(means, joint scaling test, 3 Parameter model) . The magnitude of additive effects generally paralleled the magnitude of difference between parental means and appeared to be more independent from non-allelic interaction than did dominance effects, whereas the magnitude of dominance effects were inflated by non-allelic interaction. Additive effects were significant for all characteristics observed and it was a major effects in inheritance of number of leaves. Dominance effects were higher than additive effects for plant height, days to flower, flesh leaf weight per plant, curing rate, total alkaloid and total nitrogen.

• Proceedings of the KIEE Conference
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• 2008.10a
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• pp.184-184
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• 2008

This paper presents the measurement of the mechanical property of PDMS (Polydimethylsiloxane) elastomer depending on volumetric mixing ratios of base polymer and curing agent and their hyperelastic material models.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.13-13
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• 2004

나노테크놀러지 중의 한 가지인 나노임프린트 리소그래피 기술은 수 ∼ 수십 나노 급의 선폭을 가지는 스탬프(stamp)를 전자빔 리소그래피(electron beam lithography)를 이용하여 제작한 후 스탬프에 형성된 패턴과 동일한 형상을 원하는 곳에 모사하는 기술이다. 이 기술은 크게 열을 가하는 방식과 UV 경화성 수지를 이용한 방식으로 나뉜다. 열을 가하는 나노임프린트 리소그래피 방식의 경우는 열 경화성 수지를 이용하여 고온 조건에서 스탬프를 고압으로 눌러 원래의 형상을 모사하며, UV 나노임프린트는 광경화 반응을 이용하여 수지를 경화 시켜 모사하는 차이점이 있다.(중략)