• Steel and Composite Structures
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• v.44 no.3
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• pp.339-351
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• 2022

A mortar-filled rectangular hollow structural section (RHS) can increase a structural section property as well as a compressive buckling capacity of a RHS member. In this study, the tensile performance of newly developed mortar-filled RHS members was experimentally evaluated with various connection details. The major test parameters were the type of end connections, the thickness of cap plates and shear plates, the use of stud bolts, and penetrating bars. The test results showed that the welded T-end connection experienced a brittle weld fracture at the welded connection, whereas the tensile performance of the T-end connection was improved by additional stud bolts inserted into the mortar within the RHS tube. For the end connection using shear plates and penetrating stud bolts, ductile behavior of the RHS tube was achieved after yielding. The penetrating bars increased load carrying capacity of the RHS. Based on the analysis of the load transfer mechanism, the current design code and test results were compared to evaluate the tensile capacity of the RHS tube according to the connection details. Design considerations for the connections of the mortar-filled RHS tubes were also recommended.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.21 no.2
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• pp.271-281
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• 2023

A study was conducted on the vitrification of the rare earth oxide waste generated from the PyroGreen process. The target rare earth waste consisted of eight elements: Nd, Ce, La, Pr, Sm, Y, Gd, and Eu. The waste loading of the rare earth waste in the developed borosilicate glass system was 20wt%. The fabricated glass, processed at 1,200℃, exhibited uniform and homogeneous surface without any crystallization and precipitation. The viscosity and electrical conductivity of the melted glass at 1,200℃ were 7.2 poise and 1.1 S·cm^-1, respectively, that were suitable for the operation of the vitrification facility. The calculated leaching index of Cs, Co, and Sr were 10.4, 10.6, and 9.8, respectively. The evaluated Product Consistency Test (PCT) normalized release of the glass indicated that the glass satisfied the requirements for the disposal acceptance criteria. Furthermore, the pristine, 90 days water immersed, 30 thermal cycled, and 10 MGy gamma ray irradiated glasses exhibited good compressive strength. The results indicated that the fabricated glass containing rare earth waste from the PyroGreen process was acceptable for the disposal in the repository, in terms of chemical durability and mechanical strength.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.1
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• pp.190-196
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• 2006

In the existed study, a fire outbreak in a reinforced concrete structure looses the organism by the different contraction and expansion of hardened cement pastes and aggregate, and causes cracks by thermal stress, leading to the deterioration of the durability. So accurate diagnosis of deterioration is needed based on mechanism of fire deterioration in general concrete structures. Fundamental information and data on the Properties of concrete exposed to high temperature are necessary for accurate diagnosis of deterioration. Therefore, This study is willing to propose fundamental data for quick and accurate diagnosis of deteriorated concrete structure by fire damage with making variable concrete test specimen, exposing high temperature environment, observing the explosive spalling and examining engineering property.

• Journal of Conservation Science
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• v.32 no.2
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• pp.223-234
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• 2016

Two-component epoxy resin is widely used in the cultural heritage restoration field. However according to mixing ratio of resin and hardener, curing property, mechanical strength and chemical structure differ which have possibility to effect the stability of cultural heritage. Result of questionnaire survey shows hands-on workers in the conservation field tend to mix the epoxy resin with his or her eye measurement when the using amount is small or mix additional hardener to shorten the pot life of epoxy resin. This research aims to analyze the curing property, mechanical strength and chemical structure of rapid curing type epoxy resin and medium curing type one depending on relative ratio of 0.25~4 of hardener to resin. When the amount of hardener was 0.5~2 times more than the resin, exothermic heat and curing speed were both increased. In case of included hardener to resin was lower than official ratio, mechanical strength (tensile shear strength, tensile strength and compressive strength) became higher along with active cross-linking bonding of the epoxy resin. Medium curing type epoxy relatively had lower exothermic heat and slower reaction during curing process. It was observed to be put to definite point of mechanical strength under lower content of hardener than official ratio. While, hardener ratio more than twice the resin slowed down the curing greatly and lowered the adhesion strength also. In conclusion, under the lower mixing rate of hardener than official ratio would show relatively fast reaction with similar mechanical strength. Over the official ratio on the other hand, material property drops rapidly. Accordingly, mixing ratio of epoxy resin is expected to be influential to the stability of cultural heritage.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.27 no.1
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• pp.47-56
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• 2017

In this study, the higher temperature thermal property of the fly ash-blast furnace slag system Geopolymer including alumina aggregate was investigated whether that Geopolymer will be or not useful as thermal-resistant construction materials. Under every mixing conditions, the crack on the surface of hardened body was not observed up to $800^{\circ}C$ and it corresponded with fact that level of changes was not significant before and after heating process. Residual compressive strength is most high when mixing Blast-Furnace Slag ratio is 60 wt% until temperature reaches $800^{\circ}C$. The major hydrates of hardened body of Geopolymer; amorphous halo pattern between $20{\sim}35^{\circ}$ (2theta) and mullite ($3Al_2O_3{\cdot}2SiO_2$) and quartz ($SiO_2$) was found during the experiment. Amorphous halo pattern was a aluminosilicate gel generated by geopolymeric polycondensation and it was found that the halo pattern of aluminosilicate gel was preserved up to $800^{\circ}C$. The patterns of aluminosilicate gel disappeared from $1,000^{\circ}C$ and crystal phases like gehlenite, calcium silicate, calcium aluminum oxide, microcline was observed with the increase of exposure temperature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.4
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• pp.2945-2950
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• 2015

While perfluoroalkane (PFA), a liquid state nucleating agent for a rigid polyurethane foam (RPUF) to enhance the thermal insulation property, has the excellent nucleating characteristics, it is very expensive as well as environmentally harmful due to the fluoride compound. Many researches, therefore, have been performed to develop the alternative nucleating agents to replace PFA. In the present work, a multi-wall carbon nanotube (MWCNT) was used as a sloid state nucleating agent, and thereby the effects on the property changes of the RPUF were carried out. Average cell size decreased from 165.6 for base RPUF to $162.9{\mu}m$ and cell uniformity was also enhanced, showing the standard cell-size deviation of 45.6 and 35.2, respectively. While k-factor of base PUF was $0.01763kcal/m.hr.^{\circ}C$, that of the sample with 0.01 phr MWCNT showed 1.02% reduced value of $0.01745kcal/m.hr.^{\circ}C$. Though the compressive yield stress is nearly the same as $0.030{\times}105Pa$ for the both samples, initial modulus of the sample with 0.01 phr MWCNT was higher than that of base sample. it was considered as the results that small amount of MWCNT could play a sufficient role as the effective nucleating agent for RPUF, showing that an echo-friendly RPUF with reduced-cost could be fabricated, which has an enhanced thermal and mechanical properties.

• Journal of Conservation Science
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• v.32 no.4
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• pp.459-469
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• 2016

The goal of this study was to examine property changes induced by the choice of filler used with an epoxy resin that was developed in 2014 to restore cultural assets and consider the applicability of the resin as a restorative agent. The properties of putty mixed with 9 types of fillers and as-developed resins were compared with those of existing materials with regard to stability, superiority and applicability. The potential of the putty as an alternative material was also examined. The materials produced the best adhesiveness, color change and hardness results when mixed with lime. Micro balloon produced the best wear rates and hardening times, while diatomite produced the best tensile and compressive strengths. A plaster and white mineral pigment mixture produced the best specific gravity. Every material except for lime exhibited about 2.5-20 times higher wear rates than the existing material, which is thought to exhibit an excellent cutting force. The hardening time was enhanced by about 0.5-9 times to improve convenience. The stability of the relic was also ensured by improving hand staining without any shrinkage or deformation. The material exhibited about 0.5-27 times less yellowing. Thus, it is thought to be a material that can reduce property changes and reduce the degree of relic fatigue which occurs during reprocessing and sense of difference from relic.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.285-293
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• 2001

To improve the vulnerable point and the mechanical property of the existing lightweight foamed concrete, this study was intend to manufacture the lightweight foamed concrete with wasted expanded poly-styrene, examinate and analyze the mechanical property of its. The experiment was being processed with mixing the wasted expanded poly-styrene maximum 40 % by stages and which was mainly basis on the practical mixture. The results of the experiment are following. The flow value is most affected by the mixtured rate of the wasted expanded poly-styrene. The more the mixtured ratio, the less the flow value and the more the more the unit quantity of cement and the W/C, the more the flow value. The apparent specific gravity indicated 0.31∼0.54 and which is seemed to be mainly included in the 0.4 degree and 0.5 degree that are regulated in the KS F 4039. The more the mixtured wasted poly-styrene ratio, the less the apparent specific gravity. The absorbing ratio which was depend on the mixture condition indicated 11 ∼46% and the more the mixtured ratio of the wasted expanded poly-styrene, the less the absorbing ratio remarkably. The compressive strength of the lightweight foamed concrete had a tendency to increase as the mixtured ratio of the wasted poly-styrene, the ratio quantity of cement and the apparent specific gravity increasing but as the ratio of bubble decreasing. The W/C affected little.

• Korean Journal of Agricultural Science
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• v.10 no.2
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• pp.310-323
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• 1983

To study the effect of foaming agent on the production and property of light weight concrete, the tests of compressive, tensile, bending strengths and absorption rates of mortar were done under the different mixing ratio with J, A and D foaming agents. The results obtained were summarized as follows : 1. The strengths were decreased in richer mixing ratio and more addition of foaming agent. The decrease of strengths was the greatest at the level of 0.75% of foaming agent. The decreasing rate of strengths was in order of J, A and D foaming agent. 2. At the mixing ratio of 1:1, ${\sigma}_{28}$ and 0.75% of foaming agent, the compressive strength was decreased up to 34.9% by D, 47.8% by A and 86.8% by J foaming agent, respectively, the tensile strength was decreased up to 14.8% by D, 20.2% by A and 77.9% by J foaming agent, respectively, bending strength was decreased up to 19.9% by D, 35.0% by A and 79.1% by J foaming agent, respectively. The decrease of compressive strength was more severe than that of tensile and bending strengths. 3. The absorption rates were increased in poorer mixing ratio and more addition of foaming agent. The absorption rate was significantly higher at the early stage of immersed water. The absorption rate was in order of J, A and D foaming agent. 4. The decrease of strengths was inevitable in cement-mortar with foaming agent, but the cement mortar with foaming agent has such the properties of the light-weight, lnsulation, Keeping-warmth, sound proof and fire-proof that if could be utilized to the constructions which need low strengths.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.805-811
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• 2004

In this paper, effects of mixture proportion and material condition on both fundamental properties, drying and autogenous shrinkage of high performance concrete are discussed. According to the results, for the effect of mixture proportion on the fundamental properties, decrease in W/B and unit water content results in reduction of fluidity, while air content has no variation. Compressive strength exhibits an decreasing tendency with an increase in W/B and unit water content do not remarkable affect the compressive strength. For the effect of materials on the fluidity, the fluidity of low heat portland cement(LPC) is smaller than that of ordinary portland cement(OPC). The use of Polycarbonic acid based superplasticizer(PS) has more favorable effect on enhancing fluidity than Naphtalene based superplasticlzer(NS) and Melamine based superplasticizer(MS). Air content of concrete using LPC is larger than that using OPC. The effects of superplasticizer type on the air content is larger in order of MS, PS and NS. The use of LPC exhibited lower strength development at early age than OPC, whereas after 91days, similar level of compressive strength is achieved regardless of cement type. Compressive strength of concrete is not affected by SP type. For the effect of mixture proportion and materials on drying and autogenous shrinkage, an increase in W/B results in reduction of drying shrinkage and an decrease in water content leads to reduce drying shrinkage. Autogenous shrinkage is not observed until 49 days with the concrete mixture with $35\%$ of W/B and $145 kg/m^3$ of water content. This is due to the combination effects of expansion admixture and shrinkage reducing admixture, which causes an offset of autogenous shrinkage. The use of LPC results in a reduction in autogenous shrinkage compared with OPC. SP type has little influence on the autogenous shrinkage. It is found from the results that mixture proportioning of high performance concrete incorporating fly ash, silica fume, expansion admixture and shrinkage reducing admixture is need to focus on the increase in W/B and the reduction in water content and the use of LPC and MS is also required to use to secure the stability against shrinkage properties.