• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2010년도 춘계 학술논문 발표대회 1부
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• pp.17-19
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• 2010

This paper describes the possibility of the raft thickness reduction for mega foundations system of super high-rise buildings through a case study on domestic and foreign super high-rise buildings. In case of super high-rise buildings, the size of foundations, especially raft becomes wider and deeper because of heavy upper load. It is difficult to pour concrete of this kind of mega foundation, and cracks by hydration heat could happen. Therefore, there are several ways to reduce the raft thickness of mega foundations. Piled-raft could be the one because moment and shear load that the raft subjects on by soil reaction are lower. The effect of the piled-raft foundation on the raft thickness reduction could be confirmed by comparison of super high-rise buildings with pile, piled-raft and mat foundation. Furthermore, it was showed that the raft thickness could be more reduced by locating piles right under the vertical members of super structures.

• 한국가스학회지
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• 제9권1호
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• pp.33-37
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• 2005

본 논문은 설계 변수 변화에 따른 LNG저장탱크 강제 루프의 거동을 분석하였다. 강제 루프 설계에서는 여러 가지 하중 조건 그리고 이러한 하중 조건의 조합에 대하여 안정적인 거동을 하여야 한다. 본 논문에서는 콘크리트 타설에 따른 강제 루프의 거동 그리고 H빔 및 루프 판의 두께 변화와 같은 설계 변수의 변화에 대한 강제 루프의 거동을 비교 분석하였다. 이렇게 구해진 결과를 바탕으로 LNG저장탱크 강제 루프 설계시 보다 합리적인 설계법을 제시하고자 하였다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2016년도 추계 학술논문 발표대회
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• pp.94-95
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• 2016

Calcium Silicate Hydrate (C-S-H), which takes up most of the hydration products of Portland Cement (PC), has the greatest impact on the mechanical behavior and strength development of concrete. The exact mechanism of its deformation, however, has not yet been elucidated. The present study aims to demonstrate the mechanism of nano-deformation behavior of C-S-H in tricalcium silicate paste under compressive loading, unloading and reloading by interpreting atomic pair distribution function (PDF) based on synchrotron X-ray scattering. The strain of the tricalcium silicate paste for a short-range of 0 ~ 20 Å under compressive load exhibited two stages, I) nano-packing of interlayer of C-S-H and II) micro-packing of C-S-H globules, whereas the deformation for a long-range order of 20 ~ 40 Å was similar to that of a calcium hydroxide phase measured by Bragg peak shift. Moreover, the residual strains due to the plastic deformation of C-S-H was clearly observed.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2005년도 추계 학술논문 발표대회
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• pp.25-28
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• 2005

This study investigates the field application of surface insulation curing method, which combined double layer bubble sheet(DBS) and thick-curing-material(TCM) for cold weather concreting. According to the test, deck slab, curing only upper section with DBS and TCM, does not make big different temperature history with that, curing both upper and bottom section during daily average temperature 6.5t. It is concluded that combination of DBS and TCM in only upper section can be safely cured in early period of time during cold water concreting. The field test was carried out with this favourable data. The upper deck slab was insulated by combination of DBS and TCM, and the construction was surrounded by tent. in order to protect from outside wind. The test result shows that the lowest temperature of deck slab indicated 6$ ^{circ}C $. It demonstrated that this curing method can resist early frost and save construction cost in the side of management and saving labor cost, compared with previous method. In addition, the column specimen, combined both form and bubble board, exhibited favorable temperature history, due to internal hydration heat insulation effect.

• 한국농공학회논문집
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• 제57권6호
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• pp.1-7
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• 2015

Most of chloride diffusion models based on finite difference method (FDM) could not express the diffusion in horizontal direction at each elevation. To overcome these weakness, two dimensional chloride ion penetration model based on finite element method (FEM) to be able to combine various multi-physics simultaneously was suggested by introducing moving mesh technique. To avoid the generation of mesh being able to be distorted depending on the relative movement of water level to static concrete, a rectangular type of mesh was intentionally adopted and the total number of meshes was empirically selected. The simulated results showed that the contents of surface chloride decreased following to the increase of elevation in the top part of low sea level, whereas there were no changes in the bottom part of low level. In the DuraCrete model, the diffusion coefficient of splashed zone is generally smaller than submerged zone, whereas the trend of Life365 model is reverse. Therefore, it could be understood that the developed model using moving mesh technique effectively reflects $DuraCrete^{TM}$ model rather than $Life365^{TM}$ model. In the future, the model will be easily expanded to be combined with various multi-physics models considering water evaporation, heat of hydration, irradiation effect of sun and so on because it is based on FEM.

• Computers and Concrete
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• 제16권2호
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• pp.261-274
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• 2015

This study established the standard recommended values and expansion fracture threshold values for the content of steel slag in controlled low-strength materials (CLSM) to ensure the appropriate use of steel slag aggregates and the prevention of abnormal expansion. The steel slags used in this study included basic oxygen furnace (BOF) slag and desulfurization slag (DS), which replaced 5-50% of natural river sand by weight in cement mixtures. The steel slag mortars were tested by high-temperature ($100^{\circ}C$) curing for 96 h and autoclave expansion. The results showed that the effects of the steel slag content varied based on the free lime (f-CaO) content. No more than 30% of the natural river sand should be replaced with steel slag to avoid fracture failure. The expansion fracture threshold value was 0.10%, above which there was a risk of potential failure. Based on the scanning electron microscopy (SEM) analysis, the high-temperature catalysis resulted in the immediate extrusion of peripheral hydration products from the calcium hydroxide crystals, leading to a local stress concentration and, eventually, deformation and cracking.

• Advances in concrete construction
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• 제11권2호
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• pp.163-171
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• 2021

This paper studies the effect of using multi-scale reinforcement additives on mechanical strengths, damage performance, microstructure, and water absorption of cementitious composites. Small dosages of carbon nanotubes (CNTs) or polypropylene (PP) microfibers; 0.05%, 0.1%, and 0.2% by weight of cement; were added either separately or simultaneously into cement mortar. The experimental results show the ability of these additives to enhance the mechanical behavior of the mortar. The best improvement in compressive and flexural strengths of cement mortar reaches 28% in the case of adding a combination of 0.1% CNTs and 0.2% PP fibers for compression, and a combination of 0.2% CNTs and 0.2% PP fibers for flexure. Adding CNTs does not change the brittle mode of failure of plain mortar whereas the presence of PP fibers changes it into ductile failure and clearly enhances the fracture energy of the specimens. Scanning electron microscopic (SEM) images of the fracture surfaces highlights the role of CNTs in improving the adhesion between the PP fibers and the hydration products and thus enhance the ability of the fibers to mitigate cracks propagation and to enhance the mechanical performance of the mortar.

• Advances in concrete construction
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• 제14권5호
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• pp.341-354
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• 2022

Treatment of solid waste building materials is a crucial method of disposal and an area of ongoing research. New standards for the treatment of solid waste building materials are necessary due to multisource features, huge quantities, and complicated compositions of solid waste. In this research, sustainable nanomaterial mixtures containing nano-paper waste (NPW) and nano-metakaolin (NMK) were used as a substitute for Portland cement. Portland cement was replaced with different ratios of NPW and NMK (0%, 4%, 8%, and 12% by weight of cement) while the cement-to-water ratio remained constant at 0.4 in all mortar mixtures. The fresh properties had a positive effect on them, and with the increase in the percentage of replacement, the fresh properties decreased. The results of compressive strength at 7 and 28 days and flexural strength at 28 days show that the nanomaterials improved the strength, but the results of NMK were better than those of NPW. The best replacement rate was 8%, followed by 4%, and finally 12% for both materials. The combination of NMK and NPW as a replacement (12% NMK + 12% NPW) showed less shrinkage than the others because of the high pozzolanic reactivity of the nanomaterials. The combination of NMK and NPW improved the microstructure by increasing the hydration volume and lowering the water in the cement matrix, as clearly observed in the C-S-H decomposition.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 봄 학술논문 발표대회
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• pp.169-170
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• 2023

In this study, light-heat generating materials were produced in two ways, and the performance of two light-generating insulation sheets was reviewed. As a result of the experiment, it was possible to confirm the improved heating performance of the light heating insulation sheet compared to the existing bubble sheet. The light heat insulation sheet (b) showed improved thermal properties compared to the existing bubble sheet, and it is believed that the temperature has increased due to the combined effect of initial hydration heat and heat generation after installation. In future studies additional experiments are needed to compensate for the insufficient insulation performance due to the single bubble sheet through the double bubble sheet and to adjust the amount of light-generating materials added as a consideration of the optimal heat-generating effect of the light-generating insulation sheet (b).

• 콘크리트학회논문집
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• 제23권3호
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• pp.295-301
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• 2011

최근 고성능 감수제, 실리카 퓸과 강섬유 등을 사용하여 제조한 초고성능 콘크리트(UHPC)의 사용이 전 세계적으로 증가하고 있다. UHPC는 강도가 높을 뿐만 아니라 조직이 치밀하여 내구성 측면에서도 우수한 성능을 갖고 있지만 W/B가 낮고 단위 시멘트량이 많기 때문에 초기 수화열과 자기수축이 많이 발생하여 재령 초기에 균열 발생 위험성이 높아지게 된다. UHPC의 초기 수축균열은 수축 저감제 및 팽창재의 자기수축 보상 효과에 의하여 제어할 수 있다. 이 연구에서는 수축 저감제 및 팽창재를 혼입한 UHPC의 초음파 속도를 측정하여 재령 초기 강성 변화를 추정하였고, 수축 실험을 통하여 수축 저감제 및 팽창재가 UHPC의 자기수축에 미치는 영향을 조사하였다. 또한 UHPC의 자기 수축 실험 결과로부터 자기수축 예측 모델의 재료 상수를 결정하였다. 결론적으로 수축 저감제 및 팽창재를 혼입함에 따라 UHPC 강성이 신속하게 발현되며, 자기수축 저감에 효과가 있음을 알 수 있었다.