• 대한토목학회논문집
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• 제26권2A호
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• pp.401-409
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• 2006

본 연구에서는 고강도 강섬유보강 콘크리트(HSFRC)의 설계 및 시공을 위한 기초 자료를 제공하기 위하여 역학적 특성 및 장기변형 특성에 관한 연구를 수행하였으며, 탄성계수, 압축강도, 인장강도, 휨강도, 건조수축 및 크리프에 미치는 강섬유 혼입의 영향을 검토하고, 휨파괴인성을 평가하였다. 연구결과, HSFRC의 압축강도에 미치는 강섬유의 혼입효과는 그다지 크지 않았고, 탄성계수는 섬유혼입률이 증가함에 따라 증가하는 것으로 나타났으며, 인장강도, 휨강도 및 휨인성에 미치는 섬유혼입률($V_f$) 및 섬유형상비($l_f/d_f$)의 영향은 대단히 큰 것으로 나타났다. 이는 $V_f$ 및 $l_f/d_f$의 증가와 함께 극한하중에 상응하는 처짐량이 증가하고, 강섬유의 균열구속성능에 의해 하중-처짐곡선의 하강곡선이 완만하게 감소하기 때문인 것으로 판단된다. 또한 크리프 및 건조수축에 미치는 섬유혼입률($V_f$)의 영향은 대단히 큰 것으로 나타났으며, 특히 고강도 콘크리트에 강섬유를 혼입하면 크리프 변형에 비해 건조수축 변형의 저감에 더욱 효과가 큰 것으로 나타났다.

• Korean Chemical Engineering Research
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• 제57권1호
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• pp.65-72
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• 2019

본 연구에서는 PPO 이온선택성 용액과 이온교환수지의 혼합비율을 달리하여 캐스팅법으로 불균질 이온교환막을 제조하였고 이를 이용하여 불균질 바이폴라막을 제조하였다. 불균질 양이온교환막 및 음이온교환막의 함수율은 각각 60~80% 이었고이온교환용량은 2.81~3.26 meq/g, 2.31~2.74 meq/g 이었으며전기저항은 $1.65{\sim}1.45{\Omega}{\cdot}cm^2$, $1.55~1.05{\Omega}{\cdot}cm^2$이었다. 또한 불균질 이온교환막의 최대 수지함량은 60 wt% 이었다. 불균질 바이폴라막의 인장강도는 관능화 전 PPO 수지의 인장강도($700Kg_f/cm^2$) 보다 모두 낮았고, 촉매층이 형성된 불균질 바이폴라막의 인장강도는 무촉매 불균질 바이폴라막보다 인장강도가 낮았다. 또한 촉매층이 형성된 불균질 바이폴라막의 물분해 전압은 최소 1.7~1.8 V, 최대 3.9~4.0 V로 낮고 매우 안정적이었고, 무촉매 불균질 바이폴라막의 물분해 전압은 3.8~4.0 V로 일정하였다.

• International Journal of Concrete Structures and Materials
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• 제4권2호
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• pp.113-118
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• 2010

This article aims to study the effects of adding steel fibers to concrete on the mechanical behavior of steel fiber concrete (SFC) slabs. After formulating the SFC, an experimental work was, first, conducted on $160\;{\times}\;320$ mm cylindrical specimens and $70\;{\times}\;70\;{\times}\;280$ mm prisms. Then, this study was carried out on 20 rectangular $1,100\;{\times}\;1,100\;{\times}\;60$ mm small slabs submitted to a distributed load. Two types of fibers with hooked ends were used: long fibers (LF) of a length of 50 mm and short fibers (SF) of a length of 35 mm. The studied parameters are compressive and tensile strengths and Young's modulus. Plain concrete (PC) small slabs were also prepared to be compared to the SFC specimens. The results showed that the compressive strength of SFC increased up to 25% while the splitting tests showed an improvement of the SFC reaching 45%. Tests on SFC small slabs also showed that a smaller deflection is obtained with respect to PC, which indicates an improvement in strength (up to 100%), in ductility and in resistance to cracking. The LF gives a better improvement in strength than the SF for a 70% $kg/m^3$ of steel proportioning.

• 한국안전학회지
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• 제31권5호
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• pp.109-116
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• 2016

This study presents the results of experiments to investigate the effect of polymer type and curing temperature on the mechanical properties of polymer mortar. Setting time of two types of polymers, hardening-delayed polymer(HDP) and rapid hardening polymer(RHP), was tested to check the working time. Additionally, flexural strength, compressive strength, and splitting tensile strength was investigated for mortars using these polymers. From these results, it was confirmed that, irrespective to curing temperature, RHP mortar at the curing age of 24h develops the similar mechanical properties to maximum properties and HDP mortar is more sensitive to the curing temperature. In addition, it should be noted that RHP mortar and HDP mortar are suitable in winter and summer, respectively.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2009년도 춘계 학술대회 제21권1호
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• pp.335-336
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• 2009

본 연구에서는 콘크리트 구조물의 사하중을 감소시켜 경제적 및 기술적으로 유리한 인공경량골재콘크리트를 제작하기 위한 기초연구를 수행하였다. 인공경량골재콘크리트의 기본물성 검토를 위하여 일반콘크리트, 경량골재콘크리트 1종 2종을 제작하여 단위증량, 압축강도, 쪼갬인장강도시험을 실시하였다. 그 결과 인공경량골재를 사용한 콘크리트의 경우도 압축강도가 설계기준강도 21MPa 이상으로 측정되었고, 실리카흄 첨가시 다소 강도 증진을 보였다. 향후 구조용 토목구조물에 사용하기 위해서는 내구성에 대한 체계적이고 세밀한 연구가 진행되어야 할 것이다.

• Advances in concrete construction
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• 제5권5호
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• pp.423-436
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• 2017

Today, pozzolans are widely used in construction for various reasons such as technical and economic efficiency. In this research, in order to evaluate some of important properties of concrete, silica fume and fly ash have been used as a replacement for cement in different mass percentages. Concrete mixtures were made from a water-cement ratio of (0.45) and cured under similar conditions. The main focus of this study was to evaluate the permeability and mechanical properties of concrete made from binary and ternary cementitious mixtures of fly ash and silica fume. In this study permeability of concrete was studied by evaluating the sorptivity, water absorption, water penetration depth, electrical resistivity and rapid chloride permeability (RCP) tests. Mechanical properties of concrete were evaluated with compressive strength, splitting tensile strength and modulus of elasticity. Scanning electronic microscopy (SEM) was used to characterize the effects of silica fume and fly ash on the pore structure and morphology of concrete with cement based matrix. The results indicated that the incorporation of silica fume and fly ash increased the mechanical strength and improved the permeability of concrete.

• Structural Engineering and Mechanics
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• 제86권4호
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• pp.431-441
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• 2023

The aim of this paper is to present a new sustainable ternary and quaternary binder by partially replacing ordinary Portland cement (OPC) with different percentages of supplementary cementitious materials. The motivation is to reduce our dependency on OPC to reduce CO₂ emission and carbon foot print. As the main substitute for the OPC, siliceous fly ash was used. Moreover, silica fume and nanosilica were also used. During examinations the main mechanical parameters of concrete composites, i.e., compressive strength (f_cm) and splitting tensile strength (f_ctm) were assed. The microstructure of these materials was also analysed. It was found that the concrete incorporating pozzolanic materials is characterized by a well-developed structure and has high values of mechanical parameters. The quaternary concrete containing: 80% OPC, 5% FA, 10% SF, and 5% nS have shown the best results in terms of good strength parameters as well as the most favourable microstructure, whereas the worst mechanical parameters with microstructure containing microcracks at phase interfaces were characterized by concrete with more content of FA additive in the concrete mix, i.e., 15%. Nevertheless, all concretes made on quaternary binders had better parameters than the reference one. It can be stated that sustainable concrete incorporating pozzolanic materials could be good substitute of ordinary concretes.

• Advances in concrete construction
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• 제13권 2호
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• pp.133-152
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• 2022

Ecological issues such as natural resource reduction and enormous waste disposals are increasingly leading in developing civilization toward sustainable construction. The two primary environmental issues are the depletion of natural resources and the disposal of trash in open landfills. Waste steel fiber (WSF) was investigated for usage as a cement-based concrete (CBC) constituent in this research. Recycling waste fibers both makes cement composites more long and cost-effective, also aids in pollution reduction. The objective of this study is to analyze the impacts of waste fiber on the fresh and mechanical features of concrete using recycled additives. A comparative research on the durability and mechanical qualities of fiber-reinforced concrete (FRC) constructed with natural aggregates was conducted for this aim. The obstacles to successful WSF recycling methods application in the building industry have been investigated, resulting that CBCs with these fibers make an economic and long lasting choice to deal with waste materials. The workability of fiber enhanced concrete was found to be comparable to that of normal concrete. Fibers have a considerable impact on the splitting tensile strength, flexural and compressive strength of recycled concrete. Fiber may enhance the water permeability. When the WSF content is 0.6 kg/m3, the water absorption is nearly half. Fibers would have no effect on its permeability.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 가을 학술논문 발표대회
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• pp.172-173
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• 2021

With the development of nano-reinforcement technology and the increasing concern for environmental issues, TiO₂ nanomaterials have received wide attention as an additive besides carbon nanomaterials that can be used to enhance the mechanical properties of cement-based materials. Also, TiO₂-based materials can allow cement-baned materials with photocatalytic capability, providing a potentially effective approach to reduce environmental problems. In this work, compressive strength, splitting tensile strength, and degradation of methylene blue solution were used as target to assess the effect of TiO₂ nanotubes on the mechanical strength and photocatalytic effect of hardened cement paste at different curing time. According to the strength results, the optimum amount of TiO₂ was identified as 0.5% of the weight of cement. Meanwhile, the TiO₂ nanotubes-reinforced specimen exhibited better photocatalytic effect in the early stage of curing.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 봄 학술논문 발표대회
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• pp.151-152
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• 2023

This study investigates the effect of nano-silica and nano-calcite on the hydration properties and mechanical performance of limestone calcined clay cement (LC³) paste. The pastes were synthesized by replacing limestone with nano-silica and nano-calcite in order to enhance the mechanical properties in both early and late stages of hydration. The nano-calcite enhanced the strength of LC³ pastes at 1 day of hydration, however, the strength decreased compared to the ordinary LC³ pastes afterwards due to excessive amount of carboaluminate produced in the pastes. On the other hand, nano-silica improved the mechanical properties of LC³ pastes at all ages of hydration. This is mainly due to the nucleation effect and pozzolanic reaction of nano-silica, affecting the early age and late ages of hydration, respectively. The nucleation effect of both nanomaterials were confirmed by the analysis of hydration heat, supporting the enhanced early age strength of nanomaterial incorporated LC³ pastes. Furthermore, the dense matrix was shown in the pore size distribution, and the increased C-S-H due to the pozzolanic reaction evidence the improved compressive and splitting tensile strength of nano-silica incorporated LC³ pastes.