• Advanced Composite Materials
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• 제17권3호
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• pp.259-275
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• 2008

This study aims to optimize the mechanical and electrical properties of electrically conductive polymer composites (CPCs) for use as a material of bipolar plates for PEM fuel cells. The thin CPCs consisting of conductive fillers and polymer resin were fabricated by a preform molding technique. Expanded graphite (EG), flake-type graphite (FG) and carbon fiber (CF) were used as conductive fillers. This study tested two types of CPCs, EG/FG filled CPCs and EG/CF filled CPCs, to optimize the material properties. First, the characteristics of EG/FG filled CPCs were investigated according to the FG ratio for 7 and $100{\mu}m$ sized FG. CPCs using $100{\mu}m$ FG showed optimal material properties at 60 wt% FG ratio, which were an electrical conductivity of 390 S/cm and flexural strength of 51 MPa. The particle size was an important parameter to change the mechanical and electrical behaviors. The flexural strength was sensitive to the particle size due to the different levels of densification. The electrical conductivity also showed size-dependent behavior because of the different contributions to the conductive network. Meanwhile, the material properties of EG/CF filled CPCs was also optimized according to the CF ratio, and the optimized electrical conductivity and flexural strength were 290 S/cm and 58 MPa, respectively. The electrical conductivity of this case decreased similarly to the EG/FG filled case. On the other hand, the behavior of the flexural strength was more complicated than the EG/FG filled case, and the reason was attributed to the interaction between the strengthening effect of CF and the deterioration of voids.

• 한국터널지하공간학회 논문집
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• 제12권1호
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• pp.51-60
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• 2010

최근 새로운 형태의 폴리올레핀 섬유에 대하여 성능향상 개발이 이루어지고 있으며, 기존 섬유와 혼입하여 사용하거나 폴리올레핀 섬유만을 사용한 콘크리트 특성에 대하여 연구와 검증이 필요하다. 본 연구의 목적은 강섬유와 폴리올레핀 섬유를 사용한 콘크리트의 휨 인성 및 휨 인장강도에 대한 성능을 확인하기 위하여 324개의 보 시편을 제작하고, KS F2566과 ASTM C 1399-02규격에서 제시한 4점 휨 실험을 수행하여 휨 인성지수, 등가 휨 인장강도, 평균잔류강도를 분석하였다. 실험결과, 섬유 혼입률, 섬유 형상비에 대한 휨 인성 및 인장강도에 대한 효과가 확인되었으며, 강섬유와 폴리올레핀의 최적의 혼입비율을 제시하였다.

• International Journal of Concrete Structures and Materials
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• 제10권2호
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• pp.249-256
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• 2016

This paper deals with the effects of silica fume content and polymer-binder ratio on the properties of ultrarapid-hardening polymer-modified mortar using silica fume and ethylene-vinyl acetate redispersible polymer powder instead of styrene-butadiene rubber latex to shorten the hardening time. The ultrarapid-hardening polymer-modified mortar was prepared with various silica fume contents and polymer-binder ratios, and tested flexural strength, compressive strength, water absorption, carbonation depth and chloride ion penetration depth. As results, the flexural, compressive and adhesion strengths of the ultrarapid-hardening polymer-modified mortar tended to increase as increasing polymer-binder ratio, and reached the maximums at 4 % of silica fume content. The water absorption, carbonation and chloride ion penetration resistance were improved according to silica fume content and polymer-binder ratio.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.445-450
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• 2003

The moment-curvature envelope describes the changes in the flexural capacity with deformation during a nonlinear analysis. Therefore, the moment-curvature analysis for reinforced concrete columns, indicating the available flexural strength and ductility, can be conducted providing the stress-strain relation for the concrete and steel are known. The moments and curvatures associated with increasing flexural deformations of the column may be computed for various column axial loads by incrementing the curvature and satisfying the requirements of strain compatibility and equilibrium of forces. Clearly it is important to have accurate information concerning the complete stress-strain curve of confined high-strength concrete in order to conduct reliable moment-curvature analysis to assess the ductility available from high-strength columns. However, it is not easy to explicitly characterize the mechanical behavior of confined high-strength concrete because of various parameter values, such as the confinement type of rectilinear ties, the compressive strength of concrete, the volumetric ratio and strength of rectangular ties, etc. So a stress-strain confinement model is developed which can simulate a complete inelastic moment-curvature relations of a high-strength reinforced concrete column

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2015년도 추계 학술논문 발표대회
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• pp.38-39
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• 2015

For the purpose of reducing defects (cracking) in topping concretes cast as artificial greening layer base, synthetic macro fibers were mixed. The flexural strength of synthetic macro fiber mixed topping concretes was tested via comparing its performance with current topping concrete. According to the results of the testing, topping concrete with adjusted mixing ratio after mixing with 1kg of synthetic macro fiber showed approximately 15% higher flexural strength compared to the current topping concrete.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.257-260
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• 2005

Graphite reinforced conductive polymer composites were fabricated by the compression molding technique. Graphite powder was mixed with an phenol resin to impart electrical property in composites. The ratio and particle size of graphite powder were varied to investigate electrical conductivity of cured composites. In this study, graphite reinforced conductive polymer composites with high filler loadings(>66wt.%) were manufactured to accomplish high electrical conductivity. With increasing the loading ratio of graphite powder, the electrical conductivity and flexural strength increased. However. above 80wt.% filler loadings, flexural strength decreased due to lack of resin. Regardless of graphite particle size, electrical conductivity wasn’t varied. On the other hand, with decreasing particle size, flexural strength increased due to high specific surface area.

• Computers and Concrete
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• 제21권6호
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• pp.705-715
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• 2018

This paper presents an experimentally investigation pertinent to the mechanical properties of rubberized mortar (RM) with styrene-butadiene rubber (SBR). The SBR were used with constant water-to-cement ratio of 0.485 and two different volume proportion of SBR particles were utilized as aggregates. One types of SBR particles with fineness modulus of 4.951 were utilized 0%, 10%, and 20% of aggregate volume. Effectiveness of SBR replacement ratio, curing and aging effect on the compressive strength, flexural strengths as well as load-displacement. Compressive and flexural strength of concrete were investigated at the end of 28-days and 56-days age. Obtained results demonstrated that utilization of SBR reduced the flexural strength of SBR mortar at the earlier curing age while SBR increased. Moreover, mechanical properties of mortar mentioned above were significantly affected by the water cure timing with an increasing proportion of the replacement level of SBR.

• Steel and Composite Structures
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• 제46권5호
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• pp.689-707
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• 2023

Geopolymer concrete production is interesting as it is an alternative to portland cement concrete. However, workability, setting time and strength expectations limit the sustainable application of geopolymer concrete in practice. This study aims to improve the production of geopolymer concrete to mitigate these drawbacks. The improvement in the workability and setting time were achieved with the additional use of NaOH solution whereas an increase in the strength was gained with the addition of recycled steel fibers from waste tires. In addition, the use of 25% basalt powder instead of fly ash and the addition of recycled steel fibers from waste tires improved its environmental feature. The samples with steel fiber ratios ranging between 0.5% and 5% and basalt powder of 25%, 50% and 75% were tested under both compressive and flexure forces. The compressive and flexural capacities were significantly enhanced by utilizing recycled steel fibers from waste tires. However, decreases in these capacities were detected as the basalt powder ratio increased. In general, as the waste wire ratio increased, the compressive strength gradually increased. While the compressive strength of the reference sample was 26 MPa, when the wire ratio was 5%, the compressive strength increased up to 53 MPa. With the addition of 75% basalt powder, the compressive strength decreases by 60%, but when the 3% wire ratio is reached, the compressive strength is obtained as in the reference sample. In the sample group to which 25% basalt powder was added, the flexural strength increased by 97% when the waste wire addition rate was 5%. In addition, while the energy absorption capacity was 0.66 kN in the reference sample, it increased to 12.33 kN with the addition of 5% wire. The production phase revealed that basalt powder and waste steel wire had a significant impact on the workability and setting time. Furthermore, SEM analyses were performed.

• 한국구조물진단유지관리공학회 논문집
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• 제13권3호통권55호
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• pp.155-163
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• 2009

본 연구에서는 콘크리트의 휨인장강도 특성과 함께 구콘크리트와 신콘크리트 사이의 부착강도 특성을 규명하고자 하였다. 구콘크리트와 신콘크리트를 이용하여 제작한 빔 시편 실험을 통하여 콘크리트와 콘크리트 사이의 부착강도 및 인장강도를 실험적으로 연구하였다. 신 구 콘크리트 사이의 부착강도는 인장강도에 비해 훨씬 작게 나타나며, 그 비율은 15~27% 범위이다. 또한, 신 구콘크리트 사이의 부착강도는 양생 조건에 영향을 받는 것으로 나타난다. 또한, 인장강도 실험자료의 분석으로부터 콘크리트의 휨인장강도를 예측할 때, ACI 363 위원회의 제안식을 적용하는 것이 가장 합리적이라고 사료된다.

• 농업과학연구
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• 제38권1호
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• pp.145-151
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• 2011

This study was performed to evaluate the void ratio, compressive and flexural strength, and permeability coefficient used powdered waste glass, $CaCO_3$, recycled coarse aggregate and unsaturated polyester resin to find optimum mix design of permeable polymer concrete for pavement. The void ratio and permeability coefficient of permeable concrete for pavement was decreased with increasing the powdered waste glass, respectively. The compressive strength and flexural strength was increased with increasing the powdered waste glass, respectively. In addition, this study found out that required amount of binder was decreased with increasing the powdered waste glass. This fact is expected to have economical effects during the use of powdered waste glass in the manufacture of permeable polymer concrete for pavement. Therefore, powdered waste glass and recycled coarse aggregate can be used for permeable polymer pavement.