• 한국도로학회논문집
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• 제16권6호
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• pp.79-86
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• 2014

PURPOSES : In this study, wasted vinyl aggregate, which possesses better thermal properties than natural aggregate, was used in cement concrete mixture to develop more economical concrete with thermal insulation and freeze prevention effects. METHODS : Slump and air content of the fresh concrete, which substituted its 0%, 5%, and 10% of coarse aggregate with wasted vinyl aggregate, were measured. Compressive strength, Poisson's ratio, elastic modulus, and splitting tensile strength of hardened concrete were measured by laboratory tests. Thermal properties of concrete such as coefficient of thermal expansion, thermal conductivity, and specific heat were also measured according to replacement ratio of wasted vinyl aggregate. Finally, the thermal insulation and freeze prevention effectiveness of the concrete mixed with wasted vinyl aggregate was confirmed through finite element analysis of road pavement crossing above concrete box culvert made from wasted vinyl aggregate. RESULTS : Even though the physical properties of wasted-vinyl-aggregate concrete such as compressive strength, Poisson°Øs ratio, elastic modulus, and splitting tensile strength were inferior to those of ordinary concrete, they met requirements for structural concrete. The thermal properties of concrete were improved by wasted vinyl aggregate because it decreased thermal conductivity and increased specific heat of the concrete. According to the result of finite element analysis, temperature variation in pavement subgrade was mitigated by box culvert made from wasted-vinyl-aggregate concrete. CONCLUSIONS : Through the laboratory test and finite element analysis of this study, it was concluded that the concrete structures made from wasted vinyl aggregate showed thermal insulation and freeze prevention effects.

• Environmental Engineering Research
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• 제24권4호
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• pp.630-637
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• 2019

The present study aimed to investigate the potential of Enterococcus faecalis (E. faecalis) and Bacillus cereus (B. cereus) in improving the properties of bio-concrete. E. faecalis and B. cereus strains were obtained from fresh urine and an acid mire water at cell concentration of 1.16×10¹² and 1.3×10¹² cells mL^-1, respectively. The bacterial strains were inoculated in a liquid medium into the concrete with 1, 3 and 5% as replacement of water cement ratio (w/c). The ability of E. faecalis and B. cereus cells to accumulate the calcite and the decrement of pores size within bio-concrete was confirmed by SEM and EDX analysis. The results revealed that E. faecalis exhibited high efficiency for increasing of compressive and splitting tensile strength than B. cereus (23 vs. 14.2%, and 13 vs. 8.5%, respectively). These findings indicated that E. faecalis is more applicable in the bio-concrete due to its ability to enhance strength development and reduce water penetration.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.657-660
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• 2008

철근콘크리트 구조물의 설계 및 해석에 있어 구성 재료의 역학적 특성은 기본적인 자료로서 그 불확실성 및 변동성을 합리적으로 고려하는 것이 매우 중요하다. 이 연구에서는 기존의 문헌자료 및 추가적인 실험 자료를 바탕으로 콘크리트의 품질 기준으로 가장 널리 쓰이고 있는 콘크리트 압축강도의 통계적 모델을 확립하고, 압축강도와 쪼갬 인장강도의 관계식을 정리하였으며 콘크리트 구조설계기준에 제시된 콘크리트의 탄성계수를 결정하는 방법을 검증하였다. 각 결과는 우리나라 설계기준을 포함한 각국의 설계기준 상의 규정과 비교하여 그 적합성을 확인하였다. 향후 추가적인 실험 연구 및 자료조사가 이루어지면 우리나라 실정을 반영하는 보다 합리적인 콘크리트 역학적 성질의 통계적 특성에대한 모델을 제시할 수 있을 것으로 판단된다.

• International Journal of Concrete Structures and Materials
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• 제7권3호
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• pp.215-223
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• 2013

This study presents the effect of incorporating metakaolin (MK) on the mechanical and durability properties of high strength concrete for a constant water/binder ratio of 0.3.MK mixtures with cement replacement of 5, 10 and 15 % were designed for target strength and slump of 90 MPa and $100{\pm}25mm$. From the results, it was observed that 10 % replacement level was the optimum level in terms of compressive strength. Beyond 10 %replacement levels, the strength was decreased but remained higher than the control mixture. Compressive strength of 106 MPa was achieved at 10 % replacement. Splitting tensile strength and elastic modulus values have also followed the same trend. In durability tests MK concretes have exhibited high resistance compared to control and the resistance increases as the MK percentage increases. This investigation has shown that the local MK has the potential to produce high strength and high performance concretes.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.281-284
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• 2004

The most important reason of using of ultra high strength concrete in super tall building is that ultra high strength concrete can reduce the section of members and control side sway effectively. However, the practical utilization of ultra high strength concrete is dependent not only on the production techniques, but also the overall preparation including proper code provisions, construction technique. The purpose of this study is to evaluate of mechanical properties of UHSC, such as modulus of elasticity, stress-strain behavior, modulus of rupture and tensile splitting strength. It is similar to normal or high strength concrete but necessary to discern the difference between normal or high strength concrete and ultra high strength concrete and modify existed equations. And in this study another important factor is to discern the difference according to member size, curing method in ultra high strength concrete experimentally.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표논문집(II)
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• pp.489-494
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• 1998

This paper describes the possibility to reuse concrete waste produced by demolition of reinforced concrete structures as aggregate for concrete from the viewpoint of strength. Concrete rubble obtained from the demolished buildings at Taejon were crushing machine to reuse as coarse aggregate. The strength properties, such as compressive strength, splitting tensile strength, bending strength and shear strength, of recycled and normal concrete were examined and compared experimentally when water cement ratio was varied. From the results of this study, it was thought that in case of non-washed aggregate concrete, strength properties of recycled coarse aggregate is similar to that of normal concrete, In W/C 55%~45%, stress-strain curve of recycled concrete shows more stable than that of normal concrete, while in W/C 35%, it shows brittle behavior.

• 한국농공학회지
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• 제44권1호
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• pp.116-124
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• 2002

Natural resources fur the construction materials such as good soil, sand, and coarse aggregates have been encountered to be short due to excessive use by human. Even though some soil has been found to be unsuitable for construction materials, soil with reinforcement can naturally be an answer to these alternatives. According to recently published papers on fiber mixed soil, fiber mixed with soil can improve shear strength, compressive strength and post-peak load strength retention. In this study, a series of tests were performed to clarify the characteristics of fiber mixed soil and to give basic data for design and construction and their engineering properties, that is, unconfined compressive strength, splitting tensile strength, shear strength, crack by drying, freeze-thaw, creep and Poisson\`s ratio, were investigated and analyzed. It has been shown that fiber mixed soil is one of good alternatives fur the civil and building construction materials.

• 한국농공학회지
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• 제45권7호
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• pp.20-26
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• 2003

The ultra-lightweight high strength polymer concrete could be used for the drain structures under severe condition. In this study, materials used were unsaturated polyester resin, heavy calcium carbonate, artificial lightweight coarse aggregate and perlite. In the test results, the unit weight of the ultra-lightweight high strength polymer concrete was 946 kg f/$\textrm{m}^3$ and the compressive strength was appeared in 34.5 MPa. The compressive strength, splitting tensile strength, flexural strength, acid resistance and weather resistance were shown in excellently than that of the normal cement concrete. The draining trench had 1m length, 0.24 m width, 0.02 m thickness and 0.07 m height. The developed trench could be effectively used at the draining structures.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.640-643
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• 2004

Synthetic lightweight aggregates are manufactured with recycled plastic and fly ash with 12 percent carbon. Nominal maximum-size aggregates of 9.5mm were produced with fly ash contents of 0 percent, 35 percent, and 80 percent by total mass of the aggregate. An expanded day lightweight aggregate and a normal-weight aggregate were used as comparison. Mechanical properties of the concrete determined included density, compressive strength, elastic modulus, and splitting tensile strength. Compressive and tensile strengths were lower for the synthetic aggregates; however, comparable fracture properties were obtained. Relatively low compressive modulus of elasticity was found for concretes with the synthetic lightweight aggregate, although high ductility was also obtained. As fly ash content of the synthetic lightweight aggregate increased, all properties of the concrete were improved.

• Geomechanics and Engineering
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• 제8권4호
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• pp.541-557
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• 2015

This research aims to analyze the fracture coalescence characteristics of brittle sandstone specimen ($80{\times}160{\times}30mm$ in size) containing various flaws (a single fissure, double squares and combined flaws). Using a rock mechanics servo-controlled testing system, the strength and deformation behaviours of sandstone specimen containing various flaws are experimentally investigated. The results show that the crack initiation stress, uniaxial compressive strength and peak axial strain of specimen containing a single fissure are all higher than those containing double squares, while which are higher than those containing combined flaws. For sandstone specimen containing combined flaws, the uniaxial compressive strength of sandstone increase as fissure angle (${\alpha}$) increases from $30^{\circ}$ to $90^{\circ}$, which indicates that the specimens with steeper fissure angles can support higher axial capacity for ${\alpha}$ greater than $30^{\circ}$. In the entire deformation process of flawed sandstone specimen, crack evolution process is discussed detailed using photographic monitoring technique. For the specimen containing a single fissure, tensile wing cracks are first initiated at the upper and under tips of fissure, and anti-tensile cracks and far-field cracks are also observed in the deformation process; moreover anti-tensile cracks usually accompanies with tensile wing cracks. For the specimen containing double squares, tensile cracks are usually initiated from the top and bottom edge of two squares along the direction of axial stress, and in the process of final unstable failure, more vertical splitting failures are observed in the ligament region. When a single fissure and double squares are formed together into combined flaws, the crack coalescence between the fissure tips and double squares plays a significant role for ultimate failure of the specimen containing combined flaws.