• Title/Summary/Keyword: 굵은 골재 최대 크기

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Mechanical Properties of Lightweight Aggregate Concrete according to the Substitution Rate of Natural Sand and Maximum Aggregate Size (천연모래 치환율과 경량 굵은 골재 최대 크기에 따른 경량 골재 콘크리트의 역학적 특성)

  • Sim, Jae-Il;Yang, Keun-Hyeok
    • Journal of the Korea Concrete Institute
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    • v.23 no.5
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    • pp.551-558
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    • 2011
  • The effect of the maximum aggregate size and substitution rate of natural sand on the mechanical properties of concrete is evaluated using 15 lightweight aggregate concrete mixes. For mechanical properties of concrete, compressive strength increase with respect to age, tensile resistance, elastic modulus, rupture modulus, and stress-strain relationship were measured. The experimental data were compared with the design equations specified in ACI 318-08, EC2, and/or CEB-FIP code provisions and empirical equations proposed by Slate et al., Yang et al., and Wang et al. The test results showed that compressive strength of lightweight concrete decreased with increase in maximum aggregate size and amount of lightweight fine aggregates. The parameters to predict the compressive strength development could be empirically formulated as a function of specific gravity of coarse aggregates and substitution rate of natural sand. The measured rupture modulus and tensile strength of concrete were commonly less than the prediction values obtained from code provisions or empirical equations, which can be attributed to the tensile resistance of lightweight aggregate concrete being significantly affected by its density as well as compressive strength.

Air Content, Workability and Bleeding Characteristics of Fresh Lightweight Aggregate Concrete (굳지 않은 경량골재 콘크리트의 공기량, 유동성 및 블리딩 특성)

  • Sim, Jae-Il;Yang, Keun-Hyeok
    • Journal of the Korea Concrete Institute
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    • v.22 no.4
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    • pp.559-566
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    • 2010
  • Fifteen lightweight concrete mixes were tested to evaluate the effect of maximum size of coarse aggregate and the replacement level of natural sand on the various properties of fresh lightweight concrete. The different properties, such as water absorption against the elapsed time, pore size distribution and micro-structure of lightweight aggregates used, influencing on the workability of fresh concrete were also measured. Test results showed that the initial slump of lightweight concrete decreased with the increase of the replacement level of natural sand. The slump of all-lightweight concrete sharply decreased by around 80% of the initial slump after 30~60 minutes. The air content and bleeding rate of lightweight concrete were significantly affected by the replacement level of natural sand as well as the maximum size of coarse aggregates. Empirical equations recommended in ACI 211 and Korea concrete standard specifications underestimated the air content of the lightweight concrete, indicating that the underestimation increases with the decrease of the replacement level of natural sand. In addition, equations to predict the air content and bleeding rate of lightweight concrete were proposed based on the test results.

Effects of Aggregate Size and Steel Fiber Volume Fraction on Compressive Behaviors of High-Strength Concrete (골재크기 및 섬유혼입률에 따른 강섬유 보강 고강도 콘크리트의 압축거동)

  • Ahn, Kyung-Lim;Jang, Seok-Joon;Jang, Sang-Hyeok;Yun, Hyun-Do
    • Journal of the Korea Concrete Institute
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    • v.27 no.3
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    • pp.229-236
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    • 2015
  • This paper describes the effect of aggregate size on compressive behavior of high-strength steel fiber reinforced concrete. The Specified compression strength is 60 MPa and the range of fiber volume fraction is 0~2%. The main variable is the aggregate size, which was used for the aggregate size of 8 and 20 mm. So, ten concrete mixtures were prepared and tested to evaluate the fresh and hardened properties of SFRC at curing ages (7, 14, 28, 56 and 91 days), respectively. Items estimated in this study are the fresh properties (air contents, slump), hardened properties (compressive strength, modulus of elasticity, post-peak response and compressive toughness). As a result, the aggregate size has little effect on the compressive strength and modulus of elasticity. On the other hand, the ductile behavior was shown after post peak and the compressive toughness was increasing as decreasing the aggregate size. These effects are clearly represented in the fiber volume fraction 2%, which are the point appeared fiber ball. It is considered that the decreasing the aggregate size has effect on the fiber dispersibility.

Improvement of Structural Performance of RC Beams retrofitted Hybrid Fiber using Recycled Coarse Aggregate and Ground Granulated Blast Furnace Slag (순환굵은골재 및 고로슬래그 미분말을 사용한 하이브리드섬유보강 철근콘크리트 보의 구조성능 개선)

  • Yi, Dong-Ryul;Ha, Gee-Joo
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.18 no.6
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    • pp.1-10
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    • 2014
  • In this study, thirteen reinforced concrete beams, ground granulated blast furnace slag, replacing recycled coarse aggregate with PVA fiber (BSPG series) and recycled coarse aggregate with hybrid fiber ($BSPGR_1$, $BSPGR_2$ series), and standard specimen (BSS) were constructed and tested under monotonic loading. Experimental programs were carried out to improve and evaluate the Structural performance of such test specimens, such as the load-displacement, the failure mode, and the maximum load carrying capacity. All the specimens were modeled in 1/2 scale-down size. Test results showed that test specimens ($BSPGR_1$, $BSPGR_2$ series) was increased the compressive strength by 13%, the maximum load carrying capacity by 4~21% and the ductility capacity by 4~28% in comparison with the standard specimen (BSS). And the specimens ($BSPGR_1$, $BSPGR_2$ series) showed enough ductile behavior and stable flexural failure.

Effect of Aggregate on Mechanical Properties of Ultra-High Strength Concrete Exposed to High Temperature (고온을 받은 초고강도 콘크리트의 역학적 특성에 관한 골재의 영향)

  • Kim, Young-Sun;Choi, Hyoung-Gil;Ohmiya, Yoshifumi;Kim, Gyu-Yong
    • Journal of the Korea Concrete Institute
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    • v.23 no.4
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    • pp.431-440
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    • 2011
  • Concrete structures exposed to fire produce changes in their internal structure, resulting in their service life reduction due to the deterioration of its strength and performance capacity. The deterioration level are dependent on the temperature, exposure time, concrete mix proportions, aggregate property, and material properties. This study was performed to evaluate the thermal behavior of ultra-high strength concrete for the parameters of water to cement ratio (compressive strength), fine to total aggregate ratio, and maximum coarse aggregate size. At room temperature and $500^{\circ}C$, tests of ultrasonic pulse velocity, resonance frequency, static modulus of elasticity, and compressive strength are performed using ${\varnothing}100{\times}200\;mm$ cylindrical concrete specimens. The results showed that the residual mechanical properties of ultra-high strength concrete heated to $500^{\circ}C$ is influenced by variation of a water to binder ratio, fine to total aggregate ratio, and maximum coarse aggregate size.

Tensile Performance of PE Fiber-Reinforced Highly Ductile Cementitious Composite including Coarse Aggregate (골재의 입도분포 변화에 따른 PE 섬유보강 고연성 시멘트 복합체의 인장성능)

  • Lee, Bang Yeon;Kang, Su-Tae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.24 no.5
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    • pp.95-102
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    • 2020
  • For the purpose of developing a PE fiber-reinforced highly ductile cementitious composite having high tensile strain capacity more than 2% under the condition of containing aggregates with large particle size, this study investigated the tensile behavior of composites according to the particle size and distribution of aggregates in the composite. Compared with the mixture containing silica sand of which particle size is less than 0.6 mm, mixtures containing river sand and/or gravel with the maximum particle size of 2.36 mm, 4.75 mm, 5.6 mm, 6.7 mm were considered in the experimental design. The particle size distributions of aggregates were adjusted for the optimized distribution curves obtained from modified A&A model by blending different sizes of aggregates. All the mixtures presented clear strain-hardening behavior in the direct tensile tests. The mixtures with the blended aggregates to meet the optimum curves of aggregate size distributions showed higher tensile strain capacity than the mixture with silica sand. It was also found that the tensile strain capacity was improved as the maximum size of aggregate increased which resulted in wider particle size distribution. The mixtures with the maximum size of 5.6 mm and 6.7 mm presented very high tensile strain capacities of 4.83% and 5.89%, respectively. This study demonstrated that it was possible to use coarse aggregates in manufacturing highly ductile fiber-reinforced cementitous composite by adjusting the particle size distribution.

Aggregate Effects on γ-ray Shielding Characteristic and Compressive Strength of Concrete (콘크리트의 감마선 차폐특성 및 압축강도에 대한 골재의 영향)

  • Oh, Jeong-Hwan;Mun, Young-Bum;Lee, Jae-Hyung;Choi, Hyun-Kook;Choi, Sooseok
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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    • v.14 no.4
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    • pp.357-365
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    • 2016
  • We observed the ${\gamma}-ray$ shielding characteristics and compressive strength of five types of concrete using general aggregates and high-weight aggregates. The aggregates were classified into fine aggregate and coarse aggregate according to the average size. The experimental results obtained an attenuation coefficient of $0.371cm^{-1}$ from a concrete with the oxidizing slag sand (OSS) and oxidizing slag gravel (OSG) for a ${\gamma}-ray$ of $^{137}Cs$, which is improved by 2% compared with a concrete with typical aggregates of sand and gravel. In the unit weight measurement, a concrete prepared by iron ore sand (IOS) and OSG had the highest value of $3,175kg{\cdot}m^{-3}$. Although the unit weight of the concrete with OSS and OSG was $3,052kg{\cdot}m^{-3}$, which was lower than the maximum unit weight condition by $123kg{\cdot}m^{-3}$, its attenuation coefficient was improved by $0.012cm^{-1}$. The results of chemical analysis of aggregates revealed that the magnesium content in oxidizing slag was lower than that in iron ore, while the calcium content was higher. The concrete with oxidizing slag aggregates demonstrated enhanced ${\gamma}-ray$ shielding performance due to a relatively high calcium content compared with the concrete with OSS and OSG in spite of a low unit weight. All sample concretes mixed with high-weight aggregates had higher compressive strength than the concrete with typical sand and gravel. When OSS and IOS were used, the highest compressive strength was 50.2 MPa, which was an improvement by 45% over general concrete, which was achieved after four weeks of curing.

Properties of Strength and Stress-Strain of Recycled-Plastic Polymer Concrete (폐플라스틱 재활용 폴리머콘크리트의 강도와 응력-변형률 특성)

  • Jo Byung-Wan;Koo Jakap;Park Seung-Kook
    • Journal of the Korea Concrete Institute
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    • v.17 no.3 s.87
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    • pp.329-334
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    • 2005
  • The use of Polymer Concrete (PC) is growing very rapidly in many structural and construction applications such as box culverts, hazardous waste containers, trench lines, floor drains and the repair and overlay of damaged cement concrete surfaces in pavements, bridges, etc. However, PC has a defect economically because resin which be used for binder is expensive. Therefore the latest research is being progressed to replace existing resin with new resin which can reduce the high cost. Here, Polymer concrete using the recycled PET(polyethylene terephthalate) has some merits such as decrease of environmental destruction, decrease of environmental pollution and development of new construction materials. The variables of this study are amount of resin, curing condition and maximum size of coarse aggregate to find out mechanic properties of this. Stress-strain curve was obtained using MTS equipment by strain control. The results indicated that modulus of elasticity was increased gradually in an ascending branch of curve, as an increase of resin content. Compressive strength was the highest for resin content of $13\%$. And Compressive strength was increased as maximum size of coarse aggregate increases. The strain at maximum stress increases with an increase of resin content and size of coarse aggregate. For the descending branch of stress-strain curve the brittle fracture was decreased when it was cured at the room temperature compared to high temperature.

Fracture Toughness of Concrete Brazilian Disk according to Maximum Size of Coarse Aggregate (굵은골재의 최대치수에 따른 콘크리트 브라질리언 디스크의 파괴인성)

  • Lee, Seung-Hoon;Kim, Hee-Sung;Jang, Hee-Suk;Jin, Chi-Sub
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.10 no.3
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    • pp.185-196
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    • 2006
  • Fracture toughness is a material property for crack initiation and propagation in fracture mechanics. For mode I fracture toughness measurement in concrete, RILEM committees 89-FMT proposed three-point bend tests based on the two-parameter fracture model. But, there is no proposed test method as a standard for mixed mode test for now. And RILEM three-point bend test procedure is complicate. Therefore, in this study, brazilian disks of various size were designed as the concrete with a similar specified concrete strength and maximum size of coarse aggregate($G_{max}$) were respectively 20mm and 40mm. And mode I fracture toughness of brazilian disks was compared with that of RILEM three-point bend test. As a result, it was suggested appropriate size(thickness, diameter) and notch length ratio of brazilan disk on the $G_{max}$. And it was verified that stress intensity factors for mixed mode can be easily calculated with the disk specimen. Stress intensity factors of a concrete brazilian disk were evaluated with finite element analysis and five terms approximation for comparison.

Performances of Prepacked-Type Thermal Conductive Backfills Incorporating Byproduct Powders and Aggregates (부산물 분체 및 굵은 골재를 활용한 프리팩트형 열전도성 되메움재의 성능)

  • Sang-Min Jeon;Young-Sang Kim;Ba-Huu Dinh;Jin-Gyu Han;Yong-Sun Ryu;Hyeong-Ki Kim
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.11 no.3
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    • pp.169-176
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    • 2023
  • This study aims to develop a thermally conductive backfill by applying the prepacked concrete concept, in which a coarse aggregate with relatively high thermal conductivity was first filled and then the voild filled with grout. Backfill with improved thermal conductivity can increase the heat exchange efficiency of underground heat exchangers or underground transmission facilities. The backfills was prepared by using crushed concrete as the coarse aggregate, fly ash-based grout, and a small amount of cement for solidification. The results of this study showed that the fly ash-cement-sand-based grout with a flow of at least 450 mm accor ding to ASTM D 6103 could fill the void of pr epactked coar se aggr egates with a maximum size of 25 mm. The thermal conductivity of the backfil with coarse aggregate was over 1.7 W/m·K, which was higher than that of grout-type backfills.