• Title, Summary, Keyword: 슬럼프 감소

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Application of Powdered Superplasticizer to Improve of Slump Loss Rate in Recycled Aggregate Concrete (재생 골재 콘크리트의 슬럼프 손실 개선을 위한 분말형 감수제의 활용)

  • Yang, Keun-Hyeok;Sim, Jae-Il;Lee, Jae-Sam;Chung, Heon-Soo
    • Journal of the Korea Concrete Institute
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    • v.18 no.5
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    • pp.649-656
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    • 2006
  • In this study, powered superplasticizer(PSP) agents to improve the slump loss rate of recycled aggregate concrete were developed. To evaluate the variation of fluidity against elapsed time and the mechanical properties, twenty four specimens whose main variables had the mixing condition of aggregates, such as natural and recycled gravels, and natural and recycled fine aggregates, were tested. The concrete slump with a liquid superplasticizer greatly decreased against the elapsed time and dropped by less than 50% of initial slump after two hours. However the concrete slump with the PSP agents hardly varied until after half an hour and maintained more than 85% of initial slump even after an hour. Also the PSP agents made the compressive, splitting tensile, and flexural strength of concrete increased and the shrinkage strain decreased. Considering the properties improvement of concrete, it can be recommended that optimum mixing amount of the PSP agents should be 5% of the amount of cement.

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.

The Long-Term Strength and the Workability of High-Strength Fly Ash Concrete (고가도 플라이애쉬 콘크리트의 장기 강도 특성에 관한 연구)

  • 김진근;박연동;성근열
    • Magazine of the Korea Concrete Institute
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    • v.3 no.4
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    • pp.107-115
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    • 1991
  • An investigation for the short-term and long-term compressive strength and workability characteristics for the high strength fly ash concrete was carried out when fly ash was used in high strength concrete. Selected test variables were compressive strength with 6 levels(2 levels of normal strength and 4 levels of high strength) and fly ash contents with 4 levels(O, 10, 20, 30%). For the evaluation of slump loss, four other mixes were added. As the result. the concrete containing 10% fly ash developed higher strength before 28 days than that of control concrete. With increasing of fly ash content, the slump of normal strength concrete was gradually decreased and quantity of superplasticizer for high strength concrete was also increased to keep constant slump.

Comparison Analysis of Fiber Distribution and Workability for Amorphous Steel Fiber Reinforced Concrete (비정질강섬유 보강콘크리트 작업성 및 섬유 분산성 비교분석)

  • Kim, Byoung-Il;Lee, Sea-Hyun
    • Journal of the Korean Institute of Resources Recycling
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    • v.23 no.4
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    • pp.47-57
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    • 2014
  • The research was conducted to analyze workability and fiber distributions of amorphous steel fiber reinforced concrete by changing fiber length and fiber addition ratio. The inverted slump cone and vebe tests as well as slump test was performed to understand the fluidity of amorphous steel fibers which have quite different appearance compared to conventional steel fibers. Test results showed that thin plate type of amorphous steel fibers required different test approach to figure out workability since the reduction of workability from slump test was different that from inverted slump cone and vebe tests. In conclusion, fluidity of amorphous steel fibers to concrete was significantly degraded as fiber length and addition ratio increase. Also, fibers space in cement matrix was apparently reduced as the increase of fiber length and addition ratios without fiber balling.

Durability of Concrete Using Insulation Performance Improvement Materials (단열성능 향상 재료를 사용한 콘크리트의 내구성에 관한 연구)

  • Park, Young-Shin;Kim, Jung-Ho;Kim, Se-Hwan;Kim, Sang-Heon;Jeon, Hyun-Kyu
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.19 no.3
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    • pp.22-29
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    • 2015
  • In this study, we tested to develop and apply structural insulation performance improvement concrete to field, which had compressive strength in 24 MPa and thermal conductivity twice as much as normal concrete. After experiment about slump and air contents, combination product of Plain and calcined diatomite powder showed reduction of slump and air contents and combination product with micro foam cell admixture, we cannot find result of slump and air contents reduction. Unit weight of combination product with insulation performance improvement materials decreased more than that of Plain. In the test of compressive strength, compressive strength of insulation performance improvement concrete decreased more than that of Plain but was content with 24 MPa. thermal conductivity of insulation performance improvement concrete tended to decrease. Freezing and thawing resistance of insulation performance improvement concrete was similar to that of Plain. In carbonation resistance test, combination product with calcined diatomite powder showed the result which was similar to that of Plain. In carbonation resistance test, combination product with micro foam cell admixture showed a increase compared to that of Plain and length variation of combination product generally increased.

A Study on the Compressive Strength Properties of the Ternary Blended Non-Cement Concrete using Ternary Diagram (삼각조성도를 통한 3성분계 무시멘트 콘크리트의 압축강도 특성 연구)

  • Jung, Yu-Jin;Kim, Young-Su
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.24 no.2
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    • pp.41-49
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    • 2020
  • To improve the problem of strength reduction of unary and binary blended non-cement concrete that occur at room temperature, comparative analysis was conducted based on the slump and compressive strength properties of ternary blended non-cement concrete in which cement was replaced with silica fume, fly ash, and blast furnace slag, and the following conclusions were drawn. The ternary blended non-cement concrete showed higher compressive strength than binary binder concrete, and the slump reduction was less when 10% silica fume was mixed. In addition, the appropriate composition ratio range of each by-product was suggested according to slump and compressive strength level based on ternary diagram.

Slump and Mechanical Properties of Hybrid Steel-PVA Fiber Reinforced Concrete (강섬유와 PVA 섬유로 하이브리드 보강된 콘크리트의 슬럼프 및 역학적 특성)

  • Yang, Keun-Hyeok
    • Journal of the Korea Concrete Institute
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    • v.22 no.5
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    • pp.651-658
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    • 2010
  • Sixteen concrete mixes reinforced with hybrid steel-polybinyl alcohol (PVA) fibers and a control concrete mix with no fiber were tested in order to examine the effect of the micro and macro fibers on the slump and different mechanical properties of concrete. Main variables investigated were length and volume fraction of steel and PVA fibers. The measured mechanical properties of hybrid fiber reinforced concrete were analyzed using the fiber reinforcing index and compared with those recorded from monolithic steel or PVA fiber reinforced concrete. The initial slump of hybrid fiber reinforced concrete decreased with the increase of the aspect ratio and the volume fraction of fibers. In addition, splitting tensile strength, modui of rupture and elasticity, and flexural toughness index of concrete increased with the increase of the fiber reinforcement index. Modulus of rupture and flexural toughness index of hybrid fiber reinforced concrete were higher than those of monolithic fiber reinforced concrete, though the total volume fraction of hybrid fibers was lower than that of monolithic fiber. For enhancing the flexural toughness index of hybrid fiber reinforced concrete, using the steel fiber of 60 mm length was more effective than using the steel fibers combined with 60 mm and 30 mm lengths.

Physical Properties of Self-healing Concrete Mixed with Hydrogel Carrier of Microorganism (미생물 혼입 하이드로젤 지지체 첨가에 따른 자기치유 콘크리트의 물성 변화)

  • Chu, Inyeop;Woo, Jinho;Woo, Sang-Kyun;Lee, Byungjae
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.22 no.6
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    • pp.24-29
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    • 2018
  • The properties of concrete with addition of microgel - containing hydrogel support were investigated. As a result of measuring the slump of the self - healing concrete, the target slump was satisfied in all the mixing conditions, but the slump was decreased as the mixing amount of the hydrogel support increased. The change of porosity due to incorporation of hydrogel support was minimal. As a result of the evaluation of the compressive strength of the self - healing concrete, the incorporation of the hydrogel support did not affect the strength. However, under the same mixing condition, the dispersion value of the specimens tended to increase with increasing hydrogel support contents. As a result of the permeability test of self-healing concrete according to the incorporation of hydrogel support, it was confirmed that the mixing ratio of hydrogel support was effective to decrease the permeability coefficient.

An Experimental Study on Strength Properties of Concrete using Bottom Ash Coarse Aggregate (Bottom Ash 굵은골재 혼입에 따른 콘크리트의 강도특성에 관한 실험적 연구)

  • Jang, Young-Il;Park, Seong-Bum;Lee, Jun;Lee, Byung-Jae;Min, Jeong-Wook
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.489-492
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    • 2008
  • This study analyzed the fundamental properties and strength properties of concrete utilizing Bottom Ash as coarse aggregate for concrete. As a result, compared to non-mixture, the slump decreases about 4.5${\sim}$54.2% as the mixing ratio of Bottom Ash increases. However, influence of the air contents is very little. The bleeding shows similar slump characteristics, and the primary stage of bleeding decreases as the mixing ratio of Bottom Ash increases. As the mixing ratio of Bottom Ash increases, the compressive strength decreases. When Bottom Ash is mixed by 40%, compressive strength decreases about 1.1${\sim}$5.3%. Even when Bottom Ash is mixed over 60%, compressive strength decreases sharply and is revealed about 85.2${\sim}$87.7% of non-mixture concrete strength. To utilize Bottom Ash in large quantities, it is thought that the improvement method of strength has to be discussed such as mixing strengthening element.

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