• Title/Summary/Keyword: 수축 및 균열

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Synthesis of Shrinkage Reducing Superplasticizer(SRS), and Mechanical properties and Hydration Behavior (수축저감 특성이 부여된 고유동화제 합성 및 성능에 관한 연구)

  • Shin, Jin-Yong;Park, Hun-Il;Lee, Byung-Youn;Yun, Hee-Keun
    • Proceedings of the Korea Concrete Institute Conference
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    • 2010.05a
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    • pp.203-204
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    • 2010
  • In this study, We synthesized new generation of superplasticizer(SP) which show a shrinkage reducing effect as well as water reducing effect with adequate slump retention in a wide range of water cement ratio by introduction a shrinkage-reducing group into the molecular structure. To investigate effects of the SRS on the hydration of cement, DSC have been analysed. Also the general and shrinkage properties of the concrete were evaluated.

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Characteristics of Shrinkage on Concrete using Electric Arc Furnace Slag as Coarse Aggregate (전기로 산화 슬래그를 굵은 골재로 사용한 콘크리트의 수축 특성)

  • Choi, Hyo-Eun;Choi, So-Yeong;Kim, Il-Sun;Yang, Eun-Ik
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.24 no.1
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    • pp.125-132
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    • 2020
  • The causes of concrete shrinkage are very diverse, in particular, aggregates impact the characteristics of shrinkage in concrete by constraining the shrinkage of cement paste. Meanwhile, owing to the lack of natural aggregate, various alternative aggregates are being developed, and their application in concrete also becomes more diverse. This study aimed to experimentally evaluate the drying and autogenous shrinkage in concrete that was composed of electric arc furnace slag as coarse aggregates. And, the results were compared with prediction models. From the results, the application of electric arc furnace slag can reduce the drying and autogenous shrinkage. In particular, autogenous shrinkage is greatly decreased. The predictions using GL2000 for drying shrinkage and Tazawa model for autogenous shrinkage were similar to the experimental results. However, the most prediction models do not consider the impact of aggregates, hence, the new prediction model should be developed or improved.

Drying Shrinkage Behaviors of Concrete with Powder Type Shrinkage Reducing Agent and Fly Ash (분말형 수축저감제와 플라이애쉬가 혼입된 콘크리트의 건조수축 거동)

  • Min, Kyung-Hwan;Lee, Dong-Gyu;Jeong, Yong-Wook
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.16 no.5
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    • pp.3535-3541
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    • 2015
  • In this study, series of tests were performed for drying shrinkage characteristics of concrete with power type shrinkage reducing agent (SRA) and fly ash as a part of research to reduce drying shrinkage of concrete. Firstly, for the mechanical properties, a target strength was acquired securely. In the unrestraint shrinkage tests, the SRA decreased the drying shrinkage about $200{\mu}{\varepsilon}$. Lastly, in the ring tests, due to the tensile creep effect, the concrete with SRA showed the cracking times as much again as the concrete with ordinary Portland cement only did.

Long-term Behavior of Deck-plate Concrete Slab Reinforced with Steel Fiber (강섬유 보강 데크플레이트 콘크리트 슬래브의 장기 거동)

  • Hong, Geon-Ho;Hwang, Seung-Koo
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.21 no.4
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    • pp.30-38
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    • 2017
  • Recently, research on the development of a composite slab system for shorting the construction period by simplifying the process by omitting the form work and the reinforcement placing is underway. The purpose of this study is to evaluate the long-term behavior of a simplified slab system that replaces the form work and tensile reinforcement using structural deck-plate and replaces the temperature reinforcement using steel fiber reinforced concrete. In the conventional composite deck-plate slab method, w.w.f is generally used for crack control by drying shrinkage. But previous research results by various researchers were pointed out it is not effective to control the shrinkage and temperature cracking. In this study, the long-term cracking and structural behavior of steel fiber reinforced deck plate slab specimen with two continuous spans constructed under typical load conditions were evaluated. Experimental results showed that the number and width of long-term cracks decreased remarkably in the simplified slab specimen, and the deflection was also decreased compared with conventional RC slab specimen. However, in the continuous end of the slab where the negative moment is applied, it is analyzed that reinforced details are necessary to control the crack width in the service load and to recover deflection at load removal.

Crack Control of Wall type Structures by Shrinkage and Temperature Reinforcement (수축ㆍ온도 철근에 의한 벽체형 철근 콘크리트 구조물의 균열 제어)

  • 김영진;김상철
    • Magazine of the Korea Concrete Institute
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    • v.14 no.2
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    • pp.52-60
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    • 2002
  • 지하철 구조물과 같은 매스 콘크리트 구조물을 시공할 때 온도 측정을 하는 경우는 많으나 이는 내외부 온도차를 적정한 수준으로 유지하여 균열 발생을 제어하기 위한 수단일 뿐 균열폭을 일정한도 내로 제어할 수 있는 조치는 아니다. 매스 콘크리트 구조물에서 균열폭을 제한 값 이하로 하기 위해서는 적절한 양의 철근을 배치하여야 한다. 또한 시공 이음 등을 작은 간격으로 설치하는 것은 구속도를 완화시키고 온도응력이나 균열폭을 저감시켜 균열 제어상 매우 효과적인 수단이 될 수 있다. 그러나 시공 이음, 균열 유발 줄눈 등의 이음간 간격을 좁히면 내하력 수밀성, 내구성 등에 악영향을 미칠 가능성이 높고, 타설 회수가 많아져 동일한 공정이 반복 투입되므로 시공 속도의 저하 및 공사비 상승 등의 단점이 나타날 수 있다.(중략)

Effects of Shrinkage Reducing Agent (SRA) Type and Content on Mechanical Properties of Strain Hardening Cement Composite (SHCC) (수축저감제의 종류 및 혼입률에 따른 변형경화형 시멘트복합체의 역학적 특성)

  • Han, Seung-Ju;Jang, Seok-Joon;Khil, Bae-Su;Choi, Mu-Jin;Yun, Hyun-Do
    • Journal of the Korea Concrete Institute
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    • v.28 no.1
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    • pp.41-48
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    • 2016
  • This research investigates the effects of shrinkage reducing agent (SRA) on the mechanical behavior of strain-hardening cement composite (SHCC). SHCC material with specified compressive strength of 50 MPa was mixed and tested in this study. All SHCC mixes reinforced with volume fraction of 2.2% polyvinyl alcohol (PVA) fiber and test variables are type and dosage of shrinkage reducing agents. The shrinkage reducing materials used in this study are phase change material as the thermal stress reducing materials that have the ability to absorb or release the heat. The effect of SRA was examined based on the change in length caused by shrinkage and hardened mechanical properties, specially compressive, tensile and flexural behaviors, of SHCC material. It was noted that SRA reduces change in length caused by shrinkage at early age. SRA can also improve the tensile and flexural strengths and toughness of SHCC material used in this study.

Characteristics of Autogenous Shrinkage for Concrete Containing Blast-Furnace Slag (고로슬래그를 함유한 콘크리트의 자기수축 특성)

  • Lee Kwang-Myong;Kwon Ki-Heon;Lee Hoi-Keun;Lee Seung-Hoon;Kim Gyu-Yong
    • Journal of the Korea Concrete Institute
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    • v.16 no.5 s.83
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    • pp.621-626
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    • 2004
  • The use of blast-furnace slag (BFS) in making not only normal concrete but also high-performance concrete has several advantages with respect to workability, long-term strength and durability. However, slag concrete tends to show more shrinkage than normal concrete, especially autogenous shrinkage. High autogenous shrinkage would result in severe cracking if they are not controlled properly. Therefore, in order to minimize the shrinkage stress and to ensure the service life of concrete structures, the autogenous shrinkage behavior of concrete containing BFS should be understood. In this study, small prisms made of concrete with water-binder (cement+BFS) ratio (W/B) ranging from 0.27 to 0.42 and BFS replacement level of $0\%$, $30\%$, and $50\%$, were prepared to measure the autogenous shrinkage. Based on the test results, thereafter, material constants in autogenous shrinkage prediction model were determined. In particular, an effective autogenous shrinkage defined as the shrinkage that contributes to the stress development was introduced. Moreover, an estimation formula of the 28-day effective autogenous shrinkage was proposed by considering various W/B's. Test results showed that autogenous shrinkage increased with replacement level of BFS at the same W/B. Interestingly, the increase of autogenous shrinkage is dependent on the W/B at the same content of BFS; the lower W/B, the smaller increasing rate. In concluding, it is necessary to use the combination of other mineral admixtures such as shrinkage reducing admixture or to perform sufficient moisture curing on the construction site in order to reduce the autogenous shrinkage of BFS concrete.

Hydration Heat and Crack-Reducing Properties of Cement Mortar Added Fluosilicate Salt Based Hydration Heat Reducer (규불화염계 수화열 저감제가 첨가된 시멘트 모르타르의 수화열 변화 및 균열저감 특성)

  • Kim, Jin-Yong;Lee, Hyo-Song;Rhee, Young-Woo;Kim, Do-Su;Lee, Byoung-Ky;Khil, Bae-Su;Han, Seung-Gu
    • Journal of the Korean Ceramic Society
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    • v.42 no.3 s.274
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    • pp.198-204
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    • 2005
  • Fluosilicate salts based hydration heat reducer(SWP-HR), used in this study, is composed of fluosilicate salts, soluble silica, aromatic polymer condensate and nitrate salt based inorganic compound with latent heat property. Effects of SWP-HR addition on the hydration heat and anti-crack property of cement mortar were investigated. Adiabatic hydration temperature and drying shrinkage length of SWP-HR added cement mortar had a tendency to decrease compared to those of cement mortar without SWP-HR addition. Also, it was confirmed through crack pattern experiment of plate-form specimen for elucidating crack-reducing characteristic that anti-crack property of SWP-HR added cement mortar was improved.

Cracking and Durability Characteristics of High-early-strength Pavement Concrete for Large Areas using Calcium Nitrate (질산칼슘 혼화재를 사용한 대단면 급속 포장 콘크리트의 균열 및 내구특성)

  • Won, Jong Pil;Lee, Si Won;Lee, Sang Woo;Park, Hae Geun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.29 no.1A
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    • pp.101-108
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    • 2009
  • The performance of high-early strength pavement concrete for large areas is influenced by the physical and chemical environment during service life. Generally, penetration, diffusion, and absorption of harmful materials that exist outside the concrete cause damage to its structure. Thus, we have to use a mixture for durability to keep the required quality for the planned service life. Moreover, in using high-early-strength cement and accelerators, a high heat of hydration to create the initial strength can cause cracks. Based on evaluations from optimal mix proportions of high-early-strength pavement concrete for large areas, we conducted water permeability, abrasion resistance, freeze-thaw, plastic, drying, and autogenous shrinkage tests. Test result showed that a mix of accelerator and PVA fibers showed excellent performance.