• Title/Summary/Keyword: 초기재령 압축강도

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A Research on the Recycling of Ceramic Wastes as an Aggregate for Concrete (窯業廢棄物을 콘크리트용 骨材로 再活用하기 위한 硏究)

  • 문한영;김기형;신화철
    • Resources Recycling
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    • v.10 no.2
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    • pp.41-49
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    • 2001
  • In this study, the properties of cement mortar and concrete using ceramic wastes as fine aggregates and coarse aggregates are considered experimentally. Flow value of mortar using ceramic waste as fine aggregates is increased more or less, and the com- pressive strength of mortar using ceramic wastes as fine aggregates is increased with elapsed age. The slump value of concrete using ceramic wastes fine aggregates and coarse aggregates is somewhat decreased. The compressive strength of concrete using ceramic wastes as fine aggregates and coarse aggregates is lower than that of OPC concrete in early age, but has gradually increased in long ages.

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Effect of Fineness of GGBS on the Hydration and Mechanical Properties in HIGH Performance HVGGBS Cement Paste (고성능 하이볼륨 슬래그 시멘트 페이스트의 고로슬래그 미분말 분말도에 따른 수화 및 강도 특성)

  • Choi, Young Cheol;Shin, Dongcheol;Hwang, Chul-Sung
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.21 no.5
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    • pp.141-147
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    • 2017
  • Recently, lots of researches on concrete with high volume mineral admixtures such as ground granulated blast-furnace slag(GGBS) have been carried out to reduce greenhouse gas. The high volume GGBS concrete has advantages such as low heat, high durability, but it has a limitation in practical field application, especially low strength development in early ages. This study investigated the compressive strength and hydration characteristics of high performanc and volume GGBS cement pastes with low water to binder ratio. The effects of fineness($4,330cm^2/g$, $5,320cm^2/g$, $6,450cm^2/g$, $7650cm^2/g$) and replacement(35%, 50%, 65%, 80%) of GGBS on the compressive strength, setting and heat of hydration were analyzed. Experimental results show that the combination of high volume slag cement paste with low water to binder ratio and high fineness GGBS powder can improve the compressive strength at early ages.

Evaluation of Strength and Chloride Diffusion in Concrete with FA Considering Temperature Effect (FA를 혼입한 콘크리트의 온도 영향을 고려한 강도 및 염화물 확산성 평가)

  • Keun-Hyeok Yang;Seung-Jun Kwon
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.11 no.1
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    • pp.62-69
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    • 2023
  • For the nuclear power concrete plant structures in the UAE, it is necessary to consider the deterioration from high sulfate ions in the atmosphere and high chloride ions from the coast. In this study, two strength grade concrete mixture (40 MPa and 27 MPa) and two curing/diffusion temperatures (20 ℃ and 50 ℃) were considered for evaluating the temperature effects on diffusion and strength due to high average temperature above 38 ℃ a year in UAE. When the initial curing temperature was high, the compressive strength increased in high-temperature curing to 7 days, but the strength slightly increased in the 20 ℃ curing condition at 28 days. Regarding diffusion test, unlike the compressive test results, reduced chloride diffusion coefficients were evaluated both in 40 MPa and 27 MPa grade at 28 days. In the case of 91 days of curing, an increase in diffusivity due to high temperature and a decrease in diffusivity due to age effect occur simultaneously. Compared to the results of the curing and diffusion tests at 20 ℃ and 28 days, when the curing and diffusion tests were conducted at 50 ℃ in 91 days, the diffusion coefficients decreased to 76.2 % in 40 MPa grade and 85.4 % in 37 MPa grade with increasing curing period, respectively.

Minimum Curing Time Prediction of Early Age Concrete to Prevent Frost Damage (동해방지를 위한 초기재령 콘크리트의 최소 양생 시간 예측)

  • Pae, Su-Won;Yi, Seong-Tae;Kim, Jin-Keun
    • Journal of the Korea Concrete Institute
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    • v.19 no.1
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    • pp.27-37
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    • 2007
  • The purpose of this study is to propose a method to predict the minimum curing time of early age concrete required to prevent frost damage. Tests were performed to examine major factors, which affect the compressive strength of concrete frozen at early ages and investigate the source of frost damage at early age concrete. The results from the tests showed that the loss rate of compressive strength decreases as the beginning time of frost damage was delayed and water-cement ratio was lower. In addition, the test results also showed that concrete made with type III cement was less susceptible to frost damage than concrete made with ordinary Portland cement and frost damage occurred through the formation of ice lenses. When early age concrete is being damaged by frozen, a phase transition into ice of free water presented at the capillary pores of the concrete gives a reason for the decrease of compressive strength. Accordingly, the frost resistance of fresh concrete can be determined based on the saturation degree of the capillary pores. The method to predict the minimum curing time was suggested using the concept of critical saturation degree of the capillary pores.

Evaluation of Compressive Strength and Ultrasonic Pulse Velocity according to Elapsed Time on Normal and Lightweight Aggregate Concrete at Early Age (초기재령에서 보통 및 경량골재 콘크리트의 경과시간에 따른 압축강도 및 초음파 펄스 속도의 평가)

  • Kim, Won-Chang;Choi, Hyeong-Gil;Nam, Jeong-Soo;Kim, Gyu-Yong;Lee, Tae-Gyu
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2023.05a
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    • pp.409-410
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    • 2023
  • In this study, the compressive strength and ultrasonic pulse velocity were evaluated according to the elapsed time on concrete mixed with normal and lightweight aggregates at early age. For evaluation in various strength ranges, the design compressive strength was set to 30, 45, and 60MPa and evaluated. As a result of the experiment, the compressive strength of concrete mixed with lightweight aggregates developed 5MPa earlier compared to normal aggregate concrete, and the UPV showed a similar tendency.

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Setting Time, Compressive Strength and Drying Shrinkage of Mortar with Alpha-Calcium Sulfate Hemihydrate (α형 반수석고를 치환한 모르타르의 응결 및 압축강도, 건조수축 특성)

  • Lee, Kye-Hyouk;Kim, Gyu-Yong;Lee, Bo-Kyeong;Shin, Kyoung-Su;Nam, Jeong-Soo
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.21 no.5
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    • pp.117-124
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    • 2017
  • In this study, to evaluate the setting time, compressive strength and drying shrinkage of ordinary Portland cement and Portland blast-furnace slag cement mortar with 0, 10, 20, 30 wt.% alpha-calcium sulfate hemihydrate. As a results, as the replacement ratio of alpha-calcium sulfate hemihydrate increased, the initial setting time of ordinary Portland cement and Portland blast-furnace slag cement mortar was faster. In addition, the compressive strength decreased with increasing replacement ratio of alpha-calcium sulfate hemihydrate in both ordinary Portland cement mortar and Portland blast-furnace slag cement mortar. The strength development of Portland blast-furnace slag cement mortar with alpha-calcium sulfate hemihydrate was effective than that of ordinary Portland cement mortar. On the other hand, in the case of the mortar with alpha-calcium sulfate hemihydrate, it was confirmed that shrinkage deformation was reduced at the early age by growth pressure of needle-shaped ettringite crystals produced by incorporation of alpha-calcium sulfate hemihydrate. However, the effect of inhibiting shrinkage deformation of mortar with alpha-calcium sulfate hemihydrate was not significant as the age passed. Therefore, it is considered that the alpha-calcium sulfate hemihydrate is useful as a construction material.

Effect of Compressive Strength and Curing Condition on the Direct Tensile Strength Properties of Ultra High Performance Concrete (압축강도 및 양생조건에 따른 초고성능 콘크리트의 직접인장강도 특성)

  • Park, Ji Woong;Lee, Gun Cheol
    • Journal of the Korea Institute of Building Construction
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    • v.17 no.2
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    • pp.175-181
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    • 2017
  • The purpose of this study is evaluating the characteristics of tensile strength of UHPC and examining tensile performance of notched specimens by direct tensile test. For test variables, 120, 150, and 180MPa of target design standard strength were aimed at. With general water curing and $90^{\circ}C$ high temperature steam as curing conditions, the properties were reviewed. Overall, it was represented that the specimens of notch-type direct tensile strength concrete was effective in inducing central cracks compared with existing direct tension specimens. Through this, it was judged that data construction with high reliability was possible. Above all, in a graph of direct tensile strength and strain, in the case of steam curing at high temperature, there was great difference of initial tensile strength compared with water curing. As passing of ages, an aspect that the difference gradually decreased was shown. Maximum tensile strength was found to increase steadily with increasing age for all target design strengths in water curing, in the case of steam curing, the tendency to increase significantly due to the initial strength development effect at 7 days of age. The initial crack strength increases with age in case of underwater curing, in the case of steam curing, it was higher than that of water curing in 7 days, while the strength of 28 days was lowered. In this part, it is considered necessary to examine the arrangement condition of the steel fiber.

An Experimental Study on Strength Properties of Concrete Using Blast-Furnace Slag Subjected to Freezing at Early Age (초기재령에서 동결을 받은 고로슬래그 콘크리트의 강도발현특성에 관한 실험적 연구)

  • Choi, Sung-Woo;Ban, Seong-Soo;Ryu, Deuk-Hyun;Choi, Bong-Joo
    • Journal of the Korea Concrete Institute
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    • v.15 no.1
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    • pp.43-51
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    • 2003
  • Recently, to consider financial and constructive aspect usage of Admixture such as Blast-Furnace Slag and Fly-Ash, are increased. Also the use of cold-weather-concrete is increased. Blast-Furnace Slag, a by-product of steel industry, have many advantage to reduce the heat of hydration, increase in ultimate strength and etc. But it also reduces early-age strength, so it is prevented from using of Blast-Furnace Slag at cold-weather-concrete. In this study, for the purpose of increasing usage of Blast-Furnace Slag at cold-weather-concrete, it is investigated the strength properties of concrete subjected to frost damage for the cause of early age curing. The factors of this experience to give early frost damaged were Freezing temperature(-1, -10, $-15^{\circ}C$), Early curing age(0, 12, 24, 48hour), Freezing times(0, 12, 24, 48hour). According to this study, if early curing is carried out before haying frost damage, the strength of concrete used admixture, subjected to frost damage, is recovered. And that properties are considered, the effect of using admixture like blast-furnace-slag, is very high

Estimation of Mechanical Properties of Concrete in Early Age by Resonance Frequency Test (공명주기식 동탄성계수를 이용한 초기재령 콘크리트의 역학적 성질 예측)

  • Kim, Jin-Keun;Kiim, Hoon;Noh, Jae-Ho
    • Magazine of the Korea Concrete Institute
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    • v.7 no.5
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    • pp.164-171
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    • 1995
  • Drying shrinkage and hydration heat are important factors on the initiation of the crack in con crete at early age. Therefore, the stress caused by hydration heat and drying shrinkage should be .analyzed to predict whether the crack occurrs or not. And, mechanical properties of early age concrete is also required for the predicting crack formation In this study, non-destructive test method of resonance frequency was used to find the relation between dynamic modulus and mechanical properties of concrete in early age. Test results were compared with existing equations, and a new equation based on test. results in this study and other data was also proposed

Evaluation of Strength of Normal and Lightweight Aggregate Concrete Using Ultrasonic Velocity Method in Early Age (초기 재령에서 초음파 속도법을 활용한 보통 및 경량 골재 콘크리트의 강도 발현 평가)

  • Nam, Young-Jin;Kim, Won-Chang;Choi, Hyeong-Gil;Ryu, Jung-Rim;Lee, Tae-Gyu
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2023.05a
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    • pp.55-56
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    • 2023
  • Recently, large and high-rise buildings are increasing, and accordingly, concrete weight reduction is required. Lightweight aggregate concrete can provide economic feasibility and large space, but safety can be reduced due to problems such as low strength and poor durability. Since the development of such low strength of concrete is important in the early construction stage, it is necessary to evaluate the vertical formwork demolding period at the early age. The correlation was analyzed by measuring the compressive strength and ultrasonic pulse velocity. As a result, the ultrasonic pulse rates of normal and lightweight aggregate concrete at the time of 5 MPa expression, which is the time of vertical mold deformation, were 3.07 km/s and 2.77 km/s for W/B 41, and 2.89 km/s and 2.73 km/s for W/B 33.

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