• Computers and Concrete
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• 제33권3호
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• pp.309-324
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• 2024

Internal curing, a widely used method for mitigating early-age shrinkage in concrete, also offers notable advantages for concrete durability. This paper explores the potential of internal curing by partial replacement of sand with fine lightweight aggregate for enhancing the behavior of high-performance concrete at elevated temperatures. Such a technique may prove economical and safe for the construction of skyscrapers, where explosive spalling of high-performance concrete in fire is a potential hazard. To reach this aim, the physico-mechanical features of internally cured high-strength concrete specimens, including mass loss, compressive strength, strain at peak stress, modulus of elasticity, stress-strain curve, toughness, and flexural strength, were investigated under different temperature exposures; and to predict some of these mechanical properties, a number of equations were proposed. Based on the experimental results, an advanced stress-strain model was proposed for internally cured high-performance concrete at different temperature levels, the results of which agreed well with the test data. It was observed that the replacement of 10% of sand with pre-wetted fine lightweight expanded clay aggregate (LECA) not only did not reduce the compressive strength at ambient temperature, but also prevented explosive spalling and could retain 20% of its ambient compressive strength after heating up to 800℃. It was then concluded that internal curing is an excellent method to enhance the performance of high-strength concrete at elevated temperatures.

• Computers and Concrete
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• 제17권2호
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• pp.271-280
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• 2016

This study examined the mechanical properties and adiabatic temperature rise of low-heat concrete developed based on ternary blended cement using ASTM type IV (LHC) cement, ground fly ash (GFA) and limestone powder (LSP). To enhance reactivity of fly ash, especially at an early age, the grassy membrane was scratched through the additional vibrator milling process. The targeted 28-day strength of concrete was selected to be 42 MPa for application to high-strength mass concrete including nuclear plant structures. The concrete mixes prepared were cured under the isothermal conditions of $5^{\circ}C$, $20^{\circ}C$, and $40^{\circ}C$. Most concrete specimens gained a relatively high strength exceeding 10 MPa at an early age, achieving the targeted 28-day strength. All concrete specimens had higher moduli of elasticity and rupture than the predictions using ACI 318-11 equations, regardless of the curing temperature. The peak temperature rise and the ascending rate of the adiabatic temperature curve measured from the prepared concrete mixes were lower by 12% and 32%, respectively, in average than those of the control specimen made using 80% ordinary Portland cement and 20% conventional fly ash.

• 한국건축시공학회지
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• 제12권4호
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• pp.369-376
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• 2012

본 연구에서는 초기재령에 있어 매스부재를 고려한 고강도콘크리트에 대해 수화발열상승속도를 저감시키기 위한 방안의 일환으로 열흡수성능이 있는 상전이물질을 사용하였다. 또한 수화발열상승속도의 조절에 의한 고강도콘크리트의 자기수축 특성 변화를 분석하고자 하였다. 그 결과, 상전이물질은 시멘트 수화반응을 촉진함으로서 초기재령에 빠른 응결시간과 높은 압축강도 발현을 나타냈다. 또한 수화열 및 수화발열상승속도를 저감시키고, 자기수축량을 감소시키는 결과를 나타내었다. 이를 통해 초기재령의 수화발열상승 속도의 조절에 의해 자기수축량의 저감이 가능하다고 판단된다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.163-166
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• 1999

In this paper, strength development of concrete using blast-furnace slag cement(BSC) and ordinary portland cement(OPC) are discussed under varius W/C and curing temperatures. According to the experimental results, strength development of BSC concrete is lower than that of OPC concrete in low temperature at early age and maturity. In high curing temperature, BSC concrete has higher strength development than that of low temperature regardless of the elapse of age and maturity. BSC has much effect on the strength development of concrete at the condition of mass concrete, hot weather concreting and the concrete products with the steam curing, which is influenced by high temperature.

• 한국건축시공학회지
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• 제15권6호
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• pp.589-595
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• 2015

이 연구에서는 혹한기 환경에서 매스부재에서 수화열을 고려한 고강도 콘크리트의 실제 압축강도 특성을 평가하였다. 목업 실험체는 가로${\times}$세로${\times}$높이가 $2.0{\times}1.2{\times}1.0m$로 제작하였다. 콘크리트 현장 압축강도 발현 특성은 $5^{\circ}C$에서 기건양생된 원주형 공시체와 수화열의 영향이 반영된 목업 벽체에서 채취된 코어 실험체를 비교하였다. 실험결과, 목업 벽체에서 채취된 코어의 재령 3일까지 압축강도는 실린더 강도에 비해 30% 높았는데, 이는 시멘트계 재료의 수화열에 의한 고온의 양생온도 효과 때문이다. 또한 성숙도 함수에 기반한 예측모델과 실험결과의 비교로부터 매스 부재에서 콘크리트의 현장 압축강도 발현을 합리적으로 평가하기 위해서는 수화열의 양생효과를 고려할 필요가 있음이 제시될 수 있다.

• 한국결정성장학회지
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• 제24권1호
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• pp.27-32
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• 2014

본 연구에서는 매스콘크리트의 수화열 저감 및 초기강도 향상을 목적으로 3성분계 배합에 따른 콘크리트의 기초적 특성을 분석하였는데 결과를 요약하면 다음과 같다. 굳지 않은 콘크리트의 물성은 목표범위를 모두 만족하는 것으로 나타났다. 응결시간은 W/B와 관계없이 저열 시멘트 배합이 가장 빠른 것으로 나타났고, 간이 수화열은 저열 배합의 피크 온도가 가장 높은 것으로 나타났고, 저발열-B 배합이 가장 낮은 온도를 나타내었으며, 조강형 저발열 배합은 저발열-B와 유사한 것으로 나타났다. 경화 콘크리트의 압축강도는 초기재령에서 저발열-B 배합을 제외한 모든 배합이 유사한 강도 범위를 나타내었고, 장기 재령에서는 큰 차이 없이 유사한 강도 범위를 나타내었다.

• Structural Engineering and Mechanics
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• 제85권1호
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• pp.29-53
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• 2023

High-strength shielding concrete against gamma radiation is a priority for many medical and industrial facilities. This paper aimed to investigate the gamma-ray shielding properties of high-strength hematite concrete mixed with silica fume (SF) with nanoparticles of lead dioxide (PbO₂), tungsten oxide (WO₃), and bismuth oxide (Bi₂O₃). The effect of mixing steel fibres with the aforementioned binders was also investigated. The reference mixture was prepared for high-strength concrete (HSCC) containing 100% hematite coarse and fine aggregate. Thirteen mixtures containing 5% SF and nanoparticles of PbO₂, WO₃, and Bi₂O₃ (2%, 5%, and 7% of the cement mass, respectively) were prepared. Steel fibres were added at a volume ratio of 0.28% of the volume of concrete with 5% of nanoparticles. The slump test was conducted to workability of fresh concrete Unit weight water permeability, compressive strength, splitting tensile strength, flexural strength, and modulus of elasticity tests were conducted to assess concrete's engineering properties at 28 days. Gamma-ray radiation of 137Cs emits photons with an energy of 662 keV, and that of 60Co emits two photons with energies of 1173 and 1332 keV were applied on concrete specimens to assess radiation shielding properties. Nanoparticles partially replacing cement reduced slump in workability of fresh concrete. The compressive strength of mixtures, including nanoparticles was shown to be greater, achieving 94.5 MPa for the mixture consisting of 7.5 PbO2. In contrast, the mixture (5PbO₂-F) containing steel fibres achieved the highest values for splitting tensile, flexural strength, and modulus of elasticity (11.71, 15.97, and 42,840 MPa, respectively). High-strength shielded concrete (7.5PbO2) showed the best radiation protection. It also showed the minimum concrete thickness required to prevent the transmission of radiation.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2009년도 춘계 학술논문 발표대회 학계
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• pp.119-122
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• 2009

As architectures have recently become high-risers and mega-structured, stable high strength products have been ensured. Accordingly, use of precast concrete accouplement has been increased in order to facilitate air compression and rationalize construction. Since not only external heating but a1so internal temperature rise caused by the accumulation of cement hydration heat in manufacturing process, precast concrete members with large cross-section used for high-rise mega-structure's columns and beams may exhibit different temperature history compared to the precast concrete members for wall and sub-floor with relatively small cross-sections. Therefore, this study aims to elucidate the characteristics of temperature history of mass concrete members cast with high-strength concrete fur precast concrete application. In this study, large cross-sectional precast concrete mock-up, unit cement quantity, and temperature histories in manufacturing precast concrete member under different curing condition were inclusively investigated.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2003년도 학술.기술논문발표회
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• pp.67-71
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• 2003

This study is for the great quantity use of fly-ash. For the producing of high volume concrete from the use of fly-ash, the method of replacement between bonding agents and fine aggregate by fly-ash at the same time was used. It was used that the adiabatic temperature rise of concrete about the mass member which bad been produced by the method that was mentioned before, and the hydration heat of the core test pieces in concrete was measured. Also the core test pieces which were replaced with fly-ash was studied by the compressive streneth's comparison between standard care test pieces and core test pieces. In the case of mass test pieces, hydration heat and the tine to reach the highest temperature were decreased by an increase in replaced fly-ash's amounts of concrete. In addition, among the test pieces having the same amounts of concrete, the test pieces having more replaced amounts of fly-ash's fine aggregate showed higher hydration heat and the increased time to reach the highest temperature. Compressive strength was also increased by hydration heat's decrease according to fly-ash replacement. Replacement of fly-ash was more effective in high temperature environment.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.417-420
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• 2006

Recently, the attention is paid to the problem of thermal crack by hydration heat according to the increase of high strength and mass concrete structures. At this point, various research has been carried out for the control of hydration heat in high strength and mass concrete. As a part of the research, it was investigated application of hydration heat reduction agent (HR) for the control of thermal crack by hydration heat in this study. To investigate the application, it was selected HR which can reduce hydration heat of concrete with effect in series I and II. Also, it was investigated the characteristics of hydration heat generation of low heat concrete using HR with binder types in seriesIII.