• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.1238-1241
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• 2000

The deformations of concrete specimens were measured at early at early ages, in order to verify the applicability of FBG(Fiber Bragg Grating) sensors. The FBG sensors were directly buried at various locations in the beam-type RC specimens at the time of fabrication. In this experiment, the changes of strains in concrete at early age were successfully measured as the movement in wavelength of light signals. The FBG sensors may be a very effective tool to investigate the mechanical/thermal behavior inside of concrete structures.

• 한국재료학회지
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• 제23권12호
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• pp.687-694
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• 2013

This study was performed with an aim to improve the early-age strength of concrete containing fly ash, which is known to increase the long-age strength of concrete, reduce drying shrinkage, and enhance water tightness. The composition was partially substituted with calcium sulfoaluminate (CSA), from which ettringite is actively produced, in the early stages of hydration to verify its effect on improving the early-age strength and to determine the optimal mixing ratio. For this purpose, up to 30 % of the cement weight was substituted with fly ash, and the amount of CSA substitution was 8% of the fly ash weight. The mixtures were then fabricated into concrete specimens for compressive strength measurement and analysis of the correlation between the hydration products and the compressive strength.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.781-784
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• 2005

Concrete structures often present volumetrical changes particularly due to thermal and moisture related shrinkages. Volumetric instability is detrimental to the performance and durability of concrete structures because structural elements are usually restrained. These restrained shrinkages develope tensile stresses which often results in cracking in combination with the low fracture resistance of concrete. Early-age defects in high-performance concrete due to thermal and autogenous deformation shorten the life cycle of concrete structures. Thus, it is necessary to examine the behavior .of early-age concrete at the stages of design and construction. The purpose of this study was to propose a shrinkage models of VES-LMC (very-early strength latex-modified concrete) at early-age considering thermal deformation and autogenous shrinkage.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2021년도 가을 학술논문 발표대회
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• pp.61-62
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• 2021

Because of the problem of increasing self-weight due to the enlargement and high-rise of buildings using normal aggregate concrete, the need for structural lightweight aggregate concrete increases. However, early strength prediction is required when placing structural lightweight aggregate concrete, but research is insufficient. In this study, the ultrasonic pulse velocity of normal aggregate concrete and lightweight aggregate concrete was measured at early age. As a result, the ultrasonic pulse velocity of lightweight aggregate concrete was lower than normal aggregate concrete according to elapsed time at early age.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.1215-1220
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• 2000

Blast-Furnace Slag, a by-product of the iron or steel industry, has potential sa a cementitious material. The addition of a Blast-Furnace Slag generally reduces the heat of hydration and can confer significant improvements in resistance to sulfate attack and alkali-aggregate reaction, as well as increases in ultimate strength. But it also reduces early-age strength. In this study, for the purpose of improvement of early-age quality of Blast-Furnace Slag concrete, we choose blaine fineness of $6, 000~8, 000cm^2/g$ of Blast-Furnace Slag, and investigate the various properties of concrete. As a result, workability and early-age strength of Blast-Furnace Slag concrete were improved according to the increase of blaine fineness of Blast-Furnace Slag.

• 산업기술연구
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• 제25권A호
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• pp.49-56
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• 2005

Recently, very-early strength latex-modified concrete(below ; VES-LMC) has been developed for repairing and overlaying the old concrete bridge deck. VES-LMC provides the advantage of very-early-strength, as well as high flexural strength, bond strength, durability, resistance to corrosion, reduced water permeability and resistance to damage from freeze-thaw cycles. The compressive and flexural strength of VES-LMC are 21 MPa and 4.5 MPa at 3 hours after concrete placing, respectively. However, VES-LMC would have a relatively large shrinkage at early-age because of reduced water-cement ratio, big water self-dissipation, and rapid hydration reaction. Therefore, the purpose of this study was to evaluate the early-age and restrained shrinkage of VES-LMC, having an experimental variables such as latex contents and cement types. The latex contents included 0%, 5%, 10%, 15% and 20%, and the cement types included ordinary portland cement and very-early strength cement.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.629-634
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• 2001

Recently, to consider financial and constructive aspect, usage of Admixture, like 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. According to this study, if early curing is carried out before having frost damage, the strength of concrete, subjected to frost damage, is recovered. And that properties is not connected with the frost cause.

• 콘크리트학회논문집
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• 제19권1호
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• pp.27-37
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• 2007

이 연구의 목적은 초기재령 콘크리트가 동해를 입을 경우가 예상될 때, 동해저항성을 확보하는데 필요한 최소 양생 시간의 예측법을 제안하는 것이다. 먼저, 실험을 통하여 동해시점이 지연될수록, w/c가 낮을수록, 그리고 1종 시멘트보다 3종 시멘트를 사용한 콘크리트가 동해에 의한 압축강도 감소율이 낮으며 동해는 얼음결정의 형성과 성장을 통해 발생됨을 확인하였다. 초기재령 콘크리트가 동해를 입었을 경우, 콘크리트 내에 존재하는 모세공극의 자유수가 얼음으로 상변화를 일으키면서 압축강도의 감소를 유발하므로 동해저항성은 모세공극의 포화도에 따라 결정된다. 따라서, 모세공극의 임계포화도 개념을 근거로 초기동해의 방지를 위한 최소양생시간의 예측법을 제안하였다.

• 콘크리트학회지
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• 제7권5호
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• pp.164-171
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• 1995

재령 초기에 발생하는 부등건조수축과 시멘트의 수화반응에 의한 수화열은 초기재령 콘크리트 균열의 주요 원인이다. 다라서 재령 초기 콘크리트의 균열 발생 여부를 예측하기 위해서는 수화열과 부등건조수축에 의하여 발생되는 응력의 계산이 필수적이며, 이를 위해서는 초기 재령 콘크리트의 역학적 성질 파악이 매우 중요하다. 이 연구에서는 콘크리트의 동탄성계수와 압축강도, 정탄성계수와 같은 역학적 성질들과의 관계를 구명하기 위하여 공명주기법을 이용한 비파괴 실험을 실시하였으며, 얻어진 실험결과를 기존 예측식과 비교하였다. 또한 기존의 실험치와 이 연구의 실험치를 이용하여 보다 정확한 예측식들을 제안하였다.

• Structural Engineering and Mechanics
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• 제37권5호
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• pp.459-473
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• 2011

The study of the early age concrete properties is becoming more important, as the thermal effects and the shrinkage, even in the first hours, could generate cracks, increasing the permeability of the structure and being able to induce problems of durability and functionality in the same ones. The detailed study of the stresses development during the construction process can be decisive to keep low the cracking levels. In this work a computational model, based on the finite element method, was implemented to simulate the early age concrete behavior and, specially, the evaluation of the cracking risk. The finite element analysis encloses the computational modeling of the following phenomena: chemical, thermal, moisture diffusion and mechanical which occur at the first days after the concrete cast. The developed software results were compared with experimental values found in the literature, demonstrating an excellent approach for all the implemented analysis.