• 산업기술연구
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• 제25권B호
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• pp.73-80
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• 2005

Durability of concrete structures is seriously compromised by cracking at early-age concretes, particularly in high-strength or high-performance concrete structures. Since early-age cracking is influenced by various factors that affect the hydration process, early-age shrinkage and stress/strain development, the behavior at early-age is highly complex and no rational methodologies for its control have yet been established. 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.

• 한국구조물진단유지관리공학회 논문집
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• 제17권2호
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• pp.135-141
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• 2013

본 연구에서는 CaO-$SiO_2-Al_2O_3$가 다량 함유된 산업폐기물과 산업부산물을 소성하여 개발한 분말형 속경성 분말을 초기강도의 향상을 위해 기능성 분쇄조제로 처리하여 분쇄한 속경성 미분말을 제조하였다. 이렇게 제조된 미분말을 BFS 분말과 일정비율로 혼합한 후, 시멘트에 첨가하여 모르타르 압축강도 실험을 실시하였다. 그 결과 BFS 조기강도 향상 실험 (Series I)에서는 클링커 분쇄시 기능성 분쇄조제가 첨가되어 분쇄된 속경재가 혼합된 BFS의 초기강도 발현이 우수하며 OPC 조기강도 향상 실험 (Series II)에서는 Clinker-C에 본 실험의 기능성 분쇄조제가 첨가되어 분쇄된 속경성의 분말형 자극제가 첨가된 경우에 가장 압축강도가 높은 사실을 알 수 있었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표회 논문집(I)
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• pp.42-47
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• 1998

Experimental investigation was undertaken to determine early-age strength development and the relationships between the mechanical properties of type I, V and V/fly ash cement concrete with different curing temperature. The tests for mechanical properties, i.e., compressive strength, splitting tensile strength and modulus of elasticity were carried out for type, I, V and V with 15% replacement with fly ash cement concrete. For this purpose 480 concrete cylinders cured at isothermal conditions of 10, 23, 35 and 5$0^{\circ}C$ were tested at ages of 1, 3, 7 and 28days. According to the experiments, the concrete subjected to high temperature at early age got greater strength at early age, however eventually lower strength at late age. The derived relationships between compressive strength and splitting tensile strength and elastic modulus of elasticity appeared to be identical for all types of cement.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
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• pp.43-48
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• 2001

The use of fly ash in cement and concrete industries has many benefits including engineering, economic, and ecological aspects. However, it has a disadvantage of low strength development, especially at early ages. In this study, in order to overcome this problem, the early strength accelerating agent($NA_{2}$ $SO_{4}$) was selected and applied to the production of high strength concrete(HSC) containing fly ash. It was found that the compressive strength of fly ash concrete incorporating TEX>$NA_{2}$ $SO_{4}$ has greater than that of concrete containing fly ash only until 7 days after casting. From the microstructural point of view, ettringite increased and pores decreased in fly ash concrete incorporating TEX>$NA_{2}$ $SO_{4}$ , leading to the development of early age strength. It was also found that the velocity vs. strength relationship of HSC is considerably different from that of low-strength concrete(LSC). Therefore, in order to predict early age strength of HSC, a estimation equation different from that for LSC is needed.

• 한국건축시공학회지
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• 제7권1호
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• pp.71-77
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• 2007

This paper is to investigate the effect of the curing temperature on strength development of concrete incorporating cement kiln dust(CKD) and blast furnace slag (BS) quantitatively. Estimation of the compressive strength of the concrete was conducted using the equivalent age equation and the rate constant model proposed by Carino. Correction of Carino model was studied to secure the accuracy of strength development estimation by introducing correction factors regarding rate constant and age. An increasing curing temperature results in an increase in strength at early age, but with the elapse of age, strength development at high curing temperature decreases compared with that at low curing temperature. Especially, the use of BS has a remarkable strength development at early age and even at later age, high strength is maintained due to accelerated pozzolanic activity resulting from high temperature. Whereas, at low curing temperature, the use of BS leads to a decrease in compressive strength. Accordingly, much attention should be paid to prevent strength loss at low temperature. Based on the strength development estimation using equivalent age equation, good agreements between measured strength and calculated strength are obtained.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.559-562
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• 2000

This study is about the compensation of early age strength on mortar and concrete admixed with blast-furnace slag powder. For study, we have used fine powder of gypsum and kiln dust from cement factory. According to the test results, we have obtained proper mixing ratio of slag powder, gypsum and kiln dust for the compensation of early age strength on mortar and concrete property.

• 비파괴검사학회지
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• 제27권6호
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• pp.501-508
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• 2007

This paper presents the feasibility of using electromechanical impedance based active sensing technique for nondestructive strength gain monitoring of early-age concrete by employing piezoelectric lead-zirconate-titanate (PZT) patches on concrete surface. The strength development of early age concrete is actively monitored by performing a series of experiments on concrete specimens under moist curing condition. The electrical admittance signatures are acquired for five different curing ages and compared with each other. The resonant frequency shifts of PZT patches with increasing days is observed which is on account of additional stiffening due to strength gain of concrete during curing and level of stiffening being related to strength obtained from compression tests on companion cylinder specimens. The proposed approach is found to be suitable for monitoring the development of compressive strength in early-age concrete. It is also observed in this study that root mean square deviation (RMSD) in admittance signatures of the PZT patches can also be used as an indicator of concrete strength development.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.269-272
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• 2004

After concrete casts, temperature decent and shrinkage bring volume changes of concrete pavement. Microcracking and cracking in concrete pavement are caused by these volume changes. As a result, durability of concrete pavement is deteriorated. Recently, Very-Early Strength Latex Modified concrete(below:VESLMC) from the beginning of High-Way is used as urgent repair material for bridge deck. The advantage of VESLMC is that compressive and flexural strength at 3 hours age are 4.5MPa and 21MPa respectively. It allows the traffic to open in 3 hours. But, this material has the problem which is early-age shrinkage cracking caused by water self-dissipation with rapid hydration reaction and water evaporation with body dry. Unfortunately, until now, the research about early-age shrinkage of VESLMC leaves something to be desired. Therefore, the purpose of this study is to present the early-age shrinkage of VESLMC respect to latex contents and shrinkage ratio to maximum length change that can help field engineers' skill. Latex contents of 0, 5, 10, 15, $20\%$ in standard of same workability in VESLMC are selected by experimental variables. After initial set, shrinkage value was measured with 10mm LVDT for 3 days. The results of maximum shrinkage ratio were 0.019, 0.017, 0.023, $0.027\%$ respectively.

• 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.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2023년도 봄 학술논문 발표대회
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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.