• 콘크리트학회지
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• 제21권2호
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• pp.67-71
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• 2009

• International Journal of Concrete Structures and Materials
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• 제6권1호
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• pp.31-40
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• 2012

Self-consolidating concrete (SCC) is a recently developed innovative construction material. SCC fills in a formwork without any vibrating consolidation, which allows us to eventually achieve robust casting. However, high formwork lateral pressure exerted by SCC is a critical issue regarding its application as cast-in-place concrete. In order to control the risk caused by high formwork pressure, a comprehensive prediction model for the pressure was previously proposed, investigated, and validated with various SCC mixtures. The model was originally designed to simulate the intrinsic pressure response of SCC mixtures while excluding other extrinsic influencing factors such as friction and flexibility of the formwork. The model was then extended to consider extrinsic factors such as friction between SCC mixtures and formwork. In addition, other interesting topics for peak formwork pressure and mineral admixture effects were summarized in the paper.

• 콘크리트학회논문집
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• 제20권1호
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• pp.67-75
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• 2008

마이크로역학을 기초로 하여 Slag-ECC (고로슬래그 미분말이 혼입된 ECC)가 개발되었으며, 기존의 연구에서는 Slag-ECC가 높은 연성을 나타내도록 마이크로역학을 도입하여 재료의 배합비가 제시되었다. 이 연구에서는 Slag-ECC의 자기충전과 숏크리트 시공성을 구현하기 위하여, Slag-ECC의 기본 배합에 혼화재료의 투입 순서에 상관없이 혼화재료를 한번에 투입하여 유동 특성을 제어하는 레올로지 개념을 도입하였으며, 이는 현장에서 시공성을 높이기 위하여 모든 재료를 분말의 형태로 사용하는 프리팩키지화를 위한 기초 자료로 사용될 것이다. 그리고 자기충전과 숏크리트의 서로 상반되는 레올로지 특성을 구현하기 위하여, 시멘트풀 레올로지 경시 변화 연구를 통해 대략적인 혼화재료의 첨가량을 선정하였고, 자기충전 및 숏크리트의 시공성 검증을 통해 재료의 배합비를 최적화 하였다. 개발된 Slag-ECC의 자기충전성과 숏크리트 적합성은 실험을 통하여 입증되었으며, 자기충전 및 숏크리트의 시공 방법에 의하여 타설된 재료가 굳은 이후에도 Slag-ECC의 역학적 특성인 고인성 특성을 유지하는 것으로 나타났다. 따라서 시멘트풀의 레올로지 특성을 조절하여 개발된 자기충전용 Slag-ECC와 숏크리트용 Slag-ECC는 재료의 고인성 특성을 유지하면서 다양한 현장 적용이 가능할 것으로 판단된다.

• Structural Engineering and Mechanics
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• 제22권5호
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• pp.541-562
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• 2006

This paper compares the performance of axially loaded concrete filled steel tube (CFST) columns cast using a conventionally vibrated normal concrete (NC) and a novel self-consolidating concrete (SCC) made with a new viscosity modifying admixture (VMA). A total of sixteen columns with a standard compressive strength of about 50 MPa for both SCC and NC were tested by applying concentric axial load through the concrete core. Columns were fabricated without and with longitudinal and hoop reinforcement (Series I and Series II, respectively) in addition to the tube confinement. The slenderness of the columns expressed as height to diameter ratio (H/D) ranged between 4.8 and 9.5 for Series CI and between 3.1 and 6.5 for Series CII. The strength and ductility of SCC columns were found comparable to those of their NC counterparts as the maximum strength enhancement in NC columns ranged between 1.1% and 7.5% only. No significant difference in strain development was found due to the presence of SCC or NC or due to the presence of longitudinal and hoop reinforcement. Biaxial stress development in the steel tube as per von Mises yield criterion showed similar characteristics for both SCC and NC columns. The confined strength ($f^{\prime}_{cc}$) of SCC was found to be lower than that of NC and $f^{\prime}_{cc}$ also decreased with the increase of slenderness of the columns. Analytical models for the prediction of confined concrete strength and axial strength of CFST columns were developed and their performance was validated through test results. The proposed models were found to predict the axial strength of CFST columns better than existing models and Code based design procedures.

• Computers and Concrete
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• 제8권3호
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• pp.279-292
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• 2011

The main purpose of this study includes investigation of the rheological properties of fresh self consolidating cement paste containing chemical and mineral additives using Artificial Neural Network (ANN) model. In order to develop the model, 200 different mixes are cast in the laboratory as a part of an extensive experimental research program. The data used in the ANN model are arranged in a format of fourteen input parameters covering water-binder ratio, four different mineral additives (calcium carbonate, metakaolin, silica fume, and limestone), five different superplasticizers based on the poly carboxylate and naphthalene and four different Viscosity Modified Admixtures (VMAs). Two common output parameters including the mini slump value and flow cone time are chosen for measuring the rheological properties of fresh self consolidating cement paste. Having validated the model, the influence of effective parameters on the rheological properties of fresh self consolidating cement paste is investigated based on the ANN model outputs. The output results of the model are then compared with the results of previous studies performed by other researchers. Ultimately, the analysis of the model outputs determines the optimal percentage of additives which has a strong influence on the rheological properties of fresh self consolidating cement paste. The proposed ANN model shows that metakaolin and silica fume affect the rheological properties in the same manner. In addition, for providing the suitable rheological properties, the ANN model introduces the optimal percentage of metakaolin, silica fume, calcium carbonate and limestone as 15, 15, 20 and 20% by cement weight, respectively.

• 한국구조물진단유지관리공학회 논문집
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• 제15권1호
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• pp.159-168
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• 2011

본 연구에서는 분산제 코팅을 통해 성능 개선된(EP) 나일론 섬유를 혼입한 자기충전 콘크리트의 가능성을 알아보고자 하였으며, 이를 위한 실험 방법으로 나일론 섬유 길이와 다른 유기계 섬유(폴리프로필렌, 셀룰로오스)를 혼입한 경우 그리고 광물질 혼화재(고로슬래그 미분말, 플라이애쉬)의 종류를 달리 혼합한 2성분계 및 3성분계의 경우를 가지고 자기충전 콘크리트의 특성을 검토하였다. 이 실험 결과를 토대로 하여 실구조물 적용을 위한 Mock-up Test를 성능 개선된 나일론 섬유를 혼입한 자기충전콘크리트 와 일반콘크리트를 비교하여 실구조물 활용 가능성을 검토 하였다. 그 결과 굳지 않은 자기충전 콘크리트의 특성, 경화된 자기충전 콘크리트의 특성 및 내구특성을 종합해 볼 때 성능 개선된(EP) 나일론 섬유가 우수함을 알 수 있었고, 성능 개선된 나일론 섬유에 따른 광물질 혼화재 사용에서는 플라이애쉬 보다 고로슬래그 미분말이 우수함을 알 수 있었다.

• Steel and Composite Structures
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• 제43권3호
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• pp.389-401
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• 2022

This study investigated the flowability and mechanical properties of cost-effective steel fiber reinforced ultra-high performance concrete (UHPC) by using locally available materials for field-cast application. To examine the effect of mixture constituents, five mixtures with different fractions of silica fume, silica powder, ground granulated blast furnace slag (GGBS), silica sand, and crushed natural sand were proportionally prepared. Comprehensive experiments for different mixture designs were conducted to evaluate the fresh- and hardened-state properties of self-consolidating UHPC. The results showed that the proposed UHPC had similar mechanical properties compared with conventional UHPC while the flow retention over time was enhanced so that the field-cast application seemed appropriately cost-effective. The self-consolidating UHPC with high flowability and low viscosity takes less total mixing time than conventional UHPC up to 6.7 times. The X-ray computed tomographic imaging was performed to investigate the steel fiber distribution inside the UHPC by visualizing the spatial distribution of steel fibers well. Finally, the tensile stress-strain curve for the proposed UHPC was proposed for the implementation to the structural analysis and design.

• 한국건설순환자원학회지
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• 제16권1호
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• pp.26-29
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• 2021

• Computers and Concrete
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• 제20권3호
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• pp.297-310
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• 2017

A CFD software was used to simulate free surface flow of SCC in the T-Box test. In total, seven simulations were developed to study the effect of rheological parameters on the non-restricted flow performance of SCC in both horizontal and vertical directions. Different suspending fluids having five plastic viscosity values between 10 and 50 Pa.s, three yield stress values between 14 and 75 Pa, one density of $2500kg/m^3$, and one shear elasticity modulus of 100 Pa were considered for suspension of 178 spherical particles of 20-mm diameter and $2500kg/m^3$ density. The results of the simulations are found to correlate well to changes in rheological parameters of the suspending fluid. Plastic viscosity was shown to be the most dominant parameter affecting flowability and dynamic stability compared to the yield stress. A new approach was proposed to evaluate performability of SCC based on a trade-off between flowability and dynamic stability.

• Advances in concrete construction
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• 제8권3호
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• pp.225-237
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• 2019

Although applying self-consolidating concrete (SCC) in many modern structures is an inevitable fact, the high consumption of cement in its mixing designs has led to increased production costs and adverse environmental effects. In order to find economically viable sources with environmentally friendly features, natural pozzolan pumice and blast furnace slag in 10-50% of replacement binary designs have been investigated for experiments on the properties of fresh concrete, mechanical properties, and durability. As a natural pozzolan, pumice does not require advanced equipment to prepare for consumption and only needs to be powdered. Pumice has been the main focus of this research because of simple preparation. Also to validate the results, in addition to the control specimens of each design, fly ash as a known powder has been evaluated. Moreover, ternary mixes of pumice and silica fume were investigated to enhance the obtained results of binary mixes. It was concluded that pumice and slag powders indicated favorable performance in the high percentage of replacement.