• 한국산업융합학회 논문집
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• 제8권3호
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• pp.169-176
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• 2005

The purpose of this study is to develop the high strength crushed sand concrete in conditions of water binder ratios of 25, 30, 35% and blast-furnace slag substitutions of 0, 15, 30, 45%. Additionally, in case of water binder ratio of 30%, the maximum size of coarse aggregate is two kinds of 13, 19 mm. The conclusions of this study are as follows ; 1. The compressive strength appeared lower in early age as compared with that of plain concrete according to increasing of the blast-furnace slag substitution. But, the compressive strength was respectively 5, 6, 10% larger than that of plain concrete in case of 25, 30, 35% water binder ratios, 28 days, 30% blast-furnace slag substitution and 19mm coarse aggregate. 2. According to increasing of the blast-furnace slag substitution, the modulus of elasticity and the tensile strength of concrete increased. 3. The length change by the shrinkage increased when the larger coarse aggregate was used, and decreased according to higher blast-furnace slag substitution.

• 한국건축시공학회지
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• 제2권4호
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• pp.145-152
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• 2002

High fluid concrete unlike OPC concrete is made with various material, and the phase of fresh concrete is considerably different. In order to understand fluidity phase and mix properties of high fluid concrete, concrete is required to access as suspension structure which consists of aggregate and paste. The focus of this paper is to analyze the test results and quantify the effect of mix proportions of mortar and fineness modulus of sand on the properties of fresh mortar. The effect of water-binder ratio. sand-binder ration. contents of ggbs (by mass of total cementitious materials). and various contents of water reducing agent on the yield stress and plastic viscosity of the mix is studied. Based on the experimental results, the fellowing conclusions can be drawn: (1) The mixing time needed for high fluid mortar was approximately two times more than that of ordinary portland mortar. (2) The fluidity phase of mortar could be explained by yield stress of mix and the fluidity of mortar. (3) As the content of ggbs increased, yield stress of mortar was decreased and plastic viscosity of it was increased. (4) For the high fluid mortar, it was appeared that sand-binder ratio should be below 1.5.

• International Journal of Concrete Structures and Materials
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• 제7권3호
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• pp.215-223
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• 2013

This study presents the effect of incorporating metakaolin (MK) on the mechanical and durability properties of high strength concrete for a constant water/binder ratio of 0.3.MK mixtures with cement replacement of 5, 10 and 15 % were designed for target strength and slump of 90 MPa and $100{\pm}25mm$. From the results, it was observed that 10 % replacement level was the optimum level in terms of compressive strength. Beyond 10 %replacement levels, the strength was decreased but remained higher than the control mixture. Compressive strength of 106 MPa was achieved at 10 % replacement. Splitting tensile strength and elastic modulus values have also followed the same trend. In durability tests MK concretes have exhibited high resistance compared to control and the resistance increases as the MK percentage increases. This investigation has shown that the local MK has the potential to produce high strength and high performance concretes.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표회 논문집(I)
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• pp.30-35
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• 1998

This study was carried out to investigate quantitatively the relationship between the water binder ratio and the concrete strength using finely ground granulated furnace blast slag. In the experiment, the compressive strength and elastic modulus of concrete which slag contents are 0%, 10%, 20% and 30% at 7days and 28days age. As a result, the compressive strength have a high correlation with slag contents and water binder ratio. Thus, it is possible to calculate the water binder ratio using compressive strength of concrete contented with slag.

• Computers and Concrete
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• 제19권6호
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• pp.667-675
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• 2017

One of the main disadvantages of Ultra High Performance Concrete exists in the large suggested value of UHPC ingredients. The purpose of this study was to find the models mechanical properties which included a 7, 14 and 28-day compressive strength test, a 28-day splitting tensile and modulus of rupture test for Ultra High Performance Concrete, as well as, a study on the interaction and correlation of five variables that includes silica fume amount (SF), cement 42.5 amount, steel fiber amount, superplasticizer amount (SP), and w/c mechanical properties of UHPC. The response surface methodology was analyzed between the variables and responses. The relationships and mathematical models in terms of coded variables were established by ANOVA. The validity of models were checked by experimental values. The offered models are valid for mixes with the fraction proportion of fine aggregate as; 0.70-1.30 cement amount, 0.15-0.30 silica fume, 0.04-0.08 superplasticizer, 0.10-0.20 steel fiber, and 0.18-0.32 water binder ratio.

• 한국도로학회논문집
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• 제4권1호
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• pp.149-159
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• 2002

본 연구에서는 아스팔트 바인더의 절대점도, 동점도, 침입도, 연화점, PG 고온등급을 이용하여 샌드아스팔트 흔합물의 고속 직접인장강도(DTS1), 저속 직접인장강도(DTS2), 간접인장강도(ITS), 회복탄성계수(MR), 강성지수(SI)를 추정하기 위한 연구를 수행하였다. 여러 가지 혼합물의 특성 중 DTS2가 가장 상관성이 높게 나타났으며 그 다음이 DTS1, ITS, SI, MR 순인 것으로 나타났다. 바인더 성질 중에는 PG 등급이 DTS2와 가장 높은 상관 관계를 보여 PG 고온등급이 높은 바인더를 사용하면 직접인장강도가 어느 정도 우수한 혼합물을 얻을 수 있음을 알 수 있었다. 하지만 각각의 물리적 성질만으로는 신뢰도가 낮아 종합적으로 여러 물성을 이용하여 상관성을 분석하였다. 그 결과 직접 및 간접인장강도는 결정계수가 0.99 이상인 모델을 얻을 수 있었다. 그리고 MR, SI 값의 추정치 모델도 R2이 0.91 및 0.93 이상이어서 상당한 신뢰성을 가지고 물성으로부터 역학적 특성을 추정할 수 있음을 보여준다.

• 한국건설순환자원학회논문집
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• 제8권4호
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• pp.537-544
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• 2020

Interfacial transition zone (ITZ)은 골재-시멘트 복합체 사이의 영역으로써, 콘크리트에서 가장 취약한 영역으로 알려져 있으며, 이는 점진적으로 변화하는 불균질한 상으로 이루어져 있다. 경량 고강도 콘크리트 개발을 위해 물-바인더 비가 낮은 고강도 시멘트 복합체와 경량골재 사이의 Interfacial transition zone (ITZ)의 역학적 특성 평가는 필수적이다. 하지만 ITZ는 복잡하고 다공성 구조를 가지고 있기 때문에, 이의 역학적 특성은 아직 명확하지 않다. 또한, 경량골재 ITZ는 일반골재보다 다양한 변수 (물-바인더 비, 골재의 흡수율, 양생조건 등)에 의해 변화한다. 따라서 본 연구에서 골재의 종류 및 크기에 따른 ITZ의 역학적 특성을 분석하고자 한다. 이를 위해 나노 인덴테이션 기법을 이용하여 물-바인더 비가 0.2인 고강도 시멘트 복합체와 표준사 및 최대치수가 각각 2mm, 5mm인 경량골재 ITZ의 탄성계수를 측정하였다.

• Structural Engineering and Mechanics
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• 제82권3호
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• pp.295-312
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• 2022

This study investigates the effects of nano silica (NS) and micro steel fiber on the properties of ultra-high-performance concrete (UHPC). The experimental consists of three groups, each one with five percentages of NS content (0%, 2%, 4%, 6% and 8%) in addition to the 20% silica fume and 20% quartz powder proportioned according to the weight of cement added to the mixtures. In addition, three percentages of micro steel fibers (0%, 1% and 2%) were considered. Different mixtures with varying percentages of NS and micro steel fibers were prepared to set the water-to-binder ratio, such as 0.16% and 1.8% superplasticizer proportioned according the weight of the binder materials. The fresh properties, mechanical properties and elevated temperatures of the mixtures were calculated. Then, the results from the microstructure analyses were compared with that of the reference mixtureand it was found that 6% replacement of cement with NS was optimum replacement level. When the NS content was increased from 0% to 6%, the air content and permeability of the mixture decreased by 35% and 39%, the compressive and tensile strength improved by 21% and 18% and the flexural strength and modulus of elasticity increased by 20% and 11.5%, respectively. However, the effect of micro steel fibres on the compressive strength was inconclusive. The overall results indicate that micro steel fibres have the potential to improve the tensile strength, flexure strength and modulus of elasticity of the UHPC. The use of 6% NS together with 1% micro-steel fiber increased the concrete strength and reduce the cost of concrete mix.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.433-438
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• 2000

The purpose of this study is to examine the resistance of water-permeable concretes to freezing and thawing action. The water-permeable concretes with cement-aggregate ratio of 1:5.5(by weight) and two kinds of admixture content [SP : superplasticizer(0, 1.0%), HPAE : high performance air entraining agent(0.5, 1%)] used OPC(ordinary portland cement) as binder were prepared, and then tested for relative dynamic modulus of elasiticity, mass change, length change and durablity factor. It's been concluded from the test results that the superior relative dynamic modulus of elasiticity and durability factor of water-permeable concretes were obtained at superplaciticizer 1.0% after 300 cycles. The water-permeable concretes used superplasiticizer 1.0% having relative durability factor of 88% after 300 cycles.

• 한국도로학회논문집
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• 제18권6호
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• pp.97-104
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• 2016

OBJECTIVES : The objective of this research is to develop additives for the modification of Solvent DeAsphalting Residue (SDAR) to be used as pavement materials, and evaluate the performance of asphalt mixture manufactured using the SDAR modified by developed additives. METHODS : The SDAR generally consists of more asphaltenes and less oil components compared to the conventional asphalt binder, and hence, the chemical/physical properties of SDAR are different from that of conventional asphalt binder. In this research, the additives are developed using the low molecular oil-based plasticizer to improve the properties of SDAR. First, the chemical property of two SDARs is analyzed using SARA (saturate, aromatic, resin, and asphaltene) method. The physical/rheological properties of SDARs and SDARs containing additives are also evaluated based on PG-grade method and dynamic shear-modulus master curve. Second, various laboratory tests are conducted for the asphalt mixture manufactured using the SDAR modified with additives. The laboratory tests conducted in this study include the mix design, compactibility analysis, indirect tensile test for moisture susceptibility, dynamic modulus test for rheological property, wheel-tracking test for rutting performance, and direct tension fatigue test for cracking performance. RESULTS : The PG-grade of SDARs is higher than PG 76 in high temperature grades and immeasurable in low temperature grades. The dynamic shear modulus of SDARs is much higher than that of conventional asphalt, but the modified SDARs with additives show similar modulus compared to that of conventional asphalt. The moisture susceptibility of asphalt mixture with modified SDARs is good if, the anti-stripping agent is included. The performance (dynamic modulus, rutting resistance, and fatigue resistance) of asphalt mixture with modified SDARs is comparable to that of conventional asphalt mixture when appropriate amount of additives is added. CONCLUSIONS : The saturate component of SDARs is much less than that of conventional asphalt, and hence, it is too hard and brittle to be used as pavement materials. However, the modified SDARs with developed additives show comparable or better rheological/physical properties compared to that of conventional asphalt depending on the type of SDAR and the amount of additives used.