• 한국건설순환자원학회논문집
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• 제3권1호
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• pp.43-49
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• 2015

본 연구에서는 현행 레미콘사에서 콘크리트 제조 시 13mm 이하 굵은골재의 부족으로 인한 품질저하가 발생하는 문제를 해결하기 위하여 13mm 이하 순환굵은골재를 치환하여 콘크리트의 제반특성을 검토하였다. 실험변수로 13mm 이하 순환 굵은골재를 13~25mm 굵은골재에 10~100%까지 치환사용하여 콘크리트의 품질에 대해 분석하였다. 실험결과 13mm 이하 순환 굵은골재 치환사용으로 유동성이 증가하였으며, 공기량은 골재간의 공극충전효과로 인해 감소하였다. 또한 골재간의 연속입도 구성으로 콘크리트 내부에 공극이 감소되어 강도의 향상과 건조수축이 감소하였다, 이상을 종합하면 13mm 이하 순환 굵은골재를 13~25mm 굵은골재만 사용한 콘크리트에 30% 내외 치환사용시 콘크리트의 품질이 향상되는 것으로 나타났다.

• 산업기술연구
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• 제17권
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• pp.313-322
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• 1997

As the weight of trucks increases, the need for concrete pavement also increases. Therefore, the addition of fly-ash may improve the properties of pavement concrete as well as recycle fly-ash. A full factorial experiment was performed using the primary variables, such as water-cement ratio, fly-ash substitution ratio, and maximum size of coarse aggregate, as a preliminary study for optimum mixture design for pavement concrete. The results of preliminary study indicates that the addition of fly-ash is the most important factor determining concrete strength, followed by the maximum size of coarse aggregate and water-cement ratio. It, also, shows the relative importance of fly-ash substitution ratio, compared to the water-cement ratio, and the interaction effects between the primary variables. Optimum mixture designs for pavement concrete incorporating fly-ash, that satisfied the target responses, were proposed in terms of fly-ash substitution ratio, water cement ratio and maximum size of coarse aggregate.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 춘계학술대회 논문집
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• pp.615-620
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• 2005

The purpose of this study was to provide a criterion of ballast aggregate size distribution for paved track. The parameters considered in this study were different types of particle size distribution. Then the analysis for analyzing compressive and flexural strength, physical characteristics of aggregate, and the ballast box test were performed. In the test result of the physical characteristic performed by the ballast box test, the bearing capacity was measured lower than the expected value because of its boundary conditions. Among four types of ballast aggregate, type B was selected as one of best candidate distribution because of its bearing capacity, strength, development and economics.

• KSBB Journal
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• 제5권4호
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• pp.347-353
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• 1990

The effects of nutrients and cell aggregate size on the cell growth of D. carota and the biosynthesi of carotenoid were investigated. Highest carotenoid content was obtained with sucrose as a carbon source and the equal ratio of ammonium to nitrate. High phosphate concentration stimulated the carotenoid biosynthesis in D. corota. 2,4-D inhibited the cell growth but stimulated the specific carotenoid content at high concentration. By modifying the medium composition based on these findings, three times higher specific carotenoid content and 2.5 times higher total carotenoid content were obtained as compared with the results obtained with basic MS media. Biosynthesis of carotenoid was found to be affected by cell aggregate size; high carotenoid production was obtained from the large aggregated cells resulted from high sucrose concentration.

• Computers and Concrete
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• 제33권2호
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• pp.147-162
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• 2024

This study presents a random-aggregate mesoscale model integrating the random distribution of the coarse aggerates and the damage mechanics of the mortar and interfacial transition zone (ITZ). This mesoscale model can generate the random distribution of the coarse aggregates according to the prescribed particle size distribution which enables the automation of the current methodology with different coarse aggregates' distribution. The main innovation of this work is to propose the "correction factor" to eliminate the dimensionally dependent mesh sensitivity of the concrete damaged plasticity (CDP) model. After implementing the correction factor through the user-defined subroutine in the randomly meshed mesoscale model, the predicted fracture resistance is in good agreement with the average experimental results of a series of geometrically similar single-edge-notched beams (SENB) concrete specimens. The simulated cracking pattern is also more realistic than the conventional concrete material models. The proposed random-aggregate mesoscale model hence demonstrates its validity in the application of concrete fracture failure and statistical size effect analysis.

• 한국건설순환자원학회논문집
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• 제6권3호
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• pp.61-68
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• 2011

시멘트의 강알칼리성 성분으로 인하여 파분쇄된 순환골재의 pH는 12이상을 발현한다. 이 시멘트의 강알카리성은 환경적으로 피해를 주게 된다. 순환골재의 강알카리성은 골재의 특성, 알카리 용출시간, 골재의 크기 등에 따라 다양하게 나타날 수 있다. 본 연구에서는 이러한 다양한 조건에 따른 순환골재의 pH 특성을 시험하기 위하여 습식 및 건식 생산공정에서 생산한 건식 및 습식 순환골재를 이용하여 폐기물공정 시험방법, 토양오염공정 시험방법, BS EN 1744-3에서 제시한 pH 시험방법에 따른 pH 특성, 순환골재의 용출시간에 따른 pH의 특성, 골재의 입도별 pH 특성을 분석하여 순환골재의 환경적 문제를 해결하는데 기여하고자 하였다. 시험결과에서는 순환골재는 입도가 작을수록 pH가 높은 것으로 나타났으며, 시간 경과에 따라 증가하는 것으로 나타났다. 건식과 습식 순환골재의 pH 경향은 시간 경과에 따른 차이 외에 시험방법에 의한 차이는 없었다. pH 시험방법에 있어서 폐기물공정시험에 의한 순환골재 pH값이 가장 높게 나타나 pH 편차를 고려한 단일 pH 시험방법 제안이 요구된다.

• Structural Engineering and Mechanics
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• 제62권1호
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• pp.21-31
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• 2017

Engineered Cementitious Composite (ECC) is a special class of the new generation of high performance fiber reinforced cementitious composites (HPFRCC) featuring high ductility with relatively low fiber content. In this research, the mechanical performance of ECC beams will be investigated with respect to the effect of slag and aggregate size and amount, by employing nonlinear finite element method. The validity of the models was verified with the experimental results of the ECC beams under monotonic loading. Based on the numerical analysis method, nonlinear parametric study was then conducted to evaluate the influence of the ECC aggregate content (AC), ECC compressive strength ($f_{ECC}$), maximum aggregate size ($D_{max}$) and slag amount (${\phi}$) parameters on the flexural stress, deflection, load and strain of ECC beams. The simulation results indicated that when increase the slag and aggregate size and content no definite trend in flexural strength is observed and the ductility of ECC is negatively influenced by the increase of slag and aggregate size and content. Also, the ECC beams revealed enhancement in terms of flexural stress, strain, and midspan deflection when compared with the reference beam (microsilica MSC), where, the average improvement percentage of the specimens were 61.55%, 725%, and 879%, respectively. These results are quite similar to that of the experimental results, which provides that the finite element model is in accordance with the desirable flexural behaviour of the ECC beams. Furthermore, the proposed models can be used to predict the flexural behaviour of ECC beams with great accuracy.

• 한국도로학회논문집
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• 제10권3호
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• pp.11-18
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• 2008

최근 국내외에서 역학적-경험적 설계법의 개발 및 이의 활용을 위한 각종 연구가 매우 활발하게 진행중에 있다. 미국의 경우 AASHTO 2002 설계법, 우리나라의 경우 한국형 도로포장설계법의 개발이 진행 중에 있고, 개발되는 설계법에 도로포장재료의 역학적 물성치 평가가 상당히 중요한 역할을 하도록 구성되어 있다. 따라서 설계법에 이용될 국내 아스팔트 혼합물의 재료물성의 평가가 매우 시급한 실정이다. 설계법에 이용되는 재료 물성을 평가하는 방법 중 최근에 많이 적용되는 방법이 동탄성계수 실험이다. 동탄성계수는 다양한 온도조건, 하중, 속도를 이용하여 다양한 교통조건을 반영할 수 있다. 사용된 골재의 입도, 아스팔트 바인더에 따라서 변화하며, 특히 아스팔트 혼합물의 점탄성적인 특성을 잘 묘사할 수 있는 물성치 평가방법이라고 할 수 있다. 본 연구에서는 아스팔트 혼합물에 사용되는 골재의 공칭최대치수 및 입도분포와 동탄성계수와의 상관관계를 규명하는 것이다. 국내의 실험장비 조건을 고려할 때, 시편의 직경 및 높이는 100mm 및 150mm를 이용하는 것이 바람직하다. 또한, 골재의 공칭최대치수가 커짐에 따라 동탄성계수가 증가하는 경향을 나타내었다.

• 한국지하수토양환경학회지:지하수토양환경
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• 제20권1호
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• pp.28-35
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• 2015

In this study, the mechanisms on ultrasonication enhanced metals extraction were investigated compared with the conventional washing technique. We hypothesized the mechanisms on enhanced extraction of ultrasonication: ultrasonication increased the temperature of soil slurry and decreased average particle size of soil due to breakdown of soil aggregate. Actually, the ultrasonication increased the temperature of soil slurry to $60^{\circ}C$ in this study, and the increase in the temperature enhanced the metal extraction to 15-20% even in the conventional simple mixing. The conventional washing technique decreased average size of soil particles because of breakdown of soil aggregate, and the ultrasonication decreased the size more than that of washing. The breakdown of soil aggregate improved the contact between metals and washing agent, which enhanced the extraction of metals in the ultrasonication. Therefore, we concluded that the main mechanisms of ultrasonication are increase in the temperature and breakdown of the soil aggregate. Finally, the ultrasonicaiton increased the extractability of metals upto 40% compared to conventional washing technique.

• Structural Engineering and Mechanics
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• 제77권1호
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• pp.103-114
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• 2021

Ultra high strength concrete (UHSC) originally proposed by Richards and Cheyrezy (1995) composed of cement, silica fume, quartz sand, quartz powder, steel fibers, superplasticizer etc. Later, other ingredients such as fly ash, GGBS, metakaoline, copper slag, fine aggregate of different sizes have been added to original UHSC. In the present investigation, the combined effect of coarse aggregate (6mm - 10mm) and steel fibers (0.50%, 1.0% and 1.5%) has been studied on UHSC mixes to evaluate mechanical and fracture properties. Compressive strength, split tensile strength and modulus of elasticity were determined for the three UHSC mixes. Size dependent fracture energy was evaluated by using RILEM work of fracture and size independent fracture energy was evaluated by using (i) RILEM work of fracture with tail correction to load - deflection plot (ii) boundary effect method. The constitutive relationship between the residual stress carrying capacity (σ) and the corresponding crack opening (w) has been constructed in an inverse manner based on the concept of a non-linear hinge from the load-crack mouth opening plots of notched three-point bend beams. It was found that (i) the size independent fracture energy obtained by using above two approaches yielded similar value and (ii) tensile stress increases with the increase of % of fibers. These two fracture properties will be very much useful for the analysis of cracked concrete structural components.