• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.490-497
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• 2020

This work has been initiated to find possibility whether recycled fine aggregate can be used as a source of aggregate for structural concrete or not. Two-stage mixing approach was chosen in order to maximize strength potential from recycled fine aggregate. Moisture content of the recycled fine aggregate was changed, and two different types of two-stage mixing approaches were applied to produce cement mortar. The strength of mortar made of 100% recycled fine aggregate by two-stage mixing approaches was compared to that of mortar made of 100% washed sea sand. According to the results, the effect of moisture content on compressive strength was observed from low water cement mortar(W/C 0.3). In case of W/C 0.5 cement mortar, no clear relationship was observed between moisture content and strength development. It was found that two-stage mixing approach has a potential to increase the strength of mortar made of 100% recycled fine aggregate. In case of modified version of two-stage mixing approach which first prepares cement paste and pours recycled fine aggregate into the cement paste, was more effective to increase the strength of mortar made of 100% recycled fine aggregate.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.1
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• pp.23-29
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• 2022

This study was conducted to confirm the applicability of recycled aggregates as aggregates for structural concrete as a way to respond to the shortage of natural aggregates. The two-stage mixing approach developed by Tam et al. is known to be a method that can improve the mechanical performance of recycled aggregate concrete without the installation of new additional facilities. In this work, modified version of two stage mixing approach, which was used in our earlier work, was introduced to prepare mortar specimens with recycled fine aggregate, and the compressive strength and fire resistance were compared to mortar mixed with normal mixing approach. According to the experimental results from mortar with recycled fine aggregate, the use of two-stage mixing approach was found to be more effective than normal mixing approach for compressive strength development. In addition, the residual strengths of the mortar with two-stage mixing approach was higher than mortar made of normal mixing approach after exposure to 600 and 900 ℃. It is possible to manufacture high-performance cement composites with recycled fine aggregates through the active use of the two-stage mixing approach.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.475-481
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• 2022

Recycled aggregates show high water absorption rate compared to natural aggregates due to microcrack developed during production process and adhered cement pastes at the surface of recycled aggregates. This leads to the deterioration of mechanical properties and slow work flow. Currently it is getting hard to satisfy high demand for natural aggregates. Utilizing recycled aggregate more widely may be a substitutable countermeasure for the shortage of natural resources. In this study, two-stage mixing approach(TSMA) suggested by Tam et al. is used to produce recycled aggregate concrete(RAC) with 100 % replacement of coarse natural aggregate and tests for compressive strength, elastic modulus, and chloride ion diffusion coefficient are conducted to find out the effect of TSMA compared to normal mixing method. According to experimental result compressive strength and elastic modulus of RAC with TSMA was superior to those of RAC with normal mixing irrespective of water-cement ratio, and in some cases mechanical properties of RAC with TSMA approached to those of natural aggregate concrete(NAC). However, chloride ion diffusion coefficient of RAC was higher than that of NAC. This illustrates that TSMA is not an appropriate method in reducing chloride ion diffusion coefficient, resulting in inconsequential contribution of TSMA to the durability of RAC.

• Polymer(Korea)
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• v.24 no.2
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• pp.220-227
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• 2000

Silica and carbon black filled natural rubber (NR) vulcanizates were prepared with different mixing modes and amounts of fillers. Curing characteristics, morphology. and tear properties of the NR vulcanizates were investigated. The NR vulcanizates filled with silica and carbon black sequentially showed longer induction time ($t_2$), cure index ($t_{90}$ ), and lower maximum torque ($T_{max}$ ) than the NR vulcanizates filled with them simultaneously, during curing process. The former showed superior dispersion of fillers and tear properties to the latter. The NR vulcanizates containing 30 phr of silica showed excellent properties in the experimental range.

• Magazine of the Korea Concrete Institute
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• v.8 no.2
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• pp.109-117
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• 1996

Recently, High-Workable Concrete has been developed and began to be used to a great extent in foreign countries, but it is not familiar with and fully Introduced in Korea yet. Therefore the aim of this paper is to suggest a reference data. for the development of High-Workable Concrete according to the comparative analysis which were done on the effects of mix proportion(water-binder ratio, sand-aggregate ratio, unit water, a kind of superplasticizer) on the flowing characteristics. And also this paper aims to examine the compactability and segregation resistance of High-Workable Concrete in a mock-up test and in a field test. From the result, we concluded that it is possible to produce and to use the High-Workable Concrete at the construction site.

• Korean Journal of Construction Engineering and Management
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• v.13 no.2
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• pp.48-57
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• 2012

A variety of studies on concrete have been performed to examine the advantages for structural material, but less attention has been paid to the contribution of concrete to finishing. Due to this matter, specific management guidelines for construction and quality on exposed concrete have not been clearly established despite more construction cost and quality control are required. This study analyzed a impact factors on the quality by survey of the existing research and practice. Field tests were performed using mock-up models to analyze the quality of exposed concrete according to form manufacture method, concrete mix proportion, and concrete placing method. Results indicate that the quality of exposed concrete was determined by concrete mix proportion and construction managements. Guidelines of quality control on exposed concrete in construction stages were proposed.

• Magazine of the Korea Concrete Institute
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• v.9 no.6
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• pp.185-193
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• 1997

본 연구는 각종 제진재료를 이용하여 진동을 억제할 수 있는 콘크리트를 개발하여 각종 건설공사에서 흔히 발생할 수 있는 진동공해문제를 억제하고자 하며 아울러 폐기물의 재활용차원에서 폐자재를 이용하여 유용한 제진콘크리트를 개발하고자 하는데 그 목적이 있다. 우선, 제진재료를 이용한 압축강도 (200kg/$\textrm{cm}^2$)이상의 콘크리트 배합비를 찾기 위하여 24배치의 예비실험을 수행하였으며, 선정된 적정배합비에 따른 제진재료를 이용한9개의 진동시험체보를 제작하여 보의 구조적 및 재료적 동적특성 즉 1차 공명진동수와 동적 휨강성 및 감쇠비를 측정하여 제진효과를 조사하였다. 그리고 압축강도에 의한 각 시험체의 균열모멘트를 추정하여 재하하중과 균열모멘트비(M/Mcr)에 따른 하중단계별 동적특성값을 살펴보았다. 제진재료로서는 라텍스(Latex), 고무분말(Rubber Powder)그리고 플라스틱 레진( Plastic Resin)등을 사용하였고, 재료적, 구조적 진동감쇠효과를 파악하고자 KS F2437규정과 진동파의 속도법을 사용하였으며, 감쇠비 측정은 Frequency Spectrum 곡선에 대한 Polynomial Curvefitting 방법과 기하학적 해석방법을 이용하여 각각의 결과를 비교.분석하였다.

• Polymer(Korea)
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• v.27 no.2
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• pp.142-151
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• 2003

PMMA panels are made by two fabrication methods; cell molding and belt molding processes. But these methods have disadvantages in productivity and cost. So plastic processing engineers are very interested in developing a new production method for PMU panels using plastic films as molds because the new method can reduce production cost of belt molding method as well as can improve productivity of cell molding method. To give a solution for developing such a new molding method, the effects of melthyl methacrylate compound composition and curing reaction condition on the processability and mechanical strength of PMMA panels were investigated in this study. Poly(vinyl acetate) film was used as molds in producing PMMA panels. To determine an MMA compound showing good processability and good mechanical properties after curing, ingredients and their compositions were optimized step by step. Acrylic acid, as a coupling agent and a modifier, played an important role in increasing mechanical strength of PMMA panels.

• Journal of the Korean Operations Research and Management Science Society
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• v.10 no.2
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• pp.83-87
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• 1985

분해원리(decomposition principle)은 선형계획법문제 중에서도 블록대각구조를 가진 특수 모형에 의한 해법으로 잘 알려져 있다. 그런데 일반적으로 소개되어 있는 분해원리는 변수가 비음의 조건을 가진 문제에 대한 해법이다. 블록대각 구조를 가진 선형계획법 문제는 잘 알려져 있는 바와 같이 하부구조를 가진 기관의 경영, 여러가지 종류의 사료배합 문제 등에 일어난다. 그런데 이런 문제의 대부분의 경우가 변수는 상.하한을 가지는 경우가 된다. 이 논문은 비음의 조건을 가지는 문제에 대한 분해원리를 발전시켜 이런 변수가 상.하한을 가지는 일반적인 문제를 풀 수 있도록 하고자 하는 것이다. 변수가 상.하한을 가지게 되며 우선 진입변수, 탈락변수를 결정하는 문제, 1단계(phase 1) 문제 등에 어려움이 나타난다. 이 논문은 이런 어려움들을 극복하고 나아가 주기억 공간이 제한되어 있는 소형전산기에 알맞는 계산방법을 연구하고자 한다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.2
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• pp.117-125
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• 2014

This paper examines the fundamental properties of alkali-activated slag cement (AASC) activated by sodium hydroxide (NaOH). The water to binder (W/B) ratio was 0.4 and 0.5. And concentration of activator were 2M and 4M. Five mix design of each W/B ratios was considered. The N0 mixture was KS L 5109 method and N1~N4 were varied in different mixing time, mix step and entering points of fine aggregate. Test results clearly showed that the flow value, strength and drying shrinkage development of AASC were significantly dependent on the entering point of fine aggregate. The flow value tended to decreases with delaying entering point of fine aggregate. The compressive strength and flexural strength increases with delaying entering point. Moreover, the XRD analysis confirmed that there were sustain these results. The drying shrinkage increases with delaying entering point of fine aggregate. Futhermore, a modified mixing method incorporating all hereby experimentally derived parameters, is proposed to improvement the physical properties of AASC.