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  • 제목/요약/키워드: Engineering Properties of concrete

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Ambient Vibration Testing and System Identification for Tall Buildings (고층건물의 자연 진동실험 및 시스템판별)

  • Cho, Soon-Ho
    • Journal of the Earthquake Engineering Society of Korea
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    • v.16 no.3
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    • pp.23-33
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    • 2012
  • Dynamic response measurements from natural excitation were carried out for three 18-story office buildings to determine their inherent properties. The beam-column frame system was adopted as a typical structural form, but a core wall was added to resist the lateral force more effectively, resulting in a mixed configuration. To extract modal parameters such as natural frequencies, mode shapes and damping ratios from a series of vibration records at each floor, the most advanced operational system identification methods based on frequency- and time-domain like FDD, pLSCF and SSI were applied. Extracted frequencies and mode shapes from the different identification methods showed a greater consistency for three buildings, however the three lower frequencies extracted were 1.2 to 1.7 times as stiff as those obtained using the initial FE models. Comparing the extracted fundamental periods with those estimated from the code equations and FE analysis, the FE analysis results showed the most flexible behavior, and the most simple equation that considers the building height as the only parameter correlated fairly well with test results. It is recognized that such a discrepancy arises from the fact that the present tests exclude the stiffness decreasing factors like concrete cracking, while the FE models ignore the stiffness increasing factors, such as the contribution of non-structural elements and the actual material properties used.

The Effect of the Amount of Polycarboxylate Superplasticizer on the Properties of Ultra-High Performance Fiber-Reinforced Concrete (폴리칼본산계 고성능감수제 사용량이 초고성능 섬유보강 콘크리트의 성질에 미치는 영향)

  • Kang, Su-Tae
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.38 no.1
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    • pp.11-18
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    • 2018
  • As the amount of polycarboxylate superplasticizer varied from 1.2% to 3.0% of the mass of binder, the change in the flowability & rheological properties, and strength of UHPFRC was investigated with experiments. The test results presented that the increase in the amount of superplasticizer was effective in improving the flowability up to 1.8%, but addition more than 1.8% was hardly beneficial for enhancing the flowability and rhelogical properties. Compressive strengths with different amounts of superplasticizer showed that the strength with 1.8% was slightly higher than that of 1.2%, but the amount more than 1.8% caused strength reduction, which was higher as the amount increased. The results in flexural strength according to the amount of superplasticizer showed a similar trend with the results in compressive strength. When the effect of compressive strength and fiber distribution characteristics on the flexural strength was analysed separately, it was found that high amount of superplasticizer caused an effect of fiber distribution in addition to the effect of compressive strength on flexural strength. This effect seems to be closely related to the results of flowability or rheological properties.

The Influence of Al2O3 on the Properties of Alkali-Activated Slag Cement (알칼리 활성화 슬래그 시멘트의 특성에 미치는 Al2O3의 영향)

  • Kim, Tae-Wan;Kang, Choong-Hyun
    • Journal of the Korea Concrete Institute
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    • v.28 no.2
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    • pp.205-212
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    • 2016
  • This research investigates the influence of ground granulated blast furnace slag (GGBFS) composition on the alkali-activated slag cement (AASC). Aluminum oxide (Al2O3) was added to GGBFS binder between 2% and 16% by weight. The alkaline activators KOH (potassium hydroxide) was used and the water to binder ratio of 0.50. The strength development results indicate that increasing the amount of Al2O3 enhanced hydration. The 2M KOH + 16% Al2O3 and 4M KOH + 16% Al2O3 specimens had the highest strength, with an average of 30.8 MPa and 45.2 MPa, after curing for 28days. The strength at 28days of 2M KOH + 16% Al2O3 was 46% higher than that of 2M KOH (without Al2O3). Also, the strength at 28days of 4M KOH + 16% Al2O3 was 44% higher than that of 4M KOH (without Al2O3). Increase the Al2O3 contents of the binder results in the strength development at all curing ages. The incorporation of AASC tended to increases the ultrasonic pulse velocity (UPV) due to the similar effects of strength, but increasing the amount of Al2O3 adversely decreases the water absorption and porosity. Higher addition of Al2O3 in the specimens increases the Al/Ca and Al/Si in the hydrated products. SEM and EDX analyses show that the formation of much denser microstructures with Al2O3 addition.

Structure and physical properties of the earth crustal material in the middle of Korean Peninsula : A study on the prescription of standard test by mortar-bar method (한반도 중부권 지각물질의 구조와 물성연구 : 콘크리트 공시체에 의한 표준시험 규정에 대하여)

  • 정진곤;유신애
    • The Journal of Engineering Geology
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    • v.5 no.2
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    • pp.193-200
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    • 1995
  • It has been well known that the alkali-aggregate reaction between the aggregates and cement paste is one of the reasons of a concrete siructre expansion. Because of a serious demage on the concrete stnicture from the expansion, in many countries, the safety of the materials is checked in laboratory by mortar-bar test and the upper limit of expansion in length is 0.1%. The prescriptions are presented in the ASTM C227 and 490 of U.S. which has been international currency and in the KS Handbook F2503, F2546 and L5107 of Korea published by Korean Standards Association. Both of the prescriptions are almost same in their contents. Actually, in the process of preparing and measuring the mortar-bar according to the prescription mentioned above, it seems that there are no problems for its own purpose but a few points are found to be improved upon the methods to increase the accuracy for laboratory work as follows. 1. The prescription of blending ratio(aggregate, cement and water) should be noted by volume not by weight. 2. It is unreasonable to measure the initial length of mortar bars after 24±2 hours at once regardless the kind of aggregates. 3. It may bring about errors in calculating the expansion ratio under the condition of the denominator value fixed as 254mm. 4. The measuring methods of specific gravity are selected according to the purposes but the pure specific gravity displays the highest accuracy among them.

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An Experimental Study on the Properties of Chloride Binding of Mg/Al-NO3 and Ca/Al-NO3 Layered Double Hydroxides in Solution (수용액내에서 Mg/Al-NO3 및 Ca/Al-NO3 층상이중수산화물(LDHs)의 염소이온 고정화 특성에 관한 실험적 연구)

  • Lee, Seung-Yeop;Yang, Hyun-Min;Lee, Han-Seung
    • Journal of the Korea Institute of Building Construction
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    • v.16 no.3
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    • pp.219-227
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    • 2016
  • Chloride ions ingress continuously in reinforced concrete through pores of it by Cl. Finally, it causes a localized corrosion of the rebar and then it generates cracks on concrete structures. Recently, new materials removing harmful anions have been developed. Layered double hydroxides(LDHs) has an excellent ability to remove harmful anions because various anions can be adsorbed in the interlayer space between divalent and trivalent cations. Thus, LDHs has been applied in various fields. Especially, LDHs is expected to be effective adsorbent binding chloride ions. In this study, Ca/AlNO3 and Mg/AlNO3 LDHs were prepared by using a co-precipitation method. Ca/AlNO3 and Mg/AlNO3 LDHs were compared and analyzed by using XRD, SEM analysis. Many nano size hexagonal crystals were observed by SEM. Experiments for binding chloride ions of LDHs were conducted by using potentiometric method. The experimental data were measured every 15 minutes. It was observed that the chloride ion content is reduced by increasing of LDHs mass fraction and the reaction rate of Mg/AlNO3 is faster than Ca/AlNO3. In future studies, binding chloride capacity in cement materials will be evaluated based on results of this study.

A Study on the Development of Sound Absorption Material Using Perlite for Noise Barrier Wall (펄라이트를 이용한 방음벽의 흡음소재 개발에 관한 기초적 연구)

  • Jo, Young-Kug;Yang, Ju-Kyung
    • Journal of the Korea Concrete Institute
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    • v.20 no.5
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    • pp.653-660
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    • 2008
  • The purpose of this study is to analyze the optimal mix design of the sound absorption material that is made from perlite and various binder systems for noise barrier wall. The polymer cement slurry which is made from two types of polymer dispersions, and silicone type inorganic material are used as binder. The test specimens are prepared with various polymer cement ratios, binder ratios, and tested for strengths, freezing and thawing and sound absorption performance by the tube and the reverberation room methods. From the test results, the difference of sound absorption coefficient by the tube method is a little recognized, however, noise reduction coefficient (NRC) of test specimens bound by the polymer cement slurry is in the ranges of 0.48 to 0.51. They are a little higher than those bound by cement only, and are lower values than recommended value of 0.7 by the Ministry of Environment. However, the sound absorption coefficient of test specimens at low frequency range of 250 to 500 Hz by reverberation room method shows very high values as 0.84 to 1.00, and 0.57 to 0.77 at the high frequency. The test specimens with polymer cement slurry binder have a good balance between performance and cost, and have proper properties in strengths, freezing and thawing resistance as sound absorption material for noise barrier wall. It is apparent that the good sound absorption material can be produced according to the optimum mix design that is recommended from this study.

An Experimental Study on Hydration and Strength Development of High Blain Cement at Low Temperature (저온환경에서 고분말도 시멘트의 수화반응 및 강도발현 특성에 관한 실험적 연구)

  • Mun, Young-Bum;Kim, Hyeong-Cheol;Choi, Hyun-Kuk;Kim, Jae-Young;Lee, Han-Seung;Kim, Mok-Kyu
    • Journal of the Korea Institute of Building Construction
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    • v.15 no.4
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    • pp.367-373
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    • 2015
  • In this study, fundamental properties of cement were reviewed to apply high fineness cement at low temperature environment. The classified high fineness cement has large proportion of particles below 10μm which affects early hydration: an overall reaction of cement hydration faster. As a result of using high fineness cement, setting time of concrete was reduced and compressive strength was higher than OPC at all ages. Especially, compressive strength was more than double its value compared with OPC after three days curing in low temperature. Faster reaction and higher heat of hydration was verified by calorimetry early and maximum heat of hydration was analyzed by adiabatic temperature raising test. The analysis of this study confirmed that high fineness cement can be suitable to be used in low temperature environment.

The Effects of Na2CO3 on Early Strength of High Volume Slag Cement (대량치환 슬래그 시멘트의 초기강도에 미치는 Na2CO3의 영향)

  • Kim, Tae-Wan;Hahm, Hyung-Gil
    • Journal of the Korea Concrete Institute
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    • v.28 no.3
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    • pp.349-356
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    • 2016
  • This report presents the results of an investigation on the early strength development of pastes high volume slag cement (HVSC) activated with different concentration of sodium carbonate (Na2CO3). The ordinary Portland cement (OPC) was replaced by ground granulated blast furnace slag (GGBFS) from 50% to 90% by mass, the dry powders were blended before the paste mixing. The Na2CO3 was added at 0, 2, 4, 6, 8 and 10% by total binder (OPC+GGBFS) weight. A constant water-to-binder ratio (w/b)=0.45 was used for all mixtures. The research carried out the compressive strength, ultrasonic pulse velocity (UPV), water absorption and X-ray diffraction (XRD) analysis at early ages(1 and 3 days). The incase of mixtures, V5 (50% OPC + 50% GGBFS), V6 (40% OPC + 60% GGBFS) and V7 (30% OPC + 70% GGBFS) specimens with 6% Na2CO3, V8 (20% OPC + 80% GGBFS) and V9 (10% OPC + 90% GGBFS) specimens with 10% Na2CO3 showed the maximum strength development. The results of UPV and water absorption showed a similar tendency to the strength properties. The XRD analysis of specimens indicated that the hydration products formed in samples were CSH and calcite phases.

An Experimental Study on the Engineering Properties of Lightweight Aggregate Concrete (경량골재 콘크리트의 공학적 성질에 관한 실험적 연구)

  • ;R. N. Swanmy
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.39 no.1
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    • pp.75-82
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    • 1997
  • 건설기술과 산업의 발전에 따라 구조물은 대형화되어 가고, 건설공사의 급격한 팽창으로 골재 수용량이 급증함에 따라 천연골재자원은 점차 부족현상을 면치 못할 처지에 있다. 또한, 무리한 천연골재의 채취는 자연환경을 훼손시킬 뿐만 아니라 자연보호 측면에서도 심각한 공해문제로 대두되고 있어 공급량 부족현상은 날로 심화되고 있다. 이에 세계 몇몇 나라에세는 산업부산물을 이용한 골재 생산으로 공해예방과 폐기물 활용방법을 연구하고 있다. 산업부산물중 플라이 애쉬 생산량은 전 세계적으로 매년 약 2억여톤에 달하고 있으나 이중 일부만 활용되고 있는 실정이다. 이와같은 부산물을 활용하기 위한 일환으로 산업부산물인 PFA(Pulverized Fuel Ash)로 만든 인공경량골재의 년생산량이 영국은 600,000m3, 미국은 300,000m3이며, 매년 증가주세에 있다. 고성능 경량골재 콘크리트는 단위중량의 증가없이 내구성과 강도를 향상시켜 실용화 측면에서 경제적인 효과가 있으며, 플라이 애쉬로 만든 경량골재는 시멘트와의 친화력이나 접착면에서 우수한 것으로 알려져 있다. 본 시험에 사용한 골재는 플라이 애쉬로 만든 인공경량 조골재와 강모래이고, 결합제로서 프틀랜드 시멘트를 사용하였다. 부수적인 결합재로서는 플라이 애쉬, 슬래그, 실리카 흄을 사용하였으며, 고성능 경량골재 콘크리트를 개발코자 재령 28일과 180일의 압축강도가 각각 50MPa와 60MPa가 되도록 배합설계를 하였다. 본 연구에서는 플라이 애쉬, 슬래그, 시리카 흄과 같은 산업부산물을 혼입했을때 경량골재 콘크리트의 압축강도, 휨강도, 동탄성계수, 공극체적, 공극률, 단위중량, 공극 크기별 분포등의 변화를 실험적으로 구명하여 재반 구조용 콘크리트에 활용하기 위한 기초자료를 마련코저 한다.있어 특정한 발육단계의 난포 사망기전을 연구하기 어렵다. 또한 난포는 생체 내에서 다양한 호르몬을 동시에 분비하기 때문에 특정한 난소국부호르몬이 사망기전에 미치는 영향을 조사하기 힘든 점이 있다. 최근 들어 난포체외배양이 다양하게 개발되면서, 이러한 어려운 점을 극복할 수 있게 되었다. 본 논문은 각 발육단계의 난포를 절단해 체외배양하면서, apoptosis DNA 절단 현상을 이용하여 각종 난소국부 호르몬들이 난포발육단계별로 사망기전에 미치는 영향을 요약해 보였다. 난포는 발육하면서 점차 복잡한 호르몬 경로를 생존을 위해 필요로 한다. Prevulatory난포생존에 필요한 난소국부호르몬들은 early antral 단계의 난포에서는 그 미치는 영향이 감소되다가 preantral단계의 난포에서는 영향을 전혀 미치지 못했다. 단지 예외는 cGMP처리로써, 세포내 cGMP수준을 일정하게 유지시켜주는 것이 난포발육단계에 무관하게 생존에 중요한 인자로, 장래 연구는 난포 세포내의 cGMP수준을 조절하는 기작을 규명하는데 있을 것이다.인정되지 않았다. 7. 농지보전 처리구인 배수구와 초생수로구는 비처리구에 비해 낮은 침두 유출량과 낮은 토양유실량을 나타내었다.구보다 14% 절감되는 것으로 나타났다.작용하는 것으로 사료된다.된다.정량 분석한 결과이다. 시편의 조성은 33.6 at% U, 66.4 at% O의 결과를 얻었다. 산화물 핵연료의 표면 관찰 및 정량 분석 시험시 시편 표면을 전도성 물질로 증착시키지 않고, Silver Paint 에 시편을 접착하는 방법으로도 만족한 시험 결과를 얻을 수 있었다.째, 회복기 중에 일어나는 입자들의 유입은 자기폭풍의 지속시간을 연장시키는 경향을 보이며 큰 자기폭풍일수록 현저했다. 주상에서 관측된 이러한 특성은 서브스톰 확장기 활동이 자기폭풍의 발달과 밀접한 관계가

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Electrical Resistivity of ITZ According to the Type of Aggregate (골재 종류별 시멘트 경화체 계면의 전기저항 특성)

  • Kim, Ho-Jin;Bae, Je Hyun;Jung, Young-Hoon;Park, Sun-Gyu
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.9 no.3
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    • pp.268-275
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    • 2021
  • The three factors that determine the strength of concrete are the strength of cement paste, aggregate and ITZ(Interfacial Transition Zone) between aggregate and cement paste. Out of these, the strength of ITZ is the most vulnerable. ITZ is formed in 10~50㎛, the ratio of calcium hydroxide is high, and CSH appears low ratio. A high calcium hydroxide ratio causes a decrease in the bond strength of ITZ. ITZ is due to further weak area. The problem of ITZ appears as a more disadvantageous factor when it used lightweight aggregate. The previous study of ITZ properties have measured interfacial toughness, identified influencing factors ITZ, and it progressed SEM and XRD analysis on cement matrix without using coarse aggregates. also it was identified microstructure using EMPA-BSE equipment. However, in previous studies, it is difficult to understand the microstructure and mechanical properties. Therefore, in this study, a method of measuring electrical resistance using EIS(Electrochemical Impedance Spectroscopy) measuring equipment was adopted to identify the ITZ between natural aggregate and lightweight aggregate, and it was tested the change of ITZ by surface coating of lightweight aggregate with ground granulated blast furnace slag. As a result, the compressive strength of natural aggregate and lightweight aggregate appear high strength of natural aggregate with high density, surface coating lightweight aggregate appear strength higher than natural aggregate. The electrical resistivity of ITZ according to the aggregate appeared difference.