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Hydration and time-dependent rheology changes of cement paste containing ground fly ash

  • Chen, Wei;Huang, Hao
    • Computers and Concrete
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    • v.11 no.1
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    • pp.39-49
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    • 2013
  • The use of ground fly ash in concrete can increase the risk of slump loss due to the drastic surface change of the particles after the grinding treatment and the accelerated reaction compared to the untreated ash. This study is aimed at the early age hydration and time-dependent rheology changes of cement paste containing ground fly ash. An original fly ash is ground into different fineness and the hydration of cement paste containing the ground fly ash is monitored with the ultrasound propagation method. The zeta potentials of the solid particles are measured and the changes of rheological parameters of the cement pastes with time are analyzed with a rheometer. A particle packing model is used to probe packing of the solid particles. The results show that the early age hydration of the paste is strongly promoted by replacing Portland cement with fly ash up to 30 percent (by mass), causing increase of the yield stress of the paste. The viscosity of a paste containing ground fly ash is lower than that containing the untreated ash, which is explained by the denser packing of the solid particles.

Electrostatic Beneficiation of Coal Fly Ash Utilizing Triboelectric Charging with Subsequent Electrostatic Separation

  • Lee, Jae-Keun;Kim, Seong-Chan
    • Journal of Mechanical Science and Technology
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    • v.15 no.6
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    • pp.804-812
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    • 2001
  • A triboelectrostatic separation system for removing unburned carbon from coal fly ash is designed and evaluated. Fly ash from a coal-fired power plant is used as an accepted additive in concrete where it adds strength, sulfate resistance and reduced cost, provided acceptable levels of unburned carbon are maintained. Unfortunately, unburned carbon in coal fly ash absorbs some of other additives and reduces the concrete strength. This paper describes to investigate dry triboelectrostatic process to separate unburned carbon from coal fly ash and utilize it into economically valuable products. The laboratory-scale triboelectrostatic separation system consists of a particle feeding system, a tribocharger, a separation chamber, and collection systems. Particles of unburned carbon and fly ash can be imparted positive and negative surface charges, respectively, with a copper tribocharger due to differences in the work function values of the particles and the tribocharger, and can be separated by passing them through an external electric field. Results showed that fly ash recovery was strongly dependent on the electric field strength and the particle size. 70wt% of fly ash containing 6.5wt% of carbon contents could be recovered at carbon contents below 3%. The triboelectrostatic separation system showed a potential to be an effective method for removing unburned carbon from coal fly ash.

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A Study on Properties of Domestic Fly Ash and Utilization as an Insulation material (국산 Fly Ash의 특성 및 단열재로의 이용에 관한 연구)

  • 박금철;임태영
    • Journal of the Korean Ceramic Society
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    • v.20 no.2
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    • pp.135-146
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    • 1983
  • This study is to investigate the properties of domestic fly ash for utilization as data in regard to fly ash which is by-product of domestic coal powder plants and the possibility of utilization as insulation material of domestic fly ash. Composition refractoriness size distribution density contents of hollow particles and crystalline phase were examined as the properties of domestic fly ash. As to the fired test pieces of fly ash by itself that varied contents of hollow particles with four kinds and of the fly ash-clay-saw dust system linear shrinkage bulk density app. porosity compressive strength thermal conductivity and structures were investigated for the possibility of utilization as an insulation material. The results are as follows : 1. The properties of the fly ash I) The constituent particle of the fly ash is spherical and it contains not a few hollow particles (floats by water 0.30-0.50 floats by $ZnCl_2$ aq.(SpG=1.71) 6.97-16.72%). ii) The chemical compositions of fly ash are $SiO_243.9-54.1%$ , $Al_2O_321.0-30.7%$ Ig loss is 7.4-24.1% and the principal of Ig loss is unburned carbon. iii) Fly ash was not suitable to use for mortar and concrete mixture because Ig. loss value is higher than 5% 2. Utilization as insulation material I) The test pieces of original fly ash floats by water floats by ZnCl2 aq(SpG=1.71) p, p t by ZnCl2 aq.(SpG=1.71) that were fired at 110$0^{\circ}C$ represented 0.11-0.18 kcal/mh$^{\circ}$ C as thermal conductivity value. ii) The test pieces which (76.5-85.5) wt% fly ash-(8.5, 9.5) wt% clay-(5.0-15.0) wt% saw dust system(68.0-72.0) wt% fly ash -(17.0-18.0)wt% clay-(10.0-15.0) wt% saw dust system and 59.5 wt% fly ash-25.5 wt% clay-15.0wt% saw dust system were fired at 110$0^{\circ}C$ the thermal conductivity was less than 0.1Kcal/mh$^{\circ}$ C. iii) In view of thermal conductivity and economic aspect insulation materials which added saw dust as blowing agent and clay as inorganic binder are better than that of fly ash as it is or separated hollow fly ash particles. iv) When the saw dust contents increased in the (59.5-90.0) wt% saw dust system and when amount of clay de-creased and firing temperature decreased under the condition of equal addition of saw dust app. porosity increased but bulk density compressive strength and thermal conductivity decreased.

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Alkali-Activated Coal Ash(Fly Ash, Bottom Ash) Artificial Lightweight Aggregate and Its Application of Concrete (알칼리 활성화 석탄회(Fly Ash, Bottom Ash) 인공경량골재 및 콘크리트 적용)

  • Jo Byung-Wan;Park Seung-Kook;Kwon Byung-Yoon
    • Journal of the Korea Concrete Institute
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    • v.16 no.6
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    • pp.751-757
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    • 2004
  • Artificial lightweight aggregates and solids were manufactured with coal ash(fly ash, bottom ash). In order to apply alkali-activated coal ash(fly ash, bottom ash) artificial lightweight aggregate to concrete, several experimental studies were performed. Thus, it can be noticed the optimal mix proportion, basic characteristies, mechanical properties and environmental safety of alkali-activated coal ash(fly ash, bottom ash) solid and alkali-activated coal ash(fly ash, bottom ash) artificial lightweight aggregate. Also, the freezing-thawing test property of concrete using the alkali-activated coal ash(fly ash, bottom ash) artificial lightweight aggregate was investigated. As a result, the optimal mixing proportion of coal ash(fly ash, bottom ash) solid to make alkali-activated artificial lightweight aggregates was cement $10\%$, water glass $15\%$, NaOH $10\%$, $MnO_2\;5\%$. Alkali-activated coal ash(fly ash, bottom ash) solid can achieve compressive strength of 36.4 MPa, at 7-days, after the paste was cured at air curing after moist curing during 24 hours in $50^{\circ}C$. Alkali-activated coal ash(fly ash, bottom ash) artificial lightweight aggregate that do impregnation to polymer was improved $10\%$ crushing strength $150\%$, and was available to concrete.

AN EXPERIMENTAL STUDY ON THE PROPERTIES & APPLICATION FOR FLY ASH OF CONBINED HEAT POWER PLANT - FOCUSSED HIGH STRENGTH CONCRETE - (열병합발전소 플라이애쉬의 특성 및 활용방안에 관한 실험적 연구 -고강도 콘크리트를 중심으로-)

  • 권영호;백명종;이보근;박칠림
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.211-216
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    • 1994
  • This study dealt with the properties for fly ash of conbined heat power plant and application for concrete industry. For this purpose, fly ash sampled Ulsan conbined heat power plant and analyzed for physical and chemical properties. As analyzed results of fly ash, contents of $SiO_ and Al_O_ $in the fly ash of Ulsan were less than those of Thermo-electric power plant(Boryuing), but contents of CaO were tem times as much as those of Boryung, because of these differences, it is expected that pozzolanic activity of concrete using fly ash of Ulsan will be different from another fly ash. Concrete specimens were tested to evaluate concrete preformance when 10 to 50 percent of the portland cement by weight in the concrete mix was replaced with fly ash of conbined heat power plant. As test results, workability and consideration in the fresh concrete were increased and concrete strength was showed more than 400kg/$\textrm{cm}^2$ for the required age. This study would be provided valuable data for the practical utilization of fly ash(conbined heat power plant). In the future, properties of fly ash concrete including long term strength, elapsed time, pozzolanic activity, modulus of elasticity, sulfate resistance, shrinkage, freeze-thaw durability and so on will be studied.

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A Fundamental Study on the Mix Design in High Volume Fly-Ash Concrete (플라이애시를 대량 사용한 콘크리트의 배합설계를 위한 기초적 연구)

  • 심재형;김재환;최희용;강석표;최세진;김무한
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.641-646
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    • 2001
  • Generally, when Fly-Ash was used as replacement material of cement in concrete, it might occur retardation of setting and hardening. So, it is unable to use a large amount of Fly-Ash as replacement for cement. However, if it is used as replacement material of fine aggregate in concrete, we can use a large amount of Fly-Ash and settle a problem of natural-aggregate exhaustion. Furthermore, engineering properties of High Volume Fly-Ash Concrete Is better than that of plain concrete But, the larger Fly-Ash is replaced, the more fluidity of High Volume Fly-Ash Concrete decrease, because porous organization of Fly-Ash adsorb water and Superplasticizer. In this study, after appending additional water to High Volume Fly-Ash Concrete in proportion to weight of Fly-Ash, we intend to find proper ratio which doesn't affect strength and satisfy fluidity As a result of this study, it was found that fluidity of mortar with 25~28 percentage of additional water was satisfied with fluidity of plain mortar, and compressive strength of that was similar to plain mortar's

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An Experimental Study on Hydration Heat and Strength Properties Concrete with High Volume Fly-Ash (플라이애시 콘크리트의 수화발열 특성과 압축강도 특성에 관한 실험적 연구)

  • 김우상;김광기;백민수;김우재;정재영;정상진
    • Proceedings of the Korean Institute of Building Construction Conference
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    • pp.67-71
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    • 2003
  • This study is for the great quantity use of fly-ash. For the producing of high volume concrete from the use of fly-ash, the method of replacement between bonding agents and fine aggregate by fly-ash at the same time was used. It was used that the adiabatic temperature rise of concrete about the mass member which bad been produced by the method that was mentioned before, and the hydration heat of the core test pieces in concrete was measured. Also the core test pieces which were replaced with fly-ash was studied by the compressive streneth's comparison between standard care test pieces and core test pieces. In the case of mass test pieces, hydration heat and the tine to reach the highest temperature were decreased by an increase in replaced fly-ash's amounts of concrete. In addition, among the test pieces having the same amounts of concrete, the test pieces having more replaced amounts of fly-ash's fine aggregate showed higher hydration heat and the increased time to reach the highest temperature. Compressive strength was also increased by hydration heat's decrease according to fly-ash replacement. Replacement of fly-ash was more effective in high temperature environment.

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A Study on Hydration Heat Properties and Strength Properties of High Volume Fly-Ash Concrete (플라이애시를 대량 사용한 콘크리트의 수화열특성 및 강도특성에 관한 연구)

  • Paik, Min-Su;Lee, Young-Do;Jung, Sang-Jin
    • Journal of the Korea Institute of Building Construction
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    • v.3 no.3
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    • pp.135-142
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    • 2003
  • This study is for the great quantity use of fly-ash. For the producing of high volume concrete from the use of fly-ash, the method of replacement between bonding agents and fine aggregate by fly-ash was used at the same time. It was used that the adiabatic temperature rise of concrete about the mass member which had been produced by the method that was mentioned before, and the hydration heat of the core test pieces in concrete was measured. Also the core test pieces which were replaced with fly-ash was studied by the compressive strength's comparison between standard care test pieces and core test pieces. In the case of mass test pieces, hydration heat and the time to reach the highest temperature were decreased by an increase in replaced fly-ash's amounts of concrete. In addition, among the test pieces having the same amounts of concrete, the test pieces having more replaced amounts of fly-ash's fine aggregate showed higher hydration heat and the increased time to reach the highest temperature. Compressive strength was also increased by hydration heat's decrease according to fly-ash replacement. Replacement of fly-ash was more effective in high temperature environment.

Efficiency factor of high calcium Class F fly ash in concrete

  • Sata, V.;Khammathit, P.;Chindaprasirt, P.
    • Computers and Concrete
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    • v.8 no.5
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    • pp.583-595
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    • 2011
  • This paper studied the cement efficiency factor (k factor) of high calcium Class F fly ash. This k factor represents a unit of fly ash with efficiency equivalent to k unit of cement. The high calcium Class F fly ash was used to replace cement in concrete. The modified Bolomey's law with linear relationship was used for the analysis of the result of compressive strength, cement to water ratio (c/w) and fly ash to water ratio (f/w) by using the multi-linear regression to determine the k factor and other constants in the equations. The results of analysis were compared with the results from other researcher and showed that the k factor of high calcium Class F fly ash depends on the fineness of fly ash, replacement level and curing age. While the amount of CaO content in Class F fly ash not evident. Furthermore, necessary criteria and variables for the determination of the k factor including the use of the k factor in concrete mix design containing fly ash were proposed.

Experimental Investigation of Clay Fly Ash Bricks for Gamma-Ray Shielding

  • Mann, Harjinder Singh;Brar, Gurdarshan Singh;Mann, Kulwinder Singh;Mudahar, Gurmel Singh
    • Nuclear Engineering and Technology
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    • v.48 no.5
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    • pp.1230-1236
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    • 2016
  • This study aims to determine the effect of fly ash with a high replacing ratio of clay on the radiation shielding properties of bricks. Some interaction parameters (mass attenuation coefficients, half value layer, effective atomic number, effective electron density, and absorption efficiency) of clay fly ash bricks were measured with a NaI(Tl) detector at 661.6 keV, 1,173.2 keV, and 1,332.5 keV. For the investigation of their shielding behavior, fly ash bricks were molded using an admixture to clay. A narrow beam transmission geometry condition was used for the measurements. The measured values of these parameters were found in good agreement with the theoretical calculations. The elemental compositions of the clay fly ash bricks were analyzed by using an energy dispersive X-ray fluorescence spectrometer. At selected energies the values of the effective atomic numbers and effective electron densities showed a very modest variation with the composition of the fly ash. This seems to be due to the similarity of their elemental compositions. The obtained results were also compared with concrete, in order to study the effect of fly ash content on the radiation shielding properties of clay fly ash bricks. The clay fly ash bricks showed good shielding properties for moderate energy gamma rays. Therefore, these bricks are feasible and eco-friendly compared with traditional clay bricks used for construction.