An examination of fly ash carbon and its interactions with air entraining agent

Hill, Russell L.; Sarkar, S.; Rathbone, Robert F.; Hower, James C.

doi:10.1016/s0008-8846(97)00008-2

Cited by 91 publications

(43 citation statements)

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“…1999c;. However, the low hydrogen content values reported here are consistent with other published work, where the hydrogen contents of the unburned carbon are <0.5% (dry basis) or <0.02% (daf) (Hill, et al, 1997b;Maroto-Valer, et al, 2001;1999c;. The sulfur contents of all the samples ranged from 0.01 to 3.90wt%, while the nitrogen contents varied from 1.07 to 1.77wt%.…”

Section: Proximate and Ultimate Analysessupporting

confidence: 91%

Development of Activated Carbons From Coal Combustion by-Products

Schobert¹,

Maroto‐Valer²,

Lü³

2003

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The increasing role of coal as a source of energy in the 21st century will demand environmental and cost-effective strategies for the use of coal combustion by-products (CCBPs), mainly unburned carbon in fly ash. Unburned carbon is nowadays regarded as a waste product and its fate is mainly disposal, due to the present lack of efficient routes for its utilization. However, unburned carbon is a potential precursor for the production of adsorbent carbons, since it has gone through a devolatilization process while in the combustor, and therefore, only requires to be activated. Accordingly, the principal objective of this work was to characterize and utilize the unburned carbon in fly ash for the production of activated carbons.The unburned carbon samples were collected from different combustion systems, including pulverized utility boilers, a utility cyclone, a stoker, and a fluidized bed combustor.LOI (loss-on-ignition), proximate, ultimate, and petrographic analyses were conducted, and the surface areas of the samples were characterized by N 2 adsorption isotherms at 77K. The LOIs of the unburned carbon samples varied between 21.79-84.52%. The proximate analyses showed that all the samples had very low moisture contents (0.17 to 3.39 wt %), while the volatile matter contents varied between 0.45 to 24.82 wt%. The elemental analyses show that all the unburned carbon samples consist mainly of carbon with very little hydrogen, nitrogen, sulfur and oxygenIn addition, the potential use of unburned carbon as precursor for activated carbon (AC) was investigated. Activated carbons with specific surface area up to 1075m 2 /g were produced from the unburned carbon. The porosity of the resultant activated carbons was related to the properties of the unburned carbon feedstock and the activation conditions used. It was found that not all the unburned carbon samples are equally suited for activation, and furthermore, their potential as activated carbons precursors could be inferred from their physical and chemical properties. The developed porosity of the activated carbon was a function of the oxygen content, porosity and H/C ratio of the parent unburned carbon feedstock. It was observed that extended activation times and high activation temperatures increased the porosity of the produced activated carbon at the expense of the solid yield.

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Section: Proximate and Ultimate Analysessupporting

confidence: 91%

Development of Activated Carbons From Coal Combustion by-Products

Schobert¹,

Maroto‐Valer²,

Lü³

2003

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“…The results in this report help explain the origin of apparently contradictory reports of the effects of surface oxidation in the literature on fly ash carbon [8,9,12]. It is believed that the enhanced uptake of polar compounds from the vapor phase (acetone) [9] is driven by the increased surface energy and polarity of oxidized carbon surfaces, while the decreased uptake of surfactant from solution is related not to the magnitudes of the energies but to the increased polar/dispersive ratio.…”

Section: Mechanisms Of Adsorption Suppressionsupporting

confidence: 55%

“…In recent studies, surfactant adsorption on carbon has been identified as a key phenomenon determining the suitability of coal combustion fly ash as a concrete additive [5][6][7][8][9]. Here the carbon is a contaminant and its undesirable adsorption of surfactant from the aqueous concrete paste reduces the surfactant's ability to stabilize sub-millimeter air bubbles that help improve freeze-thaw resistance in set concrete [10].…”

Section: Introductionmentioning

confidence: 99%

Strategies and Technology for Managing High-Carbon Ash

Hurt¹,

Suuberg²,

Veranth³

et al. 2002

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The overall objective of the present project is to identify and assess strategies and solutions for the management of industry problems related to carbon in ash. Specific research issues to be addressed include:• the effect of parent fuel selection on ash properties and adsorptivity, including a first ever examination of the air entrainment behavior of ashes from alternative (non-coal) fuels.• the effect of various low-NOx firing modes on ash properties and adsorptivity• the kinetics and mechanism of ash ozonation. This data will provide scientific and engineering support of the ongoing process development activities.During this fourth project period we completed the characterization of ozone-treated carbon surfaces and wrote a comprehensive report on the mechanism through which ozone suppresses the adsorption of concrete surfactants.4

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“…27 Results of mini slump test performed on mixes containing cement C4 and F1 class C ash (20% replacement by weight) 57 Table C. 28 Results of mini slump test performed on mixes containing cement C4 and F2 class C ash (20% replacement by weight) 57 Table C. 29 Summary of setting time results of pastes containing cement C4 and F1 class C ash (20% replacement by weight) 57 Table C.…”

Section: Methodsmentioning

confidence: 99%

“…The higher dosage requirement of AEAs was attributed to the following properties of unburned carbon particles in fly ash: (1) the amount; (2) the specific surface area; (3) the accessibility of the surface area; (4) the chemical nature of the surface (27,28). In general, class C fly ashes were found to have carbon with much higher specific surface areas than Class F ash does.…”

Section: A4 Incompatibility Problems Driven By Fly Ashmentioning

confidence: 99%

Compatibility of Cementitious Materials and Admixtures

Olek¹,

Paleti²

2012

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JOINT TRANSPORTATION RESEARCH PROGRAMThe Joint Transportation Research Program serves as a vehicle for INDOT collaboration with higher education institutions and industry in Indiana to facilitate innovation that results in continuous improvement in the planning, design, construction, operation, management and economic efficiency of the Indiana transportation infrastructure. https://engineering.purdue.edu/JTRP/index_html Published reports of the Joint Transportation Research Program are available at: http://docs.lib.purdue.edu/jtrp/ NOTICEThe contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views and policies of the Indiana Department of Transportation or the Federal Highway Administration. The report does not constitute a standard, specification or regulation. AbstractGrowing demand for creating more sustainable and durable concretes lead to the increased usage of various cementitious materials and chemical admixtures in the mixtures. However, the increased usage of these components resulted in more complex mixtures that sometimes cause unexpected incompatibility problems. This report summarizes the results of the investigation of the parameters that may lead to workability problems, early age hydration irregularities and difficulties in achieving quality air void system in both plain and fly ash cementitious mixtures. The present research work was performed in three major phases and the statistical modeling was used to aid in interpretation. Phase I involved evaluation of more than 100 different paste and mortar mixtures with respect to potential slump loss and hydration irregularities. The results showed that cements with high C3A and low SO3 content were more prone to incompatibility problems. It was also observed that mixes with lignin based water reducing agent (WRA) had higher tendency for rapid stiffening than mixes with polycarboxylate type superplasticizer (PCSP). Increased replacement of cement by class C ashes resulted in the development of abnormal secondary peaks in semi-adiabatic calorimetry curves and accelerated the setting behavior.The focus of phase II was on identifying material combinations that can result in problems related to air void generation and stability. The experiments were conducted on 18 different systems and included determination of foam drainage and foam index parameters. The results show that the amount of air entrainers required to obtain target air percentage, increased with the increase in the fly ash content in the mixture. Lignin based WRA had, in general, a higher air entraining effect than the super-plasticizer when used in combination with air entrainers. Also, five out of the six mixtures with most unstable air void system, identified using the foam drainage experiments, contained the PCSP.The third (and final) phase of the study involved production of 10 concrete mixtures to verify the incompatibility findings from the paste ...

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An examination of fly ash carbon and its interactions with air entraining agent

Cited by 91 publications

References 0 publications

Development of Activated Carbons From Coal Combustion by-Products

Development of Activated Carbons From Coal Combustion by-Products

Strategies and Technology for Managing High-Carbon Ash

Compatibility of Cementitious Materials and Admixtures

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