Use of Marginal and Unconventional-Source Coal Ashes in Concrete (2024) / Chapter Skim
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The coal ashes were separated into two groups: eight standard ashes and 14 unconventional ashes. The standard ashes are coal ashes that meet the AASHTO M 295-21 specification; the unconventional coal ashes are either harvested, off-specification, have been beneficiated, have marginal properties, or do not fall under the specification scope.
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Cement Paste Properties The impacts of coal ashes on early- and later-age properties of cementitious paste, including heat-release characteristics, bulk resistivity (BR) , compressive strength, calcium hydroxide content, and bound water content were studied using a variety of experimental techniques.
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At 7 days, at room temperature, most tests failed to distinguish Class F coal ashes from inert materials, presumably due to the slow reaction of the Class F ashes. Using higher replacement levels and especially performing the test at higher temperatures provides improved differentiation of inert and reactive materials when using SAI, but the magnitude of differences was generally small, especially considering the inherent variability of strength measurements.
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in any of the coal ash concrete mixtures tested, including mixtures using the cyclone collector ash and high LOI ash, apart from higher AEA dosage requirements. Testing of air content stability in cement-AEA slurries and mortars showed no increased likelihood of air loss due to use of unconventional ashes.
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conducted on pertinent properties (moisture content, density, LOI, fineness, AEA dosage, foam index) of two standard and two unconventional coal ashes indicated that a reduction of testing frequency from every 3,200 tons to every 6,400 tons did not negatively affect the ability of testing to catch outlier data nor fail to assess properties with respect to given limits.
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Additional uniformity testing on regular sampling data (daily or 400 tons) for an unconventional ash showed it had much higher variability in fineness and foam index measurements compared to composite sampling (monthly or 3,200 tons)
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