Characterization of coal fly ash by absolute foam index

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Copyright © 2015, American Concrete. Long foam index test times and the inability to characterize different loss on ignition (LOI) in cementitious materials using the same solution concentrations prompted an examination of different test solution concentrations for various fly ash samples. A 15-minute duration forced the test into a number of cycles where air-entraining admixture (AEA) drops with sensitivity compatible to the fly ash allowed diffusion and reaction consistency throughout all the tests, allowing both low- and high-carbon fly ash to be characterized uniquely. The absolute foam index, defined as the amount of undiluted volume of AEA solution added to obtain a 15-minute endpoint (limits 12 to 18 minutes) signified by 15-second metastable foam, uniquely characterized 15 fly ash samples with LOI values that ranged from 0.17 to 23.3%. The absolute foam index strongly correlated to LOI values for fly ash samples greater than 5% LOI but variability was observed in samples less than 5% LOI.

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ACI Materials Journal