Abstract
To facilitate their continued use in concrete as sources become less standard, interactions between fly ash and air-entraining admixtures (AEA) must be better understood. For this study, adsorption tests were conducted using portland cement, fly ash, calcium salts, and a commercial AEA. Varying fly ash-to-solution ratio responses indicated that the removal of AEA from solution by fly ash was divided into non-proportional adsorption (NPA) and proportional adsorption (PA). NPA was found to be reversible, resulting in a three-phase equilibrium among NPA, PA, and AEA remaining in solution. A new method was developed to obtain adsorption capacities that are not affected by the fly ash-to-solution ratio used in the test and thus can help understand the AEA distribution in the system with high solid-to-solution ratios that adsorption tests cannot simulate, such as concrete mixtures. In addition, NPA was shown to be primarily related to complexation between AEA and calcium present in the mixture due to the presence of cement and fly ash.
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