Predicting AEA dosage by Foam Index and adsorption on Fly Ash

Abstract

Abstract: The unpredictable air entrainment in fly ash concrete caused by carbon in fly ash was studied by measuring adsorption of Air Entraining Agents (AEA) on the fly ash and by Foam Index (FI) testing. The FI test measures the mass ratio of AEA/binder required to obtain stable foam when shaking a mixture of water, binder powder and AEA, while increasing AEA-dosage stepwise. A review of concrete air entrainment and new studies combining adsorption (TGA, NMR) of AEA on fly ash with various FI test procedures, including time dependent effects on foam stability, are presented. Inter-laboratory correlation between FI and concrete air void content verifies that FI is reliable for assessing compatible binder-admixture combinations. Our adsorption- and FI measurements showed that AEA with detectable adsorption required more AEA to foam than AEA that did not adsorb on the fly ash. Foam stability was more time dependent for adsorbing AEA. NMR showed signs of chemical changes of the AEA-FA mix after adsorption. Key words: AEA, fly ash, carbon, air entrainment, adsorption, foam index