Investigating Techniques for Evaluating Fly Ash Behaviour in Air-entrained Concrete

Abstract

Abstract The paper describes research from a study carried out to investigate techniques for evaluating fly ash influences on air-entrainment in concrete and covers the potential of dye adsorption tests, i.e. using methylene blue (MB) and acid blue 80 (AB80), in this role. The MB test is essentially that given in BS EN 933-9 (normally used for the assessment of fines in sand) and involves visual determination of an endpoint, while the AB80 test (similar to those used for examining activated carbon) is spectroscopic and, therefore, instrument-based. Following the determination of suitable procedures for the tests, their evaluation with fly ashes covering a range of properties is described through comparisons against parameters including, loss-on-ignition and specific surface area (measured by N 2 adsorption). Relationships are presented that examine the dye adsorption of fly ash with respect to the air-entraining admixture demand to achieve a target air content range (5.0 ± 1.0%) in corresponding concretes. These indicate strong correlations for the materials used. Consideration is given to how the dye adsorption tests could be applied in air-entrained fly ash concrete production