Air-Entraining Admixtures for Use with Fly Ashes Having High Carbon Contents

The objective of this study was to evaluate the potential use of a series of new air-entraining admixtures in concrete incorporating fly ashes with a high carbon content. After many tests on mortars and concrete, adjustments were made by the producer on the most promising admixture to finally obtain an admixture as suitable as possible for use in concrete incorporating fly ash with a high carbon content. The final product (NDb) showed real potential in producing adequate air content in fresh concrete and a very good air void system in the hardened concrete. The differences in the air content of the fresh and the hardened concrete is not high, which indicates a good stability of the air entrained. The new air-entraining admixture is less sensitive to the over-dosage compared to the reference product, which is interesting from a practical point of view for concrete producers. All properties of fresh concrete evaluated with the mechanical properties of the hardened concrete are similar for the new admixture and the reference. There is still no effect to use the admixture in concrete, even the fly ash content of the concrete is as high as 55%. The resistance to chloride ions penetration and the frost-resistance of concrete made with this new admixture are excellent. The only problem remaining to solve is the poor compatibility of this new admixture with polysulfonate-based high-range water reducing admixtures. However, the compatibility with acrylic-based water-reducing agents is very good.