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

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

Author(s): P. C. Nkinamubanzi, A. Bilodeau, C. Jolicoeur, and D. M. Golden

Publication: Special Publication

Volume: 217

Issue:

Appears on pages(s): 543-572

Keywords: activated charcoal; admixtures; air bubbles; air-entraining agents; air-void parameters; carbon content; concrete; durability; fly ash; mortars; portland cement; superplasticizers; water-reducing admixtures

Date: 9/1/2003

Abstract:
New air-entraining admixtures (AEA), suitable for use with concrete containing fly ashes having levels of unburned carbon higher than the typical 2-4% allowed in the concrete industry, have been tested in this study. A number of new AEA were selected using a mortar test. Results obtained on mortar were validated on concrete. The criteria for the evaluation of the admixtures in concrete were the dosage required for a specific air content, the sensitivity of the admixture to the carbon content of the fly ash, and the stability of the air in the fresh concrete during the first hour after the contact between the binder and the water. The airvoid system of the hardened concrete was determined for the product found to be the most promising. A full testing program in concrete of the selected air-entraining admixture was then undertaken including durability testing. Concrete having three different water-tobinder ratios were used (0.5, 0.42 and 0.32). The fly ash content of the concrete were 30% for the two higher water-to-binder ratios and 55% for the lower water-to-binder ratio concrete which was a typical high volume fly ash concrete. The new air-entraining admixture's family is suitable for fly ash having high carbon content, but it showed a poor compatibility with sulfonated water reducing admixtures. When used in combination with polycarboxylate-based water reducing admixtures, no special problem was experienced with the air entrainment. Generally, the new air-entraining admixture's family does not affect negatively the properties of the fresh concrete. The measured durability parameters and all other properties of the hardened concrete are very satisfying.