Working Mechanisms of Air-Entraining Admixtures and Their Subsequent Activation Potential

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Title: Working Mechanisms of Air-Entraining Admixtures and Their Subsequent Activation Potential

Author(s): Eberhard Eickschen

Publication: Special Publication

Volume: 288

Issue:

Appears on pages(s): 1-11

Keywords: air-entraining agent; air void; alkylsulfate; alkylsulfonate; alkylpolyglycolethersulfate; concrete; mixing time; precipitation; vinsol resin.

Date: 9/14/2012

Abstract:
From some job sites it was reported that the air void content of the hardened concrete was higher than that of the fresh concrete. Investigations with commercial air-entrainers based on synthetic and natural active agents showed that a substantial increase in air content can occur only if the fresh concrete is supplied with air-entrainer that is insuffi¬cient activated. The air void content may increase if mixing energy is subsequently applied during placement or transport. The air void formation was studied as a function of the type and quantity of the admixture added and of the mixing time. Furthermore, the precipitation of admixtures in calcium hydroxide was investigated. A subsequent increase in air content is to be expected only with admixtures based on synthetic active agents due to their better solubility in the pore solution. The knowledge of the working mechanisms allows giving recommendations for practice to avoid an increase in the air content.