Effects of Air-Entraining Agent, Defoaming Agent and Mixing Time on Characteristic of Entrained Bubbles in Air-Enhanced Self-Compacting Concrete Mixed at Concrete Plant
Keywords:air-enhanced self-compacting concrete, entrained air, air size distribution, air-entraining agent, defoaming agent
This paper presents a full-scale experimental study on the use of an air-entraining agent and defoaming agent combined with mixing time to entrain small-sized air bubbles in air-enhanced self-compacting concrete (Air-SCC). The fresh properties (flowability and V-funnel time) were determined. An air void analyzer (AVA) was used to measure the diameter size of bubbles entrained in the fresh stage. The dosages of both air-entraining agent (AE) and defoaming agent with different mixing times were investigated for their effects on the bubble size distribution. The results indicated that the portion of small bubbles with a diameter size less than 1,000 µm could be increased by increasing the AE dosage. Furthermore, prolonging the mixing time notably increased the volume of small bubbles, while producing no substantial change in the volume of large bubbles. Defoaming agent eliminated both small and large bubbles; however, small bubbles could be entrained concurrently with a reduction in large bubbles by increasing the dosage of defoaming agent or prolonging the mixing time after adding it. All investigated results confirmed that the effects of various parameters on characteristic of entrained air in concrete with full scale mixing are in agreement with the results of concrete investigated in laboratory by many researchers. These findings are beneficial for designing mixtures of Air-SCC containing high volumes of small bubbles that improve the self-compactability and freeze-thaw resistance of concrete.
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