Abstract
Rheological properties and the interaction between air bubbles and solid particles are important factors influencing the air bubble system in air-entrained concrete. The former may affect the bubble motion and the latter may influence the strength of bubbles. However, none of them were properly discussed by direct observation. In this study, we observe the rising behavior of various-sized bubbles in air-entrained cement paste. By a modified drag equation, the bubble-particle interaction is determined and represented by the interaction coefficient Ki. By Ki the bubble-particle interaction can be quantified and correlated with air entrainment properties. In combination with rheological properties and surface tension, the influence of inorganic salts on air entrainment is systematically studied. It is found that the content of bubbles <200 μm and the specific surface area of bubbles in the fresh mortar decrease with the increase of Ki, and the content of bubbles >1000 μm and the spacing factor increase with increasing Ki.
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