Effectiveness of air entraining agent and defoamer on the bubble distribution of fresh mortar under different mixing methods

Abstract

The purpose of this study was to elucidate the distribution of fine bubbles and coarse bubbles in the mortar system of cement-superfine slag powder mortar after multiple mixing of air-entraining agent and defoaming agent. The experimental study used a fresh concrete pore structure analyzer (AVA instrument) to measure the bubble size distribution and related bubble parameters of fresh mortar. The critical size of the bubbles was defined as the size that the air bubbles can maintain the volume stability over time. Based on the time-dependent change in the volume content of the larger bubbles within two hours after mixing, it was found that 500 μm was the critical dimension of bubbles. By adjusting the mortar mixing methods, a lower mortar viscosity was achieved while the total volume of fine and coarse bubbles were also reduced. In addition, when the blending ratio of defoaming agent and air-entraining agent was within the range of 0.50-0.54, the bubble structure of the cement-superfine slag powder mortar had been significantly improved, and more fine bubbles and fewer coarse bubbles had been distributed in the mortar.