Viscosity influence on rising behavior of model air bubbles in fresh mortar

• Presenting idea about the relation between vibration and air bubbles migration.
• Using model bubbles, the effect of viscosity on air bubble migration was evaluated.
• As the vibration time duration was extended, air bubble was floated and migrated.
• As viscosity of fresh mortar was increased, the migration of bubble was prevented.

In this paper, the migrating behavior of air bubbles in fresh state cement mortar was studied. Since the air content of fresh concrete and further hardened concrete influences the durability and surface conditions of concrete after formwork is removed, the air content of fresh state concrete is a very important factor in determining durability of hardened concrete. To evaluate the influence of viscosity in fresh cement paste on air bubbles’ migrating behaviors under vibrating conditions, various viscosity conditions were controlled with Viscosity Modifying Admixtures (VMA) and vibration was applied for various time durations. Modeling of the air bubble migration was conducted with expandable polystyrene (EPS) beads where distribution of EPS was measured along with density according to the unit volume weight of three divided layers in a cylinder. Results showed that air bubbles migrate with and without vibration achieving relatively stable conditions with increased viscosity. Therefore, this study was designed to add to the knowledge of how viscosity influences the quality of hardened state cementitious materials.