Concrete Consolidation in the 21st Century-Stability and Retention of Entrained Air in Vibrated Concrete (Recorded presentation)

Stability and Retention of Entrained Air in Vibrated Concrete (Recorded presentation)

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A group of researchers from the University of Illinois, in collaboration with Kansas State University, investigated the stability and retention of entrained air in vibrated concrete, focusing on the impact of vibration on entrained air systems within precast concrete, particularly concrete cross ties. Sponsored by the Federal Railroad Administration, the study aimed to understand air bubble movement during vibration, crucial for freeze-thaw durability. The research revealed that existing models, like the Bingham fluid model, inadequately describe the effects of vibration on concrete. By experimenting with surrogate materials, the team found that the granular nature of concrete influences its rheological behavior, showing a transition to Newtonian fluid behavior under vibration. This finding suggests a "cone of influence" rather than a "radius of influence" during vibration. The study highlights the importance of achieving a proper initial air bubble size distribution to ensure concrete durability, emphasizing improved mixing techniques and admixture use.

Keywords

entrained air

vibrated concrete

freeze-thaw durability

rheological behavior

concrete durability