Vibration of fresh concrete understood through the paradigm of granular physics

Fresh concrete is often cited as an example of a yield-stress fluid, typically being modeled as a Bingham material. We describe how this is an incomplete understanding to rationalize simple but important flow behaviors. As a motivating phenomenon, we consider the practice of vibrating fresh concrete during placement to induce flow and remove air voids. It is demonstrated that a simple yield-stress fluid (an aqueous polymer microgel particle suspension, Carbopol) cannot recreate the phenomenon, falsifying the hypothesis that traditional yield-stress fluid models embody the key physics. However, a granular hard-particle suspension (millimetric glass beads in silicone oil) does recreate the phenomenon. We use shear rheology to further show that concrete displays noticeable granular physics as indicated by vibration-induced loss of the yield stress, consistent with the granular constitutive model of Hanotin et al. (2015). These results have implications for understanding the unseen phenomenon of air bubbles rising in concrete.