Multiphase granular suspension flow of fresh concrete during pumping in complex geometries

During the pumping process of multiphase granular suspensions, such as concrete, through pipe systems, many parameters can influence the material's ability to flow. To understand the hydrodynamics and particle mechanics in granular, non‐Newtonian suspensions under nonlinear flow conditions, the authors have been working on a joint project within the Priority Program SPP 2005 “Opus Fluidum Futurum ‐ Rheology of Reactive, Multiscale, Multiphase Construction Materials” funded by the German Research Foundation (DFG). Based on the results obtained, it is possible to describe the relationships between concrete composition and the rheological properties of the fresh mixture for pumping applications. The effects of particle geometry and flow conditions on flow‐induced particle migration (FIPM), subsequently the formation of a lubricating layer (LL), and eventually on pumping pressure were also shown. While the behavior of concrete and other complex, multiscale suspensions in generic flows (Couette, Poiseuille) is still part of current research and only partially understood, the behavior in complex geometries is even less explored so far. Here, additional effects based on the curvature of streamlines and mass inertia of the particle phase come into play. In the framework of the project, these effects have been investigated experimentally and numerically. Various experimental approaches have been developed to observe the behavior of particles within their carrier fluid in an opaque, dense, and enclosed moving system, yielding insightful results. Currently, models are being developed and experimentally validated to describe particle migration quantitatively, allowing conclusions about the local rheological behavior to be drawn. This information is essential to predict the flow behavior necessary for modern processes such as 3D printing and energy‐optimized pumping.