Direct numerical simulation of dynamic aggregate migration in fresh concrete using multi-scale Smoothed-Particle Hydrodynamics

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The scientific objectives of the proposed research project within the SPP 2005 aim towards improving our understanding of graded fresh concrete flow in confined geometries using microstructure-resolved SPH simulations. In this regard, special attention will be devoted to shear-induced particle migration and lubrication layer formation processes motivated by their technological significance for concrete pumping. As these processes take place at length scales which are significantly smaller than the engineering length scale, resolved surface-coupled Direct Numerical Simulations (DNS) are considered appropriate approaches. In order to address the significant computational requirements of DNS, high-performance computing approaches will be used (massively parallel distributed memory computing). Our simulation approach shall explicitly take into account the multi-scale nature of fresh concrete in that the rheology of the carrier fluid as well as the numerically resolved aggregate content can be adaptively modified to adequately represent the dominating mechanisms at a suitable length and time scale. Given our interest in particle migration processes, characteristic time scales we attempt to represent in our simulations will be in the order of particle self-diffusion times. In other words, simulated time scales must be sufficient to study shear-induced dynamic aggregate segregation processes in graded concrete suspensions. This implies that our simulations will strongly be separated from time-scales associated with the chemical reactivity of hydrating cement suspensions. As a result, this project focuses on the evolution of fresh concrete microstructure during flow, i.e. resulting in segregation effects such as heterogeneous particle size and concentration distributions, due to hydrodynamic and tribological effects. Our scientific work program shall be tailored in such a way that our simulation results can ultimately provide a reliable data and knowledge basis to develop coarse-grained macroscopic models of fresh concrete flow during pumping. This data basis shall cover a feature space composed of mix design and boundary conditions. In that respect, the anticipated output of the present project is considered a valuable input to module 3 of the SPP 2005. A computationally optimized simulation framework for SPH simulations is available. This simulation framework is based on HOOMD-blue (Highly Optimized Object-oriented Many-particle Dynamics) and has previously proven good parallel performance on computer clusters we have access to. Core algorithms related to the simulation of arbitrary-shaped rigid particles suspended in continuous carrier liquids (e.g. data structures, time integration routines) have been implemented. Within the duration of the proposed project, comparatively little time will thus be devoted to software implementation.