A detailed simulation of concrete rheology, accounting for the motion of the cement, sand, and aggregates, is impossible on present-day computers. To solve the computational problem of the broad span of particle sizes in concrete, a multiscale or homogenization approach is used. Phenomena are modeled at a characteristic length scale to determine an average property, which is then used as an input in simulation at a coarser scale. For example, if the viscosity of a mortar can be determined by simulation or experiment, that viscosity can be used as an input to determine the viscosity of concrete.
There are problems with this approach, mainly linked to agglomeration.20 However, at sufficiently high shear rates, the evolution of an agglomerating system is similar to that of a non-agglomerating system. For cementitious materials that exhibit a Bingham behavior (a linear relation between shear stress and shear rate), plastic viscosity is the most relevant rheological parameter, and the slope of experimental flow curves can be compared to those of simulations.
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