Computational Model Predictions of Suspension Rheology: Comparison to Experiment | NIST

Predicting the rheological properties of fresh concrete, mortars, and cement paste from first principles remains a great challenge. While progress has been made in modeling the rheological properties of idealized hard sphere-like suspensions, there is little in the way of theoretical predictions and experimental data for suspensions composed of random shaped particles like those found in cement-based materials. In this paper, results will be presented of a study comparing computational model predictions to experimental measurements of the rheological properties of various suspensions. The model incorporates the particle size distribution as well as the shape of particles as determined from X-ray microtomography. The experimental rheological properties will be based on measurements using co-axial rheometers and various materials that could potentially be used as reference materials. 1 Introduction Predicting the rheological properties of suspensions like fresh cement paste or concrete remains a great challenge. Some of the complicating factors in modeling such systems include the broad size and shape distribution of the cement, sand and coarse aggregates. Another challenge is the fact that most rheometers need to be modified to accommodate the larger particles. These modifications lead to rheometers with geometries that do not allow for an analytical solution of the flow pattern, making it extremely difficult to determine rheological parameters, such as yield stress and plastic viscosity, in fundamental units. Therefore, a combination of flow simulation in complicated geometries, particulate reference materials and modified rheometers need to be used to characterize suspensions.