Abstract
Rheology control is essential during the period in which cement and concrete pastes are encountered in the fresh state, due to the fact that it directly affects workability, initial placement and the structural performance of the hardened material. Optimizations of clinker formulations and reductions in cement-to-water ratios induced by economic and environmental considerations have a significant effect in rheology, which invokes the need for mechanistic models capable of describing the effect of multiple relevant phenomena on the observed paste flow. In this work, the population balance framework was implemented to develop a model able to relate the transient microstructural evolution of cement pastes under typical experimental conditions with its macroscopic rheological responses. Numerical details and performance are assessed and discussed. It was found that the model is capable of reproducing experimentally observed flow curves by using measured cluster size distribution information. It is also able to predict the complex rheological characteristics typically found in cement pastes. Furthermore, a spatially resolved scheme was proposed to investigate the nature of flow inside a parallel-plates rheometer geometry with the objective of assessing the ability of the model of qualitatively predicting experimentally observed behavior and to gain insight into the effect of possible secondary flows.
Highlights
Concrete is, by volume, the most produced material in the world, and it is a fundamental aspect of infrastructure development [1]
We propose a Population balance models (PBM)-based rheological model applied to fresh cement pastes
The simulated paste exhibited a shearthickening behavior, which is consistent with experimental studies that have found that cement suspensions tend to behave in this way when the water to cement ratio is below a value situated far from the center increase the aggregation rate, which produces a higher number of large sized aggregates, hampering flow
Summary
By volume, the most produced material in the world, and it is a fundamental aspect of infrastructure development [1]. The collision frequency term in Equation (17) adopts the form of the widely known geometry and the time frame the model aims to capture, significant amounts of sedimentation should expression for orthokinetic aggregation under laminar shear flow [35,40]: not occur. The selection rate of aggregates of size k reads: 2Fc. Here, Fc is an effective bound force, η is the viscosity of the suspension, r is radius of the breaking cluster, and S0 is an efficiency term analogous to the one present in Equation (17). It is believed that the main breakage mechanism for cement aggregates is fracture, but other phenomena such as attrition can occur as well [42,43] Considering this and that no definitive evidence exists on the exact way in which breakup occurs, it was assumed that clusters are likely to form a pair of child agglomerates of any smaller size. Other common geometries (such as the concentric cylinders configuration) can be incorporated into the model after replacing the previous equation with a suitable shear profile
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