The Evolution of the Rheological Behavior of Hydrating Cement Systems (2022-12)¶

The prediction of the time-dependent rheological behavior of concrete is a challenging task of crucial importance to many applications in the construction industry. In particular, the advent of 3D concrete printing (3DCP) highlighted the importance of a more comprehensive understanding of the rheological behavior of cement systems undergoing hydration reactions. In this research, a recently proposed constitutive model is used to describe the evolution of the time-dependent rheological behavior of a cement system employed in 3DCP applications. The model is based on a single structure parameter that describes the instantaneous structuring level of the material's structure, considering both reversible and irreversible effects simultaneously. To validate the model, constant shear rate experiments are carried out and the flow curve of the fresh cement system is constructed from thixotropic equilibrium data observed before the hydration effects become significant. Then, stress ramps are performed to verify that the model can predict the time-dependent rheological behavior of a given cement system subjected to different dynamics. The main contribution of this work is the implementation of model parameters obtained directly from experiments. Calorimetric and mechanical tests were carried out with real samples, rather than just relying on fitted rheological data or estimates from literature. In comparison to other models found in the literature, this work improves the connection with real experimental quantities, providing supporting evidence for the model. The model is improved to better describe the hydration effects on the time-dependent rheological behavior of concrete by generalizing the irreversible progress function to account for different early-age and long-term hydration effects. It is shown that good agreement between experiments and model predictions can be achieved, which can impact the way 3D concrete printing applications are designed nowadays.